When should I check the H's (hypovolemia, hypoxia, hyperkalemia, hypothermia, hydrogen ions acidosis) and T's (tension pneumothorax, tamponade, toxins, thrombosis) during a cardiac arrest?

From the Guidelines

You should check the H's and T's during a cardiac arrest after initiating high-quality CPR and defibrillation for shockable rhythms, specifically during the first 2-3 minutes of resuscitation while continuing CPR cycles. The H's include hypovolemia (treat with fluid boluses), hypoxia (ensure proper ventilation and oxygenation), hydrogen ion acidosis (consider sodium bicarbonate if severe), hyperkalemia (give calcium chloride/gluconate, insulin with glucose, and sodium bicarbonate), and hypothermia (initiate active rewarming) 1. The T's include tension pneumothorax (perform needle decompression), cardiac tamponade (consider pericardiocentesis), toxins (administer specific antidotes when identified), and thrombosis (consider thrombolytics for suspected massive pulmonary embolism or acute coronary syndrome) 1. Early identification and treatment of these reversible causes is crucial as they may be the primary reason for the arrest, and addressing them specifically can significantly improve the chance of successful resuscitation, as emphasized in the guidelines for adult advanced life support 1 and post-cardiac arrest care 1. Remember that high-quality CPR and early defibrillation remain the cornerstone of resuscitation, but simultaneously identifying and treating these underlying causes can be lifesaving, as highlighted in the advanced life support guidelines 1.

Some key points to consider when checking the H's and T's include:

• Ensuring proper ventilation and oxygenation to address hypoxia
• Administering fluid boluses to treat hypovolemia
• Considering sodium bicarbonate for severe hydrogen ion acidosis
• Giving calcium chloride/gluconate, insulin with glucose, and sodium bicarbonate for hyperkalemia
• Initiating active rewarming for hypothermia
• Performing needle decompression for tension pneumothorax
• Considering pericardiocentesis for cardiac tamponade
• Administering specific antidotes for toxins
• Considering thrombolytics for suspected massive pulmonary embolism or acute coronary syndrome.

It is essential to prioritize these interventions based on the patient's specific needs and the underlying cause of the cardiac arrest, as guided by the most recent and highest quality evidence 1.

From the Research

Checking H's and T's during Cardiac Arrest

• The H's and T's are a mnemonic used to remember the reversible causes of cardiac arrest, including hypovolemia, hypoxia, hyperkalemia, hypothermia, hydrogen ions acidosis, tension pneumothorax, tamponade, toxins, and thrombosis 2.
• According to a study published in 2022, the most frequent etiologies of cardiac arrest were hypoxia, acute coronary syndrome, arrhythmias, hypovolemia, infection, and heart failure 3.
• The study suggests that cardiac tamponade, electrolyte disturbances, pulmonary embolism, neurological causes, toxins, and pneumothorax were less frequent causes of in-hospital cardiac arrest 3.
• It is recommended to check the H's and T's during cardiac arrest as part of a comprehensive approach to identifying and correcting the underlying cause of the arrest 2.
• A proposed framework for investigating the causes of perioperative cardiac arrest includes using the preload-contractility-afterload-rate and rhythm (PCARR) construct, monitoring variables such as electrocardiography and pulse oxygen saturation, and utilizing the Anesthetic care, Surgery, Echocardiography, Relevant Check and History (A-SERCH) list of actions 2.
• The H's and T's mnemonic should be used in conjunction with other diagnostic tools and frameworks to ensure a thorough investigation of the causes of cardiac arrest 2, 3.