|
Chapter 18 / Fluids and Electrolytes 109 |
What are the levels of sodium |
40 mEq/L |
and chloride in sweat? |
|
What is the major electrolyte |
Potassium—65 mEq/L |
in colonic feculent fluid? |
|
What is the physiologic |
Sodium/H2O retention via renin S |
response to hypovolemia? |
aldosterone, water retention via ADH, |
|
vasoconstriction via angiotensin II and |
|
sympathetics, low urine output and |
|
tachycardia (early), hypotension (late) |
THIRD SPACING |
|
|
|
What is it? |
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) |
When does “third-spacing” |
Third-spaced fluid tends to mobilize back |
occur postoperatively? |
into the intravascular space around POD |
|
#3 (Note: Beware of fluid overload once |
|
the fluid begins to return to the intravas- |
|
cular space); switch to hypotonic fluid |
|
and decrease IV rate |
What are the classic signs of third spacing?
What is the treatment?
What are the surgical causes of the following conditions:
Metabolic acidosis
Tachycardia
Decreased urine output
IV hydration with isotonic fluids
Loss of bicarbonate: diarrhea, ileus, fistula, high-output ileostomy, carbonic anhydrase inhibitors
Increase in acids: lactic acidosis (ischemia), ketoacidosis, renal failure, necrotic tissue
Hypochloremic alkalosis NGT suction, loss of gastric HCl through vomiting/NGT
110 Section I / Overview and Background Surgical Information
Metabolic alkalosis |
Vomiting, NG suction, diuretics, alkali |
|
ingestion, mineralocorticoid excess |
Respiratory acidosis |
Hypoventilation (e.g., CNS depression), |
|
drugs (e.g., morphine), PTX, pleural |
|
effusion, parenchymal lung disease, |
|
acute airway obstruction |
Respiratory alkalosis
What is the “classic” acidbase finding with significant vomiting or NGT suctioning?
Why hypokalemia with NGT suctioning?
What is the treatment for hypokalemic hypochloremic metabolic alkalosis?
Hyperventilation (e.g., anxiety, pain, fever, wrong ventilator settings)
Hypokalemic hypochloremic metabolic alkalosis
Loss in gastric fluid—loss of HCl causes alkalosis, driving K into cells
IVF, Cl /K replacement
What is paradoxic alkalotic aciduria?
How does paradoxic alkalotic aciduria occur?
With paradoxic alkalotic aciduria, why is H preferentially lost?
What can be followed to assess fluid status?
Seen in severe hypokalemic, hypovolemic, hypochloremic metabolic alkalosis with paradoxic metabolic alkalosis of serum and acidic urine
H is lost in the urine in exchange for Na in an attempt to restore volume
H is exchanged preferentially into the urine instead of K because of the low concentration of K
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
With hypovolemia, what |
Tachycardia, tachypnea, initial rise in |
changes occur in vital signs? |
diastolic blood pressure because of |
|
clamping down (peripheral vasoconstric- |
|
tion) with subsequent decrease in both |
|
systolic and diastolic blood pressures |
Chapter 18 / Fluids and Electrolytes 111
What are the insensible fluid losses?
What are the quantities of daily secretions:
Bile
Gastric
Pancreatic
Small intestine
Saliva
How can the estimated levels of daily secretions from bile, gastric, and small-bowel sources be remembered?
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
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)
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!
COMMON IV REPLACEMENT FLUIDS (ALL VALUES ARE PER LITER)
What comprises normal |
154 mEq of Cl |
saline (NS)? |
154 mEq of Na |
What comprises 1/2 NS? |
77 mEq of Cl |
|
77 mEq of Na |
What comprises 1/4 NS? |
39 mEq of Cl |
|
39 mEq of Na |
What comprises lactated |
130 mEq Na |
Ringer’s (LR)? |
109 mEq Cl |
|
28 mEq lactate |
|
4 mEq K |
|
3 mEq Ca |
What comprises D5W? |
5% dextrose (50 g) in H2O |
112 Section I / Overview and Background Surgical Information
What accounts for tonicity? |
Mainly electrolytes; thus, NS and LR are |
|
both isotonic, whereas 1/2 NS is hypotonic |
|
to serum |
What happens to the lactate |
Converted into bicarbonate; thus, LR |
in LR in the body? |
cannot be used as a maintenance fluid |
|
because patients would become alkalotic |
IVF replacement by anatomic |
|
site: |
|
Gastric (NGT) |
D5 1/2 NS 20 KCl |
Biliary |
LR / sodium bicarbonate |
Pancreatic |
LR / sodium bicarbonate |
Small bowel (ileostomy) |
LR |
Colonic (diarrhea) |
LR / sodium bicarbonate |
CALCULATION OF MAINTENANCE FLUIDS
What is the 100/50/20 rule?
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)
What is the 4/2/1 rule? |
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 |
What is the maintenance for |
Using 100/50/20: |
a 70-kg man? |
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 |
|
|
Chapter 18 / Fluids and Electrolytes 113 |
What is the common adult |
D5 |
1/2 NS with 20 mEq KCl/L |
maintenance fluid? |
|
|
What is the common pediatric |
D5 |
1/4 NS with 20 mEq KCl/L (use |
maintenance fluid? |
1/4 NS because of the decreased ability |
|
|
of children to concentrate urine) |
|
Why should sugar (dextrose) |
To inhibit muscle breakdown |
|
be added to maintenance |
|
|
fluid? |
|
|
What is the best way to assess fluid status?
What is the minimal urine output for an adult on maintenance IV?
Urine output (unless the patient has cardiac or renal dysfunction, in which case central venous pressure or wedge pressure is often used)
30 mL/hr (0.5 cc/kg/hr)
What is the minimal urine |
50 mL/hr |
output for an adult trauma |
|
patient? |
|
How many mL are in 12 oz |
356 mL |
(beer can)? |
|
How many mL are in 1 oz? |
30 mL |
How many mL are in 1 tsp? |
5 mL |
What are common isotonic |
NS, LR |
fluids? |
|
What is a bolus? |
Volume of fluid given IV rapidly (e.g., 1 L |
|
over 1 hour); used for increasing intravas- |
|
cular volume, and isotonic fluids should |
|
be used (i.e., NS or LR) |
Why not combine bolus fluids |
Hyperglycemia may result |
with dextrose? |
|