Hs and Ts
The Hs and Ts is a mnemonic used to aid in remembering the possible reversible causes of cardiac arrest.[1] A variety of conditions can lead to a cardiac arrest; however, they are often one or more of the "Hs and Ts".[2][3][4] They often result in pulseless electrical activity; but, may be found in any type of arrest.[5] In children hypoxia and hypovolemia are the most common.[5]
Hs
Hypovolemia
Hypovolemia is a result of a lack of circulating body fluids, principally blood. This is usually caused by some form of bleeding, anaphylaxis, or later pregnancy. Peri-arrest treatment includes giving IV fluids, blood products, and controlling the source of any bleeding. Bleeding maybe controlled by direct pressure for external bleeding, or surgery such as esophageal banding, gastroesophageal balloon tamponade (for esophageal varices), resuscitative thoracotomy, or exploratory laparotomy.
Hypoxia
Hypoxia is a lack of oxygen delivery to the heart, brain and other vital organs. Management involves rapid assessment of airway patency and respiratory effort. If the person is mechanically ventilated, the presence of breath sounds and the proper placement of the endotracheal tube should be verified. Treatment may include providing oxygen, proper ventilation, and good CPR technique. In cases of carbon monoxide poisoning, hyperbaric oxygen may be employed.
Acidosis
Acidosis (hydrogen cation excess) is an abnormally low pH as a result of lactic acidosis from hypoxia or infection, diabetic ketoacidosis, kidney failure causing uremia, or toxins, such as aspirin and other salicylates, ethanol, ethylene glycol and other alcohols, tricyclic antidepressants, isoniazid, or iron sulfate.
It may be managed with proper ventilation, good CPR technique, buffers like sodium bicarbonate, and in select cases may hemodialysis.
Hyper or hypokalemia
Hyperkalemia (excess) and hypokalemia (inadequate) potassium can be life-threatening.
Hyperkalemia commonly occurs with end-stage renal disease if dialysis is missed and presents with weakness, nausea, and broad QRS complexes on the electrocardiogram. (Note however that patients with chronic kidney disease are often more tolerant of high potassium levels as their body often adapts to it.) Several medications, for example the antibiotic trimethoprim/sulfamethoxazole or an ACE inhibitor, can also lead to the development of significant hyperkalemia. The electrocardiogram will show tall, peaked T waves (often larger than the R wave) or can degenerate into a sine wave as the QRS complex widens. Immediate initial therapy is the administration of calcium, either as calcium gluconate or calcium chloride. This stabilizes the electrochemical potential of cardiac myocytes, thereby preventing the development of fatal arrhythmias. This is, however, only a temporizing measure. Other temporizing measures may include nebulized salbutamol, intravenous insulin (usually given in combination with glucose), and sodium bicarbonate which all temporarily drive potassium into the interior of cells. Definitive treatment of hyperkalemia requires actual excretion of potassium, either through urine (which can be facilitated by administration of loop diuretics such as furosemide) or in the stool (which is accomplished by giving sodium polystyrene sulfonate enterally, where it will bind potassium in the GI tract.) Severe cases will require emergent hemodialysis.[citation needed]
The diagnosis of hypokalemia (not enough potassium) can be suspected when there is a history of diarrhoea or malnutrition. Loop diuretics may also contribute. The electrocardiogram may show flattening of T waves and prominent U waves. Hypokalemia is an important cause of acquired long QT syndrome, and may predispose the patient to torsades de pointes. Digitalis use may increase the risk that hypokalemia will produce life-threatening arrhythmias. Hypokalemia is especially dangerous in patients with ischemic heart disease.
Hypothermia
Hypothermia is a low body temperature, defined as less than 35 degrees Celsius (95 degrees Fahrenheit). Treatment is by re-warming either by using a cardiac bypass or by irrigation of the body cavities (such as thorax, peritoneum, bladder) with warm fluids; or warmed IV fluids. CPR is carried out until the core body temperature reaches 30 degrees Celsius, as defibrillation is ineffective at lower temperatures. People have been successfully resuscitated after periods of hours in cardiac arrest due to hypothermia, and this has given rise to the often-quoted medical truism, "you're not dead until you're warm and dead".
Hypoglycemia
Hypoglycemia was removed from the Hs and Ts for adults by the American Heart Association in their 2010 ACLS update.[6] It remains in the PALS cardiac arrest algorithm as of 2020.[7]
The association between hypoglycemia and sudden cardiac death is unclear. Moderate and severe hypoglycemia were both associated with increased mortality; however, giving dextrose was associated with worse outcomes in one trial.[8]
Ts
Tablets or toxins
Tablets refers to an overdose such as with tricyclic antidepressants, beta blockers, calcium channel blockers, cocaine, digoxin, or aspirin. This may be supported by items found on or around the person, their medical history (i.e. drug misuse, suicidal) taken from family and friends, or sending blood and urine samples to the toxicology lab for report.
Treatment may include specific antidotes, fluids for volume expansion, vasopressors, sodium bicarbonate (for tricyclic antidepressants or cocaine), glucagon or calcium (for calcium channel blockers), benzodiazepines (for cocaine), or cardiopulmonary bypass. Herbal supplements and over-the-counter medications should also be considered, alongside opioids.[9]
Cardiac tamponade
In cardiac tamponade, fluids build up in the pericardium and put pressure on the heart. This condition can be recognized by the presence of a narrowing pulse pressure, muffled heart sounds, distended neck veins, electrical alternans on the electrocardiogram, or visualization on ultrasound. It is treated as an emergency by inserting a needle into the pericardium to drain the fluid (pericardiocentesis), or if the fluid is too thick a subxiphoid window is cut.
