Anaesthetics: Principles and pharmacology, conduct of anaesthesia and critical care Flashcards
What does an anaesthetist do?
○ Pre-op Assessment & Care ○ Critical Care / Intensive Care ○ Pain Management ○ Anaesthesia ○ Post-operative care
What is the process of anaesthetics?
- Pre-operative Assessment
- Preparation
- Induction
- Maintenance
- Emergence
- Recovery
- Post-operative care and pain management
What happens in preperation for anaesthetics?
- Planning
- Right patient, right operation
- Right (or left) side…..
- Pre-medication
- Right equipment, right personnel
- Drugs drawn up
- IV access
- Monitoring
What happens during induction of anaesthetics?
- Quietness
□ In the UK, often in a separate, dedicated anaesthetic room - Gas or IV Agent
□ IV induction ® Propofol, Thiopentone + others ® Rapid ® One “arm-brain” circulation ~ 20s ® No obvious planes ® Easy to overdose ® Generally rapid loss of airway reflexes ® Apnoea is very common
□ Gas induction ® Sevoflurane (Halothane) ® Common in young children ® Slow ® Considerably more obvious “planes” of anaesthesia
What happens in maintenance of anaestetics?
- Careful monitoring of conciousness level
- Airway maintenance
- Monitoring
How does soemone monitor coniousness level?
□ Loss of Verbal Contact □ Movement □ Respiratory Pattern □ Processed EEG □ “Stages” or “planes” of anaesthesia
How does someone maintain airways?
□ Always required in general anaesthesia
□ Simple manoeuvres
□ Head Tilt / Chin Lift / Jaw Thrust…
□ Simple apparatus
® Face Mask
◊ Identical to those used in Resuscitation ◊ Contoured to face to allow a gas-tight seal
◊ Sizes from neonatal - large adult
◊ Technique involves lifting the face into ◊ Standard connector
® Oropharyngeal (“Guedel”) Airway ◊ Developed by Guedel in the US ◊ Rigid plastic ◊ Only tolerated by an unconscious patient ◊ Insertion in a ‘light’ patient may cause vomiting or laryngospasm
® (Nasopharyngeal Airway)
® Laryngeal Mask Airway ◊ Cuffed tube with ‘mask’ sitting over glottis ◊ Maintains, but does not protect the airway ◊ Sizes for adults and children
How is a patient under anaesthetics monitored?
□ Basic “minimum” monitoring ® SpO2, ECG, NIBP, FiO2, ETCO2 □ Respiratory parameters □ Agent monitoring □ Temperature, Urine Output, NMJ □ Invasive Venous / Arterial Monitoring □ Processed EEG □ VENTILATOR DISCONNECT □ The anaesthetist is the best monitor...
What happens during emergence?
- i-gel®
- “2nd generation” LMA
- (Relatively) Easy insertion
- Does NOT protect from aspiration
- Landing is as hazardous as take-off
- Muscle relaxation reversed
- Anaesthetic agents off
- Resumption of spontaneous respiration
- Return of airway reflexes / control
- Extubating
- Can be very quick or very, very slow
What happens during recovery?
- A dedicated area with trained staff
- Many patients have not yet regained consciousness or AIRWAY CONTROL
- Continuing responsibility of anaesthetist
- Problems with A, B, C
- Pain control
- Post-operative Nausea & Vomiting
- Set criteria for discharge back to ward
- Post-operative Care and Pain Management
What are the planes of anaesthesia?
○ Analgesia / Sedation ○ Excitation ○ Anaesthesia: Light ---> Deep ○ Overdose Or ○ Sleepy / Excited / Anaesthetised / …..
What are the airway coplications?
- Obstruction
- Aspiration
What is the difference between maintaining or protecting an airway?
○ The airway is maintained if it is open and unobstructed
○ Only a cuffed tube in the trachea protects the airway from contamination
What is endotracheal intubation?
