Anaesthesia - safety, preparation and species specific

What are factors increase the risk of death in dogs/cats?

Dog	Cat
increased ASA grade urgency / emergency major procedure increased age small breeds brachycephalic paediatric or geriatric obese	increased ASA grade urgency major procedures increased age extremes of weight tracheal intubation cats with cachexia mechanical ventilation
Death after premed = 1% Death when induced = 6% Death in maintenance= 46% Death post op = 46% (within 3hrs)	Death after premed = 1% Death when induced = 8% Death in maintenance= 30% Death post op = 61% (within 3hrs)

How can you improve anesthetia prognosis and safety?

• 19 checks to be repeated

  • before induction

  • before first incision

  • before recovery

    • decrease post op morbidity/mortality by 36-48%

• pre-op patient examination

• good history

• physical status - American Society of Anaesthesiologist (ASA)

• post op tests to check progress of known disease/ unsuspected abnormalities

• anaesthetic machine check

  • before each anaesthetic

  • x1 breathing system = breathing OR non-rebreathing

  • x1 vaporizer

• monitoring equipment

  • how the info is obtained

  • how reliable is it

  • clinical significance of values

Define psychological safety and why it is important

Psychological Safety = a work environment where an individual feels safe to express ideas, ask questions and admit mistakes without fear of embarrassment or punishment

Importance

• enhance communication

• reduce error + systematic errors (report these!)

• increase collaboration

  • reduce hierarchy in team

  • EVERYONE has the right to say something

• improve patient safety

• continuous learning and growth

What is in the anaesthetic plan?

• pre-anaesthetic patient assessment

• anticipated problems

  • related - species, patient specific

  • procedural

  • contingency planning

• anaesthesia drug and support therapy

  • types of IV fluids system

  • IV rates/dose

  • peri-operative = premed, local, post op

• physiological monitoring

  • hypoxaemia

  • hypercapnia

  • hypotension

  • hypothermia

• post anaesthesia recovery

• collaboration with hospital team

Define hypoxaemia, what causes it and how to monitor / fix it

Hypoxaemia

• decrease in O2 in arterial blood

• normal = PaO2<60mmHg or SpO2<90%

• most likely to occur during induction

• causes

  • low inspired O2

  • hypoventilation (room air → 100% O2)

  • shunt or venous administration

  • ventilation-perfusion mismatch

  • diffusion impairment

• monitor with pulse Ox machine

• minimise risk and treatment

  • issue with O2 supply, ET tube, equipment

  • optimise ventilation

  • low cardiac output or low peripheral perfusion, check pulse

Define hypercapnia, what causes it and how to monitor / fix it

Hypercapnia

• increase in PaCO2 in arterial blood or ET CO2

• normal ETCO2 = 35-45 mmHg

• causes

  • most anaesthetics cause resp depression

  • decreased elimination of CO2

• intervention

  • ET tube already in = each to fix

  • ventilation - manometer or capnograph

  • assess depth of anaesthesia

Define hypotension, what causes it and how to monitor / fix it

Hypotension

• mean arterial blood pressure (MAP) is <60 mmHg

• common anaesthesia complication

• monitor

  • non-invasive blood pressure monitor = doppler

  • invasive blood pressure monitor = arterial catheter

• causes

  • identify cause of reduced blood flow to heart

  • identify cause of reduced pump function

  • identify cause of reduced vascular resistance

• intervention

  • turn vaporiser down if possible (reduce depth of isoflurane)

  • consider bradycardia meds, circulating volume deficit and vasopressor meds

    • if already bradycardic and hypotensive → give anticholinergic

Remember:

• Cardiac Output = Heart Rate x Stroke Volume

• MAP = Cardiac Output x Systemic Vascular Resistance

Define hypothermia, what causes it and how to monitor / fix it

Hypothermia

• core temperature ideally <36 degrees

• consider surface area to volume ratio of patient

  • radiation (core → enviro = 40%)

  • convection (air and alcohol swab = 30%)

  • evaporation (cleaning fluids for open wound = 15%)

  • respiration (breathing = 10%)

  • conduction (heat of table = 5%)

• prevent

  • forced air warmers - minimise radiation and convection loss

  • prewarming

  • fluid warmers

  • be cautious of burns

List the key safety considerations during recovery

• when to deflate cuff + extubate

  • secure air way to prevent aspiration of drugs or abdomen contents

• Is the patient moving air = ventilating?

