l12 water & electrolyte imbalance 2

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  • WATER & ELECTROLYTE IMBALANCE

    2

  • Learning Outcomes

    At the end of the course students should be able to:

    1. explain the causes, the pathophysiology, effects and complications of hypernatremia and hyponatremia.

    2. define, give causes and describe the characteristics of Inappropriate ADH Syndrome

    3. explain the causes, pathophysiology, effects and complications of hyperkalemia and hypokalemia.

    3

  • Normal body water and electrolyte distribution

    60% body weight in man, 55% in woman66% intracellular, 33% in extracellular ( 8% in plasma)plasma) 4

  • Normal Homeostasis

    H2O freely permeable OSMOLALITY of ECF and ICF, same 280-290,osmol/kg ECF Osmolality dependent on molar concentration of

    - mainly Na+ and its anions e.g Cl- HC03- - others : glucose and urea

    -protein, contributes 0.5% to plasma osmolality

    ICF osmolality dependent on K+ concentration ECF: interstitial fluid and plasma

    5

  • Plasma Concentration of Na+ and K+

    Na+ conc : ECF > ICF, 140 mM vs 10 mM

    Normal Plasma Na+ : 135-145 mmol/l

    K+ conc : ECF

  • Importance of Normal Homeostasis

    Changes in ECF Na+ conc leads to water shifting between ICF & ECF

    Changes in ECF K+ affects ratio of [K+ in] to [K+ out] and has effects on membrane potential of cells

    Changes in ECF Na+ conc and K+ concentration lead to clinical consequences

    7

  • Normal Control of Water & Electrolyte Distribution

    INTAKE/PRODUCTION LOSS

    Water Dietary Intake Oxidative metabolism

    Sodium Dietary Intake

    Potassium Dietary Intake

    Obligatory daily water requirement is 1110 mL

    Kidney,Skin, Gut, Lung

    Kidney, Skin, Gut

    Kidney, Gut Minimum volume of urine

    necessary for normal excretion of waste products is 500 ml/24 hrs

    8

  • Maintanance of normal ECF and ICF VolumeMechanism Source Stimulus Effect

    1. GFR Kidney Na + & water excretion

    2. Aldosterone Adrenal reduced renal perfusion

    Renal Na+ and water retention

    3. ADH Hypothalamus Increased ECF tonicityDecrease blood volume

    Pure retention water

    4.ANF Cardiac atria Increase blood volume

    Renal Na & water retention

    9

  • Body Fluid and Electrolyte Imbalance

    Can occur as a result of :

    Water & electrolyte loss Water & electrolyte overload

    lead to clinical effects and complications

    10

  • Fluid Loss- water & electrolyte lossCan occur in two situations :

    Isotonic fluid loss - water loss accompanied by an equivalent amount of Na+

    Hypotonic fluid loss - pure water loss

    11

  • Isotonic fluid loss

    CAUSES1. Haemorrhage2. Burns3. GIT loss : diarrhoea, vomiting, fistula4. Renal loss : diuretics, Addisons disease

    polyuric phase of ARF5. Effusion of ECF into body spaces :

    haematoma, ascites, pancreatitis

    12

  • Isotonic Fluid Loss

    leads to both water and sodium depletion No immediate change to plasma sodium

    concentration No fluid movement from ICF to ECF Complication : reduced in plasma volume leading to

    circulatory collapse & shock

    13

  • Effects and Clinical complications isotonic fluid loss

    LOSS OF H2O FROM ECF

    ECF Osmolality normal

    Stimulate renin-angiotensin

    aldosterone release

    Na+ & H2O reabsorption

    Reduced urine volume

    & concentrated

    :

    Hemoconcentratio n: haematocrit,

    blood Hb concentration, Plasma protein

    :

    Reduced renal blood flow

    Reduced GFR

    Increased blood urea and creatinine

    NO Water movement from ICF

    REDUCED ECF/PLASMA VOL.

    Circulatory collapse

    SHOCK

    14

  • Hypotonic fluid loss

    Kidney

    Skin

    Lungs

    Reduced water intake

    CAUSES Diabetes Insipidus

    Osmotic diuresis: e.g diabetes mellitus

    Excessive sweating Fever, exercise in hot weather

    Hyperventilation

    Elderlies, infants, unconscious

    15

  • Clinical Effects and complications of hypotonic fluid loss

    LOSS OF H2O FROM ECF

    ECF Osmolality

    Dehydration:Dryness of mouth

    Difficulty in swallowing

    Stimulate thirst response :

    thirst

    :

    Plasma Na +HYPERNATREMIA

    :

    Immediate ADH response:

    Urinereduced volume &

    concentratedReduced urine

    output

    Water moves out of ICF

    CEREBRAL DEHYDRATION

    Haemorrhage

    Confusion, coma

    16

  • Summary of Effects of Fluid loss

    Hypotonic Loss Isotonic LossPlasma Na+ Normal tohaematocrit slightlyECF VolumePlasma urea Normal toUrine outputthirst early lateTachycardia & hypotension

    Fluid replacement

    Late

    cautious

    Early

    rapid

    17

  • Hypernatraemia High plasma sodium concentration

    Usually caused by hypotonic fluid loss

    DIABETES INSIPIDUS -Impt cause of hypotonic loss-Decrease secretion of VASOPRESSIN from posterior pituitary , causes :

    i. pituitary /hypoythalamic diseases : tumours

    ii. Nephrogenic DI kidney fails to response to vasopressin e.g

    chronic renal parenchyma dis.

