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Oxygenators for extracorporeal circulation: theory and practice fundamentals for clinicians
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Extracorporeal membrane oxygenators are essential medical devices for the treatment of patients with respiratory failure. A promising approach to improve oxygenator performance is the use of microstructured hollow fiber membranes that increase the available gas exchange surface area. However, by altering the traditional circular fiber shape, the risk of low flow, stagnating zones that obstruct mass transfer and encourage thrombus formation, may increase. Finding an optimal fiber shape is therefore a significant task. In this study, experimentally validated computational fluid dynamics simulations were used to investigate transverse flow within fiber packings of circular and microstructured fiber geometries. A numerical model was applied to calculate the local Sherwood number on the membrane surface, allowing for qualitative comparison of gas exchange capacities in low-velocity areas caused by the microstructured geometries. These adverse flow structures lead to a tradeoff between increased surface area and mass transfer. Based on our simulations, we suggest an optimal fiber shape for further investigations that increases potential mass transfer by up to 48% in comparison to the traditional, circular hollow fiber shape.
The recent outbreak of the COVID-19 pandemic in 2020 reasserted the necessity of artificial lung membrane technology to treat patients with acute lung failure. In addition, the aging world population inevitably leads to higher demand for better artificial organ (AO) devices. Membrane technology is the central component in many of the AO devices including lung, kidney, liver and pancreas. Although AO technology has improved significantly in the past few decades, the quality of life of organ failure patients is still poor and the technology must be improved further. Most of the current AO literature focuses on the treatment and the clinical use of AO, while the research on the membrane development aspect of AO is relatively scarce. One of the speculated reasons is the wide interdisciplinary spectrum of AO technology, ranging from biotechnology to polymer chemistry and process engineering. In this review, in order to facilitate the membrane aspects of the AO research, the roles of membrane technology in the AO devices, along with the current challenges, are summarized. This review shows that there is a clear need for better membranes in terms of biocompatibility, permselectivity, module design, and process configuration.
Introduction
This study analyzed the effect of different flows and pressures on the intraoxygenator flow path in three contemporary oxygenators and its consequences for oxygen transfer efficiency.
Methods
In an experimental setup, intraoxygenator flow path parameters were analyzed at post-oxygenator pressures of 150, 200, and 250 mm Hg and at flows ranging from 2 L/min to the oxygenators’ maximum permitted flow, with and without pulsatility. The oxygen gradient and the oxygen transfer per minute and per 100 mL blood were calculated using previously collected clinical data and compared with the flow path parameters.
Results
Increasing pressure did not affect the flow path parameters, whereas pulsatile flow led to significantly increased dynamic oxygenator blood volumes. Increased flow resulted in decreased values of the flow path parameters in all oxygenators, indicating increased flow through short pathways in the oxygenator. In parallel, oxygen transfer/100 mL blood decreased in all oxygenators (average 2.5 ± 0.4 to 2.4 ± 0.3 mL/dL, p > 0.001) and the oxygen gradient increased from 229 ± 45 to 287 ± 29 mm Hg, p > 0.001, indicating decreased oxygen transfer efficiency. Oxygen transfer/min increased (101 ± 15 to 143 ± 20 mL/min/m ² , p > 0.001), however, due to the increased flow through the oxygenator.
Conclusion
Varying trans-membrane oxygenator pressures did not lead to changes in the intraoxygenator flow path, while an increased flow exhibited lower flow path parameters resulting in less efficient use of the gas exchange compartment. The latter was confirmed by a decrease in O 2 transfer efficiency during higher blood flows.
Over the past decade, veno-venous extracorporeal membrane oxygenation (vvECMO) has been increasingly utilized in respiratory failure in patients. This study presents our institution´s experience focusing on the life span of ECMO systems reflecting the performance of a particular system. A retrospective review of our ECMO database identified 461 adult patients undergoing vvECMO (2010–2017). Patients that required more than one system and survived the first exchange >24 hours (n = 139) were included. Life span until the first exchange and exchange criteria were analyzed for all systems (PLS, Cardiohelp HLS-set, both Maquet Cardiopulmonary, Rastatt, Germany; Deltastream/Hilite7000LT, iLA-activve, Xenios/NovaLung, Heilbronn, Germany; ECC.O5, LivaNova, Mirandola, Italy). At our ECMO center, the frequency of a system exchange was 30%. The median (IQR) life span was 9 (6–12) days. There was no difference regarding the different systems (p = 0.145 and p = 0.108, respectively). However, the Deltastream systems were exchanged more frequently due to elective technical complications (e. g. worsened gas transfer, development of coagulation disorder, increased bleedings complications) compared to the other exchanged systems (p = 0.013). In summary, the used ECMO systems are safe and effective for acute respiratory failure. There is no evidence for the usage of a specific system. Only the increased predictability of an imminent exchange preferred the usage of a Deltastream system. However, the decision to use a particular system should not depend solely on the possible criteria for an exchange.
During extracorporeal membrane oxygenation (ECMO), oxygen (O2) transfer (V'O2) and carbon dioxide (CO2) removal (V'CO2) are partitioned between the native lung (NL) and the membrane lung (ML), related to the patient's metabolic-hemodynamic pattern. The ML could be assimilated to a NL both in a physiological and a pathological way. ML O2 transfer (V'O2ML) is proportional to extracorporeal blood flow and the difference in O2 content between each ML side, while ML CO2 removal (V'CO2ML) can be calculated from ML gas flow and CO2 concentration at sweep gas outlet. Therefore, it is possible to calculate the ML gas exchange efficiency. Due to the ML aging process, pseudomembranous deposits on the ML fibers may completely impede gas exchange, causing a "shunt effect", significantly correlated to V'O2ML decay. Clot formation around fibers determines a ventilated but not perfused compartment, with a "dead space effect", negatively influencing V'CO2ML. Monitoring both shunt and dead space effects might be helpful to recognise ML function decline. Since ML failure is a common mechanical complication, its monitoring is critical for right ML replacement timing and it also important to understand the ECMO system performance level and for guiding the weaning procedure. ML and NL gas exchange data are usually obtained by non-continuous measurements that may fail to be timely detected in critical situations. A realtime ECMO circuit monitoring system therefore might have a significant clinical impact to improve safety, adding relevant clinical information. In our clinical practise, the integration of a real-time monitoring system with a set of standard measurements and samplings contributes to improve the safety of the procedure with a more timely and precise analysis of ECMO functioning. Moreover, an accurate analysis of NL status is fundamental in clinical setting, in order to understand the complex ECMO-patient interaction, with a multidimensional approach.
Introduction:
Gaseous microemboli (GME) introduced during cardiac surgery are considered as a potential source of morbidity, which has driven the development of the first bubble counters. Two new generation bubble counters, introduced in the early 2000s, claim correct sizing and counting of GME. This in-vitro study aims to validate the accuracy of two bubble counters using monodisperse bubbles in a highly controlled setting at low GME concentrations.
