Pre-warming Prevents Hypothermia in Elective Cesarean Section
Condition: Hypothermia
MeSH terms: Hypothermia
Study type: Interventional

Summary: 
      Background: Hypothermia is common during general and regional anesthesia even when active
      warming measures are taken. The existing literature shows that, in pregnant patients, the use
      of forced air-warming during cesarean section under spinal anesthesia does not prevent
      maternal hypothermia. Therefore, this study aimed to establish the efficacy of a pre-warming
      system, initiated 30 minutes before the onset of spinal anesthesia and during surgery, in
      pregnant women subjected to elective cesarean delivery.

      Methods: Forty healthy pregnant patients undergoing elective cesarean section with spinal
      anesthesia were allocated to the control group (Gcont, n = 20), without the use of a thermal
      gown, and to the gown group (Ggown, n = 20), with the use of a thermal gown in the
      preoperative care unit, 30 minutes before spinal anesthesia installation and during surgery.
      After the anesthesia, the thermal gown was moved from the regular position and placed over
      the chest and upper limbs, as an upper body blanket, and maintained throughout the study. The
      following variables were observed: preoperative and operative room temperature, hemoglobin
      saturation, heart rate, arterial pressure, tympanic temperature in the preoperative care unit
      room (baseline) and at 0, 15, 30, 45 and 60 minutes after spinal anesthesia. Repeated Measure
      ANCOVA compared temperatures of each group, adjusted for baseline values.
    

Detailed description: 
      Introduction Body temperature decreasing following the onset of general or regional
      anesthesia is caused by a core-to-peripheral redistribution of heat, as demonstrated by
      several previous studies. Perioperative hypothermia and its complications have been widely
      studied in patients subjected to non-obstetric surgery; however, literature on the obstetric
      population is rare, although the incidence of intraoperative shivering can be as high as 60%
      in these patients. A previous study based on the use of forced air-warming unit during the
      preoperative and intraoperative periods in patients subjected to cesarean delivery observed a
      lower incidence of hypothermia and shivering in patients given epidural anesthesia when
      compared to those given spinal anesthesia.

      The forced air system is by far the most commonly used intraoperative warming approach and
      has an admirable safety record. However, the problem with blanket-forced air warming,
      circulating-water garments, or water mattresses is that it is impossible to change their
      position on the bed, which can be uncomfortable, especially if the patient is waiting in a
      sitting position.

      The Bair Paws Gown® presents an air warming system that provides patient-controlled comfort
      warming in the pre and postoperative setting. The same gown offers effective clinical warming
      during surgery involving the head, neck, knees or extremities. The air-warming flows through
      the gown, from knees to head or from head to knees, and allows the patient to be seated with
      gown covering the area between knees and neck.

      Therefore, we designed a study to establish the efficacy of a pre-warming system that keeps
      the garment throughout the perioperative period, without interruption, initiated 30 minutes
      before the induction of spinal anesthesia for elective cesarean delivery. The aim of this
      study was to test the hypothesis that active warming 30 minutes before spinal anesthesia
      should better prevent a fall in pregnant body temperature. A secondary goal evaluated the
      incidence of shivering, as well as thermal comfort during the procedure.

      Methods After obtaining Institutional Review Board approval (record 388/08) and written
      informed consent from patients, 40 healthy ASA physical status I or II pregnant women
      presenting for scheduled cesarean delivery under spinal anesthesia were enrolled in this
      prospective, randomized study.

      Randomization (1:1) was based on a random computer generated code that was maintained in
      sequentially numbered opaque envelopes.

      Eligible participants were pregnant women between 18 and 40 years of age, with singleton
      pregnancy and gestation longer than 37 weeks, scheduled for elective cesarean section.
      Patients with fever and/or infectious conditions, a familial history of potential malignant
      hyperthermia, body mass index (BMI) values below 18.5 kg.cm-2 or above 36 kg.cm-2, thyroid
      disorders, dysautonomia, Raynaud's syndrome, and those in labor were excluded.

