[Imaging and clinical features of diaphragm dysfunction after cardiac sternotomy]

To analyze the imaging and clinical features of diaphragm dysfunction in patients who underwent selective cardiac sternotomy with diaphragm ultrasound and chest CT.

A prospective cohort study was conducted. The patients undergoing selective cardiac sternotomy in the cardiac and vascular surgery department of Tianjin Medical University General Hospital from June to September 2023 were enrolled. Bedside ultrasound was performed on the day before surgery, within 24 hours of extubation, and on the 7th day after surgery to measure diaphragm excursion (DE) and diaphragm thickness (DT), and to calculate the diaphragm thickening fraction (DTF). The distance from the diaphragm's apex to the thorax's apex in the chest CT scout view was measured before and after the operation, and the diaphragm elevating fraction (DEF) was calculated. Patients were divided into two groups based on whether diaphragm dysfunction (DE < 1 cm) occurred on the 7th day after surgery. The change patterns of imaging indicators were analyzed in both groups. The clinical data of both groups before, during, and after surgery were compared.

In total, 67 patients who underwent cardiac sternotomy were enrolled. Among them, 24 patients developed diaphragm dysfunction within 24 hours after extubation; on the 7th day after surgery, 19 patients (28.4%) still exhibited diaphragm dysfunction, while 48 patients (71.6%) did not. Ultrasonic examination of the diaphragm revealed that, compared with the non-diaphragm dysfunction group, patients in the diaphragm dysfunction group exhibited varying degrees of decrease in DE and DTF before and after surgery, with a more significant decrease on the left side, and the differences were statistically significant on the 7th day after surgery [DE (cm): 1.06±0.77 vs. 1.59±0.63, DTF: 19.3% (14.8%, 21.1%) vs. 21.3% (18.3%, 26.1%), both P < 0.05]. There was no statistically significant difference in DT between the two groups at each time point. Changes in bilateral DE and DTF revealed that the non-diaphragm dysfunction group experienced early transient postoperative weakening of diaphragm function, followed by rapid recovery to the preoperative level on the 7th day after surgery, unlike the diaphragm dysfunction group. There were no significant differences between bilateral DE in the two groups on the day before surgery, and the left DE was significantly lower than the right DE within 24 hours after extubation and on the 7th day after surgery in the diaphragm dysfunction group (cm: 0.93±0.72 vs. 1.45±0.70 within 24 hours after extubation, 1.06±0.77 vs. 1.70±0.92 on the 7th day after surgery, both P < 0.05) but no significant difference was found in bilateral DT or DTF. The chest CT scan showed that, the incidence of postoperative diaphragm elevation was 61.2% (41/67), and 38.8% (26/67) did not, while no statistically significant difference in DEF was found between the two groups, nor within each group on both sides. Analysis of the clinical data showed a higher proportion of atrial fibrillation and pulmonary hypertension before surgery [atrial fibrillation: 36.8% (7/19) vs. 10.4% (5/48), pulmonary hypertension: 15.8% (3/19) vs. 2.1% (1/48), both P < 0.05], a higher incidence of high-flow oxygenation and pneumonia during surgery [high-flow oxygenation: 52.6% (10/19) vs. 25.0% (12/48), pneumonia: 73.7% (14/19) vs. 45.8% (22/48), both P < 0.05], and a longer duration of mechanical ventilation and length of intensive care unit (ICU) stay [duration of mechanical ventilation (hours): 47.0 (38.0, 73.0) vs. 24.5 (20.0, 48.0), length of ICU stay (hours): 69.0 (65.0, 117.5) vs. 60.0 (42.3, 90.6), both P < 0.05] in the diaphragm dysfunction group as compared with those in the non-diaphragm dysfunction group.

There was a high incidence of diaphragm dysfunction after cardiac sternotomy, which reflected the early transient postoperative weakening of diaphragm function, followed by rapid recovery to the preoperative level in most patients, predominantly on the left side. Diaphragm dysfunction, which was associated with atrial fibrillation and pulmonary hypertension significantly increased the incidence of postoperative pneumonia and prolonged the duration of mechanical ventilation and length of ICU stay.