Methods:
Monodisperse GME with a radius of 43 µm were produced in a microfluidic chip. Directly after their formation, they were injected one-by-one into the BCC200 and the EDAC sensors. GME size and count, measured with the bubble counters, were optically verified using high-speed imaging.
Results:
During best-case scenarios or low GME concentrations of GME with a size of 43 µm in radius in an in-vitro setup, the BCC200 overestimates GME size by a factor of 2 to 3 while the EDAC underestimates the average GME size by at least a factor of two. The BCC200 overestimates the GME concentration by approximately 20% while the EDAC overestimates the concentration by nearly one order of magnitude. Nevertheless, the calculated total GME volume is only over-predicted by a factor 2 since the EDAC underestimates the actual GME size. For the BCC200, the total GME volume was over-predicted by 25 times due to the over-estimation of GME size.
Conclusions:
The measured errors in the absolute sizing/counting of GME do not imply that all results obtained using the bubble counters are insignificant or invalid. A relative change in bubble size or bubble concentration can accurately be measured. However, care must be taken in the interpretation of the results and their absolute values. Moreover, the devices cannot be used interchangeably when reporting GME activity. Nevertheless, both devices can be used to study the relative air removal characteristics of CPB components or for the quantitative monitoring of GME production during CPB interventions.
Background:
There is no acceptable method of testing oxygen transfer performance in membrane oxygenators quickly and easily during cardiopulmonary bypass. Pre-clinical testing of oxygenators is performed under controlled situations in the laboratory, correlating oxygen transfer to blood flow using 100% oxygen. This laboratory method cannot be used clinically as oxygen transfer values vary significantly at each blood flow and the FiO2 is not kept at 1. Therefore, a formula was developed which corrects the existing FiO2 to attain a PaO2 of 150 mmHg: the corrected FiO2 at 150 mmHg. In graph form, this corrected FiO2 (x-axis) is correlated to the patient's oxygen consumption levels (y-axis), which determines the membrane oxygenator oxygen transfer performance.
Methods:
Blood gas and hemodynamic parameters taken during cardiopulmonary bypass using the Medtronic Fusion were used to calculate the oxygen consumption (inlet conditions to the oxygenator) and the corrected FiO2 for a PaO2 of 150 mmHg. Validation of the formula “FiO2-PaO2/(Pb−pH2O)+0.21” was carried out by plotting the calculated values on a graph using PaO2 values between 145 to 155 mmHg and then, using the corrected FiO2 for PaO2s outside of this range.
Results:
All trend-lines correlated significantly to confirm that the Medtronic Fusion had an extrapolated oxygen transfer of 419 milliliters O2/min at an FiO2 of 1 to achieve a PaO2 of 150 mmHg.
Conclusions:
Use of the corrected FiO2 correlated to the oxygen transfer conditions of the membrane oxygenator can easily be used on a routine basis, providing valuable information clinically. When used by the manufacturer under laboratory conditions, further clinically relevant data is provided in terms of FiO2 and resultant PaO2s instead of the present limitations using blood flow. In this way, a clinically justifiable method has been developed to finally establish a standard in testing membrane oxygenator performance.
Carbon dioxide production during cardiopulmonary bypass derives from both the aerobic metabolism and the buffering of lactic acid produced by tissues under anaerobic conditions. Therefore, carbon dioxide removal monitoring is an important measure of the adequacy of perfusion and oxygen delivery. However, routine monitoring of carbon dioxide removal is not widely applied. The present article reviews the main physiological and pathophysiological sources of carbon dioxide, the available techniques to assess carbon dioxide production and removal and the clinically relevant applications of carbon dioxide-related variables as markers of the adequacy of perfusion during cardiopulmonary bypass.
Richard W Melchior,1 Steven W Sutton,2 William Harris,3 Heidi J Dalton4,5 1Department of Perfusion Services, The Children's Hospital of Philadelphia, Philadelphia, PA, 2Cardiovascular Support Services, Inc., Dallas, TX, 3Department of Perfusion Services, Ochsner Clinic Foundation, New Orleans, LA, 4Alaskan Native Tribal Health Consortium, Anchorage, AK, 5Department of Child Health, University of Arizona-College of Medicine, Phoenix, AZ, USAAbstract: The development of the membrane oxygenator for pediatric cardiopulmonary bypass has been an incorporation of ideology and technological advancements with contributions by many investigators throughout the past two centuries. With the pursuit of this technological achievement, the ability to care for mankind in the areas of cardiac surgery has been made possible. Heart disease can affect anyone within the general population, but one such segment that it can affect from inception includes children. Currently, congenital heart defects are the most common birth defects nationally and worldwide. A large meta-analysis study from 1930 to 2010 was conducted in review of published medical literature totaling 114 papers with a study population of 24,091,867 live births, and divulged a staggering incidence of congenital heart disease involving 164,396 subjects with diverse cardiac illnesses. The prevalence of these diseases increased from 0.6 per 1,000 live births from 1930–1934 to 9.1 per 1,000 live births after 1995. These data reveal an emphasis on a growing public health issue regarding congenital heart disease. This discovery displays a need for heightened awareness in the scientific and medical industrial community to accelerate investigative research on emerging cardiovascular devices in an effort to confront congenital anomalies. One such device that has evolved over the past several decades is the pediatric membrane oxygenator. The pediatric membrane oxygenator, in conjunction with the heart lung machine, assists in the repair of most congenital cardiac defects. Numerous children born with congenital heart disease with or without congestive heart failure have experienced improved clinical outcomes in quality of life, survival, and mortality as a result of the inclusion of this technology during their cardiac surgical procedure. The purpose of this review is to report a summary of the published medical and scientific literature related to development of the pediatric membrane oxygenator from its conceptual evolutionary stages to artificially supporting whole body perfusion in the modern pediatric cardiac surgical setting. Keywords: cardiovascular perfusion, pediatric cardiac surgery, extracorporeal technological advancement
Background:
The indication for arterial line filtration (ALF) is to inhibit embolisation during cardiopulmonary bypass. Filtration methods have developed from depth filters to screen filters and from a stand-alone component to an integral part of the oxygenator. For many years, ALF has been a standard adopted by a majority of cardiac centres worldwide. The following review aims to summarize the available evidence in support for ALF and report on its current practice in Europe.
Method:
The principles and application of ALF in Europe was investigated using a survey conducted in 2014. The scientific evidence for AFL was examined by performing a systematic literature search in six different databases, using the following search terms: "Cardiopulmonary bypass AND filters AND arterial". The primary endpoint was protection against cerebral injury verified by the degree of cerebral embolisation or cognitive tests. The secondary endpoint was improvement of the clinical outcome verified elsewise. Only randomised clinical trials were considered.
Results:
The response rate was 31% (n=112). The great majority (88.5%) of respondents were using ALF, following more than 10 years of experience. Integrated arterial filtration was used by 55%. Of respondents not using ALF, fifty-four percent considered starting using integrated arterial filtration. The systematic literature database search returned 180 unique publications where 82 were specifically addressing ALF in cardiopulmonary bypass. Only four out of the 82 identified publications fulfilled our inclusion criteria. Of these, three were more than 20 years old and based on the use of bubble oxygenation.
