Mechanical effects of airway humidification devices in difficult to wean patients.
OBJECTIVE
To evaluate the influence of airway humidification devices on the efficacy of ventilation in difficult to wean patients.


METHODS
A prospective, randomized, controlled physiologic study.


METHODS
A 22-bed medical intensive care unit in a university hospital.


METHODS
Chronic respiratory failure patients.


METHODS
Performances of a heated humidifier and a heat and moisture exchanger were evaluated on diaphragmatic muscle activity, breathing pattern, gas exchange, and respiratory comfort during weaning from mechanical ventilation by using pressure support ventilation. Eleven patients with chronic respiratory failure were submitted to four pressure support ventilation sequences by using the heated humidifier and the heat and moisture exchanger at two different levels of pressure support ventilation (7 and 15 cm H(2)O).


RESULTS
Compared with the heated humidifier and regardless of the pressure support ventilation level used, the heat and moisture exchanger significantly increased all of the inspiratory effort variables (inspiratory work of breathing expressed in J/L and J/min, pressure time product, changes in esophageal pressure, and transdiaphragmatic pressure; p <.05) and dynamic intrinsic positive end-expiratory pressure (p <.05). Similarly, the heat and moisture exchanger produced a significant increase in Paco(2) (p <.01) responsible for severe respiratory acidosis (p <.05), which was insufficiently compensated for despite a significant increase in minute ventilation (p <.05). This resulted in respiratory discomfort for all patients with the heat and moisture exchanger (p <.01). Adverse effects were partially counterbalanced by increasing the pressure support ventilation level with the heat and moisture exchanger by >or=8 cm H(2)O.


CONCLUSIONS
The type of airway humidification device used may negatively influence the mechanical efficacy of ventilation and, unless the pressure support ventilation level is considerably increased, the use of a heat and moisture exchanger should not be recommended in difficult or potentially difficult to wean patients with chronic respiratory failure.
Girault
Christophe
C
Medical Intensive Care Department, Rouen University Hospital-Charles Nicolle, France.
Breton
Lucie
L
Richard
Jean-Christophe
JC
Tamion
Fabienne
F
Vandelet
Philippe
P
Aboab
Jérôme
J
Leroy
Jacques
J
Bonmarchand
Guy
G
D018806:APACHE; D000142:Acidosis, Respiratory / Q000209:etiology; D000328:Adult; D000368:Aged; D001784:Blood Gas Analysis; D002908:Chronic Disease; D005260:Female; D006358:Hot Temperature / Q000009:adverse effects / Q000627:therapeutic use*; D006801:Humans; D006813:Humidity / Q000009:adverse effects / Q000592:standards*; D008297:Male; D008875:Middle Aged; D009330:Nebulizers and Vaporizers / Q000592:standards*; D011175:Positive-Pressure Respiration / Q000379:methods; D011446:Prospective Studies; D011659:Pulmonary Gas Exchange; D012131:Respiratory Insufficiency / Q000209:etiology / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy*; D015656:Respiratory Mechanics; D012132:Respiratory Muscles / Q000503:physiopathology; D016896:Treatment Outcome; D015300:Ventilator Weaning / Q000379:methods*; D014939:Work of Breathing