Procedural Consideration

The peak oxygen consumption (VO2) during exercise appears to provide the most objective assessment of functional capacity in patients with heart failure and may be the best predictor of when to list an individual patient for cardiac transplantation.

·         Exercise tolerance is determined by three factors: pulmonary gas exchange, cardiac performance, and skeletal muscle metabolism. Exercise capacity can be quantified clinically by measurement of oxygen uptake (VO2), carbon dioxide production (VCO2), and minute ventilation.

·         After initial dissection, the patient is fully heparinized. The perfusion-sensitive organs (kidneys and liver) are removed before cardiectomy. The donor heart is excised via median sternotomy. After excision, the donor heart is placed in a plastic bag containing ice-cold saline and transported in an ice-filled cooler. Optimal myocardial function after transplantation is achieved when the donor heart ischemic time is less than 4 hours.

·         Post-CPB LV dysfunction may be a result of a prolonged donor heart ischemic time, inadequate myocardial perfusion, intracoronary embolization of intracavitary air, or surgical manipulation. The incidence of post-CPB LV dysfunction is greater in donors requiring prolonged, high-dose inotropic support before organ harvest.

Post-CPB RV failure is a significant cause of early morbidity and mortality, accounting for nearly 20% of early deaths. Therefore, prevention, diagnosis, and aggressive treatment of RV dysfunction after CPB are essential. Acute RV failure after cardiac transplantation may be due to preexistent pulmonary HTN in the recipient, transient pulmonary vasospasm, tricuspid or pulmonic valve insufficiency secondary to early postoperative RV dilation, and donor-recipient size mismatch. Additional factors that may contribute to postoperative RV dysfunction include a prolonged donor heart ischemic time, inadequate myocardial protection, and surgical manipulation of the heart.

·         In contrast to nonselective vasodilators such as nitroglycerin and sodium nitroprusside, which produce systemic hypotension, inhaled NO (20-80 ppm) selectively reduces PVR in the ventilated area of the lung, improving ventilation-perfusion (V/Q) mismatch. NO has little systemic effect because it is inactivated by hemoglobin and has a 5- to 10-second half-life.

·         three stages of liver transplantation:

The preanhepatic stage (stage 1) begins with the surgical incision and dissection and mobilization of the patient's diseased liver. During this stage, the surgeons identify the hepatic artery, portal vein, and the inferior vena cava, above and below the liver.

The anhepatic stage (stage 2) isolates the liver from the circulation and commences with the occlusion of the hepatic artery and portal vein. Occlusion of the inferior vena cava above and below the liver is performed so that the liver can be removed. During the anhepatic stage, the donated liver is reinserted into the circulation by anastomoses to the patient's vena cava, portal vein, and hepatic artery. The anhepatic stage concludes with removal of the vascular clamps resulting in reperfusion of the donor liver graft.

Stage 3 starts during reperfusion and extends to the conclusion of the operation. It mainly encompasses the process of biliary reconstruction and assessment of graft function.

·         Reperfusion syndrome during stage 2 of liver transplantation: is characterized by either a decrease of 30% or more in mean arterial pressure (from baseline) for greater than 1 minute and occurring within the first 5 minutes of reperfusion, or a mean arterial pressure less than 60 mmHg under the same circumstances. Following unclamping, approximately 30% of patients will exhibit profound cardiovascular collapse on reperfusion irrespective of attentive management during stage 2. The bradycardia, myocardial depression, and systemic vasodilation noted during reperfusion are secondary to rapid increases in serum potassium, decreases in temperature, acute acidosis, and release of vasoactive substances by the grafted liver. These vasoactive mediators include prostaglandins, kallikrein, platelet-activating factor, and leukotrienes. Increased age and larger donor organs also are considered risk factors.

Generally, treatment with calcium and/or epinephrine improves cardiovascular function. Fluid administration should be judicious because it can aggravate the already increased filling pressures (secondary to myocardial depression), resulting in impaired hepatic perfusion. Although the hemodynamic changes generally subside within 10-15 minutes, pulmonary hypertension, elevated central venous pressure (CVP), and hypotension may persist.

