The effects of perfluorocarbon dosing strategy on cerebral blood flow when starting partial liquid ventilation: A randomized, controlled, experimental study

doi:10.4236/ojped.2012.23033

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Open Journal of Pediatrics, 2012, 2, 197-213 OJPed

http://dx.doi.org/10.4236/ojped.2012.23033 Published Online September 2012 (http://www.SciRP.org/journal/ojped/)

The effects of perfluorocarbon dosing strategy on cerebral

blood flow when starting partial liquid ventilation: A

randomised, controlled, experimental study

Mark W. Davies1,2,3, Kimble R. Dunster1,4,5, John F. Fraser2,5, Paul B. Colditz3

1Grantley Stable Neonatal Unit, Royal Brisbane and Women’s Hospital, Brisbane, Australia

2Department of Paediatrics & Child Health, The University of Queensland, Brisbane, Australia

3Perinatal Research Centre, The University of Queensland, Royal Brisbane and Women’s Hospital, Brisbane, Australia

4Medical Engineering Research Facility, Queensland University of Technology, Brisbane, Australia

5Critical Care Research Group, The Prince Charles Hospital, Brisbane, Australia

Email: [email protected]

Received 14 May 2012; revised 16 July 2012; accepted 25 July 2012

ABSTRACT

Introduction: Partial liquid ventilation may benefit

the lung disease in preterm neonates but intratracheal

instillation of perfluorocarbon increases cerebral blood

flow and may cause brain injury. We aimed to deter-

mine if the effects of perfluorocarbon administration

on cerebral blood flow vary by dose-volume, rate of

administration, endotracheal tube portal of entry, or

closely targeting PaCO2. Methods: Forty-two dosing

events (in eleven rabbits) were randomised to different

dosing strategies, including a sham (i.e., placebo/con-

trol) dose of air over 20 min, 20 mL/kg of perfluoro-

carbon slowly over 20 min, 10 mL/kg of perfluoro-

carbon moderately fast over 10 min, 10 mL/kg of per-

fluorocarbon rapidly over 5 min, 10 mL/kg of per-

fluorocarbon slowly over 20 min via the endotracheal

tube tip lumen (as opposed to the proximal end of the

tube used in all other groups), or 10 mL/kg of per-

fluorocarbon slowly over 20 min whilst targeting a

PaCO2 of 45 - 50 mmHg. Blood gases, haemo-

dynamics, cortical cerebral blood flow and carotid

flow were recorded continuously for 30 minutes from

the start of each dose. Results: Carotid flow increased

with 20 mL/kg perfluorocarbon and cortical cerebral

blood flow was significantly more variable. Carotid

and cortical cerebral blood flow increased using 10

mL/kg or 20 mL/kg with no difference between the

two dose-volumes. There was no difference in cerebral

blood flow by rate of administration, but carotid blood

flow was more variable during slow administration.

There were no differences in the increase in cerebral

blood flow by portal of entry. If PaCO2 was main-

tained between 45 - 50 mmHg there was no increase

in cerebral blood flow and there was less variable

carotid flow. Conclusions: Cerebral blood flow in-

creases with perfluorocarbon dosing. This occurs

regardless of the dose-volume of perfluorocarbon.

These effects were mitigated by closely targeting

PaCO2.

Keywords: Cerebral Blood Flow; Fluorocarbons; Infant;

Newborn Preterm; Partial Liquid Ventilation

1. INTRODUCTION

Preterm infants, especially those born extremely preterm,

require a great deal of support ex utero. They are often

severely ill and their chances of survival are greatly

reduced [1]. Many die because of general immaturity; as

multiple organ systems, including the lungs, cannot adapt

to extrauterine life. Many die of overt lung disease [1].

However, the positive pressure ventilation which they

require to survive is often a cause of significant and

persistent lung injury [2].

Partial liquid ventilation has been touted as an alter-

native form of respiratory support for extremely immature

lungs and severe lung disease: not only to provide a more

effective form of respiratory support but to provide that

support with much less lung injury [3]. A recent exper-

imental study has renewed the promise that partial liquid

ventilation has significant potential to alter the course of

neonatal lung disease and reduce respiratory morbidity

[4].

Extremely preterm infants are also prone to specific

forms of brain injury such as intraventricular haemorrhage,

periventricular leucomalacia and other types of white

matter injury [5]. Rapid changes or disturbance of ven-

tilation can lead to fluctuations in cerebral blood flow

which have been shown to substantially increase the risk

of brain injury [6,7].

OPEN ACCESS

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213

198

In a previous study we have shown that preterm lambs

receiving a 30 mL/kg dose of tracheal perfluorocarbon

liquid, given over 20 minutes at the start of partial liquid

ventilation, had an increased cortical cerebral blood flow

[8]. This did not seem to be due to any general haemo-

dynamic disturbance, although the lambs that had tracheal

perfluorocarbon did have a small, non-significant increase

in arterial carbon dioxide [8]. The increase in cortical

cerebral blood flow did not differ with varying doses of

tracheal perfluorocarbon (20, 30 or 40 mL/kg given over

20 minutes) [9].

As with any treatment, the benefits of partial liquid

ventilation will need to be weighed against any harm. It

is known that increases in cerebral blood flow put very

preterm infants at greater risk of intraventricular haemor-

rhage and brain injury [6,7]. Any gains in using partial

liquid ventilation to improve gas exchange should not be

at the expense of a higher risk of brain injury. It may be

that smaller doses of perfluorocarbon will allow adequate

treatment of lung disease with minimal effects on cerebral

blood flow. Also, regardless of the dose used, it may be

that perfluorocarbon dosing can be optimised to minimise

any effects on cerebral blood flow.

Before its use in human preterm neonates, the effects

on cerebral blood flow of partial liquid ventilation need

to be determined in a relevant animal model. It has not

been established whether different methods of giving the

initial dose of perfluorocarbon affect the degree and

duration of any changes in cerebral blood flow.

We hypothesised that a 20 mL/kg dose of perfluo-

rocarbon administered when starting partial liquid ven-

tilation would disturb cerebral blood flow. Liquid ven-

tilation starts when the perfluorocarbon liquid is intro-

duced into the lungs. We also hypothesised that the degree

and duration of changes in cerebral blood flow would

vary with:

 the dose of perfluorocarbon administered;

 the duration over which the dose is given (5, 10 or 20

minutes);

 the portal of entry of the perfluorocarbon into the

ETT (side-port on the ETT manifold versus an auxi-

liary lumen further down the ETT); and

 whether, during pressure-controlled ventilation, the

peak inspiratory pressure is adjusted to maintain

PaCO2 or not.

