Effect of administration of pre-warmed intravenous fluids on the frequency of hypothermia following spinal anesthesia for Cesarean delivery

Study ObjectiveTo determine whether administration of pre-warmed colloid followed by pre-warmed crystalloid solution prevents the development of hypothermia in patients undergoing Cesarean delivery.DesignRandomized, double-blind, placebo-controlled study.Patients30 parturients scheduled to undergo elective Cesarean delivery during spinal anesthesia.InterventionsPatients assigned to the warmed fluid group (n=15) received pre-warmed colloid with average molecular weight of 70,000 daltons and substitution ratio of 0.55, followed by pre-warmed crystalloid (kept in warmed storage maintained at 41 °C) during surgery. Patients assigned to the unwarmed fluid group (n=15) received non-warmed infusion. All patients received 400 mL before spinal anesthesia followed by another 300 mL before delivery of the newborn. After completion of a 1,000 mL infusion of colloid fluid, acetate Ringer's solution was infused.MeasurementsCore temperature measured at the tympanic membrane, and forearm and fingertip skin temperatures were recorded just after arrival at the operating room (baseline), after administration of spinal anesthesia (spinal ), at incision (incision), at delivery of the newborn (delivery), and at 15, 30, and 45 minutes after delivery. Rectal temperature of the baby, Apgar scores at one and 5 minutes after delivery, and umbilical artery pH were evaluated.Main ResultsCore temperature was significantly higher in the warmed fluid group from the time of delivery to 45 minutes after delivery. Apgar scores at one minute after delivery and umbilical arterial pH were significantly higher in the warmed fluid group.ConclusionAdministration of pre-warmed intravenous colloid followed by crystalloids maintained core temperature during Cesarean delivery and induced higher Apgar scores and umbilical arterial pH.     

Shivering during epidural anesthesia

The authors tested the hypothesis that during epidural anesthesia: 1) shivering-like tremor is primarily normal thermoregulatory shivering; 2) hypothermia does not produce a subjective sensation of cold; and 3) injectate temperature does not influence tremor intensity. An epidural catheter was inserted into ten healthy, nonpregnant volunteers randomly assigned to skin-surface warming below the T10 dermatome (warmed group) or no extra warming (unwarmed group). Each volunteer was given two 30-ml epidural injections of 1% lidocaine (16.0 +/- 4.7 degrees C and 40.6 +/- 0.7 degrees C at the catheter tip), in random order separated by at least 3 h. Skin-temperature gradients (forearm-fingertip) and tympanic membrane and average skin temperatures were recorded; significant vasoconstriction was prospectively defined as a gradient greater than or equal to 4 degrees C. Integrated electromyographic (EMG) intensity was recorded from four upper-body muscles. Overall thermal comfort was evaluated using a visual analog scale. Tympanic membrane temperatures decreased significantly in the unwarmed group (n = 6). Tremor occurred following ten of 12 injections in unwarmed volunteers, but only following one of eight injections in the warmed group. Integrated EMG intensity did not differ significantly following epidural injection of warm and cold lidocaine: tremor started when tympanic membrane temperature decreased about 0.5 degrees C and continued until central temperature returned to within 0.5 degrees C of control. Tremor always was preceded by hypothermia and vasoconstriction in the arms. Thermal comfort increased in both groups after epidural injection, with maximal comfort occurring at the lowest tympanic temperatures.(ABSTRACT TRUNCATED AT 250 WORDS)     

Preoperative combined with intraoperative skin-surface warming avoids hypothermia caused by general anesthesia and surgery

