Week 4: Anaesthesia Flashcards
How do local anaesthetics work and what are some care considerations?
Electrical currents carried by ions
LA block channel for sodium ions –> blocks messages for pain, temperature, feeling
Wears off and sensation returns
Not typically reversible, have to wait for it to be absorbed and distributed in blood stream
Toxicity risk
Lipid soluble, so can administer intralipid to dilute
What are the types of LA administration?
Topical Spray Injection: locally or around nerve fibre to provide regional block Brachial plexus Femoral Spinal Epidural
What is anaesthesia?
The condition of having the feeling of pain and other sensations blocked, allowing patients to undergo surgery and other procedures without the distress and pain they would experience otherwise
What is the history of anaesthesia?
Robert Liston – surgeon; butcher; showman.
Ether
1799 – Humphrey Davey – Nitrous Oxide
1846 – William Morton dental anaesthesia
Mid 1800’s - Nitrous Oxide for anaesthesia
1847 – Simpson (obstetrician) Chlorophorm; 1st death: 1848
1860 – Cocaine used for spinals; addiction destroyed lives & limited research
1905: Novocaine
Early – mid 1900’s – Curare
Mid 1900’s – Thiopentone
1986 - Propofol
What does the Greek word, ‘anaesthesia’ mean?
Without feeling
What does the Greek word ‘analgesia’ mean?
Without pain
What are the determinants of anaesthesia?
Patient preference
Surgeon preference
Demands of surgery: type, site, access
Patient condition: medical, surgical, anaesthetic history
What is the American Society if Anaesthesiologists physical status classification system?
ASA 1: normal healthy patient
ASA 2: mild systemic disease
ASA 3: severe systemic disease
ASA 4: severe systemic disease which is a constant threat to life
ASA 5: moribund patient, not expected to survive without operation
ASA 6: brain-dead, organs being removed for donation
What is ASA 1?
Able to walk up a flight of stairs or down the street
What is ASA 2?
Can walk up a flight of stairs or down the road, but may need to stop for a rest
What is ASA 3?
Limited activity, but not completely debilitating
What are examples of ASA 2 conditions?
Respiratory disease, anxiety, diabetes
What are examples of ASA 3 conditions?
Angina, COPD, insulin dependence
What is ASA 4?
Distressed at rest
What are examples of ASA 4 conditions?
Unstable angina, CHF, uncontrolled diabetes, HTN
What is Mallampati 1?
Soft palate, fauces, uvula, pillars entire glottic opening
What is Mallampati 2?
Soft palate, fauces, uvula, posterior commissure
What is Mallampati 3?
Soft palate, uvular, base, tip of epiglottis
What is Mallampati 4?
Hard palate only, no glottal structures
What is the triad of anaesthesia?
Hypnosis: unconsciousness
Analgesia: to prevent physiological responses to pain
Paralysis: muscle relaxation
What are the steps on hypnosis?
Awake Amnesia Sedation Hypnosis Coma Death
What are the types of anaesthesia?
Local +- sedation Regional block: brachail plexus, femoral nerve Epidural Spinal General
What is local anaesthetic?
Drugs that block conduction when applied locally to nerve tissue. The block is entirely reversible
What are the differences between a spinal and a epidural?
Intradural vs extradural
In CSF vs fat, blood vessels, nerve fibre endings
Single shot of 3-5 mL vs 15-20 Ml + infusion
Lasts 2-4 hours vs 2-4- hours + 2-3 days
Motor + sensory vs Sensory only
Spinal:
Complete blockage
Blocks SNS –> peripheral vasodilation –> decrease VR –> decrease CO –> decrease BP
Instant
Epidural:
Patchy, along dermatomes
Can move but feel weak
What are different local anaesthetic medications?
Lignocaine: quick/short acting Bupivacaine +- adrenaline (vasoconstriction for prolonged effect): slow and long action, regional Ropivacaine: "" Amethocaine: topical spray Prilocaine: IV Cocaine
What are the advantages of LA?
Effective alternative to GA Avoids polypharmacy Allergic reactions Extended analgesia Patient can remain awake Early drink/feed Low level allergic reactions Analgesia after surgery Cheap
What are the disadvantages?
Limited scope Higher failure rate Time constraints: waiting for LA to take effect Anticoagulants/bleeding predisposition Risk of neural injury
What is general anaesthesia?
