Preoperative Assestment of Vascular PatientsSussan Soltani Mohammadi,M.D.
Vascular surgical patients have a high incidence of morbidity and mortality following surgery due to coexisting disease associated with advanced age, cigarette smoking, DM, and hypertension, affecting CVS , respiratory and renal system.
The preoperative period presents an opportunity to optimize pharmacologic management , perform diagnostic and therapeutic interventions , and adjust care to ↓peri operative risk and the long term risks from cardiovascular events.
Purpose of preoperative assessment: • Measurement the risk of morbidity and mortality. • Appropriate patient selection. • Appropriate pre, peri , and postop management. • Ensure that patient is fully informed of the risk
Cardiovascular system • Most of the perioperative mortality associated with vascular surgery is due to cardiovascular complications. • The body’s oxygen demand increases by up to 40% following major surgery, such as aortic aneurysm repair. • This extra oxygen demand lasts for several days postoperatively→↑ CO.
The history and physical examination are not very reliable for detecting CAD. • An estimate of the patient’s cardio respiratory reserve is important, but can be difficult, because of the high incidence of claudication , previous strokes and amputations. • The symptoms of IHD are often not manifested in diabetic patients, and silent myocardial ischemia goes unrecognized.
Despite these limitations, important risk predictors can be obtained from the History and PH.Exam: • Age >70 years • DM • Angina • CHF • Prior MI or CABG • Exercise tolerance, or functional capacity.
Exercise tolerance, or functional capacity, is valuable information that may eliminate the need for preoperative cardiac testing. • Perioperative risk ↑in patients with poor exercise tolerance. • Functional capacity, expressed by metabolic equivalents (METs).
Guidelines published AHA and ACC use the concept of metabolic equivalents • MET(metabolic aquvalant of task)is the basal metabolic oxygen consumption at rest (3 ml/kg/min) and can be measured. • Various activities can be assigned approximate MET values and an estimate of the patient’s exercise capacity made. • An inability to increase oxygen consumption more than 4 METS identifies a high-risk patient.
Other scoring systems have been devised to assess cardiac risk most of which can be established from a history, examination and simple investigations, such as the ECG.
Investigations for cardiac risk 1)ECG:A preoperative ECG should be obtained for all patients undergoing vascular surgery for comparison if MI or ischemia is suspected postoperatively.
If Q waves or other evidence of prior MI is present →to determine the timing of the infarct for the purpose of risk stratification. • Dysrhythmias should be evaluated preoperatively to optimize peri operative management (rate control for AF).
The presence of a cardiac rhythm other than sinus indicates risk for perioperative cardiac. • Approximately 50% of patients with CAD have a normal resting ECG, demonstrating that the ECG lacks sensitivity for predict
24-hour ECG: preoperative ST segment analysis of a 24-hour ECG recording gives an indication of the frequency and severity of ischemic episodes, it can detect ‘silent’ ischaemia if there is no sign of silent ischemia on a 24-hour ECG, the risk of perioperative cardiac complications is very low.
2)Exercise ECG testing: If vascular surgery patients are able to exercise and achieve 85% of their predicted maximal HR, they are low risk for perioperative cardiac. 3) Dobutamine stress echo :has a ↑sensitivity compared with resting echo. 4) Dipyridamole–thallium imaging(DTI):This test will identify ischaemic myocardium accurately, but has a poor predictive value for progression of perioperative MI.
5)Cardiopulmonary exercise testing: The level of oxygen consumption (ml/kg/min) at the anaerobic threshold has been used to risk-stratify patients for high-risk surgery. 6)Coronary angiography: is the gold standard for the assessment of CAD , allows the measurement of intra ventricular pressures, ventricular function and the gradients across valves.
A meta-analysis found DSE to be the best predictor of cardiac morbidity (relative risk [RR] = 6.2), followed by DTI (RR= 4.6), and AECG (RR = 2.7)
Specific conditions a)Coronary artery disease • only 10% of vascular patients have normal coronary arteries with more than 50% having severe coronary disease demonstrated on angiography. • This correlates with a perioperative MI rate of approximately 5%.
b) Previous myocardial infarction • Patients who have had a previous MI have a 5–6% chance of reinfarction in the perioperative period. • Surgery within 3 months of an MI carried up to a 36% chance of reinfarction. • Traditional anesthetic practice dictated post poning elective surgery until a 6month interval passed.
Much of the risk after a prior MI is related to the functional status of the ventricles and the presence of ongoing ischemia, rather than to the actual age of the infarction. • Current guidelines recommend waiting 6 weeks after an uncomplicated MI before proceeding with an elective surgical procedure.
Vascular surgery, however, is often not elective and urgent surgery is often necessary. • For this reason, each patient with a prior or recent MI must be assessed carefully from the risk-benefit standpoint.
3) Cardiac failure • symptomatic CHF has a poor prognosis. • In severe failure → ‘non-operative’ approach if possible, or a less invasive. • The patient’s medical condition should be preoptimized, with appropriate use of diuretics, vasodilators, or ACEIs. • Invasive monitoring, inotropes and postoperative critical-care facilities may be needed.
4)Aortic stenosis • The most frequent causes are congenital abnormalities and degenerative calcific stenosis. • Severe AS is defined by a mean pressure gradient of more than 50 mm Hg across a valve or a cross-sectional area of less than 0.8 cm2.
