Fluid and Electrolytes Lecture Notes PDF

Fluid and electrolytes DR SOPHIE CHEN Acknowledgement: A/PROF KELLY LAMBERT (prepared slides) Lecture objectives Fluid excess Electrolyte Oedema Imbalances Na, K, Mg, Ca Fluid deficit Case studies Dehydration Alterations in sodium,...

Fluid and electrolytes DR SOPHIE CHEN Acknowledgement: A/PROF KELLY LAMBERT (prepared slides) Lecture objectives Fluid excess Electrolyte Oedema Imbalances Na, K, Mg, Ca Fluid deficit Case studies Dehydration Alterations in sodium, chloride and water balance Na K PO4 Mg Ca Alterations in Na, LC and water balance  Disorders of Na balance are closely related to water balance  This is because water follows the osmotic gradient created by changes in salt concentration  Cl movement is passive and follows movement of Na  Distribution of electrolytes ECF (mEq/L) ICF (mEq/L) Na: 142 Na: 10 K: 5 K: 156 Ca: 5 Ca: 4 Mg: 2 Mg : 26 HC03: 24 HC03: 12 Cl: 104 C;l: 4 P: 2 P: 40-95 Source: https://basicmedicalkey.com/the-cellular-environment-fluids-and-electrolytes-acids-and-bases/ Water and solute imbalances  These imbalances can be classified according to the change in concentration of electrolytes in relation to water as either:  Isotonic imbalances  Hypertonic imbalances  Hypotonic imbalances Definitions Type of Mechanism imbalance Isotonic Gain or loss of ECF; no shrinking or swelling of cells imbalance Hypertonic Imbalance that results in concentration of the ECF via imbalance water loss or solute gain; results in cells shrinking Hypotonic Imbalance that results in dilution of the ECF via water imbalance gain or solute loss; results in cells S-W-E-L-L-I-N-G Isotonic alterations  Isotonic fluid loss: eg lose plasma or ECF eg haemorrhage, XS sweating  Isotonic fluid gain: eg XS normal saline  Hypertonic alterations  Osmolality of the ECF is elevated above normal Common causes: Increased Na Eg XS hypertonic salt ECF: increased = weight solution eg IVF gain,  BP ICF: IC dehydration, thirst,  UO, brain cell shrinks, confusion Water deficit Eg water deprivation ECF: hypovolemia, wt eg coma, confusion, loss, weak pulse, postural watery diarrhoea, hypotension, tachycardia excessive diuresis ICF: ditto as above Other factors Eg hyperglycemia ECF: polyuria, polydipsia, from undiagnosed or wt loss, hypovolemia, poorly mananged hypernatremia diabetes ICF: ditto see above Hypertonic solute alterations  End result = ECF hypertonicity attracts water from intracellular space → ICF dehydration Lecture objectives Fluid excess Electrolyte Oedema Imbalances Na, K, Mg, Ca Fluid deficit Case studies Dehydration Hypernatremia  What is it: Serum Na > 145mEq/L & serum osmolality > 295mOSm/kg  Pathophysiology: water loss or acute gain in Na. Causes ICF and ECF dehydration.  Usually always follows deficit of ECF water (eg sweating, watery diarrhea, DI, fever) or inadequate water intake  Occ. Can be caused by high salt intake (without adequate time for water ingestion) Clinical manifestations  Water is redistributed from to the ECF = IC dehydration  Thirst, fever, dry mucous membranes, hypotension & restlessness (as a result of water loss)  Specific gravity of urine = >1.03 (N:1.005-1.030)  CNS symptoms related to shrinking of brain cells are most serious eg convulsions, agitation, cerebral haemorrage,  Hypotonic alterations  Osmolality of the ECF is less than normal Common causes: Decreased Poor dietary intake, ECF: contracts Na XS diuretic therapy ICF: water moves into cell. Can cause brain swelling Water Excess Eg excessive water ECF: expands = intake, water to hypervolemia replace isotonic ICF: overhydration losses (cellular oedema) and brain swelling Other factors Isotonic dehydration ECF: can be high or low treated with ICF: as above hypotonic solution, CCF Hypotonic alterations  End result of both is = over hydration & oedema Hyponatremia What is it: Serum Na 3 L hypotonic fluids during race  Results: 7.x more likely to have race time > 4hours, more common in females and lower and higher BMI  NB: females and slower runners