Individualized ventilation for lung protection?

05.03.2020
Author: Caroline Brown, Reviewer: Jean-Michel Arnal, David Grooms

The application of general rules and guidelines for ventilator settings such as tidal volume may not be of benefit to every patient. A more individualized approach to treating the diseased lung may be safer for the lung and result in better outcomes. Today’s advanced technology supports this approach by allowing the clinician to set targets, then automatically adjusting ventilation settings according to each individual patient’s condition and lung characteristics.

Takeaway messages

  • An individualized approach to treating the diseased lung may be safer than general rules and guidelines regarding ventilator settings.
  • Advanced technology supports this approach by adjusting ventilation settings according to the individual patient’s condition and lung characteristics.
  • Together with the patient’s lung condition, certain mechanical ventilation variables, such as tidal volume, airway driving pressure and mechanical power, provide an indication of the risk of ventilator-induced lung injuries.
  • A recent study investigated the driving pressure and mechanical power delivered by a physiologic closed-loop ventilation mode, and showed that the settings selected by the ventilator result in driving pressure and mechanical power within a safe range.

Mechanically ventilated patients may suffer from various injuries to the lung, including strain, stress and atelectrauma. Risk factors for ventilation-induced lung injuries (VILI) are a combination of lung condition (size of the aerated lung and lung homogeneity) and mechanical ventilation variables. Those variables that affect the risk of VILI include tidal volume (VT), airway driving pressure (ΔP) and mechanical power (MP). Various studies have shown the benefits of lower tidal volumes (4–8 ml/kg ideal body weight (IBW)) in both ARDS and non-ARDS patients (1, 2, 3), however setting a recommended tidal volume according to IBW only may not always result in lung-protective ventilation (4).

In ARDS patients ventilated within this tidal volume range, ΔP is the variable associated most strongly with mortality (5). Driving pressure is the change in elastic pressure during tidal ventilation, i.e. the ratio between tidal volume and respiratory system compliance, and a measure of the strain applied to the lungs. It is calculated as the difference between plateau pressure and total PEEP, and can be measured quite easily at the bedside. Results have shown that ΔP of greater than 14 cmH2O may increase the risk of death in ARDS patients (6), and it has also been identified as a predictor of pulmonary complications in both brain-injured patients (7) and patients being mechanically ventilated for general anesthesia (8). Transpulmonary driving pressure (ΔPL) is the difference between transpulmonary pressure at end-inspiration and end-expiration, which can be calculated using esophageal pressure measurement and may provide a better assessment than airway driving pressure of the risk of VILI. Preliminary results show an association between survival in ARDS patients and ΔPL of lower than 8 cmH2O after 24 hours of mechanical ventilation (9).

Mechanical power is a composite of ventilator-related variables that contribute to VILI, namely VT, ΔP, inspiratory flow, respiratory rate (RR) and PEEP (10), and represents the energy load placed on the respiratory system by the ventilator. Transpulmonary MP (MPL) excludes the energy required to move chest wall and energy dissipated in lung parenchyma, and may thus also serve as a more accurate basis for assessing the risk of VILI. For any given MP, the risk of VILI depends on various factors (11) and it is difficult to interpret both MP and MPL because no safety threshold has been determined for patients. However, evidence has shown that MP of greater than 12J/min during the first day of ventilation may affect survival rates in ARDS patients (12), and increase the risk of secondary ARDS in patients admitted to the ICU without ARDS (13). ResuIts published in 2018 from an Individual Patient Data meta-analysis of 8,207 patients showed that high mechanical power was associated with higher in-hospital mortality in ICU patients receiving invasive ventilation for at least 48 hours, with a consistent increase in the risk of death with MP higher than 17.0 J/min (14).  MPL of greater than 12 J/min was associated with the occurrence of VILI in a study carried out on pigs ventilated with different combinations of VT and RR (15).

A strategy of lung-protective ventilation should thus be based on minimizing the total energy load by limiting VT, RR, ΔP and flow, and be applied in all patients, regardless of the lung condition. In ARDS patients, the strategy may also include recruitment maneuvers with PEEP titration, depending on the patient’s recruitability.

A recent publication presents results from an observational study on adult, passive patients, who met the criteria for a single lung condition (16). This group of 255 patients (98 normal lung, 28 COPD and 129 ARDS) was ventilated with the physiologic closed-loop ventilation mode, INTELLiVENT-ASV* (ASV 1.1) which "automatically controls ventilation and oxygenation settings to reach targets set by the user". 

The objective was to investigate the ΔP and MP delivered by INTELLiVENT-ASV, and assess whether they could be considered lung-protective. INTELLiVENT-ASV’s default target settings were used for each patient condition. PEEP was adjusted by INTELLiVENT-ASV within the range of 5–10 cmH2O. In moderate to severe ARDS patients, a recruitment maneuver was combined with a decremental PEEP trial and PEEP, then set manually. In a subgroup of 19 patients where the resulting PEEP was above 16 cmH2O, transpulmonary pressure was used as a reference, and ΔPL and MPL were computed.

The median ΔP was 8 (7–10), 10 (8–12), and 9 (8–11) cmH2O and the median MP was 9.1 (4.9–13.5), 11.8 (8.6–16.5) and 8.8 (5.6–13.8) J/min for normal-lung, COPD, and ARDS patients respectively. Therefore, for almost all patients and all patient conditions, ΔP was below the threshold of 14 cmH2O generally considered to represent the limit for safe ventilation (17). MP was considerably lower than 17 J/min for most patients, and also lower than values reported in the previous studies (10, 12, 13, 18). There was no statistically significant difference between MP depending on lung condition or ARDS severity. In the subgroup of moderate or severe ARDS patients managed with transpulmonary pressure, ΔPL was 6 (4–7) cmH2O and MPL 3.6 (3.1–4.4) J/min.