Our aims were to:

1) confirm in a rabbit model (with no lung disease) that

administration of a dose of 20 mL/kg of perfluorocarbon

during commencement of partial liquid ventilation

increased cerebral blood flow and its variability;

2) investigate the effects of a lower initial dose (10

mL/kg versus 20 mL/kg) of perfluorocarbon on cerebral

blood flow and its variability;

3) investigate the effects of different rates of ad-

ministration of the initial dose of perfluorocarbon (10

mL/kg over 5, 10 or 20 minutes) on cerebral blood flow

and its variability;

4) investigate the effects of the ETT portal of entry of

the initial dose of perfluorocarbon on cerebral blood flow

and its variability;

5) investigate the effects of adjusting the peak inspir-

atory pressure to maintain the arterial carbon dioxide

between 45 and 50 mmHg during the initial dose of

perfluorocarbon on cerebral blood flow and its variability.

2. MATERIALS AND METHODS

To study the effects of different dosing strategies of

perfluorocarbon, we used the adult New Zealand white

rabbit which is in the human neonatal weight-range

(similar to the preterm lambs previously studied [8,9]).

The necessary procedures and monitoring are readily

performed in rabbits of this size. The use of an adult

rabbit with no lung disease allows repeated study over

many hours.

2.1. Animal Preparation

Anaesthesia was induced in each rabbit with intra-

muscular atropine (0.1 mg/kg) followed by intra-muscular

Zoletil (tiletamine and zolazepam, 10 mg/kg) and xylazine

(2 mg/kg). An intra-venous line (22 - 24 gauge Insyte

catheter) was inserted into an ear vein and anaesthesia

maintained with an infusion of propofol (0.5 mL/kg/hr).

An intravenous infusion of 3 mL/kg/hr of 10% dextrose

was given throughout. The rabbits were then intubated

via a tracheostomy with a 3.0 HI-LO Jet multi-lumen

endotracheal tube (MuLETT) [Mallinckrodt Inc, Argyle,

New York, USA] with a ligature around the trachea (to

prevent leakage). Mechanical ventilation was commenced

as described below. Respiratory function was monitored

with a VenTrak neonatal pneumotachograph and respir-

atory mechanics monitor (Model 1550, Novametrix

Medical Systems, Wallingford, Connecticut, USA).

A NeoTrend catheter (Diametrics Medical, High

Wycombe, UK), calibrated as per the manufacturer’s

instructions, was then inserted into the descending aorta

via the femoral artery. This allowed continuous mea-

surement of intra-arterial oxygen tension (PaO2), carbon

dioxide tension (PaCO2), pH, temperature, bicarbonate,

base excess and oxygen saturation.

The right common carotid artery was exposed and a 2

mm ultrasonic flow probe (Transonic 2SB) was placed

around the right carotid artery and connected to the T206

Transonic Flowmeter (Transonic Systems Inc., Ithaca,

New York, USA).

Cerebral cortical blood flow was monitored using a

laser Doppler probe (Oxford Array, Oxford Optronix,

Oxford, UK) inserted into the parietal cortex (through a

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213 199

burr hole half-way between a line joining the outer

corner of the eye and top of the ear insertion, and the top

of skull) and the probe was held in place as previously

described [10].

Standard physiological monitoring included heart rate

(ECG), oxygen saturation (peripheral pulse oximetry)

and continuous arterial blood pressure.

After completion of all dosing events the rabbit was

killed with 5 mL pentobarbitone sodium (Lethabarb, 325

mg/mL). The mean (SD) duration from anaesthesia in-

duction to pentobarbitone injection was 7.7 (0.74) hours.

2.2. Mechanical Ventilation

The rabbits were ventilated with a neonatal ventilator

(Bear Cub, Bear Medical Systems, Riverside, California)

at 30 breaths per minute, peak inspiratory pressure (PIP)

12 cmH2O, positive end expiratory pressure (PEEP) 5

cmH2O, and inspiratory time of 0.75 seconds. The frac-

tion of inspired oxygen (FiO2) was initially 0.21, in-

creased as necessary to maintain pulse oximetry oxygen

saturations between 94% and 97%. PIP was adjusted to

maintain PaCO2 between 40 - 45 mmHg until the com-

mencement of each dosing strategy phase. No further

adjustment of ventilation, with the exception of FiO2,

were allowed except during the PLV10-slow-proxi-

mal-PC-adjust PIP dosing strategy (see below).

2.3. Perfluorocarbon Dose Volume

The perfluorocarbon dose volumes were chosen to en-

able comparisons with earlier studies in preterm lambs.

We chose 20 mL/kg, as used in our earlier preterm lamb

studies [9], in order to confirm similar effects of per-

fluorocarbon dosing on cerebral blood flow. We then

chose 10 mL/kg as the comparison dose as it was more

easily removed from the lungs between dosing events

and yet was in the range of doses with demonstrated ef-

ficacy in animal studies. Dose-dependent improvement

in lung function has been demonstrated during partial

liquid ventilation but the majority of improvement in

lung function has occurred with relatively small doses

(up to ~10 mL/kg) [11,12]. In rabbits 9 - 12 mL/kg has

been shown to improve lung function [12-14]. In animal

models with no lung disease 10 mL/kg has been shown

to disturb gas exchange less than 30 mL/kg and thus pro-

vide a more stable model to study haemodynamic ef-

fects [15].

2.4. Group Allocation

Each rabbit was allocated to multiple dosing strategies to

reduce the number of animals used. Following pre-

paration, each rabbit was randomly allocated a perfluo-

rocarbon dosing strategy and then monitored for one

minute before and 30 minutes after the start of each

dosing event. After each dosing event (and washout

period) each rabbit was randomly allocated to another

perfluorocarbon dosing strategy.

