3.2 Respiratory Disorders & Acute Emergencies

3.2 Respiratory Disorders & Acute Emergencies

Core Clinical Rule: In severe acute asthma, a normal or elevated $\text{PaCO}_2$ ($> 40\text{ mmHg} / 5.3\text{ kPa}$) in an exhausted patient with a silent chest is a medical catastrophe heralding impending respiratory arrest. In acute COPD exacerbations, never administer uncontrolled high-flow oxygen; titrate strictly to an $SpO_2$ of 88% to 92% to avoid abolishing hypoxic pulmonary vasoconstriction and inducing fatal hypercapnic narcosis.

Respiratory emergencies account for a substantial volume of acute hospital admissions across Kenyan county referral hospitals. Clinical officers must rapidly distinguish benign presentations from decompensating respiratory failure using validated risk stratification instruments and initiate prompt, evidence-based antimicrobial and bronchodilator protocols.

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1. Community-Acquired Pneumonia (CAP)

Community-Acquired Pneumonia is defined as an acute infection of the pulmonary parenchyma acquired outside of a healthcare facility or developing within 48 hours of hospital admission.

Microbial Etiology

• Typical Bacterial Pathogens:
  • Streptococcus pneumoniae (Pneumococcus): The single most common causative organism globally and across all age groups in Kenya. Characterized by sudden onset high rigors, productive cough with rust-colored sputum, and dense lobar consolidation on chest radiography.
  • Haemophilus influenzae: Common in patients with underlying COPD, bronchiectasis, and elderly smokers.
  • Staphylococcus aureus: Classically causes severe necrotizing pneumonia following an antecedent viral influenza infection; prone to cavitation, pneumatoceles, and spontaneous pneumothorax.
  • Klebsiella pneumoniae: Common in patients with severe alcohol use disorder, diabetes, or malnutrition. Characterized by thick, gelatinous 'currant jelly' sputum, upper lobe predilection, bulging fissures, and early lung abscess formation.
• Atypical Pathogens:
  • Mycoplasma pneumoniae: Frequent in adolescents and young adults residing in communal settings (schools, barracks). Manifests with non-productive hacking cough, headache, low-grade fever, prominent extrapulmonary features (bullous myringitis, autoimmune hemolytic anemia due to cold agglutinins, erythema multiforme), and diffuse interstitial reticular infiltrates.
  • Chlamydophila pneumoniae: Mild, indolent respiratory presentation with prominent pharyngitis and hoarseness.
  • Legionella pneumophila: Transmitted via aerosolized water sources (air conditioning cooling towers, hospital showers). Characterized by severe pneumonia accompanied by high fever, confusion/encephalopathy, gastrointestinal symptoms (watery diarrhea), hyponatremia (due to SIADH), and transaminitis.

Clinical Presentation and Physical Examination

Classic physical signs of pulmonary lobar consolidation include:

• Dullness to percussion over the involved lung segment.
• Increased tactile vocal fremitus and vocal resonance.
• Bronchial breath sounds (harsh, hollow, with prolonged expiration and a pause between inspiration and expiration).
• Inspiratory crackles (rales) that do not clear with coughing.
• Egophony (spoken 'E' heard as nasal 'A' through the stethoscope) and whispered pectoriloquy.

CURB-65 Severity Stratification and Triage

The CURB-65 score is an objective prognostic instrument validated to determine the appropriate site of clinical care and calculate 30-day mortality risk:

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|                             THE CURB-65 SCORING RUBRIC                            |
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| C - Confusion: Abbreviated Mental Test Score (AMTS) <= 8 or new disorientation      | [1 pt]
| U - Urea: Blood Urea Nitrogen > 7.0 mmol/L (> 19 mg/dL)                           | [1 pt]
| R - Respiratory Rate: >= 30 breaths per minute                                    | [1 pt]
| B - Blood Pressure: Systolic < 90 mmHg OR Diastolic <= 60 mmHg                   | [1 pt]
| 65 - Age: >= 65 years                                                             | [1 pt]
+-----------------------------------------------------------------------------------+

Aspiration Pneumonia

Aspiration pneumonia occurs when colonized oropharyngeal or gastric secretions enter the lower respiratory tract, typically in patients with impaired consciousness (intoxication, seizures, stroke, general anesthesia) or severe dysphagia.

