Brain tissue pO2 in relation to cerebral perfusion pressure, TCD findings and TCD-CO2-reactivity after severe head injury

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Abstract
As a reliable continuous monitoring of cerebral blood flow and/or cerebral oxygen metabolism is necessary to prevent secondary ischaemic events after severe head injury (SHI) the authors introduced brain tissue pO2 (ptiO2) monitoring and compared this new parameter with TCD-findings, cerebral perfusion pressure (CPP) and CO2-reactivity over time on 17 patients with a SHI. PtiO2 reflects the balance between the oxygen offered by the cerebral blood flow and the oxygen consumption by the brain tissue. According to TCD-CO2-reactivity PtiO2-CO2-reactivity was introduced. After initially (day 0) low mean values (ptiO2 7.7 +/- 2.6 mmHg, TCD 60.5 +/- 32.0 cm/sec and CPP 64.5 +/- 16.0 mmHg/, ptiO2 increased together with an increase in blood flow velocity of the middle cerebral artery and CPP. The relative hyperaemic phase on days 3 and 4 was followed by a decrease of all three parameters. Although TCD-CO2-reactivity was except for day 0 (1.4 +/- 1.5%), sufficient, ptiO2-CO2-reactivity sometimes showed so-called paradox reactions from day 0 till day 3, meaning an increase of ptiO2 on hyperventilation. Thereafter ptiO2-CO2-reactivity increased, increasing the risk of inducing ischaemia by hyperventilation. The authors concluded that ptiO2-monitoring might become an important tool in our treatment regime for patients requiring haemodynamic monitoring.