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6900 > Fluid & Electrolytes > Flashcards

Fluid & Electrolytes Flashcards

1
Q

What 2 factors are manipulated by intravascular fluid therapy

A

Preload and hemoglobin

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2
Q

Total body water (TBW) percentage of body and compartments

A

60%, ~40L

  • ICF (intracellular fluid) = 2/3 of TBW, ~25L
  • ECF (extracellular fluid) = 1/3 of TBW ~15L
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3
Q

ECF compartments

A 
IVF (intravascular fluid)
-Blood and plasma
-20%, ~3L
ISF (interstitial fluid space)
-Lymph and transcellular fluid
-80%, ~12L
ISF and IVF are separated by a capillary membrane
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4
Q

Fluid distribution percentages to remember

A 
60/40/20 (15/5)
60% TBW
40L TBW
20L ICF
15L ECF
5L IVF
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5
Q

Major ICF Cations

A

Potassium (most abundant)

Magnesium

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6
Q

Major ICF Anions

A

Proteins
Phosphates
Organic ions

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7
Q

Major ECF Cations

A

Sodium (most abundant)

Calcium

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8
Q

Major ECF Anions

A

Chloride

Bicarbonate

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9
Q

How is intracellular osmolality maintained

A

Na/K/ATPase pump

  • Exchanges 3 Na for 2 K, offsets tendency for Na to diffuse into the ICF
  • In ischemia or hypoxia this is disrupted, causing swelling of cells
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10
Q

4 ways fluid moves between compartments

A

Diffusion
-Particles down concentration gradient through lipid bilayer or protein channels (facilitated)
Osmosis
-Water moving between cell compartments (intracellular and interstitial space)
Active Transport
-Water, ions, molecules pumped against concentration gradient on cell wall, requires enzymes and energy
-Controls cell volume and concentration
Filtration
-Pressure causes water, ions, molecules to move to a lower pressure area (edema)

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11
Q

Starlings Forces

A

Determines amount and direction of filtration

  • Governed by differences in hydrostatic pressure (interstitial, capillary) in addition to osmotic forces (interstitial, plasma colloid)
  • Fluid tends to move out of capillaries at arterial end (BP>osmotic pressure) and back in at venous end (BP
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12
Q

Hydrostatic pressure

A

Pressure that fluid exerts on the walls

-Interstitial or capillary

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13
Q

Osmotic pressure

A

Pressure against a semipermeable membrane that prevents water from diffusing across the membrane

  • Interstitial or plasma colloid
  • Based on osmotic particles not molecular weight
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14
Q

Plasma colloid osmotic pressure

A

Significant to anesthetic

  • Can be increased or decreased depending on what we give to maintain circulating fluid volume in intravascular space
  • Crystalloid increases loss of fluid from intravascular to interstitial space
  • Replace 3:1 crystalloid to colloid
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15
Q

Osmolarity

A

Expression of the number of osmoles of solute in a liter of solution

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16
Q

Osmolality (and normal serum and urine osmo)

A

Number of osmoles of solute in a kilogram of solvent

  • Serum osmo: 285-295 mOsm/kg
  • Urine osmo: 500-800 mOsm/kg
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17
Q

Tonicity

A

How a solution affects cell volume

-Compares the osmolarity of solution to the plasma

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18
Q

How to estimate osmolarity

A

(Na x 2) + (Glucose / 18) + (BUN / 2.8)

-Na is the most important osmotically active substance influencing water in the brain tissue

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19
Q

Control of plasma osmolality

A

Closely regulated by osmoreceptors in the hypothalamus

  • Control secretion of ADH and the thirst mechanism
  • ADH is the most important regulator of serum osmolality
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20
Q

Surgery effects on fluid status (3)

A

Hemorrhage
Evaporative loss
-From exposed viscera (all water, no electrolytes)
Third spacing
-From manipulation of tissues
-Fluid redistributed from intravascular space to interstitial space
-Replacement best done with fluid composition close to ECF

