1.9 - Intravenous Fluid Management Flashcards
How is normal water balance maintained?
- Water balance is accomplished in a normal, unhospitalized patient by responding to the body’s response to the fluid state.
- If there is a water loss (extreme sweating, increased insensible losses) there is an increase in serum sodium and osmolality.
- This stimulates thirst and an increased release of antidiuretic hormone (ADH). These changes will increase water intake and decreased urine output.
- Other sources of fluid ingestion include the water content of food particularly fruit and vegetables. A normal adult takes in approximately 1600 ml a day (there is great variation among adults) that comes from water ingestion, food and water from oxidation.
- They lose fluid from urine, skin, respiratory tract and stool.
What % of TBW is located in the intracellular fluid?
- Volume is approximately 60% of TBW.
- Because the majority of water is contained in the intracellular space, the loss of water alone does not typically result in the hemodynamic changes associated with volume depletion
What is the composition of the intracellular fluid in the body?
Composition:
- High concentration of potassium and phosphate ions
- Low concentration of sodium and bicarbonate ions
What % of TBW is located in the extracellular fluid?
Volume approximately 40% of TBW
What is the composition of the extracellular fluid in the body?
- Primarily sodium salts (NCl, NaHco3). 85-90% of total body sodium is extracellular. Changes in the body’s total Na content leads to contraction or expansion of the ECF that can lead to volume depletion or volume expansion respectively.
- Low concentrations of potassium and phosphates
What is the % volume and composition of the extravascular (interstitial) compartment of the ECF?
- Volume approximately 80% of ECF volume
- Composition is protein poor electrolyte solution of ECF
What is the % volume and composition of the intravascular compartment of the ECF?
- Volume approximately 20% of ECF volume
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Composition: protein enriched electrolyte solution of ECF
- The compartment whose volume most closely reflects and best determines our cardiovascular function
Usefulness
- Compartment into which all therapeutic fluids are administered
- Distribution to all other body fluid spaces occurs by diffusion or transport into those compartments
What is the importance of body fluids?
Body fluids vital and essential to maintaining life. They help maintain our body temperature and shape of the cells. Fluids are involved in transporting nutrients, gases and wastes. The principle fluid in our body is water. The proper fluid balance is maintained by skin, lungs and kidneys. The two fluid compartments are separated by capillary walls and cell membranes.
What is fluid spacing?
A normal distribution of fluid in the body in both the intracellular and extracellular fluid compartments
What is second spacing?
Second spacing describes the excess accumulation of fluid in the interstitial spaces which we also call edema
What is third spacing?
- Third spacing occurs when fluid accumulates in areas that normally have no fluid or a minimal amount of fluid.
- You see this in ascites or edema associated with burns. If the third spacing is extreme the patient can present with extreme hypotension.
What are the 3 main reasons for IV fluid administration?
- ECF Volume depletion
- Body water (osmolality) adjustment or maintenance
- Delivery of therapeutic agents
What are the signs of ECF volume depletion?
- Look for the contributing causes including GI losses (Vomiting, diarrhea, NG suction) , urinary losses (diuretics, osmotic diuresis from hyperglycemia, contrast media), surface losses (heavy sweating if febrile; burns) respiratory tract (hyperventilation, non-humidified inhalation therapy), fluid sequestration (pancreatitis, ileus, burns), blood losses, other(inadequate oral or IV intake)
- Physical signs include: hypotension, tachycardia, postural hypotension, decreased jugular venous filling
- Invasive signs: include decreased CVP measurement and decreased pulmonary capillary wedge pressure
What are the signs of ECF volume excess?
- Physical signs: hypertension, internal jugular venous distention and edema. Edema can be peripheral, pulmonary or ascites.
- Invasive – increased CVP or PCWP
When and why is maintenance fluid started?
- In the presence of normal or near normal kidney function, maintenance fluid therapy is undertaken when the patient is not expected to be able to consume fluids for a prolonged period of time.
- These patients may be in a post-operative state or maintained on a ventilator
- The goals of maintenance fluid are to maintain adequate hydration and possibly to provide nutrition.
