E. Delva

Prevention of Intraoperative Hypothermia by Preoperative Skin-Surface Warming

Background:Intraoperative hypothermia initially results from internal redistribution of heat facilitated by anesthesia-induced vasodilatlon. Preinductlon skin-surface warming minimizes postinduction hypothermia in anesthetized volunteers. However, its efficacy might be reduced in surgical situations, because of multiple sources of heat loss. Methods:Intraoperative core and mean skin temperatures were measured during total hip arthroplasty in 16 patients, randomly assigned to be covered preoperatlvely with a warming blanket for ≥90 min (prewarmed group) or not covered (unwarmed group). Results:During the first hour of anesthesia, core temperature decreased more than twice as much in the unwarmed group (−0.7 ± 0.1° C; mean ± SE) than in the prewarmed patients (−0.3 ± 0.1° C). At the end of surgery, core temperature was 36.3 ± 0.1° C in the prewarmed group and 35.2 ± 0.2° C in the unwarmed group. During recovery, seven patients obviously shivered in the unwarmed group and none in the prewarmed group. Conclusions:Preanesthetic skin-surface warming reduces the initial postinductlon hypothermia in surgical patients, preventing intraoperative hypothermia and postoperative shivering even for procedures lasting 3 h or longer.

Oxygen uptake during recovery following naloxone. Relationship with intraoperative heat loss.

The increased metabolic and respiratory demand during naloxone recovery from opioid-based anesthesia could be related to the return of thermoregulation in hypothermic patients and thus be avoided by preventing intraoperative hypothermia. In this study, we measured O2 uptake (VO2) during naloxone-induced recovery in two groups of patients to determine the effect of intraoperative heat loss on postoperative VO2 changes. In seven patients, intraoperative hypothermia was prevented (normothermic group), whereas hypothermia was allowed to develop in seven other patients (hypothermic group). Core and skin temperatures were measured throughout the study to calculate changes in body heat content. Before naloxone antagonism of fentanyl-supplemented anesthesia, core temperature (mean +/- SEM) was 36.8 +/- 0.1 degrees C in the normothermic group and 34.2 +/- 0.2 degrees C in the hypothermic group (P less than 0.001). After titrated administration of naloxone during recovery, VO2 and minute ventilation (VE) increased in the hypothermic group, by 114 +/- 37% and 97 +/- 52% respectively (P less than 0.05), with a three-fold increase in four patients. In the normothermic group, VO2 increased significantly less (25 +/- 5%), without any significant change in VE. The change in VO2 and VE was significantly greater in patients who were hypothermic. VO2 was integrated throughout the recovery period to calculate recovery energy expenditure. Recovery energy expenditure and intraoperative heat loss were highly correlated (r = 0.88; P less than 0.01). This study demonstrates that the metabolic and respiratory stresses associated with naloxone-induced recovery from opioid-based anesthesia depend on the intraoperative heat loss and can therefore be reduced by preventing intraoperative hypothermia.

Pre-induction skin-surface warming minimizes intraoperative core hypothermia.

STUDY OBJECTIVE To test the hypothesis that only one hour of preinduction skin-surface warming decreases the rate at which core hypothermia develops during the first hour of anesthesia. DESIGN Randomized, prospective study. SETTING Operating theater of a university hospital. PATIENTS 16 ASA status I and II adult patients scheduled for laparoscopic cholecystectomy under general anesthesia. INTERVENTIONS Eight patients were assigned to receive forced-air warming for one hour before induction of anesthesia (prewarmed group); the other eight patients were covered only with a wool blanket during a similar preinduction period (control group). MEASUREMENTS AND MAIN RESULTS Tympanic membrane (core) and mean skin-surface temperatures were measured at 15-minutes intervals, starting one hour before induction of anesthesia. Mean skin temperature increased from 34.0 +/- 0.1 C to 37.0 +/- 0.2 degrees C in the pre-warmed group (p < 0.05), but remained unchanged at 34.7 +/- 0.3 degrees C in the control group. Core temperature during the preinduction period did not change significantly in either group. Following induction of anesthesia, core temperature decreased at a rate of 1.1 +/- 0.1 degrees C/hr in the control group, but only 0.6 +/- 0.1 degrees C/hr in the pre-warmed group (p < 0.05). After one hour of anesthesia, six of eight pre-warmed patients had core temperatures of at least 36.5 degrees C, whereas only one of the eight control patients did (p < 0.05). CONCLUSIONS A single hour of preoperative skin-surface warming reduced the rate at which core hypothermia developed during the first hour of anesthesia. Preoperative skin surface warming is particularly helpful during short procedures because redistribution hypothermia is otherwise difficult to treat.

Leg warming minimizes core hypothermia during abdominal surgery.

