The Introduction of Ventilatory Failure

author: Claudia

2023-12-21

Ventilatory failure is a rise in PaCO2 (hypercapnia) that occurs when the respiratory load can no longer be supported by the strength or activity of the system. The most common causes are severe acute exacerbations of asthma and chronic obstructive pulmonary disease (COPD), overdoses of drugs that suppress ventilatory drive, and conditions that cause respiratory muscle weakness (eg, Guillain-Barré syndrome, myasthenia gravis, botulism). Findings include dyspnea, tachypnea, and confusion. Death can result. Diagnosis is by arterial blood gas measurement and patient observation; chest x-ray and clinical evaluation may help delineate cause. Treatment varies by condition but often includes mechanical ventilation.

The 2 most common causes of ventilatory failure are

a. Severe acute exacerbation of asthma (ie, status asthmaticus)

b. Exacerbation of COPD (chronic obstructive pulmonary disease)

Respiratory failure due to COPD is termed acute-on-chronic respiratory failure (ACRF).

Symptoms and Signs of Ventilatory Failure

The predominant symptom of ventilatory failure is dyspnea.

When ventilatory failure is due to increased load, signs include vigorous use of accessory ventilatory muscles, tachypnea, tachycardia, diaphoresis, anxiety, declining tidal volume, irregular or gasping breathing patterns, and paradoxical abdominal motion. When it is due to impaired respiratory drive, signs include hypopnea and/or low respiratory rates will be evident.

Ventilatory failure results in hypercapnia, causing central nervous system manifestations ranging from subtle personality changes to marked confusion, obtundation, or coma. Chronic hypercapnia is better tolerated than acute and has fewer symptoms.

Diagnosis of Ventilatory Failure

a. Arterial blood gas (ABGs) measurement

b. Chest x-ray

c. Tests to determine etiology

Ventilatory failure should be suspected in patients with respiratory distress, visible ventilatory fatigue or cyanosis, or changes in sensorium and in those with disorders causing neuromuscular weakness. Tachypnea is also a concern; respiratory rates > 28 to 30/minute cannot be sustained for very long, particularly in older or weakened patients.

If ventilatory failure is suspected, ABG analysis, continuous pulse oximetry, and a chest x-ray should be done. Respiratory acidosis revealed by the ABG measurement (eg, pH < 7.35 and PCO2 > 50) confirms the diagnosis. Patients with chronic ventilatory failure often have quite elevated PCO2 (eg, 60 to 90 mm Hg) at baseline, typically with a pH that is only slightly acidemic. In such patients, the degree of acidemia rather than the PCO2 must serve as the primary marker for acute hypoventilation.

Because ABG measurements can be normal or show insufficient respiratory compensation in patients with metabolic acidosis and incipient ventilatory failure, certain bedside pulmonary function tests can help predict ventilatory failure, particularly in patients with neuromuscular weakness who may succumb to ventilatory failure without exhibiting respiratory distress. Vital capacity < 10 to 15 mL/kg and an inability to generate a negative inspiratory force of 15 cm H2O suggest imminent ventilatory failure.

Once ventilatory failure is diagnosed, the cause must be identified. Sometimes a known ongoing disorder (eg, coma, acute asthma exacerbation, COPD exacerbation, severe hypothyroidism, myasthenia gravis, botulism) is an obvious cause. In other cases, history is suggestive; sudden onset of tachypnea and hypotension after surgery suggests pulmonary embolism, and focal neurologic findings suggest a central nervous system or neuromuscular cause. Neuromuscular competence may be assessed through measurement of inspiratory muscle strength (negative inspiratory force and positive expiratory force), neuromuscular transmission (nerve conduction tests and electromyography), and investigations into causes of diminished drive (toxicology screens, brain imaging, and thyroid function tests).

Author: Bhakti K. Patel, MD, University of Chicago

If you want to learn more information, please review the links below:

//www.chinautech.com/handheld-pulse-oximeter-with-charger-base.html

//www.chinautech.com/hot-selling-finger-spo2-handheld-pulse-oximeter.html