Monitoring and Maintenance of Anesthesia Flashcards
What is the definition of MAC?
- MAC is the Minimum Alveolar Concentration of an inhalational anaesthetic agent which is required to prevent movement in response to a noxious stimulus in 50% of animals.
- MAC studies are usually performed in experimental animals which have not received any other drugs for premedication or induction of anaesthesia.
How do we use MAC in clinical anaesthesia?
- MAC gives us information about the POTENCY of different inhalational agents, ie. how much we need to give to an animal to produce anaesthesia.
- It can be thought of as the dose required of an inhalational agent.
- However, MAC studies are based on 50% of the population not moving in response to a painful stimulus: the other 50% of the population given MAC of an inhalational agent will move in response to a painful stimulus!
- For clinical anaesthesia, we would use 95% of the population as a guideline. To achieve clinical anaesthesia in 95% of the population, you need to give about 1.25 x MAC.
- Additionally, there are lots of factors that can increase or decrease MAC (or the amount of inhalational agent required) in an individual animal.
MAC and Potency
The MAC of isoflurane in the dog is 1.3%. The MAC of sevoflurane in the dog is 2.3%. Potency is inversely proportional to MAC.
- This means that isoflurane is more potent than sevoflurane
Blood:Gas
Desflurane
0.42
Blood:Gas
Halothane
2.4
Blood:Gas
Isoflurane
1.46
Blood:Gas
Sevoflurane
0.6
Blood:Gas
Nitrous Oxide
0.47
MAC: 200%
you wanted to use an inhalation induction of anaesthesia using an induction chamber / box in an aggressive cat, which would be the best agent to choose?
- Sevoflurane has a low blood:gas solubility so induction will be fast. It is also non-irritant to the respiratory passages.
- However, it is not licensed in cats.
Surgery then proceeds uneventfully and the procedure finishes shortly afterwards.
If you had used nitrous oxide, are there any special precautions you should take before recovery?
In your assessment of the patient’s pulse which of the following could be classified as ‘peripheral’ pulses?
Dorsal pedal arterial pulse, Auricular arterial pulse, Digital arterial pulse
normal PaCO2 for animal under anaesthesia
- 35-45 mm Hg
- lower would indicate a degree hyperventilation
size A and H cylinders
- not used for medical gases
size of cylinders attached to anaesthetic machines and the size used for manifolds
- size E usually attached to anaesthetic machines (have the Pin Index system for safety)
- each medical gas has a specific pin index configuration -prevents connection of wrong cylinder
- size J for those supplying manifolds (for supplying pipelines)
**now most practices use pipelines to a central gas line -more economical, much larger tanks!
black cylinder with white top
- Oxygen
- stored at 13700kPa
- Gauge pressure indicates the gas volume left inside the cylinder
- Major gas used to maintain adequate oxygenation of a patient during procedures.
- Stored in black-bodied cylindrical containers with a white collar.
- This is being phased out, so soon they will be found in solid white containers with ‘Oxygen’ written in black lettering along the side.
blue cylinder
- Nitrous Oxide
- stored in liquid phase with gas on top at 4400kPa (4.4 bar)
- Gauge pressure stays constant as long as there is some liquid left in the cylinder! - doesn’t indicate the volume remaining - must weigh for this!
- Used as a form of anaesthetic gas, though is uncommonly used in practice recently.
- Stored in solid blue cylindrical containers.
grey cylinder with black/white quarters on top
Medical Air
- often used in procedures with high end anaesthesia
- the air contains N (like normal air we breath) which is responsible for keeping the alveoli of your lungs open
- Compressed regular air, containing standard atmospheric ratios of gases.
- Notable is nitrogen, used to aid in inflation of pulmonary alveoli.
- Stored in grey-bodied cylindrical containers with a white and black quartered collar.
bodok seal
(sealing washer)
- makes a gas-tight joint!
- must be placed between cylinder and anaesthetic machine
- with make a very loud noise when turned if missing when cylinders are changed
Schrader Valves
- special end terminal unit of pipeline from central gas supply
- non-interchangeable!
