Introduction to IV fluids

Question 1

IV fluids are:

1. Isotonic if between
2. Hypotonic if
3. Hypertonic if

Answer 1

1. 240 and 340 mOsm/L
2. less than 240
3. > 340

Question 2

Intracellular normal volume?

Answer 2

In osmotic equilibrium in normal circumstances (28L)

Question 3

What are the types of extraceullualr fluid? 3

Answer 3

1. Intravascular
2. Intersititual
3. Third space or transcellular

Question 4

Describe each of the following:

1. Intravascular
2. Intersititual
3. Third space or transcellular
4. Three examples of transcellular space?

Answer 4

1. Intravascular (AKA plasma… fluid contained within the circulatory and lymphatic system (3.5 L)
2. Interstitial: Fluid that is found outside the circulatory/lymphatic system that surrounds tissues…aka “tissue space” (10.5 L)
3. Third space or transcelluar: spaces where fluid does not normally collect in large amounts…
4. • CSF,
   • joint spaces,
   • vitreous humor

Question 5

What are colloids?

Answer 5

Fluids containing larger molecular weight (>8000) proteins and molecules with plasma oncotic pressures similar to normal plasma proteins. Large molecules that don’t pass through cell membranes.

Question 6

1. When colliods are infused they remain where?

2. What do they do there? 2

Answer 6

When infused,

1. they remain in the intravascular compartment and
2. • expand the intravascular volume and
   • they draw fluid from extravascular spaces via their higher oncotic pressure

Question 7

What colliods are used as volume expanders?

3

Answer 7

1. Albumin
2. Plasma protein fraction…Plasmanate
3. Synthetic colloids…Dextran, Hetastarch

Question 8

1. WHat are crystalloids?

2. This will increase the fluid volume where? 2

Answer 8

1. Fluids with molecular weight less than 8000 and low oncotic pressure: Hypotonic, Isotonic, and Hypertonic
   Contain small molecules that flow more easily across the cell membranes, allowing for transfer from the bloodstream into the cells and body tissues.

in both the

1. interstitial and
2. intravascular spaces (Extracellular)

Question 9

Crystalloids: Describe the following solutions:
1. Hypotonic?

2. Isotonic?
3. Hypertonic?

Answer 9

1. a solution of lower osmotic pressure than blood
2. noting or pertaining to a solution containing the same salt concentration as blood
3. a solution of higher osmotic pressure than blood

Question 10

What will a hypotonic crystalloid solution cause fluids in the body to do? (know)***

Which solutions are these? 2 (know)***

Answer 10

Will cause fluids to leave the vasculature for the Interstitial and intracellular spaces

1. 0.45% NS (1/2 NS)
2. And D5W (after infusing- you metabolize the dextrose super quick and it become hypertonic).

Question 11

Hypotonic crystalloid solutions lowers the serum osmolality within the 1._______ _____, causing fluid to shift from the 2.__________ space to both the 3._________ and 4.________ spaces.

These solutions will 5._______ cells, although their use may 6._______ _____ within the circulatory system.

Answer 11

1. vascular space
2. intravascular
3. intracellular
4. interstitial
5. hydrate
6. deplete fluid

Question 12

TYPES OF HYPOTONIC FLUIDS?
4

Hypotonic fluids are used to treat patients with conditions causing intracellular dehydration, when fluid needs to be shifted into the cell , such as: 3

Answer 12

1. 0.45% sodium chloride (0.45% NS),
2. 0.33% sodium chloride,
3. 0.2% sodium chloride, and
4. 2.5% dextrose in water
5. Hypernatremia
6. Diabetic ketoacidosis
7. Hyperosmolar hyperglycemic state.

Question 13

Precautions with hypotonic fluid?

2 general precautions and 4 specific

Answer 13

1. Never give hypotonic solutions to patients who are at risk for increased ICP because it may exacerbate cerebral edema
2. Don’t use hypotonic solutions in patients with liver disease, trauma, or burns due to the potential for depletion of intravascular fluid volume
3. ICP
4. liver disease
5. trauma
6. burns

Question 14

The decrease in 1._______ ____ _________ can worsen existing hypovolemia and hypotension and cause 2._________ ______?

In older adult patients, 3.________ may be an indicator of a fluid volume deficit.

