Effects of the Lower Airway Secretions on Airway Opening Pressures and Suction Pressures in Critically Ill COVID-19 Patients: A Computational Simulation

In patients with critically ill COVID-19 pneumonia, lower airways are filled with plenty of highly viscous exudates or mucus, leading to airway occlusion. The estimation of airway opening pressures and effective mucus clearance are therefore two issues that clinicians are most concerned about during mechanical ventilation. In this study we retrospectively analyzed respiratory data from 24 critically ill patients with COVID-19 who received invasive mechanical ventilation and recruitment maneuver at Jinyintan Hospital in Wuhan, China. Among 24 patients, the mean inspiratory plateau pressure was 52.4 ± 4.4 cmH₂O (mean ± [SD]). Particularly, the capnograms presented an upward slope during the expiratory plateau, indicting the existence of airway obstruction. A computational model of airway opening was subsequently introduced to investigate possible fluid dynamic mechanisms for the extraordinarily high inspiratory plateau pressures among these patients. Our simulation results showed that the predicted airway opening pressures could be as high as 40-50 cmH₂O and the suction pressure could exceed 20 kPa as the surface tension and viscosity of secretion simulants markedly increased, likely causing the closures of the distal airways. We concluded that, in some critically ill patients with COVID-19, limiting plateau pressure to 30 cmH₂O may not guarantee the opening of airways due to the presence of highly viscous lower airway secretions, not to mention spontaneous inspiratory efforts. Active airway humidification and effective expectorant drugs are therefore strongly recommended during airway management.

Lung Ultrasound and Respiratory Pathophysiology in Mechanically Ventilated COVID-19 Patients-an Observational Trial

The relationship between respiratory system mechanics, lung ultrasound (LUS) abnormalities, and mortality in mechanically ventilated patients with COVID-19-associated respiratory failure is unknown. We assessed the pattern of respiratory mechanics and LUS, their changes over time, and the differences between survivors and non-survivors. We additionally analyzed the relationship between LUS findings and the severity of gas exchange impairment and interleukin 6 (IL-6). This was a two-center retrospective, observational trial carried out in the intensive care units of the hospitals of Bolzano and Merano, Italy, from March 15 to April 20, 2020. We enrolled 41 consecutive patients. Seven patients (17%, 95% CI 8.5–31.3%) died. Mean compliance of the respiratory system on ICU admission was 41.6 (± 18.8) ml/mbar (42.5 (± 19.6) for survivors, 38.0 (± 16.3) for deceased, p = 0.605). Non-survivors had a significantly lower compliance over time, decreasing from day 14 after symptom onset, compared with survivors (p = 0.008). Mean LUS score on admission was 11.2 (± 3.7) and survivors had lower LUS scores on admission than non-survivors (10.5 (± 3.6), 13.9 (2.8), respectively, t test, p = 0.029). LUS score correlated with IL-6 concentrations (r = 0.52, p = 0.001) and arterial pCO₂ (r = 0.30, p = 0.033) and was inversely correlated with oxygenation (r = − 0.34, p = 0.001). No correlation was found between LUS and respiratory system compliance (r = − 0.02, p = 0.299). Non-survivors from COVID-19-associated respiratory failure had a significant decrease in compliance after day 14 of symptom onset. Compliance did not correlate with the degree of abnormalities found in LUS, but LUS score correlated with oxygenation, pCO₂, and IL-6.

Respiratory physiology of COVID-19-induced respiratory failure compared to ARDS of other etiologies

BACKGROUND

Whether respiratory physiology of COVID-19-induced respiratory failure is different from acute respiratory distress syndrome (ARDS) of other etiologies is unclear. We conducted a single-center study to describe respiratory mechanics and response to positive end-expiratory pressure (PEEP) in COVID-19 ARDS and to compare COVID-19 patients to matched-control subjects with ARDS from other causes.

METHODS

Thirty consecutive COVID-19 patients admitted to an intensive care unit in Rome, Italy, and fulfilling moderate-to-severe ARDS criteria were enrolled within 24 h from endotracheal intubation. Gas exchange, respiratory mechanics, and ventilatory ratio were measured at PEEP of 15 and 5 cmH2O. A single-breath derecruitment maneuver was performed to assess recruitability. After 1:1 matching based on PaO2/FiO2, FiO2, PEEP, and tidal volume, COVID-19 patients were compared to subjects affected by ARDS of other etiologies who underwent the same procedures in a previous study.

RESULTS

Thirty COVID-19 patients were successfully matched with 30 ARDS from other etiologies. At low PEEP, median [25th-75th percentiles] PaO2/FiO2 in the two groups was 119 mmHg [101-142] and 116 mmHg [87-154]. Average compliance (41 ml/cmH2O [32-52] vs. 36 ml/cmH2O [27-42], p = 0.045) and ventilatory ratio (2.1 [1.7-2.3] vs. 1.6 [1.4-2.1], p = 0.032) were slightly higher in COVID-19 patients. Inter-individual variability (ratio of standard deviation to mean) of compliance was 36% in COVID-19 patients and 31% in other ARDS. In COVID-19 patients, PaO2/FiO2 was linearly correlated with respiratory system compliance (r = 0.52 p = 0.003). High PEEP improved PaO2/FiO2 in both cohorts, but more remarkably in COVID-19 patients (p = 0.005). Recruitability was not different between cohorts (p = 0.39) and was highly inter-individually variable (72% in COVID-19 patients and 64% in ARDS from other causes). In COVID-19 patients, recruitability was independent from oxygenation and respiratory mechanics changes due to PEEP.

