The effect of whole body position on lumbar cerebrospinal fluid opening pressure
© Sithinamsuwan et al; licensee BioMed Central Ltd. 2008
Received: 24 February 2008
Accepted: 02 July 2008
Published: 02 July 2008
We compared cerebrospinal fluid (CSF) opening pressure measurements in the lumbar subarachnoid space between the flexed position (F-OP) and relaxed position (R-OP) in recumbent patients. We devised an equation for using F-OP to determine the existence of raised intracranial pressure (ICP). Patients (n = 83) underwent lumbar puncture while in the flexed lateral decubitus position and then were moved to the relaxed position. F-OP and R-OP were measured with a water manometer. R-OP > 180 mmH2O plus relevant clinical signs were taken as indicators of raised intracranial pressure. Mean pressures for F-OP and R-OP were 178.54 and 160.52 mmH2O respectively, p <0.001. When F-OP > 180, raised ICP could be significantly over diagnosed. The authors recommend an equation [R-OP(calculated, mmH2O) = 0.885 × F-OP(measured, mmH2O)] or using 200 mmH2O as the threshold for increased ICP with flexed posture.
The existing literature recommends that physicians measure CSF opening pressure with the patient in the recumbent position. A few citations recommend using the relaxed position (neck not flexed, leg extended and without valsalva manoeuvres) because the flexed position is believed to increase lumbar CSF pressure [1–3]. There are very few existing studies available on recommended positions for CSF measurement [4, 5]. We have noticed in our clinical practice that many physicians usually measure F-OP rather than R-OP because of the convenience. Our objectives were to determine the effect of the body position on CSF pressure, by comparing F-OP with R-OP in the same patients and to ascertain if there are any differences between the two values. In addition we also investigated the cut off value for raised intracranial pressure, and derived a valid equation for the relation between F-OP and R-OP.
Eighty three consecutive patients were enrolled prospectively and underwent lumbar puncture in the lateral decubitus position between June 1st, 2004 and January 31st, 2005 in the Phramongkutklao Hospital, Bangkok. The inclusion criteria were: age >14 years, an indication for lumbar puncture for diagnostic or therapeutic purposes and good cooperation from the patient. Exclusion criteria were: pregnancy, contraindication for lumbar puncture, increased intra-thoracic or intra-abdominal pressure (marked ascites or pleural effusion, on ventilator, hyperventilation, cough, sneezing, uncontrolled movement and severe anxiety or agitation), and a marked fall in CSF pressure during measurement. Demographic characteristics were recorded. The mean value of F-OP was measured by a cylindrical glass water manometer after the pressure had stabilized with minimal fluctuation for at least 2 minutes. Patients were supported while they slowly relaxed their posture as much as possible, and R-OP was measured by the same technique. A measurement of R-OP over 180 mmH2O, together with clinical signs (several bilateral headaches and/or papilloedema) was used as an indication for increased intracranial pressure. The Medical Department Ethical Committee approved this study in 2004 and patients or responsible relatives all gave written informed consent.
Numbers of patients with or without clinical signs of increased intracranial pressure when flexed opening pressure was greater or less than 180 mmH2O
Signs of increased ICP (n = 23)
No signs of increased ICP (n = 60)
Total (n = 83)
F-OP > 180 mmH2O
F-OP ≤ 180 mmH2O
When this equation was used to calculate a new R-OP from F-OP, there was a significant improvement for specificity in determining raised intracranial pressure from 83.3% to 93.3%, p < 0.001. This calculation also decreased the difference in mean opening pressures between positions from 18.02 to -2.48 mmH2O [95% CI for mean value (-7.46)-(2.49), ns, paired sample t-test].
Eighteen per cent of patients had the same value for F-OP and R-OP. Furthermore; 14.7% had an F-OP less than R-OP. Interestingly, all patients aged >60 years and BMI ≤ 20 showed the same value of F-OP and R-OP. Among subjects who had the same value of F-OP and R-OP, we found people of older age group and those with low BMI. Our hypothesis is that the older people would be more relaxed and those with a lower BMI would be less likely to have increased intra-abdominal pressure.
It is concluded that F-OP should not be routinely used in clinical practice as it can falsely diagnose raised intracranial pressure. If physicians routinely prefer to use F-OP, we suggest the cut off at 200 mmH2O for diagnosis of raised intracranial pressure and recommend an equation that can estimate R-OP from F-OP [R-OP(calculated, mmH2O) = 0.885 × F-OP(measured, mmH2O)].
We are grateful to all medical personnel in Medical and Neurological Wards of our Hospital who contributed immensely to the patient care. We wish to thank all patients enrolled in our study.
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