Ventilators for InternsAmy Ni, MDMarch 2015

Objectives

1. Know when to mechanically ventilate

2. Understand basic settings: all about the CO2 and O2

3. Learn about two main vent modes: AC and PS

When to intubate?

Patient cannot protect their airway…what does that mean?

Sepsis, often

Hypercapnia

Hypoxia

Severe work of breathing

Obtundation

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

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 88-92%

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

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

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?”

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

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!

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?

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!”

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

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)

Summary

1. When to mechanically ventilate1. Cannot protect airway, work of breathing, obtundation,

high CO2 or low O2

2. Basic settings1. AC VC

2. RR 12, VT 500, PEEP 5, FiO2 100%

3. Two vent modes: AC and PS1. PS for weaning, also know as CPAP

4. Two cases1. Difference between peak and plateau pressure

2. Breath stacking in obstructive airway disease