Non-invasive Versus Invasive Blood Pressure Measurement in the Morbidly Obese Parturient (BMI >= 40 kg/m2) With Severe Preeclampsia: A Comparison of Direct Arterial Blood Pressure Measurements With Readings Obtained Using Either Large Cylindrical or Novel Conical Bariatric Upper Arm Blood Pressure Cuffs
Phase: NA
Conditions: Pre-Eclampsia, Morbid Obesity, Parturient, Blood Pressure
Sponsor: Vanderbilt University Medical Center

Protocol version: 11/07/2018 
 
NCT03222414 
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Title: Non-invasive versus invasive blood pressure measurement in the morbidly obese 
parturient (BMI  ≥ 40 kg/m2) with severe preeclampsia: A comparison of  direct arterial 
blood pressure measurements with readings obtained using either large cylindrical, radial 
cylindrical, or novel conical bariatric upper arm blood pressure cuffs.  
Co-Investigators:  
Laura Sorabella, MD; Jeanette Bauchat, MD   
Sub-Investigators:  
Michael  Richardson, MD; Curtis Baysinger, MD 
; Britany Raymond, MD; Holly Ende, MD, James Lozada, MD, Susie 
Dumas, MD, Mallika Thampy, MD 
Vanderbilt University Medical Center 
OB Anesthesiology 
 
 
 
Aim:  To compare agreement of invasive blood pressure measurements with non-invasive blood 
pressure measurements measured with a conical blood pressure, radial cuff, and large standard 
upper arm rectangular cuff in morbidly obese severely hypertensive (systolic blood pressure > 
160 mmHg) parturients. 
Background and Significance: A morbidly obese [Body Mass Index (BMI) ≥ 40 kg/m2] 
pregnant woman is at singular risk for all the complications of pregnancy, most notably 
preeclampsia (PE) 1, 2. Furthermore a woman who is already chronically hypertensive is quite 
likely to develop superimposed PE 3, 4. Uncontrolled systolic hypertension in pregnancy prompts 
placental abruption, hemorrhagic stroke, and systolic or diastolic heart failure. Mhyre rightly 
asserts that: “Systolic blood pressure …above 160 mm Hg constitutes a hypertensive crisis in a 
pregnant woman and requires urgent treatment to minimize risk for cerebral hemorrhage” 5. The 
American College of Obstetrics and Gynecology Task Force on Hypertension in Pregnancy also 
now recommends the use of antihypertensive therapy for persistent severe maternal hypertension 
(SBP at or above 160 mm Hg) 6.  Accurate blood pressure measurement is therefore a 
prerequisite to controlling dangerously high SBP to enable labor and delivery to be conducted 
safely in association with PE. An algorithm has been implanted on Vanderbilt Labor and 
Delivery, using SMFM guidelines, to guide treatment of these severe range blood pressures20. 
Precise SBP measurement is also a precondition for clinically testing hypotheses concerning the 
existence of druggable targets that will allow prolongation of pregnancy in the face of severe PE 
and /or intra-uterine growth restriction (IUGR) remote from term 7, 8.   
Hypertensive hemorrhagic stroke is the most common cause of maternal death related to 
preeclampsia 5. Upper arm SBPs measured with a standard rectangular cylindrical cuff exceeding 
160 mm Hg are not infrequently seen in severe preeclampsia. During general anesthesia for 
cesarean section direct arterial SBPs well in excess of 160 mm Hg have been recorded during 
both laryngeal intubation and extubation 9, 10. SBPs this high place the preeclamptic parturient at 
serious risk for hemorrhagic stroke 5. We hypothesize that measurement of noninvasive blood 
pressure (NIBP) in morbidly obese patients (BMI ≥ 40) with large upper arm circumferences 

