You matched into anesthesia. You won't be in the OR for a while, but you can start building your framework now. Every comorbidity you manage on the medicine floors has anesthetic implications you'll use for the rest of your career.
The Anesthesia Lens
The mental habit that separates anesthesiologists from internists
You already know how to evaluate and manage these patients medically. The shift is learning to see every condition through three questions:
- What is this disease doing to their physiology right now? Aortic stenosis means fixed cardiac output. COPD means air trapping. Diabetes means autonomic neuropathy. Name the physiologic problem.
- How does anesthesia interact with that? Induction drugs drop SVR. Positive pressure ventilation changes preload. Paralysis removes respiratory compensation. Every anesthetic intervention collides with the disease in a specific way.
- What could go wrong that wouldn't go wrong if they stayed awake? The patient with aortic stenosis who tolerates daily life fine can arrest on induction. The diabetic who walks around gastroparetic can aspirate. This is the question that keeps you up at night, and it's the one worth asking early.
Every comorbidity card below follows this structure implicitly. Practice it on your medicine patients now and it'll be second nature by CA-1.
Should This Patient Go to the OR Today?
Before you think about the anesthetic, answer this first
This is the most practical question an intern can learn to answer. It's the one you'll get asked on your anesthesia elective and the one medicine attendings rarely teach.
- Is it an emergency? Proceed regardless. Optimize intraoperatively. You don't delay a ruptured AAA for a cardiology consult.
- Does the patient have an active cardiac condition? Unstable angina, decompensated heart failure, significant arrhythmia, or severe valve disease (AS with valve area <1.0 cm², symptomatic MS). If yes: delay and treat, unless it's emergent.
- Can they climb a flight of stairs without symptoms? That's roughly 4 METs of functional capacity. If yes, they can generally tolerate most surgeries.
- If functional capacity is poor or unknown, count risk factors. The Revised Cardiac Risk Index: history of CAD, CHF, CVA/TIA, diabetes on insulin, creatinine >2 mg/dL. Zero factors: proceed. 1-2 factors: proceed, consider noninvasive testing only if it will change management. 3+ factors with intermediate/high-risk surgery: strongly consider cardiology input.
Based on the ACC/AHA Guidelines on Perioperative Cardiovascular Evaluation. Once you've decided surgery proceeds, the comorbidity cards below tell you what each condition means for the anesthetic.
Comorbidities & Anesthetic Implications
Tap any condition to expand. Think about it first, then check yourself.
Cardiovascular
Hypertension
The most common comorbidity you'll see, and the one most often hand-waved
Hypertension
The most common comorbidity you'll see, and the one most often hand-waved
- Chronic HTN shifts cerebral autoregulation rightward. "Normal" BP for a chronically hypertensive patient may be 160/90
- End-organ damage matters more than the number: LVH, renal insufficiency, cerebrovascular disease
- Exaggerated hemodynamic swings on induction and laryngoscopy (hypertension then hypotension)
- Continue most antihypertensives periop. ACEi/ARBs are controversial: holding reduces refractory intraop hypotension
- SBP >180 or DBP >110 on the day of surgery: consider delaying elective cases, but only if optimization will actually change the number
Aortic Stenosis
Fixed cardiac output — the heart can't compensate for sudden changes
Aortic Stenosis
Fixed cardiac output — the heart can't compensate for sudden changes
- Maintain sinus rhythm — loss of atrial kick drops CO by ~25%
- Keep SVR up: hypotension causes coronary ischemia in a hypertrophied ventricle
- Avoid tachycardia — shorter diastole means less filling and less coronary perfusion
- Spinal/epidural risky due to rapid sympathectomy and SVR drop
- Phenylephrine is your friend; ephedrine's tachycardia is not
Atrial Fibrillation
Rate control periop + anticoagulation bridging decisions
Atrial Fibrillation
Rate control periop + anticoagulation bridging decisions
- Rate control target <110 bpm preop; beta-blockers and calcium channel blockers are first-line
- New-onset afib with RVR intraop — treat the cause first (hypovolemia, pain, light anesthesia)
- Anticoagulation bridging depends on CHA2DS2-VASc score and surgical bleeding risk
- Heparin bridging for mechanical valves; DOACs held 24–48h based on renal function
- Loss of atrial kick drops CO ~15–25% — significant in patients with diastolic dysfunction
Heart Failure (HFrEF)
