202411092126

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Tags: Neuraxial block, Obstetrics

Intracranial pathology and neuraxial anaesthesia

Normal CPP ranges from 60 to 100 mmHg in pregnant and non-pregnant adults

Although fluctuations normally occur with daily activity, a sustained, raised ICP of 20–25 mmHg is generally treated, with >40 mmHg considered life-threatening.

During labour, uterine contractions can increase CSF pressure by 30mmHg via increases in central blood volume and MAP. However, the largest increase in CSF pressure transiently occurs with pushing during contractions in the second stage of labour, by 53 mmHg

Physiological goals for pregnant patients with intracranial pathology

Variable Goal Rationale
Glucose 6.1–8.30 mmol L−1 Hyperglycaemia associated with inflammation, cerebral oedema and may contribute to thrombosis
Injured brain consumes more glucose
Haemoglobin 7–10 g dl−1 Keep haemoglobin >7 g dl−1 to maximise oxygen transport and prevent cerebral hypoxia
Oxygenation Sao2 > 92% Pao2 >70 mmHg Hypoxia can lead to tissue hypoxia and lower cerebral blood flow
Sodium 135–145 mEq L−1 Hyponatraemia can exacerbate cerebral oedema
Temperature < 37.5°C Hyperthermia can increase ICP via cerebral vasodilation, increased permeability of blood–brain barrier and release of neurotoxin mediators
Arterial pressure Within 10–15% of baseline Arterial pressure should be maintained near baseline, keeping in mind that this goal will be higher in patients with hypertensive diseases of pregnancy
Ventilation _P_aco2 3.3–4.0 kPa Hypercapnia causes cerebral vasodilation and can increase ICP; however, extreme hypocapnia causes cerebral and uteroplacental vasoconstriction and can lead to respective ischaemia
Normal _P_aco2 in pregnancy is 4.0–4.3 kPa
Volume status Normovolaemia Hypovolaemia may lead to hypoperfusion, hypervolaemia may lead to oedema
Cerebral perfusion pressure (CPP) 60–70 mmHg Lower CPP may cause ischaemia
Intracranial pressure (ICP) ≤22 mmHg Increased ICP can lead to decreased CPP, herniation
The uterine arteries in pregnancy remain maximally dilated and thus uteroplacental perfusion is not autoregulated, but depends on arterial pressure

Although hyperventilation can acutely reduce ICP, extreme hypocarbia can lead to cerebral and uterine artery vasoconstriction as well as a leftward shift (tighter binding) of the maternal haemoglobin curve relative to fetal haemoglobin

Progesterone increases cerebral sensitivity to carbon dioxide, resulting in chronic respiratory alkalosis with metabolic compensation, with normal Paco2 around 4 kPa during pregnancy. To balance fetal oxygenation and perfusion while preventing further increases in ICP in patients with intracranial pathology, Paco2 should be maintained around 4 kPa

Considerations

The risks of neuraxial procedures related to intracranial pathology include complications of acute and chronic CSF leaks with potential for changes in CPP and transcompartment gradients, and the potential for cerebral hypoperfusion in those with hypotension associated with spinal anaesthesia or epidural analgesia

Untreated hypotension from spinal anaesthesia can increase the risk of maternal nausea and vomiting, fetal acidosis, decreased Apgar scores and compromise CPP

epidural catheter fluid boluses may transiently increase ICP

Recommendations for mitigating BP decreases related to neuraxial anaesthesia for CD include giving 1 L i.v. crystalloid and a prophylactic vasopressor infusion targeted at providing arterial vasoconstriction

Brain tumours

Hormones of pregnancy have been attributed to accelerated growth of glioblastomas and meningiomas

The normal physiological changes of pregnancy may also facilitate tumour growth and contribute to surrounding oedema. These changes include relative immunosuppression, vascular growth, increased blood volume and cardiac output.

Chiari malformation

There are four subtypes of Chiari malformation (CM), with progressive displacement of the cerebellar tonsils below the foramen magnum

Type 1 most prevalent
Symptoms are rare (1/1000), but type 1 CM can present with

Chiari malformations can be associated with syringomyelia, a collection of CSF within the spinal cord that can cause neurologic deficits

Syringomyelia formation may be indicative of intermittent obstruction of CSF flow at the level of the foramen magnum.

concern: obstruction would be exacerbated with pushing (i.e. Valsalva manoeuvre) during the second stage of labour.

Chiari malformation is often associated with kyphosis and scoliosis, which can increase difficulty with GA and neuraxial anaesthesia, respectively

Expert reviews advocate for usual anaesthetic and obstetric care in patients with type 1 CM who lack crowding at the foramen magnum and associated CM symptoms with shared decision-making with neurosurgical consultation in pregnant patients with CM when concerns for increased ICP and CSF flow obstruction exist

Spontaneous intracranial hypotension

Spontaneous intracranial hypotension is caused by spontaneous spinal CSF leak and may be exacerbated by pregnancy with an incidence of about four per 100,000 yr−1

The typical sagging of the brain in this disorder may mimic CM, and avoiding a lumbar puncture has been advocated to minimise worsening of brain sagging. However, these patients already have a significant spinal CSF leak, CSF pressure is low and risk of further decreasing ICP from unintentional DP is unlikely.

