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Table 5 Subgroup analysis - the effect on secondary outcomes

From: Noninvasive ventilation with helmet versus control strategy in patients with acute respiratory failure: a systematic review and meta-analysis of controlled studies

  No. of studies Patients (n) H/C I2 (%) P value for heterogeneity MD 95 % CI Overall effect Z/P value
Length of ICU stay
 Type of ARF
  Hypercapnic 2 48/48 0 0.69 −1.22 [−3.47, 1.04] 1.06/0.29
  Hypoxemic 2 52/85 0 0.37 −1.38 [−4.63, 1.88] 0.83/0.41
 Ventilation mode in the experimental group
  CPAP 1 15/15 NA NA −1.10 [−3.43, 1.23] 0.93/0.35
  PSV 3 85/118 0 0.63 −1.56 [−4.63, 1.50] 1/0.32
 Study design
  Case-control trial 3 85/118 0 0.63 −1.56 [−4.63, 1.50] 1/0.32
  RCT 1 15/15 NA NA −1.10 [−3.43, 1.23] 0.93/0.35
Oxygenation (PaO2/FiO2)
 Type of ARF
  Hypercapnic 3 68/68 0 0.38 1.23 [−9.32, 11.78] 0.23/0.38
  Hypoxemic 4 80/113 59 0.06 2.37 [−23.34, 28.08] 0.18/0.86
 Ventilation mode in the experimental group
  CPAP 2 28/28 53 0.15 −66.01 [−130.73, −1.28] 2/0.05
  PSV 5 120/153 0 0.59 2.96 [−6.91, 12.83] 0.59/0.56
 Study design
  Case-control trial 5 113/146 49 0.1 4.16 [−22.55, 14.22] 0.44/0.66
  RCT 2 35/35 0 0.33 3.57 [−7.95, 15.09] 0.61/0.54
pH
 Type of ARF
  Hypercapnic 3 68/68 16 0.3 −0.00 [−0.02, 0.02] 0.01/1
  Hypoxemic 3 63/96 28 0.25 −0.02 [−0.04, 0.00] 1.59/0.11
 Ventilation mode in the experimental group
  CPAP 1 11/11 NA NA −0.04 [−0.11, 0.03] 1.19/0.24
  PSV 5 120/153 30 0.22 −0.01 [−0.02, 0.01] 0.74/0.46
 Study design
  Case-control trial 4 96/129 0 0.43 −0.02 [−0.04, −0.00] 2.02/0.04
  RCT 2 35/35 0 0.73 0.01 [−0.01, 0.03] 0.85/0.4
PaCO2
 Type of ARF
  Hypercapnic 3 68/68 0 0.5 6.15 [4.17, 8.13] 6.08/<0.00001
  Hypoxemic 3 63/96 0 0.7 −1.76 [−5.13, 1.60] 1.03/0.30
 Ventilation mode in the experimental group
  CPAP 1 11/11 NA NA −1.40 [−16.96, 14.16] 0.18/0.86
  PSV 5 120/153 77 0.002 4.18 [2.46, 5.90] 4.76/<0.00001
 Study design
  Case-control trial 4 96/129 61 0.05 0.15 [−2.90, 3.20] 0.1/<0.92
  RCT 2 35/35 0 0.39 5.92 [3.85, 7.98] 5.62/<0.00001
Respiratory rate
 Type of ARF
  Hypercapnic 3 87/89 23 0.27 −0.56 [−1.85, 0.74] 0.84/0.4
  Hypoxemic 3 63/96 65 0.06 0.58 [−3.52, 4.69] 0.28/0.78
 Ventilation mode in the experimental group
  CPAP 1 11/11 NA NA 6.00 [−0.08, 12.08] 1.93/0.05
  PSV 5 139/174 0 0.44 −0.81 [−1.92, 0.30] 1.42/0.15
 Study design
  Case-control trial 4 96/129 57 0.07 0.07 [−1.45, 1.60] 0.1/0.92
  RCT 2 54/56 0 0.98 −1.29 [−2.86, 0.28] 1.61/0.11
 Interfaces used in the control group
  Facial mask 5 111/144 51 0.08 −0.49 [−1.66, 0.69] 0.81/0.42
  Oronasal mask 1 39/41 NA NA −1.26 [−4.28, 1.76] 0.82/0.41
  1. H/C helmet/control, MD mean difference, CI confidence interval, ICU intensive care unit, ARF acute respiratory failure, CPAP continuous positive airway pressure, PSV pressure support ventilation, high quality randomized controlled trial, PaO 2 /FiO 2 the ratio of the partial pressure of oxygen in arterial blood to the inspired oxygen fraction, pH potential of hydrogen, PaCO 2 partial pressure of carbon dioxide, NA not applicable