Download Case One: 12 Year Old Spayed Female Poodle

Everyday Challenges in Veterinary
Anesthesia
Diane E. Mason, DVM, PhD
Clinical Associate Professor, Anesthesiology
Kansas State University
Presented to the Metropolitan New Jersey Veterinary Medical Association Meeting
June 18, 2014
There are occasionally the routine cases that move us through our
daily schedule. More often it seems that the routine case is
highlighted by some “extenuating circumstances” that present an
extra challenge for anesthetic management when that is a part of the
plan for the animal on that day. Add into that the common
emergency presentations that walk into the clinic on a regular basis
and conducting anesthesia in a busy practice will always require
thoughtful planning interspersed with spur of the moment
exercisesin good judgment.
The title of this talk could be: “A Day in the Life of a Veterinary
Anesthesiologist”.Recognizing that most of you are not veterinary
anesthesiologists, it is important to see that the examples of cases
that we will talk about are not dissimilar from many that you might
encounter. The important take home message is that there are a
number of ways to anesthetize any given case, with respect to drug
choices. Often the most important thing about successful anesthesia
comes down to perioperative management as much as specific
anesthetic drug choices that are made. During the seminar we
should try to have a dialogue so that each of you feels comfortable
talking about how you might manage a given case or situation based
on the resources that you have available in your individual practice
situations.
As a general rule, the approach to general anesthesia in most of the
patients anesthetized at Kansas State University follow a fairly
predictable pattern. A typical scenario would include premedication
with a sedative/tranquilizer. Common choices might be:
acepromazine or a benzodiazepine (diazepam or midazolam) or an
alpha-2 agonist (dexmedetomidine). The advantage to
incorporation of premedication into the protocol is to improve
patient cooperation for catheter placement and handling. It provides
for a smoother induction and sometimes recovery. It reduces the
dose of other agents needed for induction and maintenance of
anesthesia, just to name a few. In addition, we almost always choose
to add an opioid to the premedication plan, if pain is a part of the
procedure that is about to be performed. This would be true for
anything from dentistry to major surgery. The choices of opioids are
wide from shorter to longer acting, partial to full agonist etc. The
decision of which to use is based on the circumstance of the
procedure and patient needs.
Anesthetic induction takes place with an intravenous induction
agent after IV catheter placement. Propofol is by far the most
commonly used induction agent at our clinic, but ketamine with or
without a diazepam is also frequently used. On occasion,
intravenous opioids are used to achieve intubation in a sick or
debilitated animal or etomidate in animals with significant
cardiovascular impairment.
Inhalation anesthesia is still the major means by which general
anesthesia is maintained for the majority of patients in small animal
veterinary medicine. In recent years, the use of continuous rate
infusions of intravenous adjunctive agents to allow less reliance on
inhalant during the maintenance phase has become more
commonplace.
In every animal that we anesthetize we always take into account the
particular analgesic needs of that animal for the procedure it is
about to undergo. What level of pain is going to be involved? Is
there anything additionally that can be done to help alleviate what
the animal is going to experience? If systemic opioids were to be
used, what dose and interval would be necessary to adequately meet
the analgesic requirements for the patient? Can a CRI of opioids or a
combination of drugs provide a better intraoperative or
postoperative analgesic experience and can that be managed for this
patient? Is there a local anesthetic technique that might be
appropriate to incorporate for this particular procedure that could
help during the intraoperative and immediate postoperative period?
These are the basic questions that come into play for planning each
anesthetic protocol even for the most uncomplicated patient.
What about a patient that then presents with specific complicating
factors? How are these weighed and how do they change the
process of anesthetic planning?
The safest anesthetic approach to an animal with underlying health
issues that could affect their risk for anesthesia would be to have a
diagnosis. As an example, if laboratory data reveals an elevation in
BUN and creatinine, that signals azotemia. Azotemia itself is not a
diagnosis. This sign could be from pre-renal, renal or post-renal
causes. This is where some further knowledge and having a
diagnosis can markedly alter your approach to the management of
the case. If further work-up would point to a likely renal cause for
the azotemia, then from an anesthetic standpoint you need to have
an understanding about the pathophysiology of renal disease. You
may need some further diagnostics to determine the progression of
the primary renal disease in this patient. What are the factors that
influence glomerular filtration and urine output and how are they
affected by general anesthesia? Are there choices we can make in a
drug protocol that will support rather than decompensate an
already compromised kidney?
