Tell me in detail about spinal anaesthesia

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Spinal Anaesthesia - A Detailed Overview

Spinal anaesthesia (also called subarachnoid block, SAB, or intrathecal anaesthesia) is the injection of a local anaesthetic - with or without adjuvants - directly into the cerebrospinal fluid (CSF) in the subarachnoid space, producing rapid, dense, and predictable sensory and motor blockade below the level of injection.

1. Anatomy Relevant to Spinal Anaesthesia

The spinal cord ends at L1-L2 in adults (lower in neonates - up to L3). Below this level, the subarachnoid space contains only the cauda equina nerve roots floating in CSF. Spinal injections are therefore performed at L2-L3, L3-L4, or L4-L5 interspaces to avoid cord injury.

Layers traversed during needle insertion (midline approach):

Skin and subcutaneous fat
Supraspinous ligament
Interspinous ligament
Ligamentum flavum
Epidural space
Posterior dura mater
Subdural space (potential)
Arachnoid mater
Subarachnoid space (target - contains CSF)

The characteristic "click" or "pop" felt as the needle penetrates the dura signals entry into the subarachnoid space. CSF flows back freely once the stylet is removed.

The intercristal (Tuffier's) line - connecting the iliac crests - typically corresponds to the L4-L5 interspace, though ultrasonographic studies show this landmark can be unreliable.

2. Indications

Spinal anaesthesia is suitable for nearly all procedures at or below the umbilicus (T10 level) and many infradiaphragmatic procedures:

Category	Procedures
Urologic	TURP, cystoscopy, nephrolithotomy
Gynaecologic	Hysterectomy, D&C, tubal ligation
Obstetric	Caesarean section (most common indication; preferred over GA), operative vaginal delivery (saddle block)
Orthopaedic	Total hip/knee arthroplasty, hip fracture repair, ankle surgery
Lower abdominal	Inguinal hernia repair, appendicectomy
Perineal/rectal	Haemorrhoidectomy, anal surgery
Vascular	Femoral-popliteal bypass

Spinal anaesthesia is the preferred technique for most elective Caesarean sections because it avoids airway manipulation, provides faster onset than epidural, has a denser block, and avoids the maternal mortality risks associated with general anaesthesia (failed intubation, aspiration).

Sabiston Textbook of Surgery, p. 1572; Miller's Anesthesia 10e, p. 6044

3. Contraindications

Absolute:

Patient refusal
Sepsis or bacteraemia
Infection at the injection site
Severe hypovolemia / haemodynamic instability
Coagulopathy or therapeutic anticoagulation
Raised intracranial pressure (risk of brainstem herniation from caudal CSF loss)
Allergy to local anaesthetics

Relative:

Pre-existing neurological disease (controversial)
Previous spine surgery or abnormal spinal anatomy
Demyelinating disorders (MS) - not an absolute contraindication depending on context
Severe aortic stenosis or fixed cardiac output states
Patient unable to cooperate or remain still
Sabiston Textbook of Surgery, p. 1605; Morgan & Mikhail, Key Concepts

4. Drugs Used

Local Anaesthetics

Drug	Type	Dose (adult)	Duration	Notes
Bupivacaine 0.5%	Amide	7.5-15 mg	90-150 min	Most widely used; isobaric or hyperbaric forms
Ropivacaine	Amide	15-22.5 mg	~120 min	Similar to bupivacaine; slightly less cardiotoxic
Lidocaine 5%	Amide	50-100 mg	60-90 min	Faster onset; associated with TNS - largely abandoned
Prilocaine 2%	Amide	40-60 mg	100-130 min	Rarely associated with TNS; used in ambulatory surgery
Mepivacaine	Amide	30-80 mg	120-180 min	Shorter-acting than bupivacaine; earlier ambulation
Tetracaine	Ester	5-20 mg	Up to 5 hr (with vasoconstrictor)	Long-acting; needs additive
Chloroprocaine 3%	Ester	30-60 mg	45-60 min	Short-acting; used in ambulatory procedures

