Respiratory

Mechanical ventilation: initial settings and weaning

Clinical Overview and When to Suspect Need for Mechanical Ventilation

— Hypoxemic respiratory failure (Type I): PaO₂ <60 mmHg on supplemental O₂; ARDS, pneumonia, pulmonary edema, PE.

— Hypercapnic respiratory failure (Type II): PaCO₂ >50 with pH <7.30; COPD exacerbation, asthma, neuromuscular disease, opioid overdose.

— Inability to protect airway: GCS ≤8, copious secretions, massive hematemesis, stroke with bulbar dysfunction.

— Anticipated decompensation: angioedema, inhalation injury, sepsis with rising lactate and tachypnea, preoperative.

— RR >35 or <8, accessory muscle use, paradoxical abdominal motion

— SpO₂ <88% despite high-flow O₂ or NIV

— pH <7.25 with rising PaCO₂

— Hemodynamic collapse requiring deep sedation/paralysis

— NIV first-line in COPD exacerbation with acidosis (pH 7.25–7.35) and cardiogenic pulmonary edema.

— HFNC preferred for de novo hypoxemic failure (e.g., pneumonia) if hemodynamically stable.

— Avoid NIV in altered mental status, shock, vomiting, recent upper GI surgery, or facial trauma.

Step 3 management: A COPD patient with pH 7.22, PaCO₂ 78, and worsening somnolence after 2 hours of BiPAP fails NIV → proceed to intubation and invasive ventilation, do not extend NIV trial. On the CCS, order: ABG, CXR, continuous pulse oximetry, capnography, sedation (propofol or fentanyl/midazolam), and head-of-bed 30°. Board pearl: Decision to intubate is clinical (work of breathing, mentation, trajectory) — do not wait for "bad" ABG numbers if the patient is tiring.

Mechanical ventilation (MV) supports oxygenation, ventilation, and work of breathing when the respiratory system fails. Step 3 expects you to recognize indications, choose initial settings, troubleshoot, and execute a weaning plan in CCS time-advance fashion.

Four physiologic indications:

Clinical thresholds suggesting intubation:

NIV vs invasive MV trial:

Presentation Patterns and Key History

— Tachypnea, restlessness, then confusion; cyanosis is late.

— Crackles (pneumonia, ARDS, CHF), unilateral findings (PE with infarct, pneumothorax).

— "Silent chest" in severe asthma is ominous, not reassuring.

— Somnolence, asterixis, headache (morning), bounding pulse from vasodilation.

— Slow shallow breathing or rapid shallow (neuromuscular fatigue).

— Hx of COPD, OSA-OHS, ALS, myasthenic crisis, Guillain-Barré, opioid use.

— Allergies (esp. succinylcholine triggers, latex)

— Medications: anticoagulants, beta-blockers, recent opioids

— Past airway: prior difficult intubation, OSA, c-spine disease, RA (atlantoaxial), Down syndrome

— Last meal (aspiration risk → RSI)

— Events: aspiration, trauma, overdose

— Mallampati, mouth opening, thyromental distance, neck mobility (LEMON criteria)

— Bronchospasm → albuterol/ipratropium nebs, steroids

— Pulmonary edema → diuresis, nitrates

— Opioid toxicity → naloxone

— Tension pneumothorax → needle decompression BEFORE intubation (positive pressure worsens it)

CCS pearl: Always order chest X-ray immediately after intubation to confirm ETT depth (3–5 cm above carina, typically tip at T2–T4) and rule out right mainstem intubation or new pneumothorax. Board pearl: Sudden desaturation post-intubation = DOPE — Displaced tube, Obstruction, Pneumothorax, Equipment failure.

Recognize the failing patient before the arrest. Step 3 stems emphasize trajectory and modifiable triggers.

Hypoxemic failure pattern:

Hypercapnic failure pattern:

Targeted history before intubation (the "AMPLE" + airway):

Code status discussion is mandatory before elective intubation when feasible — Step 3 favors clarifying goals of care, especially in metastatic cancer, advanced dementia, or end-stage COPD with frequent admissions.

Reversible triggers to address simultaneously:

Physical Exam Findings and Hemodynamic Assessment

— Look externally: beard, obesity, micrognathia, large tongue

— Evaluate 3-3-2: 3 fingers mouth opening, 3 fingers mentum-to-hyoid, 2 fingers hyoid-to-thyroid

— Mallampati III–IV predicts difficult laryngoscopy

— Obstruction: stridor, drooling, epiglottitis, angioedema

— Neck mobility: c-collar, ankylosing spondylitis, RA

— Tripod posture, nasal flaring, intercostal/supraclavicular retractions

— Paradoxical thoracoabdominal motion (diaphragmatic fatigue)

— Inability to speak in full sentences

— Pre-intubation hypotension is the #1 predictor of peri-intubation cardiac arrest.

— Shock index >0.9 (HR/SBP) → fluid bolus and/or push-dose pressors (phenylephrine 50–200 mcg, epinephrine 10–20 mcg) before induction.

— Avoid propofol in shock (use ketamine or etomidate); avoid succinylcholine in hyperkalemia, burns >24h, crush injury, chronic neuromuscular disease.

— Bilateral breath sounds, symmetric chest rise

— End-tidal CO₂ waveform (gold standard for tube placement)

— Absent epigastric sounds

— Confirm cuff seal (no audible leak at PIP <25)

— Persistent end-expiratory flow on ventilator waveform

— Hypotension after intubation in asthmatic → disconnect from vent, allow exhalation, then reattach with lower RR and longer expiratory time.