It then becomes a matter of prioritizing problems on your patient’s
problem list. If this small animal patient with azotemia requires
general anesthesia for an ophthalmologic procedure, you can choose
to anesthetize it, bearing in mind that maintaining normotension is
of utmost importance in order to keep adequate renal perfusion. In
addition, despite the fact that ophthalmic procedures might be given
systemic NSAID’s for their anti-inflammatory and analgesic effects
as part of the pre-operative medication, that would not be done in
this instance.We have placed renal protection at the top of our
problem list and NSAID’s are now contraindicated for use during
general anesthesia when their effect on renal blood flow in low
perfusion states, as might occur in we encounter hypotension, could
be deleterious.
So using that very brief primer on the approach to anesthetic
planning, let’s look specifically at several case examples that
comprise the everyday challenges we see in our practice:
Case One: 12 Year Old Spayed Female Poodle
Presenting Complaint: Halitosis, Reluctance to eat, “Painful mouth”
Initial physical exam reveals
– Quiet, alert dog
– Lean body condition
– Heart rate 120, Respiratory rate – panting
– Heart murmur heard on auscultation Grade V/VI
• Left apical systolic murmur
– Lung sounds difficult to evaluate initially (panting)
– Significant dental tartar, gingivitis, missing incisors
Pertinent History
– Exercise tolerance: Activity level has decreased with age.
– Coughing: Occasional coughing at night
– Current medications: furosemide, enalapril and
pimobendan
Clinical and Diagnostic Plan
 Mitzi needs dental cleaning and tooth extractions
 Main concerns are geriatric status and assessment of
cardiac disease
 Evaluate Mitzi’s status to determine her ability to safely
undergo general anesthesia for dentistry
• Thorough complete physical exam
• Special emphasis on signs commonly associated with heart
disease
– Pallor, cyanosis, slow capillary refill?
– Weak peripheral pulses?
– Jugular venous pulses?
– Edema, ascites, depression?
– Cough, increased work of breathing?
• Special Attention to Auscultation
Murmurs or abnormal heart sound
Irregular rhythms?
Pulse deficits?
Abnormal lung sounds?
Crackles?
www.cvmbs.colostate.edu/clinsci/callan/breath_sounds.
htm
• Minimum Data Base?
Complete Blood Count
Serum Biochemistry
Thoracic Radiography
Additional Data in Certain Cases
Electrocardiography
Urinalysis
Blood pressure measurement
SpO2
Arterial blood gas analysis
Heartworm test
Serum thyroid hormone level
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There may be expanded databaserequired when the plan is to
anesthetize a patient with cardiovascular disease. This database
is not always necessary however on occasion there will be other
diagnostics that are indicated in particular patients. The database
that is required tends to expand with the severity of the cardiac
disease, or with the difficulty of making a diagnosis of the
condition. In an emergency situation it may not be easy even to
obtain the customary minimum of data.
From the CBC, hematocrit can indicate hydration status,
presence of anemia, oxygen-carrying capacity, and blood
viscosity. Total protein indicates hydration status, and any
increased risk for development of pulmonary edema. Abnormal
serum electrolytes may indicate a predisposition to cardiac
arrhythmias, or explain the presence of pre-existing rhythm
disturbances. Serum urea nitrogen allows one to evaluate renal
function and along with urinalysis it can indicate the possibility of
pre-renal vs. primary renal azotemia. Hepatic enzymes can
indicate the presence of liver damage or suggest impaired liver
function, which may suggest altered anesthetic drug clearance.
Thoracic radiographs help to evaluate cardiac size and contour.
Other thoracic structures can be identified, pulmonary edema
may be evident and the animal’s response to therapy can be
evaluated before anesthesia.
Electrocardiography is absolutely essential to diagnose rhythm
disturbances that may have been evident on auscultation or in
palpating peripheral pulses. An ECG is necessary to evaluate
response to therapy (e.g. antiarrhythmics or correction of
electrolyte abnormalities)
Heartworm disease assessment is important in regions
endemic for the disease, based on a history of no preventative
therapy or suspected poor client compliance in administration of
preventative.
Assessing a patient’s oxygenation (SpO2) with Pulse Oximetry
can be worthwhile if there is some question about pulmonary
overcirculation or evidence of increased respiratory rate or effort.
