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PubMed1998

Hypoxemia decreases the shivering threshold in rabbits anesthetized with 0.2 minimum alveolar anesthetic concentration isoflurane.

UNLABELLED: Shivering has been proposed as an etiology of postoperative hypoxemia. The difficulty with this theory is that hypoxemia inhibits shivering in unanesthetized cats, rats, and humans. However, anesthesia inhibits many protective reflexes, including the ventilatory response to hypoxemia. We therefore tested the hypothesis that arterial hypoxemia fails to inhibit shivering in lightly anesthetized rabbits. Rabbits were intubated and instrumented during exposure to surgical concentrations of anesthesia, and anesthesia was then maintained with 0.2 minimum alveolar anesthetic concentration isoflurane. The core was cooled at a rate of 2-3 degrees C/h by perfusing water at 10 degrees C through a colonic thermode. Core temperatures were recorded from the distal esophagus. Sustained, vigorous shivering was considered physiologically significant. The core temperature that triggering significant shivering identified the thermoregulatory threshold for this response. Arterial blood was sampled for gas analysis at the shivering threshold in each rabbit. Hypoxemia linearly reduced the shivering threshold from 36.7 degrees C at 130 mm Hg to 35.4 degrees C at 50 mm Hg (threshold = PaO2.0.019 + 34.3; r2 = 0.49). We failed to confirm our hypothesis: instead, even mild hypoxemia reduced the shivering threshold >1 C. A 1 C decrease in the shivering threshold is likely to prevent or stop most postoperative shivering because it exceeds the reduction produced by many effective anti-shivering drugs. These data do not support the theory that shivering causes postoperative hypoxemia. IMPLICATIONS: Shivering has been proposed as an etiology of postoperative hypoxemia. Our data, in contrast, show that mild hypoxemia inhibits shivering. Shivering is thus unlikely to be a cause of postoperative hypoxemia.

Anesthesia, Inhalation↗
PubMed1994

Shivering following cardiac surgery: predictive factors, consequences, and characteristics.

BACKGROUND: Shivering is common after cardiac surgery and may evoke harmful hemodynamic changes. Neither those changes nor factors increasing probability of shivering are well defined. OBJECTIVES: (1) To identify factors linked with risk of shivering by comparing age, weight, body surface area, gender, intraoperative details, anesthetics, postoperative temperatures, hemodynamics, and therapeutics in shivering vs nonshivering patients. (2) To describe temperatures, hemodynamics, therapeutics, myocardial oxygen consumption correlates (rate-pressure product, heart rate, systemic vascular resistance) in shivering and nonshivering groups, and shivering and nonshivering periods. (3) To characterize the electromyogram to determine whether the tremor is cold-induced. METHODS: A descriptive design with a time series component was used to study a convenience sample of 10 shivering and 10 nonshivering adults for 4 hours during early recovery from cardiac surgery. Pulmonary artery and skin (facial, calf, trunk) temperature were measured every 60 seconds; heart rate and arterial pressure, every 15 minutes; cardiac output, 3 times. Electromyogram was recorded intermittently. Medications and treatments were noted. RESULTS: Lower skin temperature was significantly related to shivering risk. Heart rate was significantly higher initially in shiverers and remained higher by 13.6 beats per minute. Significantly more nitroprusside was used to control arterial pressure before than after shivering. No significant differences were noted between groups in core temperature, age, weight, body surface area, anesthesia type, intraoperative temperature; or surgery, circulatory bypass, or cardiac cross-clamp duration. The electromyogram pattern during shivering was typical of that produced by cold. CONCLUSIONS: These results suggest that true shivering occurs after cardiac surgery. Skin, but not core, temperature and elevated heart rate predict shivering. Shivering may be more likely in hemodynamically unstable patients.

Adult↗
PubMed2002

Shivering endurance and fatigue during cold water immersion in humans.

