OMSB Anesthesia (OEA) cheat sheet

Inhalational agent potency is inversely proportional to MAC; MAC is reduced by ~6% per decade of age after age 40, by pregnancy (~30%), hypothermia, opioids, and IV anesthetics, and increased by hyperthermia and chronic alcohol use.

Minimum alveolar concentration (MAC) of common agents in a 40-year-old: sevoflurane ~2.0%, isoflurane ~1.15%, desflurane ~6.0%, nitrous oxide ~104%. MAC-awake is roughly 0.3-0.4 MAC; MAC-bar (blocking autonomic response) ~1.3 MAC.

Induction dose of propofol is 1.5-2.5 mg/kg IV; maintenance infusion 100-200 mcg/kg/min. It causes dose-dependent hypotension from vasodilation and myocardial depression, pain on injection, and apnea.

Succinylcholine 1-1.5 mg/kg IV gives onset in 45-60 s and duration 5-10 min via plasma pseudocholinesterase. Prolonged block occurs with pseudocholinesterase deficiency, and it is contraindicated after burns, denervation, or prolonged immobility due to hyperkalemia risk.

Rocuronium 0.6-1.2 mg/kg IV achieves intubating conditions in 60-90 s; 1.2 mg/kg provides rapid-sequence conditions comparable to succinylcholine. Reversal with sugammadex 2 mg/kg (TOF count 2), 4 mg/kg (post-tetanic count 1-2), or 16 mg/kg (immediate rescue).

Neostigmine 0.03-0.07 mg/kg IV (max 5 mg) reverses nondepolarizing blockade only when a twitch is present; co-administer glycopyrrolate 0.2 mg per 1 mg neostigmine to prevent bradycardia and secretions.

Local anesthetic maximum doses: lidocaine 4.5 mg/kg plain or 7 mg/kg with epinephrine; bupivacaine 2-2.5 mg/kg; ropivacaine ~3 mg/kg. Add 1 mL of 8.4% sodium bicarbonate per 10 mL lidocaine to speed onset and reduce injection pain.

Malignant hyperthermia is treated with dantrolene 2.5 mg/kg IV, repeated up to 10 mg/kg, plus discontinuation of triggers, 100% oxygen, active cooling, and treatment of hyperkalemia and acidosis.

Airway assessment: Mallampati class III-IV, thyromental distance <6 cm, interincisor opening <3 cm, and limited neck extension each predict difficult laryngoscopy; the combination is more predictive than any single measure.

Cormack-Lehane grades: I = full glottic view, II = partial vocal cords, III = epiglottis only, IV = soft palate only. Grade III-IV predicts difficult intubation.

Preoxygenation with 100% oxygen for 3 minutes or 4 vital-capacity breaths achieves end-tidal O2 >90% and extends safe apnea time from ~1-2 min to 6-8 min in a healthy adult.

Rapid sequence induction uses a pre-calculated induction dose plus a neuromuscular blocker without positive-pressure ventilation, with cricoid pressure applied at ~20-30 N, to reduce aspiration risk in full-stomach patients.

Difficult airway algorithm: after failed intubation, maintain oxygenation with a supraglottic airway or mask ventilation; if oxygenation fails, proceed to emergency invasive airway (cricothyrotomy) rather than repeated intubation attempts.

A 7.0 mm ID cuffed tube is typical for adult females and 7.5-8.0 mm for males; tube depth at the incisors is ~21 cm in females and ~23 cm in males, and the tip should sit 3-5 cm above the carina.

Laryngospasm management: 100% oxygen with continuous positive airway pressure, deepen anesthesia, and if refractory give succinylcholine 0.1-0.5 mg/kg IV or 4 mg/kg IM.

Postoperative nausea and vomiting risk factors (Apfel): female sex, non-smoker, history of PONV or motion sickness, and postoperative opioids. Each adds ~20% risk; prophylaxis with 2-3 antiemetics from different classes for high-risk patients.

Spinal anesthesia: local anesthetic injected into CSF in the subarachnoid space at L3-L4 or below; onset 2-5 min with hyperbaric bupivacaine 0.75% 1.5-3 mL. Block height depends on baricity, patient position, and dose.

