Abstract
BACKGROUND: Transpulmonary pressure (PL) is used to assess pulmonary mechanics and guide lung-protective mechanical ventilation (LPV). PL is recommended to individualize LPV settings for patients with high pleural pressures and hypoxemia. We aimed to determine whether PL-guided LPV settings, pulmonary mechanics, and oxygenation improve and differ from non-PL-guided LPV among obese patients after 24 h on mechanical ventilation. Secondary outcomes included classification of hypoxemia severity, count of ventilator-free days, ICU length of stay, and overall ICU mortality.
METHODS: This is a retrospective analysis of data. Ventilator settings, pulmonary mechanics, and oxygenation were recorded on the initial day of PL measurement and 24 h later. PL-guided LPV targeted inspiratory PL < 20 cm H2O and expiratory PL of 0–6 cm H2O. Comparisons were made to repeat measurements.
RESULTS: Twenty subjects (13 male) with median age of 49 y, body mass index 47.5 kg/m2, and SOFA score of 8 were included in our analysis. Fourteen subjects received care in a medical ICU. PL measurement occurred 16 h after initiating non-PL-guided LPV. PL-guided LPV resulted in higher median PEEP (14 vs 18 cm H2O, P = .009), expiratory PL (–3 vs 1 cm H2O, P = .02), respiratory system compliance (30.7 vs 44.6 mL/cm H2O, P = .001), and 
(156 vs 240 mm Hg, P = .002) at 24 h. PL-guided LPV resulted in lower 
(0.53 vs 0.33, P < .001) and lower PL driving pressure (10 vs 6 cm H2O, P = .001). Tidal volume (420 vs 435 mL, P = .64) and inspiratory PL (7 vs 7 cm H2O, P = .90) were similar. Subjects had a median of 7 ventilator-free days, and median ICU length of stay was 14 d. Three of 20 subjects died within 28 d after ICU admission.
CONCLUSIONS: PL-guided LPV resulted in higher PEEP, lower 
, improved pulmonary mechanics, and greater oxygenation when compared to non-PL-guided LPV settings in adult obese subjects.
- mechanical ventilation
- obesity
- respiratory mechanics
- esophageal pressure
- transpulmonary pressure
- respiratory support
- lung-protective ventilation
- PEEP
Introduction
The morbidly obese patient represents a unique challenge in mechanical ventilation. The prevalence of obesity in the ICU, as defined as a body mass index (BMI) ≥ 30 kg/m2, is increasing globally.1,2 An estimated one third of all ICU admissions meet criteria for obesity, and up to 7% meet criteria for morbid obesity (BMI ≥ 40 kg/m2).3-5 Optimal mechanical ventilation in these patients is difficult to monitor using traditional methods. The use of esophageal pressure manometry to obtain transpulmonary pressure (PL) measurements to optimize and individualize mechanical ventilator settings in patients with suspected high pleural pressures and refractory hypoxemia has been recommended6; however, esophageal pressure manometry is less commonly used internationally.7 PL manometry was incorporated into our lung-protective mechanical ventilation clinical practice guideline (see the supplementary materials at http://www.rcjournal.com) in 2018. We describe observations associated with a PL-guided lung-protective ventilation (LPV) strategy applied to morbidly obese patients on mechanical ventilation. Our primary objective was to determine whether non-PL-guided LPV ventilator settings, pulmonary mechanics, and oxygenation differ 24 h after applying PL-guided LPV. Secondary outcomes included ventilator-free days, ICU length of stay, and overall ICU mortality.
Quick Look
Current Knowledge
Obesity is a growing problem globally, and it is complicating lung-protective mechanical ventilation management because external pressure from the chest wall and abdomen are not accounted for when measuring airway pressure as a surrogate for alveolar stress. Esophageal pressure manometry has been proposed as an adjunct to assess transpulmonary pressures to guide lung-protective ventilation.
What This Paper Contributes to Our Knowledge
Transpulmonary pressure manometry can be used to customize and optimize lung-protective mechanical ventilation settings for morbidly obese patients. An 
/expiratory transpulmonary pressure combination table can be used to optimize PEEP settings and may improve pulmonary mechanics and oxygenation for this patient population. This approach resulted in higher PEEP, lower 
, improved pulmonary mechanics, and better oxygenation.
