Fluid & Electrolyte Balance PDF

FLUID & ELECTROLYTE BALANCE DR. MEKA I.A  Lecture Objectives At the end of the lecture, students should be able to Define Electrolyte, electrolyte profile Define and calculate plasma osmolality, anion gap, osmolar gap Identify factors involved in water,...

FLUID & ELECTROLYTE BALANCE DR. MEKA I.A  Lecture Objectives At the end of the lecture, students should be able to Define Electrolyte, electrolyte profile Define and calculate plasma osmolality, anion gap, osmolar gap Identify factors involved in water, blood volume and electrolyte regulation Discuss common fluid and electrolyte derangements Enumerate investigations & Rx of each pathological  Introduction Homeostasis connotes the tendency to resist change in order to maintain a stable internal environment. The body’s ability to physiologically regulate its inner environment to ensure its stability in response to fluctuations in ext. or int. conditions B/c maintenance of normal volume and composition of ECF is necessary for efficiency of physiological processes & vital to life Homeostasis is maintained by a complex balance which include; - Fluid balance - Osmotic balance - Electrolyte balance - Acid-base balance  Daily Water Balance (liters) INPUT OUTPUT INSENSIBLE 0.8 FLUID INTAKE 1.5 SWEAT 0.1 IN FOOD 0.8 FECES 0.2 METABOLIC 0.3 URINE 1.5 Total 2.6 Total 2.6  Water balance contd ~Two liters of water per day are generally sufficient for adults; Sources of water are markedly reduced in patients who are not eating (NPO) and so must be provided by maintenance fluids Hypotonic – 0.45 % NaCl, aka half-strength Normal Saline, (lower concn of solutes than plasma) Isotonic – eg Lactate Ringer’s solution, 0.9% NaCl (similar concn of solutes as plasma) Hyper tonic fluids eg 3% NaCl , 50% Dextrose in water 3% NaCl aka 3% Saline, hyper tonic saline  Water balance contd 0.9% Normal Saline – Contains 0.9 G of salt (NaCl) per 100 ml of solution, or 9 G per liter. This solution has 154 mEq of Na per liter A fluid and electrolyte replenisher usually used to correct hypovolemia  Water balance contd Water requirements increase with:
fever, sweating, burns, tachypnea, surgical drains, polyuria, or ongoing significant gastrointestinal losses For example, water requirements increase by 100 to 150 mL/day for each C degree of body temperature elevation  Fluid/Osmotic Balance The osmolal concn (no of osmoles of solute) of a solution in osmoles/kg of water = osmolality when expressed as osmoles per litre of solution = osmolarity. Osmolality is a measure of concn of particles in the serum per kg of water. Osmolarity depends on the volume of solution, and therefore on the temperature and pressure of the solvent Osmolality depends on the mass of the solvent which is independent of temperature and pressure. Osmotic pressure (body fluids) is more closely proportional to osmolality than osmolarity  Fluid/Osmotic Balance The main way to regulate body water gain is by adjusting water intake The thirst center governs the urge to drink Regulation of loss of excess water or excess solutes depends mainly on regulating excretion in the urine. Main determinant of body fluid volume is extent of urinary Na loss Whereas the main determinant of body fluid osmolality is the extent of urinary water loss Osmolality and volume are related b/c osmolality is regulated by water balance, whereas volume is regulated by changes in Na+  Osmolality Is an estimation of osmolar concn of plasma; is propor tional to number of par ticles per kg of solvent A phy proper ty of a solution based on concentration of solute per kg of solvent Na and its associated ions contribute majorly (~90%) Determined by - Measurement (with an osmometer) (serum, plasma, urine) Osmometer measures osmolality using principle of freezing point depression - Calculation - Plasma osmolality = 2[Na] + [Urea] + [Glucose] in mmol/L - Ref range = 275 – 295 mOsm/kg Osmometers  Osmolality contd Uosm = 2(UNa + UK) + Uurea / 2.8 + Uglucose / 18 Osmolar gap = measured osmolality (MO) - calculated osmolality (CO). The "Osmolal gap" represents osmoles unaccounted for by sodium salts, glucose and urea. In healthy individuals, the osmolal gap is 3L/day or 50ml/kg/day Oliguria is defined as a urine output that is less than 1 mL/kg/h in infants, less than 0.5 mL/kg/h in children, and less than 400 mL daily in adults. Anuria: < 100ml/day  Hypervolemia (Fluid overload) Hypervolemia is an excess of water in the body The electrolyte of most concern with hypervolemia is sodium S/S: Shortness of breath & orthopnea Edema & weight gain Distended neck veins & tachycardia Increased blood pressure Crackles & wheezes Pleural effusion  Causes of hypervolemia Any disorder that decreases the body's ability to excrete water or increases the body's tendency to retain water Drinking too much water rarely causes overhydration if the pituitary gland, kidneys, liver, and heart are functioning normally Common causes: heart failure, kidney failure, liver cirrhosis, nephrotic syndrome SIADH; Inappropriate ADH secretion, stimulating the kidneys to conserve