Surgical preparation and perioperative management of birds (Proceedings)
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.
History and Physical ExaminationWithout 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.