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OCW Zoological Medicine 2008
Avian Anesthesia and Surgery (2008)
F. Tseng, DVM
Cummings School of Veterinary Medicine at Tufts University
1. Learning Objectives
Be familiar with the anesthetic options in avian medicine, including the necessary equipment required for safe administration
Understand the importance of anesthetic monitoring in birds and know the techniques used
Be familiar with the supportive therapies employed during avian anesthetic and surgical procedures
Know the three main principles of avian surgery
Understand the main differences in fracture healing between birds and mammals
Online, color coded topics also indicate learning objectives that the student should become familiar with. Cases will be presented in class to illustrate some of these topics.
2. Anesthesia review
2.1. Injectable anesthetics vs. inhalants (gas)
In general, inhalant anesthesia is used almost exclusively for anesthetic procedures by most avian practitioners today. This is because of the great speed, safety, and predictability of inhalation anesthesia in birds. The avian respiratory system is a very efficient gas exchange system. The uptake and excretion of inhalation anesthetic agents is more rapid in birds than in mammals.
The use of injectable agents in birds is still widespread, but is usually reserved for situations where a vaporizer is not available (in the field). The major drawback of injectables include
Dose response is variable
Most drugs are non-reversible
Questionable safety - higher risk
With isoflurane or sevoflurane the patient is likely to be perching and looking for its next meal in 10-15 minutes after withdrawal of the gas. With an injectable agent (e.g. ketamine/xylazine) a patient may have to be restrained for hours before it is able to perch and/or stand comfortably without injuring itself.
Some Common Injectable Agents Used in Birds
0.6 - 1 mg/kg IM
Relative short duration
0.5 - 2 mg/kg IM
Longer lasting effect, little effect on arterial blood pressure and blood gases. Reverse with flumazenil.
10 mg/kg IV induction,
Rapid onset and recovery, cardiovascular and respiratory depression may occur.
2.2. Preanesthetic considerations
2.2.1. History and physical exam
Observe in a quiet environment
Note neurological status
Assess exercise intolerance
Examine nares and glottis for obstruction
Auscult heart and lungs
Check mucous membrane color
Palpate crop and abdomen
2.2.2. Anesthetic workup
Minimal database includes PCV, TP, glucose
CBC, chemistries may be indicated
Radiographs may be indicated
Assess renal and hepatic function
2.2.3. Fasting prior to procedure
To decrease regurgitation and passive reflux
To decrease proventricular and ventricular distension, thus increasing air sac capacity
Duration of fast related to size, clinical condition, species, diet
Water may be removed up to 2-3 hours before induction
2.2.4. Stabilization prior to anesthesia
Correct severe anemia, fluid and metabolic disorders
Attain vascular access (IV or IO)
Patients that have cardiopulmonary compromise may benefit from preoxygenation
Correct body temperature abnormalities
2.2.5. Use of premedications
Parasympatholytic agents not used because they thicken secretions and risk tracheal obstruction
Premeds not usually used because they prolong recovery time and the effects are highly variable
2.3. Inhalation anesthesia
The avian respiratory system is a very efficient gas exchange system. The uptake and excretion of inhalation anesthetic agents is more rapid in birds than in mammals. Birds are very susceptible to anesthetic overdose due to their relatively higher metabolic rate, so monitor carefully! (see below)
Isoflurane anesthesia is the most commonly used agent and is performed with this agent alone. Premedications are not used for the reasons explained above. Isoflurane provides rapid induction and recovery in bird patients, with little depression of cardiac output and moderate muscle relaxation. Standard isoflurane equipment is used (requiring only a vaporizer, regulator and a Baines non-rebreathing circuit). If a ventilator is desired, it must be able to accommodate the very small tidal volumes required by these small patients. The ventilatory pressure is approximately the same as in mammals (<20mmHg).
Desflurane and sevoflurane can also be used. These agents provide a more rapid induction and recovery time than isoflurane, but the difference/benefits are not very great. The vaporizers are expensive.