Arterial blood gas analysis can indicate the degree of ventilatory
compromise especially in the presence of pulmonary edema. It
allows one to assess oxygen-carrying capacity. ABG’s also
indicate metabolic status and the need for fluid or electrolyte
adjustments prior to anesthesia. Cardiac disease associated with
low cardiac output often results in metabolic acidosis due to
diminished tissue perfusion.
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Thyroid hormone levels can indicate the presence of
hyperthyroidism (feline patients), which is the cause of
thyrotoxic cardiac disease. In addition, hypothyroidism can alter
an animal’s level of sensitivity to anesthetic agents and when
detected often suggests adjustment in dose regimen.
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Blood pressure measurement has become increasingly
important as a preanesthetic evaluation tool. In recent years
hypertension has been increasingly diagnosed in our small
animal patients. This may occur as a result of chronic renal
disease, it may be a manifestation of cardiovascular disease,
idiopathic hypertension also occurs. My preferred method of
assessment is the Doppler ultrasound device with a repeated
value greater than 160 mmHg obtained in calm setting being
evidence of hypertension in a patient.
• Echocardiography
The essential tool of the cardiologist
Allows diagnosis of specific cardiac or vascular anatomic
disorders
Allows evaluation of chamber enlargement and chamber
volume
Allows assessment of heart function
Doppler echo allows identification of regurgitant flow and
quantification of pressure gradients across
valves
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One of the most useful parameters from cardiac
echocardiography, from an anesthesia point of view is
measurement of cardiac function. Although specific measures can
be taken to control preload, afterload, heart rate in many cardiac
disorders, a significant compromise in cardiac contractility is
difficult to overcome during anesthesia even with the use of
inotropic agents.
Systolic Time Intervals can be determined with M-mode
echocardiography and simultaneous ECG. It is calculated by
determining the pre-ejection period (PEP) and the left ventricular
ejection time (LVET). The PEP is the time from the Q wave on the
ECG (beginning of ventricular depolarization) to the opening of
the aortic valve (onset of LV ejection). The LVET is measured
from the opening of the aortic valve to the closing of the aortic
valve. The PEP/LVET = Systolic Time Interval (STI). This
parameter is affected by heart rate and preload. The normal
values for the dog are 0.24 – 0.34 msec and for the cat are 0.38 –
0.40 msec. Better contractility occurs when the PEP is shorter and
the LVET is longer. An increase in STI therefore indicates less
contractility. It is however nonspecific measure of contractility
since it is affected by loading conditions. It does give a reasonable
indication of global left ventricular performance.
Ejection phase indices are given most frequently for contractile
function in the heart. These parameters are also affected by
loading conditions just like STI.
Left ventricular fractional shortening (%FS) is calculated as
the change in LV dimension from end diastole to end systole. It is
calculated as [LVEDD – LVESD / LVEDD] x100. As a rule %FS
should be > 30 in dogs, slightly less in large breed dogs and 40-50
in cats.
Ejection fraction may be a superior measurement of cardiac
function to the other ejection phase indices because it is threedimensional rather than one-dimensional. It therefore is not so
dependent on proper perpendicular and centerline orientation of
the ultrasound beam through the LV. Ejection fraction is the
measure of the percentage of end diastolic volume that is ejected
when the heart beats. It is calculated as [EDV-ESV / EDV] x 100.
Values greater than 40% are considered adequate, however there
is no standardization at this time for this particular measure in
dogs and cats.
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Mitzi’s Laboratory Data Results
Mitzi’s Thoracic Radiographs
Mitzi’s Echocardiographic Exam Data
What is the most likely diagnosis of Mitzi’s cardiac disease?
Dilated cardiomyopathy
Chronic valvular disease with mitral insufficiency
Subaortic stenosis
Bacterial endocarditis
Chronic Degenerative Mitral Valve Disease
What is the pathophysiology of this disease?
How does the animal adapt to this condition?
What is the risk of anesthesia?
