NIRS for Cerebral Oximetry in ‘More Physiological’ Cardiac Surgery: Training for the Team

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In this issue we feature several articles about cerebral oximetry and its role in minimally invasive extracorporeal circulation in cardiac surgery. Cure&Care attended the Medtronic-sponsored peer-to-peer multidisciplinary training masterclass ‘Cerebral Oximetry State of the Art’ hosted in Athens, Greece on 21–22 June 2017, to hear more about the practicalities of integrating cerebral oximetry using near infra-red spectroscopy (NIRS) into cardiac surgery.

A coordinated multidisciplinary healthcare team, both inside and outside the operating theatre, has substantial benefits for patient care [1]. The assembly and deployment of a multidisciplinary team is valuable in the care of people with conditions as diverse as haemophilia [2], cancer [3], diabetes [4] and cardiovascular disease [5]. Efficient multidisciplinary surgical team-working has been found to be correlated with time efficiencies and safety in surgery [6-8]. To achieve these benefits it is necessary to engage in training of the full team – indeed, standardised training for a multidisciplinary surgical team can have great advantages [9]. Collective training of a surgical team in a novel technique provides a great opportunity for discussion and clarification, and contributes to an enhanced coordination of team members in the operating room.

Minimally invasive extracorporeal cardiac surgery (MiECC) – a novel technique developed in the early 2000s – has been described as a method that has helped the surgical community advance towards a more physiological approach to cardiac surgery [10]. A strategy for MiECC, based on goal-directed perfusion, has been developed by Anastasiadis and co-workers. Incorporating in-line, real-time monitoring with NIRS to monitor the oxygenation of brain tissue, this strategy aims to prevent tissue malperfusion, rather than correct it after its detection by periodic evaluation [11]. This goal-directed strategy requires that the surgical team (surgeon, anaesthesiologist and perfusionist) work together in an integrated manner, being constantly aware of changes in perfusion parameters and alerting the whole team if one of the goal-directed perfusion variables is deteriorating. In this approach, NIRS has an essential role in providing additional information that the team may have to respond to promptly.

To facilitate the understanding and practical application of cerebral oximetry in MiECC, Professor Kyriakos Anastadiadis and his surgical team – Dr Polychronis Antonitsis (cardiac surgeon), Dr Helena Argiriadou (cardiac anaesthesiologist) and Apostolos Deliopoulos (clinical perfusionist) – hosted a 2-day training course. Its objective was to define how cerebral oximetry is best used when integrated into in-line monitoring and combined with advanced perfusion technology. The Faculty was able to provide the multidisciplinary teams that attended a true multidisciplinary perspective on these topics.

The rationale for considering the brain as both target and index organ was an initial discussion point. The course participants were reminded of the mechanics and importance of optimal tissue perfusion, and that the three key organs involved in oxygen consumption are the heart, the brain and the kidneys. From a clinical perspective, significant associations have been found between monitoring of brain oxygen saturation during cardiac surgery and improved survival [12]. From a practical perspective, the the frontal cortex of the brain is ideally suited as an index organ because the region most vulnerable to hypoxia – the watershed area perfused by the anterior cerebral artery and the middle cerebral artery – is sufficiently close to the skin surface to permit photons from the NIRS sensor to easily penetrate tissue and be returned to the detectors. Consequently, the brain is a good index organ for real-time monitoring of oxygen saturation.

An in-line monitoring system is required for real-time monitoring of perfusion. Apostolos Deliopoulos discussed how there has been a shift in thinking from the ‘one-size-fits-all’ approach for cardiopulmonary bypass surgery to one in which perfusion is tailored to the needs of the patient. Although technically complex, real-time in-line monitoring is valuable because it is non-invasive and can report a broad range of perfusion-related parameters. The surgical team relies on the perfusionist to monitor and understand the parameters reported, to recognise warning signs, and to raise an alert if the readings deviate from a pre-established optimum. The optimal levels can still be a matter of debate and are patient specific, but it is also the trend and the resultant capability of the team to react in real-time to a changing situation that permits the adoption of a preventative, rather than reactive, strategy, when signs of malperfusion are observed. NIRS cerebral oximetry is key to the real-time monitoring of perfusion and functions as an estimate of overall organ perfusion; if hypoperfusion is observed, the team is alerted to respond by correcting the situation. It is possible that this may help to avoid postoperative adverse effects, but more data are required to verify this.

In conclusion, as cardiac surgery is evolving to become ‘more physiological’, the needs for monitoring and response are also changing. During surgery, NIRS can detect changes in perfusion parameters, and this allows the surgical team (including perfusionists, anaesthetists and surgeons) to make immediate changes to their intended actions. This capability can have benefits that extend into the postoperative period, but it requires the surgical team to understand and implement the use of cerebral oximetry by NIRS, and understand its application through learning, practice and reflection.


Thoughts from the Faculty

We spoke with some of the Faculty to ask for their thoughts on the most important take home messages from the course and on cerebral oximetry in cardiac surgery.

Why is it important to train the surgical team?

Dr Helena Argiriadou: Cardiac surgery relies on a team; all parts of the team must do their best and cooperate for the best results for the patient.

Dr Polychronis Antonitsis: Teamwork is crucial; there are important time periods before and after surgery during which the team needs to work together.

What are the most important messages the attendees of the course will take away with them?

Dr Polychronis Antonitsis: First, that they should use NIRS in everyday clinical practice and in every patient undergoing cardiac surgery. Second, how to deal with cerebral desaturation as a team and obtain a better outcome for the patient.

Dr Helena Argiriadou: The real-world case scenarios we discuss are very important because they allow the attendees to review how to respond to specific situations. Also, the participants should adopt cerebral oximetry monitoring in all areas of their practice, because it is important that the brain and other tissues are monitored.

What controversial topics are being debated in the field of NIRS and cerebral oximetry? – and what are the most important clinical questions to be answered around NIRS?

Dr Polychronis Antonitsis: There is a need to determine the best algorithm for detecting and correcting cerebral oxygen abnormalities during surgery, and the clinical relevance of deviations from baseline readings: should all deviations be responded to and corrected, or just some? Also, although cerebral sensors are sensitive to brain ischaemia, there is considerable scope for the improvement of somatic sensors for use outside the operating theatre and in the intensive care unit; the value of somatic measurements needs to be validated in large prospective trials.

Dr Helena Argiriadou: There is a need to establish whether there is a strong relationship between intraoperative oxygen desaturation events and postoperative adverse events; there is currently some supporting evidence, but it is important to verify these observations in a multicentre, randomised study, using the same NIRS device and employing the same algorithm. Also, the collection of data using somatic sensors has still to be explored.


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