Clonidine Increases the Sweating Threshold, but Does Not Reduce the Gain of Sweating

Hypothermia in acute ischemic stroke therapy

Therapeutic hypothermia (TH) is a potent neuroprotective therapy in experimental cerebral ischemia, with multiple effects at several stages of the ischemic cascade. In animals, TH is so powerful that all preclinical stroke studies require strict temperature control. In humans, multiple clinical studies documented powerful protection with TH after accidental neonatal hypoxic-ischemic injury and global cerebral ischemia with return of spontaneous circulation after cardiac arrest. National and international guidelines recommend TH for selected survivors of global ischemia, with profound benefits seen. Recently, a study comparing target temperature 33-36°C failed to demonstrate significant effects in cardiac arrest patients. Additionally, clinical trials of TH for head trauma and stroke have so far failed to confirm benefit in humans despite a vast preclinical literature. Therefore, it is now critical to understand the fundamental explanation for the success of TH in some, but famously not all, clinical trials. TH in animals appears to work when used soon after ischemia onset; for a short duration; and at a deep target temperature.

Non-hormonal management of vasomotor symptoms

Vasomotor symptoms are the most common indication for the prescription of hormone replacement therapy since it is effective in over 80% of cases. In 1995, 37% of American women took hormone replacement therapy, principally for this purpose. However, following the publication of results from the Women's Health Initiative, as many as half of these women in the US and in the UK and New Zealand discontinued hormone therapy. Discontinuation of estrogen is often accompanied by a return of vasomotor symptoms; however, only a small number (18%) of women report restarting hormone therapy. Alternatives are available, but limited knowledge on etiology and mechanisms of hot flushing represents a major obstacle for the development of new, targeted, non-hormonal treatments, and no current alternatives are as effective as estrogen.

Folic acid supplementation may cure hot flushes in postmenopausal women: a prospective cohort study

BACKGROUND

Neurotransmitter norepinephrine seems to be involved in the pathophysiology of hot flushes in postmenopausal women, and folic acid was found to interact with its receptors.

OBJECTIVES

To examine the effect of folic acid supplementation on the occurrence of hot flushes and the plasma level of 3-methoxy 4-hydroxy phenyl glycol (MHPG, the main metabolite of brain norepinephrine).

METHOD

Forty-six postmenopausal women were allocated (by alternation) into 2 groups (n = 23 each); Group 1 received folic acid 5mg tablets daily for 4 weeks and group 2 received placebo tablets. Four women in group 2 discontinued the study.

RESULTS

The number of women who reported improvement in hot flushes was significantly higher in the treatment group. On comparing the mean plasma levels of MHPG before and after treatment, a significant lowering was found in the treatment group (mean % change = -24.1 +/- 17.9, p < 0.001) when compared with the placebo-control group (mean % change = -5.59 +/- 16.4, p = 0.10). In the treatment group, there was a significant negative correlation between improvement in hot flushes and the plasma level of MHPG (r = -0.453, p = 0.03).

CONCLUSION

Folic acid supplementation may cause subjective improvement of hot flushes by lowering the increased central noradrenergic activity.

Folic acid supplementation cures hot flushes in postmenopausal women

Over the past four decades, it was found that folic acid supplementation produced an antidepressant-like effect mediated by interaction with the brain noradrenergic receptors (inhibitory effect) and serotonergic receptors (stimulatory effect). Hot flushes occur in postmenopausal women because of disturbances in the thermoregulatory centre, most likely as a result of estrogen deficiency-related increase in central noradrenergic activity and reduced serotonergic activity. Therefore, we hypothesize that folic acid supplementation may ameliorate hot flushes by the same mechanism as estrogen replacement, i.e., by interacting with monoamine neurotransmitters in the brain; namely norepinephrine and serotonin. This article discusses the hypothesis and presents supportive preliminary data.

