Lecture 4: Breathing Systems, Scavenging, and Intubation Supplies

Where are common areas to find a leak in the breathing system?

• neck of reservoir bag

• breathing circuit hoses

• any hose connection

• inlet/outlet to vaporizer

• one-way valves

• CO2 absorbent canister

• flow meter

What are the important safety concerns of the breathing machine?

• pressure check (aka leak test) any breathing system (and machine) prior to use

• pollution to environment and personnel

• patient may wake up because not getting enough anesthetic

• patient may become hypoxemic if not getting enough O2

What is the function of the breathing systems and what are the 2 main types?

deliver gases and eliminate exhaled CO2

2 main types: rebreathing, non-rebreathing

True or false: rebreathing system (aka circle system), lower O2 flows than nonrebreathing system.

true

What are the components of the rebreathing system?

• fresh gas source

• unidirectional valves

• breathing hoses

• breathing system pressure gauge

• CO2 absorber

• APL valve

• reservoir bag

What is the pathway of gas in a rebreathing system?

gases flow in a one-way circular pattern → into patient via inspiratory hose → out of patient through expiratory hose

What prevents rebreathing of CO2 in a rebreathing system?

chemical absorption (sodasorb)

What are the advantages and disadvantages of rebreathing systems?

advantages: can use lower O2 flow rates; easy to set up and use

disadvantages: increased resistance for smaller patient; more components to work with

What are the recommended oxygen flow rates for a closed circle system, low-flow circle system, and a semi-closed circle system?

closed circle system: 4-11 mL/kg/min - oxygen flow approximates patient’s oxygen consumption, which varies with metabolic rate

low-flow circle system: 10-22 ml/kg/min - oxygen flow rate > than patient’s oxygen consumption

semi-closed circle system: 22-44 ml/kg/min - fresh gas inflow exceeds the uptake of oxygen by patient

What are the advantages and disadvantages of close circle systems?

• Advantages: more economical, retain more heat and humidity, and less likely to cause OR pollution

• Disadvantages: vaporizer accuracy compromised, depends on your assessment of O2, and CO2 absorption completely dependent on chemical absorbant

What are the advantages and disadvantages of low-flow circle systems?

• Advantages: economical, some heat and humidity retained, and reduced waste gas

• Disadvantages: slow to change anesthetic depth

What are the advantages and disadvantages of semi-closed circle systems?

• Advantages: N2 accumulation insignificant, rapid changes in inspired anesthetic concentration, CO2 partially eliminated via pop-off valve

• Disadvantages: less economical, more heat and humidity lost

What are these three rebreathing (circle) system hoses?

A. adult hose for patients 7-150 kg

B. pediatric hose for patients <7 kg

C. universal-F hose comes in adult and pediatric sizes

How does a pressure gauge on a breathing system differ from oxygen cylinder pressure gauge?

measure in mmHg where as oxygen cylinder pressure read in psi

What can occur when CO2 absorption canister is exhausted?

CO2 will accumulate in circuit → rebreathing of CO2 → respiratory acidosis

What are the methods/tools to determine when to change soda lime?

• capnography (increased inspired CO2 and ETCO2)

• color change (useful, but not reliable)

• lack of heat in canister

• hardness of granules

• clinical signs in patient

What are the components of a non-breathing system?

• fresh gas source

• expiratory limb or coaxial breathing hose

• open/close valve

• reservoir bag

What is the typical O2 flow rate?

150-300 ml/kg/min

Which patient should use a non-rebreathing system?

if < 3kg → always

if > 3kg → optional unless very large (not used for horses)

What are the advantages and disadvantages of a non-rebreathing system?

Advantages: less resistance to breathing for patient, little to no dead space and fewer components that can leak or malfunction

Disadvantages: higher O2 flow rates required to get rid of CO2 ➔ pollution to environment and can contribute to hypothermia; not as economical

What are the most commonly used non-rebreathing systems used in vet med?

Mapleson D (Bain circuit = modified Mapleson D)

Mapleson F (modified Jackson Rees circuit)

How can you prevent exposure to waste air gas?

