Blood Volume and Fluid Kinetics in Patients Undergoing Extracorporal Circulation

• Blood Volume [ Time Frame: 30 minutes after start of CPB ] [ Designated as safety issue: No ]

  volume kinetic technique: During start of cardio pulmonary by-pass a known amount of fluid will expand the blood volume and dilute the hemoglobin.

  1. The hemoglobin variation is used to calculate the blood volume. The last hemoglobin value before CPB and the hemoglobin value directly after start (extrapolated from the following 30 minutes after start) of CPB are used in the calculation.
  2. The value for the blood volume directly prior to CPB will be influenced by intra venous fluids given during early stages of the anesthesia.

  To achieve the blood volume prior to anesthesia a hemoglobin value before anesthesia and the last hemoglobin value before CPB are used to correct the blood volume calculation. In this way blood volume prior to anaesthesia can be calculated.

  
  

• Intracellular Edema [ Time Frame: 30 minutes after CPB ] [ Designated as safety issue: No ]

  Mass balance based on repeated Sodium concentration, fluid volume given, given and excreted Sodium.

  A positive value indicating intracellular fluid accumulation and a negative value indicating cell dehydration. This is the change that will occur during the first 30 min after start of cardio pulmonary bypass.

  
  

• Fluid Extravasation [ Time Frame: Two distribution half-times. Approximately 16 minutes. ] [ Designated as safety issue: No ]
  Rate of fluid transfer from the intravascular to the extravascular compartment during two distribution half-times. Graph derived from the hemoglobin change during 20 to 30 minutes after start of cardio pulmonary by-pass.
  
  

In many clinical situations, such as extensive surgery, it is of value to determine blood volume and rate of fluid loss from the intravascular space, since hypo- and hypervolemia are combined with increased morbidity and mortality. In this study we which to use the large variations in hemoglobin during extracorporal to calculate both these variables.

Hemoglobin is measured every 5 minutes during one hour beginning shortly before start of the heart-lung machine. When the extracorporal circulation begins the hemoglobin decreases due to the quick mix and dilution of the priming fluid from the heart-lung machine with the patients blood.

From the amount of priming fluid and the fall of the hemoglobin, the blood volume can be calculated. If no further fluid is given the next 20 to 30 minutes, the hemoglobin concentration will in most cases increase as a result of the fluid loss from the vascular space. This increase in combination with the diureses can be used to calculate the intravascular fluid loss to the interstitium during surgery.

Sodium concentration will also be measured in parallel with the hemoglobin concentration.

The Sodium concentrations in combination with given and excreted (urine)Sodium can be used in a mass balance to calculate if intracellular edema is induced.