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PERI OPERATIVE MANAGEMENT FOR PERIPHERAL VASCULAR SURGERY

TILOTTAMA P MANGESHIKAR, S KARTHIK
Department of Cardiovascular and Thoracic Surgery, Department of Anaesthesia, Bombay Hospital Institute of Medical Sciences.

The incidence of peripheral vascular disease (PVD) increases with age and affects 5.7% of the middle aged and elderly. There is a clear association between smoking, PVD and coronary artery disease (CAD). Patients with PVD are at high risk for developing complications after surgery and anaesthesia.

Active intervention is indicated for disabling symptoms. The intervention may be as minimally invasive as a percutaneous transluminal angioplasty (PTA) or a peripheral vascular reconstruction where the anaesthetist contributes significantly to the safety of the patient during and after surgery and also to the graft survival.

Pre Anaesthetic Assessment

The pre operative assessment of a patient subjected to peripheral vascular surgery is difficult because these patients usually present as emergencies and elaborate invasive diagnostic tests may not be feasible.

Patients with PVD present with numerous concurrent medical illnesses like diabetes mellitus, hypertension, concurrent coronary, cerebro vascular and renovascular disease and pulmonary dysfunction secondary to prolonged tobacco abuse.

Consequently, long term survival after surgery may be less than 65% at twelve months. Myocardial ischaemia and infarction are the commonest causes of mortality and morbidity. Myocardial ischaemia may be silent, especially in diabetics. Hence, clinical evidence of CAD seems to be a better predictor of peri operative cardiac events. But unfortunately, the usual clinical presentation of CAD i.e. angina on walking is frequently masked in the patient with PVD.

Why are Surgeries for PVD High Risk?
Hence, a risk assessment is mandatory. In the mid 1970s, Goldman and colleagues put forth a multifactorial risk index for the prediction of cardiac risk in patients subjected to non-cardiac surgery. Though it was effective for other surgical patients, it included a very small population of vascular surgery patients, and hence its usefulness is limited in the assessment of the PVD patients.

RISK CLASSIFICATION

The American College of Cardiology and the American Heart Association task force classified patients into three stratas of increasing risk as follows:

Major Risk
Intermediate Risk Mild Risk After stratifying patients according to the above factors, it is suggested that high risk patient should undergo further invasive assessment regardless of the surgical procedure.

Low risk patients require no special tests and one can proceed with surgery.

For those with intermediate risk, some amount of further assessment of functional capacity is essential.

The patients to be focussed on are those with intermediate risk but a poor functional capacity. They should undergo a coronary angiography and a cardiological assessment. If there is associated left ventricular dysfunction in them, then peri operative MI is a possibility. Hence, no further non invasive tests should be performed and the patient should be subjected to coronary angiography and if permissible, a coronary revascularisation also.

The following is a list of investigations:

Electrocardiogram

Exercise ECG

Ambulatory ECG

Dipyridamole Thallium Imaging (DTI), the most widely used non invasive test

Radionuclide Ventriculography and

Dobutamine stress Echocardiography.

A rationale for the use of DTI was proposed by Eagle et al by combining the test results with clinical variables such as Q waves on ECG, history of ventricular ectopics, diabetes mellitus, age beyond 70 years and angina.

It was suggested that patients with three or more risk factors can be directly subjected to coronary angiography rather than a DTI.

ANAESTHETIC MANAGEMENT

The technique of anaesthesia should be individualised in these patients due to the presence of concurrent medical illnesses. Though some studies show that the anaesthetic technique bears no influence on the outcome of surgery, many other studies have put forth that the type of anaesthesia ‘is’ important in overall outcome in terms of graft patency and lesser cardiac complications.

Pre operative evaluation and Preparation

The preoperative investigations reveal treatable medical conditions and the severity of the cardiac, respiratory and renal dysfunction if associated. These should be optimized before surgery.

Patients with coronary disease coming for surgery for PVD may be on anticoagulant regimens. A full anti coagulant course is a near total contra indication to regional anaesthesia. Patients in addition may be on anti platelets and thrombo-prophylaxis with low molecular weight heparins and aspirin. Studies have shown that low molecular weight heparins upto 5000 IU given prophylactic or intra operatively are safe provided they are not given within 4 hours prior to or 1 hour after the institution of a regional block. Hence, timing of heparin dosage, monitoring of anti coagulation with an ACT and postponement of surgery or abandoning the technique if a bloody tap is encountered are important factors that may influence outcome. Trials like the CLASP trial (1994) have confirmed that epidural is safe in patients taking aspirin.

Patients with Diabetes mellitus should be closely monitored for glucose levels. A sliding scale insulin regimen should be started intra operatively and followed strictly due to the prolonged nature of these surgeries.