Tension pneumothorax
Tension pneumothorax is the build-up of air into one of the pleural cavities, which causes a mediastinal shift. When this happens, the great vessels (particularly the superior vena cava) become kinked, which limits blood return to the heart. The condition can be recognized by severe air hunger, hypoxia, jugular venous distension, hyperresonance to percussion on the affected side, and a tracheal shift away from the affected side. The tracheal shift often requires a chest x-ray to appreciate (although treatment should be initiated prior to obtaining a chest x-ray if this condition is suspected). This is relieved by a needle thoracostomy (inserting a needle catheter) into the 2nd intercostal space at the mid-clavicular line, which relieves the pressure in the pleural cavity. Critical care teams also have the skill to incise the chest in the 5th intercostal space in the mid-axillary line, to evacuate air with a larger breach of the pleura. However, this is associated with a range of potential complications.[10]
Thrombosis (myocardial infarction)
In thrombosis (myocardial infarction), if the patient can be successfully resuscitated, there is a chance that the myocardial infarction can be treated, either with thrombolytic therapy or percutaneous coronary intervention.
Thromboembolism
In thromboembolism (pulmonary embolism), large emboli may result in cardiac arrest. Giving thrombolytics, such as tPA or TNK, can be attempted, and some centers may perform thrombectomy, however, prognosis is generally poor.
Trauma
Cardiac arrest can also occur after a hard blow to the chest at a precise moment in the cardiac cycle, which is known as commotio cordis. Other traumatic events such as high speed car crashes can cause sufficient structural damage to induce arrest.
Alternatives
An alternative mnemonic for reversible causes of cardiac arrest is ABCD-Ultrasound:[11]
- Airway and access; Ensuring open airways such as using a supraglottic device, establishing access by venipuncture (or intraosseous needle) for intravenous therapy.[11]
- Blood gas and bicarbonate; checking a venous blood gas with electrolytes, as well as giving bicarbonate and calcium in case of hyperkalemia. Bicarbonate may also be given in profound acidosis (but the most important acidosis treatment is adequate ventilation).[11]
- Core temperature; To detect and treat hypothermia.[11]
- Defibrillation; The application of an automated external defibrillator for rhythm analysis and correction.
- Ultrasound: Cardiac ultrasonography for any pericardial effusion that may be causing a cardiac tamponade, as well as any right ventricle dilatation that may indicate a massive pulmonary embolism. Bilateral lung ultrasonography to look for lung sliding and rule out a tension pneumothorax. [11]
References
- ↑ Resuscitation Council UK (2005). Resuscitation Guidelines 2005 London: Resuscitation Council UK.
- ↑ ACLS: Principles and Practice. p. 71-87. Dallas: American Heart Association, 2003. ISBN 0-87493-341-2.
- ↑ ACLS for Experienced Providers. p. 3-5. Dallas: American Heart Association, 2003. ISBN 0-87493-424-9.
- ↑ "2005 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care - Part 7.2: Management of Cardiac Arrest." Circulation 2005; 112: IV-58 - IV-66.
- ↑ 5.0 5.1 Vega, RM; Kaur, H; Sasaki, J; Edemekong, PF (January 2025). "Cardiopulmonary Arrest in Children". StatPearls. PMID 28613789.
- ↑ "Part 7: Adult Advanced Cardiovascular Life Support – ECC Guidelines". Eccguidelines.heart.org. Archived from the original on 2022-03-14. Retrieved 2018-10-10.
- ↑ Topjian, Alexis A.; Raymond, Tia T.; Atkins, Dianne; Chan, Melissa; Duff, Jonathan P.; Joyner, Benny L.; Lasa, Javier J.; Lavonas, Eric J.; Levy, Arielle; Mahgoub, Melissa; Meckler, Garth D.; Roberts, Kathryn E.; Sutton, Robert M.; Schexnayder, Stephen M.; Bronicki, Ronald A.; de Caen, Allan R.; Guerguerian, Anne Marie; Kadlec, Kelly D.; Kleinman, Monica E.; Knight, Lynda J.; McCormick, Taylor N.; Morgan, Ryan W.; Roberts, Joan S.; Scholefield, Barnaby R.; Tabbutt, Sarah; Thiagarajan, Ravi; Tijssen, Janice; Walsh, Brian; Zaritsky, Arno (20 October 2020). "Part 4: Pediatric Basic and Advanced Life Support: 2020 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care". Circulation. 142 (16_suppl_2). doi:10.1161/CIR.0000000000000901.
- ↑ Finfer S, Liu B, Chittock DR, Norton R, Myburgh JA, McArthur C, et al. (September 2012). "Hypoglycemia and risk of death in critically ill patients". The New England Journal of Medicine. 367 (12): 1108–1118. doi:10.1056/NEJMoa1204942. PMID 22992074.
- ↑ "AED in de buurt van VVE". Aedmaster.nl. Retrieved 2021-04-20.
- ↑ Mohrsen S, McMahon N, Corfield A, McKee S (December 2021). "Complications associated with pre-hospital open thoracostomies: a rapid review". Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine. 29 (1): 166. doi:10.1186/s13049-021-00976-1. PMC 8643006. PMID 34863280.
- ↑ 11.0 11.1 11.2 11.3 11.4 Cunningham, Richard J. MD (2021). "A Novel Mnemonic for Reversible Causes of ACLS". Emergency Medicine News. 43 (7). doi:10.1097/01.EEM.0000758760.12428.35. Archived from the original on 2024-12-04. Retrieved 2025-01-16.