Comparison 2. Heat and moisture exchanger (HME) versus heat humidifier (HH) ‐ cross‐over studies.

Outcome or subgroup title	No. of studies	No. of participants	Statistical method	Effect size
1 PaO2 (mmHg)	4		Mean Difference (Random, 95% CI)	Subtotals only
1.1 r = 0.3	4		Mean Difference (Random, 95% CI)	‐3.24 [‐16.08, 9.60]
1.2 r = 0.5	4		Mean Difference (Random, 95% CI)	‐3.87 [‐16.73, 9.00]
1.3 r = 0.7	4		Mean Difference (Random, 95% CI)	‐4.41 [‐17.09, 8.27]
2 PaCO2 (mmHg)	5		Mean Difference (Random, 95% CI)	Subtotals only
2.1 r = 0.3	5		Mean Difference (Random, 95% CI)	1.93 [0.27, 3.59]
2.2 r = 0.5	5		Mean Difference (Random, 95% CI)	2.02 [0.19, 3.85]
2.3 r = 0.7	5		Mean Difference (Random, 95% CI)	2.21 [0.33, 4.09]
3 Breathing rate (breaths/minute)	4		Mean Difference (Random, 95% CI)	Subtotals only
3.1 r = 0.3	4		Mean Difference (Random, 95% CI)	1.40 [0.33, 2.46]
3.2 r = 0.5	4		Mean Difference (Random, 95% CI)	1.15 [‐0.13, 2.44]
3.3 r = 0.7	4		Mean Difference (Random, 95% CI)	1.02 [‐0.38, 2.41]
4 Tidal volume (L)	5		Mean difference (Random, 95% CI)	Subtotals only
4.1 r = 0.3	5		Mean difference (Random, 95% CI)	0.02 [‐0.00, 0.03]
4.2 r = 0.5	5		Mean difference (Random, 95% CI)	0.02 [0.00, 0.04]
4.3 r = 0.7	5		Mean difference (Random, 95% CI)	0.03 [0.01, 0.06]
5 Minute ventilation (L/minute)	5		Mean difference (Random, 95% CI)	Subtotals only
5.1 r = 0.3	5		Mean difference (Random, 95% CI)	1.20 [0.78, 1.61]
5.2 r = 0.5	5		Mean difference (Random, 95% CI)	1.19 [0.63, 1.75]
5.3 r = 0.7	5		Mean difference (Random, 95% CI)	1.18 [0.55, 1.80]
6 Body temperature (ºC)	2		Mean Difference (Random, 95% CI)	Subtotals only
6.1 r = 0.3	2		Mean Difference (Random, 95% CI)	‐1.12 [‐3.77, 1.52]
6.2 r = 0.5	2		Mean Difference (Random, 95% CI)	‐1.13 [‐3.77, 1.52]
6.3 r = 0.7	2		Mean Difference (Random, 95% CI)	‐1.13 [‐3.78, 1.51]