The evaluation of cerebral oxygenation by oximetry in patients with ischaemic stroke.GG Demet, AA Talip, UU Nevzat, OO Serhat, OO Gazi
Department of Neurology, Faculty of Medicine, Osmangazi University, EskiSehir, Turkey. , Turkey
AIMS: To evaluate the clinical significance of estimation of the regional cerebral oxygen saturation (rSO2) in the patients with ischaemic stroke by the cerebral oximetry during acute, sub-acute and chronic phases. SUBJECTS AND METHODS: In this prospective study, 24 patients with ischaemic stroke in the middle cerebral artery territory were included. A detailed clinical examination and appropriate laboratory investigations were carried out. The rSO2 was determined by oximetery (INVOS 3100-SD) bilaterally on the first, third, seventh, and fifteenth days. The blood pressure, the peripheral capillary oxygen saturation and the arterial blood gas values were noted too. the changes were evaluated along with Glasgow coma scale (GCS) using unpaired student t-test and one way ANOVA test. RESULTS: There were significant differences between the rSO2 values in acute, subacute and chronic phases on the side of the lesion (p value < 0.05). The values of oxygen saturation gradually increased throughout the chronic phase. These values showed a positive correlation with GCS, but the results were not significant statistically. The rSO2 values were also significantly higher on the non-lesional side than those on the lesion side in the acute phase (p= 0.0034), the discrepancy disappeared during the sub-acute and chronic phases. CONCLUSION: Cerebral oximetry can be used as a measure to evaluate the cerebral oxygenation during the various phases of ischaemic stroke. It has a potential to serve as a useful marker for detection of cerebral oxygenation imbalances, to judge the effectiveness of the management and for the follow-up of patients with ischaemic stroke.
Keywords: Aged, Brain, metabolism,Cerebrovascular Accident, physiopathology,Female, Glasgow Coma Scale, Human, Infarction, Middle Cerebral Artery, physiopathology,Male, Middle Age, Oximetry, Oxygen, metabolism,Prospective Studies,
Cerebral oximetry is an indirect, continuous, and non-invasive method of measuring brain tissue oxygen saturation by near infrared spectroscopy (NIRS). The feasibility of using near infra red light for the monitoring cerebral oxygenation has been demonstrated by Jobsis in 1977. Till date, cerebral oximetry has been widely used in the clinical studies of the cerebral haemodynamics and the oxygen delivery to the cerebral tissue. Several case reports and small clinical series have indicated that the cerebral oximetry can detect changes in the cerebral oxygen saturation resulting from the changes in the arterial blood pressure or oxygen saturation, hypothermic circulatory arrest, carotid artery compression and subsequent morbid clinical events,,,,,,,,,,. Cerebral oximetry is not a measure of cerebral blood flow but rather is a reflection of the regional cerebral oxygen availability.
There are potential benefits of monitoring the cerebral oxygenation in patients who have ischaemic stroke. The identification of the brain oxygen imbalances can guide the physician to take a timely corrective action, which can potentially improve the patientsí outcome and can reduce the cost of health-care,,,. For these reasons, cerebral oximetry can serve as a useful tool in neuro-monitoring in cases of cerebral ischaemia. The clinical benefits of the cerebral oxygenation measurements in patients with ischaemic stroke has not been proved conclusively. In this study, we evaluated the correlation between the Glasgow coma scale (GCS) scores and the regional cerebral oxygen saturation (rSO2) values measured by the cerebral oxymetry during the acute, sub-acute and chronics phases of ischaemic strokes.
This prospective study was carried out at the Department of Neurology, Osmangazi University at Eski?ehir between May 1999 and September 1999. Patients admitted with ischaemic stroke constituted the study population. The ischaemic stroke was diagnosed by a computerised tomographic (CT) scan of the brain within first 24 hours after the onset of the stroke. The patients who did not survive for three days after the admission, those with a pre-existing cerebral disease or a major medical illness (severe respiratory and heart failure) and sepsis were excluded from the study. The local hospital ethics committee approved this study.
During the observation period of ten days or until the discharge, the patients were observed in the intensive care unit. A detailed clinical evaluation of the patients including assessment of the consciousness level using the GCS was carried out.
All the patients were monitored with the cerebral oximetry on day one (at the admission), day third, day seventh and day fifteenth with a one time spot measurement using the cerebral oximetry probe (INVOS 3100-SD, Somanetics Corp). The probe was placed on the right side of the forehead, with the caudal border approximately 1 cm above the eyebrow and the medial edge at the midline. This position places the light source and the sensors away from the frontal sinus. The first 48 hours from the onset of the stroke, before treatment was considered as the acute phase. The day three and day seven readings were considered as in the sub-acute phase, and the fifteenth day was defined as the beginning of the chronic phase. The values of oxygen saturation (SO2) determined from an arterial blood gas analysis and the values of peripheral capillary oxygen saturation (PCOS) by finger pulse oximetry were simultaneously recorded with rSO2. All patients underwent the routine clinical and diagnostic investigations including a general physical and neurological examination, a complete blood count, and blood chemistry at the admission and at each rSO2 monitoring. The electrocardiogram, blood pressure, pulse rate, finger pulse oximetry were monitored continuously. All patients were treated with acetyl salicylic acid (500 mg /daily), vitamins E and C. and fluid management during the course.
Statistical analyses was carried out using the unpaired studentís t-test and one-way ANOVA (SPSS) with a minimum acceptable probability value of 0.05 for statistically significance. All the data are expressed as the mean ? the standard deviation.
