Fluid Management Flashcards
What factors can cause patients undergoing GA to be hypovolemic?
NPO statusTraumaEvaporationDry anesthetic gases
What complications are associated with a hypovolemic patient?
PONVOrgan dysfunctionProlongation of hospital stay
What are the goals of fluid therapy?
Avoid or correct a hypovolemic stateRestore intravascular volumeMaintain O2 carrying capacity
What is the ultimate objective of fluid therapy?
To maintain adequate tissue perfusion, poor perfusion is associated with poor outcomes following surgery
What is the predominate substance in the body?
Water, about 45-75% of body weight
What factors determine total body water?
Age, gender and body habitus
What are the normal values for body water distribution in adults, infants and the elderly?
Avg. 70kg Male 60% TBWAvg. 70kg Female 55% TBW (more fat)Premature infants 80-90% TBWTerm infants 75% TBWElderly 50-55% TBW
Define volume of distribution.
The apparent volume of body water that the drug appears to distribute to produce a drug concentration to that in the blood
What population has an increased volume of distribution for water soluble drugs?
Infants, more TBW than other populations
What population has an increased volume of distribution for lipid soluble drugs?
Obese patients, more fat to distribute
What primarily regulates the extracellular volume?
Body sodium balance
What primarily regulates the intracellular volume?
Body water balance
How are the body fluid compartments divided in the body?
Total body water 60% ECF 20% ICF 40%Plasma 4% Interstitial fluid 16%
What determines the tonicity and the osmolarity of the extracellular fluid?
Sodium concentration
What is a typical blood volume of an adult and what are its contents?
About 5L 2L Red cell volume3L Plasma
What part of the body fluid are the red blood cells?
Red cell volume is actually considered part of the ICF
What mechanism cause water to move between the ICF and ECF?
Osmosis, from low solute concentration to high concentration
What determines osmotic pressure?
Osmotic pressure is proportional to the number of ions, not the molecular weight
Define osmolality?
Refers to the number of osmotically active particles per kilogram of water
How is osmolality calculated?
(Serum Na x 2) + blood glucose + blood urea
Why don’t we use osmole as a unit of measurement in medicine?
Too large in expressing osmotic activity of solutes in body fluids, miliosmoles (1/1000 osmole) is commonly used
Define Osmolarity?
Refers to the number of osmotically active particles per liter of solution, another way to express the concentration of a solution
What term is easier to use when referring to the body?
Osmolarity, body fluid already in liters
What does tonicity measure?
Measures the particles which are capable of exerting an osmotic force
Define what it means to have an isotonic solution.
The same osmolarity, no osmotic pressure is generated across cell membranes
What are the most commonly used isotonic solutions?
LR, NS
Define what it means to have a hypotonic solution?
The solution has a lower osmolarity than the plasma
Define what it means to have a hypertonic solution?
Solution with a higher osmolarity than plasma
What are the four components of Starling forces?
Capillary pressureISF pressureISF colloid osmotic pressurePlasma colloid osmotic pressure
What is the pressure exerted by the macromolecules that prevents fluid from leaving the plasma and exerts a pull from the interstitial space
Colloid oncotic pressure, about 25mmHg
What does the colloid oncotic pressure use to maintain plasma volume?
ProteinsAlbuminGamma globulins
Which of Starling’s forces can be controlled by the anesthetic provider?
Capillary hydrostatic pressure –> vasoactive agentsCapillary oncotic pressure –> giving crystalloids
Where does primary exchange of IVF and EVF take place?
Capillaries and small post capillary venules
What are the two most important components of exchange between the IVF and the EVF?
Bulk flowDiffusion
Why are large volumes required when replacing with crystalloid?
It is rapidly distributed throughout the ECF
Approximately how much crystalloid is required to expand the intravascular compartment by 1 liter?
3-4L
What occurs when D5W is administered?
Glucose initially osmotically active but then rapidly metabolized, leaving free water without eletrolytes
How much D5W would be required to replace 500mL of plasma volume?
7L which is not suitable for resuscitation or rapid volume replacement
Why don’t we typically give D5W in the OR?
Patients are usually stressed –> increased cortisol –> increased blood sugar
What is the most commonly used fluid in the OR?
Lactated Ringers, most intraoperative losses are isotonic
Why don’t we use LR to dilute blood?
The calcium in the LR binds to the citrate anticoagulant in the blood and may result in clotting
Why might we avoid using LR in renal failure patients in the OR?
There is potassium in LR (4mEq) that can cause hyperkalemia
How is LR metabolized?
Lactate is converted to bicarbonate in the liver
What is the osmolality of LR?
273 making it slightly hypotonic and causes a slight decrease in serum Na
Why don’t we typically use NS in the OR?
Greater chloride content, with large volumes this may cause hyperchloremic metabolic acidosis
What is the osmolality of NS?
308
How many grams of sodium are in 0.9% NS?
9 grams
What are hypertonic solutions predominately used for?
Severe hyponatremiaSevere hypovolemic shock or burns
What is the mechanism behind giving a hyper osmotic fluid?
