Shivering

IntroductionMild therapeutic hypothermia has been shown to improve outcome for patients after cardiac arrest and may be beneficial for ischaemic stroke and myocardial ischaemia patients. However, in the awake patient, even a small decrease of core temperature provokes vigorous autonomic reactions-vasoconstriction and shivering-which both inhibit efficient core cooling. Meperidine and skin warming each linearly lower vasoconstriction and shivering thresholds. We tested whether a combination of skin warming and a medium dose of meperidine additively would reduce the shivering threshold to below 34 degrees C without producing significant sedation or respiratory depression.MethodsEight healthy volunteers participated on four study days: (1) control, (2) skin warming (with forced air and warming mattress), (3) meperidine (target plasma level: 0.9 mug/ml), and (4) skin warming plus meperidine (target plasma level: 0.9 mug/ml). Volunteers were cooled with 4 degrees C cold Ringer lactate infused over a central venous catheter (rate asymptotically equal to 2.4 degrees C/hour core temperature drop). Shivering threshold was identified by an increase of oxygen consumption (+20% of baseline). Sedation was assessed with the Observer's Assessment of Alertness/Sedation scale.ResultsControl shivering threshold was 35.5 degrees C +/- 0.2 degrees C. Skin warming reduced the shivering threshold to 34.9 degrees C +/- 0.5 degrees C (p = 0.01). Meperidine reduced the shivering threshold to 34.2 degrees C +/- 0.3 degrees C (p ConclusionA combination of meperidine and skin surface warming reduced the shivering threshold to 33.8 degrees C +/- 0.2 degrees C via an additive interaction and produced only very mild sedation and no respiratory toxicity.

Background and purposeReducing body temperature can prolong tolerance to ischemic injury such as stroke or myocardial infarction, but is difficult and uncomfortable in awake patients because of shivering. We tested the efficacy and safety of the alpha-2-adrenergic agonist dexmedetomidine for suppressing shivering induced by a rapid infusion of cold intravenous fluids.MethodsTen subjects received a rapid intravenous infusion of two liters of cold (4°C) isotonic saline on two separate test days, and we measured their core body temperature, shivering, hemodynamics and sedation for two hours. On one test day, fluid infusion was preceded by placebo infusion. On the other test day, fluid infusion was preceded by 1.0 μg/kg bolus of dexmedetomidine over 10 minutes.ResultsAll ten subjects experienced shivering on placebo days, with shivering beginning at a mean (SD) temperature of 36.6 (0.3)°C. The mean lowest temperature after placebo was 36.0 (0.3)°C (range 35.7-36.5°C). Only 3/10 subjects shivered on dexmedetomidine days, and the mean lowest temperature was 35.7 (0.4)°C (range 35.0-36.3°C). Temperature remained below 36°C for the full two hours in 6/10 subjects. After dexmedetomidine, subjects had moderate sedation and a mean 26 (13) mmHg reduction in blood pressure that resolved within 90 minutes. Heart rate declined a mean 23 (11) bpm after both placebo and dexmedetomidine. Dexmedetomidine produced no respiratory depression.ConclusionDexmedetomidine decreases shivering in normal volunteers. This effect is associated with decreased systolic blood pressure and sedation, but no respiratory depression.

PurposeTo compare two analytical methods for the estimation of the shivering onset inflection point, segmental regression and visual inspection of data, and to assess the test-retest reliability and validity of four metrics of shivering measurement; oxygen uptake (V̇O2), electromyography (EMG), mechanomyography (MMG) and bedside shivering assessment scale (BSAS).MethodsTen volunteers attended three identical experimental sessions involving passive deep-body cooling via cold water immersion at 10 °C. V̇O2, EMG, and MMG were continuously assessed, while the time elapsed at each BSAS stage was recorded. Metrics were graphed as a function of time and rectal temperature (Tre). Inflection points for intermittent and constant shivering were visually identified for every graph and compared to segmental regression.ResultsExcellent agreement was seen between segmental regression and visual inspection (ICC, 0.92). All measurement metrics presented good-to-excellent test-retest reliability (ICC's > 0.75 and 0.90 respectively), with the exception of visual identification of intermittent shivering for V̇O2 measurement (ICC, 0.73) and segmental regression for EMG measurement (ICC, 0.74). In the assessment of signal-to-noise ratio (SNR), EMG showed the largest SNR at the point of shivering onset followed by MMG and finally V̇O2.ConclusionsSegmental regression provides a successful analytical method for identifying shivering onset. Good-to-excellent reliability can be seen across V̇O2, EMG, MMG, and BSAS, yet given the observed lag times, SNRs, along with known advantages/disadvantaged of each metric, it is recommended that no single metric is used in isolation. An integrative, real-time measure of shivering is proposed.

BackgroundPost Spinal Anesthesia Shivering (PSAS) is common and linked to increased morbidity. While various methods exist to prevent it, no study has compared Nefopam and Ondansetron. This study aims to compare Ondansetron and Nefopam in preventing PSAS.MethodsA prospective, randomized, controlled, and double-blind trial was conducted in the operating room of a tertiary university hospital from April 5, 2021 to April 30, 2022. It included patients aged between 18 and 65 years scheduled for surgery under spinal anesthesia. Patients received either 8 mg of Ondansetron or 20 mg of Nefopam administered intravenously over 30 min before spinal anesthesia. Main outcome measures included the number and grades of shivering episodes post spinal anesthesia at 15-minute intervals until post-anesthesia care unit discharge. Secondary outcomes included number of episodes of hypotension, bradycardia, nausea and/or vomiting. Tympanic temperature and pain at the injection site were also recorded.ResultsThe study included 150 patients, evenly divided between the two groups. The Ondansetron group had a higher incidence of shivering compared to the Nefopam group (23.9 % vs. 16 %; p = 0.038), as well as higher incidences of hypotension (16 % vs. 5.3 %; p = 0.035) and bradycardia (13.3 % vs. 2.7 %; p = 0.016). The Ondansetron group had a significantly lower incidence of nausea and vomiting (12 % vs. 1.3 %; p = 0.010). More patients in the Nefopam group (45.3 %) reported pain during drug infusion.ConclusionsNefopam seems to be more effective than Ondansetron in preventing PSAS with fewer cardiovascular side effects. However, Ondansetron reduces the incidence of nausea and vomiting and causes no pain during administration.