An important component of survival time during cold exposure is shivering endurance. Nine male and three female healthy and fit subjects [mean (SD) age 24.8 (6.3) years, body mass 71.7 (13.2) kg, height 1.75 (0.10) m, body fat 22.7 (7.4)%] were immersed to the upper chest level in cold water for periods ranging from 105 to 388 min on two occasions to test a prediction of shivering endurance. The water was cooled from 20 to 8 degrees C during the first 15 min of immersion and subsequently rewarmed (<20 degrees C) to elicit a near constant submaximal shivering response. The data were divided according to moderate (M) and high (H) levels of shivering intensity. Respective mean total immersion times were 250 (75) and 199 (80) min ( P=0.086) at different average shivering intensities of 61 (10) and 69 (8)% relative to maximal shivering ( P<0.001). Blood plasma glucose concentration increased during the immersion [from 3.44 (0.54) pre- to 3.94 (0.60) mmol x l(-1) post-immersion ( P=0.037)] and levels were higher during M ( P=0.012). When compared to a model prediction of shivering endurance, shivering activity continued well beyond the predicted endurance times in 18 out of the 24 trials. The average rates of oxygen consumption over the entire immersion period were lower ( P=0.002) during M [0.93 (0.20) l x min(-1)] compared to H [1.05 (0.21) l x min(-1)), and while these rates did not change during the last 90 min of immersion, there was an increase in fat oxidation. There were no trial differences in the average esophageal (T(es)) and mean skin temperatures during the entire immersion period (36.0 and 18.0 degrees C, respectively), yet T(es) decreased ( P=0.003) approximately 0.4 degrees C during the last 90 min of immersion. When the shivering intensity was normalized to account for this decrease, a significant downward trend of approximately 17% x h(-1) in the normalized shivering intensity was found after the predicted end of shivering endurance. These results suggest that shivering drive, and not shivering intensity per se, decreased during the latter stages of the immersion. Underlying mechanisms such as fatigue and habituation for this diminishing cold sensitivity are discussed.

Adaptation, Physiological↗
PubMed1992

[Postoperative shivering: analysis of main associated factors].

This study was carried out in 75 female patients, ranked ASA 1 or 2, during recovery from balanced general anaesthesia. It aimed to find out the main determinants of postoperative shivering and its thermal effects. Skin and oesophageal temperature were recorded every ten minutes. Mean skin and body temperatures, and the intraoperative energy balance were calculated. There was no additional source of heating. Shivering was ranked from 0 to 2. Statistical analysis showed that the starting mean core and body temperatures were the only factors correlated with shivering and its intensity, whereas mean skin temperatures, age and opioid doses were not. Between 33.5 and 36.5 degrees C, there was a linear relationship between the oesophageal temperature at the end of anaesthesia and the incidence of shivering. A decrease of 1 degrees C in core temperature increased the probability of shivering by 33%. At 35.4 degrees C, 50% of patients shivered. There was a homogenous group of patients whose oesophageal temperature at the end of anaesthesia was between 35 and 36 degrees C. In this group, there was no significant difference between starting skin temperatures, whether the patient shivered or not. However, the core temperature of those within that group that did shiver returned to normal levels more quickly than in those that did not shiver. These data underlined the essential role played by core temperature at the end of anaesthesia in postoperative shivering and its intensity, as well as the heat producing value of shivering. It would therefore seem logical to prevent postoperative shivering by avoiding intraoperative hypothermia.

Adult↗
PubMed1998

Epidural anesthesia reduces the gain and maximum intensity of shivering.

