Anaesthetics Flashcards
(41 cards)
Difference between local and general anaesthetic
General: insensibility in the whole body, causing unconsciousness - reversible coma using centrally acting drugs (hypnotics and analgesics)
Local: insensibility of a region of the body, using drugs applied directly to the tissues to affect the nerve supply of that area
How do general anaesthetics work?
Suppress neuronal activity by opening chloride channels, hyperpolarising the neurone and suppressing exitatory synaptic activity (less likely to fire)
Cerebral function lost from top-down; complex processes, such as level of consciousness and hearing, lost first while primitive functions lost later (reflexes mostly spared)
Sequence of general anaesthesia
Induction with inhalational or IV agent Maintenance with inhalational or IV agent
(Usually IV then inhalational)
IV maintenance can occur with newer agents and computer controlled infusion
Additional regional analgesia and anaesthesia
How do IV anaesthetics work?
Rapid onset of unconsciousness (arm to brain time)
Fat soluble drugs, cross membranes quickly
Rapid recovery (leave circulation quickly/redistributed/metabolised)
One off bolus leads to temporary unconsciousness
How do inhaled anaesthetics work?
Halogenated hydrocarbons Via lungs (cross alveolar basement membrane easily, rely on concentration gradient from lungs to blood to brain - arterial conc ~ alveolar partial pressure)
Mininum alveolar concentration measures potency (low MAC=high potency)
Slower induction
Flexible duration (stop when needed)
Washout period as CG reversed
Why do we need balanced anaesthesia?
Different drugs do different jobs
Titrate them separately
Avoid overdose
Gives flexibility, tailored to needs (consciousness, need for analgesia, need for muscle relaxation, airway management)
Problems with balanced analgesia?
Polypharmacy, increased reactions, allergies
Artificial ventilation and need for airway management if using muscle relaxant
Separates relaxation and hypnosis stages, (potential for patient to be aware/’awake!!!)’
Induction of general anaesthesia requirements?
Quietness (dedicated anaesthesia room)
IV (propofol), gas (sevoflurane/halothane)
Monitoring of consciousness
Airway maintenance (triple airway, face mask, oropharyngeal airway, laryngeal mask, cuffed tube to avoid contamination)
How is consciousness level monitored?
Loss of verbal contact
Loss of movement
Respiratory pattern and ECG Planes: eyes roll and fix, loss of corneal/laryngeal reflexes, dilated pupils and loss of light reflex, intercostal paralysis with shallow abdominal breaths
Complications of general anaesthetic?
Ineffective triple airway manoeuvre
Airway device malpositioned or kinked
Laryngospasm (forced adduction of vocal cords, can obstruct completely, caused by airway stimulation in light planes)
Aspiration due to loss of protective reflexes, foreign material present (blood, gastric)
How does general anaesthetic affect the respiratory system?
Agents are respiratory depressants
Reduction in hypoxic and hypercarbic driver
Reduced tidal volume
Increased respiratory rate
Paralysed cilia
Decreased FRC (lower lung volumes, VQ mismatch)
How does general anaesthetic affect the cardiovascular system?
Central: depresses centre in medulla oblongata, reducing sympathetic outflow
Reduction in vasoconstrictor tone=vasodilation meaning decreased peripheral resistance
Venodilation leading to reduced venous return and decreased cardiac output
Agents are negatively inotropic (weaken the force of muscular contraction)
Brief description of pre-op assessment (History, examination, investigation, optimisation)
Co-morbidities, ability to withstand stress, cardiopulmonary disease, previous surgery, anaesthesia, drugs/allergies (stop diabetic drugs, anticoagulants beforehand) ETT, potential issues (airways, lying flat, reflux, obesity), cardiac risk index
Detect unknown/suspected conditions and severity, risk assessment, aware of complications, cardio/resp assessment
Optimising current control
When is intubation required?
Protect airway from gastric contents If muscle relaxant required
Need blood gas control
Shared airway with risk of blood contamination
Restricted airway access
Endotracheal intubation
Via mouth or nose (rarely, not in emergencies) Laryngoscope and muscle relaxant Abolish laryngeal reflexes ‘Sniffing the morning air’ - triple airway of head tilt, chin lift, jaw thrust
Risks of intubation
Damaged teeth or dental work Throat or tracheal injury Fluid build-up in organs or tissues Bleeding Loss of protective reflexes (corneal, joint position) VTE risk Aspiration Unable to consent/identify
Types of intubation
Triple airway manoeuvre (head tilt, chin lift, jaw thrust)
Anaesthetic face mask
Oropharyngeal airway or laryngeal mask airway (supraglottic)
Endotracheal cuffed tube if need to avoid contamination (infraglottic)
Monitoring an anaesthetised patient
Peripheral saturation and fraction inspired (O2 rich air is above normal of 0.21, avoid oxygen toxcity)
ECG, blood pressure
Respiratory parameters
Agent monitoring
Temperature, urine, NMJ Venous/arterial monitoring (invasive)
Ventilator disconnect
Recovering from anaesthesia
Dedicated area, trained staff Check for issues with ABC (may not have regained consciousness, airway control) Pain management Post-op nausea, vomiting Need criteria for discharge or transfer
How does local anaesthesia work?
Insensitivity in relevant part of body, applied directly to tissues (spinal, epidural, plexus or nerve block)
Block sodium channels responsible for single propagation (no depolarisation)
Complications of local anaesthetic
Cardiovascular depression Cardiopulmonary arrest Tingling/numbness of mouth and tongue Convulsions due to involuntary muscle contractions Coma Drowsiness, light-headedness Tinnitus, visual disturbance
How is local anaesthetic delivered?
Wound catheters Epidural (+/- opiates) Nerve plexus catheters Intrathecal (+/- opiates) Local infiltration of wounds
When are spinal/epidural anaesthetics used?
Want to avoid general
Want to avoid airway problems (difficult intubation or obstruction)
Allergies
Severe respiratory disease
Contraindications to spinal or epidural anaesthesia?
Patient refusal Fixed cardiac output (aortic or mitral stenosis) Infection Hypocoagulability (drugs or disease) Technical difficulties Neurological defect
