Question 3

b)    66-year-old male with accidental hypothermia and core temperature < 24oC

c)    34-year-old 32/40 gestation pregnant female

Examiners Comments:

Nil

Discussion

This question is a concatenation of several older questions. Cardiac arrest following cardiac surgery came up in Question 30.2 from the second paper of 2017, cardiac arrest in extreme hypothermia appeared in Question 7 from the second paper of 2019, and cardiac arrest in the pregnant patient had been asked about at least four times since 2010. The college answer is refreshing in its approach, particularly the tabulated form of the answer and the emphasis on team composition (an excellent move).

a) Modification in the post-cardiac surgical patient:

• Modifications to diagnostic thinking:
  • Hypovolemia, tension pneumothorax and cardiac tamponade are among the most common causes of cardiac arrest following cardiac surgery.
• Modifications to ALS algorithm:
  • You do not use full dose adrenaline (rather, give smaller doses)
  • You do three "stacked shocks"
  • You try pacing (rate of 90, DDD) in asystole if pacing wires are available
  • If they are already paced and in PEA, you turn off the pacing to "unmask" VF.
  • These shocks and attempted pacing are all measures you take before  starting CPR, which is a departure from the ACLS norms.
  • If you can't control a shockable rhythm with three stacked shocks, you give amiodarone immediately rather than after three cycles.
  • Amiodarone is the only drug in the protocol, which makes it easy to remember. Atropine is mentioned in the college answer but it is not a part of the 2017 consensus statement recommendations.
  • The college suggests you grab the knife after one minute, but the official guidelines makers say "we recommend this within 5 minutes". In short, after five minutes of unsuccessful resuscitation the chest should be re-opened.  External CPR is pointless in all of the common causes of arrest in this scenario. Therefore, CPR is something you do while waiting to re-open the chest. 
• Modifications of logistics
  • Non-surgical staff are encouraged to re-open the chest in an emergency. However:
  • Operating theatres, cardiac surgeon and cardiac anaesthetist need to be notified
  • Blood bank need to be notified to be ready for a massive transfusion
• Additional steps which are not a part of the normal adult algorithm:
  • Take the patient off the ventilator and manually ventilated them
  • Drop the PEEP to zero, to optimise preload
  • Stop the sedating infusions. With diminished cerebral perfusion, the chances of awareness are pretty minimal.  In fact, stop all the infusion (to prevent drug errors). 
  • Switch the IABP to pressure trigger mode (that way it assists CPR)

b) Modification in hypothermia:

• Modifications to prognostic thinking:
  • Prognosis may be better than expected given the usually prolonged duration of CPR
  • A large percentage of survivors (~ 40%) have a good neurological outcome
• Changes to basic life support:
  • It may take longer than normal to detect signs of life (up to 1 minute)
  • CPR should ideally be performed mechanically (prolonged CPR is to be expected)
  • Intermittent CPR (stopping for 5 minutes every 5 minutes) is reasonable for prehospital and retrieval staff, particularly when interruption facilitates retrieval
  • Manual or mechanical ventilation may encounter poor lung compliance
• Changes to advanced life support
  • Do not defibrillate until core temperature is over 30°C.
    • If you decide to defibrillate and after three shocks the rhythm remains VF, withhold further attempts until core temperature is over 30°C.
  • Do not give adrenaline until core temperature is over 30°C.
  • After 30°C is achieved, double the interval between adrenaline doses until 35°C
  • Use a low-reading thermometer to record core body temperature
  • Cardiac irritability due to CVC guidewires is probably less important than the establishment of secure access, and the groins should perhaps be preserved for ECMO. 
• Rewarming is the key to restoring life (or, pronouncing death):
  • Extracorporeal circuit rewarming is the ideal
  • Warmed fluids and peritoneal lavage is the next best option
  • External warming is least effective
  • Remember that intubation will produce a increase in the rate of cooling by interruption of shivering though paralysis and anaesthesia.

c) Modification in pregnancy:

• Modifications to diagnostic thinking:
  • Keep in mind the following alternative causes of arrest:
    • Amniotic fluid embolism
    • Hypertensive disorder of pregnancy (with ensuing cardiac failure)
    • Seizures (with ensuing hypoxia and arrest)
    • Haemorrhage from liver rupture
    • Haemorrhage from uterine rupture
• Issues which complicate the pregnant arrest scenario:
  • Difficult intubation
  • Increased risk of aspiration (the stomach just doent't empty)
  • Venous return is impaired by the gravid uterus
  • Systemic oxygen consumption is increased
  • Manually displace the uterus to the left (off the aorta and vena cava)

• Manually displace the uterus to the left (off the aorta and vena cava); perform CPR with a left lateral tilt (the ideal angle is unknown, and is thought to be between 15° and 30°)
• Biaxillary defibrillator pad placement
• Prepare for an emergency perimortem caesarian. Get more staff (there are, after all, two patients)- a paediatrician is mandatory.

• Hands slightly higher on sternum for chest compressions (mediastinal and upper abdominal structures displaced by gravid uterus