Prepare and monitor anaesthesia in animals

ANAESHTESIA SCENARIOS

Prepare and monitor anaesthesia in animals

ANAESTHESIA SCENARIOS


Scenarios

• Urgency & Emergency Scenarios– See Anaesthesia emergencies

• Physiological Scenarios

• Pathological Scenarios


Physiological Scenarios

• Young animals (Paediatric)

• Old animals (Geriatric)

• Obesity

• Caesarians*

• Brachycephalic breeds

• Sighthound breeds

• Small breeds


Young animals


Young animals

Problem Solution

Greater oxygen demand, ventilation less efficient and prone to lung consolidation if anaesthetised for long periods.

Monitor oxygenationCareful selection of ET tube - not too long.Ventilatory support if needed.

Liver and kidney function immature. Use lower than adult dose rates.Use drugs that are rapidly metabolised.Avoid fluid overload.

Prone to hypoglycaemia. Monitor blood glucose.Maybe add glucose to IV fluids.

Prone to hypothermia. Monitor temperature.Keep warm.


Young animals

• ‘Pups & kittens’– Neonate: < 4 weeks– Pediatric: 4-6 weeks– Immature: 16-52 weeks


Young animals - Physiology

• Cardiovascular function - can only increase Hr not increase the force of the heart contractions

• Respiratory function – have a higher O2 requirement

• Hepatic – renal function – liver enzymes at very low levels

• Body composition• Large SA to body ratio therefore prone to

hypothermia• Poor regulation of body fluids – cannot cope

conserve or cope with overload


Young animals - Pre-op

• Correct pre-existing deficits• Rapid induction and recovery• Prevent hypothermia, hypoglycemia and

dehydration• Should be on fluids warmed 10mls/kg/hr such as

hartmans +/- 5% dextrose added• Minimize use of metabolizable drugs, no

barbiturates if < 8wks old• Maintain PCV > 20 % and serum protein >

35gm/l


Young animals - Anaesthetics

• Atropine – to all • Sedation – may not be needed, low dose opioids• Induction – a.if parenteral ketamine/valium or

propofol or Alfaxalone– inhalation probably best –mask, chamber, drug of

choice is isoflurane, may cause stress and release of adrenalin causing cardiac arrhythmias

• Maintenance – inhalation G/A , T-piece


Young animals - Support

• Supplementary heat & prepare with war fluids and warm IV fluids etc

• Fluids essential– Hartmanns (10mLs/kg/hr)– May require 5% glucose need to monitor

• Maintain PCV > 20 % & serum protein >35 g/L


Young animals – cases

• Discuss the following for a 10 week old 4kg puppy to under go an elective ovariohysterectomy– Physical status: 1 2 3 4 E– Pre-anaesthetic considerations– Premedicants and rationale– Induction technique, agents & rationale– Maintenance technique– Monitoring– Post operative support and analgesia


Geriatric animals

• Dogs > 7 years


Geriatric animals

Problem Solution

May have heart problems, poorer circulation.

Anaesthetics may take longer to work, give it time rather than increasing dose.

Avoid fluid overload.

Require less anaesthetic Reduce dose premed and GA

Reduced lung elasticity, may have respiratory disease.

Monitor oxygen carefully.Supplement oxygen prior to induction

and during recovery.Carefully monitor ventilation, assist if

required.

Reduced renal function.May be PU/PD

IV Fluids. Increase fluid rate prior to induction, make sure patient not dehydrated.

Reduced hepatic function Use drugs that are rapidly metabolised

May have other underlying diseases Do pre-anaesthetic blood tests

May be on medication Get good history from owner


Geriatric animals - Physiology

• Cardiovascular system function

• Respiratory function

• CNS

• Hepatic function

• Renal function


Geriatric animals - CV function

• Decrease with age due to– a decline in cardiac response to sympathetic nervous

system stimulation– A rise in peripheral vascular resistance due to

thickening of the walls of large arteries

• This results in – Increased blood pressure– Reduction in cardiac output– Reduction in vascular volume– Less tolerance to anaesthetic drug induced

cardiovascular depression


Geriatric animals - resp function

• There is loss of strength of the muscles of respiration

• A decrease in elastic recoil of the chest• An increase in the resting volume of the thoracic

cage• Pulmonary capillary blood volume decreases &

alveolar surface area, resulting in a reduction in diffusion capacity

• Therefore there is an increased resistance to chest expansion and a decrease in gas exchange efficiency with age


