Tissue Perfusion Monitoring During Minimally Invasive Extracorporeal Circulation

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Cure&Care spoke with Dr Kyriakos Anastasiadis, Professor of Cardiac Surgery and Head of the Cardiothoracic Department at AHEPA University Hospital, Thessaloniki, Greece, to provide insights on approaches to monitoring during minimally invasive extracorporeal circulation (MiECC), and to discuss its importance and the benefits that this technology offers over conventional cardiopulmonary bypass (CPB).

What is MiECC and what are its key features? 

Minimally invasive extracorporeal circulation was established in the late 1990s in an attempt to integrate advances in perfusion technology into a single system. The rationale behind its development was to minimise side effects and derangement of the body’s physiology from CPB, which is regarded as the conventional circulation technique for performing cardiac surgery.

Since MiECC comprises a closed system, there is no reservoir for blood collection outside of the patient’s body, as traditionally used in conventional CPB. This removes the possibility of blood–air interaction during CPB use and renders the vascular component of the patient intact (Figure 1). The system’s design consists of minimal components with contemporary advancements in perfusion technology, including short circuit design, coated tubing, a coated oxygenator and a centrifugal pump, which allow for a more ‘physiologic’ perfusion. While utilising MiECC, a significantly reduced transfusion rate, higher haematocrit levels and better performance for patients undergoing cardiac surgery has been confirmed. Thus, this new technology offers a huge potential for improving patient outcomes and tackling the significant levels of morbidity observed with conventional, ‘less-physiologic’ intervention.

How is tissue perfusion monitored in MiECC?

Monitoring is an important aspect of MiECC; it is a mandatory guide for controlling perfusion and promotes MiECC to a strategy. The MiECC strategy offers a shift from the manual, demanding and often time-consuming calculations performed in the past to monitoring real-time data for metabolic and haemodynamic parameters of the patient. These data enable immediate action for continuous adjustment rather than the correction of any derangement incrementally.

All major end-organs, including the brain, kidneys and lungs, require an optimum supply of blood and oxygen to meet their metabolic needs. When performing cardiac surgery there is a ‘non-physiologic’ period during which we stop the patient’s heart and support the body’s regulatory mechanisms with an artificial apparatus for cardiac output and tissue perfusion.

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Monitoring of tissue perfusion traditionally used preset values to meet these metabolic needs, included calculating optimum cardiac output and maintained haematocrit levels within a defined range. However, over the last decade, the emphasis has increasingly been on individualisation of perfusion to the patient’s requirements and circumstances. Data from all members of the surgical team – the surgeon, anaesthesiologist, and perfusionist – showed that additional parameters outside of these preset values were mandatory for safely guiding optimum perfusion. However, these parameters required calculation and intermittent evaluation during the procedure, and hence real-time monitoring was needed to assess metabolic requirements of the individual patient for individual conditions. This was the rationale for the shift from a ‘one-size-fits-all’ approach to that of ‘ goal-directed perfusion’ (GDP). The important part of this new approach to perfusion is the continuous determination of the patient’s metabolic state by the calculation and detailed assessment of metabolic parameters, including consumption and delivery of oxygen to the tissues, oxygen extraction rate, and mixed venous oxygen and arterial saturation.

Which organs are the focus of tissue perfusion monitoring in MiECC? 

The major organs that could be damaged by cardiac surgery are the brain, kidneys, lungs and, of course, the heart. Throughout the years, different tools have been developed to monitor perfusion in these organs. For example, measurement of urine output was used to assess adequate perfusion of the kidneys – a reduction in such output signifying the occurrence of hypoperfusion.

The conventional strategy of monitoring focuses on the intermittent correction of any deviation that occurs intraoperatively, and relies on repeated measurement, i.e. every 15–20 minutes, of blood gases to assess parameters such as lactate levels and pH. However, these measurements are imprecise, giving insufficient information to indicate the level of insult or the source of the problem. To correct hypoperfusion, more data and a specific strategy for regulating values are required. Despite the use of good monitoring techniques in the past, no algorithm was available for real-time adjustment of perfusion quality, in order to avoid or immediately reverse any insult to the body’s organs. Therefore, there was a need for an advanced intraoperative monitoring strategy to give an indication of both tissue and organ perfusion.