Preload dependent but volume intolerant — narrow therapeutic window
Heart Failure (HFrEF)
Preload dependent but volume intolerant — narrow therapeutic window
- Induction agents (propofol, thiopental) drop SVR and contractility — use reduced doses
- Etomidate or ketamine preserve hemodynamics better for severe HF
- Volatile agents are dose-dependent myocardial depressants
- Invasive arterial monitoring often needed; consider PA catheter for major surgery
- Continue ACE inhibitors/ARBs? Controversial — holding reduces intraop hypotension but may worsen postop outcomes
Coronary Stents
Dual antiplatelet timing is the single most important periop decision
Coronary Stents
Dual antiplatelet timing is the single most important periop decision
- Drug-eluting stent (DES): minimum 6 months of dual antiplatelet therapy (DAPT) before elective surgery
- Bare-metal stent (BMS): minimum 30 days of DAPT
- Stopping DAPT early risks acute stent thrombosis — 20–40% mortality
- If surgery is urgent, continue aspirin and manage bleeding risk; involve cardiology
- Periop MI risk highest in first 6 weeks after stent placement
Respiratory & Airway
COPD & Asthma
Reactive airways + air trapping under positive pressure
COPD & Asthma
Reactive airways + air trapping under positive pressure
- Laryngoscopy and intubation are the strongest bronchospasm triggers
- Auto-PEEP from air trapping → hypotension and barotrauma
- Low respiratory rates, long expiratory times on the ventilator
- Avoid histamine releasers (morphine, atracurium, mivacurium)
- Sevoflurane and ketamine are bronchodilators; desflurane is an airway irritant
- Regional anesthesia avoids the airway entirely when feasible
Obstructive Sleep Apnea
Difficult airway + opioid sensitivity + postop obstruction risk
Obstructive Sleep Apnea
Difficult airway + opioid sensitivity + postop obstruction risk
- STOP-BANG ≥5 = high risk; expect difficult mask ventilation and intubation
- Exquisitely opioid-sensitive — use multimodal analgesia (NSAIDs, acetaminophen, regional)
- Higher aspiration risk from increased intra-abdominal pressure and GERD
- Extubate fully awake, upright; CPAP in PACU
- May need extended postop monitoring (not same-day discharge for severe OSA)
Morbid Obesity
Everything is harder: airway, access, dosing, oxygenation
Morbid Obesity
Everything is harder: airway, access, dosing, oxygenation
- Decreased FRC means rapid desaturation — preoxygenation is critical (head-up/ramped position)
- Difficult airway AND difficult mask ventilation — always have a backup plan
- Drug dosing varies: succinylcholine by total body weight, most others by lean body weight
- IV access, neuraxial landmarks, and positioning are all significantly harder
- Higher risk of aspiration, DVT, and wound complications postop
Rheumatoid Arthritis
The airway danger that hides behind a common diagnosis
Rheumatoid Arthritis
The airway danger that hides behind a common diagnosis
- Atlantoaxial subluxation from C1-C2 instability. Neck extension during laryngoscopy can compress the spinal cord
- TMJ involvement limits mouth opening. Cricoarytenoid arthritis can narrow the glottis and cause post-extubation stridor
- Always get flexion-extension C-spine films if symptomatic (pain, paresthesias, weakness). Keep the neck neutral during intubation
- Pulmonary fibrosis, pleural effusions, and restrictive lung disease are common extra-articular features
- Immunosuppressants (methotrexate, biologics) increase infection risk. Coordinate periop hold/restart with rheumatology
Metabolic & Endocrine
Diabetes Mellitus
Autonomic neuropathy changes everything about the hemodynamic response
Diabetes Mellitus
Autonomic neuropathy changes everything about the hemodynamic response
- Autonomic neuropathy → blunted heart rate response, hemodynamic instability on induction
- Gastroparesis = full stomach risk — consider rapid sequence induction even if NPO
- Stiff joint syndrome (prayer sign) may predict difficult laryngoscopy
- Perioperative glucose target 140–180 mg/dL; hold oral agents and long-acting insulin morning of surgery
- Check for peripheral neuropathy before placing regional blocks (medicolegal documentation)
Chronic Steroid Use / Adrenal Insufficiency
The stress dose steroids question you will get asked on every rotation
Chronic Steroid Use / Adrenal Insufficiency
The stress dose steroids question you will get asked on every rotation
- Any patient on ≥5 mg prednisone daily for ≥3 weeks may have HPA axis suppression
- Surgical stress increases cortisol demand 5-10x. Without supplementation: refractory hypotension, cardiovascular collapse
- Classic stress dosing: hydrocortisone 100 mg IV, then 50 mg q8h, taper over 1-3 days. Some evidence supports simply continuing the patient's usual dose
