Pathophysiology of hyperkalemia induced by succinylcholine

SCh is unequivocally contraindicated in the management of patients who have sustainded thermal trauma or direct muscle trauma and those who have neurologic disorders involving motor deficits, including tetanus. The mechanism is clear in some, but not all, of these conditions, and is related to increased chemosensitivity of the muscle membrane due to the development of receptor sites in extrajunctional areas. Though SCh induces a small release of K+ in normal muscle, it produces a potentially lethal efflux in the presence of increased sensitivity. This K+-releasing action of SCh begins about 5 to 15 days after injury and persists for 2 to 3 months in patients who have sustained burns or trauma, and perhaps 3 to 6 months in patients with upper motor neuron lesions.

Malignant hyperthermia

Malignant hyperthermia (MH) is a pharmacogenetic disorder of skeletal muscle that presents as a hypermetabolic response to potent volatile anesthetic gases such as halothane, sevoflurane, desflurane and the depolarizing muscle relaxant succinylcholine, and rarely, in humans, to stresses such as vigorous exercise and heat. The incidence of MH reactions ranges from 1:5,000 to 1:50,000-100,000 anesthesias. However, the prevalence of the genetic abnormalities may be as great as one in 3,000 individuals. MH affects humans, certain pig breeds, dogs, horses, and probably other animals. The classic signs of MH include hyperthermia to marked degree, tachycardia, tachypnea, increased carbon dioxide production, increased oxygen consumption, acidosis, muscle rigidity, and rhabdomyolysis, all related to a hypermetabolic response. The syndrome is likely to be fatal if untreated. Early recognition of the signs of MH, specifically elevation of end-expired carbon dioxide, provides the clinical diagnostic clues. In humans the syndrome is inherited in autosomal dominant pattern, while in pigs in autosomal recessive. The pathophysiologic changes of MH are due to uncontrolled rise of myoplasmic calcium, which activates biochemical processes related to muscle activation. Due to ATP depletion, the muscle membrane integrity is compromised leading to hyperkalemia and rhabdomyolysis. In most cases, the syndrome is caused by a defect in the ryanodine receptor. Over 90 mutations have been identified in the RYR-1 gene located on chromosome 19q13.1, and at least 25 are causal for MH. Diagnostic testing relies on assessing the in vitro contracture response of biopsied muscle to halothane, caffeine, and other drugs. Elucidation of the genetic changes has led to the introduction, on a limited basis so far, of genetic testing for susceptibility to MH. As the sensitivity of genetic testing increases, molecular genetics will be used for identifying those at risk with greater frequency. Dantrolene sodium is a specific antagonist of the pathophysiologic changes of MH and should be available wherever general anesthesia is administered. Thanks to the dramatic progress in understanding the clinical manifestation and pathophysiology of the syndrome, the mortality from MH has dropped from over 80% thirty years ago to less than 5%.

Postoperative sore throat after ambulatory surgery

BACKGROUND

Sore throat is a common complication of anaesthesia that affects patient satisfaction after surgery.

METHODS

We studied 5264 ambulatory surgical patients prospectively to determine the patient, anaesthetic, and surgical factors associated with sore throat.

RESULTS

In 5264 patients, 12.1% reported a sore throat. Patients with tracheal tube had the greatest incidence, 45.4%, followed by patients with laryngeal mask airway, 17.5%, while patients with a facemask had a lower incidence of sore throat, 3.3%. Female patients had more sore throats than male patients (13.4 vs 9.1%). Airway management had the strongest influence on the incidence of sore throat. Sore throat in ambulatory surgical patients was associated with female sex, younger patients, use of succinylcholine, and gynaecological surgery.

CONCLUSION

Airway management, female sex, younger patients, surgery for gynaecological procedure, and succinylcholine predicts postoperative sore throat. Increased awareness of the predictive factors can help to avoid this combination and improve patient satisfaction.

