New approach to treat an old problem: Mannitol for post-dural puncture headache.

Sir,

In their comments on our article,[12] the readers are correct on the theories regarding the causation of post-dural puncture headache (PDPH, a low-pressure headache), either due to traction on pain-sensitive parietal duramater or veno-dilatation in keeping with the Monroe-Kellie doctrine. Their observations and arguments are essentially sound and astute; however, we offer the following clarifications regarding the relief of PDPH.

Mannitol acts by the following means: ‘Acute increases in blood osmolality → decrease brain water content (occurs mainly in healthy brain tissue with intact blood brain barrier) → decreased brain bulk, intracranial pressure, increased intracranial compliance’.[3] It is this decreased brain bulk, the authors believe, cause the brain to re-float in a contracted cerebrospinal fluid (CSF) volume, the end result of continuous CSF leakage [Figures 1 and 2]. We believe that re-floatation is an important factor that helps mannitol alleviate PDPH along with other factors, which are quoted in the following text. ‘Blood rheology is also improved because of decreased endothelial oedema and decreased erythrocyte oedema and increased erythrocyte deformability with augmentation of perfusion, especially through the microvasculature’.[3] Ergo, the effects of mannitol on brain circulation are beneficial and contributory to re-floatation, leading to mitigation of PDPH.[4]

Figure 1

Brain floatation

Figure 2

Re-floatation principle

The rebound phenomena as pointed out by the readers, is also a true entity. But in a patient who underwent spinal anaesthesia or inadvertent dural puncture with a Tuohy needle, the disruption to the blood-brain barrier is extremely minimal and will not cause entry of sufficient mannitol into the brain parenchyma to cause a rebound effect. Rebound phenomena also effects the CSF pressure, making it higher and maybe beneficial in a low-pressure headache.[5]

The arguments regarding dyselectrolytemia and dehydration are true as well, but as we all know, mannitol is a time-tested drug in the fields of neurology and neurosurgery (and in other clinical situations, where indicated).[6] However, it should be carefully used, like any other drug, keeping in mind the hydration and electrolyte status of the patient, as not to defeat its very purpose.

Although mannitol has never been traditionally indicated to treat PDPH, the authors have used it successfully in numerous instances with rapid clinical gains. Our colleagues at the Department of Anaesthesia, at CMC Vellore, support these benefits of mannitol on PDPH. That's why the authors only suggest that a clinical trial may be taken up to establish this fact. Instead of just reassuring the patient that PDPH is self-limiting and will subside in a couple days, and giving hydration and analgesics, if there is a way to ‘fix the problem’, why not embrace it?

The authors do not claim this as an established approach, but it is a step in the right direction and may be subjected to modifications and analysis, after the necessary clinical trials: Risk-benefit ratio needs to be analysed in depth.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.