Anaesthetics and Analgesia Flashcards
What is anaesthesia?
- any lipid-soluble agent the causes depression of the brain in a predictable order
- Cortex
- Midbrain
- Spinal cord
- Medulla
How do anaesthetics work?
- Increase tonic inhibition
- increased action of GABA receptors
- Glycine
- Inhibit excitatory synaptic transmission
- inhibiting ligand-gated ion-channels
- NMDA receptors
- opening K+ channels
- Nicotinic
- Serotonin
How is anaesthesia administered?
- Inhale
- Oxygen
- NO
- Isoflurane
- Injected
- Propofol
- Thiopental
- Etomidate
- Ketamine
Oxygen as an anaesthetic agent
- action
- side- effects
- generally good for you
Side- effects
- O2 free radicals
- CNS convulsions
- Pulmonary oxygen toxicity
- Retrolental fibroplasia
- CO2 narcosis
Nitrous oxide as an anaesthetic agent
- action
- side-effects/ contraindications
- good analgesia but usually combined with other inhaled drugs for a good anaesthetic effect
- Fast induction/ recovery
Side-effects
- Cardio-respiratory depressant: diffusional hypoxia during recovery
- risk of bone marrow depression with prolonged use
- avoided in anaemic and 12 deficient patients
- can causes expansion in gaseous cavities
- contraindicated in pneumothorax, vascular air embolus or in an obstructed intestines
What chemical properties of inhalation need to be considered?
- Non-irritant
- Low blood-gas solubility
- High potency (Minimum alveolar conc. | MAC)
- Minimal side effects
- bio-transmission
- non-toxic
Desflurane as a general anaesthetic agent
- Fast induction/ recovery
- used for day-case surgery
- moderately expensive and environmentally damaging
- Sevoflurane is similar (expensive)
Side-effects
- respiratory tract irritation
- cough
- bronchospasm
Isoflurane as a general anaesthetic agent
- a relatively cheap stable non-flammable halogenated ether
- widely used and replaced halothane
- medium induction/recovery rate
Side-effects
- irritable to the airway
- possible risk of coronary Ischaemia in susceptible patients
Give an overview of Intravenous agents
- they are usually induction agents/ iv opiate
- rapid onset and pleasant sensations
- Lipid soluble
- short-acting, metabolised
- cause CVS/RS depression
Explain Thiopentone as an anaesthetic agent
- A type of barbiturate (potentiates GABAA) Powder, Smells of garlic
- acts as an Antiepileptic
- causes CVS/RS depression and laryngospasm
- highly lipid-soluble so quickly acts on the brain
- can also cause hypotension on induction
- Anaphylaxis/ arterial
- Half-life 10 hours
What is the action of Etomidate and what are its side-effects?
It potentiates GABAa and is used as an induction agent in anaesthesia
- Primary adrenal suppression (secondary to reversibly inhibiting 11β-hydroxylase)
- Myoclonus
• Causes less hypotension than propofol and thiopental during induction and is therefore often used in cases of haemodynamic instability
Propofol as an anaesthetic agent
- Short-acting agent used for induction
- maintenance of GA and sedation
- onset within minutes of injection
2,6-diisopropylphenol as an anaesthetic agent
- Solvent
- Redistribution half-life - 4 minutes
- Elimination half-life - 4 hours
- Minimal accumulation - TIVA
- Antiemetic
- Antiepileptic
- Painful to inject
- Abnormal movements
- CVS/RS effects
Give an overview the use of muscle relaxants
- Dangerous drugs
- Muscle paralysis
- Facilitate intubation
- Maintain paralysis for surgery/ventilation
- Depolarising
- Non depolarising
- Anaesthetists only
Give an overview of depolarising agents
- Suxamethonium
- Post-synaptic membrane
- Mimics acetylcholine
- Rapid onset offset
- Short half life ~ 2min
- Plasma cholinesterase
- Multiple side effects
Give an overview of non-depolarising blockers
- Competitive with Ach
- Ach moiety blocks Na channel with size
- Duration is variable
- Slower onset and slower offset
- Steroid group: rocuronium
- Benzylisoquinoliniums: atracurium
Give an overview of the use of N-m blocking agents
- Intubation
- Surgery
- Ventilation
- Transfer
- Side effects
- Reversal
Gate theory - Pain
- C fibres lets pain through
- Ab fibres stimulate inhibitory neurons
- Descending pathways prevent the central passage
Give an overview of Opioids
- Act on opioid Receptor and antagonised by Naloxone
- Naturally occurring eg Morphine ,Codeine
- Semi-Synthetic eg Diamorphine
- Synthetic eg Fentanyl
- Weaker eg Codeine
What methods of administration are there for administration?
