Effect of respiratory protection mask use on metabolic responses and certainty of evidence
| Outcome (measurement unit) | Systematic review | Population | Comparison | Participants (included studies) | Effect size (95% CI) | Risk of bias | Certainty of evidence |
| Oxygen saturation (measured in %) | Zheng et al12 | Healthy adults | Surgical mask versus no mask | 589 (20 RCTs/crossover trials and 1 non-RCT) | MD −0.59% (−0.87% to −0.30%) | Moderate | ⊕⊕◯◯* Low |
| N95 respirator versus no mask | 232 (10 RCTs/crossover trials and 1 non-RCT) | MD −0.35% (−0.75% to 0.05%) | Moderate | ⊕⊕◯◯* Low | |||
| Cloth mask versus no mask | 164 (6 RCTs/crossover trials and 1 non-RCT) | MD −0.50% (−1.23%; 0.24%) | Moderate | ⊕⊕◯◯* Low | |||
| Mask versus no mask (progressive exercise state) | 821 (27 RCTs/crossover trials and 1 non-RCT) | MD −0.60 (−1.02 to −0.18) | Moderate | ⊕⊕◯◯* Low | |||
| Mask versus no mask (steady-state exercise) | 660 (19 RCTs/crossover trials and 1 non-RCT) | MD −0.41 (−0.73 to −0.10) | Moderate | ⊕⊕◯◯* Low | |||
| Chen et al32 | Patients with COPD | Face mask versus no mask | 97 (1 non-RCT) | MD −0.80 (−1.56 to −0.04) | High | ⊕◯◯◯† Very low | |
| End-tidal oxygen partial pressure (measured in mm Hg) | Zheng et al12 | Healthy adults | Surgical mask versus no mask | 132 (6 RCTs/crossover trials) | MD −3.17 mm Hg (−4.87 to −1.47) | Moderate | ⊕⊕◯◯‡ Low |
| N95 respirator versus no mask | 42 (4 RCTs/crossover trials) | MD −5.10 mm Hg (−9.27 to −0.94) | Moderate | ⊕⊕◯◯‡ | |||
| Oxygen uptake (measured in mL/kg/min) | Zheng et al12 | Healthy adults | Surgical mask versus no mask | 202 (9 RCTs/crossover trials and 1 non-RCT) | MD −0.64 (−0.86 to −0.42) | High | ⊕◯◯◯† Very low |
| N95 respirator versus no mask | 72 (5 RCTs/crossover trials) | MD −0.66 (−1.16 to −0.16) | Moderate | ⊕⊕◯◯‡ Low | |||
| Cloth mask versus no mask | 51 (2 RCTs/crossover trials) | MD −0.73 (−1.96 to 0.51) | Moderate | ⊕⊕◯◯* Low | |||
| Mask versus no mask (progressive exercise state) | 265 (16 RCTs/crossover trials) | MD −0.68 (−0.93 to −0.43) | High | ⊕◯◯◯† Very low | |||
| Mask versus no mask (steady-state exercise) | 62 (3 RCTs/crossover trials) | MD −0.57 (−0.94 to −0.21) | High | ⊕◯◯◯† Very low | |||
| Muscle oxygenation (measured in %) | Shaw et al15 | Adults | Surgical mask versus no mask | 40 (3 RCTs/crossover trials) | MD −0.41 (−0.86 to 0.05) | Moderate | ⊕⊕◯◯* Low |
| VCO2 (measured in mL/min) | Zheng et al12 | Healthy adults | Surgical mask versus no mask | 127 (4 RCTs/crossover trials, 1 non-RCT) | SMD −0.74 (−1.19 to −0.28) | Moderate | ⊕⊕◯◯* Low |
| N95 respirator versus no mask | 28 (2 RCTs/crossover trials) | SMD −0.87 (−1.82 to 0.07) | Moderate | ⊕⊕◯◯* Low | |||
| Carbon dioxide partial pressure (measured in mm Hg) | Wangsan et al7 | Healthy adults | N95 respirator versus no mask (high-intensity exercise) | 51 (4 RCTs/crossover trials) | SMD 1.17 (0.70 to 1.64) | Moderate | ⊕⊕◯◯* Low |
| N95 respirator versus no mask (low-intensity to moderate-intensity exercise) | 54 (4 RCTs/crossover trials) | SMD 0.43 (0.08 to 0.79) | Moderate | ⊕⊕◯◯* Low | |||
| Arterial CO2 (measured in milliequivalents per litre (mmol/L)) | Shaw et al15 | Adults | Surgical mask versus no mask | 62 (1 RCT/crossover trial and 1 non-RCT) | MD 0.41 (−2.15 to 1.33) | High | ⊕◯◯◯† Very low |
| N95 respirator versus no mask | 54 (3 RCTs/crossover trials, 1 non-RCT) | MD 1.33 (0.02; 2.64) | High | ⊕◯◯◯† Very low | |||
| End-tidal CO2 (measured in mm Hg) | Zheng et al12 | Healthy adults | Surgical mask versus no mask | 269 (9 RCTs/crossover trials) | MD 2.32 (1.38; 3.26) | High | ⊕◯◯◯† Very low |
| N95 respirator versus no mask | 213 (9 RCTs/crossover trials) | MD 2.93 (2.01; 3.86) | High | ⊕◯◯◯§ Very low | |||
| Mask versus no mask (progressive exercise state) | 369 (10 RCTs/crossover trials) | MD 4.15 (2.77 to 5.53) | High | ⊕◯◯◯† Very low | |||
| Mask versus no mask (steady-state exercise) | 387 (10 RCTs/crossover trials) | MD 2.09 (0.93 to 3.25) | High | ⊕◯◯◯§ Very low | |||
| Chen et al32 | Patients with COPD | Face mask versus no mask | 112 (1 RCT/crossover trial and 1 non-RCT) | MD 0.10 (−1.57 to 1.78) | Moderate | ⊕⊕◯◯* Low | |
| Lactate level (measured in mmol/L) | Zheng et al12 | Healthy adults | Surgical mask versus no mask | 160 (7 RCTs/crossover trials) | MD −0.10 (−1.11; 1.31) | Moderate | ⊕⊕◯◯* Low |
| N95 respirator versus no mask | 28 (2 RCTs/crossover trials) | MD −1.02 (−2.09; 0.05) | Moderate | ⊕⊕◯◯* Low | |||
| Mask versus no mask (progressive exercise state) | 147 (6 RCTs/crossover trials) | MD −1.06 (−1.69 to −0.44) | Moderate | ⊕⊕◯◯* Low | |||
| Mask versus no mask (steady-state exercise) | 127 (4 RCTs/crossover trials) | MD −1.23 (−0.40 to 2.86) | Moderate | ⊕⊕◯◯* Low | |||
| Chen et al32 | Patients with COPD | Face mask versus no mask | 27 (1 RCT/crossover trial) | MD −0.90 (−1.73 to −0.07) | Moderate | ⊕⊕◯◯* Low |
*Low quality of evidence is due to unexplained inconsistency and imprecise results due to small magnitude of change and wide CI.
†Low quality of evidence is due to imprecise results due to small magnitude of change and wide CI and some concern with risk of bias.
‡Low quality of evidence is due to imprecise results due to small magnitude of change and wide CI.
§Low quality of evidence is due to unexplained inconsistency and imprecise results due to small magnitude of change and wide CI and some concern with risk of bias.
CO2, carbon dioxide; COPD, chronic obstructive pulmonary disease; MD, mean difference; RCT, randomised controlled trial; SMD, standardised mean difference; VCO2, carbon dioxide production.