Cardiac arrest
Cardiac arrest refers to when the heart stops beating, providing no or very little cardiac output. It is diagnosed when a patient is unresponsive and not breathing or breathing abnormally. As there is no cardiac output there is no pulse either, but an unconscious patient who is not breathing likely has cardiac arrest so time is not wasted feeling for a pulse.
Cardiac arrest inevitebly leads to death unless successfully and rapidly managed. Management of cardiac arrest is called cardiopulmonary resuscitation (CPR). For every minute CPR is not initiated after cardiac arrest, survival decreases by 7-10%.
We distinguish two types of CPR, basic life support (BLS) and advanced life support (ALS). CPR always involves chest compressions and ventilation. Basic life support can be learned by anyone and provided by any bystander and layman under guidance by emergency services over the phone. Some public places have automatic external defibrillators (AEDs) which any layman can use as well.
When emergency medical services arrives (if occuring outside a hospital) or CPR team (inside hospital), advanced life support (ALS) is used instead of basic life support. ALS involves the continued use of chest compressions and ventilations, but with the addition of manual defibrillators and certain drugs.
During CPR, high quality chest compression and early defibrillation are the only measures which are known to significantly improve prognosis. The evidence of efficacy of the drugs used is poor, and so chest compression and early defibrillation should be prioritised.
The goal of CPR is to achieve return of spontaneous circulation (ROSC). Following this, post cardiac arrest treatment (PCAS) should be initiated immediately as cardiac arrest may occur again.
Causes
Four different rhythms may be found when connecting the defibrillator to a patient in cardiac arrest:
- Asystole (flat-line), where there is no electrical activity. Asystole is the most common initial rhythm
- Pulseless electrical activity (PEA), where there is electrical activity (that is not a ventricular arrhythmia) that should provide cardiac output but there is still no pulse
- (Pulseless) ventricular tachycardia (VT)
- Ventricular fibrillation (VF)
Asystole and PEA do not respond to defibrillation, but VT and VF may. When the initial rhythm is VT/VF, the prognosis is better than for asystole/PEA. VT and VF occur when the cause of the cardiac arrest is cardiac, such as acute myocardial infarction, acute decompensated heart failure, or inherited cardiac arrhythmias (like long QT syndrome, Brugada syndrome). PEA is a sign that the electrical system of the heart is functioning well but there is no cardiac output regardless; this is usually due to cardiac tamponade, respiratory failure, massive pulmonary embolism, hypovolaemic shock, tension pneumothorax, etc. Asystole can occur for the same reasons as PEA but is usually the result of cardiac arrest having lasted a longer time.
The prognosis is worst with asystole, followed by PEA and then the ventricular arrhythmias.
The mnemonic "4 T's and 4 H's" can be used to remember the most common reversible causes:
| H | T |
|---|---|
| Hypoxaemia | Tamponade |
| Hypovolaemia | Thromboembolism |
| Hypo/hyperkalaemia | Tension pneumothorax |
| Hypo/hyperthermia | Toxins/intoxication |
Advanced life support algorithm (by the European resuscitation council)
Note that the European algorithm may be slightly different from your country's algorithm. For example, the Norwegian rhythm "loop" is 3 minutes long rather than the 2 minute long loop of the ERC.
Chest compressions
Performing high quality chest compression is essential during CPR. The chest wall should be pressed 5 - 6 cm down at a rate of 100 - 120/min. Keeping the rhythm of Bee Gees song Stayin' Alive (and not Gloria Gaynor's song I Will Survive) allows you to keep a good pace.
High quality chest compressions are exhausting to perform. One cannot provide high quality chest compressions for more than 1-2 minutes; after that the quality starts to worsen. It's recommended to switch who performs chest compressions after 1-2 minutes.
Ideal chest compressions provide at least 1/4 of normal cardiac output.