CONCLUSIONS

Early after establishment of mechanical ventilation, COVID-19 patients follow ARDS physiology, with compliance reduction related to the degree of hypoxemia, and inter-individually variable respiratory mechanics and recruitability. Physiological differences between ARDS from COVID-19 and other causes appear small.

Pattern of respiratory muscle activity during exercise tests in children born prematurely

INTRODUCTION

Preterm children display only slightly lower exercise capacity than term children do during their development, despite their previous cardiopulmonary impairments. This raises doubts about the role of the respiratory muscles' influence on exercise capacity. This study aimed to compare respiratory muscle activity in preterm and term children using an exercise test.

METHODS

This cross-sectional study involved comparison of 35 term children and 39 matched preterm children aged 6-9 years, who were born prematurely with a birth weight <1500 g. An adapted treadmill incremental test was utilized and surface electromyography of the sternocleidomastoid (SCM), upper trapezius (UT), and rectus abdominis (RA) muscles was performed. The root mean square was calculated every minute and compared between and within groups. A Monte Carlo simulation was also applied, and the area under the curve was calculated to evaluate the differences between groups.

RESULTS

During the entire exercise, the SCM muscle activity was higher in preterm children with a larger area under the curve than in the term children. There was no difference in the RA and UT muscle activity between groups throughout the test.

CONCLUSION

The results suggest a greater contribution of the SCM muscle sin preterm children's performance than in term children's performance during high-intensity exercises.

TRIAL REGISTRATION

Brazilian Clinical Trial Registry (ReBec) - RBR-89hr2h.

[Clinical effect of nebulized acetylcysteine inhalation combined with bronchoscopy in the treatment of elderly patients with severe ventilator-associated pneumonia]

Objective: To explore the clinical effect of nebulized acetylcysteine inhalation combined with bronchoscopy in treating elderly patients with severe ventilator-associated pneumonia (VAP). Methods: From January 2016 to December 2017, 80 elderly patients with severe VAP who were hospitalized in Zhejiang Hospital were divided into acetylcysteine+ bronchoscopy group [24 males and 16 females, aged (78±7) years] and bronchoscopy group [26 males and 14 females, aged (80±7) years]using random number table for a prospective cohort study. Patients in bronchoscopy group were treated with bronchoscopy in addition to conventional supportive care of symptoms. Patients in acetylcysteine+ bronchoscopy group received nebulized acetylcysteine inhalation therapy on the basis of the treatment given to patients in bronchoscopy group. Patients in both groups received treatment continuously for 7 days. The simplified clinical pulmonary infection score (CPIS) in both groups was assessed before and after treatment. Venous blood of 10 mL was collected before and after treatment to detect leukocyte count, serum C-reactive protein, and procalcitonin. Arterial blood of 1 mL was collected before and after treatment to detect partial arterial oxygen pressure (PaO(2)), partial arterial carbon dioxide pressure (PaCO(2)), oxygenation index. The inhalation platform pressure (Pplat), dynamic lung compliance (Cdyn), airway resistance, work of breathing, time of antibiotic use, and time of mechanical ventilation of patients in two groups were recorded before and after treatment. Data were statistically analyzed with chi-square test and t test. Results: (1) The simplified CPIS, leukocyte count, serum C-reactive protein, and procalcitonin of patients in acetylcysteine+ bronchoscopy group were significantly lower than those in bronchoscopy group after treatment (t=2.32, 2.15, 6.08, 7.12, P<0.05 or P<0.01). The simplified CPIS, leukocyte count, serum C-reactive protein, and procalcitonin of patients in acetylcysteine+ bronchoscopy group and bronchoscopy group after treatment were significantly lower than those before treatment (t=13.76, 13.60, 12.70, 8.32, 11.44, 14.28, 9.48, 9.50, P<0.01). (2) Compared with bronchoscopy group, patients in acetylcysteine+ bronchoscopy group had significantly higher PaO(2) and oxygenation index (t=4.14, 2.55, P<0.05 or P<0.01) but significantly lower PaCO(2) (t=4.36, P<0.01) after treatment. The PaO(2) and oxygenation index of patients in acetylcysteine+ bronchoscopy group after treatment were significantly higher than those before treatment (t=10.90, 43.72, P<0.01). The PaO(2) and oxygenation index of patients in bronchoscopy group after treatment were also significantly higher than those before treatment (t=6.55, 43.03, P<0.01). The PaCO(2) of patients in both groups after treatment were significantly lower than those before treatment (t=21.54, 21.92, P<0.01). (3) The Cdyn of patients in acetylcysteine+ bronchoscopy group after treatment was significantly higher than that in bronchoscopy group (t=5.41, P<0.01), and Pplat, airway resistance, and work of breathing were significantly lower than those in bronchoscopy group (t=2.18, 5.46, 2.49, P<0.05 or P<0.01). The Cdyn of patients in both groups after treatment were significantly higher than those before treatment (t=16.10, 10.90, P<0.01), and Pplat, airway resistance, and work of breathing were significantly lower than those before treatment (t=21.18, 11.13, 9.32, 15.50, 5.17, 5.97, P<0.01). (4)The time of mechanical ventilation and antibiotic usage of patients in acetylcysteine+ bronchoscopy group were (6.9±1.9)and (8.7±2.8) d, respectively, which were significantly shorter than (10.1±2.2) and (11.6±3.5) d in bronchoscopy group (t=6.85, 4.09, P<0.01). Conclusions: Nebulized acetylcysteine inhalation combined with bronchoscopy can significantly control the degree of lung infection in elderly patients with severe VAP, improve patients' respiratory mechanics parameter and blood gas analysis indicator, and shorten the time for mechanical ventilation and antibiotic usage.

