Headache complicates approximately 10 to 40% of dural punctures [1]. This postdural puncture headache (PDPH) is typically orthostatic; provoked or aggravated by a vertical or upright position and relieved by a horizontal position. PDPH is probably caused by cerebral spinal fluid leakage through the dural rent, into the epidural space. The leakage causes a decrease in CSF pressure and volume, leading to traction on pain-sensitive structures in an upright position. Besides of headache, the patient may complain of diplopia, tinnitus, dizziness, and myalgia. PDPH may occur immediately after spinal tap, but it starts within 48 hours after the procedure in more than 90% of the patients. PDPH and accompanying symptoms are self-limiting. They generally resolve within 7 days or less, in 80% of the cases. In a small minority of cases, the symptoms may persist for weeks or even months [2]. During an episode of PDPH the patient may be completely incapacitated and confined to bed. Obviously this has financial, social and psychological repercussions.

Different prophylactic measures such as: small needle size, the use of Sprotte's needle, reinsertion of the stylet before withdrawing the needle, and direction of the brevel perpendicular to the dura, have all been shown to reduce the occurrence of PDPH [3–6]. If, despite the prophylactic measures, PDPH occurs, epidural blood patch (EDBP) may be a beneficial therapeutic intervention. EDBP has gained popularity as a therapeutic measure for PDPH. It involves the injection of 10–20 ml of autologous blood into the epidural space around the site of the spinal tap. Gormly introduced this technique in the 1960's [1]. He noticed that inadvertent bloody spinal taps were less often complicated by PDPH. He theorised that the epidural bleeding might lead to clot formation over the dural rent, preventing CSF leakage into the epidural space. He therefore continued to treat 6 subjects suffering from PDPH with EDBP, locating the epidural space with the hanging-drop or loss of resistance method. All 6 subjects were relieved of their complaints.

Many observational studies followed; they reported success rates of the EDBP for PDPH between 70% and 90% [7–12]. Seven controlled trials concerning prophylactic treatment have been published [13–19]. One of these studies was not blinded [18], three were not randomised [14–16], one was only reported as an abstract [17]. One other study [13] compared prophylactic EDBP versus no blood patch among obstetric patients and reported a high success rate. In this study adverse effects were not mentioned, which prevents firm conclusions. The latest study [19], in which prophylactic EDBP was compared to a sham procedure in a double blind setting, showed no decrease in the incidence of PDPH between the two groups. The effectiveness of prophylactic treatment does not seem to have been established firmly.

Only one randomised and blinded trial concerning the therapeutic effect of EDBP has been reported [20]. In this study 12 patients, suffering from PDPH for more than 4 days, despite conservative treatment following lumbar puncture, spinal anaesthesia or myelography, were randomly allocated to EDBP or sham treatment. In the placebo group none of the patients noted complete relief of pain. In the treatment group 5 of the 6 patients obtained immediate relief. Subsequently placebo group patients were also treated with an EDBP, resulting in complete relief of PDPH in all patients. The size of the study, the crossover effect, and the absence of any documentation regarding the effectiveness of blinding of the observers and patients, makes it difficult to draw firm conclusions from this study.

A Cochrane review on prophylactic and therapeutic blood patching [21] argued that further randomised trials of epidural blood patching must be carried out before the balance of risks and benefits of this intervention can be properly assessed".

Therefore, we decided to conduct a randomised, controlled, clinical trial comparing the efficacy of the EDBP with conservative treatment, consisting of 24 hours of bed rest and adequate fluid intake for the treatment of PDPH.

The EDBP, is widely accepted as the treatment of choice for PDPH. In a review of the literature on this subject however, we found only little evidence to justify its use in general practice [21]. Therefore, we decided to conduct an observer blinded, randomised, controlled, study comparing the therapeutic efficacy of the EDBP to the efficacy of conservative treatment.

Author	Number of patients	Type of study	Blinding	Time window to inclusion	Follow-up	Outcome	Adverse effects
Safa-Tisseront 2001 [8]	527 (504 analyzed)	Therapeutic, prospective, non-randomised, observational	NA	4 days (1–53)	15 days	75% complete relief, 18% incomplete relief, 7% failure	Fever in 3 patients
Williams 1999 [12]	55 (7 prophylactic, 41 therapeutic EDBP, 7 conservative treatment)	Retrospective, non-randomised, observational	NA	<1 week	?	34% complete relief, 54% incomplete relief, 12% failure	Back pain in 3 patients
Banks 2001 [9]	100 (81 pdph7 prophylactic, 58 therapeutic EDBP, 23 conservative treatment)	Prospective, non randomised, observational	NA	0–3 days	?	67% complete relief, 28% incomplete relief, 5% failure	22% back pain
Taivainen 1993 [7]	81 (55 patients 10 ml, 26 patients 10–15 ml EDBP)	Prospective, partly randomised, observational	NA	0–10 days	1 week	Initial relief 91%, permanent relief 61%	25% back pain
Vercauteren 1999 [11]	190 (186 EDBP, 4 atypical symptoms)	Retrospective, non randomised	NA	>24 h after symptoms	1 day	Initial relief 99%, permanent relief 73%	?
Stride 1993 [10]	34819 (461 PDPH, 137 EDBP attempted, 135 completed)	Retrospective, non randomised	NA	2 days	?	Initial relief 90%, permanent Relief 64%	?
Seebacher 1989 [20]	12 (6 EDBP, 6 sham treatment)	Prospective, randomised	Yes	>4 days	1 day	EDBP 83% relief sham treatment 0% relief	Back pain

Our study design not only enables us measure the effectiveness of the EDBP, but also its efficiency. The number of days spent with headache after treatment in the two groups will be characterised as incapacitated-days. Immediate relief of headache, and reduction of the number of incapacitated-days is the ultimate goal of this treatment. By taking into account the adverse effects of EBPD, most notably lower back pain, we will be able to make a more realistic estimate of the overall effect of EPBD.

The observer-blind method we have chosen enables us to compare the two treatment strategies of interest as if they are carried out in normal practise, without the artificial circumstances created by sham treatment, in futile attempts to maintain patient blinding. So a genuine comparison is made between the experimental treatment and normal clinical practise. Because patients are of course aware of the nature of the treatment, the study design limits our ability to assess the placebo effect of the epidural blood patch. One may argue that this may lead to overestimation of the effect of the blood patch. We think that for a treatment of a self/limiting condition this is not really a drawback. Another potential limitation is the small sample size of our study. Although our trial will turn out to be the largest randomised study of therapeutic EDBP ever, a sample size of 20 patients in each treatment group will provide us sufficient power (1-β = 80%) to detect a relative reduction in the risk of PDPH after 24 hours of 50%. Much depends therefore on our assumption that only in approximately 10% of the patients the PDPH will have resolved spontaneously after one day. Currently, the study is well underway, and we expect to be able to report its results in the end of 2005.

EDBP is accepted as the treatment of choice for PDPH although randomised, controlled data is scarce. Our randomised, observer-blind clinical trial enables us to compare the efficacy of two clinically practiced methods of PDPH treatment; EDBP versus conventional treatment, as they are applied in clinical practise.