4. What should we instruct pts to tell us, if they feel?

Answer 14

1. vascular bed volume
2. cardiovascular collapse
3. confusion
4. Instruct patients to inform you if they feel dizzy or just “don’t feel right.”

Question 15

1. Isotonic crystalloids are what?
2. What does it increase?
3. ANd what does it not affect?

What are examples of these solutions?
3

Answer 15

1. noting or pertaining to a solution containing the same salt concentration as blood
2. Increases vascular volume
3. Doesn’t result in any significant fluid shifts across cellular or vascular membranes
4. • 0.9% NS (normal Saline)
   • Lactated Ringer’s (LR)
   • D5W (before infusion)

Question 16

1. Hypertonic crystalloids are what?
2. Where will it draw fluid?
3. What are examples of these solutions? 5

Answer 16

1. a solution of higher osmotic pressure than blood
2. Will draw fluids from the cells and interstitial spaces into the vasculature
3. IV Fluids:
   - 7.5% NS
   - D5 in ½ NS
   - Dextrose 5% in NS
   - Dextrose 10%
   - D50

Question 17

1. What are hypertonic solutions?
   Whats osmolarity usually?
2. The osmotic pressure gradient draws water out of where and into where?
3. Because of this they are used as?

Answer 17

1. Solution that have a higher tonicity or solute concentration.
   - Hypertonic fluids have an osmolarity of 340 mOsm/L or higher
2. The osmotic pressure gradient draws water out of the intracellular space, increasing extracellular fluid volume,
3. so they are used as volume expanders.

Question 18

Some examples of hypertonic solutions?

2

Answer 18

1- 7.5% sodium chloride (7.5% NS):

2- 5% Dextrose with normal saline (D5NS)

Question 19

Hypertonic solution Indications:
1- 7.5% sodium chloride (7.5% NS)? 2

2- 5% Dextrose with normal saline (D5NS)? 1

Answer 19

1. May be prescribed for patients in critical situations of severe hyponatremia.
2. Patients with cerebral edema may benefit from an infusion of hypertonic sodium chloride
3. which replaces sodium, chloride and some calories

Question 20

Precautions with hypertonic fluids:

1. Hypertonic sodium chloride solutions should be administered only in what?
2. Maintain vigilance when administering hypertonic saline solutions because of their potential for causing what? 2
3. On what time line should we be giving this?
4. Prescriptions for their use should state what? 4
5. Where is it better to store hypertonic sodium chloride solutions?

Answer 20

1. high acuity areas with constant nursing surveillance for potential complications .
2. intravascular fluid volume overload and pulmonary edema.
3. shouldn’t be given for an indefinite period of time.

4.

• the specific hypertonic fluid to be infused
• the total volume to be infused
• infusion rate
• length of time to continue the infusion

5. It is better to store hypertonic sodium chloride solutions apart from regular floor stock IV fluids .

Question 21

Therefore, what category are the following:

1. 0.9% NS?
2. 0.45% NS?
3. D5 0.45% NS?
4. D5W?
5. LR (RL)?

Answer 21

1. iso
2. hypo
3. hyper
4. iso then hypo
5. iso

Question 22

State Volemic Effect of 1 L of the following Fluid on intracellular, intersititial and plasma fluid Compartments:

1. D5W?
2. NS or LR?
3. 7.5% saline?
4. 5% albumin?
5. WHole blood?

Answer 22

D5W:
Intra- 660 ml
Interst. - 255ml
Plasma - 85ml

NS or LR:
Intra- -100 ml
Interst. - 825 ml
Plasma - 275 ml

7.5% saline:
Intra- -2950 ml
Interst. - 2960 ml
Plasma - 990 ml

5% albumin:
Intra- 0
Interst. - 500 ml
Plasma - 500 ml

Whole blood:
Intra- 0
Interst. - 0
Plasma - 1000ml

Question 23

We can divide the need for IV fluid therapy into two somewhat simplistic areas. What are they?

Answer 23

1. Maintenance Therapy

2. Replacement Therapy

Question 24

What types of imblaances are replacement therapies used for?