Twenty-four patients (male: female 2:1) admitted with an ischaemic stroke in the middle cerebral artery territory, were included in the study. The mean age of patients was 67.32 ? 5.75 years (range 61-75 years).
[Table - 1] shows the mean changes of the rSO2 values on the lesional and the non-lesional sides and the values of GCS. On comparing to the values on the lesional side at different intervals, there were significant differences between acute phase and other phases (p=0.0001, p=0.032, p=0.002, p=0.018, respectively, one way ANOVA). The values of rSO2 gradually increased throughout the chronic phase. A significant improvement was observed within the first three days. There were significant differences between the lesional side and the non-lesional side in the acute stage (p=0.0034). This discrepancy disappeared after the third day.
The rSO2 values showed a positive correlation with GCS, but not significant statistically. [Figure - 1] shows the relationship of the GCS and the rSO2. With the improvement in the GCS there was a gradual improvement of rSO2 on the side of the ischaemia.
We found that there were significant differences in the blood pressures between acute and chronic stage (p<0.05). There was no correlation between rSO2 with the PCOS or the SO2.
The patients with acute stroke are at risk of hypoxaemia and the degree of their oxygen desaturation increases depending on the severity of the stroke. The equalisation of the cerebral blood flow and the oxygenation to the cerebral metabolism will prevent the secondary intracranial hypoxic insults and this forms an essential aspect of the modem neurological intensive care. The brain damage occurs within a few minutes of hypoxia, and can result in severe and complex disabilities or death. The evaluation of the cerebral oxygenation is therefore very important, especially in a critical cerebral illness.
However, determining the safe degree of hypoxaemia for an individual subject is a difficult task. The brain is the most sensitive organ, and visual, cognitive, and electroencephalographic changes develop when the oxyhaemoglobin saturation is less than 80-85% in normal subjects,. There is no evidence that a short-term hypoxaemia to this degree produces any long-term deficit. But, elderly subjects with impaired cerebral perfusion would be expected to be more susceptible to even this degree of hypoxia. However, there are no long-term studies in this regard with a sensitive measure of the outcome.
In patients with ischaemic stroke, an early determination and the prompt management of the cerebral oxygen imbalance has the potential to change the prognosis.
Several studies of measurement of rSO2 were carried out in the past during carotid endarterectomy (CEA). These includes (i) the external carotid artery clamping to evaluate the effects of scalp ischaemia on rSO2 which showed only minute effects,,, and (ii) assessment of correlation between the rSO2 and the oxygen saturation of the jugular vein during CEA, which showed a significant relationship between the two, but no correlation was found between rSO2 and the oxygen saturation of blood in the facial vein during clamping, despite the fact that changes were more pronounced in the facial vein than in the jugular. CEA study using dual INVOS detectors showed a four-fold reduction in the effect of extra cranial blood flow on the results of cerebral oximetry than a similar device with only one detector.
The accuracy of determination of cerebral hypoxaemia in the stages of normo-and hypercapnia has been assessed too. A mean decrease of 5 mm of Hg in the partial pressure of CO2, which would cause about 5% decrease in blood volume in the cortex, increases the sensitivity of the INVOS to determine the brain oxygenation changes. This results from the changes in the absorption of the light, which increases its depth of penetration. However, these changes are only minute (A 20% change in blood volume will cause a 10 point change in the patient's cerebral saturation to be in error by 0.8).
This study is the first study to determine the relation between the cerebral rSO2 and the clinical status of patients with the ischaemic stroke. Our study revealed no correlation between the rSO2 and the PCOS or the SO2, suggesting that peripheral oxygenation does not predict the cerebral tissue oxygenation. In contrast, an increase in the blood pressure correlated well with the increase in the rSO2. Our results showed a definite difference in the rSO2 changes on the lesional and the non-lesional sides. The rSO2 also correlated with the clinical improvement after ischaemic stroke. Increase in the rSO2 from acute phase towards chronic phase positively correlated with the increase of the GCS scores during that period. Albeit, this difference was not significant statistically.
With the ability to detect brain oxygen imbalances sooner and intervene earlier in patients with ischaemic stroke, a physician may be able to improve the patientsí outcome. On the other hand, the cerebral oximetry can also be used to avoid over-treatment, maximising the patient safety while minimising the cost of the care.
The use of NIRS to monitor cerebral oxygenation in adults may be controversial because of concerns about extra cranial and intracranial changes in blood flow and oxygenation interfering with the estimation of rSO2. However, NIRS monitors the tissue beneath the optical fibre, which includes scalp, skull, cerebrospinal fluid, and finally the brain, and studies have shown that with thin extra-cranial tissue the rSO2 can be effectively monitored non-invasively from the surface of the head without interference.
The study concludes that cerebral oximetry can be used as a measure to evaluate the cerebral oxygenation during the various phases of ischaemic stroke. It has a potential to serve as a useful marker for detection of the cerebral oxygenation imbalances, to judge the effectiveness of the management and for the follow-up of patients with ischaemic stroke. Our study did not focused on the treatment of the ischaemic stroke and further studies needs to be carried out to judge the efficacy of the cerebral oximetry as a guiding tool in the management of the patients with ischaemic stroke. Another limitation of the study was the small number of patients. Though, there was a positive relation between the improvement in the GCS and rSO2, this was not statistically proved and a larger study should be undertaken to evaluate this aspect.
[Figure - 1][Table - 1]