Total Body Water 26g Intracellular fluid acellular fluid P TranscellularInterstitia Fluid Figure 2.1 Body fluid compartments dy fluid compartments a 75 kg man Total body water=55%-65% body weight=45 litres Extracellular fluid=15 litres: intravascular fluid=5 litres Interstitial fluid=10 litres Intracellular fluid=30 litres Transcellular compartment= l litre Osmolality (in mOsm/)=nx molar concentration(mmol/l of water) Plasma osmolality (in mOsm/kg)=2(Na)+2(K+)+(glucose)+urea(all in mmol/D) A Osmolar gap= measured plasma osmolality- calculated plasma osmolality e osmolar gap is a measure of unmeasured osmotically active molecules, such s mannitol and alcohols Components of extracellular fluid Extracellular fluid comprises: Transcellular fluids: intra-ocular, pericardial, peritoneal, pleural and synovial fluids. These are separated from plasma by an additional epithelial layer Glandular secretions
Osmolality (in mOsm/l) ¼ n x molar concentration (mmol/l of water) Plasma osmolality (in mOsm/kg)¼ 2(Naþ)þ 2(Kþ)þ (glucose)þ urea (all in mmol/l) Osmolar gap ¼ measured plasma osmolality calculated plasma osmolality The osmolar gap is a measure of unmeasured osmotically active molecules, such as mannitol and alcohols. Components of extracellular fluid Extracellular fluid comprises: Blood plasma. Lymph. Transcellular fluids: intra-ocular, pericardial, peritoneal, pleural and synovial fluids. These are separated from plasma by an additional epithelial layer. Cerebrospinal fluid. Glandular secretions. Total Body Water Intracellular fluid Extracellular fluid Plasma Transcellular Fluid Interstitial Fluid Figure 2.1 Body fluid compartments. Body fluid compartments In a 75 kg man Total body water ¼ 55%–65% body weight ¼ 45 litres Extracellular fluid ¼ 15 litres; intravascular fluid ¼ 5 litres Interstitial fluid ¼ 10 litres Intracellular fluid ¼ 30 litres Transcellular compartment ¼ 1 litre Water and electrolyte balance 20
Normal blood volume Preterm: 90-105 ml/kg Term infant: 85 ml/kg >I month age: 75 ml/kg >l year age: 67-75 ml/kg Adult: 55-75 ml/kg Measurement of body fluid compartments The volume of body fluid compartments is measured by the dilution of indica ors, which must fulfil the following requirements: All the indicator administered remains in the volume to be measured: Uniform distribution of the indicator follows an adequate time for mixing; The indicator does not alter the volume of the compartment; The indicator does not enter the system by another route. The volume of the compartment= The amount of the indicator administered the amount of indicator excreted)/ Concentration of indicator in the volume being measured. Indicators for measurement of body compartments Plasma volume Uses a substance that binds to plasma albumin Evans Blue(t-1124) Iodocyanin green Radiolabelled albumin (31 Radiolabelled erythrocytes Total body water: Uses a substance that diffuses freely into all fluid compartments Radioactive water Deuterium oxid Tritiated water Extracellular fluid volume Non-metabolised substances Raffinose
Measurement of body fluid compartments The volume of body fluid compartments is measured by the dilution of indicators, which must fulfil the following requirements: All the indicator administered remains in the volume to be measured; Uniform distribution of the indicator follows an adequate time for mixing; The indicator does not alter the volume of the compartment; The indicator does not enter the system by another route. The volume of the compartment ¼ (The amount of the indicator administered the amount of indicator excreted)/Concentration of indicator in the volume being measured. Indicators for measurement of body compartments Plasma volume Uses a substance that binds to plasma albumin: Evans Blue (T-1124) Indocyanin green Radiolabelled albumin(131I) Radiolabelled erythrocytes Total body water: Uses a substance that diffuses freely into all fluid compartments: Radioactive water Deuterium oxide Tritiated water Extracellular fluid volume Non-metabolised substances Mannitol Inulin Sucrose Raffinose Normal blood volume Preterm: 90–105 ml/kg Term infant: 85 ml/kg >1 month age: 75 ml/kg >1 year age: 67–75 ml/kg Adult: 55–75 ml/kg Water balance 21