Mitral Valve Insuffiency
Chronic volume overload
Results in ventricular dilation
Stroke volume is divided into forward and regurgitant
flow
No period of isovolumetric contraction in LV
Expected patterns of response as seen with echocardiography
Volume Overload
– Eccentric hypertrophy
– Dilation of ventricle in systole
– Normal wall thickness
– Systolic function is usually OK
– LV wall motion during systole may appear hyperdynamic
(normal to increased %Fractional Shortening)
Mitral Valve Insufficiency
• Animals are asymptomatic for a long period because afterload
is low, oxygen demand is low, LVEDP does not ↑
• Volume of regurgitant flow is a function of size of mitral valve
orifice, time of flow and pressure gradient across mitral valve
• Regurgitant orifice size is a function of LV size
• Goal of anesthesia is to promote forward flow, reduce
regurgitation
• Dynamic factors that can increase regurgitant volume
– Increases in preload
• Avoid bradycardia
• Avoid IV fluid overload
– Increases in afterload
• Avoid vasoconstriction
– Decreases in contractility
• Avoid decreases in sympathetic tone
• Mitzi Anesthetic Protocol?
• How do we anesthetize this dog to achieve the above goals
while at the same time providing stable period of general
anesthesia with adequate analgesia for dentistry with tooth
extractions
• Supportive Measures
• What would be the best approach to treatment of hypotension
if/when it occurs in this particular patient?
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• Treatment of hypotension also is best when we know the likely
cause, but we are directed in our best approach in this
particular patient going back to the dynamic factors that will
worsen regurgitant conditions. We want to avoid increases in
afterload and IV fluid overload, which leaves increases in HR
and contractility (inotropic agents) as our best options for
treatment of hypotension.
Case Two: 8 YearOld Spayed Female Cocker Spaniel
Presenting complaint blindness and painful eye
• Diagnosis Chronic Glaucoma with poor response to medical
treatment
• Requires general anesthesia for planned enucleation of the
affected eye
• Initial physical exam reveals
– Bright, active, nervous dog
– Body condition score 4/5
– Heart rate 120, Respiratory rate 30
– Evidence of chronic atopic dermatitis
– Diagnosed and treated for past two years as a diabetic on
insulin therapy
• Minimum Data Base
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Complete Blood Count
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Serum Biochemistry
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Urinalysis or Urine Dipstick
• Goldie’s Current Values
– CBC within normal limits
– Serum Chemistry abnormal values included
• Glucose 332 mg/dl
• Alkaline phosphatase 284 U/L
• Serum bicarbonate 19.9 mmol/L
– Urine dipstick is positive for trace glucose
• Anesthetic Best Practices for Diabetics
– Schedule the surgery for the morning
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The remainder of the day to monitor
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Shortens fasting time from the night before
– Withhold food the morning of surgery
– Measure a blood glucose
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Based on result calibrate AM dose of insulin
– How much insulin to give?
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Zero up to full dose! Does it matter?
Anesthesia and the Diabetic
No data in animals regarding the risk of poor glucose
control in diabetic animals prior to anesthesia
Studies in both diabetic and nondiabetic people suggest
adverse events are associated with hyperglycemia
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Surgical site infection
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Myocardial infarction
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Stroke
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Increased mortality
In people, fluctuations of blood glucose and hypoglycemia
correlate with impaired prognosis
Insulin Perioperative Therapy
Comparison of two insulin protocols for diabetic dogs
undergoing cataract surgery. Kronen PWM, Moon-Massat PF,
Ludders JW et al. Vet Anaes Analg 2001
– Compared administration of 25% or 100% of the normal
insulin dose subcutaneously the morning of surgery
– Administration of full does only marginally advantageous
for reducing glucose to normal (70 – 120 mg/dl)
– Neither dose consistently induced glycemic values in an
acceptable range (70-200 mg/dl)
– No hypoglycemic episodes with 25%, but did occur in
100% dose, although infrequent
Anesthetic Complications of Diabetics?
A comparison of anesthetic complications between diabetic
and nondiabetic dogs undergoing phacoemulsification cataract
surgery: a retrospective study. Oliver JAC, Clark L, Corletto F,
and Gould DJ: Veterinary Ophth 2010
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– 66 diabetic and 64 nondiabetic dogs
– Same anesthetic technique in each group
– Diabetic dogs were more likely to develop moderate and
severe intraoperative hypotension than non diabetic dogs
– 71% vs. 63%
Why more hypotension?
Investigators proposed hypotension due to hypovolemia
secondary to hyperglycemia and osmotic diuresis
Cardiovascular Autonomic Diabetic Neuropathy?
