Introduction
Brain tissue oxygen pressure (PtiO2) reflects brain oxygenation and is a useful tool in traumatic brain injury (TBI) patients. Increases in inspired oxygen fraction (FiO2) are related to improvement on PbrO2, but other approaches that aim to improve oxygenation, like increasing positive-end expiratory pressure (PEEP), were not deeply evaluated in humans.
Objective
The aim of this study was to evaluate the effects of three different PEEP levels on PbrO2 of hypoxemic severe TBI patients.
Methods
From February 2007 to February 2011, 36 severe TBI patients admitted to our intensive neurological unit were monitored with PtiO2 through the Licox device (Integra Neuroscience). Seventeen patients remained in the study according to the following inclusion criteria: ratio of arterial oxygen tension to fraction of inspired oxygen (PaO2/FiO2 ratio) <300; cerebral perfusion pressure (CPP) >60 mmHg; intracranial pressure (ICP) <20 mmHg; PtiO2 >20 mmHg; absence of any signal of brain deterioration. These patients were submitted to PEEP levels of 5, 10 and 15 cmH2O, each one for at least 20 minutes. During the three PEEP levels, PtiO2, pulse oxygen saturation (SpO2), ICP and CPP were monitored and statistically analyzed by ANOVA and Bonferroni methods. P < 0.05 was considered statistically significant.
Results
The increase of PEEP level from 5 to 15 cmH2O increased SpO2 from 95.5 ± 2.1 to 98.6 ± 1.2 (P = 0.0001) and PtiO2 from 27.8 ± 6.5 mmHg to 33.9 ± 6.7 mmHg, respectively (P = 0.0001). On the other hand, ICP and CPP did not present statistical significance according to the increase of PEEP levels (8.29 ± 4.44 mmHg to 8.65 ± 4.42 mmHg; P = 0.14 and 94.8 ± 8.2 to 94.6 ± 8.0 mmHg; P = 0.78, respectively). The main characteristics of the evaluated patients are described in Table 1. Changes in PtiO2 and CPP according to the PEEP levels are represented in Figures 1 and 2.
Table 1.
Baseline characteristics of the evaluated patients
| Baseline characteristic | Mean | SD |
|---|---|---|
| Age | 28.6 | 8.4 |
| APACHE II | 19.2 | 3.2 |
| Glasgow | 6.1 | 0.9 |
| FiO2 | 55.9 | 11.8 |
| PaO2/FiO2 ratio | 154 | 46.6 |
| PbrO2 | 27.7 | 6.5 |
| ICP | 8.3 | 4.4 |
| CPP | 94.8 | 8.2 |
| SpO2 | 95.5 | 2.1 |
APACHE II, Acute Physiology and Chronic Health Evaluation.
Figure 1.
Changes in PtiO2 according to the PEEP levels.
Figure 2.
Changes in CPP according to the PEEP levels.
Conclusion
In hypoxemic severe TBI patients, increasing PEEP levels from 5 to 10 and 15 cmH2O increased PtiO2, without increasing ICP and/or decreasing CPP. Increasing PEEP levels can be an alternative ventilatory approach to improve brain oxygenation besides FiO2.