Brainstem response patterns in deeply-sedated critically-ill patients predict 28-day mortality
Brainstem response patterns in deeply- sedated critically-ill patients predict 28-day mortality
Benjamin Rohaut 0 1 3
Raphael Porcher 1
Tarik Hissem 1
Nicholas Heming 1 2
Patrick Chillet 1
Kamel Djedaini 1
Guy Moneger 1 2
Stanislas Kandelman 1
Jeremy Allary 1
Alain Cariou 1
Romain Sonneville 1
AndreÂ a Polito 1 2
Marion Antona 1
Eric Azabou 1 5
Djillali Annane 1 2
Shidasp Siami 1
Fabrice ChreÂ tien 1
Jean Mantz 1 4
Tarek Sharshar 1 2
0 0 Department of Anesthesiology and Intensive Care Unit, AP-HP, Beaujon±Claude Bernard Hospital, Diderot University , Paris , France , 11 Intensive Care Unit, AP-HP, Cochin Hospital, Descartes University , Paris , France , 12 Medical Intensive Care Unit, AP-HP, Bichat±Claude Bernard Hospital, Diderot University , Paris , France , 13 Surgical Intensive Care Unit, AP-HP, Cochin Hospital, Descartes University , Paris , France
1 Editor: Pierre Moine, University of Colorado Denver , UNITED STATES
2 General Intensive Care Unit, AP-HP, Raymond Poincar eÂ Hospital, University of Versailles Saint-Quentin en Yvelines, Garches, France, 8 General Intensive Care Unit, Chalons en Champagne Hospital, Chalons en Champagne, France, 9 General Intensive Care Unit, Geoffroy Saint-Hilaire Hospital , Paris France
3 INSERM, U 1127, Paris, France, 5 Center for Clinical Epidemiology, AP-HP, H oÃtel Dieu Hospital, Descartes University , Paris , France , 6 General Intensive Care Unit, Sud Essonne Hospital , Etampes , France
4 Department of Anesthesiology and Intensive Care Unit, AP-HP, Georges Pompidou European Hospital, Descartes University , Paris , France
5 Department of Physiology, AP-HP, Raymond Poincar eÂ Hospital, University of Versailles Saint-Quentin en Yvelines, Garches, France, 15 Laboratory of Human Histopathology and Animal Models, Pasteur Institut , Paris , France , 16 Department of Neuropathology, Saint Anne Hospital, Descartes University , Paris , France
Data Availability Statement: All relevant data are
within the paper and its Supporting Information
Funding: The authors received no specific funding
for this work.
Competing interests: The authors have declared
that no competing interests exist.
Background and purpose
Deep sedation is associated with acute brain dysfunction and increased mortality. We had
previously shown that early-assessed brainstem reflexes may predict outcome in deeply
sedated patients. The primary objective was to determine whether patterns of brainstem
reflexes might predict mortality in deeply sedated patients. The secondary objective was to
generate a score predicting mortality in these patients.
Observational prospective multicenter cohort study of 148 non-brain injured deeply sedated
patients, defined by a Richmond Assessment sedation Scale (RASS) <-3. Brainstem
reflexes and Glasgow Coma Scale were assessed within 24 hours of sedation and
categorized using latent class analysis. The Full Outline Of Unresponsiveness score (FOUR) was
also assessed. Primary outcome measure was 28-day mortality. A ªBrainstem Responses
Assessment Sedation Scoreº (BRASS) was generated.
Two distinct sub-phenotypes referred as homogeneous and heterogeneous brainstem
reactivity were identified (accounting for respectively 54.6% and 45.4% of patients).
Homogeneous brainstem reactivity was characterized by preserved reactivity to nociceptive stimuli
and a partial and topographically homogenous depression of brainstem reflexes.
Heterogeneous brainstem reactivity was characterized by a loss of reactivity to nociceptive stimuli
associated with heterogeneous brainstem reflexes depression. Heterogeneous
sub-phenotype was a predictor of increased risk of 28-day mortality after adjustment to Simplified Acute
Physiology Score-II (SAPS-II) and RASS (Odds Ratio [95% confidence interval] = 6.44
[2.63±15.8]; p<0.0001) or Sequential Organ Failure Assessment (SOFA) and RASS (OR
[95%CI] = 5.02 [2.01±12.5]; p = 0.0005). The BRASS (and marginally the FOUR) predicted
28-day mortality (c-index [95%CI] = 0.69 [0.54±0.84] and 0.65 [0.49±0.80] respectively).
In this prospective cohort study, around half of all deeply sedated critically ill patients displayed an early particular neurological sub-phenotype predicting 28-day mortality, which may reflect a dysfunction of the brainstem.