2

Answer 24

1. Mechanical imbalances

2. Electrolyte imbalances

Question 25

WHat are examples of mechanical imbalances?3

Answer 25

1. Hypotension due to hemorrhage 2. Hypotension due to anesthesia 3. Excess fluid loss....due to vomiting/diarrhea/decreased oral intake

Question 26

Two key concepts to remember about fluid homeostasis

Answer 26

1. The kidney is the primary manager of body fluid levels | 2. Sodium (Na) is the most osmotically active electrolyte in the body

Question 27

What two kidney issues can complicate IV fluid treatment? | 2

Answer 27

1. Underlying renal disease complicates things | 2. Poor renal perfusion complicates things

Question 28

The kidney is the primary manager of body fluid levels: When determining fluid status, it is important to note: 3 (Whats the most important?)

Answer 28

1. Urine output*** 2. Serum Sodium 3. Urine osmolality (easiest as urine Na)

Question 29

What other things are importnat but do not replace urine output, serum sodium and urine osmolality in our decision making? 3

Answer 29

1. Edema 2. BP 3. Orthostatic vitals

Question 30

Whats the difference between maintenance therapy and fluid resuscitation?

Answer 30

Maintenance therapy: replaces normal ongoing losses Fluid Resuscitation: corrects any existing water and electrolyte deficits.

Question 31

Maintenance therapy is usually undertaken when the individual is not expected to do what?

Answer 31

to eat or drink normally for a longer time (eg, perioperatively or patient on a ventilator)

Question 32

1. What is the goal of maintenance therapy? 2. Whats the easisest way to monitor net gain/loss of fluids? 3. What does a normal serum sodium tell you? 4. Normal adults have an obligate fluid loss of what per day?

Answer 32

1. Goal is to preserve water and electrolyte balance 2. Daily weights are the easiest way to monitor net gain/loss of fluids 3. Normal serum sodium tells you the patient has adequate water balance but not volume balance 4. Normal adults have an obligate fluid loss of 1600ml/day

Question 33

A pretty good IV fluid to use for maintenance is what? (and why?)

Answer 33

0.45% NS + 20 mEq KCl (the kidney will regulate Na, K and H20 retention)

Question 34

Water requirement increases _________ml/day for each degree fever >____C

Answer 34

100-150 37

Question 35

How to calculate maintenance fluid flow rates?

Answer 35

4/2/1 rule 4 ml/kg/hr for first 10 kg (=40ml/hr) then 2 ml/kg/hr for next 10 kg (=20ml/hr) then 1 ml/kg/hr for any kgs over that This always gives 60ml/hr for first 20 kg then you add 1 ml/kg/hr for each kg over 20 kg So: Weight in kg + 40 = Maintenance IV rate/hour 45kg patient=85 ml/hr or approx. 2L/day

Question 36

Replacement or Resuscitation Therapy 1. What is the goal? 2. What is the type of fluid given determined by?

Answer 36

1. Goal is to correct existing abnormalities in plasma electrolyte and volume status 2. Type of fluid given is determined by the type lost and current electrolytes

Question 37

1. Generally, when hypovolemia occurs; the kidneys conserve what? 2 2. What will this be seen as? 3. What will be seen earliest as? 4. What will the BUN/Creatinine ratio be?

Answer 37

1. sodium and water 2. This will be seen as increased serum Na 3. Will be seen earliest as decreased urine Na ( less than 25 mEq/L) 4. Normal BUN/Creatinine ratio is 10:1; with hypovolemia this will increase to > 20:1

Question 38

Replacement Therapy: 1. With excessive vomiting or NG (nasogastric) suction, the patient loses what? And may develop what? 2 2. With excessive diarrhea, the patient may lose what and develop what? 2 3. When all else fails what should we do?

Answer 38

1. - Hydrogen ions and may - develop metabolic alkalosis and hypovolemia 2. - sodium bicarbonate and - may develop metabolic acidosis and hypovolemia 3. Get ABGs (remember that serum CO2 levels are very helpful)

Question 39

Obviously, hemorrhage or trauma results in loss of what? 3

Answer 39

1. circulatory blood 2. hypovolema 3. shock

Question 40

Hypotension with general anesthesia is NOT initially due to loss of volume; it is due to what?

Answer 40

loss of vascular tone which “enlarges the tank”

Question 41

Hypovolemia due to decreased intake or excess excretion (sweating or hung-over): 1. How much until labs are back? 2. If serum Na is greater than 145? 3. If serum Na is less than 138? 4. Initially run at what level unless they are hemodynamically stable? 5. What should we monitor? 6. Gross estimate of renal perfusion is to make how much urine (minimum)?

