Engstr m carestation

To determine the BENGI’s accuracy at measuring V_T, the BENGI and computer flow sensor were connected in-line in series between a mechanical ventilator (Engström Carestation™, General Electric Healthcare, Chicago, IL) and the test lung. The ventilator was set in mandatory volume control ventilation, and breaths were delivered to the test lung at a constant respiratory rate (10 breaths/min) and varying inspiratory times (t_insp = 0.5, 1.0, and 2.0 s) and tidal volumes (V_T = 300 to 900 mL in 50 mL increments). Flow measurements from at least 10 consecutive respiratory cycles were captured with the computer flow sensor. The flow waveform was analyzed with custom code written in Python (version 3.7.2, Python Software Foundation, Beaverton, Oregon, United States) to determine inspiratory start and end times and calculate V_T. The onboard, real-time calculation of V_T by the BENGI was sent to the computer at end inspiratory time via USB transmission. The computer and BENGI calculated V_Ts were matched based upon end inspiration times, and the measurement differences in V_T were analyzed by Bland–Altman plot analysis.

A calorimeter module (Engström Carestation, General Electric, Madison, WI) was used for indirect calorimetry. The module consists of a fast differential paramagnetic oxygen analyzer, an infrared analyzer for carbon dioxide, and a pneumotachograph to measure the inspired and expired volumes. The pneumotachograph and gas sampling ports were connected to a disposable connector, placed between the Y-piece of the ventilator circuit and the endotracheal tube. The signals from the pneumotachograph and gas analyzers were synchronized for breath-by-breath data on gas exchange. Under each condition, the data were collected for 30 min with the first 10 min being discarded for analysis purposes. We consider the steady state to be the point after 5 consecutive minutes measurement when VCO₂ and VO₂ vary by ±10%. During the last 5 min of each steady state, the following data were recorded: VCO₂, VO₂, EE, and respiratory quotient (RQ).

A 16-electrode silicon belt (EIT evaluation kit 2, Dräger, Lübeck, Germany) was placed around the patient’s thoracic cage between the 6th and 7th intercostal spaces [16 (link)]. Patients were ventilated with pressure-controlled ventilation (PCV) (Engström Carestation, GE Healthcare, Madison, WI, USA) and, throughout the entire study period, the inspiratory pressure above PEEP, the Inspiration/expiration (I/E) ratio, frequency and inspired oxygen fraction (FiO₂) remained unchanged.
In this study we performed a recruitment maneuver in which mechanical ventilation was continued with a pressure amplitude of 20 cm H₂O while PEEP was rapidly increased from 5 to 20 cm H₂O in incremental steps of 5 cm H₂O: thus, a peak pressure of 40 cm H₂O for a 40-s period, as long as blood pressure remained stable. Thereafter, PEEP was decreased to 15 cm H₂O and the pressure amplitude was decreased from 20 to 10 cm H₂O. A PEEP level of 15 cm H₂O was applied for 15 minutes to achieve a steady state. Thereafter, a decremental PEEP trial was performed from 15 to 0 cm H₂O PEEP in steps of 5 cm H₂O. Each PEEP level was applied for 10 to 20 minutes (depending on hemodynamic stability and blood gas analyses). At the end of each PEEP step, EIT, PaO₂/FiO₂ ratio and dynamic compliance (tidal volume divided by pressure above PEEP) were calculated.

Anesthesia was induced and maintained through continuous infusion of propofol and fentanyl, with atracurium used intravenously solely to facilitate endotracheal intubation. Basic monitoring, including pulse oximetry (Radical 7; Masimo, Irvine, CA, USA) and invasive blood pressure (S/5, GE-Datex-Ohmeda; Chalfont, St. Giles, United Kingdom), was performed. Animals were ventilated using pressure-controlled ventilation-volume guaranteed mode (PCV-VG) (Engström Carestation; GE healthcare, Chalfont, St Giles, Buckinghamshire, UK) with a tidal volume of 6–8 ml kg⁻¹, a positive end-expiratory pressure (PEEP) of 5 mbar, fraction of inspired oxygen (FiO2) of 0.4, and respiratory rate adjusted to the end-tidal CO2.
Seldinger’s technique was employed for femoral vascular access after ultrasound-guided puncture to place a central venous line, a venous introducer for a pulmonary artery catheter, and an arterial introducer for a pulse contour cardiac output catheter (PiCCO; Pulsion Medical, Munich, Germany). The data from all devices were continuously monitored and stored. Balanced electrolyte fluid (BEL, Sterofundin; Braun, Melsungen, Germany) was administered at a rate of 5 ml⁻¹ kg⁻¹.