BT_SQ 1.6 Flow Measurement

Having observed a day’s silence in memory of those suffering yesterday, we return to our regular programming with some questions on an old favourite LO 😉

BT_SQ 1.6 Describe the methods of measurement applicable to anaesthesia, including clinical utility, complications and sources of error in particular:

· SI units

· Measurement of volumes, flows, and pressures, including transducers. 

· Measurement of blood pressure

· Measurement of cardiac output

· Measurement of temperature

· Oximetry

· Gas analysis, including capnography

· Methods used to measure respiratory function, including:

– Forced expiratory volume

–  Peak expiratory flow rate

–  Vital capacity

–  Flow-volume loops

–  Functional residual capacity and residual volume

TRUE/FALSE If exhaled gas is not warmed to patient temperature in a pneumotachograph, volume will be underestimated
TRUE/FALSE Volume is the area under a flow/time curve

TRUE/FALSE A pneumotachograph calculates flow from a known resistance and a measured pressure difference
TRUE/FALSE A pneumotachograph uses the hydraulic version of Ohms Law

TRUE/FALSE A pneumotachograph measures flow accurately only when it is turbulent

This is a Dräger flow sensor from one of the limbs of a circle circuit. If you look closely you can see a fine wire between the top two prongs. The wire between the lower two prongs isn’t shown so clearly. What principle is this flow sensor using?


Here are two different views of the sensor that modern GE machines use for measuring flow in a circle. The two tubes are hollow, and you can see on the photo on the left that they are open to the circuit. What principle is this flow sensor using? How do you think that it works?

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