Br.J. Anaesth. (1986), 58, 544-550
CONTINUOUS FLOW VENTILATION WITHOUT
RESPIRATORY MOVEMENT IN CAT, DOG AND HUMAN
A. PERL, J. G. WHITWAM, M. K. CHAKRABARTI AND V. M. TAYLOR
The elimination of carbon dioxide from the lungs
during conventional ventilation requires an inter- SUMMARY
mittent "to and fro" bulk movement of gas in the The insufflation of oxygen at 1 litre kg-1 min-1
conducting airways. As a result, during apnoeic via two endobronchial catheters (called continuoxygenation, when oxygen enters the blood by ous flow ventilation (CFV)) maintained a normal
diffusion without ventilation, the PSLCOJ increases PaCOl and a constant PaOt in anaesthetized
at a rate which is related to the metabolic state of paralysed dogs and in five out of seven cats. In
the animal (Holmdahl, 1956; Lambertsen, 1980). two cats with a high carbon dioxide production,
Lehnert, Dorster and Slutsky (1982) described CFVfailedto maintain carbon dioxide homeostasis
the elimination of carbon dioxide and the since gas flows greater than 1 litre kg-1 min'1
maintenance of a normal P&cOt and P&Qt in four caused thoracic distension and a decrease in
small dogs by the insufflation of a constantflowof arterial pressure. In five patients, endobronchial
air through catheters, the distal ends of which were insufflation
of oxygen 0.5 litre kg-1 min-1
placed in the main bronchi. However, the required caused approximately a 30% decrease in the
flow rates varied from 1 litre kg~l min"1 to increase in PaCOl compared with apnoeic oxygen4 litre kg"1 min"1 and the positions of the catheters, ation (P < 0.05) during a period of 6 min. CFV
which were introduced with a bronchoscope, were at 1 litre kg-1 min-1 can be used for physiological
found to be critical for the removal of carbon measurement without respiratory movement
dioxide. More recently, Chakrabarti and Whitwam while maintaining blood-gas homeostasis in
(1984) used disposable plastic Carlen's double dogs and in cats with a normal carbon dioxide
lumen tubes (Portex 100/193/005 size 5.5 mm) to production. Ethical constraints have so far
position the distal ends of two plastic manometer prevented the investigation of the effects of
lines (internal diameter 1.2 mm), which had been comparable gas flows in man.
inserted previously andfixed,one in each lumen of
the tube, in the main bronchi of dogs, by intubation without endoscopy. They found that bloodgas homeostasis was maintained readily in all the to re-examine CFV in the dog using a larger
dogs studied by insufflating either air or oxygen version of the single lumen tube developed for the
through the endobronchial catheters at aflowrate cat and, third, make preliminary observations of
the effect on blood-gas tensions of insufflating
of 1 litre kg"1 min"1.
oxygen at high flow rates to the bronchi of
The objectives of the study reported here were: anaesthetized human subjects.
first, to develop a simple single lumen tube with
Preliminary results have been presented on a
which to apply continuousflowventilation (CFV), previous occasion (Chakrabarti and Whitwam,
and to study the effects of CFV in the cat. Second, 1985).
A. PERL,* M.D.; J. G. WHITWAM, M.B., CH.B., PHJJ., F.R.CLP.,
F.F.A.R.CS.; M. K. CHAKRABARTI, B.SC., M.PHIL.; V. M.
TAYLOR, M.B., CH.B., F.F.A.R.CS.; Department of Anaesthetics,
Royal Postgraduate Medical School, Ehi Cane Road,
London W12 0HS.
•Present address: The Edith Wolfson Hospital, Holon,
58000, P.O. Box 5, Israel.
Correspondence to J. G. W.
MATERIALS AND METHODS
Cats
Investigations were undertaken on nine cats.
Two were used for the development of suitable
tracheal tubes and, subsequently, formal studies
were performed on seven animals with weights
CONTINUOUS FLOW VENTILATION
INSPIRATORY GAS i
1
545
humidifier
GAS
FIG. 1. Diagram of ventilating circuit. P = Attachment for fresh gas supply during IPPV; B = attachment for fresh gas supply during CFV; C = attachment for measurement of airway pressure.
between 2.9 and 6.0 kg. Anaesthesia was induced
with pentobarbitone 60-100 mg kg"1 administered
i.p. and maintained
with
ot-chloralose
10-15 mg kg"1 h"1 administered i.v. A femoral
artery and vein were cannulated, and neuromuscular blockade maintained with suxamethonium
1-2 mg kg"1 per 30 min i.v. A tracheal tube
(internal diameter 5 mm, length 12 cm) incorporating distal side holes for ventilation via the main
bronchi and two fine tubes (internal diameter
0.6 mm) terminating in these bronchi for gas
insufflation (fig. 1) was advanced through a
tracheostomy until its distal bifurcated end was at
the carina. The proximal end was attached to a
valveless ventilator (Chakrabarti and Whitwam,
1983) which allows easy transfer from IPPV to
CFV (fig. 1).
