Patient effort at a glance

A: Patient with little effort. Top: Volume Controlled Ventilation: airway pressure in cmH2O in yellow, constant flow in L/min in pink. Middle: Pressure controlled ventilation: airway pressure in cmH2O in yellow, decelerating flow in L/min in pink. Bottom: Esophageal pressure in cmH2O. B: Patient with high effort. Top: Volume Controlled Ventilation: airway pressure with convex negative deflection during trigger and first half of inspiration (blue arrow). Middle: Pressure controlled ventilation: airway pressure with negative deflection during the trigger (yellow arrow) and slight convex deflection (green arrow), concave deflection in the flow (orange arrow). Bottom: Convex deflection in esophageal pressure (grey arrow).

Effects on Lung Gas Volume, Respiratory Mechanics and Gas Exchange of a Closed-Circuit Suctioning System during Volume- and Pressure-Controlled Ventilation in ARDS Patients

Mechanically ventilated patients periodically require endotracheal suctioning. There are conflicting data regarding the loss of lung gas volume caused by the application of a negative pressure by closed-circuit suctioning. The aim of this study was to evaluate the effects of suctioning performed by a closed-circuit system in ARDS patients during volume- or pressure-controlled ventilation. In this prospective crossover-design study, 18 ARDS patients were ventilated under volume and pressure control applied in random order. Gas exchange, respiratory mechanics and EIT-derived end-expiratory lung volume (EELV) before the suctioning manoeuvre and after 5, 15 and 30 min were recorded. The tidal volume and respiratory rate were similar in both ventilation modes; in volume control, the EELV decreased by 31 ± 23 mL, 5 min after the suctioning, but it remained similar after 15 and 30 min; the oxygenation, PaCO2 and respiratory system elastance did not change. In the pressure control, 5 min after suctioning, EELV decreased by 35 (26–46) mL, the PaO2/FiO2 did not change, while PaCO2 increased by 5 and 30 min after suctioning (45 (40–51) vs. 48 (43–52) and 47 (42–54) mmHg, respectively). Our results suggest minimal clinical advantages when a closed system is used in volume-controlled compared to pressure-controlled ventilation.

Abstract 13110: Novel Application of Thoracic Impedance to Characterize Ventilations During Cardiopulmonary Resuscitation in the Pragmatic Airway Resuscitation Trial

Introduction: Controlled ventilation is important in OHCA resuscitation, but there are few validated methods for accurate detection of ventilations. We sought to utilize changes in thoracic impedance (TI) to characterize resuscitation ventilations in the Pragmatic Airway Resuscitation Trial (PART). Methods: We analyzed CPR process files collected from adult OHCA enrolled in PART. We limited the analysis to cases with simultaneous capnography ventilation recordings at the Dallas-Ft Worth site. We identified ventilation waveforms in the thoracic impedance signal by applying automated signal processing with adaptive filtering techniques to remove overlying artifacts from chest compressions. We correlated detected ventilations with the end-tidal capnography signal. We determined the amplitudes (Ai, Ae) and durations (Di, De) of both insufflation and exhalation phases of the ventilation impedance signal (Figure 1). We compared differences between laryngeal tube (LT) and endotracheal intubation (ETI) airway management during mechanical or manual chest compressions using Mann-Whitney U-test. Results: We included 303 CPR process cases in the analysis; 209 manual (77 ETI, 132 LT), 94 mechanical (41 ETI, 53 LT). Ventilation Ai and Ae were higher for ETI than LT in both manual (ETI: Ai 0.71Ω, Ae 0.70Ω vs LT: Ai 0.46Ω Ae 0.45Ω, p<0.01 respectively) and mechanical chest compressions (ETI: Ai 1.22Ω, Ae 1.14Ω VS LT: Ai 0.74Ω, Ae 0.68Ω, p<0.01 respectively). Ventilations per minute, duration of TI amplitude insufflation and exhalation did not differ among groups. Conclusion: Compared with LT, ETI thoracic impedance ventilation insufflation and exhalation amplitude were higher while duration did not differ. TI may provide a novel approach to characterizing ventilation during OHCA.

Simulated Ventilation of Two Patients With a Single Ventilator in a Pandemic Setting

Background: Simultaneous ventilation of two patients, e.g., due to a shortage of ventilators in a pandemic, may result in hypoventilation in one patient and hyperinflation in the other patient. Methods: In a simulation of double patient ventilation using artificial lungs with equal compliances (70mL∙mbar-1), we tried to voluntarily direct gas flow to one patient by using 3D-printed y-adapters and stenosis adapters during volume-, and pressure-controlled ventilation. Subsequently, we modified the model using a special one-way valve on the limited flow side and measured in pressure-controlled ventilation with the flow sensor adjusted on either side in a second and third setup. In the last setup, we also measured with different lung compliances.Results: Volume- or pressure-controlled ventilation using standard connection tubes with the same compliance in each lung resulted in comparable minute volumes in both lungs, even if one side was obstructed to 3mm (6.6±0.2vs.6.5±0.1L for volume-controlled ventilation, p=.25 continuous severe alarm and 7.4±0.1vs.6.1±0.1L for pressure-controlled ventilation, p=.02 no alarm). In the second setup, pressure-controlled ventilation resulted at a 3mm flow limitation in minute ventilation of 9.4±0.3vs3.5±0.1L∙min-1, p=.001. In a third setup using the special one-way valve and the flow sensor on the unobstructed side, pressure-controlled ventilation resulted at a 3mm flow limitation in minute ventilation of 7.4±0.2vs3±0L∙min-1, at the compliance of 70mL∙mbar-1 for both lungs, 7.2±0vs4.1±0L∙ min-1, at the compliances of 50 vs. 70mL∙mbar-1, and 7.2±0.2vs5.7±0L∙ min-1, at the compliance of 30 vs. 70mL∙mbar-1 (all p=.001).Conclusions: Overriding a modern intensive care ventilator's safety features are possible, thereby ventilating two lungs with one ventilator simultaneously in a laboratory simulation using 3D-printed y-adapters. Directing tidal volumes in different pulmonary conditions towards one lung using 3D-printed flow limiters with diameters <6mm was also possible. While this ventilation setting was technically feasible in a bench model, it would be volatile, if not dangerous in a clinical situation.

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

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.