Pathophysiology of arterial hypertension: implications in surgical patients

Arterial hypertension is common. It is well established that such hypertension is associated with cardiovascular complications, and that the risk of these complications can be reduced by anti-hypertensive treatment. The pathophysiology of hypertension is complex and not fully elucidated. Many physiological systems influence blood pressure, and the responses of some of these are reset. Changes have been observed both in well-known mechanisms, such as the baroreflex control of blood pressure, and in more recently described systems, such as the production of nitric oxide by the endothelium. Physical changes known as remodelling occur in the intimal and medial layers of blood vessel walls. Target organ damage may be seen in many organs, most notably the heart, the kidneys and the cerebral circulation.

It is the experience of most anaesthetists that hypertensives display cardiovascular lability and that this is less marked if the blood pressure is controlled by treatment. There is also considerable evidence for an association between hypertension and major perioperative cardiovascular complications.

Patients with hypertension should be carefully assessed prior to anaesthesia. An estimate of the severity of the hypertension should be based, if possible, on several blood pressure readings. Target organ damage should be sought. It is widely accepted that, where possible, surgery should be deferred in patients with poorly controlled or uncontrolled hypertension, and treatment given to lower the blood pressure. There is no evidence to support any particular level of blood pressure as a cut-off for treatment. We suggest that, in patients with a systolic pressure greater than 210 mmHg, a diastolic pressure greater than 115 mmHg, or target organ damage and a diastolic pressure greater than 100 mmHg, anaesthesia and surgery should be deferred if possible. In all patients on anti-hypertensive medication, this should be continued throughout the peri-operative period.