Introduction and Statement of the Problem
Background of the Problem
There is a variety of health problems that may require cardiopulmonary surgical procedures, i.e. surgeries in the thorax. Although these problems are widespread, and cardiopulmonary surgeries are often performed in many places around the world, the operation is still considered to be a rather serious intervention that presents many risks to the patient. A major part of these risks occurs due to the application of extracorporeal support.
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For the time of the operation, the functions of a patient’s heart and lungs are temporarily suspended and taken over by a machine, known as the heart-lung machine and often referred to as simply a “pump,” which ensures the normal circulation of blood and oxygen in the patient’s body. This technique is known as cardiopulmonary bypass, and it is employed in surgeries with the purpose of offering a bloodless surgical area in the thorax when either the heart or the lungs are operated while sustaining the required amount of blood and oxygen circulating throughout the rest of the body.
Every part of the human body requires normal blood flow for the supply of oxygen and nutrients and for the purpose of removing waste. Blood is a complex fluid, as it contains a variety of different cells. Also, it flows in an extremely complicated vascular system with different types of vessels. Besides, as the blood circulates, its composition is changing significantly due to chemical processes and the exchange of substances (Freund 69).
These three factors determine the complexity of the physical and mechanical characteristics of blood flow. The imitation of blood flow, which is the function of the pump in the case of extracorporeal circulation, is not limited to the application of particular pressure. There are different adjustments available for such machines, which means that perfusionists, i.e. specialists who operate the pump, have options in terms of how the blood will circulate in the patient’s body during a cardiopulmonary surgery (Nam et al. 372-373). Two major perfusion modalities are pulsatile perfusion and non-pulsatile perfusion.
It is important to understand that both modalities occur in normal blood flow. What makes them different is the presence of periodic variations in the pulsatile perfusion and the absence of them in non-pulsatile perfusion; the latter, however, is still associated with certain physiological fluctuations due to the circular nature of blood motion in the human body and due to the characteristics of blood vessels. Modern heart-lung machines allow applying both modalities in a given cardiopulmonary surgery, and there is a natural assumption that the effects on the patient, especially on his or her postoperative state and recovery but also on the physiological processes during the operation, may be different in the case of applying one profusion pattern or the other one.
Many researchers have argued that pulsatile perfusion has a number of benefits in comparison with non-pulsatile perfusion for the health of a patient (Alkan et al. 530); other researchers, however, have not found sufficient evidence for such a claim, which is why the debate over assumed advantages of pulsatile perfusion continues (O’Neil et al. 651).
The debate is long-standing and ongoing because there is a vast array of physiological functions that are affected by perfusion, and each aspect of this impact should be addressed separately in order to detect assumed benefits of pulsatile perfusion. Also, it should not be disregarded that, in cardiopulmonary surgeries, the modality of perfusion is not the only factor that may affect the patient’s state during the operation and during the period of recovery. In other words, not all the observable effects concerning the health of a patient and his or her postoperative recovery period can be attributed to the use of one or the other perfusion pattern.
Obviously, the initial state of the patient is a factor, too, which complicates the identification of correlations between perfusion and health outcomes. Experiments in this area are limited due to the recognition that there are no patients with identical combinations of medical conditions, which raises the number of factors that should be considered in every experiment (Pocock 110), and the connections between those factors may not always be fully understood.
However, the limitations outlined above are applicable to a certain degree to any type of medical research that considers the effects of certain medical procedures or treatment elements on patients. A challenge that is more specific to the area of research on pulsatile and non-pulsatile perfusion is that it is hard to separate the effects of these two modalities in a normally functioning human organism. This area is studied by not only physiologists but also fluid mechanics experts who engage in complex calculations aimed at identifying the role of the pulsatility of blood flow in various physiological processes. Again, the complication is that blood displays both pulsatile and non-pulsatile characteristics, and the boundaries are not clearly defined today, which allows the debate to go on.
Researchers who participate in the debate and present new evidence on the subject recognize that there are many possible benefits for the clinical use of the two perfusion patterns examined in the present research. In various studies, it has been observed that pulsatile perfusion may have a positive effect on vital organ blood flow and recovery (Alkan et al. 534) and on microcirculation (Koning et al. 1727; Nam et al. 373-374; O’Neil et al. 2046).
Moreover, it is suggested that the use of pulsatile perfusion during cardiopulmonary surgeries is capable of reducing the systemic inflammatory response syndrome, inotropic support, intubation period, and the period of stay in a hospital (Alkan et al. 530). These effects have been observed in actual experiments, but the existing data is not considered sufficient. In case the benefits of the use of pulsatile over non-pulsatile perfusion are confirmed, the clinical implications will include encouraging medical facilities to universally employ the pulsatile perfusion modality in cardiopulmonary bypass surgeries. It will reduce the number of risks for patients who receive such surgeries and will make their recovery easier and faster.