Drawls water from the interstitial compartment into the vascular space 12L interstitial > 3L plasma
What are some side effects of hypertonic solutions?
HyperchloremiaHypernatremiaCellular dehydrationLimited intravascular duration
What is the purpose of colloid use?
Maintaining intravascular volume with the use of large osmotically active molecules
What are some adverse effects to using colloids?
Platelet coagulationAnaphylactic reactionReticuloendothelial system (activates phagocytes)
What is the molecular weight of endogenous albumin?
69,000 and accounts for 60-80% of plasma colloidal oncotic pressure
How does albumin that leaks out get back into circulation?
Lymphatic system
Where is albumin synthesized?
Hepatocytes at a rate of 9-12g/day to maintain normal plasma concentration of 40g/L
What kind of solution is 5% albumin?
Isotonic
How does 25% albumin affect circulation?
Can expand the plasma volume up to 5x the current volume by drawling fluid in from the interstitial fluid
How are synthetic colloids typically described?
Described by the average or the number averaged molecular weight
What is the molecular weight of Dextran 70 and what is it most beneficial for?
Dextran 70 = MW: 70,000, it is a better volume expander
How are dextran 40 and 70 metabolized?
Dextran 40 is small enough to be eliminated by the kidneys where Dextran 70 must pass into the tissues and undergo hydrolysis
What is the molecular weight and effects of Dextran 40?
MW = 40,000 and it improves blood flow through microcirculation (reduced RBC sludging and reduction in blood viscosity)
What is an undesirable side effect of dextran use?
Acquired Von Willebrands, reducing both components of factor VIII:Factor VIII related antigenFactorVIII coagulant
What is the name of the hydroxyethyl starch that is mixed in 0.95% sodium chloride solution?
Hespan
What is the name of the hydroxyethyl starch that is mixed in a electrolyte solution similar to LR?
Hextend
What is the significance of the pattern on the hydroxyethyl substitution of hydroxyl starches?
It reduces the susceptibility to hydrolysis by non-specific amylases in the blood
What problem can occur if HES molecules are too small?
They can leak out into the intravascular space, eliminated by the kidneys
What problem can occur if HES molecules are too big?
Effect blood coagulation, broken down by amylase
What is currently the starch of choice and why?
Voluven, avoids molecules leaking out and avoids coagulation issues
What can occur with long term use of HES?
Storage of HES molecules in the reticuloendothelial system
What determines if a crystalloid or a colloid should be used in a particular situation?
Crystalloids are generally used as maintenance fluid for insensible losses and as replacement for body fluid deficitsColloids are used for fluid replacement and shock resuscitation
How much fluid can 1g of colloid drawl into the plasma volume?
20mL
How much does 500mL of albumin or hetastarch 6% increase the plasma volume?
500mL
What are the major preoperative goals of fluid management?
Meet basal fluid requirementsReplace lossesRestore/maintain hemodynamic stabilityEnhance microvascular blood flow –> O2 deliveryMaintain aerobic cellular metabolism
What is the formula for oxygen delivery?
DO2 = CI (cardiac index) x CaO2 (arterial oxygen content)
What causes water and electrolyte losses to occur?
UrinationEvaporative loss from skin and lungs
How much water does a normothermic patient lose per day?
2000mL/day 2500 from normal metabolic rateMay gain 400mL for metabolic water
What is the 4-2-1 maintenance estimation calculation?
0-10kg = 4mL/kg11-20kg = 2mL/kg>20kg = 1mL/kgTrick: if patient is over 20kg, just add 40mL to their weight in kgs
How do we calculate NPO deficits?
Maintenance x hours fasting = deficitThis does not account for other loses that occur in the OR
What are some causes of abnormal fluid losses?
Preoperative bleeding, vomiting, diuresis, diarrhea, bowel prepOccult lossesIncreased insensible losses
How are the first three hours of fluid deficits typically replaced?
Hour 1 = 1/2 deficit + hourly maintenanceHour 2 = 1/4 deficit + hourly maintenanceHour 3 = 1/4 deficit + hourly maintenance
What are some causes of obligatory fluid loss?
Evaporation, mostly apparent with large wounds (duration and surface are exposed)Internal redistribution of body fluids (third spacing)
What type of tissues are most likely to have third spacing?
Trauma, inflammation or infected tissue
What does the provider need to know in order to calculate third space losses?
Type of procedureDegree of exposureAmount of surgical manipulation
What is the major determinant in third space fluid replacement?
Based on whether the tissue trauma is minimal. moderate or severe
How much fluid per kg should considered for third space losses if minimal tissue trauma is thought to occur?
1-2mL/kg/hr
How much fluid per kg should considered for third space losses if moderate tissue trauma is thought to occur?
4-7mL/kg/hr
How much fluid per kg should considered for third space losses if severe tissue trauma is thought to occur?
8-10mL/kg/hr
What components make up the fluid requirements of a surgical patient?
MaintenanceNPO deficit3rd SpacingEBL
What two major risk factors contribute to a conservative provider when it comes to transfusing blood products?
Blood borne pathogensTransfusion reaction
How much blood loss can a typical adult tolerate?
10% loss of EBV
What is the main reason providers decide to transfuse a patient?
