Title: Isoflurane Therapy in a Case of Status Asthmaticus Requiring Extracorporeal Membrane Oxygenation
Case Report Body:
Introduction: Inhaled volatile anesthetics have been cited as a rescue therapy for severe refractory status asthmaticus (1,2). The use of these agents in patients requiring extracorporeal membrane oxygenation (ECMO) has been reported more recently, both in severe refractory status asthmaticus (SA) and acute respiratory distress syndrome (3,4), but the literature on this to date is limited. We present an interesting case of severe refractory SA requiring veno-venous (VV) ECMO support, and the use of systemic isoflurane delivered via the ECMO circuit.
Description: A 51-year-old male with a medical history of asthma and tobacco use presented to an outside hospital (OSH) with respiratory distress, and was admitted for management of an asthma exacerbation. He failed non-invasive ventilation and was intubated. It was difficult to ventilate the patient, and he developed a severe respiratory acidosis. He was transferred to our institution for consideration for cannulation for VV-ECMO after 3 days at the OSH.
He was cannulated for VV-ECMO due to severe respiratory acidosis from SA. He also exhibited a significant respiratory drive, with tidal volumes in the 1000s when placed on pressure control ventilation. His respiratory rate was lowered to 4 breaths/minute to allow for proper exhalation and minimize auto-positive end expiratory pressure (PEEP). He continued to have diffuse wheezing and poor air movement. Vaporized isoflurane was instilled into the ECMO circuit at an initial concentration of 0.8%, and incrementally increased to 1.2%. This was delivered for 20 hours. The patient was de-cannulated from ECMO 5 days after this therapy and extubated 12 days after.
Discussion: Isoflurane therapy has resulted in clinical improvement in patients with severe SA on ECMO (3) and has also been used for sedation in patients on VV-ECMO (4). Delivery of isoflurane in these cases was either via an anesthesia machine in the ICU or anesthetic delivery systems that deliver the drug into the endotracheal tube. Uniquely, our case highlights the delivery of isoflurane directly into the ECMO circuit itself. It has been postulated that isoflurane causes relaxation through direct action on bronchiole smooth muscle and through systemic uptake (3,5), and it is likely that both of these mechanisms contributed to improvement in our patient's case.