scholarly journals Effects of inspiratory flow on lung stress, pendelluft, and ventilation heterogeneity in ARDS: a physiological study

Critical Care ◽  
2019 ◽  
Vol 23 (1) ◽  
Author(s):  
Alessandro Santini ◽  
Tommaso Mauri ◽  
Francesca Dalla Corte ◽  
Elena Spinelli ◽  
Antonio Pesenti
Keyword(s):  
Peep Level ◽  
Transpulmonary Pressure ◽  
Plateau Pressure ◽  
Inspiratory Flow ◽  
Absolute Difference ◽  
Controlled Ventilation ◽  
Volume Controlled Ventilation ◽  
Ventilation Heterogeneity ◽  
Volume Controlled ◽  
Lung Stress

Abstract Background High inspiratory flow might damage the lungs by mechanisms not fully understood yet. We hypothesized that increasing inspiratory flow would increase lung stress, ventilation heterogeneity, and pendelluft in ARDS patients undergoing volume-controlled ventilation with constant tidal volume and that higher PEEP levels would reduce this phenomenon. Methods Ten ARDS patients were studied during protective volume-controlled ventilation. Three inspiratory flows (400, 800, and 1200 ml/s) and two PEEP levels (5 and 15 cmH2O) were applied in random order to each patient. Airway and esophageal pressures were recorded, end-inspiratory and end-expiratory holds were performed, and ventilation distribution was measured with electrical impedance tomography. Peak and plateau airway and transpulmonary pressures were recorded, together with the airway and transpulmonary pressure corresponding to the first point of zero end-inspiratory flow (P1). Ventilation heterogeneity was measured by the EIT-based global inhomogeneity (GI) index. Pendelluft was measured as the absolute difference between pixel-level inflation measured at plateau pressure minus P1. Results Plateau airway and transpulmonary pressure was not affected by inspiratory flow, while P1 increased at increasing inspiratory flow. The difference between P1 and plateau pressure was higher at higher flows at both PEEP levels (p < 0.001). While higher PEEP reduced heterogeneity of ventilation, higher inspiratory flow increased GI (p = 0.05), irrespective of the PEEP level. Finally, gas volume undergoing pendelluft was larger at higher inspiratory flow (p < 0.001), while PEEP had no effect. Conclusions The present exploratory analysis suggests that higher inspiratory flow increases additional inspiratory pressure, heterogeneity of ventilation, and pendelluft while PEEP has negligible effects on these flow-dependent phenomena. The clinical significance of these findings needs to be further clarified.

scholarly journals Different Inspiratory Flow Waveform during Volume-Controlled Ventilation in ARDS Patients

2021 ◽  
Vol 10 (20) ◽  
pp. 4756
Author(s):  
Davide Chiumello ◽  
Andrea Meli ◽  
Tommaso Pozzi ◽  
Manuela Lucenteforte ◽  
Paolo Simili ◽  
...  
Keyword(s):  
Respiratory Mechanics ◽  
Major Effect ◽  
Inspiratory Flow ◽  
Flow Waveform ◽  
Controlled Ventilation ◽  
Volume Controlled Ventilation ◽  
The Mean ◽  
Flow Waveforms ◽  
Volume Controlled ◽  
Pressure Controlled

The most used types of mechanical ventilation are volume- and pressure-controlled ventilation, respectively characterized by a square and a decelerating flow waveform. Nowadays, the clinical utility of different inspiratory flow waveforms remains unclear. The aim of this study was to assess the effects of four different inspiratory flow waveforms in ARDS patients. Twenty-eight ARDS patients (PaO2/FiO2 182 ± 40 and PEEP 11.3 ± 2.5 cmH2O) were ventilated in volume-controlled ventilation with four inspiratory flow waveforms: square (SQ), decelerating (DE), sinusoidal (SIN), and trunk descending (TDE). After 30 min in each condition, partitioned respiratory mechanics and gas exchange were collected. The inspiratory peak flow was higher in the DE waveform compared to the other three waveforms, and in SIN compared to the SQ and TDE waveforms, respectively. The mean inspiratory flow was higher in the DE and SIN waveforms compared with TDE and SQ. The inspiratory peak pressure was higher in the SIN and SQ compared to the TDE waveform. Partitioned elastance was similar in the four groups; mechanical power was lower in the TDE waveform, while PaCO2 in DE. No major effect on oxygenation was found. The explored flow waveforms did not provide relevant changes in oxygenation and respiratory mechanics.

scholarly journals The effects of pressure- versus volume-controlled ventilation on ventilator work of breathing

