Sonographic muscle mass assessment in patients after cardiac surgery

Abstract

Background: Patients undergoing cardiac surgery particularly those with comorbidities and frailty, experience frequently higher rates of post-operative morbidity, mortality and prolonged hospital length of stay. Muscle mass wasting seems to play important role in prolonged mechanical ventilation (MV) and consequently in intensive care unit (ICU) and hospital stay.

Aim: To investigate the clinical value of skeletal muscle mass assessed by ultrasound early after cardiac surgery in terms of duration of MV and ICU length of stay.

Methods: In this observational study, we enrolled consecutively all patients, following their admission in the Cardiac Surgery ICU within 24 h of cardiac surgery. Bedside ultrasound scans, for the assessment of quadriceps muscle thickness, were performed at baseline and every 48 h for seven days or until ICU discharge. Muscle strength was also evaluated in parallel, using the Medical Research Council (MRC) scale.

Results: Of the total 221 patients enrolled, ultrasound scans and muscle strength assessment were finally performed in 165 patients (patients excluded if ICU stay < 24 h). The muscle thickness of rectus femoris (RF), was slightly decreased by 2.2% [(95% confidence interval (CI): - 0.21 to 0.15), n = 9; P = 0.729] and the combined muscle thickness of the vastus intermedius (VI) and RF decreased by 3.5% [(95%CI: - 0.4 to 0.22), n = 9; P = 0.530]. Patients whose combined VI and RF muscle thickness was below the recorded median values (2.5 cm) on day 1 (n = 80), stayed longer in the ICU (47 ± 74 h vs 28 ± 45 h, P = 0.02) and remained mechanically ventilated more (17 ± 9 h vs 14 ± 9 h, P = 0.05). Moreover, patients with MRC score ≤ 48 on day 3 (n = 7), required prolonged MV support compared to patients with MRC score ≥ 49 (n = 33), (44 ± 14 h vs 19 ± 9 h, P = 0.006) and had a longer duration of extracorporeal circulation was (159 ± 91 min vs 112 ± 71 min, P = 0.025).

Conclusion: Skeletal quadriceps muscle thickness assessed by ultrasound shows a trend to a decrease in patients after cardiac surgery post-ICU admission and is associated with prolonged duration of MV and ICU length of stay.

Keywords: Cardiac surgery; Intensive care unit-acquired weakness; Muscle mass; Muscle ultrasound; Quadriceps femoris; Skeletal muscle wasting.