SECTION VI THE KIDNEY Effects of Mannitol Infusion A woman weighing 50 kg (110 Ihs)and with a plasmn [Na+]of 145 mEq/L is infused with 5 g/kg (2.3 g/lb)of mannitol (molecular weight of mannitol is 182 g/mole). Estinate the following equilibriun values.Assune that mannitol is restricted to the ECF compartment.that no excretion occurs,and that the infusion volune of the mannitol solution is megligible (total body water unchanged): Initial conditions (before mannitol infusion) Total body water: ICF volume: ECF volume: Total body osnoles: ICF osmoles: ECF osmoles: ANSVER The initial volumes of the body fluid compartpents and the osroles in these compartments are calculated as for problen I: Initial total body water 0.6 x (50 kg)30 L Initial ICF volume 0.4 x (50 kg)20 L Initial ECF volue "0.2 x (50 kg)"10 L Initial total body osmoles (total body water)(body fluid osmolality) =(30L0(2900sn/1kgH20)=87000sm Initial ICF osnoles (ICF volune)(body fluid osmolality) =(20L.)(2900sn/kg120)=58000sm Initial ECF osnoles total body osmoles ICF osmoles
SECTION VI THE KIDNEY Effects of Mannitol Infusion A woman weighing 50 kg (110 lbs) and with a plasma [Na+] of 145 mEq/L is infused with 5 g/kg (2.3 g/lb) of mannitol (molecular weight of mannitol is 182 g/mole). Estimate the following equilibrium values. Assume that mannitol is restricted to the ECF compartment, that no excretion occurs, and that the infusion volume of the mannitol solution is negligible (total body water unchanged): Initial conditions (before mannitol infusion) Total body water: _______________L ICF volume: _______________L ECF volume: _______________L Total body osmoles: _______________mOsm ICF osmoles: _______________mOsm ECF osmoles: _______________mOsm ANSWER The initial volumes of the body fluid compartments and the osmoles in these compartments are calculated as for problem I: Initial total body water = 0.6 x (50 kg) = 30 L Initial ICF volume = 0.4 x (50 kg) = 20 L Initial ECF volume = 0.2 x (50 kg) = 10 L Initial total body osmoles = (total body water)(body fluid osmolality) = (30 L)(290 mOsm/kg H2O) = 8700 mOsm Initial ICF osmoles = (ICF volume)(body fluid osmolality) = (20 L)(290 mOsm/kg H2O) = 5800 mOsm Initial ECF osmoles = total body osmoles - ICF osmoles
=87000sm-58000sm=29000s To determine the effect of the mannitol,the total amount infused must first be calculated.At 5 g/kg.a total of 250 g was infused (1.374 moles of mannitol). Because mannitol is a single particle in solution,this adds 1.374 nOsn to the ECF. The mannitol will raise ECF osmolality and result in the shift of fluid from the ICF into the ECF. New total body water 30 L (unchanged) New total body osmoles 8700 mOsn 1374 nOss 10,074 mOsm Ner ICF osnoles 5800 nOsn (unchanged) New ECF osmoles 2900 mOss+1374 nOsm 4274 nsm New plasma osnolality new total osnoles/total body water- 10.0740s/80.=3360sn/kg120 New ICP volune =ICF osnoles/Now Posn 5800m0sm/(336m0sn/kgH20) 17.301 New ECF volune total body water -ICF volue =30L-17,3=12.7L Because mannitol increases the osmolality of the ECF,2.7 L of fluid shifts from the ICF into the ECF.To calculate the new plasma [Nat].it is assured that the amount of Nat in the ECF is unchanged after mamnitol infusion.Originally,there were 2900 Osn attributed to Nat (2 x [Na+]x ECF volune)in the ECF.Because the Nat osnoles are unchanged but now present in a larger volume,the new plasma [Na+]is calculated as follows: New plasma Na+osmoles 2900m0sn due to Na+/12.7 L 228 mOsn/L
= 8700 mOsm - 5800 mOsm = 2900 mOsm To determine the effect of the mannitol, the total amount infused must first be calculated. At 5 g/kg, a total of 250 g was infused (1.374 moles of mannitol). Because mannitol is a single particle in solution, this adds 1,374 mOsm to the ECF. The mannitol will raise ECF osmolality and result in the shift of fluid from the ICF into the ECF. New total body water = 30 L (unchanged) New total body osmoles = 8700 mOsm + 1374 mOsm = 10,074 mOsm New ICF osmoles = 5800 mOsm (unchanged) New ECF osmoles = 2900 mOsm + 1374 mOsm = 4274 mOsm New plasma osmolality = new total osmoles/total body water- 10，074mOsm/30L= 336 mOsm/kg H2O New ICF volume =ICF osmoles/New Posm = 5800mOsm/（336mOsm/kgH2O） = 17.30 L New ECF volume = total body water - ICF volume = 30 L - 17.3 = 12.7 L Because mannitol increases the osmolality of the ECF, 2.7 L of fluid shifts from the ICF into the ECF. To calculate the new plasma [Na+], it is assumed that the amount of Na+ in the ECF is unchanged after mannitol infusion. Originally, there were 2900 mOsm attributed to Na+ (2 x [Na+] x ECF volume) in the ECF. Because the Na+ osmoles are unchanged but now present in a larger volume, the new plasma [Na+] is calculated as follows: New plasma Na+ osmoles = 2900mOsm due to Na+/12.7 L = 228 mOsm/L
New plasma [Na+](Natosmoles)/2 228n0sm/2 114 mfq/L New equilibriun conditions (after gastroenteritis) Total body water: ICF volune: ECF volume: Total body osnoles: ICF osnoles: ECF ospoles: 0s■
New plasma [Na+] =（Na+osmoles）/2 = 228mOsm/2 = 114 mEq/L New equilibrium conditions (after gastroenteritis) Total body water: _______________L ICF volume: _______________L ECF volume: _______________L Total body osmoles: _______________mOsm ICF osmoles: _______________mOsm ECF osmoles: _______________mOsm