Respiratory alkalosis is the consequence of primary hypocapnia of divergent etiologies. Any pathologic process that increases ventilation to levels beyond that required to excrete the CO2 byproduct of metabolism, will result in an inappropriately low systemic pCO2 and a tendency to an alkaline systemic pH. The increased drive to ventilation may be due predominantly to a primary increase in central nervous system activity, either within the respiratory center itself or from more centrally placed areas with neural projections that extend to and control the respiratory center. Alternatively, an increased drive to ventilation may result from an "appropriate" physiologic response to another more important stimulus that overrides the human's needs to protect pCO2 and pH. Hypoxia (of different causes), is the most important and most commonly encountered such stimulus.