- Email: [email protected]
Noninvasive mechanical ventilation during spontaneous breathing anaesthesia: Can electrical impedance tomography be a useful bedside tool to titrate PEEP level?
Journal of Clinical Anesthesia 39 (2017) 106–107
Contents lists available at ScienceDirect
Journal of Clinical Anesthesia
Correspondence Noninvasive mechanical ventilation during spontaneous breathing anaesthesia: Can electrical impedance tomography be a useful bedside tool to titrate PEEP level? Keywords: Noninvasive mechanical ventilation Spontaneous breathing general anaesthesia Electrical impedance tomography Positive end-expiratory pressure titration
Dear Editor: We read with great interest the study by Bordes et al. [1] recently published in the Journal of Clinical Anaesthesia. In this single-centre observational study the authors used electrical impedance tomography (EIT) to assess the effects of noninvasive mechanical ventilation (NIMV) on functional residual capacity (FRC) and ventilation distribution during spontaneous breathing general anaesthesia. A total of 18 patients undergoing gastrointestinal endoscopy (including gastric fibroscopy and colonoscopy) were studied. The authors found that following induction of anaesthesia, ventilation was shifted to non-dependent lung regions and end-expiratory lung impedancemetry was decreased. The findings also suggest that application of NIMV generates a significant increase in end-expiratory lung impedancemetry with no effect on ventilation distribution and a positive effect of NIMV on FRC during spontaneous breathing general anaesthesia. EIT is non-invasive and radiation-free, and allows dynamic imaging and analysis of ventilation at the bedside and in the operating room. EIT monitors display local air changes during ventilation in real time, and although EIT has previously been studied in patients undergoing general anaesthesia there is little data available regarding its use during NIMV [2]. In this aspect the current study is welcomed and we congratulate the authors on their efforts. However we raise several issues that we feel warrant further discussion. Firstly the level of PEEP applied during NIMV in the study warrants debate, as it is generally accepted that obese patients may require higher levels of PEEP [3]. Although the mean body mass index (BMI) of the patients included was 25.6 kg/m2 great variability was seen; thus an empirically applied 6 cm H2O of PEEP may have been insufficient in those patients whose BMI was greater than 25 kg/m2. It is unclear why the authors chose a PEEP of 6 cmH20 for all subjects as 8 patients had a BMI of less than 25 kg/m2, and the other 10 had a BMI of 25–36 kg/m2 and may therefore have been better suited to a higher PEEP. The authors also found that ventilation was shifted to non-dependent lung after induction which contradicts previously reported findings by Radke et al. that suggest spontaneous breathing general anaesthesia prevents the shift of ventilation toward non-dependent lung regions [4]. However it is of note that this study used laryngeal
http://dx.doi.org/10.1016/j.jclinane.2017.03.030 0952-8180/© 2017 Published by Elsevier Inc.
mask airways (LMA), which may help overcome the upper airway resistance encountered following induction of anaesthesia. These findings might also be related to the fixed PEEP level used in the current study, and it is possible that upwards titration of PEEP may overcome this shift to non-dependant areas. EIT has been demonstrated to be a useful tool in the detection of lung collapse and recruitment, both regionally and on a global basis, in a case report by Rosa et al. [5]. They used ETI in a patient with severe acute respiratory distress syndrome (ARDS) as a guide to titration of PEEP to achieve alveolar recruitment. Following recruitment manoeuvres, the authors calculated the optimal PEEP by using the ratios between PEEP, static compliance (Cst), alveolar collapse and overdistension indices. They then performed decremental PEEP titration in 2cmH2O steps and chose the PEEP associated with the highest Cst values and lowest alveolar collapse and overdistension values. Optimal PEEP level was determined as 16 cm H2O via thoracic EIT. The authors of the current study also found that application of NIMV had no effect on the distribution of tidal volume in the left lung. However patients were all in the left lateral decubitus position for the duration of EIT measurements. Tidal volume may influence the ventilation distribution and can be affected by pressure support and PEEP applied during NIMV. In this study, NIMV was applied via an anaesthesia ventilator in PSV mode (pressure support 8 cm H2O, PEEP 6 cm H20), which suggests that only 2 cm H20 ventilatory support was actually provided during NIMV. Finally the authors provide no information about the patients' static lung compliance measured via EIT during NIMV. A pilot study by Becher's et al. analysed the effects of a PEEP wave manoeuvre on global and regional determination of Crs in patients with spontaneous breathing using EIT [6]. Similar information, if provided by the current study, would have better contextualised the reported results. We feel that whilst the current study provides interesting and thought-provoking findings, further work is necessary to fully evaluate the utility of EIT in optimising PEEP levels in patients where NIMV is applied during spontaneous breathing general anaesthesia. Conflict of interest We declare that authors have no conflict of interest. References [1] Bordes J, Goutorbe P, Cungi PJ, Boghossian MC, Kaiser E. Noninvasive ventilation during spontaneous breathing anesthesia: an observational study using electrical impedance tomography. J Clin Anesth 2016 Nov;34:420–6. [2] Bikker IG, Leonhardt S, Reis Miranda D, Bakker J, Gommers D. Bedside measurement of changes in lung impedance to monitor alveolar ventilation in dependent and nondependent parts by electrical impedance tomography during a positive end-expiratory pressure trial in mechanically ventilated intensive care unit patients. Crit Care 2010;14(3):R100. [3] Gursel G, Aydogdu M, Gulbas G, Ozkaya S, Tasyurek S, Yildirim F. The influence of severe obesity on non-invasive ventilation (NIV) strategies and responses in patients with acute hypercapnic respiratory failure attacks in the ICU. Minerva Anestesiol 2011 Jan;77(1):17–25.