Succinylcholine-induced hyperkalemia in acquired pathologic states: etiologic factors and molecular mechanisms

Lethal hyperkalemic response to succinylcholine continues to be reported, but the molecular mechanisms for the hyperkalemia have not been completely elucidated. In the normal innervated mature muscle, the acetylcholine receptors (AChRs) are located only in the junctional area. In certain pathologic states, including upper or lower motor denervation, chemical denervation by muscle relaxants, drugs, or toxins, immobilization, infection, direct muscle trauma, muscle tumor, or muscle inflammation, and/or burn injury, there is up-regulation (increase) of AChRs spreading throughout the muscle membrane, with the additional expression of two new isoforms of AChRs. The depolarization of these AChRs that are spread throughout the muscle membrane by succinylcholine and its metabolites leads to potassium efflux from the muscle, leading to hyperkalemia. The nicotinic (neuronal) alpha7 acetylcholine receptors, recently described to be expressed in muscle also, can be depolarized not only by acetylcholine and succinylcholine but also by choline, persistently, and possibly play a critical role in the hyperkalemic response to succinylcholine in patients with up-regulated AChRs.

Intraocular pressure--physiology and implications for anaesthetic management

The major factors controlling intraocular pressure during surgery are the dynamic balance between aqueous humour production in the ciliary body and its elimination via the canal of Schlemm; the auto-regulation and chemical control of choridal blood volume; the extraocular muscle tone and vitreous humour volume. Prior to surgical incision of the anterior chamber in open intraocular procedures, a low-normal intraocular pressure is mandatory to avoid the hazards of iris or lens prolapse and vitreous loss associated with sudden decompression. In general, the central nervous system depressant drugs, hypnotics, narcotics, major tranquillizers, volatile anaesthetic agents are associated with a reduction in intraocular pressure, with the exception of ketamine and possibly trichloroethylene. The mechanism of action of anaesthetic agents in reducing intraocular pressure may involve a direct effect on central diencephalic control centres, reduction of aqueous production, facilitation of aqueous drainage or relaxation of extraocular muscle tone. Succinylcholine administration is associated with a significant rise in intraocular pressure, with a peak increase between two to four minutes following administration and a return to base line values after six minutes. The intraocular hypertensive effect may be due to a tonic contraction of the extraocular muscles, choroidal vascular dilatation or relaxation of orbital smooth muscle. Despite many claims to the contrary, no reported method to date has been shown to consistently prevent the intraocular hypertensive response to intravenous succinylcholine administration. Because the non-depolarizing relaxants are associated with a reduced intraocular pressure, a barbiturate-non-depolarizing relaxant technique utilizing preoxygenation and cricoid pressure has evolved as the most commonly employed induction technique for the emergency repair of a penetrating eye injury. The alternative non-depolarizing relaxant pretreatment-barbiturate-succinylcholine technique may offer the advantages of more rapid onset of relaxation with only minor increases in intraocular pressure and in a carefully controlled rapid sequence induction technique may be the most acceptable method of handling emergency penetrating eye injuries.

Plasma cholinesterase variants and the anaesthetist

Biochemical properties of plasma cholinesterase of significance to the anaesthetist are reviewed. The role of the genetic variants of the enzyme in suxamethonium sensitivity and hyperthermia are discussed with emphasis on the pregnant patient. Altered gene frequencies of the enzyme variants in some mental disorders is commented upon.

Prevalence of IgE antibodies to morphine. Relation to the high and low incidences of NMBA anaphylaxis in Norway and Sweden, respectively

BACKGROUND

Anaphylactic reactions to a neuromuscular blocking agent (NMBA) is more than six times as common in Norway as in Sweden, probably due to differences in preoperative sensitization. The prevalence of IgE-sensitization to morphine (MOR) and suxamethonium (SUX) in comparable populations in Bergen, Norway, and Stockholm, Sweden, was studied and related to possible sensitizing agents.

