Brachial blood pressure monitoring versus ankle monitoring during colonoscopy.

Objectives: To compare ankle and brachial blood pressure monitoring before and during colonoscopy using automated noninvasive blood pressure (NIBP) monitors.

Methods: Forty-five consecutive patients who presented for outpatient colonoscopy had both ankle and brachial blood pressure monitoring with automated NIBP using an appropriately sized cuff for arm or leg size. Three baseline measurements were obtained, and then measurements were taken at 5-minute intervals during conscious sedation, with brachial blood pressure being the standard.

Results: The average of all of the ankle blood pressures was significantly higher for all systolic and mean arterial blood pressure readings. Diastolic blood pressure readings were higher at baseline, but not significantly different during the procedure.

Conclusions: Ankle systolic and mean arterial blood pressures using automated NIBP monitoring for conscious sedation are significantly higher than brachial blood pressures. Ankle NIBP monitoring should only be used if brachial NIBP monitoring is not feasible, taking into consideration that ankle NIBP pressures are generally higher than brachial.

Key Words: ankle, blood pressure, brachial, colonoscopy, conscious sedation

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Patients undergoing colonoscopy often have multiple intravenous lines and pulse oximeter monitoring that makes brachial blood pressure monitoring difficult. In some patients there are contraindications to blood pressure monitoring in an upper extremity, such as end-stage renal disease or following radical mastectomy. Other patients may be morbidly obese and require a thigh cuff to obtain a brachial blood pressure. In these circumstances, ankle blood pressure monitoring is frequently used during conscious sedation, often without consideration of other alternatives. Some studies have compared the brachial blood pressure to the femoral blood pressure. (1-6) The data are conflicting, but in general, indirect blood pressure readings using the Korotkoff method result in higher readings in femoral blood pressures compared with brachial blood pressures (10-40 mm Hg). A definitive invasive blood pressure monitoring study in 1964 showed that intraarterial blood pressures in the brachial and femoral arteries are essentially the same. (4) Regarding ankle blood pressures, in 1936 Hamilton et al (1), found that simultaneous measurement of the pressure within the brachial and dorsalis pedis arteries show their diastolic blood pressures (DBP) to be similar. However, they also found the systolic blood pressure (SBP) of the dorsalis pedis artery to be up to 20 mm Hg higher than the brachial artery when measured manometrically. In the 1980s and 1990s, there was a shift toward utilizing the SBP as the most important reading in evaluating and treating hypertension. The SBP, among other parameters, is used by many physicians to determine the degree of hypotension that a patient may experience during a procedure such as colonoscopy. (7) Since some patients may require ankle blood pressure monitoring for colonoscopy, it would be beneficial to know whether currently used automated noninvasive blood pressure (NIBP) monitors give elevated readings of the ankle SBP similar to those that have been demonstrated with previous manual NIBP studies. This could have important implications in the monitoring of blood pressure, especially hypotension, which could occur during colonoscopy. There are few data concerning brachial and arterial blood pressure comparisons using the newer, automated NIBP monitors. This study is designed to compare ankle and brachial blood pressures during colonoscopy utilizing automated NIBP.

Materials and Methods

The study group was formed of 45 consecutive patients who presented for outpatient colonoscopy at a single endoscopy center based in a university hospital. Both ankle and brachial blood pressure monitoring was performed on each patient using the Siemens SC 6002-XL (Siemens Co., NY, NY), using an appropriately sized cuff for arm or leg size. Exclusion criteria included prior amputation, peripheral vascular disease, prior vascular surgery performed on any extremity, prior mastectomy, end-stage renal disease, or central vascular access in the past 6 weeks. Three baseline measurements were obtained, and the patient was then excluded if there was baseline hypotension or hypertension, defined as SBP <100 mm Hg or >180 mm Hg, or DBP <50 mm Hg or >100 mm Hg. Measurements were taken at 5-minute intervals during conscious sedation, with brachial blood pressure being used as the blood pressure of record for the procedure. This prospective study was approved by the University of South Alabama Institutional Review Board.

Results

There were 22 male and 23 female subjects. Thirty-five were white, 8 were black, and 2 were Asian. The mean age was 55 years (range 37-84). The average body mass index was 27.3 (range 15.7-39.2). The mean SBP and the mean arterial blood pressure were both significantly higher with ankle monitoring than with brachial monitoring at both baseline and during the procedure (Table 1). DBP readings were higher at baseline for ankle monitoring, but not significantly different during the procedure. Significant hypotension during the procedure was noted with brachial blood pressure monitoring in 13 of 45 patients (29%) if defined as SBP <100 mm Hg, but only 4 of 45 patients (9%) if defined as SBP <90 mm Hg. Only one patient with a brachial SBP <100 mm Hg during the procedure had a corresponding ankle SBP <100 mm Hg. No patient with a brachial SBP <90 mm Hg during the procedure had a corresponding ankle SBP <100 mm Hg. In fact, the corresponding ankle SBP was >110 mm Hg in all patients with a brachial SBP <90 mm Hg. The lowest brachial SBP during a procedure was 81 mm Hg, and the corresponding ankle SBP was 121 mm Hg. The average difference between ankle and brachial blood pressure at baseline in this patient was only 18 mm Hg, which was of no value in predicting this degree of intraoperative discrepancy. Neither ankle mean arterial blood pressure nor ankle DBP corresponded reliably to hypotension determined by brachial NIBP. However, the overall trend of blood pressure readings increased and decreased to a similar degree with ankle readings compared with brachial readings, although not necessarily proportionately.

