HFJV Introduction to HFJV. Overview of HFJV The Jet is composed of 5 subsystems The Jet is a...

HFJVIntroduction to HFJV

Overview of HFJV• The Jet is composed of 5 subsystems• The Jet is a microprocessor-controlled infant ventilator capable of

delivering and monitoring between 240 and 660 heated, humidified breaths per minute.

• MONITOR: displays patient and machine pressures

• ALARMS: indicate potentially hazardous conditions

• CONTROLS: regulates the Rate, PIP and On-Time of gas flowing to the patient

• HUMIDIFIER: controls and monitors the temperature and humidification of the gas flowing through the humidifier and circuit

• PATIENT BOX: makes and monitors the breaths delivered to the patient

• One controls the valves and other components that produce and monitor ventilation and pressure

• One controls and monitors humidification and temperature

Two Separate Microprocessors

• The Conventional Ventilator, when operated in tandem with the Jet, has 3 functions:

The Role of theConventional Ventilator

2. Provide background IMV breaths to open collapsed alveoli

3. Regulate PEEP to maintain alveolar recruitment

1. Provide fresh gas for a patient’s spontaneous breathing

PEEP

• The LifePort Adapter allows the Jet and conventional ventilators to be operated in tandem.

• The LifePort has 3 main features:

The LifePort Adapter

1. 15 mm opening: provides the standard connection to the conventional ventilator

2. Jet Port: entrance for high-frequency pulses coming from the Jet

3. Pressure Monitoring Port: allows distal tip airway pressures to be approximated

• Together, these elements form a system that offers a variety of options for managing patients.

• The Jet in tandem with a conventional ventilator allows the best blood gases with the least amount of pressure compared with any other form of mechanical ventilation.

Summary

HFJVHow and WhyHFJV Works

• gas is propelled into the lungs at a high velocity

• fresh gas penetrates through the anatomic dead space, compressing much of the CO2 in the dead space

against the airway walls

• incoming gas is forced to stream into the airways in a long spike

• abundant energy of the "jet stream" also causes the gas to spiral as it flows

• gas easily splits into two streams at bifurcations

CO

2 CO

2

• This possibility was first illustrated as early as 1915

• Henderson observed the shallow breathing of panting dogs

Adequate Gas ExchangeUsing Small Tidal Volumes

• Dogs could pant indefinitely without becoming hypoxic

Convection penetrated smoke deeply through tubeDiffusion occurred when flow stopped or slowed

• Convection carries fresh gas deeply into the lungs quickly

• Once the flow stops, diffusion completes the gas exchange process as usual

• The effective or physiologic dead space in the lungs can be reduced to less than the volume of the anatomic dead space

• The jet stream is only effective for a relatively short distance and a brief time

• Longer distances and times allow for development of turbulent flow

• Turbulent flow quickly mixes incoming gas with resident dead space gas

Demonstrated Importance of Convection and Diffusion During

HFJV

• The best way to maximize the jet-stream effect with a mechanical ventilator is to place the inhalation valve as close to the patient as possible

• This is accomplished with HFJV by placing the valve and pressure transducer in the small plastic "patient box" that resides close to the infant's head

Taking Advantage of Convection and Diffusion During HFJV

• The abrupt cessation of the incoming HFJV breath also helps prevent the development of turbulence so that a crisp jet stream of fresh gas can penetrate deep into the airways

• Gas flow through the pinch valve is stopped almost as soon as it starts by closing the valve almost as quickly

• With HFJV, as with conventional mechanical ventilation, inhalation is active or forced, and exhalation is passive.

• Using rates that bring in as many as 11 breaths per second, one might be concerned that there is insufficient time for breaths to get back out.

• However, two factors allow exhalation to occur relatively easily.

• The size of each breath (1-3 mL/kg) is much smaller than usual, and the natural or resonant frequency of the infant lungs is close to the frequency range being used by HFJV.

• Thus, the lungs recoil readily during HFJV under almost all conditions.

What About Exhalation?

• During HFJV, exhaled gas swirls outward around the incoming gas.

• The exhaled gas sweeps through the CO2-rich deadspace gas.

• This action may help evacuate CO2 and enhance ventilation.

Exhalation with HFJV

CO 2

CO 2

CO

2

CO 2

CO 2

CO

2

• Passive exhalation is the safest way to get gas back out of the lungs.

• During HFJV, passive exhalation ensures that mean airway pressure will overestimate mean alveolar pressure.

