Neonatal
High-Frequency
Jet Ventilation
Thomas
Pokora,
MD, Dennis
Bing,
RRT,
Mark
Mammel,
MD, and
Stephen
Boros,
MD
From The Children’s Hospital, St. Paul, and Department of Pediatrics, University of Minnesota Medical School, Minneapolis
ABSTRACT. Ten neonates with intractable respiratory failure were treated with high-frequency jet ventilation
(HFJV). Nine had progressive pulmonary air leaks with
either bronchopleural fistulas or pulmonary interstitial emphysema as the primary cause of their respiratory failure. Following HFJV, x-ray film evidence of
pulmo-nary air leaks decreased in seven of the nine neonates.
Pao,/FI02 increased in eight of the ten patients (P <
.05), and Paco2 values decreased in nine of the ten
patients (P < .01). Five patients survived. Three of the
six patients exposed to HFJV for more than 20 hours developed significant tracheal obstruction. From this
ex-perience, it may be concluded that HFJV can successfully
ventilate certain neonates with intractable respiratory failure secondary to progressive pulmonary air leaks. In
its present form, long-term neonatal HFJV carries a risk of airway obstruction and/or damage. Pediatrics 1983;72:27-32; high-frequency jet ventilation, pulmonary
air leaks, tracheal obstruction.
High-frequency jet ventilation (HFJV) is a
rela-tively new form of mechanical ventilation that em-ploys very small tidal volumes and extremely rapid rates. It has a number of theoretical advantages
when compared with current methods of
conven-tional ventilation. HFJV systems have tiny
corn-pressible volumes and minimal internal
compli-ances. HFJV is said to provide adequate ventilation using minimal proximal airway pressures. It allows
effective gas exchange with little, if any, circulatory
interference. This form of mechanical ventilation has been successfully used in the treatment of
bron-chopleural fistulas and other intractable pulmonary air leaks in adults.1’2 This report describes its
sirn-ilar use in neonates.
Received for publication July 8, 1982; accepted Sept 17, 1982.
Read in part before the Annual Meeting ofThe Midwest Society
for Pediatric Research, Detroit, Nov 3, 1981.
Reprint requests to (S.B.) The Children’s Hospital, 345 N Smith Aye, St Paul, MN 55102.
PEDIATRICS (ISSN 0031 4005). Copyright © 1983 by the
American Academy of Pediatrics.
PATIENTS
AND METHODS
The ventilator used in this trial was the VS-600
high-frequency jet ventilator (Instrument Devel-opment Corporation, Pittsburgh). The ventilator was used in conjunction with a proximal airway-ventilator monitor (Pneumogard, Novarnetrix,
Wallingford, CT) that measured and displayed
mean airway pressures and proximal airway
pres-sure wave forms.
This machine is a time-cycled ventilator con-nected to a jet injector patient circuit. Inspiratory gas is blended to a desired oxygen concentration by an air-oxygen blender and delivered to the machine at a pressure of 50 pounds per square inch gauge
(psig). Ventilator gas source pressure or driving pressure is set by an infinitely variable (0 to 50 psig) pressure regulator. A magnetic solenoid valve
allows gas to enter the patient circuit. This valve is electronically controlled by an incremental fre-quency control (variable from 8 to 600 cycles/mm) and a relative inspiratory time variable from 20% to 70%. Relative inspiratory time is the percent of the total respiratory cycle devoted to inspiration. The machine’s technical and operational details are
published elsewhere.3
Our neonatal jet injector circuit consisted of a
5-cm Luer-ended polyvinyl chloride catheter attached to a right-angle metal cannula within a sleeved
adaptor (Fig 1). This sleeved cannula (Adaptor
Interface PM-2008, Anarad Division of Cavitron Corporation, Anaheim, CA) fit into a standard en-dotracheal tube adaptor. The airway pressure mon-itor entered the circuit via a T-piece interposed
between the endotracheal tube and its adaptor.
Inasmuch as exhalation is passive, small-diameter endotracheal tubes (2.5 to 3.0 mm) were used to allow adequate air leaks around the endotracheal
tubes.