Dogs
Observations were made on five dogs weighing
between 12 and 22 kg anaesthetized with methohexitone 10-20 mg kg"1 i.v., followed by a-chloralose 15-20 mg kg"1 h"1 and suxamethonium
1-2 mg kg"1 per 30 min i.v. Thereafter the
preparation was comparable to that of the cats
using a larger (internal diameter 12 mm, length
35 cm) but similar tracheal tube (fig. 1) and the two
endobronchial insufflation tubes had an internal
diameter of 1.2 mm.
Clinical studies
Approval of the Ethical Committee was obtained
for limited observations on human subjects.
Observations were made on five adult patients
(weights 52-75 kg, ages 42-65 yr) about to undergo major hepatobiliary surgery, in whom cannuiation of the radial artery and right internal jugular
vein, and the use of two peripheral vein infusions
were routine. After night sedation with lorazepam
3-4 mg by mouth and premedication with papaveretum 15-20 mg, hyoscine 0.3-0.4 mg and droperidol 5 mg i.m., anaesthesia was induced with
thiopentone 4 mg kg"1 followed by pancuronium
0.1 mg kg"1 and maintained subsequently during
the study period with midazolam 0.1 mg kg"1,
incremental doses of papaveretum (total 10-15 mg)
and a further dose of pancuronium 2-3 mg. The
trachea was intubated with a disposable Carlen's
tube (Portex 100/193/055 each lumen with an
internal diameter of 5.5 mm or 6.0 mm) into which
plastic manometer lines (i.d. 1.2 mm) had been
inserted, one through each lumen, so that the tips
were almostflushwith the distal end of each lumen
as described previously (Chakrabarti and Whitwam, 1984). The presence of the hook on the
Carlen's tube ensured predictable positioning of
the insufflation catheters in relation to the carina
without the use of an endoscope. The proximal
end of the Carlen's tube was connected via a
Y-piece to the valveless ventilator circuit to allow
either IPPV or CFV by insufflation of oxygen to
the bronchi via the manometer lines; that is, the
ventilation system was similar to that used in the
cat and dog.
BRITISH JOURNAL OF ANAESTHESIA
546
30
60
90
Time (min)
FIG. 2. Effect of apnoeic oxygenation (( —O) and CFV (•—
Mean values and SD.
Control 5
Procedures
120
150
180
on Paco t and POQ, in n v e
cats
-
0.5 litre kg"1 min"1 (0.25 litre kg"1 m k r 1 to each
side measured with rotameters) for a period of
8 min and the effects on PaCOl and Pao, observed.
Thereafter, a conventional ventilator (60 % nitrous
oxide and 40 % oxygen) was used during surgery
lasting 3-5 h, at the end of which time recovery
and subsequent progress was normal.
Dog and cat. Once set up, the preparations were
ventilated with oxygen for at least 30 min and
stabilized so that the PaCOl was in the physiological
range. Apnoeic oxygenation was established
merely by stopping the ventilator driving jet while
maintaining the fresh gas flow; that is, oxygen at
a flow rate of 200 ml kg"1 min"1 at the proximal
end of the tracheal tube (fig. 2). The effect of 10 General measurements
min apnoeic oxygenation on P&cOt> P*o, an< i The ECG, beat-by-beat heart rate, airway and
arterial pH was observed. The animals were then arterial pressures were recorded throughout.
ventilated to a physiological P&cot> after which the P&CO,, P&Q, and pH were measured in heparinized
ventilator was again stopped and oxygen was samples of blood collected anaerobically (Radioinsufflated to the bronchi via the endobronchial meter ABL 1). In the cats and dogs the blood
tubes at a flow rate of 1 litre kg"1 min"1 withdrawn was replaced with an equal volume of
(0.5 litre kg"1 min"1 to each side measured by dextran 110 in saline. E'COl was recorded using
rotameters). Serial samples of arterial blood were an infra-red carbon dioxide analyser (Gould
withdrawn to observe the effects of CFV on PaCof Medical) and the F T was adjusted during the
and
initial setting up procedure to give a reading of
4-4.5 % in the cats and 4.5-5 % in the dogs and
Clinical study. After ventilation with oxygen for patients. In the patients, CVP was also recorded.
