Jo Kramer-Johansen

A Failed Attempt to Improve Quality of Out-of-Hospital CPR Through Performance Evaluation

Introduction. Quality of CPR performed by professionals has been reported to be substandard even with automated corrective feedback. Our hypothesis was that providing CPR performance evaluation (CPR-PE) to three ambulance services would facilitate local education andimplementation of CPR guidelines and, consequently, improve CPR quality. Methods: Quality of CPR in 85 consecutive cases of adult out-of-hospital cardiac arrests after CPR-PE was compared to 39 cases prior to CPR-PE. Real-time automated verbal andvisual feedback on CPR performance was given in all cases. No general implementation strategy was provided because the sites were expected to use the CPR-PEs in development of local strategies. Because the strategies were expected to vary, the sites were analyzed separately. Results: No significant improvement was seen in quality of CPR after CPR-PE. No chest compressions were given 40% of the time before versus 41% after CPR-PE. The median (95% confidence interval) percentage of chest compressions within the recommended depth range (38–51 mm) was 35% (27–57) before versus 51% (42–60) after CPR-PE (p = 0.12). In site-specific analysis, chest compressions within guideline depth increased from 31% to 61% after CPR-PE (p = 0.05) in one site. Conclusions: Overall our attempt to improve CPR-quality was unsuccessful. Quality improvement likely requires a full range of implementation strategies to change current attitudes andpractices.

A Least Mean-Square Filter for the Estimation of the Cardiopulmonary Resuscitation Artifact Based on the Frequency of the Compressions

Cardiopulmonary resuscitation (CPR) artifacts caused by chest compressions and ventilations interfere with the rhythm diagnosis of automated external defibrillators (AED). CPR must be interrupted for a reliable diagnosis. However, pauses in chest compressions compromise the defibrillation success rate and reduce perfusion of vital organs. The removal of the CPR artifacts would enable compressions to continue during AED rhythm analysis, thereby increasing the likelihood of resuscitation success. We have estimated the CPR artifact using only the frequency of the compressions as additional information to model it. Our model of the artifact is adaptively estimated using a least mean-square (LMS) filter. It was tested on 89 shockable and 292 nonshockable ECG samples from real out-of-hospital sudden cardiac arrest episodes. We evaluated the results using the shock advice algorithm of a commercial AED. The sensitivity and specificity were above 95% and 85%, respectively, for a wide range of working conditions of the LMS filter. Our results show that the CPR artifact can be accurately modeled using only the frequency of the compressions. These can be easily registered after small changes in the hardware of the CPR compression pads.

Development of the probability of return of spontaneous circulation in intervals without chest compressions during out-of-hospital cardiac arrest: an observational study

BackgroundOne of the factors that limits survival from out-of-hospital cardiac arrest is the interruption of chest compressions. During ventricular fibrillation and tachycardia the electrocardiogram reflects the probability of return of spontaneous circulation associated with defibrillation. We have used this in the current study to quantify in detail the effects of interrupting chest compressions.MethodsFrom an electrocardiogram database we identified all intervals without chest compressions that followed an interval with compressions, and where the patients had ventricular fibrillation or tachycardia. By calculating the mean-slope (a predictor of the return of spontaneous circulation) of the electrocardiogram for each 2-second window, and using a linear mixed-effects statistical model, we quantified the decline of mean-slope with time. Further, a mapping from mean-slope to probability of return of spontaneous circulation was obtained from a second dataset and using this we were able to estimate the expected development of the probability of return of spontaneous circulation for cases at different levels.ResultsFrom 911 intervals without chest compressions, 5138 analysis windows were identified. The results show that cases with the probability of return of spontaneous circulation values 0.35, 0.1 and 0.05, 3 seconds into an interval in the mean will have probability of return of spontaneous circulation values 0.26 (0.24–0.29), 0.077 (0.070–0.085) and 0.040(0.036–0.045), respectively, 27 seconds into the interval (95% confidence intervals in parenthesis).ConclusionDuring pre-shock pauses in chest compressions mean probability of return of spontaneous circulation decreases in a steady manner for cases at all initial levels. Regardless of initial level there is a relative decrease in the probability of return of spontaneous circulation of about 23% from 3 to 27 seconds into such a pause.

