Abdominal Aortic Aneurysm

Anesthesia for Vascular Procedures, UCH practice guide

Gregory Myers, MD and Ferenc Puskas, MD

Abdominal Aortic Aneurysm

Perioperative risks

·  Depends on patient condition – High incidence of co-existing disease (HTN, CAD, Carotid disease, atherosclerosis of major vessels)

·  Perioperative mortality of infrarenal aneurysms from the national database is 5.6-8.4% with the mortality rate of ruptured AAA over the last 4 decades remaining at 50%. If all ruptured AAA, including patients that died before reaching the hospital, were included the mortality very well could be >90%.

·  Nonlethal MI 4-15%

·  Respiratory complications 5-10%

·  Renal insufficiency 2-5% (infrarenal), 17% (suprarenal)

·  Bowel complications (Intestinal ischemia)

·  Paraplegia: Anterior spinal syndrome - loss of motor and pinprick sensation but preservation of vibration and proprioception. The patient has increased risk of neurological complication if the aorta is clamped above the Major Anterior Segmental Medullary Artery (Artery of Adamkiewicz) which has variable origin: T5-8 15%, T9-12 60%, L1-2 25%.

Perioperative Considerations

·  Preoperative - Appropriate labs drawn, assess co-existing morbidities, consider postoperative pain control (epidural vs. IVPCA), cell saver and CSF drain (See indications below), type and cross

·  Monitoring – Invasive monitoring - arterial line, central line (CVP, +/- PAC); +/- TEE, +/- CSF drain, neuromonitoring (MEP’s/SSEP’s)

OR checklist:

Emergent AAA:

·  Room warmed

·  OR flat bed in room (for fluoroscopy)

·  C-arm notified – check with OR nurse

·  Belmont and Level I - Primed

·  Colloid (albumin + Hextend)

·  Consider Cell saver

·  Double/Triple transducer connected

·  Surgeons will access femoral artery for aortic balloon occlusion – If combined IR procedure

·  For Interventional: Do not induce anesthesia until aorta is occluded by the balloon, if possible

Access:

·  Arterial line – preinduction if possible

·  Large bore IV’S (connected to Belmont and Level I)

·  Central line – can be placed later unless peripheral access not adequate

Elective AAA:

·  Arterial line

·  Central line

·  Large bore IV’s

·  Epidural – traumatic/bloody tap of epidural or CSF drain may require cancellation of case

·  CSF drain: placed in high risk patients for treatment/prevention of spinal cord ischemia

§  redo-AAA/extensive aortic repair

§  involves thoracic aorta

§  If combined stent procedure

Drugs: Similar to cardiac setup: heart box, fast track box, syringes (nitroglycerine-20mcg/ml, epinephrine-10mcg/ml, phenylephrine 100mcg/ml, and ephedrine 5-10mg/ml); Infusions: 1st tier: epinephrine, fenoldopam, nicardipine 2nd tier: nitroglycerin, dopamine, vasopressin; mannitol (12.5 - 25 grams), heparin (50 - 100 units/kg), before cross-clamp upon surgeon’s request.

Infusions:

·  NS carrier, octopus

·  Fenoldopam (keep low dose 0.01-0.1 mcg/kg/min for renal perfusion – more data needed)

·  Nicardipine: 1 - 4 mcg/kg/min

·  Epinephrine: Start 0.01 mcg/kg/min

·  Vasopressin: Start 0.04 units/min

Intraoperative:

·  Before Cross-clamp

o  Consider renal protection – Mannitol, loop diuretic and dopamine are widely given despite studies demonstrating little or no benefit. Fenoldopam infusion (a selective dopamine type 1 agonist) may be beneficial in dilating renal and splanchnic vasculature but more data needed.

o  Heparin needs to be available five minutes before aortic cross clamping, check ACT baseline, 3minutes after heparin given and every 30 minutes thereafter while cross-clamped.

·  During/After Cross-clamp

o  Cross clamp: Sudden increase in afterload. Decrease afterload with vasoactive drugs (fenoldopam, nicardipine) to decrease LV wall tension. However maintain a CVP > 10 mmHg

o  However when aneurysm is opened, back-bleeding may lead to sudden hypovolemia (maintain CVP, get ready for bleeding)

o  Organs distal from clamp will be hypoperfused and ischemic – turn off lower body warmer.

·  Infrarenal: this avoids most major organs and has the least hemodynamic effect and post clamp complications. Patients still have decreased renal blood flow, increased renal resistance and therefore renal protection should be considered.

·  Suprarenal: renal, spinal and lower extremity ischemia possible

·  Supraceliac: hemodynamic changes can be drastic and likely require dilators to decrease afterload. The kidneys, intestines and liver are ischemic thus coagulopathy, acidosis and renal dysfunction are likely.

o  Needs ABGs Q10 minutes during clamp

o  FIO2 100%

o  Correct acidosis (H2CO3/THAM)

o  Stablize electrolytes

o  Volume, calcium and consider H2CO3/THAM before clamp release

o  Keep CVP above 15 mmHg before clamp release

o  Have pressors ready and in line during unclamping

o  Coags, TEG, CBC after clamp release

·  Post Clamp: Response to unclamping will depend on clamp time and location of clamp. It is important to communicate during unclamping with surgery to optimize cardiac output. During unclamping large swings hymodynamically can occur and vasoactive medications need to be readily available. Partial or complete reclamping may be needed, to optimize hemodynamic state, if patient does not tolerate initial unclamping.

Aneurysm involving thoracic aorta, redo or extensive AAA repair, thoracic stent

Spinal cord ischemia, thus paraplegia is a major concern.

Consider CSF drain preoperatively (check coags, if bloody tap, consider cancellation of case). Consider intraoperative neuromonitoring with SSEP’s/MEP’s.

Spinal Cord Perfusion pressure= MAP – ICP (spinal fluid pressure)

·  To increase spinal cord perfusion pressure:

o  Increase MAP

o  Decrease spinal cord fluid pressure (drain CSF)

CSF drain:

§  Initial pressure goal 10-12 mmHg

§  Zero spinal pressure monitor to right atrium

§  If SSEP/MEP’s signals decrease - drain 10ml

§  Try to keep spinal pressure <10 mmHg

§  Do not drain more than 20 ml/hr – risk of subdural or sub-arachnoid hematoma or brain stem herniation

§  If CSF turns bloody - turn off drain and do not use it

§  ICU:

o  On wakeup: paraplegia: MRI spine to r/o hematoma

o  New onset weakness: drain as above

§  Do not leave drain open. Monitor pressure, drain (3-way stop)

§  Optimize MAP

o  If legs are okay: Cap CSF drain. Do not monitor. D/C CSF drain 24 hours after cap.

o  New onset weakness after drain is out. Rule out hematoma and other causes. Optimize MAP. Replace spinal drain if indicated.

Postoperative Considerations:

·  BP and HR control

·  Extubation depends on OR course and fluid shifts/ presser quirements

·  Analgesia: IVPCA vs. epidural

·  Neurological deficit – see CSF drain above

Key References: Miller’s Anesthesia 6th Edition. RD Miller; Essence of Anesthesia Practice 2nd Edition, Michael F. Roizen, Lee A. Fleisher pg 377; Department of Anesthesia, Neurology and Surgery, University of Pennsylvania, Strategies to Manage Paraplegia Risk After Endovascular Stent Repair of Descending Thoracic Aortic Aneurysm 2005.; New England Society for Vascular Surgery, Establishing a Protocol for Endovascular Treatment of Ruptured Abdominal Aortic Aneurysm, 2004.

OR AAA summary checklist:

Preoperative: consent, H&P, labs, epidural?, CSF drain?, awake a-line?, large PIV

OR: Room warm, OR flatbed, Belmont/level one wet down, double transducer (a-line, central line), central line set up (ultrasound, gown, gloves), a-line set up, IV set up

Drugs: Induction drugs, cardiac box, mannitol, heparin, syringes (epinephrine, phenylephrine, ephedrine, nitroglycerin, esmolol),

Drips on octopus: NS carrier, epinephrine, vasopressin, fenoldopam, nicardipine.