STUDY OBJECTIVES: To evaluate the effects of intraoperative skin-surface warming with and without 1 hour of preoperative warming, in preventing intraoperative hypothermia, and postoperative hypothermia, and shivering, and in offering good conditions to early tracheal extubation. DESIGN: Prospective, randomized, blind study. SETTING: Teaching hospital. PATIENTS: 30 ASA physical status I and II female patients scheduled for elective abdominal surgery. INTERVENTIONS: Patients received standard general anesthesia. In 10 patients, no special precautions were taken to avoid hypothermia. Ten patients were submitted to preoperative and intraoperative active warming. Ten patients were only warmed intraoperatively. MEASUREMENTS AND MAIN RESULTS: Temperatures were recorded at 15-minute intervals. The patients who were warmed preoperatively and intraoperatively had core temperatures significantly more elevated than the other patients during the first two hours of anesthesia. All patients warmed intraoperatively were normothermic only at the end of the surgery. The majority of the patients warmed preoperatively and intraoperatively or intraoperatively only were extubated early, and none had shivering. In contrast, five unwarmed patients shivered. CONCLUSIONS: One hour of preoperative warning combined with intraoperative skin-surface warming, not simply intraoperative warming alone, avoided hypothermia caused by general anesthesia during the first two hours of surgery. Both methods prevented postoperative hypothermia and shivering and offered good conditions for early tracheal extubation.     

Resistive-heating and forced-air warming are comparably effective

Serious adverse outcomes from perioperative hypothermia are well documented. Consequently, intraoperative warming has become routine. We thus evaluated the efficacy of a novel, nondisposable carbon-fiber resistive-heating system. Twenty-four patients undergoing open abdominal surgery lasting approximately 4 h were randomly assigned to warming with 1) a full-length circulating water mattress set at 42 degrees C, 2) a lower-body forced-air cover with the blower set on high, or 3) a three-extremity carbon-fiber resistive-heating blanket set to 42 degrees C. Patients were anesthetized with a combination of continuous epidural and general anesthesia. All fluids were warmed to 37 degrees C, and ambient temperature was kept near 22 degrees C. Core (tympanic membrane) temperature changes among the groups were compared by using factorial analysis of variance and Scheffé F tests; results are presented as means +/- SD. Potential confounding factors did not differ significantly among the groups. In the first 2 h of surgery, core temperature decreased by 1.9 degrees C +/- 0.5 degrees C in the circulating-water group, 1.0 degrees C +/- 0.6 degrees C in the forced-air group, and 0.8 degrees C +/- 0.2 degrees C in the resistive-heating group. At the end of surgery, the decreases were 2.0 degrees C +/- 0.8 degrees C in the circulating-water group, 0.6 degrees C +/- 1.0 degrees C in the forced-air group, and 0.5 degrees C +/- 0.4 degrees C in the resistive-heating group. Core temperature decreases were significantly greater in the circulating-water group at all times after 150 elapsed minutes; however, temperature changes in the forced-air and resistive-heating groups never differed significantly. Even during major abdominal surgery, resistive heating maintains core temperature as effectively as forced air. IMPLICATIONS: Efficacy was similar for forced-air and resistive heating, and both maintained intraoperative core temperature far better than circulating-water mattresses. We thus conclude that even during major abdominal surgery, resistive heating maintains core temperature as effectively as forced air.     

术中保温对患者核心体温的影响

目的　探讨术中保温对患者核心体温的影响。方法　将 4 0例择期全麻下行腹部手术的患者随机分为对照组和加温组 ,各 2 0例。对照组患者术中不采用任何升温装置 ,加温组患者术中采用输液加温器及充气升温毯加温。观察两组患者术中核心体温、失血量和输血量、拔管时间及术后寒战发生率。结果　术毕核心温度 ,加温组为 ( 36 4± 0 4 )℃ ,对照组为 ( 35 3± 0 5 )℃ (t =7 5 4 7,P <0 0 1)。两组患者术中失血量和输血量差异无显著性 (P >0 0 5 )。加温组拔管时间为 ( 18± 6 )min ,短于对照组的 ( 2 6± 10 )min(t=- 3 36 4 ,P =0 0 0 2 )。对照组有 6例患者发生术后寒战 ( 30 % ) ,加温组无术后寒战发生 ( 0 % ,χ2 =7 0 5 9,P =0 0 0 8)。结论　术中采用输液加温器和温毯 ,可有效地维持患者正常体温 ( 36 0℃～ 37 0℃ ) ,从而缩短拔管时间、减少术后寒战发生。     

Effect of postoperative skin-surface warming on oxygen consumption and the shivering threshold