This was the rationale behind my surgical team’s shift in focus from using the kidneys as an index organ to using the brain as the tissue perfusion organ to monitor. The technique arose from our ability to indirectly monitor perfusion through cerebral oximetry. We have utilised the newest near-infrared spectroscopy  ‘INVOS™’ technology for upgrading our in-line monitoring system and found that cerebral oximetry acts as an alarm to signal the occurrence of hypoperfusion.

In-line monitoring is an important tool for GDP and for the collection of data on parameters such as oxygen delivery, consumption and saturation. Employing the brain as an index organ allows the surgical team to monitor perfusion in real time and make adjustments accordingly, rather than incrementally correcting derangements. As a principle, monitoring should lead to direct action rather than data collection alone. An operator needs to be able to take the information, process it and be prompted to an action using an algorithm. This enables the team to better safeguard the organ’s perfusion and thereby produce optimum results, postoperatively. Additionally, it allows the surgeon to operate on the ‘safe side’ and achieve the goal of a ‘more physiologic’ perfusion.

What benefits does the MiECC system offer? 

The features of contemporary MiECC systems render them suitable for a wide range of cardiac procedures. When operating on a patient with no comorbidities, good results can be achieved irrespective of whether surgery is performed with conventional CPB or a MiECC system. However, we now know that MiECC offers the best performance when used in high-risk patients – for example, an elderly patient with many comorbidities and low ejection fraction, or a patient who is high-risk for cerebral insult or has severe lung disease. Additionally, MiECC offers no contraindication or limitation, as is the case with other techniques used for performing cardiac surgery, such as off-pump surgery, which may apply only for epicardial procedures.

How has the introduction of MiECC systems changed the respective roles of those in the surgical team?

The Minimal Invasive Extracorporeal Technologies International Society (MiECTiS) advocates viewing MiECC as a strategy that can bring together all stakeholders associated with cardiac surgery [1]. We believe that teamwork has to be applied to the whole procedure through collaboration between cardiac surgeons, cardiac anaesthesiologists and perfusionists so as to implement the MiECC strategy and maximise the resultant benefit for the patient.

Cooperation was not mandatory in the conventional approach to cardiac surgery: the surgeon was stitching, the anaesthesiologist was performing the induction and administered inotropic drugs for maintaining cardiac output, and the perfusionist was isolated behind the surgeon, whilst using the bypass machine to maintain intraoperative perfusion. MiECC allows for stronger interaction within the surgical team during surgery. Monitors are used as ‘bridges’ between the team members, to allow greater interaction and ultimately achieve optimal results for the patient. When I talk about MiECC, I mainly focus not on the technology but on the teamwork aspect that is engendered by these systems. However, the surgical team needs a comprehensive algorithm that enables rapid response to data from the monitors and to react to any divergence. In general, I believe that MiECC encompasses not only a change in the perfusion hardware, but instead an entirely new approach towards performing cardiac surgery. Integrating MiECC into our practice has allowed us to adopt a more multidisciplinary procedure and implement the goal of intraoperative ‘physiologic’ perfusion, which provides the maximum benefit from cardiac surgery [2]. Of course, the performance and the skill of the surgeon during the procedure will be the major factor for determining postoperative results; however, the role of the other team members should be emphasised and considered as equally important.

What clinical evidence has there been to support the improved outcomes with MiECC, compared with conventional CPB?

There have been a number of randomised control trials and large-scale meta-analyses supporting the hypothesis that MiECC offers the best organ protection. The largest meta-analysis, which included 2,770 patients treated with MiECC or conventional CPB, provides Class 1, Level A evidence that MiECC is associated with an improvement in neurological function, renal function, myocardial protection and the patient’s quality of life, compared with conventional CPB. Additionally, the use of MiECC has resulted in preserved levels of haematocrit and reduced need for blood transfusion, as well as a reduction in patient bleeding systemic inflammatory response, length of stay in the Intensive Care Unit, and overall cost of the patient’s stay within the healthcare system [3]. It is important to emphasise that this meta-analysis also showed a benefit with MiECC in terms of reduced mortality – a hard endpoint to achieve.