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adds a further margin of under-reading error when compared with direct arterial, invasive blood 
pressure (IBP) recording, thus compounding the risk of maternal stroke.   
Oscillometric NIBP measurement is the customary standard blood pressure monitoring method 
most often used in the labor suite and obstetric operating room today. For this purpose a 
rectangular, cylindrical blood pressure (BP) cuff placed on the upper arm is connected to an 
oscillometric blood pressure device. Yet inaccuracies related to the fact that oscillometric NIBP 
devices under-read high SBP relative to IBP measurements have been recognized as a potential 
source of maternal morbidity for years 11. A decade ago Martin et al. highlighted the importance 
of treating SBP rather than diastolic blood pressure (DAP) to avoid stroke in severe preeclampsia 
and eclampsia, concluding that: “A paradigm shift is needed toward considering antihypertensive 
therapy for severely preeclamptic and eclamptic patients when systolic blood pressure reaches or 
exceeds 150-160 mm Hg.” 12. 
In non-pregnant patients a recent retrospective analysis of data obtained from a cohort of more 
than 15,000 men and women showed that systolic, mean, and diastolic upper arm blood 
pressures measured non-invasively with rectangular, cylindrical blood pressure cuffs that fell 
within the normal range correlated relatively well with direct IBP recordings obtained via a 
radial artery catheter, the latter method currently representing the “gold standard” for clinical BP 
determination 13. However, outside the normal ranges NIBP tended to under read at higher 
pressures but paradoxically, over read at lower blood pressures. Cross over points for SBP, MAP 
and DAP agreement between NIBP and IBP were noted to be 111, 95 and 80 mm Hg 
respectively. Similar disparities between NIBP and IBP recordings in hyperacute stroke patients 
have been documented 14. A recent systematic review of the subject under scrutiny here confirms 
the relative inaccuracy of current NIBP methods when compared to IBP recording 15. 
Rectangular, cylindrical BP cuffs have been noted to overestimate SBP relative to troncho-
conical cuffs in morbidly obese (mean body mass index 41.4 ± SEM 0.7) men and women 
(group 4) by as much as 9.7 mm Hg , most notably in those subjects with shorter upper arm 
lengths 16.  The incidence of hypertension among this group of morbidly obese patients was 
purported to be 54.6% using the cylindrical cuff, but was found to be only 40.0% using the 
conical cuff (p < 0.001). Thus 15% of subjects who appeared hypertensive with the cylindrical 
cuff were actually normotensive. In contrast, in a limited study of “severely” obese male and 
female subjects (n = 16) NIBPs measured on the upper arm with both cylindrical and conical 
cuffs, and on the forearm with cylindrical cuffs were noted to be little different from 
corresponding radial artery catheter pressures 17.  
With regard to pregnancy, Langenegger et al. compared both manual ausculatory and automated 
oscillometric NIBP to direct arterial IBP when monitoring acute severe hypertension in 23 
preeclamptic patients (gestational ages 22 - 40 weeks; BMI 19 - 45) 18. Mean oscillometric SBP 
(148 ± 18 mm Hg) and manual auscultatory readings (152 ± 15) were on average 24 ± 17 and 20 
± 15 mm Hg respectively lower than the direct arterial SBP recordings (172 ± 11 mm Hg). To 

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the best of our knowledge, no such comparisons have yet been made in a cohort of morbidly 
obese (BMI ≥ 40) pregnant women manifesting severe hypertension.  
The conical Ultracheck Curve (reusable or single use) BP cuff (Statcorp Medical, Jacksonville, 
Florida, U.S.A.) is advertised (Sharn Anesthesia Inc., Tampa, Florida, U.S.A.) as: “A 
Breakthrough Solution for Accurate Bariatric Blood Pressure Readings. We intend to compare 
IBP readings obtained from morbidly obese, severely hypertensive (SBP > 160 mm Hg) 
parturients with NIBP consecutively measured with new innovative conical Ultracheck Curve 
BP cuffs and large standard upper arm rectangular cylindrical as well as radial BP cuffs.    
Methods: Twenty-five morbidly obese (BMI ≥40 kg/m2) severely hypertensive (SBP > 160 mm 
Hg) parturients with clinically indicated radial artery lines already in situ or who agree to 
placement of an arterial line after a thorough explanation of limited complications related to 
arterial line insertion will be recruited to the study. Both IRB approval and the patients’ written 
informed consent for the study will be obtained. The following measurements (left and right 
arm) will be made and recorded with the patient lying in a 15º left lateral tilt position, arms by 
their side and forearms pronated: 
1) Proximal upper arm circumference - just below the axilla. 
2) Distal upper arm circumference - 0.5 cm above antecubital fossa. 
3) Upper arm length - axilla to the antecubital fossa. 
4) Blood pressure cuff size 
 
