Introduction to Mechanical Ventilation

Charles S. Williams RRT, AE-C

Learning Objectives:

Indications for intubation and mechanical ventilation.

Review the different modes of ventilation and complications.

Case study.

Ventilator weaning and indicators.

Short-term vs. Long-term weaning.

Key Terms:

Tidal Volume, (Vt)

−The volume of air inhaled and exhaled each breath.

Respiratory rate, (RR,f)

−Number of breaths per minute, also known as frequency.

Minute Ventilation, (VE)

−The total amount of air moving in and out of the lungs in 1 minute, (Vt x RR).

Key Terms:

PEEP (Positive End Expiratory Pressure)

−Positive pressure applied at the alveoli at the end of exhalation.

FIO2 (Fractional Inspired Oxygen)

−Amount of oxygen. Expressed as a percentage, 21%-100%

I:E ratio, (Inspiration/Expiratoy ratio)

−Normal I:E ratio = 1:2, 1:3

To facilitate mechanical ventilation.

To maintain an open pathway between the upper and lower airway.

To protect the lower airway from aspiration.

Assist with pulmonary toileting.

When do we intubate?

Apnea or Impending Respiratory Failure:(ARDS, CHF, Status Asthmaticus, Neuromuscular disease)

Acute Respiratory Failure:– Hypoxemic (Type I failure; oxygenation)

– Hypercapnic (Type II failure; CO2 elimination)

Prophylactic Support:(Post-op, Post MI, Brain injury, etc.)

Hyperventilation Therapy:(Acute head injury)

Indications for Mechanical Ventilation:

Modes of Ventilation

CPAP/PEEP

BiPAP (Non-invasive ventilation)

Pressure Support / Volume Support

SIMV

Volume Control

Pressure Control

PRVC

Modes of Ventilation:

Servo-I ventilator from Maquet, Inc.

Pressure / Support

Describes the type of breath being delivered:

Pressure or volume

Control = Set mandatory rate on ventilator

Support = Spontaneous breaths

Example:

Modes of Ventilation:

Spontaneous Breathing

Inspiration

Exhalation

Modes of Ventilation:

No ventilator support Produces a sinusoidal pressure waveform on

graphics display.

CPAPContinuous Positive Airway Pressure

5

15Ventilator

breath

spontaneous

breaths

Modes of Ventilation:

PEEPPositive End Expiratory Pressure

Positive pressure applied at the end of exhalation on ventilator

breaths.

5

15

• CPAP/PEEP can improve oxygenation by “holding” the alveoli open.

• May decrease venous blood return if too much positive pressure is applied. This can effect blood pressure and cardiac output

CPAP/PEEP

Positive pressure applied to spontaneous breathing patients.

Can be used to treat Obstructive Sleep Apnea

Creates a pocket of air that “splints” open the

upper airway to help treat obstructive sleep apnea

Holds bronchioles and smaller airways

open

Helps oxygen to move across the alveolar-capillary

membrane

Keeps alveoli “dry” in patients with

CHF, fluid overload

Modes of Ventilation:

Modes of Ventilation:

Bipap Vision® from Respironics, Inc.

Inspiratory Positive Airway Pressure (IPAP)

Expiratory Positive Airway Pressure (EPAP)

+

Modes of Ventilation:

• A form of non-invasive ventilation (NIV)

• Adds a second pressure setting (insp.)

• EPAP = CPAP

• BiPAP has same benefits as CPAP plus:

a) Reduces WOB

b) Improves ventilation (CO2

elimination).

IPAP IPAP

EPAP EPAP5

15

Inspiratory Positive Airway Pressure (IPAP)

Expiratory Positive Airway Pressure (EPAP)

+

Weaning modes

PS may be used alone or in combination with other modes.

Pressure Support

PS - Adds pressure to spontaneous breaths to enhance inspiratory tidal volume.

VS - Automatically adjusts the amount of pressure needed to obtain a desired tidal volume.

Modes of Ventilation:

5

15

Weaning mode

Allows for combined ventilator assisted and spontaneous breaths.

Pressure support is usually added for spontaneous breaths.

Ventilatorbreath

Spontaneous breaths

Pressure Support

Modes of Ventilation:

5

15

Breaths are delivered at a preset volume.Pressure is variable, Flow remains constant during

inspiration.

Advantage:• Guarantees delivery of desired tidal volume

Disadvantages:• Increased risk of barotrauma due to potentially high peak pressures.• Fixed flowrate may not meet patient’s inspiratory demand.

Modes of Ventilation:

Ventilatorbreath

Spontaneous breath

Breaths are delivered at a preset pressure.

Pressure remains constant during inspiration, Flow is variable.

Usually used for stiff, non-compliant lungs (ARDS).

Advantages:• Less risk of lung injury due to high peak pressures• Variable flow rate can better meet patient’s demand

Disadvantage:• Delivery of tidal volume will vary depending on lung compliance, etc.

Modes of Ventilation:

Ventilatorbreath

Spontaneous breath

Pressure setting

5

15

Considered a “dual” ventilator mode.

Combines the advantages of both Volume Control (guaranteed tidal volume) and Pressure Control Ventilation. (lower peak pressures, variable flow).

Attempts to deliver the desired tidal volume, using the lowest possible pressure.

Use clinically as you would “standard” Volume Control.

Modes of Ventilation:

• Not used for weaning.

• Usually requires sedation.

• Does allow for spontaneous breathing.

•Patient triggered breaths and ventilator

breaths will be identical.

Control Modes

Modes of Ventilation:

Patients that are apneic or require lots of sedation, generally should be on a Control mode like Volume Control, PRVC, etc.

What Mode is Best for my Patient?

Pressure Control mode is usually indicated when peak inspiratory pressures are high.Patients with ARDS, Adult Respiratory Distress Syndrome, and patients with stiff, non-compliant lungs).

