Anesthesia - Quiz 4

What is important to remember during equine pre-anesthesia?

avoid excitement of the patient prior to and during induction/sedation

Should equines be fasted prior to anesthesia?

it is a clinician preference

fasting can decrease the pressure on the major abdominal vessels with less cranial displacement of the diaphragm

some texts recommend 8-12 hour fasting

What are the steps to pre-anesthesia in equines?

prepare, assess, and weight your patient

place an IV catheter

rinse out the mouth and clean out the hooves (helps reduce aspiration pneumonia) (if doing standing anesthesia, you don’t need to rinse out the mouth)

prepare equipment, drugs, fluids, induction materials, etc

make sure you have proper monitoring equipment

What is standing sedation used for?

eye procedures (laser, enucleation, corneal, ulcer treatments)

minor orthopedic procedures such as casting and x-rays

laceration repairs and hoof trims

When performing anesthesia in the field, what will you use to measure the horse’s weight?

a weight tape

Why is it important to have a head prop of assistant to hold the horse's head in a neutral position?

to avoid congestion which can lead to respiratory obstruction

Mallard anesthesia machine

Bellows

Tafonius anesthesia machine

piston driven

SurgiVet anesthesia machine

What is the difference between the SurgiVet, Mallard, and Tafonius machines?

The Tafonius is piston driven while the other two are bellows

Acepromazine is a good addition when…?

you have a patient who is young/excites or uncooperative

Who should you not give acepromazine to?

hypotensive patients and breeding stallions

low hematocrit and liver disease patients

When is Ace given?

30mins to 1 hour prior to anesthesia to help calm the horse down and allow for a smoother sedation and induction

Are full mu opioids used in horses?

No, they cause intestinal ileum and can lead to colic

What is the opioid of choice for equine pre meds?

Butorphanol (0.03mg/kg)

Euthanasia: a tool

a humane and responsible option

• failure to respond to RX

• no effective RX

• Poor quality of life

NOT a substitute for poor veterinary care

should be performed competently by willing individuals

Humane Killing

subdivided into:

• euthanasia (individuals)

• human slaughter (large numbers)

• depopulation (large numbers)

AVMA Euthanasia Guidelines

• periodically updated

• available in print and online

• presents physiology, animal and behavioral issues, modes of action, relative merits of various methods

• accepted as THE definitive reference

Acceptable

methods producing humane death as the sole means of euthanasia

Acceptable with conditions

acceptable methods when certain conditions are met

Unacceptable

methods not to be used under any conditions

Depopulation and slaughter may employ euthanasia techniques, but not all depopulation or slaughter methods meet the AVMA criteria for euthanasia…

these activities may be termed humane killing

Pain perception requires functioning

cerebral cortex

Anesthetized or properly euthanized animals

do not feel pain

Loss of consciousness should precede

loss of muscle movement

What are the 3 basic mechanisms of euthanasia?

direct depression of neurons necessary for life functions

• anesthesia overdose; CO2

Hypoxia

• argon, nitrogen, CO2; exsanguination

Physical disruption of brain activity

• concussive stunning; electrocution; cervical dislocation; gunshot

Loss of consciousness occurs at substantially different rates with different methods. T/F?

True

Suitability will depend on whether the animal experiences pain and/or distress _______________ loss of consciousness.

PRIOR TO

Events occurring _________ loss of consciousness, although unpleasant to watch, do not contribute to adverse welfare.

AFTER

Anesthetic Overdose

inhaled anesthetics

• expensive; personal exposure

• CO2

Injectable anesthetics

• Pentobarbital

• 1 min onset, minimal movement if properly restrained; carcass contamination

Death 2º to respiratory, cardiac arrest

Hypoxia

gases that displace oxygen to <2 vol %

• nitrogen, argon

gases preventing 02 binding to hemoglobin

• carbon monoxide

exsanguination

• unconsciousness must be induced first

Physical disruption of brain function

bullet; penetrating captive bolt

• destroys cortex and midbrain

electrocution (2 steps)

• humane, painless if properly done; no drug residues

• follow with 2nd method to assure death

Regardless of euthanasia method

death MUST be confirmed.

All methods have potential to cause physical injury and death. T/F?