Suppression of the cardiopulmonary resuscitation artefacts using the instantaneous chest compression rate extracted from the thoracic impedance

AIM To demonstrate that the instantaneous chest compression rate can be accurately estimated from the transthoracic impedance (TTI), and that this estimated rate can be used in a method to suppress cardiopulmonary resuscitation (CPR) artefacts. METHODS A database of 372 records, 87 shockable and 285 non-shockable, from out-of-hospital cardiac arrest episodes, corrupted by CPR artefacts, was analysed. Each record contained the ECG and TTI obtained from the defibrillation pads and the compression depth (CD) obtained from a sternal CPR pad. The chest compression rates estimated using TTI and CD were compared. The CPR artefacts were then filtered using the instantaneous chest compression rates estimated from the TTI or CD signals. The filtering results were assessed in terms of the sensitivity and specificity of the shock advice algorithm of a commercial automated external defibrillator. RESULTS The correlation between the mean chest compression rates estimated using TTI or CD was r=0.98 (95% confidence interval, 0.97-0.98). The sensitivity and specificity after filtering using CD were 95.4% (88.4-98.6%) and 87.0% (82.6-90.5%), respectively. The sensitivity and specificity after filtering using TTI were 95.4% (88.4-98.6%) and 86.3% (81.8-89.9%), respectively. CONCLUSIONS The instantaneous chest compression rate can be accurately estimated from TTI. The sensitivity and specificity after filtering are similar to those obtained using the CD signal. Our CPR suppression method based exclusively on signals acquired through the defibrillation pads is as accurate as methods based on signals obtained from CPR feedback devices.

Clinical pilot study of different hand positions during manual chest compressions monitored with capnography

PURPOSE OF THE STUDY Optimal hand position for chest compressions during cardiopulmonary resuscitation is unknown. Recent imaging studies indicate significant inter-individual anatomical variations, which might cause varying haemodynamic responses with standard chest compressions. This prospective clinical pilot study intended to assess the feasibility of utilizing capnography to optimize chest compressions and identify the optimal hand position. MATERIALS AND METHODS Intubated cardiac arrest patients treated by the physician manned ambulance between February and December 2011 monitored with continuous end-tidal CO2 (EtCO2) measurements were included. One minute of chest compressions at the inter-nipple line (INL) optimized using EtCO2 feedback, was followed by four 30-s intervals with compressions at four different sites; INL, 2 cm below the INL, 2 cm below and to the left of INL and 2 cm below and to the right of INL. RESULTS Thirty patients were included. At the end of each 30-s interval median (range) EtCO2 was 3.1 kPa (0.7-8.7 kPa) at INL, 3.5 kPa (0.5-10.7) 2 cm below INL, 3.5 kPa (0.5-10.3 kPa) 2 cm below and to the left of INL, and 3.8 kPa (0.4-8.8 kPa) 2 cm below and to the right of INL (p=0.4). The EtCO2 difference within each subject between hand positions with maximum and minimum values varied between individuals from 0.2 to 3.4 kPa (median 0.9 kPa). CONCLUSION Monitoring and optimizing chest compressions using capnography was feasible. We could not demonstrate one superior hand position, but inter-individual differences suggest optimal hand position might vary significantly among patients.

Video analysis of dispatcher–rescuer teamwork–Effects on CPR technique and performance

OBJECTIVE We wanted to study the effect of continuous dispatcher communication on CPR technique and performance during 10min of simulated cardiac arrest. METHOD We reviewed video recordings and manikin data from 30 CPR trained lay people who where left alone in a simulated cardiac arrest situation with a manikin in a home-like environment (in a small, confined kitchen with the disturbing noise of a radio). CPR was performed for 10min with continuous telephone instructions via speaker function from a dispatcher. The dispatcher was blinded for CPR performance and video. Dispatcher communication, compression technique and ventilation technique was scored as accomplished or failed in the 1st and 10th minute. RESULTS 29/30 rescuers were able to hear instructions, answer questions from the dispatcher and perform CPR in parallel. Rescuer position beside manikin was initially correct for 13/30, improving to 21/30 (p=0.008). Compression technique was adequate for the whole episode, with an insignificant trend for improvement; 29 to 30/30 using straight arms, 28 to 30/30 in a vertical position over chest and 24 to 27/30 counting loudly. 17/29 placed their hands between the nipples initially, improving to 24/29 (p=0.065). Mean compression rate improved from 84 to 101min(-1) (p<0.001), and compression depth maintained adequate (43 to 42mm). Initially, 17/29 used chin-lift manoeuvre, 14/30 used head-tilt and 19/29 used nose pinch to manage open airways, compared to 18, 20 and 22/29 (ns) in the 10th minute, respectively. Successful delivery of ventilation improved from 13/30 to 23/30 (p=0.006). CONCLUSION Bystander and dispatcher can communicate successfully during ongoing CPR using a telephone with speaker function. CPR technique and quality improved or did not change over 10min with continuous dispatcher assistance. These results suggest a potential for improved bystander CPR using rescuer-dispatcher teamwork.

