Basic Life Support (BLS) is the foundation of emergency cardiovascular care. It refers to a series of lifesaving actions that assist and maintain airway, breathing, and circulation—sometimes called the ABCs of resuscitation. Whether you’re a healthcare provider or a trained bystander, knowing how to perform BLS is a matter of life or death.
According to the Centers for Disease Control and Prevention (CDC), more than 356,000 out-of-hospital cardiac arrests occur in the United States each year. Survival rates are poor, particularly when Cardiopulmonary Resuscitation (CPR) is not undertaken immediately. This is exactly why it is so critical that you understand and apply the Adult BLS Algorithm—it provides an actionable approach to doing something in a timely, effective manner!
So, what exactly is the Adult Basic Life Support Algorithm? It’s a standardized approach recommended by the American Heart Association (AHA) that guides rescuers through each critical action — from assessing responsiveness and calling for help to delivering high-quality chest compressions, providing rescue breaths, and using an AED (Automated External Defibrillator) when available. This evidence-based algorithm ensures that no essential step is missed during a high-stress emergency.
Why the rush? Because when it comes to sudden cardiac arrest, every second is critical. For each minute that passes without defibrillation and high-quality chest compressions, the likelihood of survival declines by up to 10%. Time is brain, heart, and life.
This is where the Chain of Survival comes in — a series of critical actions that can help a person have the best chance of surviving a cardiac emergency. It begins with early recognition and activation of the emergency response system, early CPR, rapid defibrillation, effective advanced life support, and post-cardiac arrest care.
In this guideline, you’ll discover how to evaluate an unresponsive adult, when and how to perform CPR, how to utilize an AED (Automated External Defibrillator), and when to call emergency medical services. This guide has you covered, whether you are brushing up on your skills or prepping for a BLS certification.
Understanding what kind of life-threatening condition you are dealing with is critical when responding to an emergency. The Adult Basic Life Support Algorithm often starts by identifying the problem, such as cardiac arrest, airway obstruction, or some other serious issue. Let’s go through the biggest emergencies and their warning signs so you know what to watch for when every second counts.
01.
Cardiac arrest occurs when the heart suddenly stops beating effectively, usually due to ventricular fibrillation or other life-threatening arrhythmias. It disrupts blood flow to the brain and vital organs. Signs to look for include:
02.
This happens when a foreign object blocks the upper airway, preventing normal breathing. It’s a leading cause of preventable deaths. Watch for these signs:
03.
A condition where breathing stops completely, though the heart may still be beating. Without quick intervention, it can progress to cardiac arrest. Key signs include:
04.
Uncontrolled bleeding can lead to hypovolemic shock, a condition where the body cannot circulate enough blood to vital organs. Signs include:
05.
A sudden, severe allergic reaction that affects the airway, breathing, and circulation. It requires immediate treatment with epinephrine. Be alert for:
06.
Occurs when the blood flow to part of the brain is blocked or a blood vessel bursts. Immediate action can minimize brain damage. Common signs are:
07.
Resulting from prolonged exposure to cold, causing the core body temperature to drop dangerously low. It affects heart and brain function. Signs to recognize include:
08.
Occurs when the body overheats and loses its ability to regulate its temperature, often due to prolonged heat exposure or exertion. Signs include:
09.
Injuries to the skin caused by heat, chemicals, electricity, or radiation. They can lead to fluid loss, infection, and shock. Look for these signs:
10.
Caused by serious accidents or forceful impacts, these injuries can damage organs, bones, and soft tissue. Warning signs include:
Following the American Heart Association (AHA) Adult Basic Life Support (BLS) Algorithm ensures a structured and evidence-based approach to saving lives. Each step is carefully designed to optimize survival and neurological outcomes in emergencies like sudden cardiac arrest. Here’s a breakdown of the critical actions you need to take.
Step 1.
Before taking action, ensure the scene is safe for both the rescuer and the victim.
-Tap the person and shout, “Are you okay?” to check for responsiveness.
-Simultaneously, check for normal breathing and pulse (for no more than 10 seconds). If the person is unresponsive, not breathing normally, and has no pulse, start CPR immediately.
Step 2.
If you're not alone, send someone to call 911 and get an automated external defibrillator (AED).
-If you're alone and don’t have a phone, leave the victim to activate the emergency medical services (EMS) and retrieve an AED.
Step 3.
High-quality CPR begins with chest compressions:
-Compression depth should be at least 2 inches (5 cm).
-Rate: 100–120 compressions per minute.
-Allow full chest recoil between compressions.
-Minimize interruptions to maintain circulatory flow.
Step 4.
After 30 compressions, give 2 rescue breaths:
-Use the head-tilt-chin-lift method (unless there's suspected trauma).
-Maintain a 30:2 compression-to-breath ratio.
-Each breath should last about 1 second and make the chest visibly rise.
-Avoid excessive ventilation.
Step 5.
An AED can restore a normal rhythm if the cardiac arrest is due to a shockable rhythm (like ventricular fibrillation):
-Power on the AED and follow the voice prompts.