Three different humidification systems were used
PEEP valve
prsssure
coincident ongoing bench studies. The first em-ployed only entrained mist that was delivered via a simple “T” system joined to the sleeved adaptor and endotracheal tube. The second system also used only entrained mist, but the mist was delivered through one limb of a “Y” connector attached to the sleeved injector and endotracheal tube. The third system infused 0.5 N saline directly into the jet stream through a valve system (Intraflow, Sor-enson Research Company, Salt Lake City) and a standard high-pressure infusion pump, in addition to employing entrained mist.4 Prior to infusion, fluid was warmed to the ambient temperature of the patients’ isolette. Warming was accomplished by placing 15 to 20 cm of fluid-filled infusion tubing within the heated incubator. The volume of fluid infused was 0.5 rnL/L of estimated minute
venti-lation.
Fig 1. Jet injector and metal sleeve adaptor.
Ten neonates with progressive respiratory failure were treated with HFJV. Nine of these patients had intractable pulmonary air leaks and/or severe pulmonary interstitial emphysema (PIE) as the primary cause for the progression of their
respira-tory failure. Air leaks were considered intractable when they could not be controlled with chest tubes,
water seal drainage, or suction.
Prior to HFJV, the conventional ventilator was manipulated for each infant in an attempt to find
a combination of settings that allowed acceptable
gas exchange while minimizing air trapping or air leakage. The manipulations that best approached this end were lowering positive end-expiratory pres-sure (PEEP), shortening inspiratory time, and
in-creasing the ventilatory rate. This invariably ne-cessitated increasing peak inspiratory pressure.
The conventional ventilator (CMV) settings shown in Table 1, therefore, do not reflect standard or “conventional” ventilator settings. Rather, these values represent attempts to control pulmonary air
leaks using a conventional infant ventilator. If the patient’s condition continued to deteriorate follow-ing such manipulations, treatment with HFJV was instituted. Parental consent was obtained in all
cases.
The patients weight ranged from 700 to 4,030 g; gestational age ranged from 26 to 40 weeks. Seven patients had hyaline membrane disease, two had bacterial pneumonia, and one had respiratory fail-ure associated with perinatal asphyxia, assumed to be shock lung. One patient received HFJV and did not have a significant pulmonary air leak. This patient had group B streptococcal sepsis and was
profoundly hypotensive. HFJV was used in an at-tempt to ventilate this patient mechanically with minimal circulatory interference.
Initial HFJV setting selections were based on our experience using HFJV in laboratory animals and on that of Klain and others.37 FIo2 was initially
the same as that used during conventional ventila-tion. Relative inspiratory time was 30%. A minimal
PEEP of 2 to 3 cm H2O was employed in all cases
to ensure maintenance of an end-expiratory lung volume. Once FIo2, relative inspiratory time, and
PEEP were set, the machine’s driving pressure was
increased until a mean airway pressure similar to that observed during conventional ventilation was produced.
Serial arterial blood gas measurements were made. Several patients also had arterial oxygen saturation measured continuously via a No. 4 F fiberoptic umbilical arterial catheter (Oximetric Shaw Catheter Oximeter System, Mountain View,
CA). Patients were weaned from HFJV by gradually
reducing the system’s driving pressure while contin-uously monitoring airway pressure. If mean airway
TABLE 1. Ventilator Variables Before and After High-Frequency Jet Ventilation (HFJV)*
Conventional
Ventilator
HFJV
Rate (breaths/mm)
FIo2
Mean airway pressure (cm H,O)
Peak airway pressure (cm H20)
Positive end-expiratory pressure (PEEP) (cm H,O)
81 ± 27
0.91
±
0.1312.7 ± 2.9
34.8 ± 15.4
3.3 ± 1.2
260 ± 52 0.88 ± 0.18
12.0 ± 2.3
28.7 ± 6.7
2.0 ± 0.8
*Values are means ± 1 SD.
Fig 3. Chest roentgenogram of patient 6 (1,300 g, ges-tational age 28 weeks, severe hyaline membrane disease) before (A) and four hours following (B) HFJV.
Pulmo-pressure could be significantly reduced while
main-taming adequate arterial blood gas values and/or there were significant clinical or radiographic irn-provernents in the pulmonary air leaks, the patients were then returned to CMV at respiration rates of
50 to 60/mm and similar mean airway pressure. Statistical analysis was performed using a paired two-tailed Student’s t test. This project was
ap-proved by the Institutional Review Board of
Chil-dren’s Hospital.
