药物诱导的麻醉.ppt

The state of general anesthesia is drug induced absence of perception of all sensations
PRINCIPLES OF THE ADMINISTRATION OF GENERAL ANAESTHETICS
Uptake and Distribution of inhalational general anesthetics
Depth of Anesthesia - Tension of anaesthetic agent in brain - controls - rates of induction and recovery
Tension and partial pressure are interchangeable terms
Tension in the arterial blood and brain are same and are determined by:
Concentration of the anaesthetic in the inspired air depends on rate of ventilation
Transfer of the gas from the alveoli to the blood
Decreased in disease (ex. emphysema)
Rate of transfer is determined by:
Solubility(Blood gas partition coefficient.)
Rate of blood flow(directly proportional to the .
Partial pressures of the agent in arterial and mixed venous blood.
Loss of the agent from the arterial blood to all the tissue of the body
ANAESTHESIA MACHINES
Are devices by which the anesthesiologist is able to deliver
Measured quantities of anaesthetic gases and oxygen through accurate flowmeters and with the use of special vaporizers it is possible to add the vapor of volatile anesthetic liquid to the gas stream. The mixture of oxygen and anaesthetic agent is then delivered to a breathing circuit for administration by Inhalation.
General Anesthetics are the most dangerous drugs
Therapeutic index ranges between 2-4
2-3 times dose causes circulatory failure
Oral dose delivers the total dose
When gas or vapor is inhaled only a small amount is absorbed
Whereas the rest is exhaled out in next 1-2 seconds
The drug reaches the brain by leaving the blood
Anaesthetic blood levels of these cannot be measures accurately
Concentrations in the lungs can be easily frequently and accurately be measured
The partials pressures of the anaesthetic in the lung and the brain are almost equal at equilibrium
Minimum Alveolar Concentration
MAC is the measure of potency of general anesthetics
It is the minimum alveolar concentration (MAC) at