METHODS

Three hundred sera of 'allergics' and 500 blood donors in Bergen and Stockholm were tested for IgE antibodies to MOR and SUX using Pharmacia Diagnostics ImmunoCAP(Uppsala, Sweden) assay and the results compared to those of 65 patients from Bergen with documented anaphylaxis to NMBA. In addition, 84 different household chemicals were tested, by IgE antibody inhibition, for SUX and MOR.

RESULTS

In Norway 0.4% of blood donors, 3.7% of allergics and 38.5% of anaphylactics were IgE-sensitized to SUX, and 5.0, 10.0 and 66.7%, respectively, to MOR. No serum from Sweden was positive. The majority of those sensitized (69%) were women. Several household chemicals contained SUX and/or MOR activity, but the only difference between Norway and Sweden was cough mixtures containing pholcodine (PHO). IgE antibodies to PHO were present in 6.0% of blood donors from Norway and in no serum from Sweden. Of the anaphylactics, 65-68% were sensitized to MOR or PHO but only 39% to SUX.

CONCLUSIONS

IgE-sensitization to SUX, MOR and PHO was detected in Norway but not in Sweden. One possible explanation is the unrestricted use of cough mixtures containing MOR derivatives in Norway.

Anaphylactic reactions to muscle relaxants under general anesthesia

Eleven patients who suffered a reaction to the administration of muscle relaxants during induction of general anesthesia were explored using skin tests, leukocyte histamine release, lymphocyte transformation test, and the Prausnitz-Küstner test (P-K). Fifteen normal subjects served as controls. Patients who suffered a reaction showed considerable cutaneous hypersensitivity to muscle relaxants. Leukocyte histamine release was positive in three cases and the P-K test was positive in one case. These findings suggest possible specific serum IgE antibodies to muscle relaxants. However, reliable discrimination between immunological and idiosyncratic pharmacological mechanism is difficult to obtain.

Rocuronium versus succinylcholine for rapid sequence induction intubation

BACKGROUND

Patients requiring emergency endotracheal intubation often require a rapid sequence induction (RSI) intubation technique to protect against aspiration or increased intracranial pressure, or to facilitate intubation. Succinylcholine is the most commonly used muscle relaxant because of its fast onset and short duration; unfortunately, it can have serious side effects. Rocuronium has been suggested as an alternative to succinylcholine for intubation. This meta-analysis is an update since our initial Cochrane systematic review in 2003.

OBJECTIVES

To determine if rocuronium creates comparable intubating conditions to succinylcholine during RSI intubation. Comparisons were made based on dose of rocuronium, narcotic use, emergency versus elective intubation, age and induction agent. The primary outcome was excellent intubation conditions. The secondary outcome was acceptable conditions.

SEARCH STRATEGY

In our initial systematic review we searched all databases until March 2000. We have updated that search and searched the Cochrane Central Register of Controlled Trials (The Cochrane Library, 2007 issue 3), MEDLINE (1966 to June Week 3 2007), EMBASE (1988 to 2007 Week 26) for randomized controlled trials or controlled clinical trials relating to the use of rocuronium and succinylcholine. We included foreign language journals and handsearched the references of identified studies for additional citations.

SELECTION CRITERIA

We included all trials meeting the inclusion criteria (comparison of rocuronium and succinylcholine, main outcomes of intubation conditions).

DATA COLLECTION AND ANALYSIS

Two authors (JP, JL or VS) independently extracted data and assessed methodological quality for allocation concealment. We combined the outcomes in RevMan using relative risk (RR) with a random-effects model.

MAIN RESULTS

In our initial systematic review we identified 40 studies and included 26. In this update we identified a further 18 studies and included 11. In total, we identified 58 potential studies; 37 were combined for meta-analysis. Overall, succinylcholine was superior to rocuronium, RR 0.86 (95% confidence interval (95% CI) 0.80 to 0.92) (n = 2690). In the group that used propofol for induction, the intubation conditions were superior with succinylcholine (RR 0.88, 95% CI 0.80 to 0.97) (n = 1183). This is contrary to our previous meta-analysis results where we reported that intubation conditions were superior in the rocuronium group when propofol was used. We found no statistical difference in intubation conditions when succinylcholine was compared to 1.2mg/kg rocuronium; however, succinylcholine was clinically superior as it has a shorter duration of action.

