Fluids

Question 1

Assessing volume status

Answer 1

Hypovolemia: volume depletion (loss of Na and water)
-dehydration (loss of water from icf)
Accurate assessment challenging

Question 2

Systematic approach to estimating blood volume

Answer 2

Preop -> history, exam, labs

Intraop -> visual of loss, HR, BP, UO
invasive: PVP, CVP, PCWP, TEE

Question 3

Icf deficit (free water loss)

Answer 3

Insensible loss from skin, Resp, kidneys

• cellular dehydration, increased plasma osmolality and Na
• will not present as acute circulatory collapse -> its gradual

Question 4

ECf deficit (blood loss, GI loss)

Answer 4

Vomitting, diarrhea, ascites, 3rd spacing

• labs: increased BUN/Cr ratio, decreased urinAry Na excretion
• rapid circulatory collapse
• txt with isotonic solutions

Question 5

Expected plasma volume increment

Answer 5

PV = volume infused x (baseline PV/Vd of infused fluid)

Question 6

Traditional approach to fluid replacement

Answer 6

Fluid replacement = maintenance + deficit + 3rd space + loss
Maintenance: 4, 2, 1
Deficit: maintenance x hrs NPO
3rd space: 4-8 mL/kg/hr 
Loss: crystalloid x3, colloid X11

Question 7

Crystalloids

Answer 7

Aqueous solution that contains salts and water soluble molecules

• low cost, hig urinary flow
• minimal hemodynamics improvement, edema

Question 8

Colloids

Answer 8

Larger insoluble molecules

• lower volume needs to be infused, increased time in plasma, low edema, high oxygen delivery
• high cost, coagulopathy, decrease GFR, allergies

Question 9

D5W

Answer 9

Replaces free water, isotonic to plasma but becomes free water

Question 10

Lactate Ringer

Answer 10

Most widely used

• lactate metabolized in liver to CO2, unsuitable for patients in liver disease
• coagulant, may be better than NS for kidney transplants due to lower incidence of acidosis and hyperkalemia

Question 11

Normal saline

Answer 11

0.9% - widely used
Useful for neurosurg because of osmolality
Large doses can lead to hyperchloremic acidosis

Question 12

Hypertonic saline

Answer 12

3, 7.5, 23.4%
Used for 1-intravascular volume expansion in hypovolemic shock
2- reduce cerebral blood volume and ICP

Question 13

Albumin

Answer 13

5 or 25% available
Half-life of 16 hrs, made from human blood
5%- isotonic
Unclear evidence but don’t use inTBI

Question 14

Hetastarch

Answer 14

Hydroxylethyl starch
High molecular weight synthetic colloid, increases colloid osmotic pressure
- elevates serum amylase, anaphylaxis

Question 15

Dextran

Answer 15

Can cause anaphylaxis, coagulopathies, pulmonary edema

Question 16

Voluven

Answer 16

New hetastarch with low molecular weight and low degree of substitution that theoretically may be associated with lower bleeding risk

Question 17

Fluid compartments

Answer 17

TBW- 60% in males, 50% in females
- inversely proportional to adipose tissue
Intracellular fluid- 2/3
Extra cellular- 1/3
- interstitial volume (2/3 of ECf)
- plasma volume (1/3 ECf)