3.1 Severe Asthma & COPD Exacerbations in the ICU

ABIM Critical Care Medicine Study Guide Exam

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1 Chapter 1: Exam Orientation: Format, Blueprint & Study Strategy

1.1 ABIM Critical Care Medicine Exam: Format, Blueprint & Study Strategy

2 Chapter 2: Acute Respiratory Failure & ARDS

2.1 ARDS Definition, Pathophysiology & Phenotypes 2.2 Lung-Protective Mechanical Ventilation 2.3 Refractory ARDS: Prone Positioning, Neuromuscular Blockade & VV-ECMO

3 Chapter 3: Obstructive Airways, Pulmonary Vascular & Pleural Emergencies

3.1 Severe Asthma & COPD Exacerbations in the ICU 3.2 Massive & Submassive Pulmonary Embolism 3.3 Pulmonary Hypertension & Right Ventricular Failure in the ICU 3.4 Massive Hemoptysis, Complex Pleural Effusions & Thoracic Drainage

4 Chapter 4: Airway, Parenchymal & Nonthrombotic Pulmonary Emergencies

4.1 Airway Management, Upper-Airway Obstruction & Artificial-Airway Complications 4.2 Diffuse Alveolar Hemorrhage, Interstitial Lung Disease, Pulmonary Vasculitis & Noncardiogenic Edema 4.3 Severe Community-Acquired & Viral Pneumonia 4.4 Nonthrombotic Embolism (Air, Fat, Amniotic Fluid, Tumor, Septic) & Acute Chest Syndrome

5 Chapter 5: Mechanical Ventilation Modes, Dyssynchrony & Liberation

5.1 Mechanical Ventilator Modes & Advanced Breath Delivery 5.2 Patient-Ventilator Dyssynchrony & Waveform Analysis 5.3 Ventilator Liberation, Spontaneous Breathing Trials & Post-Extubation Support

6 Chapter 6: Shock Syndromes & Hemodynamic Principles

6.1 Shock Classification, Cellular Pathophysiology & Biomarkers 6.2 Hemodynamic Monitoring: Arterial Lines, CVP & Pulmonary Artery Catheter 6.3 Dynamic Assessment of Fluid Responsiveness & Resuscitation Targets

7 Chapter 7: Vasoactive Therapies & Mechanical Circulatory Support

7.1 Vasopressors & Inotropes: Pharmacology & Clinical Titration 7.2 Temporary Mechanical Circulatory Support: IABP, Impella & TandemHeart 7.3 Venoarterial ECMO (VA-ECMO) & Differential Hypoxemia 7.4 Post-Cardiac Arrest Care, Targeted Temperature Management & Neuroprognostication

8 Chapter 8: Acute Kidney Injury & Renal Replacement Therapy

8.1 KDIGO AKI Classification, Etiologies & Diagnostic Evaluation 8.2 Continuous Renal Replacement Therapy (CRRT) vs Intermittent Hemodialysis 8.3 Indications & Timing for RRT in Critical Illness: AKIKI & STARRT-AKI

9 Chapter 9: Electrolyte, Acid-Base & Endocrine Emergencies

9.1 Severe Dysnatremias: Hyponatremia, Hypernatremia & Osmotic Demyelination 9.2 Potassium, Calcium, Magnesium & Phosphate Disorders 9.3 Complex & Mixed Acid-Base Disorders: Boston vs Copenhagen vs Stewart 9.4 Endocrine Crises: DKA, HHS, Thyroid Storm, Myxedema Coma & Adrenal Crisis

10 Chapter 10: Glycemic Control, Hyperammonemia, Pituitary & Adrenal Disorders

10.1 ICU Glycemic Control & Severe Hypoglycemia 10.2 Non-Hepatic Hyperammonemia & Metabolic Encephalopathy 10.3 Pituitary Emergencies, Adrenal Excess & Critical Illness-Related Corticosteroid Insufficiency

