Body fluids 2.pdf

ILOs By the end of this lecture the student should be able to: ▪ calculate the volume of different fluid compartments ▪ Understand the concept of the water balance ▪ Identify causes of water gain and loss Measurement of body fluids How? Why? Measurement of different...

ILOs By the end of this lecture the student should be able to: ▪ calculate the volume of different fluid compartments ▪ Understand the concept of the water balance ▪ Identify causes of water gain and loss Measurement of body fluids How? Why? Measurement of different body fluids  Depending on the indicator-dilution principle, using a dye. Volume of fluid in ml=  The amount of dye injected Concentration of dye / ml of fluid 3 gram/ml 18 gram Indicator dilution principle  Steps:  Inject the dye  Allow the dye to mix very well (disperse)  Measure the dye concentration in the fluid chamber to be measured (analyzing) Properties (criteria) of the (indicator substance) dye o Disperses (mixes) only in the compartment that is being measured. o Disperses evenly throughout the measured compartment. o Indicator is not metabolized or excreted o It must be unchanged during the experiment or if it changes, the amount changed must be known. o It must be non-toxic, no physiological activity. o It has no effect on the distribution of H2O or other substances in the body. o It should be relatively easy to measure. Principle of the indicator-dilution method for measuring fluid volume: o It is based on the principle of conservation of mass. o The principle stating that mass cannot be created or destroyed.  The total mass of a substance after mixing in the fluid compartment = The total mass injected into the compartment.  Mass of substance in chamber B = Mass of injected substance A  Volume B X concentration B = Volume A X concentration A 𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑐ℎ𝑎𝑚𝑏𝑒𝑟 𝐵 𝑣𝑜𝑙𝑢𝑚𝑒 𝐴 𝑋 𝑐𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝐴 = 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝐵 If some of the injected substance is lost in compartment B:  Mass of substance in B = Mass of injected substance A – lost amount   𝑣𝑜𝑙𝑢𝑚𝑒 𝑜𝑓 𝑐ℎ𝑎𝑚𝑏𝑒𝑟 𝐵 𝑚𝑎𝑠𝑠 𝑜𝑓 𝐴−𝑙𝑜𝑠𝑡 𝑎𝑚𝑜𝑢𝑛𝑡 = 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 𝐵  Measurement of total body water  The dye is distributed  uniformly through all dye compartments Blood vessel oRadioactive water (tritium, 3H O) 2 o heavy water (deuterium, 2H2O) o Antipyrine (is very lipid ISF soluble ) o Aminopyrine Volume of fluid in ml= 42 l CELL The amount of dye injected Concentration of dye / ml of fluid  Measurement of extra cellular fluid  The dye must cross  capillary wall but not cross dye cell membrane.  Remain outside the cells  Inulin, sucrose, mannitol, bromide Volume of fluid in ml= 14 liters The amount of dye injected Concentration of dye / ml of fluid Cell  Note  Many substances can cross the cell membranes to some extent leading to inaccurate result.  