- Addisonian crisis: hypotension unresponsive to fluids and vasopressors, hyponatremia, hyperkalemia, hypoglycemia
- Etomidate suppresses adrenal function for 24-48h after a single dose. Avoid in adrenal insufficiency
Hyperthyroidism
Thyroid storm periop is rare but rapidly fatal if missed
Hyperthyroidism
Thyroid storm periop is rare but rapidly fatal if missed
- Hyperthyroid patients have exaggerated sympathetic responses: tachycardia, hypertension, arrhythmias on induction
- Must be euthyroid before elective surgery. If urgent: beta-blockers (esmolol, propranolol) to control heart rate
- Thyroid storm triggers: surgery, infection, stress. Fever >40°C + tachycardia + altered mental status. Treat with beta-blockers, PTU, steroids, cooling
- Avoid ketamine, pancuronium, atropine, and exogenous catecholamines (amplify sympathetic excess)
- Eyes: exophthalmos increases risk of corneal injury under GA. Tape and lubricate carefully
Chronic Kidney Disease
Electrolyte traps + altered drug clearance + bleeding risk
Chronic Kidney Disease
Electrolyte traps + altered drug clearance + bleeding risk
- Check K+ before induction — succinylcholine is contraindicated if hyperkalemic
- Renally cleared drugs accumulate: morphine-6-glucuronide, pancuronium, meperidine
- Uremic platelet dysfunction increases surgical bleeding risk
- Avoid the arm with an AV fistula for BP cuffs, IVs, and blood draws
- Metabolic acidosis shifts the oxyhemoglobin curve right — changes O2 delivery dynamics
Liver Cirrhosis
Coagulopathy + altered drug metabolism + hemodynamic fragility
Liver Cirrhosis
Coagulopathy + altered drug metabolism + hemodynamic fragility
- Coagulopathy (low platelets, low fibrinogen, high INR) — neuraxial usually contraindicated
- Portal hypertension → varices, ascites, splenomegaly, massive surgical bleeding risk
- Reduced albumin = more free (active) drug for protein-bound agents
- Decreased hepatic metabolism prolongs duration of fentanyl, midazolam, rocuronium
- Ascites splints the diaphragm — reduced FRC, rapid desaturation, difficult ventilation
Hematologic & Special Populations
Sickle Cell Disease
Avoid the triggers: hypoxia, cold, dehydration, acidosis, stasis
Sickle Cell Disease
Avoid the triggers: hypoxia, cold, dehydration, acidosis, stasis
- Sickling is triggered by hypoxia, hypothermia, dehydration, acidosis, and venous stasis. Every anesthetic decision should minimize these
- Preop: hematology consult. Consider exchange transfusion to target HbS <30% for major surgery, simple transfusion to Hgb ~10 for moderate-risk cases
- Aggressive warming, IV hydration, and supplemental O2 throughout. Avoid tourniquets
- Acute chest syndrome is the most dangerous periop complication: chest pain, fever, new infiltrate, hypoxia. Treat with exchange transfusion, antibiotics, O2
- Pulse oximetry is unreliable with HbS: may overestimate true O2 saturation. Use ABGs for confirmation
Pregnancy
Two patients, altered physiology, and aspiration risk from day one
Pregnancy
Two patients, altered physiology, and aspiration risk from day one
- Full stomach after ~16 weeks regardless of NPO status — always RSI for general anesthesia
- Aortocaval compression in supine — left uterine displacement after 20 weeks
- Decreased FRC + increased O2 consumption = very rapid desaturation
- MAC is reduced ~30% (progesterone effect) — lower doses of volatile agents needed
- Neuraxial is preferred for cesarean; higher block needed (T4) due to reduced epidural space volume
- Know which drugs cross the placenta: thiopental, propofol, opioids do; muscle relaxants mostly don't
Listen & Practice
Start building your framework before CA-1
- ▶ Foundations Series — Start listening on your commute. Each episode teaches one core concept from first principles.
- ▶ Anticoag Timing Tool — ASRA 5th Ed neuraxial timing for 19 anticoagulants and antiplatelets. When can you place or pull a catheter?
- ▶ Pharmacology Questions — 143 board-style questions. Start with local anesthetics and vasopressors.
- ▶ ACLS Quiz — You'll run codes on medicine floors and in the OR. Keep your algorithms sharp.
- ▶ Crisis Management — Bookmark these on your phone. You'll want quick access when things go wrong.
Recommended Reading
What to have on your shelf before you start
- ▶ Stoelting's Anesthesia and Co-Existing Disease — Read the "Anesthetic Implications" section for every comorbidity you manage on your medicine floors.
- ▶ Morgan & Mikhail or Baby Miller — Pick one. Ask your program which they prefer.
Ready for the OR?
CA-1 Guide — Your First Months →Know an incoming intern?
July 1 is coming. Send them this page before day one. Everything is free, no account required.