Miller's Anesthesia 10e, pp. 6056-6063

Opioid Adjuvants

Small doses of intrathecal opioids significantly improve block quality, duration of analgesia, and tolerance for tourniquet pain:

Fentanyl 10-30 mcg: lipophilic, rapid onset (10-20 min), duration 4-6 hrs; used in ambulatory surgery
Sufentanil 5-7.5 mcg: potent lipophilic opioid for obstetric spinal
Morphine 0.1-0.3 mg: hydrophilic, delayed onset but very prolonged analgesia (12-24 hrs); risk of delayed respiratory depression; useful post-op
Diamorphine (heroin) 0.3-0.4 mg: used in the UK instead of morphine for Caesarean section
Miller's Anesthesia 10e, p. 6060-6061

Vasoconstrictors

Epinephrine 0.1-0.2 mg: reduces systemic uptake of local anaesthetic via α1 vasoconstriction; prolongs short-acting agents; also has direct α2-mediated analgesic effect
Phenylephrine 2-5 mg: prolongs lidocaine and tetracaine; associated with TNS when combined with tetracaine

Other Adjuvants

Clonidine (α2-agonist): prolongs block duration and improves intraoperative quality
Neostigmine: intrathecal use is experimental; associated with nausea/vomiting

5. Factors Affecting Block Height and Spread

Drug Factors

Baricity (most important): ratio of local anaesthetic density to CSF density (CSF density = 1.00059 g/mL at 37°C)
- Hyperbaric: denser than CSF (dextrose added); spreads to dependent regions; more predictable
- Hypobaric: lighter than CSF (water added); spreads to non-dependent regions; useful for prone positioning
- Isobaric: same density as CSF; not significantly influenced by gravity
Dose: higher dose = greater cephalad spread and longer duration
Volume: larger volume = turbulent flow = unpredictable spread (inject slowly ~0.2 mL/s)
Speed of injection: slower is better; turbulence causes unpredictable spread
Concentration: affects onset speed and motor block depth

Patient Factors

Position: sitting position with hyperbaric solution = preferential lumbosacral ("saddle") block; lateral position biases the block to dependent side
Obesity: reduces subarachnoid volume; increases cephalad spread
Pregnancy: engorgement of epidural veins and increased abdominal pressure compress the subarachnoid space
Age: elderly patients are more sensitive to intrathecal agents
Height: affects spinal column length; extremes may require dose adjustment
Spinal abnormalities: previous surgery, scoliosis, spinal stenosis can all increase or unpredictably alter spread

Dermatome Levels Required for Common Procedures

Caesarean section: T4
Upper abdominal surgery: T4-T6
Lower abdominal/hernia: T6-T10
Hip surgery: T10
Lower extremity/knee: T10-T12
Perineal/anal: S2-S4 (saddle block)
Miller's Anesthesia 10e, p. 6044-6045

6. Technique

Patient Preparation

Obtain informed consent
Establish IV access; administer crystalloid preload or co-load
Standard monitoring: ECG, SpO2, NIBP
Resuscitation equipment and vasopressors available

Positioning

Two main positions:

Sitting position: patient sits upright with knees drawn up and neck flexed, accentuating lumbar kyphosis. Preferred for obese patients, hyperbaric technique for saddle block, and easier landmark identification
Lateral decubitus: patient in foetal position with knees and neck flexed. Can bias the block to the dependent side with hyperbaric solution

Aseptic technique is mandatory - full sterile drape, chlorhexidine skin prep, sterile gloves.