2.3.1. Mask induction
Mask induction is performed easily and quickly (about 5 minutes with Isoflurane) with adequate manual restraint and an appropriate sized mask. Most birds mask down easily with an oxygen flow rate of 1 L/min and at 3% isoflurane. Once the animal is sufficiently relaxed, it can easily be intubated. The bird’s eyes should be closed, a palpebral reflex will be absent and a nictitans reflex will be slow to absent. Animals can often be maintained on a mask alone for short procedures (<10min.). Endotracheal intubation is recommended for longer procedures and/or when ventilation is required.
Intubation in birds is very simple, since the glottis is generally very accessible. Most birds have complete tracheal rings. The use of a cuffed endotracheal tube can lead to pressure necrosis if the cuff is inflated too much since there is no elastic ligament to accommodate the expansion. Traditional ET tubes can be used in larger birds, but the cuff should not be inflated. With smaller birds, a Cole endotracheal tube is used. Cole tubes are used because of their small size (the traditional tubes are not available in the smaller sizes) and because they do not have a cuff (see image below).
Once the bird is intubated, the endotracheal tube is secured to the lower beak with tape and connected to a Baines circuit. The bird is then maintained on isoflurane anesthetic at very low flow rate (<1L/min) and usually at 1-2%.
2.3.3. Ventilatory support
Ventilatory support is required for most anesthetic procedures lasting longer than 15-30 minutes or in cases where the patient ceases to breathe voluntarily. In longer procedures it is very important to assist with ventilation even if the bird continues to breath on its own. This is because the effort made by the patient will not be sufficient to thoroughly inflate the air sacs and provide adequate circulation of air and gases through the air sac system. With the patient breathing on its own, the anesthetist should provide additional full inspiratory breaths at the rate of about 4-6 breaths/minute. This task can also be performed by a mechanical ventilator. Of course, in the situation where the patient ceases to breath on its own, ventilation must be provided immediately.
Recovery from isoflurane anesthesia is normally very rapid and uneventful. The anesthetist must monitor the patient very closely during this period of time since the bird may wake up and jump off the table unexpectedly. Once the gas has been turned off and the anesthetic lines purged of residual anesthetic, the bird should receive oxygen for a few minutes, until it wakes up. The bird will begin chewing, shaking its head, and/or attempt to flap its wings when it is ready to be extubated. The patient should then be held in a towel or wrapped securely and placed in the cage until it is ready to perch (usually about 5-10 minutes).
Recovery may be prolonged due to hypothermia, hypoglycemia, blood loss, anesthetic overdose, or a prolonged procedure.
2.4. Monitoring techniques
In general, avian patients must be monitored very closely during any anesthetic procedure. Because of their markedly faster metabolic rates, the rate of deterioration under anesthesia is also markedly accelerated. The response time required to successfully intervene during a crisis is consequently extremely short. The depth of anesthesia is gauged initially by the palpebral reflex and degree of muscle relaxation; later by the response to stimuli (a toe or wing pinch, feather plucking, surgical stimulation) and cardiac and respiratory parameters. One can estimate the expected physiological parameters using metabolic scaling. Formulas for calculating these values are provided in the Appendix .
Ideal Depth of Anesthesia in a Bird
Pupillary light reflex delayed
Palpebral reflex absent
Nictitating membrane slow or absent
Pain reflexes absent
The cardiovascular system can be monitored in a variety of ways. A traditional ECG can usually only be used in larger birds (macaws, large cockatoos, some amazons). Alternatively, a Doppler can be used on any sized bird and will give an audible heart rate, as well as a subjective evaluation of changes in blood pressure. The Doppler transducer can be placed on any artery or directly on the heart. Common peripheral arterial sites include the palatine, carotid, brachial, medial metatarsal arteries, and the dorsal aorta via the cloaca. A blood pressure cuff can be applied on the distal humerus or femur with the probe on the medial surface of the proximal ulna or tibiotarsus respectively. Normal systolic blood pressure is 90-150mm Hg. A stethescope or esophageal stethescope can also be used, however it may be inconvenient for the anesthetist to listen continuously. Pulse oximetry may be useful to monitor heart rate, however the values recorded are unreliable in birds. Note that a drop in cardiac rate may be observed in response to pain.
