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Principles I > anesthesia ventilators and pulmonary management > Flashcards

anesthesia ventilators and pulmonary management Flashcards

1
Q

why is mechanical ventilation during general anesthesia unphysiological?

A

normal ventilation is negative pressure; mechanical ventilation is positive pressure

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2
Q

Do high tidal volumes prevent atelectasis or improve gas exchange?

A

NO

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3
Q

What effects do traditional vent settings have?

A

produce hyperventilation, potentially detrimental to optimal oxygenation and lung compliance
**lower tidal volumes are better and safer

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4
Q

with mechanical ventilation, the uncoordinated, asynchronous chest movement d/t paralytics and deepened anesthetic state result in…..

A
  • lead to V/Q mismatches

* intrapulmonary shunting leading to hypoxemia

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5
Q

what might the unnatural process of positive pressure ventilation (PPV) result in?

A
  • cyclic recruitment and de-recruitment of collapsed lung units (inflate and deflate alveoli)
  • repetitive shear stress is shown to destroy cellular structures (tissue stress is r/t tidal volume and applied pressure)
  • inspiratory flow is directed to less resistant areas or areas that remain open resulting in overinflated alveoli (when lying down more dependent lung may not receive airflow leading to collapse)
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6
Q

what are the four causes of ventilator-induced lung injury (VILI)?

A
  • volutrauma
  • barotrauma
  • atelectrauma
  • biotrauma
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7
Q

what is volutrauma?

A

over distention of the alveoli

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8
Q

what is barotrauma?

A

excessive pulmonary pressure

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9
Q

what is atelectrauma?

A

repeated opening and collapse of atelectatic lung units (causes tissue damage and bio inflammatory markers release causing inflammation)

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10
Q

what is biotrauma?

A

inflammatory mediator release into alveoli and surrounding bronchiole spaces (can be caused by first three traumas)

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11
Q

what effect does positive pressure ventilation have on circulation?

A

-increased pulmonary vascular resistance
-can cause distended lungs and cardiac septal shift
-alveolar distention may occur
-venous return is impeded (high tidal volumes and peep
increase intrathoracic pressures, impeded negative
pressure pull on blood returning through vena cavas;
less venous return and less CO)
-surfactant production may be impaired (collapsed
alveoli)

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12
Q

what needs to be considered with mechanical ventilation?

A
  • paralysis needed or will the pt. have any respiratory effort? (can use LMA for simple knee surgery and allow spontaneous compared to exploratory LAP where yes will need paralysis and intubation)
  • one lung or two lung ventilation needed?
  • lung disease or normal lungs? (may not be able to tolerate ETT down throat)
  • cardiac issues? (bad ejection fraction, weak heart avoid positive pressure ventilation which decreases venous return and increase pulm. vascular resistance)
  • specific PaO2 and PaCO2 levels needed? (drop in PaCO2 in neuro cases to vasoconstrict)
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13
Q

what is the goal of protective mechanical ventilation?

A

-minimize injury to the lung
**large tidal volumes will not prevent atelectasis
**large tidal volumes and high FiO2 do not improve gas
exchange (high FiO2 can accelerate atelectasis
formation)

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14
Q

what are some concepts of protective mechanical ventilation?

A
  • large tidal volumes can cause acute lung injury
  • spontaneous ventilation preserves lung mechanics
  • mild hypercarbia is not undesirable
  • correct application of PEEP (just above Pflex- a pressure that opens up the airway) maintains an “open lung”
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15
Q

describe the anesthesia ventilators.

A
  • found an all modern anesthesia machines
  • work on concept of positive pressure inspiration
  • volume control or pressure control
  • FGF affects tidal volume EXCEPT if using FGF compensators to maintain accurate tidal volume
  • inspiratory time is based on a number of settings including respiratory rate and I:E ratio
  • expiration is passive
  • uses either piston or bellows to deliver tidal volume
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16
Q

what is volume control?

A

inspiration is terminated when a preset volume is reached

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17
Q

what is pressure control?

A

inspiration is terminated when a preset pressure is reached

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18
Q

what is inspiratory time based on?

A

a number of settings including respiratory rate and I:E ratio

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19
Q

does FGF affect tidal volume?

A

yes, unless FGF compensator used to maintain an accurate tidal volume

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20
Q

what is the driving gas that compresses the outside of the bellows?

A

oxygen

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21
Q

what fills the inside of the bellows?

A

volatile agent and fresh gas flow (being pushed to lungs)

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22
Q

what happens with the bellows during spontaneous ventilation of a pt. on the vent?

A

bellows will be moved by pts. inspiratory effort

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23
Q

what are ascending bellows?

A
  • standing (ascending) bellows ascend (fill) during expiration and descend (empty) during inspiration
  • most modern ventilators
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24
Q

what happens to ascending bellows during a disconnect?

A

**disconnect causes bellows to immediately descend and fall flat

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25
Q

what is the effect of the weight of the ascending bellows?

A

adds 2-3 cmH2O PEEP

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26
Q

describe ascending bellow filling.

