Acute Respiratory Failure: Causes, Classification, Diagnosis & Treatment

Posted on May 6, 2024 in Medicine & Health

Classification:

A- Acute Hypercapnic Respiratory Failure:

PaCO2 > 45mmHg, develops within minutes to hours

B- Acute Hypoxemic Respiratory Failure:

PaO2 < 55mmHg when FIO2 ≥ 0.6, develops within minutes to hours

Causes:

Diagnosis:

Treatment:

• Depends on the clinical manifestation & underlying status
• Oxygen Therapy
• Improve acidosis if life-threatening
• Maintain cardiac output (fluid replacement/vasopressors)
• Treat underlying disease
• Avoid complications:
  1. DVT/PE
  2. Gastric Ulcer

Respiratory Distress Syndrome:

Causes:

Diagnosis:

1. Acute Onset
2. Chest X-ray: Bilateral infiltrates with pleural effusion
3. Hypoxemia: PO2/FiO2 < 200

Treatment:

Admit to ICU:

1. Give Oxygen – Continue 40-60% O2
2. Treat underlying condition (Sepsis: culture is needed with antibiotics)
3. If hemodynamically stable, intubate
4. Hemodynamic monitoring
5. Nutritional support
6. Maintain cardiac output & treat with inotropes

Cisatracurium (neuromuscular blocker) may improve outcome

Severe Asthmatic Attack: Definition, Morphology & Diagnosis:

Definition:

Acute exacerbation of asthma that remains unresponsive to initial treatment with bronchodilators, leading to:

• Patient exhales less
• Increased CO2 build-up
• Baroreceptor damage
• Hypotension
• Hypercapnic respiratory failure

Morphology:

• Bronchospasm
• Bronchial wall thickening due to eosinophil infiltration + smooth muscle hypertrophy
• Plugging: Mucosal obstruction of bronchi

Diagnosis:

• Check consciousness
• SpO2
• Peak Expiratory Flow (PEF)
• ABG (if SpO2 < 92%)

Severe Attack:

• Inability to speak coherently
• Respiratory Rate > 25
• Pulse > 110
• PEF 33-50%

Life-Threatening Attack:

• Silent chest
• Cyanosis
• Weak respiratory effort

Cardiogenic Pulmonary Edema: Treatment

1. Oxygen therapy through a non-rebreather mask
2. Sitting position with legs towards the ground to decrease preload and lower the diaphragm
3. Give Nitroglycerin:
   • Initially sublingually (0.4 mg)
   • Later IV 10-20 microgram/min
   or Calcium channel blockers
4. Diuretics: Furosemide 1mg/kg IV (not in case of kidney failure)
5. Treat underlying cause (e.g., cardiosurgery for mitral stenosis)

Non-Cardiogenic Pulmonary Edema:

1. Oxygen therapy (mask)
2. Adequate nutrition
3. Hemodynamic monitoring: Blood gases/BP
4. Treat underlying causes:
   • Is it low oncotic pressure?
   • Is it hypoproteinemia? —> Give supplements
   • Iatrogenic hemodilution —> Plasma substitution
   • Increased permeability —> Treat with hemodialysis & restore electrolytes

Pulmonary Contusion:

Causes:

Blunt trauma/penetrating chest trauma leading to disruption of the alveolar-capillary interface

Diagnosis:

1. Clinical Features:
   • Asymptomatic to severe hypoxia
   • Should be suspected if there is respiratory distress after trauma
2. Instrumental:
   • X-ray: Small, nodular, patchy infiltrates in lung parenchyma
   • Chest CT
   • Pulse Oximetry: Hypoxemia & dyspnea —> Capnometry + ABG

Treatment:

1. Supportive care + analgesics
2. Mechanical ventilation
3. Pulmonary hygiene

Avoid overhydration

Massive Pulmonary Bleeding:

Causes:

• Neoplastic disease
• Hemorrhagic risk
• Thrombocytopenia
• DIC
• Respiratory failure
• Infectious disease (TB/Pneumonia)
• Iatrogenic

Clinical Features:

• Hemoptysis
• Pursed lips
• Agitation
• Malaise
• Decreased consciousness

Treatment:

1. Resuscitation FIRST:
   • Airway: Clear & secure
   • Breathing: Intubate 4-8 L/min
   • Circulation: IV cannula
   —> Prevent blood aspiration into lungs —> Prevent exsanguination from ongoing bleeding
2. Identify bleeding site
3. Position the patient with the bleeding lung in a dependent position + selectively intubate the other (uninvolved) lung —> Prevent exsanguination:
   1. If clinically indicated, give plasma
   2. Laser therapy, direct injection with epinephrine/vasopressin
4. Rigid bronchoscopy:
   • Control for airway
   • Larger field of view
5. Embolization via bronchial artery angiography: —> Preferred method to stop massive hemoptysis (if that doesn’t work, go for surgery)

Tactics of Asthma Attack (Status Asthmaticus)

Bronchospasm:

Give IV salbutamol if:

• Deteriorating PEF
• Worsening hypoxia
• Hypercapnia
• ABG: Low pH
• Respiratory arrest

Plugging:

• β-adrenergic agonist (salbutamol 10mg)
• Hydrocortisone 100mg IV
• Rehydration
• Do NOT give mucolytics/CSD/sedatives
• Give MgSO4 2g IV over 20 minutes

Pulmonary Edema: Pathophysiology & Causes

I- Increased Permeability:

• Inhalation of chlorine, ammonia, tin chloride
• Insect toxin
• Uremia
• Azotemia
• Too high oxygen concentration

II- Decreased Oncotic Pressure:

• Decreased albumin production
• Nephrotic syndrome
• Malnutrition
• Catabolic state

III- Increased Hydrostatic Pressure:

• Left ventricular failure (MI/cardiac contusion)
• Ventricular arrhythmia
• Cardiomyopathy
• Intoxication (CO + Ethanol)

Correctable hypoxemia by oxygen therapy —> Pulmonary Edema

Non-correctable hypoxemia with oxygen therapy —> ARDS