BACKGROUND: Shivering can be characterized by its threshold (triggering core temperature), gain (incremental intensity increase), and maximum intensity. The gain of shivering might be preserved during epidural or spinal anesthesia if control mechanisms compensate for lower-body paralysis by augmenting the activity of upper-body muscles. Conversely, gain will be reduced approximately by half if the thermoregulatory system fails to compensate. Similarly, appropriate regulatory feedback might maintain maximum shivering intensity during regional anesthesia. Accordingly, the gain and maximum intensity of shivering during epidural anesthesia were determined. METHODS: Seven volunteers participated on two randomly ordered study days. On one day (control), no anesthesia was administered; on the other, epidural anesthesia was maintained at a T8 sensory level. Shivering, at a mean skin temperature near 33 degrees C, was provoked by central-venous infusion of cold fluid; core cooling continued until shivering intensity no longer increased. Shivering was evaluated by systemic oxygen consumption and electromyography of two upper-body and two lower-body muscles. The core temperature triggering an increase in oxygen consumption identified the shivering threshold. The slopes of the oxygen consumption versus core temperature and electromyographic intensity versus core temperature regressions identified systemic and regional shivering gains, respectively. RESULTS: The shivering threshold was reduced by epidural anesthesia by approximately 0.4 degrees C, from 36.7 +/- 0.6 to 36.3 +/- 0.5 degrees C (means +/- SD; P < 0.05). Systemic gain, as determined by oxygen consumption, was reduced from -581 +/- 186 to -215 +/- 154 ml x min(-1) x degrees C(-1) (P < 0.01). Lower-body gain, as determined electromyographically, was essentially obliterated by paralysis during epidural anesthesia, decreasing from -0.73 +/- 0.85 to -0.04 +/- 0.06 intensity units/degrees C (P < 0.01). However, upper-body gain had no compensatory increase: -1.3 +/- 1.1 units/degrees C control versus 2.0 +/- 2.1 units/degrees C epidural. Maximum oxygen consumption was decreased by one third during epidural anesthesia: 607 +/- 82 versus 412 +/- 50 ml/min (P < 0.05). CONCLUSIONS: These results confirm that regional anesthesia reduces the shivering threshold. Epidural anesthesia reduced the gain of shivering by 63% because upper-body muscles failed to compensate for lower-body paralysis. The thermoregulatory system thus fails to recognize that regional anesthesia reduces metabolic heat production, instead responding as if lower-body muscular activity remained intact.

Adult↗
PubMed1986

Shivering related to epidural blockade with bupivacaine in labour, and the influence of epidural pethidine.

A prospective survey of two hundred patients who received an epidural block in labour was performed in order to determine the incidence and severity of shivering, and the influence of likely associated factors. Twenty-two of the patients who shivered took part in a double-blind trial to see if epidural pethidine 25 mg, versus saline, had any effect upon shivering. Fifty per cent of patients shivered soon after the initial dose of bupivacaine. Shivering was more common among patients who had experienced shivering before epidural block, and in those who had received nitrous oxide (P less than 0.005). Prior intramuscular injection of pethidine did not significantly affect the incidence of shivering, and it was not influenced by the concentration of epidural bupivacaine used (0.5 or 0.25%). Shiverers were more likely to feel cold than non-shiverers (P less than 0.001) but shivering was generally regarded by patients as a trivial symptom, only 13% describing it as very irritating. Shivering was abolished or considerably diminished within ten minutes in all patients who received epidural pethidine 25 mg, whereas there was no change in eight out of eleven patients who received epidural saline. These results are significant (P less than 0.01), and demonstrate that shivering following epidural blockade can be effectively treated with small epidural doses of pethidine.

Anesthesia, Epidural↗
PubMed2001

Postanaesthetic shivering: epidemiology, pathophysiology, and approaches to prevention and management.

Along with nausea and vomiting, postanaesthetic shivering is one of the leading causes of discomfort for patients recovering from general anaesthesia. The distinguishing factor during electromyogram recordings between patients with postanaesthetic shivering and shivering in fully awake patients is the existence of clonus similar to that recorded in patients with spinal cord transection. Clonus coexists with the classic waxing and waning signals associated with cutaneous vasoconstriction (thermoregulatory shivering). The primary cause of postanaesthetic shivering is peroperative hypothermia, which sets in because of anaesthetic-induced inhibition of thermoregulation. However, shivering associated with cutaneous vasodilatation (non-thermoregulatory shivering) also occurs, one of the origins of which is postoperative pain. Apart from causing discomfort and aggravation of pain, postanaesthetic shivering increases metabolic demand proportionally to the solicited muscle mass and the cardiac capacity of the patient. No link has been demonstrated between the occurrence of shivering and an increase in cardiac morbidity, but it is preferable to avoid postanaesthetic shivering because it is oxygen draining. Prevention mainly entails preventing peroperative hypothermia by actively rewarming the patient. Postoperative skin surface rewarming is a rapid way of obtaining the threshold shivering temperature while raising the skin temperature and improving the comfort of the patient. However, it is less efficient than certain drugs such as meperidine, clonidine or tramadol, which act by reducing the shivering threshold temperature.

