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.

Intravenous drug administration during out-of-hospital cardiac arrest: a randomized trial.

CONTEXT: Intravenous access and drug administration are included in advanced cardiac life support (ACLS) guidelines despite a lack of evidence for improved outcomes. Epinephrine was an independent predictor of poor outcome in a large epidemiological study, possibly due to toxicity of the drug or cardiopulmonary resuscitation (CPR) interruptions secondary to establishing an intravenous line and drug administration. OBJECTIVE: To determine whether removing intravenous drug administration from an ACLS protocol would improve survival to hospital discharge after out-of-hospital cardiac arrest. DESIGN, SETTING, AND PATIENTS: Prospective, randomized controlled trial of consecutive adult patients with out-of-hospital nontraumatic cardiac arrest treated within the emergency medical service system in Oslo, Norway, between May 1, 2003, and April 28, 2008. INTERVENTIONS: Advanced cardiac life support with intravenous drug administration or ACLS without access to intravenous drug administration. MAIN OUTCOME MEASURES: The primary outcome was survival to hospital discharge. The secondary outcomes were 1-year survival, survival with favorable neurological outcome, hospital admission with return of spontaneous circulation, and quality of CPR (chest compression rate, pauses, and ventilation rate). RESULTS: Of 1183 patients for whom resuscitation was attempted, 851 were included; 418 patients were in the ACLS with intravenous drug administration group and 433 were in the ACLS with no access to intravenous drug administration group. The rate of survival to hospital discharge was 10.5% for the intravenous drug administration group and 9.2% for the no intravenous drug administration group (P = .61), 32% vs 21%, respectively, (P<.001) for hospital admission with return of spontaneous circulation, 9.8% vs 8.1% (P = .45) for survival with favorable neurological outcome, and 10% vs 8% (P = .53) for survival at 1 year. The quality of CPR was comparable and within guideline recommendations for both groups. After adjustment for ventricular fibrillation, response interval, witnessed arrest, or arrest in a public location, there was no significant difference in survival to hospital discharge for the intravenous group vs the no intravenous group (adjusted odds ratio, 1.15; 95% confidence interval, 0.69-1.91). CONCLUSION: Compared with patients who received ACLS without intravenous drug administration following out-of-hospital cardiac arrest, patients with intravenous access and drug administration had higher rates of short-term survival with no statistically significant improvement in survival to hospital discharge, quality of CPR, or long-term survival. TRIAL REGISTRATION: clinicaltrials.gov Identifier: NCT00121524.

Quality of cardiopulmonary resuscitation before and during transport in out-of-hospital cardiac arrest.

AIM OF THE STUDY: To evaluate quality of cardiopulmonary resuscitation (CPR) performed during transport after out-of-hospital cardiac arrest. MATERIALS AND METHODS: Retrospective, observational study of all non-traumatic cardiac arrest patients older than 18 years who received CPR both before and during transport between May 2003 and December 2006 from the community run EMS system in Oslo. Chest compressions and ventilations were detected from impedance changes in routinely collected ECG signals, and hands-off ratio calculated as time without chest compressions divided by total CPR time. RESULTS: Seventy-five of 787 consecutive out-of-hospital cardiac arrest patients met the inclusion criteria. Quality data were available from 36 of 66 patients receiving manual CPR and 7 of 9 receiving mechanical CPR. CPR was performed for mean 21+/-11 min before and 12+/-8 min during transport. With manual CPR hands-off ratio increased from 0.19+/-0.09 on-scene to 0.27+/-0.15 (p=0.002) during transport. Compression and ventilation rates were unchanged causing a reduction in compressions per minute from 94+/-14 min(-1) to 82+/-19 min(-1) (p=0.001). Quality was significantly better with mechanical than manual CPR. Four patients (5%) survived to hospital discharge; two with manual CPR (Cerebral performance categories (CPC) 1 and 2), and two with mechanical CPR (CPC scores 3 and 4). No discharged patients had any spontaneous circulation during transport. CONCLUSIONS: The fraction of time without chest compressions increased during transport of out-of-hospital cardiac arrest patients. Every effort should therefore be made to stabilise patients on-scene before transport to hospital, but all transport with ongoing CPR is not futile.

