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PERIOPERATIVE FLUID THERAPHY
Rey F.Atal,M.D.,PSA,Fellow
Nomenclature of solutionsNomenclature of solutions
• One mole of substance = 6.02 x 1023 molecules
• Molarity = no. of moles of solute
L of solution
• Molality = no. of moles of solute
kg of solvent
• Equivalency = substance that ionize• The no. of equivalents of an ion in a solution is
the no. of moles x by its charge (VALENCE)• Tonicity – refers to the effect a solution has on
cell volume• Isotonic – no effect• Hypotonic – inc. cell volume• Hypertonic – dec. cel volume
Fluid compartments
Average adult male is approximately 60% water by weight Average adult female is 50%.
Intracellular fluidIntracellular fluid
• Outer membrane of the cell – regulates intracellular volume and composition
• Membrane bound ATP dependent pump• Na : K ( 3:2 ) ratio• Impermeable to Na, lesser extent K• Na – most important determinant of ECOP• K - ICOP• High intracellular protein concentration
(impermeable)
Prevents IC hyperosmolalityPrevents IC hyperosmolality
• Nondiffusable solutes ( anions ) - proteins
• Na : K pump
Swelling of cellsSwelling of cells
• Interference with Na-K ATPase activity
• Occurs during hypoxia and ischemia
Extracellular fluidExtracellular fluid
• Provide cells with nutrients , remove their waste products
• Na – major determinant of ECFV ,ECOP
• Na intake , renal Na excretion, extrarenal Na losses
Interstitial fluidInterstitial fluid
• -5 mmhg
• Edema
• Low protein content ( 2 g/dl )
• Lymphatics
• Overflow reservoir for the intravascular compartment
Intravascular fluidIntravascular fluid
• Plasma
• Most electrolytes (small ions ) freely pass between plasma and interstitium
• Tight intercellular junction between endothelial cells
• Impede passage of plasma proteins
• Albumin – osmotically active solute in fluid exhange
• Increase in ECFV = EDEMA
Exchange between fluid Exchange between fluid compartmentscompartments
• Diffusion – random movement of molecules due to their kinetic energy
• Rate of diffusion depends on :
• 1. permeability of that substance
• 2. concentration gradient
• 3. pressure difference
• 4. electrical potential across the membrane
Diffusion Through CMDiffusion Through CM
• Directly through the bilipid layer
• Protein channels
• Reversible binding through carrier protein (fascilitated diffusion)
Penetrate the CM directlyPenetrate the CM directly
• Water
• Oxygen
• Carbon dioxide
• Lipid soluble molecules
Penetrate poorly the CMPenetrate poorly the CM
• Cations wjth transmembrane voltage potential (positive to the outside)
• Na
• K
• Ca
• *diffuse through specified protein channels
• *ligands (acetylcholine) to the membrane receptors
• Glucose and Amino acids diffuse with the help of membrane bound carrier proteins
Fluid exchangeFluid exchange
• Difference in non diffusable solute concentration will lead to fluid exchange between the IC and Interstitium which is governed by osmotic forces.
• Net water movement – hypo to hyperosmolar compartment
Diffusion through capillary Diffusion through capillary endotheliumendothelium
• Oxygen, CO2, H2O, lipid soluble substance
• Low molecular weight water soluble substances ( Na, Cl, K, glucose )
• High molecular weight substances
• Plasma proteins – penetrate endothelial clefts poorly except liver and lungs (larger clefts)
Fluid exchange across capillariesFluid exchange across capillaries
• Differences in :
• Hydrostatic pressure
• Osmotic pressure
Body Fluid compartments (based on average 70 kg male)
Compartment Body weight (%) Total Body Water (%)
Volume (L)
Intracellular 36 60 25
Extracellular
Interstitial 19 32 13.5
Intravascular 5 8 3.5
Total 60 100 42
Composition of Fluid Compartments
Gram Mol. Wt.
