Fluid and Electrolyte Management of the Surgical Patient

1. Fluid and Electrolyte Management of the Surgical Patient Basic Science 9/08/09 J. P. Stokes

2. Case Presentation #1 • 28 y/o WM involved in MVC brought to 1W with GCS of 3 and hypotensive. Pt intubated and receives 2L of LR which stabilize HR and BP. Found to have extensive cerebral contusion and SAH. Admitted to ICU with plan by Neurosurgery to correct any coagulopathy and keep sodium >150. Placed on 3% Hypertonic saline with Q6 Na. After 6 hours in the ICU, the patients UOP increases to 500-1000cc/hr. The next sodium is 168. 3% discontinued and patient started on Vasopressin replacement and free water. Pt deteroriates and herniates due to cerebral edema.

3. Case Presentation #2 • 55 y/o WF with low rectal cancer s/p neoadjuvant undergoes LAR with diverting ileostomy. Blood loss is 300cc, fluid for the case was 1.8L crytalloid, and the case lasted 3.5 hours. Post-operative the patient is hypotensive with minimal UOP. Patient receives several 1L boluses and BP and UOP improve. She continues to receive IVFs and her sodium on POD#3 is 128 and her sats are decreased. She is diuresed and improves. On POD #5, she is tolerating liquids and her ileostomy output is 2.8L for that 24 hour period. Her IVFs were discontinued due to her oral intake and the next morning her creatinine is 2.3. She is bolused, restarted on maintenance, and ileostomy replacement, along with anti-motility agents. Her creatinine improves and she is discharged on POD #7 with ileostomy output of 1L/day.

4. Overview • Total Body Water (TBW) – 50-60% of total body weight depending on gender (amount of adipose tissue) • TBW is divided into extracellular (1/3) and intracellular (2/3) compartments • Extracellular is divided into plasma (1/4) and interstitial fluid (3/4) – 5% and 15% of body weight, respectively

5. Questions • What is the amount in milliliters of the intracellular volume in a 70kg male? • 14,000 ml • 10,500 ml • 42,000 ml • 28,000 ml

6. Composition • Extracellular – Sodium (+), Chloride (-) and Bicarbonate (-) • Intracellular- Potassium, Magnesium (+), Phosphate and Proteins (-) • Plasma – 154 mEq/L of cations/anions • Maintained by ATP-driven sodium-potassium pumps

7. Osmotic pressure • The movement of water across a cell membrane depends primarily upon osmosis. This depends on solutes or osmotically-active particles. • Calculated serum osmolality = 2 X Sodium + glucose/18 + BUN/2.8 • Normal 280-300 mOsm • Charge determines equivalents (1 mEq of sodium equals 1 mmol)

8. Questions • What is the calculated serum osmolality of a patient with a the following chemistry? • Na 140, K 4, Cl 105, HCO3 25, BUN 28, Cr 1.0, Glc 180 • 260 • 280 • 300 • 320 • Bonus: What is the anion gap of this patient?

9. Fluid Homeostasis • Average person • Intake - 2L of water per day (75% oral, 25% from solids • Output – 1L of urine, 250ml of stool, 600ml of insensible loss (skin and lungs – pure water) • Insensible losses increased by fever, hypermetabolism, and hyperventilation • Sweating is an active process and is electrolytes and water • Average salt intake – 3-5 grams

10. Fluid Balance System Volume down Volume UP Generalized Weight loss Weight gain Dec. skin turgor Perp. Edema Cardiac Tachycardia Increased CO Orthostasis Increased CVP Hypotension Collasped veins Bulging veins Murmur (flow

11. GI secretions Type Volume Na K Cl HCO3– Stomach 1000–2000 60–90 10–30 100–130 0 Intestine 2000–3000 120–140 5–10 90–120 30-40 Colon  60 30 40 0 Pancreas 600–800 135–145 5–10 70–90 95–115 Bile 300–800 135–145 5–10 90–110 30–40

12. Question • What fluid do you replace NGT output with? • D51/2NS • LR • 1/2NS with 20 mEq KCL • D5W with 150 mEq NaHCO3

13. Electrolyte Abnormalities • Sodium • Hyponatremia • Hypervolemic – Excess oral water intake, IV fluids • Euvolemic – Hyperglycemia, SIADH, Hyperlipidemia (pseudo) • Hypovolemic – Decreased sodium intake or increased loss of sodium containing fluids, GI losses, renal losses (UrNa >20) • Hypernatremia • Hypervolemic – Salt intake, Mineralcorticoid excess • Euvolemic – Renal water loss (diuretics, DI), Nonrenal water loss (skin, GI) • Hypovolemic – Adrenal failure, Osmotic diuretics • Signs and Symptoms: CNS, MSK, GI, CV, etc.

