Efficacy and Safety Testing of a COVID-19 Era Emergency Ventilator in a Healthy Rabbit Lung Model

Background: The COVID-19 pandemic revealed a substantial and unmet need for low-cost, easily accessible mechanical ventilation strategies for use in medical resource-challenged areas. Internationally, several groups developed non-conventional COVID-19 era emergency ventilator strategies as a stopgap measure when conventional ventilators were unavailable. Here, we compared our FALCON emergency ventilator in a rabbit model and compared its safety and functionality to conventional mechanical ventilation. Methods: New Zealand white rabbits (n = 5) received mechanical ventilation from either the FALCON or a conventional mechanical ventilator (Engström CarestationTM) for 1 hour each. Airflow and pressure, blood O2 saturation, end tidal CO2, and arterial blood gas measurements were measured. Additionally, gross and histological lung samples were compared to spontaneously breathing rabbits (n = 3) to assess signs of ventilator induced lung injury.Results: All rabbits were successfully ventilated with the FALCON. At identical ventilator settings, tidal volumes, pressures, and respiratory rates were similar between both ventilators, but the inspiratory to expiratory ratio was lower using the FALCON. End tidal CO2 was significantly higher on the FALCON, and arterial blood gas measurements demonstrated lower arterial partial pressure of O2 at 30 minutes and higher arterial partial pressure of CO2 at 30 and 60 minutes using the FALCON. However, when ventilated at higher respiratory rates, we observed a stepwise decrease in end tidal CO2. Poincaré plot analysis demonstrated small but significant increases in short-term and long-term variation of peak inspiratory pressure generation from the FALCON. Wet to dry lung weight and lung injury scoring between the mechanically ventilated and spontaneously breathing rabbits were similar. Conclusions: Although conventional ventilators are always preferable outside of emergency use, the FALCON ventilator safely and effectively ventilated healthy rabbits without lung injury. Emergency ventilation using accessible and inexpensive strategies like the FALCON may be useful for communities with low access to medical resources and as a backup form of emergency ventilation.

Carbon Dioxide Changes during High-flow Nasal Oxygenation in Apneic Patients: A Single-center Randomized Controlled Noninferiority Trial

Background Anesthesia studies using high-flow, humidified, heated oxygen delivered via nasal cannulas at flow rates of more than 50 l · min–1 postulated a ventilatory effect because carbon dioxide increased at lower levels as reported earlier. This study investigated the increase of arterial partial pressure of carbon dioxide between different flow rates of 100% oxygen in elective anesthetized and paralyzed surgical adults before intubation. Methods After preoxygenation and standardized anesthesia induction with nondepolarizing neuromuscular blockade, all patients received 100% oxygen (via high-flow nasal oxygenation system or circuit of the anesthesia machine), and continuous jaw thrust/laryngoscopy was applied throughout the 15-min period. In this single-center noninferiority trial, 25 patients each, were randomized to five groups: (1) minimal flow: 0.25 l · min–1, endotracheal tube; (2) low flow: 2 l · min–1, continuous jaw thrust; (3) medium flow: 10 l · min–1, continuous jaw thrust; (4) high flow: 70 l · min–1, continuous jaw thrust; and (5) control: 70 l · min–1, continuous laryngoscopy. Immediately after anesthesia induction, the 15-min apnea period started with oxygen delivered according to the randomized flow rate. Serial arterial blood gas analyses were drawn every 2 min. The study was terminated if either oxygen saturation measured by pulse oximetry was less than 92%, transcutaneous carbon dioxide was greater than 100 mmHg, pH was less than 7.1, potassium level was greater than 6 mmol · l–1, or apnea time was 15 min. The primary outcome was the linear rate of mean increase of arterial carbon dioxide during the 15-min apnea period computed from linear regressions. Results In total, 125 patients completed the study. Noninferiority with a predefined noninferiority margin of 0.3 mmHg · min–1 could be declared for all treatments with the following mean and 95% CI for the mean differences in the linear rate of arterial partial pressure of carbon dioxide with associated P values regarding noninferiority: high flow versus control, –0.0 mmHg · min–1 (–0.3, 0.3 mmHg · min–1, P = 0.030); medium flow versus control, –0.1 mmHg · min–1 (–0.4, 0.2 mmHg · min–1, P = 0.002); low flow versus control, –0.1 mmHg · min–1 (–0.4, 0.2 mmHg · min–1, P = 0.003); and minimal flow versus control, –0.1 mmHg · min–1 (–0.4, 0.2 mmHg · min–1, P = 0.004). Conclusions Widely differing flow rates of humidified 100% oxygen during apnea resulted in comparable increases of arterial partial pressure of carbon dioxide, which does not support an additional ventilatory effect of high-flow nasal oxygenation. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Arterial and Mixed Venous Kinetics of Desflurane and Sevoflurane, Administered Simultaneously, at Three Different Global Ventilation to Perfusion Ratios in Piglets with Normal Lungs