Methods
We conducted a retrospective analysis of quality improvement data collected at the University of Virginia Medical Center in Charlottesville, Virginia. Data were reviewed as part of an ongoing quality improvement project that monitors respiratory therapist adherence to our LPV guideline and associated clinical outcomes on a monthly basis. The University of Virginia Institutional Review Board for Health Sciences Research approved this project (IRB HSR #22249) with waiver of patient consent. Between April 2019 and July 2020, data were recorded in electronic medical records (Epic, Verona, Wisconsin) by a respiratory therapist assigned to care for each patient.
Patients
Adult patients ≥ 18 y old who met the following criteria were included in our analysis: BMI ≥ 30 kg/m2, admission to the medical ICU or surgical/trauma ICU, need for mechanical ventilation, and a respiratory therapy consult to obtain PL measurements by a licensed independent practitioner (eg, physician, nurse practitioner, or physician assistant). Patients who had one or more of the following characteristics prompted a PL measurement consult: obesity, ARDS that requires 
≥ 0.60 and/or set PEEP > 10 cm H2O, airway driving pressure > 15 cm H2O with plateau pressure ≥ 30 cm H2O despite tidal volume (VT) ≤ 6 mL/kg predicted body weight (PBW), and extrinsic pathology resulting in decreased chest wall-abdominal compliance to assess for optimal set PEEP and VT. Patients were excluded if they met any contraindication for esophagogastric tube insertion (see the supplementary materials at http://www.rcjournal.com). A total of 20 patients between April 2019 and July 2020 were found to be eligible for analysis.
Procedure and Measurements
Subjects who met the inclusion criteria had a 5-French esophageal balloon catheter (Cooper Surgical, Trumbull, Connecticut) placed by a registered respiratory therapist with specialty credentials in adult critical care. All subjects were supine with the head of the bed elevated to 30 degrees. The esophageal balloon catheter was inserted through the nose or mouth and positioned in the esophagus according to the esophageal catheter insertion procedure described by Talmor et al.8 The appropriate position of the esophageal catheter were confirmed by performing an expiratory airway occlusion maneuver with a simultaneous gentle chest compression. Changes in esophageal and airway pressures resulting from the occlusion maneuver were recorded. The esophageal catheter was considered to be in an appropriate position when the ratio between change in esophageal pressure and change in airway pressure equaled 0.8–1.2 during the occlusion maneuver.9 Visualization of cardiac artifact on esophageal pressure waveform was also used to qualitatively confirm appropriate catheter position.
All PL data were measured using one of 2 options. The preferred option was to use a 5-French balloon-tipped catheter (Cooper Surgical) in conjunction with a Hamilton G5 ventilator (Hamilton Medical, Reno, Nevada). The Hamilton G5 ventilator can display esophageal pressure and PL measurement graphics, in addition to respective numerical output on the ventilator’s display screen. The second option used a 5-French esophageal balloon-tipped catheter (Cooper Surgical) in conjunction with a bedside monitor and a disposable pressure transducer (Edwards Lifesciences, Irvine, California) configuration as described by the Cooper Surgical procedure guideline for catheter preparation.10
Mechanical ventilator settings, airway pressures, pulmonary mechanics, and oxygenation variables were recorded immediately before PL-guided LPV and 24 h after PL guided LPV. Berlin classification for mild hypoxemia (
< 300 mm Hg), moderate hypoxemia (
< 200 mm Hg), and severe hypoxemia (
< 100 mm Hg) was also recorded. Ventilator management was customized in consideration of PL and airway pressure measurement data. Mechanical ventilator settings were adjusted to target an inspiratory PL < 20 cm H2O and an expiratory PL target of 0–6 cm H2O. A 
/PL table (see the supplementary materials at http://www.rcjournal.com) was used to determine optimal expiratory PL in relationship to set 
.11 The use of sedation and neuromuscular blockade was at the discretion of the treating licensed independent practitioner.
