Fluids and Electrolytes

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Fluids and Electrolytes
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Water is the most abundant compound in the body
and is the major solvent in which metabolism
occurs.
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During an anesthetic, the anesthetist has primary
responsibility for the airway and the fluid
status of the patient.
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AANA Standards for Care

• Standard I - Thorough preoperative evaluation
• Standard II - Formulate a patient-specific plan
  for anesthesia care
• Standard III - Implement and adjust the plan
  based on the patients physiologic response.

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Agenda

• Body fluid compartments
• Electrolyte imbalances
• Types of fluids
• Fluid loss during surgery
• Developing a fluid plan
• Complications of fluid therapy

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Body Fluid Compartments and Composition
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Total Body Water

• 80 water in newborn
• Maximal at birth
• Adults - 60-70 water
• Obese - Lower percentage
• Lean - Higher percentage

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Rule of Approximate Thirds

• 2/3 of body weight is water (lean person)
• Body water
• 2/3 intracellular
• 1/3 extracellular
• Extracellular water
• 2/3-3/4 extravascular
• 1/3-1/4 intravascular

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70 kg Patient

• Total body water - 42 L
• Intracellular - 28 L
• Extracellular - 14 L
• Intravascular - 3 L
• Interstitial - 11 L

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Fluid Dynamics

• Forces affecting movement of fluids
• Capillary hydrostatic pressure
• Interstitial fluid pressure
• Plasma colloid osmotic pressure (oncotic)
• Interstitial fluid colloid pressure

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Capillary Hydrostatic Pressure

• Tends to move fluid out of the capillaries
• Arterial end - 25 mm/Hg
• Venous end - 10 mm/Hg
• Increasing hydrostatic pressure moves fluids to
  interstitial spaces.

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Edema occurs when fluid moves into interstitial
spaces faster than it can be drained by the
lymphatic system.
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Why is edema harmful?

• Edema increases the distance between the cells
  and the capillaries which reduces the
  effectiveness of meeting metabolic needs.

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Factors Increasing Hydrostatic Pressure

• Hypervolemia
• Decreased renal function
• Cardiac failure

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Plasma Osmotic Pressure

• Draws fluid from interstitial space back to the
  capillaries
• Colloid osmotic pressure is generated by protein
  molecules
• Donnan equilibrium enhances the osmotic effect

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Donnan Equilibrium

• Causes COP to be about 50 greater than that
  caused by proteins alone
• Proteins carry a negative charge
• Attract a large number of cations
• Water follows sodium

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Colloid Osmotic Pressure

• Combination of oncotic and osmotic pressures
• Oncotic pressure - from proteins
• Osmotic pressure - from electrolytes
• Normal osmolality 285 mOsm/kg (about twice the
  Na value)

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Interstitial Fluid Colloid Osmotic Pressure

• From small protein concentration in the
  interstitial fluid
• Most capillary pores are smaller than proteins,
  but some leak
• Interstitial osmotic pressure 8 mm/Hg

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Review forces causing capillary fluid movement

• McIntosh Table 11-1 p.192

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Normal Equilibrium

• Slightly more fluid leaves the capillaries than
  returns
• Excess fluid is returned via the lymphatic system

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Fluid Volume Problems

• Hypovolemia
• Hypervolemia

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Hypovolemia

• Volume defecit in ECF or circulating blood volume
• May be absolute or relative
• Actual fluid loss
• Shift to different compartment

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Causes of Fluid Loss

• Gastrointestinal loss
• Fever
• Blood loss
• Burns

• Peritonitis
• Fluid shifts
• Diuretics
• Inhalation of dry gases

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Signs of Hypovolemia

• Tachycardia
• Orthostatic hypotension
• Flat neck veins when supine
• Decreased CVP
• Decreased urine output
• Dry membranes
• CV collapse

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Compensatory Mechanisms

• Vaso constriction
• Tachycardia
• Note The patient under general anesthesia is
  unable to compensate. Therefore, fluid
  management is even more critical.