Current guidelines recommend that sedation be monitored, titrated and discontinued as soon
as possible and that benzodiazepines be avoided in critically ill patients [
]. However, deep
sedation, defined by a Richmond Assessment Sedation Scale (RASS) below -3, may be required
in a handful of conditions, including severe respiratory failure and septic shock [
deep sedation is administered in 30 to 70% of all ICU patients [4±8], and benzodiazepines
remain the most commonly used sedative in Intensive Care Units (ICU; [
]). Deep sedation is
associated with delayed awakening, increased mortality [
], acute brain dysfunction [10±
12] and a long-term impact on mental health [
]. The mechanisms linking deep sedation to
mortality and delirium remain unclear. Here, we hypothesized that brainstem dysfunction
might be involved, as early abolition of the cough and oculocephalic reflexes is associated with
mortality and delirium [
]. In order to further improve our understanding of the interaction
between sedation, critical illness and brainstem reflexes, we sought to define particular
neurological sub-phenotypes in non-brain injured, deeply sedated, critically ill patients.
The primary objective of this study was to determine whether a particular pattern of
brainstem responses predicted 28-day mortality in deeply sedated, critically ill patients; the
secondary objective was to generate and validate a prognostic score of mortality in these patients,
based on clinical examination of brainstem reflexes.
Materials and methods
Study design and setting
This was a prospective, multicenter, observational study, approved by the ethics committee of
Saint-Germain-en-Laye, France (nÊ05043). Due to the observational nature of the study, the
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need for written informed consent was waived. Patients were recruited in four medico-surgical
and two surgical ICUs. Inclusions took place over three distinct periods: between December
2007 and June 2009, between November 2011 and August 2012 and between December 2012
and August 2014. We reasoned that repeating short periods of inclusion would optimize
patients' recruitment. Forty-six patients enrolled over the first period (from 2007 to 2009)
were derived from the validation set of a previously described study, and included all patients
with a RASS<-3 [
]. The Strengthening the Reporting of Observational Studies in
Epidemiology (STROBE) guidelines were followed thoroughly [
Eligible patients were invasively mechanically ventilated and required continuous intravenous
sedation by midazolam alone or in association with sufentanil for at least 12 hrs. All
participants were deeply sedated, defined by a RASS<-3, because of high discomfort, threatening
agitation, sever ventilator asynchrony or severely impaired gas exchange. Patients were excluded
if they were treated by neuromuscular blocking agents, were affected by a peripheral
neurologic disorder involving the cranial nerves or had been referred to the ICU for a stroke, central
nervous system infection, neuro-inflammatory disease or traumatic brain injury.
Decisions to initiate, adjust and discontinue sedation were taken by the physicians in charge.
Depth of sedation was assessed every four hours using the RASS [
]. Onset time and the reason
for initiating sedation were recorded. The cumulative administered doses of midazolam and
sufentanil were expressed as milligrams/kilogram and micrograms/kilogram. Discontinuation
of sedation occurred through daily interruption and/or titration. Discontinuation was decided
every morning. Titration was monitored at least twice daily using the RASS.
The detailed procedure pertaining to neurological examination is described elsewhere [
Briefly, we assessed: 1) the level of consciousness prior to intubation and initiation of sedation,
using the Glasgow Coma Scale (GCS); 2) the depth of sedation using the RASS; 3) reactivity,
using the motor and eye response components of the GCS; 3) the brainstem reflexes, including
pupil size (miosis, normal, or mydriasis), pupillary light reflex, corneal reflex, grimace in
response to a bilateral and strong pressure to the retro-mandibular region, oculocephalic reflex
(OCR) to lateral passive head rotation, and cough reflex in response to tracheal suctioning.
Reactivity and brainstem reflexes were scored as present or abolished (see S1 Appendix).
Additionally, the Full Outline Of Unresponsiveness (FOUR)-score was assessed [
examination was performed following 24 ± 12h hours of the initiation of sedation.
Baseline clinical and biological data
Demographic characteristics, body weight, the date, time, cause and category (medical or
surgical) of ICU admission, co-morbidities, risk factors for delirium using the Pre-Deleric Score
], date, time and cause of invasive mechanical ventilation initiation were recorded. The
Simplified Acute Physiological Score II (SAPS-II; ), the Sequential Organ Failure
Assessment (SOFA; [
]), as well as key interventions and standard biological tests needed to
calculate these scores were recorded. The results of neurological examination on day 4 in patients
with RASS<-3, of brain imaging and of somatosensory and brainstem auditory evoked
potentials (SSEP and BAEP), when available, were also recorded. The SSEP medullo-cortical
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(P14-N20) and BAEP ponto-mesencephalic (III-V) conduction times were collected and
considered delayed when the mean value of the left and right side was greater than the mean +2.5
SD of the inter-latencies obtained in 20 healthy subjects (>4.6 ms and >2.2 ms respectively).
