Question 12

College Answer

a)      Venous thromboembolism with PE: (Signs of DVT, Rt. Heart failure, ECG, CTPA)

b)      Amniotic fluid embolus: Hemodynamic collapse with seizures, DIC

c)      Pulm oedema secondary to pre-eclampsia: HT, proteinuria

d)      Tocolytic pulmonary oedema: Tocolytic administration, rapid improvement

e)   Aspiration pneumonitis – classic features

f)      Peripartum cardiomyopathy: cardiomegaly, S3

g)      Air embolism: Hypotension, cardiac mill wheel murmur

h)         Pneumomediastinum: occurs during delivery

i)       Other causes as in the non-pregnant patient

Discussion

The college has actually only asked for two causes.

The list of causes generated by the college, however, is impressive.

1) Amniotic fluid embolism

Two features: DIC and right heart failure with cyanosis

2) Pulmonary embolism

Two features: increased A-a gradient and right heart strain on ECG

The belowmentioned article gives a list which looks a little like this:

• preeclampsia
• tocolytic therapy resulting in pulmonary oedema
• blood transfusion reaction
• sepsis
• aspiration
• fluid overload

The college would add:

• peripartum cardiomyopathy
• air embolism
• pneumomediastinum

To this list, I would add:

• High epidural with motor block of respiratory muscles
• Excessive peripartum opiate use

In general:

Acute Respiratory Failure in Pregnancy

Cause	Cardinal features and brief discussion
High epidural/spinal block	Abnormal (diaphragmatic) respiratory movements Flaccid paralysis of the extremities Otherwise preserved consciousness Predominantly hypercapneic respiratory failure
Amniotic fluid embolism	Clinical evidence of right heart failure Petechial rash DIC Seizures Haemodynamic compromise
Pre-eclampsia leading to pulmonary oedema	Severe hypertension Clinical features of pre-eclampsia, eg. proteinuria
Tocolytic-associated pulmonary oedema	Improves with the withdrawal of tocolytics Associated with tachycardia
Peripartum cardiomyopathy	TTE evidence of LV dilatation and decreased LVEF (by definition, under 45%) Displaced apex beat Audible S3
Air embolism	Either extreme haemodynamic instability or frank cardiac arrest A "mill wheel" murmur, which is said to be "similar to fluid splashing in a half-filled plastic bag" (Rubal et al, 2009) A precipitating cause should be apparent on history, eg recent caesarian delivery (or more weirdly, sexual intercourse in the third trimester. Who knew that blowing air into the vagina might be a bad idea?) In any case, air enters though the venous sinuses of the pregnant or peripartum uterus.
Pneumomediastinum (also known as Hamman's syndrome)	Follows a Valsalva manoeuvre during the second stage of labour Typically, associated with pneumothorax; more rarely associated with an oesophageal rupture Neck and facial crepitus (surgical emphysema) Impressive CXR and CT features A "mediastinal crunch" may be heard on auscultation, also known as "Hamman's Sign" and more familiar from the examination of cardiothoracic ICU patients who have just returned from a CABG. It is a fine crackle heard in synchrony with the heart beat.
Accidental magnesium overdose	Depressed or absent reflexes, flaccid paralysis Clinical features of hypermagnesaemia Historically, pre-eclampsia or eclampsia Usually, associated with the use of premixed bags of MgSO4
Causes which are not unique to pregnancy, but which commonly co-exist with pregnancy
Sepsis	Clinical features which support the diagnosis of sepsis (keeping in mind the uselessness of the obsolete SIRS criteria, and the questionable utility of the Sepsis III definition)
Peripartum opiate use	Predominantly hypercapneic respiratory failure Clinical features of opiate toxidrome (pinpoint pupils, etc)
PE	Clinical features of right heart failure Hypoxia, tachypnoea, tachycardia Characteristic ECG changes (S1 Q3 T3, right heart strain)
Fluid overload	Historically, vigorous fluid resuscitation Clinically, evidence of peripheral oedema
Aspiration	Auscultation findings consistent with aspiration Characteristic CXR appearance A history of vomiting or decreased level of consciousness (eg. seizures)
Transfusion reaction	History of recent large volume blood transfusion  Usually, this is a TACO as opposed to TRALI Haemolysis and haemoglobinuria may be present if this was really incorrectly crossmatched blood

Karetzky, Monroe, and Maria Ramirez. "Acute respiratory failure in pregnancy: an analysis of 19 cases." Medicine 77.1 (1998): 41-49. - this is a bit of a "royal sampler" of different causes of respiratory failure.

Oh's Intensive Care manual:

Chapter 64   (pp. 684) General  obstetric  emergencies by Winnie  TP  Wan  and  Tony  Gin

Chapter 65   (pp. 692) Severe  pre-existing  disease  in  pregnancy by Jeremy  P  Campbell  and  Steve  M  Yentis

Lapinsky, Stephen E. "Acute respiratory failure in pregnancy." Obstetric Medicine: The Medicine of Pregnancy 8.3 (2015): 126-132.

Samanta, Sukhen, J. Wig, and A. K. Baronia. "How safe is the prone position in acute respiratory distress syndrome at late pregnancy?." (2014).

Rubal, Bernard J., et al. "The'mill-wheel'murmur and computed tomography of intracardiac air emboli." Journal of the American Association for Laboratory Animal Science 48.3 (2009): 300-302.

Lifschultz, Barry D., and Edmund R. Donoghue. "Air embolism during intercourse in pregnancy." Journal of Forensic Science 28.4 (1983): 1021-1022.

Balkan, M. Erkan, and Göknur Alver. "Spontaneous pneumomediastinum in 3rd trimester of pregnancy." Annals of thoracic and cardiovascular surgery 12.5 (2006): 362.

Jain, Vikyath. "Acute respiratory distress syndrome, Respiratory failure, Pregnancy." ACUTE RESPIRATORY DISTRESS SYNDROME IN PREGNANCY 7540 (2015).

Robinson, Julian N., et al. "Inhaled nitric oxide therapy in pregnancy complicated by pulmonary hypertension." American journal of obstetrics and gynecology 180.4 (1999): 1045-1046.