H’s and T’s

The Hs and Ts is a mnemonic used to aid in remembering the possible reversible causes of cardiac arrest. A variety of disease processes can lead to a cardiac arrest; however, they usually boil down to one or more of the "Hs and Ts".

  • Hypovolemia

    • Hypovolemia is a common cause of cardiac arrest and develops from severe fluid or blood loss. This is typically a result of excessive sweating, vomiting, traumatic blood loss, severe burns or diarrhea.

  • Hypo/Hyperkalemia

    • Both hypokalemia and hyperkalemia are conditions in which potassium levels are too high or low to maintain normal contraction of the myocardium. When these levels of K+ are off, the individual is at high risk for cardiac arrest. A few causes of hypokalemia and hyperkalemia include use of diuretics, excessive vomiting, DKA, and kidney disease or failure. Hyperkalemia may be caused by diabetes, kidney disease or as a side effect of certain drugs.

  • Hypoxia

    • Hypoxia is an insufficiency in the amount of oxygen that reaches vital organs and tissues. It can occur from several reasons, including disorders of the lungs, drowning, fires, high altitudes, chemical or gas poisonings, etc.

  • Hydrogen Ion (acidosis)

    • Hydrogen Ion Excess, or Acidosis, is either a respiratory or metabolic emergency that can lead to cardiac arrest that occurs when there are inadequate pH levels caused by too much acid in the body. Some causes of acidosis include lung disease, C02 buildup, DKA/AKA, liver failure, cancer, etc.

  • Hypothermia 

    • Hypothermia occurs when the body cannot keep itself warm and the core temperature drops below 30 degrees Celsius. Hypothermia can lead to cardiac arrest because cardiac output is decreased. Hypothermia ensues when an individual is exposed to extreme and/or extended exposure to cold weather or water temperatures.

  • Tension Pneumothorax 

    • Tension pneumothorax develops when there is a buildup of air in the pleural cavity, but there is no place for air to exit. The buildup of air causes a shift in mediastinum and venous return to the heart is blocked and can result in cardiac arrest. Some common causes of tension pneumothorax are chest trauma, iatrogenic and mechanical ventilation. Signs include unequal breathing sounds, JVD, ventilation issues and tracheal deviation.

  • Tamponade Cardiac

    • Cardiac tamponade is a buildup of blood or fluid in the pericardial space, causing pressure on the heart, preventing ventricles from filling properly. Causes of tamponade include chest trauma, pericarditis and myocardial rupture.

  • Toxins

    • The ingestion of toxins is one of the most common causes of cardiac arrest, and occurs when an individual either intentionally or unintentionally overdoses on some type of medication, street drug or chemical exposure. One commonly seen sign of cardiac arrest due to toxins is a prolonged QT interval.

  • Thrombosis

    • Pulmonary Thrombosis, or a pulmonary embolism, typically develops after a blood clot in another area of the body, and can lead to cardiac arrest in some instances. A pulmonary embolism is a blockage of the lung’s main artery, and is caused by blood clots.

    • Coronary Thrombosis is a blockage within the coronary artery or arteries due to clotted blood in the vessel. This prevents blood from properly flowing to the heart, and can cause cardiac arrest depending on the intensity and location of the blockage. Coronary thrombosis is caused by blood clots and myocardial infarction.

Signs and Therapeutic Interventions

Hypovolemia 

  • Signs - rapid heart rate, narrow QRS, blood loss or excessive fluid loss

  • Treatment - volume infusion (fluid or blood or blood products)

Hypo/Hyperkalemia

  • Signs - Flattened T waves and a U wave in hypokalemia, peaked T waves and a wide QRS in hyperkalemia

  • Treatment - Several measures may be taken to treat hyperkalemia, including administering sodium bicarbonate, glucose and insulin, or nebulized albuterol. Hypokalemia treatment is intravenous administration of a dilute solution of potassium chloride.

Hypoxia

  • Signs - Respiratory distress, respiratory failure, respiratory arrest. Oxygen saturation less than 90%, or ETCO2 >50 mmhg

  • Treatment - Ensure that the patient’s airway is patent, provide adequate ventilation and supplemental oxygen.

Hydrogen ion—acidosis 

  • Signs - Tachycardia, tachypnea, hypercapnia, hypertension, hypoxemia, hypercarbia, confusion, headache. Arterial blood gases: pH < 7.35, ETCO2: < 29 mmHg in metabolic acidosis, > 50 mmHg in respiratory acidosis

  • Treatment - In patients with metabolic acidosis, the administration of an initial dose of sodium bicarbonate (1 mEq/kg) may be indicated, in respiratory acidosis mechanical ventilation.

Hypothermia

  •  Signs - Body temperature less than 86° F [30° C].

  • Treatment - Core rewarming with cardiopulmonary bypass, extracorporeal blood warming with partial bypass or thoracic lavage with warmed fluids is indicated. Warmed fluids and warmed humidified oxygen may be administered as adjunctive therapies.

Tension Pneumothorax

  • Signs - Tachypnea, diminished or absent breath sounds, unequal chest expansion, tracheal deviation (late sign), jugular venous distension, hypotension, anxiety, diaphoresis, cyanosis, high peak inspiratory pressures (in patients receiving mechanical ventilation) difficulty ventilating the patient may also be a sign. PEA rhythm with narrow QRS complexes.

  • Treatment - Decompression - needle decompression or chest tube placement.

Tamponade, cardiac 

  • Signs -Findings may include the three cardinal signs of cardiac tamponade (Beck’s triad): hypotension (weak pulse or narrow pulse pressure), muffled heart sounds and jugular venous distension. In a patient with PEA, narrow QRS complexes and electrical alternans (i.e., beat-to-beat variation in the amplitude of the QRS complexes) may be seen.

  • Treatment - pericardiocentesis

Toxins

  • Signs - Overdoses of both illicit and therapeutic drugs and poisoning.

  • Treatment (emergent dialysis, reversal agents)

Thrombosis

  • Coronary Thrombosis

    • Signs - chest pain/ discomfort; dizziness, light-headedness or syncope; nausea or vomiting; dyspnea; diaphoresis; cyanosis, ST-segment changes, T-wave inversion.

    • Treatment -If a pre- arrest 15-lead ECG shows an inferior wall myocardial infarction with right ventricular involvement (evidenced by ST-segment elevation in lead V4R), then impaired preload is likely the cause of cardiac arrest and fluid bolus therapy should be provided during resuscitation. If a pre-arrest 12-lead ECG shows anterior wall myocardial infarction, then impaired contractility is the likely cause of cardiac arrest. When myocardial infarction is the suspected cause of cardiac arrest, a 12-lead ECG should be obtained after ROSC is achieved to guide therapy and inotropic support may be needed to address cardiogenic shock.

  • Pulmonary Thrombosis

    • Signs - dyspnea, tachycardia, pleuritic chest pain, hemoptysis, anxiety, diaphoresis, syncope, PEA is the initial rhythm in one-third to one- half of patients with cardiac arrest caused by pulmonary embolism.

    • fibrinolytics, or surgical evacuation

Yakita WilkinsonComment