Download Open lung ventilation in neurosurgery: an update on brain tissue

Acta Neurochir (2005) [Suppl] 95: 103–105
6 Springer-Verlag 2005
Printed in Austria
Open lung ventilation in neurosurgery: an update on brain tissue oxygenation
S. Wolf, D. V. Plev, H. A. Trost, and C. B. Lumenta
Department of Neurosurgery, Academic Hospital Munich-Bogenhausen, Technical University of Munich, Munich, Germany
Summary
Recently, we showed the feasibility of ventilating neurosurgical
patients with acute intracranial pathology and concomitant acute respiratory distress syndrome (ARDS) according the so-called Open
Lung approach. This technique consists of low tidal volume, elevated positive expiratory pressure (PEEP) level and initial recruitment maneuvers to open up collapsed alveoli. In this report, we focus
on our experience to guide recruitment with brain tissue oxygenation
(pbr O2 ) probes.
We studied recruitment maneuvers in thirteen patients with
ARDS and acute brain injury such as subarachnoid hemorrhage
and traumatic brain injury. A pbr O2 probe was implanted in brain
tissue at risk for hypoxia. Recruitment maneuvers were performed
at an inspired oxygen frcation (Fi O2 ) of 1.0 and a PEEP level of
30–40 cmH2 O for 40 seconds.
The mean Fi O2 necessary for normoxemia could be decreased
from 0.85 G 0.17 before recruitment to 0.55 G 0.12 after 24 hours,
while mean pbr O2 (24.6 mmHg before recruitment) did not change.
At a mean of 17 minutes after the first recruitment maneuver, pbr O2
showed peak a value of 35.6 G 16.6 mmHg, reflecting improvement
in arterial oxygenation at an Fi O2 of 1.0.
Brain tissue oxygenation monitoring provides a useful adjunct to
estimate the e¤ects of recruitment maneuvers and ventilator settings
in neurosurgical patients with acute lung injury.
Keywords: ARDS; mechanical ventilation; Open Lung; ICP; brain
tissue oxygenation; recruitment maneuver.
Introduction
Contemporary management of patients with acute
respiratory distress syndrome (ARDS) consists of ventilating with low tidal volumes of 6 ml/kg body weight
to avoid alveolar overdistention of the injured lung [1].
A more advanced approach advocates for the additional use of short periods of sustained high inflation
pressure to open up collapsed alveoli. After this recruitment maneuvers, elevated levels of PEEP are used
to maintain the recruited airspace, thus avoiding the
repeated opening and closing of lung tissue, again to
limit the damage of the lung induced by mechanical
ventilation [12]. Proposed in theory by Lachmann
more than a decade ago [8], this Open Lung approach
showed improved survival in a small, randomised,
controlled trial [2].
From the aforementioned as well as other ARDS
studies, neurosurgical patients were excluded due to
concerns of intracranial deterioration through the used
elevated levels of PEEP. However, our group recently
showed the feasibility of the Open Lung approach in
patients with acute brain lesions [14]. While this previous study mainly addressed safety concerns and investigated the influence of Open Lung ventilation on ICP,
the present report focuses on its impact on brain tissue
oxygenation (pbr O2 ). We hypothesized that pbr O2 may
provide a useful tool to estimate the e‰cacy of a recruitment maneuver and to guide the settings of mechanical ventilation.
Material and methods
We studied the clinical course of 13 patients with acute brain injury and concomitant ARDS, which was diagnosed according to
the consensus conference criteria [3]. Main neurosurgical diagnosis
was aneurysmal SAH (7 patients), traumatic brain injury (3 patients), intracranial hemorrhage (2 patients) and post surgery for
brain metastasis (1 patient). In all patients, the trachea were intubated and the lungs were mechanically ventilated (Puritan Bennett,
Tyco Healthcare, Mansfield, MA, USA). Patients were sedated with
fentanyl, midazolam and/or propofol. Paralysis was used as required.
