Noninvasive cardiac output monitoring to optimise therapy for patients with poorly controlled hypertension: a randomised controlled trial

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In patients with poorly controlled hypertension, choosing the most appropriate antihypertensive agent can be an important decision and often has impact on management outcomes. Treatment options for hypertension are wide-ranging and include thiazide diuretics, angiotensin converting enzyme inhibitors (ACEI), angiotensin receptor blockers (ARB), beta-blockers, and calcium channel blockers (CCB). Although expert recommendations in authoritative guidelines have focused on comparative analyses of cardiovascular outcomes, efficacy in reducing blood pressure, adverse effects, and cost, there is one other important parameter that has not been emphasized, which is the altered balance of the patient’s haemodynamics. Essential hypertension can be classified into distinct subtypes depending on the primary haemodynamic derangement, which can either be increased cardiac output (CO), as more commonly seen in the younger age-group with sympathetic nervous system overactivity; or elevated systemic vascular resistance (SVR), as seen in older patients. Blood pressure may be lowered more effectively if therapy is targeted at the primary pathophysiological derangement. Accordingly, ACEIs, ARBs, and CCBs would be the drugs of choice for patients with elevated systemic vascular resistance, while thiazide diuretics and beta blockers would be the drugs of choice for patients with increased cardiac output. In practice, however, an antihypertensive drug is usually initiated without prior knowledge of the underlying haemodynamic derangement of the patient. We hypothesise that an antihypertensive strategy that identifies the primary underlying haemodynamic derangement, and treats accordingly, will control blood pressure more effectively. A transcutaneous Doppler ultrasound monitor may be used to measure blood flow across the aortic or pulmonary valves and therefore estimate CO, stroke volume and SVR. It is portable, simple-to-use and may be operated by physicians or nurses. We have performed a pilot study using this device to investigate the haemodynamic derangements of Emergency Department (ED) patients with poorly controlled hypertension. Patients aged 18 years or above who attended the ED with systolic blood pressure >or=160 or diastolic blood pressure >or=100 in two or more blood pressure measurements taken at least 20 minutes apart, on two separate occasions, were included. We found that 80% of the 49 patients included had increased SVR as the primary haemodynamic derangement. Moreover, in 28% of cases the patients’ existing anti-hypertensive medication did not match the derangements in CO and SVR. For example, several patients had low CO yet had been prescribed a beta-blocker or diuretic; while several others had high SVR yet they were not given ACEI, ARB or CCB. Further, in 35% of cases our ED physicians, who were blinded to the haemodynamic measurement data, chose to prescribe anti-hypertensives that would appear to be inappropriate based on the haemodynamic findings. At present the body of evidence is that well-controlled blood pressure, however that may be achieved, improves an individual’s chances of prolonged life. We are not aware of any evidence that prescription appropriate to the primary underlying pathophysiological derangement (either elevated SVR or CO) is more effective at lowering blood pressure than prescription that seems inappropriate. However, conceptually it seems more sensible than not to treat the primary pathophysiological abnormality, and evidence is required to confirm whether or not this is true in practice. Therefore, we hypothesize that a protocol targeted at addressing the primary haemodynamic derangement ascertained by non-invasive Doppler ultrasound will lower blood pressure more effectively than standard, non-targeted management. The aim of our study is to investigate whether the use of a protocol targeted at addressing the primary haemodynamic derangement ascertained by non-invasive Doppler ultrasound will lower blood pressure more effectively than standard, non-targeted, management, in emergency department patients with poorly controlled hypertension. The setting is the Emergency Department (ED) of the Prince of Wales Hospital in Hong Kong, a 1,360-bed acute and tertiary-care hospital, which is also the regional Trauma and Emergency Centre serving the East New Terrtories area. It has an annual attendance of more than 150,000 new cases, of which on average at least 17% patients present with elevated blood pressure (unpublished report from an internal audit performed in March 2011, for the period 5-11 March 2011).

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