• Anatomical Distribution: When supine, secretions preferentially pool in the superior segment of the right lower lobe or the posterior segment of the right upper lobe due to the wider, more vertical course of the right main bronchus.
• Microbiology: Polymicrobial infection combining oral anaerobes (Peptostreptococcus, Fusobacterium nucleatum, Prevotella, Bacteroides) and aerobes.
• Therapeutic Regimens: Amoxicillin-clavulanate 1.2 g IV 8-hourly, OR Ampicillin-sulbactam 1.5–3 g IV 6-hourly, OR IV Ceftriaxone 2 g daily combined with IV Metronidazole 500 mg 8-hourly. (Clindamycin 600 mg IV 8-hourly is an alternative in penicillin-allergic patients).

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2. Acute Asthma Exacerbation

Asthma is a chronic inflammatory disorder of the airways characterized by bronchial hyperresponsiveness, reversible airflow obstruction, mucosal edema, and smooth muscle bronchospasm.

Severity Grading of Acute Exacerbations

[!CAUTION] The Deadly 'Normal' Blood Gas in Asthma: An asthmatic patient who is hyperventilating should naturally blow off carbon dioxide, producing hypocapnia and respiratory alkalosis. A 'normal' $\text{PaCO}_2$ of 40 mmHg in a breathless, fatigued patient indicates that respiratory muscle exhaustion has set in. Without immediate intervention, severe hypercapnic respiratory arrest will follow rapidly.

Stepwise Emergency Pharmacological Protocol

1. Oxygen Therapy: Deliver humidified high-flow oxygen via a face mask or Venturi device to maintain an $SpO_2$ target of 93% to 95% in adults (94% to 98% in children).
2. Inhaled Short-Acting Beta-2 Agonist (SABA):
   • Salbutamol (Albuterol): 2.5–5 mg nebulized with oxygen (driven at 6–8 L/min) every 20 minutes for 3 doses, or 4 to 10 puffs via a Metered Dose Inhaler (MDI) with a large-volume spacer. In severe or life-threatening distress, administer continuous nebulization at 10–15 mg/hour.
3. Inhaled Short-Acting Muscarinic Antagonist (SAMA):
   • Ipratropium Bromide: 500 mcg nebulized together with salbutamol every 20 minutes for the first hour (3 doses). Ipratropium blocks muscarinic $M_3$ receptors, reversing cholinergic bronchoconstriction and decreasing mucus hypersecretion.
4. Systemic Corticosteroids (Immediate Administration):
   • Prednisolone: 40–50 mg PO daily for 5 to 7 days, OR
   • Hydrocortisone: 100–200 mg IV every 6 hours if the patient is vomiting, unable to swallow, or in extremis. Systemic steroids suppress airway inflammation, up-regulate beta-2 receptors, and reduce relapse rates. Tapering is unnecessary for courses lasting <= 10 days.
5. Intravenous Magnesium Sulphate:
   • Administer Magnesium Sulphate 1.2–2 g IV (in 100 mL $5%$ dextrose or normal saline) infused over 20 minutes for patients with severe exacerbations unresponsive to initial nebulization, or life-threatening asthma. Magnesium acts as a physiological calcium antagonist, inducing bronchial smooth muscle relaxation.
6. Mechanical Ventilation: Indications include respiratory arrest, deterioration in conscious level, persistent exhaustion, and worsening hypercapnic acidosis ($pH < 7.25$). Rapid Sequence Intubation (RSI) should utilize Ketamine (1–2 mg/kg IV) as the induction agent due to its sympathetic bronchodilatory properties.

Chronic Asthma Management (Global Initiative for Asthma - GINA Guidelines)

• GINA Track 1 (Preferred Strategy): Reliever and controller therapy are integrated. The preferred reliever is as-needed low-dose Inhaled Corticosteroid (ICS) combined with Formoterol (e.g., Budesonide-formoterol 160/4.5 mcg 1–2 puffs PRN). Even for mild asthma (Steps 1–2), using ICS-formoterol on-demand reduces the risk of severe exacerbations by > 60% compared to SABA monotherapy.
• Track 2 (Alternative Strategy): SABA reliever (Salbutamol 100–200 mcg PRN) accompanied by daily regular maintenance ICS (e.g., Beclomethasone 200–400 mcg daily). SABA monotherapy without concurrent ICS is no longer recommended by GINA at any level.

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3. Chronic Obstructive Pulmonary Disease (COPD)

COPD is a progressive, non-reversible airflow limitation caused by an abnormal chronic inflammatory response of the airways and pulmonary parenchyma to noxious particles or gases.

