Mechanical Ventilation

Question 1

What is the relationship between:

pressure, flow, resistance

Answer 1

Pressure = flow x resistance

Question 2

What are appropriate ET tube sizes and placement distance for men and women?

Answer 2

Women: 7.5 ID, at 21 cm
Men: 8.0 ID, at 23 cm

Question 3

What do you look for on CXR to confirm proper ET tube placement?

Answer 3

ETT tip 2- 5 cm above main carina

Question 4

What type of flow do you need for constant (ie square) pressure on vent?

Answer 4

Decelerating flow

Question 5

What is your max Pplateau and why does it matter?

Answer 5

<30 cmH2O
prevent volutrauma

Question 6

Complete for AC-VC:

Trigger (what starts a breath)
Target (how the breath is delivered)
Cycle (what stops a breath)

Answer 6

AC-VC

Trigger: patient/time
Target: flow
Cycle: volume

Question 7

Complete for SIMV-VC:

Trigger (what starts a breath)
Target (how the breath is delivered)
Cycle (what stops a breath)

Answer 7

SIMV-VC

Trigger: patient/time
Target: flow
Cycle: volume

and pressure support

Question 8

Complete for AC-PC:

Trigger (what starts a breath)
Target (how the breath is delivered)
Cycle (what stops a breath)

Answer 8

AC-PC

Trigger: patient/time
Target: pressure
Cycle: time

Question 9

Complete for PS:

Trigger (what starts a breath)
Target (how the breath is delivered)
Cycle (what stops a breath)

Answer 9

PS

Trigger: patient
Target: pressure
Cycle: flow

Question 10

What type of pathology typically leads to auto-PEEP?

Answer 10

increased airway resistance and reduced expiratory flow rates (e.g., severe asthma or COPD)

Question 11

What are 4 considerations for candidates for SBT?

Answer 11

Improving patient
Hemodynamic stability
Adequate oxygenation
Low levels of PEEP

Question 12

What are 3 considerations for candidates for extubation?

Answer 12

No immediate plan for procedures
Adequate mental status
Ability to clear secretions

Question 13

How do you calculate compliance with inspiratory hold?

Answer 13

Compliance = volume / change in pressure

C = tidal volume/(Pplat - PEEP)

Question 14

How do you calculate resistance with inspiratory hold?

Answer 14

R = (PIP - Pplat) / flow

Question 15

What is normal lung resistance?

Answer 15

<15
if higher there’s some increased resistance - clog, bronchospasm in asthma, etc

Question 16

What is ideal max plateau pressure

Answer 16

30 cm H2O

Question 17

What is normal lung compliance?

Answer 17

> 60
if <60 think stiff ie ARDS

Question 18

What is the issue (compliance or resistance) if if high peak and plateau?

Answer 18

compliance problem

alveolar filling (blood, pus, water), pleural filling (air, blood, pus, water), ILD, decreased lung size (PTX, R mainstem intubation), abdominal issues (ascites, distended bowel, pregnancy), chest wall issues (obesity)

Question 19

What is the issue (compliance or resistance) if if high peak, unchanged plateau ?

Answer 19

resistance problem

kinked tubing, biting ET tube, secretions, bronchospasm (asthma classically, can get in COPD), airway tumors, foreign body

Question 20

How do you evaluate if someone passed an SBT?

Answer 20

rapid shallow breathing index <105 (RSBI)
RSBI = RR/tidal volume

Question 21

Who can be extubated?

Answer 21

• SBT criteria + and passed SBT
• no planned procedures
• no need for frequent suctioning
• able to protect airway, good mental status
• cuff leak (ask an RT)

Question 22

How do you calculate I:E ratio?

Answer 22

If flow is 60lpm, Insp time = TV in L (ie 500mL = 0.5 sec) and exp time = RCT - insp time

I:E = insp time / exp time

If RR is 15, RCT is 4 ( 4 x 15 = 60)