On some factors determining the pressure drop across tracheal tubes during high-frequency percussive ventilation: a flow-independent model

To provide an in vitro estimation of the pressure drop across tracheal tubes (ΔP_TT) in the face of given pulsatile frequencies and peak pressures (P_work) delivered by a high-frequency percussive ventilator (HFPV) applied to a lung model. Tracheal tubes (TT) 6.5, 7.5 and 8.0 were connected to a test lung simulating the respiratory system resistive (R = 5, 20, 50 cmH₂O/L/s) and elastic (C = 10, 20, and 50 mL/cmH₂O) loads. The model was ventilated by HFPV with a pulse inspiratory peak pressure (work pressure P_work) augmented in 5-cmH₂O steps from 20 to 45 cmH₂O, yielding 6 diverse airflows. The percussive frequency (f) was set to 300, 500 and 700 cycles/min, respectively. Pressure (Paw and Ptr) and flow (V’) measurements were performed for all 162 possible combinations of loads, frequencies, and work pressures for each TT size, thus yielding 486 determinations. For each respiratory cycle ΔP_TT was calculated by subtracting each peak Ptr from its corresponding peak Paw. A non-linear model was constructed to assess the relationships between single parameters. Performance of the produced model was measured in terms of root mean square error (RMSE) and the coefficient of determination (r²). ΔP_TT was predicted by P_work (exponential Gaussian relationship), resistance (quadratic and linear terms), frequency (quadratic and linear terms) and tube diameter (linear term), but not by compliance. RMSE of the model on the testing dataset was 1.17 cmH₂O, r² was 0.79 and estimation error was lower than 1 cmH₂O in 68% of cases. As a result, even without a flow value, the physician would be able to evaluate ΔP_TT pressure. If the present results of our bench study could be clinically confirmed, the use of a nonconventional ventilatory strategy as HFPV, would be safer and easier.

Effects of Controlled Voluntary Increase in the Ventilatory Demand on Respiratory System Resistance in Healthy and Non-Cystic Fibrosis Bronchiectasis Subjects: A Cross-Sectional Study

INTRODUCTION

Bronchiectasis patients may present a reduced functional capacity due to an increase in the ventilatory demand during exercise.

OBJECTIVE

To evaluate the effects of controlled voluntary hyperinflation and increased respiratory rate on the mechanics of the respiratory system, simulating what happens during exercise, in bronchiectasis and healthy subjects.

METHODS

Bronchiectasis (n=30) and healthy (n=16) subjects were evaluated by impulse oscillometry (IOS) during a baseline condition, and in controlled conditions with baseline (b) tidal volume (V) and hyperinflation (H), with respiratory rates at 30(R30) and 40(R40) bpm, in a random order. The mixed effects and a significance level at 0.05 were used for comparisons.

RESULTS

Resistance at 5Hz (R5), and at minus 20Hz (R5-R20), in kPa/L/s, were higher in subjects with bronchiectasis in all experimental conditions (p<0.05). For the bronchiectasis group, R5 and R5-20 increased with R increase at V (VRb versus VR30 and VR40; VR30 versus VR40; R5, R20 and R5-20 increased with R increase at H (HRb versus HR40; HR30 versus HR40). For the same R, there was a decrease with H compared to V (HRb versus VR30 and VR40; and HR30 versus VR30 and VR40). For the healthy group, only R20 showed differences (HR30 versus HR40; HR40 versus VR40).

CONCLUSION

The tachypnea increases the resistance and reactance of the respiratory system in bronchiectasis patients, and the voluntary hyperinflation caused attenuates this increase. These results can guide the development of strategies to reduce the limitation of physical activity in patients with bronchiectasis.

Association of Breathing Reserve at Peak Exercise With Body Composition and Physical Function in Older Adults With Obesity

BACKGROUND

Adiposity-related ventilatory constraints in older adults can potentially contribute to greater risk of exercise intolerance and mobility disability. This study investigated whether ventilatory limitation, measured by breathing reserve (BR) at peak exercise, is associated with body composition and physical function in older adults with obesity.

METHODS

This study was a cross-sectional analysis of data from a community-based cohort (N = 177) of older men and women (65-79 years) with obesity (body mass index = 30-45 kg/m2). All participants underwent cardiopulmonary exercise testing on a treadmill, dual-energy X-ray absorptiometry for body composition, and physical function assessments. We examined relationships between BR and body composition and physical function using multiple linear regression and compared a subset with (BR ≤ 30%; BR-low; n = 56) and without (BR ≥ 45%; BR-high, n = 48) ventilatory limitation using unpaired Student's t test and analysis of covariance.

RESULTS

BR was inversely related to total body mass, lean mass, fat mass, % body fat, and waist circumference (p < 0.05 for all). BR was positively related to 400 m walk time (p = .006) and inversely related to usual gait speed (p = .05) and VO2peak (p < .0001), indicative of worse physical function. BR-low had greater adiposity, but also greater lean mass, higher VO2peak, and faster 400 m walk time, compared to BR-high (p < .05, for all).

CONCLUSIONS

Older adults with obesity who also have ventilatory limitation have overall higher measures of adiposity, but do not have lower peak exercise capacity or physical function. Thus, ventilatory limitation does not appear to be a contributing factor to obesity-related decrements in exercise tolerance or mobility.

