Keeping the lung open is a key strategy to prevent postoperative pulmonary complications
It is well established that Postoperative Pulmonary Complications (PPCs) significantly contribute to perioperative morbidity and mortality, as well as to postoperative length of hospital stay 1-3. PPCs relate to anesthesia and/or surgery, and occur within a time frame of 5 to 7 days after surgery 7,8. They lack a uniform definition and include a range of rather mild to very severe events (e.g. need for supplemental oxygen, respiratory failure, atelectasis and Acute Respiratory Distress Syndrome (ARDS)). PPCs represent the major cause of death after both cardiothoracic and non-cardiothoracic surgery and thus pose a significant burden to society 9-12. The incidence of PPCs after general surgeries is 5–10% 3,13,14, while it has been reported to be as high as 30–40% after abdominal and intrathoracic surgeries 1,3,13, and even 87% after liver transplantation 15. Of note, a large multicenter study has revealed that up to one in every five patients who develops a severe PPC dies within 30 days of surgery, and patients who survive often suffer from a sustained reduction in functional status 3.
Several investigations have aimed to define reliable risk factors for the development of PPCs 1,3-5,14,16-20. While the ‘Surgical Lung Injury Prediction’ (SLIP and SLIP-2) model 17,19 and the ‘Assess Respiratory Risk in Surgical Patients in Catalonia’ (ARISCAT) risk score 1,3 represent prediction tools that are based on patient characteristics and preoperatively assessable surgery-related features, the recently published ‘Local Assessment of Ventilatory Management during General Anesthesia for surgery’ (LAS VEGAS) prediction score 14 additionally includes intraoperative events. These have been implicated as contributing to postoperative complications 21. Of note, intraoperative desaturation has been shown to be significantly associated with the development of PPCs, which could reflect the occurrence of atelectasis during ventilation, resulting in the decrease of functional residual capacity 14. Thus, perioperative ventilation approaches should ideally include adequate strategies to prevent atelectasis and desaturation 22.
Multiple randomized controlled trials have been conducted to evaluate the effect of different ventilation strategies on the development of PPCs. The majority of these interventions aimed to keep the lung open by applying recruitment maneuvers or setting higher PEEP levels, usually in combination with low tidal volumes. While some of these trials failed to show improved patient outcome 23,24, some did show positive effects 25-30, and some are still ongoing 31,32. Thus, these studies aimed to reduce PPCs by focusing on the optimization of established ventilation parameters like pressures and volumes for specific patient groups, where an overall consensus is still lacking. This may indicate that a more fundamental change in ventilation strategies is required to improve patient outcome and prevent PPCs.
FCV® keeps the lung open and results in higher efficiency of ventilation than conventional ventilation strategies
The new ventilation method FCV®, solely applied by Evone, keeps the lungs open by controlling the full ventilation cycle. As depicted in Figure 1, FCV® relies on a continuous inspiratory and expiratory flow without notable pauses 33, which are present during Volume Controlled Ventilation (VCV) and Pressure Controlled Ventilation (PCV) at the end of inspiration and expiration. FCV® aims for a linear increase or decrease in intratracheal pressure, without sudden pressure changes as compared to conventional methods. A controlled and linearized airway pressure decline has been described to induce a recruiting effect 34. Thus, FCV® prevents the bronchioles and alveoli from collapsing at the end of expiration, enhancing oxygen uptake into the blood as well as CO2 removal.
Figure 1. Intratracheal/airway pressure, flow and volume curves for FCV®, VCV and PCV (see also Schmidt et al. 2019 37)
Animal studies revealed a significantly higher ventilation efficiency of FCV® compared to the current golden standard VCV. In lung-healthy pigs, FCV® resulted in a 9% increase (P=0.002) in arterial oxygenation while using a 21% lower minute volume (P=0.02) for normoventilation as compared to VCV with similar PEEP and tidal volume settings 35. Analysis of dynamic computer tomography (CT) scans revealed that these effects were related to a better lung recruitment (Figure 2). These results were even more striking in a porcine model of acute respiratory distress syndrome (ARDS): Compared to VCV, with comparable tidal volumes and PEEP, FCV® led to a 46% increase of arterial oxygenation (P=0.035) while using a 26% lower minute volume (P<0.001) 36. In these lung-sick animals, FCV® prevented atelectasis and facilitated normal aeration in dependent (dorsal) lung parts.
Figure 2. Improved lung aeration during FCV® vs. VCV in healthy pigs, measured by Hounsfield units during dynamic computer tomography (adapted from Schmidt et al. 2018 35)
FCV® has been applied clinically in more than 40 hospitals across 11 countries. A first multicenter observational study in ENT patients revealed that FCV® using Evone and Tritube resulted in adequate etCO2 levels with minute volume in the lower normal range and driving pressures in the normal range. It was concluded that FCV® provides a new option for mechanical ventilation and that the narrow-bore tube expands the armamentarium for airway management 37.
A randomized controlled trial in laryngeal surgical patients, aiming to evaluate surgical exposure comparing Tritube with an Microlaryngeal Tube (MLT)-6, demonstrated that FCV® improved alveolar recruitment and consequently enhanced respiratory system compliance compared to VCV (63±14 vs. 46±8 ml/cmH2O, P<0.001) 38. In the same line, FCV® better maintained end-expiratory lung volume in morbidly obese patients as compared to VCV (P<0.001) during ventilation phases of only 7 minutes, with similar tidal volumes, but lower peak inspiratory pressures 39. These results strongly implicate a recruiting effect due to the constant expiratory flow and the elevated mean airway pressure 39. Furthermore, a crossover randomized controlled trial in lung-healthy patients revealed higher efficiency of ventilation when using FCV® compared to VCV 40. With similar tidal volumes and peak pressures, FCV® resulted in a 9% higher oxygenation and 4% lower arterial CO2 concentration (P<0.001), while maintaining a 10% higher mean tracheal pressure (P<0.001) 40. Together, these studies underline the higher efficiency of ventilation by FCV® as compared to VCV and indicate that FCV® may help prevent atelectasis and hypoxemia in patients during mechanical ventilation.
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Erasmus Medical Center (Rotterdam, the Netherlands) is organizing a hybrid symposium on Flow Controlled Ventilation blowing away VILI.The event will be held on the 28th of October in Rotterdam but can also be watched online.For more information click...