Needle Selection

Pencil-point (atraumatic) needles (Whitacre 25G, Sprotte 24G, Gertie Marx) are preferred - they separate rather than cut dural fibres, significantly reducing post-dural puncture headache (PDPH)
Quincke (cutting) needles (22-25G) - bevel should be oriented parallel to the spine to minimise PDPH
Smaller gauge = longer wait for CSF return but lower PDPH risk

Midline Approach (Standard)

Palpate the L3-L4 or L4-L5 interspace
Raise a skin wheal of local anaesthetic at the insertion site
Insert introducer (for fine gauge needles) slightly cephalad (10-15 degrees)
Advance spinal needle through introducer, traversing: subcutaneous tissue → supraspinous ligament → interspinous ligament → ligamentum flavum → dura ("click/pop")
Remove stylet; confirm free CSF flow
Attach syringe; aspirate CSF to confirm placement
Inject local anaesthetic at ~0.2 mL/s; re-aspirate 0.2 mL CSF at end to confirm and clear needle
Position patient appropriately for desired block level

Paramedian Approach

Useful when midline calcification is present (elderly, spondylotic spines)
Insert 1 cm lateral to the superior edge of the inferior spinous process, angled cephalomedially 10-15 degrees off the sagittal plane
Does not traverse supraspinous or interspinous ligaments; bypasses calcified structures
Miller's Anesthesia 10e, pp. 6071-6072

7. Physiological Effects

Cardiovascular

Hypotension: most common side effect. Sympathetic blockade (T1-L2) causes arterial and venous vasodilation, reduced preload and afterload. Magnitude proportional to block height.
Bradycardia: blockade of cardioaccelerator fibres (T1-T4) reduces heart rate. Severe bradycardia or asystole can occur, especially if parasympathetic tone is unopposed.
Decreased cardiac output: secondary to reduced preload

Management of hypotension: IV fluids (crystalloid co-loading), left uterine displacement (in pregnancy), vasopressors (phenylephrine preferred in obstetrics; ephedrine for non-obstetric patients).

Respiratory

Block up to T10: no significant respiratory compromise (intercostal muscles intact)
Block extending to T1-T4: intercostal paralysis; accessory muscle loss; patient may report difficulty breathing but diaphragm (C3-C5) remains intact
Block extending to C3-C5: diaphragmatic paralysis; respiratory arrest
Apnoea after "high spinal" is nearly always due to brainstem ischaemia from hypotension, not direct phrenic nerve block

Gastrointestinal

Sympathetic block with unopposed parasympathetic (vagal) activity → increased gut motility, nausea/vomiting
Nausea can also result from hypotension

8. Complications

Immediate Complications

Hypotension

Incidence up to 80% in obstetric patients with spinal for Caesarean section
Treated with: phenylephrine infusion (now preferred over ephedrine in obstetrics as it causes less fetal acidosis), IV fluids, left lateral tilt, ephedrine if bradycardia coexists
A 2023 consensus statement recommends prophylactic phenylephrine infusion + crystalloid co-loading + left uterine displacement

Bradycardia / Asystole

Block of T1-T4 accelerator fibres; treat with atropine, ephedrine, or epinephrine

High / Total Spinal

Excessive cephalad spread causes: hypotension → bradycardia → cardiac arrest → respiratory failure → loss of consciousness
A total spinal is distinguished from a high spinal by intracranial spread of local anaesthetic (LOC, brainstem depression)
Management: immediate intubation and ventilation, aggressive vasopressor support (large doses of epinephrine may be needed), psychological reassurance until block resolves
Risk factors: obesity, short stature, spinal following failed epidural, high injection site

Nausea and Vomiting

From hypotension, unopposed vagal activity, or opioid adjuvants

Delayed Complications

Post-Dural Puncture Headache (PDPH)

Frontal or occipital headache, typically worse upright, relieved supine
Mechanism: CSF loss → traction on pain-sensitive intracranial structures, OR compensatory intracerebral vasodilation
Associated symptoms: nausea, vomiting, neck pain, tinnitus, diplopia, hearing loss, cranial nerve palsies
Onset: >90% within 3 days (66% within 48 hrs); spontaneous resolution in 72% within 7 days
Serious associations: cerebral venous thrombosis, subdural haematoma (aOR 19.0), bacterial meningitis (aOR 39.7)
Prevention: use pencil-point needles; orient cutting bevel parallel to spinal axis; smaller gauge needles
Treatment: bed rest, hydration, analgesics, caffeine; definitive treatment = epidural blood patch (autologous blood 15-20 mL)
Miller's Anesthesia 10e, p. 6115