      Participants remained seated in the preoperative care unit until they were allocated to one
      of the following groups: control group (Gcont n = 20), in which surgery was performed without
      the use of a thermal gown, or gown group (Ggown n = 20), in which surgery was performed while
      the patients were covered with a thermal gown (Bair Paws Standard Warming Gown 810 model with
      a Bair Hugger, model 850 warming unit) with forced-air flow at 40ºC in the preoperative care
      unit 30 minutes before the spinal anesthesia. When the patients were transferred to the
      operative room, the warming gown was switched off for the gown group; however, the gown was
      maintained in place and, when the pregnant women arrived in operative room, the system was
      switched back on and the gown was moved to the anterior part of the body, covering chest and
      upper limbs as an upper body blanket, which was maintained until the end of surgery.

      In the operative room, a venous cannula was inserted into the forearm, and an infusion of
      Ringer's lactate solution fluids at 37ºC was initiated. Spinal anesthesia was administered
      using 10 mg of hyperbaric bupivacaine, combined with 10 µg of fentanyl and 80 µg of morphine.
      Puncture was performed at level L1-L2 or L2-L3 of the lumbar vertebra, and surgery began when
      the sensory blockage reached a level between the T4 and T6 thoracic vertebra, as established
      by the loss of sensitivity to needle pricks. Intraoperative hydration used 500 ml of 40ºC
      Ringer's lactate solution before fetal extraction and 800 µg metaraminol was provided via
      slow infusion or 400 µg was delivered as an IV bolus whenever the arterial pressure decreased
      by more than 25% of the baseline value. Following fetal extraction but before the end of
      surgery, 1,000 ml of Ringer's lactate solution with 20 IU of oxytocin was infused.

      Demographic variables included age, weight, height and BMI. Patients were monitored with
      hemoglobin peripheral saturation (SpO2), heart rate (HR), noninvasive systolic arterial
      pressure (SAP) and diastolic arterial pressure (DAP). The tympanic temperature was measured
      by means of a digital thermometer (Techline Model TS 201, Sao Paulo, SP, Brazil) Ambient
      temperature was maintained approximately at 22ºC according to wall thermostat (ABNT NBR 7256
      - Brazilian regulatory and normalization Agency).

      All data were assessed at baseline, 30 minutes before induction of spinal anesthesia; T0
      (immediately after the spinal anesthesia); and T15, T30, T45, and T60 (15, 30, 45, and 60
      minutes following the onset of spinal anesthesia, respectively).

      In addition, postoperative data were assessed during the admission to the post-anesthesia
      care unit (PACU). Shivering was evaluated according to Wrench's scale that uses: 0 - no
      shivering; 1 - one or more symptoms of piloerection, peripheral vasoconstriction, and
      peripheral cyanosis without any other cause and without visible muscular activity; 2 -
      visible muscular activity confined to one muscle group; 3 - visible muscular activity in more
      than one muscle group; and 4 - gross muscular activity involving the entire body. Thermal
      discomfort according to Horn's verbal numerical scale: 0 - worst imaginable cold, 100 -
      insufferably hot and adverse effects during the immediate postoperative period were also
      registered. Moreover, patients received 12.5-25 mg meperidine whenever their shivering scores
      were equal to or greater than three.

      Sample size was calculated to be 20 participants to ensure that a difference of 0.5ºC could
      be detected at significance level of 5%, with a statistical power of 80%, assuming the
      standard deviation of differences to be 0.5ºC.

      Data are presented as mean and standard deviation or median and interquartile interval
      (25-75) according to tested distribution (Shapiro-Wilk test). Analysis of covariance for
      repeated measures (ANCOVA), adjusted for baseline values, compared tympanic temperatures
      between the groups. Statistical significance was established at p < 0.05, and the statistical
      analysis was performed using SPSS (Statistical Package for the Social Sciences) software
      version 20.
    

Intervention name(s): pre-warming
Intervention type(s): Device
Intervention description(s): warming patients 30 minutes prior to anesthesia
Allocation: Randomized
Intervention model: Parallel Assignment
Masking: None (Open Label)
Primary purpose: Prevention
Keywords: Hypothermia; Perioperative Care; Anesthesia; Spinal; Rewarming