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ANATOMY OF BODY FLUIDS. Total Body WaterIntracellular FluidExtracellular FluidOsmotic Pressure. Total Body Water. constitutes 50-70 % of total body weightfat contains little water, the lean individual has a greater proportion of water to total body weight than the obese persontotal body water as a percentage of total body weight decreases steadily and significantly with increasing age.
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1. Fluid and Electrolyte Management of the Surgical Patient
Hashmi
2. ANATOMY OF BODY FLUIDS Total Body Water
Intracellular Fluid
Extracellular Fluid
Osmotic Pressure
3. Total Body Water constitutes 50-70 % of total body weight
fat contains little water, the lean individual has a greater proportion of water to total body weight than the obese person
total body water as a percentage of total body weight decreases steadily and significantly with increasing age
4. Total Body Water % of Body Weight % of Total Body Water
Body Water 60 100
ICF 40 67
ECF 20 33
Intravascular 4 8
Interstitial 16 25
5. Intracellular Fluid largest proportion in the skeletal muscle
potassium and magnesium are the principal cations
phosphates and proteins the principal anions
6. Extracellular Fluid interstitial fluid: two types
functional component (90%) - rapidly equilibrating
nonfunctioning components (10%) - slowly equilibrating
connective tissue water and transcellular water
called a “third space” or distributional change
sodium is the principal cation
chloride and bicarb the principal anions
7. Osmotic Pressure physiologic and chemical activity of electrolytes depend on three factors:
the number of particles present per unit volume (moles or millimoles [mmol] per liter)
the number of electric charges per unit volume (equivalents or milliequivalents per liter)
the number of osmotically active particles or ions per unit volume (osmoles or milliosmoles [mOsm] per liter)
8. Terminology mole: molecular weight of that substance in grams mole eg: sodium chloride is 58 g (Na–23, Cl–35)
equivalent: chemical combining activity; atomic weight expressed in grams divided by the valence
divalent ions (calcium or magnesium) 1 mmol equals 2 mEq
osmole: used when the actual number of osmotically active particles present in solution is considered
millimole of sodium chloride, which dissociates nearly completely into sodium and chloride, contributes 2 mOsm
9. NORMAL EXCHANGE OF FLUID AND ELECTROLYTES
Water Exchange
Salt Gain & Losses
10. Water Exchange daily water gains
normal individual consumes 2000 to 2500 mL water per day
approximately 1500 mL taken by mouth
rest is extracted from solid food, either from the contents of the food or as the product of oxidation
11. Water Exchange daily water losses
250 mL in stools, 800 - 1500 mL in urine, and 600 mL as insensible loss
total losses ~ 2.2 liters
Insensible loss: skin (75%) and lungs (25%)
increased by hypermetabolism, hyperventilation, and fever
250 mL/day per degree of fever
unhumidified tracheostomy with hyperventilation = insensible loss up to 1.5 L/day
12. Water Exchange Minimum of 500 to 800 mL urine per day required to excrete the products of catabolism
13. Salt Gain and Losses daily salt intake varies 3-5 gm as NaCl
kidneys excretes excess salt: can vary from < 1 to > 200 mEq/day
Volume and composition of various types of gastrointestinal secretions
Gastrointestinal losses usually are isotonic or slightly hypotonic
should replace by isotonic salt solution
14. CLASSIFICATION OF BODY FLUID CHANGES Volume Changes
Concentration Changes
Composition Changes
Acid/Base Balance
Potassium Abnormalities
Calcium Abnormalities
Magnesium Abnormalities
15. Volume Changes If isotonic salt solution is added to or lost from the body fluids, only the volume of the ECF is changed, ICF is relatively unaffected
If water is added to or lost from the ECF, the conc. of osmotically active particles changes
Water will pass into the intracellular space until osmolarity is again equal in the two compartments
16. Volume Changes BUN level rises with an ECF deficit of sufficient magnitude to reduce GFR
creatinine level may not incr. proportionally in young people with healthy kidneys
hematocrit increases with an ECF deficit and decreases with ECF excess
sodium is not reliably related to the volume status of ECF
a severe volume deficit may exist with a normal, low, or high serum level
17. Volume Deficit ECF volume deficit is most common fluid loss in surgical patients
most common causes of ECF volume deficit are: GI losses from vomiting, nasogastric suction,diarrhea, and fistular drainage
other common causes: soft-tissue injuries and infections, peritonitis, obstruction,and burns
18. Volume Deficit signs and symptoms of volume deficit:
CNS: sleepy, apathy – stupor, coma
GI: dec food consumption – N/V
CVS: orthostatic, tachy, collapsed veins - hypotension