Drug induced loss of consciousness during which patients are nonresponsive, even to painful stimulation
What determines spontaneous breathing or paralysed and ventilated GA?
Depends on demands of surgery and general well being of patient
Abdo surgery: paralysed and ventilated to control organs
Cardiothoracic: need heart and lungs paralysed
Less complex surgery which does not require organs can be spontaneous, e.g. knee arthroscopy
What are the benefits of GA?
No absolute contraindications;
Quick to establish;
Never fails to work;
Often the only option available for major operations;
Can provide the best operating conditions for the surgeon;
The patient is completely unconscious and unaware
What are the complications of GA?
Polypharmacy; Effects on various systems; Allergic reactions; Recovery profile; PONV; 'Awareness' during surgery
What are the phases of GA?
Induction
Maintenance
Reversal
Recovery
How do the stages of anaesthesia compare to stages of alcohol intoxication?
- Amnesia and analgesia vs dizzy and delightful
- Uninhibited response to stimuli vs drunk and disorderly
- Surgical anaesthesia vs unconscious drunk
- Vital centre depression vs alcohol poisoning
What is involved in the induction stage of GA?
IV or inhaled Monitoring Preoxygenation Hypnotic/analgesia and/or relaxant Mack/LMA/ETT
What is involved in the maintenance stage of GA?
IV or inhaled O2 40-100% Nitrous oxide: anaesthetic machines automatically increase O2 to ensure more O2 than nitrous oxide always given Muscle relaxant Analgesia
What is involved in the recovery stage of GA?
Turn off agent Reverse relaxant Cough reflex returns: throat movement as tries to swallow, HR increases as LMA/ETT irritated Extubate upon waking Recovery position Monitor until discharge
What is a depolarising NMB agent and how does it work?
Suxamethonium
Small % of people develop sux apnoea
Motor neurons release neurotransmitters called acetylcholine at their nerve axon terminals to jump synaptic cleft and continue nerve impulse to next neuron
ACh changes permeability of cells to allow Na+ in and K+ out, creating an action potential which leads to depolarisation and muscle contraction
Mimics ACh, causing vesculations (fine motor twitching)
No reversal agent, must be able to maintain airway
Short duration
What is a non-depolarising NMB agent and how does it work?
Actracurium Cisactracurium Mivacurium Pancurium Rocuronium Vecuronium Produces histamine release: rask, swelling
Motor neurons release neurotransmitters called acetylcholine at their nerve axon terminals to jump synaptic cleft and continue nerve impulse to next neuron
ACh changes permeability of cells to allow Na+ in and K+ out, creating an action potential which leads to depolarisation and muscle contraction
Competes with ACh and blocks it from reaching receptor site
Broken down over time, quicker with anticholinergics
Administered with atropine (cause bradycardia)
What medication is used as a reversal agent for non-depolarising NMB agents and how does it work?
Neostigmine
Cholinesterase which breaks down ACh
What are the requirements for Rapid Sequence Induction?
Good IV access O2 Suction Introducer loaded with ETT Air syringe 2 working laryngoscopes Stethoscope Trachy tape Monitoring: NIBP, PSAO2, ECG, ETCO2
When is RSI used?
Patients at risk of aspiration:
Short fasting times, e.g. emergency surgery
Pregnany: added weight on gut may force aspirate out of sphincter when relaxes
Obese: “”
GORD
Oesophageal pouch surgery
What is the sequence for RSI?
Preoxygenation 100% O2 for 3 minutes Thiopentone followed rapidly by suxamethonium Rocuronium Cricoid pressure applied Fasciculations Laryngoscopy and intubation ETT inflated, test ventilation and check for ETCO2 Confirm position with stethoscope ETT secured Cricoid pressure released
What is the reversal agent for rocuronium?
Sugammadex
What is malignant hyperthermia?
Rare, life threatening
Triggered by volatile anaesthetic agents, e.g. suxamethonium
Inherited autosomal dominant disorder
What are the signs of malignant hyperthermia?
Early signs: rise in CO2, temp and RR, desaturation
Drastic, uncontrolled increase in skeletal muscle metabolism –> increase in waste production –> lactic acidosis –> disturbs ability for gas exchange
What is the prevention for malignant hyperthermia?
