PULSE OXIMETERS

Introduction:  Pulse oximetry, sometimes called the fifth vital sign, is a non-invasive method of measuring hemoglobin saturation (Spo2) by using a light signal transmitted through tissue. In addition to measuring …

Reservoir bag in Anaesthesia Machine

Most breathing systems have a reservoir (respiratory, breathing, or sometimes erroneously, rebreathing) bag. Most bags are composed of rubber or plastic and have an ellipsoidal shape so that they can …

SAFTY FEATURES OF ANAESTHESIA WORK STATION

INTRODUCTION Anaesthetic machines dispense a mixture of gases and vapours in varying proportions to control a patient’s level of consciousness, analgesia, or both during surgical procedures. The machine performs four …

Auto PEEP

Brochard (2002) defines intrinsic PEEP as “unintentional or un-measured end-expiratory hyperinflation”. Definition: Expiration usually occurs as a passive movement Resistance to air flow (eg. bronchospasm) results in decreased expiratory flow …

Physical principles of Flow Meters (Rotameter)

Rotameter is a particular kind of flowmeter based on variable area (variable orifice) and constant pressure  Principle.

Rotameter

 

 

This rotameter consists of three elements:-

i) A uniformely tapered flow tube (Thorpe’s tube),

ii) A bobbin or float (marker), and

iii) A measurement scale.

iv) The tube is positioned vertically with smallest diameter end of the tapered flow tube at the bottom.

 

 

 

 

Physical characteristics of the gas – because the annular space is tubular at low flow rates, flow is laminar and viscosity determines the gas flow rate and hence follows the Poiseuille’s law.

At low flow diameter is less than length – tubular, so laminar flow.

The annular space simulates an orifice at high flow rates, and turbulent gas flow then depends predominantly on the density of the gas and follows the Graham’s law.

So, at high altitudes since the density of the gases decreases, when higher flows are set in the flow meters, actual flow of gases will be higher than the set flows, as flow is inversely proportional to the square root of density as per Graham’s law.

Anaesthesia Machine – History and Evolution

Boyle’s machine was invented by Henry Edmund Gaskin Boyle in 1917. His machine was a modification of the American Gwathmey apparatus of 1912 and became the best known early continuous …