Which of the following can cause an increased retention of bicarbonate?

An increased retention of bicarbonate in the body, leading to metabolic alkalosis, can occur in conditions such as hypokalemia. When potassium levels are low, the kidneys tend to retain more bicarbonate as a compensatory mechanism to help maintain proper acid-base balance. In the renal tubules, low potassium prompts the reabsorption of bicarbonate while increasing the secretion of hydrogen ions, leading to an overall increase in serum bicarbonate levels.

In contrast, diarrhea typically results in a loss of bicarbonate due to the loss of intestinal fluids, which can lead to a decrease in bicarbonate levels rather than an increase. Renal failure may also lead to an accumulation of acid due to impaired excretion, which can alter bicarbonate retention, but does not inherently cause an increase in bicarbonate retention. Hyperventilation usually results in respiratory alkalosis, which can lead to a decreased amount of bicarbonate in the blood due to excessive loss of carbon dioxide.

Thus, among the options provided, hypokalemia is the primary condition associated with increased retention of bicarbonate because it leads to compensatory mechanisms in the kidney that favor bicarbonate retention to counteract the effects of low potassium levels.