Fluids and Electrolytes

Total Body Water

60% Male, 50% Female Less as we age, because greater proportion of fat

TBW

Extracellular Intracellular

Plasma Interstitial

66%33%

8% 25%

Body Fluid Compartments:

ICF:ICF:55%~75%55%~75%

IntravascularIntravascularplasmaplasma

ExtravascularExtravascularInterstitial Interstitial

fluidfluid

TBWTBW

ECFECF

3/4

1/4

Most concentrated in skeletal muscle

TBW=0.6xBW ICF=0.4xBW ECF=0.2xBW

2/3

1/3

Distribution of Solutes

Extracellular Intracellular

Na+ 142 Na+ 10

K+ 4 K+ 140

Cl- 110 Cl- 3

HCO3- 24 HCO3

- 10

Inorganic - 12 Inorganic - 137

Glucose 3 Glucose 2.5

Osmols 300 Osmols 300

Plasma osmolarity 280-295 (2 x Na) + (glucose/18) + (BUN/2.8)

Which one of the following is not needed to calculate osmolarity? Potassium, sodium, glucose, urea, chloride

Maintenance fluid 4cc/kg/day for 1st 10kg 2cc/kg/day for 2nd 10kg 1cc/kg/day for every kg after Maintenance fluid of choice for adult

D5 ½ NS w/ 20 mEq K Maintenance fluid of choice for child

D5 ¼ NS w/ 20 mEq K

Insensible fluid losses 10 cc/kg/day, 75% skin, 25% respiratory

Open abdominal operations Fluid loss 0.5-1 L/hr

In the pediatric patient, what is the recommended initial fluid challenge?

10 ml/kg lactated Ringer’s 20 ml/kg lactated Ringer’s 50 ml/kg lactated Ringer’s 10 ml/kg high molecular weight dextran

GI fluid secretion Stomach 1-2 L/day Biliary syst 0.5-1 L/day Pancreas 0.5-1 L/day SB 0.5-1 L/day Saliva 1-1.5 L/day

Na requirement 1-2 mEq/kg/day

K+ requirement 0.5-1 mEq/kg/day

GI losses Sweat – hypotonic Saliva – K+ Stomach – HCL Pancreas – Bicarb Bile – Bicarb SB – Bicarb and K+ LB – K+

Metabolic acidosis Anion gap:

Phosphates, sulfates, lactate, keto acids, proteins 10-12 mEq/L Na – (HCO3 + Cl)

Anion gap acidosis MUDPILES Methanol, uremia, dka, paraldehyde, isoniazide, lactatemia, ethylene

glycol, salicylates Normal anion gap

usually loss of Na/HCO3

Metabolic alkalosis Vomiting, NG tube: hypochloremic, hypokalemic, metabolic alkalosis, paradoxical

aciduria

IVF Solutions

LR 130 mEq Na 109 mEq Cl 28 mEq Lactate 4 mEq K 3 mEq Ca

NS 154 mEq Na 154 mEq Cl

Hyponatremia

Mild 130-138

Moderate 120-130 HA or lethargy 2o swelling intracranial cells

Severe < 120

Risk Seizure, Coma <110

Risk of death from cerebral swelling

Acute Hyponatremia Evolves in few hours Make sure to resuscitate with iso-osmotic fluid Water Intoxication Forced Diuresis (loop, mannitol, DKA) Cerebral Salt Wasting

Chronic Hyponatremia SIADH Renal Disease Adrenal Disease (rare)

Treatment

Correct Na deficit slowly Max rate of sodium correction

Should not exceed 0.25 mEq/L/hr Or 8 mOsm/kg H2O per day

Need to Avoid Central Pontine Myelinolysis

Permanent neurologic disorder Spastic quadriparesis Pseudobulbar palsy Depressed consciousness

Hypernatremia

Most common cause of Hypertonicity Moderate

146-159 Severe

>160

Altered LOC Seizure Coma Sudden dehydration can lead to intracerebral

hemorrhage

Causes of Hypernatremia

DI Greater than 500 mL/hr hypotonic urine Continual production of dilute urine (urine osmol <

