2 Rescuer CPR: How to do it, Techniques, and Expert Tips
Author:
CPR Select
Last updated:
11/7/2024
This article will delve into the importance of 2 rescuer CPR, exploring its key benefits, techniques, and considerations. By understanding the advantages of this approach and the synergy it brings to resuscitation efforts, healthcare professionals and individuals trained in CPR optimizes their skills and potentially save more lives.
How to Perform 2 Rescuer CPR?
Below is a step-by-step guide to performing two-rescuer CPR:
Assess the Situation and Ensure Scene Safety: Ensuring safety prevents further harm to both rescuers and the patient.
Designate Roles for Each Rescuer: Clear roles enhance efficiency, allowing one rescuer to focus on compressions and the other on breaths.
Primary Rescuer Starts Chest Compressions: High-quality compressions keep blood flowing to vital organs, improving the patient's chances of survival.
Secondary Rescuer Maintains an Open Airway and Provides Breaths: Effective rescue breaths provide oxygen, which is essential to sustain life during resuscitation efforts.
Use an Automated External Defibrillator (AED), If Available: An AED can deliver a shock to restart the heart’s normal rhythm, potentially saving the patient’s life.
Continue CPR Until Professional Help Arrives: Continuous CPR maintains blood circulation, bridging the time until advanced medical care takes over.
While conventional CPR techniques performed by a single rescuer are effective, the implementation of 2 rescuer CPR has proven to enhance survival rates significantly.
1. Assess the Situation and Ensure Scene Safety
This first step involves checking the surroundings to confirm that the environment is safe for both rescuers and the patient. Look for hazards such as traffic, fire, or electrical dangers. Make sure the patient is on a hard, flat surface. Confirm unresponsiveness by tapping the person’s shoulder and shouting, “Are you okay?” Check for breathing by watching the chest for movement and feeling for air on your cheek.
Ensuring safety is critical to prevent additional injuries and allows the rescuers to focus fully on providing aid. If the scene is unsafe, call emergency services for guidance on moving the person to a safer location. If you’re unsure of breathing, assume they’re not breathing normally and begin CPR.
2. Designate Roles for Each Rescuer
Assign one person as the primary rescuer to handle chest compressions, and the other as the secondary rescuer to provide breaths and manage the airway. Decide quickly on roles, with the stronger rescuer often performing compressions while the other focuses on breaths. The secondary rescuer should be ready to switch roles with the primary after about 2 minutes or 5 cycles to prevent fatigue.
Clear roles ensure efficient CPR, allowing both rescuers to stay focused on their tasks without confusion or delays. If one rescuer is less experienced, consider assigning them the role of managing the breaths while the other performs compressions. Communicate effectively if a role change is needed.
3. Primary Rescuer Starts Chest Compressions
The primary rescuer initiates high-quality chest compressions, pressing down on the chest at a steady rhythm to circulate blood.
Chest Compression Technique:
Place the heel of one hand on the center of the chest (on the lower half of the breastbone), and place your other hand on top. Push hard and fast at a rate of 100–120 compressions per minute. Allow full chest recoil between compressions.
The recommended compression rate for infants up to 1-year-old is around 100 to 120 compressions per minute, with a compression depth of approximately 1.5 inches deep (4 centimeters).
For children one year to puberty, the compression rate remains at 100 to 120 compressions per minute, while the compression depth increases to about 2 inches (5 centimeters).
For adults, including those in puberty and older, the compression rate remains at 100 to 120 compressions per minute and a depth of about 2 inches (5 centimeters) to 2.4 inches (6 centimeters).
Compressions mimic the heart's pumping action, keeping oxygenated blood circulating to vital organs, especially the brain and heart. Fatigue is common, so switch roles every 2 minutes to maintain compression quality. If compressions aren’t deep enough, focus on using body weight rather than just arm strength.
4. Secondary Rescuer Maintains an Open Airway and Provides Breaths
The secondary rescuer manages the airway and delivers breaths to supply oxygen after every 30 compressions (or every 15 in pediatric patients). Coordinating with the primary rescuer is essential to time breath delivery with chest compressions, ensuring minimal interruptions.
Rescue Breathing Technique:
Use the head-tilt, chin-lift technique to open the airway.
Pinch the nose closed, seal your mouth over the patient’s, and give two breaths (each lasting about 1 second).