For comparative purposes BP will be measured and documented sequentially and in random 
order (computer generated random numbers table). NIBPs will be recorded using either an upper 
arm large adult [American Heart Association (AHA): 16-36 cm.] cylindrical BP cuff, a radial 
cuff, or an UltraCheck Curve bariatric BP cuff. The BP cuffs will be linked to an Oscillometric 
BP recording device (Philips M1574A). There will be an initial set of readings on admission, and 
subsequent sets of readings before a medication administration on the Vanderbilt Management 
Guideline for Acute Hypertension Algorithm. A set of readings will also be attained at decision 
for ICU transfer or cesarean section. SBP, MAP and DAP will be recorded  from each cuff site 
(3 cuffs total) and then repeated after swapping the cuffs over to the opposite arm . Direct 
invasive arterial pressure readings will be charted simultaneously for comparative purposes.  
The primary outcome of this investigation will be to compare the agreement of NIBP and 
SBPmeasurements relative to IBP SBP recordings. Secondary outcomes will be: To compare the 
agreement of MAP and DAP NIBP recordings with IBP levels; to compare agreement of the 
SBP, MAP and DAP NIBP measurements obtained with cylindrical upper arm and radial BP 
cuffs with those recorded using conical BP cuffs.  
Agreement between devices (NIBP vs IBP and NIBP cylindrical (upper and radial) versus 
conical BP cuffs) will be determined. The relationship between upper arm circumference minus 
distal arm circumference and upper arm cylindrical pressure and intra-arterial SBP difference 

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will be defined as well. The same relationship between upper arm minus distal arm 
circumference and conical cuff and intra-arterial SBP recordings differences will also be 
assessed. 
Main Inclusion Criteria:  
Written, signed and dated informed consent  
 ≥ 18 years of age  
Morbidly obese (BMI ≥ 40 kg/m2) severely hypertensive (SBP > 160 mm Hg) parturients with 
clinically indicated radial artery lines already in situ or who agree to placement of an arterial line 
after a thorough explanation of limited complications related to arterial line insertion will be 
recruited to the study 
Gestational age greater than or equal to 24 weeks 
Parturients admitted for induction of labor 
 
Exclusion Criteria: 
Parturients admitted in labor 
 
 
Statistical Plan: 
Bland-Altman plots will be used to look at agreement of NIBP (SBP, MAP and DAP) and IBP. 
Regression analyses will examine the relationship between upper and lower forearm 
circumference measurements and difference between NIBP (SBP, MAP and DAP) cylindrical 
and radial cuffs versus conical (obesity) BP cuffs.  
 
Based on the 2012 report from South Africa17 we estimate that 25 patients will initially need to 
be investigated.  A difference of 10 mm Hg (SBP, MAP and DAP) will be considered clinically 
significant. 
References: 
1. Roberts JM, Bodnar LM, Patrick TE, Powers RW. The role of obesity in preeclampsia. 
Pregnancy Hypertens 2011; 1: 6-16. 
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M. The impact of increasing obesity class on obstetrical outcomes. J Obstet Gynaecol Can.2013; 
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3. Bramham K1, Parnell B, Nelson-Piercy C, Seed PT, Poston L, Chappell LC. Chronic 
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6. Roberts JM and the Task Force on Hypertension in Pregnancy. Hypertension in Pregnancy. 
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