Basic Science Lecture 9/28/10 Marcie Dorlon

Introduction Changes in fluid volume and electrolyte composition occur: preoperatively, intraoperatively, postoperatively, and in trauma and sepsis Important to recognize and understand how to manage changes

Total Body Water Water constitutes 50-60% total body weight Primarily a reflection of body fat (lean muscle=more water) Estimated total body water should be downward by 10-20% for obese individuals and downward 10% for malnourished individuals Total body water is estimated around 80% for newborns

Fluid Compartments

Composition Fluid Compartment

Osmotic Pressure Facilitates water movement across cell membranes Determined by concentration of solutes on either side membrane (mainly sodium, glucose and urea/BUN) Calculated serum osmolality= 2 * sodium + (glucose/18) + (BUN/2.8) Osmolality is maintained between 290 and 310

Normal Exchange of Fluid and Electrolytes Healthy person comsumes average of 2000mL water/day Daily losses average mL urine, 250mL stool, 600mL insensible (skin, lungs) To clear products of metabolism, kidneys must excrete 500 to 800mL urine per day despite intake Average salt intake is 3-5grams/day

SystemVolume DeficitVolume Excess GeneralizedWeight lossWeight gain Decreased skin turgorPeripheral edema CardiacTachycardiaIncreased cardiac output Orthostasis/hypotensionIncreased central venous pressure Collapsed neck veinsDistended neck veins Murmur RenalOliguria— Azotemia GIIleusBowel edema Pulmonary—Pulmonary edema Signs and Symptoms of Volume Disturbances

Composition of GI secretions Type of Secretion Volume (mL/24 h) Na (mEq/L) K (mEq/L)Cl (mEq/L) HCO 3 – (mEq/L) Stomach1000–200060–9010–30100–1300 Small intestine 2000– –1405–1090–12030–40 Colon— Pancreas600–800135–1455–1070–9095–115 Bile300–800135–1455–1090–11030–40

Body SystemHyponatremia Central nervous systemHeadache, confusion, hyperactive or hypoactive deep tendon reflexes, seizures, coma, increased intracranial pressure MusculoskeletalWeakness, fatigue, muscle cramps/twitching GIAnorexia, nausea, vomiting, watery diarrhea CardiovascularHypertension and bradycardia if significant increases in intracranial pressure TissueLacrimation, salivation RenalOliguria Body System Hypernatremia Central nervous systemRestlessness, lethargy, ataxia, irritability, tonic spasms, delirium, seizures, coma MusculoskeletalWeakness CardiovascularTachycardia, hypotension, syncope TissueDry sticky mucous membranes, red swollen tongue, decreased saliva and tears RenalOliguria MetabolicFever

Hyperkalemia Causes Increased intake: Potassium supplementation Blood transfusions Endogenous load/destruction: Hemolysis or rhabdomyolysis Crush injury Gastrointestinal hemorrhage Increased release: Acidosis Rapid rise of extracellular osmolality (hyperglycemia or mannitol) Impaired excretion: Potassium-sparing diuretics Renal insufficiency/failure

Hyperkalemia Symptoms GI Nausea Vomiting Intestinal colic Diarrhea Neuromuscular: Weakness Ascending paralysis Respiratory failure Cardiovascular: EKG changes: Early peaked T waves Late widened QRS, flat p-waves, prolonged PR interval, v-fib Cardiac arrest

Hypokalemia Causes Inadequate intake: Dietary Potassium-free intravenous fluids Potassium-deficient TPN Excessive potassium excretion: Hyperaldosteronism Medications GI losses: Direct loss of potassium from GI fluid (diarrhea) Renal loss of potassium (gastric fluid, either as vomiting or high nasogastric output)

Hypokalemia Symptoms GI Ileus Constipation Neuromuscular Weakness Fatigue Diminished tendon reflexes Paralysis Cardiovascular EKG changes U waves, T wave flattening, ST segment changes, arrhythmias Cardiac arrest

