Patient requesting labor epidural and a history of Idiopathic Intracranial Hypertension

This morning while watching the news showing the DOW plunging by another 2000 + points in the midst of a panicked public related to the spread of the novel corona virus, I was called up to L and D to place an epidural.  The patient was a G3P2 31 year old patient who was otherwise healthy with the exception of a reported prior history of Idiopathic Intracranial Hypertension.  She reported that she had been told that she could have an epidural by an anesthesiologist, but not a spinal.  Upon further questioning, I was able to determine that the patient had been treated by doxycycline for a routine URI or sinus infection.  Thereafter, she developed changes in her ability to see and sought medical care.  She was diagnosed with a reaction to the doxycycline and underwent lumbar puncture as part of the work up and therapy.  She states that after the lumbar puncture, she developed a headache which she had not suffered prior.  She was started on diamox and this was discontinued after a period of time.

At first glance, this seemed to be a case of primary idiopathic intracranial hypertension, when in fact, it was likely a case of secondary intracranial hypertension, meaning, caused by an external known cause rather than from a completely unknown cause.  Idiopathic intracranial hypertension is a diagnosis of exclusion. It typically affects females who are middle aged and obese. Upon LP, opening pressures of greater than 25 cm of H20 would be considered typical (normal opening pressure is 10 to 15 cm of H2O).  Patients with IIH can develop partial or complete blindness of one or both eyes if not treated.  In severe cases, when therapeutic LP or medicine like diamox or corticosteroids  are not working, surgical placement of an LP shunt is required.

For the OB anesthesiologist, any patient with potential intracranial pathology should be approached with caution.  Prior to any neuraxial procedure, it is important to fully understand the cause and natural history of any intracranial abnormality due to the potential catastrophic risk of brain tissue herniation.  An excellent review of the approach to the OB patient with intracranial pathology can be found here. In summary, patients who have obstruction to flow of CSF from the brain into the spinal canal are at high risk for any type of puncture of the dura mater. In the normal scenario when a puncture occurs of the dura mater in the lumbar portion of the spine, CSF will flow out and to compensate, CSF from the brain fills the space to equalize pressure throughout the continuous space. Any obstruction to this flow from from the cerebral ventricular system into the spinal canal will result in herniation.

However, patients with idiopathic intracranial hypertension (IIH) do not have a problem of obstruction of flow, and thus are not at risk for herniation after a dural puncture whether with a large bore or small bore needle.  As mentioned, LP is a therapeutic modality used to relieve headaches in these patients.  In patients with significant symptomatic IIH who wish neuraxial anesthesia for labor, there is a risk for potential exacerbation of symptoms (to include: pupillary changes or asymmetry, eye movement abnormalities, papilledema, hemiparesis, facial weakness, somnolence).   This is due to displacement of CSF from the lumbar spinal canal back up into the cerebral area. Furthermore, pregnancy and labor have been found to increase the baseline lumbar epidural pressure which it is thought is caused by engorged epidural veins. In studies of patients with elevated ICP, a 10 mL bolus of LA given over 20 to 30 s caused an average increase of 21 mmHg in ICP lasting 4.5 min vs an average increase of 6 mmHg for 2.3 min in a patient with normal pre injection ICP.  Therefore, this possibility should be discussed, and it may be a potential indication for a CSE, where a small IT dose can be given, and then a low volume infusion with PCEA can be offered to the patient to create a slow transition into epidural analgesia via lumbar epidural catheter. Indeed there are numerous case reports of successful neuraxial anesthesia for patients with IIH for both labor epidurals and cesarean sections. In this case report, the practictioner used the tuohy needle to drain 25 mLs of CSF prior to placement of an intrathecal catheter for labor analgesia. It was noted that the patient had excellent analgesia for labor and delivery, and did not suffer a PDPH, although the patient did complain of a headache.  Indications for an IT catheter might include patients where avoidance of GETA is important and likelihood of cesarian is also high.  The authors of the case report felt that their patient fell into this category.  They also noted that in a patient with difficult to control increased intracranial pressure, bolus doses through an epidural catheter may not be tolerated.

It is known that tetracycline, doxycycline and minocycline can all result in elevated intracranial hypertension.  Therefore, anytime a patient is treated with these antibiotics, any headache should prompt careful evaluation for this diagnosis. Currently it is unknown how these antibiotics can result in this disorder, although there is speculation that the antibiotics interfere with the production of ATP at the site of CSF absorption into the venous sinuses known as the arachnoid granulations.

My patient had been treated with Diamox or Acetazolamide, which is a carbonic anhydrase inhibitor. It is often noted that this action is predominantly effective at the renal tubule to reduce hydrogen ion secretion and increase the excretion of sodium, potassium, bicarbonate, and water.   Other uses include the treatment of glaucoma, seizures, and metabolic alkalosis due to its ability to dump bicarb and retain hydrogen ions. Diamox also inhibits carbonic anhydrase in the brain, and specifically in the choroid plexus, the site of CSF production, causing a decrease. Unfortunately, patients with IIH who are controlled with diamox will often be told to discontinue the medication while they are pregnant due to some case reports of congenital abnormalities and literature in animal models showing potential teratogenicity.  However, a recent study found no evidence for harmful effects of diamox in human pregnancy. Therefore, when a patient arrives for delivery, it is possible that she is still taking diamox to control her symptoms. If this is the case, it will be important to consider the effects of diamox on a potential anesthetic, primarily the risk of hypokalemia.

Patients who arrive for labor are always at risk for the potential to require anesthesia for cesarian section.  While neuraxial anesthesia is the preferred method overall, GETA may be required for a number of reasons.  In this case, there is a question as to whether succinylcholine should be used as it may cause a minor increase in ICP.  Furthermore, careful consideration of PaCO2 managment will be important as any increase in ICP will accompany hypercarbia. Definitive measures used for decreasing the ICP include, mild head elevation, maintain EtCO2 between 25 mmHg and 30 mmHg, I.V. mannitol, continuous infusion of propofol, avoid hypoxia, hypercarbia, hyperthermia and hypotension.

Anesthesia OB management for patients with IIH is generally straightforward, but careful history and a detailed understanding of the patients history and manifestation are important to avoid confusion with other intracerebral pathology that may also present during the peripartum period, such as PDPH and venous sinus thrombosis that can make diagnosis more challenging.