Conical Forearm and Cylindrical Upper Arm Non-Invasive Blood Pressure (NIBP) Measurements in Pregnant Patients

Overview

The diagnosis of hypertensive disease during pregnancy is predicated on strict blood pressure thresholds: 140/90 on at least two occasions measured four hours apart for both gestational hypertension and preeclampsia. An improvement in diagnostic accuracy of even 5mm Hg would be significant, as reflected by the US Association for the Advancement of Medical Instrumentation (AAMI), the British Hypertension Society, the European Society of Hypertension (ESH) Working Group on Blood Pressure (BP) Monitoring, and the International Organization for Standardization (ISO)consensus for validation of non-invasive blood pressure (NIBP) devices during pregnancy. Given the known inaccuracies of upper arm cylindrical cuff measurements in morbidly obese patients, a conical cuff which provides more accurate measurements will translate into direct patient benefit via more informed diagnosis and management. Fewer women may be exposed to unnecessary treatment, preterm delivery, and/or cesarean section. Recognizing the increasing prevalence of morbid obesity and hypertensive disease amongst pregnant women in the United States, the identification of a more accurate non-invasive cuff is desperately needed. Increasing the accuracy of NIBP measurements on Labor and Delivery has the potential to directly impact the management of tens of thousands of morbidly obese pregnant women diagnosed with hypertensive disease in the United States every year. Establishing the level of agreement between conical forearm and cylindrical upper arm cuffs will shed light on the presence and magnitude of any disparity between measurement methods. STUDY ENDPOINTS: Primary Outcome Measures: * Agreement between conical and cylindrical cuff systolic blood pressure across groups * Agreement between conical and cylindrical cuff diastolic blood pressure across groups Secondary Outcome Measures: • Agreement between conical and cylindrical cuff mean arterial pressure

After participants have provided written informed consent they will be enrolled into one of four groups: (1) normotensive/non-obese (2) normotensive/obese (3) hypertensive/non-obese and (4) hypertensive/obese. The threshold for hypertension will be a BP measurement greater than 140/90 mmHg on two occasions at least 4 hours apart. After informed consent has been obtained, body weight (kg) and height (cm) will be measured on calibrated scales and BMI calculated. Arm circumference will be measured proximally just beneath the axilla, at mid- point between the acromion and the olecranon, and distally just above the antecubital fossa in centimeters. Forearm circumference will be measured, in millimeters, proximally just beneath the olecranon, at mid-point between the olecranon and the styloid apophysis, and distally just above the styloid apophysis. Upper arm length will be measured from the acromion to the olecranon in centimeters. Forearm length will be measured from the olecranon to the styloid apophysis in centimeters. Upper arm cuffs will be placed at the mid-point between the acromion and the olecranon processes. All BP measurements will be obtained from the participants while in the sitting position, and the arm contralateral to the peripheral intravenous catheter (PIV) will be chosen for measurement. If the PIV has not yet been placed, the arm selection will be made by the patient. Baseline BP measurement will be performed at the upper arm after at least a 5-minute resting period utilizing a large-sized cylindrical cuff. Baseline BP measurement at the forearm will be performed using a conical forearm cuff previously validated in non-pregnant patients with arm circumferences greater than or equal to 40 cm23 (RADIAL-CUF, GE HealthCare, Milwaukee, Wisconsin). The forearm cuff will be placed 3 cm from the styloid process of the ulna palpable at the wrist. After two minutes have elapsed since the baseline measurements, sequential, paired BP measurements will then be obtained by cycling either the upper arm cylindrical cuff or forearm conical cuff, waiting 60 seconds after the measurement, then cycling the other cuff. The choice of cuff to be cycled first (conical or cylindrical) will be block randomized. Additional sequential measurements will then be obtained 2, 4, 6, 8, and 10 minutes after the first set. After the initial measurements, the upper arm cuff will automatically cycle every 15 minutes. Thus, all patients will have six sets of sequential BP measurements. Any decision to initiate antihypertensive therapy will be made by the patient's obstetrical provider, using an institutional algorithm and with reference to cylindrical cuff pressures.