Resuscitation 39 (1998) 67–74

Carbon dioxide levels during pre-hospital activecompression–decompression versus standard cardiopulmonary

resuscitation

Dietmar Mauer *, Thomas Schneider, Dirk Elich, Wolfgang Dick

Department of Anaesthesiology, Johannes Gutenberg-Uni6ersity, Langenbeckstr. 1, 6500 Mainz, Germany

Received 10 February 1998; accepted 1 September 1998

Abstract

In a prospective randomised study we investigated end-tidal carbon dioxide levels during standard versus active compression–decompression (ACD) cardiopulmonary resuscitation (CPR) assuming that the end-tital carbon dioxide reflects cardiac outputduring resuscitation. In each group 60 patients with out-of-hospital cardiac arrest were treated either with the standard or theACD method. End-tidal CO2 (petCO2, mmHg) was assessed with a side-stream capnometer following intubation and then every2 min up to 10 min or restoration of spontaneous circulation (ROSC). There was no difference in petCO2 between both patientgroups. However, CO2 was significantly higher in patients who were admitted to hospital as compared to patients declared deadat the scene. All of the admitted patients had a petCO2 of at least 15 mmHg no later than 2 min following intubation, none ofthe dead patients ever exceeded 15.5 mmHg. From these data we conclude that capnometry adds valuable information to theestimation of a patient’s prognosis in the field (threshold, 15 mmHg), but we could not detect any difference in petCO2 betweenACD and standard CPR. © 1998 Elsevier Science Ireland Ltd. All rights reserved.

Keywords: Cardiopulmonary resuscitation; Active compression–decompression; Emergency medical services; Capnometry; End-tidal carbon dioxide; Prognosis

1. Introduction

Active compression combined with active decompres-sion (ACD) improves organ perfusion during car-diopulmonary resuscitation (CPR) as compared withthe standard technique where active compression isfollowed by passive decompression [1–5]. ACD-CPRenhances intrathoracic blood flow and venous return,thus increasing cardiac output [6–10]. The positiveeffects of this method upon cerebral and coronaryblood flow have been demonstrated in numerous ani-mal studies [11–17]. However, only a few clinical stud-ies revealed increased survival rates with ACD-CPR[18–26].

Studies of the haemodynamic effects of ACD-CPR ascompared with standard CPR have been limited tolaboratory or in-hospital settings. So far, invasive mon-itoring during CPR in a pre-hospital setting has beenrestricted to a few patients due to the sophisticatedtechnical and intensive manpower requirements associ-ated with these methods.

End-tidal carbon dioxide pressure (petCO2) correlateswell with cardiac output, coronary perfusion pressure,and mean aortic pressure during CPR [27–32]. It iseasy to measure and has therefore been used as anindirect parameter for haemodynamic monitoring dur-ing CPR in emergency departments, intensive careunits, and pre-hospital emergency medical services(EMS) [33–45]. Capnometry allows comparison of dif-ferent methods of CPR under various circumstances[34,37,38,40,46].* Corresponding author. Fax: +49 6131 176634.

0300-9572/98/$ - see front matter © 1998 Elsevier Science Ireland Ltd. All rights reserved.PII S0300-9572(98)00106-3

D. Mauer et al. / Resuscitation 39 (1998) 67–7468

Table 1Baseline characteristics of the two patient groups (Na=120)

PS-CPRACD-CPR

% Na% Na

50.0 6060Number of cases 50.057.8/74.5 69b 59/78.3 0.64Median Age in (25/75 percentile) 67.5b

41 70.0Witnessed arrest 4268.3 0.84

CPR started by5.0 3Layperson 8.3 5 0.46

0.905Bystander 8.3 5 8.350 86.7EMS personel 5283.3 0.61

First rhythm0.2047VFc 49.1 52 41.2

35.1 40EMDd 33.0 35 0.952723.7 0.0819Asystole 17.9

a N is the number of cases; b data in years; c VF, ventricular fibrillation; d EMD, electromechanical dissociation.