    18

  • Hypernatremia due to Primary Na+ overload. uncommon Causes :

    1. Administration of hypertonic NaCl or NaHCO3 to unconscious patients.

    2. Infants given feeds containing salt .3. Shipwrecked sailors drinking seawater

    high urine Na+ (100-200mmol/l).

    19

  • Clinical Effects and Complications of Hypernatraemia

    Hypernatremia RESULTS Iin ECF HYPEROSMOLALITY

    H2O moves out of ICF Leads to cellular dehydration Clinical effects :

    i. stimulate thirst centre - thirstyii. Cerebral cells - mental confusion

    and comaiii. Cerebral haemorrhage

    20

  • HYPONATRAEMIALow measurable plasma sodium concentration

    CAUSES OF HYPONATREMIA

    Sodium depletion-Excessive LOSS

    KIDNEY : diuretic therapy, hypoaldesteronismAcute tubular necrosis

    SKIN: excessive sweating, burns,cystic fibrosis

    GIT: vomiting, diarhhoea, fistula

    SICK Cell Syndrome

    Primary water overloadSIADH: Syndrome of Inappropriate ADH secretion

    Dilutional Pseudohyponatremia

    21

  • Hyponatremia Sick-cell syndrome

    very ill patients, failure of the Na/K ATPase to extrude Na+. re-setting of the hypothalamic osmostat ADH secretion at lower plasma osmolality

    Dilutionale.g Diabetes mellitus, plasma glucose draws H2O from ICF into ECF, diluting the plasma Na

    + Pseudohyponatremia - gross hyperlipidaemia. in certain disease states, - replacing 5 -10% of plasma volume.

    22

  • Syndrome of Inappropriate ADH Secretion ( SIADH )

    Excessive secretion of ADH Hormone Retention of H2O in ECF and ICF Expansion of ECF by water leads to

    hyponatremia H2O move from ECF to ICF causing

    swelling of cells Complication: cerebral edema - mental

    confusion

    23

  • SIADH

    Low plasma osmolality High urine osmolality

    - Urine is inappropriately concentrated despite low plasma osmolality

    Urine sodium is high in the face of hyponatremia

    24

  • Causes of SIADH

    Intracranial Pathology Pulmonary Pathology Ectopic production of ADH Drugs

    25

  • Clinical effect of Hyponatremia

    H2O moving form ECF into ICF Cellular swelling Cerebral edema - drowsiness, coma

    26

  • Disturbance of potassium metabolism

    Most body K+ in the cells

    Plasma K+ is a small fraction of body K+, and hence not always an accurate reflection of whole body K+ status

    K+ concentration ICF vs ECF : 150 vs 5 (mmol/l) ( i.e. levels are 30 x higher in the cell)

    27

  • The kidney plays a central role in maintaining K+ balance. Filtered K+ is practically all reabsorbed

    K+ play a role in generating cell membrane action

    potential

    Normal function of some intracellular enzymes: e.g pyruvate kinase

    i/c K+ depletion may lead to cell injury and dysfunction e.g - rhabdomyolysis

    ( necrosis) and renal tubular dysfunction

    28

  • Hypokalemia - Causes

    1. Decreased potassium intake

    2. Renal K+ loss diuretic therapy mineralocorticoid excess renal tubular acidosis acute renal failure diuretic phase

    29

  • 3. Gastrointestinal K+ Loss Diarrhoea Enteric fistulae Vomiting

    4. Conditions : movement of K+ from ECF ICF

    Acute alkalosis Diabetic acidosis on treatment with insulin -adrenergic drugs

    30

  • Clinical effects/complications of Hypokalaemia

    Cardiac arrythmias

    Muscle weakness

    GIT smooth muscle weakness leading to constipation, progressing to paralytic ileus.

    Polyuria and dehydration

    Glucose intolerance. Hypokalaemia impairs insulin release

    31

  • Hyperkalaemia -Causes1. Excessive K+ Intake

    - in patients with renal impairment - treatment with K+ sparing diuretics -overenthusiastic intravenous K+ replacement for hypokalaemia, - rapid transfusion of stored blood,

    K+ leaked out of the RBCs.

    32

  • Hyperkalaemia

    2. Decreased Renal Excretion

    Acute renal failure Certain drugs Adrenal insufficiency

    33

  • Causes of Hyperkalaemia Conditions causing movement of K+

    from ICF to ECF Acidosis displace I/C K+

    from the plasma.

    K+ release from acutely damaged cells crush inju

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