The influence of haemorrhage and fluid resuscitation with either Plasma Lyte A or Ringer’s Lactate in Beagle dogs under sevoflurane anaesthesia Part 1: macrocirculation

To compare macrocirculatory effects of haemorrhage followed by fluid resuscitation with Plasma-Lyte A (PA) or Ringer's Lactate (RL) crystalloid solution in dogs under sevoflurane anaesthesia. Single centre, randomized, blinded, experimental study. Twelve adult healthy intact purpose-bred Beagle dogs. Dogs were instrumented under sevoflurane anaesthesia. Heart rate, cardiac output (CO) and mean arterial blood pressure (MAP) were measured at baseline, after removing 30 mL kg -1 of blood over 15 minutes [hypovolaemia (HV)], and after each of two boluses (B1 and B2) of either 10 mL kg -1 PA or RL intravenously over 10 minutes. Data were compared using a linear mixed model with group and timepoints as fixed factors and dog as random factor and corrections for multiple comparisons. A p value < 0.05 was considered significant. There were no significant differences between treatments. Compared to HV, CO was increased in both groups at B1: RL [0.57 (0.23–0.91) L minute -1 (estimated difference ± 95% confidence interval), p < 0.001] and PA (0.37 (0.03–0.7) L minute -1 , p = 0.030) and at B2 (RL: 0.88 (0.54–1.2) and PA [0.66 (0.23–0.91) L minute -1 , both p < 0.001]. The increase of MAP in RL was significant at B1 [15 (1–29) mmHg, p < 0.028] and B2 [16 (2–30) mmHg, p < 0.016] compared to HV, while MAP in PA was not significantly different at B1 [3 (-11–17) mmHg, p = 0.995] and B2 [4 (-9–18) mmHg, p = 0.943] compared to HV. and clinical relevance: In this small experimental study, both fluids tested led to a clinically significant increase in CO. No consistent increase in MAP was observed across fluid types. Alterations in MAP should not be used as a surrogate for flow variables to assess fluid responsiveness.