water when that is not needed. Treatment Treat underlying cause Diuretics  Blood volume regulation Adequate bld vol essential to maintain blood pressure and good perfusion to all tissues and organs Water and Na regulation are interrelated in controlling bld vol Mechanisms ↓ 1) Kidneys: RAAS responds primarily to a blood volume ↓ Renin is secreted in response to renal blood flow Angiotensinogen  Angiotensin I  Angiotensin II  Vasoconstriction, Aldosterone secretion (stimulates Na reabsorption in renal distal tubules) with water that accompanies Na RAAS Mechanism  Mechanisms contd 2) Blood volume (pressure) changes also detected by stretch receptors located in carotid sinus, aor tic arch, cardiopulmonary circulation and glomerular ar terioles These receptors restore volume by varying vascular resistance, cardiac output, renal water and Na retention 3) Atrial Natriuretic Peptide (ANP): released from myocardial atria in response to volume expansion, promotes natriuresis 4) Glomerular Filtration Rate (GFR): ↑ with volume expansion, and vice versa  Electrolyte balance Electrolytes: charged low mol mass molecules present in body fluids and help transmit electrical impulses for the proper functioning of the hear t, nerves and muscles. Are inorganic substance that dissociates into ions Fluid balance & electrolyte balance are interrelated Usually ions of; Sodium, Potassium, Calcium, Magnesium, Chloride, Bicarbonate, Phosphate, Sulphate Electrolyte profile: Na, K, Cl, HCO3  Functions of electrolytes Volume and osmotic regulation Myocardial rhythm and contractility Cofactors in enzyme activation Acid base balance Blood coagulation Regulation of ATPase ion pumps Neuromuscular excitability Electrolyte regulation & its disorders Na : the most abundant cation in ECF, largely determines osmolality Na regulation- 1) Water intake 2) Water excretion 3) Blood volume status; affects Na excretion via aldosterone, angiotensin, ANP Na & Water regulation  Anion Gap Sum of cations and anions in ECF is always equal, so as to maintain electrical neutrality. N a + K = 9 5 % o f ca ti o ns whe r e a s C l - + H C O 3 = 8 6 % o f anions. Only these electrolytes are commonly measured T h e a p p a r e n t g a p i s d u e to u n m e a s u r e d a n i o n s. ( p r o te i n anions, sulphate, phosphate, lactate and organic acids) The anion gap is calculated as the difference between (Na + + K+) and (HCO- + CL-). Normal range: 10-20mmol/L 3 High, Normal and Low Anion gap metabolic acidosis  Disorders of sodium balance Hyponatraemia Defined as serum/plasma sodium level less than 135 mmol/L Considered severe at 125 mmol/l) Water restriction to < urine output In resistant cases , consider Demeclocycline (some undesirable s.effect) or ADH Receptor Antagonists Add diuretics if hypervolemic NB: In all cases [Na] should not increase by >10-12mmol/l in 24hours to avoid osmotic demyelination syndrome, seizures and permanent neurological injury  Hypernatremia Defined as Na > 150 mmol/L Less commonly seen in hospitalized patients May result from excess loss of water relative to Na+ loss, decreased water intake, or increased Na+ intake or retention Indivs at ↑risk: altered mental status, intubated patients, infants, older adults. Symptoms most commonly involve the CNS due to the hyperosmolar state  Symptoms of hypernatremia Symptoms in infants can include tachypnea, muscle weakness, restlessness, a high-pitched cry, insomnia, lethargy, and coma In adults, symptoms tend to be mild and may include anorexia, muscle weakness, restlessness, nausea, and vomiting Hypernatremia can cause brain shrinkage, resulting in vascular rupture and intracranial bleeding 
Causes of hypernatraemia
Excess water loss - Diabetes insipidus Decreased water intake Increased intake or - Older persons retention - Hyperaldosteronism - I nf a nt s - Sodium bicarbonate - Mentally impaired excess - Dialysis fluid excess  Investigations & Treatment Investigations Laboratory studies are not necessary if the cause is apparent from the history, but frequent electrolyte checks are recommended during correction Treatment Fluid replacement Reduction of oral Na intake Management of underlying disorder - NB: Rapid over-correction can result in cerebral edema; therefore, the least amount of fluid possible should be used  Potassium The major intracellular cation, with a concentration 20x greater inside the cells than outside. This is bc most cellular functions require a low ECF concn of K+ In a healthy person, the plasma potassium is maintained within a narrow range of 3.5–5.1 mmol/L Potassium imbalance can cause life threatening conditions Functions of K+ Regulation of neuromuscular excitability Contraction of hear t mzls Maintenance of ICF volume Affects H+ concn: via K+/H+ ATPase  Potassium Regulation Renal Regulation Kidneys are important organs in mgt of chronic potassium balance Proximal tubules reabsorb nearly all filtered K+ Under the influence of Aldosterone, in the distal tubules and collecting ducts; K+ is secreted into the urine in exchange for Na+ via Na+-K+-ATPase Hence, distal nephron is the