Avian medicine: Instill a perioperative protocol to lessen anesthetic, iatrogenic risks - DVM
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Avian medicine: Instill a perioperative protocol to lessen anesthetic, iatrogenic risks


DVM360 MAGAZINE


Patient preparation

Most avian patients have extremely high metabolic rates, and in addition to their small sizes, can make hypothermia a real and constant problem.10,11 To minimize heat loss during procedures, use heating pads (circulating water), temperature control systems and warm fluids. Another option is to warm the surgical suite. When using heating blankets/pads or bottles, be sure to separate the patient from the heat source by a towel so as not to burn the patient.

Surgical positioning: Most commonly, birds are placed in dorsal or lateral recumbency for surgical procedures. Placing a bird in sternal recumbency for a procedure is risky because the bird will not be able to breathe properly due to the weight of its body on the sternum. If possible, elevate the head or the cranial aspect of the body by tilting the table or placing foam or other soft material under the patient.

Skin preparation: To prepare the skin for surgery, pluck feathers to a minimum distance of 2-3 cm around the surgical site11 by pulling feathers in the direction they normally grow. Filoplumes may be clipped with a small clipper or scissors.

After removing feathers, standard aseptic technique should be used to prepare the skin for surgery.11 The goal of surgical preparation of the skin is to reduce bacteria without damaging the skin, thereby reducing postoperative infections. Surgical prep solutions should contain chlorhexidine diacetate (0.5%) or Chlorhexidine gluconate (4.0%).11 Many veterinarians use alcohol as a surgical rinse; however, saline is preferable, since it tends to cause less heat loss than alcohol.

Patient monitoring

There are numerous methods of monitoring avian patients, including the use of a stethoscope, electrocardiography (ECG), Doppler, respiratory monitors, pulse oximetry, direct or indirect blood pressure monitors and thermometer probes.

ECG is commonly used and provides the anesthetist with information regarding the patient's pulse rate and rhythm as well as clues toward impending changes in the patient's cardiovascular system.10 The ECG should be capable of recording speeds of 100 mm/s and amplify the signal to at least 1mV equal to 1 cm.12 Standard lead positions described for dogs and cat are used for birds.

Ultrasonic Dopplers detect pulsatile blood flow and are based upon the principle that the frequency of transmitted sound waves are altered when reflected off moving red blood cells.11,13 Dopplers are considered very accurate as long as they are placed in close proximity to an artery or the heart. However, they do not give information regarding changes in the patient's physiological status.10 I use Doppler flow detection for all avian patients. As the surgeon, I find the sound of the Doppler comforting during surgical or laparoscopic procedures. One of the best sites to use for placement of the Doppler probe is over the superficial ulnar artery or the deep radial artery just inside the elbow. Two tongue depressors are taped together at one end and used as a giant clothes pin to hold the Doppler probe in place. Alternatively, the Doppler probe can be placed on the roof of the oropharynx and held in place with tape or folded gauze or on the ventral aspect of the carpus.

Pulse oximetry is a noninvasive technique that measures pulse rate and oxygen saturation during anesthesia and surgery. Pulse oximeters estimate arterial hemoglobin O2 saturation (SaO2 or SpO2) by measuring pulsatile signals across (transmission) or by reflectance (reflection) from perfused tissue at two discrete wavelengths (660 nm, red; 940nm infrared) using the constant component of absorption at each wavelength to normalize the signals.14,15 Pulse oximetry should be used to evaluate trends in oxygenation since values may be unsatisfactory for evaluation of tissue perfusion in avian species.14

Birds should breathe at least once every two to seven seconds while under anesthesia.16 A decrease in respiratory rate and depth suggests that the anesthetic level is deep. Conversely, an increase in respiratory rate and depth may indicate that the anesthetic level is too light. A significant (20 percent) drop in heart or respiratory rate is indicative of impending cardiopulmonary arrest.17 In our practice, we provide respiratory assistance to all birds under anesthesia for extended periods of time.

Blood pressure

Non-invasive measurement of systolic, diastolic, mean arterial pressure and pulse rate via an oscillometric blood pressure monitor provides a quick and somewhat reliable method of blood pressure determination and appears to correlate well with direct blood pressure monitoring in larger avian species such as eagles (Joyner et al, unpublished data) and possibly larger psittacines. Its usefulness is limited to small avian patients. Pediatric-sized or neonatal cuffs (No. 1, 2 or 3) can be placed over the distal humerus (over the easily visualized brachial artery) or cranially on the leg at the level of the tibiotarsal-tarsometatarsal joint (encompassing the dorsal metatarsal artery). Lichtenberger (2005) described a technique to measure indirect blood pressure in several psittacine species using an ultrasonic Doppler flow detector (Figure 1).18 A small cuff is placed around the distal humerus and the Doppler probe is placed along the ventral aspect of the carpus to detect ulnar arterial blood flow.18 The cuff is inflated to suprasystemic pressure with cuff-off of the Doppler signal.18 The cuff is deflated with the first sound heard and marked as the systolic pressure.18 Normal indirect systolic Doppler blood pressures of awake and anesthetized psittacine birds are 151 +/- 51 mm Hg and 112 +/- 42 mm Hg respectively.19 Lichtenberger (2006) also determined the blood pressure of various avian species under isoflurane or sevoflurane anesthesia to range between 90-140 mmHg systolic.2

Postoperative considerations

Patients should be placed in a quiet, visually secure, warm recovery cage or incubator as they awaken from anesthesia. They should not be left alone until they are able to stand on their own. During this period, fluid balance and postoperative pain should be addressed. Signs of pain may include abnormal body positions, tucked abdomen/coelomic cavity, aggression (biting, attacking), vocalization, reluctance to move or stand, pronounced fear, self mutilation and inability to perform "normal" everyday activities.

Unfortunately, few studies have been performed in exotic species; however, many of the same analgesics used in dogs and cats can be used in exotic species.20 Butorphanol (0.5-2.0 mg/kg IM q6-24 hours) appears to provide adequate anesthesia during the postoperative period. Similar dosages can also be given pre-operatively.21 Butorphanol dosages as high as 4mg/kg have been used.20 While butorphanol may be used for prolonged periods, Carprofen (1 mg/kg SC or 1-2 mg/kg IM, PO, IV q 12-24h) or meloxicam (0.1-0.2 mg/kg PO, IM q 24h) are also popular choices for analgesia.20 However, the patient should be monitored for gastrointestinal upset and bleeding and renal disease when using these non-steroidal anti-inflammatory medications.


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