11 Chapter 11: Acute Coronary Syndromes & Cardiac Arrhythmias

11.1 Acute Coronary Syndromes & Mechanical Complications of Myocardial Infarction 11.2 Critical Tachyarrhythmias: Atrial Fibrillation with RVR, VT & VF 11.3 Critical Bradyarrhythmias, Conduction Blocks & Temporary Cardiac Pacing

12 Chapter 12: Acute Heart Failure, Valvular & Pericardial Emergencies

12.1 Acute Decompensated Heart Failure & Cardiogenic Pulmonary Edema 12.2 Acute Valvular Regurgitation & Prosthetic Valve Emergencies 12.3 Pericardial Tamponade & Acute Aortic Syndromes

13 Chapter 13: Myocardial Disease, Hypertensive & Cardiac Device Emergencies

13.1 Fulminant Myocarditis, Stress & Peripartum Cardiomyopathy, and Hypertrophic Cardiomyopathy 13.2 Hypertensive Emergencies & Ruptured Abdominal Aortic Aneurysm 13.3 Implanted Cardiac Devices, LVAD Emergencies & Electrical Storm

14 Chapter 14: Sepsis & Systemic Infectious Diseases

14.1 Sepsis-3 Definitions & Surviving Sepsis Campaign 2026 Guidelines 14.2 Refractory Septic Shock & Adjunctive Therapies 14.3 Multidrug-Resistant Pathogens & Antimicrobial Stewardship in the ICU

15 Chapter 15: ICU-Acquired & Severe Focal Infections

15.1 Hospital-Acquired & Ventilator-Associated Pneumonia 15.2 Central Line-Associated Bloodstream Infections & Catheter-Associated UTIs 15.3 Intra-Abdominal Sepsis, Necrotizing Soft Tissue Infections & CNS Infections

16 Chapter 16: Focal, Special-Host & Systemic Infections

16.1 CNS Infections Beyond Bacterial Meningitis: Encephalitis, Brain Abscess & Epidural Abscess 16.2 Infections in the Immunocompromised Host, Tropical & Bioterror Infections 16.3 Infective Endocarditis, Device Infections & Other Focal Cardiovascular Infections 16.4 Antimicrobial Pharmacokinetics, Allergy, Toxicity & Infection Prevention 16.5 Gastrointestinal & Hepatobiliary Infections: Fulminant C. difficile, Typhlitis, CMV Colitis & Abscesses

17 Chapter 17: Neurocritical Care & Coma

17.1 Coma, Altered Mental Status & Acute Delirium in the ICU 17.2 Status Epilepticus & Non-Convulsive Status Epilepticus 17.3 Acute Ischemic Stroke & Intracranial Hemorrhage

18 Chapter 18: Cerebrovascular Syndromes, Encephalopathy & Withdrawal States

18.1 Cerebral Venous Sinus Thrombosis, PRES & Reversible Cerebral Vasoconstriction Syndrome 18.2 Alcohol & Sedative Withdrawal, Wernicke Encephalopathy & Drug-Induced Encephalopathy

19 Chapter 19: Intracranial Hypertension & Neuromuscular Weakness

19.1 Intracranial Pressure Monitoring, Cerebral Perfusion & Tiered ICP Management 19.2 Acute Neuromuscular Respiratory Failure, ICU-Acquired Weakness & Brain Death Determination

20 Chapter 20: Traumatic Brain Injury, Spinal Cord Injury & Toxin-Mediated Paralysis

20.1 Traumatic Brain Injury Management & Paroxysmal Sympathetic Hyperactivity 20.2 Acute Spinal Cord Injury, Neurogenic Shock & Autonomic Dysreflexia 20.3 Toxin-Mediated Paralysis & Neuromuscular Crises: Botulism, Tetanus, Tick Paralysis & Myasthenic Crisis

21 Chapter 21: Gastrointestinal, Hepatic & Abdominal Emergencies

21.1 Acute Upper & Lower Gastrointestinal Bleeding in the ICU 21.2 Acute Liver Failure & Severe Acute Pancreatitis 21.3 Abdominal Compartment Syndrome & Acute Mesenteric Ischemia