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Hypervolemia

• Fluid admisistration exceeds actual need
• May be caused by
• Large IV fluid volume
• CHF
• Renal failure
• Long term steroid use
• Cushings Syndrome

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Signs of Hypervolemia

• Destended neck veins
• Peripheral edema
• Dyspnea
• Pulmonary edema
• Hypertension

• Increased CVP
• Polyuria with decreasing specific gravity
• Cyanosis
• Hemodilution

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Fluid Composition Problems

• Hypernatremia / hyponatremia
• Hyperkalemia / hypokalemia
• Hyperchloremia / hypochloremia
• Hypercalcemia / hypocalcemia
• Magnesium
• Phosphate
• Glucose

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Hypernatremia

• Causes
• Excess renal excretion of free water
• Sweating / fever
• Diarrhea
• Respiratory evaporation

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Signs of Hypernatremia

• Mental changes
• Thirst
• Peripheral edema
• Myoclonus
• Cardiovascular collapse

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Treatment of Hypernatremia

• Restore volume with hypotonic solution
• Loop diuretics

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Causes of Hyponatremia

• Renal failure
• CHF
• Replacement with sodium-free solution
• Inappropreiate ADH
• Decreased serum osmolality
• TURP Syndrome

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Signs of Hyponatremia

• Hypertension / hypotension
• Mental confusion
• Seizure / coma

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Treatment of Hyponatremia

• Reduce excess fluid volume
• Administer hypertonic solution

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Use Caution When Correcting Hyponatremia

• Rapid correction may cause
• Central pontine myelinolysis
• Osmotic demyelination syndrome
• Correct 1-2 meq/hr to 120 meq/s
• Then 0.5 meq/hr to normal

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Hyperkalemia

• Causes
• Inadequate excretion
• Excessive intake
• Extracellular redistribution
• Cellular destruction
• Succinylcholine

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Signs of Hyperkalemia

• ECG peaked T waves
• Prolonged PR interval
• Absent P wave
• Wide QRS with severe hyperkalemia
• V-Tach / V-Fib

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Treatment of Hyperkalemia

• Alkalization
• Hyperventilation
• Bicarbonate
• Calcium chloride
• Glucose / insulin

• Potassium banding resin
• Diuretics
• Dialysis

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Hypokalemia

• Causes
• Usually iatrogenic
• Diuretics
• G.I. fluid loss
• Sweating
• Exacerbated by respiratory alkalosis

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Signs of Hypokalemia

• Lab values
• ECG changes

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Treatment

• Consider delaying surgery
• Lower limit 2.5-3.0??
• Consider total body depletion
• Consider magnesium deficit
• Give dilute solution slowly in peripheral I.V.

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Chloride Disorders

• Most commonly related to
• acid-base disorders

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Hyperchloremia

• Causes
• Renal tubular acidosis
• Excessive chloride admisistration
• Signs
• Hypercholremic acidosis
• Treatment
• Consider correcting the acidosis with bicarbonate

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Hypochloremia

• Causes
• Alkalosis secondary to excessive chloride loss
• Diuretics
• NG suction
• May follow massive blood transfusion

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Hypochloremia

• Signs
• Metabolic alkalosis
• Hypoventilation

• Treatment
• Saline with potassium or ammonium chloride
• Diamox

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Calcium Disorders

• 99 of the bodys calcium is contained the bone
  and not available in circulation
• Major function - To maintain cell membrane
  integrity and excitability
• Required for coagulation cascade

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Hypercalcemia

• Causes
• Bone degenerating diseases (Kirby 42-8)
• Excessive intake
• Decreased excretion
• Parathyroid disease
• Renal failure

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Treatment

• Correct underlying problem
• Diuresis with large volume saline
• Calcium binding drugs
• Careful positioning

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Hypocalcemia

• Causes- (Kirby Table 42-9)
• Redistribution
• Alkalosis
• Hypomagnesemia
• Inadequate intake
• Rapid infusion of banked blood

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Signs

• Irritability of electrically active cells
• Tetany
• Chvosteks sign
• Trousseaus sign
• Dysrhythmias
• Prolonged QT interval

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Treatment of Hypocalcemia

• Calcium chloride 15 mg/hr via central line
• Calcium gluconate 45 mg/kg via peripheral or
  central line

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Magnesium

• Intracellular cation
• Given to treat dysrhythmias secondary to
  hypomagnesemia or hypokalemia
• Given to treat pre-eclampsia or eclampsia

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Magnesium

• High magnesium levels
• Hypotension
• Muscle weakness
• Potentiate non-depolarizing relaxants

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Phosphate Disorders

• Phosphates required for normal ATP function
• Disorders associated with chronic malnutrition

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Glucose

• Will be covered in Diabetes unit
• Mild hyperglycemia is better than hypoglycemia in
  the operating room
• Can be dangerous when outside the range of 100-300

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Types of Fluids(see Morgan Table 29-2)

• Many solutions available
• Maintenance solutions - hypotonic solutions to
  replace water loss
• Replacement solutions - replace both water and
  electrolyte deficits

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What is free water?