The respiratory system can be monitored by simple visualization of the patient, a stethoscope, or a special respiratory monitor attached to the Baines circuit. Respiratory rate and depth should be monitored.
2.5. Supportive therapies
Cardiovascular support should be provided with fluid therapy during prolonged or invasive procedures which may result in blood loss. Intravenous or intraosseous balanced electrolyte solutions are given either as a bolus (20-30 ml/kg) or as a continuous infusion (5-10 ml/kg/hr) with an indwelling catheter. Dextrose can be added when necessary. Blood transfusions may also be needed and are discussed below.
Thermal support should be provided for any anesthetic procedure. Hypothermia can develop very rapidly in birds under anesthesia. The incidence of hypothermia can be reduced by decreasing anesthetic time, minimizing surgical prep solutions and using warm fluids, in addition to providing external heat. Body temperature should be monitored throughout the procedure with the use of cloacal or esophageal probes. Normal core body temperature is usually in the range of 102 to 108F (depending on species). External heat sources, such as circulating warm water or warm air devices should be used routinely. Heat lamps and electric heating pads must be used with great care because they can easily cause burns.
Ventilatory support should be provided as discussed above for prolonged procedures, or those in which the patient stops breathing on its own. Birds are particularly susceptible to respiratory depressant effects of anesthetics. Surgical positioning or manipulation may impede thoracic movements and draping may make visualization of respiration difficult for the anesthetist. Certain surgical procedures can also lead to accumulation of blood and fluids in the air sacs which further disrupt gas exchange in the patient.
2.6. Emergency drugs
Because of the rapid rate at which avian surgical emergencies can develop, it may be prudent to have standard emergency drugs drawn up and ready to use at the start of a procedure.
Baseline physiological parameters can be calculated through allometric scaling. For formulas, see the document in the Appendix .
3. Principles of avian surgery
3.1. Basic principles
Avian surgery requires adherence to three main principles: hemostasis, precision, and speed. Close attention to hemostasis is required to minimize blood loss. Remember that the allowable blood loss in 30g parakeet is only 0.3ml of blood. Surgical precision in dissection is required to minimize soft tissue damage. At the same time, speed results in minimizing anesthetic time. Combining these three principles and becoming accustomed to working with very small structures takes time and practice.
3.2. Patient preparation
The surgical site is generally plucked, not shaved, under full anesthesia. This is a painful procedure. Minimal feather plucking is performed, especially for wild birds intended for release. Skin is then sterilely prepared with chlorhexidine solution. Scrub solutions are too irritating for avian skin and should not be used. The final prep is performed by wiping the surgical site gently with alcohol. The patient is usually placed in lateral or ventrodorsal recumbency and draped with small drapes. If possible, draping should not completely cover the bird so that the anesthetist can properly monitor the patient. Transparent lightweight drapes are often used.
3.3. Special instruments
Small surgical instruments are essential when working with the tiny structures encountered in avian surgery. A special pack of fine surgical instruments should be compiled for use in avian patients. Some ophthalmology instruments can be very useful in an avian surgical pack. Magnification is also very useful in many instances.
Hemostasis can be promoted with the use of several different tools, depending on the situation at hand. Very small hemoclips can be used in certain situations. Electrical cautery instruments must have a very small tip such as that found with micro-ophthocautery instruments and electrosurgical tools (e.g. Ellman Surgitron). Thrombin preparations can be very useful in very delicate areas. Sterile Q-tips are a must for daubing, etc. in place of the usual 4x4 sponges.
Electrosurgical/cautery instruments (Ellman Surgitron, see end of chapter) are extremely useful in avian surgery. They allow for precise cutting with simultaneous hemostatic control. This type of instrument is relatively expensive and may be justifiable only if a fair number of avian surgeries are routinely performed. It is not an essential item.
Suture options for birds usually involve fine monofilament synthetic materials, such as PDS II. When suturing the skin, a taper needle is best, since cutting needles rip right through the delicate tissue paper thin skin. Cutting or taper/cut needles can be used for heavily keratinized areas.