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Documented in humans with diabetes
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Peripheral autonomic nerve fibers of the CV system
are affected
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Associated with hypotension perioperatively
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25% of patients with type 1 diabetes
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Limited evidence for this in dogs, although other
peripheral
neuropathies have been identified
Diabetic Monitoring and Therapy
Draw a Blood glucose prior to premedication
Repeat measurement every 30-60 minutes during
anesthesia
– Blood glucose 100 - 200 mg/dl (5.5 - 11 mmol/l)
• Lactated Ringer’s solution
– Blood glucose < 100 mg/dl (5.5 mmol/l)
• 2.5% dextrose in LRS
• 2-5 ml/kg/hour rate of administration
Target for Blood Glucose 90 – 180 mg/dl
What about hyperglycemia?
Do nothing, wait for AM insulin to peak
– When do you expect peak effect? Can it wait?
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• Administer short (regular) or ultra-short acting insulin as a
bolus or CRI
• Regular insulin CRI rate ≤ 0.1 units/kg/hour
– Dogs: 2.2 units/kg of regular insulin added to 250 ml
0.9% NaCl
• Serum glucose > 250 mg/dl administer at 10 ml/hr
• Serum glucose = 200 - 250 administer at 7 mls/hr
• Continue to frequently monitor glucose levels to
achieve target level and adjust CRI rate as needed
• Specific Drug Choices for Diabetics?
Technique appropriate for the age and physiologic status
of the
patient
Continue to monitor blood glucose
Return to normal routine as soon as possible but do not
feed if heavily
sedated
Case Three: 3Year Old, Intact FemaleShih-Tzu
• Chief complaint:Unproductive labor X 18 hrs
– Panting, shivering, not eating
– History:1 previous pregnancy
– 63d post breeding
– No current medications
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– Plan is to provide general anesthesia for emergency
cesarean section due to prolonged labor with inadequate
progress
Overview of Normal Gestation/Parturition
Normal gestation period
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63 days (dogs), 63-65 days (cats)
Assisted delivery or cesarean is unnecessary for most
small animal parturitions
Retrospective study, 151 breeds reviewed, 13,141
bitches, 22,005 litters
>80% Boston terrier, Bulldog, French bulldogs
Evans KM, Adams VJ: Proportion of litters of purebred
dogs born by caesarean section. J Small Anim Pract 2010; 51,
113–118.
Cesarean Section Anesthesia: Management goals
Provide maternal analgesia & muscle relaxation
Prevent maternal/fetal hypoxia & hypoperfusion
– Minimize changes in uterine blood flow
Minimize fetal CNS depression
Minimize post anesthetic maternal depression
It is important to understand the physiologic alterations
brought on by pregnancy
Cardiovascular
– Maternal blood volume & body water ↑
– PCV & Hemoglobin ↓
– HR, SV, & CO ↑
– SVR ↓, BP is unchanged
– CVP ↑
– Cardiac reserves ↓
Respiratory
– Sensitivity to PaC02 ↑ (progesterone)
– Minute volume ↑ with resulting ↓ PaC02
– No long term acid-base changes
– Oxygen consumption ↑
• Respiratory
– Lung compliance is unaffected
– Pa02 unchanged
– FRC ↓
• Gastrointestinal
– Lower esophageal sphincter tone ↓
• Gastric pH ↓
– Gastric emptying/motility ↓
– Intragastric pressure ↑
• Metabolism & Renal/Hepatic
– Normal biotransformation of drugs
– Inhalant anesthetics
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More effective alveolar ventilation for faster uptake
and elimination
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MAC of inhalants is decreased
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Progesterone & endorphins?
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Isoflurane MAC decreased by up to 40%
– Renal blood flow & GFR ↑
– BUN & Creatinine ↓
• Uterine blood flow
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UBF = Systemic perfusion pressure/myometrial vascular
resistance
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Placental hypotension:
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Maternal hypovolemia
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Anesthetic induced cardiac depression
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Sympathetic drugs increasing vascular resistance
(alpha 1 effect)
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Results in placental hypoperfusion, fetal hypoxia,
acidosis, &
fetal distress
• Placental drug transfer
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Placenta is highly permeable to anesthetic drugs
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Induce proportionate fetal effects
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Occur by simple diffusion
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Influenced by:
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Molecular weight
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Protein binding
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Lipid solubility
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Degree of ionization
Drug selection
Premedication
– Often not needed/indicated
– Avoid drugs with long and/or profound effects
• Avoid acepromazine, alpha 2 agonists, and
benzodiazepines in general
– If very anxious select a short duration drug:
• Fentanyl 2.5-5mcg/kg IV, IM, SQ
• Butorphanol 0.1-0.2mg/kg IV, IM, SQ
Premedication
– Opioids often withheld until puppies or kittens are
removed from dam
– Anticholinergics typically not indicated
• Glycopyrrolate does not cross the placenta
• 0.005-0.02mg/kg IM, SQ, IV
• Drug selection
Anesthesia induction
• Propofol/Propofol 28: 4-8mg/kg IV
• Alfaxalone: 1-4mg/kg IV
• Not currently available in US
• Etomidate: 1-2mg/kg IV
• Reserved for very unstable cases
• Avoid Ketamine/Benzodiazepine & Thiopental
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Associated with more negative outcomes regarding
fetal viability
Drug selection
Anesthetic maintenance
• Inhalant
• Sevoflurane > Isoflurane?
