Does a Ventilation/Compression Ratio of 5: 50 Alter Gas Exchange in Basic Life Support? A Simulation in a BLS-Model of Patients Undergoing General …

Abstract

Background: The goal of Basic Life Support is the oxygenation of vital organs during cardiac arrest. Therefore, chest compressions are combined with ventilation in a fixed ratio. This study investigated the influence of bag/mask venti-lation on pulmonary gas exchange in anaesthetized patients performed with a ventilation/compression ratio of 2:15 com-pared to 5:50. Methods: Forty patients scheduled for elective cardiac surgery received general anesthesia (Propofol/Sufentanil/ Rocu-ronium). Upon loss of consciousness bag/mask ventilation was started (15l/min O 2 with reservoir bag) over a six minute period using either 2 ventilations every 9 seconds (simulated ventilation/compression ratio 2:15) or 5 ventilations every 30 seconds (simulated ventilation/compression ratio 5:50). Arterial blood gas sampling was performed at beginning of venti-lation and after six minutes. Data were analyzed with 2-factorial ANOVA. Results: Arterial PO 2 increased in both groups during the ventilation with pure oxygen (PaO 2 : 2:15 group: 259 mmHg [0 min], 369 mmHg [6 min]; 5:50 group: 277 mmHg [0 min], 363 mmHg [6 min]; n.s.). Arterial pCO 2 also increased (PaCO 2 : 2:15 group: 47 mmHg [0min], 48 mmHg [6min]; 5:50 group: 47 mmHg [0min], 52 mmHg [6min], P=0,018). Consequently, pH decreased in both groups (pH: 2:15 group; 7,37 [0min], 7,36[6min]; 5:50 group: 7,38 [0min], 7,34 [6min], P=0,02). There was no critical decrease of SpO 2 at any time.

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The Open Critical Care Medicine Journal, 2008, 1, 7-11 7

1874-8287/08 2008 Bentham Open
Open Access
Does a Ventilation/Compression Ratio of 5:50 Alter Gas Exchange in
Basic Life Support? A Simulation in a BLS-Model of Patients Undergoing
General Anesthesia
Clemens Kill*, Christian Friedrich, Timon Vassiliou, Leopold Eberhart, Dirk Ruesch and
Hinnerk Wulf
Department of Anesthesiology and Critical Care, Philipps-University, Marburg, Germany
Abstract: Background: The goal of Basic Life Support is the oxygenation of vital organs during cardiac arrest. Therefore,
chest compressions are combined with ventilation in a fixed ratio. This study investigated the influence of bag/mask venti-
lation on pulmonary gas exchange in anaesthetized patients performed with a ventilation/compression ratio of 2:15 com-
pared to 5:50.
Methods: Forty patients scheduled for elective cardiac surgery received general anesthesia (Propofol/Sufentanil/ Rocu-
ronium). Upon loss of consciousness bag/mask ventilation was started (15l/min O2 with reservoir bag) over a six minute
period using either 2 ventilations every 9 seconds (simulated ventilation/compression ratio 2:15) or 5 ventilations every 30
seconds (simulated ventilation/compression ratio 5:50). Arterial blood gas sampling was performed at beginning of venti-
lation and after six minutes. Data were analyzed with 2-factorial ANOVA.
Results: Arterial PO2 increased in both groups during the ventilation with pure oxygen (PaO2: 2:15 group: 259 mmHg [0
min], 369 mmHg [6 min]; 5:50 group: 277 mmHg [0 min], 363 mmHg [6 min]; n.s.). Arterial pCO2 also increased
(PaCO2: 2:15 group: 47 mmHg [0min], 48 mmHg [6min]; 5:50 group: 47 mmHg [0min], 52 mmHg [6min], P=0,018).
Consequently, pH decreased in both groups (pH: 2:15 group; 7,37 [0min], 7,36[6min]; 5:50 group: 7,38 [0min], 7,34
[6min], P=0,02). There was no critical decrease of SpO2 at any time.
Conclusions: In the anesthetized patient with spontaneous circulation bag/mask ventilation simulating ventilation/comp-
ression ratios of 2:15 and 5:50 enable an adequate oxygenation and stable acid base balance.
Keywords: Basic life support (BLS), ventilation, chest compression.
1. BACKGROUND