Rigid and flexible endoscopes are very useful in avian surgery. A rigid arthroscope is routinely used for avian laparoscopy. Several models are available. The Wolf scope and the Storz rigid endoscope are both popular. (See the end of this chapter for details on these products)
Laparoscopy is a technique commonly employed in avian medicine to visualize, examine and even sample internal structures of the bird without performing a full laparotomy. The equipment used may vary, but usually involves a small rigid arthroscope, such as the Wolf or Stortz scopes mentioned above. Less expensive and less accurate instruments are available, and in some cases merely an otoscope will suffice.
This technique is most commonly employed for surgical sexing and examination of a bird’s reproductive organs, general exploration of abdominal structures and thoracic structures (e.g. liver, lungs and airsacs), and for biopsy or culture of some of these structures.
The most common indications for a laparotomy in a bird include removal of a gastrointestinal foreign body (esp. lead fragments), a hysterectomy or reproductive exploratory for unresponsive egg-binding, to perform a liver (or diagnostic) biopsy, and to perform an exploratory.
There are several acceptable approaches for a laparotomy in a bird. The choice of approach will depend on the nature of the problem, the size of the bird, and the surgeon's personal preference. Approaches commonly made include a ventral midline approach, a midline-L approach, a midline-T approach, and an oblique approach.
3.6. Some common soft tissue surgeries
Ingluviotomy is the surgical approach to the crop of a bird, often to retrieve a foreign body, resect necrotic crop tissue secondary to burns (hand fed babies), or to correct fistulas.
Incise skin parallel to neck
Enter crop with small stab incision in avascular area
Two layer inverting closure
Soft diet and antibiotics for 7 to 10 days postop
Indications for a proventriculotomy include removal of proventricular or ventricular foreign body (e.g. heavy metal), or to acquire a full-thickness biopsy for Proventricular Dilatation Syndrome.
Proventricular approach is preferable to ventriculotomy due to the thick musculature of the ventriculus.
Incision is made through left 7th and 8th ribs, or on the midline with flap to the left.
Blunt dissection of proventricular suspensory ligaments
Enter proventriculus at isthmus with stab incision
Two layer inverting closure
Postop antibiotics, feed small amounts
Cloacapexy may be needed to resolve chronic, recurring or severe cloacal prolapse that may occur with diarrhea, chronic egg laying, etc.
Midline ventral abdominal incision
Incise caudal abdominal air sacs
Stay sutures placed through cloaca and around posterior rib on both sides
Salpingohysterectomy may be indicated for chronic egg laying, complicated eggbinding, or pathologic uterine conditions.
Left lateral approach
Locate oviduct, ovary, infundibulum
Ligate dorsal suspensory ligament
Cut ligament and oviduct close to ovary
Follow oviduct/uterus to vagina, ligating blood vessels along the way
Ligate uterus at the vagina close to cloaca
Cut ventral ligament attachments
3.7. Orthopedic surgery
The underlying principle of avian orthopedics is to choose the type of repair that will best fit the future function of the bird and be allowed by the "owners" budget. Often times there is a big difference between the decision made for a wild bird vs. a pet bird. The risks and benefits of the various repairs (external vs. internal), the type of fracture (closed vs. open), the age of the fracture, and the prognosis must be considered. Avian bones have a higher calcium content than mammalian bones and, consequently, tend to shatter on impact, producing comminuted fractures. However, this higher calcium metabolism also results in faster bony healing times than in mammals.
3.7.1. Methods of fracture repair - External fixation
Temporary stabilization, e.g. Figure 8 wing wraps
Vetwrap, soft tape
Lightweight material needed
Coat hangers, paperclips, tape
3.7.2. Methods of fracture repair - Internal Fixation
Intramedullary pinning - stainless steel, polypropylene (used in human hand surgery)
Modified KE apparatus - lightweight material used for crossbar
IM/KE combinations - preferred method of long bone fixation
3.7.3. Fracture healing
Fracture healing in birds is different than in mammals. However, as with mammals, healing will vary with the type of fixation and nature of the fracture, depending on stability, blood supply, and presence of infection.
