Esophageal aspiration of air through the drain tube of the ProSeal laryngeal mask.

IMPLICATIONS: Two patients experienced partial upper airway obstruction while breathing spontaneously with the ProSeal laryngeal mask airway. This resulted in esophageal aspiration of air through the drain tube.

Learning to exchange an endotracheal tube for a laryngeal mask prior to emergence.

PURPOSE: To present a stepwise training method, first critiquing laryngeal mask (LM) insertion difficulty and malpositioning, then learning how to exchange an endotracheal tube (ETT) for a LM during emergence from anesthesia. METHODS: "Learning phase:" sixty adults were enrolled in a preliminary study in which ETT / LM exchange was not performed - only LM insertion difficulty and malpositioning in the presence of an oral ETT were evaluated. After induction of anesthesia and oral intubation, a classic LM size 4 was inserted using the standard recommended technique. Number of insertion attempts and fibreoptically determined malpositions were recorded. "ETT / LM exchange phase:" we performed airway exchange in 50 patients selected from our individual practices. RESULTS: "Learning phase:" the LM was satisfactorily positioned, on first attempt, in 95% of cases. With multiple insertion attempts it was possible to place the LM in all 60 intubated patients. Unsuccessful initial placement of the LM was always due to insufficient insertion depth (5%). When fully inserted into the hypopharynx, the epiglottis could be viewed fibreoptically in 13% of cases. "ETT / LM exchange phase:" the LM was inserted successfully in all 50 patients on first attempt. No complications occurred during any exchange. CONCLUSION: We found it is easy to learn how to insert a LM in the presence of an oral ETT. The most serious malposition, occurring in 5% of first attempts, was insufficient insertion depth. The only other malposition we encountered, fibreoptic visualization of the epiglottis, is not likely to result in complete airway obstruction following endotracheal extubation under anesthesia.

A modified intubating laryngeal mask for endotracheal tube exchange.

IMPLICATIONS: It is often necessary to change a patient's breathing tube (endotracheal tube). This can be a risky procedure. This report describes a technique for changing an endotracheal tube by using a modified "intubating laryngeal mask" (a commonly used airway and breathing device) and a fiberoptic bronchoscope.

Analysis of two purified mutants of Escherichia coli aspartate transcarbamylase with single amino acid substitutions.

Two mutant versions of Escherichia coli aspartate transcarbamylase have been purified and analyzed kinetically. Each of these mutant enzymes contains a single amino acid different from the wild-type enzyme, which was introduced by suppression of a nonsense codon within the E. coli pyrB gene. These enzymes exhibited alterations in both homotropic and heterotropic interactions with little change in specific activity. Depending upon the site of the substitution, the allosteric interactions have been either enhanced or diminished over the wild-type enzyme. Carbamyl phosphate saturation curves indicate that aspartate and carbamyl phosphate homotropic co-operativity are separable. Experiments employing the allosteric effectors indicate that the transmission of the regulatory effect is dependent upon the structure of the catalytic subunit, and that CTP inhibition can be partially decoupled from ATP activation. The kinetics of one of the mutants is unusually sensitive to dissociation at elevated temperatures. This sensitivity may be due to weakened interactions between the subunits of the enzyme.