Persistent diaphragm dysfunction after cardiac surgery is associated with adverse respiratory outcomes: a prospective observational ultrasound study

Background: Transient diaphragm dysfunction is common during the first week after cardiac surgery; however, the precise incidence, risk factors, and outcomes of persistent diaphragm dysfunction are not well described. Methods: In a single-centre prospective cohort study, we included all consecutive patients over 18 yr who underwent elective cardiac surgery. Diaphragm function was evaluated with ultrasound (M-mode) by recording the excursion of both hemidiaphragms at two different time points: preoperatively and after the seventh postoperative day in patients breathing without assistance. Significant diaphragm dysfunction after the seventh day of the index cardiac surgery was defined as a decrease in diaphragm excursion below the lower limit of normal: at rest, < 9 mm for women and < 10 mm for men; after a sniff test, < 16 mm for women and < 18 mm for men. Results: Overall, 122 patients were included in the analysis. The median [interquartile range (IQR)] age was 69 [59–74] years and 96/122 (79%) were men. Ten (8%) patients had diaphragm dysfunction after the seventh postoperative day. We did not identify risk factors for persistent diaphragm dysfunction. Persistent diaphragm dysfunction was associated with a longer median [IQR] duration of noninvasive (8 [0–34] vs0 [0–0] hr; difference in medians, 8 hr; 95% confidence interval [CI], 0 to 22; P< 0.001) and invasive mechanical ventilation (5 [3–257] vs3[2–4] hr; difference in medians, 2 hr; 95% CI, 0.5 to 41; P= 0.008); a higher reintubation rate (4/10, 40% vs1/112, 0.9%; relative risk, 45; 95% CI, 7.1 to 278; P< 0.0001), a higher incidence of pneumonia (4/10 [40%] vs7/112 [6%]; relative risk, 6; 95% CI, 2 to 16; P< 0.001), and longer median [IQR] length of stay in the intensive care unit (8 [5–29] vs4 [2–6] days; difference in medians, 4 days; 95% CI, 2 to 12; P= 0.002). Conclusion: The incidence of persistent diaphragm dysfunction was 8% in patients undergoing elective cardiac surgery and was associated with adverse respiratory outcomes. Study registration: ClinicalTrials.gov (NCT04276844); prospectively registered 19 February 2020.