Insulation Strategies for Microwave-Heated Fluid Bags in Small Animal Critical Care and Anesthesia: Enhancing Hypothermia Prevention

Abstract

Perianesthetic hypothermia is a common complication in small animal anesthesia and critical care that contributes to delayed recovery, impaired coagulation, altered drug metabolism, and cardiovascular instability. Warming intravenous crystalloids is one component of multimodal thermal support, but warmed fluid bags lose heat after removal from the heat source. This study evaluated two simple, low-cost insulation materials for preserving the temperature of microwave-heated 0.9% sodium chloride bags. A laboratory experiment was performed using 500 mL and 1000 mL bags of 0.9% sodium chloride heated to approximately
39 °C in an 800 W microwave oven for approximately 38 seconds and 75 seconds, respectively. For each volume, three groups were tested in triplicate: no insulation, a thin foil-lined convenience-store bag, and a commercially available 3 mm aluminum foil bag. Fluid bags were stored in a 25 °C room, and temperatures were recorded over 3600 seconds. Temperature change over time was analyzed with linear mixed-effects models, and final temperatures at 3600 seconds were compared using independent-sample t-tests. In both volume groups, insulated bags retained significantly more heat than uninsulated controls. In the 500 mL model, Treatment, Time, and Treatment × Time were significant. In the 1000 mL model, Time and Treatment × Time were significant, whereas the main effect of Treatment was not. Final-temperature analysis showed significant differences between no insulation and each insulation method in both volumes, but no significant difference between thin and thick insulation. Readily available foil-based insulation materials substantially improved heat retention of microwave-heated 0.9% sodium chloride bags and can serve as adjuncts to perioperative hypothermia-prevention protocols.