Inulin and sucrose are the least to penetrate the cell membrane. So, they are more accurate in estimation of the ECF volume Measurement of plasma compartment  The substances must do not cross  capillary wall or cell membrane (Remain in the vascular system after injection dye  Evans blue  Albumin labeled with radioactive iodine ISF Volume of fluid in ml= 3-3.5 liters The amount of dye injected cell Concentration of dye / ml of fluid Measurement of interstitial fluid volume  In direct   Why? dye  Because substance that equilibrate with ISF equilibrate with plasma  Method: ISF  ISF= ECF- plasma  = 14-3.5=10.5 liters cell Measurement of ICF  In direct   Why? dye  Because substance can not Blood vessel enter the cell without being present in other compartments ISF  ICF= TBW-ECF  = 42-14=28 liters CELL Effect of age on water distribution children adult  TBW=75% of body  TBW=60% of body weight (10Kg)= 7.5 weight (70Kg)= 42 liters liters ECF/ICF volume ratio is larger in infants, children than that of adults However, the absolute volume of ECF in infants & children is smaller than that of adults, because of smaller body weight. Dehydration develops rapidly and more severe in infants Measurement of blood volume Blood 8% body weight=5.6 L Blood is formed of:  A) Cells 45%  B) Fluid=plasma 55% Red blood cells are the most abundant cells Red blood cell volume is called hematocrit value=45%  Hematocrit (Packed Red Cell Volume): − Def: − It is the ratio of the volume of red blood cells to the total volume of blood. − It is the fraction of the blood composed of red blood cells. − Value: − In adult male, it is normally about 0.40 (40%) − In women, it is about 0.36 (36%) − It decreases in anemia and increases in polycythemia. To measure blood volume 1. Total blood volume is obtained from plasma volume and hematocrit. 2. Total blood volume can be obtained from red cell volume (RBCs) and hematocrit. Solve this problem  Hematocrit volume=38%, plasma volume 3500 ml  Calculate blood volume Plasma volume=100- Hematocrit value 38= (62%) Plasma volume(3500 ml)-------------------------------------62% (100-hematocrit value) Blood volume?-------------------------------100% 𝑃𝑙𝑎𝑠𝑚𝑎 𝑣𝑜𝑙𝑢𝑚𝑒 𝑥 100 𝑇𝑜𝑡𝑎𝑙 𝑏𝑙𝑜𝑜𝑑 𝑣𝑜𝑙𝑢𝑚𝑒 = 100−𝐻𝑒𝑚𝑎𝑡𝑜𝑐𝑟𝑖𝑡 3500x100/ 62= 5.6 Liters Total blood volume can be obtained from red cell volume (RBCs) and hematocrit: o Measure RBC volume by indicator dilution method using radioactive chromium o Determine hematocrit. 𝑅𝐵𝐶 𝑣𝑜𝑙𝑢𝑚𝑒 𝑥 100  𝑇𝑜𝑡𝑎𝑙 𝑏𝑙𝑜𝑜𝑑 𝑣𝑜𝑙𝑢𝑚𝑒 = 𝐻𝑒𝑚𝑎𝑡𝑜𝑐𝑟𝑖𝑡 The RBC volume can be measured, using the indicator dilution method as follows: o A sample of the patient's red cells is withdrawn and labeled with radioactive chromium (51Cr) and its radioactivity is measured. o Inject into the circulation these chromium-labeled red blood cells. o After mixing in the circulation, the radioactivity of a mixed blood sample is measured. 𝑟𝑎𝑑𝑖𝑜𝑎𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓𝑖𝑛𝑗𝑒𝑐𝑡𝑒𝑑 𝑅𝐵𝐶 𝑠𝑎𝑚𝑝𝑙𝑒  𝑅𝐵𝐶 𝑣𝑜𝑙𝑢𝑚𝑒 = 𝑟𝑎𝑑𝑖𝑜𝑎𝑐𝑡𝑖𝑣𝑖𝑡𝑦 𝑜𝑓 𝑎 𝑚𝑖𝑥𝑒𝑑 𝑏𝑙𝑜𝑜𝑑 𝑠𝑎𝑚𝑝𝑙𝑒 Measurement of body fluids Why? Fluid intake (input) Fluid loss (output)  Fluid intake (input) Fluid loss (output) Normally fluid intake must equal fluid output {stable balance} ✶ If water gain > water loss → overhydration ✶ If water gain < water loss → dehydration  Water balance disorder  Dehydration  Over hydration This is called Homeostasis  1- Sweating through sweat gland It depends on physical activity and environmental temperature. It increases in very hot weather or during heavy exercise; occasionally increases to 1 to 2 L/hour. 2- kidneys controls urine volume It can be as low as 0.5 L/day in a dehydrated person It can be as high as 20 L/day in a person who has been drinking tremendous amounts of water (overhydration). It is controlled by hormones 3- Brain centers increase Thirst secreted by the endocrine sensation glands