Prevent cardiac arrest by considering the 4 Hs and the 4 Ts. Consider reversable causes of cardiac arrest by considering the 4 Hs and the 4 Ts.
Potential causes or aggravating factors for which specific treatment exists must be considered during all cardiac arrests. For ease of memory, these are divided into two groups of four, based upon their initial letter: either H or T:
Hypoxia
Hypovolaemia
Hyperkalaemia, hypokalaemia, hypoglycaemia, hypocalcaemia, acidaemia and other metabolic disorders
Hypothermia
Thrombosis (coronary or pulmonary)
Tension pneumothorax
Tamponade - cardiac
Toxins
The four ‘Hs’
Minimise the risk of hypoxia by ensuring that the patient’s lungs are ventilated adequately with the maximal possible inspired oxygen during CPR. Make sure there is adequate chest rise and bilateral breath sounds. Check carefully that the tracheal tube is not misplaced in a bronchus or the oesophagus.
Pulseless electrical activity caused by hypovolaemia is due usually to severe haemorrhage. This may be precipitated by trauma, gastrointestinal bleeding or rupture of an aortic aneurysm. Stop the haemorrhage and restore intravascular volume with fluid and blood products.
Hyperkalaemia, hypokalaemia, hypocalcaemia, acidaemia and other metabolic disorders are detected by biochemical tests or suggested by the patient’s medical history (e.g. renal failure). Give IV calcium chloride in the presence of hyperkalaemia, hypocalcaemia and calcium channel-blocker overdose.
Hypothermia should be suspected based on the history such as cardiac arrest associated with drowning.
The four ‘Ts’
Coronary thrombosis associated with an acute coronary syndrome or ischaemic heart disease is the most common cause of sudden cardiac arrest. An acute coronary syndrome is usually diagnosed and treated after ROSC is achieved. If an acute coronary syndrome is suspected, and ROSC has not been achieved, consider urgent coronary angiography when feasible and, if required, percutaneous coronary intervention. Mechanical chest compression devices and extracorporeal CPR can help facilitate this (see below).
The commonest cause of thromboembolic or mechanical circulatory obstruction is massive pulmonary embolism. If pulmonary embolism is thought to be the cause of cardiac arrest consider giving a fibrinolytic drug immediately. Following fibrinolysis during CPR for acute pulmonary embolism, survival and good neurological outcome have been reported, even in cases requiring in excess of 60 min of CPR. If a fibrinolytic drug is given in these circumstances, consider performing CPR for at least 60-90 min before termination of resuscitation attempts. In some settings extracorporeal CPR, and/or surgical or mechanical thrombectomy can also be used to treat pulmonary embolism.
A tension pneumothorax can be the primary cause of PEA and may be associated with trauma. The diagnosis is made clinically or by ultrasound. Decompress rapidly by thoracostomy or needle thoracocentesis, and then insert a chest drain.
Cardiac tamponade is difficult to diagnose because the typical signs of distended neck veins and hypotension are usually obscured by the arrest itself. Cardiac arrest after penetrating chest trauma is highly suggestive of tamponade and is an indication for resuscitative thoracotomy. The use of ultrasound will make the diagnosis of cardiac tamponade much more reliable.
0:00 Introduction
0:08 Reversible causes of cardiac arrest
0:36 Prevent cardiac arrest by managing reversible causes
1:23 Basic life support (BLS), must be ongoing
1:48 Hypoxia Hypovolaemia Hyperkalaemia Hypothermia
2:02 Hypoxia - low levels of oxygen in body tissues
2:17 Early reversal of hypoxia prevents deterioration
2:27 Treat the cause of hypoxia early
2:40 'Blue' (cyanosed) hearts don't start
3:03 Ventilate with high flow oxygen
3:13 Aim for SpO2 of 94 - 98%
4:21 Hypovolaemia - low blood volume
4:30 Haemorrhage (hemorrhage) - loss of blood from the circulatory system
4:38 Pulseless electrical activity (PEA arrest)
5:29 Death in trauma is commonly caused by blood loss
7:00 Hyperkalaemia - high blood potassium (K+)
7:22 Hypokalaemia - low blood potassium
7:42 Hypoglycaemia - low blood glucose
8:40 Hypothermia - low body temperature
9:10 No one is dead until they are warm and dead
10:03 Thromboembolism Tension pneumothorax Tamponade Toxic substances
10:29 Thrombus pathological blood clot in a blood vessel
10:44 Coronary arterial thrombosis
10:55 Atheroma develops in the disease process of atherosclerosis
11:38 ST elevation myocardial infarction (STEMI)
12:12 Coronary thrombosis causes myocardial infarction
13:35 Pulmonary embolism blocks off a pulmonary artery
15:02 Tension pneumothorax (2nd T)
18:19 4th T - toxic substances
19:37 ROSC - return of spontaneous circulation