Apnea testing with continuous positive airway pressure for the diagnosis of brain death in a patient with poor baseline oxygenation status

Use of CPAP as an alternative to the apnea test during the determination of brain death in hypoxemic patients. Report of two cases

The apnea test, which involves disconnection from the mechanical ventilator, presents risks during the determination of brain death, especially in hypoxemic patients. We describe the performance of the apnea test without disconnection from the mechanical ventilator in two patients. The first case involved an 8-year-old boy admitted with severe hypoxemia due to pneumonia. He presented with cardiorespiratory arrest, followed by unresponsive coma due to hypoxic-ischemic encephalopathy. Two clinical exams revealed the absence of brainstem reflexes, and transcranial Doppler ultrasound revealed brain circulatory arrest. Three attempts were made to perform the apnea test, which were interrupted by hypoxemia; therefore, the apnea test was performed without disconnection from the mechanical ventilator, adjusting the continuous airway pressure to 10cmH2O and the inspired fraction of oxygen to 100%. The oxygen saturation was maintained at 100% for 10 minutes. Posttest blood gas analysis results were as follows: pH, 6.90; partial pressure of oxygen, 284.0mmHg; partial pressure of carbon dioxide, 94.0mmHg; and oxygen saturation, 100%. The second case involved a 43-year-old woman admitted with subarachnoid hemorrhage (Hunt-Hess V and Fisher IV). Two clinical exams revealed unresponsive coma and absence of all brainstem reflexes. Brain scintigraphy showed no radioisotope uptake into the brain parenchyma. The first attempt at the apnea test was stopped after 5 minutes due to hypothermia (34.9°C). After rewarming, the apnea test was repeated without disconnection from the mechanical ventilator, showing maintenance of the functional residual volume with electrical bioimpedance. Posttest blood gas analysis results were as follows: pH, 7.01; partial pressure of oxygen, 232.0mmHg; partial pressure of carbon dioxide, 66.9mmHg; and oxygen saturation, 99.0%. The apnea test without disconnection from the mechanical ventilator allowed the preservation of oxygenation in both cases. The use of continuous airway pressure during the apnea test seems to be a safe alternative in order to maintain alveolar recruitment and oxygenation during brain death determination.

Comparison of Two Apnea Test Methods, Oxygen Insufflation and Continuous Positive Airway Pressure During Diagnosis of Brain Death: Final Report

Introduction

Deterioration of the pulmonary function after the apnea test (AT) conducted with the classic oxygen insufflation AT (I-AT) is often observed during the brain death (BD) diagnosis procedure. In the present study, two AT methods were compared before a method is recommended for the currently revised Polish BD criteria.

Methods

Classic I-AT and continuous positive airway pressure AT (CPAP-AT) were performed in 60 intensive care unit patients. I-AT was performed at the end of two series of clinical tests, and approximately 1–1.5 h later, after BD was confirmed, a different method, CPAP-AT with 100% FiO₂ and CPAP value of 10 cm H₂O provided by a ventilator in CPAP mode was performed. The patients in I-AT and CPAP-AT groups were further divided into two subgroups: non-hypoxemic (NH) with good lung function before AT (PaO₂/FiO₂ index ≥ 200 mmHg) and hypoxemic (H) with poor lung function (PaO₂/FiO₂ index < 200 mmHg). PaO₂ and PaCO₂ were recorded prior to I-AT and CPAP-AT at time-point one (T1), 5 min after each test at time-point two (T2), and after 10 min prior to the end of tests at time-point three (T3). The I-AT NH subgroup consisted of 50 patients, and CPAP-AT NH subgroup 43 patients. The I-AT H subgroup consisted of 10 patients, and the CPAP-AT H subgroup 17 patients.

Results

In the I-AT NH subgroup, a gradual decrease in PaO₂/FiO₂ was observed throughout the AT but not in the CPAP-AT NH subgroup. The PaO₂/FiO₂ ratio during the AT in the CPAP-AT H group was stable with a slight tendency to increase but not in the I-AT H group. During the first 5 min of the AT, the mean increase in CO₂ was approximately 5 mmHg/min. Most patients in all groups met the AT criteria after 5 min of the test.

Conclusions

The results from the study show that I-AT may compromise pulmonary function in some cases and is one of the reasons for the recommendation of a safer option, CPAP-AT, in the currently revised Polish BD criteria. During AT, the mean CO₂ increase rate was 5 mmHg/min, which, in most patients, would allow the test to be completed after just 5 min.

Prevention of Hypoxemia During Apnea Testing: A Comparison of Oxygen Insufflation And Continuous Positive Airway Pressure

BACKGROUND

Apnea testing is an essential step in the clinical diagnosis of brain death. Current international guidelines recommend placement of an oxygen (O₂) insufflation catheter into the endotracheal tube to prevent hypoxemia, but use of a continuous positive airway pressure (CPAP) valve may be more effective at limiting arterial partial pressure of O₂ (PO₂) reduction.

METHODS

We performed a multicenter study assessing consecutive apnea tests in 14 intensive care units (ICUs) in two cities utilizing differing protocols. In one city, O₂ catheters are placed and arterial blood gases (ABGs) performed at intervals determined by the attending physician. In the other city, a resuscitation bag with CPAP valve is attached to the endotracheal tube, and ABGs performed every 3-5 min. We assessed arterial PO₂, partial pressure of carbon dioxide (PCO₂), pH, and blood pressure at the beginning and termination of each apnea test.

