Anesthetic Monitoring and Support: Improving the
Odds in Exotic Patients
Angela M. Lennox, DVM, DABVP-Avian
Exotics Track
2012 ISVMA Annual Conference Proceedings
Equipment for anesthesia
Delivery of gas anesthesia in exotic patients is an inexact science, and requires
significant practice and attention to detail. Changes in any single portion of the
anesthetic delivery system can result in uneven or unpredictable delivery of anesthetic,
with potentially dangerous results. For example, an anesthetist familiar with typical
results at certain gas and oxygen flow rates may find the same setting unacceptably high
or low with a single change in the system (leakage, change in efficiency of the
scavenging system, changes in vaporizer calibration).
Recommendations for anesthetic systems for exotic patients are readily available. A
non-rebreathing anesthetic circuit is required, with the smallest available bag, and
reduced dead space.
Bags and tubing should be inspected for leakage. Precision vaporizers are inspected
and calibrated regularly, as often as every 2-3 years.
Preparation of the patient
Pre-anesthetic blood work
Pre-anesthetic blood work provides useful information that may help identify factors
negatively impacting surgical survival; ideally these should be addressed prior to and
during the surgical procedure. In particular, these include anemia, hydration,
hypoglycemia, and hypoproteinemia. Ideally, pre-anesthetic blood work would include a
complete blood count (CBC), and biochemistry panel; however, the benefits of blood
work must be weighed against the risks of collection in each individual patient. Factors to
consider include the availability of in-house, low sample volume modalities vs. the use of
out sourced testing which may require larger sample volumes and delayed results (hours
to days). At the very minimum, if patient size and condition does not allow analysis of a
biochemistry panel, evaluation of the blood smear, PCV and TSS can be performed on
any sized patient.
Pre-Surgical Fasting-Mammals
The purpose of fasting is to reduce the risk of regurgitation in those species capable of
vomiting (primarily carnivores), and in some cases, to minimize ingesta in the stomach
and lower gastrointestinal tract. For practical purposes, the only exotic companion
mammal species that are routinely fasted are ferrets and other exotic carnivores. Most
other commonly encountered species either do not vomit, possess a rapid GI transit
time, or have a well-developed cecum and an exceptionally long GI transit time. It is
extremely useful to remove food from the enclosures of rabbits and guinea pigs two
hours prior to anesthesia, as these species tend to accumulate food in the oral cavity,
which can complicate intubation or other oral procedures.
Pre-Surgical Fasting-Birds
The purpose of fasting is to minimize ingesta in the crop and proventriculus, and to
reduce the bowel “volume” during celomic surgery. The GI transit time of most
psittacines is 3-5 hours dependent of consistency of ingested material. Passerines and
Rhamphastids have very short transit times of usually less than an hour and should not
routinely be fasted.
Fasting time therefore depends on the species of bird, overall condition, and the
presence of conditions that may impact gastrointestinal motility. In general, psittacines
with a normal GI transit time should be fasted 4 hours or greater. Water can be removed
and crystalloids administered subcutaneously at that same time. Timing of fasting for
birds with hypomotility can be difficult; ideally at minimum, the crop should be completely
empty. In these cases, care must be taken throughout surgery and handling to limit the
risk of aspiration from regurgitation.
Pre-Surgical Fasting-Reptiles
GI transit time in reptiles is extremely variable and dependent upon many factors.
Fasting may be considered in patients undergoing surgery of the gastrointestinal tract,
but in most cases, reptiles are not fasted prior to surgery.
Mammals
Pre-anesthetic drugs
The benefits and safety of “multi-modal” anesthesia have been demonstrated in humans
and many veterinary patients, and may provide the same advantages for avian patients.1
In general, pre-anesthetic agents provide a smoother induction, reduce the amount of
general anesthesia required, and provide pre-emptive analgesia. Agents most commonly
advocated in exotic companion mammal medicine include midazolam, diazepam,
dexmedetomidine, ketamine and opioids (butorphanol, hydomorphone, buprenorphine
and others). (Table 1). Choice of pre-anesthetic depends on species, patient condition,
and to a great degree, practitioner experience.
The use of pre-anesthetic agents can increase recovery time, which may be of concern
to practitioners accustomed to rapid recovery in patients receiving inhalant agents only.
A calm, gradual recovery is actually ideal, and can be differentiated from an abnormal
recovery by careful observation and monitoring.
