5. Anesthesia

Difficult intubation?

Malignant hyperthermia?

PONV (post-op nausea/vomiting)

questions to ask on previous anesthesia history

anticoagulants

ACEi/ARBs (often held day of surgery)

---

Medication/class	Typical pre-op management	Why
ACE inhibitors / ARBs (lisinopril, losartan)	Usually hold morning of surgery; some protocols hold ~24 hr	↓ intra-op hypotension
SGLT2 inhibitors (empagliflozin, dapagliflozin)	Hold 3 days; ertugliflozin 4 days	Euglycemic DKA
Metformin	Often hold day of surgery	Fasting/renal concerns; practice varies
Sulfonylureas (glipizide, glyburide)	Hold morning of surgery	Hypoglycemia
Insulin	Don't simply stop; usually reduce basal dose and hold prandial while NPO	Prevent hypo/hyperglycemia & DKA
GLP-1 drugs (semaglutide, tirzepatide)	Individualized; not routinely held in every patient	Delayed gastric emptying/aspiration concern
Warfarin	Usually stop ~5 days before	Bleeding
DOACs (apixaban, rivaroxaban)	Usually hold 1–2+ days, longer for high-bleeding-risk surgery/renal impairment	Bleeding
Clopidogrel	Commonly hold ~5 days when safe	Bleeding
NSAIDs	Often held before higher-bleeding-risk procedures; timing depends on drug	Platelet dysfunction/bleeding
Herbal supplements	Often stop ~1–2 weeks beforehand	Bleeding/drug interactions

_{^{Drugs commonly CONTINUED}}

_{^{Usually continue beta-blockers, statins, many antiarrhythmics, antiepileptics, and chronic steroids. Steroids are particularly important—don't abruptly discontinue chronic glucocorticoids.}}

_{^{🔥 Surgery-board pearls}}

_{^{ACEi/ARB → hold → hypotension
SGLT2 inhibitor → hold 3–4 days → euglycemic DKA
Sulfonylurea → hold → hypoglycemia
Anticoagulants/antiplatelets → bleeding risk, but timing depends on drug/procedure
Beta-blocker → CONTINUE
Chronic steroids → CONTINUE}}

typical medications to d/c before going under anesthesia

YES

Why continue?

Abruptly stopping them can cause rebound sympathetic activity → tachycardia, hypertension, angina, or MI.

Chronic β-blocker → CONTINUE perioperatively.
Don't routinely start a new beta-blocker immediately before surgery, because excessive bradycardia/hypotension can occur.

can you continue beta blockers under anesthesia

_{^{(Examples: metoprolol, atenolol, propranolol, carvedilol, labetalol)}}

≥4 METs = generally safe (e.g., climb stairs)

number of METs in which it is generally safe for anesthesia

Clear liquids: ≥2 hours

Breast milk: ≥4 hours

Light meal: ≥6 hours

Fatty meal: ≥8 hours

fasting guidelines for NPO

full uvula/tonsils

structures seen on Mallampati class I

partial uvula

structures seen on Mallampati class II

base of uvula

-difficult intubation

structures seen on Mallampati class III

hard palate only

-very difficult intubation

structures seen on Mallampati class IV

Look externally (beard, obesity, trauma)

Evaluate (3-3-2) rule

•  ^{3 fingers → mouth opening}

• ^{3 fingers → chin to hyoid}

• ^{2 fingers → hyoid to thyroid cartilage}

Mallampati score

Obstruction

Neck mobility

LEMON mnemonic

Mouth opening ≥3 fingers

Chin-hyoid ≥3 fingers

Thyroid-mouth ≥2 fingers

What is the 3-3-2 rule?

healthy pt with no medical problems

describe a ASA class I

mild systemic disease

ex: HTN, well controlled DM

describe an ASA class II

severe systemic disease

ex: CHF, COPD

describe an ASA class III

severe disease, constant threat to life

ex: unstable angina

describe an ASA class IV

moribund, not expected to survive

ex: ruptured AAA

DEATH = V

describe an ASA class V

brain dead organ donor

describe an ASA class VI

Post-op patient with hypoxemia + decreased breath sounds

→ atelectasis

most common complication of anesthesia intubation

III-IV

mallampati scores with difficult intubation risk

aspiration

most dangerous complication of anesthesia

Block voltage-gated Na⁺ channels

→ Prevent depolarization → no nerve conduction

---

YES - but they are not equally lipophilic.