- i.e. an oxygen line cannot be plugged into Schrader valve for NO
- also color coded (with hoses)
3 main components of anaesthetic machine
(positioned b/w cylinders and the anaesthetic machine)
- gas supply (oxygen +/- NO+/- air)
- pressure gauges
- pressure relief valve - reduces cylinder pressure to a safer operating pressure of about 400kPa (4 bar)
- gas is 5 times atmospheric pressure –> would blow lungs apart alone
- reduce this to normal atmospheric pressure so patient can breath normally
Emergency Oxygen Flush and Common Gas Outlet
-bypasses flow meters and vaporizers: gives you 40-60L of oxygen per minute
- never push when an animal is connected! - will blow their lings apart!!
- this is for cleaning ONLY
- can be to dilute anaesthetic gases (e.g. if used to fill an empty reservoir bag during anaesthesia)
- button usually found next to the common gas outlet
Pressure Relief Valve
Vaporisers
- in order to deliver volatile agent, you need vaporizers
- isoflurane, etc.
- calibrated for one agent only
- only isoflurane vaporizers will take isoflurane
purple: isoflurane, red: halothane
isoflurane - saturated vapor pressure (240 mmHg, 32%)
- very accurate!
- most theaters are 20-21 degrees so they work well
- in very cold temps (farm in winter) they do not work well!- need to be at the right temperature
- Fresh gas is split: can go through bypass channel or pass through a vaporization chamber –> therefore mixes gas containing no vapor with containing fully saturated anaesthetic vapor to produce a final mixture with appropriate vapour concentration
-splitting ratio is adjusted by the control dial on the vaporizer
Scavenging Systems
- all practices should have scavenging systems!
- DO NOT LET GAS JUST SPILL INTO ROOM
- if you don’t have the proper system to absorb the volatile agent, they will get filled with volatile agents
- needs to go in waste bin
- charcoal can be incinerated
- Portable Systems - activated charcoal absorbers
- Passive Systems - pollutes atmosphere
- Active Systems - connect to vacuum system, air brake must be utilised to limit suction
4 main functions of Anaesthetic Breathing Systems
Non- rebreathing systems vs. rebreathing systems
Non-rebreathing systems
(5)
- T-piece (0-10kg) - IPPV - class F - class F being least efficient (higher flow rates required)
- Mini-Lack (2-10kgs ) - Class A - (lower flow rates required)
- Bain - 10-18kgs - IPPV -class D
- Lack - 10-35kgs - class A (theoretically very efficient in fresh gas use)
- Magill - 10-35 kgs - class A
Typically, low classification systems are less suited to animals that must be ventilated (cannot spontaneously breathe), as a much higher flow rate is required in these patients.
Hence a higher classification system that already utilises a high flow rate would be better
Re-breathing system
- Circle - 10kgs ++++
- IPPV
Calculation of Minute Volume
(needing to know Tidal Volume)
Minute Volume = Tidal Volume x respiration rate
**make sure you convert to L per minute!!
How would you calculate the correct fresh gas flow (FGF) to use with your chosen breathing system?
FGF = Minute volume × circuit factor
Firstly, estimate the minute volume. This can be done in two ways:
- Minute volume = 200 ml/kg/minute (this is quicker and can be applied easily in daily veterinary practice)
- Multiply the respiratory rate by the estimated tidal volume (10ml/kg).
The value for minute volume then needs to be multiplied by the appropriate ‘circuit factor’. For the T-piece, the circuit factor is 2.5-3 × minute volume. For the 6kg dog in this case, if minute volume is 1200ml/minute, then FGF will need to be at least 3 litres/minute to prevent rebreathing of previously exhaled alveolar (and hence CO2 containing) gas.
What are the main Mapleson class A anaesthetic systems
(3)
All class A systems have a circuit factor of 1-1.5, so requiring a low flow rate.
Hence most are unsuitable for ventilated patients.
- Coaxial Lack
- Parallel Lack
- Magill
Magill System
- 10-35 kgs
- system factor: 1-1.5
- NOT IPPV
- Mapleson Class A
- Fresh gas passes through a tube with a reservoir bag, and into the patient.
- Exhaled gas from the patient fills this tube, and is then pushed out via the APL (adjusted pressure limiting) waste valve when fresh gas next passes through.
Uncommonly used, as APL valve is close to the patient’s face, and can be obstructive
Coaxial Lack System
10-35kg
1- 1.5 system factor
Not IPPV
Mapleson Class A
- Fresh gas passes through a tube with a reservoir bag, and into the patient.
- Exhaled gas passes via a second, internal tube to the APL waste valve, located above the reservoir bag.