Our study aimed at comparing petCO2 levels duringACD and standard CPR in patients with out-of-hospi-tal cardiac arrest. In a subgroup analysis petCO2 levelswere compared in surviving and non-surviving patients.

2. Methods

2.1. Setting

The EMS system of the City of Mainz (190000inhabitants) comprises four emergency ambulances withparamedics in the first, and one physician-staffed mo-bile intensive care unit (MICU) in the second tier. Boththe MICU and the emergency ambulance located clos-est to the emergency site are dispatched simultaneouslyby the control centre. Training in basic life support(BLS) and advanced life support (ALS) for all membersof the EMS system follows international guidelines[46,47].

2.2. Patients

Patients (N=120) of an estimated body weight ofmore than 35 kg with cardiac arrests of non-traumaticaetiology were included. Exclusion criteria were hy-pothermia, pregnancy, or non-cardiac causes for thecardiac arrest, such as intoxication, drowning, orhanging.

2.3. Randomisation

The prospective, randomised study was approved bythe Ethics Committee of the Physicians’ Chamber ofRhinelande-Palatinate. According to randomisationlists patients were allocated to either the study group(ACD-CPR) or the control group (standard CPR, S-

CPR) by the crew of the EMS vehicle which was firston scene.

2.4. De6ices

ACD-CPR was performed with the Cardio Pump©(Ambu Int.). Carbon dioxide was monitored with ahand-held side-stream capnometer (Capnochek©, BCI).

2.5. Training

Prior to the start of the study all members of theMainz EMS services were re-certified in standard CPR,according to the European Resuscitation Council(ERC) guidelines. Additionally they underwent 4 htraining in ACD-CPR [48]. MICU physicians com-pleted their ALS re-certification prior to the start of thestudy.

2.6. On-scene data collection

Time intervals and survival parameters were definedaccording to the ‘Utstein’ criteria [49]. The time ofcollapse and the bystander CPR efforts were assessedby witness or bystander interviews. The time of thereception of the call and the subsequent times (vehiclesalert, vehicles moving, vehicles stop) were documentedby the dispatch centre. When leaving their vehicle everyambulance and MICU crew activated a mini tape-recorder, thus facilitating on-line recording of arrival atthe patient side, BLS start, defibrillation, tracheal intu-bation, administration of adrenaline, (epinephrine)restoration of spontaneous circulation (ROSC), or ter-mination of CPR efforts [50]. The physicians alsorecorded the start of capnometry immediately aftertracheal intubation, and the respective petCO2 valuesevery 2 min. With a questionnaire patient data, medica-

D. Mauer et al. / Resuscitation 39 (1998) 67–74 69

Table 2Time intervals relating to key events of resuscitation efforts (Naa=120)

ACD-CPR PS-CPRNaNa

Median 25/75 PercentileMedian 25/75 Percentile

From call to 60605.4/9.8 0.49Start CPR 57 7.2 5.2/9.3 56 8.1

9.3 6.8/13.2first defib. (in VFb patients) 36 10.2 7.5/13.3 27 0.6410.2/17.313.0 0.99Intubation 5455 13.2 11.2/15.2

13.2 10.3/15.4First adrenaline dose 56 14.1 11.7/16.6 54 0.390.5613.1/23.016.6First pCO2 measurement 5657 17.5 14.2/22.2

34 23.2 16.6/28.1ROSC 0.9029 22.5 18.9/25.5

From collapse to 424142 10.3 5.2/15.0Start CPR 40 0.348.5 4.8/12.8

14.8 11.7/19.5First defib. (in VFb patients) 32 13.3 9.0/16.7 26 0.2614.2/22.918.3 0.21Intubation 5440 14.8 11.7/19.5

40 18.3 14.5/22.4First adrenaline dose 40 15.8 0.3613.7/20.117.5/29.9 0.39First pCO2 measurement 40 20.2 16.0/27.5 42 22.3

31 26.4 20.0/32.6ROSC 23 24.8 0.4820.1/27.7

a N is the number of cases; b VF, ventricular fibrillation.

tion, medical history, and drugs applied during CPRand technical problems during standard or ACD-CPRwere documented.