True

Psychological issues (the killing-caring paradox)

• transferal of personal feelings/fear onto the animal

• depression, grief, anger, guilt, sleeplessness

• job dissatisfaction may result in absenteeism, belligerence, careless/callous animal handling

People are less disturbed when they feel distanced from the physical act or when animal doesn’t move. T/F?

True

The “Trolley Problem” and “Fat Man Problem”

In many states, shelters can not obtain injectable DEA Schedule II or III drugs. T/F?

True

• injectable euthanasia can only be performed if a local vet is willing to participate

• leaves gas euthanasia chambers as only option

Some states have re-written their pharmacy laws to permit shelters to obtain their own DEA license. T/F?

True

• requires staff training and certification

Euthanasia in the face of a foreign animal disease:

Timely response necessary to prevent disease spread

• All infected within 24 hrs; all contiguous farms within 48 hrs

Euthanasia vs depopulation

• Euthanasia methods can be used for depop, but not all depop methods are euthanasia

• We owe it to the animals to do the best we can under the circumstances

Why is CO2 used?

Denser than air; noninflammable

Extensibly studied

• anesthesia due to ↓ pHi; not reliant on hypoxia

• minimally affected by respiratory disease

• recommended by OIE, AVMA, AASV for human killing of swine

Far less labor intensive than bolt guns

Fewer people involved, less safety risk

Medium or High-expansion Water-based Foams

Conditionally approved by USDAAPHIS (2006)

• Zoonosis; spreading infectious disease

• Unsound buildings

Uses air to form bubbles

• Immersion causes airway occlusion and death by suffocation

Add CO2 , N2 ?

Horses

• Pentobarbital; large volumes (approx 100 mls) needed

• Not FDA approved for this species

• Major disposal issues

• Use of a jugular vein IV catheter will facilitate the procedure

• In some situations, may be easier to anesthetize the horse 1st, then euthanize

Intrathecal lidocaine during general anesthesia

• Humane; eliminates drug residue issues

In certain situations, gunshot or penetrating captive bolt is acceptable

Zoo and Wildlife

Must consider what will happen to the carcass

• Head shot, penetrating captive bolt, KCl IV or MgSO4 IV during general anesthesia to reduce toxicity to scavengers

Species-specific guidelines available

Euthanasia of Pregnant Animals

Mammalian embryos and fetuses are unconscious and insentient throughout pregnancy and birth

• Several in utero neuroinhibitors present during prenatal life initially maintain unconsciousness

• An isoelectric EEG, which is incompatible with consciousness, rapidly appears after cessation of placental oxygen supply

Embryos and fetuses cannot consciously experience any sensations or feeling such as breathlessness or pain, and therefore cannot suffer while dying in utero, whatever the cause

• Similar conclusions have been drawn regarding the possibility that consciousness may not occur until after hatching in domestic chickens

Fetal Resuscitation

Attempts to remove the fetus from the uterus or to revive a fetus following death of the dam are likely to result in serious welfare complications for the newborn

• Physiological immaturity; effects of fetal hypoxemia; once removed from uterus and spontaneous breathing occurs, potential for consciousness and sentience

• IP pentobarbital is recommended for fetuses that have been removed from the uterus

The function of the cardiovascular system is to

circulate blood and ensure delivery of oxygen to the body

žVasodilation

Decreased systemic vascular resistance (think about a drink straw compared to a coffee stirrer)

Oxygen delivery =

žCardiac Output x oxygen content

MAP (mean arterial pressure) =

žCO x SVR (systemic vascular resistance)

žFour Mechanisms that can cause hypotension

Vasodilation

Bradycardia

Decrease in cardiac preload (directly related to ventricular filling)

Decrease in myocardial contractility

What are the causes of vasodilation?

Anesthetic agents

• propofol

• acepromazine

• inhalant anesthetics

Hypothermia (extreme cases)

Cardiac drugs

Sepsis

Anaphylaxis

What are the causes of bradycardia?

excessive anesthetic depth

arrhythmias

hypothermia (extreme cases)

opioids

alpha-2 adrenergic agonists (initially vasoconstriction)

What are the causes of decreased preload?