• Pressure drops as gas advances into the lungs on inhalation, and there is not time for the pressure in the alveoli to equilibrate with that in the upper airways because of the short inspiratory time.

• Furthermore, the highest pressure during exhalation will be in the alveoli so gas flows naturally toward the trachea during exhalation until the beginning of the next inhalation.

More on Exhalation

• Active exhalation, as with high-frequency oscillation (HFO), can lead to gas trapping by lowering intraluminal pressure disproportionately below pressure in surrounding alveoli, thereby collapsing more proximal airways before exhalation is complete.

• For that reason, users of HFO typically operate at higher mean airway pressures than those used with HFJV.

• Elevating the baseline pressure during HFO, "splints" the airways open while gas is actively withdrawn from alveoli.

Exhalation with HFOV

The highest pressure in the lung during expiration is in the alveoli

pressure = 0

+ +

+

++

+

+

+

+

+

+

Pressure drops as gas flows out the airways

• airways lack structural strength  

• the chest is squeezed  

• gas is sucked out of the airway

CHOKE POINTS may develop when:

• The high pressure in the alveoli can overwhelm the airway walls which encase gas at lower pressure

+++

++++

+

+

• Back pressure (High PEEP/Paw) may splint open the airway and allow gas to exit

PEEP

++

++

+

• PEEP/Paw and the oscillatory pressure waveform must be raised to overcome gas trapping

P

time

• The conventional ventilator (CV) during HFJV with the Life Pulse is to enhance oxygenation.

• Conventional ventilators can deliver oxygenated gas directly to the alveolar level.

• They do this by using relatively long (e.g., 0.5 second) inspiratory times and large tidal volumes (e.g., 7 to 15mL/kg body weight), and they have the capability of controlling end-expiratory pressure.

• These are the factors that most readily control PO2.

The Role of Conventional Ventilation

• Unfortunately, the support from the CV is most closely associated with barotrauma and volutrauma.

• Thus, it is useful to minimize these factors by running the conventional ventilator at minimal rates (i.e., from 1 to 3 BPM) and moderate TI’s (i.e., from .25 to .45 sec) while the Jet ventilator is providing the bulk of the ventilation.

• Using the conventional ventilator to gradually recruit collapsed alveoli allows the Jet to achieve the best possible blood gases with the lowest possible airway pressures.

Minimizing The Risks of Conventional Ventilation

HFJVTechnical Capabilities and Clinical Implications

of HFJV

Technical Capability Clinical Implication

Uses LifePort Adapter

• Minimizes mechanical dead space

• Allows use with any conventional ventilator

• Provides ability to display approximated intratracheal pressure

P

Technical Capability Clinical Implication

Operates in the natural frequency range of the lungs

• Minimizes pressure needed to move gas into the lungs

• The ease with which lungs recoil and send gas out in this frequency range lessens the chances of gas trapping that one normally encounters at higher frequencies

< Natural Frequency

Natural Frequency

> Natural Frequency

Best Blood Gases with Least Pressure

Technical Capability Clinical Implication

Jet valve is located close to patient's

airway in the Patient Box

• Introduces inspired gas as a sharp impulse that penetrates through the resident dead space gas

• Upper airway leaks (tracheal-esophageal and broncho-pleural fistulae) are bypassed by the momentum of the incoming gas.

Technical Capability Clinical Implication

These 3 factors allow less pressure to be necessary in the treatment of lung

disease

• Strain on the cardiopulmonary system (e.g., barotrauma and suppression of hemodynamics) is diminished

• Established air leaks, restrictive and/or non-homogenous such as PIE, and pneumothorax are more readily healed

Technical Capability Clinical Implication

Pressure transducer is located in the Patient Box close to the patient with an automatic monitor-ing line purge system

• Allows accurate measurement of high frequency pressure fluctuations in the ET tube without interference from mucus, condensation, etc.

PurgeTube

PressureTransducer

PressureMonitoring

Tube

Technical Capability Clinical Implication

Extended I:E ratios (1:1 to 1:12) with passive exhalation

• Gas trapping is avoided

1:6No Gas

Trapping

1:1Gas

Trapping

Technical Capability Clinical Implication

Driving pressure is feedback controlled and alarm limits are automatically set and adjustable around this

"Servo Pressure"

• Changes in lung compliance, pneumothoraces, and the need for suctioning may be detected

• Additional volume is automatic-ally provided after changes in the baby's lungs and/or leaks in the ventilator tubing or around the ET tube

Volume Increases,Servo Increases

Volume Decreases,Servo Decreases

Technical Capability Clinical Implication

Gas is delivered at 100% relative humidity at body temperature via a built-in feedback controlled humidifier

• Continuing therapy requires minimal intervention

• Labor savings reduce cost of medical care delivery

Technical Capability Clinical Implication

Ventilator tubing and humidifier circuit need only be changed every

seven days

• All gas through the circuit is inspired gas

• Exhaled goes travels through the conventional ventilator circuit

• Patient temperature losses and airway damage is avoided.

