Continuous positive airway pressure delivered with a "helmet": Effects on carbon dioxide rebreathing

Paolo Taccone, Dean Hess, Pietro Caironi, Luca M. Bigatello

Research output: Contribution to journalArticle

Abstract

Objective: The "helmet" has been used as a novel interface to deliver noninvasive ventilation without applying direct pressure on the face. However, due to its large volume, the helmet may predispose to CO2 rebreathing. We hypothesised that breathing with the helmet is similar to breathing in a semiclosed environment, and therefore the PCO2 inside the helmet is primarily a function of the subject's CO2 production and the flow of fresh gas through the helmet. Design: Human volunteer study. Setting: Laboratory in a university teaching hospital. Subjects: Eight healthy volunteers. Interventions: We delivered continuous positive airway pressure (CPAP) with the helmet under a variety of ventilatory conditions in a lung model and in volunteers. Measurements and Main Results: Gas flow and CO2 concentration at the airway were measured continuously. End-tidal PCO 2, CO2 production, and ventilatory variables were subsequently computed. We found that a) when CPAP was delivered with a ventilator, the inspired CO2 of the volunteers was high (12.4 ± 3.2 torr [1.7 ± 0.4 kPa]); b) when CPAP was delivered with a continuous high flow system, inspired CO2 of the volunteers was low (2.5 ± 1.2 torr [0.3 ± 0.2 kPa]); and c) the inspired CO 2 calculated mathematically for a semiclosed system model of CO 2 retoreathing was highly correlated with the values measured in a lung model (r2 = .97, slope = 0.92, intercept = -1.17, p <.001) and in the volunteers (r2 = .94, slope = 0.96, intercept = 0.90, p <.001). Conclusions: a) The helmet predisposes to CO2 recreating and should not be used to deliver CPAP with a ventilator; b) continuous high flow minimizes CO2 rebreathing during CPAP with the helmet; and c) minute ventilation and PCO2 should be monitored during CPAP with the helmet.

Original languageEnglish
Pages (from-to)2090-2096
Number of pages7
JournalCritical Care Medicine
Volume32
Issue number10
DOIs
Publication statusPublished - Oct 2004

Keywords

  • Acute respiratory failure
  • Carbon dioxide rebreathing
  • Continuous positive airway pressure
  • Face mask
  • Helmet
  • Noninvasive ventilation

ASJC Scopus subject areas

  • Critical Care and Intensive Care Medicine

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