A 35-year-old female is admitted to your ICU with community acquired pneumonia requiring 60% inspired oxygen via facemask. She is previously quite fit and well, and is currently 32 weeks pregnant.
Forty-eight hours later, she suffers a pulseless electrical activity (PEA) arrest.
a) What is your differential diagnosis? (30% marks)
b) Outline factors that may make successful resuscitation of this woman more challenging.(40% marks)
c) What specific alterations would you make to the standard ALS algorithm in this woman? Justify your answer. (30% marks)
Pulmonary Embolism (must state this to gain any marks in this section)
Severe Hypoxaemia (airway obstruction/lung collapse/aspiration/AFE [see below])
Amniotic Fluid Embolism
Tension pneumothorax / Tamponade (potentially post CVC etc., spontaneous unlikely)
‘Iatrogenic’ catastrophe/other: air embolism, drug error, anaphylaxis etc.
Hypovolemia (unlikely unless massive concealed bleed but possible), placental abruption
Factors relate to the underlying cause of arrest, the woman’s state pre-arrest, the physiological changes of pregnancy and the presence of a gravid uterus/unborn fetus.
Underlying cause of arrest
Lack of a rapidly reversible cause such as pneumothorax /airway obstruction.
Woman’s state pre-arrest
Severe pre-existing/worsening hypoxaemia
Physiological Changes of Pregnancy
Airway oedema and increased incidence of difficult airway and airway bleeding, high oxygen consumption and increased minute ventilation, reduced FRC, increased risk of aspiration, supine hypotensive syndrome [aortocaval syndrome], procoagulant state, chest compressions may be challenging with obesity/breast enlargement
Presence of gravid uterus/unborn fetus
Prevention of supine hypotensive syndrome [aortocaval syndrome] requires lateral tilt but chest compressions should be performed supine with manual displacement of uterus [AHA rec: see below], reduced diaphragmatic excursion due to presence of uterus with reduced FRC, poor ECHO windows especially subcostal, need for resuscitative hysterotomy and potential simultaneous neonatal resuscitation, potential for delay/hesitation in delivering indicated treatment e.g. antiarrhythmics, thrombolysis, extracorporeal support due to concerns regarding pregnancy.
Main differences are
10-15 degrees of lateral tilt during chest compressions to avoid aortocaval compression or continuous lateral uterine displacement (LUD).
Early perimortem caesarean section
Candidates often gave a routine list for cardiac arrest causes (Hs and Ts) without much specific consideration of situation. Almost no consideration given to underlying cause and pre-arrest condition of patient as factors making successful resuscitation challenging. Often no justification given for alterations to ALS algorithm
To counter the examiners' comments, one might present them with a "routine list of cardiac arrest causes" which relates the 4 Hs and 4 Ts to the specific scenario. Thus:
- Hypoxia due to
- Community-acquired pneumonia (it's what the patient presented with)
- Airway loss during seizures (eclampsia)
- Pulmonary oedema due to peripartum cardiomyopathy or preeclampsia
- Hypovolemia (or distributive shock, or cardiogenic shock )
- Purpueral sepsis
- Septic abortion
- Haemorrhage (eg placental abruption or liver rupture)
- Takotsubo cardiomyopathy
- Peripartum cardiomyopathy
- Exacerbation of pre-existing cardiac disease (eg. mitral stenosis)
- Tension pneumothorax
- due to positive pressure ventilation or CVC insertion
- due to pericardial fluid collection
- Toxins, including
- intentional overdose
- Iatrogenic overdose (eg. accidental bolus infusion of magnesium sulfate)
- Thrombus which includes all embolic phenomena:
- Pulmonary embolism (which we must mention)
- Amniotic fluid embolism
- Air embolism
The "factors that may make successful resuscitation of this woman more challenging" is a strangely worded question, as it could be interpreted as almost anything. The examiner's comments about how disappointing it was that the trainees didn't give enough attention to "underlying cause and pre-arrest condition of patient" are rendered all the more bizarre given that the presented pre-arrest history of the scenario was hardly sufficient to make any judgments about the challenging aspects of the specific situation. We know that she is very pregnant, hypoxic, and previously healthy. Almost everything else is left up to the imagination (eg. are we resuscitating her in a narrow corridor? Has the registrar had enough sleep? Is this a small regional hospital with a single GP anaesthetist? Are you the baby's father?). As such, one must reinterpret the question as "what features of third trimester pregnancy make it more difficult to successfully resuscitate a pregnant patient from cardiac arrest?"
These features can be separated into categories:
- Difficult intubation (for various reasons)
- Increased risk of aspiration
- Decreased FRC makes respiratory decompensation more rapid, and makes airway access more urgent (though, some might say, the patient has arrested - how much more urgent could it get)
- On the list of differentials are amniotic fluid embolism and pulmonary embolism, which are problems with no real immediate reversible solution in the arrest scenario.
- Oxygen consumption increased
- Foetal oxygenation needs to be considered
- If tension pneumothorax is for some reason a serious differential, the chest drains need to be placed higher because of the displacement of the diaphragm by the gravid uterus
- Venous return impaired by gravid uterus
- Placental arteries are more sensitive to catecholamines, and will constrict when you start giving large boluses of adrenaline
- Trans-thoracic echocardiography during CPR will be difficult if not impossible, because of the problematic subcostal view
- If the patient had eclampsia-related seizures and has arrested because of this, it will not be immediately apparent to the rescuers (i.e. the clues may not be obvious, eg. incontinence and a bitten tongue may go unnoticed in the melee of resuscitation)
- Though it seems an unusual thing to mention specifically as a hindrance to the normal process of resuscitation, the college in their answer mention "potential for delay/hesitation in delivering indicated treatment e.g. antiarrhythmics, thrombolysis, extracorporeal support due to concerns regarding pregnancy", which implies that a necessary consideration in resuscitating a pregnant arrest patient is the possibility that your team will refuse to carry out your order to give adrenaline or amiodarone. If your grasp of the reigns of leadership is indeed so tenuous in this arrest, it is unclear why this comment is limited to antiarrhythmics, thrombolysis and ECMO, as the staff would probably not follow any of your other orders either.
The main differences to the ALS algorithm are:
- Manually displace the uterus to the left (off the aorta and vena cava)
- Add a left lateral tilt (the ideal angle is unknown, and is thought to be between 15° and 30°)
- A left lateral tilt may compromise effective CPR, but is still recommended by the ARC Guideline 11.10 (2011) "Special Circumstances". In contrast, ECC and AHA no longer recommend the left lateral tilt (see the 2015 AHA update and the 2015 ECC guidelines).
- Biaxillary defibrillator pad placement may be considered. Anterolateral pad placement requires the lateral pad to go under the breast rather than over it.
- Early intubation is mentioned in the college answer, and is therefore the definitive opinion of the examiners, but it does not appear in any of the guidelines. Jeejeebhoy et al (2015), in the AHA scientific statement on this issue, did not mention anything about early intubation, though airway management is otherwise made much of.
- Prepare for an emergency perimortem caesarian.
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