PBLD #8Aortic Stenosis andNeuraxial Anesthesia Until 30 June 2005: John Butterworth, MD Department of Anesthesiology Wake Forest University School of Medicine Winston-Salem, North Carolina See: http://www1.wfubmc.edu/ anesthesiology/research/ faculty_presentations.htm
PBLD #8Aortic Stenosis andNeuraxial Anesthesia After 1 July 2005: John Butterworth, MD Department of Anesthesiology Indiana University School of Medicine Indianapolis, Indiana See: http://www1.wfubmc.edu/ anesthesiology/research/ faculty_presentations.htm
Clinical Case • 78 year old woman with known aortic valvular stenosis requires hemiarthroplasty of left hip for avascular necrosis • Mild dementia • Mild chronic renal insufficiency (CrCl <50 ml/min) • Preoperative echocardiogram shows • Calcified aortic valve • Peak gradient 60 mm Hg • Valve area 0.5 cm2 • Severe concentric left ventricular hypertrophy (septum is 1.5 cm thick)
What are the indications for aortic valve replacement in patients with aortic stenosis?
Indications for AVR inPatients with AS • Symptoms • Angina • Dyspnea • Arrhythmias • Gradient increasing and >50 mmHg • Moderate AS in patient requiring other cardiac surgery (e.g. CAB or MVR)
Anesthetic Goals for a Patient Undergoing AVR • Avoid hypotension • Critical importance of coronary perfusion perfusion pressure • Potential for difficult resuscitation • Avoid tachycardia • Lack of awareness, analgesia, immobility, etc.
What Would be Appropriate Monitoring During Anesthesia for AVR in a Patient with AS?
Appropriate Monitoring During Anesthesia for AVR in a Patient with AS • Arterial line before induction • Large bore intravenous line • Vasopressor infusion ready for use (some will initiate the infusion before induction) • Central line vs. PA line • TEE
Benefits of regional anesthesia in this patient • Simple anesthetic • Reduced postoperative delirium • Potential for: • Reduced bleeding • Reduced DVT • Reduced pulmonary emboli • Better outcome
Reduction of morbidity and mortality with epidural or spinal anesthesia: meta analysis • 141 trials, n=9559 • Neuraxial block significantly reduced risk of death (0.7), DVT (0.56), PE (0.45), pneumonia (0.61), incidence of transfusion of 2 or more units (0.5) % incidence Rodgers. BMJ 2000;321:1-12
Benefits of general anesthesia in this patient • Control of airway • No need for sedation of demented patient • Can (theoretically) avoid vasodilating anesthetic drugs • Can perform intraoperative TEE to reassess valve and ventricular filling/function • No need to explain to fellow anesthesiologists why you chose regional
Cardiovascular physiology of spinal anesthesia • Sympathetic nervous system • Age effects • Venous pooling • Reduced peripheral resistance • Indirect myocardial effect = bradycardia • Treatment of hypotension
Increasing age associates with an increasing incidence of hypotension Dohi et al. Anesthesiology 1979;50:319-23 Age effects on systolic blood pressure
Lidocaine spinal causes blood pooling in abdomen and legs % Rooke et al. Anesth Analg 1997;85:99-105
Spinal anesthesia increases venous pooling and reduces arterial resistance during canine cardiopulmonary bypass • Total spinal anesthesia with 20 mg tetracaine in cisterna magna • Cardiac output (CPB flow) held constant • Volume of CPB venous reservoir declines 5.6 0.9 ml/kg (venous pooling) • Mean arterial pressure declines 31 5% (reduced systemic vascular resistance) Butterworth. Anesth Analg 1986;65:612-6; Butterworth. Anesth Analg 1987;66:209-14
Bradycardia and hypotension complications after SPA Odds Ratios • In non-OB pts, risk of hypotension 33%; bradycardia 13% • Odds ratios for hypotension: >T5: 3.8, >40 yrs old: 2.5, baseline SAP <120 mm Hg: 2.4, LP above L3-4: 1.8 • ORs for bradycardia: ARBs: 2.9 , >T5: 1.7, baseline HR <60: 4.9, prolonged PR: 3.2 Carpenter. Anesthesiology 1992;76:906-16 Liu. Reg Anesth 1995;20:41-4
Failure to prevent SPA hypotension: crystalloid (n=29), colloid (n=28), or no prehydration (n=28) % Buggy et al Anesth Analg 1997;84:106-10
-, but not -adrenergic agonists reverse venous pooling during spinal anesthesia Butterworth. Anesth Analg 1986;65:612-6 μg/kg/min mg/kg μg/kg/min
