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Background: The apnea test (AT) is an important component in the determination of brain death/death by neurologic criteria (BD/DNC) and often entails disconnecting the patient from the ventilator followed by tracheal oxygen insufflation to ensure adequate oxygenation. To rate the test as positive, most international guidelines state that a lack of spontaneous breathing must be demonstrated when the arterial partial pressure of carbon dioxide (PaCO 2 ) ≥ 60 mm Hg. However, the loss of positive end-expiratory pressure that is associated with disconnection from the ventilator may cause rapid desaturation. This, in turn, can lead to cardiopulmonary instability (especially in patients with pulmonary impairment and diseases such as acute respiratory distress syndrome), putting patients at increased risk. Therefore, this prospective study aimed to investigate whether a modified version of the AT (mAT), in which the patient remains connected to the ventilator, is a safer yet still valid alternative., Methods: The mAT was performed in all 140 BD/DNC candidates registered between January 2019 and December 2022: after 10 min of preoxygenation, (1) positive end-expiratory pressure was increased by 2 mbar (1.5 mm Hg), (2) ventilation mode was switched to continuous positive airway pressure, and (3) apnea back-up mode was turned off (flow trigger 10 L/min). The mAT was considered positive when spontaneous breathing did not occur upon PaCO 2 increase to ≥ 60 mm Hg (baseline 35-45 mm Hg). Clinical complications during/after mAT were documented., Results: The mAT was possible in 139/140 patients and had a median duration of 15 min (interquartile range 13-19 min). Severe complications were not evident. In 51 patients, the post-mAT arterial partial pressure of oxygen (PaO 2 ) was lower than the pre-mAT PaO 2 , whereas it was the same or higher in 88 cases. In patients with pulmonary impairment, apneic oxygenation during the mAT improved PaO 2 . In 123 cases, there was a transient drop in blood pressure at the end of or after the mAT, whereas in 12 cases, the mean arterial pressure dropped below 60 mm Hg., Conclusions: The mAT is a safe and protective means of identifying patients who no longer have an intact central respiratory drive, which is a critical factor in the diagnosis of BD/DNC. Clinical trial registration DRKS, DRKS00017803, retrospectively registered 23.11.2020, https://drks.de/search/de/trial/DRKS00017803., Competing Interests: Conflicts of Interest: None of the authors reports any financial or nonfinancial interests that are directly or indirectly related to the work. Ethical Approval/Informed Consent: The authors confirm that the study was performed in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki and its later amendments. The study was approved by the local ethics committee (institutional review board registration number: 368/19), and informed consent from the next of kin was obtained for all patients., (© 2024. The Author(s).) more...

Objective: The time preceding brain death is associated with complex dysregulation including autonomic dysfunction that may compromise organ perfusion, thus inducing final organ failure. In this study, we assessed autonomic function in patients prior to brain death., Methods: In 5 patients (2 women, median 60 years, age range 52-75 years) with fatal cerebral hemorrhage or stroke and negative prognosis, we monitored RR-intervals (RRI), systolic and diastolic blood pressure (BP), and oxygen saturation. Adjustment of mechanical ventilation remained constant. We assessed autonomic function from spectral powers of RRI and BP in the mainly sympathetic low- (LF, 0.04-0.15 Hz) and parasympathetic high-frequencies (HF, 0.15-0.5 Hz), and calculated the RRI-LF/HF-ratio as index of sympathovagal balance. Three patients required norepinephrine (0.5-1.6 mg/h) for up to 72 h to maintain organ perfusion. Norepinephrine was reduced to 0.2-0.5 mg/h within 2 h before brain death was diagnosed according to the criteria of the German Medical Association. Wilcoxon test compared average values of ten 2-min epochs determined 2-3 h (measurement 1) and 1 h (measurement 2) before brain death., Results: We found higher systolic (127.3 ± 15.9 vs. 159.4 ± 44.8 mmHg) and diastolic BP (60.1 ± 15.6 vs. 74.0 ± 15.2 mmHg), RRI-LF/HF-ratio (1.2 ± 1.6 vs. 3.9 ± 4.0), and BP-LF-powers (2.7 ± 4.8 vs. 23.1 ± 28.3 mmHg²) during measurement 2 than during measurement 1 (p < 0.05)., Conclusions: The increase in BPs, in sympathetically mediated BP-LF-powers, and in the RRI-LF/HF-ratio suggests prominent sympathetic activity shortly before brain death. Prefinal sympathetic hyperactivity might cause final organ failure with catecholamine-induced tissue damage which impedes post-mortem organ transplantation. more...

Background: Transcranial color-coded duplex sonography (TCCD) can be used as an ancillary test for determining irreversible loss of brain function (ILBF) when demonstration of cerebral circulatory arrest (CCA) is required. However, visualization of the intracranial vessels by TCCD is often difficult, or even impossible, in this patient cohort due to elevated intracranial pressure, an insufficient transtemporal bone window, or warped anatomical conditions. Since extracranial color-coded duplex sonography (ECCD) can be performed without restriction in the aforementioned situations, we investigated the feasibility of omitting TCCD altogether, such that the ILBF examination would be simplified, without compromising on its reliability. Methods: A total of 122 patients were prospectively examined by two experienced neurointensivists for the presence of ILBF from01/2019-12/2021. Inclusion criteria were (i) the presence of a severe cerebral lesion on cranial CT or MRI, and (ii) brainstem areflexia. Upon standardized clinical examination, 9 patients were excluded due to incomplete brainstem areflexia, and a further 22 due to the presence of factors with a potentially confounding influence on apnea testing, EEG or sonography. A total of 91 patients were enrolled and underwent needle-EEG recording for >30min (= gold standard), as well as ECCD and TCCD. The sonographer was blinded to the EEG result. Results: All patients whose ECCD result was consistent with ILBF had this diagnosis confirmed by EEG (n = 77; specificity: 1). Both ECCD and EEG were not consistent with ILBF in a further 12 patients. In the remaining two patients, ECCD detected reperfusion due to long-lasting cerebral hypoxia; however, ILBF was ultimately confirmed by EEG (sensitivity: 0.975). This yielded a positive predictive value (PPV) of one and a negative predictive value of 0.857 for the validity of ECCD in ILBF confirmation. TCCD was not possible/inconclusive in 31 patients (34%). Conclusions: The use of ECCD for the confirmation of ILBF is associated with high levels of specificity and a high positive predictive value when compared to needle-electrode EEG. Thismakes ECCD a potential alternative to the ancillary tests currently used in this setting, but confirmation in a multi-center trial is warranted. [ABSTRACT FROM AUTHOR] more...