Cutaneous warming is reportedly an effective treatment for shivering during epidural and after general anaesthesia. We quantified the efficacy of cutaneous warming as a treatment for shivering. Unwarmed surgical patients (final intra-operative core temperatures approximately 35 degrees C) were randomly assigned to be covered with a blanket (n = 9) or full-body forced-air cover (n = 9). Shivering was evaluated clinically and by oxygen consumption. Forced-air heating increased mean-skin temperature (mean (SD) 35.7 degrees C (0.4) vs. 33.2 degrees C (0.8); p < 0.0001) and lowered core temperature at the shivering threshold (35.7 degrees C (0.2) vs. 36.4 degrees C(0.2); p < 0.0001). Active warming improved thermal comfort and significantly reduced oxygen consumption from 9.7 (4.4) ml x min(-1) x kg(-1) to 5.6 (1.9) ml x min(-1) x kg(-1) (p = 0.038). However, the duration of shivering was similar in the unwarmed (37 min (11)) and active warming (36 min (10)) groups. Core temperature contributed about four times as much as skin temperature to control of shivering. Cutaneous warming improved thermal comfort and reduced metabolic stress in postoperative patients, but did not quickly obliterate shivering.     

The efficacy of carbon-fiber resistive-heating in prevention of core hypothermia during major abdominal surgery

BACKGROUND: Perioperative hypothermia causes numerous severe complications, such as coagulopathy, surgical wound infections, and morbid myocardial outcomes. For prevention of intraoperative hypothermia, an inexpensive, non-disposable carbon fiber resistive warming system has been developed. METHODS: We evaluated the efficacy of resistive-heating, comparing to circulating-water mattress and forced-air warming system. Twenty four patients undergoing elective abdominal surgery were randomly assigned to warming with: 1) a circulating water mattress, 2) a lower-body forced-air system, or 3) a carbon-fiber, resistive-heating blanket. RESULTS: Tympanic membrane temperature in the first two hours of surgery decreased by 1.9 +/- 0.5 degrees C in the water mattress group, 1.0 +/- 0.6 degree C in the forced-air group, 0.8 +/- 0.2 degree C in the resistive-heating group. The decreases in core temperature by the end of surgery were 2.0 +/- 0.8 degrees C in the water mattress group, 0.6 +/- 1.1 degrees C in the forced-air group, and 0.5 +/- 0.4 degree C in the resistive blanket group, respectively. There was no significant difference in the changes of core temperature between the forced-air group and the resistive-heating group. No side effects related to resistive-heating blanket were observed. CONCLUSIONS: Even during major abdominal surgery, carbon-fiber resistive-heating maintains core temperature as effectively as forced air.     

Hypothermia and excessive sweating following intrathecal morphine in a parturient undergoing cesarean delivery

OBJECTIVE: Intrathecal morphine has been used for the relief of postoperative pain following cesarean delivery. We report a case of postoperative hypothermia down to 33.6 degrees C associated with excessive sweating in patient undergoing elective cesarean delivery under spinal bupivacaine anesthesia who received intrathecal morphine for postoperative pain management. Case Report: A healthy 31-year-old multigravida presented for elective cesarean delivery. Following prehydration with 500 mL hemaccel, she had a subarachnoid block, using hyperbaric bupivacaine 12 mg and morphine 200 microgram, via a 25-gauge Whitacre needle. In the recovery room, 3 hours after induction of spinal anesthesia, the patient's sublingual temperature was 33.6 degrees C and she was noted to be sedated and sweating excessively. During the next 2 hours, the patient was still hypothermic despite active warming. She also complained of severe nausea, vomiting, and moderate pruritis. Following administration of naloxone 400 microgram sedation, vomiting, and pruritis were relieved. Also, the patient experienced excessive shivering, and her body temperature started to increase in association with a concurrent decrease of sweating. The postoperative hypothermia and excessive sweating in our patient may be related to the cephalad spread of the intrathecal morphine within the cerebrospinal fluid (CSF) to reach the level of opioid receptors in the hypothalamus, causing a perturbation of the thermoregulatory center. This effect could be counteracted by administration of naloxone. CONCLUSIONS: Intrathecal morphine may cause disruption of thermoregulation resulting in hypothermia associated with excessive sweating.     