- Commonly used in animals over 10kg
- -essentially moved the valve as it became an issue in front of patients face
Parallel Lack System
- 10-35kg
- 1 - 1.5 System Factor
- NOT IPPV
- Mapleson Class A
Fresh gas passes through a tube with a reservoir bag, and into the patient.
Exhaled gas passes via a second, seperate tube that runs parallel to the first, to the APL waste valve located above the reservoir bag.
Commonly used in animals over 10kg.
A mini version is also available for animals under 10kg.
What are the main Mapleson class B-F anaesthetic systems
These systems typically have a circuit factor of 2.5-3, and so require a high flow rate.
These systems are more suitable for ventilated patients.
Due to high flow rates required, these systems are typically unsuitable for animals over 50kg
- T-piece (0-10kgs)
- Bain (10-18kgs)
In both systems, non-blind reservoir bag variants are uncommon, as these bags have the capability to twist, block gas expulsion, and cause pressure damage to the lungs.
T-piece breathing system
(Ayres)
- 0-10kgs
- 2..5-3 System Factor
- YES IPPV
- Mapelson Class F
Fresh gas passes into a tube leading to the patient at a T-junction close to the patient’s head.
Expired gas passes down this main tube to the scavenging system.
Some variants will have a reservoir bag at the end of this tube (Ayres) , which may be blind ended with an APL valve prior, or non-blind ended to allow gas to pass.
Bags began to twist in original- causes damage to lungs –> next model
this is really good for ventilating patients! - not for spontaenously breathing patients like Class A’s
- Most commonly used high class system in small animals, as is suited to animals under 10kg.
Breathing System for a good for a healthy, young and small animal undergoing elective castration?
T-piece (ayres)
- The T-piece has minimal apparatus deadspace and resistance to breathing, making it ideal for animals ~<10kg. Fresh gas flows for the T-piece must exceed 2.5 × the patient’s minute volume, otherwise expired gas will be rebreathed. Rapid respiratory rates with short expiratory pauses may require even higher flow rates (≥3×minute volume)
Bain System
- 10-18kgs
- 2.5-3 System Factor
- YES IPPV
- Mapelson Class D
- good for ventilating patients but again a very high circuit factor
Fresh gas passes through a small tube within a larger tube and into the patient.
- Exhaled air passes through the larger tube and into the scavenging system.
- Multiple variants, either with a reservoir bag and an APL valve adjacent to fresh gas inflow, or with a non-blind ended reservoir bag that allows gas to pass.
- Suitable for animals over 10kg, but uncommonly used due to high flow rates being uneconomical.
- Can come long or short
- fresh gas comes through inner green tube
- used gas flows in outer tube and goes into bag
- bag continues to a valve at the top
- -how do you know if there is a hole in the inner tube?
Only way to know is to occlude the inner tube with device provided
Bobbin will dip
If there were a hole in the tube, the gas would not cause the bobbin to dip
What is the Humphrey ADE system, how does it function, and when is it used?
- Variable non-rebreathing system that can be switched between Mapleson classes A, D, and E by the use of a lever.
- Also permits the attachment of an absorbent canister, converting it into a circle rebreathing system.
- The lever controls the circuit factor of the system, altering the flow rates for its function, and so allowing it to be used for both spontaneous and ventilated breathing patients.
- Suitable in small animals at a range of different weights.
What are the main rebreathing systems used in practice
- Circle
- Coaxial Circle
Circle Breathing System
- 10kg+++
- not good for smaller animals
- Doesn’t have a system factor- Minimum flow rate is 10mls/kg
- Start at 100mls/kg then reduce to a maintenance setting of 50mls/kg
- YES- IPPV
Fresh gas enters the system circuit, travelling to the patient for inhalation.
Exhaled gas passes through the second arm of the circuit, into the reservoir bag and into the absorbent cansister.
Carbon dioxide is removed, and the gas reenters the fresh gas arm of the circuit for rebreathing.
Backflow of gas is prevented by the presence of one-way valves in the inspiratory and expiratory arms of the circuit
Coaxial Circle Breathing System
- Fresh gas enters an inlet chamber above the absorbent canister and passes into a tube to the patient.
- Exhaled gas passes through a second tube that surrounds the inlet tube, and travels into the reservoir bag and the absorbent canister.
- Carbon dioxide is removed, and the gas reenters the inlet chamber and inspiratory limb of the circuit.
How are endotracheal tubes sized, and how are they selected for the individual patient?
- Sizing determined by the internal diameter of the tube in millimetres.
