Abstract
Accurate measurements of blood gases and acid-base status require an array of sophisticated laboratory equipment that is typically not available during field research; such is the case for many studies on the stress physiology, ecology and conservation of elasmobranch fish species. Consequently, researchers have adopted portable clinical analysers that were developed for the analysis of human blood characteristics, but often without thoroughly validating these systems for their use on fish. The aim of our study was to test the suitability of the i-STAT system, the most commonly used portable clinical analyser in studies on fish, for analysing blood gases and acid-base status in elasmobranchs, over a broad range of conditions and using the sandbar shark (Carcharhinus plumbeus) as a model organism. Our results indicate that the i-STAT system can generate useful measurements of whole blood pH, and the use of appropriate correction factors may increase the accuracy of results. The i-STAT system was, however, unable to generate reliable results for measurements of partial pressure of oxygen (PO2) and the derived parameter of haemoglobin O2 saturation. This is probably due to the effect of a closed-system temperature change on PO2 within the i-STAT cartridge and the fact that the temperature correction algorithms used by i-STAT assume a human temperature dependency of haemoglobin-O2 binding; in many ectotherms, this assumption will lead to equivocal i-STAT PO2 results. The in vivo partial pressure of CO2 (PCO2) in resting sandbar sharks is probably below the detection limit for PCO2 in the i-STAT system, and the measurement of higher PCO2 tensions was associated with a large measurement error. In agreement with previous work, our results indicate that the i-STAT system can generate useful data on whole blood pH in fishes, but not blood gases.
Highlights
The i-STAT system® (Abbot Point of Care Inc., Princeton, NJ, USA), a portable clinical analyser, is gaining acceptance as a means of blood analysis in biological studies on a variety of fish species (Stoot et al, 2014)
Our results indicate that the i-STAT system with the CG4+ cartridge is a useful tool to measure pH in sandbar shark whole blood, but replicate measurements are recommended if accurate mean values are required
The i-STAT system underestimated pH by ∼0.1 pH units, a correction for this bias seems possible with the linear equations we provide
Summary
The i-STAT system® (Abbot Point of Care Inc., Princeton, NJ, USA), a portable clinical analyser, is gaining acceptance as a means of blood analysis in biological studies on a variety of fish species (Stoot et al, 2014) This is despite the fact that the i-STAT system was originally developed for the analysis of human blood, : (i) samples in the test cartridges are. Conservation Physiology Volume 3 2015 heated to 37°C upon analysis; (ii) results are calculated based on algorithms derived for human blood characteristics (this includes temperature corrections); and (iii) the detection limits of the sensors within the cartridge are optimized for parameter ranges expected in air-breathing mammals These potential sources of measurement bias require a thorough validation of the i-STAT system when used to analyse blood samples obtained from fishes, taking into account species and sampling conditions. The simple availability of a method cannot justify its implementation; the choice of a suitable method should depend on the quality of the produced data, in terms of precision and accuracy, and on the tolerance of the specific research question to variation in these quality criteria
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