• _{^{Lipophilic aromatic ring — linker (amide or ester) — hydrophilic amine}}

• _{^{The lipophilic portion allows the drug to cross the nerve cell membrane, while the ionized form then binds the voltage-gated Na⁺ channel from the inside.}}

Why this matters:

• Greater lipid solubility → generally greater potency.

MOA of local anesthetics?

& are all local anesthetics lipophillic?

• _{(ester & amide classes)}

• _(-caine)

_{Mnemonic: Amides have 2 i's in the name}

_{→ e.g. lidocaine, bupivacaine.}

_{“metabolized Amid the liver.”}

how to tell the anesthetic type of amides??

Drug	Type	Duration
Procaine	Ester	Short
Chloroprocaine	Ester	Very short

_{^{note: Esters → Esterases in plasma.}}

short acting local anesthetics

• Lidocaine — amide, {classic intermediate-acting}

• Mepivacaine — amide

• Prilocaine — amide

intermediate acting local anesthetics

• Bupivacaine ⭐ — amide, long acting; most cardiotoxic

• Ropivacaine — amide, long acting; less cardiotoxic than bupivacaine

• 
  

• **Tetracaine — ester, long acting (most esters are short acting and this is the exception)

long acting local anesthetics

Bupivacaine (Marcaine)

long acting local anesthetic that poses the most:

cardiotoxic risk// cardiac arrest risk

Ropivacaine (Naropin)

less cardiotoxic long acting local anesthetic

“amid the LIVER”

_{e.g. lidocaine, bupivacaine, ropivacaine}

_{(less likely to have allergy to amide’s,, concern with severe liver disease)}

amide type of local anesthetics are metabolized

Think ESTER → PABA (para-aminobenzoic acid.) → allergy.

—> Procaine (Novocain)

short acting local anesthetic with increased allergy risk

CNS effects:

Tinnitus

Metallic taste

Perioral numbness

Seizures

early signs of local anesthetic toxicity

CV effects:

Arrhythmias

Hypotension

late signs of local anesthetic toxicity

early LAST

“Patient develops metallic taste and ringing in the ears shortly after local anesthetic injection” →

1. STOP the local anesthetic

2. Airway + 100% O₂ / ventilation

3. Seizures → benzodiazepine (e.g., midazolam)

4. 20% IV lipid emulsion (Intralipid) ⭐ — specific rescue therapy

5. If cardiovascular collapse → modified ACLS + lipid emulsion

Why lipid? It acts as a “lipid sink,” drawing lipophilic local anesthetic away from critical tissues such as the heart and brain.

_{^{Avoid/limit in LAST: large epinephrine doses, vasopressin, and additional Na⁺-channel–blocking antiarrhythmics such as lidocaine/procainamide.}}

Local Anesthetic Systemic Toxicity (LAST) — Treatment

_{Classic toxicity: CNS symptoms → seizures → cardiovascular collapse/arrhythmias, especially with bupivacaine.}

amides>esters

type of local anesthetic with lower risk of allergic reactions

• Benzocaine ⭐⭐⭐

• Prilocaine ⭐

• Lidocaine — rare

Memory: “Benzo & Prilo → MetHgb”

example:

Benzocaine spray → cyanosis + low SpO₂ that does NOT improve with O₂ + chocolate-brown blood

→ methemoglobinemia

Treatment: Methylene blue

local anesthetics associated with risk of methemoglobinemia (2)

local infiltration

Injection of anesthetic agent directly into tissues at surgical site

Rapid onset

Dense anesthesia

Ideal for lower body surgery

benefits of spinal anesthesia

Hypotension (sympathetic blockade)

Post-dural puncture headache

Urinary retention

High spinal → respiratory compromise

risks associated spinal anesthesia

into CSF (subarachnoid space)

spinal anesthesia is injection into

Adjustable/continuous

Good for labor analgesia

benefits of epidural anesthesia

Hypotension

Epidural hematoma (esp. anticoagulated patients 🚨)

