Accuracy and precision of the portable StatPal II and the laboratory-basedNOVA Stat Profile 1 for measurement of pH, Pco(2), and Po-2 in equine blood

Objective-To investigatthe accuracy and precision of the portable, battery- powered StatPal II and the laboratory-based NOVA StatProfile 1 blood gas an d pH analyzers for use in analysis of equine blood. Study Design-Patient sample comparison and whole blood tonometry. Sample Population-Patient sample comparison: 125 arterial or venous blood s amples from 49 healthy, awake, or anesthetized horses or ponies. Tonometry: venous blood samples from II healthy Thoroughbred horses. Materials and Methods-Arterial and venous blood taken from awake and anesth etized equine patients was placed in an ice-water bath, then analyzed withi n 30 minutes of collection. Bias and limits of agreement between analyzers in measurement of pH, Pco(2,) and Po-2 were calculated according to the met hod of Bland and Altman. Tonometry, using analyzed gases with a range of Po -2 of 28 to 286 mm Hg and Pco(2) of 21 to 85 mm Hg, was performed on equine whole blood or blood with abnormally high (55%) or low (20%) hematocrit. S amples were introduced directly from the tonometer into the analyzers. Inac curacy (% of target value) and imprecision (coefficient of variation) were determined for each instrument. In addition, results of analysis of blood s amples introduced into the analyzers at 36 degrees C, 0 to 3 degrees C, and 22 degrees C were compared. Results-In the patient sample comparisons, bias between analyzers (StatPal- NOVA) for measurement of Po-2 less than 60 mm Hg was - 0.33 +/- 6.2 mm Hg ( (x) over bar +/- 2 SD) and for Po, between 60 and 110 mm Hg bias was - 1.48 +/- 9.2 mm Hg. Bias was 46.5 +/- 67 mm Hg (significantly different from bi as at the lower Po-2 levels) for measurement of Po-2 values of 111 to 505 m m Hg, and at Po-2 values greater than 110 mm Hg, bias increased with increa sing Po-2. During the course of the study, a significant shift in bias betw een instruments occurred for Pco(2) and pH measurement, coincident with a c hange of Pco(2) and pH electrodes in the NOVA and use of a new lot of StatP al sensors. Bias (StatPal-NOVA) for Pco(2) before and after the electrode c hange was - 3.74 +/- 4.2 and - 0.88 +/- 6.8 mm Hg, and bias for pH before a nd after the electrode change was 0.026 +/- 0.034 and - 0.024 +/- 0.038. Th e change in bias was significant (P < .05). In the whole blood tonometry tr ials, mean recovered values of Pco(2) and Po, from blood with a normal hema tocrit ranged from 94% to 109% of target values for StatPal and from 98% to 107% for NOVA. Imprecision ranged from 3.3% to 5.3% for StatPal and from 2 .2% to 4.3% for NOVA. With extremes of hematocrit (55% and 20%), StatPal's mean recovered Pco(2) values were 115% and 112% of the target value of 21 m m Hg, whereas NOVA's recovered Pco(2) values were similar to those recovere d from samples with normal hematocrit. Introduction of cold blood samples ( 0 to 3 degrees C) into StatPal resulted in Pco(2) readings that were approx imately 2 mm Hg lower than those of 22 degrees C and 36 degrees C samples ( P < .05). No other effects of sample temperature were found for either inst rument. Conclusions-StatPal and NOVA are of similar accuracy and demonstrate accept able precision for measurement of Pco(2) and Po-2 in equine blood with valu es in the normal arterial and venous range. Mean recovered values during to nometry differed by as much as 10% between instruments, indicating that the y should not be used interchangeably for a single patient or for a group of subjects in a research setting. Clinical Relevance-The StatPal is a portable blood gas analyzer of acceptab le accuracy and precision, for clinical or investigational work in horses. (C) Copyright 1999 by The American College of Veterinary Surgeons.