Adrenergic alpha-Agonists↗
PubMed1986

Cardiorespiratory responses to shivering in vagotomized pigeons during normoxia and hypoxia.

We measured respiratory, cardiovascular and blood gas responses to shivering during normoxia and hypoxia in five bilaterally, cervically vagotomized pigeons and compared these data with those previously reported in pigeons with intact vagi (Gleeson et al. 1986). Such neural section in birds denervates, among other receptors, the carotid bodies and intrapulmonary chemoreceptors. Normoxic breathing frequency (fR) and ventilation (VE) were decreased after vagotomy. Intact pigeons showed increases in oxygen consumption (VO2), tidal volume (VT), fR and VE during shivering. Vagotomized pigeons showed similar though slightly smaller increases in fR, VO2 and VE during shivering, but VT did not change. Normoxic heart rate was greater after vagotomy and was increased during shivering as in intact pigeons. Mean arterial blood pressure (MBPa) and stroke volume were not affected by vagotomy or shivering. At the onset of shivering both intact and vagotomized pigeons exhibited immediate increases in ventilation and heart rate. Exposure of vagotomized pigeons to hypoxic gas (fractional inspired oxygen concentration, FIO2 = 0.12) during cooling completely abolished shivering electromyogram (EMG) activity. In contrast, shivering in intact pigeons was not completely inhibited until the FIO2 fell below 0.10. We conclude that bilateral, cervical vagotomy in the pigeon causes hypoventilation and tachycardia during normoxia, but that these denervated birds are still able to rapidly effect cardiorespiratory adjustments to shivering. It is suggested that these responses are mediated mainly via afferent feedback from the shivering muscles. Hypoxia inhibits shivering in both intact and vagotomized birds and the mechanism is probably related to the reduced O2 delivery to the central structures that integrate thermoregulatory demand and coordinate appropriate responses.

Animals↗
PubMed2000

Assessment and prevention of shivering in patients with severe cerebral injury. A pilot study.

Low body temperature is induced by surface cooling to reduce metabolic demands in patients with severe cerebral injury. Shivering, which increases energy expenditure, is a common effect of surface cooling. The aim of this pilot study was to investigate whether increased gradient between the set point and peripheral temperature is related to shivering and whether modifying the loss of body heat during surface cooling decreases the frequency of shivering. Seven cerebrally injured patients at a neurosurgical ICU were studied. Shivering, surface cooling and the temperature gradient measured as the tympanic and the tip toe temperatures were registered every 30 min. Shivering was assessed at three levels: no shivering, mild shivering and severe shivering. In four patients the arms and legs were covered with a cotton cloth for part of the observation time to modify the rate of heat loss. The temperature measurements were repeated in each patient between 13 and 42 times. Four patients out of seven shivered. There was a significant association between increased temperature gradient and shivering (P < 0.01). Modifying the rate of heat loss decreased the temperature gradient (P < 0.001). By simultaneously measuring the tympanic and tip toe temperatures it may be possible to detect shivering earlier and decrease its frequency by modifying the loss of body heat during surface cooling.

Adult↗
PubMed1993

Clonidine and ketanserin both are effective treatment for postanesthetic shivering.

BACKGROUND: Although meperidine is an effective treatment of postanesthetic shivering, its mechanism of action remains unknown. Investigation of other drugs might help clarify the mechanisms by which shivering can be controlled. Accordingly, we investigated the efficacy of clonidine, an alpha 2-adrenergic agonist, and ketanserin, a 5-hydroxytryptamine antagonist, in treating postanesthetic shivering. METHODS: First, 54 patients shivering after general anesthesia were allocated randomly to receive an intravenous bolus of saline, 150 micrograms clonidine, or 10 mg ketanserin. A second study explored the dose-dependence of clonidine. Forty shivering patients were given saline or clonidine, 37.5, 75, or 150 micrograms. RESULTS: The duration of shivering was significantly shorter in those given clonidine (2.1 +/- 0.9 min) than in the other two groups and shorter in the ketanserin group (4.3 +/- 0.9 min) than in the saline group (12.0 +/- 1.6 min). Clonidine and ketanserin significantly decreased systolic arterial blood pressure when compared to saline. Core rewarming was significantly slower in the clonidine group. In the second study, 37.5 micrograms clonidine was no more effective than saline. Two minutes after treatment, 150 micrograms obliterated shivering in all patients. Five minutes after treatment, all patients given 75 micrograms had stopped shivering. Systolic arterial pressure and heart rate decreased significantly in patients given 75 and 150 micrograms clonidine. CONCLUSIONS: Clonidine (150 micrograms) and ketanserin (10 mg) both are effective treatment for postanesthetic shivering. The effect of clonidine on shivering is dose-dependent: whereas 37.5 micrograms had no effect, 75 micrograms clonidine stopped shivering within 5 min.

