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Respiratory failure. The term respiratory failure is used when pulmonary gas exchange fails to maintain normal arterial oxygen and carbon dioxide levels It is a failure of the process of delivering O 2 to the tissues and/or removing CO 2 from the tissues.
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The term respiratory failure is used when pulmonary gas exchange fails to maintain normal arterial oxygen and carbon dioxide levels • It is a failure of the process of delivering O2 to the tissues and/or removing CO2 from the tissues
Acute respiratory failure often is defined in practice as occurring when the Pao2 is less than 55 mm Hg • Classified into types I and II depending on absence or presence of hypercapnia (raised PaCO2)
Pathophysiology • When disease impairs ventilation of part of a lung (pneumonia), perfusion of that underventilated region results in hypoxic and CO2-laden blood entering the pulmonary veins
Increased ventilation of neighbouring regions of normal lung can increase their CO2 excretion, correcting arterial CO2 to normal, but cannot augment their oxygen uptake because the haemoglobin flowing through these normal regions is already fully saturated • Significant hypoxemia is nearly always present in pts with acute respiratory failure
Causes of Hypoxic ARF(typeI) • Acute lung injury/ARDS • Pneumonia • Pulmonary thromboembolism • Acute lobar atelectasis • Cardiogenic pulmonary edema
Causes of Hypercapnic-Hypoxic ARF (type II ) Pulmonary disease • COPD • Asthma: advanced acute severe asthma • Drugs causing respiratory depression
Neuromuscular • Guillain-Barré syndrome • Acute myasthenia gravis • Spinal cord tumors Musculoskeletal • Kyphoscoliosis
Clinical Manifestations • Patients are typically dyspneic and tachypneic • Neurologic dysfunction may be present • Myocardial ischemia or even infarction may be precipitated by the hypoxemia
Clinical Evaluation • Clinical history and physical examination • Physiologic abnormalities • Chest radiographic findings • Other tests aimed at elucidating specific causes
The presentation often reflects one of three clinical scenarios • Effects of hypoxemia and/or respiratory acidosis • Effects of primary (e.g., pneumonia) or secondary (e.g., heart failure) diseases involving the lungs • Nonpulmonary effects of the underlying disease process
Clinical effects of hypoxemia and/or respiratory acidosis on CNS are • Irritability • Agitation • Changes in personality • Depressed level of consciousness, or coma
Effects on cardiovascular system are • Arrhythmias • Hypotension • Hypertension
In some patients, the clinical picture is dominated by the underlying disease process, particularly with diseases that cause acute lung injury, such as sepsis, severe pneumonia, aspiration of gastric contents
Treatment • The management of acute respiratory failure depends on cause clinical manifestations patient's underlying status
Certain goals apply to all patients • Improvement of the hypoxemia to eliminate or reduce markedly the acute threat to life • Improvement of the acidosis if it is considered life-threatening • Maintenance of cardiac output • Treatment of the underlying disease process • Avoidance of predictable complications
Mechanical Therapy to Improve Oxygenation • A Pao2 of greater than 60 mm Hg to produce an Sao2of 90s is usually adequate • The Pao2 can be increased by administration of supplemental O2 by continuous positive airway pressure (CPAP) or by mechanical ventilation
Supportive Measures Prevent deep venous thrombosis Prevent gastric stress ulceration Maintain the head of the bed at a 45-degree angle to reduce aspiration
Ensure a normal day/night sleep pattern, including minimizing activity and reducing direct lighting at night • Patient should change position frequently
