Pulmonary Arteriovenous Malformations (AVMs) are often associated with chronic hypoxemia due to right-to-left shunting. We present a case of a patient with Hereditary Hemorrhagic Telangiectasia (HHT) and arteriovenous malformations (AVMs) who developed severe hypoxemia on mechanical ventilation. We suggest precautions in the management of patients with right-to-left intrapulmonary shunting when initiating mechanical ventilation, and management options for worsening hypoxemia.
An 84-year-old Caucasian female with a history of HHT and pulmonary AVMs on home oxygen at night presented to the emergency department with a severe headache. CT angiogram of the brain revealed two AVMs. Her arterial blood gas (ABG) on a non-rebreather mask with fraction of inspired oxygen (FIO2) 100% revealed a pH of 7.39, a pCO2 of 33, and a PaO2 of 63, and she was admitted to the ICU for hypoxemic respiratory failure, presumably related to increased right-to-left intrapulmonary shunting as no other clear precipitants were identified. Spiral CT of the chest did not reveal pulmonary embolism or significant air-space opacities, but demonstrated multiple AVMs, with the largest measuring 3.2 cm x 1.8 cm in the right upper lobe. There were no prior CT scans for comparison. Contrast echocardiography confirmed right-to-left intrapulmonary shunting with normal right ventricular function and an estimated pulmonary artery pressure of 36 mm Hg, and percutaneous embolization of the pulmonary AVMs was scheduled. Given worsening hypoxemia (SpO2 of 80–82% with 100% FIO2) in spite of empiric diuresis, and the anticipated need for transport to the Angiography department and peri-procedure sedation, she was intubated after receiving Etomidate and Rocuronium. Time-cycled pressure-controlled ventilation was initiated with peak inspiratory pressure at 20 cm H20;PEEP at 5 cm H20; inspiratory time at 1.2 seconds, respiratory rate at 10, and FIO2 at 100%, and her SpO2 dropped to 60% with ABG values as follows: pH, 7.47; pCO2, 33;PaO2, 25; and SaO2, 55%. The left lateral decubitus position was used to minimize shunting in the right upper lobe AVM with little improvement. After her paralytic agent wore off, a change to pressure support ventilation 10 cm H20 without PEEP improved the SpO2 to 78–80%. Emergent embolization of her largest AVM improved the SpO2 to 98% immediately. She was discharged to home after 7 days without evidence of hypoxemic brain injury on 2 liters per minute of oxygen, with SpO2 94–96%.
Positive pressure ventilation likely worsened hypoxemia in this case by increasing pulmonary capillary resistance and redistributing blood flow to the AVMs, thereby worsening right-to-left shunting. Some case reports have described worsening oxygenation with mechanical ventilation and increased PEEP in patients with HHT and right-to-left shunting (1, 2), but there are no general precautions and recommendations for the ventilator management of patients with right-to-left intrapulmonary shunting and hypoxemic respiratory failure. After our experience with this patient, and a review of the literature, we offer the following suggestions: 1) Avoid mechanical ventilation unless absolutely necessary. 2) Avoid long-acting paralytics during intubation to allow spontaneous breathing through the endotracheal tube. 3) Minimize the mean airway pressure if positive pressure ventilation is necessary. 4) Positional changes, such as the decubitus position with the AVM side up, can be considered to decrease shunting but may not be helpful. 5) Consider emergent embolization of AVMs.
Positive-pressure mechanical ventilation may worsen hypoxemia in patients with HHT and intrapulmonary right-to-left shunting, and clinicians should be aware of management options for severe hypoxemia.
Yasuhiro Norisue, No Financial Disclosure Information; No Product/Research Disclosure Information