Arterial blood gases during basic life support of human cardiac arrest victims.

BACKGROUND: Ventilation with tidal volumes sufficient to raise the victim's chest is an integral part of guidelines for lay-rescuer basic life support, but optimal tidal volume, frequency and ratio to chest compressions are not known. METHODS: Adults with non-traumatic, out-of-hospital cardiac arrest, who were not successfully resuscitated following advanced life support by the staff of a physician-manned ambulance, were included. Advanced life support comprised tracheal intubation and mechanical ventilation with tidal volume of 700 ml and 100% oxygen, 12 times per min. An arterial blood sample was drawn at the end of the resuscitation attempt and analysed on the scene. After the victim was declared dead, basic life support was initiated with chest compressions and mouth-to-mask or mouth-to-tracheal tube ventilation (15:2), with volumes sufficient to make the chest rise. The tracheal tube was equipped with an impedance valve to avoid passive ventilation secondary to chest compressions. Arterial blood samples were drawn after 7-8 min of basic life support and analysed on the scene. RESULTS: Six men and two women, median (range) age 72 (32-86) years, were included in the study. Four of these received mouth-to-mask ventilation and four mouth-to-tracheal tube ventilation. Mean (S.D.) arterial blood carbon dioxide and oxygen tension during advanced life support were 6.4 (1.4)kPa and 22 (15)kPa, respectively. Similar values during basic life support were 9.6 (1.9)kPa and 8.5 (1.6)kPa, respectively, with no differences between the ventilation methods. CONCLUSION: Ventilation during basic life support performed according to international guidelines (2000) resulted in arterial hypercapnia and hypoxia.

Improving countershock success prediction during cardiopulmonary resuscitation using ventricular fibrillation features from higher ECG frequency bands.

BACKGROUND: Countershock outcome prediction using ventricular fibrillation (VF) feature analysis needs undisturbed electrocardiogram (ECG) signals and therefore requires interruption of cardiopulmonary resuscitation (CPR). Features that originate from higher frequency bands of the VF power spectrum may be less affected by CPR artefacts and as such reduce cumulative hands-off intervals. MATERIALS AND METHODS: From 192 patients with in-hospital and out-of-hospital cardiac arrest, four countershock outcome prediction features (peak-peak amplitude, mean slope, median slope, power spectrum analysis) were analysed in 550 short time ECG records, each including a CPR corrupted and a subsequent undisturbed sequence. ECG features calculated from the main frequency band (0-26Hz) and from bandpass-filtered subbands (>10-26Hz) were compared using the similarity level method and differences in shock advice numbers. RESULTS: The feature similarity between ECG periods with and without CPR artefacts was higher in bandpass-filtered (Sim=0.79, 0.8, 0.78, 0.66) than in unfiltered ECG traces (Sim=0.58, 0.69, 0.68, 0.47). For the features evaluated, the difference in number of shock advices between subsequent traces with and without CPR artefact was significantly reduced using VF analysis from higher frequency bands. CONCLUSION: The accuracy of shock outcome prediction during CPR could be increased by using filtered ECG features from higher ECG subbands instead of features derived from the main ECG spectrum.

Is CPR quality improving? A retrospective study of out-of-hospital cardiac arrest.

