Intraoperative clonidine modulates sympathetic tone in the early postoperative period after remifentanil. A double blind, placebo-controlled study

Alpha-2 adrenergic agonists for the prevention of cardiac complications among adults undergoing surgery

BACKGROUND

The surgical stress response plays an important role on the pathogenesis of perioperative cardiac complications. Alpha-2 adrenergic agonists attenuate this response and may help prevent postoperative cardiac complications.

OBJECTIVES

To determine the efficacy and safety of α-2 adrenergic agonists for reducing mortality and cardiac complications in adults undergoing cardiac surgery and non-cardiac surgery.

SEARCH METHODS

We searched CENTRAL (2017, Issue 4), MEDLINE (1950 to April Week 4, 2017), Embase (1980 to May 2017), the Science Citation Index, clinical trial registries, and reference lists of included articles.

SELECTION CRITERIA

We included randomized controlled trials that compared α-2 adrenergic agonists (i.e. clonidine, dexmedetomidine or mivazerol) against placebo or non-α-2 adrenergic agonists. Included trials had to evaluate the efficacy and safety of α-2 adrenergic agonists for preventing perioperative mortality or cardiac complications (or both), or measure one or more relevant outcomes (i.e. death, myocardial infarction, heart failure, acute stroke, supraventricular tachyarrhythmia and myocardial ischaemia).

DATA COLLECTION AND ANALYSIS

Two authors independently assessed trial quality, extracted data and independently performed computer entry of abstracted data. We contacted study authors for additional information. Adverse event data were gathered from the trials. We evaluated included studies using the Cochrane 'Risk of bias' tool, and the quality of the evidence underlying pooled treatment effects using GRADE methodology. Given the clinical heterogeneity between cardiac and non-cardiac surgery, we analysed these subgroups separately. We expressed treatment effects as pooled risk ratios (RR) with 95% confidence intervals (CI).

MAIN RESULTS

We included 47 trials with 17,039 participants. Of these studies, 24 trials only included participants undergoing cardiac surgery, 23 only included participants undergoing non-cardiac surgery and eight only included participants undergoing vascular surgery. The α-2 adrenergic agonist studied was clonidine in 21 trials, dexmedetomidine in 24 trials and mivazerol in two trials.In non-cardiac surgery, there was high quality evidence that α-2 adrenergic agonists led to a similar risk of all-cause mortality compared with control groups (1.3% with α-2 adrenergic agonists versus 1.7% with control; RR 0.80, 95% CI 0.61 to 1.04; participants = 14,081; studies = 16). Additionally, the risk of cardiac mortality was similar between treatment groups (0.8% with α-2 adrenergic agonists versus 1.0% with control; RR 0.86, 95% CI 0.60 to 1.23; participants = 12,525; studies = 5, high quality evidence). The risk of myocardial infarction was probably similar between treatment groups (RR 0.94, 95% CI 0.69 to 1.27; participants = 13,907; studies = 12, moderate quality evidence). There was no associated effect on the risk of stroke (RR 0.93, 95% CI 0.55 to 1.56; participants = 11,542; studies = 7; high quality evidence). Conversely, α-2 adrenergic agonists probably increase the risks of clinically significant bradycardia (RR 1.59, 95% CI 1.18 to 2.13; participants = 14,035; studies = 16) and hypotension (RR 1.24, 95% CI 1.03 to 1.48; participants = 13,738; studies = 15), based on moderate quality evidence.There was insufficient evidence to determine the effect of α-2 adrenergic agonists on all-cause mortality in cardiac surgery (RR 0.52, 95% CI 0.26 to 1.04; participants = 1947; studies = 16) and myocardial infarction (RR 1.01, 95% CI 0.43 to 2.40; participants = 782; studies = 8), based on moderate quality evidence. There was one cardiac death in the clonidine arm of a study of 22 participants. Based on very limited data, α-2 adrenergic agonists may have reduced the risk of stroke (RR 0.37, 95% CI 0.15 to 0.93; participants = 1175; studies = 7; outcome events = 18; low quality evidence). Conversely, α-2 adrenergic agonists increased the risk of bradycardia from 6.4% to 12.0% (RR 1.88, 95% CI 1.35 to 2.62; participants = 1477; studies = 10; moderate quality evidence), but their effect on hypotension was uncertain (RR 1.19, 95% CI 0.87 to 1.64; participants = 1413; studies = 9; low quality evidence).These results were qualitatively unchanged in subgroup analyses and sensitivity analyses.