Key distinction: Post-intubation hypotension from auto-PEEP (treat: disconnect, slow rate, bronchodilators) vs tension pneumothorax (treat: needle decompression) vs sedation-induced vasodilation (treat: fluids, pressors). Step 3 management: Always recheck breath sounds and ETCO₂ after any clinical change.

Pre-intubation airway exam (LEMON):

Work-of-breathing signs that mandate action:

Hemodynamic assessment pre-intubation:

Post-intubation exam:

Auto-PEEP detection in COPD/asthma:

Diagnostic Workup — Initial Labs, Imaging, ABG

— Acute respiratory acidosis: pH drops 0.08 per 10 mmHg rise in PaCO₂.

— Chronic: pH drops 0.03 per 10 mmHg (renal compensation with HCO₃⁻ retention).

— A-a gradient elevated → V/Q mismatch, shunt, diffusion defect; normal → hypoventilation or low FiO₂.

— ABG within 30 min of intubation and after each major setting change

— CBC, CMP, lactate, troponin if cardiac concern

— Coagulation panel before central line/arterial line

— Blood cultures × 2 if sepsis suspected

— Sputum/tracheal aspirate Gram stain + culture

— Procalcitonin (helps trim antibiotics)

— Continuous pulse oximetry, ETCO₂, telemetry

— Portable CXR: confirm ETT, NG/OG tube, central line position; assess pulmonary edema, infiltrate, pneumothorax, ARDS pattern (bilateral opacities).

— Point-of-care US (POCUS): lung sliding (rules out PTX), B-lines (edema/ARDS), IVC for volume status, cardiac for RV strain (PE) or EF.

— CT chest if PE suspected (CTA) or unclear etiology — only after stabilization.

— PaO₂/FiO₂ ratio (P/F): ARDS if ≤300 on PEEP ≥5; mild 200–300, moderate 100–200, severe ≤100.

— Driving pressure (Pplat − PEEP): target <15 cm H₂O — strong mortality predictor in ARDS.

Board pearl: A "normal" PaCO₂ (40) in a severe asthma exacerbation with RR 30 means the patient is tiring and approaching respiratory arrest — prepare to intubate. CCS pearl: Order post-intubation ABG at 30 minutes, then titrate FiO₂ down to maintain SpO₂ 92–96% (avoid hyperoxia, which increases mortality).

ABG is the cornerstone — distinguishes hypoxemic vs hypercapnic, acute vs chronic, and guides initial settings.

Initial CCS order set for the intubated patient:

Imaging:

Bedside indices to calculate:

Diagnostic Workup — Advanced and Confirmatory Studies

— Scooped expiratory flow not returning to zero → auto-PEEP (asthma/COPD)

— Plateau pressure (inspiratory hold) >30 cm H₂O → high alveolar pressure, risk of barotrauma; reduce Vt or PEEP

— Stress index on pressure-time curve: upward concavity = overdistension, downward = derecruitment

— Dyssynchrony patterns: double-triggering, ineffective triggering, reverse triggering — adjust trigger sensitivity, flow, sedation

— Atelectasis/lobar collapse unresponsive to suctioning

— Hemoptysis localization

— BAL for ventilator-associated pneumonia (VAP) diagnosis (≥10⁴ CFU/mL)

— Foreign body removal

— Difficult airway management (awake fiberoptic)

— RV dilation/strain → PE or pulmonary hypertension

— Reduced EF → cardiogenic component

— Useful in weaning failure to assess for cardiac dysfunction (weaning-induced pulmonary edema)

— Sudden loss of waveform → extubation, disconnect, cardiac arrest

— Rising ETCO₂ with stable minute ventilation → hypermetabolism (fever, sepsis, malignant hyperthermia)

— "Shark fin" → bronchospasm

Key distinction: High peak pressure with normal plateau = airway resistance problem (bronchospasm, secretions, ETT kink, biting) → suction, bronchodilators, bite block. High peak AND plateau = compliance problem (pneumothorax, pulmonary edema, ARDS progression, mainstem intubation, abdominal distension) → CXR, decompress, reduce Vt. Board pearl: This peak-vs-plateau distinction is one of the most tested ICU concepts on Step 3.

Ventilator waveform analysis — interpret these on Step 3 image stems:

Esophageal manometry (advanced): measures transpulmonary pressure, helpful in obese ARDS patients to titrate PEEP — not first-line on Step 3 but recognize the concept.

Bronchoscopy indications:

Echocardiography:

Diaphragm ultrasound: assesses thickening fraction during inspiration — predicts extubation success when >30%.

Capnography (continuous ETCO₂):

Risk Stratification and Initial Settings Logic

— Assist-Control Volume (AC/VC): default for most patients — guarantees minute ventilation, preferred in ARDS for lung-protective Vt control.

— Assist-Control Pressure (AC/PC): preferred when high airway pressures are a concern; Vt varies with compliance.

— SIMV: largely historical for weaning; not preferred — prolongs ventilation vs spontaneous trials.

— Pressure Support (PS): spontaneous mode, used during weaning and SBT.