Correspondence [4] Radke OC, Schneider T, Heller AR, Koch T. Spontaneous breathing during general anesthesia prevents the ventral redistribution of ventilation as detected by electrical impedance tomography: a randomized trial. Anesthesiology 2012 Jun;116(6):1227–34. [5] Rosa RG, Rutzen W, Madeira L, Ascoli AM, Dexheimer Neto FL, Maccari JG, et al. Use of thoracic electrical impedance tomography as an auxiliary tool for alveolar recruitment maneuvers in acute respiratory distress syndrome: case report and brief literature review. Rev Bras Ter Intensiva 2015 Oct-Dec;27(4):406–11. [6] Becher Tobias H, Bui Simon, Zick Günther, Bläser Daniel, Schädler Dirk, Weiler Norbert, et al. Assessment of respiratory system compliance with electrical impedance tomography using a positive end-expiratory pressure wave maneuver during pressure support ventilation: a pilot clinical study. Crit Care 2014;18(6):679.
Fatma Yıldırım, MD Dışkapı Yıldırım Beyazıt Research and Education Hospital, Intensive Care Unit, Ankara, Turkey Corresponding author at: Dışkapı Yıldırım Beyazıt Research and Education Hospital, Department of Pulmonary and Critical Care Medicine, Besevler, 06500 Ankara, Turkey. E-mail address: [email protected].
107
Antonio M. Esquinas, MD, PhD, FCCP Intensive Care Unit, Hospital Morales Meseguer, Murcia, Spain Alastair J. Glossop, MRCP, FRCA, DICM, FFICM Department of Critical Care and Anaesthesia, Sheffield Teaching Hospitals NHS Foundation Trust, UK 28 February 2017 Available online xxxx
Contents lists available at ScienceDirect
Journal of Clinical Anesthesia
Correspondence Noninvasive mechanical ventilation during spontaneous breathing anaesthesia: Can electrical impedance tomography be a useful bedside tool to titrate PEEP level? Keywords: Noninvasive mechanical ventilation Spontaneous breathing general anaesthesia Electrical impedance tomography Positive end-expiratory pressure titration
Dear Editor: We read with great interest the study by Bordes et al. [1] recently published in the Journal of Clinical Anaesthesia. In this single-centre observational study the authors used electrical impedance tomography (EIT) to assess the effects of noninvasive mechanical ventilation (NIMV) on functional residual capacity (FRC) and ventilation distribution during spontaneous breathing general anaesthesia. A total of 18 patients undergoing gastrointestinal endoscopy (including gastric fibroscopy and colonoscopy) were studied. The authors found that following induction of anaesthesia, ventilation was shifted to non-dependent lung regions and end-expiratory lung impedancemetry was decreased. The findings also suggest that application of NIMV generates a significant increase in end-expiratory lung impedancemetry with no effect on ventilation distribution and a positive effect of NIMV on FRC during spontaneous breathing general anaesthesia. EIT is non-invasive and radiation-free, and allows dynamic imaging and analysis of ventilation at the bedside and in the operating room. EIT monitors display local air changes during ventilation in real time, and although EIT has previously been studied in patients undergoing general anaesthesia there is little data available regarding its use during NIMV [2]. In this aspect the current study is welcomed and we congratulate the authors on their efforts. However we raise several issues that we feel warrant further discussion. Firstly the level of PEEP applied during NIMV in the study warrants debate, as it is generally accepted that obese patients may require higher levels of PEEP [3]. Although the mean body mass index (BMI) of the patients included was 25.6 kg/m2 great variability was seen; thus an empirically applied 6 cm H2O of PEEP may have been insufficient in those patients whose BMI was greater than 25 kg/m2. It is unclear why the authors chose a PEEP of 6 cmH20 for all subjects as 8 patients had a BMI of less than 25 kg/m2, and the other 10 had a BMI of 25–36 kg/m2 and may therefore have been better suited to a higher PEEP. The authors also found that ventilation was shifted to non-dependent lung after induction which contradicts previously reported findings by Radke et al. that suggest spontaneous breathing general anaesthesia prevents the shift of ventilation toward non-dependent lung regions [4]. However it is of note that this study used laryngeal
http://dx.doi.org/10.1016/j.jclinane.2017.03.030 0952-8180/© 2017 Published by Elsevier Inc.
