Week 9 Ventilators and Airway Monitors Flashcards by Laura Baillie

Describe possible issues with piston ventilators.

refill even if a circuit disconnection occurs
if a circuit leak is present, piston may entrain RA through the leak → diluting oxygen and anesthetic agent
- associated risks
  - hypoxemia
  - awareness
- Alarm should alert the operator
positive pressure relief valve prevents excessively high breathing circuit pressure (60 to 80 cm H2O)

How well did you know this?

Not at all

Perfectly

Distinguish ICU vents and anesthesia vents.

ICU ventilators are more powerful allowing for greater inspiratory pressures and tidal volumes
CO2 absorber - anesthesia vents
ICU ventilators support more modes of ventilation
- Changing!!
Gas supplied by the ICU ventilator directly ventilates the patient
Anesthesia driving gas never reaches the patient
- 100% O2 in old machines
- Air/100% O2 in newer models

How well did you know this?

Not at all

Perfectly

Describe Pressure Support Ventilation as a mode of ventilation.

aid in normal breathing with a predetermined level of positive airway pressure
pt spontaneously breathing
PSV senses patient inspiratory effort (volume or flow) and delivers pressure support
results in larger TV than the patient would produce on their own
PSV is useful to support MV and control arterial CO2 for spontaneously breathing patients during maintenance and emergence

How well did you know this?

Not at all

Perfectly

How do you calculate the I : E ratio?

Time spent in inspiration
TI = TV / Flow rate
- TV = IBW * 5-7 ml/kg = ____ mL
- Flow rate = 4 - 6 X minute ventilation
  - MV = TV X RR
  - X 60 seconds
TE = (60 seconds / RR) - TI

How well did you know this?

Not at all

Perfectly

What is the formula for oxygen delivery?

Oxygen delivery = CO x O2 content

How well did you know this?

Not at all

Perfectly

Distinguish between ascending and descending bellows.

How well did you know this?

Not at all

Perfectly

Bellows are classified by direction of bellows movement during _________.

EXPIRATION

How well did you know this?

Not at all

Perfectly

How are we going to make sure that our ventilator settings are okay and that we are ventilating adequately?

PEtCO2

How well did you know this?

Not at all

Perfectly

Discuss volume as a parameter used to describe ventilation.

measure of the tidal volume delivered by the ventilator to the patient
volume of gas patient breaths
expressed in mls
expressed in Ls for minute volume

How well did you know this?

Not at all

Perfectly

Describe the disadvantage of the descending bellows type ventilator.

These bellows will continue regular upward and downward movement despite patient disconnection: the drive gas pushes the bellows upward during the inspiratory phase, and during the expiratory phase the bellows “fills” with entrained room air instead of the patient’s exhaled gas, because of the weighted bellows. The pressure monitor and the volume monitor may be fooled even if disconnection is complete.

**An essential safety feature of any anesthesia workstation that uses a descending bellows is an integrated CO2 apnea alarm that cannot be disabled while the ventilator is in use.**

How well did you know this?

Not at all

Perfectly

Each time you increase FiO2 by _____ you increase PaO2 by _______.

10%; ~50 mmHg

PaO2 FiO2
100 21%
150 30%
200 40%
250 50%

How well did you know this?

Not at all

Perfectly

Discuss time as a paramter used to describe ventilation.

divided into insp and exp periods
expressed in seconds OR by relation of insp time to exp time expressed as I:E ratio
used to define the number of respiratory cycles within a given time period

How well did you know this?

Not at all

Perfectly

If ventilation is in adequate and we want to increase minute ventilation, in general, will we first increase RR or TV?

(think of Dr. E’s pearl in anesthesia, practical purposes)

Tidal volume first
- recruit alveoli, not being ventilated as well as when patient is awake with negative pressure ventialtion
- however, must consider pressures as well

How well did you know this?

Not at all

Perfectly

Describe features of a piston ventilator.

use computer controlled stepper motor vs drive gas
- analagous to pushing plunger of syringe
single circuit
less gas used
- great for remote locations
more accurate TV delievery tied to piston movement
**However, feedback mechanisms that help maintain stable tidal volume delivery are becoming increasingly more common**
- circuit compliance compensation
- use of inspired tidal volume measurement

How well did you know this?

