Banner by Emily Wen

Retrieving Pulses and Saving Brains: ""Cardiocerebral" Resuscitation

by Tanner Smida

We were sitting against the front windows of a small diner in a booth with faded vinyl seats and a tabletop still wet from the last wipe-down. I was drinking coffee, and my partner was getting started on a late breakfast. Our radios were on the table between us with the volume knobs turned low, crackling with the latest news of road closures and fire alarms triggered by burnt toast. In the midst of a conversation about the possibility of getting grants for a solar powered ambulance, our dispatch tone sounded. Someone in our service area had lost their pulse. 

We leaped to our feet and pushed out the door into a bright August day, breaking into a sprint as we crossed the parking lot. I jumped in the passenger side of our ambulance and reached down to grab our clipboard from between the seats as we swung out onto Main Street. The speedometer needle crept upward as we flew toward our destination, sirens blaring and howling in the humid air. All the papers on my clipboard flapped like panicked birds trying to escape. I scribbled down the information we had — address, reason for dispatch, starting mileage and time.

There are few calls that elicit a faster response than a cardiac arrest. As one of the few conditions for which the speed and skill of EMS providers has a direct influence on patient survival, there is not a paramedic on the planet who does not experience a racing pulse when the words “unresponsive, not breathing” crackle across the airwaves. Despite this, national databases suggest that overall survival to hospital discharge following cardiac arrest has hovered around 10% for a long time. Furthermore, a significant proportion of these survivors are severely disabled due to a number of factors that cause tissue death secondary to the hypoxic conditions that occur before and during resuscitation efforts. 

As a response to these dire statistics, a new wave of resuscitation protocols are rewriting the dogma of cardiac arrest management in a growing number of communities across the country. Leaving behind traditional cardiopulmonary resuscitation, the most successful of these new protocols emphasize interventions aimed at preserving neurological function. Under the banner of “pit crew CPR” or cardiocerebral resuscitation, this set of methodologies include early and uninterrupted high-quality compressions, passive oxygenation, delayed advanced airway management, early epinephrine administration and, in some emerging models, heads-up CPR with an impedance threshold device. An ITD is a new piece of technology that is, at its most basic level, a one-way valve that attaches to the end of an endotracheal tube after advanced airway management. It allows air inside the patient’s lungs to be forced out during compressions, which decreases pressure inside the chest. This creates a weak vacuum in the thorax that draws blood toward the heart and improves the efficiency of compressions. Delivered as a bundle of care, these interventions act synergistically to improve resuscitation outcomes both in terms of survival and neurological status. Cardiac arrest management is not an exercise in futility — concerted, data-driven efforts to advance the standard of care for these critically ill patients are saving lives now in Pittsburgh and other communities across the country. 

 After a patient suffers sudden cardiac arrest, high quality chest compressions are paramount and need to be initiated as soon as possible. When the heart stops pumping blood through the body, oxygen levels to the brain begin dropping very fast, and irreversible damage to metabolically demanding neuronal tissue begins to occur within minutes. Chest compressions maintain forward blood flow at roughly one third the effectiveness of a healthy heart, buying the patient time until the electrical rhythm of their cardiac conduction system can be restored. Estimates suggest that the chances of survival for an arrest victim decrease by up to 10% per minute if compressions are not being performed. With compressions, this plunge is slowed to 3 to 4%. Current AHA guidelines recommend delivering between 100 and 120 compressions per minute at a depth of 2 inches with as little interruption as possible. 

Once high-quality compressions are underway and the patient’s blood is circulating, it is essential to make sure that the minimal amount of perfusion being generated is carrying as much oxygen to the patient’s tissues as possible. Cardiocerebral resuscitation protocol suggests initial airway management with an oropharyngeal airway (OPA) in addition to a non-rebreather mask delivering pure oxygen at a flow rate of 15 liters per minute. An OPA is a plastic tube inserted into the mouth of an unconscious patient to prevent their tongue from flopping onto the epiglottis and asphyxiating them. A non-rebreather mask is a piece of molded plastic that fits around the nose and mouth of the arrest patient and conveys 100% O2 from a connected tank to their airways. As pressure within the patient’s chest changes with each compression, oxygen being delivered from the mask is drawn into their lungs. The low tidal volume (small quantity of air drawn in after a single 2-inch-deep compression) is offset by the high minute volume (amount of air inspired per unit time is high due to the rapid compressions and decompressions that far exceed normal respiratory rate), which maintains the patient’s blood oxygen saturation at a level sufficient to serve as a physiological parachute that minimizes tissue damage until advanced airway management can be accomplished. 

The use of passive oxygenation has been shown to be beneficial to the victims of cardiac arrest both in the lab and in the field. Two reasons for this observed effect have been suggested. First, passive oxygenation does not require any interruptions in compressions for tracheal tube placement. Second, hyperventilation via a bag-valve-mask (BVM)leads to increased intrathoracic pressure that opposes the benefits provided by constant, consistent compressions. Blood, like every other fluid, flows from areas of high pressure to areas of low pressure. High pressure generated inside the patient’s thorax by excess air in the lungs discourages the return of blood to the heart. This impedes the filling of the heart with this blood, a step that is required if oxygen is going to be circulated throughout the body. Think of the heart as an untied balloon — if it is only one-quarter full, a squeeze will push much less air out (and with much less noise) than if the balloon is full of air when you begin to apply pressure. Any compromise of the already minimal forward movement of blood you are generating has the potential to completely eliminate any chance the patient has for neurologically intact survival (NIS). 