Adult↗
PubMed1994

Epidural anesthesia increases apparent leg temperature and decreases the shivering threshold.

BACKGROUND: Lower core temperatures than usual are required to trigger shivering during epidural and spinal anesthesia, but the etiology of this impairment remains unknown. In this investigation, we propose and test a specific mechanism by which a peripheral action of regional anesthesia might alter centrally mediated thermoregulatory responses. Conduction anesthesia blocks all thermal sensations; however, cold signals are disproportionately affected because at typical leg temperatures mostly cold receptors fire tonically. It thus seems likely that epidural and spinal anesthesia increase the leg temperature perceived by the thermoregulatory system. Because skin temperature reportedly contributes 5-20% to thermoregulatory control, increased apparent (as distinguished from actual) leg temperature would produce a complimentary decrease in the core temperature triggering thermoregulatory shivering. Accordingly, we tested the hypothesis that abnormal tolerance for hypothermia during epidural anesthesia coincides with an increase in apparent leg temperature. We defined apparent temperature as the leg-skin temperature required to induce a reduction in the shivering threshold comparable to that produced by epidural anesthesia. METHODS: Six women were studied on 4 randomly ordered days: (1) leg-skin temperature near 32 degrees C; (2) leg-skin temperature near 36 degrees C; (3) leg-skin temperature near 38 degrees C; and (4) epidural anesthesia without leg-warming (leg-skin temperature approximately 34 degrees C). At each designated leg temperature, core hypothermia sufficient to evoke shivering was induced by central venous infusion of cold fluid. Upper-body skin temperature was kept constant throughout. In each volunteer, linear regression was used to calculate the correlation between the shivering thresholds on the 3 non-epidural days and concurrent leg temperatures. The slope of these regression equations thus indicated the extent to which leg-warming increased thermoregulatory tolerance for core hypothermia, and was expressed as a percentage leg-skin and leg-tissue contribution to total thermal afferent input. The skin and tissue temperatures that would have been required to produce the observed shivering threshold during epidural anesthesia, the apparent temperatures, were then interpolated from the regression. RESULTS: There was a good linear relation between the shivering threshold and leg-skin temperature (r2 = 0.94 +/- 0.06). The contribution of leg-skin temperature to the shivering threshold was 11 +/- 3% of the total thermal input. Apparent leg-skin temperature during epidural anesthesia was 37.8 +/- 0.5 degrees C, which exceeded actual leg-skin temperature by approximately 4 degrees C. The contribution of leg-tissue temperature to the shivering threshold was 19 +/- 7% of the total. Apparent leg-tissue temperature during epidural anesthesia was 37.1 +/- 0.4 degrees C, which exceeded actual leg-skin temperature by approximately 2 degrees C. CONCLUSIONS: Because leg-skin contributed approximately 11% to the shivering threshold, it is unlikely that the entire skin surface contributes at much less than 20%. These data suggest that the shivering threshold during epidural anesthesia is reduced by a specific mechanism, namely that conduction block significantly increases apparent (as distinguished from actual) leg temperature.

Adult↗
PubMed1995

Multivariate determinants of early postoperative oxygen consumption in elderly patients. Effects of shivering, body temperature, and gender.

