Critical Care Medicine

Critical Care of the Vascular Surgery Patient

1. Description of the problem

Introduction

Patients undergoing vascular surgery are a unique group undergoing both high-risk surgery and being at high risk of perioperative morbidity and mortality due to the advanced nature of their atherosclerotic disease, which is often combined with pulmonary dysfunction. Although many vascular procedures are undertaken without the need for critical care support, those that do warrant admission are typically extremely high risk for a poor perioperative outcome.

This chapter will focus on the following areas:

  • Elective and emergency surgery.

  • Abdominal aortic aneurysm.

  • Endovascular aneurysm repair.

  • Carotid endarterectomy.

  • Lower limb bypass surgery.

Common management problems for vascular patients

Critical care of the vascular patient ranges from active observations to prompt early intervention to prevent development of multiple organ problems. Common problems encountered include:

  1. Bleeding (and complications of multiple transfusions)

  2. Avoidance and treatment of myocardial ischemia

  3. Assessment and management of myocardial function

  4. Avoidance and early treatment of hypo- or hypertension due to increased stroke risk

  5. A thought-out ventilation strategy taking into account possible chronic obstructive pulmonary disease

  6. A management strategy for intraoperative and postoperative diabetic control

  7. A management strategy for cigarette withdrawal postoperatively

  8. Prophylaxis and management of contrast-induced nephropathy

  9. Reducing postoperative infective complications by appropriate antibiotic usage, wound management, care bundles and blood sugar control

Elective and emergency surgery

Preoperative optimization

All vascular patients undergoing elective or emergency surgery should have a full risk assessment performed prior to surgery in the appropriate time frame. Elective patients have the advantage of getting their many comorbidities optimized. Good diabetic control, management of myocardial ischemia and function, other cardiac risk factors, and any chronic lung disease help reduce perioperative risk.

Myocardial ischemia

Revascularization is recommended when there is stable significant left main stem disease, or significant triple vessel disease, especially when the left ventricular function is impaired (EF<50%). Acutely unstable or ischemic conditions (unstable angina, NSTEMI and STEMI) should also be revascularized prior to operation. The majority of stable coronary lesions are best left alone. However, the situation becomes less clear in high-risk cardiac patients. Those with a large (>4) number of abnormally contracting segments following a stress echocardiogram, or those who develop inducible ischemia prior to their anaerobic threshold on a cardiopulmonary exercise test MAY benefit from revascularization.

If cardiologic revascularization is performed, the details of the procedures must be known. If an angioplasty is performed, anti-platelet agents should be continued for at least 4 weeks, and any elective operation delayed until then. Bare metal stents require 3 months of dual anti-platelet therapy, and a continuation of aspirin if possible. Drug-eluting stents require at least 12 months of dual anti-platelet therapy, and a delay in any elective operations for this time frame. When balancing the risks of bleeding against the risk of stent thrombosis, there are many factors to take into account. Any bleed in neurosurgery can have severe consequences, while multiple stents involving vessel bifurcations are more likely to result in cardiac problems.

Myocardial function

A patient's myocardial function is one of the principal determinants in postoperative morbidity and mortality. This can be quantified from the history through to various investigations. A simple baseline echocardiogram often provides useful information, but it will not provide any details on a "heart working hard." Other tests can include a six-minute walk test, full cardiopulmonary exercise testing or stress echocardiograms, which provide dynamic data. Knowledge of a patient's myocardial function provides clues as to the amount and type of support that may be needed intra- and post-operatively, and also helps in allocating appropriate postoperative placement.

Other cardiac risk factors

Blood pressure control is dealt with in a separate chapter, but acceptable levels will depend on the degree of end organ damage and other comorbidities (such as diabetes). Statins (while reducing cholesterol) may also provide some plaque stability and anti-inflammatory properties. Extremes of BMI (<18 and >30) are consistently associated with worse outcomes in many types of surgery. Continued cigarette smoking leads to higher levels of carboxyhemoglobin, reduced cilial function, and hyperreactive airways.

Ventilation strategy

The principal respiratory complication is chronic obstructive pulmonary disease. The severity of this should be assessed. Important indicators of severe lung disease and potential complications include an FEV1 <30% predicted, dyspnea on getting dressed or on minimal exercise, a body mass index of <21, or the presence of pulmonary hypertension. Inhaler therapy should be started as appropriate. The patient should also take his or her inhalers the morning of surgery.