  • feel for air flow

  • listen

  • watch chest wall and abdominal movements

  • maintain SpO2 >95%

• Continue monitoring the patient

  • oxygenation

  • warming

  • IV fluids

  • analgesia - grimace pain scale

  • bladder care - express before start to recover

Dog	Cat
only deflate once animal is swallowing on own and lifting head deflate the cuff and extubate at the same time	extubate first, then deflate cuff to prevent laryngospasm be confident they are able to breath independently

What are the major components of an aesthetic machine and their function

Gas Cylinder = coloured (O2 is white, nitrous oxide is blue, CO is light brown). Pressure of the gas in the cylinder is proportional to the contents EXCEPT nitrous oxide as it is stored as both a liquid and gas. Cylinders differ size (C, D, E)

Oxygen Pressure Gauge = measures the level in the cylinder and in the flowmeter (useable = 400 kPa)

Flow Meter = controls gas flow to patient, measure to the TOP of the bobbin, or the MIDDLE of the ball

Vaporiser = changes inhalant from a liquid to a vapour + adds a controlled amount of vapour to fresh gas flow (e.g. isoflurane)

Common Gas Outlet = where breathing system attaches to anaesthetic machine. Delivers mix of vaporiser and O2. If you press the red button, you can flush O2 though to drain out remaining isoflurane.

Oxygen Flush = delivers high flow O2 from common gas outlet. This bypasses the flow meter and vaporiser to deliver pure O2 (do not press whilst patient attached)

APL (Adjustable Pressure Limiting) Valve OR Pop Off Valve OR Spill Valve = if open, allows the excess gas to escape into the scavenging system, release waste gas. Allows the breathing system to connect to scavenging system. If closed, allows intermittent positive pressure ventilation.

Reservoir or Rebreathing Bag = holds gas for patient, can be used to produce manual breaths/ventilate, used to monitor resp rate

Scavenge System = consists of APL Valve, interface and waste gas elimination system (passive or active)

• Passive = dose not use negative pressure

• Active = slight vacuum

Breathing Systems =

• Full rebreathing system: flow rate = metabolic O2 need

  • Adults = 10+ kg (and also paediatric = 2-9 kg)

• Partial rebreathing system: flow rate between metabolic O2 need and RMV

• Non-rebreathing system: flow rate is greater than RMV

  • Patients less than 7-10 kg

List some key safety considerations of anaesthetic machines that can be fatal

• if a gas cylinder is knocked over and reducing valve is broken off the cylinder, may act as a missile and be secured/fixed

• always ensure adequate O2 in the cylinder and that is is on, BEFORE starting anaesthesia

• never press an O2 flush button whilst the breathing circuit is still attached to the patient = death as patient lungs will explode with extreme pressure

• if the APL valve is left closed with the patient attached to to the breathing circuit = death as increased pressure in thorax reduces venous return + cardiac output

• active scavenge systems that does not contain an interface that prevents the build up of positive or negative pressure = death of patient due to the remove of gas from the patient

• when 50% of soda lime cannister has changed colour, is MUST be replaced unless not effective

What is mechanical dead space?

The dead space of a breathing system = volume from where fresh gas enters the system to the beginning of the patients airway (incisor teeth)

• one-way valves that stop closing will cause increase in dead space = allows rebreathing of CO2

Explain the components of rebreathing systems and their purpose

One Way Valves

• ensures one-way movement of gas around circuit

• attached to CO2 absorbent canister (yellow circles)

• checked and cleaned regularly for maximum efficiency

  • increased moisture may cause them to get stuck in open position

  • if stop closed will cause dead space

  • malfunctioning = detected as inspired CO2 on capnograph

Rebreathing Tube

• connects circuit breathing system to patient

• Y-piece = heated and non-heated

• Co-axial or F-cuit (inside each other)

  • Advantages = reduce bulk + warming inspired gas

  • Disadvantages = if inner tube breaks, patients will inspire CO2

Soda Lime Cannister

• chemical absorbent that removes CO2 from exhaled gas

  • white granules → purple when exhausted

  • pink granules → white when exhausted

• fresh granules will crumble and you can feel them produce chemical reactions due to heat of cannister

