Chapter 2 – Hypertension




Chapter 2 Hypertension



Tarek Francis Antonios



Key Points





  • Hypertension is one of the major risk factors for morbidity and mortality in cardiovascular disease.



  • Treatment of hypertension not only reduces the incidence of death and morbidity from strokes and coronary events, but also prevents left ventricular hypertrophy, heart failure, renal failure and dementia.



  • Common reasons for delaying surgery in patients with hypertension are poorly controlled blood pressure (BP) (grade 3 hypertension defined as BP ≥180/110mmHg), evaluation and treatment of end-organ damage that has not previously been assessed and treated or when secondary hypertension is suspected and a cause is not yet clear. However, it is not known whether reducing BP in these patients while postponing planned surgery would reduce the rate of major cardiovascular events perioperatively.



  • In patients with grade 3 hypertension, the potential benefits of delaying surgery to optimise antihypertensive therapy should be weighed against the risk of delaying the procedure.



  • Cancellations of planned surgery not only cause significant financial loss to healthcare providers, but, more importantly, have substantial psychological, social and financial implications for patients and their carers.




Introduction


Hypertension is one of the major risk factors for cardiovascular disease (CVD) morbidity and mortality. Treatment of hypertension not only reduces the incidence of death and morbidity from strokes and coronary events, but also prevents left ventricular hypertrophy, heart failure, renal failure and dementia (Ezzati, 2002). The results of prospective observational studies and of randomised controlled trials of antihypertensive treatment indicate that reduction of the blood pressure (BP) in hypertensive individuals reduces their risk of CVD events by about 16 per cent for coronary heart disease and by 38 per cent for stroke (Macmahon, 1990). A meta-analysis of observational studies involving more than 1 million individuals without prior histories of stroke or heart disease demonstrated that death from coronary heart disease and stroke increases continuously and linearly from BP levels as low as 115mmHg systolic and 75mmHg diastolic (Lewington, 2002). The discovery of untreated or uncontrolled hypertension in a preoperative assessment clinic may result in the cancellation of surgery. These cancellations of planned surgery not only cause significant financial loss to healthcare providers, but, more importantly, have substantial psychological, social and financial implications for patients and their carers (Casadei and Abuzeid, 2005).



Definition of Hypertension


Hypertension is currently defined as clinic systolic BP ≥140mmHg and/or diastolic BP ≥90mmHg or the use of antihypertensive medications. The health survey in England for 2012 suggests that the national prevalence of hypertension was 31 per cent among men and 27 per cent among women. The proportion of adults with controlled hypertension (defined as BP ≤140/90mmHg) is only 9 per cent for both men and women. Long-term risk of an individual is best determined by the lifetime risk statistic, which is the probability of developing hypertension during the remaining years of life. Data from the Framingham Heart Study indicated that a lifetime risk for developing hypertension in men and women who were not hypertensive at age 55 or 65 years and survived to age 80 to 85, respectively, was 90 per cent.


Table 2.1 shows the stages of hypertension. There is no evidence that patients with stage 1 or 2 hypertension and no evidence of end-organ damage or coexisting CVD will be adversely affected by proceeding to planned surgery (Casadei and Abuzeid, 2005). In these patients, antihypertensive medications should be continued during the perioperative period.




Table 2.1 Stages of hypertension.














































BP range (mmHg)
SBP (mmHg) DBP (mmHg)
Optimal blood pressure <120 <80
Normal blood pressure <130 <85
High-normal blood pressure 130–139 85–89
Stage 1 hypertension (mild) 140–159 90–99
Stage 2 hypertension (moderate) 160–179 100–109
Stage 3 hypertension (severe) >180 >110
Isolated systolic hypertension (Grade 1) 140–159 <90
Isolated systolic hypertension (Grade 2) >160 <90


Legend: BP=blood pressure, SBP=systolic blood pressure, DBP=diastolic blood pressure, mmHg=millimetre of mercury


In patients with stage 3 hypertension (BP ≥180/110mmHg), the potential benefits of delaying surgery to optimise antihypertensive drug treatment therapy should be weighed against the risk of delaying the procedure. In a randomised study, when compared with deferred surgery, immediate BP reduction with nifedipine was associated with similar complication rates but a shorter hospital stay (Weksler, 2003). However, it is advised that patients with stage 3 (severe) hypertension should have their elective surgery postponed for 6–8 weeks to better control their BP to <160/100mmHg and to consider arranging ambulatory BP monitoring and further laboratory tests (Mancia, 2013).