BACKGROUND: Previous investigators have proposed that postoperative shivering may be poorly tolerated by patients with cardiopulmonary disease because of the associated significant increase in total-body oxygen consumption. However, the often-quoted 300-400% increase in oxygen consumption with shivering was derived from relatively few studies performed in a small number of younger persons specifically selected on the basis of clinically recognizable shivering. We hypothesized that the average elderly postoperative patient has a shivering response that is associated with a relatively small increase in total-body oxygen consumption. METHODS: One hundred eleven elderly patients (age > 60 yr) undergoing surgery were studied to assess the determinants of shivering and total-body oxygen consumption in the early postoperative period. Anesthetic technique, postoperative analgesia, and thermal management were controlled by protocol. The clinical variables associated with shivering and increased total-body oxygen consumption were determined by univariate and multivariate analyses. RESULTS: Mean total-body oxygen consumption in shivering patients was 38% greater than in nonshivering patients. Regardless of whether data from shivering patients were included in the analysis, oxygen consumption was directly proportional to mean body temperature. Despite similar core temperatures, men had a greater incidence of clinically recognizable shivering and greater total-body oxygen consumption than did women. CONCLUSIONS: The metabolic demands associated with postoperative shivering in elderly patients are less than those reported previously in younger persons. These findings suggest that if hypothermia predisposes to cardiovascular complications in the postoperative period, these complications are not likely to be mediated by shivering and increased metabolism.

Aged↗
PubMed1998

The effects of meperidine and sufentanil on the shivering threshold in postoperative patients. pascal.alfonsi@apr.ap-hop-paris.fr.

UNLABELLED: BACKGROUND. Meperidine (pethidine) reportedly treats postoperative shivering better than equianalgesic doses of other mu-receptor agonists. The authors' first goal was to develop a method to accurately determine postoperative shivering thresholds, and then to determine the extent to which meperidine and sufentanil inhibit postoperative shivering. METHODS: A computer-controlled infusion was started before operation in 30 patients, with target plasma concentrations of 0.15, 0.30, or 0.60 microg/ml meperidine or 0.1, 0.15, or 0.2 ng/ ml sufentanil targeted; patients were randomly assigned to each drug and concentration. The infusion was continued throughout surgery and recovery. Anesthesia was maintained with nitrous oxide and isoflurane. Core temperatures were approximately 34 degrees C by the end of surgery. The compensated core temperature at which visible shivering and a 20% decrease in steady-state oxygen consumption was recorded identified the shivering threshold. A blood sample for opioid concentration was obtained from each patient at this time. The ability of each opioid to reduce the shivering threshold was evaluated using linear regression. RESULTS: End-tidal isoflurane concentrations were <0.2% in each group at the time of extubation, and shivering occurred approximately 1 h later. Meperidine linearly decreased the shivering threshold: threshold (degrees C) = -2.8 x [meperidine (microg/ml)] + 36.2; r2 = 0.64, P = 0.0005. Sufentanil also linearly decreased the shivering threshold: threshold (degrees C) = -7.8 x [sufentanil (ng/ ml)] + 36.9; r2 = 0.46, P = 0.02. CONCLUSIONS: At a given dose, sufentanil inhibited shivering 2,800 times better than meperidine. However, the equianalgesic ratio of these drugs is approximately 4,900. That is, meperidine inhibited shivering better than would be expected based on the equianalgesic potency ratio. These data are thus consistent with clinical observations suggesting that meperidine indeed possesses special antishivering activity.

Adult↗
PubMed1980

Effects of blood pressure manipulations on shivering thermogenesis in the pigeon.

The effects of blood pressure (BP) manipulations on shivering thermogenesis were studied in conscious pigeons. A rise in BP induced by noradrenaline (NA) or equipotent doses of angiotensin II (Ang II) effectively suppressed shivering at +12 degree C and partly abolished the cold-induced vasoconstriction in the feet. The inhibition commenced when the rise in BP reached +40 mmHg, and a fall in body temperature followed these responses. Comparison of the trajectories in the BP-shivering plane revealed that the inhibition of shivering by Ang II could be completely explained by changes in BP, whereas NA had also another, more prolonged inhibitory action independent of baroreceptor activity. A similar dose-dependence for effects on BP and shivering could be established with both drugs. An acute reduction of BP by sodium nitroprusside had also a very potent inhibitory effect on shivering. In hypotensive pigeons elevation of BP with NA initially enhanced shivering, but when BP was raised beyond normal levels shivering was again suppressed. We conclude that both a rise and a fall in BP can inhibit shivering in the pigeon, and that normal levels of BP facilitate shivering. NA inhibits shivering by more than one mechanism, but the initial effect is mediated through a baroreflexive action. The interactions of thermoregulatory and cardiovascular mechanisms suggest an integrated control of body temperature and circulation, which should be considered in experimental approaches to these homeostatic systems.

