Anaesthesia Flashcards
Define General Anaesthesia?
“The reversible immobile state that induces amnesia”
Define nociceptive
Nociceptive pain is a type of pain caused by damage to body tissue.
Local Anaesthetics – Mode of Action
Blocking the generation and conduction of nerve impulses, resulting in
patients feeling no pain
Are sensory or motor neurons more sensitive
Sensory Neurons
5 stages of nervous Function is Lost?
- Pain
- Heat and cold sensation
- Touch
- Deep pressure
- Motor function
Why can local anaesthetics cross blood brain barrier
Lipid soluble and low molecular weight
Therapeutic effects of local anaesthesia
Anticonvulsants, sedatives and analgesia
Negative effects of local anaesthesia in high doses
Seizures
CNS depression
Slows myocardium conduction
effects of myocardial conduction
Depressing contractility
weak pulses
hypotension
bradycardia
cardiac arrest
Species more sensitive to local anaesthetic
Cats
(and exotics)
List local anaesthetic drugs
Lidocaine
Proxymetacaine
Bupivacaine
Lidocaine benefits
Rapid onset of activity
Good tissue penetration
Short duration of activity
Good for regional blocks and
general surgery
Lidocaine activity duration
- 45 minutes without adrenaline
- 1-2 hours with adrenaline
Proxymetacaine benefits
Topical analgesia of eye
Rapid onset
(Duration:15 minutes)
Bupivacaine effects
Good epidural analgesia
post-op anaesthesia
Potency x4 lidocaine
Bupivacaine onset of activity and duration
Slow onset of activity (15 minutes)
Longer duration of action (6-8 hours)
list the Local anaesthesia blocks
Local
regional
Epidural
Intra-articular
Peri-neural (regional) block locations
Intercostal nerve block
Brachial plexus block
Maxillary/mandibular nerve blocks
Intravenous regional block AKA
Bier block
What is a Perineural (Regional) Block
Local anaesthetic injected directly around nerve
What can be used to assist with Perineural (Regional) Block
Ultrasound or Nerve stimulator
Location of Intercostal nerve block site
caudal to ribs
Location of Brachial Plexus block site
Distal to elbow
Needle used for Epidural
Tuohy needle
or 22G spinal needle
Lumbosacral epidural provides analgesia to structures…
…caudal to
thoracolumbar junction
Epidural injected between which spinal vertebrae
space between L7-S1
Patients who are at particular risk during Epidural anaesthesia
Patients Shock (Hypovolaemic)
When Would an Epidural Injection be
Contraindicated?
Patient suffering septicaemia
skin over lumbosacral junction is infected
Patient with coagulation disorder
When are Intravenous regional anaesthesia, or Bier block used
surgical procedures in body’s extremities e.g. removal of a toe
What is an Esmarch bandage
Drain blood from a limb
Dissociative Anaesthesia effects
analgesia and amnesia
minimal effect on respiratory function
can be used with brief surgery
Swallowing and eyes remain open
Dissociative anaesthesia hyperexcitation signs
- Hypersalivation
- Hyperventilation
- Tachycardia
- Muscle twitches
- Paddling of the legs
- Curling of the tongue
General Anaesthesia disadvantages
Effects major organs in the body
* Cardiovascular
* Respiratory
* Neurological
* Renal
* Hepatic
Peri-neural Anaesthesia disadvantages
- Pneumothorax
- Bleeding
- Nerve damage
Disadvantages of epidural
- Introduction of infection
- Paralysis
- Artificial ventilation required if
cranial nerve involvement - Can cause hypotension
- Possible urinary retention
Dissociative anaesthesia disadvantages
- CV stimulation
- CNS stimulation (seizures)
- Muscle hypertonicity
what parts in the brain does anaesthetics effect
- Receptors in CNS
- Cell membrane of neuronal cells
Function of the blood brain barrier
This barrier restricts movement of molecules into brain
What molecules cross easily over the blood brain barrier
Oxygen, carbon dioxide and water
The easier anaesthetic agents can cross the blood brain barrier are…
the more potent they are
cardiovascular depression.
the three side effects
1.Reduction in cardiac output
2. reduction in blood flow
3. Potential tissue hypoxia
Define Hypercapnia
Higher blood CO₂ than normal
Define Hypocapnia
Lower blood CO₂ than normal
What minimum percentage of Oxygen should be delivered to patient via breathing circuit
> 30% oxygen
How does blood reach the liver?
- Hepatic artery
- Portal vein
Inhalant anaesthetic agents reduce liver blood flow due to
Reduction in cardiac output
Due to reduction in cardiac out put to the kidneys general anaesthesia also decreases
- Glomerular filtration rate
- Urine output
- Electrolyte excretion
What is (MAC)
Minimum Alveolar Concentration
Definition of MAC
The measurement of potency
(The amount of inhalation agent required to suppress movement to noxious stimulant in 50% of patients)
Isoflurane MAC
1.15%
At what part of the body is the MAC potency measured at?
Spinal cord
Halothane MAC
0.75%
Sevoflurane MAC
2.05%
Desflurane MAC
5-10%
What is Blood – Gas Solubility Coefficient
The proportion of agent that
will dissolve in blood
compared to portion that
remains in gaseous state
What does the Blood gas solubility coefficient determine
the speed of induction and recovery
(Halothane) solubility
Slow induction
Slow recovery
Very insoluble volatile anaesthetic agent=
Rapid induction
Rapid recovery
Halothane Blood gas solubility
2-3
Isoflurane Blood gas solubility
1.4
sevoflurane Blood gas solubility
0.6
Desflurane Blood gas solubility
0.42
What is Critical Tension?
The necessary drug concentration needed in the brain to induce unconsciousness
rate of onset and recovery of inhalation
anaesthesia depends on what 5 factors
- Anaesthetic agent concentration
- Alveolar ventilation
- Blood/gas solubility
- Cardiac output
- Blood/tissue solubility
Define Pain
“A sensory or emotional experience associated with actual or potential tissue
damage”
The 3 classification of pain
- Physiological
- Inflammatory
- Neuropathic
Physiological Pain properties?
proportional to stimulation
Pain experienced is localised
Normal pain pathway activation
Inflammatory Pain properties
Pain associated with changes to pain pathway
Neuropathic Pain
Pain caused by nervous system damage
Allodynia define
Pain from stimuli which are not normally painful
Primary hyperalgesia define
increased responsiveness to stimulation in the area of injury.
Pre-emptive Analgesia prevents
“sensitisation” or “wind-up”
Multimodal Analgesia
Using multiple analgesics to control pain pathway at different levels and sites
Synergism define
An interaction between two or more drugs that causes the total effect of the drugs to be greater
Spinal Response to Pain?
receives the pain message from nociceptors which is
then sent to the brain
Medullary response to Pain?
Processed pain message and responds
Hypothalamic response to Pain
Releases hormones
e.g. cortisol releasing hormone (CRH)
Cortical response to Pain
Adrenal cortex release (Cortisol) under the
influence of ACTH
Fentanyl and buprenorphine bioavailability % for cats and dogs?
- Cats – 34%
- Dogs – 64%
Analgesia used in Rabbits and Rodents
Opioids
NSAIDS
Alpha 2 agonists
Ketamine