- Should ideally use the largest tube that will fit through the larynx of the animal.
- This maximises the airflow that a patient can receive.
Opioid commonly given with alpha-2 adrenoreceptor agonists in horses…
Butorphanol
- less legislation involved
- helps prevent them fom kicking
- can really see a difference in the way they stand as well - it is not analgesic effect, it removes some of their response to touch!
*
Usual premedication for the horse
- Acepromazine & small amount of opioid (Butorphanol) in the bix so it can walk calmly to the theater
- then give Adrenoreceptor agonist (alpha 2 agonist) - Xylazine once it is there or else it may not be able to walk to the theater
- Alpha 2 more usually used as a co-induction
- blurred lines between pre-med and sedation sometimes on what drug is given when
antinociception
(analgesia)
the action or process of blocking the detection of a painful or injurious stimulus by sensory neurons –> analgesia
- one of the purposes of GA
- SE’s: causes CVS and respiratory depression
Balanced Anaesthesia
What type of pre-med would be best suited for a cat or dog with Mitral Valve Disease?
Which would you not use?
- Use: ACP (Phenotiazines) - useful for MVD - vasodilation and hypotension (NOT GOOD FOR HCM)
- may be able to use opioids as they are good for patients with cardiac disease
- Avoid: Medetomidine (Alpha 2 agonist)
What Pre-med(s) would be useful in a healthy, young, non-pre medicated animal?
Which one would not?
- use: ACP (all young healthy dogs, cats 50/50) or Medetomadine (short procedures, aggressive cats, non-conventional species)
- avoid: Diazepam or Midazolam alone (not great sedatives)
- don’t use benzodiazepines in hepatic encephalopathy patients either (metabolized in the liver)
Good pre-med option for a seizure patient
- Benzodiazepines!
- anti-convulsant
- Diazepam or Midazolam
- NOTE: avoid overdosing though, antagonists are expensive unlike for alpha-2s
Midazolam is inhibited by…..
- ERYTHROMYCIN
Good pre-med for fracture repair
- Benzodiazepines
- Myorelaxation
Which pre-med would you avoid using in a cat with Myasthenia Gravis?
What is Myasthenia Gravis?
- Myasthenia gravis is a chronic autoimmune neuromuscular disease that causes weakness in the skeletal muscles, which are responsible for breathing and moving parts of the body, including the arms and legs
- Avoid the use of Benzodiazepines (Diazepam, Midazolam)
- Myorelaxation can lead to decreased respiratory function and relaxation of intercostal and diaphragmatic muscles
What should be best avoided as a pre-med in horses?
- Diazepam
- Benzodiazepines may scare horses as it is a muscle relaxant
Avoid the use of this pre-med in young, healthy cats
(use not indicated)
- Benzodiazepines
- Diazepam
Avoid the use of this pre-med in patients with hepatic encephalopathy
- Benzodiazepines
- Diazepam, Midazolam
Good choice in pre-med for brachycephalic breeds
- Diazepam (IV) -minimally affect CV and respiratory function, myorelaxation
- can use ACP in some cases
- likely avoid opioids (SE of Respiratory depression) and possibly medetomidine
some SE’s of opioid use in horses
- spontaneous locomotor activity (in other animals also, but esp. horses)
- changes in gut motility! –> can make horses colic
Good choice of opioid in dogs
(that is licensed)
- Methadone
- does not cause vomiting and nausea like Morphine
- Onset 10 min, duration 2-4 hours
- No His release if given IV
Butorphanol
- K and u agonist
- MILD sedative
- poor analgesic
- used with sedative drugs in horses and dogs
- not controlled
a weak mu agonist used in SA practice commonly …
- Buprenorphine
- licensed in SA, commonly used
- not as potent as Morphine, but better than Butorphanol
- Schedule 3 - less controlled than morphine
- longest acting opioid (7 hr)
Opioid that must be given IM
- Pethidine
- mu agonist of short duration
- IV will lead to increased Histamine release
- shortest acting opioid (20 min)
Fentanyl
- very potent mu agonist
- short acting opioid
- now licensed for dogs (Fentadon)
- used often as an infusion during Sx
- HIGH POTENCY
Which patients should you used Opioids?
(3)
- All patients in pain
- Invasive Sx’s
- Patients with Cardiac Diseases
Which Patients should you be cautious with using opioids?
