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Comment & Response
October 11, 2016

Face Mask vs Helmet for Noninvasive Ventilation—Reply

Author Affiliations
  • 1Section of Pulmonary and Critical Care, University of Chicago, Chicago, Illinois
JAMA. 2016;316(14):1497. doi:10.1001/jama.2016.13858

In Reply Drs Taccone and Chiumello state that physicians must understand the helmet’s physiologic behavior in terms of co2 rebreathing to ensure safety. We agree with this statement. Neurological impairment led to intubation in 5 of the 8 intubated patients in the helmet group (of a total of 44). They suggest unrecognized co2 retention and hypercapnic encephalopathy might have been responsible. Typically encephalopathy from acute hypercapnia occurs at a partial pressure of co2 (Pco2) greater than 75 to 80 mm Hg. The median Pco2 in the intubated patients in the helmet group in the study was 46.5 mm Hg. Previous work has identified a risk of co2 rebreathing with a helmet using a ventilator. We reported a high ventilator fresh gas flow of 100 to 200 L/min, which was not the peak inspiratory flow but the flow range throughout inspiration. The inspiratory fresh gas flow of 100 to 200 L/min is much higher than the 25 to 40 L/min noted by Taccone and colleagues in a study of healthy volunteers using the helmet.1

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