Surgery 18 Fluids And Electrolytes

Front 1

What are the two major body fluid compartments?

Back 1

1. Intracellular
2. Extracellular

Front 2

What are the two subcompartments of extracellular fluid?

Back 2

1. Interstitial fluid (in between cells)
2. Intravascular fluid (plasma)

Front 3

What percentage of body weight is in fluid?

Back 3

60%

Front 4

What percentage of body fluid is intracellular?

Back 4

66%

Front 5

What percentage of body fluid is extracellular?

Back 5

33%

Front 6

What is the composition of body fluid?

Back 6

Fluids = 60% total body weight
Intracellular = 40% total body weight
Extracellular = 20% total body weight (think: 60, 40, 20)

Front 7

On average, what percentage of body weight does blood account for in adults?

Back 7

~7%

Front 8

How many liters of blood are in a 70-kg man?

Back 8

0.07 × 70 = 5 liters

Front 9

What are the fluid requirements every 24 hours for each of the following substances: › Water

Back 9

~30 to 35 mL/kg

Front 10

What are the fluid requirements every 24 hours for each of the following substances: › Potassium

Back 10

~1 mEq/kg

Front 11

What are the fluid requirements every 24 hours for each of the following substances: › Chloride

Back 11

~1.5 mEq/kg

Front 12

What are the fluid requirements every 24 hours for each of the following substances: › Sodium

Back 12

~1–2 mEq/kg

Front 13

What are the levels and sources of normal daily water loss?

Back 13

Urine—1200 to 1500 mL (25–30 mL/kg)
Sweat—200 to 400 mL
Respiratory losses—500 to 700 mL
Feces—100 to 200 mL

Front 14

What are the levels and sources of normal daily electrolyte loss?

Back 14

Sodium and potassium = 100 mEq
Chloride = 150 mEq (40 mEq/L sodium and chloride lost as sweat)

Front 15

What is the physiologic response to hypovolemia?

Back 15

Sodium/H2O retention via renin aldosterone, water retention via ADH, vasoconstriction via angiotensin II and sympathetics, low urine output and tachycardia (early), hypotension (late)

Front 16

What is third spacing?

Back 16

Fluid accumulation in the interstitium of tissues, as in edema, e.g., loss of fluid into the interstitium and lumen of a paralytic bowel following surgery (think of the intravascular and intracellular spaces as the first two spaces)

Front 17

When does "third-spacing" occur postoperatively?

Back 17

Third-spaced fluid tends to mobilize back into the intravascular space around the third postoperative day; beware of fluid overload once the fluid begins to return to the intravascular space. Switch to hypotonic fluid and decrease IV rate.

Front 18

What are the classic signs of third spacing?

Back 18

Tachycardia
Decreased urine output

Front 19

What is the treatment for third spacing?

Back 19

IV hydration with isotonic fluids

Front 20

What are the surgical causes of the following conditions: › Metabolic acidosis

Back 20

Loss of bicarbonate: diarrhea, ileus, fistula, high-output ileostomy, carbonic anhydrase inhibitors
Increase in acids: lactic acidosis (ischemia), ketoacidosis, renal failure, necrotic tissue

Front 21

What are the surgical causes of the following conditions: › Hypochloremic alkalosis

Back 21

NGT suction, loss of gastric HCl through vomiting/NGT

Front 22

What are the surgical causes of the following conditions: › Metabolic alkalosis

Back 22

Vomiting, NG suction, diuretics, alkali ingestion, mineralocorticoid excess

Front 23

What are the surgical causes of the following conditions: › Respiratory acidosis

Back 23

Hypoventilation (e.g., CNS depression), drugs (e.g., morphine), PTX, pleural effusion, parenchymal lung disease, acute airway obstruction

Front 24

What are the surgical causes of the following conditions: › Respiratory alkalosis

Back 24

Hyperventilation (e.g., anxiety, pain, fever, wrong ventilator settings)

Front 25

What is the "classic" acid-base finding with significant vomiting or NGT suctioning?

Back 25

Hypokalemic hypochloremic metabolic alkalosis

Front 26

Why hypokalemia with NGT suctioning?

Back 26

Loss in gastric fluid—loss of HCl causes alkalosis, driving K+ into cells; K+ loss into urine exchange for Na+

Front 27

What is the treatment for hypokalemic hypochloremic metabolic alkalosis?

Back 27

IVF, Cl-/K+ replacement

Front 28

What is paradoxic alkalotic aciduria?

Back 28

Seen in severe hypokalemic, hypovolemic, hypochloremic metabolic alkalosis with paradoxic metabolic alkalosis of serum and acidic urine

Front 29

How does paradoxic alkalotic aciduria occur?

Back 29

H+ is lost in the urine in exchange for Na+ in an attempt to restore volume.

Front 30

With paradoxic alkalotic aciduria, why is H+ preferentially lost?

Back 30

H+ is exchanged preferentially into the urine instead of K+ because of the low concentration of K+.

Front 31

What can be followed to assess fluid status?

Back 31

Urine output, base deficit, lactic acid, vital signs, weight changes, skin turgor, jugular venous distention (JVD), mucosal membranes, rales (crackles), central venous pressure, PCWP, chest x-ray findings

Front 32

With hypovolemia, what changes occur in vital signs?

Back 32

Tachycardia, tachypnea, initial rise in diastolic blood pressure because of clamping down (peripheral vasoconstriction) with subsequent decrease in both systolic and diastolic blood pressures

Front 33

What are the insensible fluid losses?