Statistical Analysis
Data were collected from electronic medical records by study investigators (DDR and SA) and transferred to SPSS 25 (IBM, Armonk, New York) for storage and analysis. The Kolmogorov-Smirnov test was used to evaluate for normality of distribution for continuous variables. Continuous variables were described as median and interquartile range (IQR). Repeat measures for before PL and after PL measurements were compared using the Wilcoxon signed-rank test. Categorical variables were described as frequency count and percentage. The McNemar test was applied to evaluate for repeat measurement group difference after binning hypoxemia severity to compare no hypoxemia and mild hypoxemia classifications to moderate hypoxemia and severe hypoxemia classifications, respectively. The Friedman 2-way analysis of variance was applied to compare baseline 
to 
at 24 h, 48 h, 72 h, and 96 h, respectively. Alpha (2-tailed) ≤ .05 was considered significant. For the Friedman test, Bonferroni correction was applied for multiple comparisons, with an adjusted P (2-tailed) ≤ .01 being considered statistically significant.
Results
Subject characteristics are shown in Table 1. Our analysis consisted of 20 subjects (13 male) who were morbidly obese (Class 3) with a median BMI of 47.5 kg/m2 (IQR 37.4–55.7). Median Sequential Organ Failure Assessment (SOFA) score was 8 (IQR 6–11). Most subjects were cared for in our medical ICU (n = 14), and the median duration of mechanical ventilation before a respiratory therapy consult was received for a PL measurement was 16 h (IQR 8–21). The Hamilton G5 ventilator method for obtaining PL measurement was used with the majority of our subjects (15 of 20). Sixteen of 20 subjects had either moderate hypoxemia (n = 12) or severe hypoxemia (n = 4), and 12 of 20 subjects received a vasoactive drug at the time of baseline PL measurement.
Subject Characteristics
Ventilator Settings and Pulmonary Mechanics
PL manometry resulted in significant ventilator setting adjustments, improved pulmonary mechanics, and oxygenation (Table 2, Fig. 1). Set PEEP adjustment occurred in 19 of 20 subjects; 14 subjects had set PEEP increase, and 5 subjects had set PEEP decrease. Median set PEEP increased significantly from 14 cm H2O (IQR 14–20) to 18 cm H2O (IQR 16–23) (P = .009), and median 
decreased from 0.53 (IQR 0.40–0.81) to 0.33 (IQR 0.30–0.40) (P < .001). Median expiratory PL increased from –3 cm H2O (IQR –5 to 1) to 1 cm H2O (IQR –1 to 3) (P = .02) after PL-guided set PEEP adjustment. Median VT increased from 420 mL (IQR 365–454) to 435 mL (IQR 380–460), but the difference was not significant (P = .64). Median VT as mL/kg PBW (6.0 [IQR 5.6–6.0] vs 6.0 [IQR 6.0–7.0], P = .17) and median inspiratory PL (7 cm H2O [IQR 2–11] vs 7 cm H2O [IQR 5–9], P = .90) did not change significantly after PL-guided set PEEP or VT increase. Nine of 12 subjects receiving vasoactive drug prior to set PEEP increase remained on vasoactive drug, and 1 subject was started on vasoactive drugs after set PEEP increase (P = .53). No pneumothorax resulted from PL-guided set PEEP or VT increase.
Box plots of mechanical ventilator settings and pulmonary mechanics before and after PL-guided ventilator setting adjustment. P < .05 is considered significant. Black circle indicates outlier extending > 1.5 box lengths from the edge of box. PL = transpulmonary pressure; CRS = respiratory-system compliance.