Conclusion:
ALF is a standard implemented in a majority of cardiopulmonary bypass procedures in Europe. The level of scientific evidence available in support of current arterial line filtration methods in cardiopulmonary bypass is, however, poor. Large, well-designed, randomised trials are warranted.
We developed a numerical model, based on multi-physics computational fluid dynamics (CFD) simulations, to assist the design process of a plastic hollow-fiber bundle blood heat exchanger (BHE) integrated within the INSPIRE(TM), a blood oxygenator (OXY) for cardiopulmonary by-pass procedures, recently released by Sorin Group Italia. In a comparative study, we analyzed five different geometrical design solutions of the BHE module. Quantitative geometrical-dependent parameters providing a comprehensive evaluation of both the hemo- and thermo-dynamics performance of the device were extracted to identify the best-performing prototypical solution. A convenient design configuration was identified, characterized by (i) a uniform blood flow pattern within the fiber bundle, preventing blood flow shunting and the onset of stagnation/recirculation areas and/or high velocity pathways, (ii) an enhanced blood heating efficiency, and (iii) a reduced blood pressure drop. The selected design configuration was then prototyped and tested to experimentally characterize the device performance. Experimental results confirmed numerical predictions, proving the effectiveness of CFD modeling as a reliable tool for in silico identification of suitable working conditions of blood handling medical devices. Notably, the numerical approach limited the need for extensive prototyping, thus reducing the corresponding machinery costs and time-to-market.
Copyright © 2015 IPEM. Published by Elsevier Ltd. All rights reserved.
Background:
Invasive Mycobacterium chimaera infections were diagnosed in 2012 in 2 heart surgery patients on extracorporeal circulation. We launched an outbreak investigation to identify the source and extent of the potential outbreak and to implement preventive measures.
Methods:
We collected water samples from operating theaters, intensive care units, and wards, including air samples from operating theaters. Mycobacterium chimaera strains were characterized by randomly amplified polymorphic DNA polymerase chain reaction (RAPD-PCR). Case detection was performed based on archived histopathology samples and M. chimaera isolates since 2006, and the patient population at risk was prospectively surveyed.
Results:
We identified 6 male patients aged between 49 and 64 years with prosthetic valve endocarditis or vascular graft infection due to M. chimaera, which became clinically manifest with a latency of between 1.5 and 3.6 years after surgery. Mycobacterium chimaera was isolated from cardiac tissue specimens, blood cultures, or other biopsy specimens. We were able also to culture M. chimaera from water circuits of heater-cooler units connected to the cardiopulmonary bypass, and air samples collected when the units were in use. RAPD-PCR demonstrated identical patterns among M. chimaera strains from heater-cooler unit water circuits and air samples, and strains in 2 patient clusters.
Conclusions:
The epidemiological and microbiological features of this prolonged outbreak provided evidence for the airborne transmission of M. chimaera from contaminated heater-cooler unit water tanks to patients during open-heart surgery.
Failure of components integrated into the cardiopulmonary bypass circuit, although rare, can bring about catastrophic results. One of these components is the heat exchanger of the membrane oxygenator. In this compartment, unsterile water from the heater cooler device is separated from the sterile blood by stainless steel, aluminum, or by polyurethane. These areas are glued or welded to keep the two compartments separate, maintaining sterility of the blood. Although quality control testing is performed by the manufacturer at the factory level, transport presents the real possibility for damage. Because of this, each manufacturer has included in the instructions for use a testing procedure for testing the integrity of the heat exchanger component. Water is circulated through the heat exchanger before priming and a visible check is made of the oxygenator bundle to check for leaks. If none are apparent, then priming of the oxygenator is performed. In this particular case, this procedure was not useful in detecting communication between the water and blood chambers of the oxygenator.
Since its inception, administering and ensuring anaesthesia during cardiopulmonary bypass has been challenging. Partly because of the difficulty of administering volatile agents during cardiopulmonary bypass, total intravenous anaesthesia has been a popular technique used by cardiac anaesthetists in the last two decades. However, the possibility that volatile agents reduce mortality and the incidence of myocardial infarction by preconditioning the myocardium has stimulated a resurgence of interest in their use for cardiac anaesthesia. The aim of this review is to provide an overview of the administration of volatile anaesthetic agents during cardiopulmonary bypass for the maintenance of anaesthesia and to address some of the practical issues that are involved in doing so.
To compare the efficiency of 20 and 40 µm arterial line filters during cardiopulmonary bypass for the removal of emboli from the extracorporeal circuit.
Twenty-four adult patients undergoing surgery were perfused using a cardiopulmonary bypass circuit containing either a 20 µm or 40 µm arterial filter (n = 12 in both groups). The Emboli Detection and Classification system was used to count emboli upstream and downstream of the filter throughout cardiopulmonary bypass. The mean proportion of emboli removed by the filter was compared between the groups.
The 20 µm filter removed a significantly greater proportion of incoming emboli (0.621) than the 40 µm filter (0.334) (p=0.029). The superiority of the 20 µm filter persisted across all size groups of emboli larger than the pore size of the 40 µm filter.
The 20 µm filter removed substantially more emboli than the 40 µm filter during cardiopulmonary bypass in this comparison.
To remove gaseous microemboli (GME) using an oxygenator with an integrated arterial filter, it is recommended by some manufacturers to purge the oxygenator as an additional safety feature while on bypass. In this in vitro study, we evaluated whether purging of oxygenators with an integrated arterial filter is efficient in reducing GME. Five different types of commercially available contemporary oxygenators with an integrated arterial filter based on progressive filter filtration (1), cascade filtration (1), screen filtration (2), or self-venting (1) were tested for their efficiency in removing GME while keeping the purge line open or closed. A bubble counter was used for pre- and post-oxygenator GME signaling, from which the filter efficiency was computed. Freshly drawn heparinized porcine blood was used at blood flow rates of 3 and 5 L/min. Three units of each oxygenator were tested with its specific reservoir at a fixed volume level of 1,500 mL. GME load was introduced into the venous line at 1,000 mL air/min. Measurements started as soon as GME were detected by the pre-oxygenator probe and then continued for 1 minute. There was no statistically significant difference in filter efficiency between the purged and non-purged groups for specific oxygenators. At a blood flow of 3 L/min, the average filter efficiency stayed approximately invariable when comparing the non-purged and purged groups, where 89.1–88.2% indicated the largest difference between the groups. At a blood flow rate of 5 L/min, the filter efficiency changed in one screen filter group from an average of 55.7% in the non-purged group to 42.4% in the purged group. Other filter efficiencies at the blood flow rate of 5 L/min for non-purged compared with purged groups were, respectively, 98.0 vs. 98.0% (screen filtration), 88.6 vs. 85.8% (self-venting filtration), 82.8 vs. 75.5% (progressive filter filtration), and 65.4 vs. 65.1% (cascade filtration). Based on these results, purging while confronted with continuous GME challenge did not result in an increased filter efficiency.
