Critical Care Study guide Essays

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EXAM I Study Guide

ACID BASE IMBALANCE
1. Explain the body’s three regulators used to maintain a normal pH:
a. Buffers: substance that reacts with an acid or base to prevent a large change in pH
Reacts immediately
Primary regulator of acid-base balance
Acts chemically to change strong acids into weaker acids or to bind acids to neutralize their effects
Buffers in the body: Carbonic acid-bicarbonate, monohydrogen-dihydrogen phosphate, intracellular and plasma protein, and hemoglobin buffers
Function to minimize the effect of acids on blood pH until they can be excreted from the body.
CO2 is formed and excreted by the lungs – amount of CO2 in blood directly relates to carbonic acid concentration and subsequently to H+ concentration
b. Respiratory System
Responds within minutes and reaches maximum effectiveness in hours
Maintain a normal pH by excreting CO2 and water – by products of cellular metabolism
Increased respirations: more CO2 expelled and less remains in the blood
Less carbonic acid and less H+
Decreased respirations: more CO2 remains in the blood
Increased carbonic acid and more H+
Rate of CO2 excretion is controlled by the respiratory center in the medulla in the brainstem
Respiratory system compensates through hyperventilation “blow off CO2” or hypoventilation “retaining CO2”
If a respiratory problem is the cause of an acid-base imbalance, the respiratory system loses its ability to correct a pH alteration
c. Renal System
Response takes 2-3 days to reach maximum effect, but kidneys maintain balance indefinitely in chronic imbalance
Under normal conditions, kidney reabsorbs and conserves all of the bicarbonate they filter.
Kidneys can generate bicarbonate and eliminate excess H+ -- compensation of acidosis
Mechanism of acid elimination
Secretion of small amounts of free hydrogen into the renal tubule
Combination of H+ with ammonia to form ammonium
Excretion of weak acids
Kidneys excrete acid through urine – as a compensatory mechanism, the pH of urine can decrease to 4 and increase to 8
If the renal system is the cause of an acid-base balance, it loses its ability to correct a pH alteration
2. List the normal value parameters for an arterial blood gas.
Parameter
Reference Interval pH 7.35-7.45
PaCO2
32-48 mm Hg
HCO3 (bicarbonate)
22-26 mEq/L
PaO2
80-100 mm Hg
SaO2
> 95%
Base excess
2.0 mEq/L

3. Analyze the four different acid base imbalances (respiratory acidosis; respiratory alkalosis; metabolic acidosis; metabolic alkalosis) including for each:
a. Respiratory acidosis
Causes
Hypoventilation: results in buildup of carbon dioxide; subsequently carbonic acid accumulates in the blood
Clinical manifestation
Neurologic: drowsiness, disorientation, dizziness, headache, coma
Cardiovascular:  BP, ventricular fibrillation, warm, flushed skin
Neuromuscular: seizure
Respiratory: hypoventilation with hypoxia
Intervention for treatment
Kidneys conserve bicarbonate and excrete increased concentrations of hydrogen ion into the urine
Renal compensatory mechanisms begin to operate within 24 hours – until the renal mechanisms have an effect, the serum bicarbonate level will usually be normal
b. Respiratory alkalosis
Causes
Hyperventilation
Hypoxia from acute pulmonary disorders
Anxiety, CNS disorders, and mechanical overventilation
Clinical manifestation
Neurologic: lethargy, light-headedness, confusion
Cardiovascular: tachycardia, dysrhythmias
Gastrointestinal: nausea, vomiting, epigastric pain
Neuromuscular: tetany, numbness, tingling of extremities, hyerreflexia,seizures
Respiratory: hyperventilation
Intervention for…