Liver and Anesthesia: in < 27 minutes

Liver and Anesthesia:in < 27 minutes Evan Pivalizza Feb 2008

Physiology blood supply • 25% CO • HA: 25% HBF, 45-50% O2 • PV: 75% HBF, 50-55% O2 • Flow ∞ pre-portal arterioles • Flow + Resistance thru liver = portal pressure • PV: Presinusoidal(pre-capillary) + post-sinusoidal → venous resistance via SNS stimulation

HA: Resistance via arterioles • Regulation ∞ portal flow = arterial buffer response (neural, myogenic, metabolic)

Portal hypertension • ↑ blood flow into system • Resistance portal system or portacaval collaterals • → ↓ PV flow (partial compensation ↑ HA flow) • O2 supply may be maintained • Total HBF ↓

Pharmacokinetics Hepatic extraction  • HBF • Protein binding ( albumin – acidic drugs, alpha1 acid Gp often ↑ - basic drugs) • Intrinsic ability hepatic enzymes clear drug

Highly extracted –  HBF • Morphine, lidocaine, midazolam (Cl fent/sufent , alfent ) • Poorly extracted drugs – Cl independent HBF • Highly protein bound • Diazepam, lorazepam, coumadin, phenytoin • Less protein binding • STP

Pathophysiology • Cardiac function • ↑ CO, ↓ SVR, → HR, MAP • CMO (dilated) can be masked • ↓ response to catecholamines (↑ glucagon) • ↓ clearance VD mediators • ↓ O extraction (↑ SvO2)

2. Renal function • Despite ↑ CO/↓ SVR, RVR may ↑ from afferent arterioles • Urine low Na +→ tubular retention Na+ → fluid accumulation (fluid > Na +)

3. Respiratory function • Hypoxemia • HPS (intra-pulmonary R→ L shunts- angiomas, humoral VD, direct communication) • R shift ODC • V-Q mismatch • Restrictive defect ( muscle, osteoporosis) • ↑ closing volume (pleural effusion) •  FRC (ascites)

4. Coagulation •  Vitamin K dependent factors (2,7,9,10) •  fibrinogen (synthesis + dysfibrinogenemia – abnormal fibrin polymerization) • VIII often elevated • Thrombocytopenia (BM suppression, hypersplenism) •  platelet function • ↑ fibrinolysis ( PA-inhibitor) • Also  anticoagulants (protein C,S)

Conditions  Portal Hypertension • HRS • HPS • PPH

1. Hepatorenal Syndrome •  RBF, GFR, UO, plasma Na+ presence normal renal histology • Splanchnic VD, relative hypovolemia (+ hypotension) • Type 1: Acute, progressive, 80% † • Type 2: Slower, diuretic resistant ascites

Rx/prophylaxis • Fluids (albumin after paracentesis) • Acetylcysteine • ? Systemic VC (vaso and terlipressin)

2. Porto-pulmonary hypertension • MPAP > 25 (rest)(> 30 exercise) with  PVR and normal PCWP • MPAP > 45, PVR > 250  ↑ mortality • DDx: • Volume overload • CMO • High CO • Assess RV function (TEE) and reversibility • Response to VDs not 100% predictive

Rx: plt aggregation/VC/endothelial proliferation • Oral • Endothelin antagonists (Bosentan) • Sildenafil • Simvastatin • Inhaled – NO, prostacycline • IV – Epoprosetenol + usual aids RV function (PDE inhibitors etc)

3. Hepato-Pulmonary Syndrome • 4-22% transplant candidates (inc pedi) • Hypoxemia/ intrapulmonary vascular dilation (RA PaO2 < 70, ↑ † < 50) • Clubbing, orthodoxia, platypnea (standing) • Preop – lying and standing • Delayed + contrast-enhanced echo (3-6 cycles vs. direct shunt – 1-2 cycles) or nuclear medicine cardiac study • NO implicated

NOT over PEEP (won’t help) • ? Trendelenburg • ? Interventional coiling

Liver and Anesthesia: in < 27 minutes