Surgery E1: Fluids & Electrolytes

What percentage of total body weight is made up of water?

50-70%

What makes up ~40% of total body weight?

Intracellular (ICV)

What makes up ~20% of total body weight?

Extracellular (ECV)

About how many L of blood do adults have on average?

5 L

(venous 85%, arterial 15%)

What is blood osmolarity?

286 mOsmoles/L

What is the major ECF cation?

Na+

What is the major ICF cation?

K+

What is the “push” factor of homeostasis that pushes fluid out of the intravascular space and is maintained by systemic BP?

Hydrostatic pressure

What is the “in" factor that pulls fluid back into the intravascular space and is maintained by relative impermeability of capillary walls to protein?

Oncotic pressure

What is a major determinant of capillary oncotic pressure?

Albumin

What is "Third spacing"?

fluid "hides" in tissue and cavities d/t inc capillary permeability ("capillary leak") and is trapped in interstitial spaces

What kinds of injury/inflammatory responses can stimulate "third spacing"?

trauma, major surgery, intra-abdominal infections

What type of solutions are preferred in patients with "third spacing"?

Crystalloid- NS & LR

Which IVFs are crystalloids?

Normal saline 0.9% (NS), Lactated Ringer's (LR), ½ NS, 3% NaCl, 5% dextrose & 0.45% NaCl, D5 LR

Which IVFs are colloids?

Albumin, Purified plasma protein fraction

Which crystalloid solution has a similar concentration of dissolved particles as blood and does not cause fluid to shift?

Isotonic

Which crystalloid solution has a lower concentration of dissolved particles than blood causing movement of water out of the vascular space into the cellular space?

Hypotonic

Which crystalloid solution has a higher concentration of dissolved particles than blood causing movement of water out of cells into the vascular space?

Hypertonic

Which IVFs are isotonic?

LR, 0.9% NaCl (NS), plasmalyte

What are Isotonic fluids used for?

hemorrhage, severe vomiting or diarrhea, fluid loss, dehydration, pts at risk of fluid overload (HTN, CHF)

Which IVFs are hypotonic?

0.45% NaCl (1/2 NS), D5W

What are hypotonic solutions used for?

hypernatremia, DKA, intracellular dehydration

What do you need to monitor for if using hypotonic solutions?

hypovolemia, hypotension, confusion d/t fluid shifting

cerebral edema

Which IVFs are hypertonic?

3% NaCl, 5% Dextrose + 0.45% NaCl, D5 LR

What are hypertonic fluids used for?

severe hyponatremia and cerebral edema

What needs to monitored for when using hypertonic fluids?

hypervolemia, hypernatremia, respiratory distess

*do not use in pts w/ HF or renal failure

What are colloid solutions used for?

ARDS, hypoalbuminemia, 2nd line for hypovolemia

What do you need to monitor for when using colloid solutions?

anaphylaxis, flushing, urticaria, fever, chill, N/V, tachycardia, hypotension

What is 1st line for fluid resuscitation?

Isotonic crystalloid- NS or LR

What should you AVOID using for aggressive resuscitation bc the body does not utilize it during times of severe stress?

Dextrose

*will cause hyperglycemia and osmotic diuresis

4/2/1 Rule for maintenance fluids

4 mL/kg for the first 10 kg of body wt

2 mL/kg for the next 10 kg

1 mL/kg for every kg over 20

Use the 4/2/1 rule: 100 kg pt

140 mL/hr

100/50/20 (Holliday-Segard) rule for maintenance over 24 hours

100 mL/kg for first 10 kg of body wt

50 mL/kg for the next 10 kg of wt

20 mL/kg for every kg over 20

Divide total by 24 for hourly rate

Use the 100/50/20 rule: 70 kg pt

104 mL/hr

What are the daily potassium requirement?

2 mEq/100 mL (20 mEq/L)

What is the minimum urine output for an adult on maintenance IV fluids?

30 mL/hr OR 0.5-1 ml/kg/hr over 24 hrs

What is the minimum urine output for an adult trauma patient?

50 mL/hr