• Lower blood: gas solubility (0.7 vs. 1.4)
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– Faster onset, more rapid depth changes &
recovery
• Total intravenous anesthesia (TIVA)
• Propofol CRI 0.2-0.5mg/kg/min
• Alfaxalone CRI
Drug selection
Epidural drug administration
• Pros:
• Minimal depression of fetus & newborn
• Reduces inhalant requirement (local anesthetic,
such as lidocaine)
• Long duration of analgesia (opioid)
– Morphine 12-24 hours
• Cons:
• Slow onset (opioid)
• Hypotension risk (local anesthetic)
• May add time before getting into OR
Epidural drug administration
• 3mg/kg lidocaine + 0.1mg/kg morphine
– Use preservative free drugs
• 4-6mg/kg lidocaine
• Line block with lidocaine along the Incision site?
• Lidocaine or bupivacaine?
Post-operative analgesia
• Opioids administered to mother once fetuses removed
• Full mu agonist preferred
– Hydromorphone, Morphine, Methadone,
Oxymorphone,
– Can reverse opioids given to the dam in a
depressed offspring with sublingual naloxone
• Buprenorphine
Post-operative analgesia
• Single dose NSAID
• Meloxicam, Robenacoxib, Carprofen
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• Acetaminophen
• Contraindicated in cats
• Tramadol
• Mathews KA: Analgesia for the pregnant, lactating
and neonatal to pediatric cat and dog. J Vet Emerg
Crit Care 2005; 15(4) 273-284.
Perioperative care
Degree of care necessary depends on presenting
condition of the dam.
IV catheter & fluid administration
Evaluate Ca2+, Glucose, & electrolytes pre-anesthesia
Pre-oxygenate
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Avoid hypoxemia
Ensure OR set up & surgeon or surgery is ready to go
before induction
Pre-clip belly & initial prep abdomen
Perioperative care
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High regurgitation risk
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Rapid induction, head up, cuffed ET tube, secure
airway quickly
Remember MAC ↓ in pregnancy
Ventilate as needed (ETCO2 = 40mmHg)
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Avoid hypoventilation
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Uterine blood flow ↓
Avoid excessive time spent in dorsal recumbency
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Gravid uterus may decrease venous return
Newborn Resuscitation
Provide oxygen supplementation
Vigorously dry newborns & keep warm
• Huck towels, Bair-hugger, incubator, etc.
Stimulate newborns
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Reflex: Genital & umbilical → respiratory
stimulation
GV26 (Jen Chung) – acupuncture point at base of
nasal
philtrum → respiratory stimulation
Drug support
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Epinephrine 1:1000- 1 drop sublingual
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Naloxone- 1 drop sublingual if opioids have been
given to dam
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Atropine
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No effect on HR before 11-14d (Grundy 2006)
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Doxapram
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Not recommended in humans or animals
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↑ cerebral oxygen demand and ↓ CBF & oxygen
delivery (Dani et al. 2006)
Disinfect and ligate umbilicus
Inspect newborns for congenital abnormalities
Return to dam once she is awake and cognizant postanesthesia
Have patience! Many neonates will revive slowly upon
delivery but
will become quite vigorous after 10-15 minutes
of careful stimulation
and support
Clinical Case
PE:
• QAR, T: 99.9F, P: 180bpm, R: panting
• 5% dehydrated
• Otherwise unremarkable
Diagnostics:
• CBC/Chemistry
• Stress leukogram, HCT = 37%, BG= 154mg/dl,
• TP = 5.2g/dl, Ca = 9.2mg/dl, HC03 = 17U/L
• Abdominal US
• 4 puppies identified
• 3 puppies in distress (HRs 80-130bpm)
Clinical Case Management
10ml/kg IV LRS bolus prior to beginning of procedure
• Prior to induction
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Pre-oxygenation
Clip & prepped belly