Ventilator Settings, Airway Pressures, Pulmonary Mechanics, Oxygenation, and Events Before and After PL Measurements
Exploratory analysis of pulmonary mechanics and oxygenation response to PL-guided ventilator setting adjustment detected a significant median increase in respiratory system compliance of 30.7 mL/cm H2O (IQR 26.6–41.5) vs 44.6 mL/cm H2O (IQR 37.6–51.0) (P = .001), a median decrease in PL driving pressure of 10 cm H2O (IQR 7–12) vs 6 cm H2O (IQR 4–8) (P = .001), and a median increase in 
of 156 (IQR 97–190) vs 240 (IQR 207–266) (P = .002) (Fig. 2). A majority of our subjects demonstrated either moderate hypoxemia (n = 12) or severe hypoxemia (n = 4) before PL-guided ventilator setting adjustment, whereas after PL-guided ventilator setting adjustment none experienced severe hypoxemia, 7 subjects experienced moderate hypoxemia, and a greater number of subjects experienced either mild hypoxemia (n = 8) or no hypoxemia (n = 5). While a majority of subjects experienced less severe hypoxemia after PL-guided ventilator setting adjustment, the difference between before and after PL-guided ventilator setting adjustment was not statistically significant when comparing no hypoxemia and mild hypoxemia to moderate hypoxemia and severe hypoxemia classifications (P = .71) (Fig. 3). No significant difference was found in 
when comparing baseline 
(192 mm Hg [IQR 122–243]) and 24-h 
(310 mm Hg [IQR 245–330], P = .18), whereas a significant and sustained oxygenation difference was detected in the 48-h 
(300 mm Hg [IQR 245–376], P = .006), the 72-h 
(319 mm Hg [IQR 266–393], P < .001), and the 96-h 
(283 mm Hg [IQR 277–363], P < .001) after PL-guided LPV (Fig. 4).
and PL driving pressure response to PL-guided set PEEP adjustment. Change in 
(P = .002) and change in PL driving pressure (P = .001). P < .05 is considered significant. PL = transpulmonary pressure.
Distribution of hypoxemia severity before and after PL-guided mechanical ventilator setting adjustment. Hypoxemia severity classification: None = 
> 300 mm Hg; Mild = 
< 300 mm Hg; Moderate = 
< 200 mm Hg; Severe = 
< 100 mm Hg. Frequency count is at the top of the hypoxemia classification bars. PL = transpulmonary pressure.
trend after PL-guided mechanical ventilator setting adjustment Black circle indicates outlier extending > 1.5 box lengths, and asterisk indicates outlier extending > 3 box lengths from the edge of box. Adjusted P ≤ .01 is significant. *P = .18 (Baseline vs 24 h); †P = .006 (Baseline vs 48 h); ‡P = .001 (Baseline vs 72 h); §P < .001 (Baseline vs 96 h).
ICU Outcomes and Mortality
The median ICU length of stay was 14 d (IQR 10–25), and the median number of ventilator-free days was 7 d (IQR 6–10). All-cause ICU mortality was 15% (n = 3). Two subjects died after being transitioned to comfort care due to devastating neurologic injury, and 1 subject was withdrawn from mechanical ventilation due to multi-organ dysfunction.
Discussion
The primary findings of implementing PL-guided LPV in morbidly obese subjects was significant adjustments to mechanical ventilator settings that resulted in increased respiratory system compliance and oxygenation and decreased driving pressure when compared to a conventional non-PL-guided LPV ventilator management strategy.
Obesity is a global problem in health care, and up to one third of patients admitted to the ICU are obese.12 Taking care of obese patients in the ICU can be challenging. One of the main challenges is management of the ventilator to optimize the respiratory system. Obese patients exhibit altered pulmonary mechanics compared to non-obese patients. Obesity lends itself to normal chest-wall elastance and decreased lung elastance, but increased thoracoabdominal wall pressure caused by obesity increases end-expiratory esophageal pressure and decreases PL, promoting loss of lung volume and atelectasis.13-15 Despite the high prevalence of obesity and the changes in respiratory function observed in this population, very few studies have investigated how to optimize mechanical ventilation in the ICU.
In a recent editorial published in Respiratory Care, Diehl et al16 suggested that monitoring esophageal pressure to set optimal PEEP while aiming to achieve a positive end-expiratory PL could improve the prognosis of obese and severely obese patients with ARDS. However, optimal set PEEP for obese patients remains unclear. Pirrone et al17 reported that clinician-driven set PEEP (11.6 ± 2.9 cm H2O) was inadequate for morbidly obese subjects in the ICU. We know that higher set PEEP is needed to offset the pressure from the chest wall mass and abdominal pressure causing atelectasis.18 The PROBESE study noted no difference between set PEEP 4 cm H2O versus recruitment maneuvers and set PEEP 12 cm H2O during general anesthesia in obese subjects without ARDS.19 These studies bring to light the lack of customized mechanical ventilation management strategies in morbidly obese patients.