Defeating normal thermoregulatory defenses: induction of therapeutic hypothermia

Therapeutic hypothermia may be useful in various circumstances including stroke. However, core body temperature is normally tightly regulated. Even mild hypothermia in conscious subjects thus provokes vigorous thermoregulatory defenses which are potentially harmful in fragile patients. Furthermore, thermoregulatory responses are effective, which reduces the rate at which hypothermia can be induced. Drugs are thus often given to blunt normal thermoregulatory defenses. General anesthetics profoundly impair thermoregulatory control, but prolonged general anesthesia is rarely practical or appropriate. A variety of other drugs have therefore been evaluated. Most opioids only slightly impair thermoregulatory defenses, but meperidine is considerably more effective than equipotent doses of other opioids. The central alpha-2 agonists clonidine and dexmedetomidine are also useful. However, the best overall approach to inducing thermal tolerance appears to be a combination of buspirone and meperidine, which reduces the core temperature triggering shivering to about 33.5 degrees C in doses that maintain adequate ventilation.

The therapeutic effect of modified Yu Ping Feng San on idiopathic sweating in end-stage cancer patients during hospice care

End-stage cancer patients frequently suffer from idiopathic sweating of unknown cause. This study was to evaluate the effect (primary endpoint) of modified Yu Ping Feng San on idiopathic sweating and adverse reactions (secondary endpoint). Thirty two end-stage cancer patients receiving hospice care, with exclusion criteria including sweating due to known causes and taking drugs which may affect the sweating threshold were enrolled. Patients received modified Yu Ping Feng San for 10 consecutive days. The quantitative measurement of sweating showed 26 patients (81.3%) had complete remission of sweating, and the average time required to reach 50% reduction was 4.6 days. The visual analog scale (VAS) sweating score estimated by patients and care-givers showed that the mean reductions were 8.4 and 9.1 points, respectively. An increase in appetite was experienced by 65.6% of patients, after administration of modified Yu Ping Feng San. The most prevalent treatment-related complications were nausea (15.6%), diarrhea (9.3%) and allergy (3.1%) without severity greater than grade 2, and these were reversible after cessation of treatment. These results suggest that modified Yu Ping Feng San is a safe and effective treatment for idiopathic sweating of unknown cause in end-stage cancer patients.

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.

A pilot study of mindfulness-based stress reduction for hot flashes

OBJECTIVE

A variety of results from both population and laboratory studies suggest that stress and hot flashes (HFs) are correlated and that HFs are more severe in women with lower coping abilities. The objective of this pilot study was to obtain information on the feasibility and effect of participation in a mindfulness-based stress reduction (MBSR) program on HF severity and menopause-related quality of life.

DESIGN

Fifteen women volunteers reporting a minimum of seven moderate to severe HFs per day at study intake attended the eight weekly MBSR classes at the University of Massachusetts Medical School. Participants were assessed for menopause-related quality of life before beginning and at the conclusion of the MBSR program. Women also kept a daily log of their HFs through the course of the 7 weeks of the MBSR program and for 4 weeks after it.

RESULTS

Women's scores on quality-of-life measures increased significantly, and the median reported HF severity, calculated as the weekly average of a daily HF severity score, decreased 40% over the course of the 11 weeks of the assessment period. The women were individually interviewed at the completion of their participation, and the results of the interviews were consistent with the results from daily diaries.

CONCLUSIONS

These results provide preliminary positive evidence of the feasibility and efficacy of MBSR in supporting women who are experiencing severe HFs, and it warrants further investigation.

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.

Clonidine raises the sweating threshold in symptomatic but not in asymptomatic postmenopausal women

OBJECTIVE

To determine the effects of clonidine, which reduces central sympathetic activation, on the sweating threshold in postmenopausal women with and without hot flashes.

DESIGN

Laboratory physiologic study.

SETTING

University medical center.

PATIENT(S)

12 healthy postmenopausal women reporting frequent hot flashes and 7 reporting none.

INTERVENTION(S)

In two separate sessions, participants received a blind intravenous injection of clonidine HCl (2 microg/kg of body weight) or placebo, followed by body heating.

MAIN OUTCOME MEASURE(S)

Core body temperature, mean skin temperature, sweat rate, sternal skin conductance level, and blood pressure.

