Outline the challenges specifically associated with the management of a pregnant patient with status asthmaticus.
1) Pregnancy can worsen asthma – pulmonary congestion, reflux disease, low FRC
2) Because of reduced respiratory reserve, decompensation can be rapid
3) Need to be aware of the changes in blood gas reference values
4) Medications –
a) Steroids – potential malformations in the fetus if used in the first trimester – cleft lip
b) Beta 2 agonists- risk of tocolytic pulmonary oedema - delay in onset of labour
5) Sedation of the ventilated pregnant patient
Benzodiazepines – floppy infant syndrome
Opiates- fetal respiratory depression
If need for prolonged paralysis – risk of arthrogyphosis in the fetus
6) IPPV –
High risk intubation
Avoid nasal intubation
High pressures may reflect raised intraabdominal pressures
7) Maternal hypercapnia – reduces uteroplacental blood flow
Also shifts oxyHb dissociation curve in the fetus to the right, thus impairing fetal oxygenation – fetal monitoring essential
Long term maternal hypoxia associated with IUGR
8) NIV – may be difficult with increased risk of aspiration
9) Positioning of patient issues – Risk of aortocaval compression
The management of the pregnant asthmatic in the ICU is dealt with elsewhere.
To approach it systematically:
Main issues in pregnancy which complicate asthma:
- More reflux, thus more exacerbations
- More allergic exacerbations, particularly in the last trimester
- Less capacity to compensate, thus more frequent presentations
- They are already tachypnoeic, with a mild respiratory alkalosis, which can confuse their presentation.
- The preload is already decreased by uterine compression of the vena cava, let alone the intrinsic PEEP.
- Prolonged maternal hypoxia is associated with intrauterine growth retardation.
- There is a greatly increased risk of pre-term delivery with poorly controlled asthma
- Needs to be accomplished by an expert
- Cautious use of NIV (aspiration risk)
- Cautious use of permissive hypercapnea
- Cautious use of beta agonists (tocolytic effects)
- avoid hypoxia (foetal growth retardation)
- may benefit from BAl or heliox
- Assure normovolemia
- Avoid adrenaline
- Position patient into a 30° left tilt
- only in emergency, and only for short periods
- constant foetal monitoring
- may need to organise for a caesarian to protect the foetus from hypoxia.
Avoid harmful strategies:
- Corticosteroids in the first trimester - they may cause a cleft palate.
- of course, in later stages of pregnancy, you can really hit the steroids
- Beta-agonists in labour - they have a tocolytic effect, slowing everything down.
On top of that (possibly undesirable) effec, there is also the known potential to precipitate diastolic heart failure and pulmonary oedema
- Routine ICU sedatives - if it crosses the blood-brain barrier, it probably also crosses the placenta. If the plan is proceed with caesarian, a floppy infant may be produced.
Bakhireva, Ludmila N., et al. "Asthma control during pregnancy and the risk of preterm delivery or impaired fetal growth." Annals of Allergy, Asthma & Immunology 101.2 (2008): 137-143.
Schatz, Michael, and Mitchell P. Dombrowski. "Asthma in pregnancy." New England Journal of Medicine 360.18 (2009): 1862-1869.