Ch 34 Anaesthesia And Heart Disease

CHAPTER 34

ANAESTHESIA AND HEART DISEASE

Outline: Heart failure Hypertension Myocardial ischaemia Arrhythmias Other cardiac conditions

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HEART FAILURE Right heart failure The signs are: • Ankle oedema • Elevated jugular venous pressure • Enlarged and tender liver • Third heart sound Left heart failure When the left side of the heart fails, there is congestion in the lungs. Therefore the symptoms are respiratory. Dyspnoea is the main symptom, first noted on exertion. Later attacks occur at night and finally the dyspnoea persists even at rest. On auscultation of the chest fine or coarse crepitations may be heard. It is important to find the underlying cause of the cardiac failure, e.g. ischaemia, hypertension, valvular heart disease. Anaesthesia Patients with uncontrolled congestive heart failure (left heart failure) should not be anaesthetised for routine surgery as there is a high perioperative morbidity. They should be treated pre-operatively with: • Oxygen. • Diuretics, e.g. frusemide. • Potassium supplements as indicated. • Digoxin only if there is rapid atrial fibrillation. • ACE inhibitors (angiotensin converting enzyme inhibitors), if available. Pre-operative management: Once the cardiac failure has been controlled, it is safe for surgery to proceed. Frusemide can also be given IM depending on the severity of the cardiac failure. The drugs for treatment of cardiac failure should be continued right up to the morning of operation In the urgent case when it is not possible to spend time treating the cardiac failure, a regional anaesthetic may be preferable to a general anaesthetic. A spinal might be reasonable if aortic stenosis and unstable angina are excluded. If a general anaesthetic is essential it must be given very carefully.

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Intra-operative management: If a general anaesthetic is used, the principles are: • Give small doses of drugs • Air/oxygen/volatile ± relaxant or a ketamine technique would be reasonable • Give a higher inspired oxygen concentration to avoid hypoxia • Avoid hypotension • Avoid fluid overload • Give intermittent positive pressure ventilation. HYPERTENSION This is an increasing problem in anaesthesia. Hypertension, when it occurs in younger people can be due to an underlying disease, e.g. renal, endocrine, etc. In all cases prolonged hypertension, especially if untreated, affects various organs, e.g. the heart, kidneys. These patients are prone to heart failure and renal failure, because they cannot compensate for hypotension, hypoxia or hypercarbia. Some may be on anti-hypertensive drugs. It is now accepted that: • All hypertensive patients should be treated before elective surgery and their blood pressure stabilised to a diastolic pressure of 90-100 mmHg. • Patients are kept on their anti-hypertensive drugs right up to the time of operation. • Patients presenting for elective surgery with untreated hypertension with a diastolic pressure > 115 mm Hg on at least two readings should be cancelled and prescribed treatment. Points of importance to the anaesthetist Patients on anti-hypertensive drugs cannot compensate in the usual way for the stress of anaesthesia. Things to monitor closely are: − Anaesthetic drugs and their side effects − Blood loss − Changes in position − IPPV − Avoid hypoxia − Avoid hypercarbia. The same precautions, as described for patients with myocardial ischaemia or CCF must be used for hypertensive patients.

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MYOCARDIAL ISCHAEMIA Myocardial ischaemia, or damage to the myocardium, results if the arteries supplying the heart muscle become narrowed or blocked. The blood supply to the heart muscle is therefore reduced and ischaemia results. Myocardial ischaemia must be carefully evaluated before surgery. An ECG should be done. If this shows evidence of a myocardial infarct and the surgery is elective, then 6 months should elapse before the operation. If the surgery is semiurgent and has to be done under a general anaesthetic then a minimum of 3 months should still elapse. Urgent surgery is carried out in the context of risk against benefit. Even 6 months following the infarct, the mortality rate is higher. If the ECG shows evidence of myocardial ischaemia only, without damage or death of the heart muscle (i.e. no infarction) then anaesthesia still carries certain risks because these patients are very liable to go into heart failure and /or develop an arrhythmia, or progress to infarction. Anaesthetic technique The same principles and techniques as outlined for patients with congestive heart failure should be followed in patients with myocardial ischaemia. • Stabilise the patient as much as possible preoperatively i.e. nitrates, beta-blockers • Give small doses of drugs, especially myocardial depressants, e.g. thiopentone, halothane, etc. • Use a high inspired concentration of oxygen. • Have good intravenous access. • Avoid hypoxia, hypercarbia and swings in blood pressure. These patients are more liable to hypotension on account of their drug treatment, e.g. beta-blockers. • Avoid fluid overload. • Use a relaxant technique with IPPV.

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ARRHYTHMIAS The dangers of arrhythmias under anaesthesia are: • • • • • •

Myocardial ischaemia as a result of a rapid heart rate Ischaemia of the brain and kidney Myocardial infarction Cardiac failure Ventricular fibrillation (cardiac arrest) Thrombo-embolism.

The following are arrhythmias which should be treated before elective surgery: • Sinus tachycardia. Find the cause and treat it first. • Sinus bradycardia, especially if there is an associated fall in cardiac output and blood pressure. • Atrial tachycardia ) Atrial flutter ) if the rate is above 100/min. Atrial fibrillation ) • Ventricular ectopics (if greater than 5 per minute, or multifocal, or close to the preceding T-wave with the risk of the R on T phenomenon). OTHER CARDIAC CONDITIONS •

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Rheumatic heart disease. In the acute stage, general anaesthesia is contraindicated. In rheumatic valvular heart disease, give pre-operative cover with antibiotics to protect against endocarditis and observe the safety principles outlined earlier. Congenital Heart Disease. Here too give antibiotic cover pre-operatively.

Suggested regime of antibiotic cover for patients at risk of endocarditis Amoxycillin 3g orally 4 hours before surgery or 1g IV at induction followed by amoxycillin 3g orally 6 hours post-operatively OR (for patients who are allergic to penicillin) Vancomycin 1g by IV infusion over 1-2 hours followed by gentamicin 120mg IV at induction. Not all of these antibiotics will be available in many hospitals but should be

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used if possible.

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