To further investigate the positive outcomes of MiECC use, MiECTiS has now designed a large, multicentre study, designated the ‘Conventional versus Minimally Invasive extra-corporeal circulation in patients undergoing Cardiac Surgery’ (COMICS) trial. This trial initiated in 2017, will recruit 3,500 patient cases, randomised into two cohorts: a conventional CPB cohort and a MiECC one. The primary aim of the trial is to investigate MiECC as an effective strategy versus conventional extracorporeal circulation, as well as to evaluate the incidence of serious adverse events – including death – during the postoperative period. This randomised trial will compare outcomes between the two technologies to corroborate results from the other randomised controlled trials, which are relatively small in number, or to reveal additional benefits from the primary and secondary outcomes measured. Twenty-two centres in Asia, Europe and North America, are recruiting patients into the COMICS trial. I believe COMICS is one of the largest trials within the field of cardiac surgery in the last few years, and it may have a huge impact on the way we perform cardiac surgery.

Are there any risks associated with MiECC that aren’t associated with other strategies?

Over 10 years ago, the very early designs of MiECC systems were less compatible with some cardiac surgical procedures due to two major problems: one was the air entry into the circuit, which causes the system to stop, and the other was the volume management of circulating patient’s blood, as well as blood collection from the surgical field. Over the years, MiECC technology has developed from Type I systems, now considered as comparatively primitive, to the modular, hybrid, Type IV systems used nowadays that integrate extra components and have all the relevant contemporary advancements in perfusion technology [1]. Contemporary, minimally invasive extracorporeal circulation offers zero risk in regard to any problem encountered in air-handling or volume management. We have shifted from conventional extracorporeal circulation to a circulation that is truly ‘minimally invasive’ and can provide a safer, less traumatic and more effective procedure with a reduced need for inotropic medication. In general, when discussing MiECC systems, it is important to be aware of their evolution over the past 10 years into the modern systems that we utilise today, which are safe, compatible with all cardiac case-mix and offer really excellent results.

Do you have any final comments about the technology and principles of MiECC strategy? 

It is important to emphasise that monitoring is of paramount importance when using MiECC systems. Goal-directed perfusion matched with near-infrared spectroscopy using the brain as an index-organ for monitoring perfusion fulfils this need. Thus, when talking about the ‘INVOS™’ technology, we should indicate that it has the potential to be adapted for other types of surgery. Of course, for general surgery, gynaecology or orthopaedics, in-line monitoring is not needed for the assessment of potential problems. However, even in these settings, the ‘INVOS™’ technology acts as a warning system, whereby moving outside of defined parameters indicates that something is going wrong. From my own experience, I would strongly suggest that, on each occasion that the ‘INVOS™’ technology triggers an alarm, the surgical team should immediately stop and assess the scenario, in order to maintain safety. This is highly important in cardiac surgery and a core consideration when using the MiECC strategy with in-line monitoring.

To conclude, the biggest asset offered by MiECC technology is that it allows a new, thorough insight to the body’s physiology. I believe physicians should study the modern literature and follow what we advocate in regards to GDP,  ‘physiologic perfusion’, in-line monitoring, cerebral oximetry and the overall strategy of MiECC [4]. This technology is likely to become the future of cardiac surgery, and hence I urge the physicians to try and implement it in all contemporary cardiac practices. I believe that the more we try to imitate nature with our actions, the better results we can achieve for our patients; the advancement of patient care is, after all, our mainstay and of the utmost importance to technology and to surgery itself.

References

  1. Anastasiadis K et al. Use of minimal invasive extracorporeal circulation in cardiac surgery: principles, definitions and potential benefits. A position paper from the Minimal invasive Extra-Corporeal Technologies international Society (MiECTiS). Interact Cardiovasc Thorac Surg 2016; 22(5): 647–662
  2. Anastasiadis K et al. Minimally Invasive Extracorporeal Circulation (MiECC): Towards a More Physiologic Perfusion. J Cardiothorac Vasc Anesth 2016; 30(2): 280–281
  3. Anastasiadis K et al. Use of minimal extracorporeal circulation improves outcome after heart surgery; a systematic review and meta-analysis of randomized controlled trials. Int J Cardiol 2013; 164(2): 158–169
  4. Anastasiadis K et al. A multidisciplinary perioperative strategy for attaining “more physiologic” cardiac surgery. Perfusion 2017; 32(6): 446–453

 

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