Proceedings of The Physiological Society
University College Dublin (2009) Proc Physiol Soc 15, PC73
Validating the Human Patient Simulator (HPS) as an educational tool: determining the relationship between alveolar ventilation and the alveolar partial pressure of carbon dioxide.
E. Lloyd1,2, G. Coverdale1, A. Thompson1, R. Helyer1,2
1. Department of Physiology and Pharmacology, University of Bristol, Bristol, United Kingdom. 2. AIMS Centre for Excellence in Teaching & Learning, University of Bristol, Bristol, United Kingdom.
The inversely proportional relationship between alveolar ventilation (VA) and the alveolar partial pressure of carbon dioxide (PACO2) is a fundamental principle of respiratory physiology and the practice of anaesthesia. PACO2 = Vco2 x K/VA where K is a constant and Vco2 is the rate of production of carbon dioxide (equation 1). The Human Patient Simulator (HPS) was developed by anaesthetists for trainees to learn about the clinical practice of anaesthesia in a safe environment. The aim of this study was to determine how PACO2 varies with alveolar ventilation in the HPS. The manikin was intubated under complete neuromuscular blockade and connected to a mechanical ventilator (Siemens 900C Servo Ventilator) set to deliver 21% Oxygen. The minute volume (VM) was adjusted by altering the respiratory rate and tidal volume and PACO2 was recorded after 20 minutes. Physiological dead space was determined using the Bohr method and used to calculate alveolar ventilation (alveolar ventilation = [tidal volume - physiological dead space] x respiratory rate) (equation 2). The relationship between alveolar ventilation and the PACO2 in the HPS showed good correspondence with the theoretical relationship predicted by the alveolar ventilation equation (equation 1). The limitations of the study include the assumptions that the rate of carbon dioxide production remained constant throughout the experiment and that twenty minutes was sufficient to achieve a new steady state following a change in minute volume. We conclude that the HPS is a valid educational tool for demonstrating the effects of hypoventilation and hyperventilation upon PACO2 under conditions of external mechanical ventilation with 100% neuromuscular blockade.
Where applicable, experiments conform with Society ethical requirements