Spontaneous post-anesthetic tremor does not resemble thermoregulatory shivering

Underbody blankets have a higher heating effect than overbody blankets in lithotomy position endoscopic surgery under general anesthesia: a randomized trial

BACKGROUND

Surgery under general anesthesia results in temperature decrease due to the effect of anesthetics and peripheral vasodilation on thermoregulatory centers. Perioperative temperature control is therefore an issue of high importance. In this study, we aimed to compare the warming effect of underbody and overbody blankets in patients undergoing surgery in the lithotomy position under general anesthesia.

METHODS

From September 2018 to October 2019, 99 patients undergoing surgery for colorectal cancer in the lithotomy position were included in this randomized controlled trial and assigned to the intervention group (underbody blanket) or control group (overbody blanket).

RESULTS

The central temperature was significantly higher in the underbody blanket group than in the overbody blanket group at 90 min after the beginning of the surgery (p = 0.02); also in this group, the peripheral temperature was significantly higher 60 min after the beginning of the surgery (p = 0.02). Regarding postoperative factors, the underbody blanket group had a significantly lower frequency of postoperative shivering (p < 0.01) and a significantly shorter postoperative hospital stay (p = 0.04) than the overbody blanket group.

CONCLUSIONS

We recommend the use of underbody blankets for intraoperative temperature control in patients undergoing surgery in the lithotomy position under general anesthesia. Underbody blankets showed improved rise and maintenance of central and peripheral temperature, decreased the incidence of postoperative shivering, and shortened the postoperative length of hospital stay.

Using the Bair Hugger™ temperature monitoring system in neck and chest regions: a pilot study

PURPOSE

Temperature monitoring in the perioperative periods is important in order to avoid both hyperthermia and hypothermia. In our pilot study, we evaluated the usefulness of Bair Hugger™ temperature monitoring system (BHTMS), a forehead deep temperature monitoring system, in the neck and chest under general anesthesia.

METHODS

After approval from the Sapporo Medical University Research Ethics Board, 30 female patients scheduled for laparoscopic surgery were enrolled in this study. Patients were divided into three groups, depending on the attachment regions of BHTMS sensor. Temperatures obtained from the three regions and each esophageal temperature (T_Eso) were monitored and analyzed.

RESULTS

A Bland-Altman plot showed that the mean bias between temperature obtained from the neck and T_Eso was + 0.05 °C above T_Eso (2SD ± 0.35 °C), and that between temperature obtained from the chest and T_Eso was - 0.55 °C above T_Eso (2SD ± 0.55 °C).

CONCLUSION

By using the BHTMS sensor in the neck region, it is possible to monitor core body temperature seamlessly and with high reliability. These results may suggest that the use of BHTMS has high versatility in measuring perioperative core body temperature.

TRIAL REGISTRATION

This study was approved by the Sapporo Medical University Research Ethics Board (2015: No. 262-149) and registered with UMIN Clinical Trial Registry ( UMIN000016802 Registered 15 March 2015).

Efficacy of Prophylactic Clonidine in Preventing Postanesthetic Shivering in Laparoscopicassisted Vaginal Hysterectomy

Objective

Postanesthetic shivering occurs in up to 60% of patients following general anesthesia and is associated with deleterious consequences. Various drugs have been used to prevent or treat postanesthetic shivering, but the ideal one has not yet been found. In this study, we have studied the efficacy of prophylactic clonidine in preventing postanesthetic shivering.

Meterials and methods

Sixty ASA (American Society of Anesthesiologists) I and II patients scheduled for laparoscopicassisted vaginal hysterectomy (LAVH) were randomly allocated to receive either clonidine 2 μg.kg—1 (group C, n = 30) or normal saline (group S, n = 30) intravenously at the time of vault closure. Core body temperature (nasopharyngeal) along with NIBP, heart rate and ECG were monitored at regular intervals. The severity of shivering was assessed according to a five-point scale (0 to 4).

Results

Significantly less shivering occurred in clonidine group 5 (17%) compared to normal saline group 20 (67%). The recovery time (between end of anesthesia and extubation) was significantly longer in the clonidine group (12.5 ± 4.3 minutes) compared with normal saline group (8.0 ± 4.5 minutes). Mean arterial blood pressure and heart rate were significantly lower in the clonidine group compared with saline group.

Conclusion

Prophylactic clonidine is effective in the prevention of postanesthetic shivering. Following clonidine administration, the recovery time was prolonged and incidence of bradycardia and hypotension were more than placebo.

How to cite this article

Chattopadhyay S, Goswami S, Rudra A. Efficacy of Prophylactic Clonidine in Preventing Postanesthetic Shivering in Laparoscopic-assisted Vaginal Hysterectomy. J South Asian Feder Obst Gynae 2013;5(3): 120-123.