RESULT(S)

Symptomatic women had significantly lower core body temperature sweating thresholds than asymptomatic women after receiving placebo. Clonidine significantly increased this threshold in symptomatic women but lowered it in asymptomatic women.

CONCLUSION(S)

These results support the hypothesis that elevated brain norepinephrine levels reduce the sweating threshold in symptomatic women, thereby contributing to the initiation of menopausal hot flashes.

Alfentanil reduces the febrile response to interleukin-2 in humans

OBJECTIVE

Manifestation of intraoperative fever is impaired by volatile anesthetics and muscle relaxants. Opioids are common anesthetic adjuvants and remain the dominant treatment for postoperative surgical pain and sedation of critically ill patients. The effect of opioids on normal thermoregulatory control is well established. However, the extent to which these drugs might inhibit fever remains unknown. Accordingly, we tested the hypothesis that relatively low plasma concentrations of the mu-receptor agonist alfentanil reduce fever magnitude.

DESIGN

Prospective, randomized, crossover study.

SETTING

Outcomes Research Laboratory, at the Department of Anesthesia and Perioperative Care, University of California, San Francisco.

PATIENTS

Eight healthy male volunteers, aged 25-31 yrs, each studied on three separate days.

INTERVENTION

Each volunteer was given an intravenous injection of 30 IU/g interleukin (IL)-2, followed 2 hrs later by 70 IU/g. One hour after the second dose, the volunteers were randomly assigned to three doses of alfentanil: a) none (control); b) a target plasma concentration of 100 ng/mL; and c) a target concentration of 200 ng/mL. Opioid administration continued for 5 hrs.

METHODS AND MAIN RESULTS

Alfentanil significantly reduced the febrile response to pyrogen, decreasing integrated tympanic membrane temperatures from 7.5+/-2.2 degrees C x hr on the control day, to 4.9+/-1.5 degrees C x hr with 100 ng/mL alfentanil, and to 5.1+/-1.7 degrees C x hr with 200 ng/mL alfentanil (p = .011). Peak temperatures were also significantly reduced from 38.5+/-0.4 degrees C on the control day, to 38.0+/-0.4 degrees C on the 100 ng/mL-alfentanil day and 38.0+/-0.6 degrees C on the 200-ng/mL day (p = .019). Plasma cytokine concentrations increased after IL-2 administration, roughly in proportion to the elevation in core temperature. However, cytokine concentrations did not differ significantly among the treatment groups.

CONCLUSION

Alfentanil significantly reduced the febrile response to IL-2 administration. However, the reduction was comparable at plasma concentrations near 100 and 200 ng/mL. These data indicate that concentrations of opioids commonly observed in critical care patients significantly inhibit the manifestation of fever.

Reduced thermoregulatory null zone in postmenopausal women with hot flashes

OBJECTIVE

Most menopausal hot flashes are preceded by small elevations in core body temperature. If the thermoneutral zone between the thresholds for sweating and shivering is reduced in women with symptoms, the triggering mechanism for hot flashes could be explained.

STUDY DESIGN

We studied 12 postmenopausal women with symptoms and 8 without symptoms. We measured body temperatures with a rectal probe, an ingested telemetry pill, and a weighted average of rectal and skin temperatures. Each woman underwent 3 experimental sessions: determination of the sweating threshold by body heating, determination of the shivering threshold by body cooling, and replication of the sweating threshold with exercise.

RESULTS

The women with symptoms had significantly smaller interthreshold zones than did the symptom-free women for all 3 measures of body temperature: rectal temperature, 0.0 degrees C +/- 0.06 degrees C versus 0.4 degrees C +/- 0.18 degrees C (P <.005); telemetry pill temperature, 0.0 degrees C +/- 0.11 degrees C versus 0.4 degrees C +/- 0.18 degrees C (P <.005); and mean body temperature, 0.8 degrees C +/- 0.09 degrees C versus 1.5 degrees C +/- 0.20 degrees C (P <. 0006). Sweat rates were significantly higher among the women with symptoms (0.06 +/- 0.002 mg. cm(-2). min(-1)) than among the women without symptoms (0.03 +/- 0.001 mg. cm(-2). min(-1), P <.05). Sweating thresholds during exercise did not significantly differ from those during body heating. During exercise all the women with symptoms and none of the women without symptoms had hot flashes.

