Respiratory Failure 215a

Educational Objectives Define acute respiratory failure Differentiate between Type I and Type II respiratory failure List the causes of respiratory failure Differentiate between chronic and acute respiratory failure Describe the physiologic changes that occur in respiratory failure

Respiratory Failure The inability to maintain either the normal delivery of oxygen to the tissue or the normal removal of carbon dioxide from the tissue as a result of an imbalance between respiratory workload and ventilatory strength or endurance

(in otherwise healthy individuals breathing room air) Respiratory Failure PaO2 < 60 mmHg and/or PaCO2 > 50 mmHg (in otherwise healthy individuals breathing room air)

Classifications of Respiratory Failure Type I – hypoxemic respiratory failure Type II – hypercapneic respiratory failure

Hypoxemic Respiratory Failure Causes of hypoxemia Ventilation/perfusion mismatch Shunt Alveolar hypoventilation Diffusion impairment Perfusion/diffusion impairment Decreased FIO2 Venous admixture

Hypoxemic Respiratory Failure Most common causes of hypoxemia Ventilation/perfusion mismatch Shunt Alveolar hypoventilation

Hypoxemic Respiratory Failure Differentiating between causes of hypoxemia Cause P(A – a)O2 Response to ↑ FIO2 V/Q Mismatch Increased Marked Shunt Minimal Hypoventilation Normal

Hypercapneic Respiratory Failure Increased level of PaCO2 resulting in an uncompensated respiratory acidosis, either acute or acute-on-chronic

Causes of Hypercapneic Respiratory Failure Decrease in ventilatory drive Drug induced (overdose or sedation) Lesions of the brainstem Diseases affecting the central nervous system Morbid obesity Sleep apnea Increased intracranial pressure Hypothyroidism

Causes of Hypercapneic Respiratory Failure Neurological diseases Spinal trauma Motor neuron disease (ALS, poliomyelitis) Guillain-Barre syndrome Disorders of the neuromuscular junction (myasthenia gravis, botulism) Muscular diseases (muscular dystrophy, metabolic disorders)

Causes of Hypercapneic Respiratory Failure Increased work of breathing Increase in dead space in COPD Increase in airway resistance in asthma Pneumothorax Pleural effusions Rib fractures Obesity (Pickwickian syndrome)

Hypoxemia The condition of hypoxemia refers to the low partial pressure of oxygen in the arterial blood. Hypoxemia is often confused with either anoxia, asphyxia, hypoxia or anemia. Although, these are in some way related to reduction in the levels of oxygen in the body, these are distinct medical conditions. Anoxia is the absence of oxygen supply in the body. This implies extremely low levels of oxygen in the body. Asphyxia is the absence of oxygen along with the accumulation of carbon dioxide. Hypoxia is the deficiency of oxygen in some specific part of the body. Anemia refers to a condition when oxygen content in the arterial blood is low and the partial pressures in the arterial blood are high. Hypoxemia refers to refers to a condition when oxygen content in the arterial blood is low as also the partial pressures in the arterial blood.

Arterial Oxygen Content (CaO2) The arterial oxygen content can be given by the following equation: Arterial Oxygen Content = (Hgb x 1.34 x SaO2) + (0.0031 x PaO2) where, Hgb is the hemoglobin SaO2 is the percentage of hemoglobin saturated with oxygen PaO2 is the partial pressure of arterial oxygen

Clinical Manifestations of Type I Respiratory Failure Clinical signs of hypoxemia Dyspnea Tachycardia Tachypnea Use of accessory muscles of ventilation Nasal flaring Cyanosis – peripheral and central Central nervous system dysfunction – irritability, confusion, coma

Symptoms of Hypoxemia Symptoms of mild hypoxemia: Restlessness Anxiety (The symptoms of hypoxemia depend on the severity i.e. the amount by which the partial pressure has reduced.) Symptoms of mild hypoxemia: Restlessness Anxiety Disorientation, confusion, lassitude and listlessness Headaches

Symptoms of Hypoxemia Symptoms of acute hypoxemia: Cyanosis (Skin appearing bluish due to insufficient oxygen) Cheyne-Stokes respiration (irregular pattern of breathing) Increased blood pressure Apnea (temporary cessation of breathing) Tachycardia (increased rate of heartbeats, more than 100 per min) Hypotension (abnormally low blood pressure, below 100 diastolic and 40 systolic. Here, as an effect of an initial increase in cardiac output and rapid decrease later.) Ventricular fibrillation (irregular and uncoordinated contractions of the ventricles) Asystole (severe form of cardiac arrest, heart stops beating) Polycythemia (abnormal increase in RBCs. The bone marrow may be stimulated to produce excessive RBCs in case of patients suffering from chronic hypoxemia) Coma

Clinical Manifestations of Type I Respiratory Failure Auscultation Wheezing indicates bronchospasm (asthma?) Diminished (COPD?) Unilateral wheezing – endobronchial lesion Unilaterally diminished or absent – atelectasis, infection, effusion

Clinical Manifestations of Type I Respiratory Failure Radiologic Findings “Black” radiograph Hyperinflated lungs (COPD) – V/Q mismatch “White” radiograph Occlusion of alveoli – shunt

Clinical Manifestations of Type II Respiratory Failure Decreased respiratory drive Bradypnea leading to apnea Clinical signs of decrease in respiratory drive Respiratory rate < 12 bpm Altered state of consciousness Rapid, shallow breathing pattern (obesity) Evidence of trauma (brain injury) Fatigue (hypothyroidism, sleep apnea) Radiologic findings – atelectasis secondary to hypoventilation

Clinical Manifestations of Type II Respiratory Failure Neurological disease Drooling, dysarthria, weak cough (ALS) Muscle wasting Diaphragmatic weakness Supine paradoxical breathing (ALS) Lower extremity weakness, progressing superiorly (Guillain-Barre) Ocular muscle weakness (myasthenia gravis)

Clinical Manifestations of Type II Respiratory Failure Increased work of breathing Increasingly rapid, but shallow breathing (exacerbation of COPD) Diminished breath sounds Irritability, confusion

Chronic Respiratory Failure Development of respiratory failure in patients with chronic respiratory conditions over an extended period of time, as much as years Allows compensatory mechanisms to adapt to the disease state Most commonly Type II failure with compensatory metabolic alkalosis Compensation for Type I is polycythemia May be complicated by superimposed acute respiratory failure

Chronic Respiratory Failure With Superimposed Acute RF Precipitating factors Bacterial or viral infections Congestive heart failure Pulmonary embolism Chest wall dysfunction Non-compliance with medical orders “Normal” blood gases for these patients may be outside normal limits

Chronic Respiratory Failure With Superimposed Acute RF Goals of therapy Normalization of pH Elevation of SaO2 Improvement of airflow Treatment of infections Maintain fluid status

Complications of Acute Respiratory Failure Infection Barotrauma Emboli