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|I. A brief review of clinically relevant avian respiratory anatomy & physiology*
|II. Anesthesia in clinical practice
*For more detailed information on avian respiratory anatomy & physiology, view the RACE-approved webinar recording “Avian Respiratory Anatomy, Physiology & Diseases: An Overview”, presented by Dr. James Morrisey.
Download a PDF version of Dr. Crosta’s abstract.
Anatomy and physiology
The high energy demands required for flight and the high aerobic rate of this activity create high demands for oxygen. For this reason, the respiratory apparatus of the bird is likely the most different from mammals. The trachea consists of complete cartilaginous rings which interdigitate. The sound-producing organ of birds is the syrinx. Unlike the mammalian larynx, birds do not have vocal cords. Instead they possess two vibrating syringeal membranes. Depending on the localization of the syrinx, this structure can be tracheal, bronchial, or the most common type: tracheobronchial.
Birds lack a diaphragm; therefore the thoracic and abdominal cavities are fused to form a single coelomic cavity or coelom. The avian lungs are located cranio-dorsally within the coelom. The primary bronchi are formed by the upper division of the trachea, usually just distal to the syrinx. Four series of secondary bronchi are named based on their anatomical location: medioventral, mediodorsal, lateroventral, and laterodorsal. Gas exchange occurs at the level of the parabronchi or tertiary bronchi, which originate from a division of the secondary bronchi. The avian lungs are approximately ten times more efficient at gas exchange or extracting oxygen when compared to mammals.
Both inhalation and exhalation are active actions, which require the assistance of respiratory muscles. In the avian respiratory cycle, inspired air passes through the trachea, passes through the lungs, and enters the air sacs. Expired air exits from the air sacs, passes again through the lungs, and is expelled from the trachea. Most birds have nine air sacs: paired cervical, cranial thoracic, caudal thoracic, and abdominal air sacs as well as a single clavicular air sac. Air sacs play no role in gas exchange. Instead they work like bellows, sucking in inspired air when expanding and eject air when they contract.
Functionally the avian lungs are divided into neopulmo and paleopulmo systems. The paleopulmo system is found in all bird species and makes up at least 75% of lung tissue. The neopulmo system, which is less efficient in gas exchange, is absent in penguins, and very reduced in Anseriformes and Psittaciformes. The neopulmo system is extremely developed in Galliformes, Columbiformes, and Passeriformes.
There are so few advantages to injectable anesthesia in birds. Probably, the only situation in which injectable anesthesia is the first choice, is a field setting, when a proper vaporizer is not available. Injectable drugs most commonly used in birds include benzodiazepenes (i.e. diazepam, midazolam), alpha-adrenergic agents (xylazine, medetomidine), opioids (butorphanol, buprenorphine), and the dissociative anesthetic agent, ketamine. Recently, there is an increasing interest in the use of Alfaxalone in birds, but there are only few publications about it.
Pre-anesthesia is routinely used in diurnal birds of prey, like falcons to limit stress during gas anesthesia induction, avoid damage to primary feathers, and to reduce the amount of inhalant anesthetic required for maintenance. A standard regimen used is medetomidine (50 μg/kg) and ketamine (12.5 mg/kg). Midazolam (2 mg/kg intranasal) is regularly used in psittacine birds.
The minimum alveolar concentration (MAC) in birds has been defined as the minimum concentration of anesthetic needed to prevent that a bird reacts to a painful stimulus. Another way to evaluate the strength of an anesthetic, is to determine its ability to induce respiratory depression and apnea. For this purpose, the anesthetic index (AI) is used. The lower AI, the higher the chances of apnea.
The most commonly used inhalation agents are isoflurane and sevoflurane. For induction with isoflurane, the starting point is typically around 2 L/min oxygen and an isoflurane concentration about 4-5%. Compared to isoflurane, sevoflurane is less soluble and less powerful as an anesthetic, which leads to more rapid induction and recovery times. Sevoflurane is also not an irritant for the respiratory airways, and therefore this gas does not induce struggling during induction.
All open, non-rebreathing circuits, such as Magill, T Ayre, Mapleson, Jackson-Rees and Bain, can be safely used in birds. One of the major advantages of these open circuits, is that the response of the patient to the changes in anesthetic concentration are quite rapid. The oxygen flow rate should be two to three times the ventilation capacity of the patient or 150-200 ml/kg/minute.