Geriatric animals - CNS function

• Reduction in brain weight with age due to a loss of individual cells

• Increased breakdown and decreased production of neurotransmitters

• Therefore the anaesthetic requirement decreases with age


Geriatric animals - liver function

• Age related increase in BSP retention partly due to a decrease in liver blood flow

• Drugs dependant on liver metabolism & biliary excretion for their have a prolonged plasma half life in aged patients


Geriatric animals - renal function

Function decreases with age due to– Reduction of cortical renal mass, reduction in

glomeruli and tubular atrophy– Reduction in renal blood flow

• Therefore there is a reduced renal reserve (so less tolerant of dehydration or fluid overload) & a prolonged drug elimination

• More susceptible to renal failure


Geriatric animals - drugs

• Albumin mass is reduced so plasma protein binding of drugs is reduced

• Results in higher levels of unbound (active) drugs

• Receptor numbers also decline with age


Geriatric animals - pre-op

• Correct pre –existing problems –fluids, assess by pre – G/A bloods, history, PE

• Premeds to reduce stress on induction

• 5 minutes pre –oxygenation if cardiopulmonary dysfunction

• Keep warm as decreased ability to shiver

• Handle gently and provide padding


Geriatric animals - pre-med

• Anti-cholinergic such as atropine may not be needed ( an increased HR could stress the heart)

• Opioids good premeds• Diazepam + Opioids – minimal cardiac

depression• ACP –use with caution at low doses or not at all

because of its long duration of hypotension, in animals with dehydration or poor cardiac or renal function


Geriatric animals - inductions

• Thiopentone• Propofol – use with care in dehydrated animals

as it will cause vasodilatation and therefore hypotension, minimal hepatic metabolism and renal excretion

• Ketamine /valium – except in patients with cardiac disease as it increases sympathetic tone (increases HR and BP)

• Inhalation – as long as not stressful particularly with cardiopulmonary disease


Geriatric animals - maintenance

• Inhalation – best Isoflurane


Geriatric animals - monitoring

• See section above– Vital signs– Mechanical devices

• Advise fluids for example hartmans solution


Obesity

• Irregular gaseous anaesthesia?

• Restrictive pressures on URT


Caesarian


Caesarian Section

• G/A for small animals

• Local anesthesia for large animals usually


Caesarian Section

Problem Solution

Increased oxygen consumption due to foetuses.

Use at least 50% oxygen.Pre-oxygenate patient.

Risk of vomiting due to reduced gastric emptying time

Can pre-med with metoclopramide.Be prepared for possibility of vomiting

and aspiration during anaesthesia and recovery.

Rapid induction - use IV agent, intubate quickly.

Patient may be exhausted and dehydrated.

IV fluids ASAP

Distended abdomen puts pressure on diaphragm

Minimise time animal is on it’s back.Ventilate if needed.

Foetuses can be affected by the drugs used.

Keep induction to delivery time to min.Use lowest effective dose of drugs.Use short acting, rapidly metabolised

drugs. Pre-clip


Caesarian Physiology

• Blood volume > ( cardiac output >)• But causes PCV < as RBCs not increased• Increase abdominal pressure causes diaphragm

to shift cranially causing < functional residual capacity

• Increased RR, increased O2 consumption – increases minute ventilation

• Delayed gastric emptying increases risk of vomiting

• Maternal anesthetic requirements reduced


Caesarian Physiology…

• Cardiac reserve depleted

• MAC lowered

• Increased speed of inhalation induction

• Inappropriate positioning < cardiac output and compromises ventilation

• Respiratory depression - no O2 supplement will result in foetal hypoxaemia


Caesarian considerations

• History and PE

• Blood glucose, electrolytes an acid/base status assessed if available

• Fluids


Caesarian Premedication

• Fluids – maybe with glucose• Minimal doses• Opioids good• +/- anticholinergics• +/- Midazolam ( short acting benzodiazepine )• DO NOT USE – phenothiazines ( ACP ),

butyrophenones, alpha2 agonists• Clip and prepare prior to induction if possible


Caesarian Induction

• Pre oxygenation for 5 minutes• Rapid induction advised +/- on surgical

table• +/- anti emetic• Minimize dorsal recumbency prior to

intubations • Artificial ventilation should commence after

intubations particularly when placed in dorsal recumbency.


