46. INTRAOPERTIVE HYPERTENSION

Hypertension is a rise in blood pressure of more than 20% above the preoperative blood pressure. The common causes of intra-operative hypertension are relatively light anaesthesia/pain or pre-existing hypertension but there are other causes of intra-operative hypertension that must be excluded by the anaesthetist including hypoxaemia, hypercarbia, unintended administration of a vasopressor, drug interactions, pre eclampsia, raised intracranial pressure, phaeochomocytoma, volume overload and a full bladder.

Prevention

Check that hypertension is treated adequately preoperatively and that all anti-hypertensive medications are continued before surgery. Elective surgery should be postponed if the patient has severe hypertension (diastolic greater than 110 mmHg).

The anaesthetist should anticipate times of high surgical stimulus and increase the depth of anaesthesia. Avoid fluid overload and ensure that the patient is oxygenated and ventilated at all times. Give antihypertensive drugs in small doses and monitor the response.

Management

Check the blood pressure.

Ensure that the patient is oxygenated and ventilating.

Assess the depth of anaesthesia and check for new surgical stimulus. If the hypertension is due to light anaesthesia, increase the depth of anaesthesia (increase the concentration of volatile anaesthetic or give a further dose of narcotic).

If treatment is needed, consider beta blockade, nitroprusside infusion (0.1 to 0.3 micrograms/kg/min), calcium channel blockade (verapamil 2.5 mg intravenous doses, nifedipine 10mg sublingual) or hydralazine 5 mg intravenously.

Review the intravenous fluid management, preoperative history and check for a distended bladder.