GAS LEAK AND GASTRIC INSUFFLATION DURING CONTROLLED VENTILATION - FACE MASK VERSUS LARYNGEAL MASK AIRWAY

Purpose: To compare two airway management techniques, face mask (FM) w ith oropharyngeal airway and laryngeal mask airway (LMA), with respect to the effectiveness of positive pressure ventilation and airway main tenance. Methods: After induction of anaesthesia, two airway managemen t techniques (FM or LMA) and three peak pressures (20, 25 and 30 cm H2 O) were randomly applied during controlled ventilation in 60 patients, Data collected included inspiratory and expiratory volumes and presen ce of gastro-oesophageal insufflation. Leak was calculated by subtract ing the expiratory from the inspiratory volume, expressed as a fractio n of the inspiratory volume. Results: Expiratory volumes (mean +/- SD) at 20, 25 and 30 cm H2O for LMA ventilation were 893 +/- 260, 986 +/- 276 and 1006 +/- 262 respectively, and for FM ventilation 964 +/- 264 , 1100 +/- 268 and 1116 +/- 26.1 Leak fractions at 20, 25 and 30 cm H2 O for LMA ventilation were 0.21 +/- 0.15, 0.24 +/- 0.18 and 0.26 +/- 0 .18 respectively, and for FM ventilation 0.14 +/- 0.09, 0.14 +/- 0.09 and 0.12 +/- 0.08, The frequency of gastro-oesophageal insufflation wa s 1.6%, 5% and 5% for the LMA and 5%, 15% and 26.6% for the FM for ven tilation pressures of 20, 25 and 30 cm H2O respectively which was grea ter with LMA use. Conclusion: Ventilation was adequate in all patients using both techniques, Leak was pressure dependent and greater with L MA use. Most of the leak was vented to the atmosphere via the pharynx, Gastro-oesophageal insufflation was more frequent with ventilation us ing the face mask. LMA use with positive pressure ventilation would ap pear to be a better airway management method than the face mask.