Anaesthetics Flashcards
What is the function of a general anaesthetic?
- Produces insensibility in the whole body, usually causing unconsciousness
- Centrally acting drugs - hypnotics/analgesics
What is the function of a regional anaesthetic?
- Producing insensibility in an area/region of the body
- Local anaesthetics applied to nerves/plexuses supplying relevant area
What is the function of a local anaesthetic?
- Producing insensibility in only the relevant part of the body
- Local anaesthetics applied directly to the tissues
What types of anaesthetic drugs exist?
Inhalational Intravenous Muscle relaxants Local anaesthetics Analgesics
What types of techniques and equipment exist for anaesthesia?
Tracheal intubation Ventilation Fluid therapy Regional anaesthesia Monitoring
What are the triad components of anaesthetic?
Analgesia
Hypnosis
Relaxation
(But does not require all three!)
Give an example of an anaesthetic that may consist only of hypnosis?
Simple anaesthetic for dental extraction
Give an example of an anaesthetic that may consist only of analgesia?
Local anaesthetic for dental extraction
Give an example of an anaesthetic that may consist only of analgesia and relaxation, with no hypnosis?
Spinal anaesthetic
eg Epidural
What type of drugs contribute to relaxation in anaesthesia?
Local anaesthetics
General anaesthetics
Muscle relaxants
What type of drugs contribute to analgesia in anaesthesia?
Local anaesthetics
General anaesthetics (minor - except ketamine)
Opiates
What type of drugs contribute to hypnosis in anaesthesia?
General anaesthetics Opiates
What are the advantages of balanced anaesthesia (using different drugs for different jobs)?
- Titrate doses separately & therefore more accurately to requirements
- Avoid overdosage
- Enormous flexibility
What problems can arise in anaesthetic?
- Polypharmacy
- Muscle relaxation (requirement for artificial ventilation)
- Separation of relaxation + hypnosis (Can lead to awareness)
What is the mechanism of action of general anaesthetics?
- Interfere with neuronal ion channels
- Hyperpolarise neurones = less likely to fire
What membrane receptors do intravenous agents have an effect on?
GABA receptors
eg Thiopentone/Propofol
In what way are functions lost in general anaesthetics?
Most complex processes lost first
Primitive functions lost later
What are the main component of anaesthetic management?
ABC - - long drawn out resus Mandates airway management Impairment of respiratory function and control of breathing Cardiovascular impact Care of the unconscious patient
What is arm-brain circulation time?
Refers to time taken for drug to get from hand to blood brain barrier
Ie the rapid onset of consciousness in Iv anasethesia
Why does IV anaesthesia have a rapid recovery time?
- Disappearance of drug from circulation
- Redistribution vs metabolism
What type of drugs are used as inhalational anaesthetics?
-Halogenated hydrocarbons
What measure of potency is used for inhalational anaesthetics?
MAC (Minimum Alveolar Concentration)
What is the main role of inhalational anaesthetics?
Extension/continuation of anaesthesia
What is the most common sequence of general anaesthesia?
Intravenous induction
->Inhalation maintenance
What effects do general anaesthetics have centrally on the cvs?
Depress cardiovascular centre
- reduce sympathetic outflow
- negative inotropic/chronotropic effect on heart
- reduced vasoconstrictor tone → vasodilation
What effects do general anaesthetics have directly on the cvs?
-Negatively inotropic
-Vasodilation
→ decreased peripheral resistance
-Venodilation
decreased venous return,
decreased cardiac output
What effects do general anaesthetics have on the respiratory system?
All anaesthetic agents are respiratory depressants
- Reduce hypoxic and hypercarbic drive
- Decreased tidal volume & increase resp rate
Paralyse cilia
Decrease FRC
- Lower lung volumes
- VQ mismatch
What indications are there for muscle relaxants in anaesthetics?
Ventilation & Intubation When immobility is essential -microscopic surgery, -neurosurgery Body cavity surgery (access)
What problems are associated with muscle relaxants in general anaesthesia?