Anesthetic plan
No premedication
Propofol IV to effect (6.4 mg/kg)
Rapidly secured airway
Sevoflurane in 100% oxygen
Placed into lateral recumbency
Administered epidural at lumbosacral site
Lidocaine 3 mg/kg
Preservative-free morphine 0.1 mg/kg
Placed into dorsal recumbency
HR= 150bpm, RR=35bpm, ETCO2 = 40mmHg,
BP = 85mmHg (Doppler Systolic BP), Sp02 = 100%
Hypotension noted
↓ Sevoflurane 4% → 2.75%
10ml/kg LRS IV bolus
0.1mg/kg IV ephedrine
HR=120bpm, RR = 25bpm, ETC02 = 37mmHg,
BP = 105mmHg (Doppler Systolic BP), Sp02 = 99%
Case Four: 9 Year Old, Neutered Male Miniature Schnauzer
• Owners complaint: Stranguria, hematuria, pollakiuria
• Diagnosis Cystic calculi
• Plan is for general anesthesia to remove cystic calculi via
cystotomy
• Physical Exam
• Current Medications
– Clavamox to treat UTI
– Fluoxetine (2 mg/kg SID) for separation anxiety
• Minimum Data Base
– CBC
– Serum chemistry
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– Urinalysis
Anesthesia for Abdominal Exploratory
Routine anesthetic approach
– Analgesic concerns for abdominal procedure with bladder
incision as well
What role does continued administration of fluoxetine play in
anesthetic drug choice or management in this dog?
Fluoxetine (Prozac/Reconcile) is a selective serotonin
reuptake inhibitor (SSRI)
– Major actions to block 5-HT re-uptake into pre-synaptic
nerve endings allowing it to persist longer in
serotoninergic synapses
– Also has 5-HT2C antagonist action which plays an antianxiety role
– Sigma-1 receptor agonist which is produces an antidepressant effect in people
SSRI’s Side Effects
SSRI’s are metabolized by cytochrome P450 enzyme system
(isoenzyme 2D6)
– Other drugs using this same pathway can undergo
impaired or slower metabolism
– Other tricyclic antidepressants, lipophilic beta-blockers,
codeine
SSRI’s have been associated with rhythm disturbances in
people with chronic use
– Tachyarrhythmia’s, syncope from hypotension
– Typical ECG alterations: flattened T waves, prolonged QT
interval, ST segment depression
Serotonin Syndrome
Excessive serotonin agonism
Potentially life-threatening adverse drug reaction
Overstimulation of 5-HT1A receptors
Triad of symptoms
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Neuromuscular hyperactivity
Autonomic hyperactivity
Altered mental status
SSRI’s, tricyclic antidepressants and MAO inhibitors are
all associated with this syndrome
Syndrome can occur with these drugs in combo or at
higher doses individually
The addition of a drug that can inhibit the cytochrome
P450 system for these drugs increases chance of syndrome
Drug interactions with SSRI’s
Avoidance of anesthetic agents that potentiate 5-HT will
avoid this likelihood
Phenylpiperidine opioids are weak 5-HT re-uptake
inhibitors
–
Fentanyl, Tramadol, Methadone, Dextromethorphan,
Propoxyphene
Safe Opioid choices to use with SSRI’s
–
Morphine, hydromorphone, oxymorphone
Ondansetron as a 5HT-3 receptor antagonist increases 5HT availability at 5-HT1 and 5-HT2 receptors
–
For anti-emetic effect: choose maropitant or
metoclopramide
Benzodiazepines, especially midazolam are metabolized
by CYP
enzymes and may increase half-life and plasma
levels of SSRI’s
Lipophilic beta blockers may be associated with serious
bradycardia
in SSRI treated patients
–
Water-soluble beta blockers such as atenolol are the
recommended choice if needed
–
Summary
Most anesthetic agents directly or indirectly effect the a
number of body systems
The stress of anesthesia is well-tolerated in normal patients
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• The presence disease requires careful drug choices,
modification of dose, titration to effect, and a balanced multidrug approach
• Make anesthetic choices based on best understanding of
physiologic consequences of disease and the progression of the
disease process in the patient is the best approach
• Often it is not about the drug choices at all, but about the
perioperative patient management that makes all the
difference in success of the anesthetic episode