Clinical, biological and brain imaging (CT and/or MRI) data were collected as part of the
routine care, evoked potentials originated from a preliminary neurophysiological study.
Primary outcome was the 28-day mortality. The date and cause of death were collected.
Secondary outcome was altered mental status following discontinuation of sedation, defined by
the occurrence of delayed awakening and/or delirium. Delayed awakening and delirium after
discontinuation of sedation were assessed daily using the RASS and the confusion assessment
method for the ICU (CAM-ICU; [
]), respectively. Delayed awakening was defined by
RASS<-1 after 3 days of discontinuation of sedation. The duration of mechanical ventilation
and the length of stay in the ICU were also collected.
Bias and confounding factors
We sought to mitigate potential confounding factors that may have influenced neurological
examination and relevant outcomes. Neurological examination was performed by a specifically
trained senior ICU physician. Inter-observer agreement for neurological examination was
previously shown to be satisfactory (kappa scores ranged from 0.62 to 1; [
]. Management of
sedation was assessed by collecting the duration and the modalities of discontinuation of
sedation and RASS. The cause of death and its main risk factors were collected, including severity
scores (SAPS-II and daily SOFA) and the cause of critical illness. In this manner, we were able
to compare groups by study period, ensuring that the management of sedation was appropriate
and that the selected population was representative of severe clinical situations where patient
could receive deep sedation.
Latent class analysis (LCA). Patients were classified into clinical sub-phenotypes using
latent class analysis (LCA). LCA is a statistical model that aims at identifying unobservable
subgroups within a population. It posits that there is an underlying unobserved categorical
variable that divides the population into a certain number of exclusive groups, called latent classes.
LCA thus aims at inferring the number of classes and the class membership of individuals
from a set of measured variables [
] No outcome parameter was included in the LCA.
Brainstem reflexes assessed on day 1 were incorporated into this analysis as dichotomous
variables (present or absent). GCS eye and motor sub-scores were also taken into account, after
categorization as a binary variable (1 vs >1).
The optimum number of latent classes was determined by looking at the log-likelihood, the
Akaike information criterion (AIC), the Bayesian information criterion (BIC) as well as
goodness-of-fit statistics (Pearson chi-square, likelihood-ratio chi-square, G-square and bootstrap
likelihood ratio test (BLRT); S1 Table). In case of disagreement between the various indexes,
we gave priority to the BIC. Once a model was selected, patients were assigned their most likely
class to provide an exploratory analysis of differences between the latent classes, thereafter
Patient characteristics were compared between sub-phenotypes using Fisher's exact tests
and Wilcoxon rank-sum tests. Association with 28-day mortality was assessed after adjusting
for the SAPS-II or the SOFA (with and without the RASS) using logistic regression models,
which were compared to similar models without the LCA sub-phenotype.
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Construction of the "Brainstem Responses Assessment Sedation score" (BRASS).
Using the same variables as used for LCA, namely: day 1 pupillary light reflex, corneal reflex,
oculocephalic reflex, grimacing to pain, cough reflex, miosis and GCS eye and motor
responses, we constructed a prognostic score called "Brainstem Responses Assessment
Sedation score" (BRASS). Multiple logistic regression with a backward selection model was used
with a p-value cut off at 0.15. Once variables of interest had been selected, two-way interactions
between selected variables were then tested. Goodness-of-fit of the model was checked using le
Cessie and van Houwelingen's test [
]. Internal validation of the model, assessing robustness
of the model selection procedure and bias correction of model calibration was performed by
bootstrapping (200 bootstrap samples; S2 Fig; [
]). Once the final model selected, scores were
attributed to the variables by roughly rounding the regression coefficients to the nearest
integer (S2 Table; see also S2 Appendix for more details). Since the highest category of the model
only contained one patient, the highest and the second highest categories of the model were
combined. 28-day mortality was subsequently compared between the different score
categories. External validation of the BRASS was performed using a subset of 46 deeply sedated
patients from a previous study [
]. The discriminative ability of a model was assessed using
the c-index (identical to the area under the receiver operating characteristics (ROC) curve
]). No data for calculating the sample size for a latent class analysis or development of a
prognostic score was available. We therefore included in the current study a number of
patients similar to that of our previous study which assessed the prognostic value of the
abolition of the cough reflex in deeply sedated ICU patients [
]. All tests were two-sided.