Transient Neurological Symptoms (TNS)

Burning dysesthesias, pain in lower extremities/buttocks after spinal anaesthesia
Most common with lidocaine 5% especially in lithotomy position in male patients
Usually self-limiting, resolves within 4 weeks
Management: many now substitute chloroprocaine, mepivacaine, or low-dose bupivacaine for lidocaine

Cauda Equina Syndrome

Permanent neurological damage (bladder/bowel incontinence, lower limb weakness/sensory loss)
Associated with continuous spinal catheters + repeated high doses of 5% lidocaine causing drug pooling around cauda equina
Rare but devastating

Epidural Haematoma

Most feared serious complication
Risk increased by coagulopathy or anticoagulant therapy
Presents with back pain + progressive neurological deficit
Emergency MRI; surgical decompression within 6 hours if neurological compromise

Epidural Abscess / Meningitis

Breach of aseptic technique
Presents with fever, back pain, meningism, neurological deficit
Requires urgent imaging, antibiotics, possible surgical drainage

Urinary Retention

Sacral nerve block (S2-S4) inhibits detrusor contraction; common, usually resolves with block

Backache

Less common with spinal than epidural anaesthesia
Usually musculoskeletal (positioning on operating table); transient

9. Combined Spinal-Epidural (CSE) Anaesthesia

CSE combines the rapid, dense onset of spinal anaesthesia with the flexibility and controllability of epidural anaesthesia. It is particularly valuable for:

Labour analgesia (intrathecal opioid for rapid pain relief + epidural catheter for ongoing analgesia or conversion to surgical anaesthesia)
Long procedures where the spinal may wear off
High-risk patients where a low initial spinal dose is safer (block can be extended via epidural)

Epidural Volume Extension (EVE): injecting saline or LA into the epidural space after a low-dose spinal compresses the dural sac, increasing block height without additional intrathecal drug. This achieves comparable sensory block with faster motor recovery.

Technique: needle-through-needle (single interspace) or two-needle/two-interspace approach.

Miller's Anesthesia 10e, p. 6103-6104

10. Special Considerations

Obstetric Patients

Spinal preferred over GA for elective Caesarean section (lower maternal mortality)
Phenylephrine infusion is the vasopressor of choice (less fetal acidosis than ephedrine)
Norepinephrine is emerging as an alternative with better maintenance of cardiac output
Hyperbaric bupivacaine 10-12 mg + fentanyl 10-25 mcg ± epinephrine 0.1-0.2 mg is the standard regimen
Saddle block (hyperbaric solution + sitting position): used for operative vaginal delivery
Miller's Anesthesia 10e, p. 8863

Paediatric Patients

Spinal cord terminates lower (L3) in neonates; CSF volume relatively higher (10 mL/kg vs 1.5-2 mL/kg in adults)
Higher weight-based doses required (dilution effect)
Haemodynamically stable in young children even with high blocks
Main indication: inguinal hernia repair in ex-premature infants (<60 weeks post-conceptual age) who are at risk of post-GA apnoea

Anticoagulated Patients

ASRA guidelines (4th edition) govern the timing of neuraxial procedures relative to anticoagulants:
- LMWH (prophylactic): wait 12 hrs; LMWH (therapeutic): wait 24 hrs
- Warfarin: INR ≤1.4 before procedure
- Aspirin alone: not a contraindication
- Direct oral anticoagulants: drug-specific windows required

11. Advantages over General Anaesthesia

Avoids airway manipulation and risk of failed intubation
Less nausea and vomiting
Less drowsiness and prolonged emergence
Excellent post-operative analgesia (especially with intrathecal morphine)
Awake patient - useful monitor for TURP (hyponatraemia detection), and allows neurological assessment
Reduced intraoperative blood loss (vasodilatation effect)
Reduced DVT risk (lower extremity surgery)
Lower maternal morbidity/mortality in obstetrics
Possible reduction in perioperative opioid requirements

