Respiratory alkalosis ("Pa" CO2 < 35 mmHg) occurs when there is too little carbon dioxide in the blood. This may be due to hyperventilation or else excessive breaths given via a mechanical ventilator in a critical care setting. The action to be taken is to calm the person and try to reduce the number of breaths being taken to normalize the pH. The respiratory pathway tries to compensate for the change in pH in a matter of 2–4 hours. If this is not enough, the metabolic pathway takes place.