○ Placement of a cuffed tube in the trachea
○ Oral route most commonly used
○ Laryngeal reflexes must be abolished
○ Classic method uses laryngoscope, muscle relaxant, “sniffing the morning air” position
○ Also possible in the awake patient using local anaesthesia and fibre-optic scope
Why intubate?
○ Protect airway from gastric contents
- e.g. full stomach in an unfasted emergency patient
○ Need for muscle relaxation, therefor artificial ventilation
- e.g. laparotomy (muscle relaxants are not selective!)
○ Shared airway with risk of blood contamination
- e.g. tonsillectomy in ENT
○ Need for tight control of blood gases
- especially CO2 levels in Neurosurgery
○ Restricted access to airway
- e.g. Maxillo-facial surgery
What risks are there to an unconcious patient?
○ “Airway, Airway, Airway” ○ Temperature ○ Loss of other protective reflexes - e.g. corneal, joint position ○ Venous thromboembolism risk ○ Consent & Identification ○ Pressure areas
What type of anaesthetic drugs do you get?
○ Inhalational anaesthetics ○ Intravenous anaesthetics ○ Muscle relaxants ○ Local anaesthetics ○ Analgesics
What is the triad of analgesia?
- Hypnosis
□ Unconsciousness
□ Necessary component of any general anaesthetic - Analgesia
□ Pain relief, can also be taken in this context to mean “removal of perception of unpleasant stimulus” since not all unpleasant stimuli patients need protected from are necessarily painful
® E.g. handling of gut: if patient is unconscious and therefore unaware of pain, analgesia usually still required to suppress reflex autonomic responses to painful stimulus - Relaxation
□ Refers to skeletal muscle relaxation necessary to provide immobility for certain procedures, allow access to body cavities and to permit artificial ventilation amongst other things
What is balanced analgesia?
○ Different drugs to do different jobs
○ Titrate doses separately & therefore more accurately to requirements
○ Avoid overdosage
○ Enormous flexibility
○ Big advantage of balanced anaesthesia is that it allows a great degree of control over the individual components of the triad
○ Allows different drugs and techniques to be used to achieve each of the individual “targets” as it were while tailoring the technique to each patient and procedure
○ Helps keep doses of individual drugs down
What are the problems of balanced analgesia?
○ Polypharmacy
- Increased chance of drug reactions/ allergies
- The combinations they use they are very familliar with so this is not a problem
○ Muscle relaxation
- requirement for artificial ventilation
- means of airway control
○ Separation of relaxation & hypnosis
- Awareness
What are general anaesthetic agents?
○ Interfere with neuronal ion channels
○ Hyperpolarise neurones = Less likely to “fire”
○ Inhalational agents dissolve in membranes
- Direct physical effect
○ Intravenous agents – allosteric binding
- GABA receptors – open chloride channels
○ Cerebral function “lost from top down”
- Most complex processes interrupted first
- LOC early - hearing later
- More primitive functions lost later
○ Reflexes relatively spared
- Primitive
- Small number of synapses
○ ABC – Long drawn out resuscitation
○ Mandates airway management
○ Impairment of respiratory function and control of breathing
○ Cardiovascular impact
○ Care of the unconscious patient
Explain intravenous anaesthesia?
○ Thiopentone or propofol
○ Rapid onset of unconsciousness
- 1 arm - brain circulation time
- They are highly fat soluble drugs and cross membranes extremely quickly
○ Rapid recovery
- Due to disappearance of drug from circulation
- Redistribution V’s Metabolism
- Metabolism of the drug (i.e. the process of the drug being destroyed and removed from the body) actually contributes very little to the termination of action of an intravenous anaesthetic agent given as a bolus
Explain inhalation anaestheitcs
○ Halogenated hydrocarbons ○ Uptake and excretion via lungs - concentration gradient: lungs > blood > brain - cross alveolar BM easily - arterial concern equates closely to alveolar partial pressure ○ MAC = minimum alveolar concentration - Measure of potency - Low number = high potency ○ Induction - slow ○ Maintenance of anaesthesia - prolong duration - very flexible ○ Awakening - stop inhalational admin - washout - reversal of concentration gradient
Explain muscle relaxants?