The effects of nefopam on the gain and maximum intensity of shivering in healthy volunteers

BACKGROUND

Mild hypothermia has been shown to improve neurologic outcome after cardiac arrest. Nefopam, a centrally acting, nonsedative analgesic, decreases the threshold of shivering, but not vasoconstriction, and thus might be a suitable drug for induction of therapeutic hypothermia. However, not only the threshold but also the gain and maximum intensity of shivering define the thermoregulatory properties of a drug and thus are clinically important. Therefore, we evaluated the gain and maximum intensity of shivering at 2 different doses of nefopam and placebo.

METHODS

Seven healthy volunteers were randomly assigned to 3 study days: (1) control (saline), (2) small-dose nefopam (50 ng/mL), and (3) large-dose nefopam (100 ng/mL). On all study days volunteers were cooled using central venous infusion of cold IV fluid while mean skin temperature was maintained at 31 degrees C. Core temperature was recorded at the tympanic membrane. Threshold, gain, and maximum intensity of shivering were evaluated using oxygen consumption.

RESULTS

Both 50 and 100 ng/mL nefopam significantly reduced the shivering threshold as well as the gain of shivering: shivering threshold: 35.6 degrees C + or - 0.2 degrees C (control); 35.2 degrees C + or - 0.3 degrees C (small dose); 34.9 degrees C + or - 0.5 degrees C (large dose), P = 0.004; gain of shivering: 597 + or - 235 mL x min(-1) x degrees C(-1) (control); 438 + or - 178 mL x min(-1) x degrees C(-1) (small dose); 301 + or - 134 mL x min(-1) x degrees C(-1) (large dose), P = 0.028. Maximum intensity of shivering did not differ among the 3 treatments.

CONCLUSIONS

Nefopam significantly reduced the gain of shivering. This reduction, in combination with a reduced shivering threshold, will allow clinicians to cool patients even further when therapeutic hypothermia is indicated.

The effect of forced-air warming during arthroscopic shoulder surgery with general anesthesia

PURPOSE

The aim of this study was to compare the change in body temperature between the cotton blanket group and forced-air warming blanket group during arthroscopic shoulder surgery. In both groups irrigation fluid at room temperature (22 degrees C) was used.

METHODS

We randomly assigned 44 American Society of Anesthesiologists physical status I and II patients scheduled for elective shoulder arthroscopic surgery to receive 1 cotton blanket (group I, n = 22) or a forced-air warming blanket (group II, n = 22). Body temperatures were measured with an esophageal stethoscope, which was inserted immediately after intubation.

RESULTS

A significant difference in body temperatures was observed at 60 minutes after induction (P = .0192), 90 minutes after induction (P = .0004), 120 minutes after induction (P = .0003), and 150 minutes after induction (P = .0228). Shivering on arrival in the postanesthesia care unit was found in 15 patients in group I (68.1%) and only 1 patient in group II (4.5%).

CONCLUSIONS

We conclude that forced-air warming is significantly more efficient than a cotton blanket alone at maintaining perioperative normothermia during arthroscopic shoulder surgery.

LEVEL OF EVIDENCE

Level I, randomized controlled trial.

Isovolaemic haemodilution decreases the shivering threshold in rabbits

BACKGROUND AND OBJECTIVE

The inhibition of thermoregulatory control by anaesthesia is manifested by reduced vasoconstriction and shivering thresholds. As intraoperative bleeding can result in haemodynamic changes, including vasoconstriction, we investigated the effect of experimental bleeding on the shivering threshold in rabbits.

METHODS

Twenty-four rabbits were randomly assigned to one of three treatment strategies: (1) no blood removal (control), (2) 5 mL kg(-1) isovolaemic blood removal and (3) 10 mL kg(-1) isovolaemic blood removal. After tracheal intubation under isoflurane anaesthesia, anaesthesia was maintained with 50% nitrous oxide in oxygen. The removed blood volume was replaced with the same volume of warm hydroxyethyl starch colloid solution. Oesophageal temperature was measured as a core temperature at 1-min intervals. After blood removal, the animal's body was cooled at a rate of 2-3 degrees C h(-1) by perfusing water at 10 degrees C through a U-shaped thermode positioned in the colon. Hypothermic shivering was evaluated by visual inspection, and the core temperature at which shivering was triggered was identified as the thermoregulatory threshold for this response.

RESULTS

Just before the cooling, the body temperature of the animals was around 38.6 degrees C in all of the three groups. The shivering threshold in the control group was 37.2 +/- 0.2 degrees C (mean +/- SD). The shivering thresholds in the 5 mL kg(-1) (36.9 degrees +/- 0.3 degrees C) and 10 mL kg(-1) (36.5 degrees +/- 0.5 degrees C) blood removal groups were significantly lower and in proportion with the volume of blood removed than that in the control group.

CONCLUSION

Isovolaemic haemodilution decreased the shivering threshold in rabbits in proportion with the volume of blood removed.