In all patients, pbr O2 was measured with the Licox system (GMS,
Kiel, Germany). The pbr O2 probes were implanted in brain tissue estimated at highest risk of infarction, e.g. the vascular territory of the
vessel harbouring a clipped or coiled aneurysm or the more a¤ected
hemisphere after traumatic brain injury. ICP monitoring was performed via parenchymal devices (CODMAN microsensor, Codman,
Raynham, MA, USA and Spiegelberg III, Spiegelberg KG, Hamburg, Germany) or ventriculostomy. Monitoring data was collected
with multimodal monitoring software (ICUpilot, CMA, Solna, Sweden) with a frequency of 1 per minute.
S. Wolf et al.
104
Respiratory management: Chest X-ray and bronchoscopy was
performed as required and at least once before onset of Open Lung
ventilation to rule out pneumothorax and lobar atelectasis. Recruitment maneuvers were performed on an inspired oxygen fraction
(Fi O2 ) of 1.0 with a CPAP/PEEP level of 30–40 cmH2 O for 40 seconds and optional ventilation with 20 mmHg above that PEEP for a
few breathing cycles. After this recruiting maneuver, the PEEP level
was set to 5 cmH2 O higher than before and at least 15 cmH2 O. All
patients were ventilated with pressure controlled ventilation with
an I : E ratio of 1 : 1 to 1.4 : 1. Inspiratory pressure was adjusted to
achieve a tidal volume of 6 ml/kg body weight. Respiratory frequency was 15 to 30 per minute, depending on blood gas analysis to
achieve normocapnia as feasible. Recruitment was considered su‰cient if arterial pa O2 increased to more than 300 mmHg at a sustained Fi O2 of 1.0.
After recruitment, we first tried to decrease Fi O2 to at least 0.4,
with regard to an pa O2 around 100 mmHg and then to decrease the
PEEP level in steps of 1–2 cmH2 O. If derecruitment occurred after
decreasing the PEEP level, after suctioning or disconnection of the
ventilator system, another recruitment maneuver was performed
and PEEP was set 2 cmH2 O higher than before.
ICP was treated if persistently increased above 25 mmHg. We
aimed for a pbr O2 above 15 mmHg. If desaturation was pending, we
attempted to decrease ICP and to optimize mean arterial blood pressure, cardiac output, cardiac preload or pa CO2 , thus providing an
oxygenation oriented therapy [13].
For the cumulative analysis, the first recruitment maneuver of a
patient was considered as start of Open Lung ventilation, even if
this patient, as most were, was submitted to more than one. All statistic data are expressed as mean G standard deviation. Analysis was
performed with paired t-tests, as appropriate.
Table 1. Oxygenation, intracranial pressure (ICP) and Brain tissue
oxygen tension (pbr O2 ) before the first recruitment maneuver and 24
hours later
Fi O2 [mmHg]
Pa O2 /Fi O2
Pa CO2 [mmHg]
ICP [mmHg]
pbr O2 [mmHg]
Before first
recruitment
24 hours after
first recruitment
P Values
0.85 G 0.17
142 G 42
44.1 G 6.6
17.4 G 6.2
24.6 G 9.3
0.55 G 0.12
257 G 110
40.3 G 8.8
14.1 G 8.2
24.2 G 11.3
<0.001
<0.001
>0.05
>0.05
>0.05
PaO2 Arterial oxygen tension; PaCO2 arterial carbon dioxide
tension; FiO2 inspired fraction of oxygen. Data is expressed as
mean G standard deviation.
Results
In all but one patient, oxygenation improved after
initiation of Open Lung ventilation. No patient had to
be withdrawn from Open Lung ventilation due to a refractory increase in ICP or a desaturation episode of
pbr O2 . No side e¤ects of recruitment maneuvers like
pneumothorax or lasting hemodynamic instability
were noticed.
Mean Fi O2 necessary for a pa O2 of 100 mmHg
decreased gradually from 0.85 G 0.17 before the first
recruitment maneuver to 0.55 G 0.12 after 24 hours
(Table 1). The mean PEEP level used immediately
after the first recruitment to prevent loss of alveolar
recruitment was 18.2 G 4.2 cmH2 O.