○ Indications - ventilation & Intubation - when immobility is essential □ microscopic surgery, neurosurgery - body cavity surgery (access) ○ Problems - Awareness - incomplete reversal → □ airway obstruction, ventilatory insufficiency in immediate post op period - apnoea = dependence on airway & ventilatory support
What are the requirements in critical care?
○ Na+ requirements: 1 – 2mmol/kg/day
○ K+ requirements: 0.5 – 1mmol/kg/day
○ Fluid requirements: 25-30ml/kg/day
○ Glucose requirements: 50-100g/day
What is the mortality for anaesthetics?
1: 400,000 (0.00024%)
Where on the ASA system do most aneasthtic deaths occur (and what percentage)?
80% of deaths occurr in ASA3-5
What is safer: muscle relaxants or higher doses of opiodes?
Higher doses of opiodes
What parts of the traid of analgesia does opiates target?
- Mostly analgesia
- some hypnosis
What part of the triad of analgesia does general anasthetic agents target?
- Mostly hypnosis
- Some relaxation
- A little analgesia
What part of the triad of analgesia does muscle relaxants target?
- Relaxation
What part of the traid of analgesia does local analgesics target?
- mostly analgesia
- Some relaxation
What complications can happen that result in aspiration?
○ Anaesthesia means loss of protective airway reflexes
- Gag, swallow, cough etc
○ Foreign material in the lower airway
- Gastric contents, blood, surgical debris
What complications can happen that result in obstruction of the airway?
- Ineffective Triple Airway Manoeuvre
- Airway Device malposition or kinking
- Laryngospasm = Laryngeal spasm
□ Forced reflex adduction of the vocal cords
□ May result in complete airway obstruction
□ Caused by airway (or other) stimulation in light planes of anaesthesia
□ Often unrelieved by simple manoeuvres
What happens when continuing aneasthesia?
○ Induction agent wear off… ○ Maintenance: IV/ inhalation al or both ○ Self- or artificial ventilation ○ Monitoring and physiological support ○ Fluid management ○ Document recording
What are the risk factors for awareness during aneasthesia?
- Paralysed and ventilated
- Previous episode of awareness
- Chronic CNS depressant use
- Cardiac surgery 1 in 100
- Major trauma 1 in 20
- GA C/section 1 in 250
What are the 2 types of respiratory failure?
○ Type 1: oxygen failure
○ Type 2: oxygenation and ventilation failure
- Worrying as CO2 increases
What masks can you get outside of critical care?
- Vaso canula 25% oxygen
- Hudson mask 50% oxygen
- Trauma mask 100% oxygen (15L per minute)
How might someone ventilate inside of critical care?
□ High flow nasal canula (70-80 L per minute)
® Well tolerated
® Gives pressure to the airway
® Used for type 1 respiratory failure
□ NIV
® It sort of works in type 1 respiratory failure
◊ Only used if they cannot tolerate anything else
® Works very well in type 2 respiratory failure
® Cannot talk or eat while wearing this mask
□ Intubation
® Need a intratracheal tube
◊ Can defiantly get 100% oxygen
◊ Can take over the work of breathing
◊ Can open up bits of lung that were not open before and get it doing gas exchange again
What can happen if too much pressure driving ventilation and prolonged ventilation is given?
ARDS
What are the different types of shock?
- Disruptive shock
- Hypovolaemic shock
- Anaphylactic shock
- Neurogenic shock
- Cardiogenic shock
What are colloids?
Have large molecules e.g. blood. Many can result in anaphylactic shock or renal failure.
What are crystalloids?
Have small molecules e.g. saline. Isn’t particularly effective at raising blood pressure.
What can cause neurogenic failure?
○ Metabolic - SIDH (drank gallons of water) - DKA (acidosis) - Hypoglycaemic ○ Trauma ○ Infection - Meningitis - Encephalitis ○ Stroke
