Third Spacing

Question 1

What is it?

Answer 1

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)

Question 2

When does “third-spacing”

occur postoperatively?

Answer 2

Third-spaced fluid tends to mobilize back
into the intravascular space around POD
#3 (Note: Beware of fluid overload once
the fluid begins to return to the intravascular
space); switch to hypotonic fluid
and decrease IV rate

Question 3

What are the classic signs of

third spacing?

Answer 3

Tachycardia

Decreased urine output

Question 4

What is the treatment?

Answer 4

IV hydration with isotonic fluids

Question 5

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

Hypochloremic alkalosis

Answer 5

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

NGT suction, loss of gastric HCl through
vomiting/NGT

Question 6

What are the surgical causes
of the following conditions:
Metabolic alkalosis
Respiratory acidosis
Respiratory alkalosis

Answer 6

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

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

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

Question 7

What is the “classic” acidbase
finding with significant
vomiting or NGT suctioning?

Answer 7

Hypokalemic hypochloremic metabolic

alkalosis

Question 8

Why hypokalemia with NGT

suctioning?

Answer 8

Loss in gastric fluid—loss of HCl causes

alkalosis, driving K+ into cells

Question 9

What is the treatment for
hypokalemic hypochloremic
metabolic alkalosis?

Answer 9

IVF, Cl-/K+ replacement

Question 10

What is paradoxic alkalotic

aciduria?

Answer 10

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

Question 11

How does paradoxic

alkalotic aciduria occur?

Answer 11

H+ is lost in the urine in exchange for

Na+ in an attempt to restore volume

Question 12

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

Answer 12

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

Question 13

What can be followed to

assess fluid status?

Answer 13

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

Question 14

With hypovolemia, what

changes occur in vital signs?

Answer 14

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

Question 15

What are the insensible fluid

losses?

Answer 15

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—300 mL/24 hours, increased
with fever; thus, insensible fluid
loss is not directly measured

Question 16

What are the quantities of
daily secretions:
Bile
Gastric
Pancreatic
Small intestine
Saliva

Answer 16

1000 mL/24 hours
2000 mL/ 24 hours
600 mL/ 24 hours
3000 mL/day
1500 mL/24 hours
(Note: almost all secretions are reabsorbed)

Question 17

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

Answer 17

Alphabetically and numerically: BGS and
123 or B1, G2, S3, because Bile, Gastric,
and Small bowel produce roughly 1 L,
2 L, and 3 L, respectively!