• exhausted granules are hard and will show as inspired CO2 on capnograph

  • change this as soon as 50% of cannister has changed colour

Explain the components of non-rebreathing systems and their purpose

Ayre’s T Piece

• FG (central outlet) = delivers fresh gas from anaesthesia machine

• P (right side) = connects to patient

• EG (left side) = directs exhaled gas away from patient

Mapleson D

• rebreathing bad attached

• pop-off valve open

• scavenge system is attached at the level of the pop-off valve

List the gas flow rates: rebreathing, partial rebreathing and non-rebreathing systems

• Flow rate for rebreathing system = 4-10 ml/kg/min

  • O2 flow rate = metabolic O2 requirement

• Flow rate for partial rebreathing system = 20-50 ml/kg/min

  • flow rate is between metabolic requirement for O2 and resp minute volume

• Flow rate for minimal-rebreathing system = 100-200 ml/kg/min

  • flow rate is greater than resp minute volume

  • pre-oxygenation and beginning an anaesthetic or priming circuit

• Flow rate for non-rebreathing system = 300-500 ml/kg/min

  • no soda lime to remove CO2 so higher gas flow rate is needed to remove CO2

Advantages and disadvantages of rebreathing systems

Advantages	Disadvantages
economical conserve heat and moisture PaCO2 only depends on ventilation and not FGF easy to use with mechanical ventilators	many parts = more risk of breakages need to clean and sterilise vaporiser settings are not rapidly reflected by changes in % inspired inhalant rapid change in depth increased work to breath

Advantages and disadvantages of non-rebreathing systems

Advantages	Disadvantages
simple easy to clean lightweight / less parts cheap Do no require CO2 absorbents (soda lime) minimal dead space anaesthetic concentrations can be closely monitored with vaporiser settings rapid changes of inspired inhalant % = easy to control depth	potential for rebreathing exhaled gas is high fresh gas glows are not sued high fresh gas required = $$ large amount of waste anaesthetic gasses significant heat and humidity loss

Planning before the anaesthesia plan for dog/cat anaesthesia plan? (SHEAP)

SHEAP

• Signalment

  • age = speed of drug metabolism

  • dog breed = greyhound, boxer, brachycephalic, collies, shepherds have varied recovery

  • cat = specifies differences

  • size = metabolic rate + hypertension

• History

  • current medications

  • wellness - current disease or clinical signs

  • has it been fasted?

• Examination

  • cardiovascular system

  • respiratory system

  • body condition score

  • demeanour

• Assessment

  • body systems

  • problem list = why did it present today? previous?

  • differential diagnoses

  • ASA status (American Society Anaesthesiologist Pain Scale)

• Plan

  • Diagnostics

  • Blood work

  • Reassess

  • ASA status again

  • Plan drugs

Key anaesthetic complications in plan

• list of potential complications

  • patient specific = history, signalment

  • body systems = exam, assessment

  • procedure consideration

• 5 H’s + B

  • Hypotension

  • Hypoventilation

  • Hypothermia

  • Hypoxaemia

  • Bradycardia

Anaesthesia Drug Plan for Dog / Cat (PIMS)

• Preanesthetic stabilisation

  • dehydration, hypovolaemia or electrolyte abnormalities

  • pre-oxygenate 3-5 mins prior to induction w will fitting mask

    • Rebreathing = 100-200 ml/kg/min

    • Non-rebreathing = 300-500 ml/kg/min

• Premedication and Analgesia Plan

  • contraindications?

  • route? - usually before catheterisation

  • monitor respiratory and cardiovascular response

  • usually opioid ± sedative

    • Opioids = gabapentin or trazadone, methadone, morphine, butorphanol, buprenorphine

    • Sedative = acepromazine, midazolam, diazepam,

    • Both = medetomidine, dexmedetomidine,

• Induction agent

  • Injectable = most common, titrate to effect

    • Eg: alfaxalone, propofol, ketamine, midazolam, diazepam, thiopental

  • Inhalant = mask or a box if can’t place catheter

    • O2 + drug (usually isoflurane)

