Ventilation kinematics of adult patients with a median sternotomy incision following cardiothoracic surgery

Introduction: Cardiovascular diseases contribute significantly to the burden of diseases in South Africa and internationally. A standard intervention is open-heart surgery to repair and improve the functioning of the heart and a median sternotomy is the most commonly used incision during cardiothoracic surgery as it allows for optimal access to the heart and surrounding vessels. To date, few studies have described the effect of cardiothoracic surgery on ventilation kinematics as assessed by clinical bedside physiotherapy outcome measures. Aim: The aim of this research was to determine the impact of a median sternotomy on the ventilation kinematics and to describe the changes from admission to discharge from hospital. Methods: A longitudinal observational study was conducted at a private hospital in Gauteng. Male and female patients undergoing elective cardiothoracic surgery between the ages of 18 to 70 years were consecutively sampled. Participants were assessed pre-operatively and again at hospital discharge. The demographic and clinical profile of study participants were determined. Ventilation kinematics were assessed by measuring upper and lower thoracic expansion and respiratory muscle strength (Maximum Inspiratory Pressure [MIP] and Peak Inspiratory Flow [PIF]). Lastly, it was determined whether a relationship exists between the ventilation kinematics and specific demographic and clinical variables. Analysis included descriptive statistics and the Shapiro-Wilks and Wilcoxon Signed-Rank Tests, Spearman’s Rank-order and Pearson’s Product-Moment correlations. Statistical significance was set at p≤0.05. Results: The study population consisted of 61 participants and most (n=35, 57%) underwent coronary artery bypass graft surgery with the mean amount of time spent in theatre being 5.85 (SD1.30) hours, median mechanical ventilation hours 17.33 (IQR 11.21) and median days in intensive care five (IQR 2.75). Forty-seven (77%) participants were male and seventeen (27%) females with a median age of 59 (IQR 22) years. The median length of stay in hospital was nine (IQR 7) days. All participants were independently mobile at hospital admission but 5 (8.2%) required a mobility aid for independent mobility at hospital discharge. There was a significant difference between upper thoracic and lower thoracic expansion between admission and discharge (Upper: 104.51cm vs 102.51cm; p<0.001, Lower: 100.03cm vs. 98.70cm, p=0.0001). There was a significant difference between MIP and PIF between admission and discharge (MIP: 55cmH20 vs 30.66cmH20, p<0.001; PIF: 2.70l/s vs. 1.66l/s, p<0.001). There was also a significant difference between the predicted MIP achieved between admission and discharge (%Pred MIP: 58.66cmH20 vs. 33.26cmH20, p<0.001). There was a significant difference between admission and discharge for VAS pain scores and chest X-ray total scores (p<0.001). Oxygen saturation (p<0.001), temperature (p<0.001) and diastolic blood pressure (p=0.004) were significantly different from admission to discharge from hospital. There was a fair v negative correlation between predicted MIP and age (r=-0.319, p=0.012). There was a fair positive correlation between lower thoracic expansion and age (r=0.286, p=0.031). There was a fair negative correlation between upper thoracic expansion and length of time intubated (r=-0.261, p=0.05). There was a fair negative correlation between MIP and PIF between chest X-ray scores at admission (PIF: r=-0.278, p=0.03; MIP: r=-0.356, p=0.004). Conclusion There is significant alteration that happens to the respiratory pump that affects ventilation kinematics following a median sternotomy incision during cardiothoracic surgery when changes are evaluated from admission to discharge. Physiotherapy practice should continue with postoperative care after hospital discharge considering the presence of respiratory muscles weakness and presence of mobility dysfunction.
A research report submitted in fulfilment of the requirements for the degree of Master of Science in Physiotherapy to the Faculty of Health Sciences, University of the Witwatersrand, Johannesburg, 2020