The efficacy of leg skin warming in preventing hypothermia and shivering was evaluated in two separate prospective, randomized trials in patients undergoing abdominal surgery. In the first trial, 22 patients were randomized to receive no hypothermia prevention (control group) or active warming with an electric warming blanket (electric blanket group). In the second trial 33 patients were randomized to receive no hypothermia prevention (control group) or forced-air warming (Bair Hugger® group) or forced-air warming with insulation of the air blanket from the environment (insulated Bair Hugger® group). The core and skin temperatures were measured and changes in body heat content calculated. In the first trial, core temperature was 34.6 ± 0.3°C at the end of surgery in the control group vs 36.4 ± 0.1°C in the electric warming blanket group (P < 0.001). Shivering occurred in nine control patients and in one warmed patient (P < 0.05). In the second trial, core temperature was 35.1 ± 0.2°C at the end of surgery in the control group, 36.3 ± 0.1°C in the Bair Hugger® group (P < 0.01) and 37.1 ± 0.1°C in the insulated Bair Hugger® group (P < 0.01 versus control; P < 0.05 versus Bair Hugger®). Shivering occurred in one patient of each warmed group and in seven of the control group (P < 0.05). Skin-surface warming limited to the legs provides sufficient heat (ranging 34 to 43 watts) to counterbalance heat losses during abdominal surgery.

Hemodynamic effects of portal triad clamping in humans.

: The hemodynamic effects of portal triad clamping (PTC) were studied in 48 adult patients scheduled for elective liver resection. Prior to hepatic resection the effects of a short period of PTC (3-5 min) were evaluated in all 48 patients: mean arterial pressure increased 21%, whereas pulmonary capillary wedge pressure and cardiac index decreased 10 and 17%, respectively. Systemic vascular resistance increased 48%. In 34 patients a liver resection was performed during PTC and hemodynamic measurements were repeated throughout the duration of liver ischemia, which ranged from 14 to 68 min. Hemodynamic changes occurred in the first 3 min and persisted thereafter. After releasing the clamp, hemodynamic parameters returned to initial values in 3 min. These results confirm that PTC does not induce the cardiovascular collapse in humans that it does in common laboratory animals and demonstrate that humans tolerate PTC for periods up to 1 hr.

Tumor necrosis factor-α in liver transplantation and resection: No evidence for a key role in ischemia-reperfusion injury

Abstract Experimental studies have shown that liver ischemia-reperfusion induces Kupffer cell activation and tumor necrosis factor- α (TNF α ) release. The aim of this work was to determine whether severe hepatic ischemia and subsequent reperfusion triggers TNF α release in man. Serum TNF α was measured before and 3, 10, 30, 60, 120 min after revascularization and postoperatively at day 1 and 2 in 11 patients with orthotopic liver transplantation (group 1 and 4 patients with liver resection with vascular occlusion (group 2). In group 1, TNF α levels decreased during the first few minutes of reperfusion, then increased slightly to peak at 120 min (40 ± 13 pg/ml). Primary non-function occurred in 1 patient in whom low peroperative levels of TNF α levels were measured. In group 2, no significant changes in TNF α levels were observed. These data, in a small number of patients: (a) show that hepatic ischemia reperfusion does not result in major TNF α production; (b) do not support a primary pathogenic role for TNF α in damage after ischemia-reperfusion in humans.

Air embolism during liver resection: an unusual mechanism of entry from a peristaltic pump

A case of venous air embolism occurring during liver resection is reported. Diagnosis was made early from the continuous recording of pulmonary artery pressure. The aetiology was neither surgical nor an obvious discon-nection of a venous line. It was caused by a blockage of the blood filter, resulting in subambient pressure between the filter and a peristaltic pump, leading to aspiration of numerous small air bubbles. The clinical course after replacement of the defective material was uneventful, except for transient postoperative pulmonary oedema.RésuméUn cas d’embolie gazeuse d’origine veineuse survenu lors d’une hépatectomie est rapporté. Le diagnostic précoce a été permis par l’enregistrement continu de la pression artérielle pulmonaire. L’origine de l’embole n’était ni chirurgicale ni une déconnexion évidente sur une voie veineuse, mais une obstruction du filtre à sang provoquant une pression négative entre ce filtre et la pompe péristaltique, à l’origine de l’aspiration de nom-breuses petites bulles d’air. L’évolution clinique une fois le matériel défectueux remplacé fut favorable.

HEMODYNAMIC EFFECTS OF PORTAL TRIAD CLAMPING IN MAN

The hemodynamic effects of portal triad clamping (PTC) were studied in 48 adult patients scheduled for elective liver resection. Prior to hepatic resection the effects of a short period of PTC (3–5 min) were evaluated in all 48 patients: mean arterial pressure increased 21%, whereas pulmonary capillary wedge pressure and cardiac index decreased 10 and 17%, respectively. Systemic vascular resistance increased 48%. In 34 patients a liver resection was performed during PTC and hemodynamic measurements were repeated throughout the duration of liver ischemia, which ranged from 14 to 68 min. Hemodynamic changes occurred in the first 3 min and persisted thereafter. After releasing the clamp, hemodynamic parameters returned to initial values in 3 min. These results confirm that PTC does not induce the cardiovascular collapse in humans that it does in common laboratory animals and demonstrate that humans tolerate PTC for periods up to 1 hr.