Designated machine for patients which family hx of MHT, not contaminated with gas
What is the management for malignant hyperthermia?
Adrantoline sodium, 1mL per kg
May need 25 bottles
Active cooling (irrigation with catheter, packing body cavity with cold slush
What is the action, onset, duration, indication, reversal and precautions of suxamethonium?
Depolarising muscle relaxant. IV administration.
Action: mimics Acetylcholine, occupies receptor sites at the Neuromuscular Junction, lasting longer than Ach. Depolarised membranes remain depolarised and unresponsive to additional stimuli.
Onset: rapid – (1 circulation time)
Duration of Action: ½ life estimated at 2 mins. Ultra short acting
Indication: profound but brief muscle relaxation (paralysis) for intubation. Always used for intubation when patient has unknown fasting details or a full stomach, as action is rapid and complete.
Reversal: no pharmacological antidote or reversal agent. Broken down by enzymes (pseudocholinesterase).
Precautions & Side Effects: Apnoea - may have extended duration of action on specific population group – congenital abnormal pseudocholinesterase required to metabolise drug. Artificial respiration required until effects wear off.
Muscle pain resulting from fasciculations (rapid muscle twitches as drug occupies receptor sites and depolarisation occurs.)
What is the action, onset, duration, indication, reversal and precautions of actracurium?
Non-depolarising muscle relaxant. IV administration.
Indication: used as an adjunct to general anaesthesia to enable endotracheal intubation, and to relax skeletal muscles during surgery, or controlled ventilation, and to facilitate mechanical ventilation in ICU pts. Has no effect on consciousness.
Action: competes with Acetylcholine binding competitively with cholinergic receptor sites on the motor end plate at the Neuromuscular Junction.
Onset: suitable intubation conditions 2-2 ½ mins. 3-5 minutes following admin.
Duration of Action: 20-35 mins (depending on dose)
Reversal: reversed by acetylcholinesterase inhibitors such as Neostigmine (side effect bradycardia, hence added with anticholinergic – Atropine)
Precautions & Side Effects :Administer only with adequate anaesthesia or sedation/ analgesia; facilities for endotracheal intubation and ventilation, including administration of O2 under positive pressure and elimination of CO2. Reversal agents should be immediately available.
What is the action, onset, duration, indication, reversal and precautions of thiopentone?
Indication: IV anaesthetic for short duration operations; induction of anaesthesia prior to administration of other anaesthetic agents.
Action: hypnotic; anaesthetic; Ultra short acting depressant of the CNS which induces hypnosis & anaesthesia, but not analgesia.
Onset: unconsciousness 30-40 secs following IV injection.
Duration of Action: consciousness returns 20-30 mins after a single induction dose. ½ life of elimination 3-8hrs.
Reversal: nil. treat symptoms as they arise until drug is metabolised.
Precautions & Side Effects:. Thiopentone may decrease LOS tone. Avoid intra-arterial injection (causes necrosis). Respiratory depression. Hepatic & renal disease may prolong effect.
CI: status asthmaticus; lack of adequate airway; complete absence of suitable vein
What is the action, onset, duration, indication, reversal and precautions of diprivan?
Indication: Short acting IV anaesthetic agent suitable for both induction and maintenance of general anaesthesia in adults and children.
Ideal anaesthetic agent for the outpatient, day only, shorter procedures. As infusion – total IV Propofol results in a more rapid recovery and less PONV than comparison drugs. Suitable for use as sedation for ventilated ICU patients; conscious sedation for surgical & diagnostic procedures.
Onset: 60 - 120 secs. (dose dependant)
Duration of Action: 5-10 minutes following induction dose.
Reversal: Unlike other sedation agents (Midazolam, Morphine) there is no reversal agent; Adverse effects must be treated until the drugs is metabolised.
Precautions & Side Effects: reduces cerebral blood flow; pain on injection; all general anaesthetics cross the placenta with the potential to cause CNS & respiratory depression in the newborn infant
What is the action, onset, duration, indication, reversal and precautions of sevoflurane?
Indication: induction and maintenance of anaesthetic in adults and paediatric patients undergoing surgery. Fast acting non-irritating agent; rapid loss of consciousness during inhalation induction; rapid recovery following discontinuation.
Action: inhalation anaesthetic agent.
