Mosing_2010_Vet._Anaesth._Analg

RESEARCH PAPER

Comparison of two different methods for physiologic dead

space measurements in ventilated dogs in a clinical

setting

Martina Mosing*, Lukas Staub! & Yves Moens"*Faculty of Veterinary Science, The University of Liverpool, Leahurst, Chester High Road, Neston, UK

!MEM Institute for Evaluative Research in Orthopedic Surgery, University of Bern, Switzerland

"Clinic for Anaesthesiology and Perioperative Intensive Care, Veterinary University Vienna, Vienna, Austria

Correspondence: Dr Martina Mosing, Vet Swiss Faculty, University of Zurich, Equine Department, Section of Anaesthesia,

Winterthurerstrasse 260, 8057 Zuerich, Switzerland. E-mail: [email protected]

Abstract

Objective To compare physiologic dead space (VD)

and physiologic dead space to tidal volume (VT)

ratio (VD/VT) obtained by an automated single

breath test for carbon dioxide (CO2) (method SBT)

and a manual calculation (method MC) in venti-

lated healthy dogs.

Study design Prospective clinical study.

Animals Twenty client-owned dogs, ASA I and II

undergoing anaesthesia for clinical purposes.

Methods Following pre-medication, induction of

anaesthesia, and intubation of the trachea, intermit-

tent positive pressure ventilation was commenced.

Mixed expired CO2 partial pressure (P!ECO2) was

measured by two methods: method MC by analysis,

using an infrared capnograph, of the expired gas

collected in a mixing box and method SBT which

calculated it automatically by a device consisting of a

mainstream capnograph and a pneumotachograph.

At four time points arterial partial pressure of CO2

(PaCO2) was measured. Physiologic dead space

variables (VD and VD/VT) were calculated manually

(method MC) or automatically (method SBT) using

the Bohr–Enghoff equation.

Method MC and SBT were compared using Bland–

Altman plots and linear regression. Intra-class

correlation coefficient (ICC) was used to measure

consistency of each method.

Results Four measurement pairs were obtained in

all 20 dogs for method SBT and MC. The bias was

)1.15 mmHg, 7.97 mL and 0.02 for P!ECO2, VD and

VD/VT, respectively. Linear regression analysis

revealed a correlation coefficient (r2) of 0.79,

0.94, and 0.83 for P!ECO2, VD and VD/VT, respec-

tively. The ICC revealed an excellent consistency for

both methods.

Conclusions The single breath test (SBT) can be

used for clinical evaluation of VD and VD/VT in

anaesthetized ventilated dogs.

Clinical relevance Through measuring VD and VD/

VT important information about lung ventilation

can be obtained and the SBT is an easy method to

use for this purpose.

Keywords dead space, dog, single breath test, ven-

tilation.

Introduction

Physiologic dead space (VD) or ‘wasted ventilation’ is

crucial to understand the relationship between

minute volume, tidal volume (VT) and the arterial

partial pressure of CO2 (PaCO2) of a patient during

393

Veterinary Anaesthesia and Analgesia, 2010, 37, 393–400 doi:10.1111/j.1467-2995.2010.00548.x

anaesthesia. Physiologic dead space represents

the sum of the alveolar (VDalv) and the airway dead

space (VDaw). Airway dead space is a more accurate

description for what was previously termed ‘ana-

tomical dead space’ as its size is dynamic and chan-

ges with respiratory variables such as respiratory

rate (fR), VT, airway flow rates and positive pressure

ventilation (Tusman et al. 2009). Calculation of VD

during anaesthesia using the Bohr–Enghoff equation

requires the simultaneous measurement of mixed

expired carbon dioxide tension (P!ECO2) and PaCO2

(Enghoff 1938). Mixed expired CO2 can be sampled

from a Douglas bag or a mixing box incorporated in

the expiratory limb of the anaesthetic circuit (Fig. 1).

More recently an alternative method based on

volumetric capnography became available for clini-

cal use. Volumetric capnography represents the plot

of expired CO2 concentration versus expired volume

(Fig. 2) and is also called single-breath test for

expired CO2 (SBT) (Aitken & Clark-Kennedy 1928).

