You are called to a surgical ICU for consultation. A deteriorating patient (female, 67) has been treated for submassive pulmonary thrombembolism (following cervicocapital arthroplasty) with LMWH and oxygen given via nasal cannula. Blood pressure is maintained with combination of cathecholamines (norepinephrine + dobutamine). From the history: patient's been treated for hypertension, hyperlipidaemia, chronic renal failure and type II diabetes on insulin. Surgical senior house officer took blood samples for full blood count, ions and acid-base balance ("the Astrup method"). What type of blood sample is ideal for evaluation of the acid base balance in this scenario?