Blood Pressure and Anaesthesia



Patients with No History of Hypertension


The preoperative assessment clinic is a unique opportunity to identify patients with hypertension and offer appropriate therapy to reduce long-term CVD risk. It must be stressed here that appropriate measurement of BP in a non-stressful environment according to the NICE/BHS guidelines is of paramount importance (Table 2.2). The physical examination should include an examination of the fundus and a search for target organ damage and evidence of associated CVD pathology. Suggested tests include electrocardiography (ECG) and echocardiography to assess for left ventricular(LV) hypertrophy and ischaemic heart disease, plasma urea, creatinine and eGFR to assess kidney function, and fundoscopy to assess for hypertensive retinopathy. If the patient’s BP has been documented previously to be within normal limits (ideally <140/90mmHg) and was found to be elevated in the pre-assessment clinic, then the patient may be suffering with white coat hypertension. If the initial evaluation establishes hypertension as mild or moderate, with no indication of associated target organ damage, there is no evidence that it is beneficial to delay surgery as stage 1 or stage 2 hypertension (systolic BP <180mmHg and diastolic BP <110mmHg) is not an independent risk factor for perioperative CVD complications (Detsky, 1986).




Table 2.2 Correct technique for measuring blood pressure.










  1. 1. Use a properly maintained, calibrated and validated device.



  2. 2. The patient should be seated comfortably leaning on the back of the chair. Remove tight clothing, support arm at heart level, ensure the hand is relaxed and avoid talking during the measurement procedure.



  3. 3. Use an appropriately sized cuff. The rubber bladder inside the cuff should encircle at least 80 per cent of the arm circumference. It is wise to explain to the patients that there will be some slight discomfort as the cuff is inflated.



  4. 4. Automated sphygmomanometers are inaccurate in patients with atrial fibrillation. In these patients blood pressure should be measured by auscultation over the brachial artery during manual deflation of an arm cuff.



  5. 5. At first consultation blood pressure should be measured in both arms to ensure there is no discrepancy. At subsequent visits, use the arm with the higher reading.



  6. 6. Measure the blood pressure at least twice if higher than 140/90mmHg. If the blood pressure is between 140/90mmHg and 179/109mmHg, offer ambulatory blood pressure monitoring or home blood pressure monitoring to rule out white coat hypertension.



  7. 7. Measure blood pressure in the standing position at least once when assessing a new patient, in elderly patients (>80 years) and in diabetic patients.



  8. 8. The patient should be clearly informed that a single elevated reading does not constitute a diagnosis of hypertension, but that further observation is required.



  9. 9. If the blood pressure ≥180/110mmHg, the patient may have severe hypertension and should be offered immediate treatment.



Legend: mmHg=millimetre of mercury


Common reasons for delaying surgery in patients with hypertension are poorly controlled BP i.e. grade 3 (BP ≥180/110mmHg), discovery of end-organ damage that has not previously been evaluated or treated or suspicion of secondary hypertension “without properly documented aetiology. There is evidence that hypertension with target organ damage is associated with a small increased incidence of perioperative major adverse CVD events” (Howell, 2004), however, it is not known whether reducing BP in these patients during a postponement of planned surgery would reduce rate these events.



Patients with Previous History of Hypertension


In patients treated with antihypertensive medications, a thorough review of their current medications and dosages is essential. Their antihypertensive medications should be continued during the perioperative period. Several studies have demonstrated exaggerated intraoperative BP fluctuation with associated ECG evidence of myocardial ischaemia in patients with preoperative hypertension (Charlson, 1990). Intraoperative myocardial ischaemia is known to correlate with post-operative cardiac morbidity (Raby, 1992).


