Pressure versus volume-controlled ventilation with a laryngeal mask airway in paediatric patients.
Keidan I, Berkenstadt H, Segal E, Perel A. Paediatric Anaesthesia 2001; 11:691-94,.
Review: In a prospective study, 32 patients undergoing elective surgery under general anesthesia were ventilated with mechanical ventilation via a laryngeal mask airway (LMA). Patients ranged from 6months to 17 years in age. LMA size was selected according to standard guidelines for weight and age. Patients were ventilated in random order with both pressure-controlled (PCV) and volume-controlled ventilation (VCV) to achieve a target end-tidal CO2 of 38-42 mmHg. Initial ventilator parameters were 15 breaths/min. and either an inspiratory tidal volume of 10mL/kg or a peak inspiratory pressure (PIP) of 15cm H20. All patients were effectively ventilated to the target end-tidal CO2 , and no patient developed a significant increase in abdominal circumference or exhibited signs of gastric distention or aspiration. There were no significant differences in expired tidal volume (8.8+3mL with PCV vs. 8.4+2.3mLwith VCV) or percentage of leak volume. PIP was significantly lower with PCV (14.1+1.6 vs. 16.7+2.3cm H20). During VCV, PIP ranged from 20-25cm H20 in six patients. The authors concluded that PCV provided effective ventilation with a lower PIP and lower risk of gastric insufflation.
Comment: Positive pressure ventilation via an LMA is common in adults but remains controversial in children due to concern about gastric insufflation and regurgitation. Earlier studies reported the efficacy of PPV but also noted the potential risk of gastric insufflation. This study corroborates the efficacy of positive pressure ventilation and also demonstrates that PCV provides effective ventilation with lower airway pressure. Gursoy et al. recommended assessment of airway integrity prior to positive pressure ventilation via the LMA. This can easily be accomplished by measuring the airway pressure at which gas leaks around the LMA cuff and by gentle manual ventilation. Ventilation with a PIP that is less than the leak pressure may reduce the risk of gastric distention and avoid pollution of the ambient air with anesthetic gas. PCV appears to be an effective mode of ventilation. The authors did not observe gastric distention or regurgitation. However, the study population was too small to address the issue of aspiration risk.
Reviewed by: John T. Algren, MD
Vanderbilt Children's Hospital
Nashville, TN
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