Preoperative blood pressure measurement: what should GPs be doing?

The British Hypertension Society (BHS) and the Association of Anaesthetists of Great Britain and Ireland (AAGBI) have published a joint guideline, ‘The measurement of adult blood pressure and management of hypertension before elective surgery’ in the journal Anaesthesia.¹ Very few, if any, GPs read this journal, hence the need for a coordinated publication in the BJGP. The motivation for this joint venture derives from a lack of national consensus on cancellations and postponements of elective surgery because the patient had a raised blood pressure when attending hospital. The concept that raised blood pressure is a risk factor for complications during anaesthesia has sparse evidence to support it. Despite this, hospital departments have rules stipulating that surgery cannot proceed if the patient has a raised blood pressure. Those rules can vary from hospital to hospital and have no cohesive rationale. The white-coat effect of having your blood pressure measured while waiting to see a surgeon is apparent to everyone and the quality of measurement in hospitals is questionable.² The patient possibly had a normal blood pressure measurement at their surgery recently, but the hospital department is either unaware or sceptical. We felt that something had to be done.

TWO SOCIETIES WITH DIFFERENT PERSPECTIVES

The BHS is concerned with the long-term management of hypertension to avoid cardiovascular complications in the future. Anaesthetists consider the short-term effect of profound haemodynamic changes during procedures and measure the outcomes in terms of 30-day mortality and morbidity. Most literature covering the subject of hypertension and anaesthesia mixes the little data we have about the short-term outcomes with the vast amounts of long-term unrelated epidemiological studies. When we set up the working party both societies purposely selected four people from different disciplines within their own ranks. Despite this, when the eight members of the working party met in February 2013, we found that we had unanimous agreement on the principles of this subject. We could have potentially written the guideline there and then, but we knew that greater rigour would be required if our views were to be accepted.

AVOIDING THE ACCUSATION OF GOBSAT

‘Good Old Boys Sat Around Talking’ is an old-fashioned and much discredited method of guideline writing in our evidence-based era. Our problem was the lack of evidence and a plethora of local GOBSAT that took place over the years. We therefore trawled for what evidence there was and initiated a sprint audit of the number and nature of blood pressure-related cancellations. We eventually constructed a set of recommendations, in the style of the journal Anaesthesia, applying all current rules on guideline writing. There was clearly a need for this to be a consensus document and therefore the consultation process was crucial. During the writing phase we asked 20 GPs for their comments, including generalists, and including GPs with and without an interest in cardiology and research-active GPs. When our final document was ready we opened the consultation process to over 400 members of the BHS and around 10 000 members of the AAGBI. We specifically approached the patient organisation Blood Pressure UK for a response and theirs was the most probing, contributing significant influence on the final document.

THE SPARSE EVIDENCE

We produced some of our own evidence by way of combining a sprint audit of 11 West London hospitals with national audit data showing that the number of cancellations was 1–3%, which equates to approximately 100 cancellations per day in the UK.³ The actual evidence of an association between high blood pressure and perioperative complications is based on several old, small studies involving patients with severe hypertension and none of them shows any evidence that reducing blood pressure helps.^4–8 One study, where patients were given intranasal nifedipine or postponed, showed no significant difference in postoperative complications.⁹ The largest ever intervention study where beta-blockers were used to reduce blood pressure preoperatively suggested it did more harm than good.¹⁰ There is no evidence of harm in people with stage 1 or stage 2 hypertension, that is, people with a blood pressure less than 160 mmHg systolic or 100 mmHg diastolic.¹¹

OUR RECOMMENDATIONS PUT THE ONUS ON ACTION BY PRIMARY CARE!

Mindful of the increasing pressures on primary care, the last thing we wanted was to increase GP workload. We hope these recommendations will in fact reduce workload by avoiding excessive postponements with people being unnecessarily sent back to their GP to ‘get their blood pressure sorted out’. We want hospital departments to recognise that stage 1 and stage 2 blood pressure rises have little impact on acute surgery outcomes. We want them to trust and rely on the measurements taken in primary care because that is where it is best done. Our recommendations (and suggestions for care) are:

• GPs should refer patients for elective surgery with mean blood pressures in primary care in the past 12 months <160 mmHg systolic and <100 mmHg diastolic;

• secondary care should accept referrals that document blood pressures <160 mmHg systolic and <100 mmHg diastolic in the past 12 months;

• preoperative assessment clinics need not measure the blood pressure of patients being prepared for elective surgery whose systolic and diastolic blood pressures are documented <160/100 mmHg in the referral letter from primary care;

• GPs should refer hypertensive patients for elective surgery after the blood pressure readings are <160 mmHg systolic and <100 mmHg diastolic. Patients may be referred for elective surgery if they remain hypertensive despite optimal antihypertensive treatment or if they decline antihypertensive treatment;

• surgeons should ask GPs to supply primary care blood pressure readings from the last 12 months if they are undocumented in the referral letter;

• preoperative assessment staff should measure the blood pressure of patients who attend clinic without evidence of normotension being documented by primary care in the preceding 12 months; and

• elective surgery should proceed for patients who attend the preoperative assessment clinic without documentation of normotension in primary care if their blood pressure is <180 mmHg systolic and <110 mmHg diastolic when measured in clinic.

The disparity between the blood pressure thresholds for primary care (160/100 mmHg) and secondary care (180/110 mmHg) allows for a number of factors. Blood pressure reduction in primary care is based on good evidence that the rates of cardiovascular morbidity, in particular stroke, are reduced over years and decades.¹² There is no evidence that perioperative blood pressure reduction affects rates of cardiovascular events beyond that expected in a month in primary care. Blood pressure measurements might be more accurate in primary care than secondary care, due to a less stressful environment and a more practised technique.

WHAT GPS SHOULD BE DOING

It is vital that primary care should report a blood pressure measurement taken in the last 12 months in the referral letter. Referral letters are usually generated via computer systems and it should be possible for either the practice or the computer system supplier to automatically include blood pressure readings taken within the last 12 months. Clearly, if no blood pressure has been taken in that period, you will be required to take a current blood pressure. If it is raised you will need to act accordingly, but that is something expected anyway. Importantly, if the patient is unwilling to engage in this process, you should make this clear in your referral. This should not bar someone undergoing anaesthesia and the department receiving the referral should respect non-consent to blood pressure management.

The need for up-to-date research in this matter is obvious. Our guidelines are just that, guidance not law. However, if your local hospital departments persist in using their own rules, please quote us in your response.

Provenance

Freely submitted; externally peer reviewed.