Results therefore show that the ΔP and MP delivered by INTELLiVENT-ASV (ASV1.1) in almost all patients were within a range considered to be safe for lung protection, regardless of their different respiratory mechanics. Furthermore, in the subgroup of patients with severe ARDS, the combination of INTELLiVENT-ASV and a recruitment strategy resulted in apparently safe values for ΔPL and MPL.

* Not available in all markets

References

  1. Brower RG, Matthay MA, Morris A, et al. (Acute Respiratory Distress Syndrome Network) Ventilation with Lower Tidal Volumes as Compared with Traditional Tidal Volumes for Acute Lung Injury and the Acute Respiratory Distress Syndrome N Engl J Med 2000; 342:1301-1308.
  2. Serpa Neto A, Hemmes SN, Barbas CS, et al. (PROVE Network Investigators). Protective versus Conventional Ventilation for Surgery: A Systematic Review and Individual Patient Data Meta-analysis. Anesthesiology. 2015 Jul;123(1):66-78.
  3. Serpa Neto A, Simonis FD, Barbas CS, et al.  (PROtective Ventilation Network Investigators) Lung-Protective Ventilation With Low Tidal Volumes and the Occurrence of Pulmonary Complications in Patients Without Acute Respiratory Distress Syndrome: A Systematic Review and Individual Patient Data Analysis. Crit Care Med. 2015 Oct;43(10):2155-63.
  4. Terragni PP, Rosboch G, Tealdi A, et al. Tidal hyperinflation during low tidal volume ventilation in acute respiratory distress syndrome. Am J Respir Crit Care Med. 2007 Jan 15;175(2):160-6.
  5. Amato MB, Meade MO, Slutsky AS, et al. Driving pressure and survival in the acute respiratory distress syndrome. N Engl J Med. 2015 Feb 19;372(8):747-55.
  6. Laffey JG, Bellani G, Pham T, et al. (LUNG SAFE Investigators and the ESICM Trials Group). Potentially modifiable factors contributing to outcome from acute respiratory distress syndrome: the LUNG SAFE study. Intensive Care Med. 2016 Dec;42(12):1865-1876.
  7. Tejerina E, Pelosi P, Muriel A, et al. (for VENTILA group). Association between ventilatory settings and development of acute respiratory distress syndrome in mechanically ventilated patients due to brain injury. J Crit Care. 2017 Apr;38:341-345.
  8. Neto AS, Hemmes SN, Barbas CS, et al. (PROVE Network Investigators). Association between driving pressure and development of postoperative pulmonary complications in patients undergoing mechanical ventilation for general anaesthesia: a meta-analysis of individual patient data. Lancet Respir Med. 2016 Apr;4(4):272-80.
  9. Baedorf Kassis E, Loring SH, Talmor D. Mortality and pulmonary mechanics in relation to respiratory system and transpulmonary driving pressures in ARDS. Intensive Care Med. 2016 Aug;42(8):1206-13.
  10. Gattinoni L, Tonetti T, Cressoni M, et al. Ventilator-related causes of lung injury: the mechanical power. Intensive Care Med. 2016;42(10); 1567-1575.
  11. Marini JJ. Dissipation of energy during the respiratory cycle: conditional importance of ergotrauma to structural lung damage. Curr Opin Crit Care. 2018;24(1):16-22.
  12. Guérin C. Papazian L, Reignier J, et al. Effect of driving pressure on mortality in ards patients during lung protective mechanical ventilation in two randomized controlled trials. Crit Care. 2016;20(1):384.
  13. Fuller BM, Page D, Stephens RJ, et al. Pulmonary mechanics and mortality in mechanically ventilated patients without acute respiratory distress syndrome: a cohort study. Shock . 2018;49(3):311-316.
  14. Serpa Neto A, Deliberato RO, Johnson AEW, et al. (PROVE Network Investigators). Mechanical power of ventilation is associated with mortality in critically ill patients: an analysis of patients in two observational cohorts. Intensive Care Med. 2018 Nov;44(11):1914-1922.
  15. Cressoni M, Gotti M, Chiuraizzi C, et al. Mechanical power and development of ventilator-induced lung injury. Anesthesiology. 2016;124(5):1100-1108.
  16. Arnal JM, Saoli M, Garnero A. Airway and transpulmonary driving pressures and mechanical powers selected by INTELLiVENT-ASV in passive, mechanically ventilated ICU patients. Heart Lung. 2019 Nov 14. pii: S0147-9563(19)30533-3. doi: 10.1016/j.hrtlng.2019.11.001. [Epub ahead of print]
  17. Laffey JG, Bellani G, Pham T, et al. (LUNG SAFE Investigators and the ESICM Trials Group). Potentially modifiable factors contributing to outcome from acute respiratory distress syndrome: the LUNG SAFE study. Intensive Care Med. 2016 Dec;42(12):1865-1876.
  18. Determann RM, Royakkers A, Wolthuis EK, et al. Ventilation with lower tidal volumes as compared with conventional tidal volumes for patients without acute lung injury: a preventive randomized controlled trial. Crit Care. 2010;14(1):R1.
closed loop ventilation, lung protection, lung protective, driving pressure, tidal volume, mechanical power, VILI, lung injury, INTELLiVENT, ASV
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Date of Printing: 25.05.2020
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