Cerebral tissue PO2 and SjvO2 changes during moderate hyperventilation in patients with severe traumatic brain injury

Abstract

Ninety-four tests consisting of 20-minute periods of moderate hyperventilation (27-32 mm Hg) were performed on different days in 36 patients with severe traumatic brain injury (Glasgow Coma Scale score < or = 8). Moderate hyperventilation resulted in a significant reduction in average ICP, but in seven tests performed in five patients it was ineffective. The response of SjvO2 and brain tissue PO2 to CO2 changes was widely variable and unpredictable. After 20 minutes of moderate hyperventilation in most tests (79.8%), both SjvO2 and brain tissue PO2 values remained above the lower limits of normality (50% and 10 mm Hg, respectively). In contrast, in 15 tests performed in six patients (16.6% of the studied population) brain tissue PO2 decreased below 10 mm Hg although the corresponding SjvO2 values were greater than 50%. The reduction of brain tissue PO2 below 10 mm Hg was favored by the low prehyperventilation values (10 tests), higher CO2 reactivity, and, possibly, by lower prehyperventilation values of cerebral perfusion pressure. In five of those 15 tests, the prehyperventilation values of SjvO2 were greater than 70%, a condition of relative hyperemia. The SjvO2 decreased below 50% in four tests; the corresponding brain tissue PO2 values were less than 10 mm Hg in three of those tests, whereas in the fourth, the jugular venous O2 desaturation was not detected by brain tissue PO2. The analysis of the simultaneous relative changes (prehyperventilation - posthyperventilation) of SjvO2 and brain tissue PO2 showed that in most tests (75.5%) there was a reduction of both SjvO2 and brain tissue PO2. In two tests moderate hyperventilation resulted in an increase of both SjvO2 and brain tissue PO2. In the remaining 17 tests a redistribution of the cerebral blood flow was observed, leading to changes in SjvO2 and brain tissue PO2 in opposite directions. CCONCLUSIONS. Hyperventilation, even if moderate, can frequently result in harmful local reductions of cerebral perfusion that cannot be detected by assessing SjvO2. Therefore, hyperventilation should be used with caution and should not be considered safe. This study confirms that SjvO2 and brain tissue PO2 are two parameters that provide complementary information on brain oxygenation that is useful to reduce the risk of secondary damage. Changes in SjvO2 and brain tissue PO2 in opposite directions indicate that data obtained from brain tissue PO2 monitoring cannot be extrapolated to evaluate the global cerebral perfusion.

Brain Tissue Oxygen Monitoring and the Intersection of Brain and Lung: A Comprehensive Review

“…Attempts to modulate hyperventilation therapy by targeting S jvO 2 revealed that maintaining a normal S jvO 2 did not protect the P btO 2 . 23 This study, along with others, 58 demonstrated that global measurements of brain oxygenation, such as with S jvO 2 , gives information complementary, but not identical, to that from regional P btO 2 measurements. It was also further confirmed that moderate hyperventilation decreases cerebral blood flow to a level that causes a decline in regional brain tissue oxygenation.…”

Practical and comprehensive guidelines for bedside cerebral hemometabolic multitherapeutic optimization

“…Indeed, we have also recently reported that global brain ischemia is absolutely rare in acute brain trauma, as evaluated by simultaneous arteriojugular oxygen and lactate differences 11 . Despite the above-mentioned findings, an alternative monitoring "modality" involving acute placement of brain tissue probes to evaluate focal oxygen tension 21 has claimed that hyperventilation is harmful. In this recent paper 21 , the authors found that even when the jugular catheter showed high cerebral venous oxygenation, hyperventilation dropped the brain tissue oxygen tension to so-called "critically low" levels.…”

“…Despite the above-mentioned findings, an alternative monitoring "modality" involving acute placement of brain tissue probes to evaluate focal oxygen tension 21 has claimed that hyperventilation is harmful. In this recent paper 21 , the authors found that even when the jugular catheter showed high cerebral venous oxygenation, hyperventilation dropped the brain tissue oxygen tension to so-called "critically low" levels. In this respect, however, it is well known that acute placement of brain tissue probes causes focal microvascular compression and distortion, besides focal blood-brain barrier disruption (because the probes are too stiff relative to the soft brain tissue).…”

“…Because normal physiological values are not even known, and because these focal brain tissue probes are highly invasive, their use can be regarded as gross animal experimentation in humans [21][22][23] , which should therefore be abandoned and eventually punished, rather than being commercially and industrially promoted. F F F F Future prospects uture prospects uture prospects uture prospects uture prospects Because a variety of acute intracranial insults (besides brain trauma) may be frequently associated with combined abnormalities regarding ICP, CPP, and CEO 2 , Table 1 shows a broad spectrum of acute intracranial disease processes in which our proposed monitoring and protocol could also be explored.…”

Expensive cerebral blood flow measurements alone are useless and misinformative in comatose patients: a comprehensive alternative

“…In this respect, it is obvious that any brain tissue probe causes focal microvascular compression and distortion, which may well explain focal microcirculatory compressive hypoxia, with resulting increase in lactate concentration, findings that would be just artifactual, however. Another highly biased report addressed focal "brain ischemia" associated with hyperventilation, even when jugular oxygen values were normal or high, but the brain tissue oxygen probe showed socalled "critically low" levels 25 . Because this kind of intentional misinformation may have serious implications with respect to patient care, a thorough discussion regarding the total lack of validation of any type of brain tissue probe has recently been published by our team 26 .…”