Hypertensive patients should take their anti hypertensive medication until the morning of surgery. Pre operative beta blockade may help in diminishing peri operative tachycardia, surges in blood pressure and ischaemic events that are otherwise frequently seen.

Premedication

In addition to drugs for concurrent medical disorders, analgesics and anxiolytics are essential. This could include a dose of benzodiazepine and opioids for pain and sedation too.

There may be opioid tolerance as the patient may already be on these drugs for pain relief.

GENERAL ANAESTHESIA

INDUCTION - This should include a combination of oxygen, nitrous oxide, opioids and inhalational agents. Neuromuscular blockade to facilitate endotracheal intubation is necessary. This drug should be cardiostable and free of histamine release. Hence, Vecuronium would be the ideal choice with fentanyl or alfentanyl as the opioid. Propofol or Thiopentone may be used judiciously as induction should be smooth without Haemodynamic fluctuations. It should include manoeuvres to diminish the pressor.

MAINTENANCE - A balanced anaesthetic technique with endotracheal intubation and controlled ventilation is preferred. Isoflurane as the inhalational agent may be disadvantageous due to its properties of producing a coronary steal. Halothane being a myocardial depressant should be used with caution. A total intra venous technique has no added benefits. In fact it may be hazardous in the patient with severe respiratory disease, most of the drugs used being respiratory depressants. Our preference is for controlled ventilation with air and oxygen and a continuous Propofol and vecuronium infusion which keeps the patient asleep and immobile. We also almost always use an Epidural or a Spino-dural block along with the general anaesthetic. The epidural is used for intra and post operative analgesia, this being provided with a continuous infusion of 0.125% Bupivacaine and I mcg/ml of Fentanyl solution.

An important aspect during the maintenance of general anaesthesia is the maintenance of a normal body temperature due to the prolonged nature of these surgeries and cold theatre environments. Lower body temperatures are harmful. Firstly, they cause shivering and vasoconstriction increasing the myocardial oxygen demand. Secondly, vasoconstriction results in poor peripheral perfusion with thrombosis and graft failure ultimately. Therefore, active heat conserving measures are a must. At our Institution we use the Biotherm circulating mattress and an intravenous fluid warmer.

Intraoperative hypertension due to clamping of the artery needs to be anticipated and controlled with a vasodilator. Similarly the hypotension on release of the clamps can be extreme. Volume preloading as well as careful use of vaso pressors such as mephentermine can be helpful. Revascularisation causes some degree of acid metabolites entering the circulation and this needs to be assessed and corrected if severe. We use Allopurinol, Mannitol and Vitamins C and E to prevent injury due to the free radicals released after revascularisation.

Fluids and Monitoring

Good hydration should be maintained intra operatively with replacement of blood losses. The peripheral nature of these surgeries implies a minimal third space loss. Our patients are routinely started on fluids such as Lomodex which prevents roleaux formation of the red blood corpuscles which would hamper graft patency.

Monitoring should include all the routine monitoring equipment. In addition, a multi-lead ECG with ST segment analysis is superior to a routine ECG as myocardial ischaemia is a frequent complication intraoperatively. Invasive arterial blood pressure monitoring is essential. A central venous pressure monitor helps in administration of fluids, inotropes and vaso-active drugs. A pulmonary artery pressure trace may be useful in the patient with a poor LV function.

Recovery from GA should be smooth taking care not to cause tachycardia and hypertension. This is the period when chances of MI are high. Patients should continue to remain pain free, normothermic and normovolaemic.

Regional Anaesthesia

An infra inguinal arterial reconstruction can be effectively managed by regional anaesthesia with sedation or light general anaesthesia.

A continuous epidural technique is the preferred technique of choice. It has the added advantage that it can cater to a long duration of surgery and at the same time can be prolonged into the post operative period for analgesia. Drugs like lignocaine or bupivacaine or a combination of both is used. A small dose of an opioid may also be added.

Dose Regional Blockade Alter Outcome?

Theoretically speaking, regional anaesthesia has several advantages over general anaesthesia. It modifies the cardiovascular and metabolic responses to the stress of surgery. This helps to diminish myocardial ischaemic episodes. Tachycardia and hypertension caused by endotracheal intubation are avoided by regional techniques.

The sympathetic blockade caused decreases both preload and afterload. The vasodilatation produced improves the graft perfusion, decreases chances of graft failure.

With regional blockade it is seen that the levels of catecholamines are also diminished which decreases the probability of vasoconstriction. There is increased fibrinolysis too due to decrease in procoagulant factors. All these factors put together definitely improve the graft survival.

Post Operative Care

These patients are best looked after in an Intensive care unit that will continue the monitoring of the patients’ organ systems as well as the graft, regularly anticipating and correcting trends. A vigilant ICU nurse has many a time prevented loss of a limb or life by getting the patient back to theatre on time in case of bleeding or graft revision being needed.

REFERENCES

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