Angiotensin II↗
PubMed2003

Effects of carbohydrate availability on sustained shivering II. Relating muscle recruitment to fuel selection.

The purpose of this study was to quantify how shivering activity would be affected by large changes in fuel metabolism (see Haman F, Peronnet F, Kenny GP, Doucet E, Massicotte D, Lavoie C, and Weber J-M, J Appl Physiol 96: 000-000, 2004). Adult men were exposed to 10 degrees C for 2 h after a low-carbohydrate diet and exercise (Lo) and after high-carbohydrate diet without exercise (Hi). Using simultaneous metabolic and electromyographic (EMG) measurements, we quantified the effects of changes in fuel selection on the shivering activity of eight large muscles representing >90% of total shivering muscle mass. Contrary to expectation, drastic changes in fuel metabolism [carbohydrates 28 vs. 65% of total heat production (Hprod), lipids 53 vs. 23% Hprod, and proteins 19 vs. 12% Hprod for Lo and Hi, respectively] are achieved without altering the EMG signature of shivering muscles. Results show that total shivering activity and the specific contribution of each muscle to total shivering activity are not affected by large changes in fuel selection. In addition, we found that changes in burst shivering rate ( approximately 4 bursts/min), relative contribution of burst activity to total shivering ( approximately 10% of total shivering activity), and burst shivering intensity ( approximately 12% of maximal voluntary contraction) are the same between Lo and Hi. Spectral analysis of EMG signals also reveals that mean frequencies of the power spectrum remained the same under all conditions (whole body average of 78 +/- 5 Hz for Lo and 83 +/- 7 Hz for Hi). During low-intensity shivering, humans are therefore able to sustain the same thermogenic rate by oxidizing widely different fuel mixtures within the same muscle fibers.

Adult↗
PubMed1987

Shivering following cardiac surgery: hemodynamic changes and reversal.

The effects of shivering on hemodynamics and systemic oxygenation, as well as the effectiveness of therapeutic interventions in decreasing shivering and increasing mixed venous oxygen saturation, were studied. Thirty adult patients undergoing cardiopulmonary bypass with systemic hypothermia were observed for 1 1/2 to 5 hours postoperatively for signs of shivering associated with a simultaneous decrease in oxygen transport. Systemic and pulmonary hemodynamic measurements were made, blood temperature and mixed venous oxygen saturation were monitored via the pulmonary arterial catheter, and oxygen consumption and delivery were calculated. Shivering was graded by a single investigator on scale of 0 to 4, with 0 = no shivering and 4 = continuous violent muscle activity. Therapy was instituted when shivering reached grade 4 or when SvO2 decreased to less than two thirds of its value on arrival in the intensive care unit (ICU). Patients were randomly assigned to receive either morphine sulfate, 5 to 10 mg, or meperidine, 25 to 50 mg intravenously (IV), followed by the other narcotic if the initial drug failed to improve SvO2 or decrease shivering within ten minutes. The end-point for successful treatment was a return of SvO2 to within 5% to 10% of its value upon arrival in the ICU or a cessation of shivering that did not recur within 45 minutes. Twenty of the thirty patients shivered sufficiently to decrease SvO2 by more than one third of its initial value, thus requiring pharmacologic therapy. As shivering increased from a score of 0.8 +/- 1.1 to 3.4 +/- 0.9, SvO2 decreased from 74 +/- 6% to 57 +/- 12%.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1995

Isoflurane and sevoflurane produce a dose-dependent reduction in the shivering threshold in rabbits.

