ISSN: 2378-3516 Gilmore et al. Int J Respir Pulm Med 2019, 6:107 DOI: 10.23937/2378-3516/1410107 Volume 6 | Issue 1 International Journal of Open Access Respiratory and Pulmonary Medicine OrIgInal researCh artICle An Investigation of Various Inspiratory Times and Inflation Pressures during Airway Pressure Release Ventilation Tim W Gilmore1*, Robert E Walter1,2, Patrick C Hardigan3, Clifton F Frilot II1 and Guy M Nehrenz3 1Louisiana State University Health Sciences Center, Shreveport, USA 2University Health Shreveport, USA Check for 3Nova Southeastern University, USA updates *Corresponding author: Tim W Gilmore, PhD, RRT-ACCS, RRT-NPS, AE-C, Louisiana State University Health Sciences Center, 1450 Claiborne Avenue, Shreveport, Louisiana, USA Abstract Keywords An Evaluation of Various Inspiratory Times and Inflation Airway pressure release ventilation (APRV), Ventilator set- Pressures During Airway Pressure Release Ventilation. tings, Inspiratory time, Inflation pressures Introduction: There are few recommendations how best to apply certain modes of mechanical ventilation, and the An Evaluation of Various Inspiratory Times and Infla- application of Airway Pressure Release Ventilation (APRV) tion Pressures During Airway Pressure Release Ventila- requires strategic implementation of specific inspiratory tion (I-time) and expiratory times (E-time) and particular mean airway pressures (MAWP), neither of which is standardized. Introduction We sought to identify whether an ideal I-time or MAWP could be identified to favor more positive clinical outcomes. Temporary positive pressure ventilation (PPV) is a Methods: A retrospective analysis of archived electronic common, potentially life-saving, modality, but it poses health record data to evaluate the clinical outcomes of significant risks [1-3]. It has been established that PPV is adult patients that had been placed on APRV for a target anti-physiologic and contributes to morbidity and mor- of at least 8 hours. 68 adult subjects were evaluated from a convenient sample. tality under certain conditions [2], in part, to the devel- opment of ventilator-induced lung injury (VILI) [3,4]. Results: All outcomes of interest (surrogates) for short- Furthermore, there is a correlation between ventilation term clinical outcomes to include the PaO2/FiO2 (P/F) ratio, Oxygen Index (OI), Oxygen Saturation Index (OSI), and volume, airway pressure, and the development of VILI Modified Sequential Organ Failure Assessment (MSOFA) [5]. scores showed improvement after at least approximately 8 hours on APRV. Most notably, there was significant Contemporary animal studies have attempted to es- improvement in P/F ratio (p = 0.012) and OSI (p = 0.000). tablish a type of strain threshold at which lung damage Results of regression analysis showed MAWP as a occurs, but there is lacking evidence as to which enti- significant positive predictor of post-APRV OSI and P high ty primarily contributes to principal lung injury [6,7]. It as a significant positive predictor of post-APRV MSOFA score. may be the avoidance of atelectrauma, however, caused from cyclic opening and closing of the lung, that is most Conclusion: In summary, it was found that settings for P effective in VILI prevention [8]. Some studies suggest high, Plow, and T low in addition to overall MAWP and Body Mass Index (BMI) had significant correlation to impact at an open lung approach is ideal because it prevents at- least one of the short-term clinical outcomes measured with electrauma [8], and that the management of specific a lower setting for both P high and MAWP predictive of a mean airway pressures (MAWP) is more protective by better post-APRV OSI and MSOFA score. minimizing lung stretch compared to the traditional ap- Citation: Gilmore TW, Walter RE, Hardigan PC, Frilot CF, Nehrenz GM (2019) An Investigation of Various Inspiratory Times and Inflation Pressures during Airway Pressure Release Ventilation. Int J Respir Pulm Med 6:107. doi.org/10.23937/2378-3516/1410107 Accepted: May 14, 2019; Published: May 16, 2019 Copyright: © 2019 Gilmore TW, et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited Gilmore et al. Int J Respir Pulm Med 2019, 6:107 • Page 1 of 6 • DOI: 10.23937/2378-3516/1410107 ISSN: 2378-3516 proach of targeting conservative inspiratory volumes mendations for setting the four primary variables of: 1) [9,10]. Lung inflation pressure (P high); 2) Lung inflation time (T high); 3) Lung deflation pressure (P low) and 4) Lung Although there is no consensus regarding how best deflation time (T low). Habashi and Modrykamien, et to specifically apply pressure modes of PPV, Airway al. suggest target I-times of at least 4 seconds with a Pressure Release Ventilation (APRV), in particular, offers strategy of matching pre-APRV, conventional ventilator an alternative to conventional ventilation strategies. plateau pressure as a starting point for P high. Both pub- In several small-scale, observational studies, PPV with lished strategies suggest setting