Ventilatory Failure and Oxygen Therapy

Question 1

Regarding carbon dioxide:

It is mainly excreted by the lungs and kidneys in the form of CO2 and hydrogen ions respectively

Answer 1

False. CO2 is mainly exhaled via the lungs and less than 1% is eliminated by the kidneys.

Question 2

Regarding carbon dioxide:

250 ml/min of CO2 is generated at rest by the average-sized person

Answer 2

False. 250 ml of oxygen is consumed and 200 ml of CO2 is generated by the average-sized person per minute

Question 3

Regarding carbon dioxide:

Levels of PaCO2 are directly proportional to alveolar ventilation

Answer 3

False. PaCO2= CO2/A – therefore it is inversely proportional to alveolar ventilation.

Question 4

Regarding carbon dioxide:

The PCO2 generated is dependent upon the patient’s temperature, exercise and metabolic activity

Answer 4

True

Question 5

Regarding carbon dioxide:

PaCO2 gives a good indication of the adequacy of ventilation

Answer 5

True. Oxygenation is heavily influenced by intra-pulmonary shunting and the inspired oxygen concentration. In steady state, PaCO2 gives the best indication of the adequacy of ventilation.

Question 6

Regarding the causes of respiratory failure:

Botulism is caused by the ingestion of the exotoxin from Clostridium botulinum, which binds irreversibly to the nerve ending, preventing acetylcholine binding to the nicotinic receptor

Answer 6

False. Botulism prevents the release of acetylcholine.

Question 7

Regarding the causes of respiratory failure:

Myasthenia Gravis causes upper motor neuron pathology, which leads to respiratory failure

Answer 7

False. Myasthenia Gravis is caused by antibodies binding to the acetylcholine receptor, and is therefore a neuromuscular junction pathology.

Question 8

Regarding the causes of respiratory failure:

Dermatomyositis can cause respiratory failure from respiratory muscle weakness

Answer 8

True. Polymyositis is also a cause of this.

Question 9

Regarding the causes of respiratory failure:

Inhalational anaesthetic agents reduce the medulla’s sensitivity to CO2

Answer 9

True. Both intravenous and inhalational anaesthetic agents reduce the medulla’s sensitivity to CO2.

Question 10

Regarding the causes of respiratory failure:

Eschar following burns can cause respiratory failure

Answer 10

True. This is due to the loss in the elasticity of the chest wall and might require escharotomies if ventilation is impaired.

Question 11

Which of the following pathological processes are associated with Type 1 respiratory failure:

A. Pulmonary oedema
B. Acute respiratory distress syndrome
C. Exacerbation of COAD
D. Pneumonia
E. Morphine overdose

Answer 11

A, B & D - secondary to V/Q mismatch

C. False. This is due to lung tissue loss and increased demand, which leads to tiring of the patient, and an increase in carbon dioxide levels.

False. Opioids reduce the sensitivity to CO2 in the medulla, and therefore hypoventilation occurs without an immediate problem with oxygenation.

Question 12

Regarding the effects of positive pressure ventilation:

The cardiovascular effects are primarily due to the increased intrathoracic pressure

Answer 12

True. This pressure is negative under normal physiological circumstances, but becomes positive when intermittent positive pressure ventilation occurs.

Question 13

Regarding the effects of positive pressure ventilation:

The urine output can be reduced by up to 40% without sodium retention

Answer 13

False. The urine output can be reduced by up to 40% with sodium retention.

Question 14

Regarding the effects of positive pressure ventilation:

The intracranial pressure can increase due to the impaired venous return

Answer 14

True. Positive intrathoracic pressure causes an impaired venous return especially when using PEEP.

Question 15

Regarding the effects of positive pressure ventilation:

The FRC increases

Answer 15

False

Question 16

Regarding the effects of positive pressure ventilation:

There is an increase in total dead space

Answer 16

True. Atelectasis occurs in the dependent lung tissue, increasing both dead space and the alveolar arterial O2 difference.

Question 17

The respiratory cycle consists of an inspiratory and expiratory phase. True or false:

In the inspiratory phase, airway pressure is increased

Answer 17

True. This allows inspiratory gas to flow into the respiratory system. The flow to different parts of the lungs depends on compliance and resistance.

Question 18

The respiratory cycle consists of an inspiratory and expiratory phase. True or false:

If inspiratory phase is slow, flow is distributed by regional resistance

Answer 18

False. This is due to regional compliance. If the patient’s lungs are compliant and there is a slow inspiratory phase, a bigger tidal volume is achieved compared to a patient with reduced compliance. Here, the tidal volume is small.

Question 19

The respiratory cycle consists of an inspiratory and expiratory phase. True or false:

If inspiratory phase is fast, there is flow to parts of the lung with a short time constant

Answer 19

True

Question 20

The respiratory cycle consists of an inspiratory and expiratory phase. True or false:

In the expiratory phase, the airway pressure rises to ambient pressure: expiration is a passive process

Answer 20

False. In the expiratory phase, the airway pressure falls to ambient pressure: expiration is a passive process.