22 Chapter 22: Luminal GI Emergencies & Complications of Cirrhosis

22.1 Esophageal, Gastric & Bowel Emergencies: Perforation, Obstruction, Ogilvie Syndrome & Colonic Ischemia 22.2 Complications of Cirrhosis: Alcohol-Associated Hepatitis, Hepatorenal Syndrome & Pulmonary Vascular Syndromes

23 Chapter 23: Trauma, Burns & Perioperative Critical Care

23.1 Polytrauma Resuscitation, Damage Control & Massive Transfusion 23.2 Severe Burn Injury, Inhalation Injury & Environmental Emergencies 23.3 Perioperative Critical Care for High-Risk Surgical Patients

24 Chapter 24: Thoracic Trauma, Environmental Injury & Obstetric Critical Care

24.1 Thoracic Trauma: Flail Chest, Pulmonary Contusion, Great Vessel & Tracheobronchial Injury 24.2 Environmental Injury: Drowning, Diving, Altitude, Heat, Cold, Electrical & Radiation 24.3 Obstetric & Genitourinary Emergencies and the Physiology of Pregnancy

25 Chapter 25: Transplantation, Donor Management & Post-Cardiac Surgery Care

25.1 Solid Organ Transplant Recipients & Deceased Donor Management 25.2 Post-Cardiac Surgery Critical Care: Bleeding, Tamponade, Low Output & Vasoplegia

26 Chapter 26: Hematologic Emergencies, Toxicology, Critical Ultrasound & ICU Liberation

26.1 Hematologic Emergencies in the ICU: HIT, DIC, TMA & Anticoagulant Reversal 26.2 Critical Care Toxicology, Toxidromes & Specific Antidotes 26.3 Critical Care Point-of-Care Ultrasound (POCUS) 26.4 ICU Liberation, Analgosedation, Goals of Care & Critical Care Ethics

27 Chapter 27: Transfusion Medicine, Hematologic & Oncologic Disorders

27.1 Transfusion Medicine: Products, Thresholds, Reactions & Apheresis 27.2 Red and White Cell Disorders, Hemoglobinopathies, Factor Deficiencies & Hypercoagulable States 27.3 Oncologic Emergencies, Hematopoietic Cell Transplant Complications & Cellular Therapy Toxicity

28 Chapter 28: Clinical Pharmacology, Adverse Drug Reactions & Specific Poisonings

28.1 Pharmacokinetic Principles, Dose Adjustment & Drug Interactions in Critical Illness 28.2 Adverse Drug Reactions: Anaphylaxis, Severe Cutaneous Reactions & Hyperthermic Syndromes 28.3 Specific Poisonings: Sodium-Channel Blockers, Lithium, Valproate, Theophylline, Iron, Sulfonylureas & Methemoglobinemia

29 Chapter 29: Ethics, Research Methods, Administration & Abdominal Ultrasound

29.1 Advance Care Planning, Nonbeneficial Treatment, Informed Consent & Confidentiality 29.2 Critical Care Research Methods, Statistics, IRB Oversight & Quality Improvement 29.3 Abdominal, Vascular & Procedural Point-of-Care Ultrasound

3.1 Severe Asthma & COPD Exacerbations in the ICU

Key Takeaways Explain This Topic AI

Dynamic hyperinflation leads to intrinsic positive end-expiratory pressure (auto-PEEP), which causes hemodynamic collapse by reducing venous return, shifting the interventricular septum, and decreasing left ventricular preload.

Auto-PEEP is quantified during invasive mechanical ventilation by performing an end-expiratory hold maneuver, calculating total PEEP minus set extrinsic PEEP.

Bilevel NIV carries a strong recommendation (ERS/ATS 2017) for COPD exacerbations with acute or acute-on-chronic hypercapnic acidosis (pH <= 7.35), reducing intubation (RR ~0.36) and mortality (RR ~0.54); the same guideline makes no recommendation for asthma.

