A 56 year old man is admitted with fever, tachycardia, blood pressure 86 over 52 mm Hg, respiratory rate 28 per min, and suspected pneumonia on chest x ray. Lactate is 3.5 mmol per L. Blood cultures are drawn and broad spectrum antibiotics are started within 45 minutes. According to current sepsis guidelines, which additional intervention should be initiated within the first 3 hours of resuscitation?