Recruitability and effect of PEEP in SARS-Cov-2-associated acute respiratory distress syndrome

Background

A large proportion of patients with a SARS-Cov-2-associated respiratory failure develop an acute respiratory distress syndrome (ARDS). It has been recently suggested that SARS-Cov-2-associated ARDS may differ from usual non-SARS-Cov-2-associated ARDS by higher respiratory system compliance (C_RS), lower potential for recruitment with positive end-expiratory pressure (PEEP) contrasting with severe shunt fraction. The purpose of the study was to systematically assess respiratory mechanics and recruitability in SARS-Cov-2-associated ARDS.

Methods

Gas exchanges, C_RS and hemodynamics were assessed at 2 levels of PEEP (15 cmH₂O and 5 cmH₂O) within 36 h (day1) and from 4 to 6 days (day 5) after intubation. The recruited volume was computed as the difference between the volume expired from PEEP 15 to 5 cmH₂O and the volume predicted by compliance at PEEP 5 cmH₂O (or above airway opening pressure). The recruitment-to-inflation (R/I) ratio (i.e. the ratio between the recruited lung compliance and C_RS at PEEP 5 cmH₂O) was used to assess lung recruitability. A R/I ratio value higher than or equal to 0.5 was used to define highly recruitable patients.

Results

The R/I ratio was calculated in 25 of the 26 enrolled patients at day 1 and in 15 patients at day 5. At day 1, 16 (64%) were considered as highly recruitable (R/I ratio median [interquartile range] 0.7 [0.55–0.94]) and 9 (36%) were considered as poorly recruitable (R/I ratio 0.41 [0.31–0.48]). The PaO₂/FiO₂ ratio at PEEP 15 cmH₂O was higher compared to PEEP 5 cmH₂O only in highly recruitable patients (173 [139–236] vs 135 [89–167] mmHg; p < 0.01). Neither PaO₂/FiO₂ or C_RS measured at PEEP 15 cmH₂O or at PEEP 5 cmH₂O nor changes in PaO₂/FiO₂ or C_RS in response to PEEP changes allowed to identify highly or poorly recruitable patients.

Conclusion

In this series of 25 patients with SARS-Cov-2 associated ARDS, 64% were considered as highly recruitable and only 36% as poorly recruitable based on the R/I ratio performed on the day of intubation. This observation suggests that a systematic R/I ratio assessment may help to guide initial PEEP titration to limit harmful effect of unnecessary high PEEP in the context of Covid-19 crisis.

Effects of intraoperative positive end-expiratory pressure optimization on respiratory mechanics and the inflammatory response: a randomized controlled trial

Applying lung protective mechanical ventilation (LPV) during general anaesthesia even in patients with non-injured lungs is recommended. However, the effects of an individual PEEP-optimisation on respiratory mechanics, oxygenation and their potential correlation with the inflammatory response and postoperative complications have not been evaluated have not been compared to standard LPV in patients undergoing major abdominal surgery. Thirty-nine patients undergoing open radical cystectomy were enrolled in this study. In the study group (SG) optimal PEEP was determined by a decremental titration procedure and defined as the PEEP value resulting the highest static pulmonary compliance. In the control group (CG) PEEP was set to 6 cmH2O. Primary endpoints were intraoperative respiratory mechanics and gas exchange parameters. Secondary outcomes were perioperative procalcitonin kinetics and postoperative pulmonary complications. Optimal PEEP levels (median = 10, range: 8–14 cmH2O), PaO2/FiO2 (451.24 ± 121.78 mmHg vs. 404.15 ± 115.87 mmHg, P = 0.005) and static pulmonary compliance (52.54 ± 13.59 ml cmH2O-1 vs. 45.22 ± 9.13 ml cmH2O-1, P < 0.0001) were significantly higher, while driving pressure (8.26 ± 1.74 cmH2O vs. 9.73 ± 4.02 cmH2O, P < 0.0001) was significantly lower in the SG as compared to the CG. No significant intergroup differences were found in procalcitonin kinetics (P = 0.076). Composite outcome results indicated a non-significant reduction of postoperative complications in the SG. Intraoperative PEEP-optimization resulted in significant improvement in gas exchange and pulmonary mechanics as compared to standard LPV. Whether these have any effect on short and long term outcomes require further investigations. Trial registration: Clinicaltrials.gov, identifier: NCT02931409.

Effects of fixed oil of Caryocar coriaceum Wittm. Seeds on the respiratory system of rats in a short-term secondhand-smoke exposure model

ETHNOPHARMACOLOGICAL RELEVANCE

Pequi fruit are obtained from the pequi tree (Caryocar coriaceum), from which the pulp and nut are used in order to extract an oil that is commonly used in popular medicine as an antiinflammatory agent, particularly for the treatment of colds, bronchitis and bronchopulmonary infections. Making use of the fixed oil of Caryocar coriaceum (FOCC), an attractive alternative for the treatment of diseases caused by exposure to environmental tobacco smoke.

AIM OF THE STUDY

To evaluate whether oral intake FOCC provides beneficial effects in the respiratory system of rats submitted to a short-term secondhand smoke (SHS) exposure model.

