ECC Suggested Readings
February 2025
Igor Yankin DVM, DACVECC
I currently serve as a Clinical Assistant Professor in Small Animal Emergency and Critical Care at Texas A&M University. Additionally, I founded VetEmCrit.com and Academy.VetEmCrit.com, platforms that provide evidence-based clinical decision support tools and calculators for emergency veterinarians. My professional interests include electrolyte and acid-base disorders, point-of-care ultrasound, shock, extracorporeal purification therapies, and mechanical ventilation. Outside of work, I am the proud owner of a leopard tortoise, a bearded dragon, a ball python, a Siberian cat, and eight chickens.
A paper that I recently liked…
Mild hypothermia is associated with altered volume kinetic parameters of an intravenous crystalloid fluid bolus in healthy isoflurane-anesthetized cats
Gelendi S, Yiew XT, Bateman S, Gerken K, Kuo KW, Ravis WR, Johnson AK, Liao PT.
Am J Vet Res. 2024 Dec 23:1-10. doi: 10.2460/ajvr.24.09.0279.
Paper Commentary
The study design
This month, I’ve chosen an elegant paper that ranks among my top favorite articles from the past three years. This experimental study explores the effects of hypothermia (~35°C or 95°F) on fluid kinetics and the size of the central compartment (i.e., the "primary distribution space") of intravenous crystalloid boluses in healthy, anesthetized cats.
The study background
Small animal practitioners often anecdotally report a lack of response to fluid resuscitation in hypothermic cats. Additionally, mild to moderate hypothermia has been associated with increased urine production (cold diuresis) in many mammals, though this phenomenon is not well-documented in feline species.
Study considerations
Using a two-volume fluid space kinetic model, the authors demonstrated that body weight, body temperature, and end-tidal isoflurane concentrations significantly influence the central compartment in cats. Specifically, both hypothermia and higher isoflurane concentrations independently increased the size of the central compartment (i.e., reduced the effective circulating volume). In clinical patients, this increase in the central compartment likely contributes to reductions in blood pressure (which was notably lower in the hypothermic group) and cardiac output (not measured in this study).
Furthermore, the study found that hypothermia led to decreased heart rate, lower blood pressure, and reduced end-tidal isoflurane concentrations.
This research provides valuable evidence supporting common clinical practices for managing feline patients with arterial hypotension. In hypothermic cats, arterial hypotension often does not respond well to volume expansion, likely due to the increased size of the central compartment, as shown in this study. As the cat’s body temperature normalizes, fluid stored in capacitance vessels may rapidly re-enter active circulation. This shift can potentially lead to hypervolemia and fluid overload, manifesting as cavitary effusions or even pulmonary edema, despite normal cardiac function.
For bradycardic, hypothermic cats with undetectable Doppler blood pressure, active warming alongside conservative fluid boluses and other resuscitation measures (e.g., vasopressors, which may reduce the central compartment size) is often prioritized. In many cases, normalization of body temperature alone improves perfusion parameters, including heart rate and arterial blood pressure. Based on this study, these improvements can likely be attributed to a reduction in the central compartment, leading to an increase in effective circulating volume and improved perfusion.
Additionally, the study documented that hypothermia did not significantly impact urinary output (i.e., it did not induce "cold diuresis"). This finding is likely due to the effect of general anesthesia promoting antidiuretic hormone (ADH) release.
Takeaways
This study provides valuable experimental evidence that aligns with my clinical approach to resuscitating hypothermic cats —specifically, using very conservative fluid resuscitation until hypothermia is corrected. However, it's important to note that this study was conducted in healthy cats under general anesthesia, which may not fully represent clinical patients presenting in shock. Further research is needed to confirm these findings in a clinical population of cats. I highly recommend reading the original article to delve into these fascinating physiological concepts and gain a deeper understanding of this significant experimental research.
