Anaesthetics Flashcards
What is general anaesthetic?
Produces insensibility in the whole body, usually causing unconsciousness.
Centrally acting drugs - hypnotics/analgesics.
What is regional anaesthetic?
Producing insensibility in an area or region of body. Applied to nerves supplying relevant area.
What is local anaesthetic?
Producing insensibility in an only the relevant part of the body. Applied directly to the tissues.
What types of anaesthetics are there?
Inhalational Intravenous Muscle relaxants Local anaesthetics Analgesics
What techniques are used?
Tracheal intubation Ventilation Fluid therapy Regional anaesthesia Monitoring
What does the triad of Anaesthesia consist of?
Analgesia, Hypnosis, Relaxation.
What are the problems with polypharmacy?
Increased chance of drug reactions / allergies.
Problems with muscle relaxation?
Requirement for artificial ventilation.
Means of airway control.
Problems with separation of relaxation and hypnosis?
Need to have a greater awareness. Patients can be awake but paralysed.
How do general anaesthetic agents work?
Inhalational:
IV:
Interfere with neuronal ion channels.
I: Dissolve in membranes - direct physical effect.
IV: Allosteric binding - GABA receptors - open chloride channels.
What do general anaesthetic agents do?
Provide unconsciousness as well as a small degree of muscle relaxation. Also provide some analgesia to different extents. Except ketamine all are negligible.
What functions are lost in General?
Cerebral function “lost from top down”.
Most complex processes interrupted first.
LOC early - hearing later.
More primitive functions lost later.
Why are reflexes relatively spared?
Primitive and small number of synapses.
What are the main things to note when using general?
ABC - long drawn out resuscitation.
Mandates airway management.
Impairment of Resp function and control of breathing.
CVS impact.
Care for unconscious patient.
Why is there a rapid recovery and onset with IV? (propofol)
1 arm - brain circulation time.
Rapid recovery - due to disappearance of drug from circulation. Redistribution V’s metabolism.
Why are inhalational slower?
Halogenated hydrocarbons.
Uptake and excretion via the lungs.
Conc G – lungs - blood - brain.
MAC - low number = high potency.
Slow induction - breathe in a washout to reverse conc gradient.
What is most common sequence of General?
IV induction followed by inhlational maintanence.
What are the physiological effects on the CVS system using general?
Central - depresses CV centre - reduces symp outflow.
Direct - negatively inotropic, vasodilation, venodilation (decreased venous return)
MAP = CO x SVR
Physiological effects on Resp system?
Resp depressants - reduce hypoxic and hypercarbic drive. Decreased TV and Increased rate.
Paralyse cilia.
Decrease FRC - lower lung volumes, VQ mismatch. Can be prolongued.
What are the indications for Muscle relaxants?
Ventilation and intubation.
Immobility is essential.
Body cavity surgery.
What are the problems with using muscle relaxants?
Awareness
Incomplete reversal - airway obstruction, vent insufficiency in immediate postop.
Apnoea = depends on airway and vent support.
POSSIBLE TO PARALYSE SOMEONE BUT GIVE AN INSUFFICIENT DOSE OF ANAESTHITIC - AWAKE DURING PROCEDURE.
Why use local and regional analgesia?
Retain awareness / consciousness
Lack of global effects of GA.
Derangement of CVS physiology.
Relative sparing of resp function.
What is a limiting factor when using local?
Toxicity - high plasma levels.
Signs and symptoms – Tinnitus, visual disturbance, drowsiness, coma.
How can LA block be used?
Due to differential penetration into different nerve types.
What do anaesthetist do?
Pre -op Assessment and care Critical care / intensive care Pain management Anaesthesia Post-op care
What is usually used in IV induction?
Propofol.
Quietness - gas or IV - careful monitoring of conscious level.
When would gas induction usually be used?
Young children. (Sevoflurane)
Adults with special needs.
What are the planes of anaesthesia?
Analgesia / sedation Excitation Anaesthesia: Light --> deep. Overdose Or Sleepy / Excited // Anaesthetised.
How is conscious level monitored?
Loss of verbal contact Movement Resp Pattern Processed EEG 'Stages" of anaesthesia.
What is the simple manoeurve used for airway maintenance?
Head tilt / Chin Lift / Jaw Thrust. (firm)
Always required in general anaesthesia.
What simple apparatus is used in Anaesthesia?
Face mask - allow gas-tight seal.
Oropharyngeal (“Guedel”) Airway - Only unconscious patient.
Nasopharygeal Airway.
More advanced airway management includes what?
Laryngeal mask airway:
Cuffed tube with mask sitting over glottis.
Maintains but doesn’t protect.
i-gel - easy to use - often by paramedics.
What is Laryngospasm?
Larygeal spasm
Forced reflex adduction of the vocal cords.
May result in complete airway obstruction.
What foreign materials could get in lower airway?
Gastric contents, blood, surgical debris.
Anaesthesia means loss of protective airway reflexes - gag, swallow,cough.
What is difference between maintained and protecting airway?
Maintained = open and unobstructed
Protected = Cuffed tube in trachea.
Why do we intubate?
Protect airway from gastric contents.
Need for muscle relaxation.
Shared airway with risk of blood contamination.
Need for tight control of blood gases
Restricted access to airway.