tion as well as external chest compressions in a fixed ratio to
maintain tissue perfusion and oxygenation during cardiac
arrest [1]. While any interruption of chest compressions
seems to deteriorate perfusion, there is little information
about the frequency and pattern of ventilations required to
maintain an adequate oxygenation and to prevent excessive
hypercarbia during cardiac arrest [2,3]. The importance of
non-interrupted chest compressions lead to the changes in
the ILCOR guidelines 2005, that recommend a ventila-
tion/compression ratio of 2:30 instead of 2:15 during Basic
Life Support. In this study, a model of the anesthetized pa-
tients was chosen to investigate the influence of two differ-
ent ventilation/compression ratios on pulmonary gas ex-
change.
Basic Life Support (BLS) guidelines recommend ventila-
METHODS

cardiac surgery were enrolled. Inclusion criteria were as


*Address correspondence to this author at the Department of Anesthesiol-
ogy and Critical Care, Philipps-University, D-35033 Marburg, Germany;
Tel: +4964212865981; Fax: +4964212866996;
E-mail: killc@staff.uni-marburg.de
After IRB approval, forty patients undergoing elective
follows: coronary artery bypass graft (CAB), ejection frac-
tion >50%, absence of signs of a difficult airway based on
physical examination (Mallampati Score 1or 2), and absence
of any pulmonary disease. After arrival in the operating
room patients were randomly allocated to the 2:15-group
(simulated ventilation/compression ratio 2:15) or the 5:50-
group (simulated ventilation/compression ratio 5:50) using a
sealed envelope technique. Patients were monitored with
five-lead ECG, pulse-oximetry and invasive arterial blood
pressure after canulation of the A. radialis. A first arterial
blood sample was drawn while the patients were breathing
spontaneously. Anesthesia was induced with sufentanil (0.3-
1mcg/kg) and propofol (1-2mg/kg) in both groups. Upon the
start of sufentanilinfusion, patients were preoxygenated with
pure oxygen via face mask. After loss of consciousness,
bag/mask ventilation with a self-inflatable bag (AMBU
Mark 3, Ambu?, Denmark) with oxygen reservoir (15l
O2/min) and face mask was started and rocuronium (1mg/kg)
was administered. The 2:15-group received 2 ventilations
every 9 seconds (corresponding to a ventilation/compression
ratio of 2:15 when administering 100 compressions/min).
The 5:50-group was ventilated with 5 ventilations every 30
seconds (corresponding to a ventilation/compression ratio of
5:50) over a six minute period. Additional ventilations were
not allowed. Heart rate was maintained above 50bpm and

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8 The Open Critical Care Medicine Journal, 2008, Volume 1 Kill et al.
systolic blood pressure above 80mmHg (10.6 kPa). Anaes-
thesia was maintained with propofolinfusion (4mg*kg-1h-1).
Ventilations were performed by anaesthesiologists with at
least 3 years professional experience. Arterial blood gases
were drawn right after putting in the arterial line (t0), after
injection of rocuronium (t1), and after six minutes (t2). After
the six minute period an endotracheal tube was inserted and
the further preoperative routine procedures were performed.

ANOVA after confirming a normal distribution using the
Kolmogorov-Smirnov-test. A prospective power analysis
revealed that 40 patients (20 per group) provide a power of
more than 80% to detect a relative difference of 25% be-
tween the two groups using a type I error of 0.05 and assum-
ing a standard deviation of the two groups of not more than a
quarter of the actual mean. Data are presented as means (+/-
SD).
Data were analyzed using students-t-test and 2-factorial
RESULTS

No patient had to be excluded from the study due to critical
decrease of oxygen saturation, critical hypotension or brady-
cardia from the beginning of induction until completing the
last blood gas sampling.
All forty patients enrolled in the study could be analysed.