— Mode: AC/VC

— Tidal volume 6–8 mL/kg of predicted body weight (PBW) — use IBW, not actual weight

— RR 12–16

— FiO₂ 100% initially, wean to maintain SpO₂ 92–96% within first hour

— PEEP 5 cm H₂O

— Flow 60 L/min, I:E 1:2

— Vt 4–6 mL/kg PBW, plateau pressure ≤30, driving pressure <15

— Higher PEEP table (ARDSnet high-PEEP/low-FiO₂ strategy)

— Permissive hypercapnia (pH ≥7.20 acceptable)

— Prone positioning if P/F <150 — improves mortality

— Neuromuscular blockade only in severe ARDS with dyssynchrony (cisatracurium 48h max)

— Lower RR (8–12), longer expiratory time (I:E 1:3 or 1:4), Vt 6–8 mL/kg

— Accept permissive hypercapnia

— Watch for auto-PEEP; minimize applied PEEP or match ~80% of intrinsic PEEP in COPD

— Standard Vt, normal RR, low PEEP (5), low FiO₂ once stable

Step 3 management: A 170-cm man weighs 110 kg actual — calculate PBW (50 + 2.3 × (inches over 5 ft)) ≈ 65 kg, so Vt 6 mL/kg = 390 mL, not 660. Board pearl: Using actual body weight is the most common boards-tested ventilator error and a key cause of ventilator-induced lung injury.

Choose the mode:

Initial settings for a "standard" adult (70 kg, no specific lung disease):

ARDS-specific (ARDSNet):

COPD/asthma (obstructive):

Neuromuscular/overdose (normal lungs):

Pharmacotherapy — Induction, Sedation, and Analgesia

— Etomidate 0.3 mg/kg: hemodynamically neutral; transient adrenal suppression (concerning in septic shock but single dose acceptable).

— Ketamine 1–2 mg/kg: bronchodilator, preserves BP — drug of choice in asthma and shock; avoid in uncontrolled HTN or coronary ischemia (relative).

— Propofol 1.5–2 mg/kg: causes hypotension — avoid in shock; good for status epilepticus.

— Midazolam 0.1–0.3 mg/kg: slower onset, hypotension, accumulates.

— Succinylcholine 1.5 mg/kg: fast on/off; contraindicated in hyperkalemia, burns >24h, denervation injury, chronic neuromuscular disease, malignant hyperthermia history.

— Rocuronium 1.2 mg/kg: no contraindications above; longer duration (~45 min); reversible with sugammadex.

— Fentanyl 25–100 mcg/h infusion: first-line analgesic.

— Propofol 5–50 mcg/kg/min: short-acting; monitor triglycerides (propofol infusion syndrome — acidosis, rhabdo, bradyarrhythmia at >4 mg/kg/h × >48h).

— Dexmedetomidine 0.2–1.4 mcg/kg/h: light sedation, no respiratory depression — ideal for weaning; causes bradycardia/hypotension.

— Avoid benzodiazepine infusions when possible — associated with delirium and prolonged MV (PADIS guidelines).

— RASS −2 to 0 (light sedation) is goal; deeper only if ARDS-paralyzed or severe dyssynchrony.

— CPOT or BPS for pain in nonverbal patients.

— Daily sedation interruption ("SAT") paired with spontaneous breathing trial ("SBT") — the ABCDEF bundle reduces vent days and delirium.

CCS pearl: Order DVT prophylaxis (LMWH/heparin), stress ulcer prophylaxis (PPI or H2 blocker only if on MV >48h or coagulopathy), HOB 30°, chlorhexidine oral care, and subglottic suction ETT — the VAP prevention bundle. Board pearl: Light sedation + early mobilization shortens ICU stay more than any single drug choice.

Rapid sequence intubation (RSI) — induction agents:

Paralytics:

Ongoing analgosedation (A1 before sedation):

Targets:

Ventilator Adjustments and Lung-Protective Strategies

— Increase PEEP to recruit alveoli and reduce shunt; allows lower FiO₂.

— Follow ARDSnet PEEP/FiO₂ tables — e.g., FiO₂ 0.5 paired with PEEP 8–10; FiO₂ 0.8 with PEEP 14.

— Target SpO₂ 92–96% (88–92% acceptable in COPD/chronic CO₂ retention).

— Hyperoxia (PaO₂ >120) → free radical injury, worse outcomes.

— High PaCO₂ → increase RR first (safer than Vt), then Vt if Vt <6 mL/kg PBW.

— Low PaCO₂ → decrease RR.

— In ARDS, permissive hypercapnia (pH 7.20–7.30) is acceptable to protect lungs.

— Measure with 0.5-sec inspiratory hold.

— Pplat >30 → reduce Vt by 1 mL/kg PBW increments to 4 mL/kg minimum.

— Driving pressure (Pplat − PEEP) >15 → strongly predicts mortality.

— Prone 16 h/day in moderate-severe ARDS (P/F <150) — PROSEVA trial: mortality benefit.

— Recruitment maneuvers (sustained inflation 30–40 cm H₂O × 30s) — controversial, no routine use.

— Neuromuscular blockade (cisatracurium ≤48h)

— Inhaled pulmonary vasodilators (nitric oxide, epoprostenol) — bridge only, no mortality benefit

— VV-ECMO if P/F <80 despite optimization, or pH <7.20 with hypercapnia despite max settings — early referral matters

— Decrease RR, decrease Vt, prolong expiratory time, treat bronchospasm, deepen sedation ± paralysis

— Apply external PEEP at ~80% of auto-PEEP in COPD (not asthma)

Key distinction: Worsening hypoxemia despite increasing PEEP — consider overdistension (compressing capillaries) rather than under-recruitment. Reassess driving pressure. Step 3 management: In severe ARDS, escalate stepwise: lung-protective Vt → high PEEP → paralysis → prone → ECMO referral.