Vascular access
Vascular access is ideal for all surgical patients, in particular to allow surgical fluid
support and for rapid administration of emergency drugs. Intravenous and intraosseous
catheters are the two options utilized; each has distinct advantages and disadvantages
(Table 2). The ideal fluid and fluid rate for surgical support in all exotic mammal species
is unknown; however, for routine use the authors and others use crystalloids at 10
ml/kg/hour. The use of colloids and other fluids are discussed in detail in another
proceedings.
Analgesia
Most information on exotic mammal analgesia comes from laboratory animal medicine,
and a handful of controlled studies in selected species. The use of opioids is common
(table 1).
Local anesthesia can be utilized in exotic mammal patients.1 While ideal effective
dosages for all species are undetermined, lidocaine and bupivacaine at 2 mg/kg each
are commonly used for local infiltration, incisional and testicular blocks. There is also no
data on the impact of incisional/splash blocks on incision healing time; however, no
clinically significant delays have been noted.
Induction of anesthesia
Anesthetic induction is most commonly performed with inhalant agents delivered by
facemask. Proper use of pre-anesthetic agents reduces or eliminates potentially
dangerous stress and struggling, and reduces concentrations required for induction.
Most experienced practitioners no longer advocate mask or chamber induction with
inahalant drugs as a sole agent.
Injectable single agents or combinations are used for induction of anesthesia as well.
Some are simply higher dosages of agents used in low dosages for pre-anesthesia.
Some can be delivered intramuscularly, but some require IV administration. Some
agents are reversible, and some are associated with higher complication rates than
others (Table 3).
Surgical Monitoring
While a number of monitoring devices have been used successfully in exotic companion
mammals, the most valuable tool is the experienced, attentive veterinary assistant.
Table 4 summarizes monitoring devices.
The surgical emergency
Procedures for how to address anesthetic emergencies should be discussed and
planned out well in advance of the actual emergency. Dosages for all emergency drugs
based on patient weight should be posted in the surgical suite, and drugs should be
immediately available.
Decreases in blood pressure
Decreased respiratory rate
Respiratory arrest
Bradycardia
Cardiac arrest
Post surgical monitoring and care
Extubation occurs when the patient is breathing well and there is evidence of some
glottal tone. Swab the mouth and glottis to remove mucus prior to extubation.
Provide warmth and fluid support all the way through recovery.
Monitoring during recovery
Provide warmth, constant monitoring, and fluid support all the way through recovery until
the patient is ambulatory and alert. After surgery, fluid rates can be reduced to
maintenance (2-3 ml/hour) with additions calculated for dehydration and surgical loss. In
general, fluid support is discontinued when recovery is complete; at this point some
mammals often to object to and investigate the catheter and fluid line.
The delayed or poor recovery
When patients do not experience a smooth, rapid recovery, every attempt should be
made to elucidate a cause, if possible, and provide treatment (Table 5). It must be kept
in mind that patients administered pre-anesthetic drugs may have a delayed recovery
when compared to those that have received inhalant gases only. This is normal, and to
be expected, but must be distinguished from a medical/surgical complication.
Pain is a potential cause of apparent delayed recovery, especially in those that received
analgesia more than 2-3 hours prior. The painful patient is often able to stand and may
resist handling, but is not willing to move, and may display elevated respiratory and/or
cardiac rate. In contrast, the hypovolemic patient is weak and often unable to stand or
offer resistance to handling.
Birds and Reptiles
Pre-anesthetic drugs
The benefits and safety of “multi-modal” anesthesia have been demonstrated in humans
and many veterinary patients, and may provide the same advantages for avian patients.1
In general, pre-anesthetic agents can provide a smooth induction, reduce the amount of
general anesthesia required, and provide pre-emptive analgesia. Agents most commonly
advocated in avian medicine include midazolam and butorphanol. (Table 1).
The use of pre-anesthesia in reptiles is reported as well, but actual research is sparse
and sometimes contradictory (Table 1).
Vascular access
Vascular access is discussed in details in other proceedings. The ideal fluid rate for
surgical support in psittacines is unknown; however, the authors and others use 10
ml/kg/hour. Abou-Madi reports 10-12 ml/kg/hr.
Even less is known about the ideal surgical rate of fluids for various reptile species, but
is assumed to be much lower than that of birds. The author uses 1-2 ml/kg/hr.
