title: [Airway Obstruction Caused by Heat and Moisture Exchange Filter Used during General Anesthesia: A Case Report and an In Vitro Study].
abstract: BACKGROUND
  A previously healthy 54-year-old woman underwent a resection of the acoustic tumor. Following induction of general anesthesia and tracheal intubation, volume-controlled ventilation was started and the patient was placed in the left park bench position. The heat and moisture exchange filter (HMEF) was placed within the ventilatory circuit and positioned below the patient's head to avoid unintentional extubation. Six hours after the start of surgery, peak inspiratory pressure gradually rose, and 2 hours later ventilation of the patient's lung became increasingly difficult. When the HMEF was replaced, normal breathing was promptly restored.
  
  
  METHODS
  We reproduced this scenario with a similar HMEF under the same ventilator settings by adding 0-8 g of normal saline into the HMEF housing, and measured the inspiratory pressure and tidal volume across the HMEF.
  
  
  RESULTS
  When instilling 4 g of saline, an increase in inspiratory pressure occurred.
  
  
  CONCLUSIONS
  This case shows a potential risk of unexpectedly early occurrence of obstruction of the HMEF due to accumulation of condensed water within the device when the HMEF was positioned below the patient's head. We recommend selection of the appropriate HMEF and suitable mounting to avoid this problem.
authors.forename: Aya
authors.initials: A
authors.lastname: Yoshidome
authors.forename: Ayako
authors.initials: A
authors.lastname: Shinomiya
authors.forename: Tamao
authors.initials: T
authors.lastname: Iwagaki
authors.forename: Haruhiko
authors.initials: H
authors.lastname: Sano
authors.forename: Kazuyoshi
authors.initials: K
authors.lastname: Aoyama
authors.forename: Yukari
authors.initials: Y
authors.lastname: Takenaka
authors.forename: Ichiro
authors.initials: I
authors.lastname: Takenaka
mesh_terms: D000402:Airway Obstruction / Q000209:etiology*; D000768:Anesthesia, General / Q000009:adverse effects* / Q000295:instrumentation; D005260:Female; D005374:Filtration / Q000295:instrumentation; D006358:Hot Temperature / Q000009:adverse effects; D006801:Humans; D006813:Humidity; D007442:Intubation, Intratracheal; D008875:Middle Aged