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6 out of 9

Most common cause of type IV respiratory failure? (AIIMS May 2011)

A Pneumonia

B Chronic bronchitis

C Shock

D None of the above

Ans. C



Respiratory Failure is defined as a PaO2 <60 mmHg

Types of respiratory failure

1). Type I respiratory failure

It is defined as hypoxia (PaO2 <60 mmHg) with a normal or low PaCO2).

It is caused primarily by ventilation/perfusion (V/Q) mismatch. PAo2 – Pao2 is increased

It is a diffusion or perfusion defect due to

a. Parenchymal disease (V/Q mismatch)

b. Disease of blood vessel = Pulmonary embolism

c. Interstitial lung Diseases (ARDS)


1). Pneumonia

2). Pulmonary oedema

3). Pulmonary Embolism

4). Asthma

5). ARDS

2). Type II respiratory failure

It is defined as hypoxia (PaO2 <60 mmHg) with hypercapnia (PaCO2 is >45 mmHg).

This is caused by alveolar hypoventilation, with or without V/Q mismatch. PAo2 – Pao2 is Normal

Causes include:

1). COPD ( Chronic bronchitis is the commonest cause) Q, obstructive sleep apnoea (OSA).

2). Reduced respiratory drive: sedative drugs, CNS tumour, or trauma.

3). Neuromuscular disease: cervical cord lesion, diaphragmatic paralysis, poliomyelitis, myasthenia gravis, Guillain-Barre syndrome.

4). Thoracic wall disease: flail chest, kyphoscoliosis.

3). Type III Respiratory Failure: (Ref. Hari-18th ed., Pg- 2200)

a. This form of respiratory failure occurs as a result of lung atelectasis.

b. Because atelectasis occurs so commonly in the perioperative period, this is also called perioperative respiratory failure.

c. After general anesthesia, decreases in functional residual capacity lead to collapse of dependent lung units.

d. Such atelectasis can be treated by frequent changes in position, chest physiotherapy, upright positioning, and aggressive control of incisional and/or abdominal pain (Conservative management).

e. Noninvasive positive-pressure ventilation may also be used to reverse regional atelectasis.

4). Type IV Respiratory Failure:

a. This form results from hypoperfusion of respiratory muscles in patients in shock. Normally, respiratory muscles consume <5% of the total cardiac output and O2 delivery.

b. Patients in shock often experience respiratory distress due to pulmonary edema (e.g., patients in cardiogenic shock), lactic acidosis, and anemia.

c. In this setting, up to 40% of the cardiac output may be distributed to the respiratory muscles. Intubation and mechanical ventilation can allow redistribution of the cardiac output away from the respiratory muscles and back to vital organs while the shock is treated.

Summary of respiratory failure based on pathophysiologic derangement in respiratory function

1). Type I or acute hypoxemic respiratory failure

Often secondary to pulmonary edema and subsequent intrapulmonary shunting

2). Type II respiratory failure

Secondary to alveolar hypoventilation, resulting in the inability to effectively eliminate carbon dioxide

3). Type III perioperative respiratory failure

Secondary to lung atelectasis

4). Type IV respiratory failure

Secondary to hypoperfusion of respiratory muscles in patients in shock