The effect of skin surface warming during anesthesia preparation on preventing redistribution hypothermia in the early operative period of off-pump coronary artery bypass surgery.

OBJECTIVE: Redistribution hypothermia adversely affects hemodynamics and postoperative recovery in patients undergoing cardiac surgery. In off-pump coronary bypass surgery (OPCAB), maintaining the temperature is important because warming by cardiopulmonary bypass is omitted. Pre-warming studies reported earlier showing pre-warming as an effective means of preventing redistribution hypothermia was time consuming since it required at least 1-2h to pre-warm the patients before the surgery. Because pre-warming for such a long time is impractical in clinical practice, this study evaluated the efficacy of active warming during the preanesthetic period for the prevention of redistribution hypothermia in the early operative period of OPCAB. METHODS: After gaining the approval of Institutional Review Board and informed consent from the patients, 40 patients undergoing OPCAB were divided into control and pre-warming groups. The patients in control group (n=20) were managed with warm mattresses and cotton blankets, whereas patients in pre-warming group (n=20) were actively warmed with a forced-air warming device before the induction of anesthesia. Hemodynamic variables and temperature were recorded before anesthesia (Tpre) and at 30 min intervals after anesthesia for 90 min (T30, T60, and T90). RESULTS: Active warming duration was 49.7+/-9.9 min. There were no statistically significant differences in skin temperature, core temperature and hemodynamic variables between the two groups at preinduction period except for mean arterial pressure and central venous pressure. The core temperature at T30, T60, and T90 was statistically higher in pre-warming group than that in control group. Core temperature of six (30%) and seven patients (35%) in control group was reduced below 35 degrees C at T60 and T90, respectively, whereas core temperature of only one patient (5%) in pre-warming group was reduced below 35 degrees C at T90 (P=0.02). CONCLUSIONS: Active warming using forced air blanket before the induction of anesthesia reduced the incidence and degree of redistribution hypothermia in patients undergoing OPCAB. It is a simple method with reasonable cost, which does not delay the induction of anesthesia nor the surgery.     

Persistent hypothermia after intrathecal morphine: case report and literature review

Purpose

To describe a case of persistent hypothermia following spinal anesthesia with intrathecal morphine.

Clinical features

Following elective right total knee arthroplasty under spinal anesthesia with isobaric 0.5% bupivacaine 11?mg, fentanyl 15???g, and preservative-free morphine 150???g, a 57-yr-old female (93.5?kg, 151?cm) developed postoperative hypothermia with a nadir rectal temperature of 33.6°C four hours after surgery. At times, her temperature could not be measured by tympanic, temporal arterial, oral, axillary, or rectal routes. In spite of the low temperature, the patient complained of feeling hot and was diaphoretic without shivering. With the exception of her temperature, her vital signs were normal postoperatively, and aside from hyperglycemia, complete blood count, electrolytes, thyroid-stimulating hormone, serum cortisol, troponin, and twelve-lead electrocardiogram were normal. Her temperature did not respond to warming efforts with a forced-air warming blanket, infusion of warmed intravenous crystalloid, and hourly bladder irrigation with warm saline through an indwelling urinary catheter. Normothermia returned after she received a small dose of sublingual lorazepam eight hours after surgery. The remainder of her postoperative stay was uneventful.

Conclusion

Patients undergoing spinal anesthesia with intrathecal morphine may develop postoperative hypothermia that is resistant to warming measures. This complication may be treated successfully with lorazepam.     

剖宫产术病人硬膜外左旋布比卡因的胎盘转移

目的 评价剖宫产术病人硬膜外左旋布比卡因的胎盘转移情况.方法 择期硬膜外麻醉下剖宫产术病人60例.于L1,2或L2,3间隙进行硬膜外穿刺,穿刺成功后注射0.5%左旋布比卡因5ml(含1:20万肾上腺素)试验剂量,5 min后无脊麻征象后,追加9～12 ml,5 min后再追加1次.娩出时抽取脐动脉血样,进行血气分析;于娩出后l、5min行Apgar评分.选择30例病人,娩出时抽取母体静脉血样和脐静脉血样,采用高效液相色谱法测定血浆左旋布比卡因浓度.结果 在硬膜外注药结束后10～22 min60例胎儿娩出,新生儿Apgar评分均≥7分,脐动脉血Ph值均≥7.25.娩出时母体静脉血与脐静脉血血浆左旋布比卡因浓度分别为0.35 ±0.24、(0.24±0.21)μg/ml,脐静脉血与母体静脉血血浆左旋布比卡因浓度的比值为0.7 ±0.3.结论 宫产术病人硬膜外左旋布比卡因可通过胎盘,脐静脉血与母体静脉血左旋布比卡因浓度的比值为0.7.     