To maintain O2 carrying capacity
At what point should the provider switch from using crystalloids and colloids to blood products?
When the danger of anemia outweighs the risk of transfusing
What is the ratio of replacing crystalloid to blood volume lost?
Isotonic solution of 3mL for each 1 mL of blood loss 3:1
What is the ratio of replacing colloid to blood volume lost?
1mL for each 1mL of blood loss 1:1
What is the ratio of replacing blood components to blood volume lost?
Considered a colloid1:1
What does the hematocrit represent?
The RBC volume in the intracellular fluid
What factors tend to increase blood volume?
Physical activity and Muscularity
What factors tend to decrease blood volume?
Obesity, inactivity and chronic disease
How do you calculate the estimated blood volume for adult males and females?
Males 75mL/kgFemales 65mL/kg
What is the formula for allowable blood loss?
ABL = 3 [(EBV x Hct preop) - (EBV x Hct allowed)]
How much does one unit of PRBC increase the Hgb and Hct?
Hgb 1g/dLHct 2-3%
At what transfusion rate will the Hgb increase by 3g/dL and the Hct increase by 10%?
10mL/kg
What should we assess in order to determine blood loss?
Suction canisterSpongesSurgical field
How much blood is lost in a full 4x4?
10mL
How much blood is lost in a full Ray-tech?
10-20mL
How much blood is lost in a full lap pad?
100mL
How much blood is lost in wet sponges?
20-30% of dry value
What is a type specific blood compatibility test?
ABO Rh typing only 99.8% compatible
What does a type and screen blood compatibility test examine?
ABO Rh type and screen for specific antibodies commonly associated with non-ABO hemolytic reactions99.94% compatible
What does a type and crossmatch examine?
Confirms ABO Rh typingDetects antibodies to other blood groupsDetects antibodies in low titers
How long does it take to do ABO Rh typing?
Less than 5 minutes
How long does it generally take to get back antibody titers?
May take up to 45 minutes
What blood type is the universal donor?
O negative
If the results of a type and crossmatch become available before transfusing 4 units of O negative blood what should be done?
The provider should switch to the crossmatched blood, if >4 O negative transfused STICK WITH IT
What are the benefits to using whole blood?
It includes the clotting factors and antibodies
How much volume is one bag of whole blood?
450mL, reserved for mass casualties and EBV loss > 25%
How does giving pack red cells differ than giving whole blood?
Replaces RBC but not the volume250-350mL
How much does each unit of platelets increase the patients platelet count?
5000-10000
At what platelet level could spontaneous hemorrhage occur?
10-20K
About how long will platelets survive post transfusion?
About 1 week
What does a bag of fresh frozen plasma contain?
All clotting factors except platelets, usually about 250mL
How do we dose FFP?
About 10-15mL/kg
About how long does it take FFP to thaw?
45 minutes
What doses of FFP can be given for warfarin reversal therapy?
5-8mL/kg
What is cryopreciptate used for?
To correct specific coagulopathies because it contains factors VIII, XIII and fibrinogen
What transfusion product carries the greatest infectious risk from hepatitis and why?
Cryopreciptate, it is pooled from more than one donor
What are some major complications associated with transfusions?
Immune hemolytic reactionsImmune non-hemolytic reactionsInfections (HIV, Hepatitis)Metabolic complications
What metabolic complications arise from transfusions?
Decreased ph from lactate production Increased potassium from cell lysis
When in a coagulopathy complication likely to occur from transfusion?
Usually occurs after massive transfusion >10 units
What is a major complication associated with replacing blood loss with mass amounts of fluids?
Dilutional thrombocytopenia and low clotting factors
What pathophysiology can occur with massive transfusions?
DIC
What is the leading cause of transfusion related deaths in the US?
TRALI
Explain what a TRALI may look like?
Noncardiogenic pulmonary edema, hypoxia HoTN, fever and fluid in ETT
What is the treatment for TRALI?
Supportive measures
What is considered a massive transfusion?
Replacement of patients total blood volume in 1/2 EBV in 3hrsTransfusion of >10units of whole blood
What electrolyte abnormality might be seen with massive transfusions and how should it be treated?
Hypocalcemia, only replace if ionized Ca levels are low
What causes hypocalcemia with massive transfusions?
Citrate preservative may bind and chelate calcium
When might a provider see cardiac compromise related to hypocalcemia from massive transfusions?
In normal patients does not occur unless the transfusion rate exceeds 1 unit every 5 minutes
If a surgeon wants to use cell saver during a procedure what does that mean?
Blood loss from surgical field are suctioned up, RBC spun down and given back to the patient
What should you do if the surgeon says he wants to use inraoperative isovolemic hemodilution during a procedure?
Draw off blood before procedure, replace with crystalloid or colloid, when blood loss occurs, Hct will be lower, give the patients blood back after the procedure is complete
What are good techniques for transfusing products?
Warm the bloodUse a filter (170micrometer)Reconstitute with NS
Why do we reconstitute blood with NS when we use LR in the OR?
Calcium in LR may cause blood to clot by reversing the anticoagulant effect of citrate
