A 76-year-old patient is hospitalized with pneumonia and has become increasingly confused throughout ...

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Normal arterial blood pH value is 7.35 to 7.45 (acidic is less than 7.35, and alkalotic is greater than 7.45). Respiratory acidosis is an increased PaCO2 and an increased hydrogen ion concentra-tion (pH below 7.35) that reflect the excess carbonic acid (H2CO3) in the blood. Hypoventilation produces respiratory acidosis, which causes the cerebrospinal fluid and brain cells to become acidic, thus decreasing the level of consciousness. Respiratory alkalosis is a decreased PaCO2 and increased pH (above 7.45) that reflect the deficit of carbonic acid (H2CO3) in the blood. Me-tabolic acidosis results from conditions that increase metabolic acids in the body or decrease the amount of base (bicarbonate). The bicarbonate level is always low because the bicarbonate system buffers metabolic acids. Metabolic alkalosis results from a gain of bicarbonate or excessive excretion of metabolic acid.