Pre-Eclampsia

Take home messages

• 25% of women with hypertension during pregnancy will develop pre-eclampsia
• The main aims of intervention are to prevent maternal intracranial haemorrhage and allow the pregnancy to continue to as close to term as possible
• The magic number to target is <135/85 mmHg

Pressure is bad

Well, too much pressure is bad - ideally we have just enough to perfuse all of the important bits, but not enough that they leak, occlude or explode.

• Hypertension in pregnancy is a risk factor for long term cardiovascular disease
• The uterus doesn't autoregulate
• We're trying to prevent intracranial haemorrhage in a patient with leaky blood vessels

Some useful definitions

The key point in time to keep in mind is 20 weeks gestation - if hypertension is present before this, then it's not gestational, it's just hypertension. If it starts after 20 weeks, then it's gestational.

• Up to 1 in 20 parturients will already be hypertensive before pregnancy, and this number is increasing with increased rates of obesity and increasing average maternal age
• Around 6% of pregnancies will be affected by gestational hypertension
• The key in both of these cases is that there is no significant proteinuria - as soon as the kidneys start leaking protein, we're into pre-eclampsia territory

Gestational hypertension is diagnosed as new high blood pressure after 20 weeks of pregnancy. Therefore, if the blood pressure was there before (or they're already on antihypertensive meds), it's not gestational (aka Pregnancy induced hypertension PIH), rather it's simply chronic hypertension.

• In the UK between 2009 and 2012 it was the fourth most common cause of maternal death

What do I do about it?

• But as with all things in physiology, try to avoid rapid changes in blood pressure, as this can do harm in equal measure - aim for around 1-2 mmHg per minute as a maximum rate of reduction
• Just be cautious if giving nifedipine and magnesium sulphate at the same time - the double whammy calcium antagonism can cause toxicity
• Hydralazine can cause sudden hypotension as well as a maternal tachycardia so a pre-emptive 500ml fluid bolus is usually a good idea

What is pre-eclampsia?

The generally accepted pathophysiological process goes a little something like this:

• Inadequate placental invastion of trophoblast cells of the spiral arteries, producing...
• High resistance blood vessels and compromised blood flow to the placenta, leading to...
• Abnormal placentation and endothelial dysfunction, vascular remodeling, therefore triggering...
• Activation of clotting cascade, microthrombi production and end organ dysfunction

Or something like that.

Essentially there is a microanatomical problem with the blood supply to the placenta, so it throws the toys out the pram and releases a whole host of spicy chemicals that cause endothelial dysfunction and organ damage.

And that's why you see proteniuria.

How much protein is proteinuria?

• Urine protein:creatinine ratio >30 mg/mmol or
• 24 hour urine collection of over 300mg protein

Other organ dysfunction is defined by:

How bad does it get?

2% of maternal deaths are attributable to eclampsia and pre-eclampsia

As with most disease processes it lies on a spectrum, depending on how high the blood pressure and the extent of end organ dysfunction.

Who gets it?

Can we test for it?

• Placental growth factor is produced by the placenta and peaks between 26 and 30 weeks
• Levels are thought to be lower in women with pre-eclampsia, and the lower the level, the more severe the case
• This can be detected before the onset of measurable hypertension or proteinuria

It's exciting, but there isn't sufficient RCT evidence to support its routine use in diagnosing pre-eclampsia just yet.

Timing of birth

If there are features of severe pre-eclampsia then a planned delivery before 37 weeks needs to be considered.

Why are they all on Aspirin?

• NICE recommends that women at high risk of developing pre-eclampsia be given aspirin 75–150 mg daily from 12 weeks until the birth of the baby (50% relative risk reduction in high risk women)
• Women with two or more moderate risk factors should also be offered aspirin
• Aspirin alone does not contraindicate neuraxial blockade  

If they seize

It's now eclampsia, which carries risk of cardiac arrest and intracerebral haemorrhage.

Seizures are ridiculously terrifying for a pathology that usually doesn't do much harm and self resolves in a matter of minutes. Eclamptic seizures are the same, but remember that during the seizure there is a risk of aspiration due to an unprotected airway, as well as a surge in blood pressure in a patient already at high risk of stroke.

Once you go from pre-eclampsia to eclampsia the risk of stroke increases tenfold.

• Between 1 and 2% of pre-eclamptic mothers will have a seizure and therefore develop eclampsia
• The seizures are throught to be caused by cerebral vasospasm
• Magnesium is believed to induce cerebral vasodilatation and therefore prevent seizures from occurring

Magnesium sulphate is both treatment and prevention of seizures in eclampsia

4 g over 5 min

followed by an infusion of 1 g per hour for 24 h

If they seize again, then further 2g magnesium boluses can help.

HELLP

Haemolysis, elevated liver enzymes and low platelets.

This is pre-eclampsia-gone-bad and carries substantial morbidity and mortality for the mother and baby, affecting around 1 in every 10 000 pregnancies

• AST or ALT or GGT >70
• Platelets <100
• Lactate dehydrogenase >600 or bilirubin >20

But note that if the clotting is deranged or the platelet count is rapidly falling then you might find yourself avoiding the spine altogether, and don't forget the magnesium.

How should I anaesthestise a woman with pre-eclampsia?