• engage a scavenging system

• leak test the machine and breathing system prior to use

• use cuffed and correctly sized endotracheal tubes

• use a low-flow circle system if possible

• avoid mask and chamber inductions

• when disconnecting patient-turn off flow meter, vaporizer, empty gas from bag in to scavenging and occlude Y piece

• perform machine and equipment maintenance periodically

• adequate ventilation of areas where anesthetic gas exposure occurs

What are tips for safely filling or emptying vaporizers?

• Ideally wear a charcoal mask

• Always announce that you are filling a vaporizer if it must occur when other personnel are in the room

• Best to select a time late in the day (or first thing Monday morning) to refill vaporizers to minimize unnecessary exposure

• Replace cap on bottle when done

• Switch to key-fill vaporizers if possible

• Always turn vaporizer dial OFF before filling!

What are the 2 types of scavenging systems?

passive: charcoal absorption, to outside wall or window

active: central vacuum collection

What are the advantages and disadvantages of charcoal absorption?

advantages:

• absorbs halogenated anesthetic gases

• mobile; initial cost is low; easy to set up

disadvantages:

• does NOT absorb CO2 or N2O

• must be replace dafter gaining 50g of weight (8-12hrs of use)

• use limited to lower oxygen flow rates

• adds resistance

Generally, you want to use the largest size of endotracheal tube that will fit without causing trauma to the _______.

larynx

What is the most common type of ETT?

murphy

What is the term that describes the portions of the breathing passages that contain air, but there is no gas exchange (mouth, nasal passages, pharynx, trachea, end of ET tube/Y-piece)?

dead space

What is a murphy type ETT?

• “Murphy’s Eye” design - an oval hole positioned on the bevel facing the opening of the tube

• if distal end of tube becomes occluded, there is still air flow

What is the difference between a cuffed ETT under a low volume high pressure system vs high volume low pressure system?

low volume high pressure: take a small amount of air, but put a high amount of localized pressure on the tracheal mucosa

high volume low pressure: larger amount of air, but low pressure on the trachea and widely distributed

What are cole ETTs?

• uncuffed

• characterized by a “shoulder” near the distal end (laryngotracheal portion)

• designed to create a seal by using a smaller end to fit in the arytenoid carilages

• smaller portion goes in trachea

What are guarded or armored ETTs?

• made of silicone rubber

• have steel wire or nylon coil embedded in the wall

• resists kinking (good for awkward cases with poor visibility or significant neck bending)

• more expensive

How does a laryngoscope work and what are the benefits?

• Allows for visualization

• Light source (allows for quick detection of abnormal anatomy)

• Easier accessibility to airway

• Apply light pressure to base of tongue, just underneath epiglottis.

• Tilts larynx ventrally and opens glottis, frees up the epiglottis if still tucked underneath soft palate

What are the steps for correct endotracheal intubation?

1. preoxygenate patient 3-5 mins

2. at least 3 sizes ETT checked and ready + other supplies

3. assistant holds head, opens mouth, pulls tongue → person intubating grasps laryngoscope in one hand and ETT in other (pos. application of 0.2-0.5ml regular 2% lidocaine to arytenoids)

4. airway assessed for size ETT → ETT lubricated and passed between arytenoids, slight twisting motion may be needed

5. distal tip ETT should not extend past thoracic inlet

6. attach ETT adaptor to breathing circuit with oxygen turned on and capnograph attached → assess capnograph waveform to confirm placement and secure ETT In place

7. cuff inflation technique should occur next

8. confirm strong heartbeat and turn inhalant to predetermined value, assist w ventilation, instrument patient with monitors, and begin anesthetic record

What are some methods to confirm ETT placement?

• direct observation of ETT going into trachea

• capnograph reading from ETT registers high enough CO2 value

• feel breath from end of ET tube on hand

• auscultation of breath sounds bilaterally when breath give

• absence of two “tubes” palpated because ETT is inside the trachea

• feel the ETT sliding past tracheal rings, also use to guid depth of placement

What is the cuff inflation technique (aka minimal occlusion volume technique)?

• should be no escape of gas from ETT cuff when delivering a positive pressure ventilation (manual breath) and bag is squeezed to 20 cmH2O

• by ~25 cmH2O air should be able to escape around tube, if not some air should be removed from pilot balloon to prevent over inflation of the cuff

• recheck after patient asleep 10-15 min