Caesarian Maintenance

• Isoflurane

• +/- nitrous oxide



Care of neonate

• Clear oral and nasal passages

• Vigorous rubbing

• Doxapram on tongue if apnoea

• Intubate and ventilate if required

• O2 via mask if required

• Dry and keep warm

• Encourage sucking ASAP






Check for deformities


+/- Weigh





Brachycephalic Breeds


Brachycephalic Syndrome

• Narrow nostrils (stenotic nares)

• Relatively long soft palate

• Narrow trachea (tracheal hypoplasia)

• Everted laryngeal saccules

• Laryngeal ‘collapse’

Normal > Partial collapse > Full collapse



Problem Solution

Animal may be very stressed Use low-dose sedative.

May have trouble breathing spontaneously when extubated

Avoid respiratory depressants, use only low-dose and short acting opiods.

Use propofol- rapid induction, allows for top-up, rapid recovery.

Use lignocaine gel on ET tubes and leave in as long as possible during recovery.

Pre-oxygenate patient.Examine throat for mucous or other

obstruction.

May have tracheal hypoplasia Use smaller ET tube than you would usually use for a patient of this size.



• Minimal, if any, sedation

• Laryngoscope ready

• Small ET tubes ready (down to 5.0mm!)

• Pre-oxygenate (if not stressful)

• Rapid induction agent with rapid intubation

• On recovery leave ET tube in as long as possible



• Pre-oxygenate

• Rapid induction agent with rapid intubation

• On recovery leave ET tube in as long as possible– virtually want them to cough it out!


Sighthound Breeds

• Thin skin

• Initial rapid redistribution

• Altered hepatic metabolism of drugs

• Long recoveries

• Hypothermia


Small/Toy Breeds

• Hypothermia• Hypoglycemia• Small veins• Care with fluid

administration (overhydration)

• Length of endotracheal tube

• Surgeons "resting" on patient


Pathological Scenarios

• GDV• Pyometra• Pleural cavity

– Diaphragmatic hernia– Pneumothroax/haemothorax

• Pulmonary• Cardiac• Kidney• Liver


GDV


GDV

• Mainly large deep chested breeds• Circulatory shock as high intra gastric pressure causes

obstruction to gastric circulation, caudal vena cava and portal venous flow. Reduces venous return to heart and cardiac output

• Prolonged hypotension – may lead to irreversible renal failure, acute liver failure

• Portal vein occlusion maybe initiates endotoxaemia from gut flora

• Enlarged stomach – limits diaphragmatic movements- initially tidal volume < and RR > to maintain normal minute respiratory volume


GDV

• Ventricular cardiac dysrhythmias common 12 – 48 hrs after the initial ischaemic episodes, maybe occur 4 days post op

• Cause unknown suspect myocardial ischaemic hypoxia

• Advise treat with lignocaine usually an infusion


GDV

• Initial stabilisation needed• A. decompress stomach• B. correct hypovolaemic shock – hartmans

at 60-90mls/kg max. – Monitor PCV and TPP– If TPP low may require colloids

• C. pain relief – low dose opoids eg methadone or pethidine

• D. ECG - monitor


GDV - Premeds

• Avoid drugs that cause vomiting

• Best methadone and pethidine


GDV - Induction

• O2 prior to induction

• Small doses of thiopentone or propofol if no longer severely compromized

• If severe maybe intubate and put on gas


GDV - maintenance

• Ovoid nitrous oxide as increases the volume and pressure of gas containing spaces

