Fluid and Electrolyte Management of the Surgical Patient

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Fluid and Electrolyte Management of the Surgical
Patient

• Hashmi

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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

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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

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Intracellular Fluid

• largest proportion in the skeletal muscle
• potassium and magnesium are the principal cations
• phosphates and proteins the principal anions

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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

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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)

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Terminology

• mole molecular weight of that substance in grams
  mole eg sodium chloride is 58 g (Na23, Cl35)
• 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

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NORMAL EXCHANGE OF FLUID AND ELECTROLYTES

• Water Exchange
• Salt Gain Losses

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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

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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

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Water Exchange

• Minimum of 500 to 800 mL urine per day required
  to excrete the products of catabolism

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Salt Gain and Losses

• daily salt intake varies 3-5 gm as NaCl
• kidneys excretes excess salt can vary from lt 1
  to gt 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

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CLASSIFICATION OF BODY FLUID CHANGES

• Volume Changes
• Concentration Changes
• Composition Changes
• Acid/Base Balance
• Potassium Abnormalities
• Calcium Abnormalities
• Magnesium Abnormalities

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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

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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

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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

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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

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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

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Concentration Changes

• Na primarily responsible for ECF osmolarity
• Hyponatremia and hypernatremia ss 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

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Hyponatremia (water intoxication)

• acute symptomatic hyponatremia (lt 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

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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

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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

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Composition Changes

• Acid/Base Balance
• Potassium Abnormalities
• Calcium Abnormalities
• Magnesium Abnormalities

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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
• bicarbonatecarbonic acid system operates
  principally in ECF

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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 201 ratio is maintained,
  regardless of the absolute values, the pH will
  remain at 7.4

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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

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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

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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

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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

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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

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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

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Pathophysiology of Paradoxic Aciduria occurring
with GOO

• GOO -gt 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

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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 _at_ 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

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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)

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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

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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

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Hypocalcemia

• signs symptoms (serum level lt 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

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Hypocalcemia

• causes
• acute pancreatitis, massive soft-tissue
  infections (necrotizing fasciitis), acute and
  chronic renal failure, pancreatic and small-bowel
  fistulas, and hypoparathyroidism

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Hypercalcemia

• signs symptoms
• CNS easy fatigue, weakness, stupor, and coma
• GI anorexia, nausea, vomiting, and weight loss,
  thirst, polydipsia, and polyuria

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Hypercalcemia

• two major causes
• hyperparathyroidism and cancer
• bone mets
• PTH-like peptide in malignancies

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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

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Magnesium Deficiency

• causes
• starvation, malabsorption syndromes, GI losses,
  prolonged IV or TPN with magnesium-free solutions
• signs symptoms
• similar to those of calcium deficiency

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Magnesium Excess

• Symptomatic hypermagnesemia, although rare, is
  most commonly seen with severe renal
  insufficiency
• signs symptoms
• CNS lethargy and weakness with progressive loss
  of DTRs somnolence, coma, death
• CVS increased P-R interval, widened QRS complex,
  and elevated T waves (resemble hyperkalemia)
  cardiac arrest

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Secretions
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FLUID AND ELECTROLYTE THERAPY

• Preoperative Fluid Therapy
• Intraoperative Fluid Therapy
• Postoperative Fluid Therapy

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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

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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

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Fluid Composition
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Fluid Replacement Status
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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

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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
  

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Renal Indices

• Indices Prerenal Renal Postrenal
• U Osm gt 500 lt 350 Varies
• U/P osm gt1.25 lt1.1 Varies
• U/P urea gt 8 lt 3 Varies
• U/P cr gt 40 lt 20 lt 20
• Urine Na lt 20 gt 40 gt 40
• FENa lt 1 gt 3 gt 3

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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 gt
  100)