Acute Hypoxic Respiratory Failure
Pulmonary Embolism

-Symptoms / Associated Sx

  • Acute onset dyspnea (most common symptom)

  • Pleuritic chest pain (peripheral PE with infarction)

  • Tachycardia, tachypnea, hypoxia

  • Hemoptysis (pulmonary infarction — late finding)

  • Syncope or presyncope (massive PE — obstructive shock)

  • Leg pain, swelling, erythema (concomitant DVT in ~50%)

  • Hypotension, diaphoresis, altered mentation (massive PE — RV failure)

Denies

  • Fever + productive cough + focal consolidation (rules out pneumonia as primary)

  • Bilateral leg edema + JVD + elevated BNP (rules out CHF as primary)

  • Recent immobility, surgery, malignancy, OCP, prior VTE (reduces PE likelihood if truly absent)

  • Normal D-dimer with low pre-test probability (rules out PE — negative predictive value ~99%)

Social History (SHx)

Recent surgery (especially orthopedic, pelvic, abdominal), immobility, malignancy, prior VTE, OCP/HRT, pregnancy/postpartum, long-distance travel, hereditary thrombophilia, obesity, smoking.

Main Etiology

  • Virchow's triad: stasis + hypercoagulability + endothelial injury

  • Provoked: surgery, trauma, immobility, OCP/HRT, pregnancy, malignancy

  • Unprovoked: idiopathic; evaluate for occult malignancy and thrombophilia

  • Fat embolism (long bone fracture), air embolism, amniotic fluid embolism (obstetric)

Most Common DDx

  • Pneumonia (fever + consolidation; elevated WBC + procalcitonin; responds to antibiotics; no filling defect on CTPA)

  • Acute coronary syndrome (chest pain + EKG changes + troponin; bilateral leg edema less; echo shows LV dysfunction vs. RV strain)

  • Aortic dissection (sudden severe tearing back pain; pulse differential; CT aortography — PE and dissection both cause elevated D-dimer)

  • CHF / flash pulmonary edema (bilateral symmetric infiltrates; BNP markedly elevated; responds to diuretics; no filling defect on CTPA)

  • Pericardial tamponade (obstructive shock; JVD + hypotension + muffled heart sounds; echo shows pericardial effusion + RV collapse)

  • Tension pneumothorax (absent unilateral breath sounds; tracheal deviation; CXR or POCUS confirms)

DATA

  • Pre-test probability: Wells PE score (≤4 = low-moderate; >4 = high); PERC rule (if all 8 criteria met → PE excluded without D-dimer in low pre-test probability)

  • D-dimer (use only in low-to-moderate pre-test probability; negative NPV ~99% → PE excluded; age-adjusted D-dimer threshold = age × 10 mcg/L in patients >50)

  • CT pulmonary angiography (CTPA) — gold standard; first-line imaging; sensitivity ~95%, specificity ~98%

  • V/Q scan (if contrast contraindicated or renal failure; less specific with parenchymal disease)

  • EKG (sinus tachycardia most common; S1Q3T3 pattern — only 10–20%; T-wave inversions V1–V4 + new RBBB = right heart strain)

  • Troponin + BNP/NT-proBNP (RV injury markers — elevated = submassive/massive; predicts worse outcome)

  • Echo (RV dilation, McConnell's sign, D-shaped interventricular septum, elevated RV:LV ratio >0.9)

  • CBC, BMP, PT/INR, PTT (pre-anticoagulation baseline)

  • Bilateral lower extremity Doppler US (DVT confirmation — present in ~50%)

  • Thrombophilia workup (draw BEFORE anticoagulation; defer to outpatient if stable)

Home Meds

  • Prior anticoagulation (assess compliance — PE on therapeutic anticoagulation → cancer, HIT, antiphospholipid)

  • OCP/HRT (hold — thrombogenic)

  • Aspirin (does not prevent VTE adequately)

Plan (Pulmonary Embolism Add-On)

  • UFH (unstable/massive, possible tPA, thrombectomy, CrCl <30 or unpredictable course) (80/kg/per pharmacy) vs LMWH (Stable / floor / good kidneys) (1.5/kg/per pharmacy )

  • Apixaban 10mg BID for 7 days followed by 5mg BID (alternative -> for Rivaroxaban 15mg BID for 21 days followed by 20mg daily with dinner ) once stabilized with plan to treat for 3-6 months if provoked or indefinitely if unprovoked/recurrent PE. consider warfrin if Mechanical heart valve,Antiphospholipid Syndrome, or CrCl < 30

  • Fluid: can begin with 500cc bolus if e/o hypotension, careful not to overload RV

  • Supplemental O2: target SpO2 ≥92%; avoid aggressive fluid resuscitation (worsens RV dilation + septal shift)

