Inflation of an automatic pneumatic lower limb tourniquet before skin incision and its deflation after hardening of cement tends to give better outcomes in TKA patients during six postoperative days. The estimated blood loss was highest when the tourniquet was inflated just before cement application and deflated after its hardening.

The assessment and maintenance of perioperative blood volume is important because fluid therapy is a routine part of intraoperative care. In the past, patients undergoing major surgery were given large amounts of fluids because health-care providers were concerned about preoperative dehydration and intraoperative losses to a third space. In the last decade it has become clear that fluid therapy has to be more individualized. Because the exact determination of blood volume is not clinically possible at every timepoint, there have been different approaches to assess fluid requirements, such as goal-directed protocols guided by invasive and less invasive devices.This article focuses on laboratory volume determination, capillary dynamics, aspects of different fluids and how to clinically assess and monitor perioperative blood volume.

Background and objectives. There is a need for simple method allowing detection of dehydration and hypovolemia. Based on a new theory of homeostatic blood states, we hypothesized that hemodilution following standardized crystalloid fluid bolus can be used to discriminate between baseline normohydration and dehydration, also normovolemia and hypovolemia. Methods. Computer simulations based on previously published kinetic data were used to define the best time points for discrimination between baseline normohydration and dehydration, also normovolemia and hypovolemia. Hemodilution was compared at the proposed timing in 20 volunteers who received 40 infusions of Ringer’s solution of 25 mL/kg during 30 minutes. Results. Simulations indicated that preexisting hypovolemia could be best detected at the end of infusion, while dehydration 20–30 min later. In baseline hypovolemia, the peak reduction of hemoglobin concentration was 16.0% at the end of infusion, while it was only 11.8%, when participants were normovolemic (P<0.004). In baseline dehydration, the residual hemodilution was 8.6%, when measured 30 min after the end of infusion. It was only 3.1% in baseline normohydration (P<0.006). Conclusions. In response to fluid load, the baseline dehydration exaggerates the lowering of residual hemoglobin in respect to baseline. Meanwhile, baseline hypovolemia exaggerates the lowering of peak hemoglobin concentration. The volume loading test that deploys interpretation of hemoglobin dynamics in response to the test volume load could possibly serve as an easily available guide to indicate an individual patient’s baseline hydration state and volemia. The introduction of continuous noninvasive monitoring of hemoglobin concentration would expand the applicability of the new method.

Signs of dehydration were observed during mVLT in patients after pre-operative overnight fast. A revised transcapillary reflux model was proposed to explain the results.

Goal directed fluid therapy (GDT) implies administration of fluid boluses with the aim of optimizing cardiac performance. There is a major concern that maximization of cardiovascular performance can be achieved in expense of deterioration in body hydration processes. Also, these methods require semi invasive devices. However, monitoring of the whole body hydration status and interstitial fluid accumulation during fluid loading is not possible in everyday clinical practice. A new method, minimum Volume Loading Test (mVLT), uses evaluation of plasma dilution efficacy in small fluid boluses (2.5-5.0 ml kg-1) of isoosmotic crystalloid solutions followed by 5 min periods without fluids. The invasively measured arterial and venous hemoglobins, and simultaneous non-invasively measured hemoglobin (SpHb TM from Radical-7, Masimo inc., Irvine, USA) are used for estimation of plasma dilution which serves as an indication of plasma volume expansion. The objective of this paper was to discuss plasmadilution as a target parameter for goal directed therapy. Could plasma dilution also indicate a degree of interstitial fluid accumulation?