Heat and moisture exchangers and heated humidifiers in acute lung injury/acute respiratory distress syndrome patients. Effects on respiratory mechanics and gas exchange.
OBJECTIVE
To compare, in acute lung injury/acute respiratory distress syndrome (ALI/ARDS) patients, the short-term effects of heat and moisture exchangers (HME) and heated humidifiers (HH) on gas exchange, and also on respiratory system mechanics when isocapnic conditions are met.


METHODS
Prospective open clinical study.


METHODS
Intensive Care Service.


METHODS
Seventeen invasively ventilated ALI/ARDS patients.


METHODS
The study was performed in three phases: (1) determinations were made during basal ventilatory settings with HME; (2) basal ventilatory settings were maintained and HME was replaced by an HH; (3) using the same HH, tidal volume (Vt) was decreased until basal PaCO2 levels were reached. FiO2, respiratory rate and PEEP were kept unchanged.


RESULTS
Respiratory mechanics, Vdphys, gas exchange and hemodynamic parameters were obtained at each phase. By using HH instead of HME and without changing Vt, PaCO2 decreased from 46+/-9 to 40+/-8 mmHg (p<0.001) and Vdphys decreased from 352+/-63 to 310+/-74 ml (p<0.001). Comparing the first phase with the third, Vt decreased from 521+/-106 to 440+/-118 ml (p<0.001) without significant changes in PaCO2, Vd/Vt decreased from 0.69+/-0.11 to 0.62+/-0.12 (p<0.001), plateau airway pressure decreased from 25+/-6 to 21+/-6 cmH2O (p<0.001) and respiratory system compliance improved from 35+/-12 to 42+/-15 ml/cmH2O (p<0.001). PaO2 remained unchanged in the three phases.


CONCLUSIONS
Reducing dead space with the use of HH decreases PaCO2 and more importantly, if isocapnic conditions are maintained by reducing Vt, this strategy improves respiratory system compliance and reduces plateau airway pressure.
Servei de Medicina Intensiva, Hospital de la Santa Creu i Sant Pau, Sant Antoni M Claret 167, 08025, Barcelona, Spain.
Indalecio
I
Morán
Judith
J
Bellapart
Alessandra
A
Vari
Jordi
J
Mancebo
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D005260:Female; D006358:Hot Temperature; D006801:Humans; D006813:Humidity; D007362:Intensive Care Units; D008297:Male; D008875:Middle Aged; D011659:Pulmonary Gas Exchange / Q000502:physiology*; D012106:Research; D012121:Respiration, Artificial / Q000379:methods*; D012128:Respiratory Distress Syndrome; D012131:Respiratory Insufficiency / Q000503:physiopathology / Q000628:therapy*; D015656:Respiratory Mechanics / Q000502:physiology*; D013030:Spain; D014939:Work of Breathing