Analgesia
Current research supports butorphanol as the most effective and safe analgesic for
psittacines available thus far. However, it should be kept in mind research has focused
on a limited number of apparently healthy avian species, dosages, and administration
routes, and for specific applications, e.g. pain response. Reported dose ranges vary, and
studies have utilized dosages from 1-5 mg/kg administered IM, IV and/or PO.
Butorphanol can be administered as a part of pre-anesthesia, delivered as constant rate
infusion with fluids throughout surgery and/or post surgically at recovery. It should be
kept in mind the duration of action of butorphanol in psittacine species is unknown, and
appears to be relatively short. A study on plasma concentrations of butorphanol in
healthy Hispaniolan Amazon parrots showed a significant decrease 2 hours post
intravenous administration. If butorphanol is used as a pre-anesthetic drug, and the
combined presurgical and surgical period is lengthy, there may be no effective analgesia
in effect at recovery.
Analgesic studies in reptiles are few and often contradictory. Doses are suggested, but
actual efficacy is uncertain.
Local anesthesia can be utilized in avian and reptile patients. Unpublished work with
birds using sedation and local analgesia alone gives support to efficacy (Lennox);
however, studies using local analgesics in avian or reptile surgical patients, or in
psittacines in general are lacking. Lidocaine and bupivacaine at 1-2 mg/kg each have
been used by one author for a surgical incisional block (Lennox). As exact duration of
action is unknown, a portion of the total calculated dose can be retained for use at the
conclusion of surgery, in particular as a splash block of the closed musculature. There is
also no data on the impact of incisional/splash blocks on incision healing time; however,
no clinically significant delays have been noted.
Preparation of the surgical suite
The following check list is helpful for preparation of the surgical suite before induction of
anesthesia. Thorough description of surgical instruments, equipment and suture
selection are available elsewhere.
1. Temperature: conservation of body temperature during surgery is important. The
authors have found that warming the surgical suite itself is helpful, in addition to
the use of heating pads and other devices.
2. Instruments/Equipment: All pre-prepared and immediately available.
3. Monitoring equipment: 20 plus years of practice have seen an evolution in the
numbers and types of monitoring devices available and practical for avian
patients. Operator familiarity with the placement and operation of monitoring
devices in these patients is essential, as patient size can impact ease of use and
efficacy of any equipment. Perioperative and intraoperative failure of high tech
equipment is common; therefore anesthetists must be able to trouble shoot
rapidly, and if a particular monitoring device cannot be quickly restored, default to
a lower technical monitoring technique (e.g. replacement of Doppler with a
stethoscope). Surveys of experienced surgeons demonstrate a wide variety in
preferred monitoring equipment; however the most commonly cited key to
success is anesthetist familiarity and experience. Table 3 outlines common
monitoring devices used in avian and reptile patients.
4. Emergency drugs (see below).
Anesthetic induction and maintenance
Induction of anesthesia is commonly performed with injectable drugs in reptile patients,
as mask induction can be extremely prolonged in species capable of breath holding.
Multiple combinations are described. The author prefers IM administration of Alfaxan at
5-20 mg/kg, followed by intubation and maintenance with isoflurane.
In birds, isoflurane is the induction and maintenance drug of choice after a 25-year
history of use in avian medicine. Sevoflurane is advocated as well, with reported
advantages including even more rapid induction and recovery, and lack of noxious odor.
The authors are unaware of current data comparing survival rates and safety of these
two inhalant agents in birds; therefore, choice appears to be based on availability and
personal preference. A 1999 study comparing induction/recovery in various psittacine
species indicated recovery times were not significantly different, although there was
slightly less ataxia in the sevoflurane group. No pre-anesthetic agents were used in this
study.
All patients are ideally intubated; however, mucus obstruction is a potential complication
in smaller patients. For this reasons, some surgeons prefer to only intubate larger
patients, for example, patients above 100 g only. Tube choice depends on patient size.
In birds, it should be kept in mind that the relative diameter of the trachea along its
length is not the same in all avian species. In other words, the diameter of the trachea of
Amazona species is similar throughout the length. In contrast, the diameter of the
trachea of the macaw and cockatoo rapidly decreases proximally. Therefore, an
endotracheal tube that appears appropriately sized based on the appearance of the
glottis is too large when advanced into the distal trachea. Oversized endotracheal tubes
are associated with post-intubation stenosis in multiple species, including birds. In
general, advance the tube the minimal distance required for security, and keep the neck
straight to prevent kinking of the trachea and pressure against the tip of the tube.
