flushing, after which generalized, rigor mortis-like skeletal muscle rigidity mayoccur. Fever is a late sign. Triggering of susceptible muscle takes place during exci ...
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grimacing have been quantified for circumcisions done without anesthesia. Spectrographic properties of crying associated with pain have been identified. Preterm babies anesthetized with the use of nitrous oxide and curare had a greater stress response to a surgical procedure than babies receiving nitrous oxide, curare, and fentanyl. Finally, evidence has been presented of possible short- and long-term memories of pain. With new monitoring and anesthetic techniques, most preterm neonates can be safely anesthetized. Techniques reported include the use of medium to high doses of the narcotic fentanyl, the inhalational agent isoflurane, or regional anesthesia. Anesthesiologists today agree that general or regional anesthesia should be considered for all neonates undergoing an operation. On occasion, physiologic instability may demand that the doses of anesthetic agents be reduced or their use discontinued. This decision should not be based solely on an infant's age or perceived degree of maturity. DENIS LOBO, MD Loma Linda, California REFERENCES
Anand KJS, Hickey PR: Pain and its effects in the human neonate and fetus. N Engl J Med 1987; 317:1321-1329 Anand KJS, Sippell WG, Aynsley-Green A: Randomised trial of fentanyl anaesthesia in preterm babies undergoing surgery: Effects on the stress response. Lancet 1987; 1:243-248 Berry FA, Gregory GA: Do premature infants require anesthesia for surgery? (Editorial). Anesthesiology 1987; 67:291-293 Poland RL, Roberts RJ, Gutierrez-Mazorra JF, et al: Neonatal anesthesia. Pediatrics 1987; 80:446
Malignant Hyperthermia-Update MALIGNANT HYPERTHERMIA is an acute hypermetabolic syndrome that can progress within 30 minutes to a premorbid state in which the arterial pH is as low as 6.6 units and the temperature is above 42°C (108°F). Until recently, malignant hyperthermia was among the leading causes of anesthetic death, with mortality above 65 %. The incidence of malignant hyperthermic crises is about 1 per 14,000 anesthetics, but the population at risk may be as high as 1 per 200. The syndrome is multigenetic, with variable expressivity and incomplete penetrance. The only welldocumented triggering agents in humans are succinylcholine chloride and the potent inhalation anesthetics. About 1 % of children induced with halothane and succinylcholine will display masseter spasm, and half of those children are susceptible to malignant hyperthermia. The first symptoms of a crisis presenting during anesthesia are hypercarbia, sinus tachycardia, and tachypnea. Next, skin becomes mottled with cyanotic areas and patches of bright red flushing, after which generalized, rigor mortis-like skeletal muscle rigidity may occur. Fever is a late sign. Triggering of susceptible muscle takes place during excitation-contraction coupling. Once susceptible muscle has been triggered, a contraction is maintained by an abnormally increased phospholipase A2 activity, which causes an increase in mitochondrial free fatty acid content and stimulates calcium release. In the presence of free fatty acid, sarcoplasmic reticulum calcium release is increased and reuptake is inhibited. The resulting high sarcoplasmic calcium concentration allows actin and myosin fibers to interact. In late stages, when the muscle temperature rises above 43.5°C (1 lOF), actin-myosin binding is no longer calcium-depen-
dent and the muscle contraction becomes an irreversible contracture.
Treatment should include discontinuing the use of the triggering drugs, hyperventilating the patient with 100% oxygen, and administering 2.5 mg per kg of body weight of dantrolene sodium intravenously as quickly as possible. Additional doses of 2.5 mg per kg should be administered intravenously, to a maximum of 10 mg per kg until symptoms resolve. Dantrolene inhibits excitation-contraction coupling, but its major action appears to be on the sarcoplasmic reticulum. It increases the contraction activation threshold voltage in susceptible and normal muscle and prevents the depolarization of susceptible muscle by halothane. The in vitro caffeine-halothane contraction test is the only widely accepted test for malignant hyperthermia. The diagnosis is established by evaluating a fresh, intact muscle segment for contraction in response to halothane and caffeine, which have little effect on normal muscle. Elective surgical procedures are not contraindicated in patients known to be susceptible. Any type of conduction anesthesia, using any type of anesthetic for local effects (including amides) is acceptable. General anesthesia can be safely administered using a balanced technique combining nitrous oxide and narcotics augmented by nondepolarizing muscle relaxants. Other safe drugs include barbiturates, benzodiazepines, and ketamine hydrochloride. Some physicians preoperatively administer intravenous dantrolene as a prophylactic measure, while others believe it unnecessary. The Malignant Hyperthermia Association of the United States (PO Box 3231, Darien, CT 06820, [203] 655-3007) maintains a 24-hour physician referral service. DANIEL I. SESSLER, MD San Francisco REFERENCES
Cunliffe M, Lerman J, Britt BA: Is prophylactic dantrolene indicated for MHS patients undergoing elective surgery? (Abstr). Anesth Analg 1987; 66:S35 Larach MG, Rosenberg H, Larach DR, et al: Prediction of malignant hyperthermia susceptibility by clinical signs. Anesthesiology 1987; 66:547-550 Sessler DI: Malignant hyperthermia. J Pediatr 1986; 109:9-14
Perioperative Myocardial Infarction OF THE 20 MILLION PATIENTS presenting each year for anesthesia and surgical treatment in the United States, about 1 million have documented coronary artery disease, 2 million have two or more major risk factors for coronary artery disease, and 6 million are older than 65 years. Despite numerous advances in monitoring and therapeutic techniques, the incidence of perioperative myocardial infarction in patients undergoing noncardiac operations remains high: 6% in patients with a previous infarction, 10% in patients undergoing major vascular surgical intervention, and 37% in patients with a recent infarction. In 1983 it was suggested that the reinfarction rate was lower using invasive intraoperative monitoring (2% versus 6%) and prolonged intensive care unit stay (6% versus 37%). These results, however, have not been independently confirmed over the past five years. Over the next decade, the challenge will be to lower perioperative cardiac morbidity. The solution is to rigorously identify the predictors of morbidity and, once identified, attempt to therapeutically alter them. Unfortunately, there are only a few thorough outcome studies of perioperative
