1. Hypertension
There are a number of potential problems associated with the hypertensive patient having spinal anaesthesia. If left ventricular hypertrophy is present, then it is important to maintain an adequate perfusion pressure in order to ensure adequate myocardial perfusion.
Autoregulation limits in organs such as the brain and the kidney may have become reset to higher levels and, thus, these organs will cope poorly with low perfusion pressure. Also, hypertension is associated with cerebrovascular disease and, if carotid artery stenosis is present, this mandates prompt and relatively aggressive support of blood pressure.
In patients with controlled hypertension receiving thoracic epidural anaesthesia, clinical experience suggests that risks are similar to the non-hypertensive population (3). Patients with uncontrolled hypertension are also prone to a greater lability of blood pressure (4) and may have a relative hypovolaemia (contracted circulating blood volume) which can be unmasked by spinal blockade (Chapter 39).
2. Ischaemic Heart Disease
Spinal anaesthesia is not contraindicated in patients with coronary artery disease. There is evidence that high thoracic epidural anaesthesia can improve the ratio of endocardial to epicardial blood flow (5), and cardiac sympathetic blockade has been used to ease intractable angina (6). Thoracic epidural anaesthesia may improve myocardial energy balance, although a study in patients receiving epidural anaesthesia during fentanyl-based coronary artery surgery showed no difference in myocardial metabolism compared with controls (7). Wall motion abnormalities have been shown to improve during epidural anaesthesia with a sensory block to the T9 level, provided preload reduction is maintained (8).
Spinal anaesthesia is capable of substantially modifying the stress response in many types of infra-umbilical surgery. This may confer an advantage to spinal over general anaesthesia with respect to the incidence of myocardial ischaemia, although data is conflicting (9). For major abdominal and thoracic surgery, there has been no consistently demonstrated benefit or disadvantage of spinal over general anaesthesia (10, 11, 12).
There is no advantage to having the patient awake so that they can report the occurrence of angina. Silent ischaemia is common, possibly more so if the cardiac sympathetics are blocked. Appropriate ST-segment ECG monitoring is a more sensitive method of detecting myocardial ischaemia than verbal reports of chest discomfort.
It is possible, although not yet proven, that postoperative myocardial ischaemia and infarction may be reduced due to the ability of intra- and post-operative epidural analgesia to reduce the hypercoagulability seen in the postoperative period and the lowered incidence of tachycardia resulting from better pain control. Large prospective, properly-randomised studies need to be performed to clarify these issues.
3. Valvular Disease
The reduction in preload associated with spinal anaesthesia can worsen the condition of patients with severe mitral valve prolapse or hypertrophic subaortic stenosis (13) (Chapter 111). The maintainence of adequate circulating fluid volume in these patients is essential.
Patients with aortic stenosis have been safely managed with spinal anaesthesia but in this situation the maintainence of arterial pressure is crucial and epidural anaesthesia is often chosen so that the spread of the block can be titrated more gradually. The avoidance of the myocardial depressant effects of many general anaesthetic agents by the use of spinal anaesthesia is an advantage.
Spinal anaesthesia presents difficulties in women with mitral stenosis and the onset of a tachycardia may result in cardiac decompensation and pulmonary oedema. Metaraminol or phenylephrine are more appropriate vasopressors than ephedrine in this population (Chapter 79) (Chapter 76).
In aortic and mitral valvular regurgitation, the afterload reduction theoretically helps to reduce the regurgitant fraction, but preload and heart rate need to be maintained.
Clearly, patients receiving anticoagulant therapy associated with prosthetic valve replacements must have coagulation normalised prior to spinal anaesthesia being instituted (Chapter 72).
4. Cardiac Failure
A significant reduction in the incidence of cardiac failure after major abdominal surgery in high-risk patients has been demonstrated with combined epidural and general anaesthesia and postoperative epidural analgesia (14). Intraoperatively, spinal anaesthesia alone might be expected to confer an advantage over a combined technique due to the unloading of the heart and the avoidance of negatively inotropic general anaesthetic agents. There is a risk, however, that intraoperative fluid therapy, compensating for venous pooling, may result in postoperative fluid overload once the sympathetic block has regressed. A careful balance of fluid and vasopressor therapy is therefore necessary in patients with a history of heart failure.
5. Dysrhythmias
There are a number of reports in the literature noting aggravation of conduction defects or cardiac arrest in association with spinal anaesthesia (15, 16, 17). These have a common theme of relative vagal hyperactivity causing increased sinus or atrio-ventricular nodal block in patients with spinally-induced blockade of cardiac sympathetic fibres. Preoperative assessment to identify patients at risk, and avoidance of hypovolaemia should help to limit the occurrence of these brady-dysrhythmias.
Many vasopressors cause a reflex bradycardia (e.g. phenylephrine, metaraminol) and in these patients, an agent with more beta-1 activity, such as ephedrine, is often preferable. In the near-arrest situation, adrenaline is appropriate and should be given early.
Conclusions
Spinal anaesthesia, using epidural or subarachnoid block, is appropriate and safe in patients with many forms of cardiac disease. Although the benefits of spinal anaesthesia over general anaesthesia with respect to cardiac morbidity reduction remain unproven, there is no reason to believe that morbidity is increased provided that there is a clear understanding of the haemodynamic effects and of the requirement for appropriate and timely intervention. The advantages of spinal anaesthesia techniques in other areas, including improved pain control and reduced recovery time, can then be achieved.
References:
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