The effect of insufflation leaks upon ventilation. A quantified comparison of ventilators.

Some ventilator-dependent patients use uncuffed tracheostomy tubes, resulting in fluctuations in the minute volume of ventilation. Bedside measurement of ventilation is difficult because of the insufflation and exsufflation leaks. This laboratory study of five different ventilators measured the tidal volumes achieved with three insufflation leaks introduced in an increasing order of magnitude and at three levels of compliance. The largest leak reduced the peak inflation pressure from 26 to 14 cmH2O in two pressure-limited ventilators with a 35% loss of the initial tidal volume of 800 ml. The turbine-driven pressure-limited ventilator retained a peak pressure of 20.5 cmH2O and lost only 14% of the volume, whereas the volume ventilators lost 65% of the tidal volume. The loss of volume was 3% for every cmH2O decrease in airway pressure due to a leak, regardless of the ventilator or compliance. Using the Friedman test, the differences between the volume ventilators and the pressure ventilators were significant whilst the three pressure-limited ventilators did not perform significantly differently from each other.