Carefully, and ideally with some sort of neuraxial blockade to help lower blood pressure, allow neurological monitoring to continue and avoid the issues with general anaesthesia.

Regional is plan A

Most of the time in the world of obstetric anaesthesia, the safest and preferred way to proceed is with some sort of regional - usually neuraxial - blockade.

The same applies in hypertension and pre-eclampsia.

There are several benefits to regional anaesthesia in the pre-eclamptic parturient, aside from the boring answer of 'avoids risks associated with GA':

• Better pain control
• Reduces blood pressure
• Allows ongoing monitoring of neurological status
• Avoids potentially dangerous hypertensive response to laryngoscopy

Women with high blood pressure in labour are generally advised to at least consider epidural analgesia, for all of its wonderful analgesic and antihypertensive properties, as well has having an anaesthetic option in place already should you need to go to theatre.

Things to think about when performing general anaesthesia

• Unfasted patient - omeprazole, metoclopramide, citrate
• Difficult intubation - videoscope, THRIVE
• Higher risk of aspiration - ramped position, oxford pillow, cricoid if you like it
• Need to maintain steady blood pressure - pressors and labetalol at the ready
• Need to minimise laryngeal stress response to laryngoscopy

Probably best to avoid NSAIDs given potential renal and platelet issues. Paracetamol is very unlikely to cause any issues but may be witheld in the case of severely deranged liver function.

General anaesthesia carries its risks of airway issues with an oedematous larynx, hypertensive response to laryngoscopy and therefore risk of intracranial haemorrhage.

If you have to do a GA, then use a smaller tube than usual and remember you'll likely need to use hefty doses of rapid-acting opioids to suppress the response to the laryngoscope, such as:

• Alfentanil 25 microgram/kg
• Remifentanil 1 microgram/kg

And you may need esmolol 500 microgram/kg or labetalol 0.25mg/kg as well to help keep the pressure under wraps.

Try and keep the MAP below 65 and 110 mmHg and continue the magnesium infusion if its already running.

The treatment for magnesium toxicity is 10 ml 10% calcium gluconate.

If a patient's blood pressure is already of concern and they're receiving infusions of magnesium or labetalol, then an arterial line is probably a good idea.

If in doubt, dry them out

Be very cautious with maintenance fluids in patients with pre-eclampsia.

Why fluids are tricky business:

• The patient is often hugely vasoconstricted as part of the underlying pathology, meaning they can tank their blood pressure the minute you give them an antihypertensive
• They then have increasingly leaky capillaries and hypoalbuminaemia, producing a higher tendency towards pulmonary oedema
• Thankfully, while transient AKI is rather common, long term renal impairment is very rare

If you have a severely pre-eclamptic patient, then the risk of pulmonary oedema and its associated complications are more likely to cause problems than short-term dehydration.

You can always give a fluid bolus if required later.

Once baby is out

It's generally accepted, and usually the case, that hypertensive disorders of pregnancy resolve fairly rapidly after the baby and placenta are no longer in situ to cause the problem, however this shouldn't be taken as a given.

• Up to 44% of women with severe pre-eclampsia are at risk of post partum seizures
• Fluid balance, blood pressure management and normal biochemical parameters should all be diligently observed and corrected especially in the first 24 hours
• Pre-eclampsia is an independent risk factor for post partum haemorrhage so keep your wits about you

A Free Final FRCA CRQ

Our wonderful colleagues over at FRCA-revision.com have put together a whole host of high yield and syllabus-mapped CRQs, free of charge. We highly recommend you check out their site and interactive MCQ quiz!

The link below will take you straight to their high-yield question on pre-eclampsia

Final FRCA CRQ: Pre-Eclampsia

Useful Tweets and Resources

Management of Hypertensive Disorders of Pregnancy

Management of Hypertensive Disorders of Pregnancy : WFSA - Resources |

WFSA Resource Library

1/
A 21 yo G1P0 reports a severe headache 3 days after delivery.

BP 182/100😱

While waiting to be admitted, she vomits & has a generalized tonic clonic seizure.

She is sedated and intubated for eclampsia.

The next morning, she has blown pupils.

A #continuumcase. @LyellJ pic.twitter.com/K8r2hMFzh8

— Casey Albin, MD (@caseyalbin) October 2, 2023

#Esrasunny23 Platelet count for epidural placement in pre-eclampsia .. 70 is the new 80! ⁦@SOAPHQ⁩ Guidelines ⁦@DevroeSarah⁩ pic.twitter.com/feVkIUm8NX

— John Loughrey (@LoughreyJPR) October 5, 2023

References and Further Reading

Hypertension in pregnancy

Hypertensive diseases in pregnancy comprise chronic hypertension, gestational hypertension, and pre-eclampsia. They are a significant cause of morbidity and mor

OUP Academic*

Update on hypertensive disorders in pregnancy

Hypertensive disorders during the peripartum period are common and are accompaniedby increased maternal and fetal morbidity and mortality. They encompass chronic pre-existinghypertension, gestational hypertension and pre-eclampsia. The confidential enquiriesinto maternal deaths revealed that 2% w…

BJA EducationSearch for articles by this author

Overview | Hypertension in pregnancy: diagnosis and management | Guidance | NICE

National Institute for Health and Care Excellence (NICE)

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