For patients with stage 3 hypertension (systolic BP ≥180mmHg and/or diastolic ≥110mmHg), it is advisable to postpone the surgical procedure to optimise the effects of antihypertensive medications and control BP <180/110mmHg. Several studies have demonstrated the benefit of effective preoperative BP control among patients with severe hypertension (Goldman and Caldera, 1979). Particular care should be taken to avoid sudden withdrawal of beta-blockers and clonidine because of potential tachycardia or hypertension rebound. During the induction of anaesthesia, sympathetic activation can cause an increase in BP of 20–30mmHg and a heart rate increase of 15–20 beats/minute in normotensive individuals with a more pronounced effect in patients with untreated hypertension. Patients with hypertension are more likely to experience lability of their BP and intraoperative hypotension than non-hypertensive persons. Patients taking angiotensin converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs) are likely to suffer from hypotension if they are hypovolemic or dehydrated, especially if they have been kept nil by mouth for some time before their planned surgery. Few studies suggested that intraoperative hypotension was associated with a greater incidence of perioperative cardiac and renal complications, although other studies have not confirmed this (Colson, 1992; Rady and Ryan, 1998). Some authors have suggested withholding ACE inhibitors/ARBs the morning of surgery (Bertrand, 2001), but if patients are well hydrated and euvolemic, then continuation of ACE inhibitors/ARBs perioperatively is reasonable (Rosenman, 2008; Turan, 2012). If ACE inhibitors/ARBs are held before surgery, it is reasonable to restart them as soon as clinically feasible post-operatively and only after the patients are euvolemic, to decrease the risk of perioperative renal dysfunction. The long-term clinical consequences of continuing versus withholding preoperative ACE inhibitors/ARBs are unknown. This uncertainty stems in part from the absence to date of randomised trials designed specifically to examine patient-important consequences of this decision. Post-operative hypertension is frequently caused by pain after awakening, hypothermia, hypoxia or intravascular volume overload from excessive intraoperative fluid therapy, particularly in the ensuing 24 to 48 hours as fluid is mobilised from the extravascular space (Prys-Roberts, 1971).



Beta-Blocker Controversy


Until recently the European Society of Cardiology (ESC) and the American College of Cardiology (ACC) guidelines used to recommend the perioperative initiation of a course of beta-blockers in patients at risk of cardiac events undergoing high- or intermediate-risk surgery or vascular surgery (Poldermans, 2010). The revised 2014 ESC/ European Society of Anaesthesiology (ESA) (Kristensen, 2014) and the American Heart Association (AHA) /ACC Guidelines (Fleisher, 2014) continue to recommend continuation of beta-blocker therapy in the perioperative period in patients already receiving this medication. However, the current guidelines do not recommend the initiation of beta-blocker therapy. The Dutch Echocardiographic Cardiac Risk Evaluation Applying Stress Echocardiography (DECREASE) family of trials, the substratum of evidence for this, is no longer secure (Dunkelgrun, 2009). A recent meta-analysis found that the initiation of a course of beta-blockers pre-operatively in patients undergoing non-cardiac surgery increases mortality by 27 per cent, which is both statistically and clinically significant (Bouri, 2014). Please refer also to Chapter 1, page 11.



Secondary Hypertension


Table 2.3 summarises the common causes of secondary hypertension. Further evaluation to exclude secondary hypertension is rarely required before necessary surgery. However, if a pheochromocytoma is suspected, surgery should be delayed to permit its exclusion. Patients with renal artery stenosis may show a loud abdominal bruit on abdominal examination, whereas patients with coarctation of the aorta may have radio-radial, radio-femoral artery pulse delay or weak lower limb pulses and BP. The commonest cause of secondary hypertension is primary hyperaldosteronism, which may be suspected in patients with low or low-normal plasma potassium. If secondary hypertension is suspected, patients should be referred for specialist hypertension services for further management (NICE Clinical Guideline CG127, 2011).




Table 2.3 Causes of secondary hypertension.







































































































Endocrine Adrenal Cortex Conn’s syndrome (primary aldosteronism)
Cushing’s syndrome
Congenital adrenal hyperplasia
Dexamethasone responsive aldosteronism
Adrenal Medulla Pheochromocytoma
Hyperparathyroidism
Acromegaly
Renal Renovascular disease Arteriosclerotic renal artery stenosis
Fibromuscular dysplasia
Renal parenchymal disease Acute and chronic glomerulonephritis
Polycystic disease
Diabetic nephropathy
Collagen vascular disease
Renal transplantation
Renin-secreting tumours
Coarctation of aorta
Drug induced Oral contraceptives
Cyclosporine
Steroids
Carbenoxolone and liquorice
Tyramine and MAO inhibitors
Erythropoietin
NSAIDs
Angiogenic inhibitors
Pregnancy-induced hypertension


