safe feline sedation and anesthesia · •cardiovascular effects include vasoconstriction,...

Safe Feline Sedation and Anesthesia

Katy W. Waddell, LVT, VTS

(ECC) (Anesthesia/Analgesia)

Normal Behavior

• Many clients do not understand that cats are genetically programmed to hide signs of illness and injury

• Cats are unique as the only companion animals that are solitary hunters, as well as being both predators and prey.

Common stressors for cats in veterinary hospitals

• Other animals and humans

• Noise (eg, medical equipment, telephones, barking, human conversation)

• Smells and odors (eg, other animals, disinfectants)

ASA Status Class I

• Minimal Risk

• Normal healthy animal, no underlying disease

Class II

• Slight risk, minor disease present

• Animal with slight to mild systemic disturbance, animal able to compensate

• Neonate or geriatric animals, obese

Class III

• Moderate risk, obvious disease present

• Animal with moderate systemic disease or disturbances, mild clinical signs

• Anemia, moderate dehydration, fever, low-grade heart murmur or cardiac disease

Class IV

• High risk, significantly compromised by disease

• Animals with preexisting systemic disease or disturbances or a severe nature

• Severe dehydration, shock, uremia, or toxemia, high fever, uncompensated heart disease, uncompensated diabetes, pulmonary disease, emaciation

Class V

• Extreme risk, moribund

• Surgery often performed in desperation on animal with life threatening systemic disease

• Advance cases of heart, kidney, liver or endocrine disease, profound shock, sever trauma, pulmonary embolus, terminal malignancy

ASA Status

• One feline study that evaluated age and ASA physical status as risk factors for perianesthetic morbidity and mortality found that ASA status rather than age was a better predictor of perianesthetic complications.

• Cats with an ASA status of 3 or higher had a significantly increased risk of complications.

• Another study found that age (>12 years) was a risk factor independent of ASA status.

Neonates

• The neonate's physiologic differences from the adult

• The cardiac output is rate dependant in the neonate. The resting output is very near the maximum potential output. Cardiac reserve is minimal.

• High metabolic rate leads to high oxygen consumption.

• Neonates poorly regulate their body temperature.

• The blood-brain barrier is more highly permeable.

• Neonates have low protein binding of drugs due to reduced albumin.

• High body water content, low body fat. Extracellular fluid volume higher than adult.

• Decreased renal function, reduced renal clearance

• Immature hepatic enzyme function leads to reduced hepatic clearance.

0-6 months

• minimal glycogen stores in the liver of the pediatric patient,

• withholding of food should be kept to a minimum.

• Unweaned puppies and kittens should not be fasted,

• patients older than 6 weeks of age fast only for a maximum of 3 to 4 hours before general anesthesia.

• Prolonged fasting of these patients may result in hypoglycemia and dehydration and predispose them to hypothermia.

• Withholding of water is unnecessary.

Junior 6 months to 2 years

• Teenagers to young adult equivalent

• Minimum data base vs Big 4

Prime 3-6 years

• 28 – 40 human equivalent

• Prime for data base?

• Always ascertain BCS and MCS

Mature 7 – 10 years

• 44 – 56 human equivalent

• Data base include thyroid panel?

• Always ascertain BCS and MCS

Senior 11 – 14 years

• 60 – 72 human equivalent

• Thyroid ?

• Activity level

• Always ascertain BCS and MCS

Geriatric 15 + years

• 76 + human equivalent years

Develop a plan

• Working with the owner

• Less hectic schedule

• Meds to be given at home

Patient physical examination

• signalment, physiologic parameters and all body systems

• BCS, MCS

• identify any potential trends

Fearful patients

• Can you identify fearful cats prior to visit?

• Yes – consider gabapentin to be given at home

• No – always use feline friendly handling methods

• Especially with unknown health status

• On admission

• Move to quiet exam room

• IF amenable – physical exam with FF handling

• IF unsafe to patient/staff – consider chemical restraint

• Have all supplies ready at hand!

• Be flexible, each patient is an individual

• Remain calm

• Synthetic pheromones

• The increased release of catecholamines in fearful or stressed cats leads to • tachycardia,

• systemic hypertension

• and/or tachypnea, • all of which can increase the risks associated with

anesthesia

Physiological Effects of Stress

• Hyperglycemia

• Hypokalemia

• Increased CPK

• Lymphopenia

• Neutrophilia

• Hypertension

• Cardiac murmurs

• Improper response to drugs

Gabapentin

• Gabapentin (50 – 100 mg per cat or 150 mg if big cat, PO, 2 – 3 hours before arrival)

• May be given twice, evening before appointment and morning of appointment

• Geriatric or senior cats may try lower dose (50mg)

• Does have some analgesic effects

Alfaxalone IM

• 1-2 mg/kg

• Better results with addition of midazolam or butorphanol

• Usually manageable within 7-10 minutes

• Short duration

Kitty magic

• Gazillion recipes !!!!!

• TBD

• Premed or mild to moderate sedation:

• Telazol@ 1mg/kg

• Butorphanol@0.05 mg/kg

• Dexmedetomidine @ 2.5 mcg/kg

• TBD

• Profound ! Sedation

• Telazol @ 2 mg/kg

• Butorphanol @ 0.1 mg/kg

• Dexmedetomedine @ 5 mcg/kg

My usual combination if necessary

• Dexmedetomedine @ 2mcg/kg

• Butorphanol @ 0.3 mg/kg

• Ketamine @ 4 mg/kg

For geriatric or ill cats

• Butorphanol (0.2 – 0.4 mg/kg, IM) or Methadone (0.3 – 0.5 mg/kg, IM) +

• Alfaxan (1 – 2 mg/kg, IM)

• Butorphanol (0.2 – 0.4 mg/kg, IM) +/- Midazolam (0.2 mg/kg, IM)

Box or mask inductions

• hazardous approach to “sedating” the fearful feline.