Eleven rabbits (mean  SD weight of 4.0  0.59 kg)

were randomised to up to six of the seven following

dosing strategies:

1) A CONTROL-PC group which was given a sham

(i.e., placebo/control) dose of air (10 mL/kg) over 20 min

via the wye-piece at the proximal end of the ETT (see

Figure 1) on pressure-controlled ventilation;

2) A PLV20-slow-proximal-PC group which was given

20 mL/kg of FC-77 slowly over 20 min via the wye-

piece at the proximal end of the ETT on pressure-con-

trolled ventilation;

3) A PLV10-slow-proximal-PC group which was given

10 mL/kg of FC-77 slowly over 20 min (0.5 mL/kg/min)

via the wye-piece at the proximal end of the ETT on

pressure-controlled ventilation;

4) A PLV10-faster-proximal-PC group which was

given 10 mL/kg of FC-77 moderately fast over 10 min

(1.0 mL/kg/min) via the wye-piece at the proximal end

of the ETT on pressure-controlled ventilation;

5) A PLV10-rapid-proximal-PC group which was

given 10 mL/kg of FC-77 rapidly over 5 min (2.0 mL/

kg/min) via the wye-piece at the proximal end of the

ETT on pressure-controlled ventilation;

6) A PLV10-slow-tip-PC group which was given 10

mL/kg of FC-77 slowly over 20 min via ETT tip lumen

(see Figure 1) on pressure-controlled ventilation;

7) A PLV10-slow-proximal-PC-adjust PIP group

which was given 10 mL/kg of FC-77 slowly over 20 min

via the wye-piece at the proximal end of the ETT with

the PIP adjusted to maintain the PaCO2 between 45 and

50 mmHg on pressure-controlled ventilation.

In groups 1 to 6 above no further adjustment of venti-

lation (with the exception of FiO2) was allowed after the

commencement of each dosing event studied.

Portal of Entry

The dose of perfluorocarbon is usually given through a

sideport wye-piece on the ETT-connector at the proximal

end of the endotracheal tube. In this study doses of per-

fluorocarbon were given via one of two portals, either

through a wye-piece at the proximal end of the ETT or

through the ETT tip lumen (Figure 1). The use of a

wye-piece was necessary to allow the pneumotachograph

to be fitted between the ETT-circuit manifold and the

ETT connector and prevent reflux of perfluorocarbon

into the pneumotachograph during instillation.

2.5. Washout

Each dosing event was monitored for 30 minutes from

the start of perfluorocarbon dosing. After each dosing

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213

200

Figure 1. Configuration of the multi-lumen endotracheal tube (MuLETT), pneumotachograph, ETT con-

nector, ETT circuit manifold and wye-piece.

event as much FC-77 as possible was sucked out of the

ETT and trachea using a 5FG umbilical artery catheter

and syringe. Any remaining FC-77 was then left to

evaporate from the lungs via the expiratory line of the

ventilator circuit. Tracheal gas insufflation at 2 L/min via

the distal ETT tip lumen was also used to increase the

rate of evaporation.

The completeness of perfluorocarbon washout could

be confirmed when the expired tidal volume equalled the

inspired tidal volume. Because there is no expired gas in

the inspiratory limb of the ventilator circuit and FC-77

vapour is known to affect tidal volume measurement

with the VenTrak pneumotachograph [16] it was possible

to determine that all the FC-77 had evaporated from the

lung when the expired tidal volume equalled the inspired

tidal volume (i.e., when there was no more perfluo-

rocarbon vapour in the expired gases). The effect of

FC-77 vapour has been well documented [16]. The mea-

surement of tidal volumes in the range from 5 to 25 mL

using the VenTrak pneumotachograph has coefficients of

variation ranging from 0.008 to 0.04 without perfluo-

rocarbon vapour and from 0.006 to 0.06 with perfluo-

rocarbon vapour. The differences seen in TV measure-

ment are more than 7%.

After this washout period, between each dosing event,

mechanical ventilation continued as before. Once the

rabbit was stable they were then randomly allocated to

another perfluorocarbon dosing strategy as above.

Stabilisation times before each dosing event differed

between those dosing events where there was no prior

perfluorocarbon use (therefore no washout was required)

and those dosing events where a prior washout was

OPEN ACCESS

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213 201

required. The mean (SD) stabilisation time for the former

was 15.4 (6.96) minutes and for the latter was 64.9

(14.26) minutes.

2.6. Measurements

Two methods of assessing cerebral blood flow were used,

both recorded continuously: cerebral cortical blood flow

(laser Doppler flowmetry), as used in the previous pre-

term lamb studies; and right carotid blood flow (Tran-

sonic Flowmeter). Carotid flow was used to assess more

global brain blood flow to ensure that previous effects

seen were not restricted to the cerebral cortex. The coef-

ficient of variation (CV) for these two measurements

were calculated to assess their variability.

The following were all recorded continuously: heart

rate, blood pressure, peripheral oxygen saturation (pulse

oximetry), PaO2, PaCO2, pH, bicarbonate, base excess,

arterial oxygen saturation, temperature, dynamic com-

pliance, peak inspiratory pressure, and tidal volume.

FiO2 was recorded at the start of each dosing event and

the timing of any changes recorded thereafter.

2.7. Sample Size

Sample size calculation was based on carotid blood flow

data from Takeuchi et al. [17] where mean (SD) carotid

blood flow was 13.8 (3.39) mL/min. Therefore a sample

size of six in each group is required to show an absolute

difference of 6.1 mL/min between groups (



= 0.05,

power of 80% –



= 0.2).

2.8. Data Analysis

2.8.1. Data Display

For each dosing event mean values for continuously

measured variables and calculated variables were calcu-

lated at baseline (the average during the minute immedi-

ately prior to perfluorocarbon or air dosing) and every

minute for the 30 minute observation period. For each

1-min period means were calculated from all measure-

ments made over the one minute period. For the six dos-

ing events for each dosing strategy the mean (SD) was

calculated at baseline and every minute to 30 minutes

and these data were then displayed graphically over time.

For laser Doppler flow and carotid blood flow the per-

cent change from baseline was calculated for each datum

and then for each dosing event the data were averaged

for each one minute period. Calculations and graphs

were produced using Microsoft Excel 2002 (Microsoft

Corporation, Redmond, Washington, USA).

To assess the variability of laser Doppler flow and ca-

rotid flow, the coefficient of variation was calculated for

each one minute period for each dosing event. The coef-

ficient of variation is calculated by dividing the standard

deviation by the mean for each one minute period.

2.8.2. Statistical Analysis

To determine if there were any statistically significant

differences between the dosing strategy groups, the data

were compared at two time points: at the end of the dos-

ing period (i.e., at 5, 10 or 20 min) and at the point of

maximal difference between groups. These time points

were chosen as the most clinically relevant points for

between group comparisons. For the purpose of these

statistical tests the data were converted to change from

baseline—this controlled for any differences between

dosing strategy groups at baseline. If the data were nor-

mally distributed and the variances were equal the

groups were compared using Student’s t-test or one-way

ANOVA. If the data were not normally distributed or the

variances were not equal the groups were compared us-

ing the Mann-Whitney test or Kruskal-Wallis test. The

distribution of data were tested using the Kolmo-

gorov-Smirnov normality test with Dallal-Wilkinson-

Lillie for P value. The F test was used to compare vari-

ances. These data analyses were done using GraphPad

Prism version 4.03 (GraphPad Software Inc., San Diego,

CA). A p value of <0.05 was considered to be statistic-

cally significant.

