Changes In Transthoracic Impedance Research Articles

Most Effective Pad Placement in Elective Cardioversion.

Most Effective Pad Placement in Elective Cardioversion.

Characterization of the thoracic impedance waveform fluctuations during controlled ventilation modes

Purpose: Transthoracic impedance (TTI) waveform provides important information about ventilations during cardiac arrest. The objective was to characterize ventilation caused TTI changes.

A novel technique to assess the quality of ventilation during pre-hospital cardiopulmonary resuscitation

BackgroundDevices that measure ventilation in the pre-hospital setting are deficient especially during early cardiopulmonary resuscitation (CPR) before placement of an advanced airway. Consequently, evidence is limited regarding the role of ventilation during early CPR and its effect on outcomes. ObjectiveTo develop software that automatically identifies ventilation waveforms recorded by defibrillators based on changes in transthoracic impedance during standard CPR. MethodsThis was an observational, retrospective analysis of non-traumatic pre-hospital cardiac arrest patients who received 30:2 CPR by emergency medical service rescuers. Data was collected from 550 cases recorded by the bioimpedance channel of defibrillators. Two expert clinicians independently assessed all episodes from the time of initial CPR until placement of an advanced airway, defined acceptable ventilation waveforms, and annotated the pauses between compressions with ventilation waveforms. We then developed software that incorporated the expert criteria and automatically annotated pauses with acceptable ventilations. ResultsA total of 7396 pauses were analyzed, mean(SD) duration of 30:2 CPR was 13 (8) min, with 13 (10) pauses/patient, and mean pause duration of 6 (3) s. Reviewer 1 and reviewer 2 identified 2375 and 2249 pauses with any acceptable ventilation, respectively, with an inter-rater reliability of 0.94. The novel software program reproduced expert annotation with excellent agreement (>0.8) and high accuracy, both sensitivity and specificity above 90%, compared to two reviewers. The software presented a substantial agreement with the reviewers (κ > 0.73) for ventilation counts in the pauses. ConclusionWe developed a novel and reliable strategy that enables investigation of ventilation quality during standard CPR using thoracic bioimpedance. This strategy would allow a timely and reliable automatic annotation of large scale resuscitation datasets.

Transient variations of transthoracic impedance as a predictor of heart failure and death in patients with implanted defibrillators

BackgroundTransient variations in physiological parameters may forewarn of life-threatening cardiac events, but are difficult to identify clinically. Implantable cardioverter defibrillators (ICD) designed to measure transthoracic impedance provide a surrogate marker for pulmonary congestion. ObjectiveThe aim of this study is to determine if the frequency of changes in transthoracic impedance (TTI) is associated with congestive heart failure (CHF) exacerbation and predicts mortality. MethodsWe followed 109 consecutive patients (pts) with ICDs (n=58) or CRT-ICDs (n=51) for a mean of 21.3 (+10.2) months. Using 80ohm-days as a reference, we correlated the frequency of TTI changes above this index to CHF hospitalizations or death. ResultsThere was at least one TTI threshold crossing in 79 (72%) pts over 23.3months follow-up, with a mean of 1.8±3.4 per year. There were 18 pts with CHF hospitalizations who had a mean of 4.3 TTI threshold crossings/year (S.D.=±7.3; median=2.8), compared to 1.3 (S.D.=±1.5; median=0.8) among pts without CHF hospitalizations (p=0.0006). Among 20 patients who died during follow-up, there were 4.2 (S.D.=±7.0; median=2.9) TTI threshold crossings/year, compared with 1.3 (S.D.=±1.3; median=0.9) threshold crossings/year among survivors (p=0.0004). Using Cox Proportional Hazard modeling, after adjusting for age, baseline EF, and number of shocks, TTI threshold crossing was an independent predictor of death (HR 1.72, 95% CI 1.26–2.36, p=0.001). ConclusionsIncreased frequency of TTI threshold crossings may be a useful predictor of transient risk for identifying a subgroup of ICD recipients at greater individual risk for death or CHF hospitalizations.

Abstract 302: Transthoracic Impedance Is Poorly Predicted by Patient Characteristics but Significantly Reduced by Placement of Defibrillator Pads in the Anteroposterior Position

Introduction The American Heart Association Resuscitation Guidelines advocate four pad positions to achieve defibrillation success following cardiac arrest. Transthoracic impedance (TTI) reflects the electrode-skin interface and patient impedance and affects current amplitude, energy delivered and defibrillation efficacy. Modern defibrillators utilise an impedance compensated waveform to account for changes in TTI to improve defibrillation success. However the effect of electrode pad position and patient characteristics on TTI remains unclear. Objective To evaluate the effect of patient characteristics and pad position on Transthoracic impedance (TTI). Methods Patients undergoing diagnostic cardiac catheterisation were recruited for the study following regional ethical approval. Standard self-adhesive defibrillator electrodes were applied to patients in both the anterolateral and anteroposterior positions and connected to Heartsine Samaritan defibrillators. TTI was measured by applying a 30kHz sinusoidal signal through the chest. The voltage was then converted to digital samples using an 8-bit microprocessor. The digital samples were then stored on the secure digital card to be retrieved using custom-made download data recovery software. TTI was measured at 10 second intervals in both positions for the duration of the clinical procedure. Results 32 patients (mean age 63), (66% male), were recruited. TTI measured at 10 seconds was significantly higher in the anterolateral position (88.3ohms vs 68.5ohms, p <0.001). Mean TTI reduction over 5 minutes was 2.4% in the anterolateral position and 1.9% in anteroposterior position. There was no significant correlation between TTI measured from either pad position and age, height, weight, body surface area and Haemoglobin (r<0.4 for all parameters). Conclusion TTI is significantly reduced by placement of defibrillator pads in the anteroposterior position. Furthermore patient characteristics are poorly predictive of TTI from either pad position. Patients suffering failed defibrillation attempts from pads positioned in the anterolateral position may benefit from prompt relocation to the anteroposterior position to improve defibrillation efficacy.

