A 43-year-old, previously healthy man is hospitalized due to acute pancreatitis. On day 3, he develops respiratory distress. The patient is transferred to the intensive care unit and intubated. His ideal body weight is 70 kg (154 lb). Initial ventilator settings are as follows: Ten minutes after the patient is intubated, blood pressure is 110/70 mm Hg and pulse is 90/min. Results from arterial blood gas testing are as follows: Which of the following is the best next step in management of this patient?

Question

A 43-year-old, previously healthy man is hospitalized due to acute pancreatitis.  On day 3, he develops respiratory distress.  The patient is transferred to the intensive care unit and intubated.  His ideal body weight is 70 kg (154 lb).  Initial ventilator settings are as follows:  Ten minutes after the patient is intubated, blood pressure is 110/70 mm Hg and pulse is 90/min.  Results from arterial blood gas testing are as follows:  Which of the following is the best next step in management of this patient?

Quizplus · Accepted Answer

11ec25c8_d4a2_0ec2_bc81_b322ff60f09c_MD0003_00 The patient has acute pancreatitis, which is now complicated by acute respiratory distress syndrome (ARDS). In patients with ARDS, mechanical ventilation improves oxygenation by increasing FiO₂ and positive end-expiratory pressure (PEEP) to prevent alveolar collapse. The goal is to maintain PaO₂ at 60-90 mm Hg, corresponding to an oxygen saturation of 92%-96%. Immediately following intubation, a high FiO₂ (eg, ≥60%, or 0.6) is usually provided and can subsequently be adjusted based on the results of the first arterial blood gas (ABG) analysis. 92%-96% PaO₂ is influenced mainly by FiO₂ and PEEP. In this case, the patient's initial ABG values indicate excessive oxygenation (PaO₂ >90 mm Hg), or hyperoxia. Prolonged exposure to a high FiO₂ can induce oxygen toxicity via the formation of proinflammatory reactive oxygen species, leading to cellular toxicity and the propagation of lung injury. It also worsens atelectasis by displacing nitrogen gas from the alveoli (nitrogen is poorly absorbed into the bloodstream and helps keep alveoli open). Although there is no strict cutoff value, FiO₂ levels <60% are generally considered safe; therefore, this patient's FiO₂ should be lowered. A compensatory increase in PEEP may be required to maintain adequate oxygenation. (Choice B) In ARDS, a certain degree of PEEP (usually ≥10 cm H₂O) is needed to recruit collapsed alveoli and prop them open throughout the respiratory cycle. Although decreasing the PEEP would address this patient's hyperoxia, it could result in widespread alveolar derecruitment with increased intrapulmonary shunting and markedly worsened oxygenation. Lowering the FiO₂ is much safer because it carries no risk of precipitating derecruitment. (Choices C, D, and E) PaCO₂ is determined mainly by respiratory rate and tidal volume. The patient's tidal volume is 6 mL/kg (70 kg × 6 mL/kg = 420 mL), which is consistent with the lung-protective purpose of low-tidal-volume ventilation. Lower tidal volumes prevent alveolar overdistension to inhibit further lung injury and improve mortality in ARDS. Mild hypercapnic respiratory acidosis is acceptable to enable low tidal volumes ("permissive hypercapnia"). Therefore, no adjustment in respiratory rate or tidal volume is recommended. Educational objective: During mechanical ventilation, oxygenation is determined by the FiO₂ and positive end-expiratory pressure (PEEP). The lowest feasible FiO₂ (ideally <60%) should be set to prevent oxygen toxicity. As FiO2 is lowered, a compensatory increase in PEEP may be required to maintain adequate oxygenation by recruiting collapsed alveoli and keeping them open. References: Mechanical ventilation of acute respiratory distress syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/26045965) Approach to the patient with the acute respiratory distress syndrome. (http://www.ncbi.nlm.nih.gov/pubmed/25453418)

A 43-Year-Old, Previously Healthy Man Is Hospitalized Due to Acute