Makindo Medical Notes

Related Subjects: Asthma |Acute Severe Asthma |Exacerbation of COPD |Pulmonary Embolism |Cardiogenic Pulmonary Oedema |Pneumothorax |Tension Pneumothorax |Fat embolism |Hyperventilation Syndrome |Acute Respiratory Distress Syndrome (ARDS) |Respiratory Failure

It is quite possible for a patient with COPD to also have a PE. Patients may go from Type 1 to become Type 2 when they tire and hypoventilate or receive sedation. Intubation and ventilation treat both types.

About

• Respiratory failure (PaO₂ < 8 kPa) is a common medical emergency.
• Respiratory failure is a syndrome in which the respiratory system fails in one or both of its gas exchange functions: oxygenation and carbon dioxide elimination.
• It may be classified as either hypoxaemic with or without hypercapnia.
• Oximeters estimate arterial oxygen saturation and are useful in assessment or monitoring.
• Oximeters tell us nothing about Carbon dioxide levels. For that, we need an ABG.

Classification

How much Oxygen should I give?

• Normally, patients should have enough oxygen to achieve Sats 94-98%.
• In COPD/T2 RF, patients should have enough oxygen to achieve Sats 88-92% and PO₂ > 7 Kpa.
• If O₂ sats > 98%, then wean back on oxygen.
• If O₂ sats < 94%, then consider increasing oxygen.
• There are exceptions (e.g., COVID-19, with a target of > 90% to conserve stocks). Take advice if unsure.

Causes

• Type 1: The most common form, usually due to alveolar fluid and similar pathologies, often from a mismatch in ventilation and perfusion.
  • Pulmonary oedema
  • Pulmonary embolism
  • ARDS
  • Asthma
  • Pneumonia
  • High altitude
  • Upper airways obstruction
• Type 2: Usually due to ventilatory weakness, sedation, or conditions that impair ventilation. Hypercapnia causes acidosis, which prompts a compensatory rise in renal retention of bicarbonate over days.
  • Causes of Type 1 when tired, sedation, hypoventilation
  • CNS disease (e.g., stroke, tumour)
  • Exacerbation of COPD
  • Pneumonia
  • Neuromuscular weakness (e.g., Polio, GBS, MND, Spinal muscular atrophy)
  • Muscle weakness (e.g., Muscular dystrophy, Myotonic dystrophy, Pompe disease)
  • Flail chest, Rib fractures, Kyphoscoliosis
  • Obesity, sedation, hypercarbia, alcohol
  • Sputum and mucus plugs

Investigations

• Oxygen saturation probe: Does not detect CO₂ levels.
• ABG: Can tell pH, PO₂, PCO₂, HCO₃, and base excess.
• ECG: STEMI, AF, S1Q3T3 for PE, RV changes for COPD.
• CXR: May show COPD changes, pneumonia, pneumothorax but not PE.
• CTPA: If T1RF and Wells score suggest possible PE.

Management of Type 1 RF

• ABC, High flow oxygen unless suspected COPD.
• Make a diagnosis and manage the cause.
• Diuretics if fluid, Chest drain if PTX, Antibiotics if infection.
• Bronchodilators/Steroids if Asthma/COPD.
• Thrombolysis/Anticoagulation if PE.
• May need CPAP or NIV depending on cause.
• May need intubation or ventilation or ECMO.

Management of Type 2 RF

• ABC, Controlled Oxygen therapy; start with a 24% venturi mask aiming for PaO₂ > 7 kPa.
• CO₂ retention presents as warm, dilated peripheries, sleepiness, bounding pulses, and a flapping tremor.
• Often with COPD, patients exhibit prolonged expiration phase, wheeze, inflated lungs, and intercostal indrawing.
• If there is significant right heart failure, signs include peripheral oedema, raised jugular venous pressure, hepatomegaly, and ascites.
• Frequent physiotherapy ± pharyngeal suction if mucus plugs or sputum need expectoration.
• Noninvasive ventilation (NIV): CPAP nasal or mask (start at 5 cm H₂O), BiPAP nasal or mask (start at 10 cm H₂O inspiration/5 cm H₂O expiration).
• May need intubation or ventilation. Initial ventilator settings:
  • FiO₂ 1.0
  • Tidal Volume: 6–10 ml/kg
  • RR: 10-12
  • PEEP: 5 cmH₂O
  • Pressure Support: 5 cmH₂O
• Consider ECMO if necessary.
• For Drug-induced Hypoventilation: Consider naloxone for opiates and flumazenil for benzodiazepines.

Important Scenarios to Recognise

• Impending Respiratory arrest: HR > 120/min, RR > 30, low BP, pale and sweaty, agitation, confusion, rising PaCO₂ or fall in PaO₂.
• Mask intolerance in confused patients: Consider nasal prongs at 1-2 L/min if effective.
• If a patient has normal PaO₂ on high flow oxygen, investigate further, as high FiO₂ can mask worsening pathology.
• If a hypoxic asthmatic patient’s ABG shows normal PaCO₂ (it should be low), this is a sign of fatigue or worsening and requires urgent ITU review.
• A very low PaO₂ in a well-appearing patient with normal O₂ saturations may indicate a venous sample.