·         two basic types of oxygenators:

Bubble oxygenators work by bubbling oxygen (O2) through the patient's blood and then defoaming the blood to minimize air microemboli.

In membrane oxygenators, O2 and CO2 diffuse across a semipermeable membrane. Membrane units are generally preferable owing to a decreased risk of gas microemboli and less damage to blood elements.

·         There are differing opinions as to whether blood gases should be corrected for the temperature during CPB because the solubility of gases decreases with hypothermia. All blood gases are analyzed at 37%. In pH-stat measurements, the obtained value is corrected on a nomogram and the reported values refer to the partial pressure at the hypothermic temperatures. More commonly blood gases are reported uncorrected for temperature, a method referred to as alpha-stat blood gas management. Probably in terms of outcome, there is little difference in how blood gases are interpreted.

·          CARDIOPULMONARY BYPASS

1. There is no "best" anesthetic technique during CPB. Patients with a decreased ejection fraction will not tolerate propofol infusions or volatile anesthesia as well as patients with preserved stroke volume and will probably require an opioid-based technique.
2. Patients should be completely anticoagulated before initiating CPB or face the risk of massive intravascular clot formation.
3. The CPB reservoir should never be allowed to empty during CPB as massive air embolism is a consequence.
4. Factors involved in myocardial preservation include cardioplegia, hypothermia, preventing the heart from becoming warm from an adjacent structure, and ventricular venting and consequences of inadequate myocardial preservation include decreased cardiac output, ischemia, dysrhythmias, and failure to come off pump.
5. Always consider inadequate surgical technique for the patient failing to come off pump.
6. Neurologic complications, in particular neurocognitive deficits, are surprisingly common after CPB.

·         There are two basic techniques for lung isolation:

Double-lumen endotracheal tube (DLT), in which a bifurcated tube with both an endotracheal and endobronchial lumen can be used to isolate, selectively ventilate, or collapse the right or left lung independently according to the operative approach. This is the most common technique.

Blockade of a bronchus to allow lung collapse distal to the occluding bronchial blocker.

·         three methods of bronchial blockade:

Univent tube (Vitaid Airway Management, Williamsville, NY), also known as a torque control blocker

Wire-guided Endobronchial Blocker WEB (Cook Critical Care, Bloomington, IN), also known as an Arndt blocker

Fogarty embolectomy catheter (Baxter Healthcare Corporation, Irvine, CA)

·         SOMATOSENSORY-EVOKED POTENTIALS AND SPINAL SURGERY

1. SSEPs are used when spinal cord or brain parenchyma is at risk for ischemia during surgery.
2. Volatile anesthetics have the most profound effects on SSEP waveforms.
3. An anesthetic technique that minimizes volatile anesthetic exposure is best-an opiate-based technique with low-dose (< 1 MAC) volatile or a total intravenous anesthetic (TIVA).
4. During distraction of the spinal column in scoliosis surgery (or other critical parts of surgery), minimize interventions that will lower mean arterial blood pressure or deepen anesthetic levels acutely to allow differentiation of changes in SSEP waveforms from anesthetic effect.

·         SSEPs are the electrophysiologic responses of the nervous system to the application of a discrete stimulus at a peripheral nerve anywhere in the body. They reflect the ability of a specific neural pathway to conduct an electrical signal from the periphery to the cerebral cortex.

·         Deliberate hypotension is the intentional reduction of systemic perfusion pressure. The major indication for using a deliberate hypotensive technique is to reduce intraoperative blood loss and to produce a relatively bloodless surgical site. Deliberate hypotension decreases blood loss and thereby reduces the need for blood transfusion. This technique has been used in neurosurgical, orthopedic, vascular, and major craniofacial and other plastic procedures. Deliberate hypotension also may be used to help manage patients who refuse blood transfusions (e.g., for religious reasons).

