Low Pressure System anaesthesia apparatus. pptx

Anaesthesia

1. Starts downstream of flow control devices. Pressure : Slightly above atmospheric pressure (Max upto 6- 8psig) & variable Components: Flowmeters Hypoxia prevention safety devices Unidirectional valves Pressure relief devices Common gas outlet Vaporizers & Mounting devices including backbar LOW PRESSURE SYSTEM

2. Flowmeters : (flow indicators, flow tubes, rotameters ) Flowmeter is a device that measures the flow rate of liquid or gas in a closed tube. It is used to control rate of flow of gas and adjust the proportion of gas delivered. The flow rate of gas through a tube will depend on the pattern of flow, whether laminar or turbulent. Types : Mechanical & Electronic Mechanical flowmeters : Based on principle that flow past a resistance is proportional to pressure Variable orifice type tubes (Thorpe tube), internally tapered narrowest at bottom Indicator: free to move inside the tube Gas passes through an annular opening between the indicator and the tube towards the outlet .

3. Flowmeter Assembly : Tube , Scale , Indicator, Stop at the top Lights Coding (color, touch, name ) Plastic shield ( for protection ) Flow rate depends on the viscosity (at lower flow rates) and density (at higher flow rates) of the gas itself and whether it passes through a tube or an orifice . The flow also depends on the diameter of the tube, the length of the tube and the pressure difference across the tube through which it has to pass.

4. Tubes: It is made up of Pyrex glass, transparent, nonconducting material. The length of the tube can vary from 65 mm to 230 mm, differs for different manufacturers of anesthesia machines . •" Single taper ( different tubes for low and high flows) *" Double taper (single tube with gradations for fine and coarse flows)

5. Indicator (Float or Bobbin) It is light weight, made of aluminium ; hence, it is free to move up and down the tube as per increase or decrease in the flow of gas. It is a free moving device within the tube, if it moves erratically, readings may be inaccurate. It contains antistatic material to prevent sticking to wall of flowmeter . STOP It is present at the top, it prevents the float from blocking the outlet and also prevents it from ascending to a point where it cannot be seen Hazard: Stop may break off and fall on the indicator, so it can register less flow than is actually occurring .

6. ARRANGEMENT OF DUAL FLOWMETER TUBES SERIES PARALLEL

7. Safety in flowmeters Link 25 proportion limiting control system ( Ohmeda ). A chain link between nitrous oxide and oxygen knobs prevents less than 25% oxygen delivery when nitrous oxide is used. It is a mechanical linkage (chain with a gear ratio of 2:1)with 14 tooth sprocket on nitrous oxide and 28 tooth sprocket on oxygen to maintain oxygen flow with nitrous oxide. Another safety feature to prevent the delivery of hypoxic mixture of gases going to the patient when oxygen is placed u pstream is the presence of baffles

8. AUXILIARY OXYGEN FLOWMETER Auxiliary oxygen flowmeters are separate from the back bar flowmeters and common gas outlet. They are self-contained having a flow control valve, flow indicator and outlet Nasal cannula or other oxygen delivery devices can be attached for the delivery of supplemental oxygen short tube with a maximum flow of 10 L/min It works both on pipeline and cylinder supply of oxygen CONCLUSION Flowmeters are an integral part of the low pressure system in anesthesia machines, accurately controls and measures gas flows to the common gas outlet. Understanding the basic principles and working of the flowmeters , makes it easy and safe to use. Care of the flowmeters and vigilance while using it will help in safe delivery of gases to the patient .

9. Unidirectional (Check) Valve They are usually part of the absorber assembly, the direction of intended gas flow is permanently marked on the valve housing or near its associated port with either a directional arrow or with the marking inspiration or expiration so that it is visible to the user. Pressure Relief Device Some machines have a pressure relief device near the common gas outlet to protect the machine from high pressures. This valve opens to atmosphere and vents gas to atmosphere if a preset pressure is exceeded . Common (Fresh) Gas Outlet The common (fresh) gas outlet receives all of the gases and vapors from the machine and delivers the mixture to breathing system. Some outlets have a 15-mm female slip-joint fitting (that will accept a tracheal tube connector ), with a coaxial 22-mm male connector. They may also have a manufacturer-specific fitting. The common gas outlet should not be used to administer supplemental oxygen to a patient,which delays use of the breathing system if an emergency arises. Another potential problem is that a vaporizer on the back bar may be accidentally left ON, leading to undesired administration of inhalational agent .