Progress in shivering control

Hypothermia is a potent neuroprotectant and induced hypothermia holds great promise as a therapy for acute neuronal injury. Thermoregulatory responses, most notably shivering, present major obstacles to therapeutic temperature management. A review of thermoregulatory physiology and strategies aimed at controlling physiologic responses to hypothermia is presented.

Efficacy of prophylactic ketamine in preventing postoperative shivering

BACKGROUND

Treatment with ketamine and pethidine is effective in postoperative shivering. The aim of this study was to compare the efficacy of low-dose prophylactic ketamine with that of pethidine or placebo in preventing postoperative shivering.

METHODS

A prospective randomized double-blind study involved 90 ASA I and II patients undergoing general anaesthesia. Patients were randomly allocated to receive normal saline (Group S, n=30), pethidine 20 mg (Group P, n=30) or ketamine 0.5 mg kg(-1) (Group K, n=30) intravenously 20 min before completion of surgery. The anaesthesia was induced with propofol 2 mg kg(-1), fentanyl 1 microg kg(-1) and vecuronium 0.1 mg kg(-1). It was maintained with sevoflurane 2-4% and nitrous oxide 60% in oxygen. Tympanic temperature was measured immediately after induction of anaesthesia, 30 min after induction and before administration of the study drug. An investigator, blinded to the treatment group, graded postoperative shivering using a four-point scale and postoperative pain using a visual analogue scale (VAS) ranging between 0 and 10.

RESULTS

The three groups did not differ significantly regarding patient characteristics. The number of patients shivering on arrival in the recovery room, and at 10 and 20 min after operation were significantly less in Groups P and K than in Group S. The time to first analgesic requirement in Group S was shorter than in either Group K or Group P (P<0.005). There was no difference between the three groups regarding VAS pain scores.

CONCLUSION

Prophylactic low-dose ketamine was found to be effective in preventing postoperative shivering.

Postoperative shivering in children: a review on pharmacologic prevention and treatment

Postoperative shivering consists of muscular tremor and rigidity. It is often associated with body heat loss, although hypothermia alone does not fully explain the occurrence of shivering. Shivering is self-limiting, never becomes chronic, and is rarely associated with major morbidity. However, it affects the comfort of the patients, and may sometimes lead to more serious complications. The efficacy of a great variety of pharmacologic interventions to prevent shivering and to treat established symptoms has been tested in randomized controlled trials. These can be gathered systematically; recommendations on prevention and treatment can then be based on the strongest evidence. Unfortunately all these trials have been performed in adults. Thus, recommendations for the control of postoperative shivering in children have to be extrapolated from adult data. In adults, a systematic review strongly suggests that simple measurements are efficacious for both prevention and treatment. For prevention, extrapolation of these adult data indicates that three children have to receive intravenous clonidine 1.5 micro g/kg during anesthesia for one not to shiver, when they would have done so had they not received clonidine. For this degree of efficacy, the expected incidence of shivering (baseline risk) has to be high (approximately 50%). For treatment, extrapolation from adult data indicates that less than two children need to receive intravenous meperidine (pethidine) 0.35 mg/kg, or clonidine 1.5 micro g/kg for one to stop shivering five minutes after drug administration, when they would not have done so had they not received one of these drugs. Since the treatment of established shivering is efficacious, simple, inexpensive, and relatively safe, and since prevention is only efficacious if the baseline risk is very high, we recommend the 'wait and see' strategy.

Clonus after human spinal cord injury cannot be attributed solely to recurrent muscle-tendon stretch

Clonus, presented behaviorally as rhythmic distal joint oscillation, is a common pathology that occurs secondary to spinal cord injury (SCI) and other neurological disabilities. There are two predominant theories as to the underlying mechanism of clonus. The prevailing one is that clonus results from recurrent activation of stretch reflexes. An alternative hypothesis is that clonus results from the action of a central oscillator. We present evidence that the mechanism underlying clonus in individuals with SCI is not solely related to muscle stretch. We studied electromyography (EMG) of the soleus (SOL), medial gastrocnemius (MG), tibialis anterior (TA), medial and lateral hamstrings, vastus medialis, vastus lateralis, and rectus femoris from subjects with clinically complete and clinically incomplete SCI during stretch-induced ankle clonus, stepping, and non-weight-bearing standing. Clonic EMG of the SOL, MG, and TA occurred synchronously and were not consistently related to muscle-tendon stretch in any of the conditions studied. Further, EMG activity during stretch-induced ankle clonus, stepping, and non-weight-bearing standing had similar burst frequency, burst duration, silent period duration, and coactivation among muscles, indicating that clonic EMG patterns occurred over a wide range of kinematic and kinetic conditions, and thus proprioceptive inputs. These results suggest that the repetitive clonic bursts could not be attributable solely to immediate afferent feedback such as recurrent muscle stretch. However, these results support the theory that the interaction of central mechanisms and peripheral events may be responsible for clonus.