    • monitor depth when in box, increased stress

    • pollutes environment

• Maintenance drugs

  • Inhalant and/or CRI

  • Monitoring equipment = SPO2, ETCO2, doppler, ECG, BP

• Supportive therapy

  • fluids

  • cardiovascular support = minimum 30% O2 for 5 mins post inhalant, check O2 levels with SPO2

  • post op analgesia

Key notes for Intubation and Extubating in Dogs vs Cats

Intubation

• occurs after induction drug

• Cats = susceptible to laryngospasm → must spray/drop lignocaine first and wait 20-30 seconds after

  • 0.1-0.2 ml of 2% is normal

  • 5mg/kg or more = overdose

• Cats = susceptible to tracheal necrosis and rupture

  • use an uncuffed ET tube (must check for leakage)

  • use a cuffed ET tube must inflate carefully

Post Intubation

• connect breathing system and ETCO2

• tie ET tube in place, below the connector and inflate if required

• check for depth or life

• turn on maintenance

• always disconnect patient when changing position to ensure trachea does not get damaged by ET tube

• never leave a patient with ET tube in unattended

Extubating - Dog	Extubating - Cat
swallow, deflate cuff and extubate check for movement air (ensure not obstructed) If oral procedure or risk of regurg: check oral cavity before turning off inhalant can extubate with partially deflated cuff Brachycephalic = always leave intubated until vigorously attempting to expel ET tube, then extubate	Signs = moderate jaw tone, twitching ear, limb withdrawal deflate cuff + extubate (then should swallow) to avoid laryngospasm check for movement air be prepared to re-induce and re-intubate

C-Section Considerations (elective or emergency)

All C-Sections

• General anaesthetic considerations

  • Hypoventilation, Hypothermia, Hypoxaemia, Hypotension

• Physiological alterations induced by pregnancy

  • early =physiological - progesterone and oestrogen

  • later = mechanical - enlarged uterus

• Maternal pathology (obstetrical complications like blood loss)

• Pharmacology of drugs effected mother and neonates

• Analgesia

• Neonatal revival

Emergency:

• often electrolyte and haematological imbalances (Ca)

• higher mortality rate in puppies delivered by c-section due to maternal physiological state due to prolonged labour and foetal stress in utero

Cardiovascular, Respirator, GI and CNS changes with pregnancy and effects on anaesthetic

Cardiovascular

• increased blood volume → increase cardiac output + high HR

• BP unchanged

• Anaesthesia = risk of hypotension if low BV, CO, HR, uterine blood

• Prevention = monitor BP + IV fluids (avoid overload + vasopressors)

Respiratory

• increased respiratory minute volume and oxygen consumption

• decreased functional residual capacity

• Anaesthesia =

  • more rapid uptake of anaesthesia agents

  • increased risk of hypoxaemia

  • increased atelectasis (lung collapse) especially if in dorsal

• Prevention = pre-oxygenate, ventilate and sustain inhalation

Gastrointestinal

• emptying of contents is slowed

• decreased oesophageal sphincter tone

• increased gastrin and intragastric pressure

• Anaesthesia =

  • risk of aspiration pneumonia

  • acidic stomach contents

  • unknown fasting status if emergency

• Prevention = rapid induction, intubation and cuff inflation but extra care with extubating

Central Nervous System

• decreased anaesthetic requirements

• venous engorgement epidural space

• Anaesthetic = risk of overdose, lower epidural volume needed

• Prevention = monitor depth, use short acting and reversible drugs

Pharmacology of Drugs when Pregnant

Pathology

• dehydrated / hypovolaemic / electrolytes → risk of toxaemia

• stress and exhausted → limited self regulation

• pre-existing disease

• medications = Oxytocin

• potential risk of haemorrhage

Pharmacology

• decreased MAC (minimal alveolar concentration) = decreased dose

  • use weights prior to pregnancy

• placental transfer = assume all drugs willl cross into placenta

  • effected by blood flow, thickness, SA, diffusion of drugs

• analgesia is needed for C-section

  • opioids - short acting and reversible

  • local anaesthetic - epidural or midline local pre/post incision

  • NSAID - in recovery

• Premed = none or a short acting opioid

• Induction = propofol or alfaxalone (titrate to effect)

  • AVOID = ketamine, thiopentone, benzodiazepines and alpha 2 agonists

• Maintenance = low dose Isoflurane + O2 also oxytocin intraoperatively

• Post birth = methadone IV, NSAIDS

Considerations of neonates both C-Section

• good preparation

  • O2, masks and ET tubes x many of each

  • suction

  • warm and dry towels

• vigorous rubbing to stimulate

• may be hypoxic → bradycardia = potentially give adrenaline?