Watch the chest rise with each breath.
Oxygen provided by rescue breaths is crucial for the patient’s survival, as compressions alone won’t provide enough oxygen to sustain life long-term. If the chest doesn’t rise, check the airway for obstructions and reposition the head. If still unsuccessful, try a jaw thrust maneuver if a spinal injury is suspected.
What is the compression-to-breath ratio for two rescuers' CPR?
For Adult CPR, the compression-to-breath ratio is 30 compressions to 2 breaths. The primary rescuer performs 30 chest compressions, followed by the secondary rescuer delivering two rescue breaths.
Child and Infant CPR ratio for 2 rescuer is 15 compressions to 2 breaths. This means that after every 15 compressions, the rescuer delivering breaths will provide two rescue breaths.
5. Use an Automated External Defibrillator (AED), If Available
Using an AED provides an electric shock that can help restore a normal heart rhythm in patients experiencing sudden cardiac arrest. Both rescuers work together to ensure quick and effective AED use while maintaining CPR.
2 Person Technique:
Primary Rescuer continues chest compressions while the Secondary Rescuer prepares the AED.
Secondary Rescuer turns on the AED and follows voice prompts. They place the AED pads on the patient’s bare chest (upper right and lower left sides).
When the AED is ready to analyze the heart rhythm, the Primary Rescuer pauses compressions briefly, and both rescuers stand clear to avoid interference.
If the AED advises a shock, the Secondary Rescuer presses the shock button, and both rescuers stand clear of the patient.
The AED can interrupt life-threatening arrhythmias, giving the heart a chance to reset to a normal rhythm, which is critical for survival. If the AED prompts "check pads," ensure the pads are securely attached to dry skin. For patients who are wet or sweaty, the Secondary Rescuer should dry the chest before pad placement. After the shock, the Primary Rescuer should immediately resume chest compressions to maintain blood flow.
6. Continue CPR Until Professional Help Arrives
Perform continuous 2 person CPR, alternating roles every few minutes to avoid fatigue, until advanced medical help takes over. If the victim is still unconscious and not breathing, The primary rescuer will continue high-quality chest compressions while allowing full chest recoil between compressions. The secondary rescuer will deliver rescue breaths effectively, maintaining a proper mask seal and providing sufficient ventilation. Swap roles smoothly after 2 minutes or 5 cycles.
Continuous CPR provides ongoing blood and oxygen flow, helping prevent brain damage and cardiac deterioration while waiting for professional intervention. If one rescuer becomes too tired, adjust roles more frequently or have the more rested rescuer take over compressions. Communicate clearly to avoid interruptions when switching roles.
Blood Pressure Category
Systolic (Upper)
Diastolic (Lower)
Health Risks
Recommendations
Normal
Less than 120 mm Hg
and Less than 80 mm Hg
Low risk of heart disease or stroke
Maintain healthy lifestyle (diet, exercise, no smoking)
Elevated
120-129 mm Hg
and Less than 80 mm Hg
Doubled risk of cardiovascular complications
Make lifestyle changes (lose weight if overweight, increase physical activity, limit alcohol)
Hypertension Stage 1
130-139 mm Hg
or 80-89 mm Hg
Increased risk of heart attack, stroke, kidney disease
Lifestyle changes and potentially medication under doctor's guidance
Hypertension Stage 2
140 mm Hg or Higher
or 90 mm Hg or Higher
High risk; can lead to heart failure, vision loss, dementia
Medication required in addition to lifestyle changes as recommended by doctor
Hypertensive Crisis
Higher than 180 mm Hg
nd/or Higher than 120 mm Hg
Immediate danger of life-threatening complications
Seek emergency medical care immediately
Cardiac Arrest
Heart Attack
Stroke
Definition
Sudden loss of heart function, leading to collapse
Blockage in a coronary artery, affecting blood flow to the heart muscle
Interruption of blood flow to the brain, leading to brain damage
Main Cause
Electrical malfunction of the heart
Blockage in coronary arteries
Blockage or rupture of blood vessels in the brain
Circulation Affected
Entire body
Heart muscle
Brain tissue
Symptoms
105Sudden collapse, unconsciousness, no pulse
Chest pain or discomfort, shortness of breath
Sudden numbness or weakness, confusion, trouble speaking or understanding speech/73
Emergency Response
Immediate CPR and defibrillation
Activate emergency medical services, chew aspirin
Activate emergency medical services, FAST assessment (Face, Arms, Speech, Time)
Atherosclerosis, high cholesterol, hypertension, smoking, diabetes
Hypertension, diabetes, smoking, high cholesterol, atrial fibrillation
What is CPR?