2.9. Ethics Approval

Ethical approval was obtained from the University of

Queensland Animal Experimentation and Ethics Com-

mittee. All of the experimental procedures were per-

formed in accordance with the guidelines established by

the National Health and Medical Research Council of

Australia in its Australian Code of Practice for the Care

and Use of Animals for Scientific Purposes [18].

3. RESULTS

Figures 2 and 3 show the relative changes (% change

from baseline) for both carotid flow and cortical cerebral

blood flow for each perfluorocarbon dosing strategy. In

each figure the vertical scales are identical for ease of

comparison. Tables 1 and 2 summarise the maximum

variations in flow for the two cerebral blood flow vari-

ables by dosing strategy.

3.1. Does 20 mL/kg of Perfluorocarbon Disturb

Cerebral Blood Flow?

We compared the CONTROL-PC group with the

PLV20-slow-proximal-PC group.

Carotid blood flow was increased relative to baseline

during the initial 20 minute dose of 20 mL/kg perfluoro-

carbon when starting partial liquid ventilation compared

with continuing on pressure-controlled conventional

mechanical ventilation—Mann-Whitney test p = 0.04 at

the end of the dose and p = 0.04 at the time of maximum

difference (21 min). The highest mean increase in

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213

202

-40

-20

100

120

pre12 3 45 6 7 89101112131415161718192021222324252627282930

time (minutes)

% change

carotid

flow

CONTROL-PC

-40

-20

100

120

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time (minutes)

% change

carotid

flow

CONTROL-PC

(a)

-40

-20

100

120

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time (minutes)

% change

carotid

flow

PLV20-slow-proximal-PC

FC-77 dose

-40

-20

100

120

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time (minutes)

% change

carotid

flow

PLV20-slow-proximal-PC

FC-77 dose

PLV20-slow-proximal-PC

FC-77 dose

(b)

-40

-20

100

120

pre123456789101112131415161718192021222324252627282930

time

(

minutes

)

% change

c arotid

flow

PLV10-slow-proximal-PC

FC-77 dose

-40

-20

100

120

pre123456789101112131415161718192021222324252627282930

time

(

minutes

)

% change

c arotid

flow

PLV10-slow-proximal-PC

FC-77 dose

PLV10-slow-proximal-PC

FC-77 dose

(c)

OPEN ACCESS

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213 203

-40

-20

100

120

pre123456789101112131415161718192021222324252627282930

time

(

minutes

)

% change

carotid

flow

PLV10-faster-proxim al-P C

FC-77 dose

-40

-20

100

120

pre123456789101112131415161718192021222324252627282930

time

(

minutes

)

% change

carotid

flow

PLV10-faster-proxim al-P C

FC-77 dose

PLV10-faster-proximal-PC

FC-77 dose

(d)

-40

-20

100

120

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time (minutes)

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carotid

flow

PLV10-rapid-proximal-PC

FC-77 dose

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-20

100

120

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time (minutes)

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carotid

flow

PLV10-rapid-proximal-PC

FC-77 dose

PLV10-rapid-proximal-PC

FC-77 dose

(e)

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-20

100

120

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time (minutes)

% change

carotid

flow

PLV10-s low-tip-PC

FC-77 dose

-40

-20

100

120

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time (minutes)

% change

carotid

flow

PLV10-s low-tip-PC

FC-77 dose

PLV10-slow-tip-PC

FC-77 dose

(f)

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213

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-40

-20

100

120

pre123456789101112131415161718192021222324252627282930

time

(

minutes

)

% change

carotid

flow

PLV10-slow-proximal-PC-adjust PIP

FC-77 dose

-40

-20

100

120

pre123456789101112131415161718192021222324252627282930

time

(

minutes

)

% change

carotid

flow

PLV10-slow-proximal-PC-adjust PIP

FC-77 dose

PLV10-slow-proximal-PC-adjust PIP

FC-77 dose

(g)

Figure 2. Relative changes (% change from baseline) of carotid blood flow for each perfluorocarbon dosing strategy. All vertical

scales are identical for ease of comparison.

-20

100

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time (minutes)

% change

LDF

CONTROL-PC

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time (minutes)

% change

LDF

CONTROL-PC

(a)

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time (minutes)

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LDF

PLV20-slow-proximal-PC

FC-77 dose

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100

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time (minutes)

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LDF

PLV20-slow-proximal-PC

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100

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time (minutes)

% change

LDF

PLV20-slow-proximal-PC

FC-77 dose

PLV20-slow-proximal-PC

FC-77 dose

(b)

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213 205

-20

100

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time (minutes)

% change

LD F

PLV10-sl ow-pro ximal-PC

FC-77 dose

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time (minutes)

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LD F

PLV10-sl ow-pro ximal-PC

FC-77 dose

PLV10-slow-proximal-PC

FC-77 dose

(c)

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LDF

PLV 1 0-fas ter-pro ximal-P C

FC-77 dose

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100

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time (minutes)

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LDF

PLV 1 0-fas ter-pro ximal-P C

FC-77 dose

PLV10-faster-proximal-PC

FC-77 dose

(d)

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100

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time (minutes)

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LD F

PLV10-ra pid-pro ximal-PC

FC-77 dose

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time (minutes)

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LD F

PLV10-ra pid-pro ximal-PC

FC-77 dose

PLV10-rapid-proximal-PC

FC-77 dose

(e)

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LD F

PLV 10-slow-tip-P C

FC-77 dose

-20

100

pre12 3 456 7 89101112131415161718192021222324252627282930

time (minutes)

% change

LD F

PLV 10-slow-tip-P C

FC-77 dose

PLV10-slow-tip-PC

FC-77 dose

(f)

-20

100

pre1 2 3 45 6 7 89101112131415161718192021222324252627282930

time

(

minutes

)

% change

LD F

PLV10-slow-proximal-PC-adjust PIP

FC-77 dose

-20

100

pre1 2 3 45 6 7 89101112131415161718192021222324252627282930

time

(

minutes

)

% change

LD F

PLV10-slow-proximal-PC-adjust PIP

FC-77 dose

PLV10-slow-proximal-PC-adjust PIP

FC-77 dose

(g)

Figure 3. Relative changes (% change from baseline) of cortical cerebral blood flow for each perfluorocarbon dosing strategy. All

vertical scales are identical for ease of comparison.