Intraoperative warming therapies: a comparison of three devices.

STUDY OBJECTIVE: To compare the effectiveness of three commonly used intraoperative warming devices. DESIGN: A randomized, prospective clinical trial. SETTING: The surgical suite of a university medical center. PATIENTS: Twenty adult patients undergoing kidney transplantation for end-stage renal disease. INTERVENTIONS: Patients were assigned to one of four warming therapy groups: circulating-water blanket (40 degrees C), heated humidifier (40 degrees C), forced-air warmer (43 degrees C, blanket covering legs), or control (no extra warming). Intravenous fluids were warmed (37 degrees C), and fresh gas flow was 5 L/min for all groups. No passive heat and moisture exchangers were used. MEASUREMENTS AND MAIN RESULTS: The central temperature (tympanic membrane thermocouple) decreased approximately 1 degree C during the first hour of anesthesia in all groups. After three hours of anesthesia, the decrease in the tympanic membrane temperature from baseline (preinduction) was least in the forced-air warmer group (-0.5 degrees C +/- 0.4 degrees C), intermediate in the circulating-water blanket group (-1.2 degrees C +/- 0.4 degrees C), and greatest in the heated humidifier and control groups (-2.0 degrees C +/- 0.5 degrees C and -2.0 degrees C +/- 0.7 degrees C, respectively). Total cutaneous heat loss measured with distributed thermal flux transducers was approximately 35W (watts = joules/sec) less in the forced-air warmer group than in the others. Heat gain across the back from the circulating-water blanket was approximately 7W versus a loss of approximately 3W in patients lying on a standard foam mattress. CONCLUSION: The forced-air warmer applied to only a limited skin surface area transferred more heat and was clinically more effective (at maintaining central body temperature) than were the other devices. The characteristic early decrease in central temperature observed in all groups regardless of warming therapy is consistent with the theory of anesthetic-induced heat redistribution within the body.     

Comparative effects of warming systems applied to different parts of the body on hypothermia in adults undergoing abdominal surgery: A systematic review and network meta-analysis of randomized controlled trials

Study objectiveThe prevention of perioperative hypothermia after anesthesia induction is a critical concern in patients undergoing abdominal surgery. The effectiveness of various warming systems for preventing hypothermia and shivering when applied to specific areas of the body remains undetermined.DesignSystematic review and network meta-analysis.SettingOperating room.InterventionFive electronic databases were searched, including only randomized control trials (RCTs) reporting the effects of warming systems applied to specific body sites on the intraoperative core temperature and postoperative risk of shivering in adults undergoing abdominal surgery. A multivariate random-effects network meta-analysis with a frequentist framework was implemented for data analysis.MeasurementsThe primary outcome was the core body temperature 60 and 120 min after anesthesia induction for abdominal surgery. The secondary outcome was the incidence of postoperative shivering.ResultsThis review comprised a total of 24 RCTs including 1119 patients. At 60 and 120 min after anesthesia induction, a forced-air warming system applied to the upper body (0.3 °C and 95% confidence intervals = [0.3 to 0.4], 1.0 °C [0.7 to 1.3]), lower body (0.4 °C [0.3 to 0.5], 0.9 °C [0.5 to 1.2]), and underbody (0.5 °C [0.5 to 0.6], 1.2 °C [0.9 to 1.6]) was superior to passive insulation in terms of core body temperature regulation. Compared with passive insulation, the forced-air warming system applied to the lower body (odds ratio = 0.06) or underbody (0.44) and the electric heating blanket to the lower body (0.02) or the whole body (0.07) significantly reduced the risk of shivering.ConclusionsThe results of this NMA revealed that forced-air warming with an underbody blanket effectively elevates core body temperatures in 60 and 120 min after induction of anesthesia and prevents shivering in patients recovering from abdominal surgery.     