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21
Q

Hypovolemia vs dehydration

A 
Hypovolemia = ECF water deficit, blood volume
Dehydration = low water relative to sodium level, TBW
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22
Q

Hypovolemia can result from ____ or ____ (and how to replace)

A

Absolute loss of fluid
-From GI tract, polyuria, diaphoresis, decreased intake
Relative loss of fluid
-Water redistributed in the body = reduced circulating volume
-Burns, third spacing form surgery
Weight doesn’t decrease
Replace with isotonic crystalloids

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23
Q

Anesthetic considerations for hyponatremia

A

Hypovolemia emphasizes vasodilation or cardiac depression from anesthetic agents, predisposing to hypotension and hypoperfusion of tissues

24
Q

Anesthetic considerations for hypernatremia

A

Elective surgery should be postponed in patients with significant hypernatremia (>150) until cause is established and fluid deficit is corrected

25
Q

Anesthetic considerations for hypokalemia

A

Cancelling surgery for mild-severe (<2.6) isn’t warranted

  • Avoid hyperventilation, use glucose free solutions
  • Increased sensitivity to neuromuscular blocking agents may be seen
26
Q

Anesthetic considerations for hyperkalemia

A

Elective surgery shouldn’t be done in patients with hyperkalemia

  • Vigilent ECG monitoring
  • Succinylcholine and LR are contraindicated
  • Mild hyperventilation may be desirable (avoid acidosis) (10mmHg decrease in PaCO2 = 0.5mmol/L decrease in K)
  • Can accentuate effects of neuromuscular blocking agents
27
Q

Calcium roles (2) and what form is active

A

2nd messenger
-Couples cell membrane receptors to cellular responses
-Muscle contraction, release of hormones and neurotransmitters
Coagulation of blood
Ionized is most clinically significant
Only unbound ionized calcium is active (normal level 4.6-5.6)

28
Q

Anesthetic considerations of hypocalcemia

A

Controlled ventilation drives Ca and K in the cells
-Avoid hyperventilation (lowers Ca and K)
Be careful with NMBAs, barbiturates, and volatile anesthetics

29
Q

Anesthetic considerations in hypomagnesemia

A 
Frequently overlooked, especially in critically ill patients
Coexistent electrolyte disturbances
-Hypokalemia
-Hypophosphatemia
-Hypocalcemia
30
Q

Anesthetic considerations of hypermagnesemia

A

Requires close monitoring of ECG, BP, neuromuscular function
Potentiation of vasodilation and negative inotropic properties of anesthetics
Reduce muscle relaxants by 25-50%
Serially measure Ca and Mg

31
Q

Crystalloids (and 3 most common used in surgery)

A

Isotonic, closely matches electrolyte concentration of ECF (water and electrolytes)

  • 0.9% NS
  • LR
  • P-Lyte
32
Q

NS excess, benefits

A

Excess: Can cause hyperchloremic metabolic acidosis
Benefit: No potassium, good for renal failure patients and cardiopulmonary bypass

33
Q

LR

A
  • Slightly hypotonic, high volume will lower Na to 130
  • Has K, can cause hyperkalemia in renal failure patients
  • Liver converts lactate to bicarb, can cause metabolic alkalosis
  • Ca can bind citrated anticoagulants and clot donor blood
34
Q

P-Lyte

A
  • More expensive
  • Balanced
  • Contains a small amount of K
35
Q

Colloid parenteral fluids

A

Contain osmotically active substances of high molecular weight that don’t easily cross the capillary membrane, so draw fluid into intravascular space and expand the circulating volume

36
Q

Hetastarch

A

Synthetic colloid

  • Has coagulopathy risk with dose >20mL/kg
  • Prolonged PTT from decreased factor VIII
37
Q

Dextran

A

Synthetic colloid
-Used in vascular surgery to prevent thrombosis (promotes anticoagulation, decreased platelet adhesiveness with dose >20mL/kg/day)