Bleeding

Many of these patients will require anti-platelet therapy for coexistent coronary disease +/- any stents. Aspirin should nearly always be continued, and a team decision with regards further anti-platelet use should be made between the cardiologist, surgeon and anesthetist. Therefore, due to the medications and the nature of vascular surgery, bleeding is a common complication. Blood should be cross-matched for all but the most simple of vascular operations (e.g., varicose veins)

Intraoperative and postoperative care

Myocardial ischemia

Despite best intentions, perioperative ischemia can still occur. This can be detected in a number of ways. There may be acute hemodynamic instability (from cardiac output to arrhythmias). Alternatively, there may be postoperative ECG changes or a troponin rise. Ischemia can be the result of a coronary thrombosis, or a flow balance problem across a stable fixed lesion. Troponin can also rise in times of significant myocardial strain, especially in the presence of renal impairment. Either way, a risk assessment should take place to assess the likelihood of needing a coronary angiogram. An echocardiogram is integral to this process, and any regional wall motion abnormality should prompt cardiologic input and possibly a look for a stentable lesion.

Myocardial function

Postoperatively, myocardial function can change for many reasons (from the consequences of the systemic inflammatory response to new coronary ischemia). In clinical situations of borderline perfusion (for example, from measured cardiac ouput and/or end organ function), a postoperative echocardiogram may be required to help guide therapy. Acute therapy for a failing heart involves treating the underlying cause of cardiac failure (often ischemic), and support (from inotropes to intra-aortic balloon pumps -- not recommended in aortic or lower limb vascular surgery!).

Diabetic control

Good perioperative control is associated with reduced wound infections and reduced mortality. NICE-SUGAR recommends using insulin to keep blood sugar levels below 10 mmol/L.

Ventilation strategy

Many postoperative vascular patients will already be extubated on arrival to ICU. Those who are not will either have had difficult operations, or may have difficult ventilation requirements. The most common of these is the severe obstructive nature of COPD. Positive-pressure ventilation should be set to avoid significant dynamic hyeprinflation, severe hypoventilation, and excessive barotrauma. Long expiration times are required (along with acceptable inspiration times). An acceptable starting position would be a RR of 12, a tidal volume of 6 ml/kg, an inspiration time of 1.2 seconds and an expiration time of 3.8 seconds (I:E = 3.2). pH is a good guide to the suitability of the CO2 required. Early extubation is best, and early institution of noninvasive ventilation can prevent re-intubation. Ensure that all nebulizers (beta agonist, muscarinic antagonists and nebulized budesonide) and mucolytics (carbocysteine, 5% saline nebs) are prescribed and magnesium levels are satisfactory.

Bleeding

On return to intensive care, a full laboratory profile should be sent. Aim for Hb>8 g/dL, Platelets>100, Fibrinogen >1g/L, INR<1.5, APTTR<1.5, Temperature >35, Ionized Ca >0.8mmol/L. Bedside coagulation test may be available. A thromboelastogram can provide useful early diagnostic information.

Infection

Infection of a graft, a stent or a puncture site can result in major morbidity or mortality. For this reason, correct timing of the perioperative and postoperative antibiotics is important. The length and nature of these prophylactic courses will be surgeon- and institution-dependent. Our hospital uses 1 pre-op dose and 2 post-op doses. The most important of these is almost certainly the preoperative dose, given around induction, to ensure peak tissue levels around the time of the operation. Another important aspect of infection is adherence to wound management, intensive care unit "care bundles" (sitting to 30 degrees, sedation holds....), hand hygiene, general aseptic technique and good glucose control.

Acute nicotine withdrawal

In awake patients this can be tempered by nicotine patches. It is important that any smokers abstain from smoking in the long term as the graft failure rate is three times higher in those who persist in smoking.

Abdominal aortic aneurysm repair

Open repair of abdominal aortic aneurysm is less common now, given the advent of percutaneous techniques of endovascular repair. A ruptured abdominal aneurysm is, however, one of the most challenging cases to manage intra- and post-operatively. Once stability and repair have been achieved intraoperatively and the patient has been returned to the critical care unit, there are a number of common conditions to manage.

Bleeding and Coagulation Correction

It is rare to go through surgery without the administration of blood and blood products and the resultant coagulopathy that this and surgery induce.

Observation for sudden drops in blood pressure or hemoglobin may indicate insufficient correction of the coagulopathy or, more sinister, the leak of the inserted graft. Should there be any sudden changes, then provide supportive fluid, blood and product support, and vasopressor support (MAP>65 mmHg) as appropriate and call the surgeons for an urgent review. If the patient is "stable" then a CT to look for a leak may be requested.

Massive transfusion is a distinct possibility in this setting, and the immunological complications of blood transfusions may become apparent. This includes immunosuppression (and increased nosocomial infections) and transfusion-associated lung injury.

