1. Ventilators for Interns
Amy Ni, MD
March 2015

3. Objectives Know when to mechanically ventilate
Understand basic settings: all about the CO2 and O2
Learn about two main vent modes: AC and PS
There are 174 methods of positive pressure ventilation!! But this is actually much more complicated than it needs to be.

4. When to intubate?
Patient cannot protect their airway…what does that mean?
Sepsis, often
Hypercapnia
Hypoxia
Severe work of breathing
Obtundation

5. Ventilation RR and Tidal Volume affects ventilation and alters CO2
Tidal volume: volume of air moved in and out of lungs during quiet breathing
Tidal volumes should 8-10cc/kg of ideal body weight = height based, changes with sex
Ventilation in ARDS: tidal volume between 5-8cc/kg with higher PEEP
Common setting for RR: 12
Common setting for Tidal Volume: 500 mL

7. Oxygenation FiO2 and PEEP affects oxygenation and alters O2
PEEP: Positive End Expiratory Pressure
Set initial FiO2 on high side, usually 100%, then can titrate down based on ABG
Common FiO2 setting initially: 100%; check gas, then drop to 60%
Try to use as little FiO2 as possible to maintain pulse ox %

9. Modes: the basics
Assist Control: SET volume or pressure, with additional breathes triggered by patient
Volume Control: can ventilate more consistently in setting of bad lung compliance
Pressure Control: allows limits for peak inspiratory pressure and avoid barotrauma

10. Modes: the basics
Pressure Support: patient controls when a breath terminates (versus AC), allows them to determine tidal volume and inspiration time
Vent gives a certain additional pressure to overcome the diseased lung + tubing
Used during weaning, also know as CPAP trial
Common settings: Pressure Support of 10 with PEEP of 5

11. Case 1:
56 year old male admitted to UCI MICU for hypoxic respiratory failure secondary to community acquired pneumonia, requiring intubation. You are the night time intern. At 1am the ICU RN pages you. You call back:
“Hey doc, the vent is beeping and it says that the peak pressure is pretty high all of a sudden, can you come take a look?”

13. Case 1:
Check plateau with inspiratory pause (the “I” button, stands for “Intern”)
Peak pressure is usually a static measurement, think of it as patient’s chest wall + vent tubing + airway of the lungs
Plateau pressure is usually a dynamic measurement of the compliance of lung parenchyma, think of it as everything except peak pressure
Plateau is measured by holding the “Insp Hold” or inspiratory hold button for 1 sec, timed at the end of inspiration If peak is high and plateau is low = obstruction

14. Case 1:
If only peak pressure is high (therefore lung parenchyma/plateau is ok), think about something obstructing the air from getting to the lungs such as: mucous plug, bronchospasm, patient biting the vent, the vent tubing became disconnected!

15. Case 1:
If both peak and plateau are high, think about what’s wrong with lung compliance, in addition to everything else
Is the patient developing worsening ARDS, pulmonary edema, pneumothorax, pleural effusion, ETT into one bronchus?

16. Case 2:
34 year old female admitted to the UCI ICU for hypercapneic respiratory failure due to severe asthma exacerbation, requiring intubation. 3 hours into her admission the nurse calls you:
“Doc I think we need to start antibiotics and levophed now! Her blood pressure suddenly went south, it was 130s about an hour ago and now it’s in the 70s! And she’s de-satting!”

17. Case 2: COPD/asthma = desatting, increasing CO2 retention
Breath-stacking also known as auto PEEP can be caused by obstructive airway diseases
This leads to decreased venous return by increasing intrathoracic pressure
This can lead to hypoxia as well

18. Case 2: Many ways to help stop auto-PEEP or breath stacking:
Decrease RR effectively increases expiratory time
Decrease tidal volume
Increase the E in I:E ratio (advanced)
Increase sedation/analgesia/even adding neuromuscular blockade (advanced)

19. Summary When to mechanically ventilate Basic settings
Cannot protect airway, work of breathing, obtundation, high CO2 or low O2
Basic settings
AC VC
RR 12, VT 500, PEEP 5, FiO2 100%
Two vent modes: AC and PS
PS for weaning, also know as CPAP
Two cases
Difference between peak and plateau pressure
Breath stacking in obstructive airway disease