Journal: Curr Opin Anaesthesiol 21(1):1-7, 2008
Reprint: University of Texas M.D. Anderson Cancer Center, Dept of Anesthesiology and Pain Medicine, Unit 409, Faculty Center, 1400 Holcombe Blvd, Houston, TX 77030
Faculty Disclosure: Abstracted by R. Klotz, who has nothing to disclose.
The author reviews the rationale for using intravenous (IV) anesthesia for thoracic operations, the drugs and equipment required, and the methodology involved. Traditional inhalational anesthetics have been associ¬ated with a direct inhibition of hypoxic pulmonary vasoconstriction (HPV), the reflex arteriolar constric¬tion that diverts blood from hypoxic segments of lung to normal areas of lung, thereby decreasing shunt fraction. In thoracic procedures, this inhibition of HPV may be detrimental to patient oxygenation levels during one-lung ventilation. In contrast, IV anesthetics do not appear to directly inhibit HPV in patients. Total intravenous anesthesia (TIVA) might provide better oxygenation and lesser shunt fraction than inhaled anesthetics in thoracic procedures.
Several studies have shown an advantage to using TIVA. In one study arterial partial pressure of oxygen (PaO2) increased significantly and shunt fraction decreased significantly with TIVA. Other studies failed to support any advantage of TIVA. Most likely, even though inhalational anesthetics suppress HPV, other factors such as surgical manipulation, cardiac output, mixed venous oxygen tension, and positive end-expiratory pressure may have a greater influence on shunt fraction. There is solid rationale for the use of TIVA in certain circumstances, for example, when delivery of inhaled anesthetics is impossible or dis¬advantageous, or situations where traditional anesthetic delivery systems may be unavailable or impractical. Patients undergoing lung volume reduction surgery benefit from a TIVA approach. These patients suffer from chronic obstructive pulmonary disease and have increased dead space. Therefore, end-tidal volatile anesthetic concentration is inaccurate and anesthetic levels questionable. In addition, air trapping is com¬mon and the elimination of volatile anesthetics may be hindered, delaying awakening and extubation. In the case of lung transplantation, volatile anesthetics have several drawbacks. During lung transplantation, the right ventricle is subject to increased afterload and potential failure, and the cardiodepressant effects of volatile anesthetics could be detrimental. Endobron¬chial procedures that use flexible or rigid bronchosco¬py also benefit from a TIVA approach. Patients with myasthenia gravis undergoing thymectomy may benefit from a TIVA approach, as they are sensitive to neuromuscular blocking agents, and volatile anes¬thetics may cause prolonged paralysis or residual weakness.
TIVA eliminates the need for a traditional anesthesia machine, and TIVA agents are more easily stored, transported and disposed. Several IV anesthetic agents may be used in combination to execute an effective TIVA regimen. Propofol is the model drug for TIVA. Several useful adjuncts for TIVA—dexmedetomidine, ketamine, and remifentanil—are reviewed. Propofol reduces the postoperative decline in lung function after lung resection and inhibits the catecholamine surge and adrenocorticotropic hormone response during lobectomy. Dexmedetomidine inhibits endogenous norepinephrine release. Evidence suggests that its main effector sites are the locus cereleus for sedative action and the spinal cord for analgesic action. Dexmed¬etomidine reduces perioperative oxygen consumption and the sympathetic response to surgical stimulus, which may confer cardioprotective benefits. In addition, patients recovering from thoracic surgery may benefit from the reduced occurrence of respiratory depression and postoperative shivering with dexmed¬etomidine.
Remifentanil is an ultra-short-acting fentanyl deriva¬tive particularly suited to thoracic procedures. Remi¬fentanil has a rapid onset time (1 min) and short duration of action (3-10 min), which makes it ideal for managing fluctuations of high and low surgical stimulation characteristic of thoracic procedures. Ketamine blocks normally perceived sensory input and is a profound analgesic, sedative and amnestic. In addition, it has bronchodilating properties, does not depress respiration, may reduce pain for up to 3 months postoperatively when used in conjunction with thoracic epidural analgesia, reduces narcotic require¬ments, and exerts sympathomimetic effects that may be beneficial when perfusion pressure must be main¬tained in the presence of volume restriction. |
