Anesthesia Physics

Anesthesia Physics are the very basics that involve the application of the laws of physics in anesthesia. Some knowledge of Physics is very important for anesthetists in their daily practice.

The following are the important gas laws in Anesthesia Physics:


At a constant temperature, volume of gas is inversely proportional to the pressure


At a constant pressure, volume of gas is directly proportional to temperature.


The rate of diffusion of gas is inversely proportional to square root of their molecular weight.

Partial Pressure Of Gas

It is the pressure exerted by a gas in a gaseous mixture.


Vapour is the gaseous form of a liquid.


The number of molecules contained in one gram molecular weight of any compound. It is 6.23x 10 to the power of 23


In Anesthesia Physics the flow of gases may be either laminar or turbulent.


Laminar flow is produced when the gas pass through straight tube i.e when the flow is smooth. Laminar flow is more dependent on viscosity. At laminar flow Bernoulli’s law is applicable which states that flow rate is directly proportional to pressure gradient and fourth power of radius of tube and inversely proportional to viscosity and length. The Bernoulli’s law is an important consideration in Anesthesia Physics.


Turbulent flow is produced if flow rate is very high or if gas passes through bends and constrictions. In this the flow is rough. Reynold’s number must exceed to 2000 for turbulence to develop.

Turbulent flow is more dependent on density.


This is another important principle in Anesthesia Physics. When a fluid or gas passes through a tube of varying diameter, the pressure exerted by fluid (lateral pressure) is minimum where velocity is maximum (pressure energy drops where kinetic energy increases:  Bernoulli’s law).
This principle is very much utilized in anesthesia. By increasing flow rate (velocity) through narrow constriction we can create subatmospheric pressure. A lot of equipment like venturi masks, jet ventilation and suction apparatus work on this principle.

These principles of Anesthesia Physics are very valuable to an anesthetist.


  1. girija choudhary March 24, 2011
  2. Pras April 10, 2011

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