Mechanical Ventilation in the PICU

 

This fundamental tool in the PICU serves to support the patient in respiratory failure by ensuring adequate ventilation and oxygenation. 

 

Mechanical Ventilation Basics:

 

Volume Control                                                                     Pressure Control

Controls

            Rate                                                                                                     Rate

            PEEP                                                                                                   PEEP

            FiO2                                                                                                                                      FiO2

            Tidal Volume (TV)                                                                               PIP

            Inspiratory Time (IT)                                                                            IT

 

Relative Advantages/Disadvantages

            Known TV                                                                                         No guarantee of TV

                                                               

 

 

 

 

 

Ventilators used in the PICU

 Ventilators

 Types of ventilation

 Modes

 Servo 300

 volume and pressure

 PC/VC/SIMV/SIMVcPS/PS, PRVC/VS/CPAP

 Infant Star

 pressure

 SIMV and Assist Control

 LP-10

 volume and pressure

 SIMV and Assist Control

Sensormedics 300 A, B

High frequency

High frequency

 

 

 

 

 

 

 

Volume Control Ventilation                                      

            Theses ventilators work by delivering whatever pressure is necessary to achieve a set volume.  You can set the respiratory rate and the tidal volume (TV).  To control the pO2 you can adjust the FiO2, the PEEP, and the inspiratory time.  PCO2 is controlled by adjusting the tidal volume and the rate.

 

            Pressure Control Ventilation

In these ventilators, the operator sets the PIP and the machine generates the volume necessary to achieve the set pressure.  PCO2 is contolled by adjusting the respiratory rate and TV.  TV is directly proportional to ΔP (PIP-PEEP).  As in Volume Control, you can adjust the FiO2, PEEP, and inspiratory time to affect the pO2. 

 

Modes of Mechanical Ventilation: Control Modes (Assist Control Modes) vs. Support Modes

Control modes (VC, PC and PRVC) deliver a set breath which is set by the physician.  If the patient breathes over the set rate, he or she will receive a fully supported breath, regardless of how much effort is generated.  Support Modes (VS, PS, CPAP, BiPAP, and SIMV with PS) serve to augment breaths being generated by the patient spontaneously and reliably.

 

 

Characteristics of Ventilation Modes

 

 

 

IMV (Intermittent Mandatory Ventilialtion

 

Set breath delivered at a fixed interval.  No patient interaction, pressure or volume modes.

 

Uses: Commonly for neonates.

Contraindications: uncomfortable

Advantages: Regular breaths guaranteed.

Disadvantages: Patient is not allowed to breathe with  the ventilator, i.e. doesn’t work with the patient.

Ventilator: Sechrist and most others.      

 

 

 

 

 

SIMV (Synchronous IMV)

 

Set breath delivered within an interval based on the set rate (“master rate”).  Ventilator waits for a spontaneous breath by the patient as a trigger to deliver a full breath.  If this is not sensed it automatically gives a breath at the end of the interval period.  Any other breaths during the cycle are not supplemented

 

Uses: Common in many settings.  Can be used as a weaning mode (See SIMV w/ PS).

Contraindications: None.

Advantages: Works with the patient.  More friendly mode.

Disadvantages: Any other breaths during cycle are not supplemented.

Ventilators: All but the Sechrist.

 

 

PS (Pressure Support)

 

Supports each spontaneous breath with supplemental flow to achieve a preset pressure.  Gives a little “push” to get air in.

 

Uses: Helps to overcome airway resistance of the ET tube in the spontaneously breathing patient.  Useful as a weaning mode.

Contraindications: Patient who is not spontaneously breathing.

Advantages: Helps overcome resistance of the ET tube, making spontaneous breathing easier.

Disadvantages:  Can be uncomfortable for small patients, need to have appropriate sensing.

Ventilators: All but the Sechrist.

SIMV w/ PS

 

Combination of SIMV and PS.  Extra breaths in the cycle ar supplemented with pressure support.

 

Uses: Most circumstances.  Weaning mode.

Contraindications: None.

Advantages: Allows both synchrony with the patient and helps in overcoming the ET tube resistance, allowing easier spontaneous breathing.

Disadvantages:  Occasional difficulty with the pressure support for some patients.  Not useful for the patient who is not spontaneously breathing.

Ventilators: All but the Sechrist

AC (Assist Control) or

VC (Volume Control)

 

Preset rate and tidal volume (sometimes PIP), either on the patient’s initiative or at the set interval a full mechanical breath is delivered.

 

Uses: For patients who have a very weak respiratory effort.  Allows synchrony with the patient with maximal support.  Patient is on complete mechanical support in this mode.

Contraindications: None.

Advantages: Provides a great deal of support; fairly comfortable.

Disadvantages: Can lead to hyperventilation if not closely monitored. Not a weaning mode.

Ventilators: LP-10, Servo 900, Infant Star          

PC (Pressure Control)

 

 

Essentially IMV.  Breath is controlled by the Pmax, not the set tidal volume.

 

Uses: In neonates or patients with high airway pressures (ARDS) to avoid barotrauma.

Contraindications: Not a friendly mode in the awake patient.

