Peri-op pharmacology Flashcards
What level ASA status are most patients at?
1/2/3
- 1 - A normal healthy patient
- 2 - Patient with mild systemic disease
- 3 - Patient with severe systemic disease
- 4 - Severe systemic disease, constant threat to life
- 5 - Moribund patient, not expected to survive over 24 hours with/without surgery
- 6 - Declared brain dead, organ retrieval
- add “E” in emergency(except 6)
What drug is the only one that is white?
propofol
What happens in order to pre-optimise a patient for surgery?
admit to a specialised unit (HDU/POSU) Invasive BP monitoring Urinary catheter Central venous access Ionitropic support Cardiac output monitoring Maximise O2 delivery peri-op to supra-normal levels Surgery school for 'less fit' patients
What are the 3 things done pre-operatively?
Oxygen, fluids, drugs
What drugs are given pre-operatively?
Antacids, antiemetics, analgesia, sedatives
What drugs are important to OMIT pre-surgery?
Ace-inhibitors (-prils) 24-72 hrs
Angiotensin receptor antagonists (-sartans) 24-72 hrs
Anti-TNF drugs (2 weeks)
Platlet inhibitors - aspirin, clopidogrel, prasugrel (7-10 days)
DOACS dabiggatran (4days, possible reversal with praxbind)
Rivaroxiban, apixiban, edixoban (3days)
NSAIDS (bar paracoxib which can be given IV)
What NSAID can be given IV peri-operatively
parecoxib
How do NSAIDs work
COX-2 inhibitor -> reduce production of prostaglandins, prostacyclin and thromboxanes by inhibiting formation of these from arachidonic acid.
What do prostaglandins do?
Inflammatory response, temperature regulation, renal blood flow, gastric protection
What does prostacyclin do?
Vasodilator, inhibits platelet aggregation, prevents coagulation in normal blood vessels
What do thromboxanes do?
vasoconstriction, causes platelet aggregation, released at site of injury
What are the gastric adverse effects of NSAIDS and theory behind this?
- ↓ mucosal protection
- ↑ gastric acid secretion
- May lead to peptic ulceration
Prophylaxis with omeprazole/misoprostol
Action
• High index suspicion
• NSAIDs should NOT be given to patients with a history of GI ulceration or bleeding
What synthetic prostaglandin prevents GI toxicity of NSAIDS
misoprostol
What is the difference between COX 1 and COX 2
1= constitutive form, present in tissues, inhibition leads to GI side effects
2= inducible form, present at sites of inflammation, inhibition responsible for anti-inflammatory action on NSAIDS
What COX-2 inhibitor is commonly used peri-operatively?
parecoxib (dynastat 40mg)
What are the coagulation SE of NSAIDS and theory behind this?
- reduced production of thromboxane
- NSAIDs increase bleeding time
- displace warfarin increasing the effect
Action: do NOT use if risk of intra-operative bleeding
What are the respiratory SE of NSAIDS and theory behind this?
- can precipitate acute asthma
- associated with chronic rhinitis and nasal polyps
Action: do NOT use in aspirin-sensitive asthma, and use w/ caution in other asthmatics
What are the renal SE of NSAIDS and theory behind this?
- normal renal blood flow = little prostaglandin release. Prostaglandin’s release when renal blood flow is low. causes compensatory vasodilation
- NSAIDs cause renal failure if given during blood loss or hypotension, precipitate fluid retention, lead to hyperkalaemia
How do NSAIDs lead to hyperkalaemia?
renal blood flow reduced - vasoconstrictors are released (noradrenalin, angiotensin) -> prostaglandins are released (compensatory vasodilatation) ->precipitate fluid retention (exacerbate heart failure)
NSAIDs indirectly supress renin and aldosterone secretion -> hyperkalaemia
When must you avoid giving NSAIDs
renal impairment hyperkalaemia hypovolaemmia circulatory failure sever liver dysfunction pre-eclampsia/eclampsia
When should you use NSAIDs cautiously?
> 65yrs
diabetes
arteriopathy
cardiac/hepatobiliary/ major vascular surgery
What things are given intraoperatively?
Oxygen fluids blood/blood products antibiotics anaesthesia analgesia muscle relaxation
What drug puts people to sleep ?
IV Propofol
How is the patient kept asleep?
Inhalated desflurane
Advantage and Disadvantage of desflurane ?
Ad = rapid recovery, particularly in obese pt; reduces cognitive dysfunction post-op
Disad= big globe warming potential
What drug can be used to support a pt’s circulation
ketamine - used if pt is hypotensive (as propofol reduces BP further) - but more of a continuum the level to use
What site to anaesthetic agents work at
type A GABA receptors - binding opens transmembrane channel and enhances chloride activity
AND ascending reticular activating system - reduces cerebral cortical activity
What is used for muscle relaxation? depolarising and non-depolarising
Depolarising: suxamethonium
non-depolarising: atracurium and rocuronium
Use and action of suxamethonium
Muscle fasciculate and the remain paralysed for 3 minutes to get in airway then it is broken down by acetyl-cholinesterase in the neuromuscular junction
What is a rapid-sequence induction and when does it happen?
Presumed full stomach case. (And pregnancy)
Pre-oxygenate pt for 5 minutes, de-nitrogenate, sleep dose of propofol. Given 1mg/kg of suxamethonium, paralysed. O2 off. laryngoscope in, endotracheal tube, blow cuff up and lungs are isolated from gastric content -> can’t aspirate.
Not done in elective surgery as pt is starved.
How does atracurium and rocuronium work?
competetive block - builds up in 3-4mins, paralysed for 20mins. can reflux and aspirate - hence only used in elective when starved
What drug can reverse neuromuscular block due to rocuronium
Suggammadex
- rescue reversal dose of 16mg/kg. Time to reversal 1.5mins.
Expensive so limited to emergency situations
- encapsulates steroid portion of amino steroid relaxant within hydrophobic interior
What things are given post-operatively?
analgesia fluids blood products inotropes/vasopressors anti-emetics anti-coaguants antibiotics oxygen
What is a regional block
TAP (transverse abdominis plane)
What are the advantages and complications with an epidural
Ad: avoids respiratory complications associated w/ pain and large amounts of systemic opioids, continuous infusion, patient-controlled form
Complications: hypotension, itching, epidural haematoma
