Chest
Volume 128, Issue 5, November 2005, Pages 3691-3698
Journal home page for Chest

Laboratory and Animal Investigations
Effects of Gas Leak on Triggering Function, Humidification, and Inspiratory Oxygen Fraction During Noninvasive Positive Airway Pressure Ventilation

https://doi.org/10.1378/chest.128.5.3691Get rights and content

Objectives: During noninvasive positive pressure ventilation (NPPV), the gas leak that commonly occurs around the mask can render NPPV ineffective. We evaluated the effects of gas leak on inspiratory trigger function during NPPV with bilevel pressure and ICU ventilators. In addition, we evaluated the effects of gas leak on fraction of inspired oxygen (Fio2) and humidification.

Methods: Air leak was created at the airway opening of a model lung by establishing several different-size holes in the circuit. During simulated spontaneous breathing, we evaluated inspiratory trigger performance of two bilevel pressure ventilators (BiPAP Vision and BiPAP S/T-D; Respironics; Murrysville, PA) and two ICU ventilators (Puritan-Bennett 7200ae and Puritan-Bennett 840; Tyco Healthcare; Mansfield, MA). Inspiratory delay time and inspiratory trigger pressure were analyzed. Fio2at the airway opening and inside the model lung were evaluated during BiPAP S/T-D ventilation at supplemental oxygen flows of 3, 6, 9, 12 and 15 L/min. Measured oxygen concentration was compared to mathematically predicted levels. Finally, using two heated humidifiers, we evaluated the effect of gas leak on humidification.

Results: The bilevel pressure ventilators triggered properly at all levels of gas leak, and inspiratory triggering was more effective than with the ICU ventilators. Delivered Fio2with the BiPAP S/T-D ventilator was affected by gas leak and could be predicted mathematically unless the gas leak was large. With large gas leaks, although relative humidity was maintained, absolute humidity decreased.

Conclusion: Gas leak affected triggering of ICU ventilators, Fio2of the BiPAP S/T-D ventilator, and humidity with both types of humidifiers.

Section snippets

Lung Model and Ventilators

We used a custom-made bellows-in-a-box model lung12 to simulate spontaneous breathing (Fig 1). The lung consisted of two lung compartments within a rigid box. The space around the compartments simulated the pleural space. The diaphragm compartment bellows was connected to a T-tube through which gas flow was injected to create a Venturi-establishing negative pleural pressure resulting in inspiration of the lung bellows. The source gas was connected to a custom-made pressure regulator and a

Triggering Evaluation

Table 1shows DT and PI for each leak level on all ventilators. The Puritan-Bennett 7200ae and Puritan-Bennett 840 showed uncontrollable self-triggering when the gas leak was > 18 L/min at end-expiration. The BiPAP Vision and BiPAP S/T-D adequately compensated for all leaks, and PI and DT were not affected by any air leak (Fig 3,top,A, andbottom,B;Table 1), nor by either airway resistance (only data for 5 cm H2O/L/s are presented inTable 1).

Fio2Evaluation

Figure 4shows representative waveforms for Fio2and

DISCUSSION

Major findings of this study are that bilevel pressure ventilators could adequately compensate for all levels of leak evaluated, while ICU ventilators were not able to cope with large leaks. As the leak increased, the bilevel ventilation inspiratory triggering response was not affected. The Fio2delivered by the BiPAP S/T-D was affected in ways not predicted by the formula when the gas leak was large. The MR290 was able to maintain temperature and humidity under all leak conditions.

NPPV is

REFERENCES (21)

  • E Miyoshi et al.

    Performance of transport ventilator with patient-triggered ventilation.

    Chest

    (2000)
  • T Bunburaphong et al.

    Performance characteristics of bilevel pressure ventilators: a lung model study.

    Chest

    (1997)
  • S Mehta et al.

    Noninvasive ventilation.

    Am J Respir Crit Care Med

    (2001)
  • Bach JR. Conventional approaches to managing neuromuscular ventilatory failure. In: Bach JR, ed. Pulmonary...
  • G Finlay et al.

    Treatment of respiratory failure due to kyphoscoliosis with nasal intermittent positive pressure ventilation (NIPPV).

    Ir J Med Sci

    (1995)
  • L Brochard et al.

    Noninvasive ventilation for acute exacerbations of chronic obstructive pulmonary disease.

    N Engl J Med

    (1995)
  • N Kramer et al.

    Randomized, prospective trial of noninvasive positive pressure ventilation in acute respiratory failure.

    Am J Respir Crit Care Med

    (1995)
  • I Auriant et al.

    Noninvasive ventilation reduces mortality in acute respiratory failure following lung resection.

    Am J Respir Crit Care

    (2001)
  • M Antonelli et al.

    Noninvasive ventilation for treatment of acute respiratory failure in patients undergoing solid organ transplantation.

    JAMA

    (2000)
  • G Hilbert et al.

    Noninvasive ventilation in immunosuppressed patients with pulmonary infiltration, fever, and acute respiratory failure.

    N Engl J Med

    (2001)
There are more references available in the full text version of this article.

Cited by (0)

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (www.chestjournal.org/misc/reprints.shtml).

View full text