MATERIALS AND METHODS

The experiments were performed on Wistar rats divided into 4 groups; in the SHS + O and SHS + T groups, the animals were pretreated orally with 0.5 mL of FOCC (SHS + O) or vehicle (Tween-80 [1%] solution) (SHS + T). Immediately after pretreatment, the animals were submitted to the SHS exposure protocol, for a total period of 14 days. Exposures were performed 6 times per day, with a duration of 40 min per exposure (5 cigarettes per exposure), followed by a 1-h interval between subsequent exposures. In the AA + O and AA + T groups, animals were submitted to daily oral pretreatment with 0.5 mL of FOCC (AA + O) or vehicle (AA + T). These animals were then subjected to the aforementioned exposure protocol, but using ambient air. After the exposure period, we investigated the effects of FOCC in respiratory mechanics in vivo (Newtonian resistance -R_N, tissue elastance -H, tissue resistance -G, static compliance -C_ST, inspiratory capacity -IC, PV loop area) histopathology and lung parenchymal morphometry in vitro (polymorphonuclear cells -PMN, mean alveolar diameter -L_m, bronchoconstriction index -BCI), temporal evolution of subjects' masses, and percent composition of the FOCC.

RESULTS

Regarding the body mass of the animals, the results demonstrated an average body mass gain of 10.5 g for the animals in the AA + T group, and 15.5 g for those in the AA + O group. On the other hand, the body mass of animals in the SHS + T and SHS + O suffered an average loss of 14.4 and 4.75 g, respectively. Regarding respiratory system analyzes, our results demonstrated significant changes in all respiratory mechanics variables and lung parenchyma morphometry analyzed for the SHS + T group when compared to the AA + T group (p < 0,05), confirming the establishment of pulmonary injury induced by SHS exposure. We also observed that rats pretreated orally with FOCC (SHS + O) showed improvement in all variables when compared to the SHS + T group (p < 0,05), thus demonstrating the effectiveness of FOCC in preventing lung damage induced by short-term SHS exposure.

CONCLUSION

In conclusion, our results demonstrate that FOCC was able to prevent lung injury in rats submitted to short-term SHS exposure.

Lung volume dependence of respiratory function in rodent models of diabetes mellitus

Background

Diabetes mellitus causes the deterioration of smooth muscle cells and interstitial matrix proteins, including collagen. Collagen and smooth muscle cells are abundant in the lungs, but the effect of diabetes on airway function and viscoelastic respiratory tissue mechanics has not been characterized. This study investigated the impact of diabetes on respiratory function, bronchial responsiveness, and gas exchange parameters.

Methods

Rats were allocated randomly to three groups: a model of type 1 diabetes that received a high dose of streptozotocin (DM1, n = 13); a model of type 2 diabetes that received a low dose of streptozotocin with a high-fat diet (DM2, n = 14); and a control group with no treatment (C, n = 14). Forced oscillations were applied to assess airway resistance (Raw), respiratory tissue damping (G), and elastance (H). The arterial partial pressure of oxygen to the inspired oxygen fraction (PaO₂/FiO₂) and intrapulmonary shunt fraction (Qs/Qt) were determined from blood gas samples at positive end-expiratory pressures (PEEPs) of 0, 3, and 6 cmH₂O. Lung responsiveness to methacholine was also assessed. Collagen fibers in lung tissue were quantified by histology.

Results

The rats in groups DM1 and DM2 exhibited elevated Raw, G, H, and Qs/Qt, compromised PaO₂/FiO₂, and diminished airway responsiveness. The severity of adverse tissue mechanical change correlated with excessive lung collagen expression. Increased PEEP normalized the respiratory mechanics, but the gas exchange abnormalities remained.

Conclusions

These findings indicate that diabetes reduces airway and lung tissue viscoelasticity, resulting in alveolar collapsibility that can be compensated by increasing PEEP. Diabetes also induces persistent alveolo-capillary dysfunction and abnormal adaptation ability of the airways to exogenous constrictor stimuli.

[Impact of Grade I obesity on respiratory mechanics during video laparoscopic surgery: prospective longitudinal study]

INTRODUCTION AND OBJECTIVES

The association pneumoperitoneum and obesity in video laparoscopy can contribute to pulmonary complications, but has not been well defined in specific groups of obese individuals. We assessed the effects of pneumoperitoneum in respiratory mechanics in Grade I obese compared to non-obese.

METHODS

Prospective study including 20 patients submitted to video laparoscopic cholecystectomy, normal spirometry, divided into non-obese (BMI ≤ 25kg.m^-2) and obese (BMI > 30kg.mg^-2), excluding Grade II and III obese. We measured pulmonary ventilation mechanics data before pneumoperitoneum (baseline), and five, fifteen and thirty minutes after peritoneal insufflation, and fifteen minutes after disinflation (final).

RESULTS

Mean BMI of non-obese was 22.72 ± 1.43kg.m^-2 and of the obese 31.78 ± 1.09kg.m^-2, p < 0.01. Duration of anesthesia and of peritoneal insufflation was similar between groups. Baseline pulmonary compliance (Crs) of the obese (38.3 ± 8.3mL.cm H₂O^-1) was lower than of the non-obese (47.4 ± 5.7mL.cm H₂O^-1), p = 0.01. After insufflation, Crs decreased in both groups and remained even lower in the obese at all moments assessed (GLM p < 0.01). Respiratory system peak pressure and plateau pressure were higher in the obese, albeit variations were similar at moments analyzed (GLM p > 0.05). The same occurred with elastic pressure, higher in the obese at all times (GLM p = 0.04), and resistive pressure showed differences in variations between groups during pneumoperitoneum (GLM p = 0,05).

CONCLUSIONS

Grade I obese presented more changes in pulmonary mechanics than the non-obese during video laparoscopies and the fact requires mechanical ventilation-related care.

Predictors of asynchronies during assisted ventilation and its impact on clinical outcomes: The EPISYNC cohort study

PURPOSE

To investigate if respiratory mechanics and other baseline characteristics are predictors of patient-ventilator asynchrony and to evaluate the relationship between asynchrony during assisted ventilation and clinical outcomes.

