The Anesthesia Gas Machine Karen Garcia N747 Evidence Based Practice for Nurse Anesthesia

Components of the Gas Machine Valves High Pressure System Immediate Pressure System Low Pressure System Circle System/Breathing Systems Will only touch on cylinders to prevent a long lecture! Will go over review questions for us to discuss.

Valves Free Floating/Check Valves Ball and Spring Diaphragm Valves Picture is of a check valve. Note how it is unidirectional.

Free Floating/Check Valves Unidirectional Located in various parts of the machine Diameter Index Safety System Prevents oxygen cylinder gas from escaping the anesthesia machine and going out hospital wall Check Valve between Vaporizer Outlet and Common Gas Outlet Prevents reversal of flow to vaporizer Not Present on all machines (Ohmeda only)

“Ball and Spring” Type Valve You supply the energy for this valve! Oxygen Flush Valve Pressurized at 40-50 psi from wall or cylinder Oxygen delivered to patient at 35-75 L/minute May cause barotrauma Is this considered high, intermediate, or low pressure? Intermediate

Diaphragm Valves Regulate and Reduce Pressure First Stage Regulator Cylinder pressure decreased to 45 psi Why is cylinder pressure slightly less than pipeline pressure? Second Stage Regulator Receives wall pressure oxygen or from first stage regulator Only Ohmeda machines Slightly less than pipeline pressure to prevent depletion of cylinder contents when attached to pipeline

Quick Review Questions: Cylinders What is the cylinder pressure and capacity for oxygen? Cylinder pressure and capacity for nitrous oxide? Who regulates marking, labeling, filling, handling, and transportation of compressed gas cylinders? 1900-2200 psi; 660L 745-750 psi; 1590L Dept of Transportation

Cylinders (continued) Each valve stem on the cylinder has a safety device under which hazardous conditions of excessive heat or fire will cause the cylinder to become exhausted. What is this safety device called? What is this safety device composed of? At what temperature will it melt? Wood’s Metal Composed of bismuth, lead, tin, and cadmium (BLT with Cheese) Melts at 200 deg F

High Pressure System Think Cylinder Pressure! Components Cylinder Pressure Regulator (aka First Stage Regulator) Cylinder Pressure Gauge Hanger Yoke, Yoke Block, and Yoke Plug Yoke Block with Check Valves (Free Floating) Pin Index Safety System Pretty much what is exposed to cylinder pressure

Hanger Yoke Valve and the PISS Yoke Assembly has pins for E Cylinders to fit on Pin Index Safety System What is the pin index for Oxygen? Nitrous Oxide? Air? Failure to open cylinder valve will result in no gas flow to anesthesia machine Hanger Yoke Valve Acts as a “safety” valve Minimizes transfilling between cylinders Opens with pressure and closes with pressure Considered unidirectional….so what kind of valve is this? 2, 5 3, 5 1, 5 Check Valves  they are unidirectional

Cylinder Pressure Gauge Reflects cylinder pressure Bourdon Pressure PSI in tank exerted on small piece of copper that is bent into a curve, sealed and linked to clock like mechanism The higher the pressure the more it wants to straighten out which then turns the pointer

Intermediate Pressure System Think Pipeline Pressure Oxygen Second Stage Regulator Ventilator Power Inlet Pipeline Inlets, Check Valves, Pressure Gauges Flow Meter Valves Oxygen Pressure Failure Devices Flush Valve 40-50 psi!

Oxygen Second Stage Regulator Located downstream from oxygen supply source Supplies constant pressure to the oxygen flow control valves regardless of fluctuating line pressures Reduces oxygen pressure to 12-19 psi The pressure shut off VALVES have a higher threshold of 20-30 psi. Ensures that oxygen is the last gas flow to decrease if oxygen pressure falls

Oxygen Flush Valve Separate line to flush valve comes from a common source to the hospital pipeline DISS and cylinder yokes Used for emergency pressurization on circuit when you lose pressure delivery Remember, it is what type of valve? Ball and spring type

Low Pressure System Flow Meter Tubes Vaporizers Check Valves Common Gas Outlet Usually around 16 psi is considered low pressure system

Flowmeter Tubes Thorpe Tubes Gas flows range from 200 mL to 15 L Variable Orifice Design Larger diameter at top than bottom The higher the ball/float, the more turbulent the air Gas flows range from 200 mL to 15 L

