title: Effect of a heated humidifier during continuous positive airway pressure delivered by a helmet.
abstract: BACKGROUND
  The helmet may be an effective interface for the delivery of noninvasive positive pressure ventilation. The high internal gas volume of the helmet can act as a 'mixing chamber', in which the humidity of the patient's expired alveolar gases increases the humidity of the dry medical gases, thus avoiding the need for active humidification. We evaluated the temperature and humidity of respiratory gases inside the helmet, with and without a heated humidifier, during continuous positive airway pressure (CPAP) delivered with a helmet.
  
  
  METHODS
  Nine patients with acute respiratory failure (arterial oxygen tension/fractional inspired oxygen ratio 209 +/- 52 mmHg) and 10 healthy individuals were subjected to CPAP. The CPAP was delivered either through a mechanical ventilator or by continuous low (40 l/min) or high flow (80 l/min). Humidity was measured inside the helmet using a capacitive hygrometer. The level of patient comfort was evaluated using a continuous scale.
  
  
  RESULTS
  In patients with acute respiratory failure, the heated humidifier significantly increased the absolute humidity from 18.4 +/- 5.5 mgH2O/l to 34.1 +/- 2.8 mgH2O/l during ventilator CPAP, from 11.4 +/- 4.8 mgH2O/l to 33.9 +/- 1.9 mgH2O/l during continuous low-flow CPAP, and from 6.4 +/- 1.8 mgH2O/l to 24.2 +/- 5.4 mgH2O/l during continuous high-flow CPAP. Without the heated humidifier, the absolute humidity was significantly higher with ventilator CPAP than with continuous low-flow and high-flow CPAP. The level of comfort was similar for all the three modes of ventilation and with or without the heated humidifier. The findings in healthy individuals were similar to those in the patients with acute respiratory failure.
  
  
  CONCLUSIONS
  The fresh gas flowing through the helmet with continuous flow CPAP systems limited the possibility to increase the humidity. We suggest that a heated humidifier should be employed with continuous flow CPAP systems.
authors.affiliation: Unità Operativa di Anestesia e Rianimazione, Fondazione IRCCS - 'Ospedale Maggiore Policlinico, Mangiagalli, Regina Elena', via F, Sforza 35, 20122 Milan, Italy. chiumello@libero.it
authors.forename: Davide
authors.initials: D
authors.lastname: Chiumello
authors.forename: Monica
authors.initials: M
authors.lastname: Chierichetti
authors.forename: Federica
authors.initials: F
authors.lastname: Tallarini
authors.forename: Paola
authors.initials: P
authors.lastname: Cozzi
authors.forename: Massimo
authors.initials: M
authors.lastname: Cressoni
authors.forename: Federico
authors.initials: F
authors.lastname: Polli
authors.forename: Riccardo
authors.initials: R
authors.lastname: Colombo
authors.forename: Antonio
authors.initials: A
authors.lastname: Castelli
authors.forename: Luciano
authors.initials: L
authors.lastname: Gattinoni
mesh_terms: D000704:Analysis of Variance; D016022:Case-Control Studies; D045422:Continuous Positive Airway Pressure / Q000295:instrumentation*; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D008397:Masks; D012131:Respiratory Insufficiency / Q000628:therapy*; D016896:Treatment Outcome