Shortening the discharging time after total hip replacement under combined spinal/epidural anesthesia by actively warming the patient during surgery.

BACKGROUND: To compare passive thermal insulation by reflective blankets with forced-air active warming on the efficacy of normothermia maintenance and time for discharging from the recovery room after combined spinal/epidural anesthesia for total hip arthroplasty. METHODS: DESIGN: Prospective, randomized study. SETTING: Inpatient anesthesia at three University Departments of orthopedic surgery. PATIENTS: 50 ASA physical status I-III patients, who were scheduled for elective total hip arthroplasty. INTERVENTIONS: Patients received combined spinal/epidural anesthesia (CSE) with intrathecal injection of 15 mg of 0.5% hyperbaric bupivacaine. All procedures started 8-10 a.m., and operating room temperature was maintained between 21-23 degrees C, with relative humidity ranging between 40-45%. As warming therapy patients received either passive thermal insulation of the trunk, the two upper limbs and the unoperated lower limb with reflective blankets (group passive, n = 25), or forced-air active warming of the two upper limbs (group active, n = 25). Core temperature was measured before CSE placement (baseline), and then every 30 min until recovery of normothermia. RESULTS: Demographic data, duration of surgery, intraoperative blood losses, and crystalloid infusion were similar in the two groups. Arterial blood pressure decreased in both groups compared with baseline values, while no differences in heart rate were observed during the study. Core temperatures in passive group patients decreased more markedly than in actively warmed patients, with a 1 degree C difference between the two groups at the end of surgery (p < 0.0005). At recovery room entry seven patients in group active (24%) and 16 patients in group passive (64%) showed a core temperature < 36 degrees C (p < 0.01). Achievement of both discharging criteria and normothermia required 32 +/- 18 min in active group and 74 +/- 52 min in passive group (p < 0.0005). CONCLUSIONS: Forced-air cutaneous warming allows the anesthesiologist to maintain normothermia during combined spinal/epidural anesthesia for total hip replacement even if the convective blanket is placed on a relatively small skin surface with reflex vasoconstriction. Maintaining core normothermia decreased the duration of postanesthesia recovery and may, therefore, reduce costs of care.     

Spinal Anesthesia Speeds Active Postoperative Rewarming

Background: 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.

Methods: 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 [degree sign] Celsius and patients were covered with surgical drapes. However, no other active warming was applied during operation. Ambient temperatures were maintained near 20 [degree sign] Celsius. After operation, patients were warmed with a full-length, forced-air cover set to 43 [degree sign] Celsius. Shivering, when observed, was treated with intravenous meperidine.

Results: 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 [degree sign] Celsius and 34.1 +/- 0.4 [degree sign] Celsius, respectively, in patients given spinal and general anesthesia. After operation, however, core temperatures increased significantly faster (1.2 +/- 0.1 [degree sign] Celsius/h vs. 0.7 +/- 0.2 [degree sign] Celsius/h, mean +/- SD; P <0.001) in patients given spinal anesthesia. Consequently, patients given spinal anesthesia required less time to rewarm to 36.5 [degree sign] Celsius (122 +/- 28 min vs. 199 +/- 28 min; P < 0.001).     

Effectiveness of forced air warming after pediatric cardiac surgery employing hypothermic circulatory arrest without cardiopulmonary bypass

