8ClassificationThe prevalence of hypertension (HTN) is about 20-25% of the general population, making it the most common preoperative co-morbidity.Isolated Systolic Hypertesion (ISD) is the most common subtype of hypertension affecting predominantly individuals older than 60 years of age with approximately half of these individuals having very wide pulse pressure (>65 mmHg) or pulse pressure hypertension (PPH).Isolated diastolic hypertension (IDH) is most prevalent in indiviuals younger than 50 years and is an important marker of coronary heart disease.
10PathophysiologyThe underlying mechanism of essential hypertension is unkown may due to abnormal sympathetic nervous system activity, altered renin-angiotensin system regulation.The characteristic hemodyanmic changes:Increased systemic vascular resistance with normal COP.Markedly increased sympathetic response to stress such as endotracheal intubation.A greater increase in blood pressure with vasoconstriction and greater decrease in BP with vasodilation.
11End organ damageCardiac: left ventricular hypertrophy, infarction, arrhythmias and congestive heart failure.Eye : hypertensive retinopathy.Renal: Nephropathy.Cerebral: stroke or transient ischemic attack.
12Some investigators have shown that patients with untreated, poorly controlled or labile preoperative hypertension are at increased risk for perioperative blood pressure lability, dysrhyrthmias, myocardial ischemia and transient neurologic complications.Left ventricular hypertrophy, which signifies long-standing poorly controlled hypertension, can increase the risk of myocardial ischemia from imbalances of myocardial oxygen supply and demand regardless of the presence or absence of coronary artery disease.
13In hypertensive patients, autoregulation of cerebral blood flow is reset to a higher range than normal, and although it protects the brain against sudden increase in pressure, it makes it more vulneranle to hypotension. Therefore, when blood pressure is lowered acutely, hypertensive patients will show signs of cerebral ischemia at a higher level of BP than normotensive patients.So, if marked hypertension (>180/120 mmHg) is present preoperatively, arterial blood pressure should be maintained in the high normal range ( /90-80mmHg).
14The following figure shows the renin-angiotensin systems and the mechanism of action of antihypertensive drugs:
15Diuretics:They include thiazides (e.g., hydrochlorothiazide), loop diuretics (e.g., furosemide, ethacrynic acid),and potassium sparing agents (e.g., spironolactone, triametrene). All direutics initially lower the pressure (BP) by increasing urinary sodium excretion and by reducing plasma volume, extracellular fluid volume, and cardiac output. For patient with ST segment changes and evidence of pulmonary edema and hypertension or with increased intracranial cerebral pressure and hypertension, intravenous furosemide maybe appropriate.
16Antiadrenergic agents: Centrally acting drugs: clonidine, dexmedetomidine and mivazerol. Stimulation of 2 receptors in the vasomotor centers of the brain reduces sympathetic outflow.Peripherally acting drugs:1 and 2 receptors phenoxybenzamine (dibenzyline), phentolamine (regitine).1 receptor prazosin (minipress) doxazosin (cardura).By blocking -mediated vasoconstriction, these drugs induce a fall in peripheral resistance with both arteriolar and venous dilation.
17-receptor blockers atenolol (tenormin), metoprolol (lopressor), nadol (corgard),pindolol (visken),propranolol (inderal), esmolol (breviblock). These drugs lower the BP by decreasing heart rate, contractility, cardiac output, and renin levels.- and receptor blockers – labetalol (trandate)Endothelin receptor antagonist: bosentan (receptor A and B antagonist) and sitaxenstan (receptor A antagonist) are examples of a few of this class of agents used in the m¬anagement of pulmonary hypertension and less so for hypertension related heart failure.
18Cardiovascular effects of calcium channel blockers VerapamilDilatiazemNifedipineNicardipineHeart rateNodal conduction or-- or-Myocardial depression- or-Vasodilation, more increase; , more decrease; increase; , decrease; -, no change.
19Dopaminergic agonists: Fenoldopam, dopamine receptor (DA1 selective) agonist, a systemic and renal vasodilator, offers significant advantages as a parenterally administered agent for the management of BP in hypertensive emergencies and in the periopertive setting.Angiotensin converting enzyme inhibitors:They include captopril, enalapril, lisinopril, quinapril, and ramipril. These drugs inhibit the conversion of the inactive decapeptide angiotensin I to the active octapeptide angiotensin II.
20Angiotensin II receptor blockers Blockade of the action of angiotensin II leads of elevation in plasma levels of renin, angiotensin I, and angiotensin II. However, this build up of precursors does not overwhelm the receptor blockade, as evidenced by a persistent fall in both blood pressure and plasma aldosterone levels.VasodilatorsDirect vasodilators:They include hydralazine, nitroprusside, nitroglycerin, and calcium channel blockers. These drugs directly relax the smooth muscle of resistance and capacitance vessels to different degrees.Other vasodilators:They include brain natriuretic peptides such as nestiritide that is primarily used in acute exacerbation of heart failure to improve forward flow and reduce symptoms and signs of heart failure.