38
Q

Crystalloid advantages and disadvantages

A

Advantages
-Inexpensive
-No side effects
-Maintains IVF and COP as well as colloids
-No coagulation abnormalities
Disadvantages
-Larger volume needed, dilutes plasma proteins
-Peripheral edema, possibly impaired wound healing and O2 transport
-Potential for pulmonary edema
-Transient effect, intravascular half life is 20-30 minutes

39
Q

Colloid advantages and disadvantages

A

Advantages
-Maintains plasma oncotic pressure
-Less redistribution than crystalloids, requires smaller volume for resuscitation
-Less peripheral edema
-Rapid resuscitation
Disadvantages
-Expensive
-Linked to coagulopathy (Dextran>hetastarch>hextend)
-More frequent/serious side effects: Anaphylaxis (dextran), decreased calcium (albumin), renal failure (dextran)
-Intravascular half life is 3-6 hours

40
Q

Crystalloid or colloid = superior for periop?

A

No research has proven the superiority of one over another

41
Q

Calculating hourly maintenance fluid

A 
4-2-1 plan
First 10kg: 4mL/kg/hr
Next 10kg: 2mL/kg/hr
Each kg after 20: 1mL/kg/hr
Shortcut: add 40 to weight in kg
42
Q

Calculating NPO deficit

A

Hours of NPO x hourly maintenance fluid

43
Q

Intraop replacement of fluid deficit

A

1st hr: 1/2 deficit
2nd hr: 1/4 deficit
3rd hr: 1/4 deficit

44
Q

Calculating 3rd spacing/evaporated surgical fluid loss

A

Minimal tissue trauma (hernia repair): 2-4mL/kg/hr
Moderate tissue trauma (cholecystectomy): 4-6mL/kg/hr
Severe tissue trauma (bowel resection): 6-8mL/kg/hr

45
Q

Calculating other losses and blood loss

A

Account for fluids lost through NG, excess urine output, bowel prep, and lipo suction output 1:1
-Replace blood loss with crystalloid 3:1 or colloid 1:1

46
Q

Maximum allowable blood loss equation

A

MABL = (EBV x (Starting Hct-Target Hct)) / Starting Hct

Goal Hct>30 Hgb> 10 (many exceptions)

47
Q

Estimated blood volume (EBV) in neonates, infants, and adults

A 
Neonates
-Premature: 90-100mL/kg
-Full term: 80-90mL/kg
Infants: 80mL/kg
Adults: 70mL/kg
48
Q

How much blood is in a soaked sponge and laparotomy pad?

A

4x4 sponge: 10mL

Lap pad: 100-150mL

49
Q

What from PRBCs shifts the oxygen hemoglobin dissociation curve to the left and what does this promote

A

Hypothermia, low levels of 2, 3 DPG

Promotes tissue hypoxia

50
Q

Emergency blood product transfusion options

A

1: Give type-specific partially cross-matched blood
2: Give type-specific non-cross-matched blood
3: Give type O negative blood
- Least desirable
- After 2 or more units of this continue with it even if pts blood type becomes available

51
Q

How much will one unit of PRBCs increase hgb and hct? 1 unit plts?

A

Hgb: 1gm/dl
Hct: 3%
Plts: 5-10mm^3

52
Q

Risk of bacterial infection with what blood product? Why?

A

Platelets

-Stored at room temperature, also decreased shelf life

53
Q

Dose of FFP

A

5-8mL/kg to reverse warfarin

10-15mL/kg for all other purposes

54
Q

Cryoprecipitate (factors contained, indications)

A

I (Fibrinogen), VIII, vWF
Fibrinogen <80-100mg/dL
Low antibodies, ABO compatibility isn’t necessary

55
Q

Blood transmission risk of infection highest for ____

A

Hepatitis B: 1 in 220,000

56
Q

Treatment for acute hemolytic reaction

A 
Stop transfusion, send to blood bank
Support BP with IVF and pressors
If anaphylactic: consider antihistamine
*Maintain UOP with IVF, diuretics, renal dose dopamine
Monitor for lung injury

6900 (12 decks)

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