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Hypercapnic Respiratory Failure – Causes, Diagnosis, Treatment

The term respiratory failure describes inadequate gas exchange by respiratory system. This is caused when the arterial oxygen and/or carbon dioxide levels are not maintained in normal ranges. Drop in blood oxygenation is called hypoxemia and rise in arterial carbon dioxide is called hypercapnia.

Normal reference values:

Oxygen PaO2 > 60 mmHg. In kPa, PaO2 values should be above 8.
Carbon dioxide PaCO2 < 45 mmHg. In kPa, PaCO2 should be less than 6.6kPa.

Hypercapnic respiratory failure:

PaCO2 > 50 mmHg (i.e. 6.5kPa). This indicates inadequate alveolar ventilation. Any mismatch in ventilation-perfusion affects PaCO2 and hence, hypoxaemia is common.

HYPERCAPNIC RESPIRATORY FAILURE CAUSES:

Following are some common causes of hypercapnic respiratory failure:

  • Severe asthma
  • Obesity
  • Polyneuropathy
  • Head and neck injuries
  • Chronic obstructive pulmonary disease
  • Drug overdose, poisoning
  • Myxoedema
  • Adult respiratory distress syndrome
  • Pulmonary oedema
  • Poliomyelitis
  • Myasthenia gravis
  • Reduced breathing effort

DISTINCTION BETWEEEN ACUTE AND CHRONIC HYERCAPNIC RESPIRATORY FAILURE:

Chronic respiratory failure may take several days to develop or even long periods that allows for renal compensation and also increase in bicarbonate concentration. Hence, pH values are decreased slightly. Acute respiratory failure develops over minutes to hours. Thus, pH value is less than 7.3.

INVESTIGATIONS FOR HYPERCAPNIC RESPIRATORY FAILURE:

  • Chest X-ray
  • Arterial blood gas analysis
  • Echocardiography
  • Pulmonary function tests

TREATMENT FOR HYPERCAPNIC RESPIRATORY FAILURE:

Principles of cardiopulmonary resuscitation are followed during emergency. Underlying cause should be treated first. Mechanical ventilation and endotracheal intubation are required. Respiratory stimulants like doxapram can be used. If respiratory failure is due to overdose of sedative drugs like benzodiazepines and opioids, then an appropriate antidote like flumazenil and naloxone are prescribed by the health care provider.

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