Relationships between arterial and central venous blood acid-base variables in anaesthetised cats during euvolaemic and hypovolaemic states

Objectives The aim of the study was to determine differences, agreements and correlations of acid-base variables between arterial and venous blood gas in anaesthetised cats in a euvolaemic or hypovolaemic state.Methods A group of six cats was used in a prospective randomised crossover haemorrhage-resuscitation study. Anaesthetised cats underwent three treatments at intervals of 2 months. Each treatment had a controlled haemorrhage phase and a resuscitation phase. The haemorrhage phase is the focus of this study. Arterial (carotid artery) and central venous blood were drawn simultaneously from preplaced catheters before haemorrhage (euvolaemic state; mean +/- SD blood loss 1.3 +/- 0.3 ml/kg for pre-haemorrhage data collection) and soon after controlled haemorrhage (hypovolaemic state; mean +/- SD blood loss 15.8 +/- 9.9 ml/kg). Acid-base variables from arterial and venous blood were compared under euvolaemic and hypovolaemic states as follows: (1) a paired t-test to determine the differences between the two samples; (2) a Bland-Altman plot to evaluate agreement and establish maximum clinically acceptable differences (defined a priori); and (3) Pearson's correlation with least squares linear regression to determine the strength of correlation between the variables.Results The differences in pH and partial pressure of carbon dioxide were statistically significant under euvolaemic and hypovolaemic states but would not alter clinical decision-making. Agreements were clinically acceptable for all acid-base variables, except for the bias observed in the partial pressure of carbon dioxide under a hypovolaemic state. Correlations for all variables were strong under a euvolaemic state but weakened under a hypovolaemic state.Conclusions and relevance Using central venous blood sampling for acid-base analysis was clinically acceptable compared with arterial blood in our haemorrhage-resuscitation cat model during early compensated hypovolaemia. However, the partial pressure of carbon dioxide should be interpreted with caution, especially during hypovolaemia. Further investigation is necessary to determine whether these findings can be translated to critically ill cats.