Four H and Four T to remember in cardiac arrest

The four Hs
Hypoxia, Hypovolaemia Hypothermia, hyperkalaemia

Minimise the risk of hypoxia by ensuring that the patient’s lungs are ventilated adequately with 100% oxygen. 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. Evidence of haemorrhage may be obvious, e.g. trauma, or occult e.g. gastrointestinal bleeding, or rupture of an aortic aneurysm. Intravascular volume should be restored rapidly with fluid and blood, coupled with urgent surgery to stop the haemorrhage.
Hyperkalaemia, hypokalaemia, hypoglycaemia, hypocalcaemia, acidaemia and other metabolic disorders are detected by biochemical tests or suggested by the patient’s medical history e.g. renal failure.

A 12-lead ECG may show suggestive features. Intravenous calcium chloride is indicated in the presence of hyperkalaemia, hypocalcaemia, and calcium channel- blocker overdose.
Suspect hypothermia in any drowning incident use a low reading thermometer.

The four Ts Tension pneumothorax, toxins, tamponade, thrombosis.
A tension pneumothorax may be the primary cause of PEA and may follow attempts at central venous catheter insertion. The diagnosis is made clinically. 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 cannot be assessed during cardiac arrest. Cardiac arrest after penetrating chest trauma or after cardiac surgery should raise strong suspicion of tamponade - the need for needle pericardiocentesis or resuscitative thoracotomy should be considered in this setting.
In the absence of a specific history of accidental or deliberate ingestion, poisoning by therapeutic or toxic substances may be difficult to detect but in some cases may be revealed later by laboratory investigations .
Where available, the appropriate antidotes should be used but most often the required treatment is supportive. The commonest cause of thromboembolic or mechanical circulatory obstruction is massive pulmonary embolism. If pulmonary embolism is thought to be the cause cardiac arrest consider giving a thrombolytic drug immediately. Following fibrinolysis during CPR for acute pulmonary embolism, survival and good neurological outcome have been reported 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.