Ventilation
The ALS algorithm recommends pausing chest compressions for maximum 5 seconds after 30 chest compressions have been given. During these 5 seconds, 2 breaths should be delivered to the patient, either by mouth-to-mouth or by bag-valve-mask ventilation. One only needs to ventilate so much that one sees the chest wall start to elevate; that means that the ventilation was successful. If the chest wall does not elevate, the airway is not open. Time should not be wasted opening the airway; chest compressions should be initiated and the airway should be opened before 30 new chest compressions are finished and it's time for 2 new ventilations.
When a patent airway has been established (meaning that a larynx mask or supraglottic airway har been inserted, or the patient has been intubated) one ventilates 10/minute continously during chest compressions rather than 30:2.
It's actually debated whether the 30:2 compressions to breaths ratio is the best approach. Some advocate for chest compression-only CPR, as this minimises the time without compressions and may therefore provide more oxygen to the body overall, especially in the first minutes of CPR. As such, chest compressions should always be prioritised over ventilation.
Defibrillation
Together with high quality chest compressions, early defibrillation (if the patient has a shockable rhythm) is of the utmost importance. A defibrillator should be connected as soon as possible and chest compressions should be continued while it's being connected. Only during the rhythm analysis should chest compressions be paused. If the rhythm analysis shows a shockable rhythm (VT/VF), the defibrillator must charge energy, during which chest compressions should resume.
Defibrillation delivers electrical energy to the patient and everyone in contact with the patient. It's therefore essential for safety that no one touches the patient when the shock is delivered. CPR is initiated immediately after the shock is delivered.
Medications
If the initial rhythm is non-shockable, or if one has already given two shocks for a shockable rhythm, one should give adrenaline. The dose is 1 mg and is administered intravenously or intraosseously. It is repeated once for each loop.
Amiodarone 300 mg should also be given following two unsuccessful shocks for a shockable rhythm. It has no place for non-shockable rhythms.
The evidence of efficacy for the medications is very poor. Adrenaline is given in an attempt to increase perfusion to the coronary arteries, but it also increases myocardial oxygen consumption and impairs the microcirculation in the brain. Amiodarone may help stabilise ventricular arrhythmias but usually have a slow onset.
Capnography
Capnography, the monitoring of end-tidal exhaled CO2 (EtCO2), is a tool that should be used during CPR as it is a surrogate marker of cardiac output. The CO2 in question is the end-product of metabolism in the body; if the tissue oxygen delivery is poor (usually because the chest compressions are poor), less CO2 is produced, and so the EtCO2 falls.
When high quality chest compressions are given, the EtCO2 should be > 20 mmHg. If the EtCO2 drops, it is a sign of worsening chest compression quality, probably due to fatigue, and one should change compressionist.
A rapid increase in EtCO2 (to normal values > 35 mmHg (4.7 kPa) or an increase in 10 mmHg (1.3 kPa)) is usually a sign that the patient has recovered spontaneous circulation (ROSC). This increase occurs earlier than the pulse and blood pressure returns, and it avoids the need to pause chest compressions to palpate for a pulse.
A change in the capnography graph can also be a sign of dislocated endotracheal tube.
A consistently low EtCO2 (if the chest compressions are high quality) can also be a sign of non-cardiac cause of cardiac arrest, as despite effective compressions peripheral tissues are still not receiving oxygen. This can be due to hypovolaemic shock, pulmonary embolism, cardiac tamponade, tension pneumothorax, or that the patient has been dead for long.
If the EtCO2 is < 10 mmHg (or 1.3 kPa) after 20 minutes of CPR, the prognosis is very poor and one should consider terminating CPR. If the EtCO2 is > 20 mmHg (or 2.7 kPa), the prognosis is good.
Underlying cause
While CPR is being given, it's important to look for and treat any treatable underlying cause. Patient history may provide clues (chest pain in case of myocardial infarction, history of intoxication, etc.).
An arterial blood gas should be taken, as the results arrive quickly and give information on electrolytes and acid-base status. Fluids and 100% oxygen are usually routinely given in case the cause is hypovolaemic or hypoxaemic, respectively.