(4)
- respiratory diseases (SE includes respiratory depression)
- Allergic conditions (asthma) - morphine, pethidine –> both high risk for undesired effects and also can cause Histamine release possibly - worsen condition
- patients with laryngeal dysfunction as a pre-med –> due to effects on respiration
- careful with rabbits and horses - they can’t vomit and it may cause gut stasis
Options for pre-med protocols
(4)
- Opioid, ACP, Benzodiazepine or alpha 2 agonist alone
- Opioid + ACP - when sedation and analgesic effect called for
- Opioid + alpha-2 agonist - (ex: QUAD protocol)
- Opioid + Benzodiazepine - to achieve analgesic effect and lighter sedation in geriatrics, neonates, seizure Px’s
Commonly used Injectable Anaesthetics
(5)
- Propofol
- Alfaxalone
- Ketamine
All–> 100% bioavailability to the brain!
(not as much)
- Thiopentane/Thiopental - not really used in SA clinics anymore
- Etomidate- only when REALLY sick. Does not cause CVS depression like others! (drop in CO, vasodilation, reduced BP)
goal of low dose anaesthetic
Sedation
ex: propofol
goal of high dose sedative
- Anaesthesia
What are some commonly used inhalational anaesthetics?
- Isoflurane
- Sevoflurane - off license use in horses as good evidence for use (only licensed for use in SA’s)
- Nitrous oxide - use is fading, NEVER USE IN THE HORSE (hypoxia)
others:
- Halothane - not in production anymore
- Desflurane -used in horses sometimes, helps them get up faster, but not licensed for veterinary use
Common I/V Induction Protocol in Horses
Ketamine and alpha 2 agonist
works after 3 min, lasts for 15 min
Give alpha 2 first! then ketamine –> goes mad otherwise
can add benzodiazepam for muscle relaxation if needed, but not super helpful as it is not very long acting
Guaifenesin is used in the US: works a similar way
another option: Propofol and Alafaxalone (but crazy $$)
4 phases (stages) of Anaesthesia
- Unconsciousness (part of the triangle)
- Signs of Excitement (often miss with IV induction!) = involuntary twitching/excitement
- Surgical Anaesthesia
- Overdose
Which anaesthetic gives analgesia?
Ketamine
What are the main effects of anaesthetic agents?
- Cardiovascular depression (vasodilation, lower CO, and lower BP) - not HR
- Respiratory depression (lower RR, TV, and MV)
also: dose- dependent (SE’s), only some provide analgesia- cannot reach higher centers of the brain (ketamine does though), patients cannot feel pain but still have nocioception, some of the drugs are lipophilic and will hide in fat
Administration of Anaesthetic Agents
- mostly IV
- some may be IM - do not use injectable IM if the animal has poor perfusion! - does not reach the BBB quick enough
- some are inhalational
**uptake may be affected by the route of administration and there may be delay getting across the BBB
Distribution into the tissues may be affected by disease as wel (depends on BF)
What is propofol and how is it administered?
(2-4mg/kg in pre-medded animals)
- Phenol - soya oil, egg, lecithin, placed in white emulsion –> contains lipid
- Must be given IV - may not be good for aggressive animals! so lipophilic that if given IM, will not reach appropriate concentrations
- can be used for induction and maintenance
- Rapid onset and metabolism - cats cannot glucoronoconjugate well! - they will go onto oxidation (Heinz body production and oxidative injury if used repeatedly) and therefore metabolize this drug slower –> slower recovery than dogs
- will get metabolized on guts, lungs, skin and kidney (extra - hepatic)
- CV and resp depression -if you induce fast, will get some degree of apnea or CVS reduction - especially since an alpha-2 that may have already been given can cause bradycardia –> leading to slower onset due to slowed circulation
- can use for patients with liver issues or that cannot metabolize well due to extra-hepatic metabolization –> also good for C-sections because of this!! - immature livers
- “propofol twitches”
What is a side effect of propofol and how do you counteract it?
- “Propofol twitches”
- Tremors
- Give ketamine or alfaxolone
- can give Benzodiazapine as a muscle relaxant as well
- Give propofol slowly
- happens to 15-20 % of patients and is a recurring phenomena
Anaesthetic agent ok for induction in cats, but not for CRI
- propofol
- they metabolize it much slower than dogs! - they have issues metabolizing the triglycerides due to LPL deficiency - Lipoprotein lipase plays a critical role in breaking down fat in the form of triglycerides, which are carried from various organs to the blood by molecules called lipoproteins
- need to alternate agents in cats (could have Heinz bodies and oxidative damage after 3-5 days of repeated anaesthesia with propofol) –> alternate with ketamine
When would you use propofol without a preservative or use a different agent?