Cole’s tubes are the most commonly used endotracheal tubes in birds. They allow a good sealing of the trachea, and they limit the dispersion of air with no risk to the tracheal epithelium. Since the avian trachea has complete cartilaginous rings, cuffed tubes are not recommended. When forced to use a cuffed tube, the balloon should never be inflated. If the balloon is inflated, necrosis of tracheal mucosa can develop up to 15 days later.
Intermittent positive pressure ventilation is best provided with the use of pressure ventilators in the avian patient.
Monitoring the patient
Several parameters must be monitored during anesthesia, including respiration and tidal volume, carbon dioxide levels, heart rate, oxygen levels, and temperature. Birds are small patients and they cool down easily, therefore it is critical to monitor both the temperature of the environment and the temperature of the avian patient.
All birds should receive fluids during surgery. At the very least, it is wise to have vascular access ready for use in the case of an emergency. The most commonly used fluids are lactated Ringer’s solution (LRS) and LRS with dextrose. The most popular routes to deliver fluids in birds are intravenous (IV) and intraosseous (IO).
About the presenter
Dr. Lorenzo Crosta is an Associate Professor of Avian and Zoological Medicine at the University of Sydney School of Veterinary Science, Australia. He serves as the Director of the Avian, Reptile, and Exotic Pet Hospital, and in 2019 he was named the T.J. Lafeber Avian Practitioner of the Year. Dr. Crosta earned his Doctorate of Veterinary Medicine from the University of Milan in 1989. He first worked in private practice, then served as the Veterinary Director of Loro Parque in Tenerife, Spain from 2000 to 2005. Dr. Crosta also served as the Consulting Veterinarian to the Brazilian Government for the Spix’s and Lear’s Macaw Recovery Program from 2000-2014. After Loro Parque, Lorenzo returned to Italy where he earned a PhD in Veterinary Clinical Sciences from the University of Turin in 2009. Lorenzo has paired his love of teaching and enjoyment of public speaking with this ability to speak four languages. He has lectured on avian medicine in many countries ranging from the United States to Brazil and Australia, from Hungary to Portugal, and from Israel to the Arab nations [MORE].
Due to technical difficulties during the live event, Dr. Crosta has generously shared these 13 videos posted below:
Although Dr. Crosta was able to answer many questions during the live event, the remaining questions were answered by email and are posted below:
How long does the effect of midazolam last?
Depends on the species, but in psittacine birds at 2 mg/kg the average effect lasts between 20 and 40 minutes.
Have you used flumazenil as a reversal?
I have never had the need except for one time in Brazil while doing field work, but unfortunately, we did not have the reversal agent. The birds slept 2 hours and woke up uneventfully.
What is your opinion on alfaxalone IM for birds, with or without other drugs (midazolam, butorphanol…)?
LafeberVet: During his presentation, Dr. Crosta did briefly touch upon alfaxalone. He said that he has only started to use it since he’s been in Australia. In psittacine birds, he uses a dose of 2-5 mg/kg IM.
I always use premedication with my birds. I usually use butorphanol and midazolam (0.2mg/kg). Should I stop this?”
LafeberVet: Dr. Crosta did discuss midazolam… He uses midazolam quite a bit, particularly in psittacine birds and recommends a dose of 1-3 mg/kg intransal. He also mentioned use of butorphanol, but cautioned attendees on the standard possible risks associated with this drug (sedation, respiratory depression).
Do you have an anesthetic pre-medication preference for orthopedic cases such as wing fractures?
Yes, in this case, I prefer to use meloxicam only pre-op (0.5 – 2.0 mg/kg, depending on species) and after the surgery I evaluate other options. Butorphanol is a good choice.
Can dexmedetomidine be used in place of medetomidine?
Yes, at the same volume-dose, but I have very little experience with it.
Please post premed drug dosages
LafeberVet: Dr. Crosta actually recommended midazolam (1-3 mg/kg) intranasal (or less ideally IM) in psittacine birds. He also mentioned use of butorphanol in companion birds, but cautioned attendees about the possible side effects, like respiratory depression.
In falcons, he recommended a protocol using ketamine (12.5 mg/kg) and medetomidine (50 µg/kg), which was developed at the Dubai Falcon Hospital. Dr. Crosta did caution that even falcons above 1 kg body weight should not receive more than the dose for a 1 kg bird.
