Note: This guide follows the AHA 2025 Adult BLS guidelines, which remain valid through 2030, and focuses on the Health Care Professional approach. Bystanders without medical training can refer to our Adult BLS Algorithm for Lay Rescuers for a simplified approach.
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, heart attack, 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. Immediate action and treatment with epinephrine can reduce the risk. 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:
The AHA Adult BLS Algorithm provides a structured, evidence-based approach for healthcare providers responding to sudden cardiac arrest. Each step focuses on timely interventions that support survival and improve neurological outcomes. Below is a breakdown of the key actions included in the algorithm.
Step 1.
Before approaching the person, verify that the scene is safe. Make sure the area is safe and there are no dangers that could harm you or others while providing care.
Step 2.
Check if the person responds by calling out or gently tapping their shoulder. Shout for help and get an AED and emergency equipment, or send someone to retrieve them. If appropriate, activate the emergency response system using a mobile device.
Step 3.
Check breathing and pulse at the same time. Determine whether the person is breathing normally, only gasping, or not breathing. Complete this assessment within about 10 seconds.
A. Pulse Is Present and Breathing Is Normal
-If the person has a pulse and is breathing normally, monitor the person until emergency responders arrive.
B. Pulse Is Present but Breathing Is Not Normal
-If the person has a pulse but is not breathing normally, provide rescue breathing at 1 breath every 6 seconds or 10 breaths per minute.
Check the pulse every 2 minutes. If no pulse is felt, begin CPR. If opioid overdose is suspected, administer naloxone if available according to protocol.
C. No Pulse Is Present and Breathing Is Absent or Only Gasping
-If the person is not breathing or is only gasping and no pulse is felt, begin CPR immediately.
By this time, the emergency response system or backup should be activated, and the AED and emergency equipment should be retrieved, or someone should be retrieving them.
Step 4.
Begin CPR by performing 30 chest compressions followed by 2 rescue breaths. Continue CPR cycles to help maintain blood flow.
Step 5.
When the AED becomes available, turn it on and follow the device instructions to begin rhythm analysis.
Step 6.
Check the person's heart rhythm using the AED.
If the rhythm is shockable, proceed to Step 7. If the rhythm is not shockable, proceed to Step 8.
Step 7.
If the rhythm is shockable, deliver 1 shock. Resume CPR immediately for 2 minutes until prompted by the AED for a rhythm check.
Continue CPR until advanced life support providers take over or the person starts to move.
Step 8.
Resume CPR immediately for 2 minutes (until prompted by the AED to allow rhythm check).
Continue until advanced life support providers take over or the victim starts to move.
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 are alone with a person who is unresponsive and not breathing normally, start CPR immediately. Early chest compressions help maintain blood flow while emergency assistance is activated.
Steps for a single rescuer:
Tip: If you are alone without a mobile phone, leave the person to call emergency services 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 experienced rescuers can make mistakes while performing Basic Life Support (BLS), especially during high-pressure emergencies. 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. Victim assessment and treatment are essential steps in providing comprehensive care and support to individuals affected by cardiac arrest. 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.