A
  • driving gas compresses the bellows like a hand squeezing manual breathing bag
  • compressed bellows will push tidal volume through circuit and to patient
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27
Q

what happens to ascending bellows during a small circuit leak?

A

**small circuit leaks (improperly inflated ETT cuff) can cause small amounts of tidal volume to slowly leak with each cycle and the bellows will GRADUALLY DESCEND UNTIL FLAT

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28
Q

what are descending bellows?

A

-hanging (descending) bellows ascend during inspiration and descend during expiration

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29
Q

why are descending bellows considered less safe?

A
  • during disconnect, the bellows will fill due to gravity

- disconnect may not be detected by visualizing bellows

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30
Q

what happens in the ventilator during inspiration?

A
  • fresh gas hose from CGO meets at absorber
  • driving gas pushes on bellows delivering breath to patient
  • ventilator relief valve remains closed blocking path to scavenging
31
Q

what happens in the ventilator during expiration?

A
  • driving gas flow ceases, and pt’s exhalation fills the bellows
  • once pressure within bellows reach 2-3 cmH2O, ventilator relief valve opens
  • excess gas can exit to scavenger
32
Q

what is the initial respiratory rate in vent settings?

A

8-12 bpm

33
Q

what is the initial tidal volume in vent settings?

A

approximately 6-8 ml/kg ideal body weight (not to exceed 10 ml/kg

34
Q

why avoid high peak inspiratory pressures (PiP) with initial vent settings?

A

> 35-40 cmH2O can lead to barotrauma and volutrauma

35
Q

what do lower airway pressures do when setting the vent?

A
  • help preserve cardiac output

- optimize ventilation perfusion ratios

36
Q

what are sigh breaths?

A
  • larger than normal tidal volume periodically delivered to recruit collapsed alveoli
  • not necessary if PEEP of 5 is delivered and/or 6-8 ml/kg tidal volume is used
37
Q

with initial vent settings, what is the recommended FiO2?

A
  • 40-50%

* 100% FiO2 can accelerate atelectasis formations

38
Q

what is the initial vent setting for I:E ratio?

A

usually 1:2 which allows enough time during passive expiration for breaths not to stack

39
Q

Describe PEEP use in mechanical ventilation.

A
  • 5 cmH2O has been shown to recruit collapsed alveoli and splint them open to allow greater gas exchange
  • PEEP set right above Pflex (pressure where alveoli begin to open)
  • many machines require a manual PEEP valve to be placed on the circuit
  • PEEP can decrease CO, SBP, and VR and is typically not used in absence of lung disease
40
Q

Describe lung elasticity.

A
  • elastic properties of lung cause it to return passively to the pre-inspiratory volume
  • lung is extremely elastic (compliant) with low distending pressure
  • *only 3 cmH2O to distend 500 cc compared to a balloon which requires 30 cmH2O
41
Q

Describe airflow pressure in the lungs.

A
  • moving gas through the lung only requires a small amount of pressure
  • *during inspiration, a flow of 1 L/sec requires only 2 cmH2O compared to a smoker’s pipe which requires about 500 cmH2O to achieve a flow of 1 L/sec
42
Q

What increases PEEP, increasing pressures required for airflow?

A
  • external pressure on the lungs like lung rigidity (stiff chest with opioids)
  • secretions
43
Q

what causes differences in set and delivered tidal volume?

A
  • circuit compliance (distensibility) = 5ml/ cmH2O loss
  • gas sampling = 150 ml/min (2.5 ml/sec) loss
  • gas compression = 3 % loss
44
Q

so if giving a set tidal volume of 800, rate 10, I:E 1:2, PiP 20 cmH2O how much tidal volume is lost?

A
  • RR 10 gives 6 second cycles
  • I:E 1:2 gives 2 seconds in inspiratory phase
  • gas sampling lose = 5 ml (2.5/sec x 2)
  • gas compression loss is 3% of 800 = 24 ml
  • circuit compliance loss = 100 ml (5ml/cmH2O x 20 cmH2O)
  • *total loss is approx. 130ml, so a tidal vol. of only 670 is delivered.
45
Q

what does static lung compliance indicate?

A

compliance without affects of airway resistance

  • more accurate measure of lung compliance
  • it is mostly constant unless lung compliance changes like with insufflation or rigidity
46
Q

what measures static lung compliance?

A

plateau pressure

47
Q

what is plateau pressure?

A

end inhalation prior to exhalation

*always lower than Peak pressure

48
Q

what is dynamic lung compliance?

A

compliance during times of gas flow, during active inspiration (includes static)
*measure lung compliance plus airway resistance

49
Q

what measures dynamic lung compliance?

A

Peak pressure

50
Q

what causes a decrease in dynamic lung compliance?

A

airway resistance which can change from breath to breath (lung compliance usually remains unchanged)

51
Q

what is the goal of tidal volume?

A
  • keep alveoli open, expanded, recruited

- control ETCO2 (a measure of ventilation)

52
Q

what is dead space?