200) while serum osmol >300 Central

Hypothalamus can’t produce vasopressin Nephrogenic

Renal tubules can’t respond to vasopressin

EtOH intoxication Excessive losses of hypotonic fluids

Which one of the following meds is not capable of causing DI? Desmopressin Lithium Demeclocycline Amphotericin B Glyburide

Treatment of Hypernatremia

IV or oral administration of fluid Determine Free Water Deficit 0.6 or 0.5 x (wt in kg) x [(serum Na/140)-1]

Slow correction Brain swelling 10 mEq/day unless symptomatic

Hyperkalemia Defined by K > 5.0

> 6.0 Cardiac Arrhythmias Elevated T waves

>7.0 P wave amplitude decreases PR segment increases QRS complex widens

>8.0 Lethal arrhythmias (asystole, V Fib, pulseless

idioventricular rhythm)

Causes of Hyperkalemia

Renal Failure Medication

K sparing diuretics Succinylcholine

Reperfusion injury Burn

Treatment of Hyperkalemia

C Calcium

B Bicarb

I Insulin

G Glucose

K Kayexalate

F Furosemide

A Aldosterone

L L

Hypokalemia

K < 3.5 Fatigue Weakess Ileus

K < 2.0 Flaccid paralysis Respiratory compromise

Cardiac Arrhythmias Depressed T waves U waves Atrial tachycardia w/ or w/out block AV dissociation Ventricular tachycardia Ventricular fibrillation

Which is the correct electrolyte makeup of plasma? Na: 150 K: 4 Cl: 103 HCO3: 24 Na: 140 K: 4 Cl: 98 HCO3: 26 Na: 140 K: 4 Cl: 103 HCO3: 24 Na: 145 K: 4 Cl: 103 HCO3: 28

Normal Saline contains 154 meq of Na & Cl

LR contains Na 130 Cl 109 K 4 Ca 2.7 and bicarb 28

Cannot transfuse blood with LR because: calcium in Ringer's lactate solution could

overwhelm the chelating capacities of the citrate in stored blood, resulting in clot formation.

Calcium

Normal level? 8.5 to 10.5 mg/dL

Total calcium accounts for 3 forms of calcium?

Protein-bound calcium Diffusible calcium complexed to anions (bicarbonate,

phosphate, and acetate) Freely diffusible

Calcium continued …

Ionized calcium Biochemically active species Comprises ~45% of total serum calcium

Protein bound calcium 80% bound to albumin Acidemia decreases calcium binding to albumin

What factors affect calcium levels? PTH Calcitonin Vitamin D

PTH effects? Activates osteoclasts Stim tubule cells in the proximal nephron to absorb

calcium and excrete phosphates Works with vit D to enhance absorption of calcium from

the gut lumen Conversion of dietary vit D to 1, 25-

dihydroxycholecalciferol

VITAMIN D SYNTHESIS

SKIN LIVER KIDNEY

7-DEHYDROCHOLESTEROL

VITAMIN D3

VITAMIN D3

25(OH)VITAMIN D

h 25-HYDROXYLASE

25(OH)VITAMIN D

1,25(OH)2 VITAMIN D

(ACTIVE METABOLITE)

1-HYDROXYLASE

TISSUE-SPECIFIC VITAMIN D RESPONSES

FUNCTION OF VITAMIN D TISSUE SPECIFICITY

GUT STIMULATE TRANSEPITHELIAL TRANSPORT OF CALCIUM AND

PHOSPHATE IN THE SMALL INTESTINE (PRINCIPALLY DUODENUM)

BONE STIMULATE TERMINAL DIFFERENTIATION OF OSTEOCLASTS STIMULATE OSTEOBLASTS TO STIMULATE OSTEOCLASTS TO

MOBILIZE CALCIUM PARATHYROID

INHIBIT TRANSCRIPTION OF THE PTH GENE (FEEDBACK REGULATION)

Hypercalcemia

Symptoms Fatigue, weakness, anorexia, n/v Pain, polydipsia, polyuria, stones Stupor, coma

Critical level: 16-20mg/ml

Hypercalcemia cont.

