Don't take vitals, take a lactate

The resident internal medicine called from the Emergency Department (ED). “Can you please come and see my patient, I think he is becoming septic and needs admission to intensive care”. In the ED we found a confused older patient with an oxygen mask who was clearly dyspnoeic, the urinary catheter was filled with a dark brown fluid, the collecting bag was empty. The resident reported that he admitted the patient 4 h earlier as he suspected pneumonia. On admission the patient was hypoxic but this clearly improved with the supplemental oxygen. The resident was still waiting for all the laboratory results and the chest X-ray. However, now that the patient had developed hypotension he thought the patient was clearly at risk and intensive care admission was required. When we asked why he had not called us earlier, he replied that he intended to admit the patient to the general ward as he was haemodynamically stable and oxygenation had improved on supplemental oxygen so intensive care admission was not required. When reviewing the blood sample that was drawn 30 min following presentation, besides hypoxaemia, an increased lactate level of 4.6 mmol/l was present. The resident pointed out that hyperlactataemia in sepsis is not related to tissue hypoxia but rather is a marker of increased aerobic metabolism. Therefore he thought there was no need to react to this hyperlactataemia. Where did this resident go wrong?