CPR, or cardiopulmonary resuscitation, is a life-saving technique during emergencies like cardiac arrest. Immediate action during a medical emergency is crucial as it prevents irreversible brain damage caused by the lack of oxygen. In situations where multiple responders are available, 2 rescuer CPR proves advantageous. It allows for a shared workload, ensuring sustained and effective chest compressions. With one rescuer focusing on compressions, the other maintains an open airway and provide rescue breaths, leading to the uninterrupted circulation of oxygenated blood.
Additionally, two rescuers enable simultaneous actions like using an AED, further enhancing the effectiveness of resuscitation efforts. The collaborative nature of 2 person CPR optimizes response and improves survival rates in medical emergencies.
When to Perform 2 Rescuer CPR?
2 rescuer CPR is applicable and necessary in various scenarios where immediate action is required, and multiple rescuers are available. Here are some situations where 2 rescuer CPR is particularly beneficial:
Out-of-hospital cardiac arrest: When someone collapses due to cardiac arrest outside of a healthcare facility, the presence of multiple rescuers allows for the immediate initiation of 2 rescuer CPR.
Pediatric resuscitation: Performing high-quality CPR on a child or an infant often requires more delicacy and specific considerations. In these cases, having two rescuers is advantageous as one performs the appropriate compressions for the child's size while the other attends to airway management and rescue breaths.
High-stress or prolonged resuscitations: CPR is physically demanding, and fatigue affects the quality of chest compressions over time. In high-stress environments, having two rescuers allows for workload distribution, reducing the risk of fatigue-related performance decline.
Cardiac arrest in a healthcare setting: In healthcare facilities such as hospitals or clinics, immediate action is crucial when a patient experiences cardiac arrest. With multiple healthcare providers available, 2 rescuer CPR is quickly implemented.
In all of these scenarios, multiple rescuers allow for a coordinated and efficient approach to CPR. By sharing the responsibilities of chest compressions, airway management, and additional interventions, 2 rescuer CPR maximizes the chances of successful resuscitation and improves overall outcomes for individuals needing immediate medical intervention.
What are the Roles and Responsibilities in 2 Rescuer CPR?
In 2 rescuer CPR, each rescuer has specific roles and responsibilities to ensure effective coordination and maximize the chances of successful resuscitation. The following are the typical roles and responsibilities of each rescuer:
Primary Rescuer's Role
The primary rescuer in two-person CPR has critical responsibilities when initiating and maintaining high-quality chest compressions. Their primary duties include:
Initiating chest compressions: The primary rescuer takes the lead in initiating chest compressions as soon as possible. They recognize the need for CPR, assess the victim's responsiveness, and promptly begin compressions if the victim is unresponsive or not breathing normally.
Proper hand placement: The primary rescuer ensures the correct hand placement for chest compressions. They position themselves at the victim's side and place the heel of one hand on the center of the victim's chest, typically between the nipples. The other hand is placed on top, interlocking fingers or using the 'stacked fists' technique for infants. This allows for optimal force transfer to the chest, facilitating effective compressions.
Achieving the correct compression rate: The primary rescuer maintains the proper compression rate, aiming for around 100 to 120 compressions per minute. Consistently providing compressions at the appropriate rate ensures sufficient blood flow and oxygenation to the vital organs.
Achieving the correct compression depth: The primary rescuer focuses on achieving the proper compression depth, typically around 2 to 2.4 inches (5 to 6 centimeters) for adult victims. Maintaining the correct depth is crucial to circulate blood and maintaining perfusion to vital organs effectively.
Continuous compressions and minimizing interruptions: The primary rescuer ensures that chest compressions are continuous and minimizes interruptions as much as possible. They coordinate with the secondary rescuer to smoothly transition between compressions and rescue breaths, allowing minimal interruptions in the CPR cycle. Minimizing interruptions helps maintain blood flow and prevents the decay of perfusion pressure during resuscitation efforts.
