Fluid, Electrolyte, and Acid-Base Study Guide for Test 1

Comprehensive Overview of Fluid Balance and Assessment

• To master this unit, students must be able to recognize, assess, treat, and provide education on fluid states, electrolyte concentrations, and acid-base statuses.

• Fluid Balance Assessment Techniques:   - Measurement of Intake and Output ($I\&O$).   - Daily weights (most accurate indicator of fluid change; $1\text{ kg}$ gain usually equals $1\text{ L}$ of fluid retained).   - Assessment of skin turgor and mucous membrane moisture.   - Neurological checks for changes in mental status.   - Cardiovascular monitoring (blood pressure, heart rate, and central venous pressure).   - Respiratory assessment (lung sounds for crackles or fluid accumulation).

• Impact of Fluid Balance on Laboratory Values:   - Hematocrit ($Hct$): Normal ranges are Male: $42-52\%$\; Female: $37-47\%$. Levels increase with Fluid Volume Deficit ($\text{FVD}$) due to hemoconcentration and decrease with Fluid Volume Overload ($\text{FVO}$) due to hemodilution.   - Blood Urea Nitrogen ($BUN$): Normal range is $10-20\,mg/dL$. Levels increase with $\text{FVD}$ and renal impairment.   - Creatinine ($Cr$): Normal range is $0.6-1.2\,mg/dL$. This is the best indicator of overall kidney function.   - Urine Specific Gravity ($USG$): Normal range is $1.005-1.030$. Levels above $1.030$ indicate concentrated urine (fluid deficit), while levels below $1.005$ indicate dilute urine (fluid excess or diabetes insipidus).

Principles and Categories of IV Fluid Administration

• Types of IV Fluids:   - Isotonic Solutions: These solutions have the same osmolality as body fluids. Examples include $0.9\%\text{ NaCl}$ (Normal Saline), Lactated Ringer's ($LR$), and $5\%\text{ Dextrose in Water}$ ($D_5W$ — note that $D_5W$ becomes hypotonic once glucose is metabolized).   - Hypotonic Solutions: These solutions have a lower osmolality than body fluids, causing fluid to shift into cells. Example: $0.45\%\text{ NaCl}$ (Half Normal Saline).   - Hypertonic Solutions: These solutions have a higher osmolality than body fluids, pulling fluid out of cells into the vascular space. Examples include $3\%\text{ NaCl}$, $5\%\text{ Dextrose in 0.9\% NaCl}$ ($D_5NS$), and $10\%\text{ Dextrose in Water}$ ($D_{10}W$).

Fluid Volume Deficit (FVD) and Fluid Volume Overload (FVO)

• Fluid Volume Deficit ($\text{FVD}$):   - Signs and Symptoms: Decreased skin turgor (tenting), dry mucous membranes, flat neck veins (with the patient supine), hypotension (orthostatic hypotension), tachycardia, weak/thready pulse, oliguria ( < 30\,mL/hr), and weight loss.   - Laboratory Findings: Increased $Hct$, increased $BUN$, and increased $USG$.

• Fluid Volume Overload ($\text{FVO}$):   - Signs and Symptoms: Edema (peripheral or sacral), Jugular Venous Distension ($JVD$), crackles in the lungs (pulmonary edema), dyspnea, hypertension, bounding pulse, and rapid weight gain.   - Laboratory Findings: Decreased $Hct$ and decreased $BUN$ due to dilution.

Sodium Imbalances: Hypernatremia and Hyponatremia

• Lab Values for Sodium ($Na^+$): Normal range is $135-145\,mEq/L$.

• Hypernatremia (Na^+ > 145\,mEq/L):   - Neurologic Signs and Symptoms: Restlessness, agitation, lethargy, and seizures in severe cases.   - Non-Neurologic Signs and Symptoms: Thirst, flushed skin, dry/sticky mucous membranes, low-grade fever, and hyperreflexia.   - Treatment: Gradual replacement of fluid loss ($0.45\%\text{ NaCl}$ or $D_5W$) and administration of diuretics to promote sodium excretion.

• Hyponatremia (Na^+ < 135\,mEq/L):   - Neurologic Signs and Symptoms: Confusion, lethargy, headache, and potential coma or seizures.   - Non-Neurologic Signs and Symptoms: Nausea, vomiting, abdominal cramping, and muscle weakness or twitching.   - Treatment: Fluid restriction (if due to dilution), administration of hypertonic saline ($3\%\text{ NaCl}$) for severe cases with cautious monitoring, and increasing sodium intake in the diet.

Potassium Imbalances and Cardiac Priority

• Lab Values for Potassium ($K^+$): Normal range is $3.5-5.0\,mEq/L$.

