Anesthetic considerations for laser, laparoscopy, and thoracoscopy procedures

Anesthetic Considerations for Laser, Laparoscopy, and Thoracoscopy Procedures Jane E. Quandt

Laser surgery and laparoscopy are two relatively new surgical techntques gaining popularfly in veterinary medicine, which require spectal consideration when being performed on the anesthetized patient. For laser surgery, consideration must be given to the possibility of atmospheric contaminatton, inappropriate energy transfer, eye injury, perforation of a vessel or anatomm structure, perforation of the endotracheal tube, and fire. The primary concern with laparoscopy and thoracoscopy ts the creation of a pneumopentoneum or pneumothorax, which can result in (1) hypercarbia and inadequate ventilation, (2) poor cardiac output and systemic blood pressure, and (3) gas embolism. To mintmize complications, patients should be placed on positive pressure ventilation, be well hydrated before and during the procedure, and be thoroughly monitored (ECG, capnography, pulse oxlmetry). Copyright © 1999 by W.B. Saunders Company

ew advances are being made in the surgical field with the

advent of the use of laser and laparoscopic surgery N techniques. These techniques have umque requirements, which must be considered when anesthetizing patients to prevent potential complications from occurring.

Laser Laser--Light Amplification by Stimulated Emission of Radiat i o n - i s an intense beam of monochromatic, highly coherent radiation in the infrared, visible, or near ultraviolet regions of the electromagnetic spectrum3 Laser energy can be reflected, absorbed, scattered or transmitted by tissue depending on laser wavelength, cellular composition, water content, pigmentation, vascularity, thickness, and transmission characteristics of the tissue. 12 Lasers can be used to cut, ablate, or weld tissue3 General heating and even sterilization of tissue can also be achieved. 1 The surgical applications of laser energy include ulcer removal, tumor removal, granuloma removal° ablation of permnal fistulas, removal of fistulous tracts, ear ablation, arytenoidectomy, tonsillectomy, removal of brain tumors, sterihzation of infected tissue, removal or biopsy of spleen or liver, rhinotomy, amputation, removal of intraluminal colonic polyps, dentistry, and general surgery for animals with clotting deficmncles. 1

From the Department of Small Antmal Medicine and Surgery, University of Georgia, College of Veterinary Medicine, Athens, GA. Address reprint requests to Jane E. Quandt DVM, MS, Dipl AVCA, Associate Professor, Small Animal Medmme, Department of Small Animal Medicine and Surgery, UniversMty of Georgta, College of Veterinary Medicine, Athens, GA 30602. Copynght © 1999 by W.B. Saunders Company 1071-0949/99/1401-0007510.00/0 50

Laser Hazards Laser surgery is a useful and time-saving tool, but it has unique characteristics that could lead to specific hazards. These include atmospheric contamination, inappropriate energy transfer, eye injury, perforation of a vessel or structure, fire, and perforation of the endotracheal tube.

Atmospheric Contamination Vaporization of tissue produces a plume of smoke and fine particles? These particles can be transported and deposited in the alveoli. 3 The laser plume also has the potential to be mutagenic, teratogenic, or a vector for viral infection. 3 The most effective means of preventing dissemination of the plume is with an efficient smoke evacuator at the surgical site. 3 Special high-efflcmncy surgical masks are needed to catch laser plume particulates)

Inappropriate Energy Transfer There are significant safety procedures that must be used when operating lasers because of the high intensity of the beam. 1 Reflection from mirrored surfaces can occur without a change in the focal properties of the beam, therefore, the full power of the direct beam can be reflected in an unintended direction.1 To help reduce this risk, the instruments should be kept out of the surgical field or matte-finished instruments used. The surgeon should activate the laser by the foot pedal only when the laser is pointed at the intended target. 1 When not being used, the laser should be on a standby setting. 1 A conspicuous sign that states "laser in use" should be placed on the door to the operating room. I Only those personnel with safety glasses are allowed entry.1 The surgeon should announce when the laser is activated. 1 The operating room should be one without windows or if there are windows they should be covered with an opaque, non-transmissible covering as certain lasers are transmitted through glass (Fig 1). 3-~

