The Effect of Chance Variability in Blood Pressure Readings on the Decision Making of General Practitioners: An Internet-Based Case Vignette Study

Abstract

BackgroundGuidelines for the management of blood pressure (BP) in primary care generally suggest that decisions be made on the basis of specific threshold values (e.g. BP 140/90 mmHg); but this fails to adequately accommodate a common cause of variation – the play of chance.ObjectiveTo determine the impact of chance variability in BP readings on the clinical decision making of general practitioners (GPs) regarding anti-hypertensive treatment and cardiovascular risk management.MethodWe used an internet based study design, where 109 GPs were assigned to manage one of eight case vignettes (guidelines would recommend treatment for only one of the eight) and presented with blood pressure readings that were randomly selected from an underlying population.ResultsSeventeen (15.6%, 17/109) GPs consulted the vignette for whom treatment was recommended, but only 7/17 (41.2%) GPs prescribed treatment, whereas 14/92 (15.2%) GPs prescribed medication to the other vignettes. When deciding to follow-up a vignette GPs were influenced by threshold values for systolic and diastolic BP, but not by the overall cardiovascular risk. If the first reading was a low BP (systolic <140, diastolic <90) GPs were highly likely to discharge the vignette and follow-up a high BP reading (diastolic >90 or systolic BP≥140). Similar factors predicted the decision to prescribe a drug, although the vignette’s cardiovascular risk (>20%) was now statistically significant (p = 0.03).ConclusionsGP decision making, whilst generally consistent with guidelines, appears to be compromised by chance variation leading to under and over treatment. Interventions to adequately accommodate chance variability into clinical decision making are required.

General practitioners’ use of absolute risk versus individual risk factors in cardiovascular disease prevention: an experimental study

“…These results are in line with our hypotheses, and previous studies of patient records showing overtreatment of low-risk patients and undertreatment of high-risk patients, and that individual risk factors influence prescribing. 26–28 31–33 Age appeared to be largely ignored as a risk factor, and GPs prescribed less blood pressure lowering medication for 72-year-old cases in comparison with 61-year-olds despite similar descriptions in the scenarios (a relatively healthy fit x year old). This finding is worthy of further exploration, given that age is one of the strongest risk factors for CVD, as it runs counter to the concept of absolute CVD risk and proposals based solely on an age cut-off.…”

“…Hypothetical patient cases (also called vignettes) have been widely used to measure decision processes in a range of clinical settings, 25 including GP decision-making about CVD. 26–28 Indeed, three recent studies using patient cases suggest that clinicians might not base treatment decisions on absolute risk thresholds (eg, only treat patients >15% for 5-year FRE based absolute risk or >20% for 10-year risk); instead they focus on the levels of the individual risk factors blood pressure and cholesterol. 26–28 However, these studies did not systematically assess different combinations of absolute risk and individual risk factor levels.…”

“… 26–28 Indeed, three recent studies using patient cases suggest that clinicians might not base treatment decisions on absolute risk thresholds (eg, only treat patients >15% for 5-year FRE based absolute risk or >20% for 10-year risk); instead they focus on the levels of the individual risk factors blood pressure and cholesterol. 26–28 However, these studies did not systematically assess different combinations of absolute risk and individual risk factor levels. Therefore, they provide limited interpretation of how GPs use absolute risk versus individual risk factors in decision-making.…”

Blood pressure targets in primary care

“…Taking an average of multiple blood pressure readings would reduce both false positive readings that seem above target (and lead to an inappropriate up-titration of drugs) and false negative readings below target. 12 Polypharmacy and unnecessary changes to treatment resulting from unreliable blood pressure measurements may further diminish adherence, which is already poor among adults taking antihypertensives. [13][14][15][16] In Mant and colleagues' trial, 6 a lower target blood pressure led to increased losses to follow-up, more patients declining treatment intensification, worse adherence, and symptoms attributed to treatment including postural hypotension (intervention group 110/266 (41%) patients; controls 57/263 (22%)).…”