Epidural anesthesia: catheter placed in the epidural space via loss-of-resistance to saline or air; onset 10-20 min with lidocaine or bupivacaine. Test dose is 3 mL of lidocaine 1.5% with epinephrine 1:200,000 to detect intravascular or intrathecal placement.

Spinal anesthesia complications include hypotension from sympathectomy (treat with fluids, vasopressors, left uterine displacement in obstetric patients), post-dural puncture headache, and high block with respiratory compromise.

Post-dural puncture headache is positional, worse upright and relieved supine, typically occurs 24-48 h after dural puncture; conservative treatment is hydration, caffeine, and analgesics, with epidural blood patch (15-20 mL autologous blood) for persistent cases.

Total spinal anesthesia presents with bradycardia, hypotension, apnea, and loss of consciousness; management is airway support, 100% oxygen, fluids, vasopressors, and atropine or epinephrine as needed.

Peripheral nerve blocks: axillary brachial plexus block risks radial artery puncture and pneumothorax is more associated with supraclavicular approach; interscalene block carries a high risk of phrenic nerve palsy and is avoided in severe respiratory disease.

Local anesthetic systemic toxicity presents with perioral numbness, tinnitus, seizures, and cardiovascular collapse; treatment is 20% lipid emulsion 1.5 mL/kg bolus followed by infusion 0.25 mL/kg/min, plus airway and circulatory support.

Adrenaline with local anesthetics (1:100,000-1:200,000) prolongs block, reduces systemic absorption, and provides a marker for intravascular injection (transient heart rate increase).

Oxygen delivery = cardiac output × arterial oxygen content (CaO2 = 1.34 × Hb × SaO2 + 0.003 × PaO2). Normal CaO2 is ~20 mL O2/dL; anemia and hypoxemia both reduce delivery.

Pulse oximetry reads SpO2, not PaO2; the oxyhemoglobin dissociation curve is right-shifted by increased temperature, CO2, 2,3-DPG, and acidosis (Bohr effect), reducing affinity and improving tissue unloading.

Capnography: end-tidal CO2 normally 35-45 mmHg and 2-5 mmHg below PaCO2. A sudden drop suggests disconnection, obstruction, or cardiac arrest; a rising value suggests hypoventilation or CO2 absorption.

Mechanical ventilation settings for a healthy adult: tidal volume 6-8 mL/kg predicted body weight, PEEP 5 cmH2O, respiratory rate 10-14/min, and FiO2 titrated to SpO2 94-98%.

Lung-protective ventilation in ARDS: tidal volume 4-6 mL/kg predicted body weight, plateau pressure ≤30 cmH2O, and permissive hypercapnia; this reduces mortality.

Hypoxemia causes in the perioperative period: hypoventilation, V/Q mismatch (atelectasis, pneumonia), shunt, diffusion limitation, and low inspired oxygen. A normal chest radiograph with refractory hypoxemia suggests shunt.

Pulse pressure variation >13% or systolic pressure variation >10% predicts fluid responsiveness in mechanically ventilated patients; passive leg raise is an alternative in spontaneously breathing patients.

Perioperative cardiac risk: perioperative beta-blockade reduces myocardial ischemia but increases bradycardia and hypotension; continue chronic beta-blockers and statins, and avoid starting high-dose beta-blockers on the day of surgery.

Anesthesia machine check (per ASA): verify backup ventilation and suction, check vaporizers, flowmeters, and circuit leaks, confirm CO2 absorbent, and perform a high-pressure leak test with the oxygen flush valve.

Oxygen failure safety devices: the fail-safe valve stops nitrous oxide flow when oxygen pressure falls, and the oxygen ratio monitor prevents hypoxic mixtures (minimum 25% O2).

Soda lime absorbs CO2 via an exothermic reaction; exhaustion is indicated by color change (Ethyl violet indicator) and by a rise in inspired CO2. Compound A formation with sevoflurane is minimized by flows ≥2 L/min.

