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Respiratory alkalosis (hypocapnia)

Hypocapnia is the most common acid-base disorder among critically ill patients. This shouldn't be surprising, since hypocapnia may be caused by almost any pulmonary disease, pain/anxiety, or sepsis – exceedingly common conditions among critically ill patients. In most cases, the cause of hypocapnia will be evident and this won't require further investigation or management. However, very rarely a patient may be discovered with unexplained, significant hypocapnia – which warrants additional evaluation.

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Articles of Interest

Respiratory alkalosis

Respiratory alkalosis is an extremely common and complicated problem affecting virtually every organ system in the body. This article reviews the various facets of this interesting problem. Respiratory alkalosis produces multiple metabolic abnormalities, from changes in potassium, phosphate, and calcium, to the development of a mild lactic acidosis.

Pathophysiology and therapeutic strategy of respiratory alkalosis

Respiratory alkalosis is a condition characterized by low partial pressure of carbon dioxide and an associated elevation in arterial pH caused by an imbalance between CO2 production and removal, in favour of the latter.

Respiratory alkalosis & respiratory acidosis

It's very difficult to write a good chapter about respiratory alkalosis (hypocapnia) or respiratory acidosis (hypercapnia). These states remind me a bit of grand central station, because each encompasses such a broad range of patients with different conditions – who need enormously different treatments. So any discussion of these conditions is by definition a gross generalization. Furthermore, it's very difficult to tease out the effects of hyper/hypocapnia from the effects of the underlying disease state. And finally, it's often best to focus on the underlying disease states rather than the hyper/hypocapnia – so an over-emphasis on these topics might even be detrimental!

A Patient With Respiratory Acidosis:

So respiratory as alkalosis is when the pH is greater than 7.45, and the PCO2 is less than 35. So if you think about it, disorders like asthma or pulmonary embolism, pulmonary edema, and pneumothorax. And if it's in the nervous system disorders such as central neurogenic disorders, pain and panic disorders, endocrine disorders such as with pregnancy and thyrotoxicosis. And of course liver issues, such as cirrhosis, systemic disorders, such as sepsis, or if the person's on medications. And, of course, Salicylates to Topiramate, Progesterone, Theophylline, nicotine, and caffeine, they can all cause respiratory alkalosis.

Salicylate Toxicity

Tachypnea and hyperpnea: due to central stimulation of respiratory drive.

Resources

Life in the Fastlane

Hypoxaemia is an important cause of respiratory stimulation and consequent respiratory alkalosis -> give O2.

Pathway Medicine

Respiratory Alkalosis is a pathophysiological category of alkalosis and refers to those caused by primary disturbances of ventilation. Although ventilatory defects can cause significant increases in the Blood pH, renal compensatory mechanisms can largely correct the pH over several days.