Figure 2 shows a typical volumetric capnography

curve and illustrates the fact that the expired CO2 is

plotted against the expired volume and demonstrates

the difference between volumetric capnography and

a capnogram where the expired CO2 is plotted

against time. The SBT technique uses information

obtained by a mainstream capnograph and a pneu-

motachograph. The sensors of both devices are

inserted between the endotracheal tube and the

Y-piece of the breathing system. To calculate VD, the

obtained PaCO2 values are entered and an algorithm

is used, making separate measurement of P!ECO2

unnecessary. In humans SBT is used to determine

physiologic dead space variables after pulmonary

embolism, bronchoconstriction and to adapt venti-

lator settings in intensive care units (Fletcher 1990;

Arnold et al. 1995; Olsson et al. 1999; Verschuren

et al. 2004).

The objective of this study was to compare values

for VD and for its ratio to VT (VD/VT) obtained by

manual calculation (method MC) and volumetric

capnography (method SBT) in anaesthetized dogs

undergoing elective surgery in a clinical setting.

Materials and methods

The protocol was discussed and approved by the

head of the department.

Animals

Twenty dogs of different breeds, scheduled for

routine elective surgery, with a median bodyweight

of 33.2 kg (range: 19–55.7 kg) and age of 1.6 years

(range: 0.5–10 years) were included initially in this

study. Ten dogswere females and 10males. Inclusion

criteria were a bodyweight above 15 kg, American

Society of Anesthesiologists classification 1 or 2,

unremarkable lung auscultation at pre-anaesthetic

evaluation, and an arterial line in the dorsal pedal

artery. Eighteen dogs underwent orthopaedic proce-

dures and two soft tissue mass excisions. Seventeen

dogs were positioned in dorsal and three dogs in lat-

eral recumbency during the measurement period.

Pneumo-tachograph

Mainsteamcapnograph

Infraredcapnograph

Pop-offvalve

Ventilator

Sodalime

canister

Fresh gasinlet

Mixing

box

Expiratorylimb

Inspiratorylimb

One-wayvalve

Patient

Figure 1 Graphical illustration of

the arrangement of the circle system,

mixing box, and measurement

devices.

Physiologic dead space measurement in dogs M Mosing et al.

394! 2010 The Authors. Journal compilation

! 2010 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists, 37, 393–400

Anaesthetic technique

All dogs were pre-medicated with acepromazine

(0.02 mg kg)1; Vanastress; Vana, Austria) and

methadone (0.1 mg kg)1; Heptadon; Ebawe Phar-

ma GmbH, Austria) intravenously (IV). Anaesthesia

was induced with propofol given IV to effect (Prop-

ofol ‘Fresenius’; Fresenius Kabi, Austria). An endo-

tracheal tube was placed and connected to an

anaesthetic circle system. Fresh gas flow was 1–2 L

minute)1 oxygen. A 10 L gas mixing box was

placed in the expiratory limb of the anaesthetic

circle system (Fig. 1). Lactated Ringer’s solution

was infused at 10 mL kg)1 hour)1 throughout the

anaesthetic period (Ringer Lactat ‘Fresenius’;

Fresenius Kabi, Austria). Anaesthesia was main-

tained with isoflurane delivered via a precision out-

of-circle vaporiser in six dogs (Isofluran-Baxter;

Baxter AG, Austria) or with a continuous rate

infusion (CRI) of propofol in 14 dogs (10 mg

kg)1 hour)1) delivered via a syringe pump. All dogs

received a fentanyl CRI (0.02 mg kg)1 hour)1;

Fentanyl ‘Janssen’; Janssen-Cilag Pharma, Austria)

IV during anaesthesia. A 22-gauge catheter was

placed in the dorsal pedal artery for invasive arterial

blood pressure measurement and arterial blood

sampling. Intermittent positive pressure ventilation

(IPPV) in a volume-controlled mode was started in

all dogs at the beginning of surgery (Ohmeda 7800

Ventilator, Ohmeda, WI, USA). Delivered tidal vol-

ume and fR were adjusted to keep end-tidal CO2

between 4.66 and 6.65 kPa (35 and 50 mmHg).

Ventilator settings averaged a VT of 12 ± 4 mL kg)1

and a peak airway pressure of 12 ± 1 cmH2O and

were not changed throughout the period of data

collection.

