Restraint with no sedation
Operant conditioning can be used to train giant pandas to enter and remain quiet in a restraint device. The steel-constructed restraint cage used at the San Diego Zoo is rectangular (2 m long by 93 cm wide by 118 cm high) (Fig. 15.1) and on wheels for mobility. It has a solid bottom with bars on the sides and top. Along one side, some of the bars are removable to allow better access to the animal. The opposite wall is moveable allowing the available internal cage space to be decreased (i.e. the restraint function). Similar cages are being used successfully at other institutions in the USA as well as China.
This type of restraint device can facilitate various medical procedures. For example, at both the San Diego Zoo and the Smithsonian's National Zoological Park, females have been trained to enter the device and lay down in dorsal recumbency or sit upright with the front paws gripping the top bars. Usually, the cage is 'squeezed' only modestly to limit, but not prohibit, animal movement. This has allowed ultrasound examinations (see Fig. 15.1), recovery of vaginal swabs (see Chapter 9) and milk collection (when in the upright position). Some individuals will allow blood pressure measurements to be taken from the upper front foreleg (see below). Others, including those at the Smithsonian's National Zoo and Ocean Park-Hong Kong have been trained to place a
foreleg into a sleeve for blood sampling. Still others have remained so still as to permit radiography. Finally, certain individuals have been trained to place the lower jaw on a metallic bar to allow ocular examinations. In short, this approach allows multiple, important procedures to be conducted in nonsedated giant pandas that otherwise would require repeated anaesthetic events.
The following description is designed to aid in planning and implementing anaesthesia when either multiple procedures have to be accomplished quickly and efficiently, or a few complex procedures are required. There are four steps: planning; anaesthesia induction; maintenance; and recovery.
Preparation for anaesthesia must include thinking ahead about every impending event and required resource from how to transport a large and potentially dangerous animal to making sure that all necessary drugs and tools are at hand. Because of the high profile of giant pandas, it is common that everyone wants to observe the anaesthetic event, from the animal's keepers to the zoo's director. This can result in a room that is crowded (Fig. 15.2) and noisy which, in turn, can be distracting for the veterinarians. It is especially important to have a quiet room during the intubation period, when the veterinarians must be able to hear the monitors and pay close attention to maintaining a patent airway. Thus the issue of who must be present needs to be addressed pre-emptively to limit people in the examination room to those playing an essential role. Once the animal is stable and the procedure long underway, it may be possible for non-essential personnel to get a closer look.
A pre-induction planning meeting that includes all relevant personnel is an excellent time to review everyone's roles and responsibilities. Besides ensuring that all necessary tasks are organised, such preparation allows the various components of the overall procedure to be adjusted to reduce the overall anaesthesia interval. With appropriate planning, proper techniques and rigorous monitoring, the anaesthesia interval can be minimised and, if necessary, extended safely to several hours for necessary procedures.
Induction and intubation
Anaesthesia induction in the giant panda is predominately accomplished by intramuscular (i.m.), remote delivery dart or by hand injection in a restraint cage. Food and water are withheld for at least 12 hours before induction to reduce the risk of regurgitation and pulmonary aspiration of gastric contents. At induction onset, the panda is separated from its mate or offspring (even if nursing). In addition to the primary anaesthetic drug, other essential items to have available include reversal and resuscitation drugs, endotracheal tubes and stylets, a self- or flow-inflating bag with mask (to deliver oxygen), a pulse oximeter (to measure blood oxygen saturation), a stethoscope, intravenous (i.v.) catheters and fluids and a tarpaulin (to carry the animal to the examination room).
Ketamine hydrochloride (Ketaset®; Fort Dodge, Fort Dodge, IA) is the primary induction agent used for the giant panda. Other drugs, such as tiletamine/zolazepam (Telazol®; Fort Dodge, IA) and medetomi-dine hydrochloride (Wildlife Pharmaceuticals, Fort Collins, CO) are also options but are no more effective than ketamine. A 6-9 mg kg-1 dose of ketamine given in a single dart or injection is usually effective although supplemental ketamine doses (1-1.5 mg kg-1) provided i.m. or i.v. may be necessary to induce an anaesthetic plane that allows the animal to be moved safely. Initial post-ketamine effects (e.g. sitting, head drooping and uncoordination) generally occur within about five minutes, with the animal being tractable and accessible within 15 minutes. Once it has been determined that the panda can be handled, vital signs are obtained quickly and the eyes covered with a blindfold to minimise external stimuli. During transport, oxygen is provided by face-mask and an attempt made to monitor oxygen saturation by pulse oximetry, although the latter is challenging. Readings are best secured by affixing the pulse clip to the tongue, cheek or genitals (other extremities, including the ear, give poor readings).