Epinephrine preferable to phenylephrine for hypotension after hyperbaric tetracaine spinal anesthesia • 14 patients: 10 mg hyperbaric tetracaine • Transthoracic echo estimation of SV • Treatment when SAP decreased 15% • Epi (4 µg + 50 ng/kg/min) & Phenyl (40 µg + 0.5 µg/kg/min), randomized, double-blind, cross-over design • Epi increases stroke volume and maintains HR; Phenyl decreases HR Brooker et al Anesthesiology 1997;86:797-805
Brooker et al Anesthesiology 1997; 86:797-805
Brooker et al Anesthesiology 1997; 86:797-805
Effects of epidural anesthesia on the cardiovascular system • Sympathetic block • Venous pooling = ↓apparent blood volume • ↓Peripheral resistance • Effects of epinephrine in LA solutions • Dermatomal level of anesthesia determines hemodynamic effects • Differing hemodynamic effects of thoracic vs. lumbar epidural anesthesia
Pooling of blood in legs after lumbar epidural anesthesia % Arndt. Anesthesiology 1985;63:616-23
Effect of level of epidural anesthesia on CV responses % change from baseline • Volunteers (n=10) received 2% lido LEA (11-20 mg/kg) to produce increasing dermatomal levels of anesthesia • Increased arm blood flow (cervical sympathectomy) only when block >T2 Thoracic dermatome Bonica. Anesthesiology 1970;33:619-26
TEA vs. LEA: differing effects on regional blood flow TEA vs LEA CV effects ARM BF LEG BF CARD OUTPT MAP -12% -1% +47% +21% +510% -35% -9% +7%
Do either the baricity or the specific the local anesthetic make a difference during spinal anesthesia?
Choices in spinal anesthesia • Needle size and style • Puncture site • Local anesthetic species and dose • Baricity of local anesthetic solution • Patient position after injection • Additives (opioids, vasoconstrictors, clonidine, neostigmine) • Continuous spinal or combined spinal-epidural
Hyperbaric solutions Procaine 5% (<45 min) Lidocaine 1.5-5% (<1 h) Tetracaine 0.5% (<3 h) Tetracaine 0.5% + epi (<4 h) Bupivacaine 0.75% (<3 h) Isobaric solutions Bupivacaine 0.5% (<3 h) Lidocaine 2% (<2 h) Tetracaine 0.5% (<3 h) Meperidine 2.5% (<2 h) Mepivacaine 1-2% Hypobaric solutions Tetracaine 0.1-0.2% (<3 h) Bupivacaine 0.5% + fentanyl 20 μg Local anesthetic choices for spinal anesthesia
Hyperbaric solutions Density > CSF Flows to dependent sites Sitting”Saddle” block’ Supinethoracic level Isobaric solutions Density CSF No effect of position Long duration Hypobaric solutions Density < CSF Flows from dependent sites Sitting ?total spinal Supine inconsistent spread Jack-knife (Buie) sacral block Lateral block of superior side Local anesthetic baricity and spinal anesthesia
Greater dermatomal spread with hyperbaric than hypobaric or isobaric bupivacaine in supine patients Hyperbaric Sensory dermatome Isobaric Hypobaric Time (min) Van Gessel EF. Anesth Analg 1991;72:779-84
Effects of local anesthetic dose on spinal anesthesia • Dose of hyperbaric LA has almost noinfluence on dermatomal spread, even in pregnancy (tetracaine 10 or 15 mg blocks comparable dermatomes) • dose = onset, duration, and "quality" of block (hyperbaric, hypobaric, and isobaric)
Combined spinal-epidural (CSE) • Rapidly increasing popularity • Advantages: rapid onset, ability to titrate or prolong block, spinal drug dosage • Disadvantages: catheter migration, reliability of test dosing, ↑failure rate (?) • Needle through needle vs double segment • Useful for: • OB analgesia • Ambulatory anesthesia • Postop pain management after spinal anesthetic
Continuous spinal anesthesia • Analogous to continuous epidural anesthesia • Permits long duration spinal anesthesia • No special safety problems provided that there is free flow of CSF through catheter and the catheter tip is not misplaced in a root sleeve • Requirement for larger needle PDPH risk • 27g catheters formerly available associated with neurological deficits (maldistribution or restricted distribution of 5% lidocaine?)
How case was managed • Arterial line placed • CSE technique • Hyperbaric bupivacaine 5 mg + 20 µg fentanyl • Lateral position • Phenylephrine drip • Patient now in PACU, will you start PCEA infusion with bupivacaine-morphine?
How case was managed • You have got to be kidding!