Eye Injury The eye is the most susceptible to injury by laser radiation. 1 All personnel in the operating room must wear safety glasses designed to absorb the particular wavelength of the laser being used. 14 The glasses should have side shields to protect the lateral margins of the eye (Fig 2). 1,3 The animal's eyes should be taped or sutured shut and covered with moist eye patches) ,5 When structures around the eye itself are undergoing laser surgery, a scleral shell or contact shield should be placed on the eye in the operative field to protect it from any back scatter irradiation. 4

Climcal Techniques in SmallAmmal Practice, Vol 14, No 1 (February), 1999: pp 50-55

be used to pack off the area exposed to the laser to help prevent blood from entering the surgical field and also to prevent exposure of a gas-containing viscus to the laser. 1 When doing a rectal procedure, wet sponges should be placed proximal to the lesion to prevent ignition of methane gas. 1 Patients having tumors removed that have previously been treated by radiation therapy are at greater risk of perforation or tissue erosion#

Fire and Perforation of the Endotracheal Tube

Fig 1. A sign should be placed on the door to the room where laser is in use. Windows should be covered with an opaque material.

Perforation of a Vessel or Structure The patient must be anesthetized appropriately as movement such as coughing or bucking predisposes the patient to laser damage of normal tissue. 1 Destruction of normal tissue can occur if the laser is misdirected. To help prevent damage, soaked sponges should be placed on healthy tissue exposed to the laser and the instrumentation surrounding the laser. This latter precaution will help dissipate incident laser energy and inadvertent heat productionJ ,4 Moist laparotomy pads should

Fig 2. All persons working with laser must wear laser safety glasses that are specific for the type of laser being used. ANESTHESIA FOR LASER PROCEDURES

Laser can pose hazards to the patient in the form of fire from the laser striking combustible substances, or incandescent particles of tissue blown from the surgical site. 3 The risk of fire can be reduced by replacing alcohol with sterile saline in the surgical preparation and drying the surgical site prior to draping.1 Disposable operating drapes should not be used since they are flammable and once ignited are difficult to extinguish due to their water repellent nature. 5 Dry gauze sponges, and cotton pledgets are also flammable and should be soaked in sterile saline prior to laser use. 1 Smoke evacuation should also be employed to eliminate the products of combustion# Laser light can cut through thin tissue such as the tracheal membrane or a blood vessel wall leading to a potential pneumomediastlnum or hemorrhageJ Laser surgery of the airway or oral cavity can ignite the endotracheal tube which, in the presence of oxygen, has the potential to result in numerous complications (Table 1). 1 Initially, most fires are located on the external surface of the endotracheal tube where they can cause local thermal destruction. 3 If the fire is not recognized and burns through to the interior of the tube, the oxygen-enriched gas and respiratory flow will produce a blowtorch-like flame, blowing heat and flames from the endotracheal tube and toxic products of combustion down to the pulmonary parenchyma. 3,5 Puncturing and deflating the tube cuff may permit oxygen-enriched gas to flood the operative site and increase the chance of a devastating fire after a subsequent laser burst. 3 Severe patient injury or even death is possible from such fires. 5 If a fire occurs but is quickly extinguished with little or no resulting damage, the decision to proceed with surgery can be madeJ If the fire was an interior blowtorch type, then gentle bronchial lavage may be indicated, followed by fiberoptic assessment of the more distal airways. 3 If any airway damage is seen, the patient should be reintubated. If the damage is severe, a low tracheostomy may be indicated. 3 The pattern of damage tends to be worst in the upper airway and diminishes as one approaches and passes the carina. 3 If there are extensive airway burns and pulmonary damage due to heat and/or smoke inhalation there may be a need for prolonged intubation, mechanical ventilation, positive end-expiratory pressure, antibiotics, and a brief course of high-dose steroids# 5 When doing laser surgery of the airway or oral cavity the most effective way to prevent fire and patient injury is by protecting the endotracheal tube. This can be done by wrapping its outer surface with aluminum or copper adhesivebacked metal tape. 1 When adhesives are used to secure the tape, they must be evaluated to ensure they are not flammable. 6 Self-adhesive 3M ® number 425 aluminum foil tape provides excellent protection of the shafts of combustible tubes. 3,5 It is important to remember when using this technique, that the inner surface of the endotracheal tube remains unprotected. 6 A clean endotracheal tube 1 to 2 mm smaller than would normally be used, should be wiped with alcohol to remove 51