12. Disadvantages and Limitations

Fixed duration: single-shot spinal cannot be extended; unsuitable for procedures of uncertain length (unless CSE used)
Hypotension: almost inevitable for high blocks; must be proactively managed
PDPH: incidence ~1-5% depending on needle type
Failure rate: ~1-5%; requires conversion to GA
Limited upper extent: cannot be used for thoracic or upper abdominal surgery without very high (and therefore risky) block levels
Technical failure: difficult in obese, elderly (calcified ligaments), or scoliotic patients

Sources:

Miller's Anesthesia, 2-Volume Set, 10th Edition (primary - extensive spinal anaesthesia chapter)
Morgan and Mikhail's Clinical Anesthesiology, 7th Edition
Sabiston Textbook of Surgery
Barash, Cullen, and Stoelting's Clinical Anesthesia, 9th Edition

Which drug to stop when before surgery for anaesthesia

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Drugs to Stop (and When) Before Surgery / Anaesthesia

The general perioperative principle is: continue drugs whose withdrawal causes harm; stop drugs whose perioperative presence causes harm. The timing is drug-specific.

DRUGS TO STOP - With Timing

1. Antiplatelet Agents

Drug	When to Stop	Notes
Aspirin	3-7 days before	Continue in patients with prior PCI, drug-eluting stent (within recommended dual-antiplatelet period), high-grade ischaemic heart disease, or significant cerebrovascular disease. Stop otherwise.
Clopidogrel	5 days before	Do NOT stop in patients with drug-eluting stents until minimum recommended dual-antiplatelet therapy duration is complete
Ticagrelor	3 days before	Faster offset than clopidogrel
Prasugrel	7 days before	Longer-acting
Ticlopidine	10 days before	Longest offset
GP IIb/IIIa inhibitors (tirofiban, eptifibatide)	12+ hours before	Effect may persist longer

Miller's Anesthesia 10e, Box 28.11; Mulholland & Greenfield's Surgery, Table 14.9

2. Anticoagulants

Drug	When to Stop	Notes
Warfarin	5 days before	Target INR ≤1.4 pre-procedure; bridge with LMWH/UFH if high thromboembolic risk (e.g., AF with high CHADS score, mechanical valve)
LMWH (therapeutic dose)	24 hours before
LMWH (prophylactic dose)	12 hours before
Rivaroxaban	24-48 hours before (standard) 48-72 hrs for high-bleed procedures	Depends on renal function and bleeding risk
Apixaban	24-48 hours before	Similar to rivaroxaban; highly protein-bound - NOT dialysable
Dabigatran	48-72 hours before	Renal-dependent clearance - longer if eGFR <50; can be removed by dialysis in emergency
Edoxaban	24-48 hours before
Fondaparinux	36-42 hours before	Long half-life

The PAUSE trial showed that in AF patients on DOACs, simple interruption without bridging or coagulation testing was associated with low rates of both bleeding and thromboembolism.

Mulholland & Greenfield's Surgery, p. 895-897

3. Antidiabetic Medications

Drug	When to Stop	Reason
Metformin	Morning of surgery (or 24-48 hrs before major surgery)	Risk of lactic acidosis, especially with contrast or if renal perfusion compromised intraoperatively
Sulfonylureas (glibenclamide, glipizide)	Morning of surgery	Risk of intraoperative hypoglycaemia when fasting
GLP-1 agonists (semaglutide, liraglutide)	Morning of surgery (weekly injectables: hold for 1 week)	Slow gastric emptying - increases aspiration risk
SGLT-2 inhibitors (empagliflozin, dapagliflozin, canagliflozin)	At least 24 hours before elective surgery; 72 hours before intermediate/high-risk (major) surgery	Risk of euglycaemic diabetic ketoacidosis (DKA) in the postoperative period - this is a critical newer warning
DPP-4 inhibitors (sitagliptin, saxagliptin)	Morning of surgery	Hold while fasting
Repaglinide/nateglinide	Morning of surgery	Risk of hypoglycaemia
Short-acting insulin	Morning of surgery (hold while fasting)	Avoid hypoglycaemia
Long-acting insulin	Reduce dose (not stop): Type 1 DM - give 1/3 of usual dose; Type 2 DM - give none or up to 1/2 usual dose	Do NOT omit entirely in Type 1 DM - risk of DKA
Insulin pump	Continue at lowest basal (nighttime) rate