RESULTS
Mean ventilator variables before and after HFJV
are shown in Table 1. An expanded table of mdi-vidual patients’ ventilator variables, blood gas val-ues, and x-ray film findings is available on request. Arterial blood gases were measured 30 minutes to
one hour following HFJV. Any FIo2 change prior to the first HFJV blood gas measurement was based on either continuous oxygen saturation data or transcutaneous oxygen measurements. Because pa-tients were ventilated at different oxygen concen-trations, changes in oxygenation were standardized by the expression Pao2/FI02.8’9 Following HFJV, x-ray film evidence of pulmonary air leaks decreased in seven of the nine patients with such air leaks (Fig 3). Pao2/FIo2 increased in eight patients (P
<
.05). PaCO2 decreased in nine patients (P
<
.01).pH
values
increased
in nine
of the
ten
patients.
Mean values for these variables before and after
HFJV
are shown in Fig 4.The pertinent clinical data are summarized in Table 2. Five of the ten patients survived their initial respiratory failure; two of these patients later died. One died at home at 9 months of age following a presumed viral pneumonia; the other died at 3
p<o.os p<o.o1 ,00 -90 80 70 60 U. 040 0. 30 20 -10 0 C) 0. 100 90 80 70 60 50 40 30 20 10 7.6 7.5 7. 4 7. 3 I 0. 7. 1 7. C
conventional HFJV conventional HFJV conventional HFJV
mech. vent mech. vent mech. vent
Fig 4. Changes in arterial blood gas and pH values before and one hour following HFJV.
TABLE 2. Patient Data*
Patient Weight Gesta- Diagnosis Dura- HFJV Humidity System Outcome Autopsy No. (g) tional tion Complications
Age of
(wk) HFJV
(h)
1 1,020 28 HMD, PIE,
pneu-mothorax, BPD
246 Tracheal
obstruc-tion, thick
se-cretions
EM only #{149}Initially
sur-vived; died
at 9 mo
None
2 3,020 36 Pneumonia,
pneu-mothorax, BP
fis-tula
60 Tracheal obstruc-tion, thick
se-cretions
EM only Died HMD,
pneu-monia,
bronchitis,
necrotizing tracheitis
3 980 26 HMD, PIE,
pneu-mothorax, BP fis-tula
65 Tracheal
obstruc-tion, thick se-cretions
EM + infusion Died None
4 950 26 HMD, PIE 2 None EM + infusion Died None
5 940 26 HMD, PIE,
staphy-lococcal sepsis
2 None EM via Y connector Died None
6 1,300 28 HMD, PIE,
pneu-mothorax
96 Hypothermia
transient
EM via Y + infusion Died None
7 700 26 HMD, PIE 13 None EM via Y + infusion Survived, BPD ...
8 1,010 27 HMD, PIE, bilateral pneumothorax
20 None EM via Y + infusion Survived, BPD ...
9 4,230 40 “Shock lung,”
pneu-mothorax, BP fis-tula
13 None EM via T + infusion Survived ...
10 1,100 28 HMD, pneumonia 79 None EM via T + infusion Initially sur-vived, died at 3 wk
Hepatic hem-orrhage
*Abbreviations used are: BPD, bronchopulmonary dysplasia; BP fistula, bronchopleural fistula; HMD, hyaline membrane disease;
PIE, pulmonary interstitial emphysema; HFJV, high-frequency jet ventilation; EM, entrained mist.
weeks of age of an unrelated nonpulmonary illness.
The one patient who was ventilated with HFJV
and did not have a significant air leak showed improvements in both arterial blood pressure and
peripheral perfusion following HFJV.
Six patients received HFJV for more than 20
hours. Three developed tracheal obstructions from
thick, tenacious secretions. One of these
obstruc-tions was fatal (patient 2). At autopsy, this infant’s
trachea and mainstern bronchi were totally
oc-cluded with a thick gray-green material (Fig 5).
With the exception of patient 2, all other patients
exposed to long-term HFJV had regular direct
pat-Fig 5. Microscopic section through trachea of patient 2 showed advanced necrosis de-stroying mucosa and filling lumen with necrotic debris. Submucosa was invaded; many submucosa glands were dilated and filled with mucous and inflammatory cells.
ency. The only other significant obstructions were seen with humidification systems that employed entrained mist only.