less likely to agree to test  Follow on research in at risk groups  Triathlon (up to 28%)  Ultralong distance (up to 50% hyponatremia More info: EAH: http://www.uptodate.co m/contents/exercise-  Pathophysiology of EAH 1. Excessive fluid intake from oral intake and water gain from glycogen breakdown 2. Impaired urinary excretion of water due to persistent secretion of ADH (intense exercise, N &V, hypoglycaemia, pain, muscle derived interleukin 6 and NSAID use (increase ADH – reduced water excretion) 3. Sweat Na loss esp. in the unfit J. Clin. Med. 2014, 3, 1258-1275; doi:10.3390/jcm3041258 Clinical manifestations  Vary in severity due to degree of cerebral oedema (due to osmotic water moving from ECF to brain)  Mild: Weakness, dizziness, headache, N &V  Moderate – severe: collapse, N & V, sensitivity to light, lucid but confused,  Severe: Seizure, coma Lecture objectives Fluid excess Electrolyte Oedema Imbalances Na, K, Mg, Ca Fluid deficit Case studies Dehydration Alterations in K, Ca, P, Mg Na K PO4 Mg Ca suggestion Electrolyte Abnormality Cause Effects Eg K Hypokalemia xxx xxx  Potassium Imbalances ECF (mEq/L) ICF (mEq/L)  Intracellular cation Na: 142 Na: 10 - serum levels are K: 5 K: 156 tightly controlled Ca: 5 Ca: 4 (3.5-5mmol/L) Mg: 2 Mg : 26 HC03: 24 HC03: 12 Cl: 104 C;l: 4 P: 2 P: 40-95  Potassium Imbalances  Hypokalemia - < 3.5mEq/L or < 3.5mmol/L  Hyperkalemia - > 5mEq/L or > 5 mmol/L Hypokalemia Causes:  diarrhea  diuresis (diuretics)  excessive aldosterone or glucocorticoids (increased renal loss of K+)  dietary intake (alcoholism or starvation diets)  treatment of diabetic ketoacidosis with insulin Hypokalemia effects  interferes with neuromuscular function  Parethesias “pins and needles”  Intestinal smooth muscle dysfunction  Severe K+ deficiencies:  Weak respiratory muscles = shallow respirations  Cardiac dysrhythmias - prolonged repolarisation = cardiac arrest Hyperkalemia Causes:  Excessive oral intake  Renal failure  Deficit of aldosterone  use of “potassium sparing” diuretic drugs  crush injuries or burns - K+ leaks out  prolonged or severe acidosis may displace potassium from cells Hyperkalemia effects Effects:  Muscle weakness and in severe cases paralysis  Heart palpitations  Impairment of neuromuscular activity  Nausea and vomiting  ECG shows cardiac dysrhythmias = cardiac arrest  Magnesium Imbalances  Intracellular cation – N =0.6-0.82 mmol/L  Hypomagnesemia < 0.6 mmol /L  Hypermagnesemia > 0.82 mmol/L Causes of low Mg  Primarily related to 2 causes:  Renal losses eg excessive excretion from medications eg some diuretics and chemotherapy  GI losses: secretory diarrhoea and other small bowel disorders  Can also be alcoholism Effects of low Mg  Neuromuscular: tremor, tetany, seizure, delirium  Cardiovascular: abnormal heart rhythm Causes high Mg  Primarily related to poor excretion ie renal failure  Often exacerbated by high Mg content medications in renal failure Effects of high Mg  N &V, hyporeflexia, weakness (slow muscle & nerve conduction), decreased or absent deep tendon reflexes  Impaired breathing - decreased respirations  Cardiac: arrhythmia, Bradycardia (slow heart rate) Calcium imbalances  Plasma calcium is tightly controlled by hormones (PTH, vitamin D and calcitonin)  Hypocalcaemia - 2.6mmol/L See flow chart in textbook of Ca regulation Hypocalcaemia  Causes:  hypoparathyroidism, hypomagnesaemia,  vitamin D deficiency, renal failure  Manifestations:  neuromuscular excitability & cardiovascular effects  Treatment:  IV infusion (emergency), Ca supps  one glass of milk supplies only 300mg calcium Hypercalcemia  Causes:  increased bone resorption ( PTH, neoplasms)  Minor causes: immobilisation,  vitamin D, excessive dietary calcium  Manifestations: neural excitability is decreased = loss muscle tone, weakness ie sluggish nerve conduction  Treatment:  diuretics ( Na excretion & Ca excretion)  drugs to inhibit bone resorption Lecture objectives Fluid excess Electrolyte Oedema Imbalances Na, K, Mg, Ca Fluid deficit Case studies Dehydration