Daily fluid requirements Premature infant (<2kg birth weight) 150 ml/kg 26g Neonates and infants (2-10 ks 100 ml/kg for the first 10 kg Infants and children(10-20kg) 1000ml/kg +50 ml/kg for every kg 10-20 kg Children (>20 kg 500ml/kg+ 20 ml/kg for every kg >20 kg Normal water losses Urine 1.0-1.5 1/24 h Stool 0.2-0.4 1/24 h Insensible loss 0.6-0.8 1/24 h Thiocyanat Thiosulphate Sodium Extracellular fluid volume assessment and replacement Extracellular fluid volume status can be assessed by: Level of consciousness The presence of thirst; Moistness of mucosal surfaces: Skin turgo Heart rate: Supine and standing blood pressure Urine outp Options for extracellular fluid volume replacement Colloids Smaller infusion volume required, with more rapid resuscitation; Prolonged plasma volume expansion Better oxygen delivery; Minimal peripheral oedema Lower intracranial pressure Reduced risk of thromboembolism Risk of coagulopathy
Diffusible ions Sulphate Thiocyanate Thiosulphate Chloride Bromide Sodium Extracellular fluid volume assessment and replacement Extracellular fluid volume status can be assessed by: Level of consciousness; The presence of thirst; Moistness of mucosal surfaces; Skin turgor; Heart rate; Supine and standing blood pressure; Urine output. Options for extracellular fluid volume replacement Colloids Smaller infusion volume required, with more rapid resuscitation; Prolonged plasma volume expansion; Better oxygen delivery; Minimal peripheral oedema; Lower intracranial pressure; Reduced risk of thromboembolism; Higher cost; Risk of coagulopathy; Daily fluid requirements Premature infant (<2 kg birth weight) 150 ml/kg Neonates and infants (2–10 kg) 100 ml/kg for the first 10 kg Infants and children (10–20 kg) 1000ml/kgþ 50ml/kg for every kg 10–20 kg Children (>20 kg) 1500ml/kgþ 20ml/kg for every kg > 20 kg Normal water losses Urine 1.0–1.5 l/24 h Stool 0.2–0.4 l/24 h Insensible loss 0.6–0.8 l/24 h Water and electrolyte balance 22
Production of osmotic diuresis: Pulmonary oedema in capillary leak states, owing to increased total lung water. Require a larger volume to reach similar end-points Short-lived plasma volume expansion; Risk of peripheral oedema and pulmonary oedema; Lower cost aised glomerular filtration rate Replaces interstitial fluid In general, water will equilibrate across the intravascular, intracellular and interstitial spaces, while sodium equilibrates across the intravascular and inter stitial spaces. Large molecules tend to be retained, for the major part, in the intravascular space ■ Water reabsorption Water reabsorption of 65% to 75% takes place in the proximal convoluted tubule, accompanying sodium and other solutes. Further reabsorption occurs in the descending limb of the loop of Henle and, finally, in the collecting ducts via water channels or pores Properties of arginine vasopressin (antidiuretic hormone; ADH) Arginine vasopressin is a nine amino acid peptide, comprising a six-membered disulphide ring and a tail of three amino acid residues on which the C-terminal carboxy group is amidated. It is synthesised in magnocellular neural cells in the supraoptic and paraventricular nuclei of the hypothalamus, in proximity to the osmoreceptors. The osmotic threshold for thirst is at 290-5 mOsm/kg H2O, and is above the threshold for vasopressin release, which is 280-90 mOsm/kg The synthesised peptide is enzymatically cleaved from the prohormone and where it is stored in neurosecretory gran ules. Release into the bloodstream is triggered by specific stimuli, i.e. osmo- receptor stimulation by thirst, and by hypovolaemia. It has a short half-life of 15-20 minutes and is rapidly metabolised in the liver and kidne Arginine vasopressin acts via Vi receptors in vascular tissue, which are respon sible for vasopressor effects, and V2 receptors in the kidneys, which are