Categorical variables were expressed as numbers (percentage), quantitative variables as median (first to
third quartile, Q1 to Q3) or mean (standard deviation, SD). Analyses were performed using
the R statistical software version 3.0.2 [
]. Latent class analyses were performed using the
poLCA package [
Description of the population
Among 655 consecutive patients receiving deep sedation within 12 hours of admission, a total
of 507 patients were excluded, mainly because of a preexisting and/or current acute
neurological disease (n = 347, Fig 1). Overall, 148 patients were enrolled. At the time of inclusion, the
RASS was -5 in 97 (66%) patients and -4 in 51 (44%) patients (Table 1). Median [interquartile
range Q1 to Q3] duration of midazolam administration was 4 [3 to 7] days and awakening
followed after 1 [0 to 2] days (S1 Fig). The most consistently found reflex in our cohort was the
corneal reflex. By opposition, the OCR was the most frequently abolished reflex (Table 2).
Demographic data, severity of critical illness, cumulative doses of midazolam and sufentanil,
RASS and neurological examination did not differ significantly between the cohorts of each
Classification of patients by latent class analysis (LCA)
Brainstem reflex assessment was incomplete in seven patients. We performed LCA in 141
(95%) patients, which took exclusively into account neurological responses (Table 3). Two
sub-phenotypes were identified, in 77 (54.6%) and 64 (45.4%) patients and were respectively
called homogeneous and heterogeneous brainstem reactivity profiles. In comparison to the
homogeneous profile, heterogeneous profile was characterized by less ocular and motor
reactivity to nociceptive stimulation. The heterogeneous sub-phenotype was also associated with a
decrease in proportion of preserved pupillary light, corneal and cough reflexes as well as the
abolition of a large proportion of both grimace in response to pain and OCR (Fig 2). Neither
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Fig 1. Flow chart. NMBA: neuromuscular-blocking agent; RASS: Richmond Assessment Sedation Scale.
the period nor the center of inclusion accounted for observed differences between
homogeneous or heterogeneous sub-phenotypes. Patients with a heterogeneous profile were mainly
admitted for a medical cause and presented with higher severity scores (Table 3). Cumulative
administered doses of midazolam and sufentanil at the time of inclusion were comparable
between the two profiles, however the proportion of patients with a RASS of -5 was
significantly greater in the heterogeneous profile (Table 3). The median duration of sedation, the
median time to awakening and the proportion of non-sedated patients on day 4, did not
statistically differ between the two sub-phenotypes (Table 3).
Brain imaging was performed in 24 (16%) patients, including 13 MRI and 25 CT scans, and
was considered normal in 12/24 (50%) cases. No brainstem lesion was observed (non-specific
periventricular white matter lesions (8/24, 33.3%) and brain atrophy (6/24, 25%) were the
most frequent findings; ischemic stroke was observed in 2 patients). Evoked potentials,
performed in 28 (19%) patients, displayed increased medullo-cortical and/or
ponto-mesencephalic conduction times in 13 patients (46%; Table 3).
Relationship between clinical profiles and outcomes
Forty-four (30%) patients died by day 28, mainly because of multiple organ failure (n = 34,
60%) or refractory hypotension (n = 9, 16%). Limitations of active treatments were decided for
14 (9%) patients, but were never based on the results of neurological examination on day 1.
Twenty-eight-day mortality was significantly higher in the heterogeneous profile than in the
homogeneous profile (52% versus 12%, respectively, p<0.0001, Table 3). The heterogeneous
sub-phenotype was associated with increased 28-day mortality, after adjustment on SAPS-II
(Odds Ratio [95% confidence interval] = 6.93 [2.88±16.7], p <0.0001), SAPS-II and RASS
(6.44 [2.63±15.8], p <0.0001), SOFA (5.13 [2.08±12.6], p = 0.0004) or SOFA and RASS (5.02
[2.01±12.5], p = 0.0005) (primary objective; Table 4). When restricting the analysis to patients
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a Data missing for six patients;
b Data missing for seven patients.
c ICU admission related to a proven or highly suspected bacterial infection.
d PREdicition of DELirium in ICu patients. The Pre-Deleric predicts the subsequent occurrence of delirium at
the time of ICU admission [
e Interval of time between midazolam discontinuation and awakening. Awakening was de®ned by eye
opening and visual contact >10 sec (RASS -1). Awakening could occur before discontinuation of sedation.
f Delirium was de®ned using the CAM-ICU .
g Delayed awakening was de®ned by RASS<-1 within 3 days of discontinuation of sedation. ICU: intensive
care unit; SAPS-II: Simpli®ed Acute Physiology Score II; ARDS: Acute Respiratory Distress Syndrome;
COPD: Chronic Obstructive Pulmonary Disease; SOFA: Sequential Organ Failure Assessment; RASS:
Richmond Assessment Sedation Scale; Data are presented as median (interquartile range Q1 to Q3) or
7 / 17
with RASS±5, the heterogeneous profile remained associated with 28-day mortality, after
adjustment on SAPS-II or SOFA (Table 4).