• should be avoided

• 1) scary and stressful for patients,

• 2) dangerous to personnel (exposure to inhalants associated with numerous adverse health effects including impaired reproductive function), and

• 3) dangerous to the patient

Kitty would prefer some chemicals

I’m a good boy

Purpose of premedication

• Prevention of: – Increase of sympathetic tone caused by:

• Fright

• Excitation

• Difficult restraint

Which lead to: • Increased metabolism

• Increased cardiac work/oxygen demand

• Predisposition to arrhythmias

• All of which may lead to hypoxia

Premedication options

• Drug dosages used for premedication should be tailored to the individual cat.

• opioids are useful for premedication and as part of procedural sedation

• Morphine and buprenorphine undergo hepatic metabolism with glucuronidation, so the duration of action of these tends to be longer because of the lack of functional glucuronyl transferase in cats.

• At the low doses of opioids generally used for premedication, the heart rate may decrease slightly.

• Anticholinergics can be used to reverse this effect if deemed necessary.

• Atropine (0.02 mg/kg) and glycopyrrolate (0.01 mg/kg) SC may increase heart rate by about 10% in combination with an opioid

Benzodiazepines

Midazolam and diazepam: Cause little or no myocardial depressant effects

May see increase in heart rate due to excitation with inadequate use of adjunctive agent i.e. mu opioid

• Buprenorphine – mixed agonist/antagonist

• Duration of action 4-6 hours, good for mild to moderate pain

• 0.01 - 0.02 mg /kg IM or IV

• Butorphanol – mixed agonist/antagonist

• 0.1 -0.4 mg/kg IM or IV

• Duration 60 – 90 minutes

• Better sedation in cats than dogs

• Mild – moderate pain

Alpha 2 agonists

• Used in veterinary medicine to produce:

• sedation,

• analgesia

• Anxiolysis

• Reduce requirements of anesthetics

Fentanyl • Pure mu agonsist

• Causes dose dependant bradycardia (increase in vagal tone)

• Bradycardia is responsive to anticholinergics – atropine/glycopyrrolate

• Single dose IV is very short acting – up to 20 minute duration

Hydromorphone:

• morphine-like agonist, primary activity at the mu receptors.

• bradycardia due to central vagal stimulation,

• alpha-adrenergic depression causing peripheral vasodilaiton, decreased peripheral resistance

• baroreceptor inhibition.

• 0.02 -0.1 mg/kg

• Moderate duration 2-4 hours

Oxymorphone

• Similar effects to hydromorphone

• Case management of side effects the same

• 0.02 – 0.1 mg/kg

• 2 – 4 hour duration

Methadone

• Increase in vagal tone – dose dependent

• 0.2 – 0.5 mg/kg

• 2 – 4 hour duration

Alpha 2 adrenergic agonists

• Cardiovascular effects include vasoconstriction, decreased heart rate (by 40%) and cardiac output (by 60%) and increased systemic vascular resistance (300%) with minimal change in blood pressure.

• If α -adrenergic agonists are used for premedication, the decreased cardiac output may slow the onset of subsequent intravenous induction drugs.

Dexmedetomidine

• Alpha 2 agonist

– 0.00025 – 0.04 mg/kg

higher doses may induce vomiting which may be prevented by combining with butorphanol or giving maropitant pre-operatively

– Reversal: Atipamezole

Induction agents

• Propofol – hypnotic

• Dose dependent on effect of premedication

• 2 – 6 mg/kg titrated to effect

Alfaxalone

• Neuroactive steroid

• Calculated/titrated dose over 60 seconds

• Myocardial depression with higher end of dose range

DISSOCIATIVE AGENTS

• Will indirectly stimulate the cardiovascular system by increasing sympathetic tone

• cause an increase in heart rate, cardiac output, mean arterial pressure, pulmonary arterial pressure and central venous pressure.

• Increase in rate causes an increase in myocardial work and oxygen demand/consumption

Ketamine

• Does not produce a true anesthetic state – disassociation from the environment with analgesia and sensory loss

• Heart rate and arterial pressure increase due to an increase in sympathetic tone (CNS derived)

• Peripheral vascular resistance is unchanged

• Prior administration of benzodiazepine, acepromazine and/or inhalant agents may decrease or prevent cardiovascular effects

Telazol

• Tiletamine

• Zolazepam - benzodiazepine

• Clinical effects similar to ketamine

• Draw 2mg/kg and titrate to effect

• Prolonged or rough recovery when used as a sole agent

Inhalant anesthetics

• High cardiac output can delay anesthetic induction – blood flow through the lungs maintains the diffusion gradient between the alveoli and blood.

• i.e. – slower induction in excited patients vs. more rapid induction in decreased output patients – shock, hypovolemia, etc.

MAC

• MAC = minimal alveolar concentration. Produces immobility in 50% of patients receiving noxious stimuli

• Varies with agents and species

• The lower the MAC, the higher potency of the anesthetic agent.

Isoflurane

• MAC for cats is 1.63%

• Heart rate is seen to increase slightly

• Decrease in arterial blood pressure – main cause is decreased vascular resistance vs decreased cardiac output

Sevoflurane

• Causes mild myocardial depression (decreased contractility)

• Mild systemic vascular resistance and arterial blood pressure depression

• Less likely to see an increase in heart rate, vasodilation when compared to isoflurane

• MAC for cats = 2.58%

Nursing Care Goals

• Make the cat feel safe and secure in the clinical setting and at home following discharge

• Minimize stress to the patient during in-clinic and at-home treatment

• Contribute to successful recovery from illness, surgery or other treatment, and injury

kwaddell1212@Hotmail.com