Cardiovascular monitoring consisted of ECG,

invasive arterial blood pressure measurement and

pulse oximetry (HP CMS Monitor, Hewlett Packard,

Germany). All respiratory parameters were mea-

sured using the SBT monitor combination (Capno-

guard 1265 & Ventrak 1550, Novametrix Medical

Systems Inc., CT, USA). The combination consists of

a mainstream capnograph (Capnoguard 1265)

working on the principle of infrared absorption

and a fixed orifice pneumotachograph (Ventrak

1550). The capnograph and differential pressure

sensor were placed between the endotracheal tube

and the Y-piece of the circle system. The SBT

monitors were connected to a laptop and computer

software (Analysis plus!, Novametrix Medical Sys-

tems Inc., CT, USA) which allowed on- and off-line

data analysis (Fig. 1).

The capnograph was calibrated with room air

before each measurement. The accuracy of the

pneumotachograph was verified with a calibration

syringe before and after all measurements. The

system measured and displayed fR, end-tidal CO2,

respiratory volumes and pressures.

Mixed expired CO2 for method SBT was calculated

by the computer by dividing expired CO2 volume by

the tidal volume of a breath (Fig. 2). The P!ECO2

value was entered into the Bohr–Enghoff equation

(Bohr 1887; Enghoff 1938) to calculate VD/VT as

follows:

VD=VT ! "PaCO2 # P!ECO2$=PaCO2 "1$

The corresponding volume of VD in mL is calcu-

lated by multiplying the ratio by the measured tidal

volume (VT):

VD ! VT % ""PaCO2 # P!ECO2$=PaCO2$ "2$

After the start of IPPV respiratory parameters

were stabilised for at least 15 minutes. Data were

collected four times at 15 minute intervals for 1

hour. At each of the four time points (T1–T4) an

arterial blood sample of 0.3 mL was drawn from the

arterial catheter. Blood gases were analysed imme-

diately with a blood gas machine (AVL Compact 3,

Roche Diagnostics GmbH, Germany) calibrated

before each measurement period.

P!ECO2 for method MC was measured by analysing

expired gas sampled from the outlet of the mixing

box in the expiratory limb using a previously

calibrated side stream infrared analyzer (HP CMS

Monitor, Hewlett Packard) (Fig. 1) and retrospective

manual calculation of VD values using equation 1

and 2. The same PaCO2 values were used to

calculate VD with both methods.

Figure 2 Graphical illustration of an example for a single

breath test: the expired CO2 (Exp. CO2) is plotted against

the total expired volume. The volume of CO2 expired over

time represents the mixed expired CO2 (P!ECO2).


! 2010 The Authors. Journal compilation! 2010 Association of Veterinary Anaesthetists and the American College of Veterinary Anesthesiologists, 37, 393–400 395

Statistical analyses

The variables P!ECO2, VD and VD/VT measured and

calculated by method MC and SBT were compared

and visualised using Bland–Altman plots and linear

regression (Bland & Altman 1986; Mantha et al.

2000). Intra-subject reproducibility of the four

measurements was evaluated by calculating intra-

class correlation coefficients (ICC). Reproducibility

was interpreted as follows: moderate 0.40–0.59,

good 0.60–0.79, excellent ‡ 0.8. The D’Agostino–

Pearson test was used to assess normal distribution

of the data. For pair-wise comparisons of different

points in time, Bonferroni adjustment was applied.

Statistical analyses were conducted with use of SAS

9.1 (SAS Institute, Cary, NC, USA). The level of

significance was set at 0.05 throughout the study.

Results are presented as mean ± one standard

deviation or medians and ranges depending on the

distribution of data.

Results

In all dogs four paired measurements were obtained

and analysed (80 paired measurements). All mea-

sured respiratory parameters remained within

physiologic limits throughout the anaesthetic period

(Table 1).

The volume per kilogram body mass for VDMC and

VDSBT was 7.60 ± 0.09 and 7.34 ± 0.09 mL kg)1,

respectively. The physiologic dead space ratio was

>50% at all four time points with a range between

46 and 79% for both methods (Table 2). The ICC

was >0.8 in all evaluated variables and revealed an

excellent reproducibility for all VD measurements

obtained by either method

Bland–Altman plots and linear regression revealed

a uniform relationship between the difference and

magnitude of measurements (Figs 3 & 4). Different

levels of bias and lower and upper confidence limits

were observed depending on the investigated vari-

able (Table 3). The bias levels were )1.15 mmHg

()0.15 kPa), 7.97 mL and 0.02 for P!ECO2, VD and

VD/VT, respectively. At most time points method

SBT underestimated P!ECO2 and therefore overesti-

mated both physiological dead space values com-

pared to method MC (Fig. 3).

