10.4 Acute Respiratory Failure, Airway Emergencies & Oxygen Delivery Modalities

Acute Respiratory Failure, Airway Emergencies & Oxygen Delivery Modalities

Clinical Core: Acute respiratory failure represents the inability of the pulmonary system to maintain adequate systemic oxygenation, eliminate carbon dioxide, or both. It is not an isolated disease entity but rather the severe pathophysiological endpoint of diverse conditions affecting the airways, alveolar-capillary membranes, thoracic cage, or central respiratory control centers. Safe nursing practice requires precise arterial blood gas interpretation, mastery of low-flow and high-flow oxygenation modalities, and immediate, decisive interventions for catastrophic airway emergencies.

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Classification of Acute Respiratory Failure: Type 1 Hypoxemic vs. Type 2 Hypercapnic

Acute respiratory failure is fundamentally classified into two pathophysiological categories based on arterial blood gas parameters.

Type 1: Hypoxemic Respiratory Failure ("Lung Failure")

• Diagnostic Criteria: $PaO_2 < 60\text{ mmHg}$ on room air (or an $SpO_2 < 90\%$) with a normal or decreased $PaCO_2$ ($< 45\text{ mmHg}$).
• Primary Pathophysiology: Severe ventilation-perfusion ($V/Q$) mismatch or intrapulmonary shunting (blood traversing non-aerated pulmonary capillaries without participating in gas exchange). Secondary causes include alveolar diffusion impairment and alveolar hypoventilation.
• Common Etiologies: Acute Respiratory Distress Syndrome (ARDS), severe pneumonia, cardiogenic pulmonary edema, pulmonary contusion, and massive pulmonary embolism.
• Clinical Presentation: Dyspnea, profound tachypnea, air hunger, intercostal retractions, cyanosis, restlessness, tachycardia, and hypertension transitioning to bradycardia and hypotension as tissue hypoxia worsens.

Type 2: Hypercapnic Respiratory Failure ("Pump Failure")

• Diagnostic Criteria: $PaCO_2 > 50\text{ mmHg}$ accompanied by acute respiratory acidemia ($\text{pH} < 7.35$). $PaO_2$ is commonly decreased unless supplemental oxygen is administered.
• Primary Pathophysiology: Alveolar hypoventilation, where minute ventilation ($V_E = \text{Tidal Volume} \times \text{Respiratory Rate}$) is insufficient to excrete metabolic carbon dioxide.
• Common Etiologies: Acute exacerbation of COPD, severe status asthmaticus with respiratory muscle fatigue, central nervous system depression (opioid overdose, traumatic brain injury), neuromuscular diseases (Guillain-Barré syndrome, myasthenia gravis), and severe thoracic deformities (flail chest, kyphoscoliosis).
• Clinical Presentation: Tachypnea followed by progressive bradypnea and shallow breathing, morning occipital headache (due to $CO_2$-mediated cerebral vasodilation), facial flushing, bounding pulses, asterixis (flapping hand tremor), progressive somnolence, confusion, and coma ($CO_2$ narcosis).

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Arterial Blood Gas (ABG) Systematic Analysis & Compensation

Arterial blood gas analysis evaluates alveolar ventilation, systemic acid-base balance, and pulmonary gas exchange. The registered nurse must follow a disciplined, four-step analysis utilizing the ROME mnemonic (Respiratory Opposite, Metabolic Equal).

Reference Standard Physiological Ranges

• pH: $7.35\text{ to }7.45$ (Absolute neutral median: $7.40$)
• $PaCO_2$: $35\text{ to }45\text{ mmHg}$ (Respiratory component; acid substance)
• $HCO_3^-$: $22\text{ to }26\text{ mEq/L}$ (Metabolic/renal component; base substance)
• $PaO_2$: $80\text{ to }100\text{ mmHg}$ (Normoxemia on room air)
• $SaO_2$: $95\%\text{ to }100\%$

