Patient outcomes with positive pressure versus spontaneous ventilation in non-paralysed adults with the laryngeal mask

Abstract

Purpose: To compare patient outcomes for positive pressure ventilation (PPV) and spontaneous ventilation (SV) in non-paralysed patients with the LMA using either isoflurane or sevoflurane anaesthesia. Methods: One hundred and sixty-four adult patients were studied. Anaesthesia was with fentanyl-propofol and N2O 66% in O2 with 0.75 MAC isoflurane or sevoflurane and either PPV or SV. Positive pressure ventilation was with tidal volumes of 6-8 ml·kg-1. Peak airway pressures were < 15 cm H2O. Patients were evaluated for airway problems, cardiorespiratory effects, and anaesthesia emergence times. Results: There were no failed episodes of PPV or SV. Gastric insufflation was not detected by epigastric auscultation. Airway problems and cardiovascular effects were similar among groups. During maintenance: SpO2 was greater in the PPV group than in the SV group (98.4 vs 97%, P < 0.001); also, (P(ET)CO2) (34 vs 43 mmHg) and the respiratory rate (RR) (15 vs 19 min-1) were higher and the minute ventilation(MV) (5.7 vs 7.2 L) were lower in the SV groups (P < 0.0001). Shorter times to LMA removal and orientation were observed in the sevoflurane groups (P < 0.0001). Conclusions: Patients outcome is similar for SV and PPV in non-paralysed adult patients with the LMA. Isoflurane and sevoflurane at 0.75 MAC provide suitable conditions for maintenance and emergence, but emergence is more rapid with sevoflurane.