• pharmacological = naloxone or last resort doxapram

Anaesthetic plan for horse in field or hospital

• Equine anaesthetic mortality = 1:100

  • cardiovascular arrest, fractures, respiratory obstruction, myopathy, neuropathy or myelomacia

  • increased risk if = foals, geriatric, high ASA status, if in dorsal recumbency, emergency, fracture repair surgery

  • decreased risk if = short procedure, total IV anaesthetic, using acepromazine

Pre-anaesthetic

• informed risk and consent in writing

• exam + accurate weight for drug dosing

• bloods and lab tests ideal but often not possible

• preparation if in field

• IV catheter (aseptic) = 14 G with 3.25 or 5 inch catheter

• fasting = no evidence/should not be fasted. Just wash out mouth prior

  • cannot vomit, so little risk of regurgitation

• may remove shoes or bandage hooves to prevent injury in recovery

• use NSAIDS and antimicrobials prior to anaesthetic

Potential problems or complications with GA in horses

• Hypoventilation (high PaCO2)

  • drugs used, effected by anatomy, size and weight

  • dorsal recumbency = pressure on lungs → low tidal volume

• Hypoxaemia (low PaCO2)

  • can occur even if on 100% O2

  • ventilation perfusion mismatch → shunting (due to anatomy)

• Hypotension (myopathy)

  • ideally, mean arterial blood pressure is above 60 mmHg (below leads to myopathy)

  • monitor BP closely due to large body weight compression

• Neuropathy

  • peripheral nerve injury

• Fractures or major injury

  • increase muscle relation pre induction and good analgesia

  • lubricate and protect eye

• Field location vs hospital

  • consider weather and temperature

  • grass is ideal

• Other = breed, procedure, pathology, analgesia

Prevention

• reduce procedure time

• always 100% O2 and controlled ventilation when possible

• naso-trachael tubes for recovery (obligate nasal breathers)

• monitor = capnograph, pulse Ox, arterial blood gas

• use adequate padding underneath and between limbs

• if in lateral recumbency, pull down leg forward

• if in dorsal recumbency, support front legs, avoid overextension in hind

• avoid overextension of neck and remove halters

Premeds, Induction and Maintenance drugs during equine anaesthetic

Premedication = sedate, muscle relaxant and analgesia

• local blocks as much as possible = standing surgery is best

• 5 point stance = x4 legs and head down

• Acepromazine

  • mild tranquilisation but no analgesia

  • reduced risk of death peri-operatively

  • smooth induction

  • vasodilation

• Alpha 2 Agonists

  • sedates, relaxes and analgesia

  • may cause bradycardia, hypertension, increased urine, increase blood glucose, and motion

• Opioids

  • well when with alpha 2 agonist (sedate + analgesia)

  • minimal cardiovascular effects

  • may cause excitement but slow GIT → colic

  • methadone is better then butorphanol

Induction = predictable, controlled and uneventful

• standing → lateral recumbency requires adequate sedation and muscle relaxation (may use mechanical tools)

• always bolus drugs to ensure they don’t panic

• Co-induction:

  • Diazepam or midazolam = central muscle relaxant

  • Guiafensin = central muscle relaxant (causes haemolysis)

• Induction agents

  • Ketamine = increase HR/BP, minimal RR and GIT SE, only provides analgesia not muscle relaxant

  • Alfaxalone and Propofol = mainly for foals

Maintenance

• TIVA = total intravenous anaesthesia, intermittent bolus or CRI

• 45-60 mins max

• gravity infusion set or infusion pump/syringe pump

• be careful with intermittent bolusing and maintaining steady GA

• Inhalation = isoflurane, sevoflurane or desflurne

  • dose dependant cardiovascular depression

  • no analgesia

Monitoring and Recovery from GA in equine

Monitoring during Anaesthesia

• Depth = movement, muscle tending, RR, CO

  • light = eye movement is normal, minimal change in HR + BP

• Cardiovascular = MM colour, CRT, HR, pulse, direct/indirect BP

• Repiratory = RR, capnograph, pulse oximetry, arterial blood gas

Recovery

• critical period

• improve with analgesia, positioning, oxygen, using halters

Anaesthetic plan for a ruminant in field or hospital

• intramuscular = dart gun

• intravenous = jugular catheter, tail vein or auricular vein

  • cattle = jugular, 10-14 G, be aware of carotid artery

  • small ruminants = jugular or cephalic, 20-18 G

• remember cattle are food animals so need to have short half lives and not damage muscles too much

