Organ blood flow and O₂ transport during hypothermia (27°C) and rewarming in a pig model

Abstract

New Findings What is the central question of this study?Absence of hypothermia‐induced cardiac arrest is a strong predictor for a favourable outcome after rewarming. Nevertheless, detailed knowledge of preferences in organ blood flow during rewarming with spontaneous circulation is largely unknown. What is the main finding and its importance?In a porcine model of accidental hypothermia, we find, despite a significantly reduced cardiac output during rewarming, normal blood flow and O2 supply in vital organs owing to patency of adequate physiological compensatory responses. In critical care medicine, active rewarming must aim at supporting the spontaneous circulation and maintaining spontaneous autonomous vascular control. Abstract The absence of hypothermia‐induced cardiac arrest is one of the strongest predictors for a favourable outcome after rewarming from accidental hypothermia. We studied temperature‐dependent changes in organ blood flow and O2 delivery (DnormalO2) in a porcine model with spontaneous circulation during 3 h of hypothermia at 27°C followed by rewarming. Anaesthetized pigs (n = 16, weighing 20–29 kg) were randomly assigned to one of two groups: (i) hypothermia/rewarming (n = 10), immersion cooled to 27°C and maintained for 3 h before being rewarmed by pleural lavage; and (ii) time‐matched normothermic (38°C) control animals (n = 6), immersed for 6.5 h, the last 2 h with pleural lavage. Regional blood flow was measured using a neutron‐labelled microsphere technique. Simultaneous measurements of DnormalO2 and O2 consumption (V̇normalO2) were made. During hypothermia, there was a reduction in organ blood flow, V̇normalO2 and DnormalO2. After rewarming, there was a 40% reduction in stroke volume and cardiac output, causing a global reduction in DnormalO2; nevertheless, blood flow to the brain, heart, stomach and small intestine returned to prehypothermic values. Blood flow in the liver and kidneys was significantly reduced. Cerebral DnormalO2 and V̇normalO2 returned to control values. After hypothermia and rewarming there is a significant lowering of DnormalO2 owing to heart failure. However, compensatory mechanisms preserve O2 transport, blood flow and V̇normalO2 in most organs. Nevertheless, these results indicate that hypothermia‐induced heart failure requires therapeutic intervention.

Study of the Effects of 3 h of Continuous Cardiopulmonary Resuscitation at 27°C on Global Oxygen Transport and Organ Blood Flow

“…In addition, low core temperature per se prolongs end-organ survival during hypothermic CPR (Gilbert et al, 2000;Mark et al, 2012;Wanscher et al, 2012). In an intact pig model, we validated these findings and also documented that O 2 transport (Filseth et al, 2010) and tissue blood flow (Valkov et al, 2019) are maintained during 1-3 h of stable hypothermia (25 • -27 • C) as well as during rewarming. However, to date, the effects of prolonged (hours) CPR on global DO 2 and organ blood perfusion have not been assessed in an intact hypothermic animal model.…”

“…We previously reported the detailed methods for hemodynamic monitoring, immersion cooling, and blood flow measurements using the porcine animal model (Valkov et al, 2019). Briefly, after fasting the animals overnight, premedication was induced by an intramuscular bolus of ketamine hydrochloride (20 mg kg −1 ), midazolam (30 mg), and atropine (1 mg), and anesthesia was induced by a bolus infusion of fentanyl (10 µg kg −1 ) and pentobarbital-sodium (10 mg kg −1 ) in an ear vein.…”

“…It is well documented that cooling with spontaneous circulation slows metabolic rate and, therefore, reduces CO in parallel with reductions in global O 2 transport (DO 2 ) and O 2 consumption (VO 2 ) (Black et al, 1976;Kondratiev et al, 2006;Valkov et al, 2019). In addition, low core temperature per se prolongs end-organ survival during hypothermic CPR (Gilbert et al, 2000;Mark et al, 2012;Wanscher et al, 2012).…”

Extracorporeal rewarming from experimental hypothermia: Effects of hydroxyethyl starch versus saline priming on fluid balance and blood flow distribution

“…In the present study, global D O 2 was significantly elevated in the HES group compared with the saline group after rewarming to 37 • C, whereas globalV O 2 remained similar between groups. Furthermore, the O 2 extraction ratio remained <50% in both groups throughout ECC rewarming, lower than the reported critical value of 60-70%, at whicḣ V O 2 becomes dependent on D O 2 (Valkov et al, 2019) . A significantly increased TTW of the lung, skeletal muscle and both kidneys in the rats receiving saline implies a higher degree of tissue oedema in this group.…”

“…In ECC rewarming from accidental hypothermia, however, the majority of the literature originates from retrospective studies and case reports. Extrapolation of approaches for ECC rewarming of accidental hypothermia patients from studies in cardiac surgery patients might be unwarranted, as these patient groups differ in intravascular volume status, circulatory function and the duration of the hypothermic insult (Valkov et al, 2019). Recommendations concerning the choice of fluids in ECC rewarming of accidental hypothermia patients are lacking in both American (Vanden Hoek et al, 2010) and European (Truhlár et al, 2015) guidelines, and seem to vary between institutions, with some reporting sole use of crystalloids (Weuster et al, 2016) and others using addition of colloid to the prime (Suominen, Vallila, Hartikainen, Sairanen, & Korpela, 2010) or continuous colloid infusion during CPB (Farstad et al, 2006).…”