The effect of a heat and moisture exchange filter on sidestream spirometry in critically ill patients

Sidestream spirometry has enabled continuous on-line monitoring of the pulmonary mechanics in intubated patients. We studied the effect of the heat and moisture exchange filter (HMEF) on the displayed spirometry values of a commercial multiparameter pulmonary monitor in 35 stable ICU patients needing mechanical ventilatory support. There were statistically significant differences in tidal volumes, airway pressures, compliances and end-tidal CO2-values between the two sites of measurements on both sides on the HMEF. The effect of the HMEF was linear in almost every patient. However, the change of the displayed values was clinically of minor importance. In conclusion, we suggest that the HMEF can be safely used between the patient and the monitoring site in routine ventilatory monitoring of ICU patients.