The effects of urapidil on thermoregulatory thresholds in volunteers

In a previous study we have shown that the antihypertensive drug, urapidil, stops postanesthetic shivering. One possible mechanism in the inhibition of postanesthetic shivering by urapidil may be alterations in thermoregulatory thresholds. We therefore studied the effects of urapidil on vasoconstriction and shivering thresholds during cold-induced shivering in volunteers. Seven healthy male volunteers were cooled by an infusion of saline at 4 degrees C on two study days separated by 48 h. Thermoregulatory vasoconstriction was estimated using forearm minus fingertip skin-temperature gradients, and values exceeding 0 degrees C were considered to represent significant vasoconstriction. The rectal core temperatures at the beginning of shivering and at vasoconstriction were considered the thermoregulatory thresholds. Before cooling, either 25 mg of urapidil or placebo was administered randomly and blindly to each volunteer. When shivering occurred continuously for 10 min, another 25 mg of urapidil was administered IV to completely stop shivering. Urapidil led to a decrease in core temperature at vasoconstriction and shivering threshold by 0.4 degrees C plus/minus 0.2 degrees C (P < 0.001) and 0.5 degrees C plus/minus 0.3 degrees C (P < 0.01), respectively. Oxygen consumption increased during shivering by 70% plus/minus 30% (P < 0.01) in comparison with baseline and decreased levels after shivering stopped, despite the continued low core temperature. Our investigation shows that urapidil stops postanesthetic shivering by decreasing important thermoregulatory thresholds. This means that shivering, not hypothermia, is treated, and hypothermia will need more attention in the postanesthesia care unit.

IMPLICATIONS

In this study we show that the antihypertensive drug urapidil stops cold-induced shivering and decreases normal thermoregulatory responses, i.e., the thresholds for vasoconstriction and shivering, in awake volunteers.

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.

Urapidil does not prevent postanesthetic shivering: a dose-ranging study

PURPOSE

To investigate the effect of 0.2 mg x kg(-1), 0.3 mg x kg(-1) and 0.4 mg x kg(-1) urapidil on the incidence and severity of postanesthetic shivering.

METHODS

One hundred and fifty patients (ASA I-III) scheduled for elective abdominal, urologic or orthopedic surgery under standardized general anesthesia were randomly allocated to one of five groups (each group n=30) using a double-blind protocol: group A received 0.2 mg x kg(-1) urapidil, group B: 0.3 mg x kg(-1) urapidil, group C: 0.4 mg x kg(-1) urapidil, group D: 3 microg x kg(-1) clonidine (positive control group), and group E: saline 0.9% as placebo (negative control group). Postanesthetic shivering was scored using a five-point scale.

RESULTS

Twelve patients of group A, 11 of group B, nine of group C, three of group D and 14 of group E showed signs of postanesthetic shivering. Postanesthetic shivering was significantly decreased in the clonidine group compared to the three urapidil groups and the placebo group. Significantly less patients treated with clonidine needed anti-shivering therapy. There were no significant differences between the urapidil and placebo groups. Therapeutic interventions for hemodynamic effects were not required in any group. Time to extubation, but not time to discharge, was prolonged in the clonidine group.

CONCLUSION

Urapidil showed no beneficial effect on shivering in any of the doses evaluated, whereas prophylactic administration of clonidine was effective in preventing postanesthetic shivering.

A comparison between meperidine, clonidine and urapidil in the treatment of postanesthetic shivering

Postanesthetic shivering can be treated with many types of drugs. We compared the effects of meperidine, clonidine, and urapidil on postanesthetic shivering. Sixty patients shivering during recovery from general anesthesia were treated in a randomized, double-blinded fashion with 25 mg meperidine IV, 0.15 mg clonidine IV, or 25 mg urapidil IV in three separate groups of 20 patients each. If shivering did not stop within 5 min, the treatment was repeated once; clonidine was replaced with saline for the second dose. Rectal temperature, arterial blood pressure, heart rate, SaO(2) and vigilance were monitored. Clonidine stopped shivering in all 20 patients. A single dose of meperidine stopped the shivering in 18 of 20 patients, with the other 2 patients needing a second dose. Urapidil was less effective: the first dose stopped the shivering in only six patients; the second dose was effective in another six; the drug was ineffective in 8 of 20 patients. Meperidine and clonidine were both nearly 100% effective in treating postanesthetic shivering without negative side effects. By comparison, urapidil was only effective in 60% of patients treated (P <0.01).

IMPLICATIONS

Patients shivering during recovery from general anesthesia were treated in a randomized double-blinded fashion with meperidine, clonidine, or urapidil. Meperidine and clonidine were both very effective, whereas urapidil was only effective in 60% of patients treated.

