Forearm NIBP vs arterial line measurement in morbidly obese patients.

Abstract

Accurate measurement of arterial blood pressure in morbidly obese patients presents a challenge to the anaesthetist. Non- invasive (cuff) monitoring is often not feasible in morbidly obese patients. Invasive arterial lines provide an alternative, but have significant risks such as arterial wall damage, formation of thrombus, emboli and clots. Arterial cannulation in the morbidly obese patient is often technically challenging. Studies have shown that there is reliability between non invasive and invasive blood pressure monitoring in obese patients, however no studies have compared the reliability of forearm versus invasive blood pressure monitoring. Methods: After local human ethics research committee approval, 51 patients aged 18 years or older, with a BMI of 35 or greater, undergoing elective surgery requiring invasive blood pressure monitoring were recruited. Intravenous access and arterial cannulation was performed, forearm cuff pressure monitoring applied. Monitoring of no greater than 5 minute intervals were performed during surgery and in the immediate post operative period. Data was analyzed using the SCollect system. Results: 50 subjects (35 female, 15 male), mean age 50.6 years, mean BMI of 44.9 were studied. 48/50 (0.96%) patients had successful arterial line placement, 1/50 had a failure of arterial line, 1/50 had a loss of data due to software malfunction. Differences between BP measurements of art lines vs cuff for systolic, diastolic and mean BP were normally distributed; mean differences of arterial vs cuff measurements for systolic BP 5.78+/-14.54mmHg, diastolic BP -1.14+/-8.06mmHg, mean BP 1.65+/_7.92mmHg. A paired T-test showed statistically significant differences between arterial line and cuff for all three measurements. Further testing showed that for diastolic and mean BP, there was agreement at 5,10mmHg(5, 10% of measurement levels), whilst for systolic measurement agreement was only at 10mmHg(10% of measurement levels). Conclusions: There was good reliability between invasive blood pressure monitoring and non invasive forearm measurements in 48 patients, with agreement in measurement for diastolic and mean BP for both devices across a 5,10mmHg (5,10%) level, which is clinically relevant. Larger studies are needed to validate the routine use of forearm blood pressure monitoring in morbidly obese patients.