Tissue: dec skin turgor, small tongue – sunken eyes, atonia
19. Volume Excess Iatrogenic or Secondary to renal insufficiency, cirrhosis, or CHF
signs & symptoms of volume excess:
CNS: none
GI: edema of bowel
CVS: elevated CVP, venous distension – pulmonary edema
Tissue: pitting edema – anasarca
20. Concentration Changes Na+ primarily responsible for ECF osmolarity
Hyponatremia and hypernatremia s&s often occur if changes are severe or occur rapidly
The concentration of most ions within the ECF can be altered without significant osmolality change, thus producing only a compositional change
Example: rise of potassium from 4 to 8 mEq/L would significantly effect the myocardium, but not the effective osmotic pressure of the ECF
21. Hyponatremia (water intoxication) acute symptomatic hyponatremia (< 130)
hypertension can occur & is probably induced by the rise in intracranial pressure
signs & symptoms:
CNS: twitching, hyperactive reflexes – inc ICP, convulsions, areflexia
CVS: HTN/brady due to inc ICP
Tissue: salivation, watery diarrhea
Renal: oliguria - anuria
22. Hyponatremia (water intoxication) Hyponatremia occurs when water is given to replace losses of sodium-containing fluids or when water administration consistently exceeds water losses
Hyperglycemia: glucose exerts an osmotic force in the ECF and causes the transfer of cellular water into the ECF, resulting in a dilutional hyponatremia
23. Hypernatremia (water deficit) The only state in which dry, sticky mucous membranes are characteristic
sign does not occur with pure ECF deficit alone
signs & symptoms:
CNS: restless, weak - delirium
CVS: tachycardia - hypotension
Tissue: dry/sticky muc membranes – swollen tongue
Renal: oliguria
Metabolic: fever – heat stroke
24. Composition Changes Acid/Base Balance
Potassium Abnormalities
Calcium Abnormalities
Magnesium Abnormalities
25. Acid-Base Balance large load of acid produced endogenously as a by-product of body metabolism
acids are neutralized efficiently by several buffer systems and subsequently excreted by the lungs and kidneys
Buffers:
proteins and phosphates: primary role in maintaining intracellular pH
bicarbonate–carbonic acid system: operates principally in ECF
26. Acid-Base Balance buffer systems consists of a weak acid or base and the salt of that acid or base
Henderson-Hasselbalch equation, which defines the pH in terms of the ratio of the salt and acid:
pH = pK + log BHCO3 / H2CO3 = 27 mEq/L / 1.33 mEq/L = 20 / 1 = 7.4
As long as the 20:1 ratio is maintained, regardless of the absolute values, the pH will remain at 7.4
27. Acid-Base Balance Four types of acid-base disturbances
combinations of respiratory and metabolic changes may represent:
compensation for the initial acid-base disturbance or,
two or more coexisting primary disorders
10-mmHg PaCO2 change yields a 0.08 pH change
28. Respiratory Acidosis retention of CO2 secondary to decreased alveolar ventilation
management involves prompt correction of the pulmonary defect, when feasible, and measures to ensure adequate ventilation
prevention: tracheobronchial hygiene during the postoperative , humidified air, and avoiding oversedation
29. Respiratory Alkalosis PaCO2 should not be below 30 mmHg
dangers of a severe respiratory alkalosis are those related to potassium depletion
hypokalemia is related to entry of potassium ions into the cells in exchange for hydrogen and an excessive urinary potassium loss in exchange for sodium
shift of the oxyhemoglobin dissociation curve to the left, which limits the ability of hemoglobin to unload oxygen at tissues
30. Metabolic Acidosis Anion gap is a useful aid:
normal value is 10 to 15 mEq/L
unmeasured anions that account for the “gap” are sulfate and phosphate plus lactate and other organic anions
measured ions are sodium, bicarb, and chloride
31. Metabolic Acidosis treatment of metabolic acidosis should be directed toward correction of the underlying disorder
sodium bicarbonate is discouraged, attempt to treat underlying cause
shifts the oxyhemoglobin dissociation curve left
interference with O2 unloading at the tissue level
32. Metabolic Alkalosis common surgical patient has hypochloremic, hypokalemic metabolic alkalosis resulting from persistent vomiting or gastric suction in the patient with pyloric obstruction
unlike vomiting with an open pylorus, which involves a combined loss of gastric, pancreatic, biliary, and intestinal secretions
33. Pathophysiology of Paradoxic Aciduria occurring with GOO GOO -> hypochloremic, hypokalemic, metabolic alkalosis
urinary bicarb excretion to compensate for alkalosis
volume deficit progresses ? aldosterone-mediated sodium resorption is accompanied by potassium excretion
kidneys primary goal becomes volume preservation ? sodium resorption
either K+ or H+ must be excreted to keep a balanced
due to already excessive hypokalemia, the kidney excretes H+ in place of K+, producing paradoxic aciduria
