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Intro to Anesthesia > Ventilators > Flashcards

Ventilators Flashcards

1
Q

Respiratory rate

A

8-12 bpm

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2
Q

Vt

A

5-7mL/kg of IDEAL body weight

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3
Q

MV

A
  • Vt x RR
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4
Q

Flow rate

A

5 x MV

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5
Q

I:E ratio

A

Normally 1:2

-increase expiratory time for patients with increased compliance (COPD)

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6
Q

Inspiratory Time

A

(Vt / Inspiratory flow) x 60

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7
Q

Expiratory Time

A

60 seconds / RR = time for one breath cycle.

Time for breath cycle - inspiratory time = expiratory time

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8
Q

What is pressure variable

A
  • pressure is impedance to flow.
  • this occurs in the breathing circuit or patients airway (trachea, bronchi, bronchioles, alveoli, ETT)
  • back pressure from the impedance is from resistance and compliance from chest wall and lungs
  • expresses in cmH2O or mmHg or kPa
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9
Q

What do we want the ETCO2 at?

A

30-33 mmHg

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10
Q

If your ETCO2 is too high, how do you adjust ventilator?

A
  • increase MV by increasing Vt or RR

* * increase Vt first to recruit alveoli

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11
Q

Volume control ventilation

A
  • delivers a set Vt to the patient
  • anesthesia provider sets MV or Vt and RR
  • time initiated
  • volume limited
  • loses 4-5cm H2O to circuit compliance
  • patient paralyzed
  • high PIP can limit inspiratory time and Vt delivery
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12
Q

What is the flow rate like in volume control

A
  • the flow rate is constant
  • too low of flows will result in partial Vt delivery
  • too high of flows will results in inspiratory pause
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13
Q

What are two disadvantages of volume control?

A
  • high PIP

- ventilator dyssynchrony

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14
Q

Pressure control ventilation

A
  • delivers set pressure to patient
  • anesthesia providers sets a max inspiratory pressure above PEEP
  • ventilator increases the pressure to set level at start of inspiration time and maintains this pressure until exhalation begins
  • patient paralyzed*
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15
Q

What is the flow rate like in pressure control?

A

-flow rate is highest at the beginning of inspiration and then decreases

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16
Q

What is tidal volume like in this mode?

A
  • varies with resistance and compliance and vent dyssynchrony.
  • If resistance increases Vt decreases
  • if compliance decreases Vt decreases
  • *important that a respirometer be used
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17
Q

Respirometer

A
  • senses tidal volume in the expiratory limb of ventilator
  • converts gas flow into electrical pulses
  • exhaled Vt expected to measure: Vt set on vent + FGF - Vt lost in vent
  • alarm will ring if apnea is present
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18
Q

What does increasing PEEP do in PCV

A

-increasing PEEP decreases Vt

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19
Q

When do we use PCV

A
  • whenever we want to avoid high airway pressures
  • often with LMA
  • this reduces ventilator-induced lung injury
  • obese patients, lung injury, single lung ventilation, ETT cuff leak
20
Q

IMV (intermittent mandatory volume)

A
  • ventilator delivers preset Vt at preset rate, permitting spontaneous unassisted breaths
  • delivers through separate parallel circuit
  • used for weaning
  • not synchronized with patient
21
Q

SIMV (synchronized intermittent mechanical ventilation)

A
  • mix of mandatory breaths and assisted breaths;
  • synchronizes mandatory breaths with beginning of spontaneous breath
  • contains trigger window on monitor
  • if patient does not trigger, a mechanical breath is delivered
  • if patient triggers, patient determines Vt delivered
  • mandatory Vt and RR is needed
  • I:E ratio not required
  • not every spontaneous breath is assisted
22
Q

AC (Assist Control)

A

-mix of mandatory and assisted breaths
-once triggered every breath is treated the same: given a preset Vt or pressure delivery
Trigger = time, pressure, volume
Control = volume or pressure
Cycling = time
-guarantees MV and requires little respiratory effort
-can have breath stacking and does not protect against hyperventilation

23
Q

PSV (pressure support ventilation)

A
  • applies positive pressure to airway
  • patient’s inspiratory effort generates negative pressure or flow in the inspiratory limb of the ventilator
  • delivers small pressure support
  • results in larger Vt than the patient would take on his/her own
  • for maintenance or emergence of patients who are SV
  • patient can become apneic
24
Q

High Frequency (Jet) Ventilation

A
  • very low Vt with very high rates
  • usually seen when shocking kidney stones (ESWL)
  • I:E usually 1:3
  • 100-200 breaths per minute
  • driving pressure 15-30psi
25
Q

CPAP (continuous positive airway pressure)

A
  • positive pressure maintained during inspiration and expiration
  • can be done via mask
  • used when trying to recruit alveoli
  • often used just to open alveoli of top lung during surgery while dependent lung is fully ventilated
26
Q

Changes to what four variables affect Vt?