The correlation coefficients (r2) for P!ECO2, VD and

VD/VT were 0.79, 0.94 and 0.83, respectively

(Table 3).

Discussion

The results of the present study indicate that volu-

metric capnography can be used to obtain physio-

logic dead space values in mechanically ventilated

dogs. Only minor differences were seen for P!ECO2

values compared to the use of a mixing box. Hence

VD and VD/VT were in close agreement as both

methods use the same formula to reveal dead

space parameters using PaCO2 and the aforemen-

tioned P!ECO2. Therefore the minor difference in the

calculated and measured P!ECO2 obtained by the two

methods was the most important finding of

this study. Several clinical studies in humans

confirm the accuracy of SBT to determine P!ECO2

and therefore VD and VD/VT (Fletcher 1987; Eriks-

son et al. 1989; Riou et al. 2004; Blanch et al.

2006). This is the first clinical study in dogs

describing the use of SBT to reveal dead space

parameters.

Physiologic dead space was 7 mL kg)1 and cor-

responds well with the values between 7 mL kg)1 in

spontaneously breathing and 10 mL kg)1 in venti-

lated dogs described in previous studies (Haskins &

Patz 1986; Berdine et al. 1990). In contrast, the

mean ratio of 0.6 for VD/VT for ventilated dogs was

higher than expected. Haskins & Patz (1986) gave a

Table 1 Respiratory parameters of the twenty dogs at the four time points (T1–T4)

Time

(minutes)

VT

(mL)

fR (breaths

per minute)

End-tidal CO2

(kPa)

End-tidal CO2

(mmHg)

PaCO2

(kPa)

PaCO2

(mmHg)

T1 (0) 421 ± 140 10 ± 2 5.72 ± 1.04 43 ± 8 6.06 ± 0.97 46 ± 7

T2 (15) 419 ± 129 10 ± 2 5.81 ± 1.00 44 ± 7 6.04 ± 0.86 45 ± 6

T3 (30) 413 ± 120 10 ± 3 5.92 ± 0.82 44 ± 6 6.17 ± 0.82 46 ± 6

T4 (45) 411 ± 115 10 ± 2 5.97 ± 0.86 45 ± 6 6.33 ± 0.77 48 ± 6

Values are given as mean ± standard deviation.

VT, tidal volume; fR, respiratory rate; PaCO2, arterial partial pressure of CO2.




ratio of 0.4 for VD/VT in spontaneously breathing

dogs with a mean VT of 18 ± 13 mL kg)1. During

mechanical ventilation VD/VT values up to 0.5 with

a VT of 20 mL kg)1 have been reported in dogs

using a multiple inert gas elimination technique

(Schrikker et al. 1995). In the present study dogs

were ventilated with a VT of 12 ± 4 mL kg)1 and a

peak airway pressure of 12 ± 1 cmH2O. IPPV canTab

le2

Resultsof

respiratorymeasuremen

tsan

dcalculation

sat

thefourtimepo

ints

(T1–T

4),expressedas

mediansan

d(ran

ge)

Tim

e

points

P! ECO

2MC

(kPa)

P! ECO

2MC

(mmHg)

P! ECO

2SBT

(kPa)

P! ECO

2SBT

(mmHg)

VDMC

(mL)

VDSBT

(mL)

VD/V

TMC

VD/V

TSBT

T1

2.39(1.60–3.06)

18(12–23)

2.53(1.73–3.46)

19(13–26)

238(137–475)

242(136–474)

0.59(0.53–0.77)

0.57(0.47–0.77)

T2

2.39(1.33–3.06)

18(10–23)

2.53(1.46–3.46)

19(11–26)

237(165–421)

242(144–415)

0.60(0.51–0.79)

0.59(0.46–0.79)

T3

2.33(1.46–2.93)

17(11–22)

2.53(1.46–3.59)

19(11–27)

239(119–367)

227(108–377)

0.61(0.53–0.77)

0.58(0.49–0.79)

T4

2.39(1.46–2.93)

18(11–22)

2.53(1.46–3.59)

19(11–27)

244(173–386)

237(155–401)

0.61(0.56–0.78)

0.60(0.48–0.78)

ICC

0.845

0.873

0.889

0.887

0.883

0.904

ICC,intraclass

correlatio

nco

efficient;SubscriptedMC,manualcalculatio

n;su

bscriptedSBT,single

breath

test

forCO

2,P! ECO

2,mixedexp

iredCO

2;VD,physiologicdeadsp

ace

;VT,tid

alvolume;VD/V

T,

physiologic

deadsp

ace

fraction.