Mean ICP was 17.4 G 6.2 mmHg before and
14.1 G 8.2 mmHg after 24 hours. pbr O2 was
24.6 G 9.3 mmHg before and 24.2 G 11.3 mmHg
after 24 hours. After the first recruitment maneuver,
a peak in pbr O2 was seen after a mean of 17
minutes (Fig. 1). Mean pbr O2 at this peak was
35.6 G 16.6 mmHg. Afterwards, mean pbr O2 increased further, reaching a plateau after 60 minutes
with a value of 42.5 G 19.6 mmHg.
Fig. 1. Time course of brain tissue oxygen tension ( pbr O2 ) and intracranial pressure (ICP). At time point 0, the first recruitment maneuver was performed. The shaded area denotes standard deviation of
pbr O2 , indicating heterogeneity in response to recruitment between
di¤erent patients
Discussion
There is an inconsistency in the literature on the
ways of performing recruitment as well as on the lasting e‰cacy of these recruitment maneuvers [10]. The
largest study assessing recruitment, performed by the
ARDS network [5], as well as a small observational
study performed in a neurosurgical patient population
were not able to demonstrate a lasting improvement in
oxygenation [4]. However, the PEEP level to prevent
loss of recruitment in these studies was not increased
after recruitment, which may partly explain the lack
of a beneficial e¤ect of the recruitment maneuvers [9,
11]. In theory, the best method to exploit the recruitment capacity of an ARDS lung is a decremental
PEEP trial as proposed by Hickling [7]. As this method
is more aggressive than our recruitment scheme, we
did not use it as a first approach of implementing
Open lung ventilation in neurosurgery: an update on brain tissue oxygenation
Open Lung ventilation in our patients with unknown
stability of hemodynamic situation and ICP when exposed to a recruitment maneuver.
Our data shows that Open Lung ventilation with
recruitment maneuvers had a lasting improvement
on arterial oxygenation in neurosurgical patients with
ARDS. In the 24 hours after the first recruitment
maneuver we were able to reduce Fi O2 keeping pa O2
above 100 mmHg and without detrimental e¤ect on
pbr O2 . Brain tissue oxygenation increased in the short
term following an increased arterial oxygenation after
pulmonary recruitment with unchanged Fi O2 . The
peak of pbr O2 at a mean of 17 minutes reflects the
improved arterial oxygenation induced by this first
recruitment maneuver. One patient failed to respond
to multiple recruitment maneuvers, and thus did not
show an increase in arterial oxygenation. This patient
also lacked the peak in pbr O2 observed in other patients. Presently we are unable to predict a certain response in an individual patient to recruitment and
therefore unable to provide an recruitment algorithm
suitable for all patients.
There are multiple reasons for a decrease in pbr O2
after the observed peak. If the PEEP used after recruitment is not su‰ciently high enough, the improvement in arterial oxygenation is not lasting in its full
extent over time and partial derecruitment will occur
again. Furthermore multiple parameters such as pa O2 ,
pa CO2 and a mean arterial pressure might influence
pbr O2 [6]. These parameters as well as the change in
PEEP level after recruitment may induce complex hemodynamic interactions which are not fully understood up to date and are di‰cult to monitor.
The presented data provides additional evidence
that Open Lung ventilation is feasible in neurosurgical
patients with ARDS. Albeit we did not experience adverse e¤ects of recruitment maneuvers and Open Lung
ventilation, we are aware that our data does not support the use of this ventilation strategy without concern. While careful hemodynamic and ICP monitoring
is mandatory, brain tissue oxygenation monitoring
provides a useful adjunct to visualize the e¤ects of
recruitment maneuvers and fine tuning ventilatory
settings.
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Correspondence: S. Wolf, Department of Neurosurgery, Academic Hospital Munich-Bogenhausen, Technical University of Munich, Englschalkinger Ctraße 77, 81925 München, Munich, Germany. e-mail: [email protected]