Dental trauma associated with anaesthesia

Damage to teeth is the most common complaint against anaesthetists. A dental history and oral examination are important before anaesthesia. Pre-existing dental pathology or the presence of prostheses makes damage more likely but sound teeth may be affected. The maxillary central incisors are most at risk. Certain diseases and drugs should alert anaesthetists to increased likelihood of dental pathology. The flange of the Macintosh blade appears responsible for much damage and alternative equipment or techniques of endotracheal intubation should be considered, particularly when risk factors are present. Manoeuvres to protect teeth must not impact adversely on airway management. Custom mouthguards can be useful. A management plan can help control losses if damage does occur. Patients should be warned about the possibility of dental trauma.

Postoperative shivering: aetiology and treatment

Most postanaesthetic shivering-like tremor is normal thermoregulatory shivering in response to core hypothermia. Therefore, shivering will be prevented by maintaining intraoperative normothermia. Other thermoregulatory-related shivering is caused by the release of cytokines by the surgical procedure. Non-thermoregulatory shivering, occurring in normothermic patients, is caused by other aetiologies such as postoperative pain. It is thus likely that adequate treatment of postoperative pain will ameliorate non-thermoregulatory tremor. In addition, the administration of antipyretic drugs reduces shivering in patients after cardiopulmonary bypass surgery.

Nefopam and clonidine in the prevention of postanaesthetic shivering

Postanaesthetic shivering affects up to 70% of patients after general anaesthesia, and may be very distressing. Various drugs have been used to treat or prevent postanaesthetic shivering, but the ideal one has not yet been found. Sixty patients undergoing elective abdominal or orthopaedic surgery under general anaesthesia were included in a randomised, double-blind study. Patients received clonidine (3 microgram.kg-1), nefopam (0.15 mg.kg-1) or saline 0.9% as a placebo at the end of surgery, prior to extubation. Nefopam and clonidine significantly reduced the incidence and severity of shivering in comparison with the placebo. The recovery time, between the end of anaesthesia and extubation, was significantly longer in the clonidine-treated patients [13.6 (5.2) min] than in either the nefopam [9.6 (2.8) min] or the placebo [10.0 (5.4) min] groups. Mean arterial blood pressure and heart rate were significantly lower in the clonidine group compared with both other groups. Our results suggest that nefopam and clonidine are effective in the prevention of postanaesthetic shivering. However, following clonidine administration the recovery time was prolonged and hypotension was significantly greater than after nefopam.

Covering the head and face maintains intraoperative core temperature

PURPOSE

To determine the effect of covering the patient's head and face on the prevention of intraoperative hypothermia (<35.5 degrees C).

METHODS

This randomized, prospective trial included 44 adults undergoing elective abdominal surgery. After the induction of anesthesia with thiopental, in 44 patients their extremities and trunk were covered with towels and sheets. In addition, 22 patients (covered group) had their face and head fully covered. Anesthesia was maintained with N2O 50-66% (2-3 L x min(-1)) and isoflurane (<IMAC) in oxygen combined with thoracic epidural anesthesia. Core temperature was measured at the tympanic membrane continuously and was recorded at 15 min intervals from the induction of anesthesia. Heat and moisture exchangers were used in their anesthetic circuit. Ambient temperature was maintained near 25 degrees C.

RESULTS

Neither group demonstrated intraoperative hypothermia. However, tympanic membrane temperature at 75, 90, 105 min in the covered group were higher than those of control group (36.7+/-0.4 degrees C vs. 36.5+/-0.4 degrees C, 36.8+/-0.5 degrees C vs. 36.4+/-0.5 degrees C, 36.8+/-0.5 degrees C vs. 36.4+/-0.5 degrees C, respectively, P<0.05).

CONCLUSION

Covering the patient's head and face maintains intraoperative core temperature.

A comparison among nalbuphine, meperidine, and placebo for treating postanesthetic shivering

Postanesthetic shivering (PS) is distressing for patients and may induce a variety of complications. In this prospective, double-blinded, randomized study, we evaluated the value of nalbuphine, compared with meperidine and saline, for treating PS. Ninety adult patients were included in the study. Group 1 (n = 30) received i.v. nalbuphine 0.08 mg/kg, Group 2 (n = 30) received i.v. meperidine 0.4 mg/kg, and Group 3 (n = 30) received i.v. saline. Treatment that stopped shivering was considered to have been successful. The results demonstrated that, 5 min after treatment, both nalbuphine and meperidine provided a rapid and potent anti-shivering effect on PS, with high response rates of 80% and 83%, compared with those of saline (0%) (P < 0.01). Thirty minutes after injection, the response rates of nalbuphine and meperidine were 90% and 93%, respectively, compared with 17% in the saline group (P < 0.01). The differences between nalbuphine and meperidine were not significant. We conclude that nalbuphine may be an alternative to meperidine for treating PS.

IMPLICATIONS

We evaluated nalbuphine versus meperidine and saline for treating postanesthetic shivering. Our results demonstrate that both nalbuphine and meperidine provide a similar rapid and potent anti-shivering effect. Nalbuphine may be an alternative to meperidine for treating postanesthetic shivering.