Technical Capability Clinical Implication

Comprehensive alarm system and fail-safe

design

• Enhanced patient safety.

High FrequencyJet Ventilation:General Guidelines

The 6 Fundamentals1. HFJV P (PIP - PEEP) PaCO2

• HFJV Rate is secondary

2. FRC and MAP PaO2

3. PEEP to avoid hyperventilation and hypoxemia

4. If CV Rate oxygenation, PEEP is probably too low

5. CV settings whenever possible

• Especially when airleaks are a concern

6. FiO2 before PEEP until FiO2 < 0.5

20 cm H2OHFJV PIP

Setting Common

When to Raise When to Lower

To raise PCO2

(Raise PEEP if necessary to keep MAP and PO2 constant.)

To lower PCO2

420 bpmHFJV Rate

Setting Common

When to Raise When to Lower

To lengthen exhalation time and reduce inad- vertent PEEP in larger patients or when weaning

To increase PCO2

To increase MAP and PO2

To decrease PCO2

in smaller patients

0.02 secondsHFJV

I-Time

Setting Common

When to Raise When to Lower

Keep at the minimum of 0.02 in almost all cases

To enable Jet to reach PIP at low HFJV rates in larger patients

0 – 3 bpmCV Rate

Setting Common

When to Raise When to Lower

Every chance you get, especially when:

• Airleaks are a concern

• Hemodynamics are compromised

To reverse atelectasis

15 – 20 cm H2OCV PIP

Setting Common

When to Raise When to Lower

Whenever airleaks are present

When you’re not seeking to recruit alveoli

To reverse atelectasis

0.4 secondsCV I-Time

Setting Common

When to Raise When to Lower

Whenever airleaks are present

When you’re not seeking to recruit alveoli

To reverse atelectasis

4 – 8 cm H2OPEEP

Setting Common

When to Raise When to Lower

Usually when airleaks are present

When you’re not seeking to recruit alveoli

To improve oxygenation

To find optimal PEEP

(Raise PEEP until SaO2 stays constant when you switch the CV to CPAP)

21 – 100 %FiO2

Setting Common

When to Raise When to Lower

Lower in preference to MAP until FiO2 < 45%

As needed

HFJVObjectives and ActionsManaging Oxygenation and

Ventilation During High Frequency Jet

Ventilation

Lower PCO2

HFJV PIP already uncomfortably high

Raise HFJV Rate

Note: watch for inadvertant PEEP

Lower PCO2

Raise HFJV PIP

Objective CircumstancesAction To Be Taken

Objective CircumstancesAction To Be Taken

Raise PO2

Atelectasis noted on X-ray

Raise the following in this order:

Institute actions cautiously in infants with PAL

Discontinue measures once atelectasis disappears and/or PO2 improves

Stabilize alveoli with PEEP

1. PEEP2. CV Rate (max = 10)

3. CV PIP4. CV I-Time

CV Rate, PIP, and I-time increases are temporary

Use until atelectasis is alleviated

Minimize CV Rate thereafter

Objective CircumstancesAction To Be Taken

Raise PO2

Previous actions were only temporarily successful

Repeat the previous actions at a higher PEEP level

Reduce MAP by decreasing CV support

1. CV Rate < 102. CV I-time < 0.5 sec

3. PEEP < 6 cm H20

Raise PO2

Lungs are over- expanded on X-ray

4. Raise Jet PIP to maintain PO2

Objective CircumstancesAction To Be Taken

Raise PCO2

Lower HFJV PIP and/or raise PEEP

Raise PEEP before dropping HFJV PIP

Raise PCO2

PO2 drops every time HFJV PIP is dropped

Objective CircumstancesAction To Be Taken

Lower PO2

Lower, in this order, as necessary:

Lower HFJV PIPLower PO2

PCO2 is also low

1. FiO2

2. CV PIP and/or Rate3. PEEP

Objective CircumstancesAction To Be Taken

Lower PEEP

Lower, in this order, as necessary:

PEEP on CV has been turned down to minimum 1. HFJV On Time to

0.02 sec

2. HFJV Rate

3. IMV flow rate, if appropriate