Chapter 7: Cardiopulmonary Support and Circulation
Alcor 1997 Stabilization and Transport Manual
Table of Contents
Cardiopulmonary support requires restoring the patient’s circulation, which involves applying force to the heart, either directly or indirectly. The impact of cardiopulmonary support on the heart, lungs, and circulatory system is the topic of this chapter.
Because the chances of surviving cardiac arrest increase dramatically when CPS is used, multiple options for cardiopulmonary support have been heavily researched. Advantages and disadvantages exist for every method that has been developed. Comparing the different options is not possible without some understanding of myocardial anatomy and physiology and how CPS affects the heart and lungs.
Circulating blood travels through the complex system of arteries, veins, and capillaries and is propelled by a beating heart. It is the circulatory system, driven by the myocardial system (the heart and surrounding muscles), which delivers nutrients to the tissues. Oxygen is one of the most vital elements for sustaining life.
Oxygen-depleted blood enters the heart through the superior (upper) vena cava, when coming from the upper body, head, and arms. Blood returning from the legs and abdominal organs enters through the inferior (lower) vena cava. Both of these veins empty into the right atrium of the heart (the upper chamber), which is a temporary repository for blood passing to the right ventricle (the lower chamber) via the tricuspid valve. From the right ventricle, blood exits the heart through the pulmonary artery which branches to carry oxygen-depleted blood to each lung for re-oxygenation. Pulmonary veins carry oxygenated blood from each lung back to the heart, where it is deposited in the left atrium (the upper chamber). From the left atrium, blood passes through the mitral valve into the left ventricle (the lower chamber). The left ventricle pumps oxygenated blood out of the heart into the aorta — the artery which supplies the entire body with blood. Branching from the base of the aorta, the coronary arteries supply the heart muscle itself with oxygenated blood.
No artificial system of circulation is as efficient or as effective as a healthy heart and lungs.
The Effects of Cardiopulmonary Support
To prevent incidental injury, evolution developed a bone structure to surround critical and delicate organs (primarily the heart and lungs). The sternum and ribcage have generally proved to be an excellent protective mechanism. However, the inflexibility of the sternum, which defends well against glancing blows, also substantially reduces the effectiveness of cardiac compressions during CPS and greatly hinders blood flow to the body and brain.
Ideally, cardiac compressions would be administered directly to each side of the heart, using methods that mimic normal cardiac activity. Such precision is impossible without having direct access to the heart and requires opening the sternum or the rib cage. Only Open-Chest CPS (discussed later in this Chapter) provides direct access to the heart, and this is not the method of CPS usually employed by an Alcor transport team. Instead, external methods are used to compress the sternum.
When pressure is applied to the sternum, directly over the heart, it affects other organs in the chest cavity, like the lungs. The ribs are forced inward, which decreases the volume the organs occupy and causes blood to be moved throughout the body. The increased pressure also negatively impacts the blood vessels, including the pulmonary vessels, so that blood pooled near the lungs is first drawn into the heart through the left atrium and then pushed into the peripheral vessels of the body.
One measure of CPS efficacy is the amount of pressure affecting organs other than the heart. (Less is better.) The reason for this is that circulation and oxygenation must both be improved for CPS to be successful, and the lungs must be relatively unaffected by the compressions to function best. Open-Chest CPS is the only method whereby only the heart is compressed. Each of the external CPS methods affects other organs, and the degree of which is a consideration in choosing a CPS method.
Alcor transport team members, similarly to emergency medical personnel, will use different types of cardiopulmonary support (CPS), depending on the circumstances.
A few objective criteria exist for comparing the efficacy of CPS methods. Perfusion pressures and blood flow data may prove reliable indicators of cell viability. For example, for CPS to maintain neuronal viability, cerebral blood flows of at least 20% of normal must be achieved and minimum perfusion pressures of 30mmHg are necessary to achieve minimal capillary opening pressure (the pressure at which blood overcomes inertia and other forces to resume travelling through the capillaries) .
Each of the options for CPS succeeds in achieving neuronal viability to a varying degree, but time is the single largest determining factor for the efficacy of conventional, closed-chest CPS. If more than a few minutes elapse between arrest and the application of CPS, the target cerebral perfusion pressures will not be attainable without more dramatic intervention [7,8].
Manual Closed-Chest CPS
External chest compressions, performed by human operator.
Manual chest compressions usually result in cerebral blood flows between 5-10% of normal, and common carotid artery flows of 3-30% of normal [9, 10]. The transport team member should seek blood flows as close to normal as possible, with a cerebral blood flow of at least 20% being required. Manual closed-chest CPS may not achieve the minimum blood flow requirements, and should be only used as an interim measure (until mechanical CPS can be initiated) or if no alternatives are available. Use of this method results in the lowest cardiac output of any CPS technique, due primarily to fatigue of and inconsistent compressions by the rescuer. When uninflated, the lungs serve as a barrier to good perfusion, because they contain no air to help increase the direct pressure on the heart of a compression. Instead, the spongy tissue cushions some of the impact of each chest compression. Rib and sternal fractures, a ruptured spleen or liver, and gastric hemorrhaging are a few of the more common complications of external chest compressions [11, 12].
