Isoflurane muscle effects

Desflurane is less potent than the other fluorinated anesthetics having MAC values of 5.7 to 8.9% in animals (76,85), and 6% to 7.25% in surgical patients. The respiratory effects are similar to isoflurane. Heart rate is somewhat increased and blood pressure decreased with increasing concentrations. Cardiac output remains fairly stable. Desflurane does not sensitize the myocardium to epinephrine relative to isoflurane (86). EEG effects are similar to isoflurane and muscle relaxation is satisfactory (87). Desflurane is not metabolized to any significant extent (88,89) as levels of fluoride ion in the semm and urine are not increased even after prolonged exposure. Desflurane appears to offer advantages over sevoflurane and other inhaled anesthetics because of its limited solubiHty in blood and other tissues. It is the least metabolized of current agents. 

Halothane exerts a pronounced hypotensive effect, to which a negative inotropic effect contributes. Enflurane and isoflurane cause less circulatory depression. Halothane sensitizes the myocardium to catecholamines (caution serious tachyarrhythmias or ventricular fibrillation may accompany use of catecholamines as antihypotensives or toco-lytics). This effect is much less pronounced with enflurane and isoflurane. Unlike halothane, enflurane and isoflurane have a muscle-relaxant effect that is additive with that of nondepolarizing neuromuscular blockers. 

The duration of exposure to the anesthetic can also have a significant effect on the recovery time, especially in the case of the more soluble anesthetics (eg, halothane and isoflurane). Accumulation of anesthetics in muscle, skin, and fat increases with prolonged exposure (especially in obese patients), and blood tension may decline slowly during recovery as the anesthetic is slowly eliminated from these tissues. Although recovery may be rapid even with the more soluble agents following a short period of exposure, recovery is slow after prolonged administration of halothane or isoflurane. 

Halothane, isoflurane, and enflurane have similar depressant effects on the EEG up to doses of 1-1.5 MAC. At higher doses, the cerebral irritant effects of enflurane may lead to development of a spike-and-wave pattern and mild generalized muscle twitching (ie, myoclonic activity). However, this seizure-like activity has not been found to have any adverse clinical consequences. Seizure-like EEG activity has also been described after sevoflurane, but not desflurane. Although nitrous oxide has a much lower anesthetic potency than the volatile agents, it does possess both analgesic and amnesic properties when used alone or in combination with other agents as part of a balanced anesthesia technique. 

Inhaled (volatile) anesthetics potentiate the neuromuscular blockade produced by nondepolarizing muscle relaxants in a dose-dependent fashion. Of the general anesthetics that have been studied, inhaled anesthetics augment the effects of muscle relaxants in the following order isoflurane (most) sevoflurane, desflurane, enflurane, and halothane and nitrous oxide (least) (Figure 27-9). The most important factors involved in this interaction are the following (1) nervous system depression at sites proximal to the neuromuscular junction (ie, central nervous system) (2) increased muscle blood flow (ie, due to peripheral vasodilation produced by volatile anesthetics), which allows a larger fraction of the injected muscle relaxant to reach the neuromuscular junction and (3) decreased sensitivity of the postjunctional membrane to depolarization. 

Inhaled anesthetics that are relatively insoluble in blood (low blood gas partition coefficient) and brain are eliminated at faster rates than more soluble anesthetics. The washout of nitrous oxide, desflurane, and sevoflurane occurs at a rapid rate, which leads to a more rapid recovery from their anesthetic effects compared to halothane and isoflurane. Halothane is approximately twice as soluble in brain tissue and five times more soluble in blood than nitrous oxide and desflurane its elimination therefore takes place more slowly, and recovery from halothane anesthesia is predictably less rapid. The duration of exposure to the anesthetic can also have a marked effect on the time of recovery, especially in the case of more soluble anesthetics. Accumulation of anesthetics in tissues, including muscle, skin, and fat, increases with continuous inhalation (especially in obese patients), and blood tension may decline slowly during recovery as the anesthetic is gradually eliminated from these tissues. Thus, if exposure to the anesthetic is short, recovery may be rapid even with the more soluble agents. However, after prolonged anesthesia, recovery may be delayed even with anesthetics of moderate solubility such as isoflurane. 