10. Vaporizers A vaporizer is a device that changes a liquid anesthetic into its vapor and adds a “clinically useful” amount of this vapor to the fresh gas flow (FGF) or the breathing system. The ideal vaporizer should be lightweight , robust and durable •Easy to transport •Corrosion and solvent resistant •Leak proof •Economical and safe to use •Require minimal servicing •Accurate over a wide range of: –FGF –Liquid agent levels –Ambient pressures –Ambient temperatures •Unaffected by: –Heat loss due to vaporization –Pressure changes downstream of the vaporizer –Tilting or tipping •Compatible with vaporizer interlock systems.

11. VAPORIZER MOUNTING SYSTEMS Mounting systems can be permanent or detachable. Permanent Mounting Permanent mounting systems require tools to remove or install a vaporizer on the anesthesia machine. There is less physical damage to vaporizers and fewer leaks. The problems with permanent mounting are inadequate number of mounting locations to accommodate all the vaporizers that are likely to be needed . If there is a malfunction and the vaporizer needs to be exchanged , it cannot be easily removed especially with a case underway . Detachable Mounting Here the vaporizers can be mounted or removed without using tools. They are standard on most new anesthesia machines. The Select-a- tec system and a similar system from Dräger Medical are widely used. There is no interchangeability. The Select-a- tec system consists of a pair of port valves for each vaporizer position. Each vaporizer has a mounting bracket which contains two plungers (spindles), which fit over the port valves. A seal is formed between the vaporizer and the port valves due to the weight of the vaporizer and the O-rings. On the back of each vaporizer is a locking lever .

12. The Dräger Medical mounting system has different dimensions. The Vapor® 2000 vaporizer must be in “T ” (travel ) position before it can be unlocked from the machine. This position isolates the vaporizing chamber and prevents liquid from passing into the bypass during the time that the vaporizer is not on the machine Advantages •More compact anesthesia machine as fewer mounting locations needed. Replacement is possible during a case •If malignant hyperthermia is a potential problem, the vaporizers can be removed altogether. Disadvantages •Partial or complete obstruction to gas flow can occur due to misalignment •Potential for leaks is high, a common leak source is an absent or damaged O-ring or if the locking lever is unlocked •Miscellaneous instruments placed on the vaporizer— syringes for cuff inflation—may interfere with the locking and cause leaks or render the vaporizer nonfunctional

13. HAZARDS Misfilling , an unlikely occurrence in currently used vaporizers Tipping :Tipping is unlikely when permanent mounting is in use . If detachable mounting is used, vaporizers should be turned off completely Leaks :The two most common sites of leaks are an improperly sealed filling port and the O-rings if the vaporizer is wrongly seated. most likely during filling or draining. Overfilling can occur if the vaporizer is tilted. Will lead to loss of surface area and decrease in vaporization . No Output The lack of output will cause awareness. The most common cause is an empty vaporizer. Reversal of Flow Flow reversal occurs if there is misalignment of parts after servicing . This will lead to increased output Projectile : In the MRI suite, vaporizers should be firmly secured to the back bar if ferromagnetic material is present, the vaporizer may act as a projectile. SAFETY FEATURES OF VAPORIZERS •Clear color-coding indicator on the vaporizer and agent bottle •Agent specific filling systems with sealed bottles •Agent level indicators •Mounting systems with interlock to prevent simultaneous use of two vaporizers •Filling port is low to avoid overfilling •Electronic vaporizers have audiovisual alarm systems which detect malfunction—tilting, low agent and low temperature •Agent monitoring allows detection of misfilling , overdose and low output. The use of this monitor prevents incidences of accidental awareness .