21Anesthetic Management Of HTN Careful control of the hemodynamic responses to noxious stimuli such as endotracheal intubation, surgical incision and manipulation, and emergence from anesthesia is essential.The anesthetic goal is to minimize:Cerebral hypoperfusion from hypotension. Cerebral hemorrhage and hypertensive encephalopathy resulting from hypertenison.Renal failure from renal hypoperfusion.Myocardial ischemia from tachycardia, hypertension or hypotension.
22Preoperative evaluation and preparation In addition to the routine systemic preoperative physical examination and history, special attention should be paid to the following: etiology and severity of hypertension, the subtype of hypertension, current therapy (hypokalemia and hypomagnesemia with diuretics) and the end-organ damage by chronic hypertension (for cardiac evaluation: ECG and Echo, for renal evaluation: serum creatinine and blood urea nitrogen).Failure to diagnose a pheochromocytoma preoperatively, may prove fatal crisis.
23Elective surgery should be delayed for patients with severe hypertension (diastolic BP> 115 mmHg) or with severe isolated systolic hypertension (ISH) (systolic BP> 200 mmHg) until the BP is below 180/110 mmHg. If time permits, The blood pressure should be lowered over 6 to 8 weeks to less than 140/90 mmHg. Acute control within several hours is inadvisable before elective surgery, because this practice may put the cerebral circulation at risk for ischemia.
24Preoperative control of hypertension: Current opinion generally favors continuation of antihypertensive medication, especially β-blockers, up to the time of surgery. The withdrawal syndrome of beta blocker is characterized by an enhanced sensitivity to sympathetic stimulation due to increased β-receptor density.Preoperative control of hypertension:A single dose of clonidine, 5μg per kg orally, 2 hours before surgery significantly decreases anesthetic requirements and hemodynamic lability in patients with mild-to-moderate hypertension.
25Controlled hypotensive technique for hypertensive patients: A single small oral dose of a β-adrenergic blocking agent such as labetalol. Atenolol, or oxpernolol given preoperatively to untreated, asymptomatic mildly hypertensive patients.The premedication with diazepam, lorazepam, or midazolam can be regulated to have the patient arrive in the operating room sedated.Controlled hypotensive technique for hypertensive patients:Uncontrolled or untreated severe hypertension is a contraindication to controlled hypotension.
26Intraoperative management Regional anesthesia:These patients should have intravascular fluids given prior to the regional anesthetic, regional blocks should be administered to an adequately medicated and sedated patient to prevent stress-related release of catecholamines.Monitoring:Electrocardiogram (ECG). Simultaneous leads V5 and II, multiple leads ST analysisBlood pressure (BP).Pulse oximeter.End-tidal CO2 analyzer.
27Induction: Intubation: Deeper anesthesia with potent inhalation agents to attenuate tachycardia and hypertension should be done with caution because of higher incidence of hypotension arising from both vasodilatation and cardiac depression.Intubation:Laryngoscopy time should be 15 seconds or less to minimize BP elevation. Other measures are described as follows:lidocaine, 1.5 mg per kg is given 2 minutes before intubation and using it in topical airway anesthesia.
28Maintenance of anesthesia: Esmolol, 2 mg per kg.Labetalol, 0.15 to 0.45 mg per kg.Nicardipine, 1 mg intravenously 2 minutes before tracheal intuabtion.Hypotension after induction of anesthesia usually can be easily corrected by volume replacement and simultaneous titration of vasopressors such as ephedrine 5 to 10 mg or phenylephrine in 0.1 mg inrements.Maintenance of anesthesia:Potent inhalation anesthetices or narcotics should be titrated to the desired level of central nervous system depression while the blood pressure (BP) is monitored continuously.
29The combination of nitrous oxide and low to moderate doses of narcotics and potent inhalation agents may provide the most stable intraoperative couuse.Fluid therapy:Patients with essential hypertension are usually hypovolemic because of vasoconstriction and diuretic therapy.Overhydration should be avoided because it may contribute to postoperative hypertension when the vasodilating effects of anesthetics are gone. Careful estimation of fluid intake and output is essential.
30Intraoperative hypertension (causes and management): Differential diagnosis of intraoperative hypertension:Related to preexisting diseaseChronic hypertension, increased intracranial pressure, aortic dissection, early acute myocardial infarction.Related to surgeryProlonged tourniquet time, post-cardiopulmonary bypass, aortic cross-clamping, postacarotid endarerectomy.Related to anestheticPain, inadequate depth of anesthesia, catecholamine release, malignant hyperthermia, shivering, hypoxia hypercarbia, hypothermia, hypervolemia, improperly sized (too small) blood pressure cuff, intra-arterial transducer positioned too low.Related to medicationRebound hypertension (from discontinuation of clonidine, btea blockers, or methyldopa), systemic absorption of vasoconstrictors intravenous dye (e.g, indigo carmine)OthersBladder distention, hypoglycemia.
31Postoperative management: The causes of postoperative hypertension include pain, emergence excitement, hypoxemia, hypercarbia, reaction to endotracheal tube, full bladder, hypothermia, relative hypervolemia from intraoperative administration of excess fluids. The most common cause of postoperative hypertension is incisional pain.