Table 1.

Characteristics of the included studies for helmet ventilation in the meta-analysis

Study	Study design	Patients	Experimental strategy	Control strategy	Sample size		Outcomes
					Helmet	Control
Antonelli 2002 [14]	Prospective pilot case control	Patients with hypoxemic ARF without COPD	Helmet PSV	Facial mask PSV	33	66	Gas exchange, respiratory rate, intubation rate, length of NIV, level of pressure support, ICU stay and hospital mortality, complications
Pisani 2015 [15]	Multicenter RCT	AECOPD with hypercapnic ARF	Helmet PSV	Oronasal mask PSV	39	41	Respiratory rate, dysponea score, intubation rate, level of pressure support, hemodynamics, complications
Brambilla 2014 [16]	Multicenter RCT	Pneumonia with hypoxemic ARF	Helmet CPAP	Venturi mask Oxygen therapy	40	41	Gas exchangea, intubation rate, hospital stay and mortality, complications
Principi 2004 [17]	Historical case control	Hematological malignancy with hypoxemic ARF	Helmet CPAP	Facial mask CPAP	17	17	Gas exchange, intubation rate, PTS, length of NIV, complications
Antonelli 2004 [20]	Historical case control	AECOPD with hypercapnic ARF	Helmet PSV	Facial mask PSV	33	33	Gas exchange, respiratory rate, intubation rate, length of NIV, level of pressure support, hemodynamics, ICU stay, ICU and hospital mortality, complications
Ali 2011 [29]	RCT	AECOPD with hypercapnic ARF	Helmet PSV	Facial mask PSV	15	15	Gas exchange, respiratory rate, hemodynamics, ICU stay, PTS, intubation rate, complications
Özlem 2015 [30]	RCT	AECOPD with hypercapnic ARF	Helmet PSV	Facial mask PSV	25	23	Gas exchangea, respiratory rateb, PTS, complications, ICU stayb, length of NIV, hospital mortality
Antonaglia 2011 [31]	RCT	AECOPD with hypercapnic ARF	Helmet PSV	Facial mask PSV	20	20	Gas exchange, respiratory rateb, intolerance to the interface, length of ICU stayb, time of ventilator assistance
Patel 2016 [32]	RCT	ARF due to ARDS	Helmet PSV	Facial mask PSV	44	39	Respiratory rateb, intubation rate, length of NIV, level of pressure support, ICU and hospital stayb, hospital and 90d mortality, complications, ventilator-free days
Tonnelier 2003 [33]	Historical case control	Cardiogenic pulmonary edema with hypoxemic ARF	Helmet CPAP	Facial mask CPAP	11	11	Glasgow coma scale, gas exchange, respiratory rate, complications, hospital mortality
Rocco 2004 [34]	Historical case control	Immunocompromised with hypoxemic ARF	Helmet PSV	Facial mask PSV	19	19	Gas exchange, respiratory rate, intubation rate, length of NIV, level of pressure support, ICU stay, ICU and hospital mortality, complications

ARF acute respiratory failure, COPD chronic obstructive pulmonary disease, PSV pressure support ventilation, NIV noninvasive ventilation, ICU intensive care unit, AECOPD exacerbation of COPD, CPAP continuous positive airway pressure, PTS patient tolerance scale, RCT randomized control trail, ARDS acute respiratory distress syndrome

^aOutcome presented in figure form

^bOutcome presented as interquartile range