2.7. Sur6i6al data

According to the ‘Utstein’ criteria ROSC was definedas return of a palpable carotid pulse with no time limitwhatsoever. Following ROSC, admission to hospitalwith at least 6 h survival, and hospital discharge, wereassessed.

2.8. Statistics

Prior to the study a petCO2 value of 12 mmHg wasconsidered as reference [42,43]. Calculating the powerwe found that 60 patients in each group required to beevaluated to detect a 50% increase in petCO2 (a, 0.05; b,0.1). Time intervals and petCO2-values are presented asmedians (M) with corresponding first (25%) and third(75%) percentiles (Q1, Q3). Differences were evaluatedwith the Mann-Whitney U-test (time intervals), andfrequencies with the x2 or Fisher’s exact test. Differ-ences were considered significant with PB0.05.

3. Results

3.1. Patients (Table 1)

In a 30-month period, 120 patients were included inthe study. Patient groups were comparable as to age,gender, rate of witnessed arrests, incidence of bystanderCPR, and first ECG-rhythm.

3.2. Time inter6als (Table 2)

In all of the 120 patients a continuous time recordingwas started with the receipt of the call at the dispatchcentre. In the case of a witnessed arrest (n=83) thetime of collapse was additionally recorded.

There was no difference between the groups regard-ing the start of BLS measures, first defibrillation, tra-cheal intubation, first adrenaline dose, and firstpetCO2-measurement.

3.3. End-tidal CO2 during resuscitation

The values were evenly distributed between 12 and18.5 mmHg in both groups (Fig. 1), with no detectabledifference between groups. The difference of values inboth groups is related to the patients who experiencedROSC. After detection of a palpable pulse only onepetCO2 value was recorded.

There was a significant rise in petCO2 with ROSC ascompared with values during cardiac arrest with nodifference in amplitude between both groups (Fig. 2).

3.4. End-tidal CO2 in admitted patients 6ersus patientsdeclared dead on scene (Table 3)

During CPR in both groups higher petCO2 valueswere recorded in the patients who were admitted tohospital than in the patients who were declared dead atthe scene. Differences were significant at measuringpoints 1–4 (0, 2, 4, and 6 min), and 6 (10 min), andafter ROSC, in the study group, and at measuringpoints 2, 3, and 4 (2, 4, and 6 min) in the control group.

In both groups the minimum petCO2 in patientsadmitted to hospital and surviving for at least 6 h was

D. Mauer et al. / Resuscitation 39 (1998) 67–7470

Fig. 1. End-tidal pCO2 during ACD-CPR vs. standard CPR.

15 mmHg, most of the values ranging around 24mmHg. In patients declared dead on the scene valuesnever exceeded 15.5 mmHg.

3.5. Sur6i6al rates

There were no differences between the study andcontrol groups in the rates of ROSC, admission tohospital and 6 h survival, and hospital discharge (Table4). Neither was there a difference in the amount ofadrenaline administered, number of defibrillatoryshocks, or rate of re-arrest (Table 5).

4. Discussion

In animal and in human studies ACD-CPR has beenshown to improve myocardial and cerebral blood flowand cardiac output [1–10]. However, these studies donot necessarily reflect clinical experience. Studies onhaemodynamics were conducted within hospitals, withpatients suffering from either extremely short or ex-tremely long cardiac arrests, and conditions which al-lowed invasive monitoring during CPR [1–3].Pre-hospital conditions preclude routine use of invasivemonitoring. Therefore ACD-CPR has not undergone

studies of haemodynamics in this field. So far, the onlycriteria for comparing ACD versus standard CPR havebeen outcome measures, such as ROSC, hospital admis-sion, or discharge. Differences are likely to be due tothe variety of rescue systems, different patient groups,and, last but not least, providers, with different traininglevels [1–3,19–23]. The complex effects of ACD-CPRin pre-hospital studies must concentrate on EMS sys-tems with a high training level and ongoing supervisionat the scene to minimise these variables.