Potential problems with anaesthetic in cattle

• dorsal recumbency

  • oesophageal opening is submerged by rumen content → regurgitation/reflux → aspiration pneumonia (foreign body or bacteria) → disease progression = dead in 24-48 hrs

  • fermentation gas accumulate + cannot eructate → bloat

  • increased pressure on diaphragm = decreased tidal volume + increase risk of regurgitation and aspiration

  • decreased lung space + inspiration = hypoventilation due to increased CO2 + hypoxaemia

• ischaemic myopthy and nerve injury

  • increased body weight in recumbency, non-expandable muscle facia can lead to ischemia + muscle swelling → myopathy and nerve injury

  • not as prone to hypertension as horses

• salivation

  • huge volumes of fluid can pool in pharynx and mouth → risk of aspiration and depletes circulating plasma volume

    • cattle = 50L / 24hours

    • sheep = 8-16L / 24hours

Ways to prevent common GA problems in cattle

• good clinical exam

• fasting

  • will reduce volume of rumen and slow fermentation

  • list risk if they do regurgitate

  • Cattle: withhold food for 24-48 hrs and water for 12-24 hrs

  • Sheep/Goat: withhold food 12-18 hrs and water for 8-12 hrs

  • Neonates: do NOT withhold food or water (risk of hypoglycaemic and hypovolaemic)

• intubation

  • use palpation of endotracheal tube into trachea

  • inflate cuff rapidly to avoid aspiration

  • hard to intubate = use Drinkwater gag, thread stomach tube through tracheal tube, intubate, slide out then inflate cuff

  • Cattle: don’t laryngospasm

  • Sheep, goats, alpacas: prone to laryngospasms

• occiput elevation (poll)

  • elevate occiput/poll to discourage passive reflux and encourage any regurgitated material to drain

• padding and positions

  • soft surface and padding between limbs

  • pull lower leg forward

  • minimise duration

  • ensure good blood pressure throughout

  • left lateral recumbency is better (more pressure onto rumen to prevent distending)

Premeds, Induction and Maintenance drugs during cattle anaesthetic

Premedicant and Sedation

• Xylazine

  • most common, cattle are extremely sensitive (1/10th horse)

  • IV or IM = onset is 5-20 mins

  • lasts 35-40 mins

  • reversible with alpha 2 agonist (atipamezole)

  • SE = bradycardia, no swallow reflex, uterine contraction, reduced uterine blood flow (bad if calf), inhibit thermoreg

• Alpha 2 Agonists

  • can cause hypnosis and recumbency

• Acepromazine

• Benzodiazepines = Diazepam, midazolam, zolasepam

  • not for standing sedation in adult ruminants → ataxia

• Opioids

Induction

• restrain in crush with rope if needed

• 10-14 G catheter in jugular vein

• IV xylazine bolus → sternal recumbency (release from crush)

  • follow up with ketamine ± midazolam or diazepam

  • or follow up with thiopentone

• intubate trachea, inflate cuff

• intubate oesophagus + pass bore stomach tube

Maintenance

• inhalation + O2 is ideal

• IV if procedure is less than 45 mins but must give O2 as well

Monitory and recovery after GA in cattle

Monitoring

• physical movement, jaw chewing, ear movement, response to stimuli

• deep = eye will be ventral or even central if very deep

• use HR, pulse pressure, MM colour, CRT

• direct blood pressure by catheterising auricular artery or doppler

• ECG for cardiac dysrhythmias

Recovery

• sternal recumbency as soon as possible to allow rumen gas to escape

• may regurgitate so always leave ET tube in with cuff inflated

• only extubate (with cuff inflated still) when strong swallows

• can reverse xylazine to help

Analgesia

• NSAIDS = meloxicam, ketoprofen

• Opioids = butorphanol, morphine, methadone

• Alpha 2 agonists = short term only

• Local = lidocaine and bupivacaine (take care if food producing)