Surgical considerations
Actual surgical techniques are discussed elsewhere. The authors have compiled a
number of observations that have been useful during procedures and at recovery.
1. The longer the anesthetic procedure, the deeper the plane of anesthesia, even if
settings are kept the same throughout. In birds, this is likely due to recirculation
of gases within the air sacs. Gradually decrease anesthetic levels over time,
especially in extended (> 30-45 minute) surgeries.
2. In birds, the most useful gauge of anesthetic depth appears to be respiratory and
cardiac characteristics, for example, respiratory rate and effort (depth), and
cardiac rate, rhythm and intensity obtained from an audible Doppler. Trends in
the force of the signal may correlate with changes in blood pressure. Most
reptiles do not spontaneously breathe during surgery and must be ventilated.
3. Painful stimulation affects the level of anesthesia required. Birds appear to react
more to manipulation of the skin than to manipulation of internal organs;
therefore anesthetic levels must be adjusted accordingly.
4. In birds, increases in respiratory effort may indicate occlusion of the endotracheal
tube, which is common in smaller patients with tubes less than 2.5 mm ID. In
these cases, extubation and reintubation with a new tube, or maintenance by
face mask may be required.
5. In birds, during surgery, the cloaca will become distended with urine and/or feces
after about 30-45 minutes of surgery. In some cases this appears to be linked
with cardiovascular instability, likely due to increased ureteral pressure. Gentle
expression of the cloaca and removal of contents has been observed to result in
rapid correction of abnormalities such as bradycardia and shallow respirations.
6. The most dangerous period of anesthesia appears to be the recovery period (socalled “last stitch” syndrome, reported universally by avian surgeons). Birds
appear to be stable while under anesthesia, but become unstable and fail to
recover when anesthesia is discontinued. A number of factors have appeared to
reduce this, including adequate analgesia at recovery, and fluid support. This is
not reported as frequently in reptile species.
7. In addition to the surgeon and skilled anesthetist, having a third assistant on
standby is helpful to adjust failing monitoring equipment while the primary
anesthetists practices continuous monitoring using manual methods
(observation/stethoscope). The third assistant can also fetch additional supplies
as needed.
The surgical emergency
Procedures for how to address anesthetic emergencies should be discussed and
planned out well in advance of the actual emergency. All emergency drugs should be on
hand with dosages pre-calculated and pre-drawn, or with immediate access to a
weight/dosage chart (Table 1). Very little is reported on the use of emergency drugs in
reptile patients.
Post surgical monitoring and care
Extubation
Extubation occurs when the patient is breathing well and there is evidence of some
glottal tone. Swab the mouth and glottis to remove mucus prior to extubation. Patients
that have not been intubated can also form mucus; therefore swabbing is important in
these patients as well.
Monitoring during recovery
Provide warmth, constant monitoring, and fluid support all the way through recovery until
the patient is ambulatory and alert. After surgery, fluid rates can be reduced to
maintenance with additions calculated for dehydration and surgical loss. In general, fluid
support is discontinued when recovery is complete; at this point birds often begin to
object to and investigate the catheter and fluid line.
The delayed or poor recovery
When patients do not experience a smooth, rapid recovery, every attempt should be
made to elucidate a cause, if possible, and provide treatment (Table 4). It must be kept
in mind that birds administered pre-anesthetic drugs may have a delayed recovery when
compared to birds that have received inhalant gases only. This is normal, and to be
expected, but must be distinguished from a medical/surgical complication.
In general, reptile recoveries can be prolonged, and it is not uncommon to experience a
delay of many hours before the return of spontaneous breaths and movement.
Ventilation with an ambu bag (not oxygen) must be provided throughout recovery.
In birds, pain is a potential cause of apparent delayed recovery. The painful bird is often
able to stand and may resist handling, but is not willing to move, and may display
elevated respiratory and/or cardiac rate. In contrast, the hypovolemic bird is weak and
often unable to stand or offer resistance to handling.
Drug dosages used by the author for either pre-anesthesia or sedation in exotic
companion mammals. When using in debilitated patients, use lower dosages.
Drug Class
Drug
Benzodiazepine
Opioids
Midazolam
Butorphanol
Rabbit/Chin/
Guinea Pig
Ferret
Rat
Mouse
Buprenorphine
Hydromorphone
Dosage
(mg/kg)
0.25-0.10
Route
Comments
IV, IM
IV, IM
Sedation, pre-anesthesia
Short acting; drug is very
sedating in ferrets; consider
lower doses. Rats and mice
appear to require higher
dosages of opioids.
