Breathing Systems Flashcards
What 4 factors affect rebreathing?
Fresh gas flow, apparatus dead space (from Y to alveoli), breathing system design (closed vs open vs semi-closed) and empty space (circuit, canister, reservoir bag, ventilator).
Name 3 effects of rebreathing?
Heat and moisture retention, altered carbon dioxide and agent concentrations.
How do you avoid hypercarbia with increased dead space?
Minute ventilation must increase (alveolar ventilation = VE - VD).
Name 4 common features of non-rebreathing circuits.
Low resistance, less dead space/empty space, lack of unidirectional valves and lack of CO2 absorption.
Name the most popular non-rebreathing circuit and what feature makes it so.
Mapelson-D. Excess gas scavenging is easy and most efficient during controlled ventilation.
2 factors affecting resistance
Width and length of tubing
Why should a spontaneously breathing patient under anesthesia on a vent always be assisted?
Any breathing circuit creates resistance to gas flow and increases work of breathing.
Advantages of rebreathing
Cost reduction, increased warmth and humidity of inspired gases and decrease of OR contamination.
What is higher FGF associated with?
Higher FGF is associated with less rebreathing.
The higher the FGF the more gas concentration in circuit will resemble that at the common gas outlet.
What does the Bain modification to the Mapelson involve?
Placement of the FGF through the expired gases to heat inspired gases.
Advantages of NRB system
Inexpensive, rugged, excellent method to deliver positive pressure ventilation, less dead space, in Bain system inspiratory limb heated by exhaled gases, low resistance, lightweight, changes in fresh gas concentrations result in rapid changes, no CO2 or compound A.
Disadvantages of NRB
High FGF required (1.5 times MV) with resulting pollution and economic waste, inspired heat and humidity low, requires frequent adjustment in FGF, not for pt with MH history ( inability to inc FGF enough to blow off CO2.
Reasons for decline of NRB
Modern efficient ventilators, conservation of heat with rebreathing circuits and waste gas management.
Advantages of a circle system
Economical: expired oxygen and anesthetic vapor are re-circulated and reused.
Fresh gas flow and anesthetic agent utilization are minimized compared with a NRB system.
Humidifies inspired gas, preserving heat and moisture of the pt.
Disadvantages of the circle system
Complex, less portable, opportunities for disconnect, unidirectional valves may malfunction, inc dead space, inc “empty space” (longer diffusion time).