Table 1. The extent of the relative changes of carotid blood flow.

Group PFC dose duration % increase

at end of dose

Maximum %

increase (at time)

Minimum %

decrease (at time)

CONTROL-PC did not get PFC did not get PFC 4 (19 min) 4 (7 min)

PLV20-slow-proximal-PC 20 min 50 52 (27 min) 3 (2 min)

PLV10-slow-proximal-PC 20 min 95 105 (22 min) no decrease

PLV10-faster-proximal-PC 10 min 39 50 (12 min) no decrease

PLV10-rapid-proximal-PC 5 min 1 11 (11 min) 6 (3 min)

PLV10-slow-tip-PC 20 min 57 62 (17 min) no decrease

PLV10-slow-proximal-PC-adjust PIP20 min –10 no increase 14 (14 min)

PFC—perfluorocarbon.

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213

207

OPEN ACCESS

Table 2. The extent of the relative changes of cortical cerebral blood flow.

Group PFC dose duration % increase

at end of dose

Maximum %

increase (at time)

Minimum %

decrease (at time)

CONTROL-PC did not get PFC did not get PFC 17 (30 min) 1 (1 min)

PLV20-slow-proximal-PC 20 min 46 51 (26 min) 1 (2 min)

PLV10-slow-proximal-PC 20 min 24 29 (24 min) no decrease

PLV10-faster-proximal-PC 10 min 14 18 (11 min) 1 (1 min)

PLV10-rapid-proximal-PC 5 min 6 14 (7 min) 3 (29 min)

PLV10-slow-tip-PC 20 min 47 47 (20 min) no decrease

PLV10-slow-proximal-PC-adjust PIP 20 min –2 2 (2 min) 7 (23 min)

carotid blood flow was around 50% in the PLV20-slow-

proximal-PC (Figures 2(a) and (b)). In the CON-

TROL-PC dosing event group the carotid blood flow

remained with 5% of baseline throughout the 30 min.

A similar increase in cortical cerebral blood flow was

seen in the PLV20-slow-proximal-PC group (Figure

3(b)). In the CONTROL-PC dosing event group the

laser Doppler flow increased slightly up to a maximum

increase of around 18% whereas in the PLV20-slow-

proximal-PC group the laser Doppler flow increased to

a maximum of about 50%. The differences between

groups was not statistically significant—Mann-Whitney

test p = 0.31 at the end of the dose and p = 0.24 at the

time of maximum difference (26 min).

During perfluorocarbon dosing there was more vari-

ability in carotid blood flow but this difference did not

reach statistical significance—Mann-Whitney test p =

0.065 at the end of the dose and Student’s t test

Mann-Whitney test p = 0.18 at the time of maximum

difference (30 min). There was significantly more vari-

ability in cortical cerebral blood flow during perfluoro-

carbon dosing—Mann-Whitney test p = 0.0043 at the

end of the dose and Mann-Whitney test p = 0.041 at the

time of maximum difference (25 min). See additional

data file, pp. 3-5.

See additional data file (pp. 6-17) for the results of

haemodynamics, vital signs and respiratory function.

3.2. Does a Lower Dose of Perfluorocarbon

Disturb Cerebral Blood Flow?

We compared the PLV10-slow-proximal-PC group with

the PLV20-slow-proximal-PC group.

Carotid blood flow increased over the 30 minute ob-

servation period in both groups (Figures 2(b) and (c)) but

there was no difference between groups—Mann-Whitney

test p = 0.82 at the end of the dose and Mann-Whitney

test p = 0.82 at the time of maximum difference (24 min).

The highest mean increase in carotid blood flow was

around 105% in the PLV10-slow-proximal-PC group

and around 50% in the PLV20-slow-proximal-PC group.

Whilst cortical cerebral blood flow increased in both

groups (Figures 3(b) and (c)) there was no statistically

significant difference between groups—Student’s t test p

= 0.48 at the end of the dose and Mann-Whitney test p =

0.59 at the time of maximum difference (27 min).

During perfluorocarbon dosing there was considerable

variability in both carotid blood flow and cortical cere-

bral blood flow (see additional data file, pp. 18-20) but

there were no statistically significant differences between

groups. For the variability of carotid flow the Mann-

Whitney test p = 0.065 at the end of the dose and Stu-

dent’s t test p = 0.058 at the time of maximum difference

(3 min). For variability of cortical cerebral blood flow

the Student’s t test p = 0.48 at the end of the dose and

Mann-Whitney test p = 0.59 at the time of maximum

difference (27 min).

See additional data file (pp. 21-32) for the results of

haemodynamics, vital signs and respiratory function.

3.3. Do Different Rates of Administration Affect

Cerebral Blood Flow?

We compared the PLV10-slow-proximal-PC group, the

PLV10-faster-proximal-PC group and the PLV10-rapid-

proximal-PC group.

Carotid blood flow increased during the initial dose of

10 mL/kg perfluorocarbon when starting partial liquid

ventilation in both the PLV10-slow-proximal-PC and

PLV10-faster-proximal-PC groups (Figures 2(c) and (d)).

In the PLV10-rapid-proximal-PC group the increase in

carotid blood flow was much less pronounced (Figure

2(e)). The extent of the changes of carotid blood flow are

shown in Table 1. The relative increase in carotid blood

flow was greatest when the dose of perfluorocarbon was

given slowly and least when the dose was given rapidly.

However, there were no statistically significant dif-

ferences between groups for carotid blood flow—

Kruskal-Wallis test p = 0.26 at the end of the dose and

Kruskal-Wallis test p = 0.29 at the time of maximum

difference (23 min).

Cortical cerebral blood flow increased in all three

groups (Figures 3(c)-(e)). The pattern of changes were

different between all three groups and the extent of the

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213

208

changes of cortical cerebral blood flow are shown in Ta-

ble 2. The relative increase in cortical cerebral blood

flow was greatest when the dose of perfluorocarbon was

given slowly (Figure 3(c)) and least when the dose was

given rapidly (Figure 3(e)). Importantly when the dose

was given rapidly (over 5 minutes) the cortical cerebral

blood flow increased quickly but decreased back to

around baseline by about 12 minutes. When the dose of

perfluorocarbon is given over 10 or 20 minutes cortical

cerebral blood flow remained increased throughout the

30 minute observation period. However, there were no

statistically significant differences between groups—

one-way ANOVA p = 0.40 at the end of the dose and

one-way ANOVA p = 0.12 at the time of maximum dif-

ference (25 min).

