Gas leakage and the laryngeal mask airway. A comparison with the tracheal tube and facemask during spontaneous ventilation using a circle breathing system.

The ability of the laryngeal mask airway, tracheal tube and facemask to provide a leak free seal in a clinical setting was assessed by measuring the minimal fresh gas flows needed in a closed circle system during spontaneous ventilation on 60 subjects. The fresh gas flow was reduced until no spillage occurred from the pop-off valve. This fresh gas flow was taken to represent the sum of gas uptake by the subject and gas leakage from the circuit. The median fresh gas flow after 20 minutes was 350 ml.min-1 in the laryngeal mask airway group, 350 ml.min-1 in the tracheal tube group and 450 ml.min-1 in the facemask group. The fresh gas flow required for the facemask group was significantly higher than that for the laryngeal mask airway or tracheal tube groups (p < 0.01). There was no significant difference between the fresh gas flows required for the tracheal tube and laryngeal mask airway group. We conclude that the laryngeal mask airway provides as good a gas tight seal as a tracheal tube in this context and would be of benefit in reducing anaesthetic gas pollution.

Myocardial necrosis due to intraperitoneal administration of phenylpropanolamine in rats.

Overdose with the sympathomimetic agent phenylpropanolamine (PPA) may cause arrhythmias and myocardial injury in humans. To study the mechanism of these toxic effects, unanesthetized rats (6 animals per group) were given single intraperitoneal doses of 1, 2, 4, 8, 16, or 32 mg/kg PPA. Increases in blood pressure, measured by tail cuff, were dose related and comparable to increases reported in patients with PPA toxicity. Animals were killed at 24 hr and light microscopic examination showed diffuse, dose-related myocardial necrosis. Histology scores (a measure of severity of necrosis) in groups receiving 8, 16, and 32 mg/kg PPA were 1.4 +/- 0.5, 1.8 +/- 1.0, and 2.3 +/- 0.4, respectively, and were all significantly greater than the histology score of control animals (0.2 +/- 0.3, p less than 0.01). The observed lesion was similar in appearance to the myocardial necrosis produced by large doses of catecholamines or sympathomimetic agents in rats. In summary, single doses of PPA caused myocardial necrosis in rats at doses comparable to those causing toxicity in humans. Myocardial necrosis may contribute to the cardiac toxicity of PPA overdose.