Adjusting oxygenation (FiO₂ and PEEP):

Adjusting ventilation (minute ventilation = Vt × RR):

Plateau pressure management:

Recruitment maneuvers and prone positioning:

Rescue therapies for refractory hypoxemia:

Auto-PEEP management (asthma/COPD):

Special Populations — Elderly and Renal/Hepatic Impairment

— Reduced chest wall compliance, sarcopenia of respiratory muscles, blunted hypoxic drive — higher risk of weaning failure and post-extubation respiratory failure.

— Higher delirium risk → minimize benzodiazepines, prefer dexmedetomidine; aggressive non-pharmacologic delirium prevention (orientation, sleep hygiene, family presence, hearing aids/glasses).

— Increased aspiration risk pre- and post-extubation — formal swallow evaluation before PO feeds.

— Frailty predicts mortality independent of APACHE — incorporate into goals-of-care discussions early.

— Dose adjust midazolam (active metabolite accumulates), morphine (M6G accumulates → avoid; prefer fentanyl), rocuronium (modest prolongation), vancomycin, piperacillin-tazobactam.

— Acute metabolic acidosis from AKI compounds respiratory acidosis — may need higher minute ventilation; consider CRRT for severe acidemia.

— Volume overload worsens oxygenation — conservative fluid strategy (FACTT trial) in ARDS after shock resolves.

— Reduced clearance of midazolam, fentanyl (less affected), propofol (mild).

— Hepatic encephalopathy may mimic oversedation — check ammonia, hold sedation, reassess.

— Hepatopulmonary syndrome causes refractory hypoxemia (orthodeoxia) — may need higher FiO₂; consider liver transplant referral.

— Coagulopathy increases risk of airway bleeding during intubation/suctioning.

— Use predicted body weight (not actual) for Vt — same rule.

— Higher PEEP needed (often 10–15) due to atelectasis from chest wall weight.

— Reverse Trendelenburg/ramped positioning improves oxygenation and intubation success.

— Higher risk of difficult airway; pre-oxygenate longer (apneic oxygenation with nasal cannula at 15 L/min during laryngoscopy).

Board pearl: Use predicted body weight based on height and sex, never actual weight, for tidal volume calculation regardless of BMI. Step 3 management: In elderly post-op ICU patients, pair daily SAT/SBT with delirium screening (CAM-ICU) and early mobilization — the bundle that most consistently shortens ventilator days.

Elderly considerations:

Renal impairment:

Hepatic impairment:

Obesity:

Special Populations — Pregnancy, Pediatrics, and Neuromuscular

— Physiologic changes: reduced FRC (20%), increased O₂ consumption, chronic respiratory alkalosis (PaCO₂ ~30, pH ~7.42) — "normal" PaCO₂ of 40 in pregnancy = hypercapnia.

— Target SpO₂ ≥95% (fetus more sensitive to hypoxia).

— Use left lateral tilt 15° to relieve aortocaval compression.

— Airway is more difficult (edema, friable mucosa) — use smaller ETT (6.5–7.0), experienced operator.

— Avoid teratogens in continuous sedation: benzodiazepines OK short-term; avoid prolonged ketamine in 3rd trimester (uterine tone).

— Magnesium for severe asthma and preeclampsia overlaps — watch for neuromuscular weakness contributing to vent dependence.

— Use cuffed ETT for most ages now (size = age/4 + 3.5 cuffed).

— Vt 6 mL/kg, higher RR (infants 25–30, toddlers 20).

— Bradycardia during intubation = hypoxia until proven otherwise; pretreat with atropine in <1 yr or if using succinylcholine.

— NIF/MIP worse than −20 to −30 cm H₂O, FVC <15 mL/kg or <1 L → intubate.

— Avoid succinylcholine in chronic NM disease (hyperkalemia, prolonged paralysis).

— Treat underlying disease (IVIG/plasmapheresis for GBS and myasthenic crisis; pyridostigmine hold during crisis).

— Tracheostomy often needed earlier (anticipate prolonged ventilation).

— Target normoxia (SpO₂ 94–98%) and normocapnia (PaCO₂ 35–45) — both hyper- and hypocapnia worsen brain injury.

— Targeted temperature management 32–36°C × 24h.

Key distinction: In pregnancy, a PaCO₂ of 40 means impending respiratory failure, not normal — recalibrate the threshold. CCS pearl: In suspected GBS or myasthenic crisis, check bedside spirometry (FVC, NIF) every 2–4 hours — falling values predict need for intubation before ABG changes.

Pregnancy:

Pediatrics (basics for Step 3):

Neuromuscular disease (myasthenia, GBS, ALS):

Post-cardiac arrest:

Complications and Adverse Outcomes

— Develops >48h after intubation; new infiltrate + fever/leukocytosis + purulent secretions.

— Empiric antibiotics: cover MRSA (vancomycin/linezolid) + Pseudomonas (cefepime, pip-tazo, or meropenem) if late-onset (>5 days) or risk factors.

— De-escalate based on cultures; 7-day course typically sufficient.

— Prevention bundle: HOB 30°, oral chlorhexidine, subglottic suction ETT, daily SAT/SBT, DVT and stress ulcer prophylaxis.

— Pneumothorax, pneumomediastinum, subcutaneous emphysema.

— Risk factors: high Vt, high Pplat, ARDS, COPD, asthma.

— Treat tension pneumothorax immediately (needle decompression, then chest tube).

— Volutrauma, atelectrauma (repeated open/close), biotrauma (cytokine release).

— Mitigated by lung-protective ventilation.