CONCLUSIONS

Menopausal hot flashes in women with symptoms may be triggered by small elevations in body temperature acting within a reduced thermoneutral zone.

Tramadol reduces the sweating, vasoconstriction, and shivering thresholds

The analgesic tramadol inhibits the neuronal reuptake of norepinephrine and 5-hydroxytryptamine, facilitates 5-hydroxytryptamine release, and activates mu-opioid receptors. Each of these actions is likely to influence thermoregulatory control. We therefore tested the hypothesis that tramadol inhibits thermoregulatory control. Eight volunteers were evaluated on four study days, on which they received no drugs, tramadol 125 mg, tramadol 250 mg, and tramadol 250 mg with naloxone, respectively. Skin and core temperatures were gradually increased until sweating was observed and then decreased until vasoconstriction and shivering were detected. The core temperature triggering each response defined its threshold. Tramadol decreased the sweating threshold by -1.03 +/- 0.67 degrees C microgram-1.mL (r2 = 0.90 +/- 0.12). Tramadol also decreased the vasoconstriction threshold by -3.0 +/- 4.0 degrees C microgram-1.mL (r2 = 0.94 +/- 0.98) and the shivering threshold by -4.2 +/- 4.0 degrees C microgram-1.mL(r2 = 0.98 +/- 0.98). The sweating to vasoconstriction interthreshold range nearly doubled from 0.3 +/- 0.4 degree C to 0.7 +/- 0.6 degree C during the administration of large-dose tramadol (P = 0.04). The addition of naloxone only partially reversed the thermoregulatory effects of tramadol. The thermoregulatory effects of tramadol thus most resemble those of midazolam, another drug that slightly decreases the thresholds triggering all three major autonomic thermoregulatory defenses. In this respect, both drugs reduce the "setpoint" rather than produce a generalized impairment of thermoregulatory control. Nonetheless, tramadol nearly doubled the interthreshold range at a concentration near 200 ng/mL. This indicates that tramadol slightly decreases the precision of thermoregulatory control in addition to reducing the setpoint.

IMPLICATIONS

The authors evaluated the effects of the analgesic tramadol on the three major thermoregulatory responses: sweating, vasoconstriction, and shivering. Tramadol had only slight thermoregulatory effects. Its use is thus unlikely to provoke hypothermia or to facilitate fever.

Clonidine does not impair redistribution hypothermia after the induction of anesthesia

Clonidine is commonly given for premedication, and it impairs normal thermoregulatory responses to warm and cold stimuli while depressing sympathetic tone. We studied the effect of premedication by clonidine on redistribution hypothermia induced by the induction of anesthesia. Sixteen ASA physical status I or II patients were randomly assigned to receive either clonidine 150 micrograms or a placebo. Anesthesia was induced 45 min later by thiopental, fentanyl, and vecuronium i.v. and was maintained by the administration of 0.6% isoflurane. We monitored central core (tympanic) temperature and skin surface temperatures at the forearm and the fingertip during the 2 h after the induction of anesthesia before surgery. We estimated skin blood flow at the level of the forearm by using laser Doppler during the same period. The core temperature decreased comparably in the two groups of patients, from 37.1 +/- 0.2 degrees C to 35.3 +/- 0.4 degrees C and from 37.1 +/- 0.2 degrees C to 35.5 +/- 0.3 degrees C in the clonidine and placebo groups, respectively. The forearm-fingertip surface temperature gradient decreased similarly in the two groups. There was no evidence of cutaneous vasoconstriction. The laser Doppler index at the fingertip increased similarly in the two groups, as did the forearm-fingertip temperature gradient. We conclude that premedication with clonidine does not significantly impair the profile of central hypothermia induced by heat redistribution after the induction of anesthesia.

IMPLICATIONS

The induction of general anesthesia is associated with redistribution hypothermia. This study shows that premedication with oral clonidine does not worsen the decrease in core temperature resulting from general anesthesia.