residue that would interfere with adhesion, and then optionally wiped lightly with MASTIOSOL or tincture of benzoin. 3 The tube is then allowed to dry. The end of the metal tape is optimally cut at an angle of about 60 ° and the cut edge aligned with the proximal end of the cuff junction. 3 The endotracheal tube should be wrapped from the inflatable cuff upward to the reset or to the exit point of the cuffpilot tube in a spiral fashion using a single length of 0.25 inch wide tape in a 30% overlap so that bending of the tube will not expose uncovered areas (Fig 3). ],3,5 Care needs to be taken to prevent wrinkles that might abrade the tracheal mucosa. 3 Re-wiping the wrapped tube with alcohol and allowing it to dry will provide a degree of sterility before intubation. 3 Be aware that the tape itself requires certain precautions Rough edges can damage soft tissue, pieces of tape may break offand be aspirated, the tape may kink the tube, and the laser may reflect off the tape damaging soft tissue. 1 An ad&tional preventive measure is to pack off the endotracheal tube and airway with saline soaked sponges. 6 Upon extubatlon the tube should be inspected to make sure all the tape is intact. The lubricant for the endotracheal tube should be a noncombustible water-soluble gel or solution, with or without local anesthetics. 1 It must be recogmzed that the cuffs of taped endotracheal tubes are still vulnerable to the laser effects. 6 They can be protected by filling them with saline, so if the laser strikes the cuff it will produce a fine spray that will act as a budt-in "automatic sprinkler system. ''56 The saline serves as a heat sink that absorbs the laser's energy, preventing combustion of the cuff.5 A small amount of methylene blue dye can be added to the saline, and will serve as a sign if the cuff is perforated (Table 1). 6 There are endotracheal tubes that have been designed for use with laser, such as the Laser-Shield II by Xomed-Treace and the Bivona "Fome-cuff' tube. 5,r These specially designed tubes are expensive. 3,5 The use of laser-resistant endotracheal tubes requires particular care to prevent mucosal abrasions, because these tubes tend to be bulkier and more rigid than conventional tubes) The protection of tracheostomy tubes, if used, also needs to be considered. It is preferable to use metal tracheostomy tubes, if available, so that laser light inadvertently entermg the trachea will not cause ignition. 1

Laparoscopy and Thoracoscopy Laparoscopy and thoracoscopy are gaining favor as techmques for surgical diagnosis and treatment of certain conditions. Laparoscopic techmques can be used for such procedures as biopsy of abdominal organs, or for removal of the gall bladder, or gastropexy. Thoracoscopy can enable biopsy of lung tissue or creation of a pericardial window. These techniques do not

\ J

Fig 3. An endotracheal tube wrapped in aluminum foil tape. The cuff is inflated with saline-methylene blue dye after intubation. This tube is for use in laser surgery of the airway or oral cavity, 52

TABLE 1. Guidelines to Remember During Laser Surgery When Using Potentially Flammable Endotracheal Tubes 1. Minimize the respired oxygen if possible (optimal Fio230% to 50%). 2. Use wet pledgets above the cuff after replacing the pledget stnng wRh wire. 3. Remoisten the pledgets frequently. 4. Use colored saline m the cuff. 5. Place the cuff suffmlently distal m the trachea to be out of direct sight of the laser operator, Data from Ramptl.a

require major abdominal or thoracic incisions and therefore may result in lower morbidity and pain. They do, however, cause significant perturbations of certain physiologm parameters which the anesthetist must take into consideration.