During perfluorocarbon dosing there was a statistically

significant difference between groups for variability in

carotid blood flow—Kruskal-Wallis test p = 0.16 at the

end of the dose and one-way ANOVA p = 0.02 at the

time of maximum difference (18 min). There was no

statistically significant difference between groups for

variability in cortical cerebral blood flow—Kruskal-

Wallis test p = 0.22 at the end of the dose and Kruskal-

Wallis test p = 0.87 at the time of maximum difference

(1 min). See additional data file, pp. 33-35.

See additional data file (pp. 36-47) for the results of

haemodynamics, vital signs and respiratory function.

3.4. Does the Portal of Entry of the Dose of

Perfluorocarbon Affect Cerebral Blood

Flow?

We compared the PLV10-slow-proximal-PC group with

the PLV10-slow-tip-PC group. The PLV10-slow-pro-

ximal-PC group had a dose of FC-77 (10 mL/kg) given

over 20 min via the wye-piece at the proximal end of the

ETT (Figure 1) whilst on pressure-controlled ventilation.

The PLV10-slow-tip-PC group had 10 mL/kg of FC-77

given over 20 min via the ETT tip lumen (Figure 1)

whilst on pressure-controlled ventilation.

Carotid blood flow increased over the 30 minute ob-

servation period in both groups (Figures 2(c) and (f)).

The differences were not statistically significant—Mann-

Whitney test p = 0.39 at the end of the dose and Mann-

Whitney test p = 0.48 at the time of maximum difference

(24 min). The highest mean increase in carotid blood

flow was around 110% in the PLV10-slow-proximal-

PC group and around 60% in the PLV10-slow-tip-PC

group.

Cortical cerebral blood flow increased in both groups

(Figures 3(c) and (f)). The differences were not statistic-

cally significant—Mann-Whitney test p = 0.94 at the end

of the dose and Student’s t test Mann-Whitney test p =

0.94 at the time of maximum difference (15 min). The

highest mean increase in cortical cerebral blood flow was

around 47% in the PLV10-slow-tip-PC group and

around 29% in the PLV10-slow-proximal-PC group.

During perfluorocarbon dosing there were no statistic-

cally significant difference between the two groups for

carotid blood flow variability—Mann-Whitney test p =

0.24 at the end of the dose and Mann-Whitney test p =

0.13 at the time of maximum difference (3 min). There

was a little more variability in cortical cerebral blood

flow in the PLV10-slow-proximal-PC group. The dif-

ferences were not statistically significant—Mann-Whitney

test p = 0.80 at the end of the dose and Mann-Whitney

test p = 0.093 at the time of maximum difference (2 min).

See additional data file (pp. 48-50).

See additional data file (pp. 51-62) for the results of

haemodynamics, vital signs and respiratory function.

3.5. Does Tight Control of Arterial Carbon

Dioxide during Perfluorocarbon Mitigate

the Effects on Cerebral Blood Flow?

We compared the PLV10-slow-proximal-PC group with

the PLV10-slow-proximal-PC-adjust PIP group.

The relative change in carotid blood flow (Figure 2(c))

showed a significant increase in the PLV10-slow-

proximal-PC group compared with the PLV10-slow-

proximal-PC-adjust PIP group which had a slight de-

crease (Figure 2(g)). These differences were statistically

significant—Mann-Whitney test p = 0.015 at the end of

the dose and Mann-Whitney test p = 0.015 at the time of

maximum difference (24 min). The highest increase in

mean carotid blood flow was around 105% in the

PLV10-slow-proximal-PC group and the lowest de-

crease was around 14% in the PLV10-slow-proximal-

PC-adjust PIP group.

Cortical cerebral blood flow showed a significant in-

crease in the PLV10-slow-proximal-PC group (Figure

3(c)) compared with the PLV10-slow-proximal-PC-

adjust PIP group (Figure 3(g)) which had a slight de-

crease - Mann-Whitney test p = 0.041 at the end of the

dose and Mann-Whitney test p = 0.065 at the time of

maximum difference (23 min). The highest increase in

mean cortical cerebral blood flow was around 29% in the

PLV10-slow-proximal-PC group and the lowest de-

crease was around 7% in the PLV10-slow-proximal-

PC-adjust PIP group.

During perfluorocarbon dosing there was less variabil-

ity in carotid blood flow in the PLV10-slow-proximal-

PC-adjust PIP group—Student’s t test p = 0.019 at the

end of the dose and Mann-Whitney test p = 0.065 at the

time of maximum difference (5 min). There was no dif-

ference between groups for the variability of cortical

cerebral blood flow—Student’s t test p = 0.94 at the end

of the dose and Mann-Whitney test p = 0.39 at the time

of maximum difference (2 min). See additional data file

(pp. 63-65).

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213 209

See additional data file (pp. 66-77) for the results of

haemodynamics, vital signs and respiratory function.

4. DISCUSSION

4.1. Summary of Findings from the Current

Study

Right carotid blood flow was increased during tracheal

perfluorocarbon dosing with 20 mL/kg of FC-77 at the

start of partial liquid ventilation in rabbits. Similar,

non-statistically significant effects were seen in cortical

cerebral blood flow. The variability in cortical cerebral

blood flow was increased. Similar, almost statistically

significant effects were seen in carotid blood flow vari-

ability. There was also a decrease in pH (mirrored by

changes in PaCO2).

Cortical cerebral blood flow and right carotid blood

flow were not different when using 10 mL/kg of per-

fluorocarbon compared with 20 mL/kg. There were no

significant differences in variability of cortical cerebral

blood flow and right carotid blood flow.

Cerebral blood flow did not differ with the rate of ad-

ministration of 10 mL/kg of perfluorocarbon when start-

ing partial liquid ventilation. The variability in carotid

blood flow was increased when the dose is given rapidly.

The effect on cerebral blood flow variability would seem

to be of most clinical importance in the first minutes of

rapid dosing.

Changes in cerebral blood flow are similar regardless

of the portal of entry of the perfluorocarbon dose, i.e., at

the wye-piece at the proximal end of the endotracheal

tube or the tip of the endotracheal tube.

If the peak inspiratory pressure was adjusted during

perfluorocarbon dosing, to maintain the arterial carbon

dioxide between 45 and 50 mmHg, then there was no

increase in cerebral blood flow and there was less vari-

ability in carotid blood flow.