(BMI). The values of PaO2, PaCO2 and pH before the ex-
periments (t0) also showed no differences between the
groups (Table 1).
Patients did not differ in age, gender or body mass index
Table 1. Overview of Biometrical Data and Baseline Results
(= t0) of Blood Gas Analysis of Both Study Groups
(± SD)

Group 2:15 5:50
N 20 20
Age [yrs] 63,2 (± 10,5) 63,6 (± 10,6) n.s.
Height [cm] 171 (± 8) 173 (± 9) n.s.
BMI 27,4 (± 3,0) 29,7 (± 3,9) n.s.
PaO2 (t0) [mmHg] 81 (± 17,1) 79 (± 12,6) n.s.
PaCO2 (t0) [mmHg] 40 (± 3,5) 40 (± 2,8) n.s.
pH (t0)
n.s. = not significant.
7,43 (± 0,19) 7,44 (± 0,29) n.s.

Table 2. Comparison of Results of Blood Gas Analyses After
Injection of Rocuronium (t1) and Six Minutes Fol-
lowing Injection of Rocuronium (t2)

T 1(0 min) T 2(6 min)
PaO2 (2:15-group) [mmHg] 259 ± 101 369 ± 88
PaO2 (5:50-group) [mmHg] 277 ± 90 363 ± 113
n.s.
PaCO2 (2:15-group) [mmHg] 47 ± 3,6 48 ± 6,3
PaCO2 (5:50-group) [mmHg] 47 ± 3,7 52 ± 6,4
P=0,018
pH (2:15-group) 7,37 ± 0,4 7,36 ± 0,4
pH (5:50-goup) 7,38 ± 0,4 7,34 ± 0,5
P=0,02


tion with pure oxygen. Arterial pCO2 also increased and
consequently, pH decreased in both groups. There was no
critical decrease of SpO2 at any time. (Table 2, Figs. (1-3))
DISCUSSION
Arterial PO2 increased in both groups during the ventila-

2:15 and 5:50 in a model of the anesthetized patients under-
going anaesthesia for elective cardiac surgery. Oxygenation
and elimination of carbon dioxide could be maintained in
both groups without major clinical differences.
This study compared a ventilation/compression ratio of

longed compression periods without interruptions that would
be needed for ventilations [4-17]. Most of these investiga-
tions were either animal experiments or mathematical analy-
ses to predict the influence of changes in the ventilation-
compression ratio. In summary, the following aspects seem
to be of importance in finding the “BEST VENTILA-
TION/COMPRESSION RATIO”:
There are several studies showing the advantage of pro-
1.
The total minimal ventilation rate seems to be lower
than assumed over the last years, although there are
no reliable data of gas exchange in the first minutes of
CPR in humans with different ventilation-volumes
per time. In the first minutes of CPR by a lay person
Hallstrom and colleagues found no differences in out-
come even when ventilations were not performed at
all [10].
2.
Each interruption of cardiac compression seems to
worsen the probability for successful defibrillation as
well as the outcome, independent of the reason for the
interruption (analysis of an automated external defi-
brillator or ventilation)[13-16]. This might be caused
by the sudden decrease of mean and diastolic pressure
after stopping chest compressions.
3.
The workflow under realistic conditions of resuscita-
tion by a two-rescuer team in the field during the first
minutes of initial emergency treatment seems to be
strongly influenced by the duration of compression
periods. Prolonged compression periods enable an
earlier defibrillation as well as the start of ALS pro-
cedures and the reduction of emotional stress [17-20].