14. Potassium • Dietary intake 50-100 mEq/day; primarily intracellular • Hyperkalemia – Excess intake, increased release from cells, impaired excretion, medications • Hypokalemia – Decreased intake, Excess excretion, GI losses (direct vs. indirect) • S/S: GI, CNS, CV

15. Magnesium • Hypomagnesemia – Poor intake, increased renal excretion, GI losses (diarrhea) • Hypermagnesemia – impaired renal function, excess intake (TPN) • Magnesium plays an important role in potassium and calcium homeostasis

16. Calcium/Phosphorus • Hypercalcemia – Primary hyperparathyroidism, malignancy • Hypocalcemia – Pancreatitis, renal failure, hypopara-, etc. • Asymptomaic hypocalcemia can be due to hypoproteinemia, mainly albumin • Correction for albumin • Phosphorus – renal, gastrointestinal

17. Acid/Base • Normal pH – 7.35-7.45 • Metabolic vs. Respiratory • Uncompensated vs. Compensated • pH, CO2, HCO3

18. Anion Gap and Metabolic Acidosis • Anion gap = (Na + K) – (Cl + HCO3) • Normal: 12 +/- 4 • Non-gap acidosis: Hyperalimentation, Acetozolamide, RTA, Diarrhea, Ureteral diversion, pancreatic fistulas • Anion gap acidosis – Methanol, Uremia, DKA, Paraldehyde, INH, Lactate, Ethylene glycol, Salicylate

19. Metabolic Alkalosis • Normal acid-base homeostasis prevents metabolic alkalosis from developing unless both an increase in HC03 generation and impaired renal excretion of HCO3 occurs. • Generally associated with hypokalemia (pyloric stenosis) • Etiology: Mineralocorticoid excess, loss from gastric secretions, exogenous, impaired exretion

20. Question • What is the electrolyte and acid/base disturbance in pyloric stenosis, and explain why the patient has paradoxical aciduria?

21. Respiratory derangements • Hyperventilation • Hypoventilation • Involves minute ventilation (respiratory rate and tidal volume) • Treatment directed at the cause

22. Fluid therapy • What are the concentrations of normal saline and lactated ringer’s? • Na 154 and 130 • K 0 and 4 • Cl 154 and 109 • HCO3 0 and 28 • Ca 0 and 3

23. Question • What is the amount of dextrose per liter in D51/2NS? How many calories is in one liter? How many calories per hour if fluids run @ 125 cc/hr? • 5grams • 50grams • 500grams • 500mg

24. Treating Electrolyte Disturbances • Hypernatremia – Correction of free water deficit • Water deficit (L) =[(Na-140)/140] x TBW • TBW at 50% in men and 40% in women • The rate of fluid administered should be titrated to achieve a decrease in serum sodium of no more than 12 mEq/d. • Rapid correction: cerebral edema, herniation • Hyponatremia – Free water restriction, sodium administration • Neurologic symptoms – 3% (No more than 1 mEq/L/hr); Complication: CPM

25. Potassium Correction • Hyperkalemia: Reduce total body potassium, shift from extra- to intracellular, and protect cells from effects of increased potassium • What can kill my patient? EKG, calcium • How do I shift potassium? Bicarbonate, Glucose (Insulin), Albuterol • How can I remove potassium? Lasix, Dialysis, Potassium binders (Kayexalate)

27. Repleting Electrolytes • Potassium: IV and PO/NG • Magnesium: IV (Important for repleting other electrolytes) • Calcium: IV and PO • Phosphorus: IV and PO (ineffective)

28. Treatment of …. • Hypermagnesemia: Remove source, calcium for cardiovascular effects, dialysis • Hypercalcemia: Volume and diuresis, bisphosphonates, calcitonin • Hyperphosphotemia: Phosphate binders, urinary exrection, dialysis

29. Maintenance fluids/Post-op • Maintenance • 4, 2, 1 rule (Dextrose, Electrolytes) • 5, 2, 1 rule in pediatric surgery • Boluses • What fluid? • Post-Op

30. Question • What is the appropriate fluid and maintenance rate for a 4kg baby with pyloric stenosis? What would you use to bolus the baby and why?

31. Special Situations • SIADH – Euvolemia and hyponatremia along with elevated urine sodium and urine osmolality; Tx: Free water restriction, diuresis, fluids (?), lithium, democycline • DI – Dilute Urine in the face of hypernatremia; Central and Nephrogenic; Tx: Free water, Vasopressin • Refeeding: Shift from fat to carbohydrate stimulates insulin release and uptake of electrolytes (PO4, Mg, K, Ca), hyperglycemia