Introduction
A high-pressure excursion (HPE) is a sudden increase in oxygenator inlet pressure during cardiopulmonary bypass (CPB). The aims of this study were to identify factors associated with HPE, to describe a treatment protocol utilizing epoprostenol in severe cases, and to assess early outcome in HPE patients.
Methods
Patients who underwent cardiac surgery with cardiopulmonary bypass at Sahlgrenska University Hospital 2016–2018 were included in a retrospective observational study. Pre- and post-operative data collected from electronic health records, local databases, and registries were compared between HPE and non-HPE patients. Factors associated with HPE were identified with logistic regression models.
Results
In total, 2024 patients were analyzed, and 37 (1.8%) developed HPE. Large body surface area (adjusted Odds Ratio (aOR): 1.43 per 0.1 m ² ; 95% confidence interval (CI): 1.16–1.76, p < 0.001), higher hematocrit during CPB (aOR: 1.20 per 1%; (1.09–1.33), p < 0.001), acute surgery (aOR: 2.98; (1.26–6.62), p = 0.018), and previous stroke (aOR: 2.93; (1.03–7.20), p = 0.027) were independently associated with HPE. HPE was treated with hemodilution ( n = 29, 78.4%), and/or extra heparin ( n = 23, 62.2%), and/or epoprostenol ( n = 12, 32.4%). No oxygenator change-out was necessary. While there was no significant difference in 30-day mortality (2.7% vs 3.2%, p = 1.0), HPE was associated with a higher perioperative stroke rate (8.1% vs 1.8%, aOR 5.09 (1.17–15.57), p = 0.011).
Conclusions
Large body surface area, high hematocrit during CPB, previous stroke and acute surgery were independently associated with HPE. A treatment protocol including epoprostenol appears to be a safe option. Perioperative stroke rate was increased in HPE patients.
Background:
Cerebral autoregulation (CA) continuously adjusts cerebrovascular resistance to maintain cerebral blood flow (CBF) constant despite changes in blood pressure. Also, CBF is proportional to changes in arterial carbon dioxide (CO2) (cerebrovascular CO2 reactivity). Hypercapnia elicits cerebral vasodilation that attenuates CA efficacy, while hypocapnia produces cerebral vasoconstriction that enhances CA efficacy. In this study, we quantified the influence of sevoflurane anesthesia on CO2 reactivity and the CA-CO2 relationship.
Methods:
We studied patients with type 2 diabetes mellitus (DM), prone to cerebrovascular disease, and compared them to control subjects. In 33 patients (19 DM, 14 control), end-tidal CO2, blood pressure, and CBF velocity were monitored awake and during sevoflurane-based anesthesia. CA, calculated with transfer function analysis assessing phase lead (degrees) between low-frequency oscillations in CBF velocity and mean arterial blood pressure, was quantified during hypocapnia, normocapnia, and hypercapnia.
Results:
In both control and DM patients, awake CO2 reactivity was smaller (2.8%/mm Hg CO2) than during sevoflurane anesthesia (3.9%/mm Hg; P<0.005). Hyperventilation increased CA efficacy more (3 deg./mm Hg CO2) in controls than in DM patients (1.8 deg./mm Hg CO2; P<0.001) in both awake and sevoflurane-anesthetized states.
Conclusions:
The CA-CO2 relationship is impaired in awake patients with type 2 DM. Sevoflurane-based anesthesia does not further impair this relationship. In patients with DM, hypocapnia induces cerebral vasoconstriction, but CA efficacy does not improve as observed in healthy subjects.
Circulating venous blood outside the body, through an artificial lung (membrane oxygenator), and returning oxygenated blood to the patient is extracorporeal gas exchange. Oxygen and carbon dioxide exchange in a membrane lung is controlled by regulating blood flow, blood composition, and device design. With this control, lung function can be replaced for weeks by artificial organs. © 2020 American Physiological Society. Compr Physiol 10:879‐891, 2020.
Teaching Material
Robert H. Bartlett. Physiology of Extracorporeal Gas Exchange. Compr Physiol 10 : 2020, 879–891.
Didactic Synopsis
Major Teaching Points
In extracorporeal circulation venous blood is drained from the right atrium, pumped through an artificial lung (membrane oxygenator) and returned to the aorta (venoarterial) or right atrium (venovenous). Extracorporeal circulation can replace native heart and/or lung function for weeks or months. During that time, the native heart and lungs can be treated, bridging to recovery or replacement (by transplantation or wearable devices).
Oxygenator Design and Function
Modern membrane oxygenators are made of thousands of small tubes (hollow fibers) contained in a bundle perfused by venous blood. The fibers are filled with a continuous flow of oxygen. Oxygen diffuses through the walls of the fibers into the venous blood, raising the oxyhemoglobin saturation from venous conditions (typically 75% saturation) to 100% saturation. Oxygenators are designed to disrupt the laminar flow of blood and mix the red cells. Blood oxygenation is controlled by the surface area, the venous saturation, the residence time, the total amount of hemoglobin, and the blood flow. All of these factors are combined into the designation “rated flow”, which is the flow of standardized venous blood (hemoglobin 12 gr/dL, saturation 75%) which exits the lung at 95% saturation.
CO2 Clearance
CO2 clearance is a function of the flow of ventilating gas (like the normal lung). Ventilating gas flow is usually set at the same rate as blood flow and CO2 clearance is roughly equal to oxygenation. Increasing gas flow increases CO2 clearance but has no effect on oxygenation.
Pathophysiology
Membrane lungs malfunction by clotting in the blood phase or water accumulation in the gas phase. Clotting occurs gradually despite anticoagulation. It is detected by increased blood flow resistance and decreasing oxygenation. It is treated by replacing the membrane lung. Water in the gas phase blocks CO2 transfer. It is treated by increasing the gas flow.
Clinical Practice
Clinical use of a membrane oxygenator and pump is referred to as extracorporeal membrane oxygenation (ECMO). In ECMO venous blood from the right atrium is perfused through a membrane oxygenator. If the oxygenated blood is returned to the arterial circulation the device replaces both heart and lung function (venoarterial ECMO). If the oxygenated blood is returned to the right atrium the device replaces lung function only (venovenous ECMO). In practice, ECMO is used for patients with life threatening heart or lung failure. Vascular access is established through major peripheral blood vessels and an ECMO circuit is selected which has rated flow sufficient for total support of the heart and lung function (typically 6 L/min rated flow for adults). ECMO is continued until the injured organs recover, can be replaced by transplantation or implanted devices, or are irreversibly damaged.
Didactic Legends
The following legends to the figures that appear throughout the article are written to be useful for teaching.
Figure 1. Gas exchange in a membrane lung.
Figure 2. Gas exchange in a hollow fiber membrane lung.
Figure 3. In membrane lung fabrication, a bundle of hollow fibers is placed in a housing and the open ends of the fibers are exposed. Gas (typically oxygen) flows through the fibers and blood flows around the fibers. Oxygen and CO2 are exchanged at the thin fiber walls.