Regional anaesthesia in cattle

• Local options = lidocaine, bupivcaine

• Benefits = surgery is whilst standing so safer but needs restraint

• Complications = toxicity, infection or neuronal injury

• Uses

  • blocks for dehorning

  • blocks for teats or udder

  • inverted L block

  • Low or caudal epidural

  • paravertebral block, petersen block, retrobulbar block

  • auriculopalpebral

Key general considerations for paediatric vs geriatric under GA

Paediatric	Geriatric
increased work of breathing compliant ribs + weak intercostal muscles high resting respiratory rates + minute volumes immature chemoreceptors (hard to adapt to changing O2 + CO2 levels) decreased functional residual capacity increase O2 demand	increased work of breathing non compliant lungs increased closing capacity decreased pulmonary perfusion decreased gas exchange increase airway resistance

Both Predisposed to Hypoxaemia:

• respiratory fatigue - may need intermittent ventilation

• atelectasis (lung collapse)

• Hypoxaemia

Assisting Paediatric and Geriatrics under GA

• lots of preoxygenation to increase O2 reserve

• prepare a ventilator + good size breathing bag

  • use a monometer to measure this

• close monitoring with pulse oximetry (SPO2) and capnography

Paediatric	Geriatric
IV access same drugs as adults, but low doses maintain HR careful monitoring good ventilation avoid hypoxia, hypothermia and hypoglycaemia good analgesia	good history IV access same drugs as adults, but low doses good pre-oxygenate maintain blood pressure careful monitoring good analgesia good post op care

Key paediatric considerations under GA and how to manage

	Consideration	Management / Prevention
CVS (Heart)	low resistance-high flow circuit, systemic vascular resistance, BP and volume high HR, CO and plasma volume low cardiac reserve low HR poorly tolerated hypovolaemia → decrease CO	minimise bradycardia and hypotension maintain blood volume
Liver (Hepatic)	prone to hypoglycaemia	take care with drug doses + monitor BG
Renal (Kidney)	decreased clearance poor concentrating ability	pre-op renal function test avoid drugs metabolised by kidney monitor urine production stabilise with IV fluids maintain BP avoid pre-op NSAIDS
CNS	reduced drug requirements	confusion and anxiety post anaesthetic delirium reduced drug requirements
Thermoreg	increased SA to body weight prone to hypothermia low energy reserve	good management of temperature + monitoring

Key geriatric considerations under GA and how to manage

	Consideration	Management / Prevention
CVS (Heart)	low cardiac reserve = low baroreceptor activity, blood volume, circulation time, BP and CO myocardial degeneration valve dysfunction cardiac arrhythmias	minimise bradycardia and tachycardia avoid hyper+hypo tension minimise vasoconstriction maintain blood volume
Liver (Hepatic)	decreased liver, hepatic blood flow and metabolic activity prone to hypoproteinaemia, hypoglycaemia, coagulation problems and seizures	pre-op assessment of liver function, avoid hypotension MAP > 60 mmHg
Renal (Kidney)	renal disease risk risk of post GA renal failure	pre-op renal function test avoid drugs metabolised by kidney monitor urine production stabilise with IV fluids maintain BP avoid pre-op NSAIDS
CNS	decreased brain mass + cognition	confusion and anxiety post anaesthetic delirium reduced drug requirements
Thermoreg	low basal metabolic rate low msucle mass	good management of temperature + monitoring

Premed drugs used in paediatric / geriatric

Sedation / Premed

• good IV

• low stress and low anxiety

• Paediatric = not required, but if needed low dose opioid

• Geriatric = short acting + reversible = opioid ± benzodiazepine or ACP

Acepromazine

• good sedation some anti-anxiety

• no analgesia and not reversible (8 hours)

• may cause vasodilation, hypotension, hypothermia, liver metabolism

Alpha 2 Agonist

• avoid (large SE) = vasoconstriction, bradycardia, decrease CO, arrhythmia

Benzodiazepines = Midazolam or Diazepam

• centrally acting muscle relaxant

• reasonable cardiovascular stability

• unpredictable sedation

• used as a co-induction

Opoids = pure mu agonist (methadone)

