fluids in ICU

wolfgang

3 uses of IV fluids

1. providing hydration
2. fluid resuscitation
3. treating specific fluid-related issues

3 fluid spaces

* intracellular
* extracellular-intravascular
* extracellular-interstitial (extravascular)

third spacing

when fluid shifts from plasma to interstitial fluids = accumulation of fluid in interstitial peripheral space

==BAD!!==

how does third spacing happen

patients leak albumin and oncotic pressure lowers = promotes fluid movement out of vasculature = increases tendency for fluids to build up where it shouldn’t

effect of meds on third spaced fluids

therapies that increase fluid excretion remove fluid from the bloodstream, third spaced fluid remains in extravascular space

osmolarity

property of a solution that is ==independent== of any membrane

* osmoles of solute/L of solvent

osmolality

number of osmoles / kg solvent

\-usually equal

osmolarity and osmolarity are usually considered _______

equivalent

range for normal serum osmolality

275-300 mOsm/kg

tonicity

property of a solution that is ==in reference to== a membrane

range for isotonic solutions

250-375 mOsm/L

when do tonicity/osmolarity of fluid matter

at 2 points in time

* during the infusion
* after the fluid has caused systemic effects

mEq in 0.9% NaCl

154 mEq Na

properties of 0.9% NaCl

purely isotonic

amount of dextrose in D5W

252 mOsm/L

properties of D5W

begins isotonic, then becomes hypotonic

properties of D5NS

purely isotonic

\-initi 560 isn’t hypertonic enough to have a significant effect, DON’T need a central line for admin

properties of D5 1/2 NS

begins isotonic, then becomes hypotonic

mOsm/L of lactated ringer’s

273 mOsm/L

properties of lactated ringers solution

purely isotonic

value for 3% NaCl

1027 mOsm/L

properties of 3% NaCl

purely hypertonic

caution with 3% NaCl

use central line

\-anything over 900 mOsm/L should be given centrally

uses for isotonic solutions

* fluid resuscitation
* maintenance fluids

uses for hypotonic solutions

* correcting sodium abnormalities
* treating conditions with intracellular dehydration

caution for hypotonic fluids

do not use hypotonic fluids in head injury patients

\-causes increased peripheral cerebral edema

use for hypertonic solutions

* correcting sodium abnormalities
* decreasing cerebral edema

amount of sodium in lactated ringer’s

130

crystalloids

fluids that contain water, electrolytes, and small molecules

\-cross cell membranes = useful for treating imbalances

\-bad in critically ill patients bc fluid diffuses into peripheral space = vol overload

colloids

fluids made up of large molecules

\-increase oncotic pressure and don’t redistribute into EV space

* benefits: smaller volume needed to correct losses
* bad: expensive and human product

common colloid solutions

albumin 5%

albumin 25%-won’t raise blood pressure, takes too long

normal sodium range

135-145 mEq/L

normal chloride range

97-107 mEq/L

what does treatment and maintenance of hyponatremia depend on

associated with decreased serum osmolality

* causes neurologic effects (fluid goes into cells, brain cell swell)
* treatment depends on serum osmolality
* management depends on volume status

treatment for hypervolemia hyponatremia

* fluid/water restriction
* change fluids (if fluid induced)

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treatment for euvolemic hyponatemia

due to SIADH

\-water restriction

when treating hyponatremia, do not increase plasma sodium faster than _______

6-12 mEq/L/dy

maximum increase of plasma sodium rate if patients are acutely symptomatic

1-2 mEq/L/hr

\-still adhering to above 6-12 mEq/L/dy

treatment of hypovolemic hypernatremia

hypo or iso fluids

treatment for euvolemic hypernatremia

water replacement

most common cause of hyponatremia

1. excess (hypotonic) fluid
2. SIADH-can be induced by meds

treatment of hyponatremia

stop/change fluid

most common cause of hypernatremia

1. dehydration
2. diabetes insipidus

treatment of hypernatremia

hypotonic fluids

\-use carefully-don’t want to overcorrect sodium

hyperglycemia causes _______

pseudohyponatremia

\-glucose draws water from muscle space = decreases sodium concentration

relationship between glucose and plasma sodium

for each 100 mg/dL glucose above normal, plasma sodium decreases by 1.6 mmol/L

SIADH

secretion of inappropriate (too much) antidiuretic hormone

drugs that cause SIADH (5)

* SSRI
* NSAID
* opioids
* antidepressants
* antipsychotics

values to diagnose of SIADH

* sodium

treatment of SIADH

in addition to addressing underlying cause:

* fluid restriction to

diabetes insipidus

diabetes consisting of decreased secretion of antidiuretic hormone = decreased water retention

how does diabetes insipidus present

dilute urine output

* > 250 mL/h

treatment of diabetes insipidus

in addition to addressing underlying cause:

* hypotonic solutions-to replace free water
* vasopressin analogs-to supplement ADH
* vasopressin infusion

examples of vasopressin analog

desmopressin (DDAVP) 1-2 mcg IV or SQ BID

rate of vasopressin infusion for diabetes insipidus

1-15 units/h, started at 1 unit/h

* not preferred over desmopressin

target sodium decrease in diabetes insipidus

0\.5 mEq/L/hr

fluid resuscitation

easy to overload fluids=edema, increased cardiac demand, respiratory failure

maintenance fluids

ordered and forgotten

check daily