-Attach the pads to the victim’s bare chest.
-Allow the AED to analyze the rhythm.
-Deliver a shock if advised, then resume CPR immediately.
Step 6.
-Reassess the victim’s pulse and rhythm every 2 minutes.
-If there's another rescuer, switch compressors to avoid fatigue and maintain high-quality compressions.
-Continue cycles of CPR and AED analysis until advanced care arrives or the person shows signs of life.
When it comes to saving a life during cardiac arrest, the quality of CPR makes all the difference. Whether you’re a healthcare provider or a trained bystander, focusing on the right techniques ensures your efforts are as effective as possible.
Let’s break down the key components of high-quality adult CPR:
The way Basic Life Support (BLS) is performed can vary depending on whether you’re alone or have help. Both methods follow the Adult BLS Algorithm, but the approach to tasks like calling 911, getting an AED, and performing CPR is slightly different. Knowing what to do in each scenario ensures you act fast and effectively.
If you’re alone, your top priority is to start chest compressions immediately. Every second without blood flow decreases the victim’s chance of survival. Once you begin compressions, activate the emergency response system and get an AED as soon as possible.
Steps for a single rescuer:
Tip: If you’re alone with no phone, leave the victim to call 911 and retrieve an AED before starting CPR.
With two trained rescuers, BLS becomes more efficient. One person focuses on compressions, the other on rescue breaths or operating the AED. This allows for minimal interruptions and better-quality CPR.
Steps for two rescuers:
Teamwork improves survival—rotating tasks keeps both rescuers fresh and CPR quality high.
|
Aspect |
Single Rescuer |
Two Rescuers |
|
Initial Response |
Ensure scene safety, check responsiveness, breathing, and pulse |
Same as single rescuer |
|
Calling for Help |
Call 911 yourself or leave to get help if no phone |
One rescuer calls 911 and retrieves AED while the other starts compressions |
|
CPR Start |
Start CPR immediately (30:2 ratio) |
Start CPR immediately (30:2 ratio) |
|
Airway & Breathing |
Provide 2 rescue breaths after every 30 compressions |
Second rescuer gives breaths while first performs compressions |
|
AED Use |
Use as soon as available; follow prompts |
One rescuer operates AED while other continues compressions |
|
Compressor Rotation |
Not applicable |
Switch roles every 2 minutes to prevent fatigue |
|
Efficiency & Quality |
Moderate—may have pauses between tasks |
High—minimal interruptions, continuous care |
|
Key Tip |
Prioritize chest compressions, call for help ASAP |
Communicate clearly and switch roles smoothly for best results |
While Basic Life Support (BLS) is critical in emergencies like cardiac arrest, there are specific situations where it’s appropriate not to begin or to discontinue resuscitation efforts. Understanding these exceptions is just as important as knowing how to perform CPR. These situations are typically guided by ethical, medical, or legal factors—and in many cases, by local EMS protocols and healthcare directives.
BLS should generally not be initiated if there are clear, definitive signs of irreversible death or a legally valid order to withhold resuscitation.
Do not start BLS if:
Always check for legal documentation if available, and follow local laws or institutional policies.
Even if BLS has been started, there are appropriate times to stop:
Stop BLS if:
If in doubt, continue BLS until help arrives—unless a valid reason to stop presents itself.
Even with the best intentions, rescuers—especially those under pressure—can make errors during Basic Life Support (BLS). These mistakes can reduce the effectiveness of CPR and lower the chances of survival in a cardiac arrest emergency. Knowing what not to do is just as vital as knowing the correct steps.
Let’s look at the most common BLS mistakes and how to avoid them:
Knowing how to perform the Adult Basic Life Support (BLS) Algorithm isn’t just for healthcare workers—it’s a vital life-saving skill that anyone can learn. Every action, from recognizing an emergency to starting high-quality CPR and using an AED, can make the difference between life and death.
When seconds matter, being prepared to act fast and follow the correct steps builds confidence and helps save lives. Whether you’re working alone or with someone else, understanding the BLS process gives you the tools to respond effectively.
It’s important to review your BLS skills regularly, keep up with the latest American Heart Association (AHA) updates, and practice the steps often so you’re ready when it counts. Refreshing your skills with a certified course offered by Bayside CPR is a practical way to stay prepared and confident in emergencies.
Because in a real emergency, your knowledge and quick action can help protect the brain, restart the heart, and give someone a second chance.
The golden rule of BLS is to act fast and begin high-quality CPR immediately if a person is unresponsive and not breathing normally. Early action saves lives.
You can typically perform about 5 cycles of CPR in 2 minutes, with each cycle consisting of 30 compressions and 2 breaths.
You do not need to give chest compressions if there’s a pulse. Instead, give rescue breaths only—1 breath every 5–6 seconds (10–12 per minute).
You should compress the chest at least 2 inches (5 cm) deep, but not more than 2.4 inches (6 cm).
If there are two rescuers, switch roles every 2 minutes to avoid fatigue and maintain effective compressions.
