Respiratory Failure – Causes, Symptoms, Diagnosis, Treatment

Respiratory failure is a clinical? condition that happens when the respiratory system fails to maintain its main function, which is gas exchange, in which PaO2 lower than 60 mmHg and/or PaCO2 higher than 50 mmHg.

Respiratory failure is classified according to blood gases abnormalities into type 1 and type 2.

Type 1 (hypoxemic) respiratory failure has a PaO2 < 60 mmHg with normal or subnormal PaCO2. In this type, the gas exchange is impaired at the level of the aveolo-capillary? membrane. Examples of type I respiratory failures are carcinogenic or non-cardiogenic pulmonary edema? and severe? pneumonia?.

Type 2 (hypercapnic) respiratory failure has a PaCO2 > 50 mmHg. Hypoxemia? is common, and it is due to respiratory pump failure.

Also, respiratory failure is classified according to its onset?, course, and duration into acute?, chronic?, and acute on top of chronic respiratory failure.

Causes of Respiratory Failure

Respiratory failure may be due to pulmonary or extra-pulmonary causes which include:

• CNS causes due to depression of the neural drive to breath as in cases of overdose of a narcotic and sedative.
• Disorders of the peripheral nervous system: Respiratory muscle and chest wall weakness? as in cases of Guillian-Barre syndrome? and myasthenia gravis.
• Upper and lower airways obstruction: due to various causes as in cases of exacerbation? of chronic obstructive pulmonary diseases and acute severe bronchial asthma?
• Abnormities of the alveoli? that result in type 1 (hypoxemic) respiratory failure as in cases of pulmonary edema and severe pneumonia.[rx]

The main path physiologic mechanisms of respiratory failure are

• Hypoventilation: in which PaCO2 and PaO2 and alveolar-arterial PO2 gradient is normal. Depression of CNS from drugs is an example of this condition.
• V/P mismatch: this is the most common cause of hypoxemia. Administration of 100% O2 eliminates hypoxemia.
• Shunt: in which there is persistent hypoxemia despite 100% O2 inhalation. In cases of a shunt, the deoxygenated blood (mixed venous blood) bypasses the alveoli without being oxygenated and mixes with oxygenated blood that has flowed through the ventilated alveoli, and this leads to hypoxemia as in cases of pulmonary edema (cardiogenic or noncardiogenic), pneumonia and atelectasis?

Symptoms of Respiratory Failure

Symptoms and signs of hypoxemia

• Dyspnea?,irritability
• Confusion?, somnolence, fits
• Tachycardia?, arrhythmia?
• Tachypnea
• Cyanosis?

Symptoms and signs of hypercapnia

• Headache?
• Change of behavior
• Coma
• Asterixis
• Papilloedema
• Warm extremities
• Fever?, cough?, sputum? production, chest pain? in cases of pneumonia.

Diagnosis of Respiratory Failure

History of sepsis?, polytrauma, burn, or blood transfusions before the onset of acute respiratory failure may point to acute respiratory distress syndrome[rx].

Lab Test and Imaging

The following investigations are needed

• Arterial blood gases (ABG) is mandatory to confirm the diagnosis of respiratory failure.
• Chest radiography is needed as it can detect chest wall, pleural, and lung parenchymal Lesions.
• Investigations needed for detecting the underlying cause of the respiratory failure may include:
  • Complete blood count (CBC)
  • Sputum, blood and urine culture
  • Blood electrolytes and thyroid function tests
  • Pulmonary function tests
  • Electrocardiography (ECG)
  • Echocardiography
  • Bronchoscopy

Treatment of Respiratory Failure

This includes supportive measures and treatment of the underlying cause.

Supportive measures depend on depending on airways management to maintain adequate ventilation and correction of the blood gases abnormalities

Correction of Hypoxemia

• The goal is to maintain adequate tissue oxygenation, generally achieved with an arterial oxygen tension (PaO2) of 60 mm Hg or arterial oxygen saturation (SaO2), about 90%.
• Un-controlled oxygen supplementation can result in oxygen toxicity and CO2 (carbon dioxide) narcosis. So the inspired oxygen concentration should be adjusted at the lowest level, which is sufficient for tissue oxygenation.
• Oxygen can be delivered by several routes depending on the clinical situations in which we may use a nasal cannula, simple face mask nonrebreathing mask, or high flow nasal cannula.
• Extracorporeal membrane oxygenation may be needed in refractory cases[rx].

Correction of hypercapnia and respiratory acidosis

• This may be achieved by treating the underlying cause or providing ventilatory support.[rx]

Ventilatory support for the patient with respiratory failure

The goals of ventilatory support in respiratory failure are:

• Correct hypoxemia
• Correct acute respiratory acidosis
• Resting of ventilatory muscles

Common indications for mechanical ventilation include the following:

• Apnea with respiratory arrest
• Tachypnea with respiratory rate >30 breaths per minute
• Disturbed conscious level or coma
• Respiratory muscle fatigue
• Hemodynamic instability
• Failure of supplemental oxygen to increase PaO2 to 55-60  mm Hg
• Hypercapnea with arterial pH less than 7.25[rx].

The choice of invasive or noninvasive ventilatory support depends on the clinical situation, whether the condition is acute or chronic, and how severe it is. It also depends on the underlying cause. If there are no absolute indications for invasive mechanical ventilation or intubations and if there are no contraindications for noninvasive ventilation non-invasive ventilation is preferred particularly in cases of chronic obstructive pulmonary disease (COPD) exacerbation[rx][rx], Cardiogenic pulmonary edema[rx] [rx]and obesity hypoventilation syndrome[rx].

Complications

Complications from respiratory failure may be a result of blood gases disturbances or from the therapeutic approach itself

• Lung complications: for example, pulmonary embolism irreversible scarring of the lungs, pneumothorax, and dependence on a ventilator.
• Cardiac complications: for example, heart failure arrhythmias and acute myocardial infarction[rx].
• Neurological complications: a prolonged period of brain hypoxia can lead to irreversible brain damage and brain death.
• Renal:  acute renal failure may occur due to hypoperfusion and/or nephrotoxic drugs.
• Gastro-intestinal: stress ulcer, ileus, and hemorrhage[rx]
• Nutritional: malnutrition, diarrhea hypoglycemia, electrolyte disturbances[rx]