All general anesthetics markedly impair thermoregulatory responses; nonetheless, sufficient hyperthermia or hypothermia will trigger most protective reflexes. Shivering, however, remains an exception among thermo-regulatory responses: it is common during postanesthetic recovery, but is rare at typical anesthetic concentrations. This observation suggests that general anesthesia impairs shivering far more than other thermoregulatory defenses. Accordingly, we tested the hypothesis that low concentrations of isoflurane and sevoflurane would virtually obliterate shivering. Japanese white rabbits were anesthetized with isoflurane or sevoflurane at end-tidal concentrations of 0.2, 0.3, and 0.4 minimum alveolar anesthetic concentration (MAC) (n = 6 in each group); the normal core temperature for these rabbits is approximately 39 degrees C. Core temperatures were subsequently reduced by a water-perfused thermode positioned in the colon. The core temperature triggering shivering identified the threshold for this response. Five of the six rabbits given 0.2 MAC isoflurane shivered at a mean core temperature of 36.3 +/- 0.3 degrees C (mean +/- SD), and one rabbit failed to shiver at a minimum core temperature of 35.0 degrees C. Four of the six rabbits given 0.3 MAC isoflurane shivered at a mean core temperature of 36.2 +/- 0.6 degrees C, and two of these rabbits failed to shiver at a minimum core temperature of 35.0 degrees C. However, no rabbit given 0.4 MAC isoflurane shivered, even at minimum core temperatures of 35.0 degrees C. All of the rabbits given 0.2 MAC sevoflurane shivered at a mean core temperature of 36.6 +/- 0.7 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Anesthetics↗
PubMed2002

Pharmacological treatment of postoperative shivering: a quantitative systematic review of randomized controlled trials.

UNLABELLED: Shivering is a frequent complication in the postoperative period. The relative efficacy of interventions that are used for the treatment of postoperative shivering is not well understood. We performed a systematic search (MEDLINE, EMBASE, Cochrane Library, hand searching, all languages, to August, 2000) for full reports of randomized comparisons of any pharmacological antishivering intervention (active) with placebo (control) in the postoperative period. Dichotomous data on absence of further shivering after treatment and adverse effects were extracted from original reports. Relative risk (RR) and number-needed-to-treat (NNT) were calculated with 95% confidence interval (CI) using a fixed effect model. Data from 20 trials (944 adults received an active intervention, 413 were controls) were analyzed. Antishivering efficacy depended on the active regimen and the length of follow-up. Efficacy with meperidine 25 mg, clonidine 150 microg, ketanserin 10 mg, and doxapram 100 mg was reported in at least three trials; all were significantly more effective than control. After 1 min, the NNT of meperidine 25 mg for no further shivering compared with placebo was 2.7 (RR, 6.8; 95% CI, 2.5-18.5). After 5 min, the NNT of meperidine 25 mg was 1.3 (RR, 9.6; 95% CI, 5.7-16), the NNT of clonidine 150 microg was 1.3 (RR, 6.8; 95% CI, 3.3-14.2), the NNT of doxapram 100 mg was 1.7 (RR 4.0; 95% CI, 2.4-6.5), and the NNT of ketanserin 10 mg was 2.3 (RR 3.1; 95% CI, 1.9-5.1). After 10 min, the NNT of meperidine 25 mg was 1.5 (RR 4.0; 95% CI, 2.5-6.2). After 15 min, the NNT of ketanserin 10 mg was 3.3 (RR 1.5; 95% CI, 1.2-1.9). Long-term outcome data were lacking. There were not enough data for alfentanil, fentanyl, morphine, nalbuphine, lidocaine, magnesium, metamizol, methylphenidate, nefopam, pentazocine, and tramadol to draw meaningful conclusions. Reporting of adverse drug reactions was sparse. Fewer than two shivering patients need to be treated with meperidine 25 mg, clonidine 150 microg, or doxapram 100 mg for one to stop shivering within 5 min who would have continued to shiver had they all received a placebo. IMPLICATIONS: Less than two shivering patients need to be treated with meperidine 25 mg, clonidine 150 microg, or doxapram 100 mg for one to stop shivering within 5 min who would have continued to shiver had they all received a placebo.

Adrenergic alpha-Agonists↗