Infection

risks of epidural anesthesia

Feature	Spinal	Epidural
Injection site	Subarachnoid space (CSF)	Epidural space
Needle crosses dura?	Yes	No
Levels used	L3–L4 or L4–L5 ⭐	Cervical, thoracic, lumbar, or sacral
Most common levels	Lumbar only	Lumbar: L2–L5; Thoracic: varies by surgery
Obstetrics	L3–L4 or L4–L5	Usually L2–L3, L3–L4, or L4–L5
Onset	Fast	Slower
Dose	Small	Larger
Catheter	Usually no	Yes → continuous dosing
Classic use	C-section, lower-extremity surgery	Labor, thoracic/abdominal surgery, postop analgesia

Spinal anesthesia → Bupivacaine
Epidural anesthesia → Bupivacaine or ropivacaine

---

adults spinal cord level L1/2

spinal vs epidural injections

Targeted analgesia & Less systemic effect

---

Drug	Duration	High-yield use
Bupivacaine ⭐	Long	Long-lasting nerve block/post-op analgesia
Ropivacaine	Long	Long-lasting block; less cardiotoxic than bupivacaine
Lidocaine	Intermediate	Faster onset, shorter procedures
Mepivacaine	Intermediate	Faster onset, intermediate-duration block

note:

	Max lidocaine dose
Lidocaine alone	~4.5 mg/kg (max ~300 mg)
Lidocaine + epinephrine (longer lasting)	~7 mg/kg (max ~500 mg)

_{^{Epinephrine → α₁ vasoconstriction → ↓ local blood flow → ↓ systemic absorption of lidocaine}}

benefits & what meds are usually used for in

peripheral nerve blocks

——

classcially: Midazolam + fentanyl ⭐

• Midazolam → sedates + causes amnesia

• Fentanyl → treats pain

• 
  

---

others:

Drug	Class	Main purpose	Key pearl
Midazolam ⭐	Benzodiazepine	Sedation + anxiolysis + amnesia	No analgesia
Fentanyl ⭐	Opioid	Analgesia	Respiratory depression
Propofol ***	Sedative-hypnotic	Rapid sedation, short acting	No analgesia, hypotension/apnea
Ketamine	NMDA antagonist	Sedation + analgesia	Preserves respiratory drive better; ↑ HR/BP
Dexmedetomidine	α₂-agonist	Sedation	Minimal respiratory depression; bradycardia/hypotension

conscious sedation

_{^{(Depressed consciousness, pt maintains airway reflexes + responds to stimuli)}}

what drugs are typically used?

^{Midazolam → flumazenil
Fentanyl → naloxone}

^{Reversal agents:}

^{Midazolam →
Fentanyl →}

colonoscopy, biopsy, neuro

procedures in which conscious sedation is helpful

Respiratory depression

Hypoxia

Hypotension

Loss of airway (if oversedated)

risks associated with conscious sedation

Genetic defect in skeletal muscle Ca²⁺ regulation,

• most commonly an RYR1 (ryanodine receptor) mutation

-

Triggering anesthetic → abnormal RYR1

→ massive Ca²⁺ release from sarcoplasmic reticulum

→ sustained muscle contraction + hypermetabolic state → heat production

what is the cause of malignant hyperthemia?

Succinylcholine

Volatile anesthetics (e.g., sevoflurane, -flurane)

triggers for malignant hyperthemia

Malignant Hyperthermia

↑ end-tidal CO₂ despite ventilation ⭐ EARLY
→ tachycardia
→ masseter/generalized muscle rigidity*
→ metabolic + respiratory acidosis
→ hyperkalemia
→ rhabdomyolysis / ↑ CK
→ rapidly rising body temperature ⭐ LATE

Patient becomes tachycardic and rigid during anesthesia, with a rapidly increasing ETCO₂ and later develops severe hyperthermia. —>

rapid increase in CO2

what is the earliest sign of malignant hyperthemia?

dantrolene

_{^{MOA: blocks the ryanodine receptor (RYR1) in skeletal muscle}}

_{^{→ ↓ Ca²⁺ release from the sarcoplasmic reticulum}}

immediate treatment malignant hyperthemia

Step	Treatment
1. Stop triggers	Stop volatile anesthetic + succinylcholine
2. Dantrolene	2.5 mg/kg IV, repeat as needed
3. 100% O₂	Hyperventilate with high-flow 100% oxygen
4. Cool patient	IV cold saline, ice/cooling measures if hyperthermic
5. Treat hyperkalemia	IV calcium + insulin/dextrose as indicated
6. Correct acidosis	Hyperventilation ± sodium bicarbonate if severe
7. Monitor	CK, K⁺, ABG, renal function, urine output, ECG; ICU monitoring

complete treatment of malignant hyperthemia?