Scavenging systems remove waste anesthetic gas; the reservoir bag should be checked for proper filling, and the system must not allow positive pressure to the patient (adjustable pressure-limiting valve open during spontaneous ventilation).

BIS monitoring: values 40-60 correspond to adequate general anesthesia; BIS <40 indicates deep anesthesia with increased risk of awareness and hypotension, while >60 indicates light anesthesia.

Monitoring standards: continuous pulse oximetry, capnography, ECG, blood pressure, temperature, and inspired oxygen concentration for every general anesthetic; neuromuscular monitoring for every case using muscle relaxants.

Defibrillation energy: biphasic 120-200 J and monophasic 360 J for ventricular fibrillation or pulseless ventricular tachycardia; epinephrine 1 mg IV every 3-5 min during cardiac arrest.

Anaphylaxis in anesthesia: epinephrine 0.5-1 mg IM (1:1000) or 50-100 mcg IV, fluids, stop the trigger, and consider a mast cell tryptase level; common triggers are neuromuscular blockers, antibiotics, and chlorhexidine.

ASA physical status: I = healthy, II = mild systemic disease, III = severe systemic disease, IV = severe disease with constant threat to life, V = moribund, VI = brain-dead organ donor. Add E for emergency.

Preoperative fasting (ASA): 2 h for clear liquids, 4 h for breast milk, 6 h for light meal and non-human milk. Prolonged fasting is not recommended.

Cardiac risk indices: RCRI (Revised Cardiac Risk Index) uses ischemic heart disease, heart failure, cerebrovascular disease, insulin-dependent diabetes, renal impairment (creatinine >2 mg/dL), and high-risk surgery; ≥3 factors indicates elevated risk.

Perioperative medication management: continue beta-blockers and statins; hold ACE inhibitors and ARBs on the day of surgery when possible to reduce intraoperative hypotension; continue aspirin for most patients with coronary stents.

Anticoagulation: neuraxial anesthesia requires holding clopidogrel 5-7 days, warfarin with INR ≤1.4, and low-molecular-weight heparin 12 h (prophylactic) or 24 h (therapeutic) before puncture.

Postoperative delirium risk factors: advanced age, cognitive impairment, sensory deprivation, pain, and polypharmacy. Prevention includes early mobilization, orientation, and avoiding benzodiazepines and anticholinergics.

Enhanced recovery after surgery (ERAS) elements: preoperative counseling, carbohydrate loading, multimodal opioid-sparing analgesia, normothermia, early oral intake, and early ambulation.

Do-not-resuscitate orders require explicit review before surgery; anesthesia-related resuscitation is usually discussed with the patient or surrogate, and the order should be documented perioperatively.

Pediatric airway: the narrowest point is the cricoid ring in children <8 years; uncuffed tubes may be used, and tube size = (age/4) + 4 mm ID for uncuffed and (age/4) + 3.5 for cuffed tubes.

Pediatric fluid maintenance (Holliday-Segar): 4 mL/kg/h for first 10 kg, 2 mL/kg/h for next 10 kg, and 1 mL/kg/h for each kg above 20. Blood volume is ~80-90 mL/kg in neonates and ~70 mL/kg in children.

Pediatric anesthesia risks: laryngospasm is most common in children 1-5 years, and bradycardia from hypoxia or vagal stimulation is common; treat bradycardia with oxygen and atropine 0.02 mg/kg.

Neonatal physiology: higher respiratory rate (30-60/min), higher oxygen consumption, limited functional residual capacity, and immature hepatic and renal clearance; reduce drug doses accordingly.

Obstetric anesthesia: left uterine displacement after 20 weeks to relieve aortocaval compression; spinal hypotension is treated with phenylephrine or ephedrine plus fluids. Aspiration prophylaxis with sodium citrate and H2 blockers for cesarean delivery.

Obstetric contraindications to neuraxial anesthesia include coagulopathy, infection at the puncture site, severe hypovolemia, and raised intracranial pressure. Preeclampsia is not a contraindication once platelets and coagulation are acceptable.

