Fluid and electrolytes, acid base balance,

& IV fluids

Prof. M K Alam MS; FRCS

ALMAAREFA MEDICAL COLLEGE

Intended Learning Outcomes- ILOs

At the end of this presentation students will be able to:

Understand the normal & abnormal fluid and electrolyte status.

Describe how the body maintains the homeostasis.

Identify and manage fluid and electrolyte abnormalities.

Understand the mechanism of acid base balance.

Identify and mange acid base disorders

Describe different IV fluids and its uses.

Fluid and electrolytes

Fluid & electrolytes

management form an

integral part of surgical care

Fluid and electrolytes

• Homeostasis- integrated action of cellular

membrane, specific organs , local and systemic

hormones

• Diseases, trauma, surgery & medications

can adversely affect the equilibrium

Fluid and electrolytes

Total body water – total volume of water within the body.

• 60% of body weight (range 50-70%)

• Contained primarily in skeletal muscle

• Slightly higher in men

• Declines steadily with age

• Obese has less body water (Fat is devoid of water)

Fluid Compartments

• Intracellular - 40% of body weight

• Extracellular- 20% of body weight

- Interstitium 15%,

- Intravascular or plasma 5%

• Compartments separated by semipermeable

membrane to maintain the composition differences

INTRACELLULAR electrolytes

• Dominant cation- K⁺ (160 mEq/L) , Mg⁺

• Anions- phosphates (HPO₄) and proteins

Extracellular electrolytes

• Dominant cation- Na⁺(140 mEq/L)

• Anions- chloride (Cl⁻), bicarbonate (HCO₃⁻)

Fluid and electrolytes

Electrical neutrality- balance of

cations and anions on either side of the

membrane

Fluid and electrolytes

• Osmotic forces-prime determinant of water distribution.

• Determinants of osmotic activity in plasma- Na⁺, glucose & urea

• The unit of measurement of osmotically active particles in a solution: osmole

(Osm) or milliosmole (mOsm)

• Normal serum osmolarity 285 mOsm/L

• Osmolarity: concentration of osmoles of solute/ L (Osm/L)

• Osmolality: concentration of osmoles of solute/kg (Osm/kg)

Fluid and electrolytes

• Regulation of fluid volume- mainly by kidney

• Osmoreceptors in posterior Pituitary: ADH release promote retention

of free water by distal renal tubules & collecting ducts.

• Renin-angiotensin-aldosterone system: Acting on kidney increases

water &Na⁺ reabsorption, K⁺ & H⁺ excretion by distal renal tubules.

• Baroreceptors in kidney & carotid: Small role

Fluid balance

Normal state: Fluid gain = fluid loss

FLUID GAIN:

Oral intake- 2-3 L/ day (2/3rd fluid+ 1/3rd solid)

Oxidative metabolism- 400-500 ml/ day

Fluid balance

• FLUID LOSS:

Urine 1-1.5 L /day,

Faeces 250 ml/day

Insensible loss from skin & lung- 600-900 ml/day

Loss increases by 10% for each 1°C rise in body temperature

MAINTENANCE OF FLUID REQUIREMENTS

100 ml / 1st 10 kg,

50ml / 2nd 10kg,

20 ml / subsequent kg body weight

70-kg man 2500 ml / day = 35 ml / kg

Water & Electrolyte abnormalities

Fluid volume deficits (isotonic dehydration)

• Aetiology: Vomiting, nasogastric output, GI fistulas, lengthy abdominal surgery (10ml/kg/hr.), sepsis, inflammation (3rd space loss )

• Acute loss: Hypotension, tachycardia, oliguria, altered mention

• Chronic loss: Oliguria, loss of skin turgor, orthostatic hypotension, low urine Na⁺ and BUN/creatinine ratio >15:1.

Fluid volume deficits (isotonic)

• Hematocrit- elevated 5%-6%/ L volume deficit

• Treatment: Isotonic solutions (RL, NS) to restore physiologic parameters (urine >0.5ml/hr., hemodynamic status)

Volume deficits (uncommon types)

• Hypotonic dehydration: Iatrogenic. Inadequate resuscitation with hypotonic solutions

• Hypertonic dehydration: Impaired consciousness or thirst mechanism,

Inability to obtain water

Fluid volume excess

• Excessive parenteral fluid administration (5% Dextrose).

• Failure of adjustments to intake/output.