  • Vasopressors (norepinephrine preferred) if massive PE + hypotension; avoid excessive fluids

  • IVC filter: only if absolute contraindication to anticoagulation + active bleeding; retrieve when anticoagulation resumes

  • PERT consult for massive/submassive PE

  • Duration of anticoagulation: Provoked reversible risk factor → 3 months; unprovoked → ≥3 months, discuss extended; cancer-associated → indefinite while cancer active; recurrent unprovoked → indefinite

  • Trend CBC, BMP, troponin, BNP q12–24h in submassive/massive; serial echo if RV strain

  • PT/OT; graduated compression stockings; ambulation when stabilized

  • Discharge: DOAC with clear duration; INR monitoring if warfarin; hold OCP/HRT; malignancy workup if unprovoked; thrombophilia testing 3 months after anticoagulation if unprovoked; hematology/pulmonology follow-up; Homan's sign — patient education on VTE recurrence signs

Advanced Therapy Options if needed

  • consult ICU/Cards for Systemic thrombolysis (tPA)immediately in unstable patients or massive PE —no fixed time window

  • consult IR for Catheter-directed therapy (lytics OR Thrombectomy) if tPA contraindicated OR failed or no improvement after 24-48 hr initial therapy

  • VA-ECMO when Refractory shock / cardiac arrest or Bridge to thrombectomy

Red Flags

  • SBP <90 + confirmed PE → massive PE → systemic tPA vs. CDT vs. surgical embolectomy; ICU immediately

  • Cardiac arrest from PE → tPA during CPR; extended CPR (60–90 min) to allow tPA effect

  • RV:LV ratio >0.9 + hemodynamic stability + rising troponin → submassive PE deteriorating → escalate to CDT or tPA

  • PE in pregnancy → LMWH only (DOACs and warfarin contraindicated); CTPA preferred if CXR abnormal; MFM + IR consult

  • PE on therapeutic anticoagulation → CTPA to confirm; consider HIT, APS, malignancy, DOAC non-adherence, subtherapeutic dosing

Senior IM Resident Pearls

  • PERC rule: 8 criteria — if ALL met in low pre-test probability → PE excluded without D-dimer (age <50, HR <100, SpO2 ≥95%, no leg swelling, no hemoptysis, no prior VTE, no recent surgery/trauma, no OCP/HRT)

  • Age-adjusted D-dimer (age × 10 mcg/L) in patients >50 — improves specificity without losing sensitivity; reduces unnecessary CTAPAs

  • McConnell's sign on echo (RV free wall hypokinesis with preserved apex) — highly specific for acute PE; also seen in RV infarction

  • Fluid bolus in massive PE can WORSEN outcomes by overdistending RV and pushing the interventricular septum leftward (D-sign) — give conservative fluids (250–500 mL max); use vasopressors early

  • PERT teams reduce escalation time and improve outcomes in submassive/massive PE — activate early in high-risk cases

  • Common mistake: High-dose D-dimer in high pre-test probability — D-dimer is only a rule-out test in low-moderate probability; never use in high probability patients; go straight to CTPA

  • Common mistake: Aggressive IV fluids in massive PE — RV is preload-sensitive but only to a point; excess fluid causes RV dilation → septal bowing → LV compression → cardiogenic shock

PE Risk Stratification

  1. Massive PE (High Risk)
    → PE with hemodynamic instability:

    • SBP < 90 mmHg ≥ 15 min OR need for pressors

    • Cardiac arrest / pulselessness

    • Severe bradycardia (< 40 bpm) with instability

  2. Submassive PE (Intermediate Risk)
    → PE with normal BP (SBP ≥ 90) BUT evidence of strain:

    • Right ventricular dysfunction (RVD) (echo/CT) and/or

    • Positive biomarkers (↑ troponin, ± BNP)

  3. Low-Risk PE
    → PE without:

    • Hypotension

    • RVD

    • Elevated cardiac biomarkers

Absolute Contraindications for tPA

  • Active serious bleed

  • Any history of hemorrhagic CVA

  • Ischemic CVA in last 3 monhs

  • Known AVM

  • Recent brain/spinal surgery

  • Head trauma with fracture or brain injury in last 3 weeks

  • Suspected or known aortic dissection

Relative Contraindications for tPA (not exhaustive):

  • CNS tumor

  • Major non-CNS surgery in last 2-3 weeks

  • Ischemic CVA > 3 months ago

  • plt <100, INR >1.7, fibrinogen <150

  • Use of oral AC in last 48 hours

  • GI bleed in last month

  • BP >180/110

  • Age >75 yo

  • Advanced cirrhosis (coagulopathy)