AUTHORS' CONCLUSIONS

Our review concludes that prophylactic α-2 adrenergic agonists generally do not prevent perioperative death or major cardiac complications. For non-cardiac surgery, there is moderate-to-high quality evidence that these agents do not prevent death, myocardial infarction or stroke. Conversely, there is moderate quality evidence that these agents have important adverse effects, namely increased risks of hypotension and bradycardia. For cardiac surgery, there is moderate quality evidence that α-2 adrenergic agonists have no effect on the risk of mortality or myocardial infarction, and that they increase the risk of bradycardia. The quality of evidence was inadequate to draw conclusions regarding the effects of alpha-2 agonists on stroke or hypotension during cardiac surgery.

Alpha-2 adrenergic agonists for the prevention of shivering following general anaesthesia

BACKGROUND

Shivering after general anaesthesia is common. It is unpleasant but can also have adverse physiological effects. Alpha-2 (α-2) adrenergic agonist receptors, which can lead to reduced sympathetic activity and central regulation of vasoconstrictor tone, are a group of drugs that have been used to try to prevent postoperative shivering.

OBJECTIVES

To assess the following: the effects of α-2 agonists on the prevention of shivering and subsequent complications after general anaesthesia in people undergoing surgery; the effects of α-2 agonists on the risk of inadvertent perioperative hypothermia; and whether any adverse effects are associated with these interventions.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, and EMBASE on 13 June 2014. Our search terms were relevant to the review question and limited to studies that assessed shivering or hypothermia. We also carried out searches of clinical trials registers, and forward and backward citation tracking.

SELECTION CRITERIA

We considered all randomized controlled trials, quasi-randomized studies, and cluster-randomized studies with adult participants undergoing surgery with general anaesthesia in which an α-2 agonist was compared with another α-2 agonist or a placebo for the prevention of shivering.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data, consulting a third review author in the case of disagreements. We used standard Cochrane methodological procedures, including an assessment of risk of bias and use of GRADEpro software to interpret findings.

MAIN RESULTS

We included 20 studies with 1401 surgical participants comparing an α-2 agonist against a control. Thirteen studies compared clonidine with a control, whilst seven compared dexmedetomidine with a control. The doses, methods, and time of administration varied between studies: three studies gave the drug orally or as an intravenous bolus preoperatively and nine intraoperatively; one study gave the drug as an infusion starting preoperatively and seven started at varying points from anaesthetic induction to the end of surgery. Whilst all the studies were described as randomized, many provided insufficient detail on methods used. We had anticipated that attempts would be made to reduce performance bias by blinding of personnel and participants, however this was detailed in only six of the papers. Similarly, in some studies detail was lacking on methods to reduce the risk of detection bias. We therefore downgraded the quality of evidence in our 'Summary of findings' table by one level for risk of bias using the Grades of Recommendation, Assessment, Development and Evaluation (GRADE) approach.All 20 included studies presented outcome data for postoperative shivering, and in meta-analysis α-2 agonists were shown to significantly reduce the risk of shivering (Mantel-Haenszel risk ratio 0.28, 95% confidence interval 0.18 to 0.43, P value < 0.0001). We found significant evidence of heterogeneity (I(2) = 80%) for this result that was not explained by sensitivity or subgroup analysis; we therefore downgraded the inconsistency of the evidence by one level. Although we did not feel that there were concerns with imprecision or indirectness of the data, we downgraded the quality of the evidence for the risk of publication bias following visual analysis of a funnel plot. Using GRADEpro, we rated the overall quality of the data for shivering as very low. Only one study reported the incidence of core hypothermia, whilst 12 studies measured core temperature. However, as the results for core temperature were reported in different styles, pooling the results was inappropriate. We found no studies with participant-reported outcomes such as experience of shivering or participant satisfaction. We found limited data for the outcomes of length of stay in the postanaesthetic care unit (three studies, 200 participants) and the following adverse effects: sedation (nine studies, 875 participants), bradycardia (eight studies, 716 participants), and hypotension (seven studies, 688 participants). Unpooled analysis suggested that sedation and bradycardia were significantly more common with dexmedetomidine than placebo, with all seven dexmedetomidine studies and none of the clonidine studies reporting statistically significantly higher levels of sedation as an adverse effect.

AUTHORS' CONCLUSIONS

There is evidence that clonidine and dexmedetomidine can reduce postoperative shivering, but patients given dexmedetomidine may be more sedated. However, our assessment of the quality of this evidence is very low.