Invasive haemodynamic monitoring is not availableroutinely in a pre-hospital setting. We therefore choseend-tidal carbon dioxide concentration (expressed aspartial pressure in mmHg) as a suitable parameter forthe indirect measurement of cardiac output during CPR[33–45,51]. Small, hand-held capnometers are availablefor monitoring CO2 in any setting [52]. At present thereis one study conducted in the EMS system of Paris,France comparing ACD versus standard CPR in termsof cardiac output expressed by end-tidal CO2 [51].However, the initial number of 16 patients and mea-surement of a single maximum CO2-value precludes anymeaningful interpretation.

Our randomised pre-hospital study comprises thehighest number of patients investigated using end-tidalCO2 to compare standard versus ACD-CPR.

D. Mauer et al. / Resuscitation 39 (1998) 67–74 71

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D. Mauer et al. / Resuscitation 39 (1998) 67–7472

Table 3End-tidal carbondioxide in patients admitted to hospital vs. patients declared dead on the scene

Na pCO2 (2 min) Na pCO2 (4 min)Na pCO2 (0 min)

25/75 Percentile Median 25/75 PercentileMedian 25/75 Percentile Median

ACDb-CPR18.00 /25.25 9 22.00Admitted to hospital 15 20.00 19.00/26.50 12 21.00/23.0022.50

7.00/18.0011.5040Dead on scene 45 8.00/22.0015.00 10.00/21.00 41 13.000.003P 0.011 0.017

Standard-CPR16.50/27.50 13 21.00Admitted to hospital 18 17.50 15.00/23.75 15 16.00/30.0020.00

14.00 8.00/20.00Dead on scene 3542 10.00/19.0015.50 11.25/21.50 37 16.000.041P 0.101 0.032

pCO2 (8 min) pCO2 (10 min)pCO2 (6 min)

ACDb-CPR3 24.00Admitted to hospital 7 19.00 18.00/27.50 3 17.00 19.00/34.5012.50/35.00

7.00/18.0012.0023Dead on scene 35 8.75/16.2511.00 9.00/18.00 28 12.000.077P 0.039 0.331

Standard CPR4 17.00 10.25/29.00Admitted to hospital 12.25/20.759 23.00 17.00/29.00 6 15.0026 14.00Dead on scene 34 15.00 8.00/21.25 32 14.50 9.25/19.00 9.25/20.50)

0.580P 0.047 0.570

a N is the number of cases.

As opposed to the findings of the Paris group neitherACD-CPR nor standard CPR resulted in higher petCO2

values during our entire study period. However, con-cluding an equal cardiac output for both groups fromour findings would be premature as petCO2 depends onthree different physiological systems: ventilation, perfu-sion, and metabolism [31,35,37,43]. Assuming thatmetabolism is constant during cardiac arrest, and thatcirculation support is kept constant by means of chestcompressions with controlled force, depth and rate,ventilation remains the variable. With a fixed ventila-tion:compression ratio of 1:5 the ventilation rate can bewell controlled, however, a control of tidal volume isimpossible with standard bag-valve systems [52]. Yet ifventilation offers an explanation for differences inpetCO2, one would expect a difference from ACD-CPRbut this did not occur in our investigation. ACD-CPRgenerates ventilation merely by changes in intrathoracicpressure [5,7–9,51]. Combining ACD-CPR with posi-

tive pressure ventilation may augment the ventilation,resulting in hyperventilation as compared to standardCPR. Therefore an increase in petCO2 caused by in-creased cardiac output may well be masked by hyper-ventilation caused by ACD-CPR, masking the positiveeffects of this technique.