PL manometry has been studied since 1970, when Agostoni et al20,21 reported that tidal changes in esophageal pressure correlated with pleural pressures applied to the lung surface. This enables a valid estimate of PL based on the difference between alveolar and esophageal pressure. Since then, multiple studies have evaluated the use of PL manometry to guide ventilation management based on physiologic parameters in ARDS, but few have looked at its utility in the morbidly obese population.
Florio and colleagues22 published the first observational study looking at the impact of different mechanical ventilator strategies on Class 3 obese subjects with ARDS. Their lung rescue team incorporated PL manometry into their assessment for best-PEEP versus following a standard mechanical ventilation protocol approach that utilized the ARDSNet low PEEP/
combination table.23 The authors concluded that individualized titration of mechanical ventilation that utilized PL measurements to guide set PEEP was associated with decreased mortality when compared to the use of the ARDSNet low PEEP/
table.22
In our cohort, 19 of the 20 subjects required PEEP adjustment after initiating PL guided LPV. The median set PEEP was increased from 14 cm H2O to 18 cm H2O to a obtain a slightly positive expiratory PL. Fumagalli et al24 described PL during decremental PEEP titration among extremely obese subjects with mean BMI of 58.6 kg/m2 who received care in ICU. They reported that set PEEP of 21.7 ± 3.7 cm H2O resulted in the lowest elastance of the respiratory system and corresponded to a positive end-expiratory PL. This allowed for restoration of end-expiratory lung volume and improved oxygenation. Fumagalli et al24 also reported that, in extremely obese subjects, a negative PL predicted lung collapse and decruitment. In addition, Eichler et al25 observed that laparoscopic bariatric subjects in the operating room require high levels of set PEEP to maintain positive PL. set PEEP of 16.7 cm H2O before and 23.8 cm H2O during capnoperitoneum were necessary to achieve positive expiratory PL. These numbers were confirmed with electrical impedance tomography. Both studies align with our results indicating that morbidly obese patients need a higher level of set PEEP to establish and maintain a positive PL in order to optimize lung-protective mechanical ventilation.
Our findings are in agreement with those of Pirrone et al17 and Florio et al22 in that set PEEP for mechanically ventilated obese patients in the ICU appears to be underestimated both when it is empirically set and when providers use the ARDSNet low PEEP/
table to guide best set PEEP in this patient population. When extrapolating our prePL-guided LPV strategy to the ARDSNet high PEEP/
table,26 we would have been directed to increase PEEP from 14 cm H2O up to 16–20 cm H2O. Our PL-guided set PEEP was increased to 18 cm H2O, which falls within the ARDSNet high PEEP/
set PEEP range for our median 
of 0.53. It is plausible, had we referred to the ARDSNet high PEEP/
table to determine initial set PEEP at the onset of mechanical ventilation, that we may have achieved similar oxygenation and pulmonary mechanics results. However, median 
was decreased to 0.33 within 24 h after increasing set PEEP to 18 cm H2O; while expiratory PL remained slightly positive, the high PEEP/
table indicates that PEEP should be set at 12–14 cm H2O. We speculate that decreasing set PEEP as directed by the ARDSNet high PEEP/
table would have resulted in a negative expiratory PL and subsequent dorsal lung region atelectasis, worsening oxygenation, and increased risk for ventilator-induced lung injury due to atelectrauma.
As LPV has evolved, it is recognized that PEEP is used not only to recruit atelectactic lung tissue but also to stabilize dependent lung regions and guard against atelectrauma that may occur when dorsal pleural pressure exceeds alveolar pressure at end-exhalation, such as what may occur in obese patients. Future studies should seek to develop BMI-adjusted set PEEP/
combination tables that are distinguished by obesity classification categories and derived from PL or electrical impedance tomography measurements to determine if meaningful prognostic and other important clinical outcome differences result.