• Elderly, cardiac and renal disease patients at risk

• Peripheral edema, pulmonary edema, weight

gain, elevated CVP (normal 5-12mm Hg)

• Treatment: Fluid restriction, loop diuretics

Sodium homeostasis

• Normal serum level:132-144 mEq/ L

• Daily dietary intake: 100-250 mEq (6-15 g/day)

• Excreted through urine, stool and sweat

• Daily urinary excretion: 50-90 mEq/ day

• Renal regulation: reduce loss to 1 mEq/day or exceed

5000 mEq/day

Hyponatremia• Hypervolemic:

Renal failure- reduced water loss

CCF, Cirrhosis, COPD- low CO, increased water absorption

• Normovolemic:

Urinary Na⁺ loss in Syndrome of inappropriate secretion of ADH (SIADH) -head injury, stroke, carcinoma lung

• Hypovolemic: Hypotonic solutions infusion,

Loss of Na⁺ in renal disease- urinary Na⁺ ↑20mEq/L Renal loss- vomiting, diarrhea, fistula.

Hyponatremia

• Symptoms: usually ˂120 mEq/L CNS & GI: lethargy, confusion, seizures, anorexia, vomiting, coma

• TSD (total Na⁺ deficit)= 0.6 x wt. in kg x(140- actual Na⁺ level) Deficit correction 0.5 mEq/L/ hr.

• Treatment: Rapid correction leads to myelin sheath damage. Severe symptoms: corrected rapidly to Na⁺ 120 mEq/ L, then slowly

Hypervolemic- fluid restriction, loop diuretics

SIADH- fluid restriction

Hypovolemic- normal saline

Hypernatremia

• Aetiology:

Excess salt intake or reduced loss

Reduced water intake or excess loss

• Types: Hypervolemic: Iatrogenic (excessive NS infusion), hyperaldosteronism, Cushing synd. Urine osmolarity > 300 mosm/L , Urine Na > 20 mEq/L

Normovolemic:: Diabetes insipidus, diuretics or non-renal water loss. Urine Na < 20 mEq/L, osmolarity < 300 mosm/L

Hypovolemic: Renal or non-renal water loss. Diabetes insipidus, osmotic diuretics, diarrhoea.

• Pathophysiology: Hyperosmolar state leads to water shift from intracellular to extracellular . (intracellular dehydration), thirst & ADH release

Hypernatremia in Diabetes insipidus

ADH abnormalities - cause massive water loss

Abnormalities of synthesis: central diabetes insipidus-head injury

Abnormalities of action: nephrogenic diabetes insipidus.

(side effect of lithium, interstitial nephritis, obstructive uropathy)

Hypernatremia

• Symptoms: usually starts at > 160 mEq/L .

Symptomatic at a lower level if rise in Na⁺ level is rapid

• Mainly CNS related- restless, irritable, fever, seizures.

• Treatment: Isotonic saline to correct hypovolemia followed by D5

W infusion to correct water deficit

• Water deficit= normal BW x normal Na⁺ level/ current Na⁺ level

Potassium homeostasis

• Principal intracellular (155 mEq/L) cation

• Mostly located in skeletal muscle

• Normal serum level 3.5- 5 mEq/L

• Concentration gradient maintained by-

membrane bound Na⁺-K⁺ ATPase pump.

Potassium homeostasis

• Daily K⁺ intake: 1-1.5 mEq/kg body weight

• 90% excreted through kidney

• Internal regulating factors:

Insulin, aldosterone, catecholamines

and acid-base balance

Hyperkalemia

• Serum K⁺ > 5.5 mEq/ L

• Aetiology: Renal failure, adrenal insufficiency, metabolic

acidosis, hemolysis, rhabdomyolysis, seizures, sever GI bleeding,

medications (NSAID), excessive K⁺ administration.

• Pseudohyperkalemia: Thrombocytosis, leukocytosis, excessive

agitation of specimen, prolonged tourniquet or excessive fist

clenching during blood drawing

• Myocardial toxicity ( K⁺> 6 mEq)- peaked T wave, prolonged PR

interval, complete heart block, paresthesia, flaccid paralysis

Treatment of hyperkalemia

• 10% Ca-gluconate 10-20 ml- cardioprotective, effective in 1-5 min.

• 10 units insulin in 50 ml + 50% Dextrose- effective in 15-45 min.