METHODS

We performed a prospective cohort study in patients under mechanical ventilation (MV). Baseline measurements included severity of illness and respiratory mechanics. The primary outcome was the Asynchrony Index (AI), defined as the number of asynchronous events divided by the number of ventilator cycles and wasted efforts. We recorded ventilator waveforms throughout the entire period of MV.

RESULTS

We analyzed 11,881 h of MV from 103 subjects. Median AI during the entire period of MV was 5.1% (IQR:2.6-8.7). Intrinsic PEEP was associated with AI (OR:1.72, 95%CI:1.1-2.68), but static compliance and airway resistance were not. Simplified Acute Physiology Score 3 (OR:1.03, 95%CI:1-1.06) was also associated with AI. Median AI was higher during assisted (5.4%, IQR:2.9-9.1) than controlled (2%, IQR:0.6-4.9) ventilation, and 22% of subjects had high incidence of asynchrony (AI≥10%). Subjects with AI≥10% had more extubation failure (33%) than patients with AI<10% (6%), p = .01.

CONCLUSIONS

Predictors of high incidence of asynchrony were severity of illness and intrinsic PEEP. High incidence of asynchrony was associated with extubation failure, but not mortality.

TRIAL REGISTRATION

ClinicalTrials.gov, NCT02687802.

[Comparison of volume-controlled and pressure-controlled ventilation on respiratory mechanics in laparoscopic bariatric surgery: randomized clinical trial]

BACKGROUND

It is not clear which mechanical ventilation mode should be used in bariatric surgery, one of the treatment options for patients with obesity.

OBJECTIVES

To compare volume-controlled ventilation and pressure-controlled ventilation in terms of respiratory mechanics and arterial blood gas values in patients undergoing laparoscopic bariatric surgery.

METHODS

Sixty-two patients with morbid obesity scheduled for gastric bypass were included in this study. Their ideal body weights were calculated during preoperative visits, and patients were divided into two groups, volume-controlled ventilation and pressure-controlled ventilation. The patients were ventilated in accordance with a previously determined algorithm. Mechanical ventilation parameters and arterial blood gas analysis were recorded 5 minutes after induction, 30 minutes after pneumoperitoneum, and at the end of surgery. Also, the dynamic compliance, inspired O₂ pressure/fractional O₂ ratio, and alveolar-arterial oxygen gradient pressure were calculated.

RESULTS

Peak airway pressures were lower in patients ventilated in pressure-controlled ventilation mode at the end of surgery (p = 0.011). Otherwise, there was no difference between groups in terms of intraoperative respiratory parameters and arterial blood gas analyses.

CONCLUSIONS

Pressure-controlled ventilation mode is not superior to volume-controlled ventilation mode in patients with laparoscopic bariatric surgery.

Expiratory flow limitation in intensive care: prevalence and risk factors

BACKGROUND

Expiratory flow limitation (EFL) is characterised by a markedly reduced expiratory flow insensitive to the expiratory driving pressure. The presence of EFL can influence the respiratory and cardiovascular function and damage the small airways; its occurrence has been demonstrated in different diseases, such as COPD, asthma, obesity, cardiac failure, ARDS, and cystic fibrosis. Our aim was to evaluate the prevalence of EFL in patients requiring mechanical ventilation for acute respiratory failure and to determine the main clinical characteristics, the risk factors and clinical outcome associated with the presence of EFL.

METHODS

Patients admitted to the intensive care unit (ICU) with an expected length of mechanical ventilation of 72 h were enrolled in this prospective, observational study. Patients were evaluated, within 24 h from ICU admission and for at least 72 h, in terms of respiratory mechanics, presence of EFL through the PEEP test, daily fluid balance and followed for outcome measurements.

RESULTS

Among the 121 patients enrolled, 37 (31%) exhibited EFL upon admission. Flow-limited patients had higher BMI, history of pulmonary or heart disease, worse respiratory dyspnoea score, higher intrinsic positive end-expiratory pressure, flow and additional resistance. Over the course of the initial 72 h of mechanical ventilation, additional 21 patients (17%) developed EFL. New onset EFL was associated with a more positive cumulative fluid balance at day 3 (103.3 ml/kg) compared to that of patients without EFL (65.8 ml/kg). Flow-limited patients had longer duration of mechanical ventilation, longer ICU length of stay and higher in-ICU mortality.

CONCLUSIONS

EFL is common among ICU patients and correlates with adverse outcomes. The major determinant for developing EFL in patients during the first 3 days of their ICU stay is a positive fluid balance. Further studies are needed to assess if a restrictive fluid therapy might be associated with a lower incidence of EFL.

Dynamic hyperinflation and intrinsic positive end-expiratory pressure in ARDS patients

Background

In ARDS patients, changes in respiratory mechanical properties and ventilatory settings can cause incomplete lung deflation at end-expiration. Both can promote dynamic hyperinflation and intrinsic positive end-expiratory pressure (PEEP). The aim of this study was to investigate, in a large population of ARDS patients, the presence of intrinsic PEEP, possible associated factors (patients’ characteristics and ventilator settings), and the effects of two different external PEEP levels on the intrinsic PEEP.

Methods

We made a secondary analysis of published data. Patients were ventilated with a tidal volume of 6–8 mL/kg of predicted body weight, sedated, and paralyzed. After a recruitment maneuver, a PEEP trial was run at 5 and 15 cmH₂O, and partitioned mechanics measurements were collected after 20 min of stabilization. Lung computed tomography scans were taken at 5 and 45 cmH₂O. Patients were classified into two groups according to whether or not they had intrinsic PEEP at the end of an expiratory pause.

