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Difficulty: Very hardPhysiological Adaptation

A telemetry nurse is caring for an older adult client receiving a continuous intravenous infusion of furosemide for severe decompensated heart failure. Over the past 4848 hours, the client has experienced a net fluid loss of 4.5 L4.5\ \text{L}. The nurse notes the client is now exhibiting generalized muscle weakness, shallow respirations at 10 breaths/min10\ \text{breaths/min}, and frequent premature ventricular contractions on the cardiac monitor.

Laboratory TestResult
pH7.517.51
PaCO2\text{PaCO}_248 mmHg48\ \text{mmHg}
HCO3−\text{HCO}_3^-34 mEq/L34\ \text{mEq/L}
PaO2\text{PaO}_288 mmHg88\ \text{mmHg}
Serum Sodium136 mEq/L136\ \text{mEq/L}
Serum Potassium2.7 mEq/L2.7\ \text{mEq/L}
Serum Chloride92 mEq/L92\ \text{mEq/L}

Which physiological mechanism best explains the client's current clinical presentation and laboratory results?

  1. Excessive loss of fluid, chloride, and potassium has induced a primary metabolic alkalosis, prompting compensatory alveolar hypoventilation.Answer
  2. B
    Primary retention of carbon dioxide from severe heart failure has caused a respiratory acidosis, with a compensatory rise in serum bicarbonate.
  3. C
    Significant intravascular volume depletion has triggered early distributive shock, leading to anaerobic metabolism and cellular acidosis.
  4. D
    Myocardial irritability from severe hypokalemia has stimulated the respiratory center, causing hyperventilation and a primary respiratory alkalosis.

Answer

Excessive loss of fluid, chloride, and potassium has induced a primary metabolic alkalosis, prompting compensatory alveolar hypoventilation.
The client's ABG reveals a pH of 7.51 (alkalemia) with an elevated HCO3- (34 mEq/L), indicating a primary metabolic alkalosis. This is a classic complication of massive loop diuretic therapy (furosemide), which causes profound renal wasting of water, potassium, and chloride. The loss of chloride and fluid concentrates the extracellular bicarbonate, creating contraction alkalosis. The respiratory system compensates for metabolic alkalosis by hypoventilating (respiratory rate of 10 breaths/min) to retain CO2 (PaCO2 48 mmHg), which acts as an acid to help lower the pH. The concurrent severe hypokalemia (2.7 mEq/L) directly causes the muscle weakness and premature ventricular contractions.

Step-by-Step Solution

1
Analyze the Arterial Blood Gas (ABG) results.
The pH is 7.51 (alkalemia). The HCO3- is 34 mEq/L (elevated, indicating metabolic alkalosis). The PaCO2 is 48 mmHg (elevated, indicating a respiratory acid buffer response).
Determining the primary acid-base disturbance is required to understand the client's physiological state.
2
Identify the etiology of the acid-base and electrolyte disturbances.
Massive diuresis with furosemide caused profound renal excretion of water, potassium, and chloride. The disproportionate loss of chloride and fluid leads to contraction alkalosis (metabolic alkalosis), while potassium loss leads to severe hypokalemia.
Connecting the diuretic therapy to its expected physiological consequences explains the laboratory abnormalities.
3
Correlate the physical assessment findings with the laboratory data.
The severe hypokalemia (2.7 mEq/L) directly causes muscle weakness and premature ventricular contractions. To compensate for the metabolic alkalosis, the respiratory center decreases the respiratory rate (10 breaths/min) to retain CO2 and lower the pH.
This confirms that the clinical signs are physiological adaptations to the iatrogenic electrolyte and acid-base shifts.
4
Select the mechanism that encompasses all clinical data.
The only mechanism that explains the alkalotic pH, the compensatory hypoventilation, and the complications of diuresis is primary metabolic alkalosis with respiratory compensation.
The other options incorrectly identify the primary disturbance as acidosis or hyperventilation, contradicting the objective data.

Key Concept

Acid-Base Imbalances and Loop Diuretic Complications
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Topics

Physiological Adaptation

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