Brain death (BD) is characterized by a severe brain injury resulting in irreversible loss of all brain and brainstem functions, while other organs may remain viable. The diagnosis of BD is based on the presence of coma, absence of brainstem reflexes, and absence of spontaneous breathing confirmed by an apnea test. In France, the apnea test is mandatory prior to organ procurement. The apnea test aims to demonstrate that hypercapnia, a strong ventilatory stimulus, does not induce any respiratory movements.
In current practice, the apnea test is performed by disconnecting the patient from mechanical ventilation for 8-10 minutes while administering oxygen. Oxygenation strategies during apnea vary across French centers. Although the use of continuous positive airway pressure (CPAP) is recommended, a substantial proportion of tests are still performed without positive end-expiratory pressure (PEEP) effect, using either an open T-piece or an intratracheal oxygen catheter. These methods are associated with a higher risk of complications, such as hypoxemia, and potential adverse effects on organ function, which is particularly relevant in the context of organ donation.
Humidified high-flow oxygen (HHFO), delivered via a specialized device connected to the endotracheal tube, provides high flow rates (up to 60 L/min), allows precise adjustment of the fraction of inspired oxygen (FiO₂ up to 1.0), and generates a minimal PEEP effect. HHFO is routinely used in intensive care units. While its feasibility during apnea testing has been reported, its efficacy during BD diagnosis has not been well evaluated.
Preliminary observations in intensive care patients with clinical brain death suggest that HHFO can be safely used during the apnea test, allowing achievement of hypercapnia and confirmation of absence of spontaneous respiration while maintaining better oxygenation compared with conventional oxygen delivery via an open T-piece.
This study aims to evaluate the efficacy of HHFO for apneic oxygenation during the apnea test, in comparison with the recommended method using CPAP.
Adult intensive care unit patients
fulfilling all criteria for clinical brain death, for whom confirmation of the absence of spontaneous breathing requires performance of an apnea test
And for whom consent to participate in the study was sought from a trusted person or a family member
History of chronic obstructive pulmonary disease (COPD) classified as GOLD stage III or IV.
Current extracorporeal life support, including veno-arterial (VA) or veno-venous (VV) extracorporeal membrane oxygenation (ECMO).
PaO₂/FiO₂ ratio ≤ 150 on the most recent arterial blood gas analysis, obtained within 24 hours prior to the screening visit.
Presence of at least one clear or absolute contraindication to the procurement of at least one organ.
Crossover
Apnea test under HHFO followed by an apnea test under CPAP.
Other interventionFor each 10-minute apnea test, regardless of the oxygenation device used, arterial blood gas will be analysed and heart rate, arterial pressure, and pulse oximetry will be recorded in 2-minute intervals.
Apnea test under CPAP followed by an apnea test under HHFO.
Other interventionFor each 10-minute apnea test, regardless of the oxygenation device used, arterial blood gas will be analysed and heart rate, arterial pressure, and pulse oximetry will be recorded in 2-minute intervals.
Change in PaO₂ (mmHg) between the beginning and the end of an apnea test under HHFO and CPAP
To demonstrate the non-inferiority of humidified high-flow oxygen compared to continuous positive airway pressure in apneic oxygenation for apnea testing.
Evolution of arterial blood PaO2 parameters during the apnea test under HHFO and the apnea test with CPAP
Recording of PaO2 values measured in 2-minute intervals during the apnea test under HHFO and apnea test with CPAP
Evolution of arterial blood PaCO2 parameters during the apnea test under HHFO and the apnea test with CPAP
Recording of PaCO2 values measured in 2-minute intervals during the apnea test under HHFO and apnea test with CPAP
Evolution of arterial blood pH parameters during the apnea test under HHFO and the apnea test with CPAP
Recording of pH values measured in 2-minute intervals during the apnea test under HHFO and apnea test with CPAP
Evolution of arterial blood pressure during the apnea test under HHFO and the apnea test with CPAP
Recording of arterial blood pressure measured in 2-minute intervals during the apnea test under HHFO and with CPAP.
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Centre Hospitalier Régional d'Orléans
Lead sponsor
Fisher and Paykel Healthcare
Collaborator
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