• hemorrhage

• dehydration (vomiting, diarrhea)

• 3rd spacing (effusions, ascites, GI fluid) - occurs when too much fluid moves from the intravascular space (blood vessels) into the interstitial or “third” space - can cause edema, reduced cardiac output, and hypotension

• vascular compression/obstruction - occurs when blood vessels are under abnormal pressure, limiting the size of the blood vessel and the amount of blood that flows through it

• positive pressure ventilation -due to cardiac compression

• vasodilation

Stage A

patient at risk but no clinical signs

Stage B

B1

• murmur, no past or present clinical signs of heart enlargement or failure

B2

• murmur and cardiomegaly but asymptomatic

Stage C

patients with past or present clinical signs of heart failure with structural cardiac disease

Stage D

patients with end-stage heart failure that are refractory to standard therapies

Stage A & B1

generally do not require intensive management

Stage B2

• keep patient heart rates normal

• keep patients normothermic

• avoid alpha-2 adrenergic agonists (depends on clinician)

Stage C & D

• rely on balanced anesthesia

• avoid alpha-2 adrenergic agonists (depends on clinician)

• use opioids/benzodiazepines to reduce amounts of induction and inhalant agents needed

What is hypertrophic cardiomyopathy?

žThickening of the cardiac muscle leading to stiffening and failure of relaxation and adequate filling (think of body builders)

žAnesthetic Management of hypertrophic cardiomyopathy

Dissociatives are contraindicated in severe HCM because the increase in HR, contractility, & BP can lead to reduced cardiac output while also increasing cardiac workload and oxygen demand – can and will cause death

Cautious with fluid administration

Balanced Anesthesia

What is dilated cardiomyopathy?

primary loss of myocardial contractibility that can lead to dilation of the ventricles

What is the anesthetic management of dilated cardiomyopathy?

Cautious with fluid administration

Manage arrhythmias

Inotropic support

Balanced Anesthesia

Alpha-2 adrenergic agonist are contraindicated due to the increase in afterload(amount of pressure that the heart needs to exert to eject the blood during ventricular contraction) whichcan cause a decrease in cardiac output

Do not give dissociative to cats with

thyroid problems

• if they have a thyroid problem, they most likely also have HCM

Minute ventilation

volume of gas inhaled or exhaled in lungs per minute ventilation

Maintain CO2 levels (35-45 mmHg) and pH (7.35-7.45)

these parameters are directly related

Hb

what binds to O2 – the body’s oxygen carrying capability

SaO2

the percentage of available binding sites on hemoglobin that are bound with oxygen in arterial blood

• how much hemoglobin is available

PaO2

the alveolar partial pressure of oxygen is the driving force for the diffusion of oxygen across the alveolar membranes, through pulmonary capillary walls, and into the arterial blood flow and erythrocytes (RBC) for transport throughout the body into peripheral tissues

• ARE THE LUNGS UP TAKING OXYGEN

What are the causes of hypoxemia?

• Low inspired oxygen fraction –FiO2

• Hypoventilation – increased CO2

• Diffusion impairments – gases do not move normally across the lung tissues into the blood vessels of the lung – decreased oxygen levels – increased CO2 levels  - secondary to primary respiratory disease

• Ventilation-perfusion mismatching – areas of the lungs are poorly perfused but well ventilated or poorly ventilated and well perfused

• Right-to-left shunts – non oxygenated blood may flow directly back to the rest of the body – it may flow from the right chamber to the left chamber and never pass through the lungs to be oxygenated – cardiac defect

Examples of obstructive issues:

Asthma

Laryngeal paralysis

Brachiocephalic

Tracheal collapse

What is the anesthesia management for obstructions?

Minimize excitement and stress

Mild sedation may be warranted

• —Butorphanol, acepromazine

Ventilation refers to

CO2

Perfusion refers to

oxygen

Examples of decreased lung capacity:

Aspiration pneumonia

Muscle rigidity

Obesity

Intra-abdominal changes – tumor – GDV - hemoabdomen

What is the anesthetic management of decreased lung capacity?