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

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.

Dexamethasone decreases the incidence of shivering after cardiac surgery: a randomized, double-blind, placebo-controlled study

Shivering after cardiac surgery is common, and may be a result of intraoperative hypothermia. Another possible etiology is fever and chills secondary to activation of the inflammatory response and release of cytokines by cardiopulmonary bypass. Dexamethasone decreases the gradient between core and skin temperature and modifies the inflammatory response. The goal of this study was to determine whether dexamethasone can reduce the incidence of shivering. Two hundred thirty-six patients scheduled for elective coronary and/or valvular surgery were randomly assigned to receive either dexamethasone 0.6 mg/kg or placebo after the induction of anesthesia. All patients received standard monitoring and anesthetic management. After arrival in the intensive care unit (ICU), nurses unaware of the treatment groups recorded visible shivering, as well as skin and pulmonary artery temperatures. Analysis of shivering rates was performed by using chi2 tests and logistic regression analysis. Compared with placebo, dexamethasone decreased the incidence of shivering (33.0% vs 13.1%; P = 0.001). It was an independent predictor of reduced incidence of shivering and was also associated with a higher skin temperature on ICU admission and a lower central temperature in the early postoperative period.

IMPLICATIONS

Dexamethasone is effective in decreasing the incidence of shivering. The effectiveness of dexamethasone is independent of temperature and duration of cardiopulmonary bypass. Shivering after cardiac surgery may be part of the febrile response that occurs after release of cytokines during cardiopulmonary bypass.

[Efficacy of ketanserin on postanesthetic shivering]

OBJECTIVE

To evaluate the clinical and electromyographic (EMG) effects of ketanserin (K), a serotoninergic receptor antagonist (5-HT2), on postoperative shivering (POS).

STUDY DESIGN

Prospective, randomised, double-blind study.

PATIENTS

Fifty ASA class 1 and 2 patients with major clinical postoperative tremor were studied.

METHODS

POS was assessed clinically (0 = nil, 1 = moderate, 2 = severe). Inclusion criterion was a POS of 2 at admission in the recovery room. The mean arterial blood pressure, rectal temperature, SpO2 were recorded at admission (T0) and subsequently at T5, T10, T15, T30 and T60 minutes. Either 10 mg of K (n = 25) or a corresponding volume of a placebo (P) (n = 25) were intravenously injected. The EMG activity of the deltoid and quadriceps muscles was recorded continuously. Blood lactic acid concentration was measured at the end of POS. Results are expressed as mean +/- SEM. Parametric values were analysed with unpaired Student's t-test, and nonparametric values with chi 2 analysis. P < 0.05 was accepted.

RESULTS

Demographic data, duration of anaesthesia, postoperative temperature, oxygen saturation, blood pressure and blood lactate concentration were similar between groups. The POS duration in the K group was significantly shorter than in the P group: 8.8 +/- 1.5 min and 15.5 +/- 1.5 min respectively (P < 0.01). The number of patients in the K group experiencing POS at T5 and T10 was significantly lower, when compared with those who had received the P (P < 0.05).

CONCLUSION

At a dose of 10 mg, K administered in patients with POS during recovery, reduced significantly the duration and intensity of the shivering without noticeable side effects. This study suggests that this 5-HT2 antagonist is an efficient therapeutic tool for POS in adults.

Precautions in warming light therapy as an adjuvant to postoperative flap care

Warming lights, circulating-water blankets, space heaters, and the Bair Hugger are used by surgeons in the perioperative period to maintain a patients core body temperature. Warming lights in particular are often used by plastic surgeons to augment the postoperative vasodilatation of reconstructive flaps by increasing the ambient temperature of the area around the flap. A review of the literature fails to elucidate even anecdotal experience regarding the actual intensity of thermal energy directly imparted to tissues from these modalities with respect to distance. The purpose of our study was to quantify actual tissue temperatures generated, as a function of distance, with the Emerson warming light. Our interest in this is a result of a full-thickness burn which occurred to a portion of a pedicled TRAM flap used for breast reconstruction when a warming light was inadvertently positioned, during the course of the first postoperative night, at a distance less than that recommended by the manufacturer. A biological model was created simulating a sympathectomized flap and the temperature curves generated by Emerson warming lights were recorded by calibrated glass bulb thermometers at 15 min intervals for distances of 32 and 71 cm using both focused and defocused light beams. The distance of 32 cm was used as a parameter as it was the distance noted between the patient and the warming light when the TRAM flap burn occurred. Temperatures obtained at a distance of 32 cm rose to 120 degrees F (48.8 degrees C) within 30 min for the focused beam and 118 degrees F (48 degrees C) after 1 h for the defocused beam. This exceeds the temperature at which tissue necrosis is known to occur (111.2 degrees F/44 degrees C). However, temperatures obtained at 71 cm for the focused and defocused beams plateaued at 93.2 and 96.8 degrees F (34 and 36 degrees C) respectively, which is well within physiologic limits and below the temperature resulting in tissue necrosis. Our conclusion is that warming lights can be successfully used as a safe adjuvant in order to optimize flap vasodilatation without compromising the thermal threshold of tissue damage if maintained at the manufacturer's minimum recommended distance of 71 cm. If this source of thermal energy is used, however, strict precautions and nursing guidelines must be instituted to maintain this minimum distance parameter and prevent patient morbidity.