Delirium occurred in 62 (56%) and delayed awakening in 41 (38%) patients (Table 1). The
prevalence of delirium did not significantly differ between homogeneous and heterogeneous
profiles (49% vs. 68%, p = 0.10), while delayed awakening was significantly less frequent in the
homogeneous profile (24% vs. 59%, p = 0.0004; Table 3). Overall, altered mental status
following sedation discontinuation was significantly more frequent in the heterogeneous profile
(64% vs. 89%, p = 0.002).
Development and validation of the Brainstem Responses Assessment
Sedation Score (BRASS)
After rounding of logistic regression coefficients, absence of pupillary light reflex, cough reflex
and the combined absence of grimace and OCR were each attributed a score of 1. Absent
corneal reflex was attributed a score of 2 and absent grimace in the presence of OCR was
attributed a score of 3. The resulting sum theoretically ranged from 0 to 7, but since only one patient
in our cohort obtained a score over 5, we set a maximum value for the BRASS at 5 (Fig 3).
Both the BRASS and FOUR-score reliably predicted 28-day mortality, with a higher likelihood
ratio for the BRASS than the FOUR-score (49.5 vs. 37.1) and better discrimination, with
cindexes [95%CI] of 0.82 [0.74±0.90] for the BRASS vs. 0.76 [0.67±0.84] for the FOUR-score,
respectively, though the difference in c-index did not reach statistical significance (p = 0.10; S3
Table). The predictive value of the BRASS and FOUR-score was validated using the historical
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1 (1 to 4)
1 (1 to 1)
Latent class analysis (LCA) was performed on neurological responses assessed at day-1 only (8 variables in the bold rectangle).
a ICU admission related to a proven or highly suspected bacterial infection.
b PREdicition of DELirium in ICu patients. The Pre-Deleric predicts the subsequent occurrence of delirium at the time of ICU admission [
c Cumulative dose from onset of sedation and neurological examination (i.e. inclusion)
d Somatosensory evoked potentials enabled to assess the P14-N20 interlatency, which re¯ects the medullo-cortical conduction time; Auditory evoked
potentials allowed to assess the III-V interlatency, which re¯ect the ponto-mesencephalic conduction time. The neurophysiological tests were performed in
28 (19%) patients.
e Awakening was de®ned by eye opening and visual contact >10 sec (RASS -1). Awakening could occur before discontinuation of sedation
f Delirium was de®ned using the CAM-ICU .
g Delayed awakening was de®ned by RASS<-1 within 3 days following the discontinuation of sedation.
h Proportion of patients free of sedation among patients alive at day 4.
ICU: intensive care unit; SAPS-II: Simpli®ed Acute Physiology Score II; SOFA: Sequential Organ Failure Assessment; GCS: Glasgow Coma Scale; FOUR:
Full Outline Of Unresponsiveness; RASS: Richmond Assessment Sedation Scale.
PLOS ONE | https://doi.org/10.1371/journal.pone.0176012
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Fig 2. Representation of homogeneous and heterogeneous profiles. The percentage of abolition of each
tested neurological responses in homogeneous and heterogeneous profiles are depicted. The heterogeneous
profile is characterized by a greater and more heterogeneous abolition of neurological responses.
RASS = -5 (N = 91)
OR (95% CI)
6.37 (2.28 to 17.8)
1.02 (1.00 to 1.05)
5.82 (2.04 to 16.6)
1.14 (1.00 to 1.31)
4.69 (1.60 to 13.7)
8.04 (3.44 to 18.8)
1.03 (1.01 to 1.06)
6.93 (2.88 to 16.7)
1.03 (1.01 to 1.06)
1.41 (0.54 to 3.72)
6.44 (2.63 to 15.8)
1.21 (1.07 to 1.38)
5.13 (2.08 to 12.6)
1.21 (1.06 to 1.38)
1.13 (0.42 to 3.03)
5.02 (2.01 to 12.5)
LCA: Latent Class Analysis; SAPS-II: Simpli®ed Acute Physiology Score II; SOFA: Sequential Organ Failure Assessment; RASS: Richmond Assessment
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Fig 3. 28-day mortality probability according to the BRASS. Mortality probability expressed in mean [95%
CI], BRASS: Brainstem Responses Assessment Sedation Score.