Anesthetic Considerationsfor Laparoscopy In small animals, laparoscopy will usually require use of general anesthesia although minor procedures such as biopsy of the kidney or liver may be done under heavy sedation and local anesthetic infiltration of the port sites. When using sedation, it is best if the procedure can be done in a short time, 20 minutes or less, due to the potential for respiratory compromise in the spontaneously breathing patient. A face mask can be used to dehver oxygen to overcome the hypoxemia that might occur. General anesthesia should be used for more invasive or longer duration laparoscoplc procedures and for patients with significant respiratory disease. General anesthesia allows patients to easily be ventilated and provides analgesia, good muscle relaxation, and a quiet surgical field. 8 It will also allow for an immediate laparotomy should there be a ma] or complication or unexpected finding. 8 Most of physiologic changes that may result from laparoscopic procedures result from the fact that insufflation of a gas into the abdomen is used for better visuahzation of structures. Carbon dioxide is the most commonly used gas for this purpose, for several reasons; CO2 is rapidly absorbed and excreted, it does not support combustion, and IS more soluble in blood than other gases. 8 The insufflation of CO2 to deliberately create a pneumoperitoneum may cause the following complications: hypercarbia, cardiac arrythmias, depression of cardiac output, pulmonary impairment, gas embohsm, gastric reflux, and increased intracranlal pressure.

Hypercarbia The absorption of carbon dioxide into blood can contribute to hypercarbia. 8 Hyl?ercarbia enhances hypertension, tachycardia, cardtac arrhythmias, vasodilation, and myocardial depression. 8 The pneumoperitoneum and hypercarhia may enhance sympathetic tone, leading to an increase in plasma catecholamines which may produce vasoconstriction, elevate central venous pressure° and increase cardiac chronotrophy, inotrop5 and sympathetically mediated arrhythmias. 8 Plasma concentrations of cortisol, prolactin, and glucose also increase in response to the stress of peritoneal distention, s Commonly seen arrythmias include sinus tachycard]a, ventricular arrhythmias, and asystole. 8 These arrhythmlas occur most often during the preinsuffiation period and may be related to light anesthesia. 8 Respiratory acidosis and hypoxia can also contribute to arrhythmias. 9 As halothane can sensitize the myocardium to catecholamines, it may be prudent to use QUANDT

isoflurane, s,9 Alternatively, bradycardia might occur from peritoneal distension and sumulation. 8 The use of atropine either as part of the premed or in response to bradycardia will antagonize the vagal effects of abdominal distention. 8 Arrhythmlas may also occur with either COs or nitrous oxide insufflation at high mtra-abdominal pressure.i°

Cardiovascular Changes In dogs and in humans the msufflation of the peritoneum will depress stroke volume, cardiac output, and inferior vena caval flow up to 60%. s,l° In the dog mtra-abdominal pressures of 20 to 40 m m Hg produced with either nitrous oxide or CO2 have been shown to decrease the cardiac output by more than 40%. n At pressures of 30 m m Hg or greater, there are decreases m systolic pressure, pulse pressure, and cardiac output, s In anesthetized dogs with intra-abdominal pressures of 16 m m Hg, a significant decline in total hepatic blood flow was found, m addition to a sharp increase in systemic vascular resistance and a decrease in cardiac output. 12Venous return to the heart is impaired due to compression of the vena cava, which produces arterial hypotension with a rise in central venous pressure. 8 Mean arterial pressure, right atrial pressure, intrapleural pressure, femoral-vein pressure, heart rate, and total peripheral resistance increased as insufflation pressure was raised.l° Total peripheral resistance in the dog increased by approximately 200%3 o At an intra-abdominal pressure of 40 m m Hg nght atrial pressure increased by 150%. I° Following release of the intra-abdominal pressure the cardiac output, Inferior vena caval flow and stroke volume returned to pre-insufflation values3 ° In anesthetized dogs it is recommended that an intra-abdominal pressure of no more than 8 to 12 m m Hg be used to avoid complications caused by hemodynamlc derangements. 12 The degree of hemodynamic change is directly dependent on the patient's intravascular volume status. 9 Hypotension will be worse in those animals that are hypovolemic, therefore tt is important to maintain proper hydration. 8 Volume loading with a crystalloid at 10 to 20 mL/kg will replete the intravascular volume and help to minimize the cardmvascular changes) The hemodynamic changes that occur with laparoscopie surgery are well tolerated in healthy patients, but patients with compromised cardiovascular function may be extremely sensitive to any alteration in hemodynamtcs. 9