2020 ◽  
Vol 19 (1) ◽  
Author(s):  
Mojdeh Monjezi ◽  
Hamidreza Jamaati
Keyword(s):  
Work Of Breathing ◽  
Normal Subjects ◽  
Inspiratory Flow ◽  
Flow Profile ◽  
Controlled Ventilation ◽  
Volume Controlled Ventilation ◽  
Copd Patients ◽  
Flow Waveforms ◽  
Lung Airways ◽  
Volume Controlled

Abstract Background Measurement of work of breathing (WOB) during mechanical ventilation is essential to assess the status and progress of intensive care patients. Increasing ventilator WOB is known as a risk factor for ventilator-induced lung injury (VILI). In addition, the minimization of WOB is crucial to facilitate the weaning process. Several studies have assessed the effects of varying inspiratory flow waveforms on the patient’s WOB during assisted ventilation, but there are few studies on the different effect of inspiratory flow waveforms on ventilator WOB during controlled ventilation. Methods In this paper, we analyze the ventilator WOB, termed mechanical work (MW) for three common inspiratory flow waveforms both in normal subjects and COPD patients. We use Rohrer’s equation for the resistance of the endotracheal tube (ETT) and lung airways. The resistance of pulmonary and chest wall tissue are also considered. Then, the resistive MW required to overcome each component of the respiratory resistance is computed for square and sinusoidal waveforms in volume-controlled ventilation (VCV), and decelerating waveform of flow in pressure-controlled ventilation (PCV). Results The results indicate that under the constant I:E ratio, a square flow profile best minimizes the MW both in normal subjects and COPD patients. Furthermore, the large I:E ratio may be used to lower MW. The comparison of results shows that ETT and lung airways have the main contribution to resistive MW in normals and COPDs, respectively. Conclusion These findings support that for lowering the MW especially in patients with obstructive lung diseases, flow with square waveforms in VCV, are more favorable than decelerating waveform of flow in PCV. Our analysis suggests the square profile is the best choice from the viewpoint of less MW.

Volume-controlled mechanical ventilation

2016 ◽  
Author(s):  
Kristy A. Bauman ◽  
Robert C. Hyzy
Keyword(s):  
Mechanical Ventilation ◽  
Tidal Volume ◽  
Flow Rate ◽  
Plateau Pressure ◽  
Patient Comfort ◽  
Controlled Ventilation ◽  
Volume Controlled Ventilation ◽  
Pressure Limitation ◽  
Controlled Mechanical Ventilation ◽  
Volume Controlled

The goal of mechanical ventilation is to achieve adequate gas exchange while minimizing haemodynamic compromise and ventilator-associated lung injury. Volume-controlled ventilation can be delivered via several modes, including controlled mechanical ventilation, assist control (AC) and synchronized intermittent mandatory ventilation (SIMV). .In volume-controlled modes, the clinician sets the flow pattern, flow rate, trigger sensitivity, tidal volume, respiratory rate, positive end-expiratory pressure, and fraction of inspired oxygen. Patient ventilator synchrony can be enhanced by setting appropriate trigger sensitivity and inspiratory flow rate. I:E ratio can be adjusted to improve oxygenation, avoid air trapping and enhance patient comfort. There is little data regarding the benefits of one volume-controlled mode over another. In acute respiratory distress syndrome, low tidal volume ventilation in conjunction with plateau pressure limitation should be employed as there is a reduction in mortality with this strategy. This chapter addresses respiratory mechanics, modes and settings, clinical applications, and limitations of volume-controlled ventilation.

scholarly journals Mechanical power at a glance: a simple surrogate for volume-controlled ventilation

2019 ◽  
Vol 7 (1) ◽  
Author(s):  
Lorenzo Giosa ◽  
Mattia Busana ◽  
Iacopo Pasticci ◽  
Matteo Bonifazi ◽  
Matteo Maria Macrì ◽  
...  
Keyword(s):  
Peak Pressure ◽  
Minute Ventilation ◽  
Clinical Intervention ◽  
Lung Parenchyma ◽  
Mechanical Power ◽  
Icu Patients ◽  
Controlled Ventilation ◽  
Volume Controlled Ventilation ◽  
New Equation ◽  
Volume Controlled

