Module 2.1.2 (Anaesthesia and postoperative nausea and vomiting) Flashcards
What does aneasthesia and post-operative management involve?
General anaesthetics
- IV
- Inhaled
- Neuromuscular blockers
- Other agents
Local anaesthetics
Peri-operative analgesia
Post-operative nausea and vomiting
Define the following terms which general anaesthesia incorporates:
A) preoperative assessment with or without premedication
B) induction
C) maintenance
D) reversal
E) recovery
A)
to ensure that the process of anaesthesia is as safe and as smooth as possible
B)
to render the patient unconscious and unreactive to surgical stimuli; use IV or inhaled drugs
C)
to keep the patient anaesthetised for as long as the operation lasts; use IV and/or inhaled drugs with muscle relaxants and analgesics as necessary
D)
when the operation is complete, drugs for reversing neuromuscular blockade are usually required if non-depolarising neuromuscular blockers are used
E)
which begins when the anaesthetic is stopped and lasts until the patient is fully conscious, has stable cardiovascular status, is able to maintain own airway and is comfortable
Why is premedication given as part of pre-operative assessment?
May be given before induction of anaesthesia to
- Relieve anxiety, eg benzodiazepines
- produce sedation and amnesia, eg benzodiazepines, clonidine, ketamine
- relieve pain, eg opioids, paracetamol
- reduce secretions, eg glycopyrronium (glycopyrrolate)
- help empty stomach, eg metoclopramide
- reduce the volume and decrease the acidity of gastric contents, eg H2 antagonists
- reduce pain during venipuncture, eg a topical local anaesthetic is commonly applied preoperatively (particularly in children).
> Some of these objectives can be achieved by drugs given during induction or maintenance of anaesthesia, and explanation and reassurance is often sufficient to relieve anxiety
What ios the role of the pre-admissions pharmacist
Best possible medication history
Check medications have either been given or withheld as appropriate
- Eg withhold anticoagulants, antiplatelets, diabetes medication, NSAIDS
- Ensure they have had their beta-blocker, anti-anginal, antiarrhythmic, antiepileptics, PPI, corticosteroid, inhalers etc
- Oral medications with a small amount of water up to 2 hours pre-op
> Consider post-op management, prolonged periods of fasting, iodinated contrast media, unable to swallow oral preparations post-op
> Check allergy status
What conditions is risk of aspirations increased in?
Obesity, significant GORD, hiatus hernia, obstetric patients, and emergency surgery without adequate fasting
How to empty stomach for surgery for aspiration pneumonia prophylaxis?
In general, patients should fast before surgery for 6 hours from food, infant milk formula and animal milk; for 4 hours from breast milk; and for 2–3 hours from clear fluids
Continue regular PPI/H2-antagonist
If high risk of aspiration give H2 antagonist the night before and morning of surgery
Metoclopramide
Sodium citrate solution (non-particulate antacid)
What are FOUR major IV general anaesthetics? What are the inidcations? What happens when administered?
Ketamine, midazolam, thiopental, propofol
- Produce rapid, reversible loss of consciousness and insensibility to surgical stimuli
- All the IV anaesthetic agents, except ketamine, cause dose-related respiratory, laryngeal reflex suppression and cardiovascular depression
- A period of apnoea frequently follows induction, and is succeeded by slow and shallow breathing.
- BP decreases because of myocardial depression and peripheral vasodilation
- They do not have analgesic properties, except for ketamine, and addition of opioids is usually necessary
Indications
- Induction and maintenance of anaesthesia
- Conscious sedation (midazolam, propofol)
- Sedation during ventilation (midazolam, propofol)
Outline pharmacology of the following:
A) Ketamine
B) Midazolam
C) Propofol
D) Thiopental
A)
- Potent analgesic
- Maintains pharyngeal and laryngeal reflexes compared to the others (but still watch for aspiration)
- Recovery can be prolonged
B)
- Least effective but anterograde amnesic effects can be beneficial
C)
- Most effective at suppressing laryngeal and pharyngeal reflexes (ETT)
- Most likely to cause hypotension and pain on injection
- Has antinauseant properties
D)
- Most rapid onset but slower recovery’
- Can get laryngospasm from minor stimuli
What is used for inhaled anaesthetics? What does it cause? What are the precuations? What are the adverse effects?
Volatile aneasthetics: Desflurane, isoflurane, methoxyflurane and sevoflurane
Other: nitrous oxide
- Cause hypnosis, amnesia and immobility despite painful stimuli
- Potency measured by minimum alveolar concentration (MAC)
Precautions
- Risk of malignant hyperthermia
> All volatile anaesthetics are contraindicated (NO2 is ok)
- Myasthenia gravis – muscle weakness may worsen
- Muscular dystrophy – risk of life-threatening rhabdomyolysis
Adverse ffects
- Shivering, N, V, arrythmias, malignant hyperthermia, hepatotoxicity
What are the types of neuromuscular blockers? What dot they do?