(a)

(b)

(c)

Figure 3 Bland and Altman scatter plots of (a) the mixed

expired CO2; (b) physiologic dead space and (c) physiologic

dead space ratio, comparing method MC (manual calcu-

lation) and SBT (single breath test); solid line: bias, dashed

lines: 95%-CI of the differences. P!ECO2 = mixed expired

CO2; VD = physiologic dead space; VT = tidal volume VD/

VT = physiologic dead space ratio. For conversion to SI

units, 7.5 mmHg = 1 kPa.



increase VD/VT by 1) overventilation of parts of the

lung which have a very small blood flow, or 2)

overdistension of the conducting airways (increase

in VDaw) produced by the abnormal pattern of

inflation (Hedenstierna & McCarthy 1975; Tan &

Simmons 1979). The addition of the apparatus dead

space contributes to the increase in VD in anaes-

thetised subjects (Hedenstierna & McCarthy 1975).

This is especially true for VD/VT if small VTs are used

as even small changes have a high impact on the

ratio itself. In the present study a part of the VD

consisted of mechanical or apparatus dead space.

This includes parts of the endotracheal tube extend-

ing beyond the incisors and the SBT sensor itself.

The endotracheal tube connector was kept at the

level of the incisors. The volume of the sensor was

measured by water displacement and added

13.9 mL to the mechanical dead space. Wenzel

et al. (1999) demonstrated that in newborns with a

bodyweight of 2.7 kg an increase in inspired CO2

was apparent 5 minutes after inserting the com-

bined sensor and suggested that therefore the

measurement period should be restricted to a

maximum of 5 minutes in infants. We accounted

for this potential problem by excluding dogs with a

body weight below 15 kg. Nevertheless, the high

physiologic dead space ratio found is more likely as

a result of the the added apparatus dead space than

to an overdistension of the lung tissue and airways

as relatively low peak inspiratory pressures were

used. Evaluation of the changes of VDaw and VDalv

with different airway pressures using the same set

up would be necessary to prove this point.

The data for VD/VT found in this study do not

agree with other recently reported values on

physiologic dead space in dogs (Kudnig et al.

2004, 2006). However there was a major differ-

ence in the measurement methods used. Kudnig

et al. used end-tidal CO2 instead of the P!ECO2 to

calculate the ‘physiologic dead space’ resulting in

(a)

(b)

(c)

Figure 4 Linear regression of (a) the mixed expired CO2;

(b) physiologic dead space and (c) physiologic dead space

ratio comparing method MC (manual calculation) and SBT

(single breath test). Dashed lines represent the 95%

confidence interval and the solid line the fitted regression

line. P!ECO2 = mixed expired CO2; VD = physiologic dead

space; VT = tidal volume, VD/VT = physiologic dead space

ratio. For conversion to SI units, 7.5 mmHg = 1 kPa.

Table 3 Estimation of the difference (bias) and linear

regression (r2) between method SBT (single breath test)

and MC (manual calculation) for all dead space variables,

including 95% confidence limits.

Bias

Lower

limit

Upper

limit r2

P!ECO2 (mmHg) )1.15 )1.60 )0.70 0.79

VD (mL) 7.97 2.76 17.29 0.94

VD/VT 0.02 0.01 0.03 0.83

P!ECO2, mixed expired CO2; VD, physiologic dead space; VD/VT,

physiologic dead space fraction.




values of 0.11–0.24. The substitution of P!ECO2 by

end-tidal CO2 in the Bohr–Enghoff equation gives

values corresponding more likely with the VDalv

rather than VD (Fletcher 1985) so Kudnig et al.

incorrectly labelled their value as VD when in fact

they calculated the alveolar dead space fraction.

This explains the huge difference in the values in

the aforementioned studies and the study pre-

sented here.

