Question 6

College Answer

Electro-mechanical dissociation refers to a clinical state in which the patient has an ECG compatible with a normal output but has no palpable pulse. Various ways have been proposed to assist practitioners to remember the sort of conditions that could be responsible for EMD (eg. 10 step zigzag sequence [Kloeck 1995], 4Hs and 4Ts [ILCOR 2000]). Specific conditions that should be considered (history, examination, and investigation, with specific management) include:
·           Hypoxia (ensure 100% oxygen),
·           Hypovolaemia (administer fluids, stop haemorrage, clamp bleeding vessels),
·           Hypo/hyperthermia (ensure adequately warmed if severely hypothermic, or cooled
[eg. with dantrolene for malignant hyperpyrexia])
·           Hypo/hyper-kalemia and other metabolic disorders (exclude abnormalities in K [low:
give K; high: give Ca, HCO3, consider insulin/glucose], Mg [low: give Mg;
high:give Ca], Ca [low: give Ca]; severe acidosis: consider HCO3)
·           Tamponade (drain pericardial collection, release ventilation induced intra-thoracic pressure)
·           Tension Pneumothorax (needle thoracostomy then chest tube),
·           Toxins/Poisons/Drugs (consider all recently administered drugs for allergy and/or anaphylaxis [adrenaline, fluids, oxygen, remove hapten], excessive vasodilatation or cardiac depression [consider antidotes: isoprenaline {betablockers}, Ca {Ca channel blockers}, HCO3 for Na channel blockers {especially tricyclic anti-depressants}) ·           Thrombosis Pulmonary/Coronary (consider thrombolytics, urgent surgery)

Discussion

PEA is a situation where one is presented with organised electrical activity (i.e. a potetially perfusing rhythm) in the absence of cardiac output. The old term (electro-mechanical dissociation) is no longer in use.

A good systematic framework for this is the "Four Hs and four Ts" mnemonic:

• Hypoxia
• Hypovolemia (or distributive shock)
• Hyper/hypokalemia
• Hyper/hypothermia
• Tension pneumothorax
• Tamponade
• Toxins
• Thrombus

Thus, one may start by saying that the management of such a situation, whatever the cause, should begin with cardiopulmonary resuscitation.

Specific management then depends on the cause.

Thus:

• Hypoxia in an arrest is usually well-managed with adequate bag-mask ventilation and high concentration of supplied oxygen
• Hypovolemia and distributive shock can be ameliorated by the administration of fluids
• Potassium disturbances will be discovered whent he first ABG returns from the blood gas machine, and these can be managed routinely
• Tension pneumothorax can be suspected from history, and confirmed by examination. Management consists of decompression.
• Cardiac tamponade is also suggested by history and examination findings. Management consist of emergency pericardicentesis
• Toxins are suggested by history and characteristic examination findings, eg. pinpoint pupils, the rashj of anaphylaxis, etc. Management consists of administering an antidote, if it is available.
• Thrombosis - in the context of arrest-inducing massive PE - can be suspected from history; confirmation relies on the presence of an ultrasound machine and a skilled operator. Management consists of intra-arrest thrombolysis. For coronary thrombosis, this may not be a viable option.

Everyone has heard of the 4Hs and 4 Ts, but what the hell is this 10-step zigzag sequence? Apparently, it was described by Walter J.G. Kloeck in 1995. The article is not available to me, and the abstract is uninformative, but this entry in JournalGems confirms that this 10-step mnemonic is in fact the same 4 Hs and 4 Ts with an extra H (hypoglycaemia) and an extra T (separating PE and MI). One could also argue that we could extend the mnemonic further, and end up with 20 Hs and 20Ts, but one ought to remember that these mnemonics are used by critical care staff who have brief two minute breaks between rhythm checks to diagnose the cause of the arrest while running the show. Any complex memory device used to recall causes of arrest is only adding to their already massive cognitive load.

The index of ARC guidelines is available from the ARC website.

Kloeck, Walter GJ. "A practical approach to the aetiology of pulseless electrical activity. A simple 10-step training mnemonic." Resuscitation 30.2 (1995): 157-159.