Figure 4. Oxygen delivery related to flow and oxygen content.
Figure 5. Describes the concept of rated flow.
Figure 6. Oxygen supply related to hemoglobin concentration and flow.
Figure 7. The amount of gas exchange related to gas content difference and blood flow. CO2 clearance can be achieved at low blood flows, compared to oxygen.
Figure 8. 3 ways of describing the amount of oxygen in blood.
Figure 9. All the variables in oxygen kinetics are described in this figure.
Figure 10. The relationship of oxygen delivery to oxygen consumption during normal and hyper metabolism.
Figure 11. This describes all the components of ECMO in the venoarterial mode.
Figure 12. This describes all the components of ECMO in the venovenous mode.
Figure 13. This describes the blood gases when 2 blood flows of different oxyhemoglobin concentration are mixed.
Figure 14. This describes the calculation of arterial oxygen content or saturation when 2 blood flows are mixed.
Figure 15. This demonstrates the amount of flow related to hemoglobin concentration to deliver 240 cc oxygen per minute.
Figure 16. The clinical course of a patient with severe respiratory failure managed with V‐V ECMO.
Microfluidic artificial lungs (µALs) have the potential to improve the treatment and quality of life for patients with acute or chronic lung injury. In order to realize the full potential of this technology (including as a destination therapy), the biocompatibility of these devices needs to be improved to produce long-lasting devices that are safe for patient use with minimal or no systemic anticoagulation. Many studies exist which probe coagulation and thrombosis on polydimethyl siloxane (PDMS) surfaces, and many strategies have been explored to improve surface biocompatibility. As the field of µALs is young, there are few studies which investigate biocompatibility of functioning µALs; and even fewer which were performed in vivo. Here, we use both in vitro and in vivo models to investigate two strategies to improve µAL biocompatibility: 1) a hydrophilic surface coating (polyethylene glycol, PEG) to prevent surface fouling, and 2) the addition of nitric oxide (NO) to the sweep gas to inhibit platelet activation locally within the µAL. In this study, we challenge µALs with clottable blood or platelet-rich plasma (PRP) and monitor the resistance to blood flow over time. Device lifetime (the amount of time the µAL remains patent and unobstructed by clot) is used as the primary indicator of biocompatibility. This study is the first study to: 1) investigate the effect of NO release on biocompatibility in a microfluidic network; 2) combine a hydrophilic PEG coating with NO release to improve blood compatibility; and 3) perform extended in vivo biocompatibility testing of a µAL. We found that µALs challenged in vitro with PRP remained patent significantly longer when the sweep gas contained NO than without NO. In the in vivo rabbit model, neither approach alone (PEG coating nor NO sweep gas) significantly improved biocompatibility compared to controls (though with larger sample size significance may become apparent); while the combination of a PEG coating with NO sweep gas resulted in significant improvement of device lifetime.
Statement of Significance
The development of microfluidic artificial lungs (µALs) can potentially have a massive impact on the treatment of patients with acute and chronic lung impairments. Before these devices can be deployed clinically, the biocompatibility of µALs must be improved and more comprehensively understood. This work explores two strategies for improving biocompatibility, a hydrophilic surface coating (polyethylene glycol) for general surface passivation and the addition of nitric oxide (NO) to the sweep gas to quell platelet and leukocyte activation. These two strategies are investigated separately and as a combined device treatment. Devices are challenged with clottable blood using in vitro testing and in vivo testing in rabbits. This is the first study to our knowledge that allows statistical comparisons of biocompatible µALs in animals, a key step towards eventual clinical use.
Objectives:
Among the factors that could determine neurological outcome after hypothermic circulatory arrest (HCA) rewarming is rarely considered. The optimal rewarming rate is still unknown. The goal of this study was to investigate the effects of 2 different protocols for rewarming after HCA on neurological outcome in an experimental animal model.
Methods:
Forty-four Sprague Dawley rats were cooled to 19 ± 1°C body core temperature by cardiopulmonary bypass (CPB). HCA was maintained for 60 min. Animals were randomized to receive slow (90 min) or fast (45 min) assisted rewarming with CPB to a target temperature of 35°C. After a total of 90 min of reperfusion in both groups, brain samples were collected and analysed immunohistochemically and with immunofluorescence. In 10 rats, magnetic resonance imaging was performed after 2 and after 24 h to investigate cerebral perfusion and cerebral oedema.
Results:
Interleukin 6, chemokine (C-C motif) ligand 5, intercellular adhesion molecule 1 and tumour necrosis factor α in the hippocampus are significantly less expressed in the slow rewarming group, and microglia cells are significantly less activated in the slow rewarming group. Magnetic resonance imaging analysis demonstrated better cerebral perfusion and less water content in brains that underwent slow rewarming at 2 and 24 h.
Conclusions:
Slow rewarming after HCA might be superior to fast rewarming in neurological outcome. The present experimental study demonstrated reduction in the inflammatory response, reduction of inflammatory cell activation in the brain, enhancement of cerebral blood flow and reduction of cerebral oedema when slow rewarming was applied.
To remove gaseous microemboli (GME) using an oxygenator with an integrated arterial filter, it is recommended by some manufacturers to purge the oxygenator as an additional safety feature while on bypass. In this in vitro study, we evaluated whether purging of oxygenators with an integrated arterial filter is efficient in reducing GME. Five different types of commercially available contemporary oxygenators with an integrated arterial filter based on progressive filter filtration (1), cascade filtration (1), screen filtration (2), or self-venting (1) were tested for their efficiency in removing GME while keeping the purge line open or closed. A bubble counter was used for pre- and post-oxygenator GME signaling, from which the filter efficiency was computed. Freshly drawn heparinized porcine blood was used at blood flow rates of 3 and 5 L/min. Three units of each oxygenator were tested with its specific reservoir at a fixed volume level of 1,500 mL. GME load was introduced into the venous line at 1,000 mL air/min. Measurements started as soon as GME were detected by the pre-oxygenator probe and then continued for 1 minute. There was no statistically significant difference in filter efficiency between the purged and non-purged groups for specific oxygenators. At a blood flow of 3 L/min, the average filter efficiency stayed approximately invariable when comparing the non-purged and purged groups, where 89.1-88.2% indicated the largest difference between the groups. At a blood flow rate of 5 L/min, the filter efficiency changed in one screen filter group from an average of 55.7% in the non-purged group to 42.4% in the purged group. Other filter efficiencies at the blood flow rate of 5 L/min for non-purged compared with purged groups were, respectively, 98.0 vs. 98.0% (screen filtration), 88.6 vs. 85.8% (self-venting filtration), 82.8 vs. 75.5% (progressive filter filtration), and 65.4 vs. 65.1% (cascade filtration). Based on these results, purging while confronted with continuous GME challenge did not result in an increased filter efficiency.
