Small Animal Laparoscopy and Thoracoscopy. Группа авторов

as prompt recognition and management are essential to a positive outcome.

Perhaps the most concerning complication is the potential for gas embolism. This results when insufflation gas enters the vasculature and is transported to the heart and lungs. In small amounts, the gas is delivered to the lungs and usually cleared without much consequence to the patient. As volumes of gas increase, hypotension, tachycardia, arrhythmias, and a decrease in end‐tidal CO₂ tension may be noted [106, 107]. If a larger (patient size dependent) volume of gas were to reach the heart, there is the potential for the gas to occupy one of the chambers of the heart and prevent blood flow that ultimately results in cardiac arrest [107–110]. Several studies using transesophageal echocardiography have demonstrated a very high incidence of subclinical gas emboli during different laparoscopic surgical procedures in both animals and humans [111–114]. The fact that no adverse effects were reported in those studies may be related to the use of CO₂ for abdominal insufflation. The potential for embolization exists with CO₂ but is lower than for air, nitrous oxide, or helium. This is why despite not being inert (and so contributing to a rise in arterial tensions of CO₂ more than caused by distention alone), CO₂ is still preferred as the insufflation gas for laparoscopic interventions [32, 111, 112, 115]. Despite its relative safety, fatal embolism has been reported with CO₂ use in both human and animals [107, 109]. If gas embolism is suspected, abdominal insufflation should be immediately discontinued. When possible, the animal should be placed in left lateral recumbency and cardiac massage started in an attempt to dislodge the emboli from the heart. Placement of a central venous or pulmonary artery catheter may allow aspiration of the gas emboli [32, 84]. One of the authors had experienced a fatal suspected CO₂ embolism event in a small dog undergoing laparoscopic cholecystectomy. While most severe cases of CO₂ embolism typically occur at the beginning of the procedure, due to inadvertent placement of the Veress needle into a vessel or organ parenchyma [116], it can also occur later in the procedure as was the case in this dog. Later occurrence of CO₂ embolism is thought to be due to smaller amounts of CO₂ entraining the circulation through injured vessels in the abdominal wall or surgical site [112, 116]. Attempts to dislodge the emboli (as described above) were unsuccessful. Severe CO₂ embolism is extremely uncommon, but consequences can be devastating. The mortality rate associated with severe gas embolism in humans has been reported at 28% [117].

      Insufflation with CO₂ gas is typically performed at 22 °C and 0% relative humidity. The use of a warmed humidified CO₂ insufflation (37 °C, 97% relative humidity) has been proposed as a manner to minimize postoperative discomfort, perioperative hypothermia, as well as peritoneal injury and adhesion formation [118–120]. However, studies on potential benefits of using warmed humidified CO₂ insufflation have provided conflicting results. While various studies have reported less pain with the use of warmed humidified CO₂ insufflation in human patients [118,121–123], others have failed to detect a benefit [124, 125]. A recent study in dogs showed that the ones insufflated with warmed humidified CO₂ had higher pain scores than the ones insufflated with the cold dry gas, although no dogs required rescue analgesia [126]. In addition, no benefit regarding maintenance of core body temperature in the perioperative period has been demonstrated from the use of warmed humidified CO₂ in humans [121, 124, 125, 127] or dogs [126]. A potential benefit may be the reduction in peritoneal injury that has been shown with the use of warmed humidified CO₂ in rats [119, 120] and in dogs [126]. These might include less adhesion formation [120] and lower susceptibility to implantation of cancer cells and metastasis at portal sites [128, 129], but further studies are needed to confirm its clinical significance.