Alpha-2 adrenergic agonists for the prevention of cardiac complications among patients undergoing surgery

BACKGROUND

The surgical stress response plays an important role on the pathogenesis of perioperative cardiac complications. Alpha-2 adrenergic agonists attenuate this response and may thereby prevent cardiac complications.

OBJECTIVES

This review assessed the efficacy and safety of preoperative (within 24 hours), intraoperative, and postoperative (first 48 hours) alpha-2 adrenergic agonists for preventing mortality and cardiac complications after surgery performed under either general or neuraxial anaesthesia, or both.

SEARCH STRATEGY

We searched the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library 2008, Issue 3), MEDLINE (1950 to August week 4 2008), EMBASE (1980 to week 36 2008), the Science Citation Index, and reference lists of articles.

SELECTION CRITERIA

We included randomized controlled trials that compared alpha-2 adrenergic agonists (clonidine, dexmedetomidine, or mivazerol) against placebo or non-alpha-2 adrenergic agonists. Included studies had to report on mortality, myocardial infarction, myocardial ischaemia, or supraventricular tachyarrhythmia.

DATA COLLECTION AND ANALYSIS

Three authors independently assessed trial quality and extracted data. Two authors independently performed computer entry of abstracted data. We contacted study authors for additional information. Adverse event data were gathered from the trials.

MAIN RESULTS

We included 31 studies (4578 participants). Study quality was generally inadequate, with only six studies clearly reporting methods for blinding and allocation concealment. Overall, alpha-2 adrenergic agonists reduced mortality (relative risk (RR) 0.66; 95% CI 0.44 to 0.98; P = 0.04) and myocardial ischaemia (RR 0.68; 95% CI 0.57 to 0.81; P < 0.0001). However, their effects appeared to vary with the surgical procedure. The most encouraging data pertained to vascular surgery, where they reduced mortality (RR 0.47; 95% CI 0.25 to 0.90; P = 0.02), cardiac mortality (RR 0.36; 95% CI 0.16 to 0.79; P = 0.01), and myocardial infarction (RR 0.66; 95% CI 0.46 to 0.94; P = 0.02). With regard to adverse effects, alpha-2 adrenergic agonists significantly increased perioperative hypotension (RR 1.32; 95% CI 1.07 to 1.62; P = 0.009) and bradycardia (RR 1.66; 95% CI 1.14 to 2.41; P = 0.008).

AUTHORS' CONCLUSIONS

Our study provides encouraging evidence that alpha-2 adrenergic agonists may reduce cardiac risk, especially during vascular surgery. Nonetheless, these data remain insufficient to make firm conclusions about their efficacy and safety. A large randomized trial of alpha-2 adrenergic agonists is therefore warranted. Additionally, future research must determine which specific alpha-2 adrenergic agonist should be used, and whether it is safe to combine them with other perioperative interventions (for example beta-adrenergic blockade).

Anästhesie und Analgesie bei Suchtpatienten

Addicts have an exaggerated organic and psychological comorbidity and in cases of major operations or polytrauma they are classified as high-risk patients. Additional perioperative problems are a higher analgetics requirement, craving, physical and/or psychological withdrawal symptoms, hyperalgesia and tolerance. However, the clinical expression depends on the substance abused. For a better understanding of the necessary perioperative measures, it is helpful to classify the substances into central nervous system depressors (e.g. heroin, alcohol, sedatives, hypnotics), stimulants (e.g. cocaine, amphetamines, designer drugs) and other psychotropic substances (e.g. cannabis, hallucinogens, inhalants). The perioperative therapy should not be a therapy for the addiction, as this is senseless. On the contrary, the characteristics of this chronic disease must be accepted. Anesthesia and analgesia must be generously stress protective and sufficiently analgesically effective. Equally important perioperative treatment principles are stabilization of physical dependence by substitution with methadone (for heroin addicts) or benzodiazepines/clonidine (for alcohol, sedatives and hypnotics addiction), avoidance of stress and craving, thorough intraoperative and postoperative stress relief by using regional techniques or systematically higher than normal dosages of anesthetics and opioids, strict avoidance of inadequate dosage of analgetics, postoperative optimization of regional or systemic analgesia by non-opioids and coanalgetics and consideration of the complex physical and psychological characteristics and comorbidities. Even in cases of abstinence (clean) an inadequate dosage must be avoided as this, and not an adequate pain therapy sometimes even with strong opioids, can potentially activate addiction. A protracted abstinence syndrome after withdrawal of opioids can lead to increased response to administered opioids (e.g. analgesia, side-effects).