Back 33

Loss of fluid not measured:
Feces—100 to 200 mL/24 hours
Breathing—500 to 700 mL/24 hours
(Note: increases with fever and tachypnea)
Skin—approximately 300 mL/24 hours, increased with fever; thus, insensible fluid loss is not directly measured

Front 34

What are the quantities of daily secretions?

Back 34

Bile—approximately 1000 mL/24 hours
Gastric—approximately 2000 mL/ 24 hours
Pancreatic—approximately 600 mL/ 24 hours
Small intestine—approximately 3000 mL/day
Saliva—approximately 1500 mL/24 hours
Note: almost all secretions are reabsorbed

Front 35

How can the estimated levels of daily secretions from bile, gastric, and small-bowel sources be remembered?

Back 35

Alphabetically and numerically: B, G, S and 1, 2, 3; or B1, G2, S3 as bile, gastric, and small bowel produce roughly 1 L, 2 L, and 3 L, respectively!

Front 36

What are the principles of fluid and electrolyte replacement?

Back 36

1. Replace deficits.
2. Fulfill daily maintenance requirements.
3. Replace ongoing losses.

Front 37

What comprises normal saline (NS)?

Back 37

154 mEq of Cl–
154 mEq of Na+

Front 38

What comprises ½ NS?

Back 38

77 mEq of Cl–
77 mEq of Na+

Front 39

What comprises ¼ NS?

Back 39

39 mEq of Cl–
39 mEq of Na+

Front 40

What comprises lactated Ringer's (LR)?

Back 40

130 mEq Na+
109 mEq Cl–
28 mEq lactate
4 mEq K+
3 mEq Ca+

Front 41

What comprises D5W?

Back 41

5% dextrose (50 g) in H2O

Front 42

What accounts for tonicity?

Back 42

Mainly electrolytes; thus, NS and LR are both isotonic, whereas ½ NS is hypotonic to serum

Front 43

What happens to the lactate in LR in the body?

Back 43

Converted into bicarbonate; thus, LR cannot be used as a maintenance fluid because patients would become alkalotic

Front 44

What is the 100/50/20 rule?

Back 44

Maintenance IV fluids for a 24-hour period:
100 mL/kg for the first 10 kg
50 mL/kg for the next 10 kg
20 mL/kg for every kg over 20 (divide by 24 for hourly rate)

Front 45

What is the 4/2/1 rule?

Back 45

Maintenance IV fluids for hourly rate:
4 mL/kg for the first 10 kg
2 mL/kg for the next 10 kg
1 mL/kg for every kg over 20

Front 46

What is the fluid maintenance for a 70-kg man?

Back 46

Using 100/50/20:
100 × 10 kg = 1000
50 × 10 kg = 500
20 × 50 kg = 1000
Total = 2500
Divided by 24 hours = 104 mL/hr maintenance rate
Using 4/2/1:
4 × 10 kg = 40
2 × 10 kg = 20
1 × 50 kg = 50
Total = 110 mL/hr maintenance rate

Front 47

What is the common adult maintenance fluid?

Back 47

D5 1/2 NS with 20 mEq KCl/L

Front 48

What is the common pediatric maintenance fluid?

Back 48

D5 1/4 NS with 20 mEq KCl/L (use 1/4 NS because of the decreased ability of children to concentrate urine)

Front 49

Why should sugar (dextrose) be added to maintenance fluid?

Back 49

To inhibit muscle breakdown

Front 50

What is the best way to assess fluid status?

Back 50

Urine output (unless the patient has cardiac or renal dysfunction, in which case central venous pressure or wedge pressure is often used)

Front 51

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

Back 51

30 mL/hr (0.5 cc/kg/hr)

Front 52

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

Back 52

50 mL/hr

Front 53

How many mL are in 12 oz (beer can)?

Back 53

356 mL

Front 54

How many mL are in 1 oz?

Back 54

30 mL

Front 55

How many mL are in 1 tsp?

Back 55

5 mL

Front 56

What are common isotonic fluids?

Back 56

NS, LR

Front 57

What is a bolus?

Back 57

A volume of fluid given IV in a rapid manner (e.g., 1 L over 1 hour); used for increasing intravascular volume, and isotonic fluids should be used (i.e., NS or LR)

Front 58

Why not combine bolus fluids with dextrose?

Back 58

Hyperglycemia may result.

Front 59

What is the possible consequence of hypergly-cemia in the patient with hypovolemia?

Back 59

Osmotic diuresis

Front 60

Why not combine bolus fluids with a significant amount of potassium?

Back 60

Hyperkalemia may result (the potassium in LR is very low: 4 mEq/L).

Front 61

Why should isotonic fluids be given for resuscitation (i.e., to restore intravascular volume)?

Back 61

If hypotonic fluid is given, the tonicity of the intravascular space will be decreased and H2O will freely diffuse into the interstitial and intracellular spaces. Thus, use isotonic fluids to expand the intravascular space.

Front 62

What portion of 1 L NS will stay in the intravascular space after a laparotomy?

Back 62

In 5 hours, only approximately 200 cc (or 20%) will remain in the intravascular space!

Front 63

What is the most common trauma resuscitation fluid?

Back 63

LR

Front 64

What is the most common postoperative IV fluid after a laparotomy?

Back 64

D5LR for 24 to 36 hours, followed by maintenance fluid

Front 65

After a laparotomy, when should a patient's fluid be "mobilized"?

Back 65

Classically, postoperative day 3; the patient begins to "mobilize" the third-space fluid back into the intravascular space

Front 66

What IVF is used to replace duodenal or pancreatic fluid loss?

Back 66

LR (Bicarbonate loss)

Front 67

What is a common cause of electrolyte abnormalities?

Back 67

Lab error!