Answer 41

1. 0.45% NS until labs are back 2. If serum Na > 145 change to 0.25% NS 3. If serum Na less than 138 change to 0.9% NS 4. Initially run at 125 ml/hr unless hemodynamically unstable 5. Monitor electrolytes and vitals 6. Gross estimate of renal perfusion is to make 30ml/hr (minimum) urine

Question 42

Hypovolemia due to vomiting or diarrhea: 1. How much until labs are back? 2. If serum Na is greather than 145? 3. Initally run at what unless hemodynamically stable? 4. Monitor what? 5. Gross estimate of renal perfusion?

Answer 42

1. 0.9% NS until labs are back 2. If serum Na > 145 change to 0.45% NS 3. Initially run at 125 ml/hr unless hemodynamically unstable 4. Monitor electrolytes and vitals 5. Gross estimate of renal perfusion is to make 30ml/hr (minimum) urine

Question 43

Hypovolemia due to hemorrhage: 1. What will it cause on PE? 6 How should we treat them? 2. What should we give them? 3. Continue this based on what? 4. What do we need to give them as soon as available? 5. Monitor what? 3 6. Gross estimate of renal perfusion?

Answer 43

1. - Tachycardic, - tachypneic, - systolic bp less than 90 - pale, cool, and clammy - confused - cyanotic 2. Bolus 1-2 LITERS 0.9% NS or LR through large bore IVs until labs are back 3. Continue fluid resuscitation based on vital signs and urine output 4. Packed Red Blood Cells (PRBC) as soon as available 5. Monitor electrolytes, ABGs and vitals 6. Gross estimate of renal perfusion is to make 30ml/hr (minimum) urine

Question 44

Hypovolemia due to burns 1. Treatment until labs are back? 2. Continue this based on what? 3. What should we consider early to maintain pressure and limit? 4. Monitor what? 3 5. Gross estimate of renal function?

Answer 44

1. Bolus 1-2 LITERS 0.9% NS or LR through large bore IVs until labs are back 2. Continue fluid resuscitation based on vital signs and urine output 3. Consider Albumin early to maintain pressure and limit edema 4. Monitor - electrolytes, - ABGs and - vitals 5. Gross estimate of renal perfusion is to make 30ml/hr (minimum) urine

Question 45

Correction of existing abnormalities in volume status or serum electrolytes (as in hypovolemic shock) What are the some parameters used to assess volume deficit? 4

Answer 45

1- Blood pressure 2- Urine output 3- Jugular venous pressure 4- Urine sodium concentration

Question 46

How to know that the patient has Hypovolemic Shock? The patient has the following signs and symptoms: 9

Answer 46

``` 1- Anxiety or agitation 2- Cool, Pale skin 3- Confusion 4- Decreased or no urine output 5- Rapid breathing 6- Disturbed consciousness 7- Low blood pressure 8- Low body temperature 9- Rapid pulse, often weak and thready ```

Question 47

Rate of Repletion of Fluid deficit. 1- Severe volume depletion or hypovolemic shock? 2.- Mild to moderate hypovolemia?

Answer 47

1- Severe volume depletion or hypovolemic shock: Rapid infusion of 1-2L of isotonic saline (0.9% NS) as rapidly as possible to restore tissue perfusion 2- Mild to moderate hypovolemia: Choose a rate that is 50-100mL/h greater than estimated fluid losses. calculating fluid loss.

Question 48

How should we calculate fluid loss in order to treat mild to moderate hypovolemia? 4 components

Answer 48

1. Urine output= 50ml/h 2. Insensible losses = 30ml/h 3. Additional loss such as 4. Vomiting or Diarrhea or high fever (additional 100- 150 ml/day for each degree of temp >37 C)

Question 49

Hypervolemia due to excessive accumulation of fluid in the body from? 7

Answer 49

1- Excessive parenteral infusion 2- Deficiencies in cardiovascular or renal fluid volume regulation 3- too much fluids in febrile phase 4- Use of hypotonic crystalloid solutions 5- Inappropriate…FFP, platelets 6- Continuation of IV fluids after critical phase 7- Comorbid condtions

Question 50

Comorbid conditions that could cause excessive accumulation of fluid in the body (hypervolemia)? 3

Answer 50

1. Congenital or ischemic heart disease 2. Chronic lung and renal disease 3. Obesity-fluid not calculated for IBW

Question 51

Fluid Overload Signs and Symptoms They are not always typical but most commonly are? 8

Answer 51