Non-depolarising and Depolarising
Neuromuscular blocking drugs produce skeletal (including respiratory) muscle relaxation, which is used during general anaesthesia to:
- facilitate endotracheal intubation and hence control of the airway
- allow mechanical ventilation
- prevent reflex muscle contraction
- improve access to the surgical field.
- They have no sedative or analgesic effects
- Facilities for airway maintenance must be available
What are examples of non-depolarising neuromuscular blockers? Wgat are the precuations
Atracurium, cisatracurium, mivacurium, pancuronium, rocuronium, vecuronium
- Acetylcholine receptor antagonists, which act at the neuromuscular junction preventing depolarisation of the muscle membrane
Precuations
- Myasthenia gravis – prolongs paralysis (avoid if possible)
- Myopathy with prolonged use in ICU (>48h)
How to reverse neuromuscular blockade?
- Can be achieved when recovery of muscle twitch in response to peripheral nerve stimulation has started; complete reversal is usually achieved within 8–10 minutes of neostigmine administration with most agents (except pancuronium)
- Give an anticholinergic, eg atropine or glycopyrronium (glycopyrrolate), with neostigmine to prevent its muscarinic effects (especially bradycardia)
- sugammadex is an alternative to neostigmine for reversing block induced by rocuronium or vecuronium without the associated muscarinic effects
What is an example of depolarising neuromsuclar blockers? What is it used for? CI and precautions? Adverse effects?
Suxamethonium mimics acetylcholine; acts at acetylcholine receptor, depolarising the motor end plate resulting in neuromuscular blockade
Indication: skeletal muscle relaxation in anaesthesia
CI and precuations:
- Malignant hyperthermia
- Muscular dystrophy
- Myasthenia gravis (unpredictable effects)
- Acquired or inherited plasma cholinesterase deficiency
Adverse effects:
- Hyperkalemia
- Prolonged paralysis
- Muscle fasciculations and muscle pain post-op
What is malignant hyperthermia? What does it result in? How to treat?
Rare, inherited, hypermetabolic response of skeletal muscle, which can be triggered by certain drugs, especially suxamethonium and volatile anaesthetic agents
- May occur abruptly and unpredictably and can be fatal
- It results in increased oxygen consumption and carbon dioxide production, tachypnoea, tachycardia, arrhythmias, muscle rigidity, rising temperature and metabolic acidosis.
- Treatment includes stopping the anaesthetic if possible (if not possible, switch to MH-safe agents), 100% oxygen, hyperventilation, IV dantrolene, correction of fluid and electrolyte abnormalities and lowering temperature.
What are agents with sedative, analgesic and haemodynamic stabilising effects?
Alpha2 and imidazoline agonists
- Clonidine and dexmedetomidine (shorter t ½)
- Hypotension and bradycardia
- Minimal resp depression, no amnesia, CV stabilising fx and reduction of post-op shivering esp in patients at risk of myocardial ischemia
Opioids
- Fentanyl, remifentanil, alfentanil
What are the post-op options for peri-operative analgesia?
Paracetamol
Opioids
> Oral if tolerated
> PCA
> Sucut
NSAID
> Wach for CI
Regional and local administration of local anaesthetics and opioids
Local anaesthetics
- Via epidural, interpleural, paravertebral, nerve sheath, or simple wound catheters (different devices available)
- Eg continuous peripheral nerve blockade
Opioids
- Epidural
> Eg fentanyl + bupivacaine (watch for motor block and rare risk of epidural abscess)
- Intrathecal morphine 100-300mcg
> Pain relief can last 12-24 hours after single dose intrathecal Itch, nausea and urinary retention can occur
> Both can cause delayed (24hrs) respiratory depression
ketamine
- Specialist use only
- Helps prevent hyperalgesia
- acute pain poorly responsive to opioids
other post op issues
- urinary retention –> cathether
- muscle spasm
How to prevent PONV?
Modify baseline risk factors to reduce incidence of PONV
> minimise anaesthetic risk factors: Use propofol total IV anaesthesia and regional anaesthesia
> optimise: non-opoid analgesia: IV paracetamol, gapapentinoids, NSAIDs, alpha2-adrenergic agonists
> ensure adequate hyddration in the perio operative period
Combination anti-emetics are superior to monotherapy: consider AE and patient co-morbidities
> Generally patients with no risk factors do not require prophylaxis with antiemetic medication
> calculate APFEEL score
If an antiemetic was given as prophylaxis but patient still experiencing signs of PONV, what to do?
Treat PONV with a medication from another class
- Eg 5HT3 antagonist, dexamethasone, droperidol
- If > 6 hours since ondansetron or granisetron can re-dose
- Re-administration of longer-acting agents (palonosetron and dexamethasone) is not recommended
> If treatment options have been exhausted – can try promethazine or cyclizine
> If still an issue – contact APS/anaesthetist
> Fosaprepitant – bariatric surgery – caution OCP interaction