Calcium Daily Intake 1-3grams Adjust total serum calcium down by 0.8g/dL for every 1g/dL decrease in albumin Acidosis increases ionized fraction of calcium due to decreased protein binding Hypercalcemia Think primary hyperparathyroidism in outpatient setting vs malignancy in inpatient setting Sx: neurologic impairment, musculoskeletal weakness and pain, renal dysfunction, nausea, vomitting, abdominal pain, hypertension, arrhythmias, worsening digitalis toxicity EKG changes: shortened QT interval, prolonged PR and QRS interval, increased QRS voltage, T wave flattening and widening, AV block->arrest Hypocalcemia Causes: pancreatitis, massive soft tissue infections, renal failure, pancreatic or small bowel fistulas, hypoparathyroidism, TSS, tumor lysis syndrome, abnormal magnesium levels, massive blood transfusion with citrate binding Sx: paresthesias face and extremities, muscle cramps, stridor, tetany, seizures, hyperreflexia, Trousseau’s sign, Chvostek’s sign, decreased cardiac contractility, heart failure EKG changes: prolonged QT interval, T wave inversion, heart block, V-fib

Phosphorus Abundant in metabolically active cells and tightly controlled by renal excretion Hyperphosphatemia Causes: decreased urinary excretion, increased intake, hypoparathyroidism, hyperthyroidism, rhabdomyolysis, tumor lysis syndrome, hemolysis, sepsis, hypothermia, malignant hyperthermia Sx: Most asymptomatic but severe cases can lead to metastatic deposition of calcium-phosphorus complexes Hypophosphatemia Causes: decreased intake, intracellular shift (respiratory alkalosis, insulin administration, hungry bone syndrome, refeeding syndrome) increased excretion, decreased GI uptake due to binders, Sx: Usually asymptomatic until severe- cardiac dysfunction and muscle weakness when high energy phosphates unavailable

Magnesium Hypermagnesemia Causes: severe renal insufficiency, iatrogenic- in antacids, laxatives and TPN, severe trauma, severe acidosis, thermal injury Sx: nausea, vomiting, weakness, lethargy, hyporeflexia, hypotension and cardiac arrest EKG changes: increased PR interval, widened QRS complex, elevated T waves Hypomagnesemia Causes: starvation, alcoholism, prolonged IVF tx, inadequate TPN, diuretic use, amphotericin B, primary aldosterism, diarrhea, malabsorption, acute pancreatitis Sx: neuromuscular and CNS hyperactivity, similar to hypocalcemia EKG changes:prolonged QT and PR intervals, ST segment depression, flattening or inversion of p waves, torsades de pointes, arrythmias

Acid-Base Disorders Acute UncompenstedChronic (Partially Compensated) Type of Acid-Base Disorder pHPCO 2 (Respiratory Component) Plasma HCO 3 –a (Metabolic Component) pHPCO 2 (Respiratory Component) Plasma HCO 3 –a (Metabolic Component) Respiratory acidosis N Respiratory alkalosis N Metabolic acidosis N Metabolic alkalosis N?

IVF Composition SolutionNaCLKHCO 3 – CaMgmOsm Extracellular fluid –310 Lactated Ringer's % Sodium chloride D % Sodium chloride D5W 253 3% Sodium chloride

Alternative Resuscitative Fluids SolutionMolecular WeightOsmolality (mOsm/L)Sodium (mEq/L) Hypertonic saline (7.5%) — Albumin 5%70, –160 Albumin 25%70, –160 Dextran 4040, Dextran 7070, Hetastarch450, Hextend670, Gelofusine30,000NA154

Correcting Hypernatremia Treat the associated water deficit Water deficit (L)= serum sodium-140 x TBW 140 Estimate TBW as 50% lean body mass men and 40% women Correct no more than 1 mEq/hr or 12 mEq/day to avoid cerebral edema and brain herniation

Correcting Hyponatremia Free water restriction and occasionally administration of sodium Correct by no more that 0.5mEq/L/hr or maximum increase of 12 mEq/L/day to avoid central pontine myelinolysis