Neurological assessment

The supply to the anterior part of the cordis is derived from branches off the aorta, the largest being the artery of Adamkiewicz. Clamping the aorta can result in anterior ischemic cord syndrome (loss of motor function and pain/temperature sensation, but preservation of vibration and joint position sense). Vasculopaths (as these patients certainly are) are also more prone to cerebrovascular accidents. These can be thrombotic or watershed in nature.

Renal impairment

Following major surgery, probably a significant transfusion, (possibly) clamping above the renals, and some potentially nephrotoxic drugs, acute renal injury often occurs. This probably be on the background of some rather fragile kidneys, and can (rarely) result in the development of renal failure. Often the renal injury can be managed with fluid management, inotropes and occasionally temporary hemodiafiltration. While the above combinations of problems are the most common reason for renal impairment, appropriate investigations to establish the cause (such as an ultrasound with Doppler to assess renal blood flow) should be done.

Nutrition

While there is usually no bowel resection during AAA repair, there is often a lot of bowel handling, and potentially a period of ischemia. This can result in an ileus. Prokinetics and/or post-pyloric feeding tubes can be beneficial.

Abdominal compartment syndrome

This is more likely to happen following an emergency repair (due to a significant retroperitoneal hematoma and edema) than in an elective scenario. It usually takes 24-48 hours to develop. Once abdominal pressures are high enough to impair respiratory, cardiovascular, gastrointestinal and renal function, then compartment syndrome has been established. Medical solutions include starting prokinetics (including low-dose neostigmine), having the NG tube on free drainage, creating a negative fluid balance, and using neuromuscular blockers. A decompressing colonoscopy, and even a laparostomy may be required to relieve the tension.

Endovascular aneurysm repair and hybrid operations

Endovascular repairs can now be done to increasingly complicated aneurysms. Distal infra-renal AAA to thoracic arch aneurysms can now be stented. Prior to the procedure, the operability needs to be assessed. There must be suitable "landing zones" for the stents that do not compromise other major vessels, and the size of the femoral and common iliac arteries needs to be assessed to ensure access.

Stents with fenestrations to provide access to adjacent arteries, and hybrid operations involving revascularization operations to organs made ischemic by the stent are now done. All this has resulted in increasingly complex surgery, so an understanding of what has actually been done (and so some of the potential complications) is crucial on admission to intensive care.

Much of the immediate postoperative care provided for an open AAA repair applies for an endovascular repair, and an ABC approach is appropriate. Many of these patients will have had a general anesthetic or an epidural (or both). There can be an unrecognized amount of blood loss "under the drapes" from the femoral cannulation site. There will also be a propensity to low body temperature as the patient spends plenty of time in a cold radiology suite under a GA +/- regional block.

Particular postoperative problems to watch for include:

Hypovolemia with coagulopathy: This can be due to the "hidden" bleeding intraoperatively, dilutional coagulopathy and hypothermia. There can also be endoleaks (bleeding into the endovascular sac) resulting in drops in hemoglobin (or if serious may result in sudden changes in hemodynamics).

Device-related problems: Malposition, migration, or embolization can occur. Malposition is the most common of these and can render an organ ischemic (commonly renal). This problem will often need urgent attention.

Renal Injury: This can be the result of bleeding, malposition of the stent or importantly contrast-induced nephropathy. Significant amounts of contrast can be used during and after the placement of stents, and pre- and post-treatment with bicarbonate and N-Acetyl cysteine may be appropriate.

Neurological: Placement of stents can still be associated with cord ischemia. The larger the length of aorta stented, the greater the risk of cord ischemia.

Groin hematoma: The sheath size can be high, and in some people (notably Asian females) this can constitute a sizable part of the femoral artery. Consequently, large hematomas can develop. Occasionally these hematomas can be masking false aneurysms created by the puncture. Ultrasound and further vascular input may be required. These hematomas or false aneurysms can become infected. Infected pseudoaneurysms can be particularly difficult, involving surgery and continued antibiotics.

Infection: The graft is foreign material, and can become infected following a bacteremia. This is not a common acute event. The groin puncture site (or any hybrid operation wounds around this area) can become infected.

Carotid endarterectomy

NASCET (North American Symptomatic Endarterectomy trial) and ECST (European Carotid Surgery Trial) have provided clear guidance on who would benefit most from this procedure.

  1. Symptomatic patients who have >70% carotid artery stenosis. Symptomatic includes those who have had TIAs, or a more minor cerebrovascular accident. This category of patients benefit most from a carotid endarterectomy, and this should be done within 2 weeks of the event for the best population outcomes. Patients who have a dense total anterior circulation infarct would not benefit from revascularization. (In the same way, those with 100% stenosis wouldn't, either).