Background Previous studies have established the role of various tissue compartments in the kinetics of inhaled anesthetic uptake and elimination. The role of normal lungs in inhaled anesthetic kinetics is less understood. In juvenile pigs with normal lungs, the authors measured desflurane and sevoflurane washin and washout kinetics at three different ratios of alveolar minute ventilation to cardiac output value. The main hypothesis was that the ventilation/perfusion ratio ( .VA/.Q ) of normal lungs influences the kinetics of inhaled anesthetics. Methods Seven healthy pigs were anesthetized with intravenous anesthetics and mechanically ventilated. Each animal was studied under three different .VA/.Q conditions: normal, low, and high. For each .VA/.Q condition, desflurane and sevoflurane were administered at a constant, subanesthetic inspired partial pressure (0.15 volume% for sevoflurane and 0.5 volume% for desflurane) for 45 min. Pulmonary arterial and systemic arterial blood samples were collected at eight time points during uptake, and then at these same times during elimination, for measurement of desflurane and sevoflurane partial pressures. The authors also assessed the effect of .VA/.Q on paired differences in arterial and mixed venous partial pressures. Results For desflurane washin, the scaled arterial partial pressure differences between 5 and 0 min were 0.70 ± 0.10, 0.93 ± 0.08, and 0.82 ± 0.07 for the low, normal, and high .VA/.Q conditions (means, 95% CI). Equivalent measurements for sevoflurane were 0.55 ± 0.06, 0.77 ± 0.04, and 0.75 ± 0.08. For desflurane washout, the scaled arterial partial pressure differences between 0 and 5 min were 0.76 ± 0.04, 0.88 ± 0.02, and 0.92 ± 0.01 for the low, normal, and high .VA/.Q conditions. Equivalent measurements for sevoflurane were 0.79 ± 0.05, 0.85 ± 0.03, and 0.90 ± 0.03. Conclusions Kinetics of inhaled anesthetic washin and washout are substantially altered by changes in the global .VA/.Q ratio for normal lungs. Editor’s Perspective What We Already Know about This Topic What This Article Tells Us That Is New

Second-generation laryngeal mask airway as an alternative to endotracheal tube during prolonged laparoscopic abdominal surgery: a comparative analysis of intraoperative gas exchanges

Introduction: Despite several advantages over endotracheal tube (ETT), laryngeal mask airway (LMA), which is used in emergencies under difficult airway maintenance conditions, is rarely utilized in prolonged surgery. We compared the variables representing intraoperative gas exchange with second-generation LMA and ETT during prolonged laparoscopic abdominal surgery. Methods: Prolonged surgery was defined as a surgery lasting more than 2 h. In total, 394 patients who underwent laparoscopic liver resection via either second-generation LMA or ETT were retrospectively analysed. Parameters including end-tidal pressure of carbon dioxide (ETCO2), tidal volume (TV), respiratory rate (RR), peak inspiratory pressure (PIP), arterial partial pressure of carbon dioxide (PaCO2), pH, and ratio of arterial partial pressure of oxygen to fractional inspired oxygen (PFR) during surgery were compared between the two groups. In addition, the incidence of postoperative pulmonary complications (PPC) including pulmonary aspiration was also compared. Results: The values of ETCO2, TV, RR and PIP during pneumoperitoneum were comparable between the two groups. Although PaCO2 at 2 h after induction was higher in patients with LMA (40.5 vs. 38.5 mmHg, p < 0.001), the pH and PFR values of the two groups were comparable. The incidence of PPC was not different. Conclusion: During prolonged laparoscopic abdominal surgery, the second-generation LMA facilitates adequate intraoperative gas exchange and represents an alternative to ETT.

