In vitro validation of a Pitot‐based flow meter for the measurement of respiratory volume and flow in large animal anaesthesia  Yves PS Moens, DVM, PD, PhD, Diplomate ECVAA, Peter Gootjes, Ing, Jean‐Claude Ionita, DVM, Erkki Heinonen, Lic Tech, PhD, Urs Schatzmann, DVM, PhD, Diplomate ECVAA  Veterinary Anaesthesia and Analgesia  Volume 36, Issue 3, Pages 209-219 (May 2009) DOI: 10.1111/j.1467-2995.2009.00449.x Copyright © 2009 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia Terms and Conditions

Figure 1 Design of the Pitot tube based sensor. (a) Lateral view of the D‐lite (left) and of the H‐lite (right). The two pressure‐sensing ports (large arrows) and the gas sampling port (small arrow) are shown for each sensor. (b) Design of the sensor head (D‐lite). End view through the tube (left) showing the star shaped resistor element, and a cross sectional view (right) showing the two Pitot tubes (P1 and P2) for pressure measurement, alongside the gas sampling port (a). Veterinary Anaesthesia and Analgesia 2009 36, 209-219DOI: (10.1111/j.1467-2995.2009.00449.x) Copyright © 2009 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia Terms and Conditions

Figure 2 Diagram of the combination of the Pitot tube‐based flow sensor (two pressure pick‐ups and one gas sampling port) and the host monitor. Sensor no. 2 monitors flow. Sensor no. 1 has a higher range of pressure sensitivity and applies corrections related to varying airway pressure. Veterinary Anaesthesia and Analgesia 2009 36, 209-219DOI: (10.1111/j.1467-2995.2009.00449.x) Copyright © 2009 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia Terms and Conditions

Figure 3 Relationships between the output of the differential pressure transducer (mmH2O) and static airflow for the large remodelled sensor (H‐lite) and for the D‐lite. • = D‐lite = H‐lite . Veterinary Anaesthesia and Analgesia 2009 36, 209-219DOI: (10.1111/j.1467-2995.2009.00449.x) Copyright © 2009 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia Terms and Conditions

Figure 4 Linear regression analysis of reference versus measured flows (50/50 mixture of O2 and N2,) using the D‐lite (a) or the H‐lite (b) sensor, combined with the host monitor (Capnomac Ultima). Positive values correspond to inspiratory flow, and negative values correspond to expiratory flows. The linear regression equations are reported. Veterinary Anaesthesia and Analgesia 2009 36, 209-219DOI: (10.1111/j.1467-2995.2009.00449.x) Copyright © 2009 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia Terms and Conditions

Figure 5 Box plot showing bias expressed as percent of the reference volume determined with Capnomac Ultima/H‐lite for a reference volume of 5 L (inspiration, ambient air) as a function of different calibration volumes used. Each box represents data from the 25th to 75th percentiles. The horizontal line within each box represents the median value, and the whiskers represent the range of values. Veterinary Anaesthesia and Analgesia 2009 36, 209-219DOI: (10.1111/j.1467-2995.2009.00449.x) Copyright © 2009 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia Terms and Conditions

Figure 6 Box plot showing conversion factors for inspiratory volumes of 3, 5 and 7 L. These factors were determined with S/5/H‐lite as a function of the gas mixture used: A = 21% O2/79% N2 (ambient air), B = 100% O2, C = 40% O2/60% N2O, D = 80% O2/4% CO2/2% isoflurane‐balance N2, E = 100% N2O). Grey circles are outliers. All notations as in Fig. 5. Veterinary Anaesthesia and Analgesia 2009 36, 209-219DOI: (10.1111/j.1467-2995.2009.00449.x) Copyright © 2009 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia Terms and Conditions

Figure 7 Box plot showing conversion factors for inspiratory volumes of 3, 5 and 7 L grouped, using ambient air. These factors were determined with S/5/H‐lite as a function of the peak flow rate displayed on the host monitor. Grey circles are outliers. All notations as in Fig. 5. Veterinary Anaesthesia and Analgesia 2009 36, 209-219DOI: (10.1111/j.1467-2995.2009.00449.x) Copyright © 2009 Association of Veterinary Anaesthetists and American College of Veterinary Anesthesia and Analgesia Terms and Conditions