Respiratory Failure

Question 1

Type I Failure

Answer 1

Lung failure: failure to sufficiently exchange gases (typically manifested in hypoxemia). Unacceptabbly low levels of arterial PO2 (<60mmHg). Normocapnia or hypocapnia.

Question 2

Type II Failure

Answer 2

Pump failure: Ventilatory failure manifested by hypercapnia. PaCO2 > 45 mmHg. Often accompanied by hypoxaemia.

Question 3

Causes of type I respiratory failure.

Answer 3

Ventilation perfusion inequality (mismatch). Increased shun. Diffusion impairment. Pneumonia Pulmonary oedema (cardiac failure; acute lung injury (ALI); acute respiratory distress syndrome (ARDS)) Pulmonary embolism Pulmonary fibrosis Asthma and COPD (initially)

Question 4

When can supplementary O2 correct hypoxaemia?

Answer 4

When it it caused by a V/Q mismatch, and not a shunt.

Question 5

Arterial partial pressure of CO2 equation

Answer 5

PaCO2 = k x (volume of CO2 produced/ alveolar ventilation) PaCO2 = kV’CO2/(V’E - V’ds)

Question 6

Causes of type II respiratory failure

Answer 6

1. Respiratory drive - anaesthesia - drug overdose 2. Chest wall defects - neural defects of myopathies - severe hyperinflation (reduced mechanical efficiency) e.g. acute asthma, chronic COPD 3. Muscle fatigue - long term obstruction (e.g. asthma and COPD)