that longer compression periods of any an alternative ventila-
tion/compression ratio (e.g. 2:30, 5:50, 2:100, 5:100) are
advantageous, provided a minimal necessary ventilation is
applied [21-23].
Considering these aspects together, it must be concluded

need for longer continous compression periods to minimize
“hands-off-times”, to increase oxygen delivery to vital or-
gans, to avoid deleterious effects of excessive hyperventila-
tion on hemodynamics and to optimize the workflow [20,
24-26]. The need for ventilations in the first minutes of CPR
seems to depend on the etiology of cardiac arrest (cardiac vs
asphyctic), so it might be difficult to recommend a uniform
BLS-strategy without any ventilation for all patients suffer-
ing cardiac arrest [27,28].
Recently published data strengthen the evidence of the

about the gas exchange during BLS with bag/mask ventila-

The goal of this study was to provide further information

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Ventilation/Compression Ratio of 5:50 Alter Gas Exchange in Basic Life Support The Open Critical Care Medicine Journal, 2008, Volume 1 9

Fig. (1). PaO2 [mmHg ± SD] at t1 (0min) and t2 (6min).

Fig. (2). PaCO2 [mmHg ± SD] at t1 (0min) and t2 (6min).

Fig. (3). pH [ ± SD] at t1 (0min) and t2 (6min).

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10 The Open Critical Care Medicine Journal, 2008, Volume 1 Kill et al.
tion and supplemental oxygen using a prolonged period
between ventilations. This concerns the period of Basic Life
Support provided by healthcare professionals (EMS, nurses)
until the airway can be secured. Research in the field with
focus on gas exchange during ongoing resuscitation might be
quite difficult to carry out. Therefore, we chose a model of
the anesthetized patient with spontaneous circulation. All
patients enrolled into this study underwent elective cardiac
surgery (CAB), so they belong to a population of patients of
enhanced risk for sudden cardiac death and might provide
similar conditions for the face mask placement. Unlike re-
suscitation training mannequins, these patients with their
anatomical variations represent most realistic conditions
concerning possible difficulties in placing and tightening the
face mask for bag/mask ventilation. To avoid bias caused by
untrained personnel ventilations were performed by anesthe-
siologists with at least 3 years professional experience. The
six minute period of bag/mask ventilation was chosen to
reach at least double the average necessary time period of
Basic-Life-Support with an unsecured airway [20]. Ventila-
tion with a self-inflatable bag was chosen because it caused
the same difficulties in applying adequate ventilation vol-
umes as it occurs in real emergency situations. We assumed,
that several ventilation attempts in a row (as in 5:50) might
lead to higher tidal volumes than only two ventilations (as in
2:15) and therefore lead to results, that might be different to
theoretically calculated values.

high oxygen concentration the oxygenation is favourable in
both groups without statistical differences. Although the
PaCO2 increases slightly more in the 5:50-group after six
minutes, these results might be without clinical relevance
because a PaCO2 of 51 mmHg could be tolerated as well as
the decrease of pH to 7,33 in the 5:50 group.
The results show that using a self-inflatable bag with

because all patients had spontaneous circulation. We do not
know whether these results can simply be transferred to the
situation during cardiac arrest, because pulmonary perfusion
under external chest compression might be quite different
from spontaneous circulation. The results under comparable
pulmonary perfusion of spontaneous circulation show no
relevant disadvantage concerning gas exchange of the 5:50
ventilation/compression ratio. If there are differences be-
tween the 2:15 and 5:50 group in pulmonary perfusion dur-
ing cardiac arrest with chest compressions, existing data
suggest that perfusion gets better the longer the compression
interval will be. Probably the improved perfusion using 50
non-interrupted compressions may also further improve
pulmonary gas exchange during CPR.
There are limitations to the interpretation of these results

tion/compression ratio of 5:50 do not seem to be limited by
any deterioration in gas exchange. The results of oxygena-
tion and acid-base balance in this investigation under spon-
taneous circulation might even allow a further reduction of
the number of ventilations (3:50, 2:50, 5:100 e.g.) without
critical decrease of PaO2. Therefore future research should
focus on the influence of prolonged ventilation/compression
ratios during BLS.
In conclusion, the advantages of a prolonged ventila-


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Received: January 23, 2008

Revised: March 26, 2008 Accepted: March 28, 2008
© Kill et al.; Licensee Bentham Open.

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