Anesthesia Management

      While there are some unique aspects to laparoscopic intervention as noted in the preceding text, the basic principles of anesthesia must first be applied. General anesthesia should be a reversible event that provides amnesia, analgesia, unconsciousness, and muscle relaxation while supporting thermoregulation, cardiovascular, respiratory, neurologic, hepatic, and renal functions. To meet these basic principles, care should be individualized for the animal with consideration given to the reason for the presentation, the animal's signalment, general health status, etc. Procedure‐related risks should also be considered, and it may be warranted to consider the expertise of the surgical team when selecting anesthetic drugs and the support and monitoring plan. Additionally, one must factor in the pathophysiological implications of laparoscopic intervention as discussed earlier in this chapter.

      The young healthy dog or cat presented for an elective procedure is unlikely to have restrictions when selecting anesthetic drugs. In our practice, an opioid would likely be used for premedication to provide analgesia and some sedation. The additional use of a tranquilizer or sedative might be warranted if the animal is excited or fractious. An anticholinergic could be considered to offset the bradycardia seen with many opioids and sometimes associated with peritoneal distention and visceral traction. Propofol (or another preferred induction agent) could be used for anesthesia induction and to facilitate intubation. While many drugs including ketamine, propofol, and more recently alfaxalone have been shown to increase splenic size to some degree, [130–133] thiopental, which is still available internationally, has been historically associated with the greatest potential to cause splenic enlargement [134] While earlier studies have shown that propofol did not seem to affect splenic volume, [130, 131] a more recent study, which used computed tomography as the evaluating method, has shown comparable spleen enlargement with both thiopental and propofol. [132] Spleen enlargement may increase the potential for puncture of the spleen on entry into the abdomen and could compromise surgical visualization during cranial abdominal procedures, so awareness of the effects of anesthetic drugs on splenic size is important. Following intubation, the patient is commonly transitioned to maintenance with an inhaled anesthetic (isoflurane or sevoflurane). Local anesthetic infiltration at portal sites and a nonsteroidal anti‐inflammatory drug when not contraindicated are used in addition to postoperative opioids to provide additional analgesia. More recently, a sustained‐release bupivacaine formulation (liposomal bupivacaine), which is reported to provide analgesia for 72 hours, has been used with increased frequency for portal site infiltration and for ultrasound‐guided transversus abdominis plane block (TAP block) at our institution. In humans, the use of liposomal bupivacaine for TAP blocks has been described to provide better pain control than traditional bupivacaine in patients undergoing laparoscopic nephrectomy and colon resection and is associated with lower use of postoperative opioids [135–137]. For debilitated or critically ill animals, as well as for more complex laparoscopic procedures, the anesthetic plan should be modified as appropriate.

      In addition to the anesthetic drug plan, when considering the investment in time, training, and equipment for surgical aspects of laparoscopy, the veterinarian must consider whether the appropriate anesthesia equipment is available to support and monitor the patient during these procedures.

In addition to monitoring body temperature and providing external heat as appropriate, the heart rate and cardiac rhythm, which can vary during gas insufflation and organ manipulation (e.g., bradycardia with urinary bladder traction), should be monitored using an electrocardiogram. Blood pressure monitoring is essential and will alert the anesthetist to both anesthetic drug and insufflation‐related changes. Intravenous fluids (crystalloid or colloids as appropriate for the animal) are used to help maintain vascular volume and counteract the vasodilating effects of tranquilizers (e.g., acepromazine) and anesthetic drugs (e.g., propofol), as well as the additional influence of abdominal distention with insufflation gas, and postural changes on venous return and subsequently cardiac output. Hypotension may be treated with rapid administration (bolus) of intravenous fluids, reducing the anesthetic dose or decreasing insufflation pressure. When these interventions are not possible or not adequate, inotropes (e.g., dobutamine, dopamine) or vasoactive medications may be necessary.

      Due to pneumoperitoneum and additional potential postural changes for surgery, mechanical ventilation is recommended. As has been mentioned previously, pneumoperitoneum will increase CO₂ tension. This occurs to a greater extent when the insufflation gas is CO₂ as is currently most common. If no adjustments are made to positive pressure ventilation at the start of CO₂ insufflation,