In general with good fixation, one can expect a clinical union in 2-3 weeks with complete repair in 6 weeks. Radiographic union will occur between 3-6 weeks. Healing is much faster than in mammals. It depends chiefly on soft tissue callous formation (very important) and later on endosteal and periosteal callous formation.
Complications of fracture healing may occur when the fracture involves a joint or is very close to a joint (especially the elbow joint). Incorporation of the joint in the healing callous will likely render the joint immobile and the bird non-flighted. As with mammal fractures, infection will delay or prevent healing. In birds, especially those intended to regain functional flight, muscle contraction secondary to the repair or confinement of a wing can render the bird temporarily or even permanently non-flighted. In addition, due to the compact arrangement of the muscles and nerves in the avian wing, any significant soft tissue damage can result in compromised blood or nerve supply and result in a devitalized or nonfunctional wing.
4. References and Resources
4.1. Products mentioned in the text
Ellman Surgitron F.F.P.F. Ellman International Inc., The Ellman Building, 1135 Railroad Ave., Hewlett, NY 11557.
Karl Storz Endoscopes available from many medical distributors.
Thrombin, USP Thrombostat. Parke-Davis, Morris Plains, NJ 07950.
Vet-Lite orthopedic tape
Wolf rigid arthroscope Models 8853.41, 8672.31, Richard Medical Instrument Corp., 7046 Lyndon Ave., Rosemont, IL 60018. Richard Wolf GmbH
4.2. Texts and Articles
Altman, Robert B., et al. Avian Medicine and Surgery. Philadelphia. W.B. Saunders Co., 1997. Chapter 40-47
Bennett, R. Avery, and Alan B. Kuzma. Fracture management in birds. Journal of Zoo and Wildlife Medicine, 23 (1), 1992, pp. 5-38.
Harrison, Gregg J. and Teresa L. Lightfoot. Clinical Avian Medicine. Palm Beach, FL : Spix Pub., c2006. Chapters 33-35.
Hernandez-Divers, Stephen J. Minimally invasive endoscopic surgery of birds. Journal of Avian Medicine and Surgery 19(2), 2005: 107-120.
Ludders, John W. and Nora Matthews. Chapter 20E Birds. In: Lumb & Jones' Veterinary Anesthesia, 3rd ed., Baltimore : Williams & Wilkins, 1996, pp.645-669.
Ludders, J.W. Inhaled anesthesia for birds, IN Recent Advances in Veterinary Anesthesia and Analgesia: Companion Animals, R.D. Gleed, J.W. Ludders (Eds.) IVIS Website .
Machin, Karen L., and A. Livingston. Assessment of the analgesic effects of ketoprofen in ducks anesthetized with isoflurane. AJVR 63 (6), 2002: 821-826.
Mitchell, Mark and Tully, Thomas. Manual of Exotic Pet Practice. St. Louis, MO. Saunders Elsevier, 2009. Chapter 10.
Murray, Michael J. Soft tissue surgery. Seminars in Avian and Exotic Pet Medicine, Vol. 2(2), 1993.
Paul-Murphy, J. and J. Fialkowski. Injectable anesthesia and analgesia of birds, In: Recent Advances in Veterinary Anesthesia and Analgesia: Companion Animals, R.D. Gleed, J.W. Ludders (Eds.) IVIS Website .
Redig, Patrick. Avian orthopedics. Seminars in Avian and Exotic Pet Medicine, vol. 3 (2), April 1994.
Redig, Patrick. The use of an external skeletal fixator-intramedullary pin tie-in (ESF-IM Fixator) for treatment of longbone fractures in raptors. Lake Worth, FL. Zoological Education Network, 2000.
Ritchie, Branson W., et al. Avian Medicine: Principles and Application. Lake Worth, Fla., c1994: Chapters 13, 39, 40, 41, 42.
Samour, Jaime. Avian Medicine, Second Edition. St. Louis, MO. Mosby Elsevier, 2008, Chapter 4.
Zebisch K, Krautwald-Junghanns ME, Willuhn J. Ultrasound-guided liver biopsy in birds. Veterinary Radiology & Ultrasound, 45 (3), 2004 : 241 - 246.