The next step after compressions are started and oxygenation is established is to attempt to get the cardiovascular system working again with a defibrillator. There are two abnormal cardiac electrical rhythms — ventricular fibrillation and ventricular tachycardia — that can be terminated with a shock. After one cycle of compressions, the attachment of defibrillator pads and a quick glance at the electrical rhythm the heart is generating will tell any provider if defibrillation is a valid treatment modality. If the shock fails to reestablish sinus (normal) rhythm, the next step is to rapidly reinitiate consistent, constant compressions to stave off the rapidly increasing probability of brain death. 

To better facilitate the delivery of these invaluable compressions, several models are now turning to the use of automated CPR devices such as the widely used LUCAS and AutoPulse systems. Given the relatively poor quality of compressions delivered by even the most experienced prehospital healthcare providers, the importance of these systems is being increasingly recognized. The existence of portable devices that provide compressions at an optimal rate and depth is a relatively new contribution to cardiac arrest care that proves integral to this model of resuscitation, which emphasizes high quality compressions above all. This innovation is especially important for rural EMS systems that do not have enough backup providers to allow for rotation after each compression cycle, which is one way to ensure that optimal compressions are always being performed without an automated system. Once a mechanized CPR device is deployed on the patient, cardiocerebral resuscitation protocol mandates that the device remains on and compressing until the person is either declared dead or regains a pulse. 

Several reportedly successful protocols are now embracing a method known as “heads-up CPR,” which requires transferring the patient to a stretcher while the automated compression device is active and inclining their head to 30 degrees above the horizontal. Inspired by EMS agencies in Singapore, where high-rise apartment buildings necessitate crowding cardiac arrest victims into elevators, this method decreases intracranial pressure (ICP) and improves perfusion to the brain. 

At this point, while automated compressions continue, paramedics are permitted to proceed to advanced airway management with an endotracheal (ET) tube. Studies of “chest time” during advanced life support resuscitations have shown that medics often pause compressions while the tube is placed, but recent research suggests that even the 20 to 30 second pause in blood flow required for this maneuver has severe negative implications for patient outcomes. This interruption of compressions may be part of the mechanism underlying the inferior NIS observed in arrest victims with advanced airway management in comparison to those managed solely with a BVM. Despite the increased difficulty of placing a tube while compressions continue, cardiocerebral resuscitation protocols dictate that the automated CPR devices are not to be paused during the performance of this intervention. Incorporating passive ventilation prior to and during the intubation attempt reduces time pressure on providers.

Once an ET tube is placed in the trachea of an arrest victim, BVM-mediated ventilation can be initiated. In order to mitigate the drawbacks of BVM ventilation mentioned above, a piece of technology known as an Impedance Threshold Device (ITD) can be attached between the ET tube and the BVM. It contains a one-way valve that allows oxygenated air to be expelled from the patient’s lungs during each compression, preventing an increase in intrathoracic pressure. This creates a vacuum in the patient’s chest that drags blood in from the periphery, further decreasing ICP and improving perfusion to the myocardium and brain. 

Capnography sensors should be deployed at this point to monitor the end tidal carbon dioxide (ETCO2) of the patient, which allows providers to see how much carbon dioxide is emitted by the patient with each compression. The levels of this molecule can be used as correlates of metabolic activity and cell death, making ETCO2 monitoring a valuable prognostic measure. Sudden, precipitous increases in ETCO2 levels can be a predictor of the return of spontaneous circulation, which decreases the need to pause the automated compression device to check for pulses. 

A common trope in many television medical dramas is a dramatic call to “Push epi, STAT!” when a patient flatlines. Epinephrine is a catecholamine hormone secreted by the adrenal glands. It acts on alpha- and beta-adrenergic receptors throughout the vasculature and, among a myriad of other physiological effects, constricts blood vessels, which leads to increased peripheral blood vessel resistance and therefore perfusion pressure in the coronary arteries that significantly improves the chances of getting a return of circulation. However, this constriction also has the potential to choke off blood flow to the end of capillary beds in heavily vascularized organs such as the kidneys and brain. Several studies have demonstrated the negative effects epinephrine use has on the neurological deficits of cardiac arrest survivors. For this reason, cardiocerebral resuscitation emphasizes early administration to maximize the chances of getting pulses back early and minimize the total dosage given. 

These bundled interventions are designed to ensure the provision of constant, high quality compressions — passive ventilation allows oxygenation to be established early without the necessity of a pause in compressions and permits advanced airway management via ET tube to be delayed until an automated compression device is attached to the patient. The activation of the automated compression device allows airway management and IV access to be initiated while high quality compressions continue, and ETCO2 monitoring prevents the need to stop compressions to check for pulses. The integration of heads-up-CPR and ITDs improve perfusion to the brain and heart. Considered utilization of epinephrine prevents unnecessary neurological impairment. Combination into one resuscitation protocol has led to striking results both in terms of overall survival and post-arrest neurological status. These simple changes provide a new avenue by which EMS providers can continue to find success in that most elusive goal — bringing the dead back to life. 

Footnotes

1 Advanced airway management is defined as any maneuver conducted to ensure the patency of a patient’s airway other than oxygen administration or bag valve mask ventilation with a basic life support adjunct. These methods include endotracheal intubation, during which a plastic tube is inserted into the patient’s trachea, and supraglottic airway (SGA) insertion, in which the inserted airway is a tube that seals around the opening to the trachea. 

Prehospital and critical care researchers at the University of Pittsburgh maintain a working relationship with Pittsburgh EMS, which makes this region have one of the highest cardiac arrest survival rates in the country. If you want to help further improve OHCA survival rates in Pittsburgh, download the PulsePoint Respond app for iOS or Android.