Heater-cooler units (HCUs) play a vital role in temperature management during cardiopulmonary bypass. In recent years, HCUs have been shown to play a significant role in the propagation of bacteria causing patient infection and significant harm. As a result, various institutions across the world have begun moving the HCU either far away or outside of the operative theater entirely. The purpose of this study was to examine the effect that the increased length of HCU water lines have on the ability of the device to heat and cool. We hypothesized that the increase in water line distance leads to a decrease in HCU efficiency and that insulating the water lines would blunt the effect of this increase in distance. Five water line conditions were compared under two cooling and two warming ranges. Short water lines, long water lines, and long water lines with foam, rubber, or tape insulation were compared. Cooling from an arterial line temperature of 26.7-19.7°C showed no difference between conditions with the exception that every long line condition takes significantly longer to cool than short water lines. Cooling from 35.6 to 28.6°C revealed that all insulations reduce the cooling time compared with long water lines without insulation, but only foam insulation reduces to the level of the short water lines. During warming conditions, all insulations reduced the warming time compared with long uninsulated water lines, but none were comparable with short water lines. Increased water line length leads to a decrease in HCU efficiency. Insulation is effective at increasing efficiency of long water lines, but only at warmer temperatures and not to the level of short water lines. Only foam-insulated long water lines were able to match the efficiency of short water lines, but only across a single temperature range.
We characterized the effects of surface wettability on the entire dynamics of a bubble disappearing through porous membranes.
The purpose of this study was to evaluate the hemodynamic properties and microemboli capture associated with different VAVD vacuum levels and venous reservoir levels in a neonatal CPB circuit. Trials were conducted in 2 parallel circuits to compare the performance of Capiox Baby RX05 oxygenator with separate AF02 arterial filter to Capiox FX05 oxygenator with integrated arterial filter. Arterial cannula flow rate to the patient was held at 500mL/min and temperature maintained at 32°C while VAVD vacuum levels (0mmHg, ‐15mmHg, ‐30mmHg, ‐45mmHg, ‐60mmHg) and venous reservoir levels (50mL, 200mL) were evaluated in both oxygenators. Hemodynamic parameters measuring flow, pressure, and total hemodynamic energy (THE) were made in real‐time using a custom‐made data acquisition system and Labview software. 10cc bolus of air was injected into the venous line and gaseous microemboli (GME) detected using an Emboli Detection and Classification (EDAC) Quantifier. Diverted blood flow via the arterial filter's purge line and mean pressures increased with increasing VAVD levels (p<0.01). Mean pressures were lower with lower venous reservoir levels and were greater in RX05 groups compared to FX05 (p<0.01). Microemboli detected at the pre‐oxygenator site increased with higher VAVD vacuum levels and lower venous reservoir levels (p<0.01). The amount of microemboli captured by the FX05 oxygenator with integrated arterial filter was greater than by the RX05 oxygenator alone, although both oxygenators were able to clear microemboli before reaching the pseudo‐patient.
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Gaseous microemboli (GME) are a potential complication of cardiopulmonary bypass (CPB). Though it is difficult to prove that GME is the only major cause of neurological deficits, it may increase the chance of post-operative cognitive dysfunction if not removed. The objectives of this research were to compare LivaNova-Sorin Inspire (Inspire) oxygenator with a Medtronic arterial filter to the Medtronic Fusion (Fusion) oxygenator with and without a Medtronic arterial filter based on each system's ability to handle GME. The Inspire and Fusion systems were evaluated in vitro. GME handling was observed by introducing air in the sampling manifold connected to the venous return at a 60 mL bolus or 1 liter per minute (LPM). The emboli detection and classification (EDAC) system measured GME preand post-oxygenator/arterial filter. The Inspire with a filter was able to remove a statistically significant greater amount of total emboli per second during the 60 mL bolus and 1 LPM tests than the Fusion with and without an arterial filter. The Inspire with an arterial filter was more efficient in removing GME during a 60 mL bolus and 1 LPM than the Fusion and Fusion with an arterial filter. However, the Fusion with an arterial filtered performed better than the Fusion system without the arterial filter.
Introduction:
Mycobacterium chimaera ( M. chimaera) is a recently characterised bacterium that can cause life-threatening infections in small numbers of patients who undergo cardiopulmonary bypass during cardiac surgery. The likely mode of transmission is thought to occur through aerosolisation from contaminated water reservoirs. The airborne bacteria then contaminate the surgical field, leading to an infection months or even years later. The preferred practical solution to disrupt the transmission of these airborne bacteria to the patient is to remove the heater-cooler units (HCUs) from the operating room (OR). We describe a process of achieving this in order to provide information to guide other institutions who wish to do a similar thing.
Methods:
A multidisciplinary team was assembled to work on the project. The planning phase involved trialling different OR layouts and simulating the alterations in the HCU circuit function. The changes to the OR were made over a weekend to minimise disruption to the operating schedule.
Results:
The HCU was moved to the dirty utility room adjacent to the OR. Standard operating procedures (SOP) and risk assessments were made to enable this to be used for a dual purpose. One of the ORs was reconfigured to allow the cardiopulmonary bypass machine to be located close to the HCU in the dirty utility room. The total cost of the alterations was £6,158. Although we have provided a physical barrier to interrupt patient exposure to aerosolised M. chimaera from HCUs, we continue to perform cultures and decontamination as per the national recommendations. The SOP was designed to be auditable to ensure compliance with the protocols.
Conclusions:
We show a method by which the HCU can be removed from the OR in a relatively low-cost, straightforward and practical manner.
A change of oxygenator during cardiopulmonary bypass is a technically high-risk procedure with potential for a serious adverse event for the patient. This case report describes a case of increased pressure drop and pre-oxygenator blood pressure during cardiopulmonary bypass successfully treated with pre-oxygenator-administered epoprostenol.
Introduction:
The use of cardiopulmonary bypass is associated with a risk of neurocognitive deficit caused by gaseous microemboli. Flushing the empty bypass circuit with carbon dioxide, which is more soluble than air, may reduce the amount of gaseous microemboli in the priming solution before the initiating of cardiopulmonary bypass.
Method:
We measured the amount of gaseous microemboli in twenty primed bypass circuits. Ten circuits were flushed with carbon dioxide before being primed and ten circuits were non-flushed. All circuits in both groups were primed with crystalloid priming. An ultrasonic clinical bubble counter was used to count gaseous microemboli in the prime for 20 minutes.
Results:
The median numbers of gaseous microemboli counts were highest during the first minute in both groups, with a significantly lower median value in the group flushed with carbon dioxide (397.5) versus the non-flushed group (1900). In the 20th minute, the median values of gaseous microemboli were significantly lower (p<0.023) in the flushed (0.5) versus non-flushed (10.75) groups. The gaseous microembolic count in the flushed group remained lower than in the non-flushed group when tested minute by minute throughout the whole 20-minute period.
Conclusion:
Flushing the bypass circuits with carbon dioxide before priming significantly decreased the number of gaseous microemboli in the priming solution.
