How Often Should HMEs be Changed?
How Often Should HMEs be Changed?
Abstract & Commentary
Synopsis: No overall deterioration in the effectiveness of humidification or heat conservation was observed when heat and moisture exchangers were used for seven days, although the devices had to be replaced before seven days in three patients with COPD because of inadequate humidification detected in the course of the study.
Source: Ricard JD, et al. Am J Respir Crit Care Med 2000;161:104-109.
Ricard and associates performed a prospective observational cohort study of the efficiency and safety of heat and moisture exchangers (HMEs) in medical intensive care unit (ICU) patients requiring mechanical ventilation for more than 48 hours. They sought to determine whether HME use could be extended to seven days without deterioration of the device’s humidification function or increased bacterial colonization.
During a nine-month period, all patients admitted to the ICU who were judged likely to require ventilatory support for more than 48 hours were considered for the study. Excluded were individuals with initial core temperatures less than 33°C, poisoning by ingestion of hydrocarbons (which would be eliminated via exhalation), or bronchopleural fistula. The same hydroscopic and hydrophobic HME (Hygrobac-Dar; Mallinckrodt) was used in all patients. Placed vertically between the endotracheal tube and the Y-piece of the ventilator circuit, the HME was changed every seven days.
Ricard et al measured absolute and relative humidity, using a psychrometric method, along with tracheal temperature, within the first 48 hours and then daily from day 3 until day 7. They recorded the daily number of tracheal suctionings and instillations, and peak airway pressures (daily mean of every-6-hour measurements, as an indicator of airway obstruction). HME resistance to airflow was measured daily on one-third of the patients. For these assessments, data were reported as comparisons between findings on day 0 and day 7. In addition, bacterial colonization of the HMEs was assessed at the time of removal from the circuit at seven days.
Data were collected on 33 patients, whose mean age was 67.3 years, 15 of whom were women. Ten patients were ventilated because of chronic obstructive pulmonary disease (COPD), 13 because of other pulmonary diseases, four postoperatively, and six because of other conditions. The 33 patients were ventilated a total of 377 days. Twelve patients provided more than one seven-day study period.
The HMEs performed well in terms of humidification and maintenance of airway temperature, without detectable deterioration during the seven-day observation periods. No incidents of endotracheal tube occlusion occurred. However, absolute humidity was significantly lower in patients with COPD than in the other patients, and three HMEs required replacement because of insufficient absolute humidity. Mean airway resistance was not different on day 0 vs. day 7. There were no statistically significant differences in number of suctionings or instillations between the two observations. Bacteriological studies showed that 20 of the HMEs were sterile, while the other 13 had negligible numbers of coagulase-negative staphylococci (in 11 instances), Candida albicans (1), and Bacillus sp. (1). Similar bacteriological results were obtained from cultures of the Y-piece.
Ricard et al conclude that mechanical ventilation can be safely conducted in non-COPD patients using an HME changed only once per week. They estimate that a yearly cost savings of $110,000 could be realized if this practice were adopted in all the university-affiliated hospitals in Paris. However, they recommend that HMEs continue to be changed every 48 hours in patients with COPD.
COMMENT BY DAVID J. PIERSON, MD, FACP, FCCP
Although HMEs humidify the airways slightly less effectively during mechanical ventilation than heated humidifiers, they are substantially less costly in terms of both parts and labor. The slightly reduced humidification is probably of no clinical importance for the majority of patients requiring ventilatory support, and there has been increased use of these devices over the last decade. This study shows that, for medical ICU patients who do not have COPD, there is no appreciable deterioration in the function of the HME used over the first seven days. It might be argued that even the COPD patients were acceptably managed with an HME, since there were no clinical obstructions and the diminished humidification prompting replacement of the device in three instances was detected because of the study and likely would not have been noticed during usual patient care.
HMEs probably should not be used when ventilating certain categories of patients. The patients in this study were medical patients with a mean ventilatory requirement of 9 or 10 L/min. The efficiency of an HME declines with minute volumes substantially exceeding 12-15 L/min, and they are not used in most centers for patients with trauma, sepsis, and other conditions associated with a high minute ventilation requirement. In addition, the presence of copious secretions may necessitate more frequent HME changes because of accumulation and obstruction, thus decreasing or eliminating any cost savings. However, the majority of patients who require mechanical ventilation can be managed more economically and without a clinically important loss of humidity or airway temperature through the use of an HME, even when ventilatory support is necessary for several days.
When heat and moisture exchangers were left in place for seven days:
a. airway resistance progressively increased.
b. colonization of the HME progressively increased.
c. suctioning was required more often.
d. All of the above
e. None of the above
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