• Water from drinking fountain
• Rain
• Water in excess of electrolyte content
• Water you dont have to pay for

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Ringers Lactate

• Most commonly used solution in the O.R.
• Slightly hypotonic - 100 ml free water / liter
• Most physiologic solution when large volumes are
  needed
• Lactate metabolizes in liver to bicarbonate

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Normal Saline

• Large volumes cause dilutional hyperchloremic
  acidosis
• Preferred solution for
• Hypochloremic metabolic acidosis
• Diluting packed cells

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5 Dextrose in Water

• Dextrose is metabolized leaving a large volume of
  free water
• Used for patients on sodium restriction
• Some dextrose needed when insulin is given

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Intraoperative Fluid Requirements
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Intraoperative Fluids

• Must Replace
• Maintenance
• Deficit
• Actual blood loss
• Third space loss

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Maintenance Fluids

• Water and electrolytes needed for normal
  metabolism
• Need 1 ml/hr for each kilocalorie expended

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Fluid Deficits

• Ongoing normal losses
• Intestinal / renal
• Perspiration
• Respiratory tract

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Fluid Deficits

• Increased loss
• Vomiting, diarrhea, ostomy
• Bowel prep
• Fever
• Hyperventilation
• Loss of skin integrity

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Intraoperative Fluid Loss

• Actual blood loss
• Hidden internal bleeding
• Evaporation from exposed surfaces
• Third space loss

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Estimating Blood Loss

• Volume in suction minus irrigation
• Volume on drapes
• Volume on surgical sponges
• Observe for blood on the flood

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Blood Loss

• Small sponges
• Large laporotomy sponges

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Actual Blood Loss

• Multiply surgeons guess by 2
• Divide anesthetists guess by 2
• Average those numbers

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Your patient is a lean 70 kg and has a hematocrit
of 38. How much blood can be lost to drop the
hematocrit to 26?
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Calculating Allowable Blood Loss
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Allowable Blood Loss

• 1. Starting HCT minus lowest HCT
• 2. Divide by the average of the above
• 3. Multiply times the estimated blood volume

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Example

• 70 kg patient (lean)
• EBV 70kg X 70 ml/kg 4900 cc
• Starting HCT 38 minus lowest HCT 26
• 38 minus 26 12
• 12 divided by average of 26 and 38
• 12 divided by 32 .375
• 0.375 X 4900 1837 cc

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Remember, as the patient becomes more obese, the
ml/kg is reduced
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What is the immediate effect of acute blood loss
on the HCT?
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Throughout a long case with moderate blood loss
your patient is becoming progressively
hypovolemic. What will you see on the blood gas?
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What is third space loss?
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Third Space Loss

• Shifting fluid to interstitial spaces
• Any traumatized tissue becomes edematos
• Third space loss is isotonic - replace with
  Ringers

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How much third space loss?

• Minimal 3-4 ml/kg/hr
• Moderate 5-6 ml/kg/hr
• Severe 7-8 ml/kg/hr

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Developing a Care Plan

• You must have a written plan for anticipated
  fluid therapy
• Calculate maintenance fluids
• Calculate deficit
• Estimate third space loss
• Replace actual blood loss

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Maintenance Fluids

• Many formulas available
• Hourly formulas
• 24 hour formulas

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Hourly Maintenance Formula

• 4 ml/kg/hr for 1st 10 kg
• 2 ml/kg/hr for 2nd 10 kg
• 1 ml/kg/hr for all weight over 20 kg

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Example

• 72 kg patient
• 4 ml/kg/hr for 1st 10 40 ml
• 2 ml/kg/hr for 2nd 10 20 ml
• 1 ml/kg/hr for 52 kg 52 ml
• Total 112 ml/hr

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24 Hour Formula

• 100 ml for 1st 10 kg
• 50 ml for 2nd 10 kg
• 20 ml for remaining kg
• Divide by 24 to get hourly rate

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Example

• 72 kg patient
• 100 ml for 1st 10 kg 1000 ml
• 50 ml for 2nd 10 kg 500 ml
• 20 ml for 52 kg 1040 ml
• Total 1040 ml
• Divide by 24 106 ml/hr

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Fluid Deficit

• Calculate hourly maintenance
• Multiply by hours NPO
• Consider other factors
• Overnight I.V.
• Bowel prep
• Replace 1/2, 1/4, 1/4

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Does Anesthesia Affect Fluid Needs?
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Effects of General Anesthesia

• Vasodilation may unmask compensated hypovolemia
• Decreased release of atrial natriuretic hormone
• Increased release of ADH

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Effects of Regional Anesthesia

• Block of sympathetic nerves
• Vasodilation
• Hypotension

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Complication of Fluid Therapy

• Peripheral edema
• Pulmonary edema
• Increased intracranial pressure
• Coagulopathy
• Allergies to colloids

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Thats all folks!