"Protective Mechanical Ventilation from OR to ICU to Improve Outcome”
Prof Paolo Pelosi, Professor of Anaesthesia and Intensive Care, University of Genoa, Italy
Dr Ewen Forrest opened the meeting and ran through the AGM (see seperate Minutes). Following this, Professor Hunter introduced the speaker, Professor Paolo Pelosi from the University of Genoa, Italy.
Professor Pelosi firstly described the contributions made by T.Cecil Gray, as described by Steve Schafer (BJA 107 (1) 97-102 (2011)) one of which being the introduction of controlled ventilation to routine anaesthetic practice. He spoke about the first documented use of positive pressure ventilation in 1732.
Professor Pelosi discussed the editorial by Villar (Critical Care 2010; 14:120), which asked the question whether or not ARDS was largely a man-made syndrome as a consequence of the aggressive ventilator regimens that are adopted to treat acutely ill patients? To answer this, he looked at the pulmonary extracellular matrix which is particularly important in controlling fluid dynamics in the lungs. This is made up of proteoglycans which bind with other proteins such as collagen to make up this space. These proteoglycans can be fragmented during controlled mechanical ventilation. (Marcozzi C. Exp Lung Res. 2015 May; 41(4):228-40) With injury to the extra cellular matrix, there is activation of inflammatory processes with resultant lung injury. This has been demonstrated to occur in previously healthy lungs and worsened when larger tidal volumes are used (O’Neill M. et al. Nature Medicine 11, 1161 - 1162 (2005))
Professor Pelosi described the European Surgical Outcomes study (Lancet 2012; 380:1059-1065). He then spoke about the Periscope trial which was an observational trial organised through the ESA looking at postoperative pulmonary complications in over 5000 patients. This showed that the incidence was in the order of 8%. These complications both increased postoperative length of stays and ultimately in-hospital mortality. He described a scoring system developed by Canet et al, (Anaesthesiology 2010: 113 (6:1138-50)) and further validated by Mazo V. et al. (Anesthesiology. 2014 Aug;121(2):219-31) which gave a score to risk factors such as age, preoperative Hb saturation, recent respiratory infections, preoperative anaemia, emergency or elective procedure, the area of surgical incision and the duration of surgery. Those with a very high score had a 50% chance of developing postoperative pulmonary complications.
Professor Pelosi then discussed the factors associated with postoperative complications, and in particular the role of controlled mechanical ventilation. He described the incidence atelectasis during general anaesthesia, which could be up to 10% but more commonly was less than 5% of lung tissue. He described the PROVHILO trial looking at the role of PEEP on postoperative outcomes (Lancet 2014 Aug 9;384(9942):495-503). It indicated that there was no difference in pulmonary complications with PEEP levels of 2 or 12cmsH2O but a significantly greater incidence of hypotension in the latter with the requirement of vaso-active drugs.
Professor Pelosi then talked about a meta-analysis of intra-operative lung protective ventilation in abdominal surgery by Serpa Neto A. et al. (Lancet Respir Med. 2014 Dec;2(12):1007-15). This showed that lung-protective mechanical ventilation strategies reduce the incidence of postoperative lung injury but did not improve mortality. Futiers et al (NEJM 2013: 369 428-37) looked at lung protective ventilation with a tidal volume of 7 mls/kg, PEEP of 6-8 cm H2O and a recruitment manoeuvre compared to traditional ventilation of over 10 mls/kg with no PEEP and no recruitment manoeuvre. It showed that the use of the lung-protective ventilation strategy in intermediate-risk and high-risk patients undergoing major abdominal surgery was associated with improved clinical outcomes and reduced health care utilization. The central message was that there was a dose-response curve between tidal volume (but not PEEP) and post-operative pulmonary complications. However, in the LAS VEGAS and PROVEnet observational trials, there seemed to be evidence that increasing PEEP also increases postoperative pulmonary complications.
Professor Pelosi then discussed the relationship between airway pressure and postoperative pulmonary complications. Higher driving pressures increased postoperative pulmonary complications and length of hospital stay (PROVHILO Lancet 2014 Aug 9;384(9942):495-503 & Futier E. et al. N Engl J Med 2013;369:428-37). The addition of PEEP, which caused an elevation in peak airway pressures could worsen this. High tidal volumes leading to high airway pressures were more likely if actual body weight was used compared to ideal or predicted body weight and Professor Pelosi felt this was a very important factor in deciding the selection of tidal volumes for individual patients.
In conclusion, to this part of his lecture, he had demonstrated that postoperative pulmonary complications were more common in ‘at risk’ patients and associated mortality was consequently greater. Secondly intra-operative mechanical ventilation settings affect postoperative outcome and tidal volumes of approximately 7 mls/kg with a PEEP of less than 2 cmsH2O without recruitment manoeuvres should be used. However, if saturations fall the first step is to increase inspired oxygen followed by a PEEP of 5 cmsH2O. Thirdly PEEP of equal or higher than 5 cmsH2O could perhaps be used in surgery lasting longer than 3 hours, in laparoscopic surgery in the Trendelenburg position and in those patients with a BMI of greater than 35. Higher levels of PEEP may lead to hypotension with consequent fluid loading which may lead to overload and further pulmonary compromise.
Professor Pelosi then turned his attention to critical care. He looked at a paper by Gajic O, (Critical Care Medicine 2004; 32: 1817-1824) which looked at ventilator associated lung injury in patients without acute lung injury at the onset of mechanical ventilation. He demonstrated that with tidal volumes of less than 9 mls/kg, the incidence appeared to be half of that when tidal volumes of more than 12 mls/kg were used. This appeared to be confirmed by Serpa Neto (JAMA 2012; October 24: 308 16;1651-9). The authors interpreted the meta-analysis as demonstrating that anaesthetised patients who received ventilation with lower tidal volumes during surgery had a lower risk of lung injury. A review by the same author in Intensive Care Medicine (2014, 40 950-7), demonstrated that those patients without ARDS where low tidal volumes were used, were ventilated for a shorter period of time although this was not statistically significant. A further paper currently in publication by the same author demonstrates from meta-analysis a correlation between tidal volume and risk of pulmonary complication. He thought that the conclusion of current research was that tidal volumes of 6 mls/kg of predicted body weight should be used in all ventilated patients. Secondly, PEEP higher than 5 cmsH2O or recruitment manoeuvres to compensate for atelectasis may not be required in patients without ARDS.
Professor Pelosi concluded his talk by showing a summary soon to be published in Current Opinion in Critical Care showing current guidelines. In anaesthetised patients, tidal volumes of less than 8mls/kg of predicted body weight with PEEP with less than 2 cmsH2O should be the norm. In critical care patients with uninjured lungs, tidal volumes of 6 mls/kg of predicted body weight and PEEP, no higher than 5 cmsH2O, should be used. In critical care patients with mild ARDS, tidal volumes of 6-8 mls/kg with PEEP levels of between 5 cmsH2O should be used. In patients with moderate to severe ARDS the only change should be PEEP levels of greater than 5 cmsH2O.
There were some questions from the floor and the vote of thanks was given by the President, Dr Ewen Forrest.
Professor Hunter and Professor Nigel Webster representing the BJA presented Professor Pelosi with the T Cecil Gray BJA medal.
8th May 2015