Mechanical ventilation in severe obstructive disease requires a low respiratory rate (10-14 breaths/min), high peak inspiratory flow (70-90 L/min), long expiratory time (I:E ratio 1:3 to 1:5), and permissive hypercapnia while maintaining plateau pressure ≤30 cmH2O.

Sudden hypotension or PEA arrest after intubation in severe bronchospasm warrants immediate disconnection from the ventilator circuit and bilateral manual chest wall compression to evacuate trapped alveolar gas.

Last updated: October 2026

Acute exacerbations of obstructive airway disease—encompassing acute severe asthma (status asthmaticus) and acute exacerbations of chronic obstructive pulmonary disease (AECOPD)—represent frequent, high-stakes medical emergencies in the intensive care unit. While both conditions present with expiratory airflow limitation, tachypnea, and respiratory distress, their underlying cellular pathophysiology, airway mechanics, dynamic response to positive pressure ventilation, and evidence-based indications for noninvasive versus invasive support differ significantly.

Pathophysiology of Airflow Limitation

Expiratory airflow limitation in obstructive airway diseases arises from marked increases in airway resistance ( R aw R_{\text{aw}} R aw ) and altered respiratory system elastance ( E rs E_{\text{rs}} E rs ).

Acute Severe Asthma

In status asthmaticus, the primary pathology is intense, acute smooth muscle contraction coupled with airway wall mucosal edema, eosinophilic and neutrophilic inflammation, and extensive intraluminal inspissation of tenacious mucus plugs throughout the bronchial tree.

Because lung parenchymal architecture and alveolar elastic recoil are largely preserved, airflow limitation in asthma is primarily dynamic and resistance-driven . The high resistance markedly prolongs the expiratory time constant of the respiratory system ( τ = R aw × C rs \tau = R_{\text{aw}} \times C_{\text{rs}} τ = R aw × C rs ), requiring substantially longer duration for passive exhalation.

Chronic Obstructive Pulmonary Disease (COPD)

In AECOPD, airflow limitation results from a combination of chronic small airway inflammation (bronchiolitis with peribronchiolar fibrosis) and irreversible destruction of the alveolar capillary bed and parenchymal matrix (pulmonary emphysema).

The progressive loss of radial alveolar tethering reduces the outward mechanical traction on small conducting airways, leading to dynamic expiratory airway collapse . In COPD, the equal pressure point—the anatomic locus along the airway where intraluminal pressure matches peribronchial tissue pressure—shifts upstream toward small, non-cartilaginous bronchioles during active exhalation, resulting in premature airway closure and profound gas trapping.

Dynamic Hyperinflation, Auto-PEEP, and Hemodynamics
The Mechanism of Gas Trapping

When respiratory rate and airway resistance are elevated, the expiratory time ( T E T_E T E ) allotted by the patient's breathing cycle or ventilator settings is shorter than the time required for passive deflation back to the relaxed functional residual capacity (FRC). Subsequent inspiration begins before full exhalation is completed, causing progressive air trapping—a state termed dynamic hyperinflation .

This trapped alveolar gas exerts positive pressure throughout the lung parenchyma at end-expiration, creating intrinsic positive end-expiratory pressure (auto-PEEP) . Dynamic Airflow Obstruction (High Raw) + Short Expiratory Time (TE)

│
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Incomplete Passive Alveolar Emptying
│
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Progressive Air Trapping (Dynamic Hyperinflation)
│
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Auto-PEEP (Intrinsic Alveolar Pressure)
┌────────────┴────────────┐
▼ ▼
Inspiratory Threshold Load Hemodynamic Collapse
(Increased Work of Breathing) (Decreased Venous Return)
Measuring Auto-PEEP

In an intubated, passively ventilated patient (without spontaneous respiratory efforts), auto-PEEP is quantified on the mechanical ventilator by executing an end-expiratory hold maneuver for 2 to 3 seconds:

At end-expiration, the expiratory valve closes, preventing gas escape.

Alveolar pressure equilibrates with the pressure transducer in the ventilator circuit.