• Protect airway and suction mouth as needed

• Pre-oxygenate

• Mechanical ventilation

• Monitor oxygenation

Neurological Disease

žBrain injury, trauma, tumors, hydrocephaly

• Cerebral perfusion – (blood flow to the brain) BP affects the cerebral perfusion pressure, if BP is low the blood flow to the brain may be limited

• Intracranial pressure – if ICP is too high – blood flow to the brain may be limited

What is the anesthetic management for neurological disease such as žBrain injury, trauma, tumors, or hydrocephaly?

• Maintain MAP

• Oxygen and ventilatory support

• Mannitol – diuretic – helps treat brain swelling and reduce ICP

• Hypertonic saline – helps treat brain swelling and reduce ICP

What is the anesthetic management for neurological diseases such as žSpinal injuries or intervertebral disc disease?

• Patients at risk for developing neuropathic pain – can happen if your nervous system is damaged or not working correctly – you can feel pain from any of the various levels of the nervous system – the peripheral nerves, the spinal cord and the brain

  • Adjunct analgesics to opioids beneficial

    • Ketamine, lidocaine

žThe liver provides multiple essential functions such as….

• Bile formation and excretion – filters bilirubin, cholesterol, drugs and toxins – intestinal absorption

• Metabolic functions – changes food and water into energy

• Plasma proteins- stabilizes osmotic pressure – helps maintain pH – fights infection

žComplications associated with hepatic disease

• Hepatic encephalopathy – loss of brain function (liver not filtering toxins)

• Hypokalemia – can worsen insulin resistance leads to fatty liver

• Hypoglycemia – liver responsible for maintaining plasma glucose

• Hypoalbuminemia – doesn’t produce enough ALB to keep fluid in vessels

• Ascites – fluid build up on the abdomen

• Coagulopathy – houses clotting factors

• Hypotension – hypertension in portal vein

• Impaired drug biotransformation – poor filter

• Storage of glycogen – enzymes break down glycogen into glucose when the body needs energy

žMost anesthetic drugs rely on liver for metabolism and duration of effect may be prolonged. T/F?

True

• Use lower doses if possible

• Use shorter acting drugs if possible

• Use reversible drugs if possible

žBalanced anesthesia

žMonitor glucose

žMonitor blood pressure and provide oncotic support – (large protein fluids)

žGI disease could cause

• Anorexia – loss of appetite for food

• Dehydration – the loss or removal of water

• Hypovolemia – decreased volume of circulating blood in the body

• Acid-base & electrolyte imbalance – when your electrolyte levels are out of balance due to dehydration, you experience acid/base imbalance

• Protein loss – albumin and other protein-rich materials leak into the intestine

• Abdominal pain – multitude of causes

Anesthetic Management with GI Disease

žCorrect any imbalances before anesthesia – if possible correct dehydration over 24 hours prior –Does your patient need a blood or plasma transfusion? – run blood gas and correct any issues

žMonitor blood pressure – IBP or NIBP

žProvide volume or oncotic support (large protein fluid therapy)

Lower anesthetic drug dosage if possible

žNeoplasia in mouth may cause difficult intubation

Retrograde intubation - nasal

Pharyngeal intubation

Tracheostomy

žEsophageal disease

• Megaesophagus

  • Regurgitation and aspiration

• Be fast but patient

• Protect airway – high instance of aspiration

• Suction mouth and esophagus

žUpper GI Hemorrhage

Monitor PCV

• <20% give blood transfusion

The kidneys function in:

• Excretion of metabolic waste and toxins

• Regulation of blood volume and extracellular fluid  by controlling sodium and water balance and maintaining extracellular fluid volume homeostasis ( an increase in sodium and water consumption leads to an increase in extracellular fluid volume which in turn increases blood volume -  osmolality (measures the body’s water/electrolyte balance) – an increase osmolality of serum can help diagnose dehydration, diabetes, and shock -  electrolyte balance (directly related to osmolality)

• Aids in acid-base regulation – kidney’s reabsorb HCO3 from urine back into blood – ultimately balancing pH

• Filtration is related to blood flow although most of the time the kidneys can compensate (autoregulation) for changes in blood pressure. These factors can alter the kidney’s ability to compensate.