- Intravenous pca/infusion
- Intramuscualr
- Oral
- Intra nasal/aersol
- EPidural/spinal
Where are Opioid receptors found?
- POns and the Midbrain
- Periaqueductal Grey Matter
- Nucleus Raphe Magnus
- Spinal COrd Posterior Horn 1 and 2
- G.I.T
- Peripheral tissues
Subtypes
- Mu 1 and 2: OP3
- Delta: OP1
- Kappa: OP2
Give an overview of the use and effects of morphine
Effects: significantly reduces pain
Side effects
- Resp. depression/ airway loss
- N&V
- Constipation/Pruritis
- Miosis
What is Naloxone?
- drug used to treat opioid overdose
- needs to be regularly monitored and regulated
Give an overview of Ketamine and it’s effects
- acts on NMDA Receptors
- Kappa and delta receptors
- Not GABA
- Analgesic local/general
- Anaesthetic
- Sedative
- SIDE EFFECTS: emergence phenomena
Give an overview of NSAIDS and their effects
- Act by inhibiting Cyclooxygenase 1 and 2
- Analgesic, Antipyretic, Anti-inflammatory
- Side Effects
- Gastric Irritation
- Bronchospasm
- Renal Impairment
- Platelet function ASPIRIN
What is the effect of Aspirin in the body?
- Acetylsalycilic acid
- causes Oxidative phosphorylation
- causes Air Hunger
- Reyes Syndrome
Give an overview of the effect Paracetamol has on the body?
- Mechanism of Action: Central prostaglandin effect/unknown
- Side effectsOVERDOSE Hepatotoxicity/glutathione depletion
- N acetylcysteine
Give examples of other Analgesia?
- Anxiolysis
- Local anaesthetics
- Antidepressants,antiepileptics
- Guanethidine, ketamine, clonidine
- Acupuncture
- Inhalational Nitrous oxide/penthrane
- Tramadol
What are anti-emetics give examples?
- drug used to treat nausea and vomiting
- Cyclizine
- Ondansetron
- hyoscine
- Metoclopramide
- Steroids
- Prochlorperazine
- cannabinoids
The tiers of the Ramsay Sedation scale
- Patient Anxious
- Cooperative
- Responds only to commands
- Brisk response to Glabellar Tap/Shout
- Sluggish Response
- No response
Give an overview of Benzodiazepines
- Midazolam, Diazepam, Lorazepam
- Routes of administration
- suppositories, IV injection(triazolam, flunitrazepam, and diazepam emulsion)
- PHYSIOLOGY
- Gabba- aminobutyric Acid
- Inhibitory Neurotransmitter
- Receptors A and B
What are the side effects of Benzodiazepines
used for
- loss of airways
- respiratory depression
- ABC
- Flumazenil can reverse the effects of benzodiazepines
Give examples of other sedatives
- Low dose vapours
- Ketamine
- Hyoscine
- Propofol Low dose
- Major Tranquilisers
What are the classifications of local anaesthetics?
- Amides
- Lignocaine, Prilocaine, Bupivacaine
- Esters
- Cocaine, Amethocaine
Explain the mechanism of action of local anaesthetics
- Na channel blockade
- Un-ionized drug through the membrane into the axoplasm
- Protonated
- Blocks channel–> blocking the action potential
How are local anaesthetics administered?
- Anatomy Local Blocks /Ultrasound
- Spinal Epidural Caudal
- Skin
- Aerosol/Nebulised
- Combination with GA Part of Triad
How do side effects of local anaesthetics present?
- restlessness, disorientation, tremors, drowsiness
- lightheadedness circumoral numbness, dizziness visual changes
- respiratory depression
What effect does the toxicity of local anaesthetics cause in the
- cardiovascular and
- central nervous system
Cardiovascular
- dysrhythmias, Cardiac depression
CNS
- fitting/ anxiety/ loss of consciousness
- circumoral numbness
How is local anaesthetic toxicity treated?
- ABC - Alert local cardiac team for potential cardiopulmonary bypass
- Oxygen - 100%
- 20% Lipid emulsion
- bolus 1.5mL/kg over one minute (approx 100mL) consider repeat
- initiate continuous infusion of emulsion 0.25mL/g/min
- Dysrhythmias/fitting
- suppress seizures with benzodiazepines try and avoid proprofol
What patient factors are associated with cardiac risk?
- Older Age
- Cerebrovascular disease
- Heart failure
- Ischameic heart disease (MI/angina)
- Insulin dependent diabetes mellitus
- renal impairment or dialysis
What patients are at risk of gastric aspiration even after fasting?
- use of opioids
- Acute abdomen and raised intraabdominal pressure
- Hiatus Hernia
- GI obstruction
- Pregnancy (2nd and 3rd trimester)
- Sever trauma
Which drugs are not continued preoperatively and when are they stopped?