Once the panda has been relocated to the main examination area, full physiological monitoring can begin, including using electrocardio-graphy, pulse oximetry, measuring end-tidal carbon dioxide and tracking blood pressure noninvasively (using a cuff around a fore-limb). Systemic hypertension often occurs initially, with blood pressure usually returning to normative values within 10 to 15 minutes. Noninvasive blood pressure readings are helpful to determine when the animal is sufficiently relaxed for intubation. Giant pandas anaesthetised with ketamine are usually physiologically stable with excellent respiratory function as determined by arterial blood-gas sampling.
An isoflurane delivery system is one method that can be used to deepen anaesthesia and optimise conditions for intubation. This is usually required if the jaw muscles remain tense, respiration is rapid and/or the animal responds to stimulation (e.g. repositioning or a skin pinch). For supplemental anaesthesia before intubation, we have occasionally used propofol (Diprivan; AstraZeneca Pharmaceuticals, Wilmington, DE) in 0.5-1 mg kg-1 boluses i.v. or ketamine in 50-100 mg boluses i.v. Care is exercised using propofol because, even at therapeutic doses, the animal may become apnoeic. During this time, the panda is supported using supplemental oxygen mixed with the volatile anaesthetic given by mask. The most useful mask is a plastic jug with the bottom cut away to fit the panda's muzzle and face while avoiding the eye region and ocular injury. The mask is attached using adhesive tape, which provides an adequate seal, although a towel can be placed around the mask's edge to further reduce air leakage.
Endotracheal intubation is desirable to assure control of the animal's airway. This is particularly important for performing procedures in the oral cavity or for any prolonged procedure. It also decreases the risk of pulmonary aspiration from oral secretions or regurgitated stomach contents. For the giant panda, direct laryngoscopy and intubation are most easily accomplished with the animal in lateral recumbency. To aid in opening the jaws and for obtaining the best possible view of the upper airway, two assistants apply ropes anchored around the upper and lower incisors behind the canine teeth (Fig. 15.3). Topical anaesthesia is applied to the larynx to decrease the incidence of laryn-gospasm during intubation. The preferred drug and dose are lidocaine at about a 2-5 ml volume of a 2% solution sprayed on the vocal cords and periglottic structures. Intubation is usually accomplished with a long, straight blade (Miller 4 or 5; Welch Allyn Medical Products, Skaneateles Falls, NY) and a well-lighted laryngoscope (Welch Allyn Medical Products) (see Fig 15.3). Most adult giant pandas can be intubated with a size 12, 13 or 14 mm endotracheal tube with placement often facilitated by a stylette within the tube. The full length of the tube is generally used for proper positioning within the trachea. However, it should be noted that intubation into the right primary bronchus has occurred with a 63-cm long tube in an adult male. Therefore, it is
important to estimate the position of the tracheal bifurcation. On most occasions, an ideal view of the vocal cords is obtained, the tube placed and the cuff inflated to prevent air leakage. Placement and appropriate ventilations are further confirmed by listening to bilateral breath sounds over the anterior lung fields and by placing the end-tidal carbon dioxide monitor in the circuit. Simply seeing the chest rise and fall is not an accurate indicator of proper tube placement. This, in fact, can result from an upper airway occlusion or laryngospasm.
Once the tube is appropriately placed, it is secured with a tie around the animal's neck. An alternative method is holding the tube with a plastic prop placed between the teeth, a technique that also serves as a block to prevent accidental bite obstruction of the endotra-cheal tube. Throughout all of these procedures, care is taken to avoid hyperextending the jaw.
While the endotracheal procedure is underway, an i.v. catheter is simultaneously placed. The medial cephalic vein is most accessible and can be catheterised using an 18-gauge, 2-cm long catheter. The external jugular vein can also be used for multipurpose access relying on a 7 French, double-lumen catheter. Once vital signs are satisfactory via the various monitoring approaches, the airway is secured and there is i.v. access, then the planned medical procedures may commence.
Anaesthetic maintenance techniques to ensure effective procedures
Volatile agents, including isoflurane and sevoflurane, provide a stable base for anaesthetic maintenance delivered by the endotracheal tube. Propofol and ketamine supplementation have also been useful for sustaining effective anaesthesia. However, the medical procedure itself can influence animal stimulation which, in turn, requires modifying the anaesthesia protocol. For example, electroejaculation involves periods of no or low activation followed by more intensive stimulation, which can evoke acute tachycardia and hypertension. Therefore, when semen collection is scheduled for sperm banking, a background volatile agent (isoflurane or sevoflurane) combined with bolus doses of propofol or ketamine can be used. In contrast, for simple examinations without electroejaculation, volatile anaesthesia can be used alone.