  • Pain

  • Chronic hypertension

  • Acute renal failure

  • Sepsis

Some abnormalities with kidney injury or disease…

• Increased BUN – kidneys aren’t working well – dehydration, urinary obstruction

• Increased Creatinine – same as above

• Increased potassium – hyperkalemia – kidneys remove potassium from the blood, when K+ is too high, kidney’s aren’t working

• Changes in urine output – amount, color, smell

• Metabolic acidosis – decreased HCO3- decreased pH

• Hypertension – because arteries are small, kidney’s aren’t getting enough blood, they react by making a hormone that causes your BP to rise – damaged kidneys do not filter blood well

• Dehydration  - kidneys can’t keep body fluids balanced and you become dehydrated

• Nausea/vomiting – due to toxin build up

Anesthetic Management with Renal Disease

žMonitor and maintain blood pressure

žMonitor and correct acid-base and electrolyte status – ventilation? – HCO3? – iCa? – Na? – K+?

žMaintain hydration – BUN? – CREA? – Hypernatremia? – PCV? – TS? – Lactate?

žThyroid

• Hypothyroid – hormone imbalance - decreased

  • Decrease metabolism – weight gain without an increase in appetite

  • Weak muscles – myopathy – weakness – functional limitation – autoimmune – body attacks itself

  • Bradycardia – hypothyroidism causes constriction of blood vessels and increased blood pressure which causes a reflex bradycardia

  • Hypothermia – due to decrease in metabolism

• Hyperthyroid – hormone imbalance - increased

  • Hypertension – increases systolic BP by decreasing systemic vascular resistance, increasing HR and raising cardiac output

  • Hyperthermia – increases metabolism

  • Cardiac changes (ventricular hypertrophy) – thickening of the wall of the heart’s main pumping chamber – poor pumping action – typically due to high BP

Hypercoagulability

increased production of clotting factors caused by cushing’s

Pregnancy

žRegurgitation & Aspiration

• Cranial displacement of the stomach due to size of uterus

• Decreased esophageal sphincter tone

• Decreased gastric motility

žDecreased lung capacity

• Cranial displacement of enlarged uterus

žCardiovascular

• Physiologic anemia

  • Increased blood plasma w/o increase in RBC

• Increased cardiac workload

  • Increased stroke volume, heart rate and cardiac output

• Blood pressure Regulation

  • Increased estrogens decrease SVR

  • Weight of uterus can compress caudal vena cava and aorta decreasing venous return and cardiac output

žHypoglycemia

žHypocalcemia

žDehydration

žExhaustion

Anesthesia Management with Pregnancy

žInduce and intubated quickly to protect airway

žH2 antagonist (famotidine) and metoclopramide considered preoperatively

žPre-oxygenate and ventilate for patient

žPrep patient while she is awake

žLeft lateral recumbency as much as possible

žMonitor glucose and calcium

žMaintain normovolemia

žShort-acting drugs until neonates are delivered

Newborns

žAirway

• Suction mouth

• Stimulate breathing

  • Don’t sling/swing puppies

žCardiovascular

• Chest compression ~120bpm

• Epinephrine drop under tongue

žTemperature

• Keep warm

Common Emergencies that require Anesthesia…

C-section

Respiratory Distress

GDV

Sepsis

Hemoabdomen

What are the elements of a basic triage?

get a complete history

take a physical assessment

• TPR

• Hydration Status

• Auscultation

run bloodwork/diagnostics

• big 4

  • Azo stick, glucose, PCV, TS

• ECG

What is the procedure for a C-section?

be considerate when choosing pre-med agents

• almost everything that will effect the mother will also effect the babies

Pre-oxygenation/clipping/prepping

Fast and efficient induction

• Alfaxalone/propofol

• inhalant

• epidural/lineblock

Intra-operative care/support

• Full mu opioid after delivery

• supportive therapy

Post-operative care

What is the procedure for neonatal care after c-section?

make sure you have all supplies ready

establish a clean airway

stimulate the babies

check to make sure the babies are breathing - have a palpable pulse

Give dopram or epinephrine as a respiratory stimulant under the tongue (1 drop)

oxygen supplementation

once stable:

• dry

• ligate and disinfect the umbilicus

• keep warm until the mother is recovered