Recently, an oxygenator with an integrated centrifugal blood pump (IP) was designed to minimize priming volume and to reduce blood foreign surface contact even further. The use of this oxygenator with or without integrated arterial filter was compared with a conventional oxygenator and nonintegrated centrifugal pump. To compare the air removal characteristics 60 patients undergoing coronary artery bypass grafting were alternately assigned into one of three groups to be perfused with a minimized extracorporeal circuit either with the conventional oxygenator, the oxygenator with IP, or the oxygenator with IP plus integrated arterial filter (IAF). Air entering and leaving the three devices was measured accurately with a bubble counter during cardiopulmonary bypass. No significant differences between all groups were detected, considering air entering the devices. Our major finding was that in both integrated devices groups incidental spontaneous release of air into the arterial line in approximately 40% of the patients was observed. Here, detectable bolus air (>500 µm) was shown in the arterial line, whereas in the minimal extracorporeal circulation circuit (MECC) group this phenomenon was not present. We decided to conduct an amendment of the initial design with METC-approval. Ten patients were assigned to be perfused with an oxygenator with IP and IAF. Importantly, the integrated perfusion systems used in these patients were flushed with carbon dioxide (CO2 ) prior to priming of the systems. In the group with CO2 flush no spontaneous air release was observed in all cases and this was significantly different from the initial study with the group with the integrated device and IAF. This suggests that air spilling may be caused by residual air in the integrated device. In conclusion, integration of a blood pump may cause spontaneous release of large air bubbles (>500 µm) into the arterial line, despite the presence of an integrated arterial filter. CO2 flushing of an integrated cardiopulmonary bypass system prior to priming may prevent spontaneous air release and is strongly recommended to secure patient safety.
Gaseous microemboli (GME) may originate from the extracorporeal circuit and enter the arterial circulation of the patient. GME are thought to contribute to cerebral deficit and to adverse outcome after cardiac surgery. The arterial filter is a specially designed component for removing both gaseous and solid microemboli. Integration of an arterial filter with an oxygenator is a contemporary concept, reducing both prime volume and foreign surface area. This study aims to determine the air-handling properties of four contemporary oxygenator devices with an integrated arterial filter. Two oxygenator devices, the Capiox FX25 and the Fusion, showed significant increased volume of GME reduction rates (95.03 ± 3.13% and 95.74 ± 2.69%, respectively) compared with both the Quadrox-IF (85.23 ± 5.84%) and the Inspire 6F M (84.41 ± 12.93%). Notably, both the Quadrox-IF and the Inspire 6F M as well as the Capiox FX 25 and the Fusion showed very similar characteristics in volume and number reduction rates and in detailed distribution properties. The Capiox FX25 and the Fusion devices showed significantly increased number and volume reduction rates compared with the Quadrox-IF and the Inspire 6F M devices. Despite the large differences in design of all four devices, our study results suggest that the oxygenator devices can be subdivided into two groups based on their fibre design, which results in screen filter (Quadrox-IF and Inspire 6F M) and depth filter (Capiox FX25 and Fusion) properties. Depth filter properties, as present in the Capiox FX25 and Fusion devices, reduced fractionation of air and may ameliorate GME removal.
Established as the standard reference on cardiopulmonary bypass, Dr. Gravlee's text is now in its Third Edition. This comprehensive, multidisciplinary text covers all aspects of cardiopulmonary bypass including sections on equipment, physiology and pathology, hematologic aspects, and clinical applications. This edition features a new section on cardiopulmonary bypass in neonates, infants, and children and a new chapter on circulatory support for minimally invasive cardiac surgery. Other highlights include state-of-the-art information on low-volume circuits and other new equipment and discussions of outcomes data for on-pump and off-pump surgeries. © 2008 by Lippincott Williams & Wilkins, a Wolters Kluwer business
To improve our understanding of the evidence-based literature supporting temperaturemanagement during adult cardiopulmonary bypass, The Society of Thoracic Surgeons, the Society of Cardiovascular Anesthesiology and the American Society of ExtraCorporeal Technology tasked the authors to conduct a review of the peer-reviewed literature, including 1) optimal site for temperature monitoring, 2) avoidance of hyperthermia, 3) peak cooling temperature gradient and cooling rate, and 4) peak warming temperature gradient and rewarming rate. Authors adopted the American College of Cardiology/American Heart Association method for development clinical practice guidelines, and arrived at the following recommendation.
Neurologic injury is a devastating complication of cardiac surgery Cerebral cooling is an important aspect of hypothermic cardiopulmonary bypass in some patients, because hypothermia is the only reliable method of neuroprotection against injuries related to cerebral ischemia. Hypothermia may afford neuroprotection by a variety of mechanisms, including reduction in cerebral metabolic rate, decreased excitatory transmitter release, reduced ion influx, and reduced vascular permeability Conversely, hyperthermia, even if mild (2-3 degrees C), is harmful; it aggravates ischemic neuronal injury and accelerates neuronal death. In patients with acute strokes, hyperthermia worsens prognosis with respect to stroke severity, infarct size, mortality, and outcome in survivors. The degree of temperature discrepancy among standard monitoring sites in individual patients is often striking. The differences between jugular bulb temperature and rectal or bladder temperature are particularly large. Blood temperature in the arterial line leading from the oxygenator may be the most consistently accurate indicator of cerebral temperature. When hypothermia is used to protect vital organs during cardiopulmonary bypass, the cooling phase should be adequate, and the rewarming phase must be carefully managed. Hyperthermia may be as hazardous (luring the postoperative period as during surgery, exacerbating the extent of tissue injury if an overt stroke has occurred. Postoperative hyperthermia correlates with a greater degree of cognitive dysfunction measured 6 weeks after cardiac surgery. In conclusion, cardiac anesthesiologists can reduce the risk of inadvertent hyperthermia by selecting the best sites for temperature monitoring, carefully controlling the rewarming process, and continuing temperature monitoring during the postoperative period.
During cardiopulmonary bypass (CPB), gaseous microemboli (GME) are released into the patients' arterial bloodstream. GME may contribute to the adverse outcome after cardiac surgery. Recently, two oxygenator models with or without integrated arterial filter (IAF) were designed and only differ in size, leading to a change of 20 % in surface area of the hollow-fibers and 25 % in blood velocities. The aim of this study was to assess the air removal characteristics of the Inspire oxygenators with or without IAF. Sixty-eight patients were randomly assigned to four different groups: Optimized Adult and Full Adult and an additional IAF. GME reduction rates were measured with a bubble counter. The number of GME reduction rates showed no differences. However, both models reduced significantly less volume of GME (Optimized Adult: 40.6 and Full Adult: 50.3 %) compared to both models with IAF (respectively: 88.7 and 88.5 %). No significant differences of reduction rates were found between both devices without IAF and also not between both models with IAF. In conclusion, the larger Inspire oxygenator tends to remove more GME. No effect from size of oxygenator device with integrated screen filter on GME reduction was observed. The Inspire oxygenators with IAF may be considered as an adequate GME filter.