- If suspect a prolonged anaesthetic
- Propofol Plus is only licensed for induction!! - not good for CRI use over 30 min (mainly in cats)
- for CRI need to use regular propofol
Propofol Plus
contains benzyl alcohol to increase shelf-life! (28 days)
- no pain on injection like Propoclear product
- does not need to be stored in fridge + little extravasation rxn
- BUT, cats struggle with it (prolonged recovery and hyperkinesia), neuro signs in dogs, fatalities in both
- seems to be OK to use in dogs!
- lethal dosage dog: admin per hour for 9 hours
- lethal dosage cat: admin per hour for 6.5 hours
What is alfaxalone?
(2-5 mg/kg)
2 if given premed, 5 if not
- anaesthetic agent
Steroid - can be used for both induction and maintenance
- Licensed IV in UK
- can be given IM (not licensed in the UK)
- Added solubilising agent - poorly soluble in water so margeted with solubilizing agent (cyclodextrin)
- Rapid onset and metabolism, short duration of action (excitement on recovery if not properly sedated)
- Excitement on recovery if not sedated
- LESS CARDIOPULMONARY DEPRESSION THAN PROPOFOL - good for cats with HCM!
- can be a nice sedation induction when given with other agents
- Drug is CLEAR - do not confuse (except now ketamine is color coded)
What is ketamine?
- Dissociative anaesthetic
- Analgesic - at sub- anaesthetic doses (binds NMDA receptors)
- NMDA receptor antagonists are a class of anesthetics that work to antagonize, or inhibit the action of, the N-Methyl-D-aspartate receptor (NMDAR). They are used as anesthetics for animals and humans; the state of anesthesia they induce is referred to as dissociative anesthesia
- IM or IV (only IM is licensed for dogs)
- Used for both induction and maintenance (only licensed in cats) - not greattt though as induction/maintenance agent
- Combine with sedative to avoid excitation and rigidity - ALWAYS combine with other sedative (ex: horses, give alpha 2 agonist prior to ketamine)
What is the triple combination for aggressive dogs and cats?
- IM injection
- Ketamine, medetomidine, opioid
- 3-5mg/kg
can make it a quad by adding midazolam
AGGRESSIVE CATS AND DOGS- short duration procedures
What do you need to remember when giving ketamine to horses?
- Only after profound sedation with a2 agonist
- Give with benzodiazepine to counteract ridigity
Why is placing an ET tube difficult with ketamine?
- one of the disadvantages with ketamine is that they retain a gag reflex - may need propofol with inhalation maintenance
- Cranial reflexes preserved
- Stimulates Sympathetic NS - mild hypertension/tachycardia, mild respiratory depression
- React to intubation, blinking and swallowing
- makes cats REAL DIFFICULT if using for induction
- as a baby vet - best to go with propofol
When is the use of Ketamine contraindicated in patients?
- animals with cardiomyopathies!
- stimulation of sympathetic NS - these patients will already have a high HR and Low Ventricular filling
- mild increase in BP and tachycardia
- DIRECT MYOCARDIAL DEPRESSION
- mild respiratory depression
- Endobronchial intubation
- Only intubating half of the lung
- Hypoxia
- Reduced anaesthetic agent delivery to the patient
- Can be desired effect (rarely)
- likely due to the ET tube being too long (should be nose to shoulder- connector tube a t level of the nose)
- Pressure on walls of trachea
- Increased risk of tracheal rupture
- E.g. overinflation of cuff, or moving animal without disconnecting ET tube
Describe intubation in cats
- Spray layrnx with local aeansthetic to desnsitise and reduce laryngospasm during intubation
- Lidocaine spray
- Care: easy to overdose - local anaesthetic toxicity - e.g. kitten, may use drop of normal lidocaine rather than spray
- Alternative options e.g. Laryngeal mask (Vgel) - tube that sits on top of oesophagus (pushing down the epiglottis), gas directed down trachea, so tube in trachea avoids issues with damage and not reducing diameter of trachea
- CONS to VGel: not very air tight and if the fit isn’t good, epiglottis can move –> partial airway obstruction
Graphically describe the plasma concentration of a intermitent or continuous dose of anaesthetic agent
- Intermittent boluses can be more stressful on the patient! benefit of CRI - plane of anaesthesia swings between toxic and subtherapeutic levels
- CRI= constantly infused (MRI= minimum infusion rate) - e.g. propofol, alfaxalone, ketamine
- Injectable agents for maintenance: Propofol (be wary with cats) , Alfaxalone, Ketamine (at low analgesic doses)
If an animal has liver problems: which inhalation agent is safer to use?
