UK Resuscitation Advanced Life Support Guidelines: Should the Paradigm be Extended?

Cardiac arrest continues to be a predominant cause of mortality worldwide, necessitating its rapid identification, and intervention by reversible aetiologies to optimise successful outcomes. The established 4H 4T framework has served as a foundational guide for advanced life support (ALS) protocols since its formal introduction in the 2000 International Guidelines on Cardiopulmonary Resuscitation (CPR) and Emergency Cardiovascular Care (ECC), effectively targeting critical conditions such as hypoxia, hypothermia, hypo-/hyperkalaemia, hypovolaemia, tension pneumothorax, cardiac tamponade, thrombosis, and exposure to toxins. However, this framework inadequately addresses other significant factors: specifically hypoglycaemia and tachy- and bradyarrhythmias. Hypoglycaemia, a reversible and treatable metabolic state, poses substantial threats to cardiovascular stability, particularly in people with diabetes and in association with sepsis. It disrupts myocardial repolarisation, prolongs the QT interval, and may instigate the R-on-T phenomenon, which can precipitate life-threatening arrhythmias. Likewise, tachyarrhythmias and bradyarrhythmias often precipitate cardiac arrest, thereby warrant dedicated attention within ALS protocols. This paper advocates expanding the current 4H 4T framework to include hypoglycaemia and tachy- and bradyarrhythmias as critical and reversible causes of cardiac arrest (5H 5T). The rationale for such a paradigm shift is supported by evidence from clinical studies, case reports, and experimental models that demonstrate the adverse effect of these conditions on cardiovascular integrity and alert clinicians to look for these reversible factors. The inclusion of these factors into ALS protocols will necessitate revising resuscitation guidelines, modifying training for healthcare practitioners, and including systematic monitoring of blood glucose alongside routine assessment of cardiac rhythm during resuscitation procedures. Future research should focus on elucidating the pathophysiological mechanisms underlying these conditions, to establish operational thresholds for intervention, and validate their integration into resuscitation frameworks. By expanding the conceptualisation of reversible causes, the proposed 5H/5T framework would offer a more rational and practical approach to the management of cardiac arrest, to improve the survival and recovery of these critically ill patients.