— Positive pressure decreases venous return → hypotension, especially with high PEEP, hypovolemia, RV failure.

— In RV failure/PE, high PEEP worsens RV afterload — keep PEEP minimal, optimize preload, consider pulmonary vasodilators.

— Critical illness myopathy/polyneuropathy — risk factors: prolonged paralysis, steroids, hyperglycemia, sepsis, immobility.

— Prevention: early mobilization, minimize paralytics, glycemic control.

— Hyperactive, hypoactive (most common, missed), mixed — screen with CAM-ICU.

— Manage with non-pharm bundle; avoid benzodiazepines; haloperidol/atypicals for agitation only short-term.

— Cuff overinflation → ischemia → stenosis, tracheomalacia, tracheoesophageal fistula.

— Keep cuff pressure 20–30 cm H₂O.

Board pearl: Sudden rise in peak pressure + hypotension + unilateral absent breath sounds = tension pneumothorax — decompress before CXR. Step 3 management: New fever on day 4 of MV with new infiltrate → obtain tracheal aspirate culture, start empiric VAP coverage, narrow at 48–72h.

Ventilator-associated pneumonia (VAP):

Barotrauma / volutrauma:

Ventilator-induced lung injury (VILI):

Oxygen toxicity: FiO₂ >0.6 prolonged → absorption atelectasis, free radical lung injury.

Hemodynamic effects:

ICU-acquired weakness:

Delirium:

Tracheal complications:

When to Escalate Care — Consults, Transfer, ECMO

— Need for mechanical ventilation (invasive or NIV with high failure risk)

— Hemodynamic instability requiring vasopressors

— Severe metabolic derangements requiring close monitoring

— High-risk post-procedure (e.g., post-cardiac arrest, massive PE)

— Refractory hypoxemia (P/F <150)

— Failure to wean after 2 weeks

— Suspected complex ARDS requiring advanced strategies

— Tracheostomy decision-making

— Indications: P/F <80 for >6h, P/F <50 for >3h, pH <7.20 with PaCO₂ >60 despite optimization (EOLIA criteria).

— Best in reversible disease (ARDS, severe asthma, bridge to transplant).

— Contraindications: irreversible disease without transplant option, advanced age + comorbidity, severe CNS injury, prolonged MV (>7 days) before referral worsens outcomes — refer early.

— Stabilize airway, secure ETT (tape/holder), confirm placement with ETCO₂ + CXR.

— Transport ventilator settings should match ICU settings; bring extra O₂, sedation, backup BVM.

— Document time-zero for sepsis, stroke, STEMI — does not stop with transfer.

— Tracheostomy typically considered at day 10–14 of MV if extubation unlikely.

— Early trach (<10 days) does NOT improve mortality but may reduce sedation needs and improve comfort.

— Indications: prolonged MV, failed extubation × 2, severe neuro injury with poor airway protection prognosis.

— Trigger criteria: ICU stay >7 days, multiple organ failure, advanced cancer, dementia with recurrent intubation, family conflict about goals.

— Integrates with intensivist — not "withdrawal of care," but goals-concordant care.

CCS pearl: On the CCS, when a patient on max ventilator settings continues to deteriorate (P/F <80, rising Pplat, lactic acidosis), order pulmonary and ECMO consult simultaneously rather than waiting — time-to-cannulation is outcome-critical.

ICU admission criteria — any of:

Pulmonary/critical care consult indicated for:

ECMO referral (VV-ECMO for respiratory failure):

Interhospital transfer considerations:

Surgical airway consult:

Palliative care consult:

Key Differentials — Causes of Acute Respiratory Failure (Same Category)

— ARDS: bilateral opacities, P/F ≤300, not fully explained by cardiac failure; treat with lung-protective MV, prone.

— Pneumonia (CAP/HAP/VAP): focal/multifocal infiltrate, fever, purulent sputum; empiric antibiotics per setting.

— Pulmonary edema (cardiogenic): bilateral perihilar opacities, Kerley B, cardiomegaly; treat with diuresis, NIV, afterload reduction.

— Pulmonary embolism: sudden dyspnea, hypoxia with clear CXR, RV strain on echo, elevated D-dimer; CTA confirms; anticoagulate ± thrombolysis.

— Pneumothorax: unilateral absent breath sounds, hyperresonance; chest tube.

— Diffuse alveolar hemorrhage: hemoptysis, dropping Hgb, ground-glass on CT; vasculitis workup (ANCA, anti-GBM).

— COPD exacerbation: prolonged expiration, wheezing, hyperinflation; bronchodilators, steroids, antibiotics if purulent, NIV first.

— Severe asthma/status asthmaticus: silent chest is preterminal; permissive hypercapnia, ketamine, magnesium, heliox.

— Upper airway obstruction: stridor, angioedema, foreign body, epiglottitis — secure airway emergently.

— Interstitial lung disease acute exacerbation

— Massive pleural effusion → thoracentesis

— Chest wall: flail chest, kyphoscoliosis, severe obesity

— Bilateral, symmetric, no cardiomegaly, no Kerley → ARDS

— Bilateral with cardiomegaly, cephalization, Kerley → cardiogenic edema

— Unilateral consolidation → pneumonia

— Hyperlucent unilateral with mediastinal shift → tension pneumothorax

Key distinction: Cardiogenic vs ARDS pulmonary edema — BNP, echo (EF), PCWP if available, response to diuresis. Both can coexist. ARDS-criteria edema is not fully explained by cardiac failure, requires objective cardiac assessment. Board pearl: Berlin criteria for ARDS require acute onset (<1 week), bilateral opacities, P/F ≤300 on PEEP ≥5, and exclusion of pure cardiogenic etiology.