Not at all

Perfectly

Discuss flow rate as a parameter used to describe ventilation.

rate at which the gas volume is delivered to the patient
- from the patient connection of the breathing system to the patient
refers to the volume change/time
expressed in L/sec or L/min

FR = 4 - 6 X Minute Volume

How well did you know this?

Not at all

Perfectly

Describe the mechanism of the Maquest FLOW-i Anesthesia System with volume reflector.

newer vents, not commonly in use
uses a “volume reflector”
- functional and “in circuit” during all modes of ventilation
- gases are mixing
  - exhaled gases
  - FGF
breathing bag not in play during mech ventilation
PEEP/APL valve closed during inspiration, open during expiration for scavenging
during expiration, lots of CO2 and less oxygen in the volume reflector
during inspiration, gas from volume reflector THEN goes through CO2 absorber and mixes with FG to go to patient
at the end of exhalation, the volume reflector is filled at its proximal end (near the patient) with exhaled gas and is filled distally with a mixture of exhaled gases and reflector gas
during inspiration, reflector gas module pushes the exhaled gas back out of the volume reflector, much like a piston, through the CO2 absorber, to the patient. Fresh gas combines with the volume reflector outflow to maintain the desired oxygen and anesthetic concentration
The fresh gas modules and the reflector gas module work together in a coordinated manner to control gas flow and pressure in the breathing circuit so that operator determined ventilation parameters are maintained

Discuss pressure as a parameter used to describe ventilation.

impedance to gas flow rate
impedance encountered in
- breathing circuit
- patients airways and lungs
amount of backpressure generated as a result of
- airway resistance
  - ETT
  - bronchi
  - bronchioles
  - alveoli
- lung-thorax compliance
expressed in cm H2O, mmHg, kPa

Describe the flow of gas through the piston ventilator during expiration.

FIRST STEP OF EXHALATION
patient exhales into breathing bag
fresh gas continues to flow in retrograde fashion
SECOND STEP OF EXHALATION
ventilator returns to its starting position, drawing in gas stored within the breathing bag and fresh gas from the gas supply system
once the piston reaches the bottom of its stroke, fresh gas flow reverses course and flows in retrograde fashin toward the breathign bag and the absorber
excess gas vents through the exhaust valve to the scavenger

Discuss possible issues with a bellows ventilator.

leaks
- improper seating
hole in the bellows
- hyperinflation of the lungs
  - think drive gas going to patient lungs
- O2 concentration can change
ventilator relief valve problems
- hypoventilation
  - gas goes to scavenger rather than drive
  - caused by disconnection, ruptured valve, or other damage
  - could be noted with PEtCO2
- stuck valve in closed position
  - additional PEEP and excess pressure
  - excess suction from scavenging can also cause the valve to close and cause increased pressure
  - could be noted with pressure monitors/alarms

Parameters used to describe ventilation.

time
volume
pressure
flow rate

List 4 monitors discussed.

ETCO2 monitor/capnography
- best for revealing disconnects
- adequate ventilation?
oxygen analyzers
- most important monitor on the machine
- calibrate at 21%
respirometer
- vent settings
- PAP monitors
VIGILANCE
- sweep check

Many vents can operate in VC or PC modes. Distinguish between the two.

Volume controlled
- terminates inspiration when a preselected TV is delivered
- most adult vents are V cycled but have a second limin in inspiratory pressure to guad against barotrauma
- a percentage of TV is always lost to the _compliance of the system (not patient)_
  - usually about 4 - 5 cm H2O.
Pressure controlled
- cycle into expiratory phase when airway pressure reaches a predetermined level.
- TV and inspiratory time vary
- used in situations where pressures can be high
- useful in neonates/premies

**All vents are under electric control**

Explain the flow of gas through a piston ventilator during inspiration.

The PEEP/maximum pressure (Pmax) valve is held closed
The pressure in the breathing circuit that is generated by the ventilator closes the fresh gas decoupling valve
This directs gas flow tward the breathign bag during inspiration so it does not interfere with TV accuracy
Excess fresh gas flows past the open APL bypass valve, though the exhaust valve, and to the scavenger
**Note how the breathing bag is integral to cirucit function during mechanical ventilation**

Describe CPAP as a mode of ventilation.

CONTINUOUS POSITIVE AIRWAY PRESSURE
positive pressure is maintained during both inspiration and expiration
can be provided with mask
- CAUTION: if pressures > 15 cm H2O, can cause regurgitation and aspiration

Describe the mechanism of **expiration** in the bellow ventilator.