Discussion

Colonoscopy is increasing in utility as a diagnostic, screening, and therapeutic procedure. Patients undergoing the procedure vary in indications and options for NIBP monitoring. In some patients, brachial NIBP monitoring may not be feasible and ankle monitoring may be considered. This study demonstrates that discrepancies between ankle and brachial blood pressures exist using automated NIBP monitors. Ankle systolic and mean arterial blood pressures using automated NIBP monitoring for conscious sedation are significantly higher than brachial blood pressures. The discrepancies in blood pressures may be even greater during the procedure than at baseline. This prevents comparison of baseline ankle and brachial blood pressures to determine which patients are more likely to have discrepant readings.

Conclusion

We conclude that brachial blood pressure monitoring should be used as the method of choice for NIBP monitoring for conscious sedation for colonoscopy. Ankle blood pressure monitoring should be reserved for situations in which there are no suitable alternatives, recognizing that the readings are generally higher than the corresponding brachial pressures.

The difference between 'involvement' and 'commitment' is like an
eggs-and-ham breakfast: the chicken was 'involved'-the pig was
'committed'.
--unknown

Table 1. Differences in ankle and brachial blood pressures (a)

                                          Gradient NIBP Ankle
                       Mean NIBP (mm Hg)  > Brachial
                       Ankle   Brachial   (Mean + SD, mm Hg)   P value

SBP baseline           154.8   131.5      25.9 [+ or -] 11.6   < 0.0001
SBP during procedure   145.5   124.7      19.6 [+ or -] 9.8    < 0.0001
MABP baseline          104.73   95.7      11.6 [+ or -] 8.5    < 0.0001
MABP during procedure   98.0    91.1       6.5 [+ or -] 7.2    < 0.0001
DBP baseline            79.7    77.8       4.4 [+ or -] 9.5    = 0.003
DBP during procedure    74.1    74.3      -0.16 [+ or -] 7.4   = 0.09

(a) NIBP, noninvasive blood-pressure monitoring; SBP, systolic blood
pressure; MABP, mean arterial blood pressure; DBP, diastolic blood
pressure; SD, standard deviation.

Accepted April 5, 2004.

References

1. Hamilton WF, Woodbury RA, Harper HT. Physiologic relationships between intrathoracic, intraspinal, and arterial pressures. JAMA 1936;107:853-856.

2. Wendkos MH, Rossman PL. Normal blood pressure in lower extremity. Am Heart J 1944;28:763-772.

3. Kotte JH, Iglauer A, McGuire J. Measurements of arterial blood pressure in the arm and leg: comparison of sphygmomanometric and direct intraarterial pressures, with special attention to their relationship in aortic regurgitation. Am Heart J 1944;28:476-490.

4. Pascarelli EF, Bertrand CA. Comparison of blood pressures in the arms and legs. N Engl J Med 1964;270:693-698.

5. Hocken AG, Lond MB. Measurement of blood-pressure in the leg. Lancet 1967;1:466-468.

6. Bertrand CA, Pascarelli EF. Arm and leg blood pressures [abstract]. JAMA 1974;227:942.

7. Gross JB, Farmington CT, Bailey PL, et al. Practice guidelines for sedation and analgesia by non-anesthesiologists. Anesthesiology 2002;96:1004-1017.

RELATED ARTICLE: Key Points

* Ankle systolic and mean arterial blood pressures using automated noninvasive blood pressure (NIBP) monitors are significantly higher than brachial blood pressures.

* Ankle NIBP monitoring should only be used if brachial NIBP monitoring is not feasible.

* Significant hypotension may not be recognized during conscious sedation when ankle NIBP monitoring is used instead of brachial NIBP monitoring.

Jason M. Wilkes, MD, and Jack A. DiPalma, MD

From the Division of Gastroenterology, University of South Alabama College of Medicine, Mobile, AL.

This study was approved by the University of South Alabama Institutional Review Board.

Reprint requests to Jack A. DiPalma, MD, Division of Gastroenterology, USA Knollwood Pavilion, 5600 Girby Road, Mobile, AL 36693. Email: [e-mail]