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The Rational Clinical Examination
David L. Simel, Drummond Rennie
Lumbar Puncture
Sharon E. Straus, Kevin E. Thorpe, Jayna Holroyd-Leduc
Table 70-3 Studies Assessing Cerebrospinal Fluid Analysis in Patients With Suspected Central Nervous System Infection

Topics Discussed: cerebrospinal fluid analysis, cerebrospinal fluid pressure, clinical competence, clinical prediction/decision rules, diagnostic spinal puncture, likelihood ratio, meningitis, bacterial, positioning patient, summarizing the evidence, teaching issues

Excerpt: "We found 537 citations of potential interventions to optimize LP technique. Review of these led to retrieval of 22 full-text articles for assessment, 15 of which were subsequently identified for inclusion. Reasons for excluding trials were lack of randomization (5 studies18-22), repeat publication (1 study23), and inability to obtain outcomes data (1 study24). Studies were categorized by intervention including needle type, needle size, reinsertion of stylet, mobilization after LP, and use of supplemental fluids. No studies of other interventions—such as positioning of the patient during LP, direction of bevel, volume of CSF removed, or prophylactic use of an epidural blood patch—met the inclusion criteria.Fifteen randomized trials were identified with sample sizes ranging from 44 to 600 people. Eight studies had sample sizes of 100 patients or fewer.We were unable to identify any randomized studies that evaluated the impact of the experience of the clinician performing LPs on clinical outcomes. Some studies we identified included experienced neurologists,23 whereas others involved students under the supervision of physicians.25 In a case series of LPs performed at an urban university-affiliated hospital, the incidence of traumatic LP was 15% using a definition of more than 400 red blood cells per high-powered field and 10% using a definition of more than 1000 red blood cells.26 However, the level of training and specialty of all physicians were not recorded. One retrospective study compared the incidence of traumatic LP at the end of the resident academic year when housestaff are more experienced with that at the start of the next year when new housestaff begin training. Using a cutoff of 1000 red blood cells/L, there was no difference in risk of traumatic LP between experienced housestaff (14%) and inexperienced housestaff (12%).27 In a prospective cohort of 501 patients who underwent LP either by a nurse, physician, resident, or medical student, there was no significant difference in the risk of post-LP headache among the 3 groups.8 We found no data on the number of LPs required to demonstrate or maintain proficiency.Normal resting CSF pressure is assumed to be 60 to 180 mm of H2O or 6 to 14 mm Hg.46,47 In the single identified study, CSF pressure changed little (<1.1 mm of water) with flexion of the lower extremities.48 Various maneuvers, such as compressing the abdomen or the jugular vein (Queckenstedt's maneuver49), can increase CSF pressure.50 An obstruction to CSF flow prevents the normal rise and fall in pressure (positive Queckenstedt), but we were unable to find any studies describing the accuracy of this maneuver for detection of CSF outflow obstruction...."
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