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Assessment of an Earlobe Arterialized Blood Collector in Microgravity
... The basic functionality and operability required was achieved with all prototypes, including earlobe incision, blood collection, and blood sample storage for analyses. It was successfully subjected to validation of operability in microgravity ( 7 ). ...
... Having a wide range of cartridges, the i-STAT w is capable of providing accurate testing for blood gases, electrolytes, chemistries, hematology, and cardiac markers. All EABC versions use the technique of arterialized earlobe blood collection ( 7 ). With the adaptation of the EABC to enable its use in conjunction with the i-STAT w cartridges, there were minor changes in the procedure for blood collection and analysis. ...
... The required tests are shock and vibration tests, measurements and mass proprieties, low and high pressure and temperature tests, humidity test and offgassing evaluation [20]. To confirm its suitability for space use, the following tests were applied: ...
The coming decades will see a large increase in the numbers of people who will have the opportunity to go into space, whether on traditional Earth-orbiting space stations, tourist spaceflights or proposed space hotels. In addition, humans are likely to be spending longer periods of time in the microgravity of space and the reduced gravity environments found on the moon and Mars, with plans for long-duration spaceflight to reach the red planet and habitation of a moon colony. The anatomy, physiology and psychology of humankind are shaped by the gravity we are subject to on Earth, and it is known that the removal or reduction of this force can have a detrimental effect on our health and wellbeing. Therefore, all steps must be taken to monitor these aspects. Currently, there is no safe and acceptable method to collect arterial blood in space, which can be used to obtain valuable blood gas and blood component variables. This chapter will outline the development of a method for safely collecting arterialized blood in space, the research and steps taken to ensure its suitability and applicability, in preparation for this growing presence of humans in space.
Techniques for sampling arterialised capillary blood from the finger pulp and the earlobe were first described over two decades ago but, although close agreement between arterial values and earlobe samples has been demonstrated in normal subjects, this technique is not in common usage.
Forty patients with chronic lung disease and a wide range of arterial blood gas values were studied. Simultaneous earlobe and arterial samples were drawn with the patient at rest and analysed in the same blood gas analyser. The respiratory function laboratory staff in 50 UK hospitals with a respiratory department were telephoned and asked whether the technique was used in their hospital and the reasons, if known, for not adopting it.
Earlobe and arterial blood gas tensions agreed closely over a wide range of values of arterial pH, PCO2 (mean difference 0.21, 95% confidence intervals -0.24 to +0.67 kPa) and PO2 (mean difference -0.17, 95% confidence intervals -1.09 to +0.75 kPa), especially at arterial PO2 values lower than 8 kPa. Of 50 UK centres surveyed 18% used the arterialised earlobe technique and 4% had plans to introduce it. Reasons for not using it were lack of knowledge in 64%, no blood gas analyser in 6%, the technique was considered inaccurate in 4%, and insufficient staff in 4%.
Although earlobe blood gas analysis is sufficiently accurate to be reliably substituted for arterial sampling in routine clinical practice, most centres in the UK do not use the technique. The main reasons for this appear to be lack of knowledge of its existence and uncertainty over its accuracy.
This study was designed to validate the utility of a commercial portable clinical blood analyzer (PCBA) in ground-based studies and on the space shuttle. Ionized calcium, pH, electrolytes, glucose, and hematocrit were determined. Results agreed well with those from traditional laboratory methods, and the PCBA demonstrated good between-day precision for all analytes. In-flight analysis of control samples revealed differences in one analyte (sodium). There were few changes in crew members' results during flight, and these were expected. Potassium increased in flight compared with before flight, and potassium, pH, and hematocrit decreased after flight. Ionized calcium was decreased in flight and on landing day. Changes during flight were likely related to sample collection technique. Postflight changes likely reflected the fluid redistribution that occurs after exposure to weightlessness. These data confirm that the PCBA is a reliable instrument for most analytes, and can provide important medical data in remote locations, such as orbiting spacecraft.
PO2 in capillary blood was compared with arterial PO2 under different conditions.PO2 in capillary blood from the hyperemic earlobe at rest and during exercise compares favorably with arterial PO2, while discrepancy is rather large when capillary blood at rest is sampled from the warmed finger-tip. For PCO2, good accordance was found regardless of the site of sampling.In circulatory collapse, PO2 in capillary blood does not accurately reflect arterial PO2, even if sampled at the earlobe.At oxygen tensions above 200 mm Hg accordance is very poor and the capillary method is thus unsuitable for determining true anatomic shunt.
The accuracy of arterialized blood samples both at rest and during exercise is described in comparison to simultaneous arterial blood samples. The technique was found to be reliable and sufficiently accurate for clinical exercise testing, with no significant differences for Po2 or Pco2 between the two methods.
A technique is described for obtaining good samples of arterialized ear lobe blood both at rest and during exercise on a cycle ergometer. The method has been validated against simultaneously obtained arterial samples, and the accuracy for Pco2, Po2 and pH has been found adequate for clinical and physiological investigations.
In this study we investigated the possibility of obtaining accurate values of arterial Po(2) from specimens of capillary blood stored in glass capillary tubes and measured in an oxygen microelectrode. It has been shown that Po(2) measurements made on the Radiometer oxygen microelectrode are as accurate as those made on the macroelectrode and that the storage of blood is as satisfactory in glass capillary tubes as in glass syringes. The important feature in obtaining accurate values for arterial Po(2) is the choice of the capillary bed and its method of preparation for sampling. If the ear lobe is massaged with thurfyl nicotinate (Trafuril) it is possible to obtain values of Po(2) from the capillary blood which are in close agreement with arterial Po(2) in normal, hyperoxic, and shocked vasoconstricted patients.
The prescription of long-term oxygen (LTOT) is underpinned by the measurement of arterial PO2, generally obtained by radial artery puncture. This test is commonly associated with patient discomfort and a test that is reliable, well-tolerated and non-invasive would be advantageous. Cutaneous oximetry has not proved sufficiently accurate. Arterialized earlobe capillary sampling has been proposed, with some authors stating that it is under-utilized. However, to date studies have yielded conflicting results and the clinical utility remains uncertain. Our regional oxygen service based at a specialist respiratory hospital undertook a prospective study of consecutive patients with chronic respiratory disease undergoing assessment for LTOT. Simultaneous radial artery and arterialized earlobe sampling was performed. Rigorous steps were taken to ensure optimal arterialization of the earlobe samples. Agreement between arterial and arterialized PO2 and PCO2 was compared using the Bland-Altman method. One hundred patients were studied. Procedural difficulties (insufficient sample or air in sample) were similar for both procedures, however clotting occurred more frequently in arterialized earlobe samples. Sixty-four sample pairs were available for comparison. The bias and limits of agreement between arterialized and arterial PO2 were wide, mean (+/- 2 SD), -048 (-2.05-1.09) kPa. The bias and limits of agreement for PCO2 were smaller. Using the absolute criterion (arterial PO2 < 7.3 kPa), 9/55 (16%) patients would receive oxygen inappropriately based on the arterialized earlobe sample. Conversely, no patients would have been denied LTOT. Radial artery puncture gave rise to significantly greater discomfort (P < 0.0001) and level of concern (P < 0.0001). Patient preference strongly favoured arterialized earlobe sampling. However, despite rigorous attention to arterialization earlobe sampling was insufficiently accurate to replace radial artery puncture in the prescription of LTOT.