T low to target induce- APRV has been shown to improve overall oxygenation ment of auto positive end-expiratory pressure (PEEP) and allow a shorter intensive care unit stay with fewer with an initial P low setting of 0 cm H O [12,27]. To date, ventilator days [11]. Specifically, APRV allows for sus- 2 no single APRV recommendation is widely accepted in tained lung inflation over a more prolonged period than practice, and, over the last 30 years of APRV use, studies other pressure modes of PPV [11], resulting in less cyclic have rarely evaluated similar settings in order to assess opening and closing of lung units [6,11,12]. the efficacy of a single APRV strategy19 [ ]. APRV Methods Downs and Stock introduced APRV to the healthcare This study was completed in partial fulfillment of a market circa 1987 via a small animal study with results PhD program requirement at Nova Southeastern Uni- suggestive of APRV as a viable mode to treat ALI [13]. versity. After Institutional Review Board approval, a The following year, the same group conducted the first retrospective analysis of electronic health record (EHR) human trial of APRV with similar findings in that patients data was conducted to evaluate adult subjects who with ALI were able to be successfully ventilated at low- were placed in APRV (BiVent - Maquet; Rastatt, Germa- er peak airway pressures compared to traditional PPV ny; BiLevel - GE Healthcare; Chicago, Illinois). Data was [14]. After two landmark APRV studies were published transferred into SPSS® for statistical analyses. Subject [14,15], scores of variable studies have followed, even- pre-APRV dosing and post-APRV dosing P/F ratio, OI, tually establishing APRV as a means of protective lung OSI, and MSOFA scores were calculated to represent strategy as well as a recommended early treatment for validated predictors of clinical outcomes [28-32]. ALI or ARDS [12,16]. More recently, it has been suggest- ed that early implementation of APRV is ideal [17,18]. Subjects There remains, however, a lack of specific recommen- Adults receiving APRV for a minimum of approxi- dation on how best to apply this protective ventilation mately 8 hours continuously were included. Subject strategy [19]. that had been placed on APRV but found without docu- Under a majority of circumstances, pressure-target- mented settings for both I-time or ventilation pressures ed modes of PPV are preferred over volume-targeted were excluded. Any subject lacking the information nec- modes for lung protection [20]. And, although lower essary to calculate neither the P/F ratio, OI, OSI or MSO- tidal volume ventilation compared to conventional tidal FA score were excluded. ventilation is associated with better clinical outcomes [21,22], pressure-targeted ventilation is more protec- Specific procedures tive against VILI. Needhem, et al. compared the use of A data collection tool (DCT) form (see Appendix) volume-limited ventilation to the use of pressure-limit- was created and thereafter, an electronic database was ed ventilation in a large prospective cohort, noting that compiled utilizing File Maker Pro software. The database lung protective ventilation via pressure-limited modes was converted to an Excel spreadsheet and into SPSS®. was associated with a substantial long-term survival The pre-APRV and post-APRV P/F ratio, OI, OSI, and benefit in patients with ALI [23]. In 2016, the “LUNG MSOFA scores were manually calculated utilizing an “if, SAFE” study by Laffey, et al. concluded that both lower then” formula in Excel. All other applicable metrics were plateau and lower driving pressures are associated with analyzed via SPSS (See Table 1, Table 2 and Table 3). improved survival in ARDS [24]. Statistical analyses Current recommendations of APRV use Descriptive statistics were calculated with pertinent To date, studies comparing APRV to conventional clinical data reported as a conglomerate. All change PPV have yet to demonstrate any significant difference scores for clinical outcomes were calculated to identify in mortality outcomes [16,25,26]. Even though the ox- statically significant results. Correlation matrixes were ygenation benefit of APRV use has been well estab- created, and a bivariate analysis was performed for all lished [11], there remains an overall lack of consensus categorical variables. An additional correlational matrix concerning when to implement or how to manage this was created linking potential predictor variables to mode. Two of the more common published manage- change scores at pre-APRV and post-APRV dosing. A ment strategies of APRV simply include generic recom- bivariate analysis of categorical variables and change Gilmore et al. Int J Respir Pulm Med 2019, 6:107 • Page 2 of 6 • DOI: 10.23937/2378-3516/1410107 ISSN: 2378-3516 Table 1: Subject demographics. scores was also performed. Finally, a multiple regression (n = 68) analysis was conducted to identify significant predictors Age, yr, ( x ; min-max, SD) of P/F ratio, OI, OSI, and MSOFA scores.