What about the [use of] continuous rate infusion (CRI)?
As a rule, to place an intravenous catheter, you have to anesthetize the patient beforehand. Therefore, there are very few reports about CRI in birds, and most are in large birds, where it is easier to place an IV catheter without anesthesia.
Please see Müller K, Holzapfel J, Brunnberg L. Total intravenous anaesthesia by boluses or by continuous rate infusion of propofol in mute swans (Cygnus olor). Vet Anaesth Analg 38(4):286–291, 2011.
Do you have any experience with zoeletil (tiletamine HCl and zolazepam HCl) as a pre-anesthetic in birds of prey?
We use tiletamine-zolazepam as a general anesthetic, more than a pre-anesthetic, but not in birds. It is the injectable anesthetic of choice for some marsupials.
Can we do injectable sedation and anesthesia for falcons/raptors?
LafeberVet: I think you wrote this question long before Dr. Crosta discussed falcons in particular, but Dr. Crosta recommended a protocol using ketamine (12.5 mg/kg) and medetomidine (50 µg/kg), which was developed at the Dubai Falcon Hospital. Dr. Crosta did caution that even falcons above 1 kg body weight should not receive more than the dose for a 1 kg bird.
Atipamizole—I’m not familiar…
LafeberVet: Atipamizole hydrochloride (Zoetis) is a selective alpha-2 antagonist used to reverse anesthetic agents, like dexmedetomidine and medetomidine. Additional information can be found at https://www.sciencedirect.com/topics/pharmacology-toxicology-and-pharmaceutical-science/atipamezole.
We get a lot of donated endotracheal (ET) tubes which are cuffed (I work exclusively with seabirds including LOTS of penguins). We don’t inflate the cuff but sometimes still have problems such as blood on the end of the ET tube on extubation (despite trying to keep the birds head as still as possible and being extremely careful if we have to change position during anesthesia). In your opinion, would removing the cuff altogether from the tube reduce the incidence of these injuries?
I am afraid if you cut the tube above the cuff and reshape it, it could even be more traumatic than before. I would act in this way: use a smaller diameter tube and customize a step by rolling some layers of Vet Wrap above the cuff. In this way you are basically imitating the Cole’s tube.
Do you have the same concerns with mammals where you have to be careful to detach the tube from the breathing circuit as to not damage the trachea when flipping?”
LafeberVet: Yes! Absolutely.
In the case of intubation of penguins, should we intubate both sides of trachea?”
LafeberVet: Actually a short endotracheal tube that ends before the bifurcation is typically selected instead.
Thoughts on length of time for pre-oxygenation and post-oxygenation?
Depends a lot on the mental status of the patient. The average is 2 minutes pre-operatively. Post-op until the patients wakes up.
Regarding induction, can you explain what you mean by smooth and gentle restraint please?
I think the LafeberVet video “Parrot Handling & Restraint” explains it perfectly.
Does not the induction chamber increase the metabolic acidosis status as happens with cats induced in these chambers?
Clinically this does not seem to be so, however, I do not think there are studies on this topic.
How does desflurane compare?
I am sorry I have never used it.
Granone TD, de Francisco ON, Killos MB, et al. Comparison of three different inhalant anesthetic agents (isoflurane, sevoflurane, desflurane) in red-tailed hawks (Buteo jamaicensis).Vet Anaesth Analg. 2012 Jan;39(1):29-37.
Does sevoflurane have the potential of lowering calcium metabolism as well as isoflurane?”
LafeberVet: We mentioned this briefly during the Q+A session. Dr. Crosta mentioned that he was not sure, but a quick literature search did find that there is research to suggest sevoflurane can also decrease calcium. One of these papers can be found here: https://www.ncbi.nlm.nih.gov/pubmed/12170060.
Do you find small birds especially (budgies, canaries) pass away almost immediately after turning on isoflurane? What could be the potential cause/solution?
Darryl Heard wrote a nice paragraph in the book by Brian Speer’s “Current Therapy in Avian Medicine and Surgery” (Elsevier 2016). Look at: “Why Do Birds Not Recover or Die?”, page 613.
Would you always induce birds with 4-5% isoflurane even if they might have some cardiovascular/respiratory compromise, or would you incrementally increase it from a lower percentage?
