Anesthesia and Hepatic Function

Anesthesia and Hepatic Function
Scott F. MacKinnon, M.D
35 yo male with chronic Hep c presents for lumbar laminectomy
66 yo homeless male with extensive etoh abuse history presents for pelvic exenteration
32 yo gravida2 para1 for emergent c-section. Severe RUQ pain, ALT>6000
Vascular Supply

• 25% of total CO: 120ml/min/100gm
• Hepatic Artery(25%;50%DO2)
• Portal Vein(75%;50%DO2)
• Portal Vein: nutrients, multiple tributaries

Regulation of Hepatic Blood Flow

• Dual Supply
• One primarily for oxygenation, substrates
• One for providing vital services
• Watershed regions
• Intrinsic vs Extrinsic

Intrinsic Modulation

• Hepatic Arterial buffer response
• Modulated by adenosine
• More Evident in Post-prandial state

Extrinsic Modulation

• Catecholamines
• Hormones
• vasopressin

Major Physiologic functions of Liver

• Blood Reservoir-500ml may be expelled
• Anesthetics may suppress this
• Vasoconstrictor response impaired of abscent in cirrhotics
• All factors from liver except vwbf
• Vitamin K precursors(2,7,9,10)
• Bile enables absorption of vitamin K
• Thrombopoietin
• Also clears activated factors

Endocrine Functions of Liver
LFT’s

• Hepatocellular damage
• Obstruction
• Synthetic function
• Uptake/conjugation/excretion
• Other

Indices of Hepatocellular Damage

• AST(formerly SGOT); ALT(formerly SGPT) both indicators of cell damage
• ALT: just liver AST: other tissues
• Degree of elevation-no correlation with prognosis
• Glutathion S-transferase(iso-B) short half life(1/2 hour)-good monitor

Hepatic Diseases

• Parenchymal
• Cholestatic
• 10% American pop
• Hep B,C-5 mil

Parenchymal Hepatic Disease

• Viral accounts for vast majority of AH
• HepA(30%), HepB(50%), HepC(20)%
• HepA highly contagious, fecal oral, resolves
• HepA, if superimposed on other Hepatitis-may be fatal

Viral Hepatitis

• HepA: 4 wk incubation
• HepB: 12wk incubation
• HepC: 7 wk incubation
• Anorrhexia, N/V, fever,jaundice(1/2)
• Serologic testing

Non-Viral Hepatitis

• Ingestion, Inhalation,IV
• Ccl4, Acetaminophen, alpha aminitin
• Histological pattern similar, reproducible
• 1-2 days after exposure

Uncommon causes of Cirrhosis

• Wilson’s disease
• Heredetary Hemochromatosis
• Primary Biliary Cirrhosis
• Alpha-1-Antitrypsin deficiency
• Budd-Chiari syndrome

National Halothane Study

• 85k anesthetics
• Fulminant hepatic necrosis 1:35k
• Non-fatal: 1:3k
• Not dose dependent
• Previous exposure—Immunologic?

Immunologic postulate

• Previous Exposure—70-95% of jaundice patients
• Idiosyncratic
• Not dose dependent
• Peripheral eosinophilia, immune complexes

Cirrhosis: Endstage parenchymal Disease

• >3 million americans
• Twelfth leading cause of death
• Chronic HepC, alcoholism
• Alters nearly every organ system

Hepatic Circulatory Dysfunction

• Portal Hypertension-hallmark of cirrhosis
• Increased vascular resistance in sinusoids
• Increased portal flow from dilated splanchnic arterioles
• Hepatic arterial flow unchanged

Treatment of Portal hypertension

• Pharmacologic: Non-selective B-blocker, somatostatin, octreotide.
• May reduce bleeding up to 80%
• Band ligation, sclerotherapy, TIPS
• Portocaval Shunt

Cardiovascular changes

• Decreases SVR
• AV malformations
• Decreased responsiveness to catecholamines(glucagon)
• Remember cardiomyopathy

Pulmonary Changes in Cirrhosis

• Impaired HPV
• V/Q mismatching
• Decreased FRC
• Av malformations in pulmonary circ.
• Interstitial edema secondary to fluid retention

Other Organ Systems

• Renal
• Neurologic: encephalopathy, post columns
• Endocrine
• Heme/coagulation

Risk Stratification

• Child-Pugh Score
• Model of End-Stage Liver Disease Score(MELD)

Child-Turcotte-Pugh

• M&M for pts undergoing intra-abd surgery
• Incorporates three biochemical(PT, albumin, bilirubin)
• Incorporates three clinical features(Nutrition, +/-ascites, encephalopathy

MELD SCORE

• Created in 1999 to predict 3 month mortality in pts with chronic dz.
• Prioritizes those on transplat list
• Looks at bilirubin,INR,and serum creatinine

MELD SCORE

• >8: predictive of poor outcome(some type of morbidity;s/s 91%/77%)
• >24: qualifies for transplantation

Pre-Operative Assessment

• Initial H&P(hx of hepatitis, tatoos, tansfusion, etoh)
• AST, ALT, bilirubin, PT
• What the procedure is
• Anyone with unexplained elevation of LFT’s-postpone
• Test only those you suspect

Anesthesia

• Effective serum concentration
• Effective clearance: slower conjugation, less perfusion, less binding
• Halothane, Enflurane reduce hepatic perfusion the most
• Coagulopathy

Physiology of Anesthesia

• Markedly reduced SVR
• Markedly reduced FRC
• Markedly increased Aa gradient
• Markedly reduced responsiveness to catecholamines
• Less Responsive liver