Geriatric anesthesia: reduced MAC requirement (~6% per decade after 40), decreased cardiac output and hepatic/renal clearance, and increased sensitivity to benzodiazepines and opioids; titrate doses and monitor for postoperative cognitive dysfunction.

Day-surgery selection: ASA I-II, well-controlled III, surgery <60 min, no significant postoperative pain, nausea, or bleeding risk, and adequate home support. Obstructive sleep apnea and morbid obesity increase unplanned admission risk.

Critical incident: anaphylaxis during anesthesia is treated with epinephrine 50-100 mcg IV (or 0.5-1 mg IM), rapid IV fluids, 100% oxygen, and removal of the trigger; a tryptase sample is drawn 1-2 h after onset.

Local anesthetic systemic toxicity: stop injection, secure the airway with 100% oxygen, control seizures with benzodiazepines, and give 20% lipid emulsion 1.5 mL/kg bolus then 0.25 mL/kg/min infusion; avoid vasopressin and calcium-channel blockers.

Malignant hyperthermia: earliest sign is often unexplained rising end-tidal CO2 with masseter spasm and tachycardia; dantrolene 2.5 mg/kg IV repeated as needed, active cooling, and treatment of hyperkalemia (calcium, insulin/glucose, bicarbonate).

Awareness under anesthesia: risk factors are obstetric and cardiac surgery, trauma, and total intravenous anesthesia without monitoring; management includes explanation, apology, follow-up, and psychological support.

Difficult mask ventilation predictors: age >55, BMI >26, edentulous, beard, and snoring; difficult intubation predictors: Mallampati III-IV, short thyromental distance, and limited neck mobility.

Postoperative respiratory failure: causes include residual neuromuscular blockade, opioids, atelectasis, and aspiration; ensure TOF ratio >0.9 before extubation and use multimodal analgesia to limit opioids.

Perioperative myocardial infarction most often occurs within 48-72 h after surgery; troponin monitoring is indicated in high-risk patients, and management includes beta-blockade, aspirin, and cardiology consultation.

Acute intraoperative hypotension: consider hypovolemia, vasodilation from anesthetics or sepsis, myocardial depression, pneumothorax, and anaphylaxis; treat with fluids, vasopressors, and correction of the underlying cause.

Pharmacokinetics: propofol is highly protein-bound and rapidly redistributed, giving a short clinical effect; context-sensitive half-time increases with prolonged infusion, especially in obese patients.

Opioid equianalgesia: morphine 10 mg IV ≈ fentanyl 100 mcg IV ≈ hydromorphone 1.5 mg IV ≈ oxycodone 10 mg IV. Fentanyl onset 3-5 min and duration 30-60 min; remifentanil is metabolized by plasma esterases with a context-insensitive half-time of 3-5 min.

Ketamine 1-2 mg/kg IV provides dissociative anesthesia with analgesia and bronchodilation; it increases heart rate, blood pressure, and secretions, and emergence reactions are reduced by benzodiazepines.

Etomidate 0.2-0.3 mg/kg IV has minimal cardiovascular effects and is useful in hemodynamically unstable patients, but it causes adrenal suppression and myoclonus.

Dexmedetomidine is an alpha-2 agonist with sedative and analgesic effects; a loading dose of 1 mcg/kg over 10 min followed by 0.2-0.7 mcg/kg/h causes bradycardia and hypotension.

Neuromuscular blockers: depolarizing (succinylcholine) versus nondepolarizing (rocuronium, vecuronium, cisatracurium). Cisatracurium undergoes Hofmann elimination and is safe in renal and hepatic failure.

Volatile agents reduce systemic vascular resistance and myocardial contractility; desflurane has the fastest onset and offset due to low blood solubility, while halothane is avoided due to hepatotoxicity and arrhythmogenicity.

Antiemetics: ondansetron 4 mg IV (5-HT3), dexamethasone 4-8 mg IV, droperidol 0.625-1.25 mg IV, and metoclopramide 10 mg IV. Combine agents from different classes for high-risk patients.

Blood transfusion: 1 unit of packed red blood cells raises hemoglobin by ~1 g/dL and hematocrit by ~3%. Transfuse based on clinical status; a restrictive threshold of 7-8 g/dL is appropriate for most stable patients.

