The Association Between Doppler Parameters of Superior Mesenteric Artery(SMA) and Prolonged Mechanical Ventilation(PMV) in Patients After Cardiac Valve Surgery

Patient enrollment This prospective observational study was performed in the 15-bed adult critical care unit in Adult General Hospital from January 2021 to March 2022.

The inclusion criteria were as follows: 1) patients admitted to ICU immediately after cardiac valve surgery; 2) age 18-80 years; 3) sinus rhythm; 4) without active bleeding or pneumothorax, and 5) complete measurement data.

The exclusion criteria were as follows: 1) history of peripheral vascular disease, 2) patients with severe stenosis defined as SMA peak systolic velocity (SMA-PSV >275 cm/s or SMA-PSV/abdominal aorta peak velocity of >3, 3) hepatic dysfunction or liver cirrhosis, portal hypertension, 4) cancer or end-stage renal diseases, 5) poor quality of abdominal ultrasound images.

Doppler ultrasound monitoring Doppler ultrasound was performed with an ultrasound system consisting of a 2-5 MHz C60xp Probe (X-Porte Ultrasound System, FUJIFILM SONOSITE, INC., USA). Blood flow parameters were measured by two physicians, each physician measured twice and averaged, and then averaged the two results. Each of the two ICU physicians had more than four years of experience in critical ultrasound and obtained certification from the Chinese Critical Ultrasound Study Group. Two skilled physicians conducted a total of 40 measurements on ten patients after cardiac valve surgery to evaluate inter-observer reproducibility.

The SMA flow was measured 1 cm proximal to the abdominal aorta. The angle of insonation was < 60°. The time-velocity waveform readings were used to measure the peak systolic velocity (PSV), end-diastolic velocity(EDV), resistance index(RI), time-averaged mean velocity(TAMV), pulsatility index (PI), according to the calculation software carried by the ultrasound. PI=(PSV-EDV)/TAMV, and RI=(PSV-EDV)/PSV.