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Regulation of fluids and acid base balance

front 1 noenates fluids proportion At 12 months of age	back 1 75-80% water Proportionally more ECF than adults Interstitial fluid is three times larger than in adults At 12 months decrease to 60%
front 2 TBW at 60 years of age	back 2 50% of total body weight Due to increased adipose tissue
front 3 Fluids can be collectively discussed in physiologically relevant compartments, which are....	back 3 Intracellular Fluid (ICF: about 23 liters, 2/3 TBW, discontinuous small collections) Extracellular Fluid (ECF: about 19 liters, interstitial fluid and plasma)
front 4 Characteristics of ICF	back 4 High in potassium High in magnesium Low in sodium and chloride ions

front 5 Characteristics of ECF	back 5 Low in potassium Low in magnesium High in sodium and chloride ions
front 6 Interstitial fluid (ISF)	back 6 consists of all the fluids which lie in the interstices of all body tissues. is the link between the ICF and the intravascular compartment. Oxygen, nutrients, wastes and chemical messengers all pass through the ISF. low protein concentration (in comparison to plasma). Lymph is considered as a part of the ISF
front 7 Plasma	back 7 The only major fluid compartment that exists as a real fluid collection all in one location. Higher protein content and its high bulk flow interstitial fluid of the blood
front 8 The fluid compartment called the blood volume is interesting in that it is a composite compartment containing.....	back 8 ECF (plasma) ICF (red cell water)

front 9 Blood levels – normal range Sodium	back 9 135-145 mEq/L
front 10 Blood levels – normal range Potassium	back 10 3.5-5.5 mmoles/L
front 11 Blood levels – normal range Magnesium	back 11 0.7-0.95 mmoles/L
front 12 Blood levels – normal range Calcium	back 12 2.20-2.55 mmoles/L

front 13 Blood levels – normal range Chloride	back 13 96-106 mmoles/L
front 14 Blood levels – normal range Phosphate	back 14 0.8-1.3 mmoles/L
front 15 What makes water move?	back 15 Osmosis The osmotic pressure is the hydrostatic (or hydraulic): pressure required to oppose the movement of water through a semi-permeable membrane in response to an ‘osmotic gradient’ Serum osmolality can be measured by use of osmometer calculated as the sum of the concentrations of the solutes present in the solution
front 16 Components of Daily Obligatory Water Loss	back 16 Insensible loss: 800 mls Minimal sweat loss: 100 mls Faecal loss: 200 mls Minimal urine volume to excrete solute load: 500 mls Total: 1,600 mls

front 17 Fluid input	back 17 External: Oral intake of fluids and food (+ IV fluids) Food is an important source of water Processed foods may have a very low water content. Internal: Metabolic water production The oxidation of food Carbohydrates are completely metabolised to CO2 and H2O Metabolic water is about 350 to 400 mls/day (ie 5 mls/kg)
front 18 Pure gastric vomiting	back 18 Loss of HCl volume causes hypochloremic metabolic alkalosis Cl decrease > limits reabsorption of HCO3 in the kidneys
front 19 Bilious vomiting	back 19 loss of K loss of HCO3 loss of Na causes hypokalemia, acidosis
front 20 Panting	back 20 Loss of free water no electrolyte loss

front 21 Free water gain	back 21 Dilution Diuresis promotes ion loss
front 22 Diarrhea	back 22 loss of volume Loss of Na Loss of K Loss of HCO3
front 23 Oral rehydration solutions should	back 23 Enhance the absorption of water and electrolytes Replace the electrolyte deficit adequately and safely Contain an alkalinising agent to counter acidosis Be slightly hypo-osmolar (about 250 mmol/litre) to prevent induction of osmotic diarrhoea be simple to use in the hospital and at home be palatable and acceptable, especially to children be readily available
front 24 The WHO oral rehydration salts formulation contains	back 24 Sodium chloride 2.6 g. Na+ 75 mmol/l, Cl– 65 mmol Potassium chloride 1.5 g. K+ 20 mmol/l Sodium citrate 2.9 g. citrate 10 mmol/l Anhydrous glucose 13.5 g glucose 75 mmol/l It is dissolved in sufficient water to produce 1 litre