Conventional and Hi-Impulse Closed-Chest CPS
External chest compressions, performed by machine.
There are three types of mechanical chest-compression devices in use by Alcor personnel: Brunswick models, and Michigan Instruments Conventional and Hi-Impulse models. The Brunswick models will be replaced at the earliest opportunity and they currently remain in the field only as back-ups to the Michigan Instruments’ devices. Their use during a transport should be limited to those cases where no alternative except manual CPS exixts. The Conventional and Hi-Impulse CPS devices are essentially identical, with the Hi-Impulse providing compressions that more closely resemble normal cardiac compressions. Hi-Impulse compressions are sharper, i.e. it takes less time to compress and release the sternum (see the wave-form illustration).
Each device provides external chest compression with better perfusion pressure results than manual CPS. They also eliminate many of the problems associated with “operator fatigue” when prolonged CPS is required, as in a transport.
Mechanical CPS has identical complications and risks to manual CPS. These complications include fractured bones, ruptured internal organs, and hemorrhaging.
Simultaneous Compression-Ventilation CPS
External chest compressions with simultaneous ventilation.
Like Closed-Chest CPS, this method uses high pressures to squeeze blood from the lungs into the heart and vascular beds. It also uses the inflated lungs to assist with the heart compression.
It has drawbacks. The high airway pressures occurring at the same time as the chest compression could cause vomiting. Simultaneous chest compression and ventilation causes low cerebral blood flows, which are usually accompanied by high intracranial pressures [9, 10] because the lungs are inflated at the same time chest compressions are being applied. The lungs are unable to provide a cushion against the compressions, and instead, constrict the blood vessels and block the flow of blood.
The mechanical CPS device generally applied during an Alcor transport (Michigan Instruments’ Hi-Impulse “Thumper”) may be modified to administer this form of CPS, but the disadvantages of low cerebral blood flow and increased intrathoracic pressures (pressure within the chest cavity) have eliminated simultaneous compression-ventilation CPS in favor of Hi-Impulse, closed-chest CPS during transport.
Active Compression-Decompression CPS
External chest compressions using a suction device to improve cardiac filling during decompression.
This brand new technique is being actively investigated and has yet to be approved by the Food and Drug Administration for use in this country, except by rare, and closely-scrutinized, research organizations. As a method for cardiopulmonary support, ACD-CPS seems to refill the heart between compressions with more fluid than other methods, which ultimately improves the effectiveness of the cardiac compressions [13, 14].
Currently, the Food and Drug Administration has prohibited the use of these devices in the medical community, and they may not even be imported to this country without extreme bureaucratic intervention. Given Alcor’s status as a research organization, an Active Compression-Decompression CPS device may eventually be used during transport. Alcor is investigating this as an alternative to the current protocol, and may purchase an ACD-CPS device for future research purposes, if FDA restrictions are eased.
Direct heart massage.
This method requires the sternum or ribs be opened to pressurize the heart by hand and surgically closed when complete. It is the most effective of all CPS methods, but it is not widely used due to the invasiveness of the procedure. Directly squeezing the heart delivers higher cerebral perfusion pressures and blood flow. This method can deliver between 50-70% of normal cardiac output [10, 15, 16]. However, implementing open-chest CPS requires more training and equipment than other methods [17, 18, 19].
Surgically opening the chest to apply cardiac compressions to the atria and ventricles eliminates many of the pressure problems arising with closed-chest CPS. Of all the CPS alternatives, this method has the highest incidence of complication, due primarily to infection and myocardial damage caused by poor technique — the infections are of lesser concern than the damage to the heart caused by improper technique, and for cryonics, both are of secondary concern.
External pump and tubing array directly accessing the circulatory system.
In this form of CPS, tubes (“cannula”) are inserted into large arteries and veins, and connected to an external pump. This pump can replace both the heart and the lungs when an oxygenating device is included in the circuit.
Cardiopulmonary bypass improves cooling rates to about 1°C per minute, as the circulatory system is used to deliver chilled blood (or blood-substitute) to the core tissues. The chart shows a hypothetical cooling curve for cardiopulmonary bypass initiated immediately upon pronouncement of legal death, as compared to actual surface-cooling rates seen in past cryonic suspension transports.
