Effect of preoperative inspiratory muscle training on postoperative outcomes in patients undergoing cardiac surgery: A systematic review and meta-analysis

Table 1 Characteristics of the six included studies

No.	Ref.	Country	Intervention	Control	Intervention group			Control group
					Patients (male: female)	Mean age	Surgery type	Patients (male: female)	Mean age	Surgery type
1	Hulzebos et al[12], 2006	Netherlands	Threshold IMT + incentive spirometry + education in an active cycle of breathing techniques + forced expiration techniques	Usual care (i.e. instruction on deep breathing maneuvers, coughing, and early mobilization) + postoperative incentive spirometry, chest physical therapy, and mobilization scheme	139 (108:31)	66.5 (9.0)	CABG: 139	137 (107:30)	67.3 (9.2)	CABG: 137
2	Savci et al[17], 2011	Turkey	Threshold IMT + mobilization + active exercises of upper and lower limbs + breathing exercises + coughing techniques	Usual care (mobilization, active exercises of upper and lower limbs, breathing exercises, and coughing techniques)	22 (19:3)	62.82 (8.69)	CABG: 22	21 (19:2)	57.48 (11.48)	CABG: 21
3	Moises et al[18], 2014	Brazil	Threshold IMT + breathing exercises + postoperative physical therapy	Guidelines ward routine + postoperative physical therapy	35 (23:12)	58.90 ± 9.53	CABG: 35	35 (29:6)	61.40 ± 8.43	CABG: 35
4	Valken et al[6], 2016	Netherlands	Threshold IMT + incentive spirometry + education (deep breathing maneuvers, coughing, and early mobilization)	Postoperative deep breathing maneuvers, coughing, and early mobilization incentive spirometry and chest physical therapy	119 (93:26)	66 (9.2)	CABG: 99; CABG + valve:20	116 (93:23)	67.5 (9.7)	CABG: 87; CABG + valve: 29
5	Chen et al[19], 2019	China	Threshold IMT + usual care (education coughing, and early mobilization) and abdominal breathing training + postoperative chest physical therapy and mobilization scheme	Threshold IMT [the intensity was fixed at the minimum load of the device (9 cmH2O)] + usual care (education coughing and early mobilization) and abdominal breathing training + postoperative chest physical therapy and mobilization scheme	98 (73:25)	61.68 ± 8.12	CABG: 69; valve: 18; CABG + valve: 11	99 (68:31)	61.68 ± 7.73	CABG: 70; valve: 21; CABG + valve: 8
6	Weber et al[20], 2021	Germany	Threshold IMT + walking below the threshold of subjective exhaustion + mobilization protocol and individual physiotherapy	Postoperative physiotherapy	58 (27:31)	82.2 ± 5.8	TAVR: 58	50 (26:24)	81.7 ± 5.0	TAVR: 50

For threshold inspiratory muscle training, patients must generate a preset pressure to allow airflow for each breath. Once that threshold is achieved, inspiratory flow is not dependent on patient effort. This means that threshold loading is the easiest of these inspiratory muscle training methods to standardize and prescribe for patients. CABG: Coronary artery bypass grafting; IMT: Inspiratory muscle training; TAVR: Transcatheter aortic valve replacement.

Table 2 Inspiratory muscle training used in each study

No.	Ref.	Length	Frequency	Duration	Supervision	Intensity
1	Hulzebos et al[12], 2006	≥ 2 wk preoperatively	Once a day	20 mins	6 times a week without supervision and once a week with supervision	30% of MIP. Resistance increases incrementally, based on the RPE scored on the Borg scale
2	Savci et al[17], 2011	5 d preoperatively + 5 d postoperatively	Twice a day	30 mins	Each session was under the supervision of a physical therapist	15% of MIP. The resistance was increased incrementally between 15% and 45% based on patient’s tolerance in the following days
3	Moises et al[18], 2014	Preoperative (length not mentioned)	Once a day	20 mins	Each session was under supervision	40% of MIP. Intensity increase not mentioned
4	Valkenet et al[6], 2016	Not mentioned	Once a day	20 min	6 times a week without supervision and once a week with supervision	30% of MIP. Increased incrementally based on the RPE as scored on the Borg scale. If patients recorded an RPE score < 5 after a training session, they were instructed to increase the inspiratory load of the threshold device by 5% before the next training session. The threshold load was unchanged for RPE scores ≥ 5
5	Chen et al[19], 2019	5 d preoperatively	Twice a day	20 min	Each session was under the supervision of a physical therapist	30% of MIP. Increased incrementally, based on the RPE scored on the Borg18 scale. If the RPE was less than 5, the resistance of the inspiratory threshold trainer was then increased incrementally by 5%. Training loads were adjusted to maintain 30% of the maximal inspiratory pressure every day
6	Weber et al[20], 2021	≥ 2 wk preoperatively	Once a day	20 min	Not mentioned	Not mentioned

MIP: Maximum inspiratory pressure; RPE: Rate of perceived exertion.