A client with a 3-day history of nausea and vomiting and suspected gastroenteritis presents to the emergency department. The client is hypoventilating and has a respiratory rate of 10 breaths per minute. The electrocardiogram (ECG) monitor displays tachycardia, with a heart rate of 120 beats per minute. Arterial blood gases are drawn, and the nurse reviews the results, expecting to note which finding?