Pulmonary System Changes The pneumoperitoneum also affects the pulmonary system. The total respiratory compliance and diaphragmatic movement are reduced, s 12,13 If the intraperitoneal pressures are above 20 m m Hg, the airway pressure, lntrathoraclc pressure, and lung and chest wall mechanical impedances increase. 814 Pulmonary atelectasis, decreased functional residual capacity, and high peak airway pressures may also result. 9 The changes m impedance may be critical in obese patients or in those with pulmonary disease. 14 In these patients the increases in lung impedance can increase alveolar pressures, which increases the risk of lung injury. 14 The increase in chest wall impedance can increase mtrathoracic pressure and have possible inhibitory effects on cardiac output i4 Both central venous pressure and arterial Pc02 may increase by as much as 8 m m Hg secondary to the increase in intra-abdominal pressure and absorption of ANESTHESIA FOR LASER PROCEDURES

CO2 .9,I5 These changes will be less dramatic if the insuffiation pressure is kept between 10 and 14 m m Hg. 9 The increase in intra-abdominal pressure and the associated decrease in intrathoracic volume have a deleterious effect on pulmonary gas exchange during spontaneous respiration. 1° A spontaneously breathing patient will increase minute ventilation and respiratory rate to compensate for a reduction in tidal volume. 8 Obese patients will have more significant reductions in pulmonary compliance and tidal volumes, s Respiratory and metabolic acidosis and hypoxemia may result, especially if there is pre-existing pulmonary disease. 8 Hypoxemia may also cause hypotension. In a study using nitrous oxide as the insuffiation gas for laparoscopy in spontaneously breathing isoflurane-anesthetized dogs, the cardiorespiratory changes, although significant, were minimal if the insuffiation pressure did not exceed 20 m m Hg. I6 The effects of the pneumoperitoneum, the increases in intra-abdominal pressure and the decreases in functional residual capacity, as well as the effects of absorbed CO2, hypercarbia, respiratory acidosis, and hypoxemia can be minimized with controlled positive pressure ventilation. 8,9 This is especially important in obese or older patients that may have preexisting impairment of pulmonary comphance, decreased vital capacity, and decreased functional restdual capacity, as these are patients with limited pulmonary reserve that may be unable to compensate if allowed to breathe spontaneously. Without positive pressure venulation in these patients, respiratory failure may ensue, s,9 It 1s more efficient to increase the ndal volume and keep the respiratory rate low when attempnng to maintain normocapnia during pneumoperitoneum33 Gas

Embolism

One of the most serious and potentially life-threatening complications of laparoscopic surgery is gas embohsm. 9 Carbon dioxide ]s safer than oxygen and nitrous oxide in preventing air embohsm. 8 This is because CO2 is highly soluble in blood and is relatively innocuous to the peritoneal tissues. 9 Carbon &oxide is readily absorbed by the splanchnic vasculature, and entrance of small amounts of this gas into the central circulation generally occurs without consequence. 9 If large amounts of CO2 gain access to the central venous circulation through open venous channels that may result from surgical trauma, or ff the splanchnic blood flow is reduced by excessive intra-abdominal insufflation pressure (20 to 40 m m Hg) or peripheral vasoconstriction, severe hemodynamic and resplra-