4.2. Interpretation of the Results

Despite the lack of statistically significant between-

group differences in PaCO2 there was a consistent asso-

ciation between increased PaCO2 and increased cerebral

blood flow. In five of the dosing strategies used the

PaCO2 increased during perfluorocarbon dosing, and in

four of those five the tidal volumes decreased. The effect

on tidal volumes, and hence minute ventilation, is not

unexpected in animal models where there is no lung dis-

ease, particularly when no adjustment is made in peak

inspiratory pressures. Partial liquid ventilation is known

to decrease lung compliance in normal lungs, and it also

partially blocks endotracheal tubes during perfluorocar-

bon instillation, increasing the airway resistance [19-21].

Both lead to decreased tidal volumes and/or increased

tidal volumes to maintain PaCO2 [22]. Also PaO2 is

known to be lower during partial liquid ventilation in

animals with normal lungs [15,23]. The most compelling

data that it is simply a decrease in tidal volume that

caused the rise in PaCO2 is that during the dosing strat-

egy where the PaCO2 was closely targeting by adjusting

peak inspiratory pressure the tidal volumes were not de-

creased.

We have no evidence from the current study to suggest

that any other factors were operating during the per-

fluorocarbon dosing episodes in rabbits to increase cere-

bral blood flow. Using adult animals excludes a change

in shunt across a patent ductus arteriosus as a cause for

the increase in cerebral blood flow. Similarly none of the

rabbits had any hypoxic-ischaemic events making any

post-hypoxic-ischaemic hyperperfusion very unlikely

during any of the dosing episodes. None of the rabbits

were hyperthermic at any stage during any of the dosing

episodes; also during those dosing strategies where there

was an increase in cerebral blood flow there was no cor-

responding increase in temperature.

There have been other published reports of studies in-

vestigating the effect of partial liquid ventilation on

cerebral blood flow [8,9,22,24-26]. Two of the reports

are our previous studies in preterm lambs [8,9]. Only one

of the other studies reported measurements during per-

fluorocarbon dosing but in this study there was no con-

trol group for comparison [24]. The studies are discussed

below.

4.3. Comparison with Other Studies

Burkhardt et al. [24] report the only other study that has

investigated the effects of perfluorocarbon dosing on

cerebral concentration of total and oxygenated haemo-

globin using near infrared spectroscopy. They used

newborn piglets of around 730 g and <24 hours old

without lung disease. They were randomised to one of

three different dosing regimens of PF5080:

 10 mL/kg given over about six minutes, target filling

rate of 1.5 mL/min [~2.1 mL/kg/min]; or

 30 mL/kg given over about 16 minutes, target filling

rate of 1.5 mL/min [~2.1 mL/kg/min]; or

 30 mL/kg given over about 41 seconds, target filling

over 30 - 45 s [~40 - 60 mL/kg/min].

The cerebral concentration of oxygenated haemoglo-

bin decreased initially (at 1 minute) when 30 mL/kg was

given rapidly, with return to baseline by 3 min. There

was no decrease with 30 mL/kg given slowly nor when

10 mL/kg was administered. At 5 min and thereafter the

cerebral concentration of oxygenated haemoglobin in-

creased in both 30 mL/kg groups but not in the 10 mL/kg

group. In both 30 mL/kg groups the total cerebral hae-

moglobin concentration increased compared with the 10

mL/kg group. Similarly in both 30 mL/kg groups the

PaCO2 increased and PaO2 decreased but not in the 10

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213

210

mL/kg group.

There was no control group, therefore conclusions

cannot be drawn about the effect of perfluorocarbon

dosing compared with gas ventilation alone. The study

design makes direct comparisons between the two vol-

umes of perfluorocarbon given difficult because the

doses were also given over different durations. Interpre-

tation is also difficult as they did not measure cerebral

blood flow directly, did not record and report real-time

haemodynamic variables during the perfluorocarbon liq-

uid dosing, and only reported changes in cerebral oxy-

genation at discrete time points.

Burkhardt et al. [24] concluded that giving perfluoro-

carbon extremely rapidly (20 - 30 times faster than the

rabbits in our “rapid” group) is not recommended because

of the decrease in cerebral blood flow (as determined by

total cerebral haemoglobin concentration) during per-

fluorocarbon dosing.

The three different rates of administration in our rabbit

studies were:

 slow—10 mL/kg over 20 min—0.5 mL/kg/min;

 faster—10 mL/kg over 10 min—1.0 mL/kg/min;

 rapid—10 mL/kg over 5 min—2.0 mL/kg/min.

The volume and rate of administration in our “rapid”

group in rabbits were almost identical to the volume and

rate in the Burkhardt [24] 10 mL/kg group and similar

results were seen: they found no changes in PaCO2 or

total cerebral haemoglobin concentration. We found a

slight increase (maximum 14%) in cerebral blood flow

during dosing with a much lower increase in cerebral

blood flow compared with the slower administration

rates.

Our previous studies [8,9] investigated the effect of

perfluorocarbon dosing in preterm lambs. We showed

that an intratracheal loading dose of 30 mL/kg of per-

fluorocarbon liquid, instilled over 20 min, caused an in-

crease in cortical cerebral blood flow (measured con-

tinuously with laser Doppler) during the administration

of perfluorocarbon and immediately thereafter. The

highest mean increase in the partial liquid ventilation

group was 27%. There was a slightly lower mean arterial

blood pressure in the partial liquid ventilation group; the

heart rate did not differ between groups. The PaCO2 was

marginally higher in the partial liquid ventilation group

at 30 min—the difference between groups was not statis-

tically significant. These lambs who received 30 mL/kg

were compared with lambs that received either 20 or 40

mL/kg. Cortical cerebral blood flow increased over time

in all three groups but there was no difference between

groups. There was no statistically significant difference

in PaCO2 between groups, but this was only measured at

baseline and at 30 minutes.

Therefore, in preterm lambs there was a consistent ef-

fect of perfluorocarbon dosing causing increased cerebral

blood flow. There did not seem to be any haemodynamic

cause for the increased cerebral blood flow but we could

not rule out an increase in PaCO2. Our rabbit studies

have demonstrated similar increases in cerebral blood

flow with perfluorocarbon dosing and associated in-

creases in PaCO2. It is also possible that in a lamb with a

left-to-right shunt across a patent ductus arteriosus (i.e.,

with decreased cerebral blood flow) that an increase in

pulmonary vascular resistance could decrease the left-

to-right shunt and cause a relative increase in cerebral

blood flow. Our rabbit model has ruled out an effect

from a patent ductus arteriosus.

4.4. Choice of Rabbit Model

In order to study the effects of many different dosing

strategies a simple and reliable model of the effects of

perfluorocarbon administration on cerebral blood flow

was needed. The use of adult New Zealand white rabbits

provides an animal model with the following advantages.

