Heated intravenous fluids alone fail to prevent hypothermia in cats under general anaesthesia

Abstract

Objectives The objective was to evaluate the clinical efficiacy of a constant rate infusion of heated fluid as the sole means of preventing intraoperative hypothermia in cats. Methods This randomised, prospective, clinical study was conducted at a university teaching veterinary hospital. Female cats (American Society of Anesthesiologists [ASA] grade I) undergoing elective surgery by laparotomy under general anaesthesia (acepromazine 0.05 mg/kg SC; morphine 0.2 mg/kg IV; propofol IV titrated, isoflurane 2% in 100% oxygen) were randomised in two groups. Both groups were infused with fluid (NaCl 0.9%, 5 ml/kg/h) either at room temperature (control group) or prewarmed at 43°C (warmed group) using an Astoflo Plus eco (Stihler Electronic) fluid heating device. No other heating device was used. Temperature, heart rate, respiratory rate and SpO₂ were evaluated after induction (T0) and every 15 mins for 1 h (T15, T30, T45, T60). Mean arterial blood pressure was recorded every 30 mins (T0, T30 and T60). Results Thirty-four female cats (ASA grade I) were enrolled in the study. There was no difference in age, weight, propofol dose or room temperature (22.4 ± 1.1°C vs 22.0 ± 1.5°C; P = 0.363) between control and warmed groups, respectively. In both groups, oesophageal temperature significantly decreased during anaesthesia ( P <0.0001). The temperature decrease after 1 h was -3.6 ± 0.7°C in the warmed group and was not significantly different from the control group (-3.4 ± 0.7°C; P = 0.307). The slopes of the temperature decrease did not significantly differ between the two groups (-0.058 ± 0.013°C/min vs -0.060 ± 0.010°C/min for the control and warmed groups, respectively; P = 0.624). Conclusions and relevance This study provides clinical evidence that a constant rate infusion of heated fluid alone fails to prevent intraoperative hypothermia in cats. The low infusion rate (5 ml/kg/h) could partly explain the ineffectiveness of this active warming device in minimising or delaying the onset of intraoperative hypothermia.

Figure 1

The decrease in oesophageal temperature in cats undergoing abdominal surgery. All cats were anaesthetised and subjected to a constant rate infusion of NaCl 0.9% at room temperature (control group, n = 17, black squares) or warmed to 43°C (warmed group, n = 17, open circles) using an Astoflo Plus eco (Stihler Electronic) fluid heating device. Symbols indicate a P value <0.05 compared with values measured at T0 using ANOVA for repeated measures followed by a bilateral Bonferroni–Dunnett post-hoc test in control (*) and warmed (°) groups, respectively