TABLE 2. Emergency Preparation and Treatment Plan for Airway Fires That May Occur When Using Laser 1. The endotracheal tube should be secured with a mfnimum amount of tape so easy extubatJon can be accomphshed. 5 2. Saline or a bucket of water should be available to douse any flames. 35 3. At the first sign of an airway fire, the laser must be shut off, pulmonary ventilation should be stopped and the anesthetm gases, including oxygen be turned off. 135 4. It may be useful to temporarily disconnect the breathing circuit from the anesthesia machine 3 These maneuvers remove the flame and the retained heat in the tube as well as stop the enriched source of oxygen. 3 5. After the fire is extinguished the endotracheal tube should be removed, as even brief combustion will damage the tube. 15 6. The patient's lungs should be ventilated by mask and the airway thoroughly examined 3 s 7. The oropharynx and face should be assessed, chest radiographs and/or bronchoscopy should be done to determine the extent of tissue injury. 1 The lung parenchyma and the trachea can be damaged by smoke inhalation or thermal burn. 1

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tory compromise can occur. 9 One case report of a dog in which nitrogen gas was used for msuffiation describes the spleen being punctured with the p n e u m o p e n t o n e u m needle, leading to rapid and fatal embofism of peritoneal gas. n The spleen was markedly crepltant, three bullae were found in the lungs, and the liver had widely dilated portal veins devoid of blood and filled with gas, and the stomach vessels had gas emboli, n The immediate consequences of venous air embolism are related to the volume of air embolized and the rate at which it is embolized, n Large volumes, 3 to 8 mL/kg, injected rapidly can be quickly fatal, n Gas embolism will present with clinical signs which include a sudden and profound decrease m blood pressure, cardiac dysrhythmias, a mill-wheel or other new-onset heart murmur, cyanosls, pulmonary edema, and an increase in the end-tidal CO~ as the gas embolizes. 9 This is followed by an abrupt decrease in the end-tidal CO2 as right-sided heart failure ensues from the accelerated pulmonary hypertension and hypoxemia. 9 Constant vigilance and momtoring of the ECG, blood pressure, heart sounds, and end-tidal CO2 will assist in making an early dmgnosis should an embolus occur. 9 Insufflation of the abdomen should occur at a rate of less than 1 L/min, with intra-abdominal pressures of no greater than 20 m m Hg.ll Devices are available to measure the quantity or gas msuffiated and the intra-abdommal pressures produced, and their use Is a good safety measure31 Before introduction of the Verres pneumopentoneum needle, the underlying area should be palpated to avoid placing the needle into an abdominal organ or mass. n Venous gas embolism may also occur during laparoscopic laser surgery. 3 If coolant gas must be used, using carbon dioxide will result in the least damage after an embolization compared with nitrogen or air. 3 In procedures where the risk of air embolism exists, avoid cutting or vaporizing organs with large vascular structures, do not use coaxial gas or mr as the fiber coolant, and use only fluid cooling. 4 It is important to act quickly to treat gas embohsm in order to avmd serious consequences of cardiac arrest and death (Table 3). 9 Other causes of cardiovascular collapse must be considered and treated if they are present. 9 These include hemorrhage, pulmonary embohsm, myocardial infarction, pneumothorax, pneumomediastinum, excessive intra-abdominal pressure, and profound vagal reflex. 9

Gastric Reflux The increase in intra-abdominal pressure that is a result of the pneumoperitoneum may be enough to increase the risk of passive reflux of gastric contents. 9 Patients with a history of TABLE 3. Steps to be Followed Rapidly, as Necessary, for the Treatment of Gas Embolism 1. Deflate the pneumopentoneum ~mmedmtely m order to help preserve hemodynamic function. 2. Place the patient in left lateral recumbencywRh the head below the level of the nght atnum. 9 3. Intravenous access of the central circulation should be obtained for aspiration of gas from the heart. 9 4. Prevent further entry of air. 5. Begin positive pressure ventilation if patient is not already being ventilated. 6. Begin or continue rapid infusion of IV fluids. 7. Cardiac massage. 11 8. If after 2 or 3 minutes these measures have faLled, a rapid nonstenle thoracotomy should be performed, and air should be aspirated directly from the right atrium. 11 54

diabetes comphcated by gastroparesis, or with hiatal hernia, obesity, or any type of gastric outlet obstruction are at a higher risk for aspiration of gastric contents. 9 It is therefore very important to secure the airway with a cuffed endotracheal tube during general anesthesia. 9 Once the airway is secured, and if the stomach appears large, an orogastric tube may be placed to empty the stomach contents. 9 There are some prophylactic measures that can be taken in order to reduce the complicat o n s from aspiration should it occur. 9 Preoperanve admmmtrauon of metocloprom]de may increase the tone of the lower esophageal sphincter and promote gastric emptying, and nonparuculate antacids and H2 blockers may be given to raise the gastric pH. 9