Bypass also allows medications to be administered swiftly and in large volume, and the blood may be completely replaced with an organ preservation solution. Nearly 100% of normal cardiac output can be achieved artificially [18, 20], and 100% oxygen may be used. Naturally, this significantly increases the chances of maintaining cerebral and myocardial function. In fact, cardiopulmonary bypass is the most effective of all CPS methods [20, 21]. Its drawbacks revolve around the equipment and training needed by personnel. To access the circulatory system directly, transport team members must be able to perform surgery and assemble complex tubing arrays (see Chapter 9), all of which requires advanced training.
Cardiopulmonary bypass is used in cases where qualified Alcor personnel are involved in the transport, and the necessary equipment is on-hand. The application of cardiopulmonary bypass is time-consuming (currently 60-90 minutes to begin) with the methods currently employed, and Alcor is investigating ways to reduce this time. Until bypass is initiated, manual or mechanical CPS is used to maintain blood flow.
Transport CPS Requirements
As mentioned above, manual and mechanical CPS will be used during the stabilization of a cryonic suspension patient in conjunction with cardiopulmonary bypass. All transport team members are encouraged to keep their manual CPS technique fresh by attending an occasional CPR course. The American Red Cross, the American Heart Association, local fire departments and EMS services, and schools offer classes regularly. Many of these are open to the public.
During a transport, mechanical CPS is begun at the earliest possible moment. Usually, this is immediately after pronouncement, or upon exiting hospital premises. (Hospital administrators will often try to prohibit the administration of CPR to a legally-dead person on hospital grounds.)
Administering CPS to a patient is another area of a transport where the transport team member risks infection, as the transport team member is likely to encounter the patient’s body fluids (including blood, sputum, mucus, and vomitus). Rigorous implementation of safety precautions is essential to avoiding accidental infection.
|Caution: Any transport team member coming into contact with a patient’s body fluids must wear latex exam gloves. Face masks and hair covers are also required. For individuals handling sharp objects, like needles or scalpels, puncture-resistant nitrile gloves should be worn underneath the exam gloves. For the surgeon and perfusionist, or anyone assisting them, face shields or goggles are also required to protect the eyes. Water-resistant suits are also recommended.|
Use of the Michigan Instruments HLR
Manual CPS should only be used until a mechanical device can be placed, if one is nearby, and should never be used if a mechanical device is immediately available. Mechanical devices which administer external compressions will only be used until cardiopulmonary bypass is an available option.
In most transports, a Michigan Instruments’ heart-lung resuscitator (HLR) will be used. An HLR of this type is usually referred to as a “Thumper”. Standard and Hi-Impulse models are available to the Alcor transport team members. The application of each is similar.
The Thumper requires oxygen or compressed air to function, and its demands are high. Oxygen cylinders come in various sizes. Refer to the chart below for information about cylinder size and capacity.
In order to function, a Thumper should be receiving oxygen at pressures between 50 and 90psi. Pressures will be displayed on the regulator (which fits between the cylinder and oxygen line).
Ventilation will be controlled automatically by the Thumper, and the maximum ventilation pressure should be 30 (psi or mmHg, check gauge).
Placing the Thumper is not difficult, and the steps are shown in the photographs below. Things to remember when placing the device include: the plunger height regulates the depth of the compression, which should be about 1-1/2″ according to CPR guidelines; the placement of the pad on the sternum will determine where chest compressions will occur and should be two finger-widths above the xiphoid process; the orientation of the pad will determine whether or not ribs will be broken immediately; and all compressions and ventilations are performed automatically, so pressures must not exceed recommended levels.
- Connect oxygen (hand off airhose to person managing airway).
- Swing HLR arm over the patient’s chest and position plunger. The dome should read 9.
- Read column position.
- Raise arm until dome reading is identical to the previous column reading.
- Secure arm by turning knob.
- Turn master switch to “on”.
- Turn on cardiac compressions.
- Connect airhose to airway.
- Turn on ventilations.
- Check ventilation pressure.
- Listen for signs of chest expansion and lungs filling with air.
Care must be taken when using a mechanical device for CPS. Mechanical devices cannot readjust their position if something changes. During mechanical CPS, some of the ribs may break under the force of the plunger. This will cause the chest to cave in slightly. In order to optimize CPS, a transport team member must occasionally check the height of the plunger (via the dome, not the column) and reset the entire arm if the plunger isn’t returning to its original height.
Cardiopulmonary support, as initiated by transport team members, is very similar to cardiopulmonary resuscitation techniques used by emergency medical personnel. Much of the technology is applicable.
Team members will apply the techniques most suitable to the circumstances surrounding the emergency response. Manual CPS will be administered until a Thumper can be placed, and Thumper support is an interim measure until cardiopulmonary bypass is started. No CPS method will be used on a patient who has been autopsied, as there will be no viable circulatory system (see Chapter 11).
Administering cardiopulmonary support, especially through external compression, will not eliminate all damage to a patient, and unless medications are administered to reduce and reverse the damage caused by implementing CPS, the patient will suffer preventable damage.
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