Agreement between arterial and central venous blood pH and its contributing variables in anaesthetized dogs with respiratory acidosis

Objective To determine the accuracy of variables that influence blood pH, obtained from central venous (jugular vein) blood samples compared with arterial (dorsal pedal artery) samples in anaesthetized dogs with respiratory acidosis. Study design Prospective, comparative, observational study. Animals A group of 15 adult male dogs of various breeds weighing 17 (11-42) kg [median (range)]. Methods Dogs were premedicated with buprenorphine (0.03 mg kg(-1)) and medetomidine (0.01 mg kg(-1)) administered intramuscularly by separate injections, anaesthetized with propofol intravenously to effect and maintained with isoflurane in 50% air-oxygen. Arterial and central venous catheters were placed. After 15 minutes of spontaneous breathing, arterial and central venous blood samples were obtained and analysed within 5 minutes, using a bench-top gas analyser. Differences between arterial and central venous pH and measured variables were assessed using Wilcoxon rank sum test and effect size (r: matched-pairs rank-biserial correlation) was calculated for each comparison. The agreement (bias and limits of agreement: LoAs) between arterial and central venous pH and measured variables were assessed using Bland-Altman; p < 0.05. Data are reported as median and 95% confidence interval. Results Arterial blood pH was 7.23 (7.19-7.25), and it was significantly greater than central venous samples 7.21 (7.18-7.22; r = 0.41). Agreement between arterial and venous pH was acceptable with a bias of 0.01 (0.002-0.02) and narrow LoAs. PCO2 [arterial 54 (53-58) mmHg, 7.2 (7.1-7.7) kPa; venous 57 (54-62) mmHg, 7.6 (7.2-8.3)kPa], bicarbonate ion concentration and base excess did not differ between samples; however, agreement between arterial and venous PCO2 was not acceptable with a bias of -2 (-5 to 0) mmHg and wide LoAs. Conclusions and clinical relevance Blood pH measured from central venous (jugular vein) blood is an acceptable clinical alternative to arterial blood (dorsal pedal artery) in normovolaemic anaesthetized dogs with respiratory acidosis.