A
  • fresh gas flows
  • bellows
  • RR
  • I:E ratio
27
Q

Relationship: FGF and Vt

A
  • direct

- increase FGF increase Vt, MV, and PIP

28
Q

Relationship: RR and Vt

A
  • indirect
  • increase RR, decrease Vt
  • decrease RR, increase Vt
29
Q

Relationship: I:E ratio and Vt

A
  • direct
  • increase I:E ratio, increase Vt
  • decrease I:E ratio, decrease Vt
30
Q

Relationship: Bellows Height to Vt

A
  • direct
  • increase bellows height, increase Vt
  • decrease bellows height, decrease Vt
31
Q

In an anesthesia machine that couples FGF with Vt, what is the true Vt delivered to patient?

A

-Vt programmed + FGF on inspiration - circuit compliance

32
Q

How to find FGF on inspiration

A

1)convert fresh gases from L/min to mL/min
(1L/min air + 3L/min O2 = 4000mL/min FGF)
2)use I:E ratio to find fraction of mL/min in inspiration
(I:E of 1:2 means 1/3 is inspired)
3)multiply inspired fraction of FGF and total FGF in mL/min
-1/3 * 4000mL/min = 1,333mL/min
4)divide inspired FGF by RR
-1,333 / 10 bpm = 133mL
5)add inspired FGF total to bellows total
-500mL + 133mL = 633mL

33
Q

Resistance

A

The force that acts opposite to the relative motion of an object

  • [P (airway) - P (alveolar)] / Gas Flow Rate
  • ETT, trachea, bronchi, bronchioles, alveoli
34
Q

Compliance

A

Delta volume / Delta pressure

  • measures elasticity of lungs and chest wall
  • influenced by: muscle tone, degree of lung inflation, alveolar surface tension, amount of interstitial lung water, and pulmonary fibrosis
35
Q

Dynamic Compliance

A
  • means “movement”
  • the compliance of the lung/chest wall during air movement
  • the pressure required to inflate the lung to a given volume is a function of airway resistance AND the tendency of the lung/chest to collapse
36
Q

Static Compliance

A
  • not moving
  • measures lung compliance when there is no airflow
  • the pressure required to keep the lung inflated is a function of the tendency of the lung/chest to collapse
  • there is no airflow, so no resistance to overcome
37
Q

O2 content formula

A

(Hbg x SaO2 x 1.34-1.39) + (PaO2 x 0.0031)

37
Q

O2 delivery formula

A

(CO x O2 content)

37
Q

Each time you increase FiO2 by ______ your SaO2 increases by _____

A

10%

50mmHg

38
Q

Vent Alarms

A
  • low pressure (disconnect alarm)
  • sub atmospheric pressure alarm (neg pressure alarm)
  • sustained/continuing pressure alarm
  • high PIP alarm
  • low oxygen supply alarm
  • ventilator inability to deliver set Vt
39
Q

Low pressure alarm

A
  • detects a drop in circuit pressure

- check for disconnections

40
Q

Sub atmospheric pressure alarm

A
  • patient trying to breathe against vent

- switch to PSV, bag, or deepen sedation

41
Q

Sustained/continuing pressure alarm

A

~ 15cm H20 for more than 20 seconds

- check for things sitting on circuit

42
Q

High PIP alarm (set at 30cmH2o)

A
  • occlusion, kinked tube, accumulating fluid in lungs, mucus plug
43
Q

Low oxygen supply alarm

A
  • low oxygen coming into the machine
44
Q

Monitors

A
  • ETCO2
  • respirometer = Vt and PAP
  • oxygen analyzer = calibrate at 21%
  • VIGILENCE. = sweep check
45
Q

ICU vs OR vent

A
  • delivers higher Vt and PIP
  • does not have CO2 rebreathing no absorber
  • ## support more modes

Intro to Anesthesia (15 decks)

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