STUDY OBJECTIVE: To evaluate the effectiveness of forced-air warming compared to radiant warming in pediatric cardiac surgical patients recovering from moderate hypothermia after perfusionless deep hypothermic circulatory arrest. DESIGN: Prospective unblinded study. SETIING: Teaching hospitals. PATIENTS: 24 pediatric cardiac surgical patients. INTERVENTION: Noncyanotic patients undergoing repair of atrial or ventricular septal defects were cooled by topical application of ice and rewarmed initially in the operating room by warm saline lavage of the pleural cavities. On arrival at the intensive care unit (ICU), patients were warmed by forced air (n = 13) or radiant heat (n = 11). The time, heart rate, and blood pressure at each 0.5 degrees C increase in rectal temperature were measured until normothermia (36.5 degrees C) to determine the instantaneous rewarming rate. MEASUREMENTS AND MAIN RESULTS: Baseline characteristics were not different in the two groups. The mean (+/- SD) age was 5.6 +/- 3.4 years, weight was 20 +/- 8 kg, esophageal temperature for circulatory arrest was 25.7 +/- 1.3 degrees C, and duration of circulatory arrest was 25 +/- 11 minutes. The mean core temperature on arrival at the ICU was 29.9 +/- 1.3 degrees C and ranged from 26.1 to 31.5 degrees C. The mean rewarming rate for each 0.5 degrees C was greater (p < 0.05) for forced-air (2.43 +/- 1.14 degrees C/hr) than radiant heat (2.16 +/- 1.02 degrees C/hr). At core temperatures <33 degrees C, the rewarming rate for forced-air was 2.04 +/- 0.84 degrees C/hr and radiant heat was 1.68 +/- 0.84 degrees C/hr (p < 0.05). At core temperatures > or = 33 degrees C, the rewarming rate for forced air was 2.76 +/- 1.20 degrees C/hr and radiant heat was 2.46 +/- 1.08 degrees C/min (p = 0.07). Significant determinants of the rewarming rate in a multivariate regression model were age (p < 0.001), temperature (p < 0.05), time after arrival to the intensive care unit (p < 0.05), pulse pressure (p < 0. 05) and warming device (p < 0.001). The duration of ventilatory support and ICU length of stay was not different in the two groups. CONCLUSIONS: Both forced-air and radiant heat were effective for rewarming moderately hypothermic pediatric patients. When core temperature was less than 33 degrees C, the instantaneous rewarming rate by forced air was 21% faster than by radiant heat.     

Phenylephrine in the prevention of hypotension following spinal anesthesia for cesarean delivery

STUDY OBJECTIVE: Phenylephrine and ephedrine were compared in the prevention of maternal hypotension following spinal anesthesia for elective cesarean delivery. DESIGN: Randomized, double-blind trial. SETTING: Obstetric suite at a university-affiliated hospital. PATIENTS: Sixty healthy patients electively scheduled for cesarean delivery under spinal anesthesia. INTERVENTIONS: Patients were randomly assigned to receive either ephedrine (n = 29) in 10 mg intravenous (IV) bolus injections or phenylephrine (n = 31) in 80 microgram IV bolus injections to maintain systolic blood pressure (SBP) above 100 mmHg. MEASUREMENTS AND MAIN RESULTS: Maternal venous, umbilical artery, and umbilical vein blood gases were measured, and neonatal Apgar scores and Early Neonatal Neurobehavior Scale scores were assessed. In the ephedrine group, umbilical artery pH was 7.28 +/- 0.01 (mean +/- SEM), umbilical artery partial pressure of carbon dioxide (PCO2) was 56.6 +/- 1.4 mmHg, and umbilical artery base deficit was 2.2 +/- 0.04 meq. In the phenylephrine group, umbilical artery pH was 7.32 +/- 0.01, umbilical artery PCO2 was 52.1 +/- 1.3 torr, and umbilical artery base deficit was 0.38 +/- 0.35 meq. There were significant differences between the groups in mean umbilical artery pH, PCO2, and base deficit, although all values obtained were within normal limits. There were no significant differences between the groups in the remaining acid-base values, neonatal Apgar scores, Early Neonatal Neurobehavior Scale scores, or frequency of maternal nausea and vomiting. CONCLUSIONS: Phenylephrine is as effective as ephedrine in the treatment of maternal hypotension, and when used in small incremental bolus injections, it appears to have no adverse neonatal effects in healthy, nonlaboring parturients.     