A

space where there is ventilation but no perfusion (no gas exchange)

53
Q

what is the opposite of dead space?

A

shunting (perfusion without ventilation)

54
Q

what is the safest way to increase pulmonary ventilation?

A

increase RR

55
Q

what happens with hypoventilation?

A

-inadequate O2 delivery to alveoli (decreased PAO2)
-inadequate CO2 removal causing increased PACO2
*common in MAC (monitored anesthesia care) or when
using an LMA with spontaneous ventilating patient with
shallow breathing
(too much opioids and anesthetic drugs)

56
Q

if breathing room air oxygen, how does hypoventilation affect the patient?

A

increasing alveolar CO2, decreases the alveolar oxygen leading to decreased O2 to tissues (hypoxia)

57
Q

describe I:E ratio.

A
  • reflects the inspiratory time (time Vt is delivered) in relation to the expiratory time (end inspiration to start of next
  • typical default 1:2 (normal breathing) or 1:1.5
58
Q

what determines the I:E ratio?

A
  • RR: determines the time of each ventilator cycle

- Inspiratory flow: determines how fast the Vt is delivered

59
Q

describe setting of I:E ratio.

A
  • since expiration is passive, I:E ratios usually set to allow greater expiratory time to exhale ETCO2
  • higher the I:E ratio, the greater inspiratory time
  • higher the I:E ratio, lower the inspiratory pressures since the breath is delivered over longer amount of time
60
Q

what has inverse ratio ventilation (IVR) like 2:1 been utilized for?

A

inverse ratio ventilation (IRV) (2:1) utilized to allow longer inspiratory times under lower pressures in order for inspired volume to reach and recruit collapsed alveoli
*problem breaths start stacking and not enough time to blow off ETCO2

61
Q

how does I:E ratio affect PiPs?

A

increase in PIP will occur as Vt delivered per second is increased
*so smaller I:E ratios allowing less time in inspiratory phase will have increased PiPs due to more volume pushed in per second

62
Q

how does I:E ratio affect ETCO2 with a constant Vt and rate?

A

longer expiratory phase times allow evacuation of more ETCO2

**smaller I:E ratios with more time in expiratory phase allow more time to blow off more CO2

63
Q

how does I:E ratio affect inspiratory flow and pressure with constant Vt and rate?

A

pressure and flow during inspiration increases as inspiration time is decreased
**smaller I:E ratios have shorter inspiratory phases increasing pressure and flow to get in Vt; increase the I:E ratio allowing longer inspiratory phase and pressure and flow will decrease

64
Q

when does laminar flow change to turbulent flow in the lungs?

A
  • when critical velocity is reached
  • direction and/or diameter is changed
  • flow is obstructed or resistance is increased
65
Q

what leads to turbulent flow in lungs?

A
  • bronchospasm
  • airway edema
  • airway mucus and secretions
66
Q

what can turbulent flow in the lungs cause?

A

-leads to resistance, sheering, and barotrauma

67
Q

if you have 2 L/min FGF and vent settings are Vt 600, RR 10, I:E ratio 1:2 how will FGF affect Vt and Vm?

A
  • 2000 ml/ min
  • 10 breaths/min meanings 200 ml FGF per breath
  • I:E 1:2 means 1/3 of FGF will be given during inspiration (66 ml)
  • an extra 66 ml Vt for 10 breaths increases Vm by 660 ml/min
68
Q

what is the effect of increasing FGF on Vt and Vm?

A

increasing FGF will increase tidal volume and minute ventilation and PiPs
**FGF decoupling (flow compensator) is used on most newer anesthesia ventilators

69
Q

if you have 2 L/min FGF and vent settings are Vt 600, RR 10, I:E ratio 1:2 how will FGF affect Vt

A
  • 2000 ml/ min
  • 10 breaths/min meanings 200 ml FGF per breath
  • I:E 1:2 means 1/3 will be given during inspiration (66 ml)
  • an extra 66 ml Vt for 10 breaths increases Vm by 660 ml
70
Q

if you have 10 L/min FGF and vent settings are Vt 600, RR 10, I:E ratio 1:2 how will FGF affect Vt and Vm?

A
  • 10,000 ml/min addede
  • 10 breaths, each breaths has 1,000 ml FGF
  • I:E ratio 1:2 means 1/3 FGF will be given during inspiration (333ml) for 10 breaths increasing Vm by 3,330 ml/min
71
Q

using a ventilator that only has a rate and minute ventilation, turning the rate up and leaving the minute ventilation unchanged will affect the Vt how?

A

Vt will decrease

72
Q

what are the effects of rate and Vm adjustment on Vt in ventilators with only Vm and rate controls?

A
  • lower RR with unchanged Vm will increase Vt
  • lower Vm with unchanged rate will decrease Vt
  • increase RR, decrease Vt
73
Q

how does inspiratory flow affect I:E ratio?

A

increasing the inspiratory flow, decreases the I:E ratio

**increased flow requires less time in inspiratory, decreasing I:E ratio

Principles I (18 decks)

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