Wed3November0919PM 10

In acute severe asthma:

True / False

The decision to intubate should be based on the blood gas results Correct

Antibiotics should be routinely administered Correct

Ketamine should be administered in anaesthetic doses to provide adequate sedation on ITU Correct

Intravenous magnesium is a useful adjunct Correct

Pulsus paradoxus correlates to the severity of the attack Correct

Explanation

Pulsus paradoxus is defined as a difference of >10 mmHg between the inspiratory and expiratory blood pressures, and it correlates to the severity of the asthma attack. It is most readily seen on invasive arterial blood pressure monitoring, but can also be estimated from the pulse oximetry trace where a sinusoidal baseline trace is seen.

The decision to intubate is most often made on clinical grounds (e.g. patient exhaustion, decreasing respiratory effort, decreasing level of consciousness). Hypoxia may occur at any stage of a severe asthma attack, and a normal PaCO2 may be an indicator of impending collapse (the arterial CO2 is usually low during a severe asthmatic attack).

The majority of acute asthmatic attacks are viral or allergic in origin, therefore unless there is conclusive evidence of a bacterial infection, antibiotics should be withheld.

Studies on patients suffering from acute severe asthma have demonstrated significant increases in peak expiratory flow rate (PEFR) and FEV1 following administration of 2-3 g of intravenous magnesium sulphate, without significant side effects.

Ketamine is a bronchodilator at sub-anaesthetic doses, and is used for intubating and sedating patients admitted to the intensive care unit. The adverse effects of ketamine include delirium, hallucinations and cardiovascular instability (sympathomimetic effect or paradoxical myocardial suppression in the critically ill). Ketamine also increases intracranial pressure and should therefore be avoided after a hypoxic arrest.

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