Increased Intracranial Pressure A standard pneumoperltoneum increases the intracramal pressure. lr This appears to be due to a direct mechanical effect3 r Decreases in or restrlcuon of lumbar venous plexus outflow potentially causes increased spinal canal pressure, increased cerebral spinal fluid pressure, and secondary increases m mtracramal pressure3 r If the arterial Pco2 rises, it will elevate mtracramal pressure through increased cerebral blood flow. ~r Laparoscopy must be used cautiously in patients with trauma or head mlury,17

Thoracoscopy These techniques can also be applied to the thorax in the form of thoracoscopy, The morbidity of such procedures as lung biopsy, pericar&al window formation, and thoracic exploratory can be greatly reduced by use of thoracoscopy versus thoracotomy, The stgnificant benefits of a thoracoscopic biopsy over a convenuonal thoracotomy and transbronchial, or percutaneous biopsy are the improved diagnostic yield and earher and more accurate dtagnosts and treatment of patients with parenchymal lung disease, is Thoracoscopy results in less postoperative pain, less morbldity, and shorter hospital stays compared with thoracotomy, is 2o Thoracoscopy is not suitable for patients w~th hemodynamic instability or vigorous hemorrhage. Instead, thoracotomy should be performed in those patients. 19

Anesthetic Considerations for Thoracoscopy The patmnt is posmoned in dorsal or lateral recumbency with the thorax prepared as for a thoracotomy, t9 Then, if it becomes necessary, the surgeon can proceed to a thoracotomy. The animal is placed under general anesthesia and mtubated. 19 Intermittent positive pressure ventilation reduces the changes seen with mediastinal shift and prevents paradoxical respiration. 2° Hypotension may result from cardiac arrhythmias, pulmonary embolism, or myocardial infarcuon. 2° Perforation of organs and hemorrhage are rare complications. 2° To improve visualizauon, insuffiation of the pleural cavity can be done with carbon dioxide. 2° The infusion of carbon dioxide at a low flow, 1 L/min, and low pressure, less than 5 m m Hg, will aid in the collapse of the lung. 18 Sigmficant hemodynamic compromise occurs at insufflation pressures greater than 5 m m Hg. 2° Chest tubes are placed at the end of surgery and the lung is re-expanded under direct vision to assess for air leaks, t8,2° It is important to seal the trocar insertion sites so that intrathoracic suction may be maintained via the chest tube. .9 Pleural QUANDT

specific safety management and application. With special consideration given to these concerns these techniques can be done safely and to the benefit of the patient.

References

Fig 4. After thoracoscopy the trocar insertion sites must be sealed postoperatively so that intrathoracic suction can be maintained via the chest tube.

drainage time is less than with a conventional thoracotomy. 2° Local anesthetics such as lidocame or bupivacaine administered intercostally as well as through the chest tube will provide postoperative analgesia. Systemic administration of opioids may also be used (Fig 4). 2°

MonitoringDuring Laparoscopyand Thoracoscopy The patient must be monitored to improve the safety of the procedure. Electrocardiography and blood pressure monitoring should be done to evaluate the cardiovascular status of the patient, especially in response to the increased intra-abdominal pressure. 8 Capnography and pulse oximetry should be used on all patients to monitor the respiratory variables of CO2 and oxygen saturation. 8 The capnograph will help in the recognition of hypercarbia and also facilitates the detection of CO2 embohsm as indicated by a transient but rapid rise in the end-tidal CO2.89 The pulse oximeter can detect hypoxemia, s An esophageal stethoscope may assist in the detection of new heart murmurs that may signify a gas embolus. 9 Complications that may occur as a result of laparoscopy include hemorrhage, injury to viscera, subcutaneous emphysema, and pneumothorax. 8 Laparoscopy and thoracoscopy should only be done where equipment is immediately available for emergency laparotomy or thoracotomy and resuscitation. 8

