A 43-year-old woman with borderline personality disorder is brought to the emergency department after taking an undetermined number of pills.  She is lethargic but arousable.  She refuses to answer questions.  Blood pressure is 110/60 mm Hg and heart rate is 120/min and regular.  Laboratory results are as follows:

Which of the following best describes this patient’s acid-base disturbance?

A 36-year-old man is brought to the emergency department due to confusion, nausea, and decreased arousal.  He is unable to answer questions and no other history is available.  Temperature is 36.7 C (98.1 F), pulse is 86/min, and respirations are 22/min.  Arterial blood gas and serum chemistry results are as follows:

Which of the following is the most likely primary acid-base disorder in this patient?

A 58-year-old woman comes to the emergency department due to cramping mid-abdominal pain.  Imaging shows a small bowel obstruction.  Vital signs and laboratory studies, including complete blood count and comprehensive metabolic panel, are within normal limits.  The patient is admitted to the hospital for nonsurgical management.  Oral intake is withheld to promote bowel rest, and an isotonic saline infusion is administered for hydration.  She has no vomiting or diarrhea and after 2 days the abdominal pain improves.  Total administration of sodium chloride infusion was approximately 6 L.  Which of the following changes have most likely occurred in this patient since the onset of her hospitalization?

An 80-year-old man has been participating in a longitudinal study of aging.  He has no major medical conditions.  Arterial blood gas samples are obtained every decade, on room air at sea level, to monitor long-term changes in pulmonary gas exchange.  Compared to 30 years ago, which of the following results is most consistent with normal aging?