Production of osmotic diuresis; Pulmonary oedema in capillary leak states, owing to increased total lung water. Crystalloids Require a larger volume to reach similar end-points; Short-lived plasma volume expansion; Risk of peripheral oedema and pulmonary oedema; Lower cost; Raised glomerular filtration rate; Replaces interstitial fluid. In general, water will equilibrate across the intravascular, intracellular and interstitial spaces, while sodium equilibrates across the intravascular and interstitial spaces. Large molecules tend to be retained, for the major part, in the intravascular space. & Water reabsorption Water reabsorption of 65% to 75% takes place in the proximal convoluted tubule, accompanying sodium and other solutes. Further reabsorption occurs in the descending limb of the loop of Henle and, finally, in the collecting ducts, via water channels or pores. Properties of arginine vasopressin (antidiuretic hormone; ADH) Arginine vasopressin is a nine amino acid peptide, comprising a six-membered disulphide ring and a tail of three amino acid residues on which the C-terminal carboxy group is amidated. It is synthesised in magnocellular neural cells in the supraoptic and paraventricular nuclei of the hypothalamus, in proximity to the osmoreceptors. The osmotic threshold for thirst is at 290–5 mOsm/kg H2O, and is above the threshold for vasopressin release, which is 280–90 mOsm/kg. The synthesised peptide is enzymatically cleaved from the prohormone and transported to the posterior pituitary, where it is stored in neurosecretory granules. Release into the bloodstream is triggered by specific stimuli, i.e. osmoreceptor stimulation by thirst, and by hypovolaemia. It has a short half-life of 15–20 minutes and is rapidly metabolised in the liver and kidneys. Arginine vasopressin acts via V1 receptors in vascular tissue, which are responsible for vasopressor effects, and V2 receptors in the kidneys, which are Water reabsorption 23
Renal aquaporins (water channel proteins) 26g AQPI Proximal tubule, thin descending limb AQP2 Collecting duct apical membrane and subapical vesicles Regulated by Collecting duct basolateral membrane AQP4 Inner medullary collecting duct basolateral membrane Factors that control arginine vasopressin release: Increased extracellular fluid (plasma) tonicity(osmolarity): hypothalamic osmoreceptors Reduced extracellular fluid volume Plasma volume contraction: cardiovascular volume re Fall in arterial blood pressure: cardiovascular barorec Hormonal: beta-adrenergic stimulation hypothyroidism Drugs: nicotine barbiturates vincristine Miscellaneous: nausea and vomiting hypoglycaemia Decreased tonicity of the extracellular fluid Extracellular fluid volume: volume expansion rise in blood pressure Hormonal: alpha-adrenergic stimulation Drugs: ethanol Miscellaneous: cold responsible for antidiuretic effects. The Vi receptor is a 394 amino acid protein with 7 transmembrane domains. The V2 receptor is a 370 amino acid protein coupled to adenyl cyclase by a Gs protein. Antidiuretic effects of arginine vasopressin Arginine vasopressin increases water reabsorption in the collecting ducts of the kidney. This is achieved by binding to the G-protein-coupled v2 receptor in the
responsible for antidiuretic effects. The V1 receptor is a 394 amino acid protein with 7 transmembrane domains. The V2 receptor is a 370 amino acid protein, coupled to adenyl cyclase by a Gs protein. Antidiuretic effects of arginine vasopressin Arginine vasopressin increases water reabsorption in the collecting ducts of the kidney. This is achieved by binding to the G-protein-coupled V2 receptor in the Renal aquaporins (water channel proteins) Aquaporin Renal localisation AQP1 Proximal tubule, thin descending limb AQP2 Collecting duct apical membrane and subapical vesicles. Regulated by vasopressin AQP3 Collecting duct basolateral membrane AQP4 Inner medullary collecting duct basolateral membrane Factors that control arginine vasopressin release: Stimulation Increased extracellular fluid (plasma) tonicity (osmolarity): hypothalamic osmoreceptors Reduced extracellular fluid volume Plasma volume contraction: cardiovascular volume receptors Fall in arterial blood pressure: cardiovascular baroreceptors Hormonal: beta-adrenergic stimulation angiotensin II hypothyroidism hypoadrenalism Drugs: nicotine barbiturates vincristine Miscellaneous: nausea and vomiting hypoglycaemia stress heat Inhibition Decreased tonicity of the extracellular fluid Extracellular fluid volume: volume expansion rise in blood pressure Hormonal: alpha-adrenergic stimulation Drugs: ethanol Miscellaneous: cold Water and electrolyte balance 24