Phenotypes and Pathophysiology

• Chronic Bronchitis ('Blue Bloater'): Defined clinically by chronic productive cough for at least 3 consecutive months in each of 2 successive years, in the absence of other cardiopulmonary conditions. Characterized by goblet cell hyperplasia, mucus hypersecretion, hypoxemia, early hypercapnia, cyanosis, and secondary pulmonary hypertension progressing to cor pulmonale (right ventricular heave, elevated JVP, tender hepatomegaly, and peripheral edema).
• Emphysema ('Pink Puffer'): Defined pathologically by permanent, abnormal enlargement of airspaces distal to the terminal bronchioles, accompanied by destruction of alveolar walls without gross fibrosis. Characterized by loss of elastic recoil, air trapping, barrel chest (increased anteroposterior diameter), pursed-lip breathing, decreased breath sounds, hyperresonance to percussion, and profound dyspnea with preserved normal blood gas tensions until end-stage.
• Etiological Factors: Tobacco smoking is the leading global cause; however, in Kenya and across sub-Saharan Africa, indoor biomass smoke exposure (burning firewood, charcoal, and crop residues in poorly ventilated domestic kitchens) is an equally critical driver of severe COPD, especially among non-smoking rural women.
• Diagnostic Confirmation: Post-bronchodilator spirometry demonstrating an $FEV_1 / FVC < 0.70$ confirms persistent, non-reversible airflow limitation.

Acute Exacerbation of COPD (AECOPD)

An acute worsening of respiratory symptoms beyond normal day-to-day variations that necessitates a step-up in medical therapy.

• The Anthonisen Criteria for Antibiotic Initiation: Patients must exhibit at least two of the following three cardinal symptoms, one of which must be increased sputum purulence:
  1. Increased dyspnea
  2. Increased sputum volume
  3. Increased sputum purulence (green/yellow appearance)
• Common Infective Triggers: Viruses (rhinovirus, influenza) and bacteria (Haemophilus influenzae, Streptococcus pneumoniae, Moraxella catarrhalis, and Pseudomonas aeruginosa in advanced disease).

Principles of Controlled Oxygen Therapy

Uncontrolled, high-flow oxygen delivery in patients with acute hypercapnic COPD exacerbations can precipitate acute carbon dioxide retention, severe respiratory acidosis, coma, and death through three distinct physiological mechanisms:

1. Abolition of Hypoxic Pulmonary Vasoconstriction (Major Mechanism): Excess oxygen reverses compensatory vasoconstriction in poorly ventilated alveolar units, flooding poorly ventilated lung areas with perfusion and dramatically worsening ventilation-perfusion ($V/Q$) mismatch.
2. The Haldane Effect: Oxygenation of deoxygenated hemoglobin reduces its affinity for carbon dioxide, displacing $CO_2$ from hemoglobin into the dissolved plasma phase and elevating arterial $PCO_2$.
3. Attenuated Peripheral Chemoreceptor Drive: Chronic carbon dioxide retainers rely partly on peripheral carotid body hypoxemia to drive ventilation; sudden correction of hypoxemia can suppress minute ventilation.

• Clinical Practice Standard: Administer controlled low-flow oxygen via a 24% or 28% Venturi mask or nasal cannula at 1 to 2 L/min, strictly targeting an $SpO_2$ of 88% to 92%. Obtain a repeat arterial blood gas (ABG) within 30 to 60 minutes.

Comprehensive Management of AECOPD

• Inhaled Bronchodilators: Nebulized Salbutamol 2.5–5 mg combined with Ipratropium Bromide 500 mcg every 4 to 6 hours.
• Systemic Corticosteroids: Oral Prednisolone 40 mg once daily for 5 days. The landmark REDUCE trial confirmed that 5 days of therapy is non-inferior to 14 days, provides equivalent clinical recovery, and minimizes steroid toxicity.
• Antimicrobial Therapy: Indicated when Anthonisen criteria are fulfilled. First-line oral choices: Amoxicillin-clavulanate 625 mg PO 8-hourly, Azithromycin 500 mg PO daily, or Doxycycline 100 mg PO 12-hourly for 5 to 7 days.
• Non-Invasive Positive Pressure Ventilation (NIV / BiPAP): First-line ventilatory support for acute hypercapnic respiratory failure ($pH < 7.35$ and $\text{PaCO}_2 > 45\text{ mmHg}$). NIV significantly decreases intubation rates, reduces length of stay, and reduces in-hospital mortality.