Brain death (BD) determination differs slightly amongst European countries. In Italy, assessment requires a 6-hour legal observation which includes:
– Coma status with absent brainstem reflexes
– Absence of cortical electric activity as documented on an electroencephalogram
– Absence of spontaneous breathing as documented by an apnea test (AT)
Positivity of AT is confirmed by the absence of respiratory movements and arterial carbon dioxide partial pressure (PaCO2) >60 mmHg, with an increase of >20 mmHg from baseline. In previously chronic hypercapnic patients, pH rather than PaCO2 variations are taken into account. Serious complications may occur during AT, including hypoxemia, barotrauma, pneumothorax, air trapping and hypotension. In addition, the rate of aborted ATs has been reported as up to 3%. In patients undergoing veno-arterial extracorporeal membrane oxygenation (VA-ECMO), decrease of gas flow and increase in fraction of inspired oxygen (FiO2) are usually required.
The authors of this paper performed a retrospective analysis of prospectively collected data aimed to investigate the feasibility and efficacy of an AT technique based on the application of positive end expiratory pressure (PEEP) and pulmonary recruitment in a large cohort of brain-dead patients.
Before the AT: Respiratory rate was titrated to obtain PaCO2 of 40-45 mmHg; low tidal volumes were used in addition with periodic hyperinflation of the lungs. FiO2 and PEEP were adjusted to obtain a PaO2 > 90 mmHg. A short pre-oxygenation period of 5 minutes was also performed.
During the AT: The patient was disconnected from the ventilator and connected to a resuscitator bag providing 8 L/min of oxygen. An adjustable PEEP valve was added in order to maintain the same previous PEEP level.
After the AT: Patients were reconnected to the ventilator with the same settings and recruitments manoeuvres were performed in case of SpO2< 92%.
In patients undergoing ECMO, the same procedure was applied. Further, blood flow was not changed, gas flow was reduced to 1L/min and FiO2 to the membrane lung was increased to 100%.
Out of 169 patients enrolled in the analysis, 25 were receiving VA-ECMO support. No AT interruptions, pneumothorax, pneumomediastinum, cardiac arrhythmias and cardiac arrest were reordered. Fluid boluses and increase or starting of vasopressors were necessary in less than 10% of patients, without differences between ECMO and non-ECMO patients with regards to the need for haemodynamic interventions. Severe hypoxemia occurred in 2.4% and 8% of ATs performed in non-ECMO and ECMO patients; more frequently in previously hypoxemic patients (11.1% vs. 4.8%, p=0.002).
Although this study was single-centre and retrospective, it represents a useful and detailed insight into effective ventilatory management of AT in BD patients.
Take home message
During brain death assessment, an apnea test strategy based on PEEP application and lung recruitment is safe and effective in reducing the rate of potentially deleterious haemodynamic and respiratory complications.
This article review was prepared and submitted by Gennaro De Pascale on behalf of the NEXT Committee.
Giani et al. Apnea test during brain death assessment in mechanically ventilated and ECMO patients. Intensive Care Medicine. (January 2016) 42:72 – 81