• 100 mEq of sodium bicarbonate - if metabolic acidosis

• K⁺exchange resin 50-100 gm enema- slow action

• Hemodialysis

Hypokalemia

• K⁺ ˂ 3.5 mEq/L

• Aetiology: Vomiting, diarrhea, GI fistula, diuretics

• Metabolic alkalosis often coexists (↓ renal conservation)

• Weakness, flattening of T wave , arrhythmias in patients on digoxin.

• Treatment: IV K⁺ - for severe cases Oral K⁺- 60-80 mEq / day for milder cases

Calcium Homeostasis

• 99% body Ca⁺- in bone, not readily exchangeable

• Homeostasis- exchange between bone, ECF, renal

excretion, and intestinal absorption

• Homeostasis mainly controlled by PTH

• Plasma calcium: 10 mg/dl.

• ECF Ca⁺: Ionized, Non-ionized, Protein-bound

Calcium Homeostasis

• Low ionized Ca⁺ → ↑ PTH and ↑ 1,25-dihydroxyvitamin D3

stimulate bone absorption by increasing osteoclastic activity.

• Increased ionized ca → ↓ PTH and ↓1,25-dihydroxyvitamin D3,

which decreases bone absorption

• Intestinal absorption depends primarily on 1,25-dihydroxy vitamin D3.

• Renal excretion: PTH & vitamin D increases distal tubular reabsorption of Ca.

Calcitonin inhibits Ca reabsorption.

• Alkalosis ↑ ca excretion.

• Acidosis ↓excretion.

Hypercalcemia

• Aetiology: Hyperparathyroidism, malignancy, thiazide, acute adrenal insufficiency, prolonged immobilization

• Clinical features:

CNS: Muscle fatigue, weakness, personality disorders, psychoses, confusion, depression, and coma

CVS: Hypertension, shortening of QT interval

GIT: Nausea, vomiting, and abdominal pain

Renal: Nephrocalcinosis → chronic renal failure, Nephrolithiasis

Treatment of Hypercalcemia

• Promote diuresis by infusion of normal saline

• Add KCl 20-30 mEq/ L of i.v. fluid

• Furosemide to enhance calcium excretion

• Treat the underlying cause -Primary HPT: Surgery -Bone metastasis: Bisphosphonates,

calcitonin, steroids

Hypocalcaemia

• Aetiology

-Thyroid or parathyroid surgery

-Acute pancreatitis

-Pancreatic and small bowel fistulae

-Vitamin D deficiency secondary to malnutrition, malabsorption, or lack of exposure to sunlight

-Renal failure → vitamin D₃ deficiency→ ↓ intestinal absorption

• Clinical features: (ca < 8 mg/dl) Muscle cramps, perioral tingling, paresthesia, laryngeal stridor, tetany, seizures, and psychotic behavior, hyperactive deep tendon reflexes.

Treatment of Hypocalcaemia

• IV calcium (calcium gluconate or calcium chloride)

50 mg/minute (2.5 mEq/minute)

• Oral calcium ( citrate, carbonate)

• Vitamin D₃ (Calcitriol)- increases intestinal absorption

Magnesium

• Total body content : 2,000 mEq- 50% in bone, the

remaining in the intracellular space.

• < 1% of total in the extracellular space (1.4 to 2 mEq/L or

1.7 to 2.3 mg/dl).

• Daily intake: 25 mEq

• Excretion primarily by the kidneys

• Excretion increased by hypermagnesemia, hypercalcemia,

metabolic acidosis, and phosphate depletion.

Excretion decreased by metabolic alkalosis.

Hypermagnesemia

• Aetiology: chronic or acute renal failure, Mg-containing

antacids/ laxatives intake , severe burns, crush injuries,

rhabdomyolysis, severe metabolic acidosis, extracellular

volume depletion

• Clinical features: Depressed neuromuscular function.

Loss of deep tendon reflexes, paralysis , coma. Hypotension or

even cardiac arrest can occur if levels exceed 18 mg/dL.

Treatment of Hypermagnesemia

• Calcium- 5 to 10 mEq, slow i.v (antagonizes the effects of magnesium)

• Volume expansion

• Correction of acid-base disturbances

• Loop diuretics

• Hemodialysis

• Avoid Mg- containing medications

Hypomagnesemia

• Aetiology: Malnutrition, steatorrhea, increased GI losses ,

prolonged IV fluid therapy without Mg, loop diuretics, insulin for

DKA , aminoglycosides, diuretic phase of acute renal failure.