cohort of 46 sedated patients with RASS<-3, with c-indexes of 0.69 [0.54±0.84] for the BRASS
and 0.65 [0.49±0.80] for the FOUR-score, respectively (NS). This historical cohort was
comparable to the other cohorts of the present study regarding the SAPS-II (52 [40±63]), SOFA
(11 [10±15]), RASS (-5 [-5 to -5]) and 28-day mortality rate (n = 16 [34%]) but not for age
(67.0 ± 15.4 vs 59.7 ± 15.6, p = 0.004). Motor reactivity (1 [1 to 2] versus 1 [1 to 1], p = 0.015)
and cough reflex (72% versus 51%, p = 0.03) were more frequently abolished in the historical
The probability of 28-day mortality was improved in a model combining the SAPS-II and
BRASS compared to the SAPS-II alone (Net Reclassification Improvement (NRIc) 0.984, SE
0.200, p<0.0001; S4 Table). Similarly, the probability of 28-day mortality was improved in a
model combining the SOFA and BRASS compared to the SOFA alone (NRIc 1.004, SE 0.184,
Brainstem reflexes were also assessed on day 4 in 42 (61%) patients among the 69 (47%)
who had still a RASS < -3. All brainstem reflexes were present in more than 80% of patients,
except for the grimace and OCR which were detected in about 60% of the patients (S5 Table).
Finally the BRASS calculated at day 4 was significantly greater in non-survivors than survivors
(1 [0 to 2] versus 0 [0 to 0.25], p = 0.027).
The present study indicates that, in non-brain injured deeply sedated mechanically ventilated
patients, the motor and ocular reactivity to nociceptive stimuli combined with brainstem
responses can be classified into two separate clinical sub-phenotypes (i.e. homogeneous and
heterogeneous profiles). The former is characterized by a decreased reactivity to nociceptive
stimuli associated with homogeneous brainstem responses. The latter is characterized by a loss
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of reactivity to GCS nociceptive stimuli and a heterogeneous abolition of brainstem responses,
involving the grimace, OCR and to a lesser extent the cough reflex. The heterogeneous
subphenotype is a predictor of 28-day mortality, after adjustment on severity scores (i.e. SAPS-II
and SOFA) and RASS. This prediction of mortality is also found within the subgroup of
deepest sedated patients. In order to ensure that our phenotypic approach was clinically relevant,
we developed a clinical score (BRASS) in aiming to help physicians to assess brainstem
reactivity in a given deeply sedated patient. We found that the BRASS and the FOUR-score had a
relatively similar predictive value for 28-day mortality.
Overall, our findings help enhance the neurological assessment and prognostication of
deeply sedated non-brain injured mechanically ventilated critically ill patients. Indeed, the
neurological items incorporated in commonly used severity scores (SAPS-II and SOFA) are
those of the GCS, which does not include brainstem reflexes. Similarly, the assessment of
brainstem reflexes is not integrated into the RASS, which only assesses reactivity to verbal and
non-nociceptive physical stimulation. From a neurological, our approach is similar to that
proposed in comatose patients, where the assessment of brainstem reflexes completes the GCS.
Here, the assessment of brainstem responses completes the RASS in deeply sedated critically
ill patients. Therefore, our findings are likely to contribute to improving the care of deeply
sedated patients, since the assessment of brainstem reflexes can easily be performed by any
ICU physician. Our findings may also contribute to some extent to account for the relationship
between deep sedation and increased mortality reported by Shehabi and colleagues, inasmuch
as brainstem reflexes were not assessed in their study [
We hypothesized that the heterogeneous sub-phenotype may reflect a dysfunction of the
brainstem, accounting for mortality and delirium/delayed awakening since the brainstem
controls both vital functions and arousal. Evidence from our study and from previous studies may
suggest a dysfunction of the brainstem in critically ill patients. Critical illness is associated with
a degree of autonomic dysfunction such as impaired heart rate variability, which is associated
with increased mortality [
]. The increased brainstem conduction time that we observed is
consistent with this hypothesis, although evoked potentials were only assessed in a restricted
sample of subjects (Table 3).
The respective role of the general sickness and of deep sedation in the genesis of both
subphenotypes is unclear. Firstly, the heterogeneous profile does not match any previously
described syndrome and may not be explained by any single focal injury of the brainstem.
