Fluids and Electrolytes Flashcards
T/F: Approx 1/3 of ideal body weight is water.
False, 2/3!
Intracellular Fluid is what fraction of Total Body Water?
2/3
Extracellular Fluid is what fraction of Total Body Water?
1/3
Interstitial Fluid is what fraction of ECF?
2/3
Plasma is what fraction of ECF?
1/3
What is the average blood volume of a male? Of a female?
66 ml/kg
60 ml/kg
What is the Total Blood Volume of a 70 kg patient?
4.2-4.6 L
What separates the interstitial fluid and intravascular fluid compartments?
Capillary Endothelium - impermeable to proteins (primarily albumin), which determines the plasma/interstitial compartment oncotic pressures.
What separates the intracellular and extracellular compartments?
Cell membrane – impermeable to ions (Na) which determine the ICF/ECF osmotic pressure
The infusion of IL of 0.9% NaCl (Isotonic Saline) will expand ______ volume by only 275 ml.
Plasma
What types of IV fluids are there?
- Blood
- Lactated Ringers
- Normal Saline
- Half normal saline
What is the 4:2:1 Rule and what is is used for?
4 cc/kg/hr for the 1st 10 kg
2 cc/kg/hr for the 2nd 10 kg
1 cc/kg/hr for each additional kg
For a 70 kg patient, how many ccs should you give per hour (using the 4:2:1 Rule)?
40 + 20 + 50 = 110 cc/hr
What is the best indicator of adequate volume replacement?
Urine Output greater than or equal to 0.5 cc/kg/hr
What is typical IVF management for a major GI surgery?
- Use isotonic fluids (LR or NS) for the first 24 hours
2. Switch to D5 1/2 NS + 20 mEq KCl
What does 50 g glucose/L function to do?
Stimulates insulin release resulting in amino acid uptake and protein synthesis (prevents protein catabolism)
When you have gastric losses (H+ and Cl-), what IV fluids do you give?
Ex. Diarrhea, Vomiting
Normal Saline
When you have pancreatic/bile/small intestine losses (HCO3), what IV fluids do you give?
Ex. biliary drain, ileostomy, fistula
Lactated Ringers
May need to give K+ as needed
When you have large intestine losses (HCO3- and K+), what IV fluids do you give?
Lactated Ringers +/- Potassium
Clinical signs/symptoms of hypovolemia (dehydration)
- Dry mucuous membranes
- Decreased skin turgor
- Extreme Thirst
- Low urine output
- Climbing BUN +/- Cr (rising BUN:Cr ratio)
- Low BP
- Low CVP
- Tachycardia
- FENA < 1%
- Altered mental status
How do you assess a hypovolemic patient?
- ABCs - Airway, Breathing, Circulation
- Two large bore IVs
- Foley to monitor urine output
- MUST RULE OUT BLEEDING! All Sx patients are bleeding until proven otherwise
- Give 1-2 L bolus of isotonic fluid and assess response
- In no response, check bleeding again.
- If not bleeding, may be massively under-resuscitated and just need more fluid.
What is the diagnosis for a patient with a serum Na great than 145 mEq/L
Hypernatremia
Signs and Symptoms of Hypernatremia
- Restlessness
- Ataxia
- Seizures
- Lethargy
- Altered Mental Status
What is the most common cause of hypernatremia?
Loss of hypotonic body fluids.
Especially in the surgical patient
What’s another common cause of hypernatremia?
Large wounds/burns
What is the equation for Free Water Deficit?
FWD = TBW x (Serum Na - 140) / 140
Can you give more than 10 mEq/day or 0.5 mEq/L/hr? Why or why not/
No, risk of cerebral edema.
When a patient has a total body sodium deficit in addition to free water deficit, what is this called?
Hypovolemic Hypernatremia
In a patient with Hypovolemic Hypernatremia, what do you do first?
Isotonic Crystalloid (NS/LR)
What do you do after correcting with isotonic crystalloids in hypovolemic hypernatremic patients?
Calculate and replace their free water deficit
Total Body Water of a male is determined by?
TBW = 0.6 x Body Weight
Total Body Water of a female is determined by?
TBW = 0.5 x Body Weight
Diabetes Insipidus – Hypernatremia!
