Redistribution of body heat decreases core temperature more during general than regional anesthesia. However, the combination of anesthetic- and sedative-induced inhibition may prevent effective upper-body thermoregulatory responses even during regional anesthesia. The extent to which each type of anesthesia promotes hypothermia thus remains controversial. Accordingly, the authors evaluated intraoperative core hypothermia in patients assigned to receive spinal or general anesthesia. They also tested the hypothesis that the efficacy of active postoperative warming is augmented when spinal anesthesia maintains vasodilation.
Patients undergoing lower abdominal and leg surgery were randomly assigned to receive general anesthesia (isoflurane and nitrous oxide; n = 20) or spinal anesthesia (bupivacaine; n = 20). Fluids were warmed to 37 degrees C and patients were covered with surgical drapes. However, no other active warming was applied during operation. Ambient temperatures were maintained near 20 degrees C. After operation, patients were warmed with a full-length, forced-air cover set to 43 degrees C. Shivering, when observed, was treated with intravenous meperidine.
The mean spinal analgesia level, which was at the sixth thoracic level during surgery, remained at the T12 dermatome after 90 min after operation. Core temperatures did not differ significantly during surgery and decreased to 34.4 +/- 0.5 degrees C and 34.1 +/- 0.4 degrees C, respectively, in patients given spinal and general anesthesia. After operation, however, core temperatures increased significantly faster (1.2 +/- 0.1 degrees C/h vs. 0.7 +/- 0.2 degrees C/h, mean +/- SD; P < 0.001) in patients given spinal anesthesia. Consequently, patients given spinal anesthesia required less time to rewarm to 36.5 degrees C (122 +/- 28 min vs. 199 +/- 28 min; P < 0.001).
Comparable intraoperative hypothermia during general and regional anesthesia presumably resulted because the combination of spinal anesthesia and meperidine administration obliterated effective peripheral and central thermoregulatory control. Vasodilation increased the rate of core rewarming in patients after operation with residual lower-body sympathetic blocks, suggesting that vasoconstriction decreased peripheral-to-core heat transfer after general anesthesia.
"Interestingly, Szmuk et al.  reported that regidual spinal anesthesia, which maintained lower body vasodilation, significantly increased the rate of core rewarming. Vasodilation facilitates core rewarming in patients after operation with residual lower body sympathetic blocks. "
[Show abstract][Hide abstract] ABSTRACT: Postoperative hypothermia and shivering is a frequent event in patients during cesarean section under spinal anesthesia. We assessed the effect of preoperative warming during cesarean delivery under spinal anesthesia for prevention of hypothermia and shivering.
Forty five patients undergoing elective cesarean section were randomly assigned to three groups. Group F received warmed intravenous fluid (40℃). Group A patients were actively warmed by forced air-warming. Group C was the control group. Forced air-warming and warmed fluid was maintained for the 15 min preceding spinal anesthesia. Core temperature (tympanic membrane) and the skin temperature of arm and thigh were measured and shivering was graded simultaneously.
The core temperature at 45 min decreased less in Groups F and A than Group C (-0.5℃ ± 0.3℃ vs -0.6℃ ± 0.4℃ vs -0.9℃ ± 0.4℃, respectively; P = 0.004). The arm temperature at 15 min and 30 min exhibited a greater increase in Group A than Group F and Group C (P = 0.001 and P = 0.012, respectively). Leg temperature increased similarly among the three groups. The incidence of shivering was significantly less in Group A and Group F than Group C (20%, 13.3%, and 53.3%, respectively; P = 0.035).
Preoperative forced air-warming and warmed fluid prevents hypothermia and shivering in patients undergoing elective cesarean delivery with spinal anesthesia.
Korean journal of anesthesiology 05/2012; 62(5):454-60. DOI:10.4097/kjae.2012.62.5.454
[Show abstract][Hide abstract] ABSTRACT: Resumen La Hipotermia inadvertida se asocia con un aumento de la morbimortalidad potsoperatoria. El objetivo de este estudio descriptivo retrospectivo es determinar la incidencia de hipotermia postoperatoria y su caracterización en base a factores predictores conocidos. Se estudiaron 313 pacientes operados de coordinación para determinar la incidencia de hipotermia postoperatoria (temperatura central (Tc) < 36ºC) y su relación con factores predictores como edad, tipo y grado de invasividad del procedimiento quirúrgico, técnica anestésica y duración de la estadía en sala de operaciones (SO). La incidencia de hipotermia al ingreso a Sala de Recuperación Post Anestésica (SRPA) fue de 67%. Un 20% presentó Tc < o = 35ºC . Al alta un 24% se mantenía en hipotermia. Estos valores son similares a los encontrados, en la literatura internacional en pacientes anestesiados sin la aplicación de medidas activas de calefaccionamiento. No se encontraron diferencias significativas en la incidencia de hipotermia entre las categorías estudiadas con excepción de una incidencia mayor para la Anestesia Regional (AR) con respecto a la Anestesia General (AG) (p = 0.042). Los pacientes > 65 años, los sometidos a AG y/o con estadía en SO > 3 horas, tuvieron períodos de hipotermia más prolongados. Concluimos que la incidencia de hipotermia postoperatoria inadvertida es un problema frecuente en nuestro Servicio. Dado que es difícil predecir qué pacientes desarrollarán hipotermia y en qué magnitud, se hace imprescindible la adopción de medidas de calefaccionamiento y monitorización de la Tc durante el período perioperatorio en todos los pacientes. Summary Unintentional hypothermia is associated with high postoperative morbidity and mortality. The aim of this study is to evaluate the incidence of postoperative hypothermia (core temperature (Tc) <36ºC) and to identity predictor factors to categorized it. We analyzed 313 elective surgical patients and factors such as: age, nature of surgical procedure, anesthetic technique and stay in the operating room (SO). At admission in Post Anesthetic Recovery Room (SRPA) , the hypothermia incidence was 67%. Twenty percent had Tc less than 35ºC, 24% were still with hypothermia when they left the recovery room. These outcomes are the same as in the international studies in anesthetized patients without active warning equipment. There were no statistical differences between several groups, except for higher degree of hypothermia in Regional Anesthesia (AR) Vs General Anesthesia (AG) (p=0.042) Prolonged hypothermia was seen in patients older then 65 years, those whom stayed greater than 3 hours in the operating room and those who had general anesthesia. Unadvertised postoperative hypothermia has a great incidence in our Department. It is difficult to predict whose patient will develop hypothermia and its different degree of severity, so it is essential for us to adopt active warning techniques and Tc monitoring during the preoperative period.
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