15—30 min so that the Pacoi w a s within normal
Oesophageal temperatures were maintained in
limits, atracurium 0.5 mg kg"1 was administered the range 37-38.5 °C in all three groups (measured
to ensure the complete abolition of respiratory with a thermistor—Yellow Springs Instrument
movement during apnoeic oxygenation and CFV. Co.).
The effect of apnoeic oxygenation was observed
During CFV, alveolar pressures were measured
for 6 min by stopping the ventilator while as the equilibrium pressure after simultaneously
maintaining the fresh supply of oxygen occluding the fresh gas flow and either the
(100 ml kg"1 min"1) at the Y-piece at the proximal proximal end of the tracheal tube in the cats and
end of the Carlen's tube. The ventilator was then dogs or the Y-piece attached to the Carlen's tube
restarted and IPPV provided until the Pac O . n a d in the patients.
returned to the control values. The ventilator was
Statistical analysis was performed using Stuagain stopped and oxygen was insufflated to the dent's paired r-test where appropriate. P < 0.05
bronchi via the manometer lines at a flow rate of was regarded as statistically significant.
CONTINUOUS FLOW VENTILATION
RESULTS
Respiratory system
Cats. Results from five cats in which a
physiological Pac Ot was maintained for periods of
approximately 3 h are shown in figure 2. During
apnoeic oxygenation the mean rate of increase in
Paco, for the first 10 min was 0.82 kPa min"1
(range 0.67-0.96 kPa min"1). It can be seen that,
during the insufflation of oxygen to the bronchi,
the Pace, was 5.14 kPa at the end of 3 h and
remained within the normal range of all preparations throughout the period of observation. The
P&o, during apnoeic oxygenation decreased in
relation to the increase in PaCOl and, during CFV,
the mean value remained greater than 57 kPa.
Airway pressures during CFV in these preparations
were less than 0.2 kPa and the alveolar pressures
were in the range 0.4-0.65 kPa.
In two preparations the Pa COl could not be
maintained by CFV with a gas flow of
1 litre kg"1 min"1, but increased during 10 min
from 4.4 kPa to 12.3 kPa and from 3.7 kPa to
10
0
10
Time (min)
FIG. 3. Two cats with a high carbon dioxide production. Effect
of apnoeic oxygenation (O
O) and CFV ( #
•)
on Pa
-
co1-
547
6.5 kPa, respectively (fig. 3). In spite of normal
oesophageal temperatures, these two preparations
had a high rate of increase in Paco, during apnoea
of 1.25 kPa min"1 and 1.02 kPa min"1, respectively
(fig. 3).
An attempt to reduce the Paco, by increasing the
gasflowto more than 1 litre kg"1 min"1 caused an
increase in alveolar pressure above 0.7 kPa, which
caused a visible large expansion of the thoracic
cage and an unacceptable decrease in mean arterial
pressure to less than 50 mm Hg.
Dog. It can be seen in figure 4 that the mean rate
of increase in P a ^ , during apnoeic oxygenation
was 0.59 kPa min"1, whereas during CFV a
physiological PaCOt was maintained throughout
the period of observation and the mean Pa O|
remained greater than 63 kPa. The airway and
alveolar pressures in these preparations varied
between 0.1 and 0.2 kPa and 0.4 and 0.7 kPa,
respectively.
Clinical study. As described above, the fresh gas
flow rate during CFV was half that used in the
animal preparations. The changes in PaCOt and
Pao, during apnoeic oxygenation and CFV are
shown infigure5. It can be seen that the mean rate
of increase in Pac Ot during 6 min apnoeic
oxygenation was 0.56 kPa min"1, and during CFV
this was decreased to 0.36 kPa min"1 (P < 0.05).
Control 5
10
20
30
Time (min)
50
60
FIG. 4. Effect of apnoeic oxygenation (O
O) and continuous flow ventilation (CFV #
• ) on Pico, and Pa Oi in five
dogs. Mean values and SD.
BRITISH JOURNAL OF ANAESTHESIA
548
arterial pressure during IPPV and CFV is shown
in figure 6.