Secondary Rescuer's Role
The secondary rescuer in two-person CPR plays a critical role in providing ventilation through rescue breaths, ensuring a proper mask seal, delivering breaths effectively, and monitoring the victim's response. Their responsibilities include:
Airway management and rescue breaths: The secondary rescuer focuses on maintaining an open airway and delivering rescue breaths to the victim. They ensure that the victim's head is properly positioned to open the airway, utilizing techniques such as the head tilt-chin lift or jaw thrust maneuver, depending on the situation and the victim's condition.
Proper mask seal: The secondary rescuer ensures a proper mask seal during rescue breaths. They place a mask over the victim's mouth and nose, ensuring a secure fit that covers both areas. Creating an airtight seal is important to prevent air leakage during breath delivery, maximizing the effectiveness of ventilation.
Effective breath delivery: The secondary rescuer delivers rescue breaths effectively to provide oxygen to the victim's lungs. They maintain a proper seal with the mask and give breaths with sufficient volume and duration.
Monitoring the victim's response: The secondary rescuer closely monitors the victim's response during CPR. They observe for any signs of chest rise and fall with breath delivery, indicating effective ventilation. They also watch for changes in the victim's color, responsiveness, or other signs of improvement or deterioration.
Communication and coordination: The secondary rescuer communicates with the primary rescuer to synchronize their actions. They coordinate the delivery of rescue breaths with the primary rescuer's chest compressions, ensuring a smooth and uninterrupted cycle of CPR. Clear and effective communication helps maintain the proper rhythm and maximize the overall quality of CPR.
Assisting with additional tasks: Depending on the situation, the secondary rescuer helps with additional duties such as calling emergency response, retrieving and preparing an automated external defibrillator (AED), or managing any other required equipment or interventions. Their support allows for a more efficient and coordinated response to the medical emergency.
Both rescuers must maintain open lines of communication, constantly assess the victim's condition, and adapt their actions as needed. Effective teamwork, clear roles, and coordinated efforts are essential to providing high-quality CPR and improving the chances of successful resuscitation.
What is Modified 2 rescuer CPR technique?
The modified 2 rescuer CPR technique refers to a variation of traditional 2 rescuer CPR where one rescuer uses a 2 handed mask seal during ventilations while the other rescuer performs chest compressions. In this technique, the rescuer providing ventilations creates a secure seal over the patient's mouth and nose using both hands to ensure effective delivery of breaths with a bag-valve-mask (BVM) device. Meanwhile, the other rescuer focuses solely on performing high-quality chest compressions. This modification aims to optimize the efficiency of CPR delivery by incorporating a superior method for providing ventilations while maintaining effective chest compressions, ultimately improving the overall quality of resuscitation efforts.
A recent study investigated whether a modified 2 rescuer CPR technique, using a 2 handed mask seal during ventilations, affects chest compression quality during simulated cardiac arrest. Medical students were split into two groups: one using the modified technique and the other using standard 2 rescuer CPR. Results showed no significant differences in compression quality, completion time, or hands-off time between the two groups. This suggests that the modified technique can be performed effectively without compromising chest compression quality.
What are the key differences between 2 person CPR and single-rescuer CPR?
In single-rescuer CPR, one person performs both chest compressions and rescue breaths, requiring constant switching between the two tasks. On the other hand, 2 person CPR involves two rescuers working together, with one focusing solely on chest compressions and the other on providing rescue breaths. This collaborative approach ensures more effective and continuous chest compressions, while also maintaining uninterrupted oxygenation of the patient, thereby improving the overall quality of CPR delivery and enhancing the chances of successful resuscitation.
What are the benefits of performing 2 person CPR over single-rescuer CPR?
Performing 2 person CPR offers several benefits over single-rescuer CPR, particularly in terms of improving survival rates. Here are some key advantages:
Continuous and Effective Chest Compressions: With two rescuers working together, one dedicated solely to chest compressions, the quality and continuity of compressions are enhanced. This results in better circulation of blood throughout the body, maintaining vital organ perfusion and increasing the likelihood of successful resuscitation.
Uninterrupted Ventilation: In 2 person CPR, one rescuer focuses exclusively on providing rescue breaths, ensuring consistent oxygenation of the patient's lungs. This reduces the risk of hypoxia (low oxygen levels) and hypercapnia (high carbon dioxide levels), which are critical factors in cardiac arrest management.
