Postoperative respiratory complications affect improvement of postoperative respiratory muscle strength in patients undergoing cardiac surgery
Authors: Nishinakagawa T , Mikawa K 
Published: October 2021

Abstract

Introduction
The number of operations in the field of cardiac surgery is increasing year by year. In Japan, the number of operations in 2016 was about 68,000, which is a significant increase from about 54,000 in 2006. In addition, since patients undergoing cardiac surgery have low cardiac function after surgery, it is a problem that they often develop respiratory complications in the period until functional improvement. It has been reported that the incidence of respiratory complications is high in Japan as well. The purpose of this study is to clarify the relationship between the effects of postoperative respiratory complications on physical function at pre and post-operation and at discharge in patients undergoing cardiac surgery.

Methods
Twenty-two cardiovascular surgery patients (16 males and 6 females; mean age, 69.7±10.3 years; Body Mass Index, 23.1±4.2 kg/m2) were assigned. The evaluations were performed pre and post-operation and at discharge. We evaluated maximum inspiratory muscle strength (PImax; Maximum Inspiratory Pressure), 6-minute walking distance, balance function (Berg Balance Scale), 10 m gait speed, hand grip strength, and Activities of Daily Living (Barthel Index). In addition, preoperative cognitive function (Mini-Mental State Examination) and preoperative echocardiography, preoperative respiratory function tests, respiratory complications, length of stay in ICU, ventilator wearing time, the length of hospital stay was also investigated. The statistical analysis were performed using the SPSS 27 to examine the comparison of the differences between the two groups in the presence or absence of respiratory complications. This study protocol was approved by the Ethics Committee of Yonemori Hospital (approval number: Yonerin 18002). All patients signed the informed consent.

Results
Postoperative respiratory complications were observed in 45.5% (10 cases). Regarding physical function, preoperative hand grip strength (24.8±9.0 vs 31.7±6.1) and vital capacity % predicted (78.2±9.9% vs 91.1±17.5%) compared to the group with respiratory complications (complication group) and the group without respiratory complications (control group). Was significantly reduced. In addition, the improvement in postoperative PImax (21.3±18.7 vs 8.8±13.6) was significantly lower in the complication group than in the control group, and the PImax at discharge (44.5±26.5 vs 26.5±20.3) was also significantly reduced.

Conclusion
In this study, it was suggested that postoperative respiratory complications may affect postoperative respiratory muscle strength improvement and postoperative respiratory muscle weakness. It was also suggested that decreased preoperative hand grip strength and vital capacity may be associated with the development of postoperative respiratory complications.

Funding Acknowledgement
Type of funding sources: Public grant(s) – National budget only. Main funding source(s): This work was supported by JSPS KAKENHI Grant Number JP20K19326.