Sevoflurane or Isoflurane?
(the ones used in practice)
- Isoflurane!
- 0.2 % metabolism
3 types of pain
Pain Pathway
(4 steps)
-free nerve endings will Will differentiate between different thresholds (hot/cold)
Transmission of pain via fibers
What is the term “inflammatory soup” refering to in the process of nociception?
- during transduction of a noxious stimulus, peripheral sensitization can result in hyperalgesia due to cytokines/GFs being released simultaneously
- Hyperalgesia is a condition where a person develops an increased sensitivity to pain
- due to massive amount of inlammatory mediators
- think they are always painful on a limb or something
- where as central is a much more generalized, all over continuous pain
When will central sensitization occur?
- Failure of interneurons/ascending neurons to modulate a noxious stimulus at the dorsal horn in the SC
- Central sensitization is a condition of the nervous system that is associated with the development and maintenance of chronic pain. When central sensitization occurs, the nervous system goes through a process called wind-up and gets regulated in a persistent state of high reactivity
- Trigger: repeated stimuli
- this is why we give Pre-emptive analgesia!!
- NO involved with NMDA receptors - NMDA receptors can lead to hyperalgesia effects
- bc you have frequent stimulation, the central NS perceives that as constant pain
- will have hypersensitivity in the neck area but not elsewhere
By which tract does a noxious stimulus travel from the spinal cord to the brain?
Spinothalamic
- The anterior and lateral spinothalamic tracts. The former helps localize crude touch and pressure, the latter painful or temperature sensation.
- The spinoreticular tract, which is responsible for increasing our level of arousal/alertness in response to the pain or temperature.
Hyperalgesia and Allodynia
- innocuous = not harmful or offensive (like touch)
- In allodynia - receptors are really fucked, the mechanoreceptors meant to relay touch now relay pain –> hard to treat and continues to spread
Three Domains of Pain Assessment
- use glasgow scale or Colorado scale
What is the reversal drug of opioids?
Naloxone
Opioids
- Some conditions require it
- delta, kappa, and mu
- But it is almost always part of our pre med
- Receptors are in CNS but also in the GIT! And other places
- This is why you get effects on other systems
- Reptiles –> kappa
- Epsilon is a receptor that we think is linked and we are trying to alter drugs to aim for that
- We are trying for other receptors as our opioids have pretty adverse SE’s
- opioids works for the C -fibers –> dull pain
Opioids are not good for sharp pain!! - common misconception
Partial Mu agonist
(Buprenorphine)
- Has a higher affinity for the receptors
- If you give a strong dose of opioid by accident, you can give buprenophine to antagonize it
Tramadol
- Tramadol is used in human medicine for the management of osteoarthritis pain and is gaining acceptance in veterinary medicine to treat mild to moderate pain in dogs and cats. In addition to its analgesic properties, tramadol may also have some mild anti-anxiety effects
- weak u-receptor agonist (opiod-like)
inhibitor of serotonin and noradrenaline reuptake
NMDA receptor antagonist
Opioid Effects
(6)
- thermoregulation - some hyperthermia
- Respiratory depression (mu mediated effect in resp center) - use naloxone. esp. if co-admin of a sedative
- Bradycardia - vagal stimulation. responsiveness to anticholinergics, pethidine an exception
NSAIDs in Pain Management
(and 4 SE’s)
Effects of NSAIDs
Ketamine and Analgesia
Paracetamol
Easy to find
Minimal side effect which is true –> UNLESS IT IS A CAT
Useful as long as liver function is fine! - don’t give to animal with decreased hepatic metabolism
Make sure your animal has no liver disability
Epidural Analgesia
- Touch back of L7
- Drugs used: Local Anaesthetics, Opioids, Alpha-2 agonists, ketamine, NSAIDs
Epidurals: Small v. Large animals
Systemic Local Anaesthetics: Lidocaine
Can be used IV! - can use systemically
Ruminants - LA blocks