The 4-Step ABG Interpretation Protocol

1. Analyze the pH: If $\text{pH} < 7.35$, the primary condition is Acidemia. If $\text{pH} > 7.45$, the primary condition is Alkalemia. If the pH is normal ($7.35\text{ to }7.45$), look at whether it falls on the acidic side ($7.35\text{--}7.39$) or basic side ($7.41\text{--}7.45$) to detect fully compensated disorders.
2. Analyze the $PaCO_2$ (Respiratory Component):
   • Elevated $PaCO_2$ ($> 45\text{ mmHg}$) represents respiratory acidosis.
   • Decreased $PaCO_2$ ($< 35\text{ mmHg}$) represents respiratory alkalosis.
3. Analyze the $HCO_3^-$ (Metabolic Component):
   • Decreased $HCO_3^-$ ($< 22\text{ mEq/L}$) represents metabolic acidosis.
   • Elevated $HCO_3^-$ ($> 26\text{ mEq/L}$) represents metabolic alkalosis.
4. Determine the Level of Compensation:
   • Uncompensated: The pH is abnormal; one component ($PaCO_2$ or $HCO_3^-$) is abnormal, while the opposite regulatory system remains entirely within its normal reference range.
   • Partially Compensated: The pH remains abnormal; both $PaCO_2$ and $HCO_3^-$ are abnormal, indicating that the compensatory system is actively shifting to buffer the primary defect, but has not yet restored normal pH.
   • Fully Compensated: The pH has returned to the normal range ($7.35\text{ to }7.45$); both $PaCO_2$ and $HCO_3^-$ remain abnormal.

Comprehensive Acid-Base Disorders Guide

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Acute Life-Threatening Airway & Thoracic Emergencies

1. Foreign Body Airway Obstruction (FBAO)

• Mild Obstruction: The client can speak, cough forcefully, and breathe. Nursing Action: Do not interfere with the client's spontaneous efforts; encourage continuous coughing while monitoring closely.
• Severe / Complete Obstruction: The client clutches their neck (Universal Choking Sign), cannot speak, vocalize, or breathe, exhibits silent ineffective coughing, and rapidly develops facial cyanosis.
  • Conscious Adult: The 2025 American Heart Association guidelines recommend cycles of 5 back blows (between the shoulder blades, with the person leaning forward) followed by 5 abdominal thrusts (inward and upward, just above the umbilicus). Repeat until the object is expelled or the client becomes unresponsive. In late pregnancy or obesity, use chest thrusts over the lower sternum instead of abdominal thrusts. For infants, use 5 back blows and 5 chest thrusts.
  • Unresponsive Adult: Lower the client carefully to a firm surface, call immediately for emergency assistance, and initiate CPR starting with 30 chest compressions. Every time the airway is opened to deliver rescue breaths, visually look into the oropharynx. If a foreign body is clearly visualized, remove it with a finger sweep. Blind finger sweeps are strictly contraindicated because they push lodged objects deeper into the larynx.

2. Severe Bronchospasm & Status Asthmaticus

Status asthmaticus is severe, prolonged asthma exacerbation refractory to standard inhaled bronchodilator therapy.

• The Silent Chest Phenomenon: During early exacerbations, auscultation reveals loud, high-pitched expiratory wheezes. If wheezing diminishes while the client remains severely dyspneic, tachypneic, and exhausted, this represents a "Silent Chest"—air movement is so severely restricted that wheezes cannot even be generated. This is an ominous herald of imminent asphyxial cardiac arrest.
• Interventions: Continuous high-dose nebulized short-acting beta-2 agonists (Albuterol) with Ipratropium bromide, intravenous systemic corticosteroids (Methylprednisolone), IV Magnesium Sulfate (2 g infused over 20 minutes for bronchial smooth muscle relaxation), and preparation for rapid sequence intubation.

3. Acute Laryngeal Angioedema

Rapid submucosal extravasation of fluid into the tongue, uvula, and epiglottis induced by ACE inhibitors (e.g., enalapril, lisinopril) or IgE-mediated anaphylaxis.

• Management: Immediate discontinuation of offending agents, high-flow oxygen, nebulized racemic epinephrine, and emergent preparation for an advanced airway. If endotracheal intubation is blocked by massive supraglottic swelling, perform immediate Emergency Surgical Cricothyroidotomy.

