Respiratory acidosis is caused by alveolar hypoventilation. Alveolar hypoventilation is not the same as a reduced respiratory rate - a person may be breathing at a normal or high rate but have a reduced minute volume (= frequency x tidal volume). Acute alveolar hypoventilation results from an imbalance between respiratory muscle strength and load (see previous chapter). Chronic alveolar hypoventilation as seen in chronic obstructive pulmonary disease (COPD) involves multiple mechanisms.
In acute respiratory acidosis, compensation occurs firstly by cellular buffering over minutes to hours. Renal compensation then occurs over 3-5 days.
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