title: Under-humidification and over-humidification during moderate induced hypothermia with usual devices.
abstract: OBJECTIVE
  In mechanically ventilated patients with induced hypothermia, the efficacy of heat and moisture exchangers and heated humidifiers to adequately humidify the airway is poorly known. The aim of the study was to assess the efficacy of different humidification devices during moderate hypothermia.
  
  
  METHODS
  Prospective, cross-over randomized study.
  
  
  METHODS
  Medical Intensive Care Unit in a University Hospital.
  
  
  METHODS
  Nine adult patients hospitalized after cardiac arrest in whom moderate hypothermia was induced (33 degrees C for 24[Symbol: see text]h).
  
  
  METHODS
  Patients were ventilated at admission (period designated "normothermia") with a heat and moisture exchanger, and were randomly ventilated during hypothermia with a heat and moisture exchanger, a heated humidifier, and an active heat and moisture exchanger.
  
  
  RESULTS
  Core temperature, inspired and expired gas absolute and relative humidity were measured. Each system demonstrated limitations in its ability to humidify gases in the specific situation of hypothermia. Performances of heat and moisture exchangers were closely correlated to core temperature (r (2)[Symbol: see text]=[Symbol: see text]0.84). During hypothermia, heat and moisture exchangers led to major under-humidification, with absolute humidity below 25[Symbol: see text]mgH(2)O/l. The active heat and moisture exchanger slightly improved humidification. Heated humidifiers were mostly adequate but led to over-humidification in some patients, with inspiratory absolute humidity higher than maximal water content at 33 degrees C with a positive balance between inspiratory and expiratory water content.
  
  
  CONCLUSIONS
  These results suggest that in the case of moderate hypothermia, heat and moisture exchangers should be used cautiously and that heated humidifiers may lead to over-humidification with the currently recommended settings.
authors.affiliation: INSERM U 651, Université PARIS XII, Service de Réanimation Médicale, AP-HP, Hôpital Henri Mondor, 51 av. du Maréchal de Lattre de Tassigny, 94010 Créteil, France.
authors.forename: François
authors.initials: F
authors.lastname: Lellouche
authors.forename: Siham
authors.initials: S
authors.lastname: Qader
authors.forename: Solenne
authors.initials: S
authors.lastname: Taille
authors.forename: Aissam
authors.initials: A
authors.lastname: Lyazidi
authors.forename: Laurent
authors.initials: L
authors.lastname: Brochard
mesh_terms: D000328:Adult; D000368:Aged; D018592:Cross-Over Studies; D005260:Female; D006323:Heart Arrest / Q000628:therapy*; D006801:Humans; D006813:Humidity; D007036:Hypothermia, Induced / Q000295:instrumentation*; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies