title: Noninvasive ventilation with helmet versus control strategy in patients with acute respiratory failure: a systematic review and meta-analysis of controlled studies.
abstract: BACKGROUND
  Noninvasive ventilation (NIV) has proved to be a useful technique for breathing support. However, complications, discomfort, and failure of NIV were commonly caused by the mask. Therefore, the helmet was developed to improve performance and reduce complications; however, there has been no conclusive results on its effect until now. Thus, we performed a systematic review and meta-analysis to investigate the effect of NIV with a helmet versus the control strategy in patients with acute respiratory failure (ARF).
  
  
  METHODS
  We searched Cochrane Library, PubMed, Ovid, and Embase databases and bibliographies of relevant articles published before June 2016. Randomized and case-control studies that adopted the helmet as an NIV interface and compared it with another interface were included. The primary outcomes were hospital mortality, intubation rate, and complications. The secondary outcomes included the length of intensive care unit (ICU) stay, gas exchange, and respiratory rate. Pooled odds ratios (ORs) and 95 % confidence intervals (CIs) were calculated by the Mantel-Haenszel method and mean difference by the inverse variance method in a fixed effect model or random effects model according to the heterogeneity.
  
  
  RESULTS
  A total of 11 studies involving 621 patients were included. The overall hospital mortality was 17.53 % in the helmet NIV group versus 30.67 % in the control group. Use of the helmet was associated with lower hospital mortality (OR 0.43, 95 % CI 0.26 to 0.69, p = 0.0005), intubation rate (OR 0.32, 95 % CI 0.21 to 0.47, P < 0.00001), and complications (OR 0.6, 95 % CI 0.4 to 0.92, P = 0.02). In contrast, there was no significant difference in gas exchange and ICU stay (P >0.05). Subgroup analysis found the helmet reduced mortality mainly in hypoxemic ARF patients (P < 0.05) and a lower intubation rate was shown in randomized trials; fewer complications caused by the helmet might be restricted to case-control trials. Additionally, the effect of the helmet on PaCO2 was influenced by type of ARF and ventilation mode (P <0.00001).
  
  
  CONCLUSIONS
  NIV with a helmet was associated with reduced hospital mortality and intubation requirement. The helmet was as effective as the mask in gas exchange with no additional advantage. Large randomized controlled trials are needed to provide more robust evidence.
authors.affiliation: Department of Pulmonary and Critical Care Medicine, the First Affiliated Hospital of Zhengzhou University, 1st Jianshe East Road, Zhengzhou, Henan, 450001, People's Republic of China. qi.liu@vip.163.com.
authors.forename: Qi
authors.initials: Q
authors.lastname: Liu
authors.affiliation: Department of Pulmonary and Critical Care Medicine, the First Affiliated Hospital of Zhengzhou University, 1st Jianshe East Road, Zhengzhou, Henan, 450001, People's Republic of China.
authors.forename: Yonghua
authors.initials: Y
authors.lastname: Gao
authors.affiliation: Respiratory Mechanics Lab, State Key Laboratory of Respiratory Disease, Guangzhou Institute of Respiratory Disease, First Affiliated Hospital of Guangzhou Medical University, 151st Yanjiang West Road, Guangzhou, Guangdong, 510120, People's Republic of China.
authors.forename: Rongchang
authors.initials: R
authors.lastname: Chen
authors.affiliation: Department of Pulmonary and Critical Care Medicine, the First Affiliated Hospital of Zhengzhou University, 1st Jianshe East Road, Zhengzhou, Henan, 450001, People's Republic of China. chengzhehi@126.com.
authors.forename: Zhe
authors.initials: Z
authors.lastname: Cheng
mesh_terms: D004867:Equipment Design / Q000592:standards*; D006260:Head Protective Devices / Q000592:standards*; D017052:Hospital Mortality; D006801:Humans; D007362:Intensive Care Units / Q000458:organization & administration; D007902:Length of Stay; D063087:Noninvasive Ventilation / Q000295:instrumentation* / Q000592:standards; D012131:Respiratory Insufficiency / Q000628:therapy*
keywords: Facial mask; Helmet; Noninvasive ventilation