Throughout the interval of anaesthesia maintenance, vital signs are continuously and carefully monitored. This involves recording blood pressure, pulse, oxygen saturation, end-tidal carbon dioxide and respiratory rate every five minutes. Normative values are found elsewhere in this book (see Chapter 4). We have found excellent correlation between noninvasive blood pressure monitoring via a cuff on a limb extremity and values measured directly and invasively via intra-arterial means. End-tidal carbon dioxide values likewise correlate well with direct arterial blood-gas analysis.
During this period, it is also essential to consider fluid and temperature management (normal temperature values for this species are presented in Chapter 4). The target is usually to provide a fluid bolus to replace the deficit resulting from the 12-hour fast. Approximately 5-10 ml kg-1 of a balanced electrolyte solution (e.g. lactated Ringer's) are given i.v. over the first 30 minutes after the animal has been stabilised under anaesthesia. Blood-gas analysis of fasted giant pandas has revealed a metabolic acidosis of unclear aetiology, which is usually corrected by this initial fluid bolus. Maintenance fluids are then given to sustain adequate hydration, generally lactated Ringer's at a rate of about 200 ml per hour, which prevents electrolyte abnormalities.
Adequate personnel during the anaesthetic episode are critical, especially given individual animal variations and the complexity of these anaesthetic drugs. Ideally, there should be a team of three qualified individuals focusing only on anaesthesia and with the following assignments.
One person is responsible for airway management, including mask oxygenation (immediately after the animal becomes tractable), aiding or performing the intubation, securing the endotracheal tube, confirming (and reconfirming) tube placement and 'guarding' the airway. This team member may want to keep a hand physically on the tube, whenever possible, and at all times during any animal movements. The latter includes (but is not limited to) animal repositioning or activities associated near the head or neck (e.g. ophthalmic or dental procedures).
The second anaesthesia team member assumes the role of monitoring and adjusting the anaesthetic drug, as necessary, to maintain an adequate plane of anaesthesia. This includes closely observing the animal and its reaction to various stimuli, with the ability then to anticipate and react by changing anaesthetic delivery. This usually means simply adjusting the percentage of volatile agent provided. However, this person is also prepared to give required i.v. drugs, including vasopressors and beta-blockers perhaps needed to control blood pressure or heart rate.
The third person keeps detailed records, documenting not only anaesthetic events, but also procedural activities to allow future correlations. A standardised record form is used and formatted to allow recording anaesthetic drugs, doses and times of delivery as well as anaesthesia and procedural start and end times. The forms are designed so that the times the agents are given can be correlated with changes in vital signs, which are also recorded. Additional useful information includes that associated with monitoring data, i.v. site information, amounts of fluids provided, airway status and general comments.
Emergence from general anaesthesia is fraught with potential complications such as laryngospasm, vomiting and ingesta aspiration. This is yet another time to be highly vigilant and to take precautions to ensure smooth recovery with minimal physiological stress. One potential prophylaxis to reduce the incidence of vomiting is the use of metoclopramide (0.1 mg kg-1, i.v.; Faulding Pharmaceutical Co., Parmus, NJ) given as an anti-emetic about 30 minutes before emergence. Lidocaine (1 mg kg-1) administered i.v. also helps diminish laryngospasm and gagging on the endotracheal tube or during its withdrawal.
When all procedures that required anaesthesia are complete, the panda is moved to a transport or recovery cage. At this time, the endotracheal tube is left in place with the animal spontaneously breathing 100% oxygen. Oxygen saturation is monitored continuously while the panda is observed transitioning from unconsciousness to full awareness. Once the swallowing and protective airway reflexes return ( just prior to arousal), the cuff on the endotracheal tube is deflated and the tube carefully withdrawn. An alternative approach is to transport the panda back to the home enclosure with the tube in place after which, upon arrival, it is extubated. The former option is preferable, that is, it is safer to remove the endotracheal tube with the animal in the transport cage held at or near the examination room where all medical resources are readily available.
Even after returning to consciousness, the giant panda is monitored continuously until ambulatory in order to identify complications or signs of discomfort. If the animal still seems to be under the influence of the anaesthetic, pulse oximetry continues to be used while oxygen is provided via the face-mask. Detailed record-keeping also continues, marking the times from the end of the procedure to extubation, head lift, sternal recumbency, attempting to stand and full standing. Throughout, attention is paid to limiting stimulation, especially noise. When judged to be in a satisfactory condition, the giant panda is returned to its enclosure.
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