£46
* 44
Dog. During CFV there were no significant
differences in heart rate and arterial pressure,
which remained near control values during the
period of observation. A typical recording of
arterial pressure and airway pressure in the dog is
shown in figure. 7.
£42
9
8-
.2
Clinical study. In man the mean heart rate (HR)
and mean arterial pressure (MAP) increased from
100 to 110 beatmin" 1 and 88 to 104mmHg,
respectively, during apnoeic oxygenation for
6 min, whereas during CFV there were no
significant changes in HR and MAP, which
7-
o
5
ok
Control
2
4
Time (mln)
6
8
200
iilil!!1
FIG. 5. Effect of apnoeic oxygenation (O
O) and continuous flow ventilation CFV ( 0
# ) on Pa COi and Pa Ol in five
patients. Mean values and SD. The difference between the
increase of PtL<x>t ™ apnoeic oxygenation and during CFV was
statistically significant {P < 0.05).
Cardiovascular system
Cat. In the five preparations where CFV
maintained carbon dioxide homeostasis, mean
arterial pressure decreased from 118mmHg to
68mmHg (P < 0.001). A typical recording of
IPPV
CFV
FIG. 6. Arterial pressure (AP) in one cat during IPPV and
CFV.
AO
"-IPPVCFV
FIG. 7. Arterial (AP) and airway (P AW ) pressures during CFV, apnoeic oxygenation (AO) and IPPV
in one dog, showing effect of the increase in / 3 a COi on arterial pressure during apnoeic oxygenation.
CONTINUOUS FLOW VENTILATION
remained near control values of 103 beat min"1
and 90 mm Hg, respectively.
549
Bitterman and colleagues (1983) found that gas
insufflated through a single catheter with its tip
placed near the carina failed to eliminate carbon
dioxide and hence it appears that continuous flow
ventilation depends on directing gas at high
DISCUSSION
velocity into both main bronchi. The mechanism
This study confirms that, in some cats, as in all the by which carbon dioxide elimination is maintained
dogs studied, a physiological PaCOl can be during continuous flow ventilation without conmaintained by delivering a continuous flow of ventional inspiratory and expiratory phases has
1 litre kg"1 min"1 of fresh gas to the main bronchi not been investigated. It seems unlikely that
at high velocity through fine catheters. In human cardiogenic oscillation plays a significant part in
subjects, because of ethical constraints, a fresh maintaining gas exchange (Chakrabarti et al.,
gas flow rate of only 0.5 litre kg"1 min"1 has been 1981; Horsfield et al., 1982). However, it can be
used so far, in spite of which the results reported postulated that a high gas velocity must provide a
here show that the rate of increase in PaCOl was convection interface with the diffusion zone and
decreased by approximately 30 % compared with this must depend on the kinetic energy of the fresh
that observed during apnoeic oxygenation.
gas molecules in the bronchi.
The tube which was developed for use in the dog
The use of continuous flow ventilation would
was easy to apply, and was much easier to use than allow recording, free from the movement artefact
the system described previously using Carlen's resulting from ventilation, of, for example, unit
tubes with manometer lines inserted to the activity in the brain and in nerves and structures
bronchi (Chakrabarti and Whitwam, 1984). In the in the thorax and abdomen.
dog both Paco, and PaOt could be maintained
In man, it seems unlikely that an endobronchial
within their physiological ranges using continuous gas flow of 1 litre kg"1 min"1 could be applied
flow ventilation with either air or oxygen without safely under all conditions. However, it is clear
adversely affecting the circulation. At the end of from this present study that half this flow rate
the investigations when the thorax was opened, causes significant carbon dioxide elimination. It is
the right upper lobe, the bronchus of which arises possible that, with a modified form of ventilation—
from the trachea, was found to be collapsed, but for example low frequency at 3-5 b.p.m., this
this did not prevent the maintenance of a stable effect could be exploited to assist artificial
P&O, while insufflating with air (Chakrabarti and ventilation.
Whitwam, 1984).
In contrast, various factors seem to be more
critical in the cat than in the dog. The cat has a
ACKNOWLEDGEMENT
relatively narrow trachea which limits the internal
We
wish
to
thank
Professor L. Blumgart for permission to
diameter of the tracheal tube, so that there is a
study his patients.
tendency for a rapid increase in the pressure in the
airways as the flow rate of the insufflating gas is
increased. This causes excessive inflation of the
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Anaesth., 55, 1005.
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