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Review of the role of non-invasive ventilation in the emergency department
  1. Anthony M Cross
  1. Emergency Department, Royal Melbourne Hospital, c/o Post Office, Parkville, Victoria 3050, Australia
  1. Correspondence to: Dr Cross, Emergency Registrar

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One of the first descriptions of a “pulmonary plus pressure machine” in 1936 describes varying success in the treatment of cardiac asthma and bronchial asthma.1 The author describes how an Electrolux or Hoover vacuum cleaner can be used to supply air at positive pressure and wisely cautions that “the machine should be run for some minutes first of all to get rid of the dust”.

The aim of this article is to review the effects of non-invasive ventilation in acute respiratory failure, the evidence for its use in an emergency setting, and make some recommendations concerning its optimal use.

Pathophysiological effects of non-invasive ventilation


Extrinsically applied positive end expiratory pressure (ePEEP) increases alveolar size and recruitment.2, 3 This expands the area available for gas exchange, reduces intrapulmonary shunt, improves lung compliance, and decreases the work of breathing.36 It acts to negate the effects of intrinsic PEEP (iPEEP), which is the cause of dynamic airway compression and gas trapping.7, 8 Ventilation is improved with beneficial effects on the alveolar-arterial gradient, hypercarbia and, to a lesser extent, hypoxia.9, 10

Pressure support (alone or as part of bilevel positive airway pressure, BiPAP) further augments alveolar ventilation and allows some respiratory muscle rest during the inspiratory phase.11


PEEP reduces venous return to the right side of the heart.12 Left ventricular preload, transmural pressure, and relative afterload are all decreased without altering myocardial contractility.1214 Thus, the ejection fraction improves without an increase in myocardial oxygen consumption.12, 15 It appears that those with worst ventricular dysfunction show the most significant improvement in stroke volume index with continuous positive airway pressure (CPAP).16

Overall, CPAP leads to a decrease in arterial pressure, heart rate, and rate-pressure product within 10 minutes, without exacerbation of hypotension.17

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  • Conflict of interest: none.

  • Funding: none.