Hypertension

Learning objectives

Hypertension is defined as a systolic BP > 160 mmHg
Episodes of hypertension are relatively common during anesthesia and are reported by nearly one-third of adult patients
Whether it is ultimately harmful to the patient depends on its degree, cause, and duration, and on the patient’s condition

Hypertension rarely has noticeable symptoms, however, the following signs and symptoms can be associated with hypertension:

Stage	Systolic blood pressure (mmHg)	Diastolic blood pressure (mmHg)
Prehypertension	120 - 129	60 - 79
Stage 1 hypertension	130 - 139	80 - 89
Stage 2 hypertension	> 140	> 90
Hypertensive crisis	≥ 180	≥ 120

Pre-existing hypertension	Control blood pressure prior to surgery < 160 mmHg systolic and <100 mmHg diastolic
Side effects of agents	Ketamine, ergometrine, desflurane anesthesia (> 1.0 MAC)
Inadequate anesthesia/analgesia	Adjust administration
Inadequate ventilation	CO2 retention causes catecholamine release
Interaction of agents	For example monoamine oxygenase inhibitors + vasopressors or opioids
Tourniquet pain
Pre-eclampsia	Treat with magnesium sulfate and hypotensive agents
Pheochromocytoma	If suspected, a small bolus dose of phentolamine (1–5 mg) usually gives a significant fall in BP If systolic BP falls more than 35 mmHg, a Pheochromocytoma is likely Administer alpha-blockers in addition to beta-blockade
Rare causes	Fluid overload Aortic cross-clamping Hyperthyroidism/thyroid storm Malignant hyperthermia Increased intracranial pressure Interference with the carotid body, brainstem, or spinal cord Bladder distension Alcohol withdrawal syndrome or addictive drug withdrawal Autonomic hyperreflexia

Myocardial ischemia (especially subendocardial), myocardial infarction, or heart failure
Hemorrhage from the operation site
Rupture of an existing aneurysm
Encephalopathy, cerebral edema, or cerebral hemorrhage
May precipitate acute renal failure

Inform the surgeon and consider halting the surgical procedure if possible
Cycle BP, scan monitors for HR, ECG rhythm, EtCO2, and temperature
Check if the patient is adequately oxygenated and ventilated
Deepen the anesthetic
Examine the patient:
- Pupils (high ICP)
- Diaphoresis & flushing (carcinoid, pheochromocytoma, hyperthyroidism)
- Rigidity (malignant hyperthermia, serotonin syndrome)
- Bladder distension
- Hot (thyroid storm, malignant hyperthermia, serotonin syndrome)
If severe and life-threatening, (e.g. MAP >150 mmHg with signs of myocardial ischemia), immediate therapy is warranted
Otherwise, seek the cause and treat this cause
If there is no likely cause, nonspecific therapy may need to be instituted

Agent	Example	Action and dose
Vasodilators	Anaesthetic agents Isoflurane Sevoflurane Propofol	Easy to titrate
	Hydralazine	Arteriolar dilator Peak action after 20 min following 5-10 slow IV (maximal dose of 30 mg) Slow IV push every 20 minutes
	Nitroglycerine	Arterial and venous dilator Dose: 10-200 mcg/min IV Start infusion at 10 mcg/min
	Labetalol	Combined alpha and beta blockade Dose: 10-50 mg slow IV, repeated after 5 min if necessary Maximal dose of 200 mg
	Sodium nitroprusside	Arterial dilator with a very rapid response Dose: continuous IV: 0.5-1.5 mcg/kg/min starting dose Increase every 5 min in 500 ng/kg/min graduations according to response Large doses may cause cyanide poisoning
Beta blockers	Atenolol	Reduces vascular tone Cardioselective Dose: 2.5 mg slow IV, repeated after 5 min if necessary
	Esmolol	Reduces vascular tone Rapid onset with a short half-life of about 9 min Dose: 50-200 mcg/kg/min infusion Start infusion at 50 mcg/kg/min
	Nicardipine (rydene)	Arterial dilator Dose: 0.1 mg/mL
Alpha blockers	Phentolamine	Vasodilator Relaxes vascular tone Dose: 1-5 mg IV

Agent	Example	Action and effect
Thiazide diuretics	Bendrofluazide Indapamide	Blocks Na+ channels Complications: electrolyte disturbances
Loop diuretics	Furosemide	Inhibit Na+, K+ and CL- uptake
Aldosterone antagonists	Spironolactone	Inhibit Na+ reabsorption and K+ secretion
Osmotic diuretics	Mannitol	Increase osmotic pressure and inhibit water and solute reabsorption
Carbonic anhydrase inhibitors	Acetazolamide	Inhibits carbonic anhydrase thereby inhibiting HCO3- and reduces Na+ reabsorption
Sodium channel blockers	Triamterene	Directly inhibit Na+ reabsorption and K+ secretion
Beta blockers	Atenolol Propranolol Esmolol	Slow heart rate Improved ventricular filling Complications: lethargy, nausea, and general malaise
ACE inhibitors	Peridopril Enalapril	Block angiotensin-converting enzyme Complications: cough and deterioration of renal function
A2 inhibitors	Candesartan Losartan	Block angiotensin 2
Calcium channel blockers	Nipedipine	Vasodilation

Continue to monitor the patient
Provide adequate analgesia
Administer oxygen titrated to SpO2 of 94%–98% (reduce myocardial ischemia)
Patient may need investigations to exclude complications (e.g. myocardial infarction) or to identify the cause

Postoperative hypertension can occur in up to 20% of patients after surgery
Is associated with adverse outcomes such as myocardial injury, bleeding, stroke, or arrhythmias
Systolic BP > 180 mmHg is a high risk for postoperative hypertension