Fluid Therapy in Cardiac Surgery Patients

Done by Dr. Ayman RawehAugust 26, 2009

Goal of Fluid Resuscitation

to restore tissue perfusion cellular oxygenation

maintain end organ function

The body of a healthy 70 kg male contains about 42 liters of water, which is distributed into the following:

Extracellular Fluid

Intracellular Fluid

Extracellular Fluid (1/3 of Total Body Water)Volume % of body weight

Interstitial fluid 11.2 liters (16%)Plasma 2.8 liters (4%)Total 14.0 liters (20%)

Intracellular Fluid (2/3 of Total Body Water)Volume % of body weight

Red Cells 2.2 liters (3%)Intracellular Fluid 25.8 liters (37%)Total 28.0 liters (40%)

Intravascular volume (plasma + red cells) is about 5 liters, with a hematocrit of 44%

Types of Resuscitation Fluid

Crystalloid solutions

Colloid solutions

Types of Crystalloid SolutionsHypotonic

5% Dextrose ½ Normal Saline

Isotonic Ringer’s Lactate Normal Saline

Hypertonic 3% Normal Saline 6% Normal Saline 7.5% Normal Saline

Types of Colloid SolutionsProtein Solutions

Human Serum Albumin (5%, 25%) Gelatin Solutions

Non-Protein Solutions Starches

6% hetastarch (HES= hydroxyethyl starch)10% pentastarch

Dextransdextran-40 in normal salinedextran-70 in 5% dextrose in water





Dextrose Solution 5%

Hypotonic solution

consists of 5g Dextrose in every 100 mL water

does not contain any electrolytes

distributes rapidly and evenly throughout the entire body fluid compartments

Dextrose Solution 5% (continued)

One liter of intravenous dextrose solution expands intravascular compartment by only 70 ml and the interstitial fluid by 260 mL

has no use in fluid resuscitation to expand the intravascular volume

Dextrose Solution 5% (continued)

More concentrated dextrose solutions (10%, 20%, and 50%) are available

their use is limited to management of diabetic patients or patients with hypoglycaemia

These solutions are irritant to veins.





Ringer’s Lactate and Sodium Chloride 0.9% (‘normal saline’)

Isotonic solutionsrapidly redistribute within the extracellular

space (intravascular space and interstitium)One liter of intravenous normal saline or

Ringer’s lactate expands the intravascular volume by 220 mL after equilibration.

Redistribution is complete within 30-60 minutes

Ringer’s Lactate and Sodium Chloride 0.9% (continued)

a four-fold amount of fluids is needed in comparison to whole blood or colloid plasma substitution in order to achieve the same intravasal volume effect

Ringer’s Lactate and Sodium Chloride 0.9% (continued)

a risk of interstitial fluid overload

may lead to a decrease in arteriolar PaO2 in case of increasing extravasal lung water






Colloid Solutionssufficiently large molecules that normally do

not cross capillary membranes in significant numbers

exert an oncotic pressure

remains intravascular for about 6-25 hours unless an altered permeability condition is present

Colloid Solutions (continued)

good resuscitation fluids because all the volume administered stays in the circulation

One liter of intravenous hydroxyethyl starch, for example, expands the intravascular volume by 1200-1300 mL after 30-60 minutes






Human Serum Albumin

Natural protein

Stays within the intravascular space unless the capillary permeability is abnormal

cause anaphylaxis in rare circumstances.

5% solution – isooncotic, 10% and 25% solutions – hyperoncotic

Human Serum Albumin (continued)

Expands volume 5x its own volume in 30 minutes (when 25% Albumin Solution is used for example)

65 times more expensive than crystalloids






Gelatin SolutionsBovine collagen is the basis for gelatin solutions

up to 50% leaves intravasal space within 1-2 hours

completely metabolized and can be eliminated by the kidneys

do not impact kidney function suitable for use in patients suffering from impaired

kidney function






Hetastarch (HES= hydroxyethyl starch) A synthetic highly branched glucose polymer

Cheaper alternative to Albumin

Available as 6% and 10% solution in normal saline solution

Excreted in the urine (smaller particles), metabolised by blood amylase, then excreted into the bile and faeces (medium sized molecules), or undergoes phagocytosis by the reticulo-endothelial system (RES) (larger molecules).

Dose: limit the amount to 20 ml/kg/day

13 times more expensive than crystalloids

Hetastarch (HES= hydroxyethyl starch) (continued)

Excretion Excreted in the urine (smaller particles)

metabolised by blood amylase, then excreted into the bile and faeces (medium sized molecules)

undergoes phagocytosis by the reticulo-endothelial system (RES) (larger molecules)


Impact on blood coagulation There are reports that HES caused

significant prolongation of prothrombin time and prolonged thromboplastin time

reduced the levels of fibrinogen, factor VIII, factor C, and factor V

but the changes remained within the normal range


Impact on blood coagulation In another report, patients who received large

doses of HES (about 1L) for trauma and surgery

had a prolonged partial thromboplastin time

up to a 50% decrease in factor VIII and factor C


Impact on blood coagulation

HES seems to cause changes in fibrin clot formation and fibrinogenolysis

This characteristic may be related to the incorporation of the HES molecules into the clot, with subsequent prevention of solid clot formation.






Pentastarch (Pentaspan)

Lower MW analogue of hydroxyethyl starch (HES)

10% solution in 500 ml normal saline solution vials

eliminated from the circulation at a faster rate than HES because of its smaller molecular weight

is mostly excreted in the urine, so it should be avoided \ in patients with renal disease complicated by oliguria or anuria unless it is related to hypovolemia






DextransHigh MW polysaccharide

Dextran 40 - MW 40,000

Dextran 70 - MW 70,000

10% solution in NS or D5W

Excretion is through the urine, faeces and reticulo-endothelial system (RES) (according to molecular size)

Dose: limit to 20 Dose: limit to 20 ml/kg/day

occasional anaphylaxis

Dextrans (continued)Impact on Coagulation

causes defects in platelet interaction and an antifibrinolytic effects

seems to be incorporated into the polymerising fibrin clot so that it alters clot structure and enhances fibrinogenolysis

Crystalloids Vs. Colloidsstill a matter of debate and needs to be

determinedColloids and crystalloids have the same

(SAFE Study, 2004) mortality rate ICU or hospital days days of mechanical ventilation days of renal-replacement therapy

Colloids are much more expensive than crystalloids

Crystalloids Vs. Colloids (continued)Crystalloids can cause interstitial and lung edema

more crystalloids are needed compared to colloids

Colloids have a dose-related coagulopathy (greatest with hetastarch), and occasional anaphylaxis

starch molecules may adversely affect renal function by causing tubular injury

Non-protein colloids can also interfere with antigen detection during cross matching of blood products

Simulation of Fluid Management

http://pie.med.utoronto.ca/CA/CA_content/CA_fluidManagement.html

Documents

Fluid Therapy in Cardiac Surgery Patients