Indeed, abolition of the OCR, grimace and cough reflex indicates involvement of the midbrain,
pons and medulla. However, such an extensive brainstem injury is ruled out by the absence of
an upper motor neuron syndrome and no visible sub-tentorial abnormalities on brain imaging
(while acknowledging that the CT scan is not the most reliable method for investigating the
brainstem). The heterogeneous sub-phenotype is therefore likely to rely on a functional rather
than a structural origin; it can be therefore speculated that some neuro-anatomical centers are
more sensitive to deep sedation, critical illness or both. The arguments in favor of a role of
general sickness in generating the heterogeneous profile are that the infusion rate of midazolam
did not differ between the two sub-phenotypes; that severity scores were greater in the
heterogeneous profile and the fact that brainstem conduction times were increased, and these
measurements are not modified by midazolam [
]. Additional arguments stem from previous
studies. A systemic inflammatory response may trigger neuro-inflammation, as circulating
mediators can reach the brainstem through the area postrema . Thus, neuro-inflammation
and neuronal apoptosis have been evidenced within the brainstem in fatal cases of septic shock
[33±35]. These processes are infra-radiological, explaining why brain imaging does not reliably
succeed in detecting insults to the brainstem. Deep sedation may also play a role in generating
the heterogeneous profile; indeed most patients were conscious prior to the initiation of
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sedation and brainstem reflexes generally reappeared following cessation of sedation (S5
Table). It may even be speculated that the heterogeneous profile is in fact an up-to-now
unidentified level of deep sedation, not included in the RASS, reflecting over-sedation. Such
over-sedation may be related to impaired drug clearance. Indeed renal and hepatic failures
were observed more frequently in the heterogeneous profile. A trial assessing plasma levels of
midazolam and sufentanil might help confirm this hypothesis. Given these arguments and the
fact that our study is strictly observational, we definitely cannot delineate the respective roles
of the initial sickness versus deep sedation in generating the heterogeneous profile. Further
clinical and experimental studies on the subject are needed (a larger multicenter prospective
study is ongoing; ClinicalTrials.gov number: NCT02395861).
Limitations of the study
Our study has limitations. First, one may question the generalizability of our findings as they
were obtained in a selected population of deeply sedated mechanically ventilated critically ill
patients. Also, the BRASS was validated with a c-index of 0.69 in a restricted historical cohort,
but exhibited c-stats parameters not different from the FOUR-scores.
Second, the purpose of our study was in no way to promote the use of midazolam or of
early deep sedation, which may have deleterious effects [
]. The indications for deep
sedation in our patients were based on particularly severe situations where patients were obviously
highly uncomfortable or experiencing agitation, ventilator asynchrony or severely impaired
gas exchange. Recent studies indicate that ICU physicians use deep sedation in more than 30%
of sedated patients and that midazolam remains one the most commonly used sedative agents
together with propofol, and in combination with opioids [4±7,36]. Management of sedation,
and severity of critical illness in our study are comparable to those reported elsewhere [
This suggests that our population may be representative of deeply sedated ICU patients. It
would be of interest to assess neurological profiles in patients sedated by propofol, which
shares common molecular mechanisms with midazolam by acting at the GABA-A
receptorcoupled chloride channel.
Third, patients' characteristics, neurological responses, sedation regimens and outcomes
did not differ between centers, observers and study periods. This suggests that our results may
be extrapolated to other ICUs and other physicians.
Fourth, the discrepancy in the prevalence of abolished cough reflex between the historical
and the development cohorts could account for the relative weakness of BRASS validation.
This discrepancy might be related to the small size of the validation cohort but also to the fact
that patients of the historical group were less reactive to nociceptive stimulation [
]. All in all,
the BRASS remains efficient, as a c-index of 0.69 [0.54 to 0.84] denotes fair discrimination,
supporting the generalizability of our findings. Interestingly, we also found that BRASS at day
4 remained associated with mortality.
Fifth, LCA is an exploratory rather than a confirmatory procedure. LCA is associated with a
risk of reification, where identified latent classes are considered to be the actual types of
individuals in the population. Although it might be considered relatively small, the sample size of
our cohort was large enough to compute LCA [
]. It has to be noted that characteristics of the
sub-populations and management of sedation did not differ between centers or study periods.
We report, in approximately 50% of non-brain injured mechanically ventilated deeply sedated
critically ill patients, a particular neurological pattern within 24 hours of sedation,
characterized by a loss of reactivity to nociceptive stimuli and a heterogeneous abolition of brainstem
13 / 17
reflexes. When adjusted to severity scores, depth of sedation, this sub-phenotype was a robust
predictor of increased 28-day mortality, Our findings may suggest the existence of a brainstem
dysfunction that can be clinically detected using the BRASS or the FOUR-score.
S1 Fig. Proportion of sedated (a) and awake (b) patients over the first 28-day following
admission to the ICU. In a), patients were classified into four categories: 1) alive under
sedation, 2) dead under sedation, 3) dead following discontinuation of sedation, 4) alive following
discontinuation of sedation. In b), patients were classified into four categories: 1) alive not
awake, 2) dead not awake, 3) dead after awakening, 4) alive after awakening. Awakening was
defined by eye opening and visual contact >10 sec (RASS -1).