The effects of active peripheral skin warming on perioperative hypothermia in dogs

OBJECTIVE

This study evaluates the efficacy of three perioperative warming protocols to improve control of body temperature in anesthetized dogs.

STUDY DESIGN

A randomized controlled clinical trial.

ANIMALS OR SAMPLE POPULATION

Thirty-two client-owned dogs.

METHODS

We prospectively studied dogs entering the University of Pennsylvania Veterinary Teaching Hospital for orthopedic or dental procedures and assigned them to one of three perianesthetic warming protocols. Group 1 (n = 10) had a single circulating warm water mattress applied over the trunk (single-trunk warming). Group 2 (n = 12) had two circulating warm water mattresses, one placed over and one under the trunk (double-trunk warming). Group 3 (n = 10) had warm circulating mattresses applied only around the feet and legs of all available limbs (peripheral warming). The warm water mattresses were prewarmed and maintained at 40 degrees C (104 degrees F) and applied immediately after induction of general anesthesia. All dogs had a layer of thick terry cloth toweling beneath and above the trunk. Body temperature measurements were recorded every 15 minutes for the first 2.5 hours of anesthesia.

RESULTS

The lowest mean temperature for dogs in group 3 was 37.4 +/- 0.2 degrees C (99.5 degrees F), compared with 36.4 +/- 0.2 degrees C (97.4 degrees F) and 36.7 +/- 0.2 degrees C (98.0 degrees F) in groups 1 and 2, respectively.

CONCLUSIONS

Dogs in the peripheral warming group maintained significantly higher core body temperatures than dogs in either trunk warming groups throughout the 2.5-hour study period.

CLINICAL RELEVANCE

To maintain body heat in dogs during anesthesia, it is more effective to warm the feet and legs than to warm the trunk.

The relationship among brain, spinal cord and anesthetic requirements

The spinal cord is a crucial site wherein anesthetics suppress movement in response to noxious stimuli. The balance of excitatory and inhibitory influences on the spinal cord likely determines the extent of motor response, and is thus important to anesthetic requirements. When the volatile anesthetic isoflurane is selectively delivered to the in situ goat brain (with low concentrations in the torso), anesthetic requirements increase dramatically, but when low isoflurane concentrations are delivered to the brain, anesthetic requirements decrease in the torso. When high, supraclinical concentrations of isoflurane (6-10%) are delivered to the brain and not to the torso, spontaneous movement occurs. These results are best explained by a differential effect of anesthetics on spinal cord neurons and cerebral neurons (midbrain reticular formation). Examination of neurons in the dorsal horn and midbrain reticular formation, and the electromyogram, during differential delivery of isoflurane to brain and spinal cord, will test this hypothesis.

The effects of forced-air warming on postbypass central and skin temperatures and shivering activity

STUDY OBJECTIVE

To test the hypothesis that forced-air skin-surface warming used prophylactically after hypothermic cardiopulmonary bypass (CPB) would: (1) decrease the incidence and severity of postbypass shivering, (2) rapidly increase skin-surface temperatures when compared with standard warmed cotton blankets, and (3) not contribute to excessive central temperature elevation.

DESIGN

Prospective, randomized, nonblinded comparison of two rewarming techniques.

SETTING

Multidisciplinary intensive care unit at a tertiary care, private teaching hospital.

PATIENTS

Following hypothermic CPB, 47 patients underwent postoperative rewarming by using either conduction (warmed cotton blankets) or convection (forced-air cover) techniques.

MEASUREMENTS AND MAIN RESULTS

Central and skin temperatures were measured at 30-minute intervals for 5.5 hours postoperatively. Four lead electromyographic recordings were used to objectively document shivering activity. Antihypertensives, opioids, sedatives, and muscle relaxants were administered per patient need and recorded. The forced-air cover markedly decreased the overall incidence, duration, and magnitude of significant shivering compared with the warmed cotton blankets. Forced-air therapy produced clinically significant increases in skin surface temperatures, but avoided excessive central temperature elevation when compared with passive rewarming with cotton blankets.

CONCLUSION

Convection warming, when compared with conductive warming with cotton blankets, limited the incidence, magnitude, and duration of shivering following hypothermic cardiac surgery. This suggests an important role of cutaneous thermal input in the mediation of the shivering response. The central tissue compartment is buffered from the effects of skin-surface warming and, thus, forced-air therapy will not lead to excessive central temperature elevation in this patient population when compared with cotton blanket rewarming.