Pulmonary causes of hypoxemic failure:

Obstructive causes of hypercapnic failure:

Restrictive causes:

Distinguishing features on CXR:

Key Differentials — Non-Pulmonary Mimics

— Brainstem stroke/hemorrhage: abnormal breathing patterns (apneustic, ataxic), depressed consciousness.

— Status epilepticus: post-ictal hypoventilation, aspiration.

— Increased ICP: Cushing's triad, irregular breathing — hyperventilate transiently to PaCO₂ 30–35 only as bridge.

— High cervical spinal cord injury (C3–C5): diaphragm denervation — permanent vent dependence possible.

— Myasthenic crisis: precipitated by infection, surgery, medications (aminoglycosides, beta-blockers).

— Guillain-Barré: ascending weakness, areflexia, albuminocytologic dissociation on LP.

— Botulism: descending paralysis, bulbar first.

— ALS: progressive — anticipate need for NIV then trach; advance care planning critical.

— Organophosphate poisoning: DUMBELS, bronchorrhea, weakness; atropine + pralidoxime.

— Opioid overdose: pinpoint pupils, slow shallow breaths — naloxone, may need ventilation.

— Salicylate toxicity: mixed respiratory alkalosis + anion gap metabolic acidosis — intubation worsens outcomes by reducing compensatory hyperventilation; avoid intubation if possible, dialyze.

— DKA: Kussmaul respirations are compensatory — do NOT intubate just for tachypnea; intubation can be lethal by losing respiratory compensation.

— Severe metabolic acidosis (any cause): respiratory compensation may fatigue → eventual intubation, but match high minute ventilation pre- and post-intubation.

— Cardiogenic shock: pulmonary edema + low output; MV reduces preload and work of breathing.

— Tamponade: positive pressure can precipitate arrest — drain first.

Key distinction: Salicylate overdose and DKA patients with metabolic acidosis depend on hyperventilation for survival. If you intubate, match their pre-intubation minute ventilation (high RR, adequate Vt) to avoid catastrophic acidemia. Step 3 management: In suspected GBS/myasthenia, intubate based on FVC <15 mL/kg or NIF worse than −20, not on ABG — by the time PaCO₂ rises, arrest is imminent.

Neurologic causes of respiratory failure:

Neuromuscular:

Toxic-metabolic:

Cardiac:

Sepsis: increased metabolic demand, ARDS development, encephalopathy with airway compromise.

Weaning, Extubation, and Discharge Planning

— Underlying cause improving

— Adequate oxygenation: P/F >150–200, PEEP ≤8, FiO₂ ≤0.5, SpO₂ ≥90%

— Hemodynamic stability: minimal/no vasopressors

— Able to initiate spontaneous breaths

— Adequate cough, manageable secretions

— 30–120 minutes on PS 5–8 + PEEP 5 or T-piece.

— Pass: stable RR <35, SpO₂ >90%, HR <140, no significant BP change, no diaphoresis/anxiety.

— Rapid shallow breathing index (RSBI) = RR / Vt(L); <105 predicts success.

— Fail → return to prior settings, identify reason (cardiac, respiratory muscle weakness, sedation, agitation), retry next day.

— Deflate cuff; if leak volume <110 mL or <10–15% of Vt → risk of post-extubation stridor → give methylprednisolone 20 mg IV q4h × 4 doses before extubation in high-risk (>6 days MV, female, large ETT, traumatic intubation).

— Confirm awake, following commands, strong cough, adequate clearance.

— Suction, deflate cuff, remove tube on inspiration.

— Place on HFNC or NIV if high-risk (COPD, CHF, obesity, >65, multiple comorbidities) — prophylactic NIV after extubation in COPD reduces reintubation.

— Reassess for cardiac dysfunction (weaning-induced pulmonary edema — diurese, afterload reduce), occult infection, electrolyte (low phos/Mg/K), nutrition, oversedation, ICU-acquired weakness.

— Consider tracheostomy at day 10–14.

— Pulmonary rehab referral for COPD/ILD survivors

— Outpatient pulmonary follow-up in 2–4 weeks

— Vaccinations (influenza, pneumococcal, COVID) before discharge

— Reconcile chronic inhalers, address smoking cessation

— Screen for post-ICU syndrome: cognitive, physical, psychiatric (PTSD/depression) sequelae

CCS pearl: The SAT + SBT pairing (sedation interruption followed by SBT on same morning) is the single most evidence-based intervention to shorten MV duration — order it daily.

Daily readiness screen (perform every morning):

Spontaneous breathing trial (SBT):

Cuff leak test before extubation:

Extubation:

Failure to wean (>7 days SBT failures):

Post-extubation discharge planning:

Follow-Up, Monitoring, and Rehabilitation

— Continuous SpO₂, ETCO₂, telemetry, arterial line for frequent ABGs in unstable

— ABG q6–12h initially, then daily once stable; after any setting change

— Daily CXR is not routine; obtain for clinical change or line/tube placement

— Daily weight, strict I&O — conservative fluid strategy after shock resolves

— Glucose 140–180 target (avoid hypoglycemia)

— Daily CAM-ICU and RASS, CPOT scoring

— Pressure injury prevention — turn q2h, specialty mattress

— Enteral nutrition within 24–48h (preferred over parenteral); 25 kcal/kg/day target; trophic feeds acceptable early in ARDS

— VAP bundle: HOB 30°, oral chlorhexidine, subglottic suction ETT, daily SAT/SBT, DVT ppx, PUD ppx

— ABCDEF bundle: Assess pain, Both SAT/SBT, Choice of analgesia/sedation, Delirium monitoring, Early mobility, Family engagement

— Watch for stridor, hypoxia, hypercapnia, secretions

— Aspiration precautions; bedside swallow eval before PO

— Reintubation rate ~10–15%; risk highest first 24h

— Post-ICU clinic at 4–8 weeks if available — screens for PICS (post-intensive care syndrome): cognitive impairment, ICU-acquired weakness, anxiety/depression/PTSD.