RESULTS

Thirty-six apnea tests were performed using an O₂ catheter and 50 with a CPAP valve. One test per group was aborted because of physiological instability. There were no significant differences in the degree of PO₂ reduction (-59 vs. -32 mmHg, p = 0.72), rate of PCO₂ rise (3.2 vs. 3.9 mmHg per min, p = 0.22), or pH decline (-0.02 vs. -0.03 per min, p = 0.06). Performance of ABGs at regular intervals was associated with shorter test duration (10 vs. 7 min, p < 0.0001), smaller PCO₂ rise (30 vs. 26 mmHg, p = 0.0007), and less pH reduction (-0.20 vs. -0.17, p = 0.0012). Lower pH at completion of the apnea test was associated with greater blood pressure decline (p = 0.006).

CONCLUSION

Both methods of O₂ supplementation are associated with similar changes in arterial PO₂ and PCO₂. Performance of ABGs at regular intervals shortens apnea test duration and may avoid excessive pH reduction and consequent hemodynamic effects.

Apnea testing using the oxygen insufflation method for diagnosis of brain death may compromise pulmonary function

INTRODUCTION

The aim of our study was to compare the reliability and safety of the classical I-AT with the continuous positive airway pressure apnea test (CPAP-AT).

MATERIAL AND METHODS

In the group of 48 patients (group O), an I-AT was performed at the end of BD diagnostic procedures, and approximately 1-1.5h later CPAP-AT with 100% FiO₂ and CPAP of 10cm H₂O, provided by ventilator in CPAP mode. After pre‑oxygenation with 100% FiO₂ for 10min, the PaO₂/FiO₂ ratio was recorded prior to I-AT at time-point one (T1) and prior to CPAP-AT at time-point two (T2). Group O was categorized into subgroup N-H (non-hypoxemic), consisting of 41 patients with good lung function, and subgroup H (hypoxemic) consisting of 7 patients with poor lung function. Within each subgroup PaO₂/FiO₂ at T1 and T2 were compared.

RESULTS

In Group O, PaO₂/FiO₂ decreased from 321±128mmHg at T1 to 291±119mmHg at T2 (p=0.004). In subgroup N-H, PaO₂/FiO₂ declined from 355±103 to 321±100mmHg (p=0.008), and in subgroup H, PaO₂/FiO₂ remained almost unchanged. Additionally, in 4 patients from subgroup N-H, PaO₂/FiO₂ decreased below 200mmHg at T2.

CONCLUSIONS

Our study indicates that I-AT may compromise pulmonary function and this may support the recommendation of safer CPAP-AT alternative.

Novel method of delivery of continuous positive airway pressure for apnea testing during brain death evaluation

Background

There are several methods for apnea testing for the evaluation of neurological death, including oxygen via T-piece, oxygen cannula inserted into the endotracheal tube, and continuous positive airway pressure (CPAP). Lung suitability for transplantation is determined in part by the partial pressure of arterial oxygen (PaO₂) to fraction of inspired oxygen (FiO₂; P:F) ratio. We hypothesized that delivery of CPAP during apnea testing using a novel method would improve post-test P:F ratios.

Methods

A retrospective review was performed at a level I trauma center for all patients undergoing apnea testing from 2010 to 2016. The CPAP system used a flow-inflating bag and was made available in 2012. It was used at the discretion of the clinician. Patients were classified as having an apnea test by CPAP or by non-CPAP method (T-piece, oxygen cannula in endotracheal tube, etc). The two groups were compared for baseline characteristics and the primary outcome of postapnea test P:F ratio.

Results

During the study period, 145 patients underwent apnea testing; 67 patients by the CPAP method and 78 by non-CPAP method. There were no significant differences in demographics, mechanism of brain injury, pneumonia rate, smoking status, or antibiotic usage between the two groups. The pretest P:F ratio was similar between groups, but the CPAP group had significantly higher post-test P:F ratio (304 vs 250, p=0.02). There were no reported complications arising from CPAP use.

Conclusions

We describe a novel method of delivering CPAP by a flow-inflating bag during examination for brain death. This method led to improved oxygenation, P:F ratios, and may decrease barotrauma. The flow-inflating bag was inexpensive, easily implemented, and without adverse effects. Multicentered, prospective trials are needed to elicit significant benefit in lung donation and transplantation.

Level of evidence

Level IV, diagnostic tests.

Boussignac CPAP system for brain death confirmation with apneic test in case of acute lung injury/adult respiratory distress syndrome - series of cases

Introduction

There are some patients with severe respiratory disturbances like adult respiratory distress syndrome (ARDS) and suspicion of brain death, for whom typical performance of the apneic test is difficult to complete because of quick desaturation and rapid deterioration without effective ventilation. To avoid failure of brain death confirmation and possible loss of organ donation another approach to apneic test is needed. We present two cases of patients with clinical symptoms of brain death, with lung pathology (acute lung injury, ARDS, lung embolism and lung infection), in whom apneic tests for recognizing brain death were difficult to perform. During typical performance of apneic test involving the use of oxygen catheter for apneic oxygenation we observed severe desaturation with growing hypotension and hemodynamic destabilization. But with the use of Boussignac CPAP system all necessary tests were successfully completed, confirming the patient’s brain death, which gave us the opportunity to perform procedures for organ donation. The main reason of apneic test difficulties was severe gas exchange disturbances secondary to ARDS. Thus lack of positive end expiratory pressure during classical performance of apneic test leads to quick desaturation and rapid hemodynamic deterioration, limiting the observation period below dedicated at least 10-minute interval.

Conclusion

The Boussignac CPAP system may be an effective tool for performing transparent apneic test in case of serious respiratory disturbances, especially in the form of acute lung injury or ARDS.