front 25 Oral rehydration solutions used in the UK are	back 25 lower in sodium (50–60 mmol/litre)
front 26 Rehydration should be rapid over	back 26 3 to 4 hours in most cases
front 27 Maximum rate of sweating is	back 27 up to 50 mls/min or 2,000 mls/hr in the acclimatised adult losses up to 25% of total body water are possible under severe stress from 100 to 8,000 mls/day solute loss can be as much as 350 mmols/day (or 90 mmols/day acclimatised) of sodium under the most extreme conditions
front 28 Losses due to Sweating	back 28 Fluid loss (hot environment, physically active) Solute loss (Decreases with 'acclimatisation', 0.2-1%) Heat loss

front 29 Insensible fluids losses	back 29 From the skin (trans-epithelial) From the respiratory tract Heat loss No solute loss
front 30 The Central Controller in Water Balance	back 30 Hypothalamus Osmoreceptors Thirst centre OVLT & SFO (respond to angiotensin II) Supraoptic & paraventricular nuclei (for ADH synthesis)
front 31 What is thirst?	back 31 Thirst is "the physiological urge to drink water". Most water intake is due to social and cultural factors, not thirst Thirst offers a backup to these behavioural factors and to the ADH response.
front 32 Water intake can be considered to consist of two components:	back 32 a regulatory component (due to thirst) non-regulatory component (all other fluid intake)

front 33 The 4 major stimuli to thirst are:	back 33 The 4 major stimuli to thirst are: Hypertonicity: Cellular dehydration acts via an osmoreceptor Hypovolaemia: sensed via the low pressure baroreceptors in the great veins and right atrium Hypotension: The high pressure baroreceptors in carotid sinus & aorta provide the sensors for this input Angiotensin II: This is produced consequent to the release of renin
front 34 Drinking stimulates	back 34 mechanoreceptors in the mouth and pharynx Peripheral receptors provide input to the hypothalamus and the sensation of thirst is relieved This occurs even before any reduction in plasma tonicity
front 35 Antidiuretic Hormone (ADH)	back 35 nonapeptide synthesised in the hypothalamus regulation of water balance by its effect on the kidneys Also known as vasopressin Intravenously has a half-life of only about 15 minutes Rapidly metabolised in the liver and kidney to inactive products
front 36 Properties of caffeine and alcohol? affect which hormone?	back 36 diuretic properties inhibit the pituitary secretion of ADH Caffeine > when ingested at levels in excess of 300mg Alcohol diuretic effects are largly due to the alcohol volume

front 37 Why give fluids?	back 37 Replace intravascular volume Improve tissue perfusion Replace fluid deficits (dehydration) Replace ongoing losses (Vomiting, Diarrhoea, burns, etc.) Fluid diuresis to eliminate toxins Anaesthetic and surgical support Replacement of specific components (blood, plasma) Nutritional support (TPN, PPN)
front 38 Extracellular fluid pH Blood pH	back 38 7.4 7.35 – 7.45
front 39 Acidosis pH Alkalosis pH	back 39 acidemia below 7.35 alkalemia above 7.45 < 6.8 or > 8.0 death occurs
front 40 Small changes in pH can produce major disturbances such as	back 40 Most enzymes function only with narrow pH ranges Affect electrolytes (Na+, K+ , Cl-) Affect hormones Affects bone synthesis and reabsorption

front 41 The body produces more acids than bases	back 41 •Acids taken in with foods •Acids produced by the metabolism of lipids and proteins •Cellular metabolism produces CO2.
front 42 pH equation	back 42 pH = - log [H+]
front 43 pH Regulation organs	back 43 Lung > respiratory compensation > Pco2 > carbonic acid bicarbonate buffer system Kidneys > renal compensation > H+
front 44 Three major buffering systems	back 44 Protein buffer system > AA, H+ by haemoglobin buffer system Carbonic acid bicarbonate system > organic and fixed acids Phosphate > buffer pH in ICF

front 45 Common acids include...	back 45 Carbonic acid is the most important factor affecting pH of ECF Sulfuric acid and phosphoric acid > catabolism of AA Organic acids > Metabolic byproducts lactic acid, ketones
front 46 Carbonic Acid-Bicarbonate Buffering	back 46 H+ + HCO3- <> H2CO3 <> H2O + CO2 convert carbonic acid to CO2 (through the enzyme carbonic anhydrase) Then remove CO2 from the body through respiration. Only functions when the respiratory system and control centres are working normally
front 47 Enzyme converting carbonic acid to carbon dioxide	back 47 carbonic anhydrase
front 48 Explain protein buffering	back 48 ⬆️ pH > the carboxyl group acts as a weak acid ⬇️ pH > the amino group acts as a weak base Hemoglobin buffer system Prevents pH changes when PCO2 is rising or falling

