Cardiopulmonary responses during the cooling and the extracorporeal life support rewarming phases in a porcine model of accidental deep hypothermic cardiac arrest

Abstract

BackgroundThis study aimed to assess cardiac and pulmonary pathophysiological responses during cooling and extracorporeal life support (ECLS) rewarming in a porcine model of deep hypothermic cardiac arrest (DHCA). In addition, we evaluated whether providing a lower flow rate of ECLS during the rewarming phase might attenuate cardiopulmonary injuries.MethodsTwenty pigs were cannulated for ECLS, cooled until DHCA occurred and subjected to 30 min of cardiac arrest. In order to assess the physiological impact of ECLS on cardiac output we measured flow in the pulmonary artery using Doppler echocardiography as well as a modified thermodilution technique using the Swan-Ganz catheter (injection site in the right ventricle). The animals were randomized into two groups during rewarming: a group with a low blood flow rate of 1.5 L/min (LF group) and a group with a normal flow rate of 3.0 L/min (NF group). The ECLS temperature was adjusted to 5 °C above the central core. Cardiac output, hemodynamics and pulmonary function parameters were evaluated.ResultsDuring the cooling phase, cardiac output, heart rhythm and blood pressure decreased continuously. Pulmonary artery pressure tended to increase at 32 °C compared to the initial value (20.2 ± 1.7 mmHg vs. 29.1 ± 5.6 mmHg, p = 0.09). During rewarming, arterial blood pressure was higher in the NF than in the LF group at 20° and 25 °C (p = 0.003 and 0.05, respectively). After rewarming to 35 °C, cardiac output was 3.9 ± 0.5 L/min in the NF group vs. 2.7 ± 0.5 L/min in LF group (p = 0.06). At the end of rewarming under ECLS cardiac output was inversely proportional to the ECLS flow rate. Moreover, the ECLS flow rate did not significantly change pulmonary vascular resistance.DiscussionUsing a newly developed experimental model of DHCA treated by ECLS, we assessed the cardiac and pulmonary pathophysiological response during the cooling phase and the ECLS rewarming phase. Despite lower metabolic need during hypothermia, a low ECLS blood flow rate during rewarming did not improved cardiopulmonary injuries after rewarming.ConclusionA low ECLS flow rate during the rewarming phase did not attenuate pulmonary lesions, increased blood lactate level and tended to decrease cardiac output after rewarming. A normal ECLS flow rate did not increase pulmonary vascular resistance compared to a low flow rate. This experimental model on pigs contributes a number of pathophysiological findings relevant to the rewarming strategy for patients who have undergone accidental DHCA.

Use of Extracorporeal Membrane Oxygenation in Patients with Refractory Cardiac Arrest due to Severe Persistent Hypothermia: About 2 Case Reports and a Review of the Literature

“…Optimal rewarming speed is ill-defined in the literature. A proposed maximum speed of 4 °C/h has been proposed [15] while maintaining a temperature gradient between patient and ECMO of maximum 10 °C [16]. An animal study performed on a pig model compared two ECMO flow regimes (1.5 L/min vs. 3 L/min) and two different temperature goals (5 degrees Celsius above body temperature versus 38 degrees Celsius throughout the resuscitation).…”

“…Admission arterial gas analysis showed a severe mixed acidosis associated with hypoxia: pH 6.98, PaCO 2 57, and PaO 2 49. Laboratory testing showed anemia with Hb 9.8 g/dL (13)(14)(15)(16)(17)(18), a thrombocytopenia at 65000/mm 3 (150-440 000), and leucopenia with a total white cell count of 2470/mm 3 (3.5-11). Coagulation disorders were also present.…”

“…The arterial blood gas analysis showed a severe acidosis with a pH of 6.95, a PaCO 2 of 26 mmHg, and hyperoxia at 155. Lactic acidosis was present with a first value of 20 mmol/L (<2) as well as a severe anemia with Hb 3 g/dL (13)(14)(15)(16)(17)(18). Concentrated red blood cells were administered to maintain Hb above 8.5 g/L.…”

Extracorporeal membrane oxygenation for accidental deep hypothermia—current challenges and future perspectives

“…There are significant differences in rewarming strategies among reports, while the optimal speed of rewarming and ECLS flow are still to be established. Animal studies on a porcine model of accidental deep hypothermia with cardiac arrest revealed that low ECLS flow does not attenuate post-rewarming pulmonary lesions, but decreases cardiac output (25). On the other hand, also in a porcine model, it has been shown that a high temperature delta between the core temperature and ECLS increases lung injury (26).…”

On the footsteps of Hippocrates, Sanctorius and Harvey to better understand the influence of cold on the occurrence of COVID-19 in European countries in 2020

“…Hypoxia activates aerobic glycolysis and results in lactate production, muscular pain and decrease sensibility of the skin, all signs clinically observed in patients with ischemic limbs due to arterial thrombosis [ 23 ]. Acute or chronic exposure to cold temperature also elicits vasoconstriction of pulmonary arteries, as shown in humans [ [24] , [25] , [26] ], in various mammals [ [27] , [28] , [29] ], and also in broilers showing signs of pulmonary hypertension (PAH), such as larger diameter of the main pulmonary artery and thicker pulmonary artery wall [ 30 ].…”