Reduced Rescuer Fatigue: Sharing the workload between two rescuers allows for more efficient CPR delivery and minimizes rescuer fatigue. Fatigue compromises the quality of CPR, leading to decreased effectiveness and lower chances of survival. By rotating roles and supporting each other, rescuers maintains optimal performance throughout the resuscitation process.
Improved Teamwork and Coordination: 2 person CPR promotes effective communication and coordination between rescuers, ensuring seamless execution of CPR maneuvers and other interventions. This teamwork maximizes the efficiency of resuscitation efforts and enhances overall patient care.
Adaptability to Challenging Situations: In complex scenarios or challenging environments, such as confined spaces or difficult access to the patient, having two rescuers allows for greater adaptability and problem-solving capabilities. This versatility is crucial in optimizing patient outcomes during resuscitation efforts.
Overall, the collaborative approach of 2 person CPR enables more effective chest compressions, consistent ventilation, reduced rescuer fatigue, enhanced teamwork, and adaptability, all of which contribute to improved survival rates compared to single-rescuer CPR.
What equipment should be used when performing 2 person CPR, and how should it be shared between rescuers?
The equipment required for 2 person CPR includes protective gloves, a CPR mask or barrier device for rescue breaths, and an automated external defibrillator (AED) if available. These items should be shared between the rescuers as follows:
Protective gloves: Each rescuer should have their own pair of gloves to prevent cross-contamination and ensure personal protection.
CPR mask or barrier device: This device should be readily accessible and is passed between rescuers as needed for delivering rescue breaths. It's essential to ensure proper sealing and ventilation during breath delivery.
Automated external defibrillator (AED): If an AED is available, both rescuers should be familiar with its location and operation. While one rescuer continues chest compressions, the other retrieve and prepares the AED for use, applying the pads to the patient's chest as necessary.
How does the presence of an AED influence 2 person CPR procedures?
The presence of an automated external defibrillator (AED) in 2 person CPR procedures enhances the resuscitation process by allowing for early defibrillation, which significantly improves survival rates. Rescuers should continue performing CPR while one rescuer prepares and applies the AED pads to the patient's chest. Once the AED is ready, CPR briefly pauses while the device analyzes the heart rhythm. If a shockable rhythm is detected, the AED delivers a shock, and CPR resumes immediately afterward. This integration of AED use into 2 person CPR maximizes the chances of restoring normal cardiac rhythm and increasing the likelihood of a successful outcome for the patient.
How do 2 person CPR guidelines differ when an advanced airway is in place?
When an advanced airway, such as an endotracheal tube or supraglottic airway, is in place during 2 person CPR shifts to continuous chest compressions without pauses. The primary rescuer performs uninterrupted compressions at 100–120 per minute, while the secondary rescuer gives one breath every 6 seconds (10 per minute) through the airway, without interrupting compressions. This approach maintains blood flow and oxygenation. Effective coordination is crucial, so rescuers should communicate clearly to stay in sync.
What challenges arises during 2 person CPR, and how can they be mitigated?
Several challenges arises during 2 person CPR, but they are effectively mitigated through proper training, communication, and coordination. Here are some common challenges and strategies for addressing them:
Coordination and Timing: Coordinating chest compressions and ventilations between two rescuers is challenging, leading to interruptions or inconsistencies in CPR. To mitigate this challenge, rescuers should undergo regular training together to synchronize their movements and timing. Clear communication and practice helps establish a rhythm and ensure smooth transitions between compressions and ventilations.
Fatigue Management: Performing CPR is physically demanding, leading to rescuer fatigue over time. To prevent fatigue from compromising CPR quality, rescuers should rotate roles regularly, switching between performing compressions and providing ventilations. This rotation allows each rescuer to rest and recover, maintaining the effectiveness of CPR delivery throughout the resuscitation effort.
Maintaining Quality Chest Compressions: Ensuring the depth, rate, and recoil of chest compressions are crucial for optimizing blood flow during CPR. With two rescuers, it's essential to monitor and provide feedback to each other to maintain high-quality compressions. Rescuers should focus on using proper technique and applying adequate force to achieve the recommended compression depth (at least 2 inches or 5 centimeters for adults).
Communication Challenges: Effective communication between rescuers is essential for coordinating CPR efforts and addressing any issues that arise during resuscitation. Clear verbal cues and hand signals facilitate communication, even in noisy or chaotic environments. Establishing designated roles and responsibilities beforehand also help minimize confusion and ensure efficient teamwork.