Surgery in patients with AS is hazardous due vasodilatation and myocardial depression caused by induction of anaesthesia. • Patients with associated angina or syncope have severe disease, and consideration should be given to surgical correction of the valve if possible.
5) Hypertension • Is a risk factor for IHD. • Patients are prone to BP lability both intra- and postoperatively • Uncontrolled hypertension is only a minor risk factor in the ACC and AHA guidelines • There is little evidence to support cancelling hypertensive patients, who are undergoing elective surgery, on the day of surgery.
Patients with a diastolic blood pressure> 110 mm Hg, which fails to settle, should be referred for further investigation and treatment. • Current guidelines suggest a target blood pressure of 140/90 mm Hg. • Patients taking antihypertensive medication should continue in the perioperative period, but omit ACEIs as they may cause perioperative hypotension.
6)Atrial fibrilation • patients in atrial fibrillation should have their HR controlled to <90 beats per min. • These patients are frequently anticoagulated to reduce the risk of thromboembolic events. • Ideally, patients should remain without anticoagulation for as little time as the surgical procedure allows.
Modifying cardiac risk Coronary artery intervention: • patients with severe CAD should be investigated and treated along standard medical, surgical or radiological guidelines. • Cardiac surgery should be undertaken only if the disease makes it necessary. • Correcting severe CAD before elective surgery does not reduce short term mortality.
Focus is correction of CAD by pharmacological optimization with β-blockers and statins. • Vascular surgery immediately following percutaneous coronary stenting is hazardous, despite adequate antiplatelet treatment. • Surgery should be delayed at least 6 weeks in these patients.
B-blockers: • β-blockade reduced arrhythmias and myocardial ischaemia but had no effect on mortality, MI rate or length of hospital stay. • prescribe β-blockers to patients with a history or evidence of myocardial ischaemia on testing, but not to all patients→ will cause an excess of side effects.
Statins • They↓inflammation,stabilize athero-sclerotic plaques and may reduce peri operative cardiovascular complications. • Because one of the proposed mechanisms of perioperative MI is rupture of a coronary artery plaque, All vascular patients should be prescribed a statin to reduce vascular events.
Preoptimization: • maximizing oxygen delivery by using incremental fluid boluses and inotropes. • SV monitoring is optimized with a PAC or an oesophageal Doppler probe. • The younger, fitter patient undergoing aortic aneurysm surgery may benefit from preoptimization, • In the older patient with significant cardiac disease the use of β-blockade and the avoidance of tachycardia would seem logical.
Perioperative medical therapy Antiplatelet/anticoagulant agents: • Aspirin should be continued throughout the perioperative period. • Clopidogrel, an ADP/platelet binding inhibitor, should be stopped for at least 5 days before surgery.
Warfarin should also be stopped 5–7 days before surgery and the patient started on either LMW heparin or unfractionated heparin. • A risk/benefit analysis should be made for each patient,Patients with coronary artery stents should not be left without antiplatelet cover.
Respiratory system • Because the number of vascular patients who smoke is high, COPD is very common and functional assessment of the severity of the condition is useful. • Much of the damage to the alveoli will be permanent, but there is usually an element of reversible airway disease, and this should be optimized preoperatively. • If functional ability is seasonal, schedule elective surgery for the best time of year.
Stop smoking 6–8 weeks before surgery to allow ciliary function to return, failing that, get the patient to stop on the day of surgery to decrease carboxyhaemoglobin and improve oxygen carriage.
Admit the patient several days in advance to allow time for chest physiotherapy. • Bronchodilators, and steroids will help treat any reversible element. • Exclude active infection. • Encourage the patient to lose weight.
Investigations: • PFT → assess the severity of respiratory disease. • FEV1 is a good measure of ventilatory capacity ,FEV1 <1 liter indicates extremely poor function and predicts a high risk of postoperative ventilation. • FVC indicates the severity of diffuse parenchymal disease, FVC<50% of that expected for height, weight and sex indicates a high likelihood of needing postoperative support.
PFT before and after the administration of bronchodilators give an indication of the reversibility of the disease. • ABG should be done if PFT are below 50% of the predicted value. • CXR rarely adds to the assessment after history, examination and respiratory function testing.
Renal system • Preoperative renal impairment and postoperative renal failure ↑perioperative mortality. Avoid: • Hypovolaemia • Hypotension • Nephrotoxic drugs (NSAIDs) • Sepsis • Hypoxaemia • Prolonged periods of oliguria.
Angiographic contrast media are potentially nephrotoxic. • Pre-angiographic intravenous hydration, the use of low-osmolar dyes, and minimizing the dose used help reduce the renal insult. • Aminophylline and N-acetyl cysteine have been used to counteract the toxicity.
Diabetes Mellitus • The anaesthetist should seek the presence of IHD, renal impairment and peripheral or autonomic neuropathies. • The management of patients involves either omitting the morning dose of oral hypo-glycaemics on the day of surgery or a glucose-potassium-insulin infusion through the perioperative period.
Patients with autonomic neuropathy may not tolerate the vasodilatation associated with the induction of anaesthesia or the fall in venous return on commencing PPV. • Preoperative standing/sitting blood pressure, tachycardia during a Valsalva maneuver can assess the autonomic nervous system.