S2 Fig. Calibration plot for the model with neurologic responses . The solid and dotted
lines plot the actual versus model-predicted 28-day mortality. The dashed line represents
perfect calibration. Neurological responses included in the BRASS: pupillary light reflex, corneal
reflex, grimace in response to pain, oculocephalic and cough reflexes.
S1 Table. Indices for latent class models ranging from 1 to 5 classes. The bootstrap
likelihood ratio test (BLRT) yielded p<0.001 for a model with 2 vs 1 class, p = 0.085 for 3 vs 2 classes
and p = 0.033 for 4 vs 3 classes. AIC: Akaike Information Criterion, BIC: Bayesian Information
S2 Table. Construction of the Brainstem Responses Assessment Sedation Score (BRASS).
The score range from 0 to 7; OCR: oculephalic reflex.
S3 Table. Association of the BRASS and FOUR score with 28-day mortality. The p-values
compare the c-index of the models to the model with SAPS-II only. SAPS-II: Simplified Acute
Physiology Score II; BRASS: Brainstem Responses Assessment Sedation Score; FOUR: Full
Outline Of Unresponsiveness.
S4 Table. Statistical indexes of the final models. AIC and BIC for models with SAPS-II,
BRASS and both, as well as the NRIc and IDI for a model with the BRASS compared to a
model with SAPS-II alone. Results show a significant improvement of BRASS as compared to
SAPS-II. AIC: Akaike Information Criterion, BIC: Bayesian Information Criterion, NRIc: Net
Reclassification Improvement, IDI: Integrated Discrimination Improvement.
S5 Table. Brainstem reflexes at day 4 among patients deeply sedated (RASS < -3).
Neurological examination was available in 42 out of 69 patients who were alive and had a RASS < - 3
at day 4. Neurological examination was not systematically performed after day 1 in patients
with RASS remained below -3. It has to be reminded that brainstem reflexes were never
assessed in patients with RASS ± 3. All brainstem reflexes were more frequently present on
day 4 than on day 1 but also in patients without than with midazolam, except for the cough
reflex. Discontinuation of sedation does not imply that there was no persisting effect of
midazolam. Mid+: patient receiving continuous midazolam infusion.
14 / 17
S1 Appendix. Brainstem responses assessment in ICU Form.
S2 Appendix. Details regarding the calibration of the BRASS.
We thank all the caregivers of the Units which included patients in this study: 1) Raymond
PoincareÂ Hospital, APHPÐUniversity of Versailles Saint-Quentin en YvelinesÐGarches; 2)
Sud Essonne Hospital, Etampes; 3) Geoffroy Saint-Hilaire Hospital, Paris; 4) Chalons en
Champagne Hospital; 5) Beaujon Hospital, APHP±Claude Bernard Hospital, University
Diderot±Paris; 6) Bichat Hospital, APHP±Claude Bernard Hospital, University Diderot±Paris. 7)
Cochin Hospital, APHPÐUniversity ReneÂ Descartes±Paris.
We also thank all the members of the "Groupe d'Exploration Neurologique en ReÂanimation
(GENER)", led by Prof Tarek Sharshar (email: ) and Prof Jean Mantz.
Members of the GENER include: Nicolas Adam, Jeremy Allary, Nora Ait Hamou, Xavier
Ambrosi, Marion Antona, Eric Azabou, Omar Ben Hadj Salem, Guillaume Berquier, Francis
Bolgert, Alain Cariou, Patrick Chillet, Fabrice ChreÂtien, Vincent Degos, Sophie Demeret,
Chung Hi Do, Raphael Gaillard, SteÂphane Gaudry, Alexandra Grinea, Nicholas Heming, Tarik
Hissem, Bertrand Herman, Stanislas Kandelman, Jonathan Levy, Yann Lhermitte, Eric
Magalhaes, CleÂmence Marois, AureÂlien Mazeraud, Nicolas Mongardon, ReÂgine Morizot-Koutlidis,
Lionel Naccache, Vincent Navarro, HerveÂ Outin, Andrea Polito, Benjamin Rohaut, Shidasp
Siami, Romain Sonneville, Pierre Rocheteau, Franck Verdonk, Chuyen Vu Dinh, Nicolas
Weiss and Julie Zyss.
This study is dedicated to the memory of Prof Jean Mantz.
Formal analysis: BR RP DA EA FC MA TS.
Investigation: BR TH PC KD GM SK JA MA EA AC AP RS SS TS.
Conceptualization: BR TS RP.
Data curation: BR RP.
Methodology: RP BR TS.
Project administration: BR TS.
Software: BR RP.
Supervision: JM TS.
Writing ± original draft: BR RP NH JM TS.
Writing ± review & editing: BR RP NH JM TS.
15 / 17
16 / 17
Working Group on Sepsis-Related Problems of the European Society of Intensive Care Medicine.
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