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Pharmacokinetic and Pharmacodynamic Changes The pharmacology of many anesthetics is changed in the presence of liver disease and during liver transplantation. This is the result not just of altered metabolism by the liver, changes in liver blood flow, and drug protein binding, but also by changes in the volume of distribution of the drugs. However, this usually does not interfere significantly with the use of anesthetics intraoperatively, because although the duration of action of many of the anesthetics may be prolonged, most patients after liver transplantation are not extubated immediately but require a postoperative ventilation period of at least a few hours. Similarly, the pharmacodynamic changes that may occur are handled by titrating the drugs to effect. Therefore, unless massive drug overdosing occurs, the altered pharmacology is only relevant if the anesthesiologist wants to extubate the patient at the end of the procedure.

Preoperative Preparation

The anesthesia team should be experienced; at least two anesthesia providers and an experienced anesthesia technician should be available. The blood bank should be prepared to supply packed red blood cells, fresh frozen plasma, cryoprecipitate, and platelets in large quantities. Special equipment should be available, and is presented in Table 13.1. The operating room table and the arm boards should be padded to avoid nerve or skin injury.

Induction and Maintenance of Anesthesia

One of the main concerns is the possibility of aspiration of gastric contents after induction of anesthesia but before tracheal intubation. Patients with liver disease, severe ascites, and/or recent gastrointestinal bleeding may not have an empty stomach. Therefore, cricoid pressure is routinely applied during induction of anesthesia. Most commonly thiopental, propofol, or etomidate are used to induce anesthesia, and succinylcholine provides the most rapid paralysis permitting fast intubation. Nondepolarizing muscle relaxants have been used in patients with hyperkalemia.

Maintenance of anesthesia is accomplished with a combination of intravenous narcotics (e.g., fentanyl), benzodiazepines (e.g., midazolam, lorazepam), muscle relaxants (e.g., pancuronium, cisatracurium), and inhaled anesthetics (e.g., isoflurane, desflurane). Cardiovascular drugs such as lidocaine, atropine, dopamine, epinephrine (10 |ig/mL and 100 |ig/mL) should be available. Other drugs that should be available include epsilon-aminocaproic acid, protamine sulfate, calcium

Table 14.1. Equipment required for liver transplantation anesthesia

Anesthesia machine with air supply

Multichannel patient monitor with pulse oximeter

Multigas analyzer

Cardiac output monitor

Cardiac defibrillator

Drug infusion pumps

Warming blanket

Forced air warmer

Heated humidifier

Rapid infusion system

Autotransfusion system

Thromboelastographs (TEG)

Transesophageal echocardiography (TEE)

chloride, sodium bicarbonate, tromethamine (THAM), dextrose, and insulin. Positive end-expiratory pressure (5 cm H2O) is frequently applied to improve oxygenation in the presence of tense ascites and upper abdominal retractors and to prevent atelectasis. The humidification of inspired gases, a forced air warmer, increasing the room temperature, and appropriate draping by the surgeon in order to prevent the patient to become wet may all aid in the prevention of hypothermia.

Postinduction Preparation

Arms are extended at a 90° angle in an attempt to avoid brachial plexus injury. An orogastric tube is placed to drain gastric secretions; nasogastric tubes are avoided to reduce the chance of nasal bleeding. Two large-bore intravenous catheters (7-8.5 Fr) are placed after induction of anesthesia to allow blood transfusion. The choice of veins for these catheters depends on whether venovenous bypass is used; in general the antecubital vein on the side where the axillary vein is cannulated for venovenous bypass is avoided. Also, subclavian veins are only used as a last resort because accidental subclavian arterial puncture may lead to intrathoracic bleeding in patients with significant coagulopathy. The most commonly used veins are the right antecubital vein and the internal j ugular veins, with the external j ugular veins as acceptable alternatives.

The radial arterial catheter is usually inserted after induction of anesthesia unless the patient is hemodynamically unstable. An additional femoral arterial catheter is placed because it gives more accurate information regarding central aortic pressure, especially during the anhepatic state and immediately after graft reperfusion. A pulmonary artery catheter is placed, most frequently through an internal jugular vein; commonly the pulmonary artery catheter has been modified to determine mixed-venous oxygen saturation, while another modification allows continuous cardiac output, or right ventricular ejection fraction and end-dias-tolic volume determination (RVEDV). Intermittent determination of arterial blood gas tension, acid-base status, electrolytes (including ionized calcium) and hematocrit or hemoglobin is obligatory.

Intraoperative Laboratory Tests

The tests presented in Table 14.2 should be performed every hour, or more frequently when indicated. Tests should be performed at the following times: baseline, every hour thereafter, 5 min after onset of anhepatic state, every 30 min during anhepatic state, 15 min before graft reperfusion, 5 and 30 min after graft reperfusion, and then every hour. Many institutions use thromboelastography (TEG) instead of or in addition to more standard coagulation tests.

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