For the purpose of the present research, research questions were formulated to address the debate on the use of pulsatile versus non-pulsatile perfusion in cardiopulmonary bypass, and the answers to the questions were assumed (see Research Questions and Hypotheses). Also, key terms used in the research were defined (see Definitions of Terms). Further, a review of the relevant academic literature was conducted to examine, both from the theoretical and practical perspectives, what has been found on the subject (see Literature Review).
The literature review is part of the research because it does not only provide valuable background data but also addresses the research question directly. Also, research methods were described to justify the validity and reliability of findings by means of testing the adequacy of methods, tools, sampling, and data collection (see Research Design and Methodology).
Finally, upon analyzing and discussing the results, as well as paying particular attention to the limitations of the research, recommendations will be proposed for future research and clinical implications of findings (see Discussion about Results, Conclusion, and Recommendations). Proper compliance with this structure will allow obtaining reliable results that will make a contribution to the understanding of whether pulsatile or non-pulsatile perfusion should be used in cardiopulmonary bypass.
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Research Questions and Hypotheses
The first research question is what are the differences in the physiological effects produced by pulsatile and non-pulsatile perfusion during cardiopulmonary bypass. The second question is whether there are consistent benefits of pulsatile perfusion as opposed to non-pulsatile. The questions are applicable to two areas: physiological characteristics and recovery indicators. Physiological characteristics will include blood flow in different vital organs, microcirculation, thyroid hormone homeostasis, and some other characteristics identified in relevant studies (see Literature Review).
Recovery indicators will include the speed of vital organs recovery after cardiopulmonary bypass surgery, the duration of intubation, the time a patient stays in a hospital, and other indicators that may show whether the recovery is adequate and successful. It is hypothesized that pulsatile perfusion will demonstrate better results in terms of patients’ physiological responses and recovery, i.e. will be confirmed to be a better perfusion pattern for cardiopulmonary bypass.
Definitions of Terms
Sorted by relevance.
Cardiopulmonary surgery (also referred to as cardiothoracic surgery or thoracic surgery) is a manual or operative treatment procedure employing incision into the thorax, i.e. the area between the neck and the abdomen, needed for treating certain medical conditions of the heart and lungs. Conditions that may require cardiopulmonary surgery include various diseases of injuries of the heart, blood vessels, and respiratory system.
Cardiopulmonary bypass is a technique employed in cardiopulmonary surgeries that implies the temporal suspension of the functions of the heart and lungs and provides extracorporeal circulation (O’Neil et al. 2047), i.e., the circulation of blood and oxygen is performed by a machine rather than human organs for the purpose of conducting a surgery.
Pulsatile perfusion is one of the perfusion modalities, i.e. the modalities of passage of blood through the circulatory system, where the flow has periodic variations (Koning et al. 1728).
Non-pulsatile perfusion is one of the perfusion modalities, i.e. the modalities of passage of blood through the circulatory system, where the flow does not have periodic variations. Non-pulsatile perfusion and pulsatile perfusion constitute the two main modalities of perfusion that characterize the physical features of blood flow.
Centrifugal pump is a heart-lung machine used in cardiopulmonary bypass that functions by means of resistance attributes and uses rotation to produce resistance and various flow rates. It plays a notable role in pulsatile perfusion.
Roller pump is a heart-lung machine used to control resistance that is often preferred under clinical conditions due to its convenience and lower speed of rotation.
Microcirculation is the process of blood flow within organ tissues, as opposed to the process of blood flow to and from organs. Microcirculation occurs in the smallest blood vessels where the exchange of dissolved materials and substances carried by blood is enabled by thin and permeable vessel walls.
Vital organs recovery is the process of vital organs’ return to normal functioning after the application of extracorporeal circulation.
Thyroid hormone homeostasis is the process within the neuroendocrine system that regulates metabolism by producing particular hormones.
Alkan, Tijen, et al. “Effects of Pulsatile and Nonpulsatile Perfusion on Vital Organ Recovery in Pediatric Heart Surgery: A pilot clinical study.” ASAIO Journal, vol. 52, no. 5, 2006, pp. 530-535.
Freund, Jonathan B. “Numerical Simulation of Flowing Blood Cells.” Annual Review of Fluid Mechanics, vol. 46, no. 1, 2014, pp. 67-95.
Koning, Nick J., et al. “Pulsatile Flow during Cardiopulmonary Bypass Preserves Postoperative Microcirculatory Perfusion Irrespective of Systemic Hemodynamics.” Journal of Applied Physiology, vol. 112, no. 10, 2012, pp. 1727-1734.
Nam, Kweon-Ho, et al. “Extracorporeal Bypass Model of Blood Circulation for the Study of Microvascular Hemodynamics.” Microvascular Research, vol. 83, no. 3, 2012, 372-375.
O’Neil, Michael P., et al. “Pulsatile versus Nonpulsatile Flow during Cardiopulmonary Bypass: Microcirculatory and Systemic Effects.” The Annals of Thoracic Surgery, vol. 94, no. 6, 2012, pp. 2046-2053.
Pocock, Stuart J. Clinical Trials: A Practical Approach. John Wiley & Sons, 2013.