The purpose of this study is to evaluate the effect of the ganglion sphenopalatine block (GSP block) on postdural puncture headache.

Adult patients with postdural puncture headache will be enrolled in the study. The patients will be randomised to receive a ganglion sphenopalatine block (GSP-block) with either local anesthetic (lidocaine + ropivacaine) or placebo (isotone NaCl).

Primary outcome is hyperactivity in the sphenopalatine ganglion assessed by pain intensity (0-100mm on a visual analogue scale, VAS) of the postdural headache in standing position 30 minutes after block.

If the patients in the timeframe of 1 hour to 1 week after block does not achieve remission (VAS <30mm while standing) they will be offered a "rescue GSP-block" defined as a new GSP-block with "open-label" local anesthetic and if continued lack of remission at least 1 hour thereafter then an epidural blood patch will be offered.

Inclusion Criteria:

• Age > 18 years
• Patients with postdural puncture headache defined as moderate to severe postural headache (VAS >= 30mm) after lumbar puncture or accidental dural puncture during epidural insertion with an onset within 3 days following the puncture.
• Lack of headache remission within 1 day after dural puncture and after treatment with fluids, caffeine and paracetamol
• Patients who have given their written informed consent for participation in the study after fully understanding the protocol content and limitations.

Exclusion Criteria:

• Patients who cannot cooperate to the study
• Patients who does not understand or speak Danish
• Allergy to the drugs used in the study
• Has taken opioids within 12 hours prior to intervention