What are the risks to an unconscious patient?
Airway Temperature Loss of protective reflexes Venous thromboembolism Consent and identification Pressure areas Patient position
What needs to be monitored?
SpO2, ECG, NIBP, FiO2, ETCO2. Resp parameters Agent monitoring Temperature, Urine output, NMJ Invasive venous / Arterial monitoring Processed EEG
What causes most problems?
Airway
Breathing
Circulation
Unconsciousness
What is Post Anaesthsia Care unit?
Dedicated area with trained staff Continuing responsibility of anaesthetist Problems with A,B,C Pain control Post-operative Nausea and Vomiting Set criteria for discharge back to ward.
What is critical care?
Organ system support.
Initial assessment: ABCDE
What type of Resp failures are there?
Type 1: Oxygenation failure.
Type 2: oxygenation and ventilation failure. (more serious)
How are type 1 and 2 treated in critical care?
1 - HFT nasal cannula
2 - HFT mask
For emergency - Inflatable cuff through mouth.
What is the most common cause of CV failure?
Shock - acute circulatory failure with inadequate or inappropriately distributed tissue perfusion resulting in cellular hypoxia.
Distributive / septic (most common) Hypovolaemic Anaphylactic Neurogenic Cardiogenic (acute / chronic)
CV failure: What are vasopressors?
Alpha 1 agonists:
Metaraminol
Noradrenaline
CV failure: What are inotropes?
Improve contractility.
Dobutamine - beta 1, CO2 can go down.
Adrenaline - alpha and beta receptor - heart rate, contractility (avoid as first line)
What are some of the different fluids?
Colloid - big molecules e.g. albumin
Crystalloids - small molecules e.g. Na, Cl.
Plasmolyte - Na, Cl, K, Mg.
What is the fluid limit?
30ml/kg
What can cause neurological failure?
Metabolic - DKA, SIADH
Trauma - head injury
Infection - meningitis
Stroke
What can be complications of general anaesthesia?
Drug induced reversible coma.
CNS, cardiac and resp depression.
Drug interactions.
What can be complications of regional anaesthesia?
Profound sympathectomy.
Neurological sequelae.
What do anaesthtists do pre-op? (elective, emergent, urgent)
Why?
Assess Identify high risk. Optimise Minimise risk Inform and support patients decisions Consent
To reduce anxiety, delays, cancellations, length of stay, mortality.
What key point are taken from a history?
Known and unknown co-morbidities.
Ability to withstand stress - exercise tolerance.
D&A
Previous surgery and anaesthesia.
Potential problems:
Airway, obesity,fam history.
What are most important pre-op?
ASA grade 1-6.
Surgery grade
Co-morbidities
What is cardiac risk index?
For each co-morbidity you score 1 point.
Above 4 = high risk.
Congestive heart failure, Ischaemic heart failure etc…
What are METs?
Exercise tolerance test scores:
From 2 - 9
4 or more = concerned.
What is done in a high risk emergency patient?
Informed consent Anaesthetic pain Invasive monitoring Senior management Post - op critical care.
What can cause falls in elderly?
Drugs (anti-hypertensives) Neurological (stroke, dementia) Sensory (Visual impairment) Cardio (Heart failure, Postural hypertension) Generally unwell Incontinence
How do drugs cause falls?
Decrease blood pressure, heart rate, awareness.
Increase urine output, sedation, hallucinations, dizziness, qTC.
What are the main drugs that cause falls?
Antihypertensives Beta Blcokers Sedatives Anticholinergics Opiods Alcohol
How can pain be classified into 3 categories?
Duration - acute, chronic, acute on chronic.
Cause - cancer, non-cancer
Mechanism - nociceptive, neuropathic.
What is nociceptive pain?
Obvious tissue injury or illness.
Protective function
Sharp / dull
Well localised
What is neuropathic pain?
Nervous system damage or abnormality Tissue injury may not be obvious Does not have protective function Burning, shooting / numbness, pins and needles. Not well localised.
What are the 4 physiology steps of pain?
Periphery - tissue injury, stimulation of pain receptors.
Spinal cord - Dorsal horn first relay station, A delta and C nerves synapse with second nerve - travels up opposite side of SC.
Brain - Thalamus 2nd relay station - connects to cortex, limbic, brainstem.
Pain perception occurs in cortex.
Modulation - Descending pathway from brain to dorsal horn. Decreases pain signal.
Treatment for periphery
Non-drug (ice)
NSAIDS
Local anaesthetics.
Treatment for Spinal Cord
Accupunture, TENS
Local anaesthtics
Opiods
Ketamine
Treatment for Brain
Psychological Drug treatments - paracetomol -opiods - Amitriptyline (TCA) - Clonidine
What is the RAT approach to pain?
Recognize
Assess - severity, type, other factors.
Treat - non-drug treatments, drug treatments.
How do we pain assess?
Verbal rating score Numerical rating score Visual analogue score Smiling faces Abbey pain scale (confused patients) Functional pain
What is the WHO pain ladder?
Used for nociceptive pain:
ASA system
Fitness of patient before surgery.
1-5
1 - being fit
5 - morbid shouldn’t be having surgery.
What is MAC
Minimum alvolar concentration
Potency inhaled anaesthesia
