TheHs and Ts is amnemonic used to aid in remembering the possible reversible causes ofcardiac arrest.[1] A variety of disease can lead to a cardiac arrest; however, they usually boil down to one or more of the "Hs and Ts".[2][3][4]
Hypovolemia is a result of a lack of circulatingbody fluids, principally blood volume. This is usually (though not exclusively) caused by some form of bleeding,anaphylaxis, or pregnancy with gravid uterus.Peri-arrest treatment includes givingIV fluids andblood transfusions, and controlling the source of any bleeding - by direct pressure for external bleeding, or emergency surgical techniques such asesophageal banding,gastroesophageal balloon tamponade (for treatment of massivegastrointestinal bleeding such as inesophageal varices),resuscitative thoracotomy in cases of penetrating trauma or significant shear forces applied to the chest, orexploratory laparotomy in cases of penetrating trauma, spontaneous rupture of major blood vessels, or rupture of a hollow viscus in the abdomen.[citation needed]
Hypoxia is a lack ofoxygen delivery to theheart, brain and othervital organs. Rapid assessment of airway patency and respiratory effort must be performed. If the patient 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 goodCPR technique. In cases ofcarbon monoxide poisoning orcyanide poisoning,hyperbaric oxygen may be employed after the patient is stabilized.[citation needed]
Acidosis (hydrogen cation excess) is an abnormal pH in the body as a result oflactic acidosis which occurs in prolonged hypoxia and in severe infection,diabetic ketoacidosis, kidney failure causinguremia, or ingestion of toxic agents or overdose of pharmacological agents, such asaspirin and othersalicylates,ethanol,ethylene glycol and otheralcohols,tricyclic antidepressants,isoniazid, oriron sulfate. This can be treated with proper ventilation, goodCPR technique, buffers likesodium bicarbonate, and in select cases may require emergenthemodialysis.[citation needed]
Hyperkalemia (excess) andhypokalemia (inadequate) potassium can be life-threatening.
A common presentation of hyperkalemia is in the patient withend-stage renal disease who has missed adialysis appointment and presents withweakness,nausea, and broadQRS complexes on theelectrocardiogram. (Note however that patients withchronic kidney disease are often more tolerant of high potassium levels as their body often adapts to it.) Several medications, for example the antibiotictrimethoprim/sulfamethoxazole or anACE 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 ofcalcium, either ascalcium gluconate orcalcium 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 includenebulizedsalbutamol, intravenousinsulin (usually given in combination withglucose), andsodium 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 ofloop diuretics such asfurosemide) or in the stool (which is accomplished by givingsodium polystyrene sulfonate enterally, where it will bind potassium in the GI tract.) Severe cases will require emergenthemodialysis.[citation needed]
The diagnosis ofhypokalemia (not enoughpotassium) can be suspected when there is a history ofdiarrhoea ormalnutrition. Loopdiuretics may also contribute. Theelectrocardiogram may show flattening of T waves and prominent U waves.Hypokalemia is an important cause of acquiredlong QT syndrome, and may predispose the patient totorsades de pointes.Digitalis use may increase the risk thathypokalemia will produce life-threateningarrhythmias. Hypokalemia is especially dangerous in patients withischemic heart disease.[citation needed]
Hypothermia is a lowcore body temperature, defined clinically as a temperature of less than 35 degrees Celsius (95 degrees Fahrenheit). The patient is re-warmed either by using acardiac bypass or by irrigation of the body cavities (such as thorax, peritoneum, bladder) with warm fluids; or warmedIV fluids.CPR only is given until the core body temperature reaches 30 degrees Celsius, asdefibrillation is ineffective at lower temperatures. Patients have been known to be successfully resuscitated after periods of hours in hypothermia and cardiac arrest, and this has given rise to the often-quoted medicaltruism, "You're not dead until you're warm and dead."[citation needed]
Hypoglycemia was removed from the Hs and Ts by the American Heart Association in their 2010 ACLS update.[5]
The association between hypoglycemia and sudden cardiac death is unclear. Moderate and severe hypoglycemia were both associated with increased mortality; however, giving dextrose is also associated with worse outcomes in one trial.[6]
Tablets such astricyclic antidepressants,phenothiazines,beta blockers,calcium channel blockers,cocaine,digoxin,aspirin,paracetamol/acetominophen. This may be evidenced by items found on or around the patient, the patient's medical history (i.e. drug abuse, medication) taken from family and friends, checking themedical records to make sure no interacting drugs were prescribed, or sending blood andurine samples to thetoxicology lab for report. Treatment may include specificantidotes, fluids for volume expansion, vasopressors,sodium bicarbonate (fortricyclic antidepressants),glucagon orcalcium (forcalcium channel blockers),benzodiazepines (forcocaine), orcardiopulmonary bypass. Herbal supplements and over-the-counter medications should also be considered, alongside narcotics.[7]
Incardiac tamponade, blood or other fluids building up in thepericardium can put pressure on the heart so that it is not able to beat. This condition can be recognized by the presence of a narrowingpulse pressure, muffledheart sounds, distended neck veins,electrical alternans on theelectrocardiogram, or by visualization onechocardiogram. This is treated in an emergency by inserting a needle into thepericardium to drain the fluid (pericardiocentesis), or if the fluid is too thick then asubxiphoid window is performed to cut the pericardium and release the fluid.[citation needed]
Tension pneumothorax is the build-up of air into one of thepleural cavities, which causes amediastinal shift. When this happens, thegreat vessels (particularly thesuperior vena cava) become kinked, which limits blood return to theheart. 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 chestx-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 needlethoracostomy (inserting a needle catheter) into the 2ndintercostal space at the mid-clavicular line, which relieves the pressure in thepleural cavity.[citation needed] 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.[8]
Inthrombosis (myocardial infarction), if the patient can be successfully resuscitated, there is a chance that the myocardial infarction can be treated, either withthrombolytic therapy orpercutaneous coronary intervention.
Inthromboembolism (pulmonary embolism), hemodynamically significant pulmonary emboli are generally massive and typically fatal. Administration ofthrombolytics can be attempted, and some specialized centers may performthrombectomy, however, prognosis is generally poor.
Cardiac arrest can also occur after a hard blow to the chest at a precise moment in the cardiac cycle, which is known ascommotio cordis. Other traumatic events such as high speed car crashes can cause sufficient structural damage to induce arrest.
An alternative mnemonic for reversible causes of cardiac arrest isABCD-Ultrasound:[9]