AIM OF THE STUDY: To evaluate the quality of cardiopulmonary resuscitation (CPR) performed by a physician-manned ambulance, and assess whether it changed with time influenced by developing scientific evidence and guideline changes. MATERIALS AND METHODS: A retrospective, observational study of all cardiac arrest patients (except trauma) older than 18 years treated between May 2003 and December 2006 by the physician-manned ambulance in Oslo. CPR quality was assessed from continuous electronic recordings from the defibrillators (LIFEPAK 12, Physio-Control or a modified Heartstart 4000, Philips Medical Systems). Ventilations were assessed from changes in transthoracic impedance, chest compressions from transthoracic impedance for LIFEPAK 12 and from an accelerometer for Heartstart 4000 (nine patients). Values are given as mean+/-S.D. and differences analysed with ANOVA and unpaired Student's t-test with Bonferroni correction. RESULTS: Forty-eight of 169 consecutive cases were excluded from CPR quality analysis, 47 due to missing defibrillator data and one due to a short arrest time (<1min). Hands-off intervals (fraction of time without spontaneous circulation where no chest compressions are given) were reduced from 0.18+/-0.11 in 2003 to 0.10+/-0.06 in 2006 (p=0.03). Compression and ventilation rates were significantly reduced from 122+/-12 and 16+/-3min(-1), respectively in 2003 to 111+/-10 and 12+/-3 in 2006 (p<0.0001 and p=0.001). In 2003-2004 10% were discharged alive versus 16% in 2005-2006 (p=0.3, Chi-square test). CONCLUSION: High quality CPR is achievable out-of-hospital, and the improvement with time could reflect developing scientific evidence focusing on reducing hands-off intervals and hyperventilation.

Prediction of countershock success using single features from multiple ventricular fibrillation frequency bands and feature combinations using neural networks.

Targeted defibrillation therapy is needed to optimise survival chances of ventricular fibrillation (VF) patients, but at present VF analysis strategies to optimise defibrillation timing have insufficient predictive power. From 197 patients with in-hospital and out-of-hospital cardiac arrest, 770 electrocardiogram (ECG) recordings of countershock attempts were analysed. Preshock VF ECG features in the time and frequency domain were tested retrospectively for outcome prediction. Using band pass filters, the ECG spectrum was split into various frequency bands of 2-26 Hz bandwidth in the range of 0-26 Hz. Neural networks were used for single feature combinations to optimise prediction of countershock success. Areas under curves (AUC) of receiver operating characteristics (ROC) were used to estimate prediction power of single and combined features. The highest ROC AUC of 0.863 was reached by the median slope in the interval 10-22 Hz resulting in a sensitivity of 95% and a specificity of 50%. The best specificity of 55% at the 95% sensitivity level was reached by power spectrum analysis (PSA) in the 6-26 Hz interval. Neural networks combining single predictive features were unable to increase outcome prediction. Using frequency band segmentation of human VF ECG, several single predictive features with high ROC AUC>0.840 were identified. Combining these single predictive features using neural networks did not further improve outcome prediction in human VF data. This may indicate that various simple VF features, such as median slope already reach the maximum prediction power extractable from VF ECG.

Estimation of the duration of ventricular fibrillation using ECG single feature analysis.

The duration of untreated ventricular fibrillation (VF) is of paramount importance for CPR success. Moreover, therapeutic interventions taking into account the interval between cardiac arrest onset and initiation of CPR improve outcome. This study was performed to investigate whether VF feature analysis could be used to estimate the duration of VF in patients with out-of-hospital cardiac arrest. Demographic data recorded according to the Utstein guidelines and ECG recordings of 376 cardiac arrest patients from three European areas were analysed. Ten features in the time and frequency domain derived from different sub-bands of the initial VF ECG (n=127) were evaluated. The correlation between VF ECG features and cardiac arrest times was investigated using Pearson's correlation coefficient in a subset of 40 patients with reliably estimated downtimes and artefact-free initial VF tracings. No significant correlation (p<.05) between any of the VF ECG features and downtime could be found. The duration of cardiac arrest could not be estimated reliably from human VF ECG single feature analysis.

Pre-injury ASA physical status classification is an independent predictor of mortality after trauma.