Advantages: Pressure limited, decreases barotrauma risk.

Disadvantages: No guaranteed TV.

Ventilators: All.

PRVC (Pressure Regulated Volume Control)

 

 

A volume control assist control mode.  Adjusts flow rate of the delivered air to achieve set TV at or below the set maximum pressure.  Decelerating flow pattern.

 

Uses: All patients.  Especially in patients with high airway pressures.  Perhaps more friendly to awake patients than SIMV.

Contraindications: None.

Advantages: Delivers a guaranteed tidal volume while minimizing barotrauma.

Disadvantages: None.

Ventilators: Only available on the Servo 300.

 

 

CPAP (Continuous Positive Airway Pressure)

 

 

Same as PEEP.

 

Uses: For patients with upper airway soft tissue obstruction or tendency for airway collapse.  As a final mode prior to extubation in some patients.

Contraindications: Any patient w/o spontaneous respiratory effort.  Not a good idea in a patient with obstructive pulmonary disease (asthma, COPD)

Advantages: Simple, easy to use.

Disadvantages: Provides no supportive ventilation.

 

 

Where to Start: Initial Ventilator Settings

 

Obviously, the individual patient and clinical setting will determine the mechanical ventilation needs, but the following is a good place to start, realizing that the settings will most likely require adjusting to achieve the desired effect.

 

 

 

Premie

Infant/Toddler

Child

Adolescent/Adult

Rate

40

30

20

12

Inspiration Time (IT)

sec

0.4

0.6

0.7

.9

PIP

(P-Peak)

cm H20

16

20

20

20

Tidal Volume

(TV)  ml/kg

5-10

5-10

5-10

5-10

PEEP

4-5

4-5

4-5

4-5

FiO2

      1.0  

Titrate

 Down  

As Tolerated

 

 

Things to Watch Out For:

 

1.      Peak Pressures: Keep below 30-35 to reduce risk of barotrauma.

2.      Oxygenation: Want to wean down as quickly as is safe to about 0.6.  Inability to wean implies V/Q mismatch.  May need to increase PEEP, I-time.

3.      Ventilation: Utilize blood gases to guide your ventilation rate.  Obtain first gas 15-20 minutes after initially starting ventilation or after major changes.   Non-invasive monitoring—ETCO2 and Oxygen saturation may allow you to do many fewer blood gases.

4.      Follow the trend.  The trend is your friend, know what it is.  The trend is more important than any specific blood gas, oxygen saturation, or chest film.

 

 

 

 

Resources:

 

1.        Hammer GB, Frankel LR. Mechanical ventilation for pediatric patients.  Int Anesthiesiol Clin. 1997; 35(1):139-67.

2.      Lectures and printed material provided by Ken Tegtmeyer MD (http://homepage.mac.com/tegthmeyer/residents/vents.html); Mohan Mysore MD; Mark Wilson MD.

 

 

 

High Frequency Oscillatory Ventilation (HIFOV)

 

Candidates for HFOV:

1.      Hyaline Membrane Disease (HMD), aspiration etc. as evidenced by bilateral diffuse, homogenous lung disease on CXR.

2.      Patients requiring hyperventilation including ECMO candidates and patients with pulmonary hypertension.

3.      Pediatric patients with acute lung injury/ARDS, general guidelines include PEEP >10, FiO2 >60%.

What to set

1.      MAP—Mean airway pressure.  Affects degree of recruitment of alveoli and expansion of the lung.

2.      Hz—Hertz, cycles per second.  Affects ventilation.  The LOWER the Hz, the more the piston moves, and the BETTER the ventilation.

3.      Power—How MUCH the piston moves, works like “tidal volume”.  The amount of gas displaced is less than dead space. 

 

 

How to start

1.      Patient <30K, use 300A, patient >30kg, use 300B.

2.      MAP—4-8 higher than the MAP on conventional ventilation.  The worse the complicance, the more the increase will need to be.

3.      Hz—smaller patient, higher Hz.  Infant-10-14, toddler-6-10, child-5-8, adolescent 4-6. 

4.      Power—look for CWF (chest wiggle factor).  The chest should wiggle, and you should see the wiggle down to the groin.

5.      Check x-ray “soon” and repeat in 6-12 hours.

6.      Suction as INFREQUENTLY as possible

7.      Treat bronchospasm aggressively.

Hospital Disclaimer

THE INFORMATION CONTAINED IN THIS SITE IS NOT INTENDED NOR IMPLIED TO BE A SUBSTITUTE FOR PROFESSIONAL MEDICAL ADVICE. ALWAYS SEEK THE ADVICE OF YOUR PHYSICIAN OR OTHER QUALIFIED HEALTH PROVIDER PRIOR TO STARTING ANY NEW TREATMENT OR WITH ANY QUESTIONS YOU MAY HAVE REGARDING A MEDICAL CONDITION. NOTHING CONTAINED IN THE SITE IS INTENDED FOR MEDICAL DIAGNOSIS OR TREATMENT.

This page was created by Laura M. Ibsen, M.D. for the use of Pediatric Residents in training. Comments or suggestions should be forwarded to Dr. Ibsen at ibsenl@ohsu.edu