The intra-subject reproducibility of the four mea-

surements was high for both method MC and

method SBT as demonstrated by an excellent ICC.

Therefore the variation around the values of VD for

both methods was small. Reproducibility can be

influenced by several factors including stability of

the baseline after calibration of volumetric capnog-

raphy devices, the blood gas machine, blood gas

sampling, entering data into the software and, most

importantly, analysis of the data. A significant

change in VD over a study period of 1 hour without

changing ventilator settings is not expected. There-

fore the high ICC can be interpreted as confirmation

for the consistency of both methods.

The bias of 8 mL for VD was caused mainly by

data obtained from two dogs and these SBT wave-

forms were inspected more closely. In these dogs

P!ECO2 was underestimated by the SBT by 4

(0.53 kPa) and 4.5 mmHg (0.6 kPa) causing an

overestimation of VD and VD/VT by 40.1 and

29.9 mL and 0.07 and 0.09 respectively.

Re-evaluating the single breath curves of the two

dogs revealed a short elevation in CO2 concentra-

tion in the first phase of the expiration (Fig. 5). The

algorithm of the SBT device only summarises the

area under the curve of phase II (quick increase in

CO2 concentration) and phase III (alveolar plateau)

(manufactures information sheet). The area under

phase I was not included into the P!ECO2 calculation

leading to the underestimation. A small residual

volume between the cuff and the tip of the endo-

tracheal tube (ETT) causes the aberration in the

baseline of the volumetric capnography (Schramel

& Mosing 2009). Carbon dioxide rich gas is trapped

in a small anatomical space between the outer

surface of the ETT distal to the inflated cuff and the

trachea. During exhalation, the trapped CO2-rich

gas is washed out during the first period of

expiration causing an aberration in baseline in

phase I of the expirogram. Thus, if an elevation in

phase I is observed during anaesthesia one can try

to deflate and reinflate the cuff to change the

volume of the space between the ETT and tracheal

wall. In case of persistence of the aberration, dead

space calculations based on SBT curves should be

interpreted with caution.

The handling of the combined monitoring device

for method SBT was convenient in a clinical setting.

With newer devices (NICO, Novametrix Medical

Systems Inc., CT, USA) PaCO2 values are entered

directly into one measurement unit without the

additional need of a laptop, making clinical set-up

even more convenient. The anaesthetist can use the

derived values to adjust ventilator settings during

the anaesthetic period. The classical calculation of

VD with collection of expired air in a mixing box has

several disadvantages in a clinical setting. The

addition of the 10 L-mixing box into the expiratory

limb of the circle system increases the time constant

of the breathing system. This might be a problem

when quick changes of gas composition are neces-

sary in a clinical setting. No such problems were

observed during data collection although only

healthy subjects in a stable plane of anaesthesia

were included into the study. Furthermore an

additional side stream capnograph is necessary at

the outlet of the box to measure P!ECO2 from the

mixing box if dead space parameters are derived by

manual calculation (Fig. 1). For the SBT the PaCO2

value simply has to be entered into the software and

the computer calculates all values, whereas manual

calculations are time consuming and not always

possible during clinical anaesthesia.

Both methods of measurement require arterial

blood gas analysis in order to obtain physiologic

dead space values. This might limit the use for

monitoring dead space variables in very small

animals because of the difficulties in arterial blood

sampling or when blood gas analysis is not available.

Figure 5 Screenshot of a single breath test for CO2 of dog 2

showing irregularities in phase I of the expiration; alter-

ation in baseline marked with arrow given in mmHg. For

conversion to SI units, 7.5 mmHg = 1 kPa).



At the time of data collection no ethical commit-

tee was in place at the institution. No alteration in

anaesthetic protocol occurred as a result of the

study, and the only potential difference from routine

practice was the addition of the mixing box in the

circuit and the arterial blood sampling. However, if

the study was carried out today, owner consent

would have been obtained.

In summary the SBT is an easy to use semi-

automated tool to estimate physiologic dead space

variables in a clinical setting and shows a high

correlation and low bias with manually calculated

values using the Bohr–Enghoff equation in healthy

ventilated dogs.

References

Aitken RS, Clark-Kennedy AE (1928) On the fluctuation

in the composition of the alveolar air during the

respiratory cycle in muscular exercise. J Physiol 65,

389–411.