- Drugs that affect coagulation
- Warfarin → 5 days before surgery and INR measured on the day of surgery
- Heparin → 6 hours before surgery, and can be started within 6-12 hours post-surgery
- Aspirin + Clopidogrel → 7-10 days before surgery
- Hypoglycameics
- Some hypotensive drugs: ACEi stopped the day of surgery (can also be started in the preop period to improve blood pressure)
- Oral Contraceptive Pill: 6 weeks before
What is the fasting guidlines in elective surgery?
- > 2 hours of clear fluids
- > 4 hours since milk
- > 6 hours since food
What is used to assess a patient’s risk for surgery?
American Society of Anesthesiologists (ASA) grading
(POSSUM, APECHE, Goldman and Lee (for cardiovascular risk))
depends on the patient and the proposed surgery. The patients cardiac status can play a role in this as well
What is the general management of diabetic patients undergoing surgery?
- Manage blood glucose and diabetic control before surgery in elective patients
- HbA1c of 48mmol/mol is good control, >64mmol/mol is poor control
- Assessment of diabetic complications, especially vascular
- The airway: glycosylation of collagen in the cervical vertebra joints may cause difficulties in tracheal intubation
- Gastroparesis: may have a delay in gastric emptying with autonomic neuropathy and may require tracheal intubation
-
Regional anaesthesia: avoiding GA to allow quicker return to eating and drinking preferable however duabetic patients may compensate poorly following symptahtic blockade and the infection risk
- infections are more common
diabetic patients should be first on the operating list to minimize fasting times and limit the chance of ketosis developing
What is the management of blood glucose for patients intraoperatively?
-
GIK regime: Insulin given separately accoding to variable rate machine with Glucose and Potassium. Insluin is independent according to the blood glucose
- allows for tigter control but runs the risk of hypoglycamia
-
Alberti regime: Insulin simultatesously given with dextrose and potassium. The amount of insulin in the bag is altered according to the blood glucos
- always administered with glucose, however may require frequent changes of the bag with different insulin concentrations
diabetic patients should be first on the operating list to minimize fasting times and limit the chance of ketosis developing
What preoperative assessments are done for vascular surgery?
- Resting and exercising ECG
-
Cardiopulmonary testing (CPET): gives an objective assessment of physiological reserve
- oxygen production and CO2 production is measured,
- when the oxygen delivery becomes inadequate energy demands aerobic metabolism it is called the anaerobic threshold (AT))
- the oxygen consumption at the onset of supplementary anaerobic metabolism is described as mL/kg/min
- an AT of less than 11mL/kg/min suggests a highly increased risk
- Pharmacological stress tests to assess coronary perfusions → dipyridamole-thallium scanning or dobutamine stress echocardiography
- Echocardiography: assess left ventricular and valvular fucntion
- Coronary angiography: can be done prior to vascular surgery to decide if revascularization is required
What are the key principles of managing pain post-operatively?
- WHO pain ladder:
- Multimodal analgesia: paracetamol, NSAIDs, opioids and local anaesthetics
-
Managing side effects of analgesics:
- Opioids: respiratory depression, nausea and vomiting and constipation
- NSAIDs: renal impairment, bleeding and gastric perforations
- Prescribing analgesics regularly
- Infusion devices
- Nausea and vomiting: Phenothiazine (prochlorperazine), Ondansetron, Dexamethasone
- Monitoring the patient and the pain score: BP, sedative effect, N&V, severe weakness
What is the Minimal Alveolar Concentration (MAC)?
the amount of vapour (%) needed to render 50% of spontaneously breathing patients unresponsive to a standard painful surgical stimulus
a lower MAC number means a more potent an anaesthetic
What factors increase the MAC?
- Chronic alcohol consumption (liver enzyme induction)
- Increased sympathetic activity (amphetamine, cocaine)
- Hypermetabolic states (thyrotoxicosis, pyrexia)
- Anxiety
- Some Antidepressants (tricyclics, MOAI)
What factors decrease the MAC?
- Age (peak at 6 months)
- Premedication (BZD)
- Opioids
- Pregnancy
- Acute alcohol intoxication
- Other volatiles (MACs are additive)
- NO
- Hypothermia
What are the Mallampati grading systems?
What is Suxamethonium and what are the contraindications to using it in surgery?
- A depolarizing muscle relaxant
- it Binds to nicotinic acetylcholine receptors resulting in persistent depolarization of the motor end plate
- Contraindications:
- causes a transient rise in intra-ocular pressure therefore contraindicated in narrow angle glaucoma and penetrating eye injuries
What are side effects of Suxamethonium
- Hyperkalaemia (usually transient)
- Malignant hyperthermia
- may cause fasciculations