Onset: administered at 5% - surgical anaesthesia produced in <2 mins. A short acting barbiturate or other intravenous induction agent should be administered followed by inhalation of Sevoflurane.
Duration of Action: emergence times short; pts may require pain relief earlier than others.
Reversal: there is no reversal agent, although 100% O2 would assist in the dilution and elimination of drug from the alveoli. Assisted or controlled ventilation required.
Precautions & Side Effects: Caution in patients with severe renal or hepatic impairment; .
CI: Malignant Hyperthermia
What is the action, onset, duration, indication, reversal and precautions of isoflurane?
Indication: inhalation anaesthetic agent; induction and maintenance of general anaesthetic.
Onset: inspired concentrations of 1.5-3% may produce surgical anaesthesia in 7-10 mins.
Reversal: 100% O2 with assisted or controlled ventilation.
Precautions & Side Effects:. Mild pungency which limits rates of admin during inhalation induction; Respiratory depression; hypotension. Potentiates the effects of all muscle relaxants – notably all non-depolarising muscle relaxants.
CI: known or suspected Malignant Hyperthermia
What is the action, onset, duration, indication, reversal and precautions of bupivacaine?
Indication: local anaesthetic; production of spinal anaesthetic.
Action:.causes a reversible blockade of impulse along nerve fibres by preventing the inward movement of sodium ions through the nerve membrane.
Onset: slower than lignocaine;
Duration of Action: up to 4X potent as lignocaine; motor blockade 3-4hrs in spinal application, shorter than sensory blockade.
Reversal: lipid reversal for toxicity
Precautions & Side Effects:. monitor cardiovascular & respiratory function. Slow injections with frequent aspirations to avoid intravascular administration. Restlessness, anxiety, tinnitus, dizziness + early signs of toxicity
Adverse reactions: hypotension; bradycardia; cardiovascular toxicity; high / total spinal blockade.
CI: IV administration; epidural & spinal anaesthesia in pts with uncorrected hypotension, coagulation disorders & on anticoagulation therapy
What is the action, onset, duration, indication, reversal and precautions of ropivacaine?
Indication: local anaesthetic; epidural block inc. for caesarian; minor & major nerve block; infiltration. Continuous epidural infusion or intermittent bolus administration for analgesia in postoperative pain; continuous peripheral nerve block infusion for intra & post-operative pain management.
Action: Causes a reversible blockade of impulse along nerve fibres by preventing the inward movement of sodium ions through the nerve membrane.
Anaesthetic and analgesic effects; at higher doses produces surgical anaesthesia with motor block, lower doses produces sensory block (inc. analgesia) with little motor block.
Onset:
Duration of Action:.
Reversal:
Precautions & Side Effects: Monitor cardiovascular & respiratory function.
Adverse reactions:. Total spinal block may occur if an epidural dose is inadvertently administered into the subarachnoid. may lead to CNS depression, cardiovascular collapse, and respiratory arrest. Toxicity symptoms include visual or auditory disturbances, dizziness, to convulsions.
CI: IV administration; uncorrected hypotension; local inflammation, sepsis; Bier’s block
What is the action, onset, duration, indication, reversal and precautions of droperidol?
Indication: Anaesthesia: General anaesthesia adjunct (to reduce PONV); premedication; regional anaesthesia adjunct.
Neuroleptanalgesia : when given concurrently with narcotic analgesic - produce tranquillity and decreasing anxiety and pain. Psychiatry: severe agitation, hyperactivity & agitation. Mania.
Onset: 3-10 mins.
Duration of action: 2-4 hrs. Altered consciousness up to 12hrs.
Reversal: No specific antidote – treatment is primarily supportive; severe extrapyramidal reactions, hypotension, drowsiness.
Precautions: High dose, prolonged use; spinal anaesthesia; a history of significant cardiac disease, serious ventricular arrhythmia. May cause drowsiness. Hypotension. Respiratory depression.
CI: severe CNS depression; clinically significant bradycardia. Drugs prolonging QT interval eg amiodarone, sotalol; some antihistamines
What is the action, onset, duration, indication, reversal and precautions of rocoronium?
non-depolarising muscle relaxant; IV bolus or infusion.
Indication: adjunct to general anaesthesia to facilitate endotracheal intubation during routine induction; to facilitate mechanical ventilation. Adjunct to GA when suxamethonium is CI.
