Anaesthesia

Anaesthesia

The reversible production of a state of unconsciousness

General anaesthesia

The state of unconsciousness across the whole body, produced by anaesthetic agents, with the absence of pain throughout the whole body

Regional anaesthesia

Insensibility caused by the interruption to sensory nerve conduction on an area of the body

Local anaesthesia

Lack of sensation in a specific area of the body

Sedation

State of reduced excitement or irritability. No loss of consciousness

Anxiolysis

State of reduced anxiety

Analgesia

State of a reduced sensibility to pain

Narcosis

A sleep-like state

Hypnosis

An artificially induced state of passivity (this term is often used interchangeably with 'narcosis')

Premedication

A combination of drugs given prior to GA induction to:

• Calm patients

• Aid restraint

• Provide pre-emptive analgesia

• Reduce induction agent and maintenance drug quantities

• Contribute to a smooth induction and recovery

Induction phase

Phase where the patient is taken from a conscious to anaesthetised state. This involves:

• IV placement

• Pre-oxygenation

• Premed admin (if not already given)

• Induction agent admin

• Airway security

Maintenance phase

Phase where anaesthesia is taking place:

• Maintenance drugs

• Placement of local/regional blocks

• Prep + procedure

Recovery phase

Cessation of gaseous maintenance or CRI:

• Airway device removal

• Move to recovery area (this phase is smoother and less sudden with a good premed)

Anaesthetic triad

Narcosis, analgesia, and muscle relaxation.
The 3 main components of anaesthesia

Balanced anaesthesia

The idea that anaesthesia produced by smaller doses of 2+ agents is safer than a large dose of 1 agent.

MDR1 gene mutation

A mutation of a gene found in collies, sheepdogs, shepherds, etc. This mutation means toxins can't be taken away, causing neurological symptoms.

Alfaxalone

A type of injectable anaesthesia agent that isn’t propofol

Chamber induction

Gas induction where a box is used. This is great for smallies, is cheap, and easy to set up.
However it is stressful to animals (stingy eyes, weird smell, etc), difficult for observation, and risks staff exposure.

Facemask induction

Gas induction by covering the nose + mouth with a mask. This is cheap, easy to use, and allows a quick change to oxygen or volatile gas.
However, this doesn't protect the airway, risks staff exposure, and has a lot of dead space.

Laryngeal mask airway (LMA)

This airway management device sits over the larynx.
It is more commonly used in humans, and less designed for animals.

Supraglottic airway device (V-gel)

Airway management device that has a species and weight specific design. This requires training before use.
It blocks the oesophagus + is useful in rabbits!

Endotracheal tube (ETT)

Gold standard airway management device for airway protection!
This prevents atmospheric exposure.
Measure from the incisors to the tip of the shoulders

Bevelled edge

The diagonal cut of the end of the ET tube. This gives a wider surface area, helping with placement

Murphy's eye

The little hole in some ET tubes, allowing for breathing if the main tube gets blocked.
Like the little hole in lollypop sticks!

Adaptor

The end of the ET tube that connects to the breathing circuit

Pilot balloon

Part of the ET tube that connects to a tube, connecting to the cuff.

Silicone ETT

Soft and flexible ET tubes

PVC ETT

"single use" ET tubes with high volume, low pressure cuffs.
These are clear so you can see blockages and condensation.
Cleaning can make them brittle

Red rubber ETT

ET tubes with low volume, high pressure cuffs. The cuffs are more rounded creating a small area of high pressure on the tracheal tissue

Armoured ETT

ET tube that is metal reinforcement on the inside. These allow movement of the neck.
*DON'T USE IN AN MRI MACHINE*

ASA I

Anaesthetic risk - Normal + healthy

ASA II

Anaesthetic risk - Mild systemic disease (not a risk, but worth noting)

ASA III

Anaesthetic risk - Systemic disease that's well compensated or controlled by treatment

ASA IV

Anaesthetic risk - Severe disease that's uncompensated

ASA V

Anaesthetic risk - Unlikely to survive 24h without surgery

E

ASA notation added to any patient for

Checklists

Used in procedures to ensure everything is done and complete before/after.
Introduced by WHO in 2008 + mandated by NHS in 2009.
Reduced surgical complications/deaths by 1/3.

Oxygen cylinder

Made of molybdenum steel, these store oxygen at over 10,000kPa for use in anaesthetics.
They should be stored undercover, dry, clean, and well ventilated, with no extreme temperatures.
Store full and empty separately.

Pipeline gas

Oxygen is transmitted from a large storage outside to the anaesthetic circuit through pipes.
This is better to deal with larger caseloads.
It has 2 cylinders - one is a reserve

Cylinder yoke

Attachment point for cylinders of oxygen, nitrous, etc.
These are specific, preventing the wrong cylinder being attached.

Bodok seal

Non-combustible copper ring that ensures a gas-tight seal between the cylinder and yoke

Pin index safety system

Each cylinder has 2 pins, which align with 2 holes on the yoke, like a lock/key mechanism. This prevents the wrong cylinder being attached.
There are 6 potential pin locations

Schrader sockets

Sockets for probes to attach to, allowing for pipeline oxygen access.