Cardiopulmonary bypass (CPB) is used so routinely in hospitals around the world that most of the participants — surgeons, anesthesiologists, perfusionists, operating room nurses and, above all, patients — forget that this landmark in clinical technology is not even 40 years old. In fact, many of the pioneers are still active in the field. Yet, so much has been done to transform a once-hazardous procedure into standard medical practice — through basic science, quality control, and good manufacturing — that one hardly remembers the days (not so long ago) when “pump-oxygenators,” as they were graphically called, were assembled just outside the operating room by tinkerers with a dream. The purpose of this chapter is to recall the inventiveness displayed by a small coterie of gifted investigators to whom we owe the mechanical and physiologic foundations of open-heart surgery, and to reflect on the new demands that continuing clinical advances will undoubtedly make on this technology.
Approximately one hundred and forty-two Trendelenburg operations for massive pulmonary embolism have been reported, and only nine of the patients operated on have left the hospital as cured.¹ This exceedingly high mortality is due to the critical condition of the patient and to the operative procedure, which entails the complete throttling of the great vessels leading from the heart for a brief period. Because of the difficulty in diagnosis and the uncertain prognosis, Nyström² advised postponing the operation until the patient is practically moribund. Then, as Churchill³ has stated, "the procedure could perhaps be more properly termed an immediate postmortem examination than a surgical operation."
Nyström and Blalock⁴ have demonstrated experimentally that occlusion of the pulmonary artery alone may be safely maintained for a longer period than occlusion of both the pulmonary artery and the aorta. Kiser¹ found that constriction of the afferent vessels of
This editorial will address two issues that are still a source of global controversy and confusion in present day perfusion practice. Membrane oxygenators are designed and tested to a set of stringent flow standards prior to their release from every manufacturer. But how well do we know the iatrogenic consequences of pushing these devices beyond their maximum rated limits? In addition, how well do we know the meaning of the term 'AAMI Reference Flow' as it relates to the Manufacturers Maximum Rated Flow?
This article describes the structure and physiological functions of haemoglobin, including abnormal forms of haemoglobin and their significance. The mechanism of oxygen binding and the factors affecting oxygen affinity will be discussed.
Heat exchanger leak on cardiopulmonary bypass is very rare, but serious. The exact incidence is not known. It is an emergency associated with the potential risk of blood contamination, air embolism and haemolysis, difficulty with re-warming, acidosis, subsequent septic shock, multi-organ failure and death. We present a prompt, highly co-ordinated algorithm for the successful management of this important rare complication. There is need for further research to look for safety devices that detect leaks and techniques to reduce bacterial load. It is essential that teams practice oxygenator change-out routines and have a well-established change-out protocol.
© The Author(s) 2015.
Cardiopulmonary bypass (CPB) required for cardiac surgery presents unique challenges to the cardiac anesthesiologist responsible for providing the 3 most basic facets of any anesthetic: amnesia, analgesia, and muscle relaxation. Unique pathophysiologic changes during CPB result in pharmacokinetic alterations that impact the serum and tissue concentrations of IV and volatile anesthetics. Similarly, CPB causes pharmacodynamic alterations that impact anesthetic efficacy. The clinical significance of these alterations represents a "moving target" as practice evolves and the technology of CPB circuitry advances. In addition, perfusionists choose, modify, and maintain the CPB circuitry and membrane oxygenator. Thus, their significance may not be fully appreciated by the anesthesiologist. These issues have a profound impact on the anesthetic state of the patient. The delivery and maintenance of anesthesia during CPB present unique challenges. The perfusionist may be directly responsible for the delivery of anesthetic during CPB, a situation unique to the cardiac suite. In addition, monitors of anesthetic depth-assessment of clinical signs, hemodynamic indicators, the bispectral index monitor, end-tidal anesthetic concentration, or twitch monitoring-are often absent, unreliable, or directly impacted by the unique pathophysiology associated with CPB. The magnitude of these challenges is reflected in the higher incidence of intraoperative awareness during cardiac surgery. Further complicating matters are the lack of specific clinical guidelines and varying international policies regarding medical device specifications that add further layers of complexity and introduce practice variability both within institutions and among nations. We performed a systematic survey of the literature to identify where anesthetic practice during CPB is evidence based (or not), identify gaps in the literature to guide future investigations, and explore the implications of evolving surgical practice, perfusion techniques, and national policies that impact amnesia, analgesia, and muscle relaxation during CPB.
Various types of pump oxygenators are now being employed in the surgical correction of intracardiac anomalies. Certain basic physiological criteria will have to be satisfied with all such machines if the majority of such operations are to be successful. Only part of the responsibility for successful intracardiac surgery rests with the machine. The clinical management of the patient before, during, and after the operative procedure is equally important. Furthermore, new intracardiac surgical techniques have to be devised and perfected. Consequently, the problem of successful direct-vision open intracardiac surgery is threefold, and success is dependent upon the development of a reliable pump oxygenator that maintains the physiological requirements of the body, the clinical management of the patient, and the employment of a satisfactory surgical technique. The requirements of a pump oxygenator are that it must (1) provide the needs of the body for oxygen without the dangers of emboli or foaming
Polymethylpentene (PMP) oxygenators, utilised for ECMO, are commonly believed to be resistant to plasma leakage. Whilst uncommon, plasma leakage has been previously reported with PMP fibres, both in vivo and in vitro. We describe a paediatric ECMO case during which plasma leakage occurred and oxygenator function gradually deteriorated, ultimately necessitating device replacement. To our knowledge, this is the first case of plasma leakage described using a PMP device during paediatric ECMO. Subsequent investigation is described, demonstrating that a protein coating reduces the free passage of solution across the PMP membrane.
© The Author(s) 2015.
Anemia and red blood cell (RBC) transfusions are both associated with morbidity and mortality after cardiac surgery. Patients with the lowest hematocrit (HCT) values during cardiopulmonary bypass (CPB) are the most likely to receive a transfusion, which results in a double-negative exposure. We aimed to clarify the effects of anemia, transfusion, and their combination to identify which imposes the greatest risk of end-organ dysfunction and mortality.
From November 1, 2004, to November 1, 2009, 7942 patients underwent procedures requiring CPB and did not receive intraoperative or postoperative RBC transfusion, and 1202 received intraoperative RBC transfusion alone. They were divided into 4 groups: intraoperative nadir HCT ≥25% without RBC transfusion, ≥25% with RBC transfusion, <25% without RBC transfusion, and <25% with RBC transfusion. The relationship among HCT, RBC, and outcomes was studied using generalized propensity-score analysis. Outcomes included estimated glomerular filtration rate (eGFR), troponin, ventilatory support time, length of stay, and mortality.
After risk adjustment, comparison of all 4 groups showed that double exposure to anemia (HCT <25%) and RBC transfusion was associated with the highest risk: lowest eGFR (P = .008), highest troponin values (P = .01), longest ventilator requirement (P < .001), longest length of stay (P < .001), and highest mortality (P = .007). Single exposure to either HCT <25% or RBC transfusion alone was associated with the next risk category, and the lowest morbidity risk was associated with neither exposure.
Although single exposure to anemia or RBC transfusion alone was associated with risk, it was generally lower than that of anemia and RBC exposure in combination.