In cases of mild respiratory distress, there is a clear evidence the anesthesia will improve the respiration of the patient (we believe this is due to the elimination of anxiety). If there is a severe respiratory issue, we may look into a different approach. Always try to stabilize the patient beforehand.
At which pressure do you ventilate intermittent positive pressure ventilation or IPPV?
Generally between 8-12 cm H2O
How many times per minute should intermittent positive pressure ventilation (IPPV) be done in anesthetized birds if no ventilator is available? What pressures are safe?
In this case I would stay around 20 breaths per minute.
Pressure should not exceed 10 mmHg
Anesthetic index is also lower in birds for other volatile anesthetics, like sevoflurane? There are not publications.
I am not aware of papers about anesthetic index for sevoflurane in birds, but there are some papers about its “minimum alveolar concentration” or MAC.
Botman J, Gabriel F, Dugdale AH, Vandeweerd JM. Anaesthesia with sevoflurane in pigeons: minimal anaesthetic concentration (MAC) determination and investigation of cardiorespiratory variables at 1 MAC. Vet Rec (178(22):560, 2016 doi: 10.1136/vr.103654
Can you please expand on the adjustments you make to the small animal ventilator (SAV) for birds?
The problem is that the measurement of the tidal volume in birds is not well standardized.
Do you use the same formula for calculating the tidal volume of birds as you use for mammals?
LafeberVet: Yes, the same formula of approximately 10-15 ml/kg is used to calculate (or rather estimate) tidal volume.
Can I use warm water inside the bubbler?
Sure you can.
What face mask do you use for hornbills, toucans, other long beaked birds that provides a good seal?
LafeberVet: For species like this, you need to create a makeshift face mask. Depending on the size of the bird, a 1- or 2-L soda pop bottle can be used (trimmed to fit with a latex glove over the cut end to create a seal). The photograph shown in the lecture outline section above illustrates a makeshift face mask used in a penguin.
How are you attaching the capnograph onto the 2 mm connectors without a side port?
There are capnographs that have a direct connection, but I do not have any picture with me.
You talked about Doppler, for the heart rate measurement or at list flow listening, and then you talked about blood pressure measurement. Is Doppler your pressure measurement? Where do you put your cuff?
A Doppler monitor will only detect the heartbeat. Blood pressure can be detected with a small animal cuff on the leg, or on the wing (humerus).
In the States, injectable meloxicam has been on backorder . Can you give oral prior to surgery? Or is injectable Onsior (robenacoxib) a better option?
You can give meloxicam orally before the surgery; the volume is so small that there is no risk of regurgitation.
How many days post op can you use meloxicam?
Depends on the surgery, however, there are studies done in birds with proventricular dilatation disease that show long term use of meloxicam is relatively safe, provided that you maintain good hydration in the patient.
Do you use nerve stimulators for local blocks?
No, but some pilot studies have been done in large birds.
d’Ovidio, Noviello E, Adamio C. Nerve stimulator-guided sciatic-femoral nerve block in raptors undergoing surgical treatment of pododermatitis. Vet Anaesth Analg 2015 42(4):449-53.
Any protocol preference for post-operative pain aside from meloxicam?
Butorphanol is a good choice.
What’s your opinion on the use of tramadol as a post-surgical analgesic?
Good, but there are very few studies and mostly in birds of prey or penguins. In theory, tramadol should last longer than butorphanol, but in a study in Amazons it was shown to last only 6 hours.
Sanchez-Migallon Guzman D, Souza MJ, Braun JM, et al. Antinociceptive effects after oral administration of tramadol hydrochloride in Hispaniolan Amazon parrots (Amazona ventralis). Am J Vet Res 73(8):1148-1152, 2012.
If you are in a hot field situation, such as Mato Grosso in western Brazil, what alternative means can you suggest for bringing the bird around in your hands without using a towel?
I would transfer the patient to a transport box.
AIR SAC CANNULAS
Don’t you think that it can be better to tie the air sac tube to the last two ribs, to avoid movement or displacement?
To do so one would be rather cranial and the risk of the leg displacing the tube is higher.
Do you use antibiotics post-op when placing an air sac cannula to prevent external contaminants?
Yes. There are three parameters that I use to select the antibiotic in each case.
- If the bird is already on an antibiotic, I keep it on that antimicrobial.
- In case it is a wild animal or zoo bird, I use enrofloxacin so I can limit treatment to once daily (less stress)
- Otherwise I go with amoxicillin and clavulanic acid.
