Comparison between Laryngeal Mask Airway and Uncuffed Tracheal Tube for Positive Pressure Ventilation in Paralyzed Pediatric Patients: A Randomized Crossover Study / 대한마취과학회지

BACKGROUND: This randomized cross over study was performed to compare the effect of positive pressure ventilation (PPV) through a laryngeal mask airway (LMA) with that through an uncuffed endotracheal tube (ETT) in paralyzed pediatric patients. Additionally, this study was to determine the protective effect of LMA for the aspiration of oral secretion. METHODS: Pediatric patients (n = 158) weighing less than 30 kg, of ASA physical status 1 or 2 were studied. LMA or ETT was randomly selected and connected to a volume-type ventilator. After measurement and extubation, the other that was not initially used was inserted. Expiratory tidal volume (VT) and airway pressure were measured at the same ventilator setting by a simple pneumo-tachometer, and the expiratory tidal volume ratio (VTR) was calculated as expiratory VT of LMA/expiratory VT of ETT. In randomly selected 39 patients out of 158, methylene blue diluted 1:10 with saline was injected into the oral cavity during PPV through an LMA. At the end of the surgery, fiberoptic bronchoscopy was performed to observe any staining of methylene blue in the trachea. RESULTS: Successful placement of the LMA was achieved in 98% (155/158) of the cases. Expiratory VT through the LMA 1 or 1.5 was decreased if compared with that through the ETT. Leaking pressure of the LMA was lower than that of the ETT except LMA 2.5. VTR of the LMA size 1, 1.5, 2 and 2.5 (mean +/- SD) was respectively 0.94 +/- 0.22, 0.94 +/- 0.14, 1.02 +/- 0.18 and 1.06 +/- 0.19. There was no patient whose trachea was soiled with methylene blue. CONCLUSIONS: Only in older children who are indicated for LMA 2.5, did LMA have the same leakage and the same leaking pressure as ETT during PPV. LMA may not be recommended for the maintenance of PPV in young children less than 10 kg. Inflated LMA seems to have a protective effect against oral secretion.

The Effect of Oxygen Inflow Rate and Tidal Volume on Excretion of Nitrous Oxide by Pharmacokinetic Study / 대한마취과학회지

BACKGROUND: There are few literatures which show the role of tidal volume on the excretion of nitrous oxide(N2O). The purpose of this study is to pharmacokinetically evaluate the effect of varying oxygen inflow rates and tidal volumes on the excretion of N2O. METHODS: Ten patients undergoing general anesthesia on supine position were selected. Administering N2O 3 L/min and oxygen 2 L/min with enflurane, ventilatory pattern was tidal volume 10 mL/kg and respiratory rate 11/min. Administration of N2O was stopped after 30 minutes, when end-tidal N2O concentration(ETN2O) were near 60% at steady state. Oxygen was given at 4 L/min with tidal volume(VT) 8 mL/kg(treatment 1), 4 L/min with VT 16 mL/kg (treatment 2), 8 L/min with VT 8 mL/kg(treatment 3) and 8 L/min with VT 16 mL/kg(treatment 4). ETN2O was measured every 15 seconds for first 3 minutes and every 1 minute thereafter. The order of 4 treatments were determined with bloc randomization. The time interval between treatments was 30 minutes. Pharmacokinetic parameters were obtained using PKCALC data program. RESULTS: Area under curve and clearance in treatments 1 and 2 were significantly larger than those in treatments 3 and 4. Mean residence time and half-life in treatment 4 were significantly shorter than those in other treatments. CONCLUSIONS: The oxygen inflow rate enhances the excretion of N2O more than the tidal volume does, and the tidal volume does so when the oxygen inflow rate is 8 L/min.