Correcting Hyperkalemia Potassium removal Kayexalate Oral administration is 15–30 g in 50–100 mL of 20% sorbitol Rectal administration is 50 g in 200 mL of 20% sorbitol Dialysis Shift potassium Glucose 1 ampule of D 50 and regular insulin 5–10 units IV Bicarbonate 1 ampule IV Counteract cardiac effects Calcium gluconate 5–10 mL of 10% solution

Correcting Hypokalemia Serum potassium level <4.0 mEq/L: Asymptomatic, tolerating enteral nutrition: KCl 40 mEq per enteral access x 1 dose Asymptomatic, not tolerating enteral nutrition: KCl 20 mEq IV q2h x 2 doses Symptomatic: KCl 20 mEq IV q1h x 4 doses Recheck potassium level 2 h after end of infusion; if <3.5 mEq/L and asymptomatic, replace as per above protocol

Correcting Hypomagnesemia Magnesium level 1.0–1.8 mEq/L: Magnesium sulfate 0.5 mEq/kg in normal saline 250 mL infused IV over 24 h x 3 d Recheck magnesium level in 3 d Magnesium level <1.0 mEq/L: Magnesium sulfate 1 mEq/kg in normal saline 250 mL infused IV over 24 h x 1 d, then 0.5 mEq/kg in normal saline 250 mL infused IV over 24 h x 2 d Recheck magnesium level in 3 d If patient has gastric access and needs a bowel regimen: Milk of magnesia 15 mL (approximately 49 mEq magnesium) q24h per gastric tube hold for diarrhea

Correcting Hypocalcemia Normalized calcium level <4.0 mg/dL: With gastric access and tolerating enteral nutrition: Calcium carbonate suspension 1250 mg/5 mL q6h per gastric access; Recheck ionized calcium level in 3 d Without gastric access or not tolerating enteral nutrition: Calcium gluconate 2 g IV over 1 h x 1 dose; Recheck ionized calcium level in 3 d

Correcting Hypophosphatemia Tolerating enteral nutrition: Neutra-Phos 2 packets q6h per gastric tube or feeding tube No enteral nutrition: KPHO 4 or NaPO mmol/kg IV over 6 h x 1 dose Recheck phosphate level in 3 d Phosphate level <1.0 mg/dL: Tolerating enteral nutrition: KPHO 4 or NaPO mmol/kg over 6 h x 1 dose Recheck phosphate level 4 h after end of infusion; If <2.5 mg/dL, begin Neutra-Phos 2 packets q6h Not tolerating enteral nutrition: KPHO 4 or NaPO mmol/kg (LBW) over 6 h x 1 dose; recheck phosphate level 4 h after end of infusion; If <2.5 mg/dL, then KPHO 4 or NaPO mmol/kg (LBW) IV over 6 h x 1 dose

Preoperative Fluid Therapy For the first 0 to 10 kgGive 100 mL/kg per day For the next 10 to 20 kgGive an additional 50 mL/kg per day For weight >20 kgGive an additional 20 mL/kg per day Just an initial guideline, does not replace pre-existing deficit or ongoing losses No routine fluid choice. Surgeon/Anesthesia preference

Intraoperative Fluid Therapy Usually at discretion of Anesthesia team Be sure to note what (colloid vs crystalloid) and how much is given, particular blood or blood products and pressors Postoperative Fluid Therapy Take into account NPO status, ongoing losses from NGT, drains, fistua, etc Type of fluid can be surgeon or service dependent

Special Circumstances Neurologic Patients SIADH- hyponatremic with elevated urine sodium & osmolality Tx with fluid restriction and diuretics & underlying problem Diabetes Insipidus-hypernatremia with dilute urine Central (ADH secretion) vs nephrogenic (ADH responsiveness) Vasopressin tx Cerebral Salt wasting Dx of exclusion Refeeding Syndrome Insulin release leads to cellular uptake of electrolytes (Phosphate, Magnesium, Calcium, Potassium) Start feeding slowly at 20kcal/kg/day Acute Renal Failure Cancer Patients