— Physical/occupational therapy, pulmonary rehabilitation, mental health referral as needed.

— Caregivers also affected — "PICS-Family" — provide resources.

— Smoking cessation (varenicline, nicotine replacement, bupropion)

— Vaccinations: influenza annual, pneumococcal (PCV20 or PCV15 + PPSV23), COVID, RSV ≥60

— Advance directives discussion — particularly meaningful after MV experience

— Driving may be restricted if cognitive sequelae

Board pearl: Post-intensive care syndrome (PICS) affects 30–50% of MV survivors — Step 3 expects you to recognize, screen, and refer for multidisciplinary rehab rather than treating recovery as automatic.

In-ICU monitoring while on MV:

Bundles to order routinely (Step 3 favors bundle thinking):

Post-extubation monitoring (first 24–48h):

Post-ICU follow-up:

Counseling at discharge:

Ethical, Legal, and Patient Safety Considerations

— In emergencies, implied consent applies — proceed without waiting for surrogate when delay endangers life.

— For non-emergent intubation (e.g., elective surgery, planned procedure), obtain consent including risks: aspiration, dental injury, vocal cord injury, tracheal stenosis, ICU stay, death.

— If patient has decision-making capacity and refuses intubation despite life-threatening illness, respect the refusal — document capacity assessment (understanding, appreciation, reasoning, communication). Examples: end-stage COPD, terminal cancer, ALS with prior DNR/DNI.

— Always check for DNR/DNI status before intubation — at admission, on transfer, and before code events.

— DNR ≠ DNI — clarify both separately. A patient can be "full code intubate but no chest compressions" (uncommon but valid).

— Surrogate hierarchy in absence of advance directive: spouse → adult children → parents → siblings (varies by state).

— Substituted judgment (what would patient want) > best-interest standard when patient values are known.

— Ethically and legally equivalent to withholding; not euthanasia.

— Compassionate extubation protocols: stop paralytics, titrate opioids/benzodiazepines for comfort (proportionate sedation — doctrine of double effect), extubate, support family.

— Document goals-of-care discussion, surrogate consensus, ethics consult if conflict.

— Wrong-tube events: confirm ETT vs OG tube with two methods (auscultation + ETCO₂ + CXR).

— Unplanned extubation: secure tube, appropriate sedation, restraints only when other measures fail and per protocol.

— Medication errors: high-alert drugs (paralytics, opioids, vasopressors) — independent double-check.

— Transitions of care: structured handoff (I-PASS) — ventilator settings, sedation goals, code status, family contacts. Step 3 emphasizes that transitions are the highest-risk moments for ICU patients.

— Disclose adverse events to patient/family transparently (apology laws in most states protect this).

— Report ventilator-associated events (VAE) per CDC/NHSN if hospital participates.

Step 3 management: When a previously full-code patient with metastatic cancer is intubated and family produces a written advance directive specifying DNI, withdraw ventilation per goals of care with palliative care involvement — continuing MV against documented wishes is both unethical and legally problematic.

Informed consent for intubation:

Advance directives and POLST:

Withdrawal of mechanical ventilation:

Patient safety priorities specific to MV:

Mandatory reporting / disclosure:

High-Yield Associations and Rapid-Fire Clinical Facts

— Men: 50 + 2.3 × (height in inches − 60)

— Women: 45.5 + 2.3 × (height in inches − 60)

Board pearl: The single most tested ventilator concept on Step 3 is lung-protective ventilation with 6 mL/kg PBW in ARDS — know it cold.

Tidal volume: 6 mL/kg PBW in ARDS, 6–8 mL/kg PBW otherwise. Never use actual body weight.

PBW formulas:

Plateau pressure ≤30 cm H₂O; driving pressure ≤15.

PaO₂/FiO₂ ratio: ARDS ≤300 (mild 200–300, moderate 100–200, severe ≤100).

PEEP/FiO₂ table (ARDSnet low): FiO₂ 0.4→PEEP 5; 0.5→8; 0.6→10; 0.7→12; 0.8→14; 0.9→16; 1.0→18–24.

Permissive hypercapnia: pH ≥7.20 acceptable in ARDS and severe asthma.

SpO₂ target: 92–96% general; 88–92% chronic CO₂ retainers; ≥95% pregnancy.

RSBI <105 predicts successful extubation.

Cuff leak <110 mL or <10%: post-extubation stridor risk → steroids pre-extubation.

NIV first-line: COPD exacerbation with pH 7.25–7.35, cardiogenic pulmonary edema, immunocompromised hypoxemia.

NIV contraindications: altered mental status, shock, vomiting, facial trauma, recent upper GI surgery, inability to clear secretions.

DOPE (sudden desat post-intubation): Displaced, Obstructed, Pneumothorax, Equipment.

Auto-PEEP signs: hypotension, expiratory flow not returning to zero, hyperinflation on CXR — disconnect from vent as first maneuver.