The total measured pressure represents total PEEP ( P tot P_{\text{tot}} P tot ).

Auto-PEEP is calculated as:

auto-PEEP = P tot − PEEP extrinsic \text{auto-PEEP} = P_{\text{tot}} - \text{PEEP}_{\text{extrinsic}} auto-PEEP = P tot − PEEP extrinsic

Note

In actively breathing, non-paralyzed patients, auto-PEEP cannot be accurately measured with a ventilator end-expiratory hold because patient respiratory muscle effort distorts circuit pressure equilibration. An esophageal balloon catheter measuring end-expiratory esophageal pressure fluctuations is required for definitive quantification in spontaneously breathing subjects.

Hemodynamic Compromise and the "Tamponade of the Lung"

Dynamic hyperinflation produces profound circulatory derangements:

Reduced Venous Return: Elevated intrathoracic pressure compresses the superior and inferior vena cava and right atrium, collapsing the extrathoracic-to-intrathoracic venous pressure gradient and drastically reducing right ventricular (RV) preload.

Increased RV Afterload: Alveolar overdistension stretches and compresses intra-alveolar capillaries, increasing pulmonary vascular resistance (PVR).

Ventricular Interdependence: RV dilation within the constrained pericardial space shifts the interventricular septum leftward, compressing the left ventricle (LV), impairing LV diastolic filling, and precipitating sudden cardiogenic/obstructive shock.

Arrest Phenomenon: In extreme breath-stacking, cardiac output drops to near-zero, culminating in pulseless electrical activity (PEA) arrest.

Noninvasive Ventilation: COPD vs. Asthma

Clinical Metric COPD Exacerbation Severe Status Asthmaticus
Guideline Status (ERS/ATS 2017) Strong recommendation No recommendation (insufficient evidence)

Primary Physiologic Target Unloads fatigued diaphragmatic muscles, overcomes threshold load of auto-PEEP Relieves respiratory muscle fatigue; variable effect on dynamic hyperinflation

Intubation Reduction Reduces intubation risk by ~60–65% Unproven; small case series show variable outcomes
Mortality Benefit Reduces mortality (Cochrane 2017: RR ~0.54) No demonstrated mortality benefit

Extrinsic PEEP Setting 4–8 cmH2O (counterbalances dynamic airway collapse) 0–4 cmH2O (risks worsening hyperinflation if excessive)

Failure & Complication Rate Low in early intervention (10–15% failure) High (up to 40–50% failure in severe acidosis)

Noninvasive Ventilation in COPD

Noninvasive positive-pressure ventilation (NIV/BiPAP) is a cornerstone of therapy in acute hypercapnic respiratory failure from COPD ( pH < 7.35 \text{pH} < 7.35 pH < 7.35 and PaCO 2 > 45 mmHg \text{PaCO}_2 > 45\text{ mmHg} PaCO 2 > 45 mmHg ).

By delivering an inspiratory positive airway pressure (IPAP) that supplements tidal breathing and an expiratory positive airway pressure (EPAP) that counterbalances auto-PEEP, NIV drastically reduces diaphragmatic work, reverses acute hypercapnic encephalopathy, shortens hospital length of stay, and prevents endotracheal intubation and its attendant complications (ventilator-associated pneumonia, tracheal injury, difficult weaning).

Noninvasive Ventilation in Asthma

In severe asthma, evidence supporting NIV is markedly weaker. Severe asthma is characterized by dynamic diffuse bronchospasm and thick secretions rather than the dynamic airway collapse seen in emphysema. High positive airway pressures can exacerbate air trapping and induce barotrauma (pneumothorax, pneumomediastinum).

NIV should only be trialed in highly selected, fully conscious, cooperative asthmatic patients with mild-to-moderate respiratory acidosis who do not exhibit signs of imminent exhaustion. If clear improvement in tachypnea, work of breathing, and gas exchange is not evident within 60 to 90 minutes, prompt endotracheal intubation is mandatory.