Action: competes with acetycholine blocking receptor sites at the motor end plate
Onset:.fast onset; intubating conditions achieved within 60 secs. General muscle paralysis achieved within 2 mins.
Duration of action: intermittent duration. 14-20 mins
Reversal: administration of acetylcholinesterase inhibitors, such as neostigmine., should not commence until definite signs of spontaneous recovery are present.
Precautions & Side Effects:. Injection site pain; profound prolonged paralysis; tacchycardia; Administer only with adequate anaesthesia or sedation/ analgesia; facilities for endotracheal intubation and ventilation, including administration of O2 under positive pressure and elimination of CO2. Reversal agents should be immediately available.
CI: Bromide ion hypersensitivity
What is the action, onset, duration, indication, reversal and precautions of fenanyl?
Synthetic opioid. Analgesic (related to morphine, 80x potent).
Indications: short duration analgesia during premedication, induction and maintenance of anaesthesia & immediate postoperative periods. Opioid analgesic supplement in general and regional anaesthesia.
Duration of action: 30-60 mins.
Onset: mins
Reversal: Opioid antagonists such as naloxone, consider duration of respiratory depression vs duration of action of Naloxone. Assist or control adequate ventilation.
Precautions & side effects: Respiratory depressant; may cause respiratory depression in newborn infant.
CI: bronchial asthma; respiratory depression;
Fentanyl may be used in combination with neuroleptic agents such as droperidol as an anaesthetic premedication, for the induction of anaesthesia, and as an adjunct in the maintenance of general and regional anaesthesia.
The state of neuroleptanalgesia may be converted to neuroleptanaesthesia by the concurrent administration of 65% nitrous oxide in oxygen
What is the action, onset, duration, indication, reversal and precautions of epidural anaesthetic?
Injection of local anaesthetic (+/- narcotic – Fentanyl) into the posterior lumbar epidural space.
Indications: postoperative pain relief; lower abdominal procedures; normal & high risk obstetric procedures.
Advantages: Slower onset compared to spinal, of sympathetic blockade – allows for compensation through vasoconstriction.
Ability to administer via continuous epidural infusion or intermittent bolus administration for analgesia in postoperative pain.
Disadvantages: relative difficulty of technique; can be an incomplete block - following dermatomes.
CI: absolute: anticoagulant therapy; hypovoleamia; systemic or localised infectin near needle puncture site; raised ICP; relative: inexperience; CNS disease; previous spinal surgery
What is spinal anaesthetic?
Consists of injecting local anaesthetic into the subarachnoid space with the resultant blockade of the spinal nerve roots. cerebro-spinal fluid (CSF). Usually occurs in the lumbar spine below L2 (spinal cord ends).
Spinal anaesthesia is best reserved for operations below the umbilicus e.g. hernia repairs, gynaecological and urological operations and any operation on the perineum or genitalia.
Spinal anaesthesia is especially indicated for older patients and those with systemic disease such as chronic respiratory disease, hepatic, renal and endocrine disorders such as diabetes. Most patients with mild cardiac disease benefit from the vasodilation that accompanies spinal anaesthesia except those with stenotic valvular disease or uncontrolled hypertension.
What are the advantages of spinal anaesthetic?
Produces few adverse effects on the respiratory system as long as unduly high blocks are avoided.
Airway not compromised; there is a reduced risk of airway obstruction or the aspiration of gastric contents. This advantage may be lost with excessive sedation.
Spinal anaesthesia provides excellent muscle relaxation for lower abdominal and lower limb surgery. Complete blockade (motor & sensory).
What are the disadvantages of spinal anaesthetic?
Some patients are not psychologically suited to be awake, even if sedated, during an operation. Post spinal headache.
Even if a long-acting local anaesthetic is used, a spinal is not suitable for surgery lasting longer than approximately 2 hours. If an operation unexpectedly lasts longer than this, it may be necessary to convert to a general anaesthetic.
What is the role of the anaesthetic nurse?
Be fully engaged Preempt decisions Plan care Be highly involved with technology Check anaesthetic equipment and support anaesthetist
What needs to be checked on the anaesthetic machine?
Gas supplies Ventilator function Suction and scavenging systems Inhalation agents Anaesthetic circuit CO2 absorber: soda lime Gas analyser: ETCO2 Monitoring: BP, PSAO2, ECG