34. Potassium Abnormalities normal daily dietary intake of K+ is approx. 50 to 100 mEq
majority of K+ is excreted in the urine
98% of the potassium in the body is located in ICF @ 150 mEq/L and it is the major cation of intracellular water
intracellular K+ is released into the extracellular space in response to severe injury or surgical stress, acidosis, and the catabolic state
35. Hyperkalemia signs & symptoms:
CVS: peaked T waves, widened QRS complex, and depressed ST segments ? Disappearance of T waves, heart block, and diastolic cardiac arrest
GI: nausea, vomiting, diarrhea (hyperfunctional bowel)
36. Hypokalemia K+ has an important role in the regulation of acid-base balance
alkalosis causes increased renal K+/H+ excretion
signs & symptoms:
CVS: flatten T waves, depressed ST segments
GI: paralytic ileus
Muscular: weakness - flaccid paralysis, diminished to absent tendon reflexes
37. Calcium Abnormalities majority of the 1000 to 1200g of calcium in the average-sized adult is found in the bone
Normal daily intake of calcium is 1 to 3 gm
Most is excreted via the GI tract
half is non-ionized and bound to proteins
ionized portion is responsible for neuromuscular stability
38. Hypocalcemia signs & symptoms (serum level < 8):
numbness and tingling of the circumoral region and the tips of the fingers and toes
hyperactive tendon reflexes, positive Chvostek's sign, muscle and abdominal cramps, tetany with carpopedal spasm, convulsions (with severe deficit), and prolongation of the Q-T interval on the ECG
39. Hypocalcemia causes:
acute pancreatitis, massive soft-tissue infections (necrotizing fasciitis), acute and chronic renal failure, pancreatic and small-bowel fistulas, and hypoparathyroidism
40. Hypercalcemia signs & symptoms:
CNS: easy fatigue, weakness, stupor, and coma
GI: anorexia, nausea, vomiting, and weight loss, thirst, polydipsia, and polyuria
41. Hypercalcemia two major causes:
hyperparathyroidism and cancer
bone mets
PTH-like peptide in malignancies
42. Magnesium Abnormalities total body content of magnesium 2000 mEq
about half of which is incorporated in bone
distribution of Mg similar to K+, the major portion being intracellular
normal daily dietary intake of magnesium is approximately 240 mg
most is excreted in the feces and the remainder in the urine
43. Magnesium Deficiency causes:
starvation, malabsorption syndromes, GI losses, prolonged IV or TPN with magnesium-free solutions
signs & symptoms:
similar to those of calcium deficiency
44. Magnesium Excess Symptomatic hypermagnesemia, although rare, is most commonly seen with severe renal insufficiency
signs & symptoms:
CNS: lethargy and weakness with progressive loss of DTR’s – somnolence, coma, death
CVS: increased P-R interval, widened QRS complex, and elevated T waves (resemble hyperkalemia) – cardiac arrest
45. Secretions
46. FLUID AND ELECTROLYTE THERAPY Preoperative Fluid Therapy
Intraoperative Fluid Therapy
Postoperative Fluid Therapy
47. Preoperative Fluid Therapy Correction of Volume Changes: Volume deficits result from external loss of fluids or from an internal redistribution of ECF into a nonfunctional compartment
nonfunctional because it is no longer able to participate in the normal function of the ECF and may just as well have been lost externally
Correction of Concentration Changes: If severe symptomatic hypo or hypernatremia complicates the volume loss, prompt correction of the concentration abnormality to the extent that symptoms are relieved is necessary
48. Postoperative Fluid Management replace losses & supply a maintenance:
open abdomen losses: 8 cc/kg/hr
NGT & urine output
Blood loss x 3
Replace with isotonic salt solution (LR or NS)
unwise to administer potassium during the first 24 h, until adequate urine output has been established even a small quantity of potassium may be detrimental because of fluid shifts
49. Fluid Composition
50. Fluid Replacement Status
51. Acute Renal Failure Classified according to its cause:
Prerenal: hypotension, hypovolemia, renal artery occlusion/stenosis, cardiac failure
Renal: trauma, toxins (contrast, endotoxin), drugs (NSAIDS, aminoglycosides), pigment (myoglobin, hemaglobin)
Postrenal: ureteral obstruction, bladder dysfxn (anesthesia, meds, nerve injury), urethral obstruction, foley obstruction
52. Laboratory Studies Urinalysis: blood or myoglobin is a positive diagnostic test - can test via Hemoccult card
Urinary lytes: urine sodium, creatinine, urea, osmolality, and specific gravity help classify type of renal failure using Renal failure indices
53. Renal Indices Indices Prerenal Renal Postrenal
U Osm > 500 < 350 Varies
U/P osm >1.25 <1.1 Varies
U/P urea > 8 < 3 Varies
U/P cr > 40 < 20 < 20
Urine Na < 20 > 40 > 40
FENa < 1% > 3% > 3%
54. Indications for use of Dialysis in Acute Renal Failure Severe acidosis
Electrolyte abnormalities
Inability to clear toxins
Volume overload
Uremic signs and symptoms (encephalopathy, BUN > 100)