In addition, adrenaline administration offers a fur-ther explanation as to the absence of difference inpetCO2 between both techniques. With adrenaline theeffects of ACD-CPR upon organ perfusion are dimin-ished [12]. In our investigation adrenaline was adminis-tered every 3 min, with the first dose starting muchearlier than in the French investigation which showedelevated CO2 values with ACD-CPR. Early availabilityof adrenaline may therefore contribute considerably toa lack of difference in petCO2 between both groups inour investigation.

While there was no difference in petCO2 between bothgroups there was a significant rise with ROSC in bothgroups. Capnometry is a suitable method for detectingspontaneous circulation without interrupting CPR forpulse checks [31,32,37,41–43,45]. A rapid rise in petCO2

indicates ROSC prior to a palpable pulse [31,44,45].Facing the difficulties even well-trained providers havewith pulse checks and the consequences of a falsenegative pulse check (e.g. adrenaline overdose), cap-nometry is a method with high sensitivity and specific-ity which can be applied easily during CPR. This holdstrue for both standard CPR and ACD-CPR as ourresults indicate.

Table 4Clinical outcome (Na=120)

S-CPR PACD-CPR

% NaNa%

6050.06050.0Number of cases63.3 38 0.2051.7ROSC 3130.01525.0Admitted to hospital 0.5418

13.3 0.3858.38Discharged from hospital

a N is the number of cases.

D. Mauer et al. / Resuscitation 39 (1998) 67–74 73

Table 5Total amount of adrenaline, number of defibrillations until ROSC and number of re-cardiac arrests after first ROSC in the two groups

Na S-CPR (mean9S.D.)Na ACD-CPR P

38 0.736.494.45.392.2Total amount of adrenaline (mg) 314.493.4 0.84Number of defibrillations until ROSC (in VFb patients) 27 4.592.8 29

8 1.291.6Number of re-cardiac arrests after first ROSC 15 0.891.492.0

a N is the number of cases; b VF, ventricular fibrillation.

Our results underline the useful prognostic value ofpetCO2. With ACD- and standard CPR petCO2 differssignificantly between patients declared dead at the sceneand patients transported to a hospital [32,42,43,45]. Inour investigation 15 mmHg was the threshold beyondwhich most of the patients survived hospital admissionplus 6 h. Small numbers, however, preclude any furtheranalysis of discharge rates. Our data confirm thethreshold of 10 mmHg found by Sanders et al. andLevine et al. and 15 mmHg found by Callaham et al.where an initial petCO2 of 15 mmHg indicated success-ful resuscitation with high specificity and sensitivity[42,43,53]. For the first time our data reveal the samethreshold for both standard and ACD-CPR, and for avariety of ECG-rhythms, at a very early stage in resus-citation. The pathophysiological background of thethreshold, however, remains unclear. Differences inpetCO2 between survivors and non-survivors may reflectthe duration, the type of cardiac arrest (VF, asystole, orEMD), and susceptibility of the organs to CPR efforts.However, basing the decision whether to terminate orcontinue CPR upon petCO2 as single parameter wouldbe unjustified. In conjunction with information as topre-existing diseases, witnessed or unwitnessed collapse,initial ECG-rhythm, and duration of the cardiac arrest,petCO2 provides objective information for the evalua-tion of a patient’s prognosis at a very early stage ratherthan after a longer period of resuscitative effort.

5. Conclusion

In our prospective, randomised study there was nodifference in petCO2 between patients resuscitated withthe standard versus the ACD method. With the help ofcapnometry restoration of spontaneous circulation isnoticed prior to a palpable pulse during both standardCPR and ACD-CPR. With both CPR methods apetCO2 of more than 15 mmHg during the first minutesof CPR indicates a successful resuscitation in the formof hospital admission. Due to its high prognostic valuecapnometry has become an indispensable monitoringmethod during CPR in our EMS system.

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