Common causes of acidbase disturbances

Changes in pH occur because of:

• abnormal respiratory function

• abnormal renal function

• an overwhelming acid or base load.

Table 3.2 Changes in pH, PaCO2 and bicarbonate in different acid-base disturbances

pH

PaCO2

base excess

standard bicarbonate

Respiratory

low

high

normal

normal

acidosis

Metabolic

low

normal

low

low

acidosis

Respiratory

high

low

normal

normal

alkalosis

Metabolic

high

normal

high

high

alkalosis alkalosis

Since [H+] is regulated by two systems - the respiratory system and the kidneys - there are four possible primary acid-base disorders:

• respiratory acidosis (acute or chronic)

• metabolic acidosis (further divided into increased or normal anion gap)

• respiratory alkalosis (acute or chronic)

• metabolic alkalosis (further divided into saline responsive and saline unresponsive).

A summary of the changes in pH, PaCO2 and bicarbonate in the different acid-base disturbances is shown in Table 3.2.

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