Metabolic alkalosis is characterised by a pH >7.45 and raised plasma bicarbonate level (> 26 mmol/L).
There are numerous causes of metabolic alkalosis, which are broadly divided based on the volume status (i.e. fluid replete or replete) of the patient. It is characterised by alkalosis (pH > 7.45) and a high plasma bicarbonate level (> 26 mmol/L).
For metabolic alkalosis to develop, there needs to be an ‘initiating event' and then ‘maintenance of alkalosis’. In some cases, these two factors are the same physiological process.
Metabolic alkalosis, put simply, can result from a loss of hydrogen ions or gain of bicarbonate.
For development of metabolic alkalosis, the kidneys ability to regulate bicarbonate through excretion needs to be interrupted. Factors that interrupt bicarbonate excretion include:
The causes of metabolic alkalosis are numerous and broadly divided into chloride-responsive and chloride-resistant.
There are numerous causes of metabolic alkalosis. These are broadly divided based on the volume status of the patient.
The most common causes of metabolic alkalosis are GI losses from vomiting or diuretic therapy. This is usually obvious from the history and examination. However, a series of further investigations may be required to determine the underlying cause.
This is often used to help differentiate between chloride-responsive and resistance causes.
Patients may be given volume expansion with normal saline empirically to see whether metabolic alkalosis will improve.
Some of the major causes of chloride-resistant metabolic alkalosis are due to overactivation of the RAAS system. Therefore, assessment of blood pressure, plasma renin and aldosterone are useful in differentiating the causes.
Further tests may be required for chloride-resistant metabolic alkalosis and usually guided by the suspected aetiology. These include 24-hour urinary collections (e.g. aldosterone, cortisol), drug screen, adrenal imaging or dexamethasone suppression test.
The most common cause of chloride-responsive metabolic alkalosis is GI losses (e.g. vomiting).
The causes of chloride-resistant metabolic alkalosis are broadly divided based on the presence or absence of hypertension.
There are several additional causes of metabolic alkalosis.
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