Preventing and Treating Hypoxia: Using a Physiology Simulator to Demonstrate the Value of Pre-Oxygenation and the Futility of Hyperventilation.
BACKGROUND
Insufficient pre-oxygenation before emergency intubation, and hyperventilation after intubation are mistakes that are frequently observed in and outside the operating room, in clinical practice and in simulation exercises. Physiological parameters, as appearing on standard patient monitors, do not alert to the deleterious effects of low oxygen saturation on coronary perfusion, or that of low carbon dioxide concentrations on cerebral perfusion. We suggest the use of HumMod, a computer-based human physiology simulator, to demonstrate beneficial physiological responses to pre-oxygenation and the futility of excessive minute ventilation after intubation.


METHODS
We programmed HumMod, to A.) compare varying times (0-7 minutes) of pre-oxygenation on oxygen saturation (SpO2) during subsequent apnoea; B.) simulate hyperventilation after apnoea. We compared the effect of different minute ventilation rates on SpO2, acid-base status, cerebral perfusion and other haemodynamic parameters.


RESULTS
A.) With no pre-oxygenation, starting SpO2 dropped from 98% to 90% in 52 seconds with apnoea. At the other extreme, following full pre-oxygenation with 100% O2 for 3 minutes or more, the SpO2 remained 100% for 7.75 minutes during apnoea, and dropped to 90% after another 75 seconds. B.) Hyperventilation, did not result in more rapid normalization of SpO2, irrespective of the level of minute ventilation. However, hyperventilation did cause significant decreases in cerebral blood flow (CBF).


CONCLUSIONS
HumMod accurately simulates the physiological responses compared to published human studies of pre-oxygenation and varying post intubation minute ventilations, and it can be used over wider ranges of parameters than available in human studies and therefore available in the literature.
2. Department of Anaesthesiology, Cleveland Clinic, Cleveland, OH, USA.
Anna A
AA
Lerant
1. Department of Physiology and Biophysics, University of Mississippi Medical Center, University of Mississippi Medical Center, MS.
Robert L
RL
Hester
1. Department of Physiology and Biophysics, University of Mississippi Medical Center, University of Mississippi Medical Center, MS.
Thomas G
TG
Coleman
2. Department of Anaesthesiology, Cleveland Clinic, Cleveland, OH, USA.
William J
WJ
Phillips
3. Department of Emergency Medicine, University of Mississippi Medical Center, University of Mississippi Medical Center, MS, USA.
Jeffrey D
JD
Orledge
4. Clinical Simulation Centre, Pennsylvania State University College of Medicine, Hershey, PA, USA.
W Bosseau
WB
Murray
D000328:Adult; D001049:Apnea / Q000473:pathology; D002138:Calibration; D002245:Carbon Dioxide / Q000737:chemistry; D002560:Cerebrovascular Circulation; D003198:Computer Simulation; D006801:Humans; D006985:Hyperventilation; D000860:Hypoxia / Q000517:prevention & control* / Q000628:therapy*; D007442:Intubation, Intratracheal; D008297:Male; D008962:Models, Theoretical; D010100:Oxygen / Q000008:administration & dosage* / Q000737:chemistry; D010477:Perfusion; D012119:Respiration; D012984:Software; D013997:Time Factors
D002245:Carbon Dioxide; D010100:Oxygen
hyperventilation; intubation; preoxygenation; resuscitation; simulation