- The assessment of volume status is best learned at the bedside but assessment of lab values is important. In addition to sodium, look at the creatinine-to-urea ratio. A ratio higher than 12 is suggestive of volume depletion.
What are classic symptoms of volume overload?
- HR - Resting tachycardia; Postural rise in HR < 15 beats/min
- BP - May be low, normal or high. No postural fall in systolic or diastolic BP
- RR - Tachypnea
- Resp - Crackles bilaterally at bases; wheezing may or may not be present; pleural effusions may or may not be present
- CVS - JVP > 3cm H20 above the sternal angle; S3 present
- Abd - Hepatojugular reflux present; Liver may or may not be enlarged or tender
- Ext - Accentuated skin creases on posterior thorax; sacral or pedal edema
What therapeutic agents can be delivered IV?
1. Electrolytes: specifically adjustment of potassium, magnesium, calcium, bicarbonate, phosphate, etc. The majority of electrolyte losses (primarily sodium and potassium salts) are in the urine with a lesser amount seen in losses through the skin or GI tract.
2. Nutrition: emphasis on calories, glucose, lipids
3. Drugs: multiple water soluble agents
What are the characteristics of NS (0.9% NaCl)? (where is it distributed/characteristics)
- NS (0.9 NaCl) approximately isotonic to plasma
- Distribution: ECF volume
- ECF volume expansion; approximately one third of infused volume remains in vascular space at full distribution to support circulatory function
- Drug delivery: for drugs stable only in NS
What are the characteristics of D5W? (where is it distributed/characteristics)
- D5W approximately isotonic to plasma
- Distribution: intracellular and extracellular body water spaces
- Repletion or maintenance of body water (osmolality): equivalent to giving pure water once dextrose has been metabolized
- Drug delivery: for compatible drugs when ECF volume expansion undesirable (less than 10% remains in vascular space at full distribution)
What are the characteristics of LR and what is it used for?
- Lactated Ringer’s solution (LR); containing NaCl, KCL, CaCl, Na Lactate approximately isotonic to plasma
- Distribution – ECF compartment, similar to NS
Usage:
- Mostly as repletion or resuscitation fluid with actual or ongoing blood loss
- Lactate ion is metabolized in the liver to generate HCO3
- Repletion or maintenance fluid in trauma or surgical patients
What are the characteristics of ½NS 0.45% NaCl and what is it used for?
- It is hypotonic to plasma
How this solution distributes into the body:
- Half of volume equivalent to pure water distributes into total body water
- Half of volume equivalent to NS distributes into ECF compartment
- About 1/6 of volume remain in vascular space
USES:
Maintenance fluid (most common use)
- Saline component replaces ongoing NaCl losses, maintains ECF volume
- Free water component replaces insensible free water losses, maintains osmolality
Replacement fluid
- Saline component restores ECF volume deficit
- Free water component restores water deficit in hyperosmolar state such as hypernatremia
What are the characteristics of D5 NS, D5 ½ NS and D5 ¼ NS and what are they used for?
These solutions are equivalent to the corresponding saline solution plus supplying 200 kcal energy per liter of solution
Why are colloid solutions given and what are some examples?
They are solutions of large molecular weight particles that are substantially retained in the vascular volume and _are used for selective vascular volume expansion and hemodynamic support_
Examples:
- 25% human albumin - Best given in bolus (25 g) in hypoalbuminemic patients
- 5% albumin in saline - Comparable with NS alone
- Fresh frozen plasma - Should not be used in fluid therapy but only when depleted clotting factors are replaced
How should you calculate the fluid volume needs of a patient when ordering IV fluid replacement?
Consider the water and electrolyte needs of your patient separately when deciding on their IVF therapy.
- Minimum water requirements can be approximated from the sum of the required urine output, stool water loss and insensible losses. It calculates to approximately 500 cc/day
- Water loss in stools is typically 200 cc/day
- Insensible water loss, roughly 400-500 cc/day
- Fluids from drains must be added.
- After adding these, the minimum amount of water needed to maintain homeostasis is roughly 1400 cc/day or 60 cc/hr.