AUTHORS' CONCLUSIONS

Succinylcholine created superior intubation conditions to rocuronium when comparing both excellent and clinically acceptable intubating conditions.

Prevention of Succinylcholine-induced Fasciculation and Myalgia

Fifty-two randomized trials (5,318 patients) were included in this meta-analysis. In controls, the incidence of fasciculation was 95%, and the incidence of myalgia at 24 h was 50%. Nondepolarizing muscle relaxants, lidocaine, or magnesium prevented fasciculation (number needed to treat, 1.2-2.5). Best prevention of myalgia was with nonsteroidal antiinflammatory drugs (number needed to treat, 2.5) and with rocuronium or lidocaine (number needed to treat, 3). There was a dose-dependent risk of blurred vision, diplopia, voice disorders, and difficulty in breathing and swallowing (number needed to harm, < 3.5) with muscle relaxants. There was evidence of less myalgia with 1.5 mg/kg succinylcholine (compared with 1 mg/kg). Opioids had no impact. Succinylcholine-induced fasciculation may best be prevented with muscle relaxants, lidocaine, or magnesium. Myalgia may best be prevented with muscle relaxants, lidocaine, or nonsteroidal antiinflammatory drugs. The risk of potentially serious adverse events with muscle relaxants is not negligible. Data that allow for a risk-benefit assessment are lacking for other drugs.

Detection of IgE antibodies to suxamethonium after anaphylactoid reactions during anaesthesia

Choline covalently coupled to an insoluble support was used in a radioimmunoassay to detect IgE antibodies to suxamethonium in serum samples from patients who experienced life-threatening anaphylactoid reactions after receiving the drug. Direct binding and inhibition experiments and correlations with clinical findings showed that use of choline in such an assay is relevant to the detection of suxamethonium-reactive antibodies. IgE antibodies were found in 9 of 10 patients who reacted to suxamethonium and whose skin-tests to the drug were positive and in 8 other patients who had reactions to other muscle-relaxant drugs. The positive reactions in the latter group were probably due to cross-reacting antibodies that recognise quaternary ammonium groups on more than one muscle relaxant.

Adverse reactions to suxamethonium and other muscle relaxants under general anesthesia

The mechanisms of anaphylactic reactions to muscle relaxants under general anesthesia are not completely understood. Extending an earlier study, we report 41 cases of anaphylactic shock investigated by intradermal skin tests with muscle relaxants (suxamethonium, pancuronium, gallamine, nortoxiferine), in vitro leukocyte histamine release, and Prausnitz-Küstner tests. Intradermal tests were significantly positive at concentrations ranging from 10 to 10(5) times less than those in controls. Reproducibility tested for suxamethonium at a 1-year interval in five patients was good. Histamine release induced by muscle relaxants in Tris-albumin-Ca++-Mg++ buffer showed positive results in 8/25 instances and was inhibited by antigen excess in seven cases. Addition of 50% deuterium oxide (D2O) caused significant increase of histamine release in positive cases and induced release in all five negative cases studied. Muscle relaxant-induced histamine release was inhibited by in vitro anti-IgE leukocyte desensitization. The mean maximal histamine release dropped from 58.2% +/- 9.7 to 5.8% +/- 2 (p less than 0.01). Similarly, leukocyte desensitization also inhibited histamine release induced by anti-IgE but not by formyl-L-methionyl-L-leucyl-L-phenylalanine or poly-L-arginine. Prausnitz-Küstner tests were positive in five out of 21 cases studied and became negative after heat inactivation. These results confirm the usefulness of intradermal skin tests in diagnosis of patients' reaction to muscle relaxants and suggest an IgE-mediated rather than an idiosyncratic mechanism.