They are in the neonatal size-range (similar to the pre-

term lambs previously studied). The procedures involved

are readily performed in rabbits of this size and they are

familiar to the investigators. Using rabbits of this size,

with no lung disease, gives a far more stable animal that

allows repeated study over many hours, as they are ro-

bust enough to tolerate multiple dosing procedures.

There is no requirement to do experiments on particular

days as with date-mated ewes and their lambs. The con-

founding factors of lung disease and/or patent ductus

arteriosus are eliminated. There is no perinatal asphyxia.

Adult New Zealand white rabbits allowed the use of an

animal in which we could measure continuous cerebral

blood flow—laser Doppler as a reliable measure of cere-

bral blood flow has been validated in adult New Zealand

white rabbits. They also allowed the use two different

methods of measuring continuous cerebral blood flow—

carotid flow and cortical cerebral blood flow.

The different dosing strategies were studied in multi-

ple sequences in single animals: others have also used

this approach. Individual rabbits were not allocated dos-

ing strategies: each dosing event was randomly allocated

a different dosing strategy. This allowed an absolute

minimum number of animals to be used. The PLV10-

slow-proximal-PC group served as the reference strat-

egy for perfluorocarbon dosing. All the dosing strategies

experimental runs were done contemporaneously using

identical methods in the same laboratory with the same

personnel. As best we could be assured at the time only

the dosing strategy differed significantly for any given

run. Differences between dosing strategy groups at base-

line were controlled for with the statistical analysis used

with the data converted to “change from baseline”. All

dosing strategies were randomly allocated and allocation

was concealed until just before each episode of per-

M. W. Davies et al. / Open Journal of Pediatrics 2 (2012) 197-213 211

fluorocarbon dosing. A post hoc analysis of the distribu-

tion of individual rabbits within each dosing strategy

group showed no statistically significant difference

compared with that expected by chance for the 11 rabbits

(Chi squared test, p = 0.98). Similarly the distribution of

the order of the dosing events for each rabbit within each

dosing strategy group showed no statistically significant

difference compared with that expected by chance (Chi

squared test, p = 0.32). Furthermore the oxygen indices

were remarkably similar between all comparison dosing

event groups with low average oxygen indices ranging

from 1.5 to 2.0. This is consistent with minimal lung

disease across all dosing strategy groups for all com-

parisons.

4.5. Implications

From the results of the current study no direct conclu-

sions about the effects in preterms can be made. How-

ever, given that the effect of perfluorocarbon dosing is

the same in rabbits as that which we found in preterm

lambs [8,9] it is likely that the effects seen with different

dosing strategies will also been in preterm lambs.

Our studies were born out of a desire to ensure that if

partial liquid ventilation was to be used in extremely

preterm infants that we should first know whether the

instillation of perfluorocarbon disturbs cerebral blood

flow which would put the infants at risk of brain injury.

If cerebral blood flow is disturbed then it is necessary to

determine if the dose of perfluorocarbon can be given

safely without any cerebral blood flow disturbance.

Given the potential for harm associated with perfluoro-

carbon dosing in the most vulnerable of preterm infants it

is reassuring to know that there are ways of giving per-

fluorocarbon that can mitigate any increase in cerebral

blood flow. This can be achieved best by either monitor-

ing PaCO2 continuously during perfluorocarbon dosing

and keeping it under tight control; not giving the dose

over 5 minutes or faster; and not using the secondary

lumen of an endotracheal tube.

If partial liquid ventilation is to be used, then the best

protection for the extremely preterm brain is to start it

safely without disturbing cerebral blood flow. Data from

these studies will enable optimisation of the dosing

method to be used. Given the availability of a suitable

product, randomised controlled trials of partial liquid

ventilation in neonates are both feasible and desirable

[27,28]. Now the design of such trials can incorporate the

findings of this study to make the dosing procedure as

safe as it can be for use in extremely preterm infants.

5. CONCLUSIONS

The following effects were seen during perfluorocarbon

dosing at the start of partial liquid ventilation in rabbits:

 Compared with conventional gas ventilation right

carotid blood flow increased during perfluorocarbon

dosing with 20 mL/kg. Similar, non-statistically

significant effects were seen in cortical cerebral

blood flow. There was also increased variability in

cortical cerebral blood flow and similar, almost

statistically significant, effects were seen in carotid

blood flow variability. The effects on cerebral blood

flow were similar to that seen in preterm lambs with

lung disease.

 Cortical cerebral blood flow and right carotid blood

flow were not different when using 10 mL/kg of

perfluorocarbon compared with 20 mL/kg. There were

no significant differences in variability of cortical

cerebral blood flow and right carotid blood flow.

The lack of any significant differences between dose

volume groups on cortical cerebral blood flow was

similar to that seen in preterm lambs.

 Cerebral blood flow did not differ with the rate of

administration of 10 mL/kg of perfluorocarbon when

starting partial liquid ventilation. The variability in

carotid blood flow was increased, but this did not

seem to be a consistent or clinically important differ-

ence.

 The increase in cortical cerebral blood flow and

right carotid flow (and their variability) were similar

when the dose was given at the endotracheal tube tip

(via a secondary lumen in the wall of the endo-

tracheal tube) compared with doses given more

proximally.

 If the peak inspiratory pressure was adjusted during

perfluorocarbon dosing to maintain the arterial carbon

dioxide between 45 and 50 mmHg then there was no

increase in cerebral blood flow and there was less

variability in carotid blood flow.

6. ACKNOWLEDGEMENTS

We gratefully acknowledge financial support from The Prince Charles

Hospital Foundation, the Royal Women’s Hospital Paul Weedon

Bursary, and the Royal Women’s Hospital Auxiliary.

Many thanks to Kathy Wilson who contributed significantly to the

work in the animal laboratory. Thanks also to Michael Lindeberg and

Bill Sommers who helped out in the animal laboratory. Thanks to Peter

O’Rourke for his statistical advice.

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Abbreviations

ANOVA: Analysis of variance;

Cdyn: Dynamic compliance;

CI: Confidence interval;

CV: Coefficient of variation;

ETT: Endotracheal tube;

FiO2: Fraction of inspired oxygen;

LDF: Laser Doppler flow;

MuLETT: Multi-lumen endotracheal tube;

PaCO2: Arterial carbon dioxide tension;

PaO2: Arterial oxygen tension;

PC: Pressure-controlled;

PEEP: Positive end expiratory pressure;

PFC: Perfluorocarbon;

PIP: Peak inspiratory pressure;

PLV: Partial liquid ventilation.