Miller's Anesthesia 10e, p. 3967-3968

4. ACE Inhibitors and ARBs

Drug Class	When to Stop	Reason
ACEi (ramipril, enalapril, lisinopril)	Morning of surgery (hold day of surgery)	Inhibit angiotensin II-mediated vasoconstriction that compensates for anaesthesia-induced vasodilation → severe refractory intraoperative hypotension
ARBs (losartan, valsartan, candesartan)	Morning of surgery (hold day of surgery)	Same reason

Administration of ACEi/ARBs within 24 hours before surgery is associated with significantly increased risk of intraoperative hypotension.

Miller's Anesthesia 10e, p. 4031; Mulholland & Greenfield, Table 14.9

5. Diuretics

Drug	When to Stop	Notes
Loop diuretics (furosemide, bumetanide)	Morning of surgery	Risk of hypovolaemia and electrolyte imbalance
Potassium-sparing diuretics (spironolactone, amiloride)	Morning of surgery	Risk of hyperkalaemia, especially with renal impairment
Thiazides (for hypertension, e.g., hydrochlorothiazide)	Continue on day of surgery	Exception to the rule - continue for hypertension control

6. NSAIDs

Drug	When to Stop	Notes
Non-selective NSAIDs (ibuprofen, diclofenac, naproxen)	48-72 hours before	Reversible platelet inhibition and risk of perioperative AKI; earlier discontinuation adds no benefit
COX-2 inhibitors (celecoxib)	Continue on day of surgery (usually)	Minimal platelet effect; exception: stop if surgeon concerned about bone healing (orthopaedic surgery)

7. Hormonal Drugs

Drug	When to Stop	Reason
Oestrogen-containing HRT (postmenopausal)	4 weeks before major surgery	Increased thromboembolic (VTE) risk; 4 weeks needed for coagulation to normalise
Combined oral contraceptives	Usually continue (weigh unintended pregnancy risk vs. VTE risk)	Consider stopping 4 weeks before surgery if patient is high VTE risk
Testosterone/anabolic steroids	4 weeks before	Polycythaemia and VTE risk
Tamoxifen	4 weeks before major surgery	Hypercoagulable state
Note: Sugammadex reversal agent can reduce efficacy of hormonal contraceptives - advise additional non-hormonal contraception for 7 days after

8. Psychiatric / Neurological Drugs

Drug	Action	When/How
MAOIs (phenelzine, tranylcypromine) - irreversible	Traditionally stopped 2-3 weeks before; but current practice is often to continue and modify anaesthetic	Risk: serotonin syndrome with pethidine (meperidine); hypertensive crisis with indirect vasopressors (ephedrine). If continued: avoid pethidine, use direct vasopressors (phenylephrine/norepinephrine)
MAOIs (moclobemide) - reversible	24 hours before	Short-acting; much safer
Lithium	Hold at least 1 day before	Prolongs neuromuscular blockade; sedative interaction; risk of cardiac arrhythmia; narrow therapeutic index
SSRIs / SNRIs	Generally continue	Minor increased bleeding risk; abrupt withdrawal causes discontinuation syndrome. Stop 3 weeks before only if bleeding is a major concern, in discussion with psychiatrist
Antipsychotics	Continue	Risk of decompensation if stopped; QT prolongation - inform anaesthetist
Antiepileptics	Continue	Seizure risk; also important as enzyme inducers (affect drug metabolism)

