Perioperative fluid therapy

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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