BACKGROUND: The ability of an organism to withstand trauma is determined by the injury per se and inherent properties of the organism at the time of injury. We analyzed whether pre-injury morbidity scored on a four-level ordinal scale according to the American Society of Anesthesiologists Physical Status (ASA-PS) classification system predicts mortality after trauma. MATERIALS: From a total of 3,773 prospectively collected patients (years 2000-2004), 3,728 patients were included. Main outcome measure was mortality 30 days after injury. The effect of pre-injury ASA-PS on mortality was assessed using linear logistic regression analysis, controlling for Revised Trauma Score (RTS), Injury Severity Score (ISS), and age. RESULTS: Mortality increased with increasing pre-injury ASA-PS, age, and ISS, and with decreasing RTS. Unadjusted mortality rates were 5.7% in ASA-PS 1, 12.3% in ASA-PS 2, and 26.4% in ASA-PS 3-4. This increasing mortality trend across pre-injury ASA-PS group was evident in nearly all categories of ISS, RTS, and age. Odds ratio for death was 1.76 (95% CI, 1.14-2.72) for pre-injury ASA-PS 2, and 2.25 (95% CI, 1.36-3.71) for ASA-PS 3-4 compared with for ASA-PS 1 and adjusted for ISS, RTS, and age. There were no interaction effects between pre-injury ASA-PS and the other variables. CONCLUSIONS: Pre-injury ASA-PS score was an independent predictor of mortality after trauma, also after adjusting for the major variables in the traditional TRISS (Trauma and Injury Severity Score) formula. Including pre-injury ASA-PS score might improve the predictive power of a survival prediction model without complicating it.

Effects of compression depth and pre-shock pauses predict defibrillation failure during cardiac arrest.

BACKGROUND: Cardiopulmonary resuscitation (CPR) and electrical defibrillation are the primary treatment options for ventricular fibrillation (VF). While recent studies have shown that providing CPR prior to defibrillation may improve outcomes, the effects of CPR quality remain unclear. Specifically, the clinical effects of compression depth and pauses in chest compression prior to defibrillation (pre-shock pauses) are unknown. METHODS: A prospective, multi-center, observational study of adult in-hospital and out-of-hospital cardiac resuscitations was conducted between March 2002 and December 2005. An investigational monitor/defibrillator equipped to measure compression characteristics during CPR was used. RESULTS: Data were analyzed from 60 consecutive resuscitations in which a first shock was administered for VF. The primary outcome was first shock success defined as removal of VF for at least 5s following defibrillation. A logistic regression analysis demonstrated that successful defibrillation was associated with shorter pre-shock pauses (adjusted odds ratio 1.86 for every 5s decrease; 95% confidence interval 1.10-3.15) and higher mean compression depth during the 30s of CPR preceding the pre-shock pause (adjusted odds ratio 1.99 for every 5mm increase; 95% confidence interval 1.08-3.66). CONCLUSIONS: The quality of CPR prior to defibrillation directly affects clinical outcomes. Specifically, longer pre-shock pauses and shallow chest compressions are associated with defibrillation failure. Strategies to correct these deficiencies should be developed and consideration should be made to replacing current-generation automated external defibrillators that require long pre-shock pauses for rhythm analysis.

Performing procedures on the newly deceased for teaching purposes: what if we were to ask?

BACKGROUND: Performance of procedures on the recently dead for physician training is controversial. It has been suggested that permission be obtained. We investigated whether patients and family members would grant such permission or if even this request might anger the recently bereaved. METHODS: Physicians administered identical surveys to adult emergency department patients and family members in Brooklyn and Oslo to determine their willingness to consent for teaching of specific invasive techniques in the event of their own death or that of a family member. Demographic factors and location (culture) were assessed for effects. RESULTS: Willingness to consent was directly related to age of decedent and inversely related to perceived invasiveness of the procedure at both sites. In every scenario, respondents in Brooklyn were much less willing to grant permission (2- to 2.5-fold) than were those in Oslo. In Oslo, respondents were more willing to consent for their own bodies to be used as training tools than that of a relative. In Brooklyn, 48.5% would be angry if approached for permission compared with only 8.4% in Oslo (P<.001). CONCLUSIONS: Asking for permission to perform procedures on the recently deceased for physician training purposes may often anger the bereaved. The emotional response to the consent request may be culturally determined. Increased willingness of individuals to permit the use of their bodies in the immediate postmortem period suggests that a preauthorization program similar to organ donor cards might be acceptable, successful, and ethical.

