The relationship between preoperative and primary care blood pressure among veterans presenting from home for surgery: is there evidence for anesthesiologist-initiated blood pressure referral?

BACKGROUND: American College of Cardiology/American Heart Association guidelines describe the perioperative evaluation as "a unique opportunity to identify patients with hypertension"; however, factors such as anticipatory stress or medication noncompliance may induce a bias toward higher blood pressure, leaving clinicians unsure about how to interpret preoperative hypertension. Information describing the relationship between preoperative intake blood pressure and primary care measurements could help anesthesiologists make primary care referrals for improved blood pressure control in an evidence-based fashion. We hypothesized that the preoperative examination provides a useful basis for initiating primary care blood pressure referral.
METHODS: We analyzed retrospective data on 2807 patients who arrived from home for surgery and who were subsequently evaluated within 6 months after surgery in the primary care center of the same institution. After descriptive analysis, we conducted multiple linear regression analysis to identify day-of-surgery (DOS) factors associated with subsequent primary care blood pressure. We calculated the sensitivity, specificity, and positive and negative predictive value of different blood pressure referral thresholds using both a single-measurement and a 2-stage screen incorporating recent preoperative and DOS measurements for identifying patients with subsequently elevated primary care blood pressure.
RESULTS: DOS systolic blood pressure (SBP) was higher than subsequent primary care SBP by a mean bias of 5.5 mm Hg (95% limits of agreement + 43.8 to -32.8). DOS diastolic blood pressure (DBP) was higher than subsequent primary care DBP by a mean bias of 1.5 mm Hg (95% limits of agreement +13.0 to -10.0). Linear regression of DOS factors explained 19% of the variability in primary care SBP and 29% of the variability in DBP. Accounting for the observed bias, a 2-stage SBP referral screen requiring preoperative clinic SBP ≥140 mm Hg and DOS SBP ≥146 mm Hg had 95.9% estimated specificity (95% confidence interval [CI] 94.4 to 97.0) for identifying subsequent primary care SBP ≥140 mm Hg and estimated sensitivity of 26.8% (95% CI 22.0 to 32.0). A similarly high specificity using a single DOS SBP required a threshold SBP ≥160 mm Hg, for which estimated specificity was 95.2% (95% CI 94.2 to 96.1). For DBP, a presenting DOS DBP ≥92 mm Hg had 95.7% specificity (95% CI 94.8 to 96.4) for subsequent primary care DBP ≥90 mm Hg with a sensitivity of 18.8% (95% CI 14.4 to 24.0).
CONCLUSION: A small bias toward higher DOS blood pressures relative to subsequent primary care measurements was observed. DOS factors predicted only a small proportion of the observed variation. Accounting for the observed bias, a 2-stage SBP threshold and a single-reading DBP threshold were highly specific though insensitive for identifying subsequent primary care blood pressure elevation.