Induction: HD stable

Intraoperative:

Before cross-clamp: start fenoldopam, consider mannitol, lasix, dopamine for renal protection. Check baseline ACT before giving Heparin 5 min before cross-clamp. Recheck ACT 3 minutes after giving heparin and then q30min.

During cross-clamp: determine cross-clamp level. If supraceliac, the kidneys, intestines and liver will be ischemic: coagulopathy, acidosis, renal dysfunction likely: check ABG q10min, fIO2 100%, correct acidosis (tham/H2CO3), stable electrolytes, keep CVP approx 15mmHg, maintain pressure

If CSF drain in place: initial goal 10-12 mmHg, zero at atrium, if SSEP/MEP’s decrease. Drain 10ml – no more than 20ml/hr, optimize BP

Post clamp: depends on clamp location – have drips ready and treat BP aggressively with fluid/pressors

Carotid Endarterectomy

Indications:

·  Asymptomatic patients with >60-70% stenosis are candidates if low perioperative risk of morbidity/mortality (<3%).

·  Patients who have experienced Reversible Ischemic neurological deficit, TIA or stroke

Risk Factors:

·  Smoking , DM, Hypertension, hypercholesterolemia, hypertriglyceridemia, obesity, family History

·  Male>Female

Perioperative risks

·  Mortality 0-2.6%

·  Permanent neurological deficit 0-6.3%

·  Perioperative MI 0-4%

·  Stroke risk 1-2% per year in asymptomatic patient vs. 6-10% if patient has TIA’s: stroke risk increases significantly in asymptomatic patient if stenosis is >75%

·  High incidence of CAD

Perioperative Management

·  Preoperative –Appropriate labs drawn, assess co-existing morbidities, patient should continue blood pressure medications (hold lisinopril) and ASA perioperatively. Determine if awake or general anesthesia will be used

o  Regional - peripheral block: superficial and deep cervical plexus block C2-C4 dermatomes

Advantages:

§  Continuous neurologic assessment –most sensitive method for cerebral perfusion

§  Avoidance of expensive cerebral neuromonitoring

§  Reduced need to shunt

§  Better BP control and decreased use of vasopressors

§  92% patient satisfaction

Disadvantages:

§  Patient cooperation

§  Unable to use cerebral protection with anesthesia which may increase neurological injury if ischemia occurs

§  Seizure or loss of consciousness with clamping and need for immediate airway

§  Need to convert to general anesthesia 2-6% of the time

§  Local anesthetic toxicity/phrenic nerve paralysis

§  Difficult anatomy – short neck and high bifurcation

§  Increased catecholamines – increased HR/BP

Most reports show that no differences in perioperative stroke or death rate based on anesthetic technique - Regional vs. General

·  Monitoring- Arterial line (consider preoperative), +/- neuromonitoring, central line usually not indicated but if needed subclavian or femoral line are most practical secondary to surgical site.

OR Checklist:

·  General anesthesia- regular OR bed

·  Single transducer - Arterial line (glucose and BP)

·  Infusion pump

·  2 large bore IVs

·  Lido Tube, Lidocaine ointment, LTA – prevent postoperative coughing

·  Consider bilateral BIS or Sedline

Drugs: Regular narcotic bag; syringes: nitroglycerine 20mcg/ml, epinephrine 10mcg/cc, phenylephrine 100mcg/ml, ephedrine 5-10mg/ml, glycopyrrolate, atropine, esmolol

Infusions: Infusions on a separate IV line from volume IV

·  NS carrier, three way octopus

·  1st tier:

o  Nicardipine: 1-4 mcg/kg/min

o  Vasopressin: Start 0.04 units/min

·  2nd tier

o  Phenylephrine: 0.15-0.75 mcg/kg/min

o  Nitroprusside: 0.1-10mcg/kg/min

Induction:

·  Place arterial line before induction if indicated

·  Maintain MAP and heart rate

Intraoperative: Hemodynamic fluctuations are frequent during manipulation of the carotid area. BP and heart rate should be maintained keeping in mind that cerebral autoregulation is shifted with chronic hypertension. Short acting BP meds should be used secondary to these frequent shifts. Other important considerations are:

·  Maintain patients normal BP, CO2 levels

·  If patient does not have adequate collateral flow - BP may need to be maintained at 10-20% higher than normal.

