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, the arterial CO2 tension (PaCO2) rises. This increase tends to occur rapidly upon insufflation and generally plateaus in ventilated patients. Spontaneously breathing animals tend to fatigue and may not be able to maintain the plateau [138]. Hence, for procedures where insufflation will be sustained for greater than 20–30 minutes, use of positive pressure ventilation is recommended to minimize hypercapnia and a consequent reduction in pH and potential adverse effects on intracranial pressure and anesthesia depth. Typically, minute ventilation will need upward adjustment to compensate for the delivery of CO2 with the insufflator. One should follow the basic principles of ventilation and consider the change in chest wall compliance when making these adjustments.
Because of the potential to cause barotrauma and compromise venous return (and so cardiac output) further with a significant increase in tidal volume, it is common to first increase respiratory rate and then if needed adjust the airway pressure/tidal or minute volume depending on the type of ventilator being utilized. Both pressure and time‐cycled (volume limited) ventilators may be used, but the user should be familiar with the special considerations for each of these in the face of reduced pulmonary compliance caused by insufflation and potential postural changes. While some elevation in arterial CO2 tension is acceptable in a healthy patient, a general recommendation in patients without intracranial disease is to maintain this value at or below 60 mmHg. In the absence of blood gas monitoring, the end‐tidal CO2, which may be up to 10 mmHg (but is usually 0–5 mmHg) lower than arterial CO2 tensions, should be maintained below 55 mmHg. Ventilation may also help prevent atelectasis of the lung resulting from cranial displacement of the diaphragm and so help maintain oxygenation. The use of positive end‐expiratory pressure (PEEP) has been shown to be beneficial in improving gas exchange and pulmonary mechanics in healthy dogs [139] as well as in humans [140]. Alveolar recruitment maneuvers in addition to PEEP may further improve gas exchange, particularly when a steep Trendelenburg position is required [139, 141]. However, it is important to consider the potential negative impact on cardiovascular function associated with these ventilatory techniques.
Along with providing respiratory support, it is important to monitor respiratory function. Carbon dioxide may be monitored in the airway with a capnograph or in the blood using a blood gas analyzer. The former has the benefit of being continuous and noninvasive. Additionally, the capnograph will alert the anesthetist to low cardiac output states as may occur for a number of reasons including that resulting from an intravascular gas (CO2) embolus.
A pulse oximeter similarly is easily applied and provides continuous measurement of oxygen saturation while also recording pulse rate. In most dogs and cats undergoing laparoscopic procedures, the use of pulse oximetry is considered sufficient for monitoring of oxygenation, as hypoxemia is not a likely complication even with insufflation in patients breathing high fraction of inspired oxygen (FiO2). However, in patients breathing a lower FiO2, hypoxemia is possible and likely to occur more rapidly if a complication (e.g., pneumothorax) occurs. If N2O is used as part of the anesthetic protocol, oxygen saturation monitoring is especially important.
In the high risk or critically ill animal, arterial blood gas analysis is useful and provides information about CO2 and oxygen tensions. Blood pH and other parameters including electrolytes, blood glucose, and lactate are frequently included with blood gas results and provide additional information to facilitate appropriate management of the animal.
Summary
As laparoscopic interventions become well established in veterinary medicine, it is important that the veterinary team is well versed in both surgical and anesthetic aspects of management to ensure a successful outcome.
References
1 1 Beedorn, J.A., Dykema, J.L., and Hardie, R.J. (2013). Minimally invasive surgery in veterinary practice: a 2010 survey of diplomates and residents of the American college of veterinary surgeons. Vet. Surg. 42:
