Osmolarity (mOsm/L H2O) = 2x[Na+] + glucose/18 + BUN/2.8 _CALCULATED_ compared to OsmoLALity, which is collected/measured Qualitative measure of TBW ↓ pOsm implies EXCESS water ↑ pOsm implies LACK of water

2 - Fluid Disorders Flashcards by Karlo Sison

TBW
Total Body Weight
for Male & Female

**Male = 60%
Female = 50%**

% of body weight

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TBW
Total Body Weight
for
Pediatrics

Pediatrics = 60-70%

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TBW
Total Body Weight
for
Elderly Male & Female

Elderly Male = 50%

Elderly FEMALE = 45%

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TBW
Total Body Weight
for
OBESE

Decrease by 5%
if >130% over the IBW (ideal body weight)

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*Split of Total Body Water**
*ECF / ICF / ISF / IVF**

2/3 ICF (intracellular Fluid)

1/3 ECF (Extracellular Fluid)
broken down to:
3/4 ISF (Interstitial Fluid)
&
1/4 IVF (Intravascular fluid)

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Body Fluid Composition

TBW = ICF + ECF (ISF + IVF)

for a Male, 60% of weight is TBW

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Tonicity

Fluid Tension between ECF & ICF
Extracellular Fluid - Intracellular Fluid (2/3 of TBW)

Weight of particles in a compartment that can Attract fluid
depend on relative solute permeability

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OsmaLALity

Definition and Range

Total Solute concentration
given a weight of water in a given compartment

*Collected or Measured** Plasma OsmoLALity:
*280-295** mOsm/kg h2o

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OsMOLARity

Osmolarity (mOsm/L H2O) =
2x[Na+] + glucose/18 + BUN/2.8

*CALCULATED**
compared to OsmoLALity, which is collected/measured*

Qualitative measure of TBW
↓ pOsm implies EXCESS water
↑ pOsm implies LACK of water

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Regulation of Water Metabolism

Water Intake
THIRST is the mechanism to increase water intake
↑pOsm (lack of water)
↓ECF or BP

WATER EXCRETION
AVP = Arginine Vasopressin
major determinant of water loss

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Water Balance

Water Gain
Sensible = Drinking Fluids / Eating Solids
Insensible = 250mL
From Metabolism / not measurable, but need to be taken account for

Water LOSS
Sensible = Urine / Intestinal / Sweat
Insensible = 600
from lungs / skin

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AVP
Arginine Vasopressin

an ADH hormone synthesized in the Hypothalmus
stored in the posterior pituitary

Major Determinant of WATER LOSS
Water Excretion

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Vasopressin Receptors
AVP

V2: Renal COLLECTING DUCT
<–Resorption of water via aquaporin-2 channel
decreases water excretion

V1A: Vascular Smooth Muscle
vasoconstriction / cardiac hypertrophy

V1B: Stress Reactive
release ACTH & Endorphin

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What stimulates the RELEASE of AVP?

↑pOsm or ↓BP

NAUSEA**

Pain / Anxiety

*Medications**:
*Nicotine** / carbamezapine / TCA’s
*SSRI’s** / opiates / haloperidol

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Labs / Vitals / Symptoms
for HypoVolemia

*Vitals**
*↑HR** , orthostatics , ↓BP (severe), ↓Urine output

Labs
conc. urine , ↑BUN,
↑SCr // ↑Na+ (severe)

*Symptoms**
*weakness / syncope** / confusion / THIRST
*↓ skin turgor / dry mouth**

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Causes of dehydration which can lead to hypoVolemia

Increasing Age / Medications

INSENSIBLE Losses
Sweat / burn / HYPERVentilation

GI Losses
Vomiting / Diarrhea / biliary

*Diabetes Insipidus** = AVP issues
*Central** (neurogenic) - ↓ AVP secretion
*Nephrogenic** = RESISTANCE to AVP effect

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What type of VOLUME THERAPY?

Goal is to maintain ORGAN PERFUSION
by treating the intravascular hypovolemia

RESUSCITATION

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What type of VOLUME THERAPY?

Goal is to Replace Volume Lost

REPLACEMENT

What type of VOLUME THERAPY?

Goal is to PREVENT Dehydration
consider BOTH sensible & insensible losses

MAINTENANCE

CRYSTALLOID
Volume Therapy

FLUID + ELECTROLYTES
replaces water & electrolytes

readily available / better tolerated / 1st line

Ex:
0.45% / 0.9% NaCl // LR // D5W

COLLOID
Volume Therapy

PRBC / Albumin 5% / 25% hetastarch
HUMAN PRODUCTS

used for I_ntravascular Volume (IVF) EXPANSION_

large molecules stay in the VASCULAR space

ISOTONIC
Replacement Fluid Tonicity

SImilar to Plasma, no fluid shifts

0.9% NaCl & LR’s

HYPERtonic
Replacement Fluid Tonicity

GREATER than PLASMA

IC –> EC fluid shifts
intracellular to extracellular

3% NaCl

HypoTonic
Replacement Fluid Tonicity

< 150 mOsm/L
flows BACK <– into Intracellular Space
EC –> IC

0.2% NaCl

**Crystalloid Characteristics**

**Dextrose 5% is isotonic hypotonic solution** BUT it causes increases in **ICF / ISF / IVF** - Dextrose is slowly distributed

