Fig. 1. Median blood volume status of 13 patients with ovarian cancer before and after major abdominal surgery, receiving a standard infusion regimen (crystalloids: approximately 12 ml · kg−1· h−1; iso-oncotic colloids: blood loss replacement in ratio 1:1). Direct blood volume measurements (double-label technique) revealed a perioperatively occurring, at first unexplainable fluid loss out of the circulation. 97 Median values (range): Preoperative blood volume 5,104 (4,099–6,004) ml, crystalloid infusion 3,800 (800–8,000) ml, colloid infusion 2,000 (0–4,700) ml, blood loss 1,700 (100–3,800) ml, urine production 750 (100–1,950) ml, postoperative blood volume 4,621 (3,802–5,170) ml. Total perioperative fluid balance is calculated from the measured parameters.