``` 1- Edema (swelling) - particularly feet, and ankles 2- Difficulty breathing while lying down 3- Crackles on auscultation 4- High blood pressure 5- Irritated cough 6- Jugular vein distension 7- Shortness of breath (dyspnea) 8- Strong, rapid pulse ```

Question 52

Management of Fluid Overload 5

Answer 52

``` 1- Prevention is best! 2- Sodium restriction 3- Fluid restriction 4- Diuretics 5- Dialysis ```

Question 53

How do colloid solutions work?

Answer 53

Expands the intravascular volume by drawing fluid from the interstitial spaces into the intravascular compartment through their higher oncotic pressure.

Question 54

1. Has the same effect as hypertonic crystalloids solutions but it requires what and have what? 2 2. because why? 3. This affect can last how long is the capillary wall linings are intact and working properly?

Answer 54

1. - administration of less total volume and - have a longer duration of action 2. the molecules remain within the intravascular space longer. 3. several days

Question 55

1. What is the most commonly used colloid solution? 2. contains plasma protein fractions obtained from human plasma and works to rapidly expand the plasma volume used for what? 3 3. What is it considered? 4. Why is its use limited?

Answer 55

1. 1- 5% albumin (Human albumin solution) 2. - volume expansion - moderate protein replacement - achievement of hemodynamic stability in shock states. 3. considered a blood transfusion product and requires all the same nursing precautions used when administering other blood products. 4. -It can be expensive and its availability is limited to the supply of human donors

Question 56

Colloid Solutions Albumin Contraindications: 4

Answer 56

a) Severe anemia b) Heart failure c ) Known sensitivity to albumin d ) Angiotensin-converting enzyme inhibitors ( ACEI) should be withheld for at least 24 hours before administering albumin because of the risk of atypical reactions, such as flushing and hypotension

Question 57

1. What is another form of hypertonic synthetic colloids used for volume expansion? 2. What does it contain and what is it used for? 3. Why are its advantages over albumin? 2

Answer 57

1. 2- Hydroxyethalstarches 2. - Contain sodium and chloride - used for hemodynamic volume replacement following major surgery and to treat major burns 3. Less expensive than albumin and their effects can last 24 to 36 hours

Question 58

Precautions when using Colloid solutions: | 7

Answer 58

1. The patient is at risk for developing fluid volume overload 2. As for blood products, use an 18-gauge or larger needle to infuse colloids. 3. Monitor the patient for signs and symptoms of hypervolemia, 4. Closely monitor intake and output. 5. Colloid solutions can interfere with platelet function and increase bleeding times, so monitor the patient's coagulation indexes. 6. Elevate the head of bed unless contraindicated. 7. Anaphylactoid reactions are a rare but potentially lethal adverse reaction to colloids.

Question 59

Monitor the patient for signs and symptoms of hypervolemia using Colloid solutions with what? 3

Answer 59

1. Increased BP 2. Dyspnea or crackles in the lungs 3. Edema.

Question 60

1. What is the usual IV fluid of choice? (WHat kind of solution is this?) 2. The only use for D5W as a stand alone fluid is what? 2 3. Patient fluid needs are how much per day?

Answer 60

1. Usual IV fluid of choice is normal saline (0.9% NS)-isotonic 2. The only use for D5W as a stand-alone fluid is when - serum Na is >145 and - patient is symptomatic with hypernatremia (almost never) 3. Patient fluid needs are about 1600ml/day (obligate fluid loss) plus any urine output over 500 ml plus any measured or quantified loss (diarrhea, vomiting, NG suction, drains, or bleeding) [Don’t forget increased need with fever = 150ml per degree C over 37]

Question 61

What is Lactated Ringer's RL? What is it the fluid of choice for? 2

Answer 61

Lactated Ringer’s (LR): Isotonic and also a fluid of choice for volume depletion due to - trauma - burns

Question 62

1. 0.45% NS (Half-Normal Saline) is what kind of solution and used for what? 2. 0.25% NS (Quarter-Normal Saline) is what kind of solution and used for what? 3. Albumin/Dextran is what kind of solution and used when?

Answer 62

1. Hypotonic and may be useful until serum Na comes down and in maintenance 2. Very hypotonic and used only when serum sodium is very high 3. Colloid with special use only

Question 63

If patient is dehydrated how does this manifest? | 8

Answer 63

1. Tachycardia, 2. weak pulses 3. postural hypotension 4. Flushed, dry skin 5. Dry mucous membranes 6. Decreased urine output 7. Increased hematocrit 8. Increased serum sodium level

Question 64

What should we do first before we give IV fluids? 4

Answer 64