Twelve-month retention of CPR skills with automatic correcting verbal feedback.

AIM: To evaluate the retention of CPR skills 12 months after initial training, using a manikin equipped with a computer-based voice advisory feedback system. METHODS: Thirty-five volunteers had individual 20 min training sessions without an instructor on a manikin with computer-based voice advisory feedback. The feedback depended on the performance as measured by the manikin computer system versus set limits for ventilation and compression variables. Twelve of the volunteers received additional ten 3-min self-training sessions during the following month making a total of 50 min training. All ventilation and compression variables when the volunteers were tested before, immediately after and 6 months after training have previously been reported. The volunteers were now tested 12 months after the initial training session with activated feedback. RESULTS: There were virtually no changes in CPR skills when tested with active feedback 12 months after initial training versus immediately or 6 months post-training. The only exception was a slightly lower number of compressions per minute at 12 months versus immediate post-training in the subgroup with 20 min of initial training, 47+/-4 versus 52+/-4, p = 0.008. There were no differences between the 20 and 50 min training subgroups at 12 months. CONCLUSIONS: Computer-based voice advisory feedback can improve the performance of basic life support skills on a manikin with no deterioration in feedback supported performance after 12 months.

A probabilistic neural network as the predictive classifier of out-of-hospital defibrillation outcomes.

INTRODUCTION: Although modern defibrillators are nearly always successful in terminating ventricular fibrillation (VF), multiple defibrillation attempts are usually required to achieve return of spontaneous circulation (ROSC). This is potentially deleterious as cardiopulmonary resuscitation (CPR) must be discontinued during each defibrillation attempt which causes deterioration in the heart muscle and reduces the chance of ROSC from later defibrillation attempts. In this work defibrillation outcomes are predicted prior to electrical shocks using a neural network model to analyse VF time series in an attempt to avoid defibrillation attempts that do not result in ROSC. METHODS: The 198 pre-shock VF ECG episodes from 83 cardiac arrest patients with defibrillation conversions to different outcomes were selected from the Oslo ambulance service database. A probabilistic neural network model was designed for training and testing with a cross validation method being used for the better generalisation performance. RESULTS: We achieved an accuracy of 75% in overall prediction with a sensitivity of 84% and a specificity of 65% using VF ECG time series of an order of 1 s in length. CONCLUSION: Pre-shock VF ECG time series can be classified according to the defibrillation conversion to a return of spontaneous circulation (ROSC) or No-ROSC.

Retention of basic life support skills 6 months after training with an automated voice advisory manikin system without instructor involvement.

AIM: To evaluate the retention of skills 6 months after training in ventilation and chest compressions (CPR) on a manikin with computer based on-line voice advisory feedback and the possible effects of initial overtraining. METHODS: Thirty five volunteers had 20 min provisional CPR training on a manikin with computer based voice advisory feedback but without an instructor. The appropriate feedback was taken from a pre-recorded list depending on performance measured by the manikin--computer system versus set limits for ventilation and compression variables. One group in addition was randomised to receive 10 similar 3 min training sessions during 1 week in the following month (overtrained group). All ventilation and compression variables were measured without feedback before and after the initial training session, with feedback immediately thereafter, and both without and with feedback 6 months after the initial training session. RESULTS: The initial training improved all variables. Compressions with correct depth increased from a mean of 33 to 77%, and correct inflations from a mean of 9 to 58%. After 6 months, the results for the controls were not significantly different from pre-training, except for a higher of correct inflations (18%), while the overtrained group had better retention of skills including the correct compression depth (mean 61%) and inflations (mean 42%). When verbal feedback was added both the compressions and ventilations immediately improved both when tested immediately and 6 months after the initial training session. CONCLUSIONS: The computer-based voice advisory manikin (VAM) feedback system can improve immediate performance of basic life support (BLS) skills, with better long-term retention with overtraining.