How do you manage air sac tubes postoperatively?
Depends on the purpose of the tube. If there is the risk of tracheal occlusion post op, I leave the tube for 5-6 days.
Visit LafeberVet’s “Air Sac Cannula Placement in Birds” for additional information.
Do you always place intraosseous (IO) catheters under sedation/anesthesia?
In critical birds, I sometimes place the IO cath without anesthesia.
…or can you use local?
LafeberVet: Yes, certainly. The needle is advanced down to the level of periosteum and a small bleb of anesthetic solution is infiltrated into the area. It is important to palpate carefully and feel very comfortable with your landmarks before placing the anesthetic, because this small bleb can distort the appearance of the anatomic landmarks.
If you have a critical bird, would you still consider anesthesia? Basically what is the benefit to risk considerations of placing IO catheter in critical bird not going for surgery but rather rehydration?”
The typical mistake most of us do, is to consider the IO catheter a last and extreme measure, to be used only in critical cases…those cases by definition have a bad prognosis and can go bad independently of IO catheterization. I tend to use the IO cath in small birds, or whenever I want to leave the catheter some days post op.
Any reason for not recommending the metatarsal vein for catheters?
I do recommend the metatarsal vein in long-legged birds, like flamingos, storks, cranes, some birds of prey (goshawks), and most Anseriformes and pelicans. In psittacine birds and most falcons the vein is too short.
I have heard fluids like Plasmalyte A are more physiologically similar to Ringer’s Lactate to birds. True?
Plasmalyte contains almost no calcium, therefore I would not recommend it with isoflurane anesthesia.
Will calcium gluconate administered intramuscularly (IM) not cause necrosis or reaction in the place of injection? I only heard of doing it IV.
You are right [calcium gluconate] should be given IV very, very slowly, however this means the bird should already be anesthetized. This is why one colleague suggested to dilute calcium gluconate and inject it IM. You will not inject it in one site only, but divide it in several small injections: in this way I never saw muscle necrosis.
You mentioned small injections IM of Ca gluconate versus hypercalcemia: What volumes? Obviously patient size dependent but do you have a guide?
40 mg/kg diluted. See above
In chickens, and in food animal in general in the USA, it is restricted to use scheduled drugs, like butorphanol. What would you recommend as a pre-op cocktail for these birds?
I am sorry, but I never worked in the US… in this case I would think to meloxicam only. Is butorphanol totally restricted in chickens, or there is a withdrawal time?
LafeberVet: In Backyard Poultry Medicine & Surgery, Angela Lennox writes in Chapter 12 (p. 167): “Sedation, anesthesia, and analgesia of avian species are well described, and the author has found that poultry do well with pre-anesthetic, induction, maintenance, and analgesic protocols described for psittacines. Many minor wounds can be addressed with sedation (the author recommends butorphanol 2-3 mg/kg and midazolam 0.5 mg/kg IM) with lidocaine 2 mg/kg as a local or regional block.”
I just see chickens. Mainly I do anesthesia for crop impaction and coyote attacks. Would a dorsal recumbency be best for anesthesia and what would be the best opioid for analgesia?
I would go for dorsal recumbency for sure. If you can, use butorphanol, or tramadol.
Please see above.
Could you explain again why including the whole head in the mask prevents the dive response or apnea?
Since in most cases the pressure receptors are located at the base of the beak, if the mask is putting pressure on those receptors it may stimulate them and lower the heart rate.
Does hybridizing gyrfalcons with peregrines for Middle Eastern desert conditions have any clinical effect on induction or ease of anesthesia?
I have seen more Gyr x Saker hybrids, than Gyr x Peregrines, however, there are some rumors that different hybrids respond differently to many drugs, however this has not really been proven.
For your information, it is very likely that hybridization will be banned in Europe soon. In some countries it has been already been banned.
What type of non-absorbable suture do you recommend for birds?
The suture size and type depend of what tissue I need to suture. However, even if Vicryl seems to hold the knot better, as a general rule I tend to use monofilament sutures, such as Monocryl and Monosyn. The most [frequently] used are 4-0 and 5-0.
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Crosta L. Avian anesthesia webinar. Jan 5, 2020. LafeberVet website. Available at https://lafeber.com/vet/avian-anesthesia-webinar/