Kataoka et al. (1994) studied the negative inotropic effects of sevoflurane, isoflurane, enflurane and halothane in canine blood-perfused papillary muscles. 

McMurphy RM, Hodgson DS (1996) Cardiopulmonary effects of desflurane in cats. Am J Vet Res 57 367-370 Mazzeo AJ, Cheng EY, Bosnjak ZJ et al. (1996) Differential effects of desflurane and halothane on peripheral airway smooth muscle. Br J Anaesth 76 841-846 Mitsuhata H, Saitoh J, Shimizu R et al. (1994) Sevoflurane and isoflurane protect against bronchospasm in dogs. Anesthesiol 81 1230-1234... 

Other effects. Isoflurane relaxes voluntary muscles and potentiates the effects of nondepolarising muscle relaxants. Isoflurane depresses cortical EEG activity and does not induce abnormal electrical activity or convulsions. 

The inhalational anesthetics halothane, isoflurane, and enflu-rane all have been reported to have a positive effect in children and adults with severe asthma that is unresponsive to standard medical therapy. The proposed mechanisms for inhalational anesthetics include direct action on bronchial smooth muscle, inhibition of airway reflexes, attenuation of histamine-induced bronchospasm, and interaction with /32-adrenergic receptors. Well-controlled trials with these agents have not been completed. Potential adverse effects include myocardial depression, vasodilation, arrhythmias, and depression of mucociliary function. In addition, the practical problem of delivery and scavenging these agents in the intensive care environment as opposed to the operating room is a concern. The use of volatile anesthetics cannot be recommended based on insufficient evidence of efficacy. 

Electrolyte imbalance, and diseases that lead to electrolyte imbalance, such as adrenal cortical insufficiency, alter neuromuscular blockade. Depending on the nature of the imbalance, either enhancement or inhibition may be expected. Magnesium sulfate, used in the management of toxemia of pregnancy, enhances the skeletal-muscle-relaxing effects of pancuronium. Antibiotics such as aminoglycosides, tetracyclines, clindamycin, lincomycin, colistin, and sodium colistimethate augment the pancuronium-induced neuromuscular blockade. Anesthetics such as halothane, enflurane, and isoflurane enhance the action of pancuronium, whereas azathioprine will cause a reversal of neuromuscular blockade. 

Because diethyl ether (commonly known simply as ether) is a short-lived muscle relaxant, it has been widely used as an inhalation anesthetic. However, because it takes effect slowly and has a slow and unpleasant recovery period, other compounds, such as enflurane, isoflurane, and halothane, have replaced ether as an anesthetic. Diethyl ether is still used where there is a lack of trained anesthesiologists, since it is the safest anesthetic to administer by untrained hands. Anesthetics interact with the nonpolar molecules of cell membranes, causing the membranes to swell, which interferes with their permeability. 

Muscle Isoflurane produces some relaxation of skeletal muscle via its central effects. It also enhances the effects of depolarizing and nondepolarizing muscle relaxants. Isoflurane is more potent than halothane in its potentiation of neuromuscular blocking agents. The drug relaxes uterine smooth muscle and is not recommended for analgesia or anesthesia for labor and vaginal delivery. 

E) Isoflurane has less skeletal muscle-relaxing effects than other inhalation anesthetics... 

A 71-year-old woman received a standard bowel preparation consisting of oral erythromycin and neomycin (a total of 3 g). Surgery was postponed for one day and she received a second similar bowel preparation pre-operatively. Anaesthesia was induced with sufentanil and etomidate and maintained with isoflurane and sufentanil. Rocuronium (total dose of 60 mg over 2 hours) was used to facilitate tracheal intubation and maintain muscle relaxation. Despite clinical appearance of a reversal of the neuromuscular blockade by neostigmine 3.5 mg and glycopyrrolate 400 micrograms, the patient complained of dyspnoea and required reintubation twice. The effects of additional doses of neostigmine were inconsistent and the use edrophonium 50 mg or calcium chloride 500 mg intravenously did not result in an improvement. ... 

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