Contraindications to NIV
Respiratory arrest or gasping respirations
Inability to clear copious respiratory secretions or frank hemoptysis
Severe encephalopathy or coma (Glasgow Coma Scale score < 8 < 8 < 8 )
Uncooperative, combative, or agitated delirium
Facial trauma, severe burns, or craniofacial anatomic abnormalities precluding mask fit
Acute upper gastrointestinal hemorrhage, bowel obstruction, or intractable vomiting (high aspiration risk)
Severe hemodynamic instability requiring escalating vasoactive infusions
Endotracheal Intubation & Airway Management
Indications for Invasive Mechanical Ventilation
Progression to respiratory arrest or severe bradypnea

Profound exhaustion manifested by "silent chest" (disappearance of wheezing and breath sounds due to minimal airflow)

Altered mental status: lethargy, stupor, or agonal agitation

Worsening respiratory acidosis ( pH < 7.15 – 7.20 \text{pH} < 7.15–7.20 pH < 7.15–7.20 ) despite intensive pharmacotherapy and noninvasive trials

Refractory hypoxemia ( PaO 2 < 60 mmHg \text{PaO}_2 < 60\text{ mmHg} PaO 2 < 60 mmHg on maximal supplemental oxygen)

Hemodynamic collapse, refractory shock, or life-threatening arrhythmias
Critical Airway Risks During Intubation

Intubating an individual with severe bronchospasm is one of the most perilous airway procedures in critical care. Two lethal complications frequently occur during or immediately following induction:

Profound Post-Induction Hypotension: Rapid loss of endogenous sympathetic tone from sedative agents, compounded by immediate conversion from negative-pressure spontaneous ventilation to high positive-pressure ventilation, severely curtails venous return. Intravascular volume expansion with 500 to 1,000 mL crystalloid should be administered preemptively.

Catastrophic Breath-Stacking: Manual bag-valve-mask hyperventilation at rates of 20 to 30 breaths/min traps immense volumes of gas in seconds, creating high intrathoracic pressure and immediate electromechanical dissociation.

Rapid Sequence Intubation Strategy

Induction Agent: Ketamine (1.5–2.0 mg/kg IV) is the agent of choice. It triggers endogenous catecholamine release, relaxes bronchial smooth muscle via NMDA receptor antagonism and muscarinic pathway inhibition, and maintains systemic vascular tone.

Paralytic Agent: Rocuronium (1.2 mg/kg IV) or succinylcholine (1.5 mg/kg IV). Rocuronium is preferred when prolonged paralysis is anticipated to allow ventilator synchronization. Histamine-releasing muscle relaxants (such as atracurium) must be avoided.

Tube Caliber: Select a large endotracheal tube (ETT ≥ 8.0 mm \ge 8.0\text{ mm} ≥ 8.0 mm inner diameter for adults). Airway resistance through an ETT is inversely proportional to the fourth power of the radius (Poiseuille's law); larger tubes dramatically reduce resistance and facilitate subsequent bronchoscopy and suctioning.

Mechanical Ventilation Strategy in Severe Bronchospasm

The overarching principle of mechanical ventilation in status asthmaticus and severe COPD is lung protection through dynamic decompression . Clinicians must avoid the temptation to normalize arterial blood gases, adhering instead to the paradigm of permissive hypercapnia . Ventilator Goals in Severe Bronchospasm:

┌──────────────────────────────┬──────────────────────────────┐
│ Ventilator Parameter │ Target Goal │
├──────────────────────────────┼──────────────────────────────┤
│ Mode │ Volume Control (Assist/Ctrl) │
│ Tidal Volume (VT) │ 6–8 mL/kg PBW (often 5–7) │
│ Respiratory Rate (RR) │ 10–14 breaths/min │
│ Peak Inspiratory Flow │ 70–90 L/min (Square wave) │
│ Inspiratory:Expiratory (I:E) │ 1:3 to 1:5 │
│ Plateau Pressure (Pplat) │ ≤30 cmH2O │
│ Permissive Hypercapnia │ pH ≥7.15–7.20 (PaCO2 60–90) │
└──────────────────────────────┴──────────────────────────────┘
Setting the Ventilator

Tidal Volume ( V T V_T V T ): 6 to 8 mL/kg of predicted body weight (PBW). In extreme asthma, reducing V T V_T V T to 5 to 6 mL/kg PBW may be necessary to control plateau pressures.

