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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
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
P(A – a)O2
Response to ↑
FIO2
V/Q Mismatch
Increased
Marked
Shunt
Increased
Minimal
Hypoventilation
Normal
Marked
Cause
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
(The symptoms of hypoxemia depend on the severity i.e. the amount by which the
partial pressure has reduced.)
• Symptoms of mild hypoxemia:
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Restlessness
Anxiety
Disorientation, confusion, lassitude and listlessness
Headaches
Symptoms of Hypoxemia
• Symptoms of acute hypoxemia:
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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
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Bradypnea leading to apnea
Clinical signs of decrease in respiratory drive
Respiratory rate < 12 bpm
Altered state of consciousness
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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
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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