Higher driving pressure in patients with ARDS has been found to increase mortality.27 In obese patients with and without ARDS, this relationship has not been well studied. The respiratory physiology changes of obese patients differ from those of non-obese patients. The transthoracic pressure, which consists of the chest and abdomen, is higher in obese patients than in non-obese patients.28 A PL-driven LPV strategy resulted in a median decrease in driving pressure from 13 cm H2O to 10 cm H2O in our subjects. De Jong et al29 hypothesized that, in obese subjects with ARDS, driving pressure would not represent the real pressure applied to the lungs and would not be associated with mortality. They found that driving pressure at day 1 was not significantly different in survivors at day 90 (13.7 ± 4.5 cm H2O) when compared to nonsurvivors (13.2 ± 5.1 cm H2O. Our all-cause ICU mortality was 15%, but this consisted of obese subjects with and without refractory hypoxemia. More studies are needed to establish the relationship of driving pressure and mortality in obese patients without ARDS.
In the EPVent trial,8 the use of higher set PEEP based on PL improved 
and respiratory system compliance. Our findings were similar, with a significant increase in respiratory system compliance and 
and a decreased driving pressure with higher set PEEP. We also noted a shift from moderate and severe hypoxemia to mild or no hypoxemia. Baedorf Kassis et al30 also reported that set PEEP driven to target positive PL improved elastance and driving pressures.
Results from a multicenter study of subjects with ARDS indicated that VT > 6.5 mL/kg PBW at the onset of ARDS was associated with a greater risk of ICU mortality when compared to subsequent VT values.31 Our subjects had a median VT of 6 mL/kg PBW at the onset of mechanical ventilation, and median airway driving pressure was 13 cm H2O when measured just prior to baseline PL measurement. Inspiratory PL was 7 cm H2O before and after any VT increase. In a recent study by Kalra et al,32 53% of subjects characterized with Class 3 obesity (BMI > 40 kg/m2) received VT > 8 mL/kg PBW and had an airway driving pressure of 16 cm H2O on day 1 of mechanical ventilation; both of these values are associated directly with increased risk for alveolar stress and mortality. When comparing day 1 and day 2 of mechanical ventilation, the authors reported a VT decrease from > 8 mL/kg PBW (53%) to VT of 6–8 mL/kg PBW (49%). Median VT among our subjects did not change significantly when comparing VT values before PL guided LPV (6.0 mL/kg PBW [IQR 5.6–6.0]) with VT values after PL-guided LPV (6.0 mL/kg PBW [IQR 6.0–7.0], P = .17). Three of our subjects had a VT increase to > 8.0 mL/kg PBW to optimize ventilation. They had a plateau pressure > 30 cm H2O prior to increasing VT, and plateau pressure did not change significantly after VT and PEEP increase. However, PL driving pressure did decrease significantly from 10 cm H2O (IQR 7–12) to 6 cm H2O (IQR 4–8). Having PL driving pressure measurements available for these subjects allowed our clinicians to comfortably customize mechanical ventilator settings by increasing VT while objectively assessing for risk of alveolar stress when confronted with clinically important acute respiratory acidosis.
Direct and elastance ratio-based methods are used to obtain PL measurements, but these methods yield different results. When the esophageal catheter balloon is properly placed in the retrocardiac position, a reasonable estimate of plateau pressure in the chest can be obtained with either method. Yoshida et al33 conducted an animal and cadaver study that compared esophageal pressure at the mid-thoracic region and direct pleural pressure measured from sensors placed in the pleura space. The authors reported that the direct method reasonably estimated PL in the dependent lung region (ie, the region most prone to atelectasis), whereas the elastance ratio-based method estimated PL better in the nondependent lung region (ie, the region most at risk for overdistention). While the elastance ratio-based method may provide a more accurate estimate of PL in the nondependent lung compared to the direct method, there is controversy surrounding this method because of assumptions that must be made to obtain valid measurements. For example, one assumption is that plateau pressure and PL are equal at end-inspiration and end-expiration. However, extrathoracic pressure resulting from obesity increases plateau pressure, thus causing a negative PL, which challenges this assumption. These changes lead us to use the direct method described by Talmor et al8 to measure both inspiratory and expiratory PL.
