What is the effect of measurable respiratory muscle training on respiratory muscle strength in mechanically ventilated adults in intensive care units? A systematic review and meta-analysis

Background: Respiratory muscle weakness, associated with mechanical ventilation during critical illness, is well established. Respiratory muscle strength training (RMST) including inspiratory muscle training (IMT) and expiratory muscle strength training (EMST) aims to address this weakness. The aim of this systematic review and meta-analysis was to assess the effectiveness of RMST, delivered using measurable load devices, to increase respiratory muscle strength in mechanically ventilated adults in the intensive care unit. Methods: Conducted per Preferred Reporting Items for Systematic reviews and Meta-Analyses guidelines, the review included randomised controlled trials of intensive care unit patients aged ≥16 years, ventilated ≥24 h, receiving RMST (IMT or EMST) via measurable load devices before extubation, published from January 2000 to January 2024. Preoperative/postoperative training and cohorts with other causes of respiratory weakness were excluded. Searches covered electronic databases, clinical registers, reference lists, and SCOPUS. Meta-analyses and sensitivity and subgroup analyses were performed using Cochrane Review Manager (RevMan). Risk of bias (RoB2) and Grading of Recommendations, Assessment, Development, and Evaluation tools were applied to assess respiratory muscle strength. Results: Fourteen studies (n = 844) met inclusion criteria (seven with low and seven with a high risk of bias). No trial employed EMST. Thirteen randomised controlled trials (n = 747) reported maximal inspiratory pressure (MIP) in response to IMT. Findings showed low-certainty evidence that IMT increases MIP by 6.9 cmH2O ([95% confidence interval {CI}: 4.9 to 9], i2 = 83%), improving to high-certainty evidence after sensitivity analysis (6.3 cmH2O [95% CI: 3.8 to 8.8], I2 = 34 %, n = 397). IMT was also associated with reduced weaning time (−1.9 days [95% CI: −3 to −0.8], I2 = 76 %, n = 482) and shorter ventilation duration (−1.7 days [95% CI: −3.8 to 0.3], I2 = 32 %). Reductions in rapid shallow breathing index (−6.4 breaths/min/L [95% CI: −16 to 3.2], I2 = 78%) were also observed. Conclusion: This systematic review supports the use of IMT delivered using measurable load devices, initiated during mechanical ventilation, in critical care patients, to increase MIP measures. Other potentially positive effects found in this review such as reduced weaning and mechanical ventilation durations in response to IMT need further confirmation. Registration: This protocol was registered with the International Prospective Register of Systematic Reviews (CRD42023431244).