Alveolar–arterial partial pressure difference as an early predictor for patients with acute paraquat poisoning

Objective Paraquat (PQ) is associated with high mortality rates in acute poisoning. This study aimed to determine the importance of the alveolar–arterial partial pressure difference (A-aDo2) in the expected consequences of acute PQ poisoning. Methods Patients who were hospitalized for PQ poisoning in 2018 were enrolled in this retrospective study. A-aDo2 data were collected. Multivariate analysis was performed using binary logistic regression to determine whether A-aDo2 is an independent risk factor for mortality from PQ. Results A total of 352 cases were analyzed. The mean PQ dose was 36.84 ± 50.30 mL (0.3–500 mL). There were 185 survivors and 167 non-survivors. The mean A-aDo2 was not significantly correlated between survivors and non-survivors on day 1. However, there were significant differences in A-aDo2 between survivors and non-survivors on days 3, 7, 14, and 21. Increased A-aDo2 values were correlated with an increased mortality rate. The mean A-aDo2 on day 14 showed the most significant difference between survivors and non-survivors. Conclusion Our study suggests that A-aDo2 plays an important role as a reference index, which could be a useful predictor in assessing acute PQ poisoning, especially on the 14th day after onset of poisoning.

Medical Image Enhancement Algorithm for B-Mode Ultrasound Image Analysis of Neonatal Respiratory Distress Syndrome

The aim of this paper was to explore the imaging characteristics of lung B-ultrasound images under image enhancement algorithm for neonatal respiratory distress syndrome (NRDS) and the therapeutic effect of vitamin A (VA) on NDRS. 30 newborn babies with NRDS in hospital were selected as the experimental group and 30 healthy newborn babies were selected as the control group. All of them received the lung B-ultrasound based on the image enhancement algorithm under the partial differential equation (PDE). The subjects of the control group were given formula milk every day. On the basis of formula milk, the subjects of the experimental group took VA soft capsule orally once a day at noon. Oxidative stress indexes, blood gas indexes, and mechanical ventilation parameters were recorded in the subjects of the two groups. The results of 30 newborn babies with NRDS in the experimental group indicated that the images of 12 cases presented the disappearance of line A and dense or discontinuous distribution of line B; the abnormal pleural line was found in the images of 8 cases; there was lung consolidation under the pleural line, patchy hypoecho, and point-strip hyperecho in the images of 5 cases; the images of 2 cases showed alveolar edema and alveolar interstitial syndrome. Compared with before treatment, the arterial partial pressure of oxygen (PaO2) of subjects in the experimental group (87.61 ± 5.79) increased dramatically, but their arterial partial pressure of carbon dioxide (PaCO2) decreased sharply after treatment (40.07 ± 6.12), with statistically huge differences ( P < 0.05 ). The respiratory rate (RR) and positive end expiratory pressure (PEEP) after treatment were greatly less than those before treatment of subjects in the experimental group ( P < 0.05 ), and the difference was statistically obvious ( P < 0.05 ). By comparing with before treatment, malondialdehyde (MDA) of subjects in the experimental group decreased after treatment while superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) increased considerably, with statistically marked differences ( P < 0.05 ). In conclusion, lung B-ultrasound based on partial image enhancement algorithm could clearly display the imaging characteristics of NRDS, such as pleural abnormalities and alveolar stroma. Besides, VA could effectively improve the neonatal shortness of breath, which had a good clinical effect.