Post-op + shallow breathing → atelectasis → incentive spirometry

Immediately after extubation + can't ventilate/stridor → laryngospasm → positive pressure → succinylcholine

Post-op + RR 6/min after morphine → naloxone

Wheezing + ↑ peak airway pressure → bronchospasm → albuterol

HY resp complications

Obesity, OSA

Smoking

Abdominal/thoracic surgery

Poor pain control → shallow breathing

— anything that affects airways/lungs

risk factors for respiratory complications of anesthesia

Incentive spirometry

Early ambulation

Oxygen supplementation

CPAP if needed

Reverse opioids if severe (naloxone)

mgmt of respiratory complications of anesthesia

Female

Non-smoker

History of motion sickness/PONV

Opioid use

risk factors for post-operative nausea/vomiting

Ondansetron (Zofran) – first line

Dexamethasone

Scopolamine patch

---

concern’d for aspiration/dehydration so we treat this

first line treatments for postop nausaea and vomiting

Anesthetic-induced vasodilation

Cold OR environment

IV fluids

causes of post op hypothermia

_{^{(Temp <36°C, shivering, delayed drug metabolism)}}

Coagulopathy

Increased infection risk

Delayed drug metabolism

Shivering → ↑ O₂ demand

consequences of post-op hypothermia

hypotension

_{^{(tx: fluids ± vasopressor & make sure they aren’t bleeding)}}

most common circulatory complication post-op

-T2-7 dysfunction (lungs)

-inhalation dysfunction

osteopathic findings associated with atelectasis

Hemodynamic instability

Acute respiratory distress

Unstable fractures

Increased ICP

Severe hypoxia

absolute contraindications to post-op OMM

early ambulation

& incentive spirometry

first step prevention of post-op:

atelectasis & DVT/PE

Propofol ⭐

Most common; rapid onset/ recovery ↓ BP, respiratory depression

Etomidate

Hemodynamically stable → useful in hypotensive/cardiac patients

Ketamine

↑ HR/BP, provides analgesia; useful in hypotension/bronchospasm

Drugs Used for General Anesthesia?

— INDUCTION (3)

_{^{Think induction → maintenance → analgesia → paralysis.}}

Sevoflurane ⭐

Common volatile inhaled anesthetic

Desflurane, isoflurane

Volatile anesthetics

Propofol ⭐

Can maintain anesthesia via IV infusion (TIVA)

Drugs Used for General Anesthesia?

— MAINTENANCE

_{^{Think induction → maintenance → analgesia → paralysis.}}

Fentanyl ⭐

Opioid; respiratory depression

Morphine, hydromorphone

Opioids

Drugs Used for General Anesthesia?

— ANALGESIA

_{^{Think induction → maintenance → analgesia → paralysis.}}

Succinylcholine ⭐

Depolarizing; rapid onset/short duration; malignant hyperthermia + hyperK⁺

Rocuronium ⭐

Nondepolarizing; common alternative

Drugs Used for General Anesthesia?

— PARALYSIS

_{^{Think induction → maintenance → analgesia → paralysis.}}

Midazolam (optional premedication)
→ Propofol induction
→ Rocuronium or succinylcholine for intubation
→ Sevoflurane ± fentanyl for maintenance/analgesia
→ reverse neuromuscular blockade → extubate

---

_{^{Propofol = most common IV induction agent
Etomidate = cardiovascular instability
Ketamine = hypotension + bronchodilation
Succinylcholine = rapid-sequence intubation; malignant hyperthermia risk
Sevoflurane = common inhaled maintenance agent}}

classic Drugs Used for General Anesthesia?

_{^{Think induction → maintenance → analgesia → paralysis.}}

Propofol	Stop infusion → supportive care; no antidote
Volatile anesthetics (sevoflurane, etc.)	Turn off anesthetic → ventilate with O₂; eliminated through lungs
Opioids (fentanyl, morphine)	Naloxone ⭐
Benzodiazepines (midazolam)	Flumazenil ⭐
Rocuronium / vecuronium	Sugammadex ⭐
Other nondepolarizing paralytics	Neostigmine + glycopyrrolate
Succinylcholine	No routine reversal → wears off via plasma butyrylcholinesterase

reversal agents of general anesthesia