``` 1. Do Orthostatic VS (Tilts) Get a 2. CBC, 3. CMP, and 4. UA ```

Question 65

Pt is considered to be Tilt positive if they have a change of how much with pulse and how much in systolic blood pressure?

Answer 65

Patient is considered to be “Tilt Positive” or “tilting” if he/she has a change of 15 bpm with pulse AND decrease of 10 in the systolic B/P.

Question 66

1. In a dehyrdated pt what IV fluid should we start and over what period of time? 2. Do we do this before or after we get labs? 3. We should not stop the IV until what?

Answer 66

1. Then start 1 L NS or RL IV over approximately 1 hr. 2. Adjust the fluid when you get the lab values. 3. Do not stop the IV until patient can urinate Usually I will go to the 2nd L then will slow the flow rate substantially until he/she urinates if I have not received labs yet.

Question 67

What is the best marker for volume status?

Answer 67

Urine sodium

Question 68

Hypertonic salt solution may be lifesaving in patients with what? 2

Answer 68

1. severe dilutional hyponatremia and in | 2. trauma patients when blood is not readily available…..but rarely used

Question 69

0.9% sodium chloride (Normal Saline) should be given when? | 6

Answer 69

1- to treat low extracellular fluid, as in fluid volume deficit from 2- Shock 3- Mild hyponatremia 4- Metabolic acidosis (such as diabetic ketoacidosis) 5- It’s the fluid of choice for resuscitation efforts. 6- it's the only fluid used with administration of blood products.

Question 70

Where would we get fluid volume deficit from? (in which we would need NS) 3

Answer 70

1. Hemorrhage 2. Severe vomiting or diarrhea 3. Heavy drainage from GI suction, fistulas, or wounds

Question 71

Because 0.9% sodium chloride replaces extracellular fluid, it should be used cautiously in certain patients for fear of fluid volume overload. Which kind of pts? 2

Answer 71

those with cardiac or renal disease

Question 72

What are the ions in lactated ringer and in what concentrations? 5

Answer 72

1. Na- 130 2. K- 4 3. Ca - 3 4. Cl - 109 5. HCO3 - 28 Total - 273

Question 73

1. WHy is lactated ringer the most physiologically adaptable fluid? 2. When to be used? 4

Answer 73

because its electrolyte content is most closely related to the composition of the body's blood serum and plasma. 1. To replace GI tract fluid losses ( Diarrhea or vomiting ) 2. Fistula drainage 3. Fluid losses due to burns and trauma 4. Patients experiencing acute blood loss or hypovolemia due to third-space fluid shifts.

Question 74

1. LR is metabolized where? 2. What is the lactate converted to? 3. Administered to pts with what kind of acidosis? 4. Who can we not give LR to? 3

Answer 74

1. LR is metabolized in the liver, which 2. converts the lactate to bicarbonate. 3. LR is often administered to patients who have metabolic acidosis… not patients with lactic acidosis 4. Don't give LR to patients with -liver disease as they can't metabolize lactate -severe renal impairment because it contains some potassium -LR shouldn't be given to a patient whose pH is greater than 7.5

Question 75

Be aware that patients being treated for hypovolemia can quickly develop ________(fluid volume overload) following rapid or overinfusion of isotonic fluids.

Answer 75

hypervolemia

Question 76

1. What is NS 0.9% NaCl used for mostly? 2. LR? 3. D5W? 4. D5 1/2 NS (D5NS) 2 -What do we need to remember about giving this? 5. WHo can we not give D5W to? Why?

Answer 76

1. - expand volume - dilute medications - keep the veins open 2. Fluid resuscitation 3. isotonic to hypotonic in the body 4. - Na and volume replacement - -GO SLOW and monitor BP, pulse and lung sounds. Also Urine output and serum Na 5. infants or head injuries - can cause cerebral edema