There is a long-standing concern that higher airway pressures result in hemodynamic instability and negatively affect right-ventricular function. Twelve of our 20 subjects were on a vasoactive drug prior to PL-guided ventilator management. Nine subjects remained on vasoactive drugs after the study, and 1 subject was started on a vasoactive drug after set PEEP increase. We can also report that there were no pneumothorax events with significant ventilator setting adjustments. The ART trial34 reported an increased need for vasoactive drug administration and increased incidence of pneumothorax when comparing lung recruitment maneuver with set PEEP titration to low set PEEP groups. In contrast, Florio et al22 reported that lung rescue with lung recruitment and set PEEP titration resulted in a decrease in the need for vasoactive drugs. This was explained by the decrease in pulmonary vascular resistance and reduced right-ventricular workload when atelectatic lungs are recruited. The decrease in PL driving pressure after PL-guided set PEEP increase suggests lung tissue recruitment in our cohort of subjects. This may partially explain the decrease in vasoactive drug administration experienced by some of our patients after they received PL-guided LPV.
A multinational ARDS workgroup7 conducted a large observational study to better understand the impact of ARDS globally. Importantly, it was found that clinicians underrecognized ARDS when it was present. Our licensed independent practitioners requested a PL manometry consult within 16 h of initiating mechanical ventilation. When considering ARDS pathogenesis and its typical clinical presentation time of 24–48 h after exposure to a risk factor,35 we believe that clinicians caring for patients in our analysis recognized unresolving hypoxemia early and subsequently recommended PL manometry to optimize mechanical ventilator settings. Our data suggest that obese subjects who received PL-guided LPV experienced ventilator setting adjustment that may have mitigated progression of hypoxemia severity and risk of atelectrauma.
Limitations
This study has several limitations, the first being the study design. Quality improvement data analysis and not having a control group for comparison limits the generalization of our findings. It is possible that the use of a high PEEP/
table or electrical impedance tomography to guide LPV may yield similar findings. Second, our sample size was relatively small due to being a single-center retrospective analysis. Third, we used 2 methods to obtain PL measurements. However, the respiratory therapists who performed the PL measurements received procedure training and followed a standard of practice clinical practice guideline that includes validated methods for obtaining PL measurements using esophageal pressure manometry as described previously. Fourth, cardiac function and volume status evaluation with bedside echocardiography were not available for comparison of findings before and after PL-guided LPV ventilator setting adjustments. Fifth, it has been reported that obese patients with ARDS have a high prevalence of complete airway closure at end-expiration during passive ventilation, which lends itself to the possibility of overestimating set PEEP requirement when targeting a PEEP. A calculation to correct for this possibility has been proposed13; however, we did not adjust our measured expiratory PL measurements to correct for this possibility. While it is possible that an adjusted expiratory PL may have resulted in a lower set PEEP requirement, our set PEEP finding is similar to what other investigators have reported for this patient population.
Conclusions
The use of esophageal pressure manometry to determine PL measurements could potentially help clinicians optimize LPV ventilator settings, improve pulmonary mechanics, and improve oxygenation among morbidly obese patients. Future studies should compare the early use of PL-guided LPV to a control group treated with a strategy that consists of a high PEEP/
table or electrical impedance tomography to determine if there is a difference in LPV ventilator settings and important clinical outcomes for obese mechanically ventilated patients.
Footnotes
- Correspondence: Daniel D Rowley MSc RRT RRT-ACCS RRT-NPS RPFT FAARC, Pulmonary Diagnostics & Respiratory Therapy Services, University of Virginia Medical Center, Charlottesville, VA 22903. E-mail: ddr8a{at}virginia.edu
See the Related Editorial on Page 1224
Mr Rowley presented a version of this paper as an Editors’ Choice abstract at AARC Congress 2020 LIVE!, held virtually November 18, 2020.
Supplementary material related to this paper is available at http://www.rcjournal.com.
This work was supported in part by the Pulmonary Diagnostics & Respiratory Therapy Services Department at the University of Virginia Medical Center. Mr Rowley has disclosed relationships with Philips, Ikaria, and Draeger. Mr Lamb discloses a relationship with Fisher & Paykel.
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