The Comparison of Respiratory Mechanics after Laryngeal Mask Airway and Endotracheal Tube Insertion during Positive Pressure Ventilation / 대한마취과학회지

ABSTRACT

BACKGROUND: The laryngeal mask airway (LMA) is relatively easy to use and may have advantages over an endotracheal tube (ETT). This randomized cross over study was performed to compare the respiratory parameters of a LMA and ETT in anesthetized mechanically ventilated patients. METHODS: Thirty ASA physical status I and II adult patients undergoing peripheral limb surgery were studied. Anesthesia was induced with fentanyl 1.5ng/kg and thiopental sodium 5 mg/kg. Anesthesia was maintained with O2 1 L/min - N2O 1 L/min - enflurane (end tidal concentration 1.0 1.5 vol%) and muscle relaxation was accomplished using vecuronium 0.12 mg/kg. A LMA and ETT were placed in a random sequence in each patient and connected to a ventilator. After 15 minutes of each insertion at the same ventilator setting, ventilatory variables and arterial CO2 partial pressure were measured and physiological dead space/tidal volume ratio was calculated by a CO2SMO plus! respiratory profile monitor. RESULTS: Physiological dead space/tidal volume ratio and airway dead space in the LMA group were significantly higher compared with those in the ETT group. There were no statistically significant differences in dynamic and static compliance. Inspiratory and expiratory airway resistance were lower in the LMA group. There were no significant differences in air leakage fraction and total inspiratory work done by the ventilator on the respiratory system. Airway pressure, arterial, end-tidal and mixed expired CO2 partial pressure were similar in both groups. CONCLUSIONS: Efficiency of ventilation is similar with a LMA and ETT during positive ventilation in patients without pulmonary disease. We found no differences of clinical importance in either group of patients in the range of measured parameters.