Evaluation of tidal volume measurements of the anaesthesia device Tafonius® in vitro and in vivo

Abstract

The anaesthesiologic risk is higher in horses than in other domesticated animal species and thereby ventilation is a vital problem. The aim of this study was to evaluate the accuracy of the anaesthesia device Tafonius ® tidal volume measurements in vitro as well as in vivo. In an in vitro study the whole system was flushed by air to reduce the air moisture to a minimum. The preparation of the anaesthesia device was exactly the same, as if there was a surgery on a patient. But instead of a horse, a seven liter calibration syringe was connected to the Y-piece of the anaesthesia device and the whole system was flooded by pure oxygen. By touch screen on the monitor of the anaesthesia device, a CPAP (Continuous Positive Airway Pressure), a tidal volume of 20 liters and an airway pressure of 20 cmH 2 O were adjusted. The leakage test was repeated and the connections tightened until the leak was 168 mL gas per minute. All the measurements were made randomly, without breaks or changes of the adjustments. For tidal volume measurements a seven liter calibration syringe was used. A connecting piece was specially manufactured, to attach the syringe to the Tafonius ® without gas leakage.14 different tidal volumes were evaluated in a random order, covering the range from 500 mL to 7000 mL using 500 mL steps. To imitate respiration during anaesthesia, three respiratory rates were simulated: 30, 15 and 6 times per minute. All the measurements were performed in duplicate, once with NICO ® interconnected and once without it. The respiratory rates and tidal volumes were chosen in random order, as well as whether the flow meter was interconnected or not. In a in vivo study twenty-one patients with a mean weight of 516 kilograms submitted for elective surgery were included. All of them received a balanced anaesthesia regime (inhalation anaesthesia with isoflurane and constant rate infusion with medetomidine (3.5 mcg/kg/h) and controlled mechanical ventilation. 16 horses were positioned in dorsal and five in lateral recumbency. The flow meter NICO ® was connected ones a steady state in the plane of anaesthesia was reached. The flow meter was left during 38 to 190 breaths. A total of 2368 breaths were measured. Mean tidal volumes reached from 4107 mL to 8964 mL. In vitro data were analysed by descriptive statistics to determine measurement accuracy. Bland-Altman plots with limits of agreement (loa) were used to analyze in vivo data. The mean difference between the volume given by the calibration syringe and the volume shown on the Tafonius ® screen was -19.45 % (standard deviation 11%). The data stored on the computer showed an average difference of -20.5 % (standard deviation 15.57 %). Whether NICO ® was interconnected or not resulted in a change in accuracy of 0.36 % in the volume measurement of the Tafonius ® . The mean difference of the volume produced with the calibration syringe and the measured volume of the NICO ® was 0.73 % (standard deviation 4.3 %). The Bland-Altman analysis from NICO ® to Tafonius ® gave a lower limit of a...

Physiologic Factors Influencing the Arterial-To-End-Tidal CO2 Difference and the Alveolar Dead Space Fraction in Spontaneously Breathing Anesthetised Horses

“…All devices were calibrated following manufacturer’s guidelines before each anesthesia; the capnograph of the NICO device was calibrated with room air before each experiment (infrared sensor with a response time <60 ms and accuracy of ±2 mmHg) and the accuracy of the pneumotachograph was verified with a 100-mL calibration syringe before and after all measurements (allowed accuracy of ±3% following manufacturers guidelines for the calibration set-up). The accuracy of the volume measurement of the flow-partioning device used in our set-up in connection with the NICO device was verified in an in vitro experiment published elsewhere ( 25 ). The difference between the reading of the flow-partitioning device in combination with the NICO device and the 10 L calibration syringe was 0.73 ± 4.3% (mean ± SD).…”

Monitoring of tidal ventilation by electrical impedance tomography in anaesthetised horses

“…Interpretation of the results of this study assumes that spirometry is accurately measuring VT. The accuracy of the flow‐partitioning device in combination with the NICO spirometer was evaluated in an in vitro model using the same ventilator and circle system set‐up as in the study described here (mean difference less than 1%) . In an in vivo study using the flow‐partitioning device and NICO combination in anaesthetised horses limits of agreement were found to be within ±10% .…”

“…To measure the tidal volume (VT NICO ), a flow‐partitioning device connected to a human spirometry unit (NICO)j was used. The NICO device was calibrated following manufacturer's guidelines before each anaesthesia and the accuracy of the volume measurement of the flow‐partitioning device in conjunction with the NICO device and breathing system used in this study was verified in an in vitro experiment published elsewhere . The flow‐partitioning device was placed between the endotracheal tube and the Y‐piece of the circle system.…”

A Sensor for Spirometric Feedback in Ventilation Maneuvers during Cardiopulmonary Resuscitation Training

“…Therefore, the YF-S201 achieves the objective of measuring air volume entering the lung of CPR dummies in respiratory maneuvers providing spirometric results. As stated before, the incorporation of sensors such as those presented in [1,2,4,19,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41] is not feasible for this purpose due to, mainly, its high cost.…”

“…To perform spirometry, a spirometer is used, which can be: (i) of volume (sealed in water, piston, and bellows [35]); (ii) of flow (differential pressure or pneumotacometers [36], thermistors, Pitot and turbinometers [35]); or (iii) portable [37] of volume or flow [25]. The respiratory volume sensors used in these types of equipment have a high cost and some of them perform indirect measurements, discarding their application in medical simulators or dummies, as in the case of Hamiltonian sensors coupled to differential pressure sensors [38], flow mass sensors [39] and airflow meter [40] rotary or vibratory beam and shell flow meters [41].…”