Abstract Background Mechanical power is a summary variable including all the components which can possibly cause VILI (pressures, volume, flow, respiratory rate). Since the complexity of its mathematical computation is one of the major factors that delay its clinical use, we propose here a simple and easy to remember equation to estimate mechanical power under volume-controlled ventilation: $$ \mathrm{Mechanical}\ \mathrm{Power}=\frac{\mathrm{VE}\times \left(\mathrm{Peak}\ \mathrm{Pressure}+\mathrm{PEEP}+F/6\right)}{20} $$Mechanical Power=VE×Peak Pressure+PEEP+F/620 where the mechanical power is expressed in Joules/minute, the minute ventilation (VE) in liters/minute, the inspiratory flow (F) in liters/minute, and peak pressure and positive end-expiratory pressure (PEEP) in centimeter of water. All the components of this equation are continuously displayed by any ventilator under volume-controlled ventilation without the need for clinician intervention. To test the accuracy of this new equation, we compared it with the reference formula of mechanical power that we proposed for volume-controlled ventilation in the past. The comparisons were made in a cohort of mechanically ventilated pigs (485 observations) and in a cohort of ICU patients (265 observations). Results Both in pigs and in ICU patients, the correlation between our equation and the reference one was close to the identity. Indeed, the R2 ranged from 0.97 to 0.99 and the Bland-Altman showed small biases (ranging from + 0.35 to − 0.53 J/min) and proportional errors (ranging from + 0.02 to − 0.05). Conclusions Our new equation of mechanical power for volume-controlled ventilation represents a simple and accurate alternative to the more complex ones available to date. This equation does not need any clinical intervention on the ventilator (such as an inspiratory hold) and could be easily implemented in the software of any ventilator in volume-controlled mode. This would allow the clinician to have an estimation of mechanical power at a simple glance and thus increase the clinical consciousness of this variable which is still far from being used at the bedside. Our equation carries the same limitations of all other formulas of mechanical power, the most important of which, as far as it concerns VILI prevention, are the lack of normalization and its application to the whole respiratory system (including the chest wall) and not only to the lung parenchyma.

scholarly journals Comparison of Volume-Guaranteed or -Targeted, Pressure-Controlled Ventilation with Volume-Controlled Ventilation during Elective Surgery: A Systematic Review and Meta-Analysis

2021 ◽  
Vol 10 (6) ◽  
pp. 1276
Author(s):  
Volker Schick ◽  
Fabian Dusse ◽  
Ronny Eckardt ◽  
Steffen Kerkhoff ◽  
Simone Commotio ◽  
...  
Keyword(s):  
Systematic Review ◽  
Elective Surgery ◽  
Meta Analysis ◽  
Lung Ventilation ◽  
One Lung Ventilation ◽  
Controlled Ventilation ◽  
Pressure Controlled Ventilation ◽  
Volume Controlled Ventilation ◽  
Volume Controlled ◽  
Pressure Controlled

For perioperative mechanical ventilation under general anesthesia, modern respirators aim at combining the benefits of pressure-controlled ventilation (PCV) and volume-controlled ventilation (VCV) in modes typically named “volume-guaranteed” or “volume-targeted” pressure-controlled ventilation (PCV-VG). This systematic review and meta-analysis tested the hypothesis that PCV-VG modes of ventilation could be beneficial in terms of improved airway pressures (Ppeak, Pplateau, Pmean), dynamic compliance (Cdyn), or arterial blood gases (PaO2, PaCO2) in adults undergoing elective surgery under general anesthesia. Three major medical electronic databases were searched with predefined search strategies and publications were systematically evaluated according to the Cochrane Review Methods. Continuous variables were tested for mean differences using the inverse variance method and 95% confidence intervals (CI) were calculated. Based on the assumption that intervention effects across studies were not identical, a random effects model was chosen. Assessment for heterogeneity was performed with the χ2 test and the I2 statistic. As primary endpoints, Ppeak, Pplateau, Pmean, Cdyn, PaO2, and PaCO2 were evaluated. Of the 725 publications identified, 17 finally met eligibility criteria, with a total of 929 patients recruited. Under supine two-lung ventilation, PCV-VG resulted in significantly reduced Ppeak (15 studies) and Pplateau (9 studies) as well as higher Cdyn (9 studies), compared with VCV [random effects models; Ppeak: CI −3.26 to −1.47; p < 0.001; I2 = 82%; Pplateau: −3.12 to −0.12; p = 0.03; I2 = 90%; Cdyn: CI 3.42 to 8.65; p < 0.001; I2 = 90%]. For one-lung ventilation (8 studies), PCV-VG allowed for significantly lower Ppeak and higher PaO2 compared with VCV. In Trendelenburg position (5 studies), this effect was significant for Ppeak only. This systematic review and meta-analysis demonstrates that volume-targeting, pressure-controlled ventilation modes may provide benefits with respect to the improved airway dynamics in two- and one-lung ventilation, and improved oxygenation in one-lung ventilation in adults undergoing elective surgery.

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