A 71-year-old man is evaluated in the intensive care unit (ICU) for management of acute re… — USMLE Step 2 CK

A $71$ -year-old man is evaluated in the intensive care unit (ICU) for management of acute respiratory failure. He was intubated and mechanically ventilated yesterday for a severe chronic obstructive pulmonary disease (COPD) exacerbation triggered by community-acquired pneumonia. His medical history includes COPD, heart failure with reduced ejection fraction (LVEF $30\%$ ), and chronic kidney disease.

Current ventilator settings (Volume Control):
Fraction of inspired oxygen ( $\text{FiO}_2$ ): $0.40$
Tidal volume: $450\text{ mL}$ ( $6\text{ mL/kg}$ predicted body weight)
Respiratory rate: $10\text{/min}$
Positive end-expiratory pressure (PEEP): $5\text{ cm H}_2\text{O}$

Vital signs:
Temperature: $37.8^\circ\text{C}$ ( $100.0^\circ\text{F}$ )
Blood pressure: $110/70\text{ mm Hg}$
Heart rate: $98\text{/min}$

Physical examination shows coarse breath sounds and prolonged expiration. There is no jugular venous distention. Bedside echocardiography demonstrates a collapsible inferior vena cava with no B-lines.

Arterial blood gas (ABG) on current settings:
pH: $7.25$
$\text{PaCO}_2$ : $70\text{ mm Hg}$
$\text{PaO}_2$ : $75\text{ mm Hg}$
$\text{HCO}_3^-$ : $30\text{ mEq/L}$

The patient's sputum culture from admission has finalized, growing *Streptococcus pneumoniae* susceptible to ceftriaxone. He is currently receiving intravenous vancomycin, piperacillin-tazobactam, and azithromycin.

Concurrently, the patient's estranged son arrives from out of state and demands immediate extubation, stating his father "would not want to live on a machine." The patient's wife, who is his legally designated healthcare proxy, is present and strongly desires to continue full medical support.

Which of the following interventions are appropriate in the management of this patient? (Select all that apply)

Discontinue vancomycin and piperacillin-tazobactamAnswer
Increase the mechanical ventilator respiratory rateAnswer
C
Administer intravenous furosemide
D
Administer intravenous sodium bicarbonate
E
Withdraw mechanical ventilation per the son's directive

Answer

The most appropriate interventions are to discontinue the unnecessarily broad-spectrum antibiotics (vancomycin and piperacillin-tazobactam) and to increase the mechanical ventilator respiratory rate to treat the acute-on-chronic respiratory acidosis.

This complex ICU scenario requires multidisciplinary management. First, the patient has an acute-on-chronic respiratory acidosis (pH

7.25

\text{PaCO}_2

70\text{ mm Hg}

). On volume-control ventilation, minute ventilation is determined by tidal volume multiplied by respiratory rate. Because the tidal volume is appropriately set to

6\text{ mL/kg}

ideal body weight, increasing the respiratory rate is the best method to increase minute ventilation and clear

\text{CO}_2

. Second, the patient is on broad-spectrum empiric antibiotics, but sputum cultures have identified *Streptococcus pneumoniae* susceptible to narrower agents. Discontinuing vancomycin and piperacillin-tazobactam is a necessary step in antimicrobial stewardship.

Step-by-Step Solution

Analyze the arterial blood gas (ABG) to determine the acid-base status.

The pH (

7.25

) is acidemic. The elevated

\text{PaCO}_2

(

70\text{ mm Hg}

) indicates respiratory acidosis. The elevated

\text{HCO}_3^-

(

30\text{ mEq/L}

) represents a partial compensatory response.

Identifying the primary disturbance dictates ventilator management.

Assess the adequacy of the current mechanical ventilation settings.

The patient is hypoventilating (RR

10\text{/min}

, Tidal Volume

450\text{ mL}

). Minute ventilation must be increased.

Increasing the respiratory rate will clear more

\text{CO}_2

and correct the severe acidemia.

Evaluate the microbiology data and the current antibiotic regimen.

The sputum culture grew *Streptococcus pneumoniae* susceptible to ceftriaxone, but the patient is on vancomycin and piperacillin-tazobactam.

Antimicrobial stewardship requires de-escalating broad-spectrum antibiotics once a specific, susceptible pathogen is identified.

Resolve the ethical conflict regarding the withdrawal of life-sustaining treatment.

The wife is the legal healthcare proxy and wishes to continue care.

Medical teams must follow the directives of the legally appointed proxy over other family members.

Key Concept

Management of acute-on-chronic respiratory failure in the ICU requires addressing inadequate minute ventilation, practicing antimicrobial stewardship based on culture data, and correctly identifying the legal healthcare proxy in ethical disputes.

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