• Clinical features: Similar to hypocalcemia. Muscle fasciculations,

weakness, tetany, carpopedal spasm, nausea, vomiting, and

personality changes. Hypokalemia by renal K wasting.

• Treatment: Mild cases: oral magnesium

Large deficit: IV Mg-sulfate 50-100 mEq/ day

ACID-BASE BALANCE

ACID-BASE System

• Acid: donate a H⁺ ion – HCl , H2CO3

• Base: accept a H⁺ -HCO3

• Acid-base homeostasis: equilibrium in H+, PCO2, and HCO3-

• H+ concentration - expressed as pH

• Normal pH - 7.35 to 7.45

• Acidemia - pH < 7.35

• Alkalemia- pH > 7.45

Acid-base disturbance

• Acidosis- respiratory, metabolic.

• Alkalosis- respiratory , metabolic

• Assessment- arterial blood gas analysis (radial artery)

• Normal ABG report: pH- 7.36- 7.44 H⁺- 44-36 nml/L HCO₃- 23-28 mmol/L pCO₂- 36-44 mmHg (4.8-5.9 kPa) pO₂- 80- 100 mmHg (10.6- 13.3 kPa)

Acid-base disturbance- Compensatory mechanisms

1. Respiratory compensation- most rapid – in minutes.

2. Blood buffers - in hours.

Bicarbonate (65%)- most important, protein 30%

3. Kidney – in days.

Metabolic acidosis

• ↓ pH, ↓ bicarbonate concentration.

• Increased production of endogenous acids: ( increased anion gap acidosis) - shock, severe hemorrhage, liver failure, diabetic ketoacidosis.

• Increased bicarbonate loss: (normal anion gap acidosis)- diarrhoea, intestinal fistula.

• Respiratory compensation- fall in pCO₂ - resp. alkalosis.

• Treatment: Fluid resuscitation, base deficit correction by bicarbonate.

Metabolic alkalosis

• ↑ pH, ↑ bicarbonate concentration.

• Respiratory compensation - ↑pCO₂ - resp. acidosis

• Associated with hypokalemia, hypochloraemia.

• Aetiology: Loss of acid as vomitus in gastric outlet obstruction.

• Treatment: Replace fluid, K⁺ & chloride. Treatment of primary cause

Respiratory acidosis

• ↑pCO₂, ↑plasma bicarbonate, ↓pH

• Respiratory depression (head injury, opioids drugs)

• Pulmonary disease (asthma, COPD)

• Metabolic compensation- renal bicarbonate retention.

• Treatment: Ventilatory support.

Respiratory alkalosis

• Result of hyperventilation- pain, hysterical hyperventilation,

CNS disorders, salicylate poisoning, liver failure.

• ↑pH, ↓pCO₂.

• May develop tetany- ↓ ionized Ca⁺ due to alkalosis.

• No specific treatment.

Types of intravenous fluid

• 5% Dextrose: 5Gm dextrose/ 100 ml, isotonic, not useful in resuscitation.

• 10, 20 & 50 % Dextrose:- Hypertonic , used for diabetics or hypoglycemics.

• Normal saline: 0.9% NaCl, 9Gm NaCl in 1L (Na 154 mmol), pH 5.

• Ringer’s lactate (Hartman’s): < NaCl ( Na 131 mmol) + K⁺, HCO₃, Ca⁺ & Mg⁺, pH 6.5

• NS & RL: For replacing ECF loss. RL closely match ECF and less risk of hyperchloremia.

• Hypertonic saline: Used for hyponatraemic seizures, cerebral oedema.

• Dextrose Saline: 5% Dextrose with N saline- hypertonic, used with caution.

4.3% Dextrose with 1/5 N saline more safe.

• Colloids: Albumin (4.5%), gelatin, hydroxyethyl starch [HES], dextran- all stay longer in

intravascular space after resuscitation. Side effects- coagulopathy, pruritus, anaphylactic

reaction

Maintenance fluid & electrolyte in 24 hours

Example for an adult in normal condition:

• Normal saline 500- 1000 ml + 5% Dextrose 2 - 2.5 L

• Potassium chloride: 60-80 mmol added to IV fluids.

Better avoided on 1st postoperative day.

• Adjust according to intake/output, & serum electrolytes.