DISCUSSION
HFJV
has
recently
been
called
the treatment
of
choice for major airway disruptions in adults.’#{176}
Nine of our neonatal patients had similar air
leaks-bronchopleural fistulas, recurrent
pneurno-thoraces, and/or pulmonary interstitial emphy-sema. Most patients’ conditions improved following
HFJV,
even
though
the proximal
airway
pressures
delivered via HFJV were little different than those delivered via
CMV.
Similar
experiences
have
been
described in adults. The fact that these patients’ conditions showed clinical improvement is clear.
The reasons for the improvement are not. Carlon
et al’ suggested that during HFJV, pressures rapidly equilibrate within the upper airway and deliver tidal
volumes to the lower airways at a relatively con-stant distending pressure. This constancy of pres-sure eliminates the pressure differential between airway and intrapleural space, arid it decreases the
tidal
volume losses that often occur at peakinspi-ration during CMV.’ A constant distending
pres-sure also eliminates the intermittent stretching of the lower airways, increasing the opportunity for self repair.
Hoff et al” ventilated dogs with large
broncho-pleural fistulas with both CMV and a high-fre-quency oscillator. High-frequency oscillatory
yen-tilation provided more than adequate gas exchange whereas CMV consistently resulted in life-threat-ening hypercarbia and acidosis. Calkins and co-workers’2 recently examined the changes in airway diameters associated with CMV and HFJV. In this study, CMV produced large fluctuations in the di-ameter of the distal airways; minimal changes oc-curred during HFJV.
The exact mechanism by which high-frequency ventilators, whatever their design, produce gas ex-change is not known. HFJV, because of its minimal internal compressible volume, high flow rates, and direct delivery, may simply be a more efficient system for the rapid bulk delivery of small tidal volumes. By increasing airway turbulence, HFJV may enhance the distribution and diffusion of res-piratory gases. Mixing, at any given flow rate, is greater during turbulent flow than during laminar flow.13’8 Slutsky and co-workers’4”9’2#{176} suggest that during high frequency ventilation, gas mixing oc-curs throughout the entire tracheobronchial tree,
producing a continuous CO2 gradient from alveolus
to atmosphere. With this concept, there is no “dead
space.” Whatever the exact gas exchange
mecha-nism, most traditional concepts of pulmonary gas exchange no longer seem to apply.
Of the 17 adult patients treated with HFJV de-scribed by Carlon et al,”4 two also developed upper
airway complications. These patients were also
yen-tilated with systems that humidified only entrained
available until after our HFJV trial was well under-way.
The
adverse
effects
of inadequately
humidified
gas on respiratory mucous membranes are well
known.21’22
Considerably
less
is known about the effects of an injector jet stream. However, Rock et al23 and Jacobs24 used HFJV in animalsand
in
adult patients for as long as 24 hours; neither observed significant tracheal damage. Carlon et al25
ventilated
an adult
with
HFJV
for 36 days.
Multiple
tracheobronchoscopies
failed
to demonstrate
any
significant upper airway damage. The only other
significant tracheobronchial damage attributed to
HFJV
was reported
by Spoerel
et a126 in dogs.
One
animal
showed
mucosal
hyperemia and petechialhemorrhage in the area
of the jet stream’s
impact.
Others showed some loss of surface epithelium in the area of the jet stream’s impact.
We cautiously
speculate
that
the tracheal
damage
we observed
was due to inadequately
humidified
gas
rather than any jet stream-induced trauma. An
animal
study
of the cytopathologic
effects
of HFJV,
its jet stream, and its various humidification sys-tems is currently underway.
Our
limited
experience
suggests
that
HFJV
is
useful in the short-term treatment of neonatal res-piratory failure secondary to intractable pulmonary air leaks. In its present form, however, long-term
neonatal
HFJV
may carry the risk of upper airwayobstruction
and/or
damage.
HFJV
may be the
rec-ommended
form
of therapy
in adult
airway
disrup-tions.’#{176} More data are needed before this
recom-rnendation
can be extended
to neonates.
ACKNOWLEDGMENTS
The authors thank Drs Charles Jarvis and Janice Ophoven for the microscopic tissue analysis, and Mar-ietta Sattler for her secretarial assistance.
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