- Awareness
- Incomplete reversal →
- Airway obstruction, ventilatory insufficiency in immediate post op period
- Apnoea = dependence on airway & ventilatory support
What is the purpose of intraoperative analgesia?
- Prevention of arousal
- Opiates contribute to hypnotic effect of GA
- Suppression of reflex responses to painful stimuli
- e.g. tachycardia , hypertension
List some examples of local anaesthetic drugs?
- Lignocaine
- Bupivacaine
- Ropivacaine
What are the effects of local/regional anaesthesia?
-Retain awareness / consciousness
-Lack of global effects of GA
-Derangement of CVS physiology
proportional to size of anaesthetised area
-Relative sparing of respiratory function
What steps are involved in the process of anaesthesia?
Pre-operative Assessment Preparation Induction Maintenance Emergence Recovery Post-operative Care and Pain Management
Give some examples of drugs used in IV induction of anaesthesia?
Propofol
Thiopentone
Give some examples of a drug used in gas induction of anaesthesia?
Sevoflurane (Halothane)
What is used for monitoring consciousness level in anaesthesia?
- Loss of verbal contact
- Movement
- Respiratory Pattern
- Processed EEG
- ‘Stage’ or ‘planes’ of anaesthesia
What is involved in the triple airway manoeuvre in airway management?
Head Tilt
Chin Lift
Jaw Thrust
What simple apparatus may be used in airway maintenance?
- Face mask
- Orophayngeal (Guedel) Airway
- Nasopharyngeal Airway
What state does the patient need to be in for insertion of an oropharyngeal (guedel) airway?
Unconsciousness
What may be used in more advanced airway management?
Laryngeal Mask Airway
What may be used for resuscitation airway management?
i gel Laryngeal airway
What are some airway complications?
Obstruction
- Ineffective Triple Airway Manoeuvre
- Airway Device malposition or kinking
- Laryngeal spasm
Aspiration
What is the only thing to protect the airway? (Rather than maintain it?)
Endotracheal intubation
A cuffed tube in the trachea
What reasons may you intubate a patient?
- Protect airway from gastric contents
- Need for muscle relaxation: artificial ventilation
- Shared airway with risk of blood contamination (tonisllectomy in ENT)
- Need for tight control of blood gases (eg neurosurgery)
- Restricted access to airway (eg Max-Fax)
What risks are there to an unconscious patient?
- Airway maintenance
- Temperature maintenance
- Loss of protective reflexes
- Venous thromboembolism risk
- Consent and identification
- Pressure areas
What may be used in the maintenance of anaesthesia?
IV/Inhalational anaesthesia or both
What is monitored in anaesthesia?
Basic “minimum” monitoring -SpO2, ECG, NIBP, FiO2, ETCO2 Respiratory parameters Agent monitoring Temperature, Urine Output, NMJ Invasive Venous / Arterial Monitoring Processed EEG VENTILATOR DISCONNECT
What are the risk factors for awareness in anaesthesia?
Paralysed and ventilated Previous episodes of awareness Chronic CNS depressant use Major trauma GA C/Section Cardiac Surgery
What happens during emergenece/awakening of anaesthesia?
Muscle relaxation reversed Anaesthetic agents off Resumption of spontaneous respiration Return of airway reflexes / control Extubation
What is critical care?
-Organ system support (single vs multiple)
Initial assessment: ABCDE
What are the oxygen and carbon dioxide levels in type 1 respiratory failure?
- Oxygen = Low
- Carbon Dioxide = Normal/Low
(Failure of oxygenation)
What are the oxygen and carbon dioxide levels in type 2 respiratory failure?
- Oxygen = Low
- Carbon Dioxide = High
(Failure of oxygenation + ventilation)
What breathing support systems may be use in respiratory failure?
Heated-humidified high flow therapy
Non-invasive Ventilation
Endotracheal ventilation
What is the definition of shock?
Shock is acute circulatory failure with inadequate or inappropriately distributed tissue perfusion resulting in cellular hypoxia
List some types of shock
Distributive (septic) Hypovolaemic Anaphylactic Neurogenic Cardiogenic
What is the formula for working out cardiac output?
HR x Stroke Volume