The AAGBI have produced guidelines for pre-operative management of blood pressure readings available here
This guideline aims to ensure that patients admitted to hospital for elective surgery are known to have blood pressures below 160 mmHg systolic and 100 mmHg diastolic in primary care. The objective for primary care is to fulfil this criterion before referral to secondary care for elective surgery. The objective for secondary care is to avoid spurious hypertensive measurements. Secondary care should not attempt to diagnose hypertension in patients who are normotensive in primary care. Patients who present to pre-operative assessment clinics without documented primary care blood pressures should proceed to elective surgery if clinic blood pressures are below 180 mmHg systolic and 110 mmHg diastolic.
Why worry about BP
Hypertension is a common reason to cancel or postpone surgery. In our audit, 1–3% of elective patients had further investigations precipitated by blood pressure measurement, of whom half had their surgery postponed.
The association between hypertension and peri- operative harm was first reported in the 1950s. Systolic blood pressures in excess of 170 mmHg and diastolic blood pressures in excess of 110 mmHg were associated with complications such as myocardial ischaemia. Hypertension was the second-most common factor associated with postoperative morbidity.