Use of Flow-Volume Loops on a Mechanically Ventilated Pediatric Patient as a Diagnostic Tool for Fixed Airway Obstruction

The flow-volume loop (FV-loop) provides a graphical representation of the inspiratory and expiratory flow of both mechanically provided breaths and patient-triggered breaths during invasive mechanical ventilation. The FV-loop on the ventilator-delivered breath displays the active inspiratory flow reflective of lung compliance and the passive expiratory flow reflective of airway resistance. Our case report highlights the importance of the FV-loop in determining a fixed airway obstruction. A five-month-old male presented to the emergency department with worsening respiratory distress in the setting of rhino-enterovirus. He was admitted to the pediatric intensive care unit (PICU) and intubated for acute hypoxic respiratory failure. The findings on his ventilator FV-loop graphics denoted a fixed airway obstruction, as seen by the truncation of inspiratory and expiratory flow. The patient was subsequently found to have a left pulmonary artery (LPA) sling with a vascular ring and several complete tracheal rings. He was transferred to a referral institution for operative management, returned to our PICU, and discharged home after 47 days of hospital management. During mechanical ventilation, FV-loops can be effectively utilized to assist in the diagnosis of fixed intra- or extra-thoracic airway obstructions.