Respiratory Failure 215a. Educational Objectives Define acute respiratory failure Differentiate between Type I and Type II respiratory failure List the

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


• Most common causes of hypoxemia

– Ventilation/perfusion mismatch

– Shunt

– Alveolar hypoventilation


• Differentiating between causes of hypoxemia

Cause P(A – a)O2 Response to ↑ FIO2

V/Q Mismatch Increased Marked

Shunt Increased Minimal

Hypoventilation Normal Marked

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


• 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)


• 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 hemoglobinSaO2 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:

– 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


• Auscultation

– Wheezing indicates bronchospasm (asthma?)

– Diminished (COPD?)

– Unilateral wheezing – endobronchial lesion

– Unilaterally diminished or absent – atelectasis,

infection, effusion


• 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


• 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)


• 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

Documents

Respiratory Failure 215a. Educational Objectives Define acute respiratory failure Differentiate between Type I and Type II respiratory failure List the