Chest
Volume 111, Issue 3, March 1997, Pages 686-691
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Clinical Investigations in Critical Care
Safety of Combined Heat and Moisture Exchanger Filters in Long-term Mechanical Ventilation

https://doi.org/10.1378/chest.111.3.686Get rights and content

Study objective

To evaluate the safety of a combined heat and moisture exchanger filter (HMEF) for the conditioning of inspired gas in long-term mechanical ventilation (MV).

Setting

Medical ICU in a large teaching hospital.

Patients

One hundred fifteen consecutive patients who required ≥48 h of MV.

Interventions

Patients were randomized at intubation time (day 1) to receive inspired gas conditioned either by a water-bath humidifier heated at 32°C (HWBH) or by an HMEF (Hygroster; DAR; Mirandola, Italy).

Measurements and main results

The two study groups were comparable in terms of primary pathologic condition at the time of hospital admission, disease severity as measured by the Simplified Acute Physiology Score, and ICU mortality. They did not differ with respect to ventilator days per patient (mean±SD: HMEF, 7.6 ± 6.5; HWBH, 7.8 ± 5.8), incidence of endotracheal tube obstruction (HMEF, 0/59; HWBH, 1/56), and incidence of hypothermic episodes (HMEF, five; HWBH, two). In 41 patients receiving MV for ≥5 days, the morphologic integrity of respiratory epithelium was evaluated on day 1 and day 5, using a cytologic examination of tracheal aspirate smears. The state of ciliated epithelium was scored on a scale from 0 (poorest integrity) to 1,200 (maximum integrity), according to a well-described method. In both patient groups, the scores slightly but significantly decreased from day 1 to day 5 (mean±SD: HWBH, from 787 ± 104 to 745 ± 88; HMEF, from 813 ± 79 to 739 ± 62; p<0.0l for both groups); there were no statistically significant differences between groups.

Conclusions

These data indicate acceptable safety of HMEFs of the type used in the present study for long-term mechanical ventilation.

Section snippets

Study Design

This study took place during an 18-month period in the medical ICU of a large teaching hospital. Advantage was taken of a recent institutional decision to introduce HMEFs into the daily practice of respiratory care in this ICU, so that approval by the local ethical committee was not sought. During the study period, each patient with an indication for mechanical ventilation was considered for inclusion at the time of intubation or at ICU admission if already intubated. Subjects who were

RESULTS

Two hundred thirty-seven consecutive patients were randomized; 115 continued to receive mechanical ventilatory assistance for at least 48 h, 59 in the HMEF group and 56 in the HWBH group.

The two groups were comparable in terms of gender ratio, primary abnormality, and severity of illness as determined from the SAPS score (Table 1, left). On the average, patients in the HWBH group were slightly older than those in the HMEF group (p<0.02). There were six crossovers from HMEF to HWBH, four

DISCUSSION

The safety of heat and moisture exchangers for long-term use in mechanical ventilation has not been well defined. Concern is legitimate, considering that these devices may not condition inspired air quite as well as HWBHs do,18 and have indeed been associated with an increased incidence of ETT obstruction.13, 14, 15 One controlled trial of HMEF vs HWBH was even discontinued following one death related to this latter complication in one patient using an HMEF.14 A common denominator to all these

ACKNOWLEDGMENTS

The authors wish to thank the ICU staff, especially Cathy Grant, RRT, and Camille Anglada, for their outstanding technical help. We are also grateful to Antonijeta Peric for her patience in reading the tracheal aspirate smears.

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  • Cited by (0)

    Reprint requests: Dr. Feihl, Institute of Pathophysiology, CHUV BH-19/313, CH-1011 Lausanne, Switzerland

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