• Hyperkalemia (K^+ > 5.0\,mEq/L):   - Signs and Symptoms: Muscle weakness, fatigue, numbness/tingling, and cardiac arrhythmias.   - EKG Changes: Peaked T-waves, widened QRS complex, and flat/absent P-waves.   - Treatment and Priority Actions: Sodium Polystyrene Sulfonate (Kayexalate) for excretion; Emergency shifts via IV Regular Insulin and Dextrose ($D_{50}$); IV Calcium Gluconate (to protect the heart/stabilize membrane potential).   - Diuretic Interactions: Potassium-sparing diuretics (e.g., Spironolactone) can worsen hyperkalemia.

• Hypokalemia (K+ < 3.5\,mEq/L):   - Signs and Symptoms: Leg cramps, muscle weakness, constipation, and decreased deep tendon reflexes.   - EKG Changes: Flattened T-waves, prominent U-waves, and ST-segment depression.   - Treatment: Potassium replacement (oral or IV). IV potassium must NEVER be given as a bolus ($\text{IV push}$) as it is lethal.   - Diuretic Interactions: Loop diuretics (e.g., Furosemide) and Thiazide diuretics promote potassium loss.

Calcium and Magnesium Imbalances

• Hypocalcemia:   - Lab Value: Ca^{2+} < 9.0\,mg/dL (Normal: $9.0-10.5\,mg/dL$).   - Signs and Symptoms: Tetany, muscle spasms, and circumoral numbness.   - Classic Assessment Signs:     - Chvostek\u2019s sign: Abnormal spasm of the facial muscles elicited by light taps on the facial nerve in front of the ear.     - Trousseau\u2019s sign: Carpal spasm induced by inflating a blood pressure cuff on the upper arm for $2-5\text{ minutes}$.   - Clinical Link: Frequently occurs after a thyroidectomy if the parathyroid glands are accidentally damaged or removed.   - Treatment: Calcium Gluconate or Calcium Chloride administration.

• Magnesium Imbalances:   - Normal Range: $1.3-2.1\,mEq/L$.   - Hypomagnesemia ( < 1.3\,mEq/L): Hyperactive Deep Tendon Reflexes ($DTRs$), tremors, and seizures.   - Hypermagnesemia ( > 2.1\,mEq/L): Hypoactive $DTRs$, lethargy, and depressed respiratory effort.

Acid-Base Balance and ABG Interpretation

• Normal Arterial Blood Gas ($ABG$) Ranges:   - $\\text{pH}$: $7.35-7.45$   - $PaCO_2$: $35-45\,mmHg$   - $HCO_3^-$: $22-26\,mEq/L$

• Interpreting Compensation:   - Uncompensated: pH is abnormal; one parameter is abnormal, the other is normal.   - Partially Compensated: pH is abnormal; both $PaCO_2$ and $HCO_3^-$ are abnormal (one system is trying to fix the other).   - Fully Compensated: pH is within normal range ($7.35-7.45$); both $PaCO_2$ and $HCO_3^-$ are abnormal.

• Metabolic Acidosis:   - ABG: \\text{pH} < 7.35, HCO_3^- < 22\,mEq/L.   - Causes: Kidney disease (renal failure prevents acid excretion), Diarrhea (loss of base), and Diabetic Ketoacidosis ($DKA$).   - Treatment: Treat the underlying cause; administration of Sodium Bicarbonate ($NaHCO_3$).

• Metabolic Alkalosis:   - ABG: \\text{pH} > 7.45, HCO_3^- > 26\,mEq/L.   - Causes: Vomiting, gastric suctioning ($NG\text{ tube}$), or excessive antacid use.   - Treatment: Fluid replacement with saline to promote bicarbonate excretion.

• Respiratory Acidosis:   - ABG: \\text{pH} < 7.35, PaCO_2 > 45\,mmHg.   - Causes: Respiratory depression (drug overdose, anesthesia), COPD, or pneumonia (hypoventilation).   - Treatment: Improve ventilation (oxygen therapy, cough and deep breathe, bronchodilators).

• Respiratory Alkalosis:   - ABG: \\text{pH} > 7.45, PaCO_2 < 35\,mmHg.   - Causes: Hyperventilation (anxiety, panic attack, fever).   - Treatment: Slow the breathing rate (breathe into a paper bag, calming techniques).

Class Mathematics and Practical Application

• Students must be proficient in math questions practiced in class, including IV drip rates, dosage calculations, and fluid intake totals.

• ABG Practice Resources: Utilizing links for Quiz 1 and Quiz 2 provided in the course materials for identifying compensation states.