principal determinant of urinary K+ excretion Extrarenal Regulation Include potassium uptake by both liver and muscle generally, and intestinal secretion of potassium Extrarenal tissues regulate acute potassium tolerance Renal regulation  Potassium Regulation contd Hormones involved: insulin, epinephrine These hormones enhance potassium uptake by the liver and muscle Changes in acid-base balance: Affects movement of K+ in and out of cells This depends on the exchange of H+ for K+ across the cell membrane. Under acidic condition (acidemia) a shift of potassium out of the cell occurs. Disorders of potassium balance  Hyperkalaemia Defined as a serum potassium > 5.0 mmol/L, the ref. range is 3.5–5.1 mmol/L for adults Critical hyperkalemia = plasma K+ concentration > 6.5 mmol/L Since the kidneys are the major organs involved in K+ metabolism, kidney impairment which affects K+ excretion  hyperkalemia Is a potentially life-threatening electrolyte disorder Early rises in extracellular K+ concn lower the resting cardiac membrane potential. With larger acute rises in extracellular K+ concn, adequate repolarization is inhibited, conduction delay becomes prominent,  diastolic cardiac arrest  Causes of hyperkalaemia Decreased renal excretion - Acute or chronic renal failure - Hypoaldosteronism Increased intake - Oral/IV K replacement Cellular shift therapy - Acidosis Artefactual - Drugs eg ACEI, K sparing - Sample hemolysis diuretics (eg Spironolactone) - Muscle/Cellular injury  Clinical features of hyperkalaemia Asymptomatic Generalized fatigue and weakness – most common Paresthesia Paralysis Palpitations, dyspnea, chest pain Nausea/Vomitting Cardiac examination may reveal extrasystoles, pauses, or bradycardia Neurologic examination may reveal diminished deep tendon reflexes or decreased motor strength  Investigations In a patient who does not have a predisposition to hyperkalemia, repeat the blood test before taking any actions to bring down the potassium level, unless ECG changes are present ECG SE/U/Cr Other tests include Glucose, cor tisol and aldosterone, urinalysis, Ar terial or venous blood gas, depending on underlying disease ECG changes in hyperkalaemia - Peaked T waves - Decreased or disappearing P wave - Shor tened QT interval - Widening of the QRS - ST-segment depression - Amplified R wave - Prolonged PR interval  Treatment of hyperkalaemia Treatment should be initiated when K+ is 6.0 - 6.5mmol/L or greater or if there are ECG changes. Acute treatment of life-threatening hyperkalemia necessitates infusion of IV calcium to protect against malignant cardiac hyperexcitability Ca2+ provides immediate but short-lived protection Followed by agents proven to rapidly and effectively shift K+ into the intracellular space.  Insulin mostly used, Na bicarbonate may also be used (also for met. acidosis) Intravenous dextrose is usually given to prevent hypoglycemia and further stimulates endogenous insulin production Increase potassium excretion Ultimately, hemodialysis for extracorporeal elimination of potassium in life- threatening situations. Treat underlying disease  Hypokalaemia Hypokalaemia Defined as serum/plasma K+ level < 3.5 mmol/L Ref interval 3.5 – 5.1 mmol/L Is a common electrolyte disorder in clinical practice S/S of hypokalaemia include; muscle weakness, irritability, paralysis Causes may result from inadequate potassium intake, increased potassium excretion, or a shift of potassium from the extracellular to the intracellular space  Causes of hypokalaemia GI loss - Vomiting, diarrhea Renal loss - Gastric suction - Diuretics - Large doses of laxatives - Nephritis Cellular shift - Hyperaldosteronism - Alkalosis Decreased intake - Insulin overdose  Treatment of hypokalaemia Involves – a) Reduction of potassium losses Discontinue diuretics/laxatives Use potassium-sparing diuretics if diuretic therapy is required (eg, severe hear t failure) Treat diarrhea or vomiting b) Replenishment of potassium stores Medications - oral potassium chloride[ Slow-K] (over several days) Angiotensin-conver ting enzyme (ACE) inhibitors - inhibit renal potassium excretion In chronic mild cases, foods with high K+ content eg nuts, banana, orange juice Determination of the cause to prevent recurrence, if possible  Treatment of hypokalaemia…. Patients who have mild or moderate hypokalemia (potassium level of 2.5-3.5 mEq/L) may need only oral potassium replacement. If cardiac arrhythmias or significant symptoms are present, more aggressive therapy is warranted. This treatment is similar to the treatment of severe hypokalemia. If the potassium level is less than 2.5 mEq/L, intravenous potassium should be given. Maintain close follow-up care, provide continuous ECG monitoring, and check serial potassium levels. IV potassium must NEVER be given by direct IV injection. It must always be diluted in infusion fluid (RL or 0.9% sodium chloride). It must never be administered subcutaneously or intramuscularly. The serum potassium level is difficult to replenish if the serum magnesium level is also low. Look to replace both. SUMMARY THANKS FOR LISTENING