1. Respiratory Failure
215a

2. 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

3. 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

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

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

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

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

8. 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

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

10. 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

11. 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)

12. 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)

13. 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.

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

15. 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

16. 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

17. 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

18. 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

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

20. 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

21. 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)

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

23. 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

24. 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

25. 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

26. Complications of Acute Respiratory Failure
Infection
Barotrauma
Emboli