Table 2 Characterization of the studies on the use of heat and moisture exchangers as compared with the conventional humidifiers

Martin et al., 1990 [23]

ICU

Quantitative variables were compared using the Student t test.

Pneumonia was diagnosed on the basis of purulent secretion. It did not involve VAP incidence density.

Hypothermia in 22% and 12% of the patients belonging to the HME and HH groups, respectively (p < 0.01). Six and no cases of tube occlusion were reported in the HME and HH groups, respectively (p < 0.01).

Not reported.

1C

The study was interrupted after the death of a patient belonging to the HME group due to total obstruction of the endotracheal tube.

Roustan et al., 1992 [26]

ICU

Both groups were compared using the Student t, Mann–Whitney, Chi-square, and Fisher exact tests for differences in frequency. Regression was conducted for the incidence of nosocomial pneumonia, atelectasis, and tube occlusion.

Sample size was not calculated.

Nine and no events of endotracheal tube occlusion in the HME and HH groups, respectively. Nine and ten episodes of atelectasis in the HH and HME groups, respectively.

Not reported.

1C

The randomization procedure was not described.

Dreyfuss et al., 1995 [22]

ICU

The Student t test was used for the continuous variables. The Chi-square test with Yates correction was employed for the categorical variables. The Mann–Whitney test was used to compare non-parametric variables.

The randomization procedure was not described. Various patients were excluded after randomization. Sample size calculation was not reported.

Report of severe occlusion that required cannula exchange due to clotting (patients with hematemesis) in the HME group. Six patients required cannula exchange due to obstruction by secretion in the HME group.

The use of HME reduces costs and staff working time.

1C

Boots et al., 1997 [21]

ICU

The patients’ characteristics were compared by paired t test. The VAP rate was evaluated using the log rank test.

The randomization procedure was not described.

Not reported.

The use of HME reduces costs.

1C

Kirton et al., 1997 [24]

ICU

Analysis of variance and non-paired Student t test.

Non-blinded study. ICU specifically admitted trauma patients.

The HME and HH groups did not differ in terms of endotracheal tube obstruction.

The use of HME reduces costs.

1C

Kollef et al., 1998 [25]

ICU

Student t and Wilcoxon tests were used (according to normal and non-normal distribution).

The randomization procedure was not described. No mention of blinded study.

Tube obstruction was not detected in any of the groups.

The use of HME reduces costs by 50%.

1C

Chi-square and exact Fisher tests were employed to compare categorical variables.

Time elapsed during filter exchange was not controlled.

Results were confirmed by multiple logistic regressions.

VAP diagnosis criteria did not include bronchoalveolar lavage.

Memish et al., 2001 [20]

ICU

The Student t test was employed.

The statistical power was not calculated.

Not reported.

Nursing staff spends less time discarding the condensate that builds up in the circuit. The use of HME reduces costs.

1C

Lacherade et al., 2005 [14]

ICU

The Student t test was employed for continuous variables. The Chi-square test was used for the categorical variables. Multivariate logistic regression was also performed.

Differences between the two populations with respect to HIV infection. Physicians and researchers were not blinded.

Tube occlusion rates were lower in the HME group (1 case) as compared with the HH group (5 cases).

On the basis of literature studies, the paper mentions that the use of HME reduces costs.

1C

Boots et al., 2006 [15]

ICU

Sample size was determined using the difference between two ratios. Univariate analysis involved the use of Student t and Kruskal-Wallis tests. The difference in VAP rate among groups was evaluated by Kaplan-Meier and log rank tests.

Pneumonia was diagnosed according to CPIS (Clinical Pulmonary Infection Score).

HME may present higher resistance to airflow than the manufacturer’s specifications after use for 24 h.

The use of HME reduces costs.

1C

Lorente et al., 2006 [19]

ICU

Quantitative variables were compared using the Student t test. Five risk models proportional to Cox were constructed for VAP analysis.

Temperature and moisture were not monitored. VAP diagnosis was confirmed by tracheal aspirate. After randomization, patients under mechanical ventilation for less than five days were excluded. Sample calculation was conducted, but it did not reach a sufficient number of patients. Wide confidence interval. Incidence density was not approached. Immunosuppressed patients were excluded.

Not reported.

No benefits have been reported for the use of HME.

1C