Week 8 Scavenging System

Question 1

What is the size of the outlet connection (of the gas collecting assembly) and why is this important?

Answer 1

• 30 mm male fitting connection

SIZE OF CONNECTIONS IS IMPORTANT SO THAT IT DOESN’T CONNECT TO OTHER COMPONENTS OF BREATHING SYSTEM.

Question 2

Describe the components of an open, active scavenging system.

Answer 2

• no need for positive or negative pressure relief valves
• open to atmosphere via “relief ports” in resevoir, avoiding buildup of positive or negative pressures
• removes risk of barotrauma or removal of fresh gas from breathing circuits
• requires use of central vacuum system and a resevoir
  
  • open canister
  • size should allow for high waste gas flows
• gas enters the system at the top of the canister and travels through a narrow inner tube to the base
• VACUUM CONTROL VALVE CAN BE ADJUSTED
  
  • must be > or = to excess gas flow rate to prevent OR pollution
    
    • too much suction entrains room air into the scavenger
    • too little suction vents scavenged gas into the OR

Question 3

Describe a passive disposal assembly. What are the advantages/disadvantages?

Answer 3

• pressure is raised above atmospheric by the patient exhaling, manual squeezing of the resevoir bag or ventilator (needs positive pressure)
• waste gases directed out of the building via:
  
  • an open window
  • a pipe passing through an outside wall
  • an extractor fan vented to the outside air
• ADVANTAGES
  
  • inexpensive to setup
  • simple to operate
• DISADVANTAGES
  
  • may be impractical in some buildings

Question 4

Describe the scavenging interface.

Answer 4

• most critical component of the scavenging system
• prevents pressure increases or decreases in the scavenging system from being transmitted to the breathing system
• also called the balancing valve, or balancing device
• interface limits pressures immediately downstream of the gas - collecting assembly to between -0.5 cm - +3.5 cm H2O.
• should be situated as close to gas - collecting assembly as possible
• inlet should be 30 mm male connector

Question 5

Describe a proper scavenging system check.

Answer 5

• ensure proper connections between the scavenging system and both APL valve and ventilator relief valve and waste - gas vacuum
• FULLY OPEN APL valve and occlude Y piece
  
  • (not creating any pressure within the system)
• With minimum O2 flow, allow scavenger resevoir bag to collapse completely and verify that pressure gauge reads zero
  
  • APL scavening off all gas
  • APL valve fully functional
• With the O2 flush valve activated, allow scavenger resevoir bag to distend fully, and then verify that pressure gauge reads less than 10 cm H2O pressure
  
  • (APL valve should be open fully still, gas should be scavenged off to ensure APL valve functional)

Question 6

Distinguish between open, closed, active, and passive systems.

Answer 6

Question 7

What is the purpose of the gas collecting assembly and where is it located?

Answer 7

• Captures excess gases at the site of emission (breathing circuit)
• Located at the APL valve in spontaneous ventilation
  
  • controls the amount of gas that remains in the circuit and the amount that is released to the scavenger
• located at the ventilator spill valve in mechanical ventilation
  
  • controls the amount of gas that remains in the circuit and the amount that is released to the scavenger
• Delivers them to the transfer means

Question 8

What is the gas disposal tubing and how does it differ in a passive system vs an active system?

Answer 8

• connects the scavenging interface to the disposal assembly
• should be different in size and color from the breathing system
• PASSIVE SYSTEM
  
  • hose short and wide
  • tube running overhead ideal to prevent accidental obstruction and kinking
• ACTIVE SYSTEM
  
  • must be connected to a DISS connector

Question 9

What is the transfer means and what are the features of this system?

Answer 9

• Exhaust tubing or hose and transfer system
• conveys gas from collecting assmbly to the interface
• Features
  
  • usually a tube with female - fitting connectors on both ends
  • tubing - short and large
    
    • ​carries a high flow of gas without a significant increase in pressure or resistance
  • kink resistant
  • must be different from breathing tubes
    
    • color coded yellow and stiffer plastic, sometimes black, should be a different color

Question 10

List determinants of exposure to waste gases.

Answer 10

• amount of OR ventilation and air turnover
• functional status of anesthesia equipment
  
  • machine check, circuit check
• Your CRNA Practice
  
  • good mask fit
  • turn on anesthetic gas only with good mask fit
  • prevent fresh gas from entering atmosphere
  • turn off anesthetic gas before suctioning patient
  • evacuate anesthetic gases into scavenger at end of case
  • use cuffed ETT
  • monitor anesthesia machine for leaks
  • do not spill anesthetic agents
  • use TIVA
  • avoid N2O
  • use low fresh gas flows
  • pediatric steal induction

Question 11

Differentiate between the two types of closed scavenging interfaces.

Answer 11

• POSITIVE PRESSURE AND NEGATIVE RELIEF PRESSURE
  
  • used with active disposal systems - vacuum control valve adjusted so that the resevoir bag is NOT over distended or completely deflated
  • contains:
    
    • positive pressure relief valve
    • negative pressure relief valve
    • resevoir bag
  • gas is vented to the atmosphere is the system pressure exceeds 5 cm H2O
  • RA is entrained if the system pressure is less than -0.5 cm H2O
    
    • back up negative pressure relief valve opens at -1.8 cm H2O if the primary negative pressure relief valve becomes occluded
• POSITIVE PRESSURE RELIEF ONLY
  
  • single positive pressure relief valve opens when a max pressure is reached
  • passive disposal
    
    • no vacuum used, no resevoir bag needed

Question 12

List the 5 basic components of a gas scavenging system.

Answer 12

1. gas collecting assembly
2. transfer means
3. scavenging interface
4. gas disposal tubing
5. gas disposal assembly

Question 13

OSHA Recommended Levels of Anesthetic Gases in OR: Volatile Halogenated Anesthetic aone, Nitrous, Volatile Anesthetic with Nitrous Oxide.

Answer 13

• Volatile Halogenated Anesthetic Alone = 2 ppm
• Nitrous Oxide = 25 ppm
• Volatile Anesthetic with Nitrous Oxide = 0.5 ppm
  
  • (Think of 2nd gas effect)

Question 14

What is the most critical component of the scavenging system?

Answer 14

Scavenging interface

Question 15

Describe an active gas disposal assembly. What are the advantages/disadvantages?

Answer 15

• mechanical flow-inducing device moves the gases
  
  • (produces negative pressure in disposal tubing; must have negative pressure relief valve)
• connect the exhaust of the breathing system to the hospital vacuum system via an interface controlled by a needle valve
• ADVANTAGES
  
  • convenient in large hospitals where many machines are in use in different locations
• DISADVANTAGES
  
  • vacuum system and pipework is a major expense
  • needle valve may need continual adjustment
  • **most commonly used in hospitals**