·         DELIBERATE HYPOTENSION

1.       Deliberate hypotension is a technique that can limit blood loss and improve operative conditions but appropriate patient selection is necessary.

2.       Three signs of cyanide toxicity from SNP infusion include (1) the need for doses > 10 µg/kg/min, (2) tachyphylaxis occurring within 60 minutes, or (3) resistance to SNP.

3.       Treatment of cyanide toxicity includes stopping the infusion of SNP; delivery of 100% oxygen; administration of amyl nitrite by inhalation for 30 seconds every 2 minutes; administration of sodium nitrite, 10 mg/kg intravenously, followed by an infusion of 5 mg/kg over 30 minutes; and administration of sodium thiosulfate, 150 mg/kg, not to exceed 12.5 gm, immediately after sodium nitrite.

·         Postoperative visual loss (POVL), ranging from vision deficits to blindness, are catastrophic complications following surgery and anesthesia. Ischemic optic atrophy appears to be the final mechanism though numerous patient-related and intraoperative events have been implicated. Spine surgery and cardiac surgery are the most common procedures associated with POVL.

·         ANESTHESIA FOR MINIMALLY INVASIVE SURGERY

1. PaCO2 increases during CO2 pneumoperitoneum in laparoscopy because of CO2 absorption and ventilation-perfusion mismatch; if the patient is spontaneously breathing, ventilatory depression may also contribute to hypercapnia.
2. Hemodynamic changes during laparoscopy include increased systemic vascular resistance, mean arterial pressure, and left ventricular wall stress; cardiac output decreases initially, then gradually increases back to baseline.
3. Pulmonary changes during laparoscopy include increases in peak inspiratory pressure, intrathoracic pressure, and respiratory resistance and decreases in vital capacity, functional residual capacity, and pulmonary compliance.

·         Only nonelectrolyte solutions can be used for irrigation during TURP. Electrolyte solutions are avoided to minimize the dispersion of current throughout the bladder when electrocautery is used. Dissemination of electrocautery current would be uncomfortable for the patient and dangerous to both patient and surgeon. After completion of surgery and before the patient is moved to the postanesthesia care unit, bladder irrigation should be changed to normal saline. Because fluid absorption from continuous bladder irrigation may continue in the postoperative period, eliminating nonelectrolyte solutions reduces the risk of postoperative hyponatremia.

·         TRANSURETHRAL RESECTION OF THE PROSTATE

1. Hyponatremia secondary to TURP syndrome may present with restlessness, mental confusion, nausea, vomiting, dizziness, headache, unresponsiveness, transient visual changes, hypertension, hypotension, heart rate changes, cardiac arrhythmias, pulmonary edema, or cyanosis.
2. Prompt treatment of TURP syndrome is essential and includes terminating the procedure, changing the bladder irrigant to normal saline, infusing normal saline, evaluating serum sodium and other chemistries, administering diuretics, and considering the use of hypertonic saline in unstable patients.
3. The hyponatremia of TURP syndrome is due to fluid excess and not a loss of sodium.
4. The preferred anesthetic technique is subarachnoid block so that mental status can be followed as an early indicator of hyponatremia.

·         Laser light has three defining characteristics:

Coherence: All waves are in phase, both in time and in space

Collimation: The waves travel in parallel directions

Monochromaticity: All waves have the same wavelength

·         ELECTROCONVULSIVE THERAPY

1. Methohexital should be considered the drug of choice for the induction of anesthesia for ECT.
2. ECT causes pronounced sympathetic activity, which may result in myocardial ischemia or even infarction in patients with coronary artery disease.
3. To perform ECT safely it is necessary to complete a preoperative history and physical examination, use standard monitors, have readily available equipment and medications appropriate for full cardiopulmonary resuscitation, utilize an induction agent (e.g., methohexital) and muscle relaxant (e.g., succinylcholine), and have a beta blocker readily available (e.g., esmolol).