What are the H’s and T’s of ACLS?

What are the H's and T's of ACLS?
  • Updated on: January 3, 2024

In the dynamic world of advanced cardiovascular life support (ACLS), every heartbeat counts. Over 356,000 out-of-hospital cardiac arrests take place each year, and we can save these people by being well-equipped. This is where ACLS steps in and arms healthcare providers with crucial knowledge. Enter Pulseless Electrical Activity (PEA), Ventricular Fibrillation (VFib or VF), and Ventricular Tachycardia (VTach or VT) – technical terms that elevate ACLS understanding. The H’s and T’s of ACLS serve as primary indicators during critical situations. In the realm of ACLS, understanding the H’s and T’s is like having a roadmap to revive a struggling heart. Keep reading to understand more about the H’s and T’s and their role as key indicators during critical situations.

H’s and T’s of ACLS

Different health problems can cause heart attacks in both adults and kids. This involves problems with the heart’s neuro-electrical system. It could stem from disorders you are born with, and changes in the heart’s mechanism. Finding and fixing the reason behind heart failure is crucial to help patients recover. From Hypovolemia to Tamponede, understanding H and T of cardiac arrest are key in advanced cardiovascular life support. Explore the ACLS H’s and T’s:

Hypoxia: Hypoxemia is caused when there’s not enough oxygen in the blood. This can cause a lack of oxygen in tissues. The following are some of the causes of hypoxemia:

  • Airway obstruction
  • Anemia
  • Asthma
  • Avalanche burial
  • Brain or spinal cord damage causes breathing problems.
  • Chronic obstructive pulmonary disease
  • Drowning
  • Hanging
  • High altitude
  • Breathing problems from muscle disease impact the lungs’ function.
  • Pneumonia
  • Tension pneumothorax
  • Trauma
  • Traumatic asphyxia or pressure suffocation (for example, a crowd crush)

Hypovolemia: One usual reason for cardiac arrest is hypovolemia. It can happen if there’s not enough blood inside the veins (like bleeding) or when you sweat a lot, or throw up too much. Bad burns can also cause low blood volume. Losing blood is one of the main reasons people die from heart problems caused by accidents. Loss of blood is usually easy to see (like when you get hurt or vomit blood, cough it up), but internal bleeding stays invisible (such as from bleeding in your stomach or an aneurysm burst). 

Read More: Importance of Learning ACLS

Hypothermia: Every year in the United States, around 1500 people die from accidental hypothermia. This is when your body gets too cold suddenly and lowers its main temperature below 35 degrees Celsius. You can measure this using a system called Swiss staging, which breaks it down even more into different stages or levels of severity, with level one being less severe than the others.

  • Hypothermia level 1: Gentle hypothermia (awake, shivering, and core body temperature between 32 and 35 degrees Celsius)
  • Hypothermia Part 2: – When you’re not shivering but feel cold and your main body temperature is between 82 and 90 degrees.
  • Hypothermia Part 3: Hypothermia Part 3 is when a person’s body temperature drops very low (around 75 to 82 degrees Fahrenheit). They might lose consciousness, but they still have signs of life.
  • Hypothermia IV: Sudden heart stop or low blood flow state (almost no important signs; core temperature is less than 24 degrees Celsius)
  • Hypothermia V: Death from severe hypothermia that is irreparable (core temperature less than 13.7 degrees Celsius)

Hyperkalemia/hypokalemia: Electrolyte issues can cause heart rhythm problems or cardiac arrest. Potassium disorders, especially high potassium levels, are most often linked with life-threatening arrhythmias, and the normal working of our heart needs a balance of electrolytes like sodium and calcium. If levels get too high or low, heart failure can happen. The exact numbers that lead to treatment choices will depend on the person’s health situation and how fast their electrolyte values change.

Hyperkalemia: A heart attack is often caused by too much potassium in the blood. This is usually because the kidneys can’t get rid of things properly, like drugs or high levels of potassium in cells, while there are too many bad substances causing acid to build up. Hyperkalemia happens often in patients who need hospital help, like 10%. Here are ways to treat hyperkalemia:

  • Cardiac protection
  • Shifting potassium into cells
  • Removing potassium from the body
  • Checking potassium and sugar levels in the blood.
  • Prevention of recurrence

Hypokalemia: Hypokalemia is the most common problem in medical clinics. It’s found in up to 20% of hospital patients and causes heart problems like arrhythmias or sudden death because it means you have too little potassium (less than a certain amount). The main causes of hypokalemia include:

  • Gastrointestinal loss (e.g., diarrhea)
  • Drugs (e.g., diuretics, laxatives, and steroids)
  • Losses of kidney function (for example, renal tubular problems, diabetes insipidus, and dialysis)
  • Hormone problems (for example, Cushing’s syndrome and high aldosterone levels)
  • Metabolic alkalosis
  • Magnesium depletion
  • Poor dietary intake

Treating low potassium levels in the body depends on how bad it is and if you have signs or problems with your heart’s electrical activity. The best thing to do is slowly bring potassium levels back to normal in your blood.

Tension Pneumothorax: Tension pneumothorax means trouble with blood pressure in a patient whose lungs are filling up. This is something that can cause cardiac arrest. If there’s too much air buildup in the space surrounding the lungs and other organs, it can lead to a condition called tension pneumothorax. Building up makes the chest move and stops blood from going back to the heart. This can stop your heartbeat. Tension pneumothorax can happen in different health situations, like accidents, asthma, and other breathing problems.

Tamponade (Cardiac): Cardiac tamponade is when the heart’s protective layer gets filled with pressured fluid. This makes it hard for your heart to work right and could completely stop the heart’s beating. It can happen from chest injuries like a gunshot wound or because of an inflamed pericardium. Thoracotomy, or pericardiocentesis, can fix heart attacks related to possible injuries and other types of cardiac tamponade. It is best to use ultrasound during pericardiocentesis if possible.

Toxins: Choking and interruption of breathing due to low awareness often cause death after self-poisoning (benzodiazepines, alcohol, opiates, tricyclics, or barbiturates). Keep unconscious patients alive, but don’t let them choke. Some of the drugs often found in an overdose are benzodiazepines, opioids, tricyclic antidepressants, and local anesthetics. Also included are beta-blockers and calcium channel blockers.

Read More: How to get online ACLS certification


The H’s and T’s ACLS serve as the compass guiding healthcare providers through the landscape of cardiac emergencies. Understanding these reversible causes is crucial for saving lives in emergency situations. These include problems with blood and oxygen levels that can be fixed, as well as dealing with blood clots or fluid buildup around the heart. H’s and T’s ACLS not only represent classes but also show the dedication of health workers to keeping life safe in difficult moments.