Intraoperative clonidine administration to neurosurgical patients

The goals of this two-part study were to determine the dose of clonidine to prevent postoperative shivering after mild hypothermia and to evaluate the effect of clonidine on recovery from anesthesia in patients undergoing surgery for intracranial lesions. We enrolled 48 patients undergoing elective supratentorial neurosurgical procedures into one of two studies. In study 1 (n=14) we determined the ED50 of clonidine to prevent postoperative shivering after mild hypothermia (35 degrees C) using Dixon's up-and-down method. Clonidine dose for the first study patient was 3 microg/kg. The dose was then adjusted in 1-microg/kg increments for the following patients. Shivering was assessed for 1 h postoperatively. Study 2 (n=34) was a prospective, randomized, double-blind, placebo controlled study to evaluate the effect of 3 microg/kg clonidine on recovery from anesthesia. At the beginning of dural closure, patients randomly received a 15-min infusion of either clonidine or normal saline. Recovery variables were studied for 2 h after the end of anesthesia. The ED50 of clonidine to prevent shivering was 1.1 +/- 1.5 microg/kg in neurosurgical patients whose target core temperature was 35 degrees C at the end of surgery. Compared with saline, 3 microg/kg of clonidine administered to neurosurgical patients 1 h before the end of anesthesia did not delay emergence from anesthesia nor did it have clinically significant sedative or hemodynamic effects. Our results imply that clonidine may be used in neurosurgical patients to prevent postoperative shivering after mild hypothermia.     

Warmed humidified inspired oxygen accelerates postoperative rewarming

STUDY OBJECTIVE: To investigate the efficacy of warmed, humidified inspired oxygen (O(2)) for the treatment of mildly hypothermic postoperative patients. DESIGN: Prospective, randomized, unblinded clinical trial. SETTING: Postanesthesia care unit in a tertiary care hospital. PATIENTS AND INTERVENTIONS: 30 ASA physical status I, II, and III patients following intraabdominal surgical procedures were randomly assigned to receive either routine O(2) therapy (control group, n = 15), or warmed (42 degrees C) humidified O(2) (treatment group, n = 15) for the initial 90 postoperative minutes. MEASUREMENTS: Core (tympanic) temperature, dry mouth score and shivering score. MAIN RESULTS: Tympanic temperature was similar in both groups on admission ( approximately 35.8 degrees C). Rewarming rate in the first postoperative hour was greater in the treatment group (0.7 +/- 0.1 degrees C. hr(-1)) compared to the control group (0.4 +/- 0.1 degrees C. hr(-1)) (p = 0.03). Patients receiving the warmed, humidified O(2) had a lower incidence of dry mouth compared to the control group (p = 0.03). The incidence of shivering was low and similar in both groups. CONCLUSIONS: Warming and humidifying inspired O(2) hastens recovery from hypothermia in postoperative patients.     

Temperature monitoring and management during neuraxial anesthesia: an observational study

Temperature monitoring and thermal management are rare during spinal or epidural anesthesia because clinicians apparently restrict monitoring to patients with an expected risk of hypothermia. This implies that anesthesiologists can predict patient thermal status without monitoring core temperature. We therefore, tested the hypotheses that during neuraxial anesthesia: 1) amount of core hypothermia depends on the magnitude and duration of surgery; 2) temperature monitoring and thermal management are used selectively in patients at high risk of hypothermia; and 3) anesthesiologists can estimate patient thermal status. We evaluated thermal status on arrival in the recovery room along with intraoperative thermal management and monitoring in 120 patients. Anesthesiologists were asked if their patients were hypothermic (<36 degrees C). There was no correlation between the magnitude or duration of surgery and initial postoperative core temperature in unwarmed patients. Temperature monitoring and thermal management were not used selectively in high-risk patients. Initial postoperative tympanic membrane temperatures were <36 degrees C in 77% of patients and <35 degrees C in 22%. Body temperature was monitored intraoperatively in 27% of the patients and forced-air warming was used in 31%. Anesthesiologists failed to accurately estimate whether their patients were hypothermic. Our results suggest that temperature monitoring and management during neuraxial anesthesia is currently inadequate. IMPLICATIONS: In this observational study, we evaluated core temperatures and intraoperative thermal management in patients undergoing spinal or epidural anesthesia. Hypothermia was common, however, rarely detected either by temperature monitoring or estimates by anesthesiologists. In addition, it was not treated with active warming. Consequently, temperature monitoring and management have to be done during neuraxial anesthesia.