Conclusion The availability of new technology; laser, laparoscopy, and thoracoscopy will improve the ability to diagnose and treat disease m the veterinary patient. These techniques require

ANESTHESIA FOR LASER PROCEDURES

1. Klause SE, Roberts SM: Lasers and veterinary surgery. Compend Contln Educ Pract Vet 12:1565-1576, 1990 2. Spencer L: Lasers light the way to easier surgery and therapy. J Am Vet Med Assoc 198:195-202, 1991 3. Rampll IR: Anesthetic considerations for laser surgery. Anesth Analg 74:424-435, 1992 4. CL MD Operation and Maintenance Manual: Surgscal Laser Technologies Inc. 1-68, 1989 5. Sosis MB: Anesthesia for outpatient laser airway surgery. Ambulatory Anesthesia 8-9, 1993 6. Sosis MB: What is the safest endotracheal tube for Nd-YAG laser surgery9 Anesth Analg 69:802-804, 1989 7. Arnold JE, Alphin AL: Effect of extralumlnal oxygen on carbon dioxide laser ignition of endotracheal tubes. Arch Otolaryngol Head Neck Surg 118:722-724, 1992 8. Lucas LF, Asher EF, Schroeder JA, Rigor BM" Anesthesia for laparoscopic general surgery. In: Vitale GC, Sanfihppo JS, Perlssat J, (eds). Laparoscopic Surgery and Atlas for General Surgeons. Philadelphia PA, JB Lipplncott, 1995, pp 55-64 9. Hanley ES: Anesthesia for laparoscopic surgery. Surg Clinics North Am 72:1013-1019, 1992 10. Ivankovich AD, Miletlch DJ, Albrecht RF, et al Cardiovascular effects of intraperitoneal insufflat~onwith carbon dioxide and nitrous oxide in the dog. Anesthesiology 42.281-287, 1975 11. Gilroy BA, Anson LW: Fatal air embolism during anesthesia for laparoscopy in a dog. J Am Vet Med Assoc 190:552-554, 1987 12. Ishlzakl Y, Bandal Y, Shlmomura K, et al: Safe intraabdomlnal pressure of carbon dioxide pneumoperltoneum during laparoscopic surgery. Surgery 114:549-554, 1993 13. Hirvonen EA, Nuutlnen LS, Kauko M Ventilatory effects, blood gas changes, and oxygen consumption during laparoscoplc hysterectomy. Anesth Analg 80:961-966, 1995 14. Fahy BG, Barnas GM, Flowers JL, et al: The effects of increased abdominal pressure on lung and chest wall mechanics during laparoscoplc surgery. Anesth Analg 81:744-750, 1995 15. Kelman GR Swapp GH, Smith I, et al: Cardiac output and arterial blood-gas tension during laparoscopy. Br J Anaesth 44:1155-1161, 1972 16. Gross ME, Jones BD, Bergstresser DR, et al: Effects of abdominal insufflation with mtrous oxide on cardloresplratory measurements in spontaneously breathing Isoflurane-anesthetized dogs. Am J Vet Res 54:1352-1358, 1993 17. Josephs LG, Este-McDonald JR, Birkett DH, et al" Diagnostic laparoscopy increases Intracranial pressure. J Trauma 36.815-819, 1994 18. Rothenberg SS, Wagner JS, Chang JGT, et al: The safety and efficacy of thoracoscopic lung biopsy for dJagnos~sand treatment on infants and children. J Pediatr Surg 31 100-104, 1996 19. Frame SB: Thoracoscopy for trauma. Int Surg 82:223-228, 1997 20. Plummer S, Hartley M, Vaughan RS. Anaesthesia for telescopic procedures in the thorax. Br J Anaesth 80:223-224, 1998

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