• consider mode of action, duration and reversibility

• SE = bradycardia (have an anticholinergic to reverse), hypoventilation

Induction, Maintenance and analgesia drugs used in paediatric / geriatric

Induction

• pre-oxygenate

• titrate slowly

• ideally alfaxalone or propofol (short half life + non cumulative)

• avoid ketamine and thiopentone

Maintenance

• Inhalation may cause vasodilation but minimal metabolism

• Intravenous

• ensure balanced / multimodal

• ideally isoflurane

Analgesia

• CRI or incremental dose intra /post operatively

• ideally opoids (morphine and fentanyl) or ketamine

• regional anaesthesia, local and nerve blocks

• be careful with toxicity

Anatomy primary and secondary changes in brachycephalic patient

Aim = leave hospital alive (morality rate is 2.5% vs normal is 0.5%)

• Primary Changes = Brachycephalic Airway Obstructive Syndrome (BOAS)

  • stenotic nares

  • elongated soft palate

  • large tongue

  • abnormal nasopharyngeal tubinates

  • hypoplastic trachea → diagnose on radiograph (ideal larger than 0.16)

    • = increased airway resistance and negative pressure

• Secondary Changes

  • excessive pharyngeal tissue

  • mucosal inflammation and oedema

  • laryngeal saccule eversion

  • tonsil eversion

  • arytenoid cartilage collapse

  • bronchial collapse

  • pulmonary oedema

  • gastro-oesophageal reflux

• Comorbidities

  • oesophageal, gastric and duodenal inflam → regurg + vomit

  • aspiration pneumonia

  • congenital cardiac conditions

• Other

  • increased vagal tone → bradycardia

  • excessive skin → hard to intubate

  • prominent eyes → hard to restrain + ulcerations

Premed, Induction and Maintenance drugs for the brachycephalic patient under GA

Premedication / Sedation

• if very stressed give IM or IV

• if low HR, premed with atropine or glycopyrrolate

  • contraindicated with alpha 2 adrenergic agonist

• give anticholinergic if increased vagal tone

• low dose opioid (methadone) ± very low dose acepromazine

  • boxes do not give ace

• dexmedetomidine ± opioid (minimal relaxation of pharyngeal muscles)

• corticosteroid (dexmethasone) for airway surgery to decrease inflam/irritation

• esomeprazole to decrease regurg and gastric upset

Induction

• minimise change of obstruction and maintain blood oxygen

• good airway assessment or rapid intubation + airway protection

• preoxygenate then rapid induction IV

• Use alfaxalone or propofol

Maintenance

• TIVA and/or inhalant anaesthesia

• Injectable = alfaxalone or propofol

• Inhalants = isoflurane or sevoflurane

• Local blocks (opioid bolus or infusion) = methadone, fentanyl, morphine

Supportive Care, Recovery for the brachycephalic patient

Parameters

• decreased PaO2

• increased PaCO2 and PCV

• often increased ASA status and BCS

Supportive Care

• Pre-oxygenate to avoid obstructions = decreased stress + pain

• catheter before premed to decrease stress

• anticholinergic (atropine or glycopyrrolate) if already low HR

• fluids = Hartmans 6ml/kg/hr

• mannitol pharyngeal swabs = decrease swelling via osmosis

• be ready to reintubate

Recovery

• respiratory distress and obstruction common

• pharyngeal oedema

• regurgitation → aspiration pneumonia

• always be ready to reintubate ± tracheostomy

• leave ET tube in as long as possible until they reject OR use intranasal O2

• death

Capnography

• measures ventilation by the the expired CO2 / end titdal CO2

• either side-stream or main stream

• confirms airway confirmation and indicates hypercapnia or respiratory acidosis

Each wave:

1. Inspiratory baseline - assess inspired Co2 and indicate breathing

2. Start of expiration (anatomical dead space)

3. Plateau (alveola gas)

4. Inspiration

Electrocardiogram (ECG)

• Wave measures the electrical function of the heart to identify cardiac arrhythmias

  • can have electrical activity without mechanical activity

• each heart beat should have P, QRS and T wave

  • leads 1 and 2 cranial to heart, then one caudal to heart “smoke over fire”

  • read on lead 2 (closest to heart)