Results

We enrolled 217 sedated, paralyzed patients: 87 (40%) had intrinsic PEEP with a median of 1.1 [1.0–2.3] cmH₂O at 5 cmH₂O of PEEP. The intrinsic PEEP significantly decreased with higher PEEP (1.1 [1.0–2.3] vs 0.6 [0.0–1.0] cmH₂O; p < 0.001). The applied tidal volume was significantly lower (480 [430–540] vs 520 [445–600] mL at 5 cmH₂O of PEEP; 480 [430–540] vs 510 [430–590] mL at 15 cmH₂O) in patients with intrinsic PEEP, while the respiratory rate was significantly higher (18 [15–20] vs 15 [13–19] bpm at 5 cmH₂O of PEEP; 18 [15–20] vs 15 [13–19] bpm at 15 cmH₂O). At both PEEP levels, the total airway resistance and compliance of the respiratory system were not different in patients with and without intrinsic PEEP. The total lung gas volume and lung recruitability were also not different between patients with and without intrinsic PEEP (respectively 961 [701–1535] vs 973 [659–1433] mL and 15 [0–32] % vs 22 [0–36] %).

Conclusions

In sedated, paralyzed ARDS patients without a known obstructive disease, the amount of intrinsic PEEP during lung-protective ventilation is negligible and does not influence respiratory mechanical properties.

Effect of Using the Rapid Shallow Breathing Index as Readiness Criterion for Spontaneous Breathing Trials in a Weaning Protocol

BACKGROUND

This study aimed to compare the effect of using versus not using the Rapid-Shallow Breathing Index (RSBI) as a readiness criterion for Spontaneous Breathing Trials (SBT) on SBT success.

MATERIALS AND METHODS

Daily readiness screens were performed within a respiratory therapist-driven weaning protocol. Patients who passed these screens underwent a one-time measurement of the RSBI and then a SBT regardless of RSBI result. The proportion of passed readiness screens reaching SBT success was compared to the proportion that would have been obtained if RSBI ≤ 105 br/min/L had been used as an additional screen criterion.

RESULTS

Two hundred and fifty SBTs performed on 157 patients were analyzed. The sensitivity of RSBI ≤ 105 br/min/L to predict SBT success was 94.8% (95% CI 90.6-97.5). Relative to potentially using RSBI, 14.4% additional SBTs were performed. A third of these were successful, and no complications were detected in the rest that failed. The proportion of passed readiness screens reaching SBT success would have been 4% (95% CI 1.2-6.8) (P = 0.002) lower if RSBI had been used.

CONCLUSIONS

The inclusion of the RSBI in a readiness screen may not be useful in a weaning protocol.

Noninvasive ventilation during weaning from prolonged mechanical ventilation

BACKGROUND AND OBJECTIVE

Non invasive ventilation (NIV) is currently employed for weaning from invasive ventilation (IMV) in the acute setting but its use for weaning from prolonged ventilation is still occasional and not standardized. We wanted to evaluate whether a combined protocol of NIV and decannulation in tracheostomized patients needing prolonged mechanical ventilation was feasible and what would be the one-year outcome.

METHODS

We studied patients still dependent from invasive mechanical ventilation with the following inclusion criteria: a) tolerance of at least 8h of unsupported breathing, b) progressive hypercapnia/acidosis after invasive ventilation discontinuation, c) good adaptation to NIV, d) favorable criteria for decannulation. These patients were switched from IMV to NIV and decannulated; then they were discharged on home NIV and followed-up for one year in order to evaluate survival and complications rate.

RESULTS

Data from patients consecutively admitted to a weaning unit were prospectively collected between 2005 and 2018. Out of 587 patients admitted over that period, 341 were liberated from prolonged mechanical ventilation. Fifty-one out of 147 unweaned patients (35%) were eligible for the protocol but only 46 were enrolled. After a mean length of stay of 35 days they were decannulated and discharged on domiciliary NIV. After one year, 38 patients were still alive (survival rate 82%) and 37 were using NIV with good adherence (only one patient was switched again to invasive ventilation).

CONCLUSIONS

NIV applied to patients with failed weaning from prolonged IMV is feasible and can facilitate the decannulation process. Patients successfully completing this process show good survival rates and few complications.

Challenges and perspectives in porcine model of acute lung injury using oleic acid

The oleic acid (OA) models of lung injury try to simulate the findings of human Acute Respiratory Distress Syndrome (ARDS). However, these models are difficult to replicate because they vary in terms of animals species, OA doses, time for establishment of lung injury, different observation periods and settings of mechanical ventilation. The objective of this study was to evaluate a protocol of administration of OA in lung injury model, challenges in its development and its effects on respiratory mechanics, hemodynamic changes, histology, gas exchange and mortality. We then submitted ten Large White pigs to acute lung injury through intravenous infusion of acid oleic in the pulmonary artery. The mortality of the model was 50%, due to an intense hemodynamic instability during OA administration, even with early use of vasoactive drugs. Three animals required additional doses of OA to achieve criteria for acute lung injury. Histology showed findings consistent with acute lung injury. However, more pulmonary edema was observed in lower segments than in upper segments of both lungs (p = 0.01). IL-6 and IL-8 were significantly increased compared to normal lungs (p < 0.05), and IL-6 showed higher levels in upper segments compared to lower segments (p = 0.03). Positive cells for Caspase 3 were present in all samples, localized mainly in respiratory epithelial cells and macrophages. In conclusion, this model shows histological findings of acute lung injury and inflammatory response similar to those of clinical ARDS, it presents high mortality, inconsistent reproducibility and hardly controlled hemodynamic instability.

