FLOW DYNAMICS OF PATIENT HOODS. S. D. Reimers, MS, PE.
Reimers Systems, Inc., Springfield, Virginia, USA
INTRODUCTION
What flow rate to use with a patient hood is a question with many implications. Hood flow rate primarily affects patient inspired CO2 levels, humidity level, hood noise level and oxygen consumption. It can also have substantial effects on breathing pressures and patient comfort. For many years, “standard practice” for management of patient hoods had been to supply them with a steady flow of about 28 to 30 actual liters per minute (alpm, actual volumetric liters at chamber conditions) regardless of the size of the patient. However, the scientific basis for that practice is obscure. This paper presents an analysis of the flow dynamics of patient hoods and the associated implications regarding hood flow rate selection.
METHODS
The model
The flow dynamics of patient hoods closely resemble those of neckdam style air diving helmets. The performance aspects of such helmets have been extensively studied by the navies of the world and are well known.1 Using the principles established for air diving helmets a mathematical model of a hood was created as shown in Figure 1.
Figure 1: Hood Ventilation Model