  2. Symptomatic patients who have a 50-70% stenosis also benefit from a carotid endarterectomy, although the statistical benefit is less pronounced than with higher grades of stenosis. Again, the operation is best performed within 2 weeks of the symptomatic event.

  3. Asymptomatic patients who have >60% carotid artery stenosis. The risk/benefit for operating on asymptomatic patients is the least conclusive of these three indications, but the current trials suggest that it is beneficial.

The majority of patients will have a carotid endarterectomy with or without a shunt. The operation is performed under either general anesthetic or local anesthetic (there is no difference in outcome). If the patient is awake, then there is in-built neurological monitoring, and the need for a shunt is obvious. Under a general anesthetic, other neurological monitoring must be used (EEG, transcranial Doppler, NIRS) to provide indications for shunting, although some surgeons will shunt all their patients. There are trials out suggesting equivalence with using angioplasty and stenting (using a net to catch the debris). Other trials in this area suggest that this latter technique is inferior.

The majority of patients return to HDU/ICU following a carotid endarterectomy for blood pressure control. Removal of the plaque and the stenosis can alter the sensitivity of the baroreceptors in the carotid sinus. This can result in both significant hypo- and hypertension for up to 24 hours (and sometimes longer), which may need critical care. However, there are other critical issues that the doctor should be aware of and watch for:

Airway hematoma. This can result in catastrophic airway compromise requiring urgent intubation to prevent external tracheal compression. It is worth noting that the intubation will often be more difficult than the previous intubation in the OR due to distortion of the airways and edema. High-level anesthetic support may be needed. Clips from the neck can also be released as a temporizing measure.

Cardiovascular complications: As has already been mentioned, there is a high incidence of coronary stenosis in this population, and so a propensity to coronary thrombotic events, and myocardial watershed (flow demand) problems.

Neurological complications: Cerebrovascular events can result from embolization of some of the plaque. This is more common in symptomatic patients (6%) than asymptomatic (3%) patients. Hypoglossal nerve injury can occur, either through surgical trauma or mechanical stretching. This can result in a lower motor neuron palsy of the ipsilateral side of the tongue (not to be confused with an upper motor neuron problem). Cerebral hyperperfusion syndrome is a rare event that occurs following a carotid endarterectomy. It is most prevalent when the step-up in flow to the cerebral hemisphere is pronounced. This can result from having a previous tight stenosis, or being hypertensive postoperatively (or both).

The actual cause of cerebral hyperperfusion syndrome is probably many fold, with abnormal baroreceptor function, abnormal cerebral autoregulation, and ischemia-reperfusion injury all playing a part. The result is an ipsilateral pounding headache, focal neurology and seizures. Within 24 hours, cerebral edema can develop and occasionally an intracerebral hemorrhage. Treatment includes the use of antihypertensives (labetalol or clonidine is favored) that do not vasodilate. However, prognosis is not good, with up to a 50% mortality.

Lower limb bypass surgery

Many patients will receive major operations such as aorto-bifemoral bypass, fem-fem cross-overs, or fem-popliteal bypass. However, like aortic aneurysmal surgery, there is an increasing tendency to perform more endovascular procedures. The use of angioplasty and stents has meant that fewer traditional operations are performed, but also that there are more vascular procedures being performed. One source suggests that there are 3 additional endovascular procedures for every 1 decline in lower limb bypass surgery. There also appears to be a reduction in amputation rates, which will have a significant impact on patient quality of life.

Intensive care admissions will be required for:

  1. Elective major bypass operations: Close monitoring for sudden hemodynamic changes indicative of bleeding. Postoperative management of fluid in patients with multiple comorbidities, early postoperative extubation and pain management, early recognition of postoperative cardiac complications and leg ischemia/graft failure

  2. Emergency revascularization operations: These can range from embolectomies to emergency bypass operations. On top of the similar issues to elective patients highlighted above, these patients will often have a pronounced inflammatory response and acidosis (from the ischemic time to the lower limb, and any reperfusion injury). There can also be a pronounced rise in CK, indicative of rhabdomyolysis.

  3. Certain endovascular procedures: Endovascular procedures to the lower limbs have many similar problems to both bypass operations and endovascular procedures to the aorta. Emergency lower limb endovascular procedures can be associated with the acute physiological disturbances of limb ischemia. Both elective and emergency procedures need monitoring for potential bleeds, hematoma or pseudoaneurysm development and renal injury. The limbs also need monitoring for signs of stent malposition/failure or blockage.

2. Emergency Management

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3. Diagnosis

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Pathophysiology

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Epidemiology

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Special considerations for nursing and allied health professionals

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What's the evidence?

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