Chest
Volume 100, Issue 1, July 1991, Pages 160-163
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Heat and Moisture Exchanger vs Heated Humidifier during Long-Term Mechanical Ventilation: A Prospective Randomized Study

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Adequate humidification of inspired gases with HMEs during long-term MV remains controversial. In this study, a comparison is made between tracheal secretions during long-term MV either with HME or conventional HH. Both the HME and HH groups were similar with respect to age, sex, diagnosis, duration of MV, SAPS and mortality. Temperature of gases in the tracheal tube was lower and the amount of tracheal instillations was greater in the HME group than in the HH group. Tracheal secretions became thicker between day 1 (control) and day 5, in the HME group than in the HH group. Four and two tube occlusions occurred in HME and HH groups, respectively. Tracheal bacterial colonization was similar in the two groups. Given the advantages of HME (reduced nurses’ work and financial cost), HME could be routinely used under cautious surveillance and replaced by HH if difficulty in suctioning occurs.

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Patients and Methods

All consecutive patients mechanically ventilated in our ICU from June 1988 to June 1989 were preincluded in this study at the onset of MV if their expected duration of MV was more than five days. They were then randomly assigned to MV either with HH or with HME. Only patients who underwent MV for at least five days were ultimately included for analysis. The duration of evaluation was limited to ten days.

In the HH group, the humidifier was either a Bennett Cascade II when a Servo 900 B

Study Population

Seventy-four patients entered the study and underwent randomization (Table 1 and 2). Eighteen of them were excluded because MV was stopped before the fifth day. In the remaining 56 patients, 26 were assigned to MV with HH and 30 with HME. In the HH group, a Cascade II Bennett humidifier was used in 21 patients and a Fisher Paykel humidifier in five. The two groups were similar in terms of diagnosis on admission in the ICU, age, sex, SAPS at the time of inclusion, duration of MV before

Discussion

Heat and moisture exchangers might replace the functions of the UAs by avoiding loss of heat and moisture during expiration and returning them to the inhaled gas. Their main advantages are high bacterial filtering capacity9 and simplification of the ventilator tubing. Therefore, the use of a HME should be generalized if an equivalent humidification of inspired gases could be demonstrated between HME and HH.

During the last decade, many HME proved to be effective by in vitro assays.3, 10, 11, 12,

Conclusion

Our results suggest that tracheal secretions during MV with periodic tracheal instillations become thicker with PALL BB 2215 HME than with HH. The number of patients is too small to state that these features are associated with a greater incidence of tube occlusion with HME. In view of the advantages of HME (reduction of nurses’ work and of financial cost) it seems reasonable to carry on their use in long-term MV, but it is advisable to replace them by HH when difficulty in suctioning occurs.

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Supported in part by a grant from the Institut G. Roussy (CRC 88D23).

Manuscript received November 5; revision accepted December 13.

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