Novel method of transpulmonary pressure measurement with an air-filled esophageal catheter

Background There is a strong rationale for proposing transpulmonary pressure-guided protective ventilation in acute respiratory distress syndrome (ARDS). The reference esophageal balloon catheter method requires complex in vivo calibration and dedicated ventilator with auxiliary pressure port. A simple, inexpensive, accurate and reproducible method of measuring esophageal pressure would greatly facilitate the measure of transpulmonary pressure to individualize protective ventilation in the intensive care unit. Results We propose an air-filled esophageal catheter method without balloon, using disposable catheter and transducer that allows reproducible esophageal pressure measurements, and that does not require any specific ventilator equipment. We use a 49 cm-long thin low compliance polyvinyl 10 Fr suction catheter, positioned in the lower third of the esophagus and connected to an air-filled disposable blood pressure transducer bound to the monitor. To guarantee air transmission, the transducer is pressurized by an air-filled infusion bag allowing its integrated flush device to deliver continuous air flow and to obtain a stable esophageal waveform. Calibration requires simple zeroing the transducer open to atmospheric pressure. Esophageal pressures recorded on the monitoring are expressed in mmHg and need to be converted in cmH2O. We tested our novel method in 10 consecutive intubated patients with severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) infection. We calculated the target transpulmonary pressures for protective lung and diaphragm ventilation, both in passive and spontaneously breathing conditions. Esophageal to airway pressure change ratio was close to one in both conditions (median [P25;P75] = 0.94 [0.92;1.00] and 0.98 [0.96;1.01]). We adjusted ventilator settings towards recommended pressure targets to limit atelectrauma, barotrauma, inspiratory effort and lung stress, by modifying positive end-expiratory pressure, tidal volume, or inspiratory pressure accordingly. Conclusions We propose a simple, inexpensive and reproducible method for esophageal pressure monitoring with an air-filled esophageal catheter without balloon. It holds the promise of widespread bedside use of transpulmonary pressure-guided protective ventilation in patients with ARDS.

Lead, Zinc, Copper, and Cadmium Content of Water from South Australian Rainwater Tanks

Rainwater is consumed for drinking water in many parts of Australia, either preferentially over municipal water or in regional or remote areas, because rainwater is the primary source of water. Previous rainwater studies in other areas in Australia have shown the levels of some metals to be above the Australian Drinking Water Guidelines (ADWG). This study assessed the level of metals in rainwater harvested in the Adelaide region. Water samples were collected from 53 tanks from three different sampling corridors. A total of 365 water samples were analysed for lead, zinc, copper, and cadmium using atomic absorption spectrophotometry. In 47 out of the 53 tanks, lead was above the ADWG of 0.01 ppm in at least one sample (with 180/365 samples above 0.01 ppm). Zinc was above the ADWG (3.0 ppm) in 53/365 samples, copper was above the ADWG (2.0 ppm) in eight samples out of 365 samples, and cadmium was above the ADWG (0.002 ppm) in 19 samples out of 365 samples. These data are consistent with other studies of rainwater quality in Australia. Comparisons of levels of metals and volume of rainfall in the sampling and preceding month, roof material, and tank material, the presence of a first-flush device, sampling corridor, and sample pH showed that the roof material was related to higher levels of metals. There was a significant relationship between sampling corridors and the levels of lead and zinc. Nine of the tanks surveyed had filters installed. There was a small, but statistically significant, decrease in the levels of metals that passed through a filter prior to collection but, in those samples, filters did not remove metals to below guideline concentrations. An estimate of exposure, and a brief discussion of health risks as a result of exposure to metals, is presented.

Percutaneous Transtracheal Jet Ventilation with Various Upper Airway Obstruction

A “cannot-ventilate, cannot-intubate” situation is critical. In difficult airway management, transtracheal jet ventilation (TTJV) has been recommended as an invasive procedure, but specialized equipment is required. However, the influence of upper airway resistance (UAR) during TTJV has not been clarified. The aim of this study was to compare TTJV using a manual jet ventilator (MJV) and the oxygen flush device of the anesthetic machine (AM). We made a model lung offering variable UAR by adjustment of tracheal tube size that can ventilate through a 14-G cannula. We measured side flow due to the Venturi effect during TTJV, inspired tidal volume (TVi), and expiratory time under various inspiratory times. No Venturi effect was detected during TTJV with either device. With the MJV, TVi tended to increase in proportion to UAR. With AM, significant variations in TVi was not detected with changes in any UAR. In conclusion, UAR influenced forward flow of TTJV in the model lung. The influence of choked flow from the Venturi effect was minimal under all UAR settings with the MJV, but the AM could not deliver sufficient flow.

Risk in the mist? Deriving data to quantify microbial health risks associated with aerosol generation by water-efficient devices during typical domestic water-using activities

The aim of this study was to address existing data gaps and to determine the size distribution of aerosols associated with water-efficient devices during typical domestic activities. This information is important to assist in understanding infection spread during water-using activities and in designing water regulations. Three water-using scenarios were evaluated: i) showering using a water-efficient showerhead; ii) use of a high pressure spray unit for cleaning cars and iii) toilet flushing using a dual flush low volume flush device. For each scenario a control condition (conventional lower efficiency device) was selected for benchmarking purposes. Shower module results highlighted the complexity of particle generation and removal processes and showed that more than 90% of total particle mass in the breathing zone was attributed to particle diameters greater than 6 μm. Conversely, results for car washing experiments showed that particle diameters up to 6 μm constituted the major part of the total mass generated by both water-efficient and conventional devices. Even under worse case scenario conditions for toilet flushing, particle measurements were at or below the level of detection of the measuring instrumentation. The data provide information that assists in health risk assessment and in determining future research directions, including methodological aspects.

Time-dependent Pressure Distortion in a Catheter–Transducer System

Background Distortion of the pressure wave by a liquid-filled catheter-transducer system leads most often to an overestimation in systolic arterial blood pressure in pulmonary and systemic circulations. The pressure distortion depends on the catheter-transducer frequency response. Many monitoring systems use either mechanical or electronic filters to reduce this distortion. Such filters assume, however, that the catheter-transducer frequency response does not change over time. The current study aimed to study the changes with time of the catheter-transducer frequency response and design a flush procedure to reverse these changes back to baseline. Methods An in vitro setup was devised to assess the catheter-transducer frequency response in conditions approximating some of those met in a clinical environment (slow flushing, 37 degrees C, 48-h test). Several flush protocols were assessed. Results Within 48 h, catheter-transducer natural frequency decreased from 17.89 +/- 0.36 (mean +/- SD) to 7.35 +/- 0.25 Hz, and the catheter-transducer damping coefficient increased from 0.234 +/- 0.004 to 0.356 +/- 0.010. Slow and rapid flushing by the flush device built into the pressure transducer did not correct these changes, which were reversed only by manual fast flush of the transducer and of the catheter. These changes and parallel changes in catheter-transducer compliance may be explained by bubbles inside the catheter-transducer. Conclusions Catheter-transducer-induced blood pressure distortion changes with time. This change may be reversed by a manual fast flush or "rocket flush" procedure, allowing a con. stant correction by a filter.