Intracellular Extracellular
Intravascular Interstitial
Sodium(meq/L) 23 10 145 142
Potassium 39.1 140 4 4
Magnesium 24.3 50 2 2
Chloride 35.5 4 105 110
Bicarbonate 61 10 24 28
Normal Water Balance
Normal adult daily water intake 2500ml
Normal water loss 2500ml
Urine 1500ml Resp tract eva 400ml Skin evaporation 400ml Sweat 100ml Feces 100ml
Total Blood Volume(TBV) = RBC volume + plasma volume 2L + 3L = 5L
7% of body weight
ETBV = 4.9L
Hyperosmolarity and Hypernatremia
- total body solute increases relative to TBW - Na > 145 meq/L - Loss of water in excess of sodium (hypotonic fluid loss) - Retention of large amounts of sodium - Compute for the water deficit
Ex. A 70kg man is found to have a plasma sodium of 160meq/L What is his water deficit?
( Normal TBW ) ( 140 ) = ( present TBW ) ( plasma Na ) (70) (0.6) ( 140 ) = ( present TBW ) ( 160)
Present TBW = 36.7L Water deficit = NormalTBW – Present TBW
42L – 36.7L = 5.3L
Hypertonic solutions are given in cases of hypovolemic shock
3% NSS
5% NSS
Hypo-osmolarity and Hyponatremia
- water retention - increase in TBW - loss of sodium in excess of water
Ex. An 80kg woman is lethargic and is found to have a plasma sodium of 118meq/L. How much NaCl must be given to raise her plasma sodium to 130 meq/L.
Sodium Deficit = ( TBW ) ( 130 – 118 ) = ( 80 ) ( 0.5 ) ( 12 ) = 480 meq Normal isotonic saline = 154 meq/L = 3.12 L of normal saline
Intravenous fluids
Crystalloids
- aqueous solutions of low molecular wt., w/ or w/out glucose.- Ratio is 3:1- Maintains intravascular volume-Excessive amounts of fluid will manifest as peripheral edema -before it ges into the lungs.
Types of solutions:
maintenance solutions – primarily due to water loss -replaced by hypotonic solutions
replacement solutions – losses that involve water and electrolytes - replaced with isotonic electrolye solutions.
Colloids
-contains high molecular wt. substances such as proteins or large glucose polymers
-5% dextran, starch solutions.
-normal ratio is 1:1 when used as a replacement in cases of blood loss
-maintains intravascular volume by increasing the oncotic pressure
-should be given slowly and in small amounts to prevent pulmonary edema
Estimating Maintenance Fluid Reqiurements
Weight RateFor the first 10 kg 4 ml/ kg / hrFor the next 10-20 kg add 2ml / kg /hrFor each kg above 20 kg add 1 ml /kg /hr
Ex. MFR for a 25 kg child?
40 + 20 + 5 =65 ml/hr
Fluid Deficits = ( MFR ) (length of fasting )
Surgical fluid losses
fully soaked sponge (4*4) = 10 ml of bloodsoaked lap = 100 – 150ml
Redistributive and Evaporative Surgical Fluid Losses Degree of tissue trauma Additional fluid requirement
Minimal (herniorapphy) 2 ml/kg/hr Moderate (cholecystectomy) 4 ml/kg/hr Severe (bowel resection) 6 ml/kg/hr
Average Blood Volumes Age Blood volumes
Prematures 95ml/kg Full term 85ml/kg Infants 80ml/kg
Adults Men 75ml/kg Women 65ml/kg
-blood transfusion, if blood loss is > 20% of the TBV
Allowable Blood Loss
Based on hemoglobin level
= (EBV) (initial Hgb – targeted Hgb) initial Hgb Ex. Compute for the ABL of a 70 kg male patient with an initial Hgb of 15gms% And a targeted Hgb of 10 gms%.
= (75) (70) (15 – 10) 15 = 1750 ml.
Based on hematocrit
=Ex. What is the ABL of an 85 kg female patient with a pre-op Hct of 35% and a post Op Hct of 30%.
Hct = ( RBCV lost ) ( 3 ) RBCV 35% = ( EBV ) (0.35) = 1934 RBCV 30% = ( 5525 ) (0.30) = - 1657 RBCV lost = 277 ABL = ( 227 ) ( 3 ) = 831 ml
Types of blood
- Fresh whole blood = plasma + rbc - Packed rbc = rbc vol only
-. Platelet concentrate
Patient Positioning
lithotomysitting
tredelenburgfowlerssupine
semi recumbentprone
lateral decubitus
Essential monitors for all patients undergoing ansthesia
observationauscultation
pulse oximetercapnograph
ECG
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