4. Tension Pneumothorax

• Pathophysiology: A one-way valve pleural injury allows air to enter the pleural space during inspiration but prevents it from escaping during expiration. Intrapleural pressure progressively exceeds atmospheric pressure, completely collapsing the ipsilateral lung, shifting the mediastinum and trachea toward the contralateral side, and compressing the vena cava. This abolishes venous return, producing fatal obstructive shock.
• Clinical Presentation: Severe dyspnea, tachycardia, severe hypotension, absent breath sounds on the affected side, hyperresonance to percussion, jugular venous distension, and tracheal deviation away from the affected side.
• Immediate Intervention: Emergency Needle Thoracostomy (Decompression) must be performed immediately without waiting for a diagnostic chest radiograph! Insert a large-bore (14-gauge or 16-gauge) cannula with catheter over needle into the second intercostal space at the midclavicular line or the fourth or fifth intercostal space just anterior to the midaxillary line, which current ATLS guidance prefers in adults, on the affected side. A characteristic hiss of escaping pressurized air confirms decompression. Follow immediately with formal Tube Thoracostomy (Chest Tube insertion) connected to a closed water-seal drainage system.

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Oxygen Delivery Modalities: Low-Flow vs. High-Flow Systems

Oxygen is a prescribed medication. Selecting the appropriate delivery modality depends on required $FiO_2$ (fraction of inspired oxygen), patient ventilatory pattern, and whether hypercapnic drive requires precise titration.

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Non-Invasive Ventilation (NIV) & Emergency Endotracheal Intubation

Non-invasive positive pressure ventilation delivers pressurized gas via a tightly fitting oro-nasal or full-face mask, recruiting collapsed alveoli, improving functional residual capacity, and offloading respiratory muscle work.

CPAP vs. BiPAP Modalities

• Continuous Positive Airway Pressure (CPAP): Delivers a constant, preset positive airway pressure throughout both inspiration and expiration (typically 5 to 12 $\text{cmH}_2\text{O}$). It does not assist ventilation directly; rather, it splints open micro-atelectatic alveoli and shifts pulmonary capillary fluid back into the vascular space.
  • Prime Indication: Acute cardiogenic pulmonary edema and obstructive sleep apnea.
• Bilevel Positive Airway Pressure (BiPAP): Delivers two discrete pressure levels:
  • Inspiratory Positive Airway Pressure (IPAP): Higher pressure (e.g., 10 to 18 $\text{cmH}_2\text{O}$) that augments tidal volume, reduces the work of breathing, and blows off accumulated $CO_2$.
  • Expiratory Positive Airway Pressure (EPAP): Baseline pressure (e.g., 4 to 8 $\text{cmH}_2\text{O}$) that maintains alveolar patency and improves oxygenation.
  • Prime Indication: Acute hypercapnic exacerbations of COPD, status asthmaticus, and post-extubation respiratory distress.
• Strict Contraindications to Non-Invasive Ventilation:
  • Respiratory or cardiac arrest.
  • Severe encephalopathy, profound somnolence, or delirium (inability to cooperate).
  • Inability to manage copious oral secretions or severe vomiting (extreme aspiration risk).
  • Facial burns, trauma, or anatomical abnormalities preventing an airtight mask seal.
  • Upper airway obstruction or severe hemodynamic instability requiring multiple vasopressors.

Absolute Indications for Emergency Endotracheal Intubation

When non-invasive modalities fail or are contraindicated, endotracheal intubation provides definitive airway control:

1. Inability to Protect the Airway: Loss of protective cough and gag reflexes, severe bulbar dysfunction, or a Glasgow Coma Scale score $\le 8$.
2. Inability to Ventilate or Oxygenate: Refractory hypoxemic respiratory failure ($PaO_2 < 60\text{ mmHg}$ despite high-flow $O_2$ or CPAP) or progressive hypercapnic respiratory acidosis with exhaustion.
3. Impending Airway Obstruction: Rapidly expanding neck hematoma, severe thermal facial/inhalation burns with soot in sputum, or progressive laryngeal angioedema.