front 49 Rates of correcting pH	back 49 Respiratory > several minutes to hours Renal > several hours to days
front 50 Acidosis symptoms	back 50 Depression of the CNS through ↓ in synaptic transmission. Generalized weakness Deranged CNS function Severe acidosis causes > Disorientation, coma, and death
front 51 Alkalosis symptoms	back 51 causes over excitability of the central and peripheral nervous systems Numbness Lightheadedness Nervousness muscle spasms or tetany Convulsions Loss of consciousness Death
front 52 The Bohr effect is	back 52 a physiological phenomenon where haemoglobin's affinity for oxygen decreases as carbon dioxide levels or acidity (pH) in the blood increase causing it to release more oxygen to tissues that need it, like actively respiring muscles.

front 53 Respiratory Acidosis why? in which conditions?	back 53 Carbonic acid excess occurs by blood levels of CO2 are above 45 mm Hg. Hypercapnia Chronic conditions Drugs or head trauma > Depression of the respiratory centre in the brain that controls breathing rate Paralysis of the respiratory or chest muscles Emphysema Acute conditions Adult Respiratory Distress Syndrome Pulmonary edema Pneumothorax
front 54 Compensation for Respiratory Acidosis	back 54 Kidneys eliminate hydrogen ion and retain bicarbonate ion
front 55 Signs and Symptoms of Respiratory Acidosis	back 55 Breathlessness Restlessness Lethargy and disorientation Tremors, convulsions, coma Respiratory rate rapid, then gradually depressed Skin warm and flushed due to vasodilation caused by excess CO2
front 56 Treatment of Respiratory Acidosis	back 56 Restore ventilation IV lactate solution Treat underlying dysfunction or disease

front 57 Respiratory Alkalosis Why? In which conditions?	back 57 Carbonic acid deficit pCO2 less than 35 mm Hg (hypocapnea) Most common acid-base imbalance Primary cause is hyperventilation Conditions that stimulate respiratory center: Oxygen deficiency at high altitudes Pulmonary disease and Congestive heart failure – caused by hypoxia Acute anxiety Fever, anemia Early salicylate intoxication Cirrhosis Gram-negative sepsis
front 58 Compensation of Respiratory Alkalosis	back 58 • Kidneys conserve hydrogen ion • Excrete bicarbonate ion
front 59 Treatment of Respiratory Alkalosis	back 59 Treat the underlying cause Breathe into a paper bag IV Chloride-containing solution – Cl- ions replace lost bicarbonate ions
front 60 Major causes of metabolic acidosis	back 60 Depletion of bicarbonate reserve Inability to excrete hydrogen ions at kidneys Production of large numbers of fixed / organic acids Bicarbonate loss due to chronic diarrhea

front 61 Symptoms of Metabolic Acidosis	back 61 Headache, lethargy Nausea, vomiting, diarrhea Coma Death
front 62 Compensation for Metabolic Acidosis	back 62 Increased ventilation Renal excretion of hydrogen ions if possible K+ exchanges with excess H+ in ECF
front 63 Treatment of Metabolic Acidosis	back 63 IV lactate solution
front 64 Metabolic Alkalosis causes	back 64 Bicarbonate excess greater than 26 mEq/L Causes: Excess vomiting = loss of stomach acid Excessive use of alkaline drugs Certain diuretics Endocrine disorders Heavy ingestion of antacids Severe dehydration

front 65 Symptoms of Metabolic Alkalosis	back 65 • Respiration slow and shallow • Hyperactive reflexes ; tetany • Often related to depletion of electrolytes • Atrial tachycardia • Dysrhythmias
front 66 Compensation for Metabolic Alkalosis	back 66 Alkalosis most commonly occurs with renal dysfunction, so can’t count on kidneys • Respiratory compensation difficult – hypoventilation limited by hypoxia
front 67 Treatment of Metabolic Alkalosis	back 67 Electrolytes to replace those lost IV chloride containing solution Treat underlying disorder
front 68 Diagnosis of Acid-Base Imbalances	back 68 Note whether the pH is low (acidosis) or high (alkalosis) Decide which value, pCO2 or HCO3 is outside the normal range and could be the cause of the problem If the cause is a change in pCO2, the problem is respiratory If the cause is HCO3- the problem is metabolic Look at the value that doesn’t correspond to the observed pH change. If it is inside the normal range, there is no compensation occurring. If it is outside the normal range, the body is partially compensating for the problem.