Respiratory Rate ( R R RR RR ): 10 to 14 breaths/min. A low rate is the single most effective intervention to prolong expiratory time ( T E T_E T E ) and allow complete exhalation.

Inspiratory Flow Rate: Deliver gas at a high peak inspiratory flow rate of 70 to 90 L/min (up to 100 L/min) using a square or descending decelerating waveform. High inspiratory flow shortens the inspiratory time ( T I T_I T I ), thereby expanding available T E T_E T E to achieve an I : E I:E I : E ratio of 1:3, 1:4, or 1:5.

Extrinsic PEEP ( P ext P_{\text{ext}} P ext ):

In Asthma: Set PEEP to zero (ZEEP) or minimal ( 0 – 5 cmH 2 O 0–5\text{ cmH}_2\text{O} 0–5 cmH 2 O ). In asthma, airflow obstruction is diffuse and resistance-mediated (bronchospasm, mucus plugging, wall edema) rather than caused by dynamic expiratory collapse, so extrinsic PEEP is more likely to add to end-expiratory lung volume and barotrauma risk.

In COPD: In patients who are triggering the ventilator, set extrinsic PEEP to approximately 70% to 80% of measured auto-PEEP (in a fully passive patient it offers little benefit). In COPD, airway closure is dynamic. Applying extrinsic PEEP splints open dynamically collapsed downstream airways, acting like a "waterfall" to reduce the inspiratory threshold work of breathing without elevating upstream alveolar pressure.

Plateau Pressure vs. Peak Inspiratory Pressure

Clinicians must differentiate between peak inspiratory pressure ( P peak P_{\text{peak}} P peak ) and plateau pressure ( P plat P_{\text{plat}} P plat ):

P peak = ( Flow × R aw ) + P plat P_{\text{peak}} = \left( \text{Flow} \times R_{\text{aw}} \right) + P_{\text{plat}} P peak = ( Flow × R aw ) + P plat

P peak P_{\text{peak}} P peak is frequently elevated to 50 to 70 cmH2O in severe bronchospasm due to extreme resistance across conducting airways and the endotracheal tube. Elevated P peak P_{\text{peak}} P peak alone does not rupture alveoli and is not an independent marker of barotrauma.

P plat P_{\text{plat}} P plat (measured with a 0.5-second end-inspiratory pause) reflects static alveolar distending pressure. To protect the lung from alveolar rupture and barotrauma, P plat P_{\text{plat}} P plat must be maintained ≤ 30 cmH 2 O \le 30\text{ cmH}_2\text{O} ≤ 30 cmH 2 O .

Tip

If P peak P_{\text{peak}} P peak is 60 cmH2O but P plat P_{\text{plat}} P plat is 22 cmH2O, the elevated pressure is entirely dissipated across high-resistance airways; the alveoli are safely protected from barotrauma.

Medical Management of Severe Bronchospasm in the ICU First-Line Inhaled Therapies:

├── Continuous nebulized albuterol (10–20 mg/hr) or MDI with in-line spacer (4–8 puffs q15–30min)
└── Inhaled ipratropium bromide (0.5 mg nebulized q4–6h)

Systemic Pharmacotherapy:

├── Systemic corticosteroids: asthma - methylprednisolone 40–60 mg IV q6–12h; COPD - prednisone 40 mg daily x 5 days (or IV equivalent)

├── Intravenous magnesium sulfate: 2 g IV over 20 minutes (blocks smooth-muscle calcium influx)
└── Ketamine infusion: 0.5–2.0 mg/kg/hr IV for bronchodilatory sedation

Refractory Rescue Options:

├── Inhalational volatile anesthetics (sevoflurane, isoflurane via ICU vaporizers)
├── Neuromuscular blockade: Cisatracurium infusion (to eliminate ventilator dyssynchrony)
└── Extracorporeal Membrane Oxygenation: Veno-venous (VV) ECMO for refractory hypercapnic arrest
Pharmacologic Adjuncts

Inhaled Beta-2 Agonists: Albuterol delivered continuously (10 to 20 mg/hr) or via frequent metered-dose inhalers (MDIs) with an in-line spacer chamber (4 to 8 puffs every 15 to 30 minutes).