·  If BIS/Sedline/EEG changes occur unilaterally – notify surgeon and optimize BP

·  Slow HR - be prepared for bradycardia upon carotid bulb dissection (titrate glycopyrolate)

o  If bradycardia continues surgeon may inject Lidocaine which should blunt this response effectively intraoperatively. Postoperatively after carotid bulb injection it is unpredictable if the patient would become hypertensive or hypotensive.

·  Blood loss usually <200 ml

·  Consider opioid infusion (remifentanil/sufentanil) to blunt catecholamine response

CNS protection

·  Shunt (surgeon preference) or maintain stump pressure

·  Avoid exogenous glucose

·  Goal for glucose control <160 mg/dl

·  Maintain normocarbia, BP

·  Consider transcranial Doppler/ EEG

Emergence:

·  Make environment calming – radio off, overhead lights off

·  Avoid bucking – Decrease risk of hematoma, hypertension and tachycardia. Lidocaine tube, lidocaine ointment, IV lidocaine or LTA (depending on length of surgery) on intubation can blunt this response.

·  Slow opioid wakeup (titrate fentanyl to effect) to decrease chance of bucking and sympathetic response vs. quick wakeup for neurological exam.

Postoperative Considerations

·  HTN: exclude – hypercarbia, bladder distention and pain, adjust vasodilator infusion

·  Hypotension (hyperactive carotid sinus) is as common as HTN – rule out MI and cerebral ischemia. Then treat with volume and vasopressors – likely will resolve in 12-24 hours

·  Hematoma formation – immediate bedside evacuation of hematoma if compromising airway

·  Airway edema secondary to venous and lymphatic congestion

·  Nerve damage – Evaluate hypoglossal (motor tongue), recurrent/superior laryngeal (dysphonia) and marginal mandibular (facial expression)

·  Hyperperfusion/Reperfusion syndrome: Causes post-operative neurological dysfunction, characterized by ipsilateral headache, focal seizure activity, focal neurological deficit and ipsilateral intracerebral hemorrhage or edema can occur.

·  CNS (emboli, ischemia, thrombosis, etc)

·  Residual effects of Carotid bulb Lidocaine injection are unpredictable and can result in hypotension or hypertension.

·  MI – most asymptomatic

·  Regional – phrenic nerve paralysis

Key References: Miller’s Anesthesia 6th Edition. RD Miller; Essence of Anesthesia Practice 2nd Edition, Michael F. Roizen, Lee A. Fleisher pg 377;Executive Committee for the Asymptomatic Carotid Atherosclerosis Study. Endarterectomy for asymptomatic carotid artery stenosis. JAMA. 1995;273:1421–1428.

OR Carotid Endarterectomy Check list:

Preoperative: consent, H&P, labs, awake a-line?, PIV, regional vs. general

OR: Room warm, regular OR bed, transducer (a-line), a-line set up, IV set up

Drugs: Induction drugs, cardiac box, heparin, syringes (epinephrine, phenylephrine, ephedrine, nitroglycerin)

Drips on octopus: NS carrier, vasopressin, nicardipine, opioid infusion

Induction: HD stable, lidocaine on tube - prevent bucking

Intraoperative: Can have wide swings in BP, If poor collateral flow – may need BP 10-20% higher than normal. Carotid bulb manipulation can cause bradycardia – if continues surgeon may inject lidocaine to blunt response. Turn off body warmers below clamp site. Blood loss usually <200ml. CNS protection: avoid exogenous glucose, keep glucose <160mg/dl, maintain normocarbia/BP, transcranial Doppler, EEG

Wake up: environment calming, avoid bucking