You need more information to answer questions in your case. First of all, what was the initiating insult that caused your patient to be the way that he or she is? Patient's don't just show up with those electrolyte and respiratory abnormalities without having some underlying pathology. Also, you need more numbers, specifically a PaCO2, arterial pH, and Na levels before really evaluating his or her acid base abnormalities. Yes, your patient does have a metabolic acidosis, the tachypnea is not compensatory because compensatory tachypnea would not allow the PaO2 level to drop to such a life-threatening (almost dead) level. Your patient is very sick.