Impact of Systemic Hypothermia Degree on Postoperative Outcomes in Adult Cardiac Surgery: A Retrospective Observational Study

Abstract

Objective: To study the effect of different levels of therapeutic hypothermia during cardiopulmonary bypass (CPB) on postoperative characteristics such as cerebrovascular events, blood loss, weaning from mechanical ventilation, and discharge from the intensive care unit. Methods: Data from 108 patients (aged between 19 and 78 years) who had cardiac surgery between November 2023 and July 2024 at Queen Alia Heart Institute (QAHI) were analyzed retrospectively. Core temperature was measured continuously by a nasopharyngeal thermistor probe. Data was collected using a special form designed for the purpose of this study. Patients were divided into three groups according to the lowest temperature utilized during CPB: Group one: Mild hypothermic CPB (Temperature ranged between 36° C and 33 ° C), Group two: Moderate hypothermic CPB (Temperature ranged between 33 ° C and 30 °C). Group three: Deep hypothermic CPB (temperature less than 30 ° C). Intraoperative characteristics (duration of surgery, duration of cardiopulmonary bypass, aortic clamp time, and haemodynamics) and postoperative characteristics (blood loss, extubation, cerebrovascular events, renal impairment and mortality) were compared between the three groups. A p-value of < 0.05 is considered statistically significant. Results: The average temperature during cardiopulmonary bypass was 33.4 ± 1.3 º C and ranged from 28 º C to 36 º C. Mild hypothermia was utilized in 58 (54%) of patients, moderate hypothermia in 43 patients (40%), and deep hypothermia in 7 patients (6%). Average postoperative blood loss in patients who underwent mild and moderate therapeutic hypothermia was around 379 millilitres and 416 millilitres, respectively; whereas patients who underwent severe hypothermic bypass had an average of 564 millilitres of postoperative blood loss. The correlation between temperature and amount of blood loss was not statistically significant (p-value=0.2). Average durations of cardiopulmonary bypass and aortic clamp times were longer in deep hypothermia (98 ± 49 minutes and 67± 40.1 minutes, respectively) than in mild hypothermia (81 minutes and 43 minutes, respectively). Hypothermia had a statistically significant correlation with time of mechanical ventilation (P-value=0.016) and length of intensive care unit stay (P-value=0.001). There were fewer incidences of cerebrovascular events, postoperative renal impairment, and mortality, with deep hypothermic bypass (group 3) as compared with the mild and moderate hypothermic bypass patients (groups 1 and 2). Low cardiac output syndrome was more common when deep hypothermic bypass was utilized. Conclusion: The use of hypothermia during cardiac surgery with CPB was associated with a lower incidence of perioperative cerebrovascular complications and increased hospital length of stay.