Massive transfusion protocol: balanced ratios of red cells, plasma, and platelets (1:1:1), calcium replacement for citrate toxicity, and prevention of hypothermia, acidosis, and coagulopathy.

Transfusion reactions: febrile non-hemolytic (most common, stop and give antipyretics), acute hemolytic (ABO mismatch with fever, hypotension, hemoglobinuria), and TRALI (non-cardiogenic pulmonary edema within 6 h).

Fluid resuscitation: crystalloids (0.9% saline, lactated Ringer's) distribute to the extracellular space; colloids stay in the intravascular space longer. Avoid large volumes of 0.9% saline due to hyperchloremic metabolic acidosis.

Hypothermia in the perioperative period causes coagulopathy, increased surgical site infection, and delayed drug metabolism; maintain normothermia with forced-air warmers and warmed fluids.

Surgical site infection prevention: antibiotics within 60 min before incision (vancomycin within 120 min), redosing every 3-4 h or after large blood loss, and discontinuation within 24 h.

Venous thromboembolism prophylaxis: risk-stratify with Caprini score; use mechanical prophylaxis for moderate risk and low-molecular-weight heparin for high-risk patients, timed around neuraxial procedures.

Postoperative pain management: multimodal analgesia with acetaminophen, NSAIDs, local anesthetics, and opioids; regional techniques reduce opioid consumption and improve recovery.

Preoperative ECG indications: age >65, known cardiovascular disease, or risk factors; routine ECG is not indicated for low-risk patients undergoing low-risk surgery.

Pulmonary function tests are indicated before lung resection to predict postoperative lung function; predicted postoperative FEV1 or DLCO <30-40% predicts high risk.

Obstructive sleep apnea: screen with STOP-BANG; high-risk patients need postoperative monitoring, CPAP continuation, and cautious opioid dosing.

Diabetes: aim for perioperative glucose 140-180 mg/dL; hold metformin on the day of surgery if contrast or renal impairment is present, and use insulin sliding scale for uncontrolled diabetes.

Renal disease: avoid succinylcholine in hyperkalemia, use cisatracurium (Hofmann elimination), and adjust doses of renally cleared drugs such as morphine and vecuronium.

Hepatic disease: reduced albumin and coagulation factors increase free drug levels and bleeding risk; avoid halothane and reduce doses of hepatically metabolized drugs.

Smoking cessation at least 4-8 weeks before surgery reduces pulmonary complications; brief cessation still reduces carboxyhemoglobin levels.

Informed consent for anesthesia: discuss risks, benefits, alternatives, and the possibility of awareness or regional versus general anesthesia; document the discussion.

Post-anesthesia care unit (PACU) discharge criteria (Aldrete score ≥9): activity, respiration, circulation, consciousness, and oxygen saturation; include pain and nausea control and temperature.

Airway obstruction in the PACU: snoring suggests soft tissue obstruction, stridor suggests laryngospasm or edema; treat with jaw thrust, oral or nasal airway, CPAP, and reintubation if refractory.

Postoperative hypoxemia: consider residual anesthesia, opioids, atelectasis, pulmonary embolism, and aspiration; treat with oxygen, incentive spirometry, and early mobilization.

Emergence delirium: agitation and confusion during recovery, more common in children and the elderly; treat with reassurance, analgesia, and low-dose propofol or dexmedetomidine if needed.

Shivering in the PACU increases oxygen consumption and is treated with forced-air warming and meperidine 12.5-25 mg IV.

Postoperative urinary retention: risk factors include spinal anesthesia, opioids, and pelvic surgery; treat with bladder catheterization if the bladder volume exceeds 500-600 mL.

Nerve injury after regional anesthesia: most resolve; document baseline neurologic status, and evaluate persistent deficits with neurology consultation and imaging.

Cardiac arrest in the PACU: follow ACLS with high-quality CPR, defibrillation for shockable rhythms, and search for reversible causes (hypovolemia, hypoxia, acidosis, hyperkalemia, tension pneumothorax, tamponade, toxins, thrombosis).