By addressing these challenges through training, communication, and coordination, rescuers overcome obstacles and optimize the delivery of 2 person CPR, improving the chances of successful resuscitation and patient outcomes.
Why is communication essential between rescuers during 2 person CPR?
Communication between rescuers during 2 person CPR is essential for coordinating actions, maintaining rhythm, and optimizing CPR technique. Clear communication ensures that both rescuers are synchronized in their efforts, preventing interruptions and maximizing the effectiveness of chest compressions and ventilations. It also allows for task assignment and role clarification, ensuring that each rescuer knows their responsibilities and able to work together seamlessly to provide high-quality CPR. Overall, effective communication enhances teamwork and improves the chances of successful resuscitation.
What Does CPR Select Recommends to Reduce Rescuer Fatigue
CPR Select recommends rotating rescuers every 2 minutes to keep compressions strong and effective, as this prevents fatigue from affecting compression quality. Using proper body mechanics—positioning shoulders directly above hands and using body weight rather than arm strength—helps conserve energy. Clear communication between rescuers also ensures smooth transitions and consistent compression depth and rate.
Fatigue leads to shallow compressions. Frequent role-switching and using body weight instead of arm strength help maintain consistent compression quality.
How do CPR certification courses ensure proficiency in 2 rescuer CPR techniques?
CPR certification courses ensure proficiency in 2 rescuer CPR techniques through interactive modules and instructional videos. During the course, participants learn about the principles of 2 rescuer CPR, including the roles and responsibilities of each rescuer, the correct compression-to-ventilation ratio, and the importance of effective communication and teamwork. While online courses do not offer hands-on practice, they often include demonstrations and interactive elements to reinforce learning.
Through repeated practice, participants develop the skills and confidence needed to effectively perform 2 rescuer CPR in real-life situations. Additionally, many virtual CPR certification courses include recertification requirements to ensure that individuals maintain proficiency in CPR techniques, including 2 rescuer CPR.
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Blood pressure tends to vary by age due to several factors, including changes in blood vessels, heart function, and overall health. Here's how blood pressure generally varies across different age groups:
Age Group
Min Systolic/Diastolic
Normal Range
Max Systolic/Diastolic
Recommendations
1-12 months
75/50
90/60
110/75
Consult pediatrician if outside normal range. Cuff sizing is critical.
1-5 years
80/55
95/65
110/79
High BP in children may indicate underlying condition. Lifestyle factors.
6-13 years
90/60
105/70
115/80
Obesity, family history increase risk. Promote healthy habits early.
14-19 years
105/73
117/77
120/81
Adolescent rise normal. Rule out secondary causes if elevated.
20-24 years
108/75
120/79
132/83
Stressors, medications may impact. Start monitoring if high-normal.
25-29 years
109/76
121/80
133/84
Dietary changes, exercise for elevated readings. Birth control effects.
30-39 years
110/77 - 111/78
122/81 - 123/82
134/85 - 135/86
Monitor closely if readings increasing with age.
40-49 years
112/79 - 115/80
125/83 - 127/84
137/87 - 139/88
Lifestyle changes proven to reduce hypertension risk.
50-64 years
116/81 - 121/83
129/85 - 134/87
142/89 - 147/91
White coat effect common. Home monitoring advised.
65+ years
Varies
130+ Systolic Risk
Varies
Frailty, medications, conditions factored in management.
Obtaining CPR Certification
Preparing for 2-rescuer CPR and obtaining proper CPR certification are vital steps to equip yourself with the necessary skills, knowledge, and confidence to respond effectively in emergencies. CPR certification ensures you are prepared to deliver high-quality care, adapt to different scenarios, communicate and coordinate with fellow rescuers, and fulfill professional requirements. By taking these steps, you contribute to a safer and more prepared community, ready to make a difference in critical moments when lives are at stake.
Sources:
American Heart Association CPR Guidelines for 2 person CPR
Root CW, Deutsch BC, Lakha S, Shah A, Lin HM, Hyman JB. Feasibility of a Modified Strategy for 2-Rescuer Cardiopulmonary Resuscitation. J Emerg Med. 2019 Jul;57(1):51-58. doi: 10.1016/j.jemermed.2019.03.009. Epub 2019 May 3. PMID: 31060845.