Mild hypothermia is associated with altered volume kinetic parameters of an intravenous crystalloid fluid bolus in healthy isoflurane-anesthetized cats.

Objective: To assess the impact of mild hypothermia on the distribution and elimination of an IV crystalloid fluid bolus in healthy anesthetized cats using volume kinetic (VK) analysis.

Methods: 10 adult cats were anesthetized and included in a prospective, randomized, cross-over study. The subjects were maintained either normothermic (38.3 ± -16.9 °C) or mildly hypothermic (35 ± -16.9 °C), with a 7-day washout period between anesthetic episodes. All cats received 20 mL/kg of a balanced isotonic solution (Normosol-R) IV over 20 minutes, following the achievement and stabilization of target temperature. Hemoglobin concentration, PCV, and urinary output were measured at established time points and served as input variables for VK analysis.

Results: Hypothermia was associated with a larger central compartment volume (Vc); higher body weights were associated with an increased Vc and a decreased elimination rate; higher end-tidal isoflurane concentration (ETISO) was associated with an increased Vc and a higher distribution rate constant. Heart rate, blood pressure, and ETISO were significantly lower in the hypothermic group. No statistically significant difference was observed in urinary output between groups.

Conclusions: Body weight, temperature, and ETISO were significant covariates affecting VK parameters. Hypothermia did not induce cold diuresis but was associated with an increase in Vc. The negative relationship between body weight and the elimination rate constant requires further verification. Hypothermia was associated with lower heart rate and blood pressure despite reduced ETISO.

Clinical relevance: Hypothermia was associated with smaller plasma volume expansion from fluid bolus. Fluid dosing based on ideal body weight should be considered to avoid overdosing.