A randomized trial of the capability of elderly lay persons to perform chest compression only CPR versus standard 30:2 CPR

AIM OF THE STUDY Early cardiopulmonary resuscitation (CPR) improves survival after cardiac arrest, but there is a discrepancy between the age group normally attending CPR-classes and the age group most likely to witness a cardiac arrest. We wanted to study if elderly lay persons could perform 10min of CPR on a realistic manikin with continuous chest compressions (CCC) and conventional CPR (30:2). METHODS Volunteers were tested 5-7 months after CPR-classes. They were randomized to CCC or 30:2, and to receive feedback (FB) or not. Quality of CPR, age adjusted maximum heart rate (HRmax), and subjective exhaustion ratings were measured and evaluated in a blinded fashion. Temporal development and group differences were evaluated with ANOVA procedures. RESULTS All 64 volunteers were able to perform CPR for 10min and rated their efforts as mild to moderate in concordance with a mean HRmax of 78%. Quality of CPR was similar in all groups, except for chest compression rate that was slightly higher and had less variability in the FB group. Overall chest compression depth was 41+/-4.5mm. Analysis of temporal development of chest compression depth revealed a small initial decline before leveling off. As expected, CCC group had less pauses and higher total number of chests compressions. CONCLUSION Lay people in the age group 50-76 were able to perform CPR with acceptable quality for 10min and we found only very slight temporal quality deterioration. This makes training programs for the elderly meaningful to improve survival after cardiac arrest.

Dynamics and state transitions during resuscitation in out-of-hospital cardiac arrest

BACKGROUND The state or rhythm during resuscitation, i.e. ventricular fibrillation/tachycardia (VF/VT), asystole (ASY), pulseless electrical activity (PEA), or return of spontaneous circulation (ROSC) determines management. The state is unstable and will change either spontaneously (e.g. PEA-->ASY) or by intervention (e.g. VF-->ASY after DC shock); temporary ROSC may also occur. To gain insight into the dynamics of this process, we analyzed the state transitions over time using real-life data. METHODS Detailed recordings from 304 episodes of attempted resuscitation from out-of-hospital cardiac arrests of presumed cardiac etiology were obtained from modified Heartstart 4000 defibrillators. State transitions were visualized and described, and analyzed in terms of a Markov probability model. RESULTS The median number of state transitions was 5 (range 1-39), and more transitions were observed with VF than PEA or asystole as the initial rhythm. Of 105 patients (35%) who regained ROSC at some point during CPR, only 65 (21%) achieved sustained ROSC; suggesting an unrealized survival potential. A 3-min transition probability matrix was estimated: for example, a patient early in VF has a probability of 31% to be in ASY, 32% of still being in VF, 5% to have temporary ROSC, and 2% to have sustained ROSC after 3 min. CONCLUSION The dynamics of resuscitation can be described in terms of state transitions and a Markov probability model. This framework enables prediction of short-term clinical development, supports informed decisions during CPR, and suggests a novel area for research.

Comparison of mechanical characteristics of the human and porcine chest during cardiopulmonary resuscitation

BACKGROUND Most studies investigating cardiopulmonary resuscitation (CPR) interventions or functionality of mechanical CPR devices have been performed using porcine models. The purpose of this study was to identify differences between mechanical characteristics of the human and porcine chest during CPR. MATERIAL AND METHODS CPR data of 90 cardiac arrest patients was compared to data of 14 porcine from two animal studies. Chest stiffness k and viscosity mu were calculated from acceleration and pressure data recorded using a Laerdal Heartstart 4000SP defibrillator during CPR. K and mu were calculated at chest compression depths of 15, 30 and 50mm for three different time periods. RESULTS At a depth of 15mm porcine chest stiffness was comparable to human chest stiffness at the beginning of resuscitation (4.8 vs. 4.5N/mm) and clearly lower after 200 chest compressions (2.9 vs. 4.5N/mm) (p<0.05). At 30 and 50mm porcine chest stiffness was higher at the beginning and comparable to human chest stiffness after 200 chest compressions. After 200 chest compressions porcine chest viscosity was similar to human chest viscosity at 15mm (108 vs. 110Ns/m), higher for 30mm (240 vs. 188Ns/m) and clearly higher for 50mm chest compression depth (672 vs. 339Ns/m) (p<0.05). CONCLUSION In conclusion, human and porcine chest behave relatively similarly during CPR with respect to chest stiffness, but differences in chest viscosity at medium and deep chest compression depth should at least be kept in mind when extrapolating porcine results to humans.

Automatic Identification of Return of Spontaneous Circulation During Cardiopulmonary Resuscitation

The main problem during pulse check in out-of-hospital cardiac arrest is the discrimination between normal pulse-generating rhythm (PR) and pulseless electrical activity (PEA). It has been suggested that circulatory information can be acquired by measuring the thoracic impedance via the defibrillator pads. To investigate this, we performed an experimental study where we retrospectively analyzed 127 PEA segments and 91 PR segments out of 219 and 113 segments. A PEA versus PR classification framework was developed, that uses short segments (< 10 s) of ECG and impedance measurements to discriminate between the two rhythms. Using realistic data analyzed over a duration of 3 s, our system correctly identifies 90.0% of the segments with rhythm being pulseless electrical activity, and 91.5% of the normal pulse rhythm segments. Automatic identification of pulse could avoid unnecessary pulse checks and thereby reduce no-flow time and potentially increase the chance of survival.