Acute Respiratory Failure

Acute Respiratory Failure

Respiratory failure is a sudden and life-threatening deterioration of the gas exchange function of the lung. It exists when the ex-change of oxygen for carbon dioxide in the lungs cannot keep up with the rate of oxygen consumption and carbon dioxide pro-duction by the cells of the body.

Acute respiratory failure (ARF) is defined as a fall in arterial oxygen tension (PaO₂) to less than 50 mm Hg (hypoxemia) and a rise in arterial carbon dioxide tension (PaCO₂) to greater than 50 mm Hg (hypercapnia), with an arterial pH of less than 7.35. In ARF, the ventilation or perfusion mechanisms in the lung are impaired. Respiratory system mechanisms leading to ARF include:

·        Alveolar hypoventilation

·         Diffusion abnormalities

·         Ventilation–perfusion mismatching

·         Shunting

It is important to distinguish between ARF and chronic res-piratory failure. Chronic respiratory failure is defined as a de-terioration in the gas exchange function of the lung that has developed insidiously or has persisted for a long period after an episode of ARF. The absence of acute symptoms and the presence of a chronic respiratory acidosis suggest the chronicity of the res-piratory failure. Two causes of chronic respiratory failure are COPD and neuromuscular diseases. Patients with these disorders develop a tol-erance to the gradually worsening hypoxemia and hypercapnia. However, a patient with chronic respiratory failure may develop ARF. This is seen in the COPD patient who develops an exacer-bation or infection that causes additional deterioration of the gas exchange mechanism. The principles of management of acute versus chronic respiratory failure are different; the following dis-cussion will be limited to ARF.

Pathophysiology

Common causes of ARF can be classified into four categories: de-creased respiratory drive, dysfunction of the chest wall, dysfunc-tion of the lung parenchyma, and other causes.

DECREASED RESPIRATORY DRIVE

Decreased respiratory drive may occur with severe brain injury, large lesions of the brain stem (multiple sclerosis), use of sedative medications, and metabolic disorders such as hypothyroidism. These disorders impair the normal response of chemoreceptors in the brain to normal respiratory stimulation.

DYSFUNCTION OF THE CHEST WALL

The impulses arising in the respiratory center travel through nerves that extend from the brain stem down the spinal cord to receptors in the muscles of respiration. Thus, any disease or dis-order of the nerves, spinal cord, muscles, or neuromuscular junction involved in respiration seriously affects ventilation and may ultimately lead to ARF. These include musculoskeletal disorders (muscular dystrophy, polymyositis), neuromuscular junction dis-orders (myasthenia gravis, poliomyelitis), some peripheral nerve disorders, and spinal cord disorders (amyotrophic lateral sclero-sis, Guillain-Barré syndrome, and cervical spinal cord injuries).

DYSFUNCTION OF LUNG PARENCHYMA

Pleural effusion, hemothorax, pneumothorax, and upper airway obstruction are conditions that interfere with ventilation by pre-venting expansion of the lung. These conditions, which may cause respiratory failure, usually are produced by an underlying lung disease, pleural disease, or trauma and injury. Other diseases and conditions of the lung that lead to ARF include pneumonia, status asthmaticus, lobar atelectasis, pulmonary embolism, and pulmonary edema.

OTHER CAUSES

In the postoperative period, especially after major thoracic or abdominal surgery, inadequate ventilation and respiratory fail-ure may occur because of several factors. During this period, for example, ARF may be caused by the effects of anesthetic agents, analgesics, and sedatives, which may depress respiration as de-scribed earlier or enhance the effects of opioids and lead to hypoventilation. Pain may interfere with deep breathing and coughing. A mismatch of ventilation to perfusion is the usual cause of respiratory failure after major abdominal, cardiac, or tho-racic surgery.

Clinical Manifestations

Early signs are those associated with impaired oxygenation and may include restlessness, fatigue, headache, dyspnea, air hunger, tachycardia, and increased blood pressure. As the hypoxemia pro-gresses, more obvious signs may be present, including confusion, lethargy, tachycardia, tachypnea, central cyanosis, diaphoresis, and finally respiratory arrest. Physical findings are those of acute respiratory distress, including use of accessory muscles, decreased breath sounds if the patient cannot adequately ventilate, and other findings related specifically to the underlying disease process and cause of ARF.

Medical Management

The objectives of treatment are to correct the underlying cause and to restore adequate gas exchange in the lung. Intubation and mechanical ventilation may be required to maintain ade-quate ventilation and oxygenation while the underlying cause is corrected.

Nursing Management

Nursing management of the patient with ARF includes assisting with intubation and maintaining mechanical ventilation. The nurse assesses the patient’s respiratory status by monitoring the patient’s level of response, arterial blood gases, pulse oximetry, and vital signs and assessing the respiratory system. The nurse implements strategies (eg, turning schedule, mouth care, skin care, range of motion of extremities) to prevent complications. The nurse also assesses the patient’s understanding of the management strategies that are used and initiates some form of communication to enable the patient to express his or her needs to the health care team. Nursing care also addresses the problems that led to ARF. As the patient’s status improves, the nurse assesses the patient’s knowledge of the underlying disorder and provides teaching as appropriate to address the underlying disorder.