The purpose of this paper is to provide a brief review of important aspects of perioperative management.
The purpose of this paper is to provide a brief review of important aspects of perioperative management. As such, the reader is encouraged to study other sources for additional information.
Without a doubt the history and physical examination are extremely important when evaluating potential surgical patients. The history must thoroughly evaluate all aspects of husbandry including the source of pet(s), length of ownership, diet, environment and previous or current illness(s) and therapy. Patients should be observed in their cage or transport carrier before the hands on portion of the physical examination is performed. This will allow veterinarians to identify signs of illness that may be difficult to detect once the patients is restrained for the physical examination. Thorough physical examination will help to assess physical condition, cardiopulmonary status, severity of illness if present and any other conditions that are unknown to the owner. The veterinary team can use this information to identify potential problems and address them accordingly.
All patients should be as physiologically stable as possible prior to anesthesia, and veterinarians should use their judgment when performing preanesthetic screening for their avian patients. Ideally, the minimum database for procedures that require significant anesthesia time should include a complete blood count (CBC) and biochemical profile. In instances when the size of the patient limits the amount of blood that can be safely taken, a packed cell volume, total protein and blood glucose are acceptable; however the addition of uric acid, aspartate aminotransferase and white blood cell count is preferable. If your hospital or clinic is equipped with biochemical analyzers such as the Abaxis VetScan® (Abaxis, Union City, CA 94587, USA) with avian/reptilian profile rotors a compete biochemical panel can be obtained from 100 microliters of blood.
Hydration status should be noted and corrected with appropriate fluid therapy if necessary. Subcutaneous fluids are suitable for birds that are mildly dehydrated. Intraosseous and intravenous fluids are required for patients that are moderately or severely dehydrated. In general, daily maintenance fluid requirement is 50 mg/kg/day. Fluid deficit is calculated by multiplying the body weight in grams by the percent dehydration (% dehydration x bodyweight[g] = fluid deficit in milliliters). To correct dehydration the daily maintenance plus one-half of the fluid deficit is given during the first 12-24 hours, and then repeated during the second 24 hour period. Additional fluids are also given for on-going losses resulting from continued regurgitation, vomiting or diarrhea. In emergency situations a bolus of 10 ml/kg IV over a 5 minute period is well tolerated by most birds. Crystalloids such as Lactated Ringer's (Abbot Laboratories, Abbot Park, IL, USA), Normosol-R (Abbot Laboratories) or other balance fluid solutions with or without added dextrose (2.5% to 5%) are commonly used. During surgery, fluid should be given at rate of 10 ml/kg/hour for the first hour then 5 ml/kg/hour for the second hour and thereafter. Colloids such as hetastarch 6% (Hepsan®) (Sigma-Aldrich Brand: SIGMA, St. Louis, MO 63103, USA) (10-15 ml/kg IV or IO slowly) are administered if the patient is hypovolemic/hypoproteinemic and volume expansion is necessary to stabilize the patient.1,2 When using hetastarch with crystalloids reduce the volume of crystalloids given by the volume of hetastarch used to avoid fluid overload.1
Fasting allows the upper gastrointestinal tract to empty, thereby reducing the likelihood that the patient will regurgitate or vomit and aspirate ingesta. Fasting also reduces proventricular and ventricular distension thereby reducing potential interference with normal respiratory airflow or organ perforation during laparoscopic procedures.3 A prolonged fast greater than six hours is not recommend for most birds due to their small size and rapid metabolic rates. Some authors recommend fasting larger birds (> 500 grams) for at least 12 hours while smaller birds (e.g. budgerigars and canaries) are fasted for 6-12 hours. In most instances I feel a three hour fast is sufficient for most small birds.3 Raptors and especially waterfowl should be fasted for 12-24 hours if necessary.
There are numerous sources of information regarding anesthetic protocols for avian species. To become familiar with these protocols I recommend purchasing an appropriate source (e.g. formulary or textbook) for more specific information.
When choosing an anesthetic protocol select one that will allow you to complete the desired procedure with minimal to no physiologic changes to the patient. Most often isoflurane (IsoFlo®) (Abbot Animal Health/Abbot Laboratories, Abbot Park, Illinois, 60064, USA) is the anesthetic of choice; however, sevoflurane is an acceptable alternative.