9. Cardiovascular Drugs

Drug	Action
Beta-blockers	Continue on day of surgery. Abrupt withdrawal can cause rebound hypertension, tachycardia, myocardial ischaemia. Do not start new beta-blockers immediately preoperatively (increased risk of stroke and hypotension)
Digoxin	Continue
Calcium channel blockers	Continue
Nitrates	Continue
Antiarrhythmics	Continue
Statins	Continue (even have organ-protective effects perioperatively; consider initiating in vascular surgery patients)
Clonidine	Continue (abrupt withdrawal causes rebound hypertension)
Alpha-blockers (doxazosin)	Continue but be aware of risk of hypotension with anaesthesia

10. Herbal Supplements and Over-the-Counter Products

These are frequently undisclosed by patients (>70% fail to mention them). Most should be stopped 7 days before surgery. Key offenders:

Supplement	Concern
Garlic, ginger, ginkgo, ginseng, feverfew	Antiplatelet effects - increased bleeding
St John's Wort	CYP450 enzyme induction - alters drug metabolism; also serotonin syndrome risk
Echinacea	Immune modulation; potential hepatotoxicity
Ephedra (Ma huang)	Cardiovascular instability; dangerous with MAOIs and vasopressors
Kava	Sedation potentiation; hepatotoxicity
Valerian	Sedation; withdrawal symptoms
Fish oil / Omega-3	Antiplatelet effect
Vitamin E	Antiplatelet and anticoagulant

11. Phosphodiesterase-5 Inhibitors

Drug	When to Stop
Sildenafil, tadalafil, vardenafil	24 hours before surgery

12. Topical Medications (creams, ointments)

Stop on the day of surgery (application to skin near surgical site can cause electrosurgery complications or alter skin preparation)

DRUGS TO ALWAYS CONTINUE

These should not be stopped and should be taken with a small sip of water even when fasting:

Drug Class	Reason
Beta-blockers	Rebound ischaemia/arrhythmia if stopped
Antiepileptics	Seizures
Antipsychotics, antidepressants (most)	Psychiatric decompensation
Statins	Pleiotropic cardioprotective effects
Corticosteroids (inhaled and oral)	Adrenal suppression / asthma
Thyroid medications	Thyroid crisis or myxoedema
Opioids (chronic)	Withdrawal syndrome
HIV antiretrovirals	Resistance development
Asthma inhalers	Bronchospasm
Eye drops	Glaucoma / IOP control
Reflux / PPI medications	(Also reduces aspiration risk)

Quick Summary Table

STOP	Timing
SGLT-2 inhibitors	24-72 hrs before
Warfarin	5 days before
Clopidogrel	5 days; prasugrel 7 days; ticagrelor 3 days
NSAIDs	48-72 hrs before
Metformin, sulfonylureas, GLP-1 agonists, DPP-4 inhibitors	Morning of surgery
ACEi / ARBs	Morning of surgery (hold day of surgery)
Loop and K+-sparing diuretics	Morning of surgery
Short-acting insulin	Morning of surgery
Phosphodiesterase-5 inhibitors	24 hrs before
Postmenopausal HRT (oestrogen)	4 weeks before major surgery
Lithium	24 hrs before
Herbal supplements	7 days before
Irreversible MAOIs (if stopping)	2-3 weeks before
Topical creams/ointments	Day of surgery

Sources:

Miller's Anesthesia, 2-Volume Set, 10th Edition - Box 28.11, Preoperative Management of Medications, pp. 4031-4036
Mulholland and Greenfield's Surgery, 7th Edition - Table 14.9, pp. 895-899
Sabiston Textbook of Surgery

Clinical note: These are general guidelines. Always individualise management based on the patient's specific indication for the drug, the type and urgency of surgery, and bleeding/thrombotic risk balance. For anticoagulated patients, involve haematology or cardiology when appropriate.

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