Improved prediction of defibrillation success for out-of-hospital VF cardiac arrest using wavelet transform methods.

We report an improved method for the estimation of shock outcome prediction based on novel wavelet transform-based time-frequency methods. Wavelet-based peak frequency, energy, mean frequency, spectral flatness and a new entropy measure were studied to predict shock outcome. Of these, the entropy measure provided optimal results with 60 +/- 6% specificity at 91 +/- 2% sensitivity achieved for the prediction of return of spontaneous circulation (ROSC). These results represent a major improvement in shock prediction in human ventricular fibrillation.

Outcome when adrenaline (epinephrine) was actually given vs. not given - post hoc analysis of a randomized clinical trial.

PURPOSE OF THE STUDY: IV line insertion and drugs did not affect long-term survival in an out-of-hospital cardiac arrest (OHCA) randomized clinical trial (RCT). In a previous large registry study adrenaline was negatively associated with survival from OHCA. The present post hoc analysis on the RCT data compares outcomes for patients actually receiving adrenaline to those not receiving adrenaline. MATERIALS AND METHODS: Patients from a RCT performed May 2003 to April 2008 were included. Three patients from the original intention-to-treat analysis were excluded due to insufficient documentation of adrenaline administration. Quality of cardiopulmonary resuscitation (CPR) and clinical outcomes were compared. RESULTS: Clinical characteristics were similar and CPR quality comparable and within guideline recommendations for 367 patients receiving adrenaline and 481 patients not receiving adrenaline. Odds ratio (OR) for being admitted to hospital, being discharged from hospital and surviving with favourable neurological outcome for the adrenaline vs. no-adrenaline group was 2.5 (CI 1.9, 3.4), 0.5 (CI 0.3, 0.8) and 0.4 (CI 0.2, 0.7), respectively. Ventricular fibrillation, response interval, witnessed arrest, gender, age and endotracheal intubation were confounders in multivariate logistic regression analysis. OR for survival for adrenaline vs. no-adrenaline adjusted for confounders was 0.52 (95% CI: 0.29, 0.92). CONCLUSION: Receiving adrenaline was associated with improved short-term survival, but decreased survival to hospital discharge and survival with favourable neurological outcome after OHCA. This post hoc survival analysis is in contrast to the previous intention-to-treat analysis of the same data, but agrees with previous non-randomized registry data. This shows limitations of non-randomized or non-intention-to-treat analyses.

Patients Referred to a Norwegian Trauma Centre: effect of transfer distance on injury patterns, use of resources and outcomes.

BACKGROUND: Triage and interhospital transfer are central to trauma systems. Few studies have addressed transferred trauma patients. This study investigated transfers of variable distances to OUH (Oslo University Hospital, Ullevål), one of the largest trauma centres in Europe. METHODS: Patients included in the OUH trauma registry from 2001 to 2008 were included in the study. Demographic, injury, management and outcome data were abstracted. Patients were grouped according to transfer distance: ≤20 km, 21-100 km and > 100 km. RESULTS: Of the 7.353 included patients, 5.803 were admitted directly, and 1.550 were transferred. The number of transfers per year increased, and there was no reduction in injury severity during the study period. Seventy-six per cent of the transferred patients were severely injured. With greater transfer distances, injury severity increased, and there were larger proportions of traffic injuries, polytrauma and hypotensive patients. With shorter distances, patients were older, and head injuries and injuries after falls were more common. The shorter transfers less often activated the trauma team: ≤20 km -34%; 21-100 km -51%; > 100 km -61%, compared to 92% of all directly admitted patients. The mortality for all transferred patients was 11%, but was unequally distributed according to transfer distance. CONCLUSION: This study shows heterogeneous characteristics and high injury severity among interhospital transfers. The rate of trauma team assessment was low and should be further examined. The mortality differences should be interpreted with caution as patients were in different phases of management. The descriptive characteristics outlined may be employed in the development of triage protocols and transfer guidelines.