Emergency drugs (atropine and epinephrine) should be readily available or prepared in syringes prior to initiating anesthesia. This is a time saving move that allows the veterinary team to address anesthetic emergencies (cardiopulmonary arrest) as soon as they occur. Patients under anesthesia for longer than 10-15 minutes should be intubated. Be careful not to manipulate the head and neck of intubated birds too much as excessive movement of the endotracheal tube can result in hemorrhage or moderate inflammation within the tracheal lumen.
Certainly, anesthetists are trained to monitor patients closely while they are under anesthesia and maintain adequate ventilation. This is extremely important and necessary for all avian patients; however, special consideration should be given to African grey parrots (Psittacus erithacus sp). which may suffer from hypocalcemia. Although the exact etiology of this condition is uncertain, dysfunctional parathyroid glands or parathyroid hormone (PTH) are suspected as a possible etiology.4 Additionally, isoflurane has been shown to decrease ionized calcium, myocardial contractility, cardiac index, mean arterial pressure and alter calcium homeostasis in cardiac and skeletal muscle in several mammalian species.5-7 And, while there are great physiologic differences between mammals and birds, these findings may help to explain some of the unexpected anesthetic deaths observed in African grey parrots under isoflurane anesthesia. Additionally, Krapf, Jaeger and Hulter (1992) revealed that chronic respiratory alkalosis due to hyperventilation may result in impaired renal response to PTH in humans8 and loss of calcium through the kidneys. To manage anesthesia in African grey parrots. Edling et al (2001) suggest that intermittent positive pressure ventilation combined with capnography will help the anesthetist to maintain end-tidal CO2 within a range of 30-45 mmHg which is adequate for and will improve anesthetic monitoring of greys.9 Supplemental calcium gluconate given 5-10 minutes prior to anesthesia may help to alleviate the problems associated with hypocalcemia.
Most avian patients have extremely high metabolic rates, and in addition to their small size, can make hypothermia a real and constant problem.10,11 To minimize heat loss during procedures use heating pads (circulating water), Bair Hugger Total Temperature Control Systems™ (Augustine Medical, Inc., Elden Prairie, MN 55344, USA) 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 during and after the procedure.
Most commonly, birds are placed in dorsal or lateral recumbency for surgical procedures. Placing a bird in sternal recumbency for a procedure is risky as the bird will not be able to breath 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.
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.
Following removal of 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 the numbers of bacteria without damaging the skin, thereby reducing postoperative infections. Surgical prep solutions should contain chlorhexidine diacetate (0.5%) (Nolvasan Solution, Fort Dodge Laboratories, Fort Dodge, IA) or Chlorhexidine gluconate (4.0%) (Hibiclens, Stuart Pharmaceuticals Division, ICI America, Wilmongton, DE).11 Many veterinarians use alcohol as a surgical rinse; however, saline is preferable, as it tends to cause less heat loss than alcohol.
There are numerous methods of monitoring avian patients including the use of a stethoscope, electrocardiography, Doppler, respiratory monitors, pulse oximetry, direct or indirect blood pressure monitors and thermometer probes.
Electrocardiography (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 (Parks Medical Electronics, Inc., Aloha, OR, 97007 USA) 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 to be very accurate as long as they are placed in close proximity to an artery or the heart. Unfortunately, they do not give information regarding changes in the patient's physiological status.10 I personally 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 as values may be unsatisfactory for evaluation of tissue perfusion in avian species.14
Birds should breathe at least once every 2 to 7 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%) drop in heart or respiratory rate indicative of impending cardiopulmonary arrest.17 In our practice we provide respiratory assistance in all birds under anesthesia for extended periods of time.
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. However its usefulness is limited in small avian patients. Pediatric sized or neonatal cuffs (No. 1, 2 or 3) can be placed 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 different 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
Patients should be placed in a quiet (away from dogs, cats, and high traffic), 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 should be addressed again as well as postoperative pain. 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 all be used in exotic species.20 Butorphanol (Torbugesic®) (Fort Dodge Animal Health, Overland Park, KS 66225, USA) (0.5-2.0 mg/kg IM q6-24 hours) appears to provide adequate anesthesia during the post-operative period. Similar dosages can also be given pre-operatively.21 Butorphanol dosages as high as 4mg/kg have also been used.20 While butorphanol may be used for prolonged periods of time. Carprofen (Rimadyl®) (Pfizer Animal Health, Exton, PA 19341, USA) (1 mg/kg SC or 1-2 mg/kg IM, PO, IV q 12-24h) or meloxicam (Metacam®) (Boehringer Ingelheim Vetmedica, Inc., St., Joseph, MO 64506, USA) (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.
References provided on request