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 cc/hr. The next sodium is % 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 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 – – – –130 0
Intestine 2000– – – –
Colon 
Pancreas 600– – – –90 95–115
Bile 300– – – –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 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
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