Postanaesthetic shivering in children

This study was designed to assess the incidence, severity and possible aetiological factors of postanaesthetic shivering in children. Three hundred and seventy-six children undergoing general anaesthesia were enrolled in the study. Tympanic membrane temperatures were recorded pre-operatively and every 15 min postoperatively in the recovery room until discharge to the ward. Also recorded were all anaesthetic data including fluid administration, methods of temperature preservation used, sedation scores and shivering (using a four-point scale). The overall incidence of shivering was 14.4%. Multiple regression analysis identified three factors that were significantly related to shivering: age, the administration of atropine and peri-operative temperature changes. Children who shivered rewarmed faster in the recovery room.

The treatment of postanaesthetic shivering: a double blind comparison between alfentanil and pethidine

It has been postulated that pethidine may mediate its effects on postanaesthetic shivering (PAS) via kappa-opioid receptors. However, clinical evidence indicates that alfentanil, a pure mu-agonist, may also have beneficial effects on PAS. In order to assess whether opioid effects on PAS are effected via kappa receptors, fifty-one patients were randomised to receive alfentanil 250 micrograms (n = 18), pethidine 25 mg (n = 18) or placebo (n = 15) on a double-blind basis for the treatment of established postanaesthesia shivering (PAS). Both drugs proved significantly better in treating PAS than placebo (P < 0.005). Following treatment, blood pressure fell and oxygen saturation increased in patients in the two treatment groups when compared with the control group (P < 0.05). There was a highly significant incidence of reshivering in the alfentanil treated group (P < 0.005). In conclusion, the high incidence of reshivering indicates that alfentanil is unlikely to supercede pethidine in the treatment of PAS, but its initial success rate implies that pethidine's anti-shivering effect is unlikely to be mediated via kappa-opioid receptors.

Post-anaesthetic shaking

Although shaking in the post-anaesthetic period is common, the cause of this phenomenon is obscure. Many predisposing factors have been identified, but the medical treatments and measures of care for patients with post-anaesthetic shaking are as controversial as the causes.

A comparison of thiopentone and propofol with respect to the incidence of postoperative shivering

One hundred patients (69 female) undergoing surgical excision of three or more wisdom teeth were randomly allocated to receive either thiopentone or propofol for induction of anaesthesia. Other than the induction agent, the anaesthetic regimen was standardised for all cases. All patients were observed for 15 min after entry into the recovery area to assess the presence and intensity of shivering. Twenty-five patients in the thiopentone group (n = 50) and 11 patients in the propofol group shivered postoperatively (p < 0.005). There was no statistically significant difference in axillary temperature between shivering and non-shivering patients. The use of propofol as an induction agent is associated with a lower incidence of postoperative shivering than thiopentone.

Effects of a forced-air system (Bair Hugger, OR-type) on intraoperative temperature in patients with open abdominal surgery

Intraoperative hypothermia is difficult to avoid and may present a significant clinical risk during the early postoperative phase. We evaluated a forced-air system [Bair Hugger, OR-type (BH)] for warming intraoperative patients with open abdominal surgery. Twenty patients received BH warming [BH(+) group] and another 20 patients, who served as controls, did not [BH(-) group]. Patients in both groups also received circulating blanket warming. Tempertures were measured at 30-min intervals throughout the operation in the rectum and on the tip of the index finger opposite the nail bed. The average operation time was 168.8±16.2 min. Rectal and fingertip temperatures in the BH(+) group were significantly higher than those in the BH(-) group, and central-peripheral temperature gradients in the BH(+) group were significantly smaller than those in the BH(-) group during the study, except at 180 min. No shivering occurred in either group. Therefore, BH is an effective warming device during open abdominal surgery.

The intensity of postoperative shivering is unrelated to axillary temperature

The relationship between axillary temperature and postoperative shivering was examined in 302 patients who entered one recovery room in the Derbyshire Royal Infirmary over a one-month period. No relationship was found between temperature and the occurrence of shivering, or between conscious level and the occurrence of shivering.

Neurological examination in patients recovering from general anesthesia

We performed serial neurological evaluations on 86 patients who underwent surgery for herniated lumbar disk during the first 3 hours after the end of anesthesia (isoflurane-N20-02 for 25 patients, halothane-N20-02 for 38, fentanyl-droperidol-N20-02 for 23). At time 0, the idiomuscular response to percussion of the extensor carpi muscle was present in every patient, while tendon reflexes were always absent. Hyperreflexia was as frequent as shivering, but it took place earlier; we could determine no correlation between these two phenomena. There was no correlation between shivering and rectal temperature of the patients. Although almost all the patients were cooperative and could correctly calculate 100-7, the post-hyperventilation-apnea test was positive in 35 patients at time 120 minutes: this suggests that many patients considered "awake" still exhibit neurological abnormalities, such as inadequate respiratory drive.