Idiopathic intracranial hypertension

Patients with idiopathic intracranial hypertension (IIH) have increased ICP in the absence of a structural cause and, unlike other pathologies with increased ICP, have no contraindications to neuraxial procedures

The aetiology of IIH may be insufficient CSF resorption. It occurs most frequently in women of childbearing age, more commonly with coexisting obesity (1–2 per 100,000).

Patients with IIH have increased ICP of ≥25 cmH2O (18.4 mmHg) CSF opening pressure during lumbar puncture. With no pressure gradient between intracranial and spinal compartments and no structures that can cause obstruction in the setting of CSF leak, neuraxial analgesia/anaesthesia may be used without concern. Lumbar puncture is often used as a therapeutic procedure.

AVM

Arteriovenous malformations (AVMs) are collections of abnormal vessels that form direct shunts between arterial and venous vasculature with low resistance and high blood flow.
The risk of AVM rupture may be increased by higher oestrogen concentrations and cardiac output during pregnancy, and intracranial AVM-related sequelae account for 5–12% of maternal deaths.

Neuraxial analgesia or anaesthesia is generally considered safe in patients with stable AVM as it avoids acute ICP increases related to pain with labour as well as induction and intubation with GA.

PET

Preeclampsia with severe features has 19–43% increased ICP based on diameter of the optic nerve sheath

In the absence of an additional acute neurologic event, labour epidural analgesia and neuraxial anaesthesia remain the preferred choices for labour and CD and both are widely used in preeclampsia, with close hemodynamic control

Hypertension during pregnancy may increase the autoregulation threshold and need to maintain a higher BP for optimal maternal and fetal perfusion.

Decision making

Shared decision-making can be made with the patient for

Imaging studies must be reviewed for mass effect, which may indicate increased ICP and risk for herniation with DP

In patients with brain tumours (especially gliomas and meningiomas), repeat imaging may be warranted (within 2 months of planned delivery) to evaluate for changes in intracranial space and signs of increased ICP given that increased tumour growth can occur during pregnancy

Neurosurgical consultation before delivery should include a discussion regarding

Risk modification

Several possibilities exist for decreasing the physiologic risk of herniation including

EVD
pencil point tip spinal needles
smaller atraumatic spinal needle
experienced clinician

Maintenance of maternal BP after spinal anaesthesia by infusion of a vasopressor (phenylephrine, ephedrine or noradrenaline) will help prevent large decreases in MAP and is part of enhanced recovery for CD and international guidelines

close monitoring

Alternatives

Remifentanil provides better pain control than traditional non-neuraxial options offered for labour

remifentanil patient-controlled analgesia is typically reserved for patients with contraindications for neuraxial labour analgesia because of the higher risk of maternal respiratory depression compared with other pain control options

Increased monitoring in the form of 1:1 nursing, continuous pulse oximetry and continuous end-tidal CO2 are methods used to mitigate this risk

In patients with intracranial pathology, respiratory depression related to systemic opioid and medications with sedative effects must be considered as potentially causing hypoxaemia or hypercarbia, leading to cerebral vasodilation and ↑ ICP.

concerns regarding the effects of nitrous oxide on CBF and ICP should be included in interdisciplinary discussions and shared decision-making for pain relief during labour or scheduled CD with GA

Complications

For acute neurological decompensation caused by increases in intracranial hypertension, the following acute actions are considered standard:

Unintentional dural puncture

If unintentional DP occurs during the placement of an epidural catheter with non-obstructive intracranial pathology (see decision-making above), the patient should be monitored closely for signs of acute neurological changes

Some clinicians place an intrathecal catheter via the epidural needle; most choose to withdraw and perform the epidural at the same or different level.

Having the patient remain supine with left uterine displacement will minimise the intracranial–spinal canal pressure gradient

Acute boluses of fluid in the epidural or intrathecal space (e.g. preservative-free normal saline) can temporarily increase epidural/spinal canal pressure, reducing the intracranial–spinal canal pressure gradient

Treatment of post-DP headache with epidural blood patch should be an individualised risk/benefit decision based on intracranial pathology.

Postpartum / post-op

Immediately after delivery, the uterus contracts, increasing central blood volume and increasing cardiac output to its highest level throughout the peripartum period.
This peak in cardiac output occurs during what is considered the highest risk period for intracranial haemorrhage

The vasodilation of neuraxial anaesthesia moderates this immediate increase in central blood volume until the neuraxial block wears off, typically 1–2 h later.
Giving i.v. diuretics after delivery can help mitigate this acute increase in circulating volume.

adequate analgesia

close monitoring

References

Neuraxial Anaesthesia for the Parturient With Intracranial Pathology - BJA Ed