Using Bubble Contrast Transthoracic Echocardiogram to Individualize Peep Titration in a Patient With Acute Hypoxemic Respiratory Failure, Intracardiac Shunt

Abstract Introduction: Positive end-expiratory pressure (PEEP) titration is crucial in managing acute hypoxemic respiratory failure (AHRF), balancing lung recruitment and overdistension. Lung-heart interactions further complicate the identification of optimal PEEP levels; higher PEEP can reduce cardiac output by decreasing preload and increasing right ventricular afterload. This issue is particularly problematic in patients with intracardiac shunts. This case report illustrates a novel method using a bubble contrast transthoracic echocardiogram (TTE) to individualize PEEP titration, aiming to avoid intrapulmonary shunting while minimizing intracardiac shunt. Case Description: A 52-year-old male with a history of smoking, chronic obstructive pulmonary disease, and poorly managed chronic heart failure presented to the emergency department with worsening shortness of breath and retrosternal pain. Due to significant oxygen desaturation, the Emergency Team initiated non-invasive ventilation with bilevel-positive airway pressure (BiPAP) and contacted the Critical Care Team for further management. Upon examination, he had notable lower limb edema, a blood pressure of 177/107 mm Hg, respiratory rate of 27 bpm, and oxygen saturation of 95% on FiO2 of 1.0 (IPAP/EPAP 30/20 cm H2O). Lung auscultation revealed bilateral crackles, and widespread wheezing. Chest x-ray indicated mild pulmonary congestion and lab results showed respiratory acidosis and mild leukocytosis. Due to his progressive acute hypoxemic respiratory failure, the patient was intubated and admitted to the intensive care unit. Due to profound and persistent hypoxemia, out keeping with the x-ray, the patient had a bubble contrast TTE to rule out intracardiac shunt. This TTE confirmed a suspected patent foramen oval and shunt. A repeat bubble test was performed during a PEEP response test to address ongoing oxygenation issues, increasing PEEP from 6 to 16 cm H2O (Figure 1). Monitoring included SpO2, respiratory compliance, and intracardiac shunt direction. Numerous bubbles entered the left heart at 16 cm H2O of PEEP; only a few were noted at 14 cm H2O, with none at 12 cm H2O or lower. Thus, the optimal PEEP was determined to be 12 cm H2O, leading to improved clinical status and eventual extubation. Discussion: Titrating PEEP according to lung mechanics and considering cardiopulmonary interactions in right-to-left cardiac shunts may enhance AHRF management. This case highlights the challenges of PEEP titration in these complex cases. The combined use of a bubble test with PEEP titration can help minimize intracardiac shunting whilst balancing the risks of intrapulmonary shunting from alveolar collapse.

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