Fentanyl-Induced Wooden Chest Syndrome Masquerading As Severe Respiratory Distress Syndrome In Covid-19

Introduction: Wooden chest syndrome (WCS) is a rare and often fatal reaction to fentanyl where airways and chest wall musculature become rigid through α1-noradrenergic activation and cholinergic modulation causing ineffective ventilation.1-4 This dose-independent response is more easily diagnosed in non-ventilated patients either in the operating room or who overdose recreationally.2,4,5 In ventilated patients with acute respiratory distress syndrome (ARDS) it can be difficult to distinguish from poor lung compliance. We describe a case of a previously healthy male with COVID-19 on mechanical ventilation who developed WCS.Case: A 47-year-old previously healthy male was admitted for COVID-19 pneumonia requiring high-flow nasal cannula. On hospital day 11, he was intubated and placed on lung protective ventilation for moderate ARDS (PaO2/FiO2 192). On ventilator day (VD) 2 a fentanyl infusion was started. After 36 hours, hypoxemia improved but plateau pressures were consistently <30 cm H2O necessitating a decrease to 4 cc/kg after minimizing dead space within the ventilator circuit. A trial of airway pressure release ventilation worsened hypercarbia and bronchoscopy did not reveal mucous plugging, airway collapse, or purulent secretions. Worsening lung compliance (PPlat 50 on 4 cc/kg) without change in oxygenation raised suspicion for WCS, so fentanyl was discontinued. Within one hour, plateau pressures nadired at 16 and the ventilator was changed to pressure support. The patient was successfully extubated on VD 10.Discussion: Differentiating low lung compliance in classical ARDS from disproportionately compliant hypoxemia in COVID-19-induced ARDS is an ongoing point of research in the thoracic community.6-9 The novelty of this paradigm allows potential to overlook less common, if not rare, complications such as fentanyl-induced WCS. Our patient's poor compliance despite relatively quick improvement in oxygenation countered available evidence on COVID-19 lung physiology, prompting suspicion for an alternative explanation for his poor ventilation. With descriptions of WCS limited to case reports we found that onset and severity of initial signs (contraction of the chest wall, diaphragm, and abdominal and laryngeal muscles2) can be masked in mechanically ventilated patients. Inadequate ventilation can be interpreted as manifestations of high airway and alveolar pressure making it difficult to differentiate it from classical ARDS and ultimately increasing ventilator use duration. To our knowledge, this is the first report of WCS in a patient with COVID-19 associated ARDS. It demonstrates that when mechanically ventilated COVID-19 patients receiving fentanyl have poor lung compliance and oxygenation improves disproportionately faster than ventilation, WCS should be considered.