- Often Euvolemic
- Excess loss of free water in urine (ADH promotes water reabsorption in the distal tubule)
- Central DI: dailure of ADH release from posterior pituitary
- Nephrogenic DI: Kidneys unresponsive to ADH (amphotericin, dopamine, lithium, contrast dyes)
What is the daily potassium intake?
0.5-1 mEq/day
What can cause hypokalemia?
- Diuretics
- Diarrhea
- Magnesium Depletion (impairs K reabsorption across the renal tubules)
Signs/Symptoms of Hypokalemia
Muscle Weakness if severe (< 2.5) and can be arhythmogenic when accompanied by other conditions (hypomagnesemia, digitalis, myocardial ischemia)
Treating Hypokalemia
Replace in increments of 20-60 mEq
For every 10 mEq, expect a 0.1 increase in serum level.
A serum level of potassium greater than 5.5 would be diagnostic of what?
Hyperkalemia
What does hyperkalemia do?
Slows the electrical conduction of the heart and can eventually lead to life-threatening dysrrhythmias
What can cause hyperkalemia?
- Iatrogenic
- Rhabdomyolysis
- Certain Drugs
- Renal Insufficiency
- Massive Blood Transfusions
How do you treat hyperkalemia?
- Immediately stop K-containing infusions. Check EKG for peaked T wave
- If EKG changes are present—give calcium gluconate to stabilize the cardiac membrane
- Then give 1 amp of D50 and 10 units of insulin to drive the potassium intracellularly
- Kayexalate can be given to enhance K excretion via the GI muscosa, however this will take hours, but will help to lower the total body potassium
- Lasix is another option but must check renal function first
- In most patients with good kidney function they will not develop hyperkalemia
- Dialysis if extremely high K and patient in renal failure
Why is Magnesium important?
Major intracellular cation, serves as a cofactor for countless enzymatic reactions (ATP). It also regulates the movement of calcium into smooth muscle cells.
Causes of Magnesium deficiency?
- Diuretics
- Alcoholics
- Chronic malutrition
- Diarrhea
- Diabetics
Diagnostic criteria for hypomagnesemia?
< 2 at Shands
<1.5 in general
What can happen with hypomagnesemia?
- Can accompany hypokalemia andhypocalcemia difficult to correct.
- Arrhythmias: Replace as needed, typically in increments in 2 mg IV
Tell me about hypermagnesemia?
- Rare, typically renal failure or iatrogenic (OB Wards)
- Weakness/Lethargic state, Hyporeflexia.
- Give calcium, may require dialysis
A serum level of Na less than 135 would be diagnostic of?
Hyponatremia
What is the most common cause of post-op hyponatremia?
SIADH (Syndrome of inappropriate ADH secretion)
Pain or stress of surgery → elevated antidiuretic hormone (ADH) levels postop, Kidneys retain too much free water and the urine is inappropriately concentrated.
DDx of post op hyponatremia
- Loop Diuretics
- Iatrogenic
- Osmotic Diuresis from hyperglycemia
- Adrenal Insufficiency
Asymptomatic Treatment of Hyponatremia
- Hypovolemic = Give volume
- Hypervolemic = Na & Water Restriction (loop diuretics if CHF or nephrotic syndrome)
- Euvolemic = Water restriction (to counter retention of free water using Hyponatremia) Treat underlying problem, like hypothyroids – give thyroxine
In a euvolemic patient, you can use loop diuretics or demclocycine. What can this cause sometimes?
The exact opposite problem! Diabetes Insipidus
Signs/Symptoms of Hyponatremia
- Acute - Osmotic Forces cause water movement into brain cells leading to cerebral edema
- Mild - Anorexia, nausea, lethargy
- Moderate - Disoriented, agitates, neuro deficit
- Severe - Sz, Coma, Death
What is the treatment for hyponatremia? If this urgent?
IT IS URGENT!
If symptomatic and urgent (mental status changes), give hypertonic saline (3% NaCl = 513 mEq/L Na+ and Cl-)
How do you calculate a sodium deficit?
Na+ Deficit = TBW x (130 - actual Na+ concentration)
What is important to remember for Na correction?
Do no correct more than 0.5 mEq/L/hr due to the risk of pontine myelinolysis (CPM)