• Isoflurane agent of choice

• Maybe need IPPV


Pyometra


Pyometra

• Usually D/H as are PU/PD even if appears bright

• Usually have acidosis – correct

• Hypotensive

• If closed will present with septic shock


Pyometra

• Aggressive fluid therapy continue for at least 24 hrs post op and monitor urine output

• Antiboitics

• Monitor blood glucose levels pre/op/post if sepsis is suspected and supplement if required


Pyometra

• Benzodiazepines and opioids as premeds cause little C/V depression

• Induction – mask best

• Maintain on isoflurane


Cardiac patients

• 1. Reduced cardiac reserve – avoid stress as this increases sympathetic tone and increases work load on the heart

• 2. If pulmonary edema present maybe require IPPV

• 3. may have or predispose to arrhythmias • 4. Reduced myocardial contractility• 5. reduced cardiac output favours brain

perfusion so < amounts of IV agents required even though induction may be slow


Cardiac Disease & drugs

• 1. opioids – causes no significant reduction in myocardial contractility

• 2. Benzodiazepines – minimal C/V effects• 3. Phenothiazines – only in VVV small

doses, AVOID in cardiac tamponade• 4. Barbituates/propofol – slowly to effect,

small doses• 4. Isoflurane – less arrythmiogenic effects• 5. Anticholinergics

ANAESHTESIA SCENARIOSThoracotomy/Diaphragmatic hernia/Pneumothorax etc

Problem Solution

Can’t breathe spontaneously once chest opened

IPPV immediately after induction

May have stomach/intestines in chest cavity

Don’t use nitrous oxide.


Diaphragmatic hernia


Thoracic Surgery

• Pre Oxygenation is recommended

• Light sedation

• Quick induction and intubation

• Maintenance – inhalational

• Pneumothorax – avoid Nitrous oxide

• Take control of ventilation – Neuromuscular blockers or– Hyperventilation – reduces PaCO2


Thoracic Continued

• Mechanical ventilation– Use of a ventilator or– Anaesthetist squeezing rebreathing bag

• Post op– Analgesics– Local anaesthetics around the intercostal

nerves


Surgical fixes

Widen nostrils

Trim soft palate

Remove everted laryngeal saccule

Permanent tracheostomy


Lung disease


Lung disease

Problem Solution

Prone to hypoxia Pre-oxygenate.Rapid induction - use 100% oxygen.May need to ventilate.Supplement oxygen post operatively.Avoid drugs causing i may be helpful

to animals with pulmonary oedema.


Kidney disease


Kidney disease

Problem Solution

Kidney function reserve reduced Maintain renal perfusion - IV fluids essential.

Avoid hypotension, don’t use ACP.

May be azotaemic (high urea, creatinine)

Avoid prolonged fluid restriction.Correct prior to GA.

May be dehydrated.

May be polyuric Need higher than maintenance rates for fluids

May have electrolyte disturbances, hypoalbuminaemia, anaemia

Correct prior to GA.

Reduced renal clearance of drugs. Don’t use ketamine.Ok to use propofol, thiopentone,

opioids, benzodiazepines.


Kidney disease

• Correct if possible prior to induction:– May be dehydrated– May have electrolyte abnormalities– May be anaemic – Why?

• Premedication – may not be required

• Induction – rapid– Best inhalational techniques


Liver disease


Liver disease

Problem Solution

May have low plasma protein (esp. albumin)

Use lower doses of protein bound drugs.

Avoid fluid overload (prone to oedema)

May have reduced clotting time Evaluate before surgery

Prone to hypoglycaemia Supplement IV fluids with glucose.Monitor blood glucose.

Reduced ability to metabolise some drugs

Avoid thiopentone, ACP, diazepam.Opiates and propofol are OK.

Maybe anaemic - reduced oxygen carrying capacity.

Evaluate prior to GA100% oxygen

May be jaundiced - bilirubin and endotoxins from gut affecting kidneys

IV fluids


Liver disease

• Considerations:– May have decreased plasma proteins

(increases amount of free agents in blood)– Clotting factors may be affected– May have anaemia– May have ascites or pleural effusions

• Premedication – usually not desirable• Induction – ultra-short acting drugs or gas• Maintenance – best is Isoflurane


The End

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Prepare and monitor anaesthesia in animals