**Colloid Characteristics** **NO Intracelular Movement**

**Lactated Ringers & 0.9% NaCl USES** **LR contains K+, not good for patients with RENAL failure**

Useful for **_hypotensive patients_** **_IVF EXPANSION_** (intravascular) Since they are **ISOTONIC**, there is ***no fluid shift*** ***_does NOT enter any cells_*** commonly used in **general surgery / neurosurgical** poulations *since there is a LOSS of a lot of blood* --\> need to **expand volume**

**D5W** Uses

* *ISOTONIC** * **_BUT it_*** **_INCREASES_** **ICF / ISF / IVF** The Dextrose **provides OSMOTIC Activity** to ***prevent hemolysis*** Effective admin of a **_hypotonic solution_**"free water" _Watch out for:_ **HYPERglycemia &*****hypoNatremia***

**0.45% NaCl or 0.45% NaCl/D5W** USES

Able to **REPLACE MORE Free water vs NS** Useful in: **HYPERNatremic Patients** & **Replacing *INSENSIBLE* water *loss*** dextrose can **add calories**

* *RESUSCITATION** * *_Management of HypoVolemia_**

\**ONLY if S/Sx of SHOCK* _Bolus Dosing with_ **_250-1000mL_** of **0.9% NaCl** or **LR** goal is to EXPAND **IVF** volume, need **blood purfusion --\> vital organs** FIRST Monitor: **BP / HR / Urine Output / CNS symptoms** *MAY REPEAT if still **SYMPTOMATIC***

**REPLACEMENT** Management of HypoVolemia

* *Calculate:** * *FREE WATER DEFICIT** * based on SODIUM concentrations*

**MAINTENANCE** Management of HypoVolemia

Goal is to: **Prevent Dehydration** while administering daily water requirements check **comorbidities** revie patient's **electrolytes** & **nutritional status**

**Daily Fluid Requirements** (Maintenance) Based on **Volume Status** Dehydration / Post-OP / Euvolemia / Elderly or CHF

* *_Dehydation_** * *45** mL/kg/day * *_Post-Operative_** * *40** mL/kg/day * *_Euvolemia_** * *35** mL/kg/day * *_Elderly or CHF_** * *30** mL/kg/day

**Daily Fluid Requirement** (Maintenance) **Alternative Method - PEDIATRICS**

* *_for the 1st 10kg_** * *100** mL/kg/day * *_for the 2ND 10kg_** * *50** mL/kg/day * *_for WEIGHT \> 20kg_** * *20** mL/kg/day

**What Fluid & how much** for this patient? **Post-OP patient with EBL of 500ml** (estimated blood loss)

_FIRST_ **LR** or **0.9% NaCl** @ **40** mL/kg/day useful in **surgery - loss of a lot of blood //** **post-op pt** _after 24 hours, THEN_ **D5W/0.45% NaCl** @ **35** mL/kg/day ??? // **euvolemic** (normal volume)

**What Fluid & how much** for this patient? **HypoTensive Patient**

**LR** or **0.9% NaCl** @ **45** mL/kg/day useful in **HypoTensive Patients** & ***low BP*** will lead to **AVP release** --\> **WATER excretion** **dehydration is 45** mL/kg/day

**What Fluid & how much** for this patient? **NPO Cardiac patient w/ K+ level 3.4** mEq/L

**D5W/0.45% NaCl + KCl 20** mEq @ **30** mL/kg/day Normal **K+** levels are **3.5-5.0** mEq/L, patient is **hypoKalemic** to correct the hypokalemia along with the **KCL tabs** **30** mL/kg/day --\> **CARDIAC PATIENT** (CHF)

**What Fluid & how much** for this patient? **NPO Patient** for an **elective procedure**

**D5W/0.45% NaCl** @ **35** mL/kg/day *not an EMERGENCY / sudden surgery*, likely **no blood loss** **need to add calories? replace free water &****insensible water losses** **35** because **euvolemic** (normal volume)

**Assessment of TOXICITY**

* *FLUIDs = DRUGS** * *volume overload is a COMMON PROBLEM** * if not MONITORED properly*: Monitor: **Daily weight / Labs / Physical Exam** S/Sx: Pulmonary + Peripheral **Edema** // **Heart Failure** ↓**serum Osm** // ↓**Na+** *_reduction of pOsm, means EXCESS water_*

↓ **pOsm** **IMPLIES WHAT?** (osmolarity, qualitative measure of TBW)

**EXCESS OF WATER** can be **HYPERvolemic**

**↑ pOsm IMPLIES WHAT?** | (osmolarity, qualitative measure of TBW)

***_LACK OF WATER_*** *HypoVolemic*

**_Use for COLLOID Solutions_** 5% Albumin // 25 % Albumin *no intracellular movement*

for **_INTRAVASCULAR VOLUME EXPANSION_** **4x GREATER** IVF expansion vs equal volume of crystaloid **_BLOOD TRANSFUSIONS_** packed RBC's = PRBC

* *Colloid Solutions** * *Albumin Uses**

_**5%** is adminstered in **250mL doses**_ _**25%** is admin in **50-100mL doses**_ *25% is DIFFERENT because* **fluid flows from ISF (negative) --\> IVF** interstitial --\> intravascular