Prone positioning: ARDS with P/F <150 — 16 hours/day; mortality benefit (PROSEVA).

VV-ECMO: P/F <80 despite optimization, refer early (before day 7 of MV).

VAP: develops >48h post-intubation; empiric coverage MRSA + Pseudomonas if late-onset or risk factors.

Tracheostomy: consider days 10–14 if extubation unlikely.

Best induction in shock: ketamine or etomidate (avoid propofol).

Best induction in asthma: ketamine (bronchodilator).

Succinylcholine contraindications: hyperkalemia, burns >24h, crush, chronic NM disease, MH history.

Sedation goal: light (RASS −2 to 0); prefer dexmedetomidine/propofol; avoid benzo infusions.

ABCDEF bundle reduces vent days, delirium, mortality — order daily.

Board Question Stem Patterns

Key distinction: When the stem mentions specific numbers (Pplat, P/F, pH, RSBI, cuff leak), there is almost always a threshold-based decision — memorize the thresholds in chunk 18.

Stem 1 — Wrong tidal volume: 78-kg actual / 60-kg PBW man with ARDS on Vt 600 mL, Pplat 34. Best next step? → Reduce Vt to 6 mL/kg PBW (~360 mL) to lower plateau pressure.

Stem 2 — Auto-PEEP: Intubated asthmatic becomes hypotensive minutes after intubation; SpO₂ 92, BP 70/40. Next step? → Disconnect from ventilator to allow exhalation; then resume with lower RR, longer expiratory time, fluids.

Stem 3 — Tension pneumothorax: Sudden rise in peak pressure, hypotension, absent left breath sounds in COPD patient. Best next step? → Needle decompression before CXR.

Stem 4 — Peak vs plateau: PIP 50, Pplat 20. Cause? → Airway resistance (bronchospasm, secretions, mucus plug, tube kinking) → suction, bronchodilators.

Stem 5 — Cuff leak / post-extubation stridor: Cuff leak 50 mL after 7 days MV. Next step? → IV methylprednisolone 4 hours before extubation.

Stem 6 — ARDS rescue: P/F 90 on PEEP 16, FiO₂ 1.0, Vt 6 mL/kg, Pplat 28. Next step? → Prone positioning (16h/day).

Stem 7 — NIV failure: COPD patient on BiPAP 2 hours, pH 7.20, increasing somnolence. Next step? → Endotracheal intubation.

Stem 8 — Salicylate overdose: Tachypnea, AG metabolic acidosis + respiratory alkalosis. Best management? → Bicarbonate, dialysis; AVOID intubation if possible; if intubated, match high minute ventilation.

Stem 9 — Weaning readiness: Improving pneumonia, FiO₂ 0.4, PEEP 5, off pressors, RR 18, alert. Next step? → Spontaneous breathing trial with PS 5 / PEEP 5.

Stem 10 — RSBI: SBT shows RR 28, Vt 350 mL → RSBI = 80 → proceed to extubation (if other criteria met).

Stem 11 — Cardiogenic weaning failure: Patient fails SBT with new pulmonary edema and rising BNP. Cause? → Weaning-induced pulmonary edema — diurese, optimize afterload, retry.

Stem 12 — VAP: Day 5 MV, new fever, infiltrate, purulent secretions. Empiric therapy? → Vancomycin + cefepime/pip-tazo (or meropenem), de-escalate per cultures, 7-day course.

Stem 13 — Pregnancy: 28-week pregnant woman with pneumonia, PaCO₂ 38, RR 32. Interpretation? → "Normal" PaCO₂ in pregnancy = relative hypercapnia; prepare to intubate.

Stem 14 — Goals of care: Metastatic cancer patient intubated emergently; family produces DNI directive. Next step? → Compassionate extubation with palliative care, opioid titration for comfort.

Stem 15 — Failure to wean: Day 12 of MV, repeated SBT failures, no clear reversible cause. Next step? → Tracheostomy.

One-Line Recap

Mechanical ventilation success on Step 3 hinges on three things: (1) recognizing failure early and choosing the right initial settings for the underlying disease, (2) applying lung-protective principles — 6 mL/kg PBW, Pplat ≤30, driving pressure <15, SpO₂ 92–96% — across all patients while individualizing PEEP, rate, and I:E ratio, and (3) executing daily SAT + SBT pairing within the ABCDEF bundle to extubate at the earliest safe moment.

Board pearl: If forced to remember a single number on Step 3 ventilator questions, it is 6 mL/kg of predicted body weight — it appears, directly or indirectly, in the majority of MV stems and anchors every other lung-protective decision you will make at the bedside or on the CCS.

Initial settings default: AC/VC, Vt 6 mL/kg PBW, RR 12–16, PEEP 5, FiO₂ 100% then wean to SpO₂ 92–96%, then ABG at 30 min.

Disease-specific tweaks: ARDS → low Vt + high PEEP + prone if P/F <150; obstructive disease → low rate, long expiratory time, permissive hypercapnia, watch auto-PEEP; neuromuscular → standard lung settings, intubate based on FVC/NIF.

Weaning algorithm: daily readiness screen → SAT → SBT (PS 5/PEEP 5 × 30–120 min) → cuff leak test → extubate to HFNC or prophylactic NIV in high-risk; tracheostomy at days 10–14 if extubation unlikely.

Never miss: lung-protective Vt by PBW, plateau pressure measurement, DOPE for sudden desaturation, peak-vs-plateau differential, code status before/after intubation, post-ICU syndrome screening at follow-up.