What Mode is Best for my Patient?

Spontaneous breathing patients generally do well in SIMV mode. The patient may feel more “in control” of their breathing.

What Mode is Best for my Patient?

Adding Pressure Support to SIMV can reduce muscle fatigue and may allow for more synchronous breathing efforts with the ventilator.

What Makes a Complete Order for ventilation?

36 yr. old female, admitted to SJRMC,

with respiratory distress due to

bacterial pneumonia.

Case Study:

Laboratory Results: − WBC: 24,000

− ABG: pH 7.12, PaCO2 74, PaO2 45,

HCO3 24 on 100% O2

(hypoxic and hypercapnic respiratory failure)

Chest x-ray:

− Extensive Bilateral Pneumonia.

Patient is intubated and place on the ventilator.

Vent settings: Mode: SIMV/PS

Tidal volume: 600 ml

Resp Rate: 20

FiO2: 100%

Pressure Support: 10, PEEP: 5

Case Study:

ABGs after 30 minutes on ventilator: pH 7.22, PaCO2 64, PaO2 74, HCO3 24.

Peak airway pressures are measuring *50 cm H2O.

IV steroids and antibiotics are started.

She is very agitated. IV sedation is increased. (Peak airway pressures continue to be 50cm H2O or higher).

Decision is made to switch to Pressure control ventilation mode due to high peak pressures.

*In general, keeping peak pressures < 30cm H2O is desirable.

Case Study: cont…

Vent settings: Mode: Pressure Control

Inspiratory Pressure: 26

Resp Rate: 24

FiO2: 100%

PEEP: 5

Insp. Pressure is adjusted to maintain exhaled tidal volume

of 550-600 ml

After switching to PCV, Her peak airway pressure is now

measuring 31cm H2O (26+5), instead of 50cm H2O.

(Much lower risk of developing a pneumothorax due to barotrauma.)

ABG’s eventually improve to normal range:

pH 7.42, PaCo2 44, PaO2 110, HCO3 24.

Case Study: cont…

As the patient began to oxygenate better, sedation was weaned and she returned to SIMV/PS mode.

Within 5 days of intubation she was extubated. And was soon discharged home.

Case Study: conclusion

Ventilator Induced Lung Injury, (VILI)

BarotraumaCaused by excessive pressure

VolutraumaCaused by excessive volume

Oxygen Toxicity

Complications to Mechanical Ventilation:

Complications to Mechanical Ventilation:

Complications from ventilator-induced lung injury

Barotrauma, Volutrauma

OxygenToxicity

Ventilator Associated Pneumonia, (VAP)

A sub-type of Hospital Acquired Pneumonia, (HAP).

Usually occurs within 48 hours of being ventilated.

Complications to Mechanical Ventilation:

Decreased Cardiac Output and Blood Pressure

Increased intrathoraic pressures can increase the pressure surrounding the heart and major blood vessels.

This can impede blood flow to the heart causing a decreased CO/BP.

Complications to Mechanical Ventilation:

Ventilator Weaning

Control modes Combined Support modes

Pressure ControlVolume Control

PRVC

SIMVPressure SupportVolume Support

CPAP

Ventilator Weaning

Indications for Weaning

Resolution of acute phase of disease

FIO2 of 40% or less, Peep 5-10

Stable vital signs

Stable ABG’s (minimal acidosis)

No continuous IV sedation

Adequate cough

RSBI less than 100

• Reliable predictor of weaning outcomes.

• Pt is allowed to breath without vent support for 1 minute, RR is then divided by exhaled tidal volume.

• Normal value is < 100.

• Performed every a.m. in conjunction with RN sedation vacation.

RSBIRapid Shallow

Breathing Index

Indications for Weaning

• Decreasing SIMV rate

• Decreasing levels of Pressure Support

• Spontaneous Breathing Trials

Approaches to weaning:

The SIMV rate is decreased by 2 breaths/min every 4-6 hours as tolerated.

When the SIMV rate is down to 4, and is tolerated for 2-4 hours , the patient is then considered for extubation or changing to pressure support mode.

Example order: Wean IMV rate by 2, every 4-6 hours as tolerated. Maintain RR < 30 w/ no respiratory distress.

Decreasing SIMV rate

Approaches to weaning:

Pressure Support level is slowly decreased over time.

When the patient has tolerated a pressure support level of 5 -7, for 2-4 hours, the patient is considered weaned.

Example order: Wean pressure support by 2 every 6-8 as tolerated. Maintain RSBI < 100. Lowest pressure 5cm H2O*.

*PS 5 is maintained to overcome airway resistance from breathing tube

Approaches to weaning:

Decreasing Levels of Pressure Support

The patient is removed from the vent and placed on T-Bar or left attached to the ventilator and placed on Flow-By mode.

The patient’s vital signs are monitored during the trial, usually for 30-120 mins.

Example order: May attempt SBT x 30 min as tolerated BID.

Approaches to weaning:

Spontaneous Breathing Trials

Short-term weaningvs.

Long-term weaning

Short-term weaning:

Example: post-op open heart patient.

The FiO2 is weaned to a stop point of 40%. The RR is weaned by 2 breaths with a stop point of 2-4 breaths /minute.

The patient is then placed on CPAP and weaning parameters are obtained along with ABG’s. Respiratory Therapist obtaining weaning parameters

Short-term weaning:

The patient is then extubated with physician approval.

Most open heart patients meet a goal extubation time of 6 hours or less.

Long-term weaning:

Some patients may take longer to wean due to MSOF, poor nutritional status, etc.

Even though it can be a slow and long process, the most complex patient can be weaned.

PS weaning proves to be an effective tool to help wean long-term patients.

Thank You!