Flowmeter Tubes (continued) Series of 2 flowtubes per gas/air Left hand tube = fine flow tube Right hand tube = cooarse flow tube Traditional flowmeters calibrated at atmospheric pressure and room temperature of 20 degrees Celsius How many “torr” is one atmosphere? When flowtubes are used at high altitudes, is the actual flow higher or lower than indicated? 1 atm = 760 torr High altitudes = actual flow is higher than indicated….this is because atm pressure decreases with altitude At low altitudes, actual flow is lower

Common Gas Outlet Most susceptible to leakage Point of exit for gas from anesthesia machine A fresh gas entry port/delivery tube through which gases are delivered from the anesthesia machine to the breathing circuit system

Vaporizers Variable Bypass Flow Over Wick Design

Vaporizers Gas/Vapor Blend (AKA Desflurane Vaporizer)

Circle System Components CO2 Absorber APL Valve Common Gas Outlet Reservoir Bag Inspiration and Expiration Check Valves (Flutter Valves) Corrugated Tubing with Patient Mask

Carbon Dioxide Absorbers Soda Lime Final Products Calcium Carbonate Sodium Hydroxide Potassium Hydroxide Water and Heat Baralyme Final Products Calcium Carbonate Barium Hydroxide Water and Heat These are final products when CO2 reacts with soda lime….baralyme…. 4-8 mesh Allows rebreathing Exothermic reaction What size mesh is considered acceptable for granule size?

Other Nuances to Remember Scavenging System Link 25 system for hypoxic guard system Draeger or Ohmeda? Oxygen Failure Protection Device is NOT an all or none phenomenon What happens when the vaporizer is tipped then leveled? Will the carrier flow carry more or less agent to the patient? Scavenging System – receives gas from APL and ventilator; can be passive or active – basically with or without suction Link 25 – Ohmeda OFPD – Draeger More agent to patient

Question 1 The devices that prevents reverse flow of gases from the anesthesia machine to the pipeline or atmosphere is: A. Diameter Index Safety System B. Check Valve C. Pin Index Safety System D. Pressure Gauge B. A check valve is located downstream from the inlet. It prevents reverse flow of gases from the machine to the pipeline or to the atmosphere.

Question 2 All of the following are functions of the check valve EXCEPT: A. It reduces pressure in the system. B. It minimizes leakage from an open cylinder to the atmosphere if one cylinder is absent. C. It minimizes gas transfer from a cylinder at high pressure to one with lower pressure. D. It allows uninterrupted gas flow from one cylinder to another. A. Pressure in the system is reduced by pressure-reducing valves. The check valves mainly control the forward flow of gases through the system.

Question 3 The component of the anesthesia machine that changes the pressure of an incoming gas to a pressure suitable for use in the anesthesia machine: A. Safety Valve B. Pressure Increasing Valve C. Pressure Regulator D. Check Valve C. Each cylinder supply source has a pressure reducing valve known as the cylinder pressure regulator. It reduces the high and variable storage pressure to a lower more constant pressure suitable for use.

Question 4 The first stage regulator reduces gas pressure to: A. 15 psi B. 60 psi C. 20-30 psi D. 45-50 psi D. The first stage pressure regulator reduces the gas pressures from their high cylinder level to 45-50 psi. The second stage pressure regulators then reduce the pressure event further for specific gases.

Question 5 The second stage regulator reduces O2 pressure to: A. 45 psig B. 12-19 psig C. 10 psig D. 45-55 psig B. Second stage regulators reduce O2 pressure to 12-19 psi. the pressure shut off valves have a higher threshold of 20-30 psi. this ensures that oxygen is the last gas flow to decrease if oxygen pressure falls.

Question 6 Where is the second stage regulator located? A. At the hanger yoke B. Just before flowmeter C. Just after flowmeter C. The second stage regulator is located downstream from the oxygen supply source. This regulator supplies a constant pressure to the oxygen flow control valves regardless of fluctuating line pressures.

References Nagelhout, J.J. (1999). Review of Nurse Anesthesia. Philadelphia: Saunders. Nagelhout, J. J. & Plaus, K. L. (2014). Nurse Anesthesia. St. Louis: Elsevier Saunders. Memory Master: Questions & Answers for the Student Registered Nurse Anesthetist (2012). Valley Anesthesia. Morgan, G. E., Mikhail, M. S., & Murray, M. J. (2006). Clinical Anesthesiology (4th ed). New York: McGraw-Hill. Teich, A. & Schaus, S. S. (2014). A Comprehensive Certifying Examination Review Course Manual. Valley Anesthesia Educational Programs. Wiltse-Nicely KL and Macksey LF. CRNA Certification Exam Review. Jones and Bartlett Learning: Burlington, MA; 2014.

Questions?