Inhaled Anticholinergics: Ipratropium bromide (0.5 mg nebulized every 4 to 6 hours) acts synergistically with beta-agonists by blocking muscarinic bronchoconstriction.

Systemic Corticosteroids: In severe asthma, methylprednisolone 40 to 60 mg IV every 6 to 12 hours (oral prednisone is equally effective when it can be absorbed; higher doses add toxicity without proven benefit) accelerates resolution of airway inflammation and restores beta-2 receptor responsiveness. In COPD exacerbations, prednisone 40 mg daily for 5 days was noninferior to 14 days in the REDUCE trial; use the IV equivalent in intubated patients.

Antibiotics in AECOPD: Give antibiotics when sputum purulence accompanies increased dyspnea or sputum volume, and for every patient who needs NIV or invasive ventilation; they reduce treatment failure and, in ventilated patients, mortality. Antibiotics are not routinely indicated in asthma unless pneumonia or another bacterial infection is present.

Intravenous Magnesium Sulfate: 2 grams IV infused over 20 minutes (can be repeated once). Magnesium inhibits voltage-gated calcium channels in bronchial smooth muscle, producing direct relaxation.

Continuous Ketamine: An infusion of 0.5 to 2.0 mg/kg/hr provides combined analgosedation and smooth muscle bronchodilation.

Inhalational Anesthetics: Volatile agents (isoflurane, sevoflurane) delivered via dedicated ICU volatile gas scavenging delivery systems (such as the Anaesthetic Conserving Device) directly relax bronchial smooth muscle in life-threatening refractory status asthmaticus.

Neuromuscular Blockade: A continuous infusion of cisatracurium eliminates patient-ventilator dyssynchrony, tachypnea, and chest wall rigidity that exacerbate breath-stacking. Continuous paralytic use should be limited to the minimum effective duration ( < 24 – 48 hours < 24–48\text{ hours} < 24–48 hours ) and monitored with peripheral nerve stimulation (train-of-four) to mitigate the high risk of acute quadriplegic myopathy of intensive care, especially when co-administered with high-dose corticosteroids.

Acute Decompression for Breath-Stacking & Sudden Hypotension

If an intubated patient with severe obstructive airway disease develops sudden hemodynamic collapse, profound bradycardia, or pulseless electrical activity (PEA): Sudden Hypotension / PEA Arrest in Mechanically Ventilated Obstructive Patient

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STEP 1: IMMEDIATELY DISCONNECT PATIENT FROM VENTILATOR CIRCUIT
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STEP 2: PERFORM MANUAL BILATERAL CHEST WALL COMPRESSION
(Evacuates trapped alveolar volume; wait 15–30 sec)
│
┌───────────────────┴───────────────────┐
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Hemodynamics Restore Within 30s Persistent Collapse / Absent Breath Sounds
│ │
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Diagnosis: Dynamic Hyperinflation Evaluate for Tension Pneumothorax
(Auto-PEEP Overdistension) Perform Immediate Needle/Finger Thoracostomy
Reconnect ventilator with: Followed by Tube Thoracostomy
Lower RR (10–12 bpm)
Lower VT (5–6 mL/kg PBW)
Higher peak flow (80–90 L/min)
Zero/low extrinsic PEEP

Warning

Do not administer empiric CPR chest compressions or high-dose vasopressors before disconnecting the endotracheal tube! If the arrest is driven by dynamic hyperinflation, cardiac output cannot recover until the trapped alveolar gas is decompressed.