Computational Modeling of Primary Blast Lung Injury: Implications for Ventilator Management

Primary blast lung injury (PBLI) caused by exposure to high-intensity pressure waves is associated with parenchymal tissue injury and severe ventilation-perfusion mismatch. Although supportive ventilation is often required in patients with PBLI, maldistribution of gas flow in mechanically heterogeneous lungs may lead to further injury due to increased parenchymal strain and strain rate, which are difficult to predict in vivo. In this study, we developed a computational lung model with mechanical properties consistent with healthy and PBLI conditions. PBLI conditions were simulated with bilateral derecruitment and increased perihilar tissue stiffness. As a result of these tissue abnormalities, airway flow was heterogeneously distributed in the model under PBLI conditions, during both conventional mechanical ventilation (CMV) and high-frequency oscillatory ventilation. PBLI conditions resulted in over three-fold higher parenchymal strains compared to the healthy condition during CMV, with flow distributed according to regional tissue stiffness. During high-frequency oscillatory ventilation, flow distribution became increasingly heterogeneous and frequency-dependent. We conclude that the distribution and rate of parenchymal distension during mechanical ventilation depend on PBLI severity as well as ventilatory modality. These simulations may allow realistic assessment of the risks associated with ventilator-induced lung injury following PBLI, and facilitate the development of alternative lung-protective ventilation modalities.

Distinct neural-mechanical efficiency of costal and crural diaphragm during hypercapnia

Classic physiology suggests that the two distinct diaphragm segments, costal and crural, are functionally different. It is not known if the two diaphragm muscles share a common neural mechanical activation. We hypothesized that costal and crural diaphragm are recruited differently during hypercapnic stimulated ventilation, and the EMG recordings of the esophageal crural diaphragm segment does not translate to the same level of mechanical shortening for costal and crural segments In 30 spontaneously breathing canines, without confounding anesthetic, we measured directly electrical activity and corresponding mechanical shortening of both the costal and crural diaphragm, at room air and during increasing hypercapnia. During hypercapnic ventilation, the costal diaphragm showed a predominant recruitment over the crural diaphragm. The distinct mechanical contribution of the costal segment was not due to a different level of neural activation between the two muscles as measured by segmental EMG activity. Thus, the two diaphragm segments exhibited a significantly different neural-mechanical relationship.

Effects on Humidification and Ventilatory Parameters of Three Single-limb Heated-wired Circuits for Non-invasive Ventilation: A Bench Study

BACKGROUND

The objective of this study was to evaluate the effects of three single-limb heated wired circuits (SLHWC) for NIV, on ventilatory parameters and humidification performance in a simulation lung model.

METHODS

Three SLHWC compatible with the MR-850 Heated Humidifier (HH) (Fisher & Paykel, Auckland, New Zealand) were tested: RT-319 (FP) (Fisher & Paykel, Auckland, New Zealand), Respironics 1045770 (RP) (DEAS, Castel Bolognese, Italy) and Intersurgical B/SYS 5809001 (IT) (Intersurgical, Wokingham, UK). A Bipap Vision ventilator (Philips Respironics, Murrysville, PA, USA) in pressure control ventilation (PCV) connected to a test lung was used for simulation. Each SHWC performance was evaluated in four ventilatory conditions: IPAP of 15cmH₂O with FiO₂ 0.3 and 1, respectively; and, IPAP of 25cmH₂O with FiO₂ 0.3 and 1, respectively. EPAP was set at 5cmH₂O. Hygrometric and ventilatory measurements including: relative humidity (RH), temperature (T), Pplat, PIP, PEEP, peak inspiratory flow (PIF), and tidal volume (Vt) were measured.

RESULTS

In each FiO₂ group absolute humidity (AH) was similar with FP regardless of the IPAP level employed compared to IT and RP (P<.001). Except for RP at FiO₂ 0.3, AH increased significantly in IT and RP groups as IPAP increased (P<.001). PIP, Pplat, PEEP, PIF, and Vt values were significantly higher with FP and RP in each FiO₂ group compared to IT (P<.001).

CONCLUSIONS

Humidification performance varied significantly among the three circuits, being FP the only one able to maintain stable AH values during the study with no influence on ventilatory parameters.

Evaluation of model-based methods in estimating respiratory mechanics in the presence of variable patient effort

Monitoring of respiratory mechanics is required for guiding patient-specific mechanical ventilation settings in critical care. Many models of respiratory mechanics perform poorly in the presence of variable patient effort. Typical modelling approaches either attempt to mitigate the effect of the patient effort on the airway pressure waveforms, or attempt to capture the size and shape of the patient effort. This work analyses a range of methods to identify respiratory mechanics in volume controlled ventilation modes when there is patient effort. The models are compared using 4 Datasets, each with a sample of 30 breaths before, and 2-3 minutes after sedation has been administered. The sedation will reduce patient efforts, but the underlying pulmonary mechanical properties are unlikely to change during this short time. Model identified parameters from breathing cycles with patient effort are compared to breathing cycles that do not have patient effort. All models have advantages and disadvantages, so model selection may be specific to the respiratory mechanics application. However, in general, the combined method of iterative interpolative pressure reconstruction, and stacking multiple consecutive breaths together has the best performance over the Dataset. The variability of identified elastance when there is patient effort is the lowest with this method, and there is little systematic offset in identified mechanics when sedation is administered.