Synergistic with
benzodiazepines.
0.1-0.3
0.1-0.2
0.3-1.0
0.5-1.0
0.04-0.05
0.10
Dexmedetomidine
Rabbit
IM
NMDA
antagonist
Ketamine
5-10
IM
Local anesthetic
Lidocaine
Bupivacaine
1 mg/kg
1 mg/kg
Local
block or
infusion
Not for use in debilitated
patients. Use with ketamine
Is reversible
Used in addition to midazolam
and an opioid for additional
sedation
Enhances patient comfort for
procedures such as
phlebotomy and catheterization
Peri-surgical drugs commonly cited and used in avian and reptile surgical patients1,7
including doses currently recommended by the authors.
Agent (mg/kg) Birds
Reptile
Midazolam
0.05-0.15 IV, IO
2 mg/kg
0.1-0.5 IM
Butorphanol
0.02-0.04 IV, IO1
0.2-2.0 mg/kg SQ, IM, IV
1 mg/kg IM1
1-3 mg/kg IM
1 mg/kg IV with 1 mg/kg/hour as
CRI throughout surgery2
Buprenorphine 0.02-0.2 mg/kg SQ
Morphine
0.05-4.0 mg/kg IM, IC, SQ
Alfaxan
Doxapram
Atropine
Glycopyrroate
Vasopressin
Epinephrine
2 mg/kg IM, IV, IO10
0.2 mg/kg IM10
0.01 mg/kg IM10
0.08 u/kg IM, IV, IO10
0.01 mg/kg IM, IV, IO10
5-20 mg/kg IM
Monitoring equipment used in avian and reptile surgical patients.
Device
Advantages
Disadvantages
Stethoscope
Reliable in birds, difficult
Not “hands free”, subject to
to impossible in reptiles
displacement with movement
May be more difficult to detect with
hypovolemia
The attentive
Only device able to detect
anesthetist
changes in respiratory
depth
Ultrasonic Doppler Extremely reliable, even
Movement may dislodge probe, can
in smaller birds ad
be challenging to secure
reptiles. Allows handsfree cardiac rate
monitoring
Mean oscillometric Allows monitoring of
Requires machine able to process
blood pressure
pressure trends; handsrapid cardiac rates; best current
(MAP)
fee operation
machines unlikely to be helpful in birds
less than 100 g and most reptiles
Indirect blood
Allows monitoring of
Studies show poor correlation with
pressure monitor
pressure trends
central pressures; difficult in birds
smaller than 100 g and reptiles.
Requires manual operation
Pulse oximeter
Allows monitoring of
Probes can be challenging to use in
oxygen saturation; hands- smaller patients, and in reptiles
free operation
Capnography
Allows monitoring of end- Required intubated patient; smaller
tidal CO2. Some are
side-stream monitors may be too large
equipped with respiratory in smaller patients
monitors
Efficacy questionable in
some studies.
ECG
Allows monitoring of ECG Requires machine able to process
and cardiac rate
rapid cardiac rates, less commonly
utilized in reptiles
Temperature
Allows accurate
Must be placed in the
probe-flexible with
monitoring of temperature crop/proventriculus or esophagus
constant read out
trends
which may be difficult in smaller
patients
Table 4. Trouble shooting guide for slow recoveries in exotic patients.
Potential
Diagnosis
Treatment
cause
Administration Rule out other causes of slow recovery
None required; monitor
of
carefully
preanesthetics
Pain
Rule out other causes of slow recovery;
Administer low dose
note painful posture with rapid cardiac
butorphanol IV or IO and
and/or respiratory rate. Consider especially observe response over
if time of last dose of opioid is more than 2
next 10 minutes
hours ago.
Hypovolemia
Take indirect blood pressure, observe
Administer crystalloids
basilic vein turgor, evaluate CRT from vent
and colloids at shock
mucosa
rates IV or IO as
indicated above
Hypoglycemia Measure blood glucose with hand-held
Administer glucose IV,
glucometer
IO, or if mild, PO
Hemorrhage
Look for evidence of hemorrhage, see
Administer colloids
“hypovolemia” above, note mucus
and/or whole blood;
membrane color
decide if
Reprinted in part from the Conference of the Association of Avian Veterinarians, 2012,
with special thanks for Dr. Larry Nemetz.
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