Ultrasonography can be used to look for signs of:
| Condition | Sign |
|---|---|
| Hypovolaemic shock | Collapsed inferior vena cava |
| Tension pneumothorax | Air in the pleural cavity, lack of lung sliding |
| Cardiac tamponade | Pericardial effusion, compression of the right atrium and ventricle |
| Myocardial infarction | Regional wall motion abnormality, only visible if the heart is contracting at all) |
| Massive pulmonary embolism | Larger right ventricle, flattening of the intraventricular septum |
However, ultrasonography during CPR is very difficult and can necessitate pauses in chest compressions.
If acute myocardial infarction is presumed as a cause it's possible to perform percutaneous coronary intervention during CPR.
Signs of ROSC
- The patient waking up
- A pulse is palpated
- The EtCO2 rapidly increases
Post-resuscitation care
If CPR is successful and return of spontaneous circulation (ROSC) is achieved, it's important to initiate post-resuscitation care.
- Oxygenate and ventilate to achieve SpO2 94-98% and normocapnia
- Obtain an ECG
- Establish intra-arterial blood pressure monitoring
- Administer fluids
- If systolic BP < 100 mmHg, give vasopressors or inotropics
- Sedate the patient and cool them to 32 - 36℃
- Continue to look for and treat underlying cause
Complications
High quality chest compressions necessarily cause rib and sternal fractures and possibly other blunt thoracic trauma (including lung contusion, heart contusion) in almost all patients, especially the elderly (who usually have osteoporosis).
Prognosis and do-not-resuscitate
Despite perfect CPR, the prognosis of cardiac arrest is very poor. While around 10-30% of out-of-hospital cardiac arrests achieve ROSC, less than 10% of them survive to hospital discharge. Many of the survivors have poor neurological function. The survival rate for in-hospital cardiac arrest is a bit better, probably due to rapid initiation of ALS and that the patient's medical history is known. The prognosis is much worse for patients with chronic illnesses; <2% of patients with advanced COPD, heart failure, malignancy, or cirrhosis survive for at least 6 months after cardiac arrest. Patients massively overestimate the success rate of CPR (due to inaccurate displays of CPR on television) and are therefore usually unaware that CPR should not be initiated in all cases. Up to half of CPR survivors wish they hadn't been resuscitated.
It is ethically and medically inappropriate to give futile medical therapy, including CPR. The worst case scenario following CPR is that ROSC is achieved but the patient has no neurological function or needs mechanical ventilation or similar for the rest of their life. In cases where the physician percieves a patient's odds of surviving cardiopulmonary resuscitation with good neurological outcomes as very low the physician can discuss a do-not-resuscitate order with the patient, also called a DNR or a "no code". In some countries, the physician can decide this for the patient (even if the patient disagrees); this is the case in Norway, for example. In other countries, like the USA, the patient (or guardian) must agree and sign a written form. I do not know the routine in Hungary. In most cases, when patients are informed of the poor prognosis of CPR, they understand and accept their DNR order, as most would much rather allow a natural death than surviving but risking significantly reduced functioning.
Peri-arrest and warning signs
The peri-arrest state is the state just before cardiac arrest, indicating the need for immediate intervention and/or preparation for CPR. It’s important to recognize so that CPR can be initiated early. A peri-arrest state occurs in 80% of cases before cardiac arrest.
The so-called “OMG” signs of peri-arrest:
- Respiratory rate > 30/min or < 8/min
- Heart rate > 140/min or < 40/min
- Systolic BP > 220 mmHg or < 90 mmHg
- GCS decrease by > 2
- Imminent airway obstruction (decrease in SpO2)
Other important signs of peri-arrest:
- Seizure
- Asystolic periods (> 2 – 3 seconds)
- Acute significant bleeding
- Any unexplained deterioriation
Immediately perform ABCDE management. Secure airways and breathing, monitor and support circulation, check for disabilities and exposure/environment.