Post-Operative Sheep Care
Last updated: December 19, 2011
Sheep undergoing invasive survival surgeries must be appropriately evaluated and monitored before, during, and after surgery in a manner consistent with the current standard of veterinary care in order to provide humane care that is compliant with regulatory requirements. In order for these guidelines to reflect the current standard of veterinary care for postoperative monitoring in USDA-regulated species undergoing cardiopulmonary by-pass procedures, clinical laboratory animal veterinarians at four institutions were contacted. The institutions included Stanford University, The University of Minnesota, Texas A&M University, and Duke University.
Trained personnel should be present with sheep for continuous postoperative monitoring until midnight on the day of surgery and should return at 6 am after cardiopulmonary by-pass (CPB) procedures. With less invasive surgeries, such as vascular grafting procedures, peri-operative care requirements will be documented in the IACUC-approved Animal Use Protocol. The principal investigator is responsible for providing trained personnel for postoperative care.
Postoperative care and extubation
Sheep should be placed in sternal recumbency in the recovery stall. 100% oxygen should be maintained via endotracheal tube until extubation. If furosemide was not already given in the operating room, administer furosemide 0.25-0.50 mg/kg IV now. Extubate with partial cuff deflation to protect the airway. After extubation, oxygen saturation should be checked every 5 minutes. Maintain oxygen supplementation via face mask until oxygen saturation remains steady at > 95% for at least 5 minutes, until the sheep is standing, or the sheep no longer tolerates the face mask, whichever occurs first.
Jugular vein access should be maintained with a long, large bore catheter (i.e., minimum of 5.25 inch, 14-18 gauge) overnight. The catheter should be flushed with 1-2 mL of heparinized saline a minimum of once every 6 hours and after any blood sampling procedures. Auricular arterial catheters may be removed once oxygen saturation is stable at > 95% following extubation or until the sheep is standing, whichever occurs first. A final blood gas analysis should be done immediately prior to removing the arterial catheter. Some arterial catheters may be removed in the operating room, such as femoral or pedal arterial catheters. In this case, a final blood gas analysis is done before removing the arterial catheter in surgery.
Perform temperature, pulse, respiratory rate, mucous membrane color, capillary refill time, arrhythmia assessment, thoracic auscultation, and pain assessment every 15 minutes until the sheep is standing then every 30 minutes until vitals have been stable for 1 hour. Records should then reflect continued monitoring every 2 hours until midnight on the day of surgery. Monitoring should begin again the next morning at 6 am and continue twice daily for 2 days. At a minimum, routine daily health checks are required thereafter until the end of the study.
Check packed cell volume (PCV), total solids (TS), and serum electrolytes 2 hours postoperatively, then PCV/TS every 4 hours until midnight on the day of surgery. A PCV/TS should be done between 11:30 pm and midnight before leaving the sheep for the night.
Chest tube care
The chest tube should be aspirated every hour for the first 2 hours postoperatively, then every 4 hours if no fluid/blood/air is retrieved. The chest tube should be aspirated between 11:30 pm and midnight before leaving the sheep for the night. If no fluid/blood/air is aspirated the next morning, the chest tube may be removed.
Clinical Parameters for Leaving Sheep Alone at Midnight
- Rectal temperature (T) should be > 97.5F
- Pulse rate (P) should be 80-140 beats per minute
- Respiratory rate (R) should be 20-80 breaths/minute, without signs of labored breathing
- Mucous membranes (mm) should be pink to light pink
- Capillary refill time (CRT) should be < 2 seconds
- Arrhythmia assessment can be done by thoracic auscultation or palpating a peripheral pulse. There should not be consistent arrhythmias. Antiarrhythmic therapy such as lidocaine should be considered in the event of consistent arrhythmias.
- Thoracic auscultation should include both sides of the thorax. It is particularly important to note the presence or absence of crackles which may indicate pulmonary edema. Additional doses of furosemide (0.25-2.0 mg/kg IV every 8 hours) may be beneficial in this case.
- Pain assessment should include observation of behavior, particularly the presence of teeth grinding, which is a typical species behavior for sheep experiencing pain. In addition, reluctance to stand, rear legs tucked under the abdomen, increased heart rate and respiratory rate can all be associated with pain. Buprenorphine may be administered at 0.005-0.01 mg/kg SC or IM every 8 hours using a 20-22 gauge needle. There are other causes of these signs as well. If there are concerns about the clinical evaluation of the sheep, call the IHI clinical veterinarian or the Attending Veterinarian (AV) at 243-6344 or 360-1560.
- Blood gas and electrolyte abnormalities will be treated on a case-by-case basis. Call the IHI clinical veterinarian or the AV for assistance.
Parameters Requiring Euthanasia
- Refractory arrhythmias associated with poor mucous membrane color, weak peripheral pulses, stupor or unconsciousness, or heart rate > 180 beats per minute.
- Persistent respiratory rate > 100 breaths per minute not responsive to pain management or labored breathing refractory to furosemide therapy.
- Evidence of hemorrhagic shock, including capillary refill time > 3 seconds, pale mucous membranes, increased heart rate (> 160 beats per minute), PCV < 17 or drop in PCV of > 20% since the final intraoperative measurement, or hemorrhagic thoracic effusion with a PCV > 10% aspirated from the chest tube.