* the drive gas exits the bellows chamber * pressure within bellows and the pilot drop to zero causing the ventilator relief valve (pop off valve) to open * Exhaled pt gas fills the bellows before any scavenging occurs because the valve ball produces a **2 - 3 cm H2O** *back pressure* * *scavenging* occurs ONLY when the bellows are *_filled completely_* * the **relief/pop off valve** is ONLY open during **expiration,** and any scavenging occurs at this point

How much O2 do we give? Think of hypoventilation. What is the formula?

* Factors to consider: * *hypoventilation* * reduces PaO2 except when the subject breathes enriched O2 mixture * from sedation * switching from NPV to PPV * derecruiting alveoli * PaO2 = PIO2 - PaCO2 / R + F * R = extraction ratio (0.8) for CO2 * F = correction factor (small and negligble * THUS * **PaO2 = PIO2 - PaCO2/R**

What is the breathing gas?

FGF + Anesthetic + what the patient exhales

List 6 ventilator alarms discussed.

* **low pressure alarm (disconnect alarm)** * detected by a drop in peak circuit pressure * circuit disconnect * bellows leak * **sub atmospheric pressure alarm** * pressure of \< or = -10 cm H2O * pt trying to breathe against ventilator * **sustained/continuing pressure alarm** * 15 cm H2O for more than 10 seconds * **high peak airway pressure alarm** * detects excess pressure in system * activated at 60 cm H2O OR *_set by practitioner_* * **low oxygen supply alarm** * **ventilator setting alarm** * vent's inability to deliver the desired MV set * older machines

Describe the **bellows** ventilator and the mechanism during **inspiration.**

* **pneumatically driven** * bellows separate the _driving gas_ from the *pt gas circuit* * *double circuit* * like practitioner squeezing the reservoir bag * bellows serves as the _reservoir_ for pt breathing gases * driving force is the pressurized gas that flows into the bellows housing * during **inspiration** phase, the _driving gas_ *enters the chamber and increases pressure* * The above increase in pressure casuses **2** things to occur * the ventilator relief valve closes (pop off valve) * so no gas can escape into the scavenger * the bellows are then compressed and the gases in the bellows are delivered to the patient * (analagous to you squeezing the bag)

Describe **high frequency ventilation** as a mode of ventilation.

* **low tidal volumes, less than dead space** * _high rate (60-300 bpm)_ * **Typical settings** * 100-200 bpm * IT 33% * Drive pressure: 15-30 psi * GOAL * *_maintain pulmonary gas exchange at lower mean airway pressures_* * Used in ESWL

What is the **respirometer** and *where* is it located? What sensors, monitors and alarms are included?

* **TV sensor** * **in expiratory limb** * gas flow converted to electrical pulses * exhaled Vt expect to measure * Vt = Vt set on vent + Vt FGF - Vt lost in system * _Exhaled volume monitor_ * activated automatically once breaths are sensed and always active during mechanical ventilation * _Apnea_ * If sufficient breath, based on TV setting, not achieved within 30 seconds * _low minute volume_

Discuss ventilator settings: **TV, RR, Flow Rate, and I:E ratio.**

* **Tidal Volume** * *5-7 ml/kg* (older vents up to 10 ml/kg) * \*\*use **IBW**\*\* * **RR** * ~ 8-12/min * **Flow rate _(machine doing, not me)_** * 4 - 6 X minute ventilation * MV = TV X RR * **I : E ratio** * *\*\*physiologic is 1 : 2\*\**

Discuss the options for **drive gas** and the *advantages/disadvantages* of each.

* Either **oxygen** or **air** * Advantage of O2 * if there is a leak it prevents hypoxic mixture from being administered to patient * Disadvantage of O2 * can deplete oxygen quickly if not hooked up to pipeline * some machines can entrain room air * reduces need for O2 * ideal in austere conditions

What is the formula for **oxygen content?**

**(hgb x %sat x 1.39 ml O₂) + (PaO₂ x .0031 ml O₂)** * 1 gram of pure Hb combines with 1.39 ml O₂ * For each mmHg of PO₂ there is .0031 ml O₂/100 ml blood * normal arterial blood with a PaO₂ of 100 mmHg contains 0.3 ml O₂/100 ml