Causes Hyperparathyroidism (unregulated PTH secretion) Malignancies

PTH-related peptide- share 8 of the first 13 amino acids with

PTH Nonhormonal mechanisms

- direct invasion with activation of osteoclast activity via cytokines (IL-1, TNF, IL-6)

Drugs Thiazide diuretics Extreme doses of Vit A & Vit D

Immobility Young, normally active patients with high bone turnover

PTHrP Very high hypercalcemia, suppressed PTH

One of the first cancers recognized to cause hypercalcemia

MULTIPLE MYELOMA

Mediated by family of cytokines causing osteoclast activation Hypercalcemia, suppressed PTH

Hypercalcemia cont.

CHIMPANZEES Calcium excess (administration) Hyperparathyroidism Immobility / iatrogenic Metastasis / milk-alkali syndrome Paget’s disease Addison’s disease Neoplasms Excess vit D Excess vit A Sarcoidosis

Hypercalcemia Treatment

Saline infusion to expand ECW loop diuretic Renal failure hemodialysis Correct primary problem

PTH excision of diseased tissue Drugs Malignancy excision, XRT, or chemotherapy

Long term Bisphosphonate

Reduce osteoclast-mediated release of calcium from bone Given as long term prophylaxis in pts with metastatic cancer

Calcitonin Induces renal excretion of calcium Suppresses osteoclast bone reabsorption

Long term tx tachyphylaxis Chelating agents (EDTA or phosphate salts)

Rarely indicated

Hypocalcemia

Symptoms Numbness, paresthesias of the distal extremities and

circumoral region Chvostek sign

- a twitch of facial muscles elicited by tapping gently on the facial nerve

Trousseau’s sign

- carpopedal spasm induced by 3 min of inflation of a BP cuff above the brachial artery

Painful muscle spasms Cardiac dysfunction

Impaired contractility Prolonged QT interval complete heart block or v-fib

Hypocalcemia cont.

Causes Parathyroid surgery Tumor lysis syndrome Severe pancreatitis Rapid infusion of citrate with blood products Dietary deficiencies, short gut syndrome Impaired vit D conversion

Available forms of calcium replacement? CaCl2

10% solution 272 mg calcium (13.6 mmol) Ca gluconate

10% solution 90mg calcium (4.5 mmol)

Hypocalcemia cont.

Tumor lysis syndrome? Constellation of electrolyte abnormalities that occur

when antineoplastic therapy causes a sudden surge in tumor cell death and release of cytosol contents

Assoc with: solid tumors and lymphoma

Electrolyte abnormalities Hypocalcemia Hyperphosphatemia Hyperuricemia Hyperkalemia

Acute renal failure prevents spontaneous correction

Elderly alcoholic man who takes loop diuretics is seen in ER with sxs of hypocalcemia. They are unable to correct the deficit. What else should they correct?

Ca K Mg Phos Na

Magnesium

Normal plasma concentration 1.4 to 2.0 mEq/L

Hypermagnesemia symptoms appear when Mg > 6 mg/dL. altered mental status, lethargy, depressed DTR, flaccid paralysis. Respiratory depression

Treatment: Loop diuretics. Calcium, 10 – 20 meq, can reverse the clinical signs.

Hypomagnesemia Gastrointestinal loss:

Diarrhea, malabsorption, vomiting, biliary fistulas Urinary loss:

Diuresis or renal tubular dysfunctions. Drugs: cisplatin, cyclosporin, loop diuretics, amphotericin B,

aminoglycosides. Shifting into cells

Acute MI, alcoholic withdrawal, glucose injection.

Hypomagnesemia cont.

Treatment Intravenous magnesium sulfate (MgSO4)

Sustained therapy req for severe ↓Mg (<1.0 mEq/L) Due to slow equilibration of extracellular Mg with

intracellular stores