Legend: MAO =monoamino oxidase , NSAID = nonsteroidal anti-inflammatory drugs



Long-Term Management of Hypertension



Management of Mild to Moderate Hypertension


The goal of antihypertensive treatment is to reduce CVD risk and thus morbidity and mortality. The current NICE guidelines recommend that individuals younger than 55 years should be offered an ACE inhibitor or an ARB, while individuals older than 55 years and people of African or Caribbean origin (of any age) should be offered a calcium channel blocker (CCB) or a thiazide-like diuretic (e.g. chlorthalidone or indapamide). However, BP control on monotherapy is rarely achieved, except in mild hypertensives. This is because hypertension is multifactorial in aetiology and the haemodynamic effect of a single drug is limited by physiological feedback mechanisms, which oppose the action of the drug. In this respect the most effective way to control BP is to combine agents that lower BP by different mechanisms. Large intervention trials make clear that if BP targets are to be reached, then the majority of patients will need to take two or more antihypertensive agents in combination. Drug combinations allow lower doses to be used with minimal or no side effects. In general, ACE inhibitors/ARBs (A) combine well with CCB (C) and diuretics (D). This gives rise to the A/CD rule for combining two drugs, in which an A drug is added to another from either C or D (NICE Clinical Guideline CG127, 2011). The A/CD rule allows the addition of a third drug class, when the majority of patients should end up on a drug from each group: A plus C plus D (Antonios, 1996; Macgregor, 2000).



Resistant Hypertension


Resistant or refractory hypertension exists when the BP remains above the treatment target, despite treatment with a rational combination of maximum tolerated doses of three drugs, including a diuretic (Calhoun, 2008). If not addressed at the outset of treatment, attention should be directed to lifestyle modifications, particularly dietary salt reduction, and moderation of alcohol intake. Advice about antihypertensive drug compliance and avoidance of exacerbating factors such as NSAIDs, which are frequently purchased over the counter, is also worthwhile. A referral to a specialist hypertension unit is warranted for exclusion of secondary causes of hypertension.



Hypertensive Crises


The presence of severely elevated BP may encompass chronic uncomplicated hypertension or a hypertensive crisis. Patients with chronic hypertension may tolerate systolic BP of 250mmHg or diastolic BP of up to 150mmHg without developing a hypertensive crisis, while children or pregnant women may develop encephalopathy with diastolic BP 100mmHg. Hypertensive crisis is defined as a clinical situation involving severe hypertension and ongoing or impending target organ damage. Hypertensive crises occur most commonly in individuals previously diagnosed with systemic hypertension but who are non-compliant and therefore inadequately treated.


The rate of the rise in BP in relation to the previous levels of BP is more important than the absolute BP level. Hypertensive crises can be further classified as hypertensive emergencies or urgencies depending on the need for acute medical intervention. Hypertensive Emergency is defined as a situation that requires immediate BP lowering (not necessarily to normal values) to prevent or limit target-organ damage. Hypertensive Urgency is a situation in which severely elevated BP is not accompanied by any evidence from history, physical examination or laboratory investigation of acute target organ damage. Individuals under this category could be known hypertensive patients who are not compliant with their medication, and prior therapy should be restarted if there are no side effects. For patients taking their medications regularly, therapy should be increased (either by increasing the dose(s) of drugs or adding new drugs). For patients on no treatment, hypertension therapy should be started with oral agents (e.g. nifedipine SR or MR) and follow-up appointments arranged urgently with a hypertension specialist clinic to ensure compliance and to make further adjustments if necessary.


Individuals with untreated severe or accelerated hypertension have an unfavourable long-term prognosis. The most common causes of death are renal failure, strokes and myocardial infarction. The exact cause of hypertensive crisis is not well understood; however, it is widely thought that a sudden increase in peripheral systemic vascular resistance (e.g. secondary to non-compliance) triggers an increase in circulating levels of vasoconstrictor substances such as angiotensin II and noradrenaline.



Management of Hypertensive Crisis


The key to a successful outcome is the prompt recognition and initiation of treatment. Full medical history and physical examination including palpation of all peripheral pulses and a funduscopic examination is mandatory. Specific points in the patient’s past history include what was the patient’s BP prior to presentation, and what medications, prescription and over the counter, is the patient taking. Initial investigations should include FBC, electrolytes, urea, creatinine, urine dipstick, echocardiography and an ECG. CT head is useful in patients with neurological signs. These tests should be performed simultaneously with the initiation of antihypertensive therapy. The approach in treating hypertensive emergency is to initially reduce arterial BP by about 25 per cent with further reductions accomplished more gradually. The initial reduction should be achieved over a period of 2–4 hours with less rapid reduction over the next 24 hours to a BP of approximately 160/100mmHg.


Indications to specialist referral when urgent treatment of BP is required are listed in Table 2.4.


Sep 15, 2020 | Posted by in ANESTHESIA | Comments Off on Chapter 2 – Hypertension
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