mask airways (LMA), which may help overcome the upper airway resistance encountered following induction of anaesthesia. These findings might also be related to the fixed PEEP level used in the current study, and it is possible that upwards titration of PEEP may overcome this shift to non-dependant areas. EIT has been demonstrated to be a useful tool in the detection of lung collapse and recruitment, both regionally and on a global basis, in a case report by Rosa et al. [5]. They used ETI in a patient with severe acute respiratory distress syndrome (ARDS) as a guide to titration of PEEP to achieve alveolar recruitment. Following recruitment manoeuvres, the authors calculated the optimal PEEP by using the ratios between PEEP, static compliance (Cst), alveolar collapse and overdistension indices. They then performed decremental PEEP titration in 2cmH2O steps and chose the PEEP associated with the highest Cst values and lowest alveolar collapse and overdistension values. Optimal PEEP level was determined as 16 cm H2O via thoracic EIT. The authors of the current study also found that application of NIMV had no effect on the distribution of tidal volume in the left lung. However patients were all in the left lateral decubitus position for the duration of EIT measurements. Tidal volume may influence the ventilation distribution and can be affected by pressure support and PEEP applied during NIMV. In this study, NIMV was applied via an anaesthesia ventilator in PSV mode (pressure support 8 cm H2O, PEEP 6 cm H20), which suggests that only 2 cm H20 ventilatory support was actually provided during NIMV. Finally the authors provide no information about the patients' static lung compliance measured via EIT during NIMV. A pilot study by Becher's et al. analysed the effects of a PEEP wave manoeuvre on global and regional determination of Crs in patients with spontaneous breathing using EIT [6]. Similar information, if provided by the current study, would have better contextualised the reported results. We feel that whilst the current study provides interesting and thought-provoking findings, further work is necessary to fully evaluate the utility of EIT in optimising PEEP levels in patients where NIMV is applied during spontaneous breathing general anaesthesia. Conflict of interest We declare that authors have no conflict of interest. References [1] Bordes J, Goutorbe P, Cungi PJ, Boghossian MC, Kaiser E. Noninvasive ventilation during spontaneous breathing anesthesia: an observational study using electrical impedance tomography. J Clin Anesth 2016 Nov;34:420–6. [2] Bikker IG, Leonhardt S, Reis Miranda D, Bakker J, Gommers D. Bedside measurement of changes in lung impedance to monitor alveolar ventilation in dependent and nondependent parts by electrical impedance tomography during a positive end-expiratory pressure trial in mechanically ventilated intensive care unit patients. Crit Care 2010;14(3):R100. [3] Gursel G, Aydogdu M, Gulbas G, Ozkaya S, Tasyurek S, Yildirim F. The influence of severe obesity on non-invasive ventilation (NIV) strategies and responses in patients with acute hypercapnic respiratory failure attacks in the ICU. Minerva Anestesiol 2011 Jan;77(1):17–25.
Correspondence [4] Radke OC, Schneider T, Heller AR, Koch T. Spontaneous breathing during general anesthesia prevents the ventral redistribution of ventilation as detected by electrical impedance tomography: a randomized trial. Anesthesiology 2012 Jun;116(6):1227–34. [5] Rosa RG, Rutzen W, Madeira L, Ascoli AM, Dexheimer Neto FL, Maccari JG, et al. Use of thoracic electrical impedance tomography as an auxiliary tool for alveolar recruitment maneuvers in acute respiratory distress syndrome: case report and brief literature review. Rev Bras Ter Intensiva 2015 Oct-Dec;27(4):406–11. [6] Becher Tobias H, Bui Simon, Zick Günther, Bläser Daniel, Schädler Dirk, Weiler Norbert, et al. Assessment of respiratory system compliance with electrical impedance tomography using a positive end-expiratory pressure wave maneuver during pressure support ventilation: a pilot clinical study. Crit Care 2014;18(6):679.
Fatma Yıldırım, MD Dışkapı Yıldırım Beyazıt Research and Education Hospital, Intensive Care Unit, Ankara, Turkey Corresponding author at: Dışkapı Yıldırım Beyazıt Research and Education Hospital, Department of Pulmonary and Critical Care Medicine, Besevler, 06500 Ankara, Turkey. E-mail address: [email protected].
107
Antonio M. Esquinas, MD, PhD, FCCP Intensive Care Unit, Hospital Morales Meseguer, Murcia, Spain Alastair J. Glossop, MRCP, FRCA, DICM, FFICM Department of Critical Care and Anaesthesia, Sheffield Teaching Hospitals NHS Foundation Trust, UK 28 February 2017 Available online xxxx