Schrader probe

Unique end to each type of pipeline. These fit into their type of socket, preventing transmission of the wrong type of gas.

Hypoxic guards

A feature on some anaesthetic machines that link the Oxygen with Nitrous, maintaining the minimum ratio, and preventing delivery of hypoxic gases.

Flowmeters

Measure the flow of gas with an accuracy of +/-2.5%.
Consist of the flow control valve, tapered transparent tube, and lightweight rotating bobbin/ball

Flow control valve

The knob of the flowmeter that is used to control flow of gas

Tapered transparent tube

The tubes of the flowmeter

Lightweight rotating bobbin/ball

Component of the flowmeter that tells us the volume of each gas being delivered.

Read the bobbin from the top.
Read the ball from the middle

Vaporiser

Component of the anaesthetic machine containing liquid anaesthetic agent. Gases from the flowmeter flow through and pick up vapour, delivering it to the patient.

Back bar

Where the vaporiser attaches to the anaesthetic machine

Wicks

Part of the vaporiser that increases SA for anaesthetic liquid evaporation

Baffles

Part of the vaporiser that directs the FGF closer to the anaesthetic liquid surface.

Common gas outlet

Where we attach the inspiratory limb to receive FGF.

Oxygen flush button

Button near the common gas outlet that supplies oxygen really fast, bypassing the flowmeters and vaporiser.

400kPa - So can cause barotrauma.

Active scavenging

Scavenging using a fan and vent system to suck waste gases out of the building.

Air break

Component of active scavenging that prevents negative pressure sucking the patients lungs and FGF.

Passive scavenging

Scavenging where the patients expiratory effort pushes waste gases into tubing to either:

• Outside

• Into activated charcoal container (doesn’t absorb nitrous)

Oxygen concentrators

Machines that purify normal room air to supply oxygen to patients

Dead space

Volume of gas that does not eliminate CO2

Tidal volume

Volume of gas entering the lungs per inspiration

Metabolic oxygen requirement

Amount of oxygen required to carry out metabolic processes

Rebreathing

When inspired gases reaching the alveoli contain more CO2 than accounted for by mere re-inhalation from dead space gases

Coaxial

Tube within a tube

T-piece

Non-rebreathing system for

Bain

Non-rebreathing system for >8-10kg

Circuit factor 2-3

Parallel lack

Non-rebreathing system for >10kg

Circuit factor 0.8-1

Magill

Non-rebreathing system for >5kg

Circuit factor 1

Minimum alveolar concentration (MAC)

Effective dose of volatile agent to prevent a noxious stimuli response in 50% of the population

Volatile agent

Liquid that changes to vapour at room temperature

Second gas effect

The concept that if volatile agent is given with N20, N20 quickly diffuses into capillaries, resulting in a high alveolar concentration of volatile gas.

Stage 1

Time of induction to unconsciousness.

• Breath holding

• High HR and RR

• Dilating pupils

Stage 2

Rhythmic breathing returns under unconsciousness

* Hyperactive cranial nerve reflexes

Stage 3: Plane 1

• Regular deep inspiration

• Absent limb movement

• May have brisk pinch reflex

• Ventromedial eyeball

Stage 3: Plane 2

• Absent palpebral reflex

• Relaxed muscles

• Ventromedial eye position

• Reduced tidal vol, RR, HR and BP

• Regular and deep inspiration

Stage 3: Plane 3

• Central eyeball

• Increased pupil diameter

• Loss of pedal reflex

• Relaxation of abdo muscles

• Low BP + HR

Stage 4

• Progressive respiratory failure

• Rapid or v slow impalpable pulse

• Central eye

• No palpebral reflex

• Extended capillary refill time

• Accessory muscle twitching (e.g. twitching of throat)

Doppler unit

Microphone of a doppler set

Sphygmomanometer

Doppler puffer

Sidestream capnography

Capnography sample tube connects to the side of the breathing tube adapter

Mainstream capnography

Connecter between the Et tube and breathing tube, using an infrared light source and sensor to give real time CO2 activity, without sampling FGF.

Plethysmograph

The waveform trace given on some pulse oximeters

Low flow anaesthesia

A method of environmental anaesthesia, using a FGF of 0.5-1L/min. This often needs a circle system and high levels of training

Waste heirarchy

Classification of how we can dispose of different types of waste

Acepromazine

A mild sedation used for hoses.

30 minute onset

4-6 hour action.

Used in initial horse premed

Alpha2-adrenoreceptor agonists

Drug that relaxes horse muscles and provides analgesia to some degree

Used pre-GA in horses

Diazepam

Induction agent (alternative to ketamine) used in horses.

Give as a bolus

Equine post-anaesthetic myopathy

Condition occurring in the post-GA recovery period where muscles harden and cause lameness

Convection

Heat transfer from the body → air

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e.g. from cold air or draughts

Conduction

Heat transfer from the body → surfaces

Radiation

Heat transfer from the body → structures not touching the patient

Moisture evaporation

Heat loss from the body from water loss from the body surfaces.

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e.g. surgical scrub/alcohol evaporation, respiration, or an open body cavity.