Q: 24 year old male has been brought to ICU from ER after he was stuck at his workplace in a kitchen and was exposed to smoke inhalation for 15 minutes. Patient has clinically no respiratory symptoms and wants to go home after 6 hours in hospital (ER and ICU). Most of the labs and CXR are essentially normal. Carboxyhemoglobin level is 14% and earlier ABG was reported "essentially normal". Which one other lab you may like to do before sending patient home?

Answer: VBG (Venous blood gas) 

Patient should not be discharged from hospital if there is a history of closed-space exposure for longer than 10 minutes or if manifest  symptoms of carbonaceous sputum, bronchospasm, odynophagia or if workup shows arterial PO2 less than 60 mm Hg or any  metabolic acidosis or carboxyhemoglobin levels 15% or above. Often missed is VBG (venous blood gas) as if arteriovenous oxygen difference (on 100% oxygen) is greater than 100 mm Hg, patient should not be allowed to go home.

Borderline cases can be hard to decide as frequently symptoms develop late. This patient should be allowed to go home with high caution as there is already long exposure to smoke as well as carboxyhemoglobin level is almost at cut off of 15%.