Assessment of fluid balance by measurement of skin tissue thickness during clinical anaesthesia.

Study Objective: To determine if measuring skin tissue thickness by a recently developed 10 MHz ultrasound scan may be used as a valuable parameter to guide fluid therapy and detect fluid shifts to the extravascular space during surgical procedures in addition to central venous pressure (CVP).

Study Design: Prospective, clinical and observational study.

Setting: An operation theatre of the Ear Nose Throat (ENT) department of an university hospital.

Patients: Following approval by the local ethics committee 12 otherwise healthy male patients undergoing ENT surgery for oropharyngeal carcinoma were involved in this study. The patients stayed nil per os for 10 h before induction of anaesthesia. INTERVENTIONS/MEASUREMENTS: Crystalline fluids (Ringer's solution) were supplied at a constant rate of 10 ml kg-1 bw h-1. Patients were kept in the supine position during surgery, no further interventions were performed. Additional to routine monitoring, tissue thickness (TT) of proximal pre-tibial skin and CVP were measured every 30 min, haematocrit was determined hourly for 5 h starting at t0.

Main Results: Haematocrit constantly declined during the observation period, showing a significant difference in t0 after 120 min. The increase in TT was strongly correlated with intraoperative positive fluid balance (r=0.96), while the course of CVP did not reflect the amount of fluid application comparably.

Conclusions: Non-invasive determinations of skin tissue thickness by the presented ultrasonic device appears to give additional information on fluid intake and distribution during clinical anaesthesia.