Arnold JH, Bower LK, Thompson JE (1995) Respira-

tory deadspace measurements in neonates with

congenital diaphragmatic hernia. Crit Care Med 23,

371–375.

Berdine GG, Johnson JE, Dale D et al. (1990) Inspiratory

flow rate and dead space in dogs. J Appl Physiol 68,

1228–1232.

Blanch L, Romero PV, Lucangelo U (2006) Volumetric

capnography in the mechanically ventilated patient.

Minerva Anestesiol 72, 577–585.

Bland JM, Altman DG (1986) Statistical methods for

assessing agreement between two methods of clinical

measurement. Lancet 1, 307–310.

Bohr C (1887) Uber die Lungenathmung. Centralblatt fur

Physiologie 1, 236–268.

Enghoff H (1938) Volumen inefficax. Bemerkungen zur

Frage des schadlichen Raumes. Uppsala Lak Forhandl

44, 191–218.

Eriksson L, Wollmer P, Olsson CG et al. (1989) Diagnosis

of pulmonary embolism based upon alveolar dead space

analysis. Chest 96, 357–362.

Fletcher R (1985) Deadspace, invasive and non-invasive.

Br J Anaesth 57, 245–249.

Fletcher R (1987) Gas exchange during thoracotomy in

children. A study using the single-breath test for CO2.

Acta Anaesthesiol Scand 31, 391–396.

Fletcher R (1990) Deadspace during anaesthesia. Acta

Anaesthesiol Scand Suppl 94, 46–50.

Haskins SC, Patz JD (1986) Effects of small and large face

masks and translaryngeal and tracheostomy intubation

on ventilation, upper-airway dead space, and arterial

blood gases. Am J Vet Res 47, 945–948.

Hedenstierna G, McCarthy G (1975) The effect of anaes-

thesia and intermittent positive pressure ventilation

with different frequencies on the anatomical and alve-

olar deadspace. Br J Anaesth 47, 847–852.

Kudnig ST, Monnet E, Riquelme M et al. (2004) Cardio-

pulmonary effects of thoracoscopy in anesthetized nor-

mal dogs. Vet Anaesth Analg 31, 121–128.

Kudnig ST, Monnet E, Riquelme M et al. (2006) Effect of

positive end-expiratory pressure on oxygen delivery

during 1-lung ventilation for thoracoscopy in normal

dogs. Vet Surg 35, 534–542.

Mantha S, Roizen MF, Fleisher LA et al. (2000) Comparing

methods of clinical measurement: reporting standards

for Bland and Altman analysis. Anesth Analg 90, 593–

602.

Olsson K, Greiff L, Karlefors F et al. (1999) Changes in

airway dead space in response to methacholine provo-

cation in normal subjects. Clin Physiol 19, 426–432.

Riou Y, Leclerc F, Neve V et al. (2004) Reproducibility of

the respiratory dead space measurements in mechani-

cally ventilated children using the CO2SMO monitor.

Intensive Care Med 30, 1461–1467.

Schramel JP, Mosing M (2010) Aberration in the baseline

of volumetric capnography. Abstracts presented at the

10th World Congress of Veterinary Anaesthesia,

Glasgow. Vet Anaesth Analg 37, Available online DOI:

10.1111/j.1467-2995.2010.00535a.x

Schrikker AC, Wesenhagen H, Luijendijk SC (1995)

Intrapulmonary gas mixing and dead space in artificially

ventilated dogs. Pflugers Arch 430, 862–870.

Tan CSH, Simmons DH (1979) Effect of assisted mechan-

ical ventilation on arterial carbon dioxide tension of

normal anesthetized dogs. Lung 156, 255–264.

Tusman G, Scandurra A, Bohm SH et al. (2009) Model

fitting of volumetric capnograms improves calculations

of airway dead space and slope of phase III. J Clin Monit

Comput 23, 197–206.

Verschuren F, Liistro G, Coffeng R et al. (2004) Volumetric

capnography as a screening test for pulmonary embolism

in the emergency department. Chest 125, 841–850.

Wenzel U, Wauer RR, Schmalisch G (1999) Comparison of

different methods for dead space measurements in ven-

tilated newborns using CO2-volume plot. Intensive Care

Med 25, 705–713.

Received 31 July 2009; accepted 4 January 2010.




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