Abstract 16745: Usefulness of Analysis of Transthoracic Impedance Signals for Accurate Diagnosis of Sleep Disordered Breathing in Patients with Permanent Pacemaker Implantation

Purpose: There are several reports regarding an excessively high prevalence of undiagnosed sleep disordered breathing (SDB) in patients with permanent pacemaker implantation. Some programs for pacemakers utilize transthoracic impedance changes between the generator and the electrode tip to derive minute ventilation as a sensor for rate adaptation. We investigated whether this system can detect sleep-related breathing disorders. Methods: We investigated 39 patients (19 male, 20 female, 78±13 (SD) years) who underwent permanent pacemaker implantation for sick sinus syndrome and advanced or complete atrio-ventricular nodal block. Body mass index of these patients was 23±4 kg/m 2 . Chronic heart failure was observed in 10 (26%) of 39 patients. We measured the number of the transthoracic impedance signals remaining unchanged for more than 10 seconds with use of the pacemaker minute ventilation sensor (SORIN), and compared with the results of polysomnography (Morpheus C, Teijin). By using polysomnography, we calculated the number of apnea/hypopnea episode per hour (apnea/hypopnea index: AHI). We defined the number of respiratory cycles more than 10 seconds of unchanged transthoracic impedance signals as the respiratory disturbance index (RDI). Receiver operating characteristic (ROC) analysis was performed on the RDI for the diagnosis of moderate to severe SDB (AHI >20). Results: Moderate to severe SDB was diagnosed in 18 (46%) of 39 patients. The area under the ROC curve was 0.87 (95% CI 0.75 to 0.99). Given a cutoff value of 210/hour for the RDI, the RDI can significantly (p<0.05) discriminate between patients with and without moderate to severe SDB, and showed 72.2% sensitivity and 90.5% specificity for the diagnosis. The RDI was well correlated with the AHI in patients with moderate to severe SDB (n=15, r=0.771, p=0.0004). Conclusions: Detection of apnea/hypopnea episode by pacemaker minute ventilation sensor is feasible and accurate for diagnosing SDB in patients with permanent pacemaker implantation.

Advances in defibrillation

The place of defibrillation in the chain of survival is paramount and this review covers advances in this aspect of resuscitation over the past 18 months. The main advance is the publication of 2010 European Resuscitation Council guidelines of which defibrillation is a key aspect. Additionally, there have been a number of important articles discussing safety issues with defibrillation, the occurrence of refibrillation following successful cardioversion, prediction of shock success and changes in transthoracic impedance with sequential defibrillation shocks. The focus of these articles is to improve the delivery of defibrillation without interrupting chest compression and aiming to do so at an optimal stage of the resuscitation attempt.

Analysis of transthoracic impedance during real cardiac arrest defibrillation attempts in older children and adolescents: Are stacked-shocks appropriate?

Background In 2005, the AHA changed the treatment recommendation for shockable rhythms from 3 transthoracic stacked-shocks to a single shock followed by immediate chest compressions. The stacked-shock recommendation was based on low first-shock efficacy of monophasic waveforms and the theoretical decrease in transthoracic impedance (TTI) following each shock. The objective of this study was to characterize TTI following biphasic defibrillation attempts in children ≥8 yrs during cardiac arrest to assess whether a stacked-shock approach may be appropriate to improve defibrillation success. Methods TTI (Ohms (Ω)) was collected via standard anterior-apical defibrillator electrode pads during consecutive in-hospital cardiac arrest biphasic defibrillation attempts in children ≥8 yrs. Analytic data points for TTI were: 0.1 s pre-shock (baseline); post-shock at 0.1, 0.5, 1.0, 1.5, and 2.0 s. TTI variables analyzed with descriptive summaries/paired t-test. p values < 0.05 considered statistically significant after correction for multiple comparisons. Results Analysis yielded 13 evaluable shock events during 5 cardiac arrests (mean age 14.3 ± 5 yrs, weight 47.4 ± 7.3 kg) between September 2006 and May 2009. Compared to 0.1 s pre-shock baseline values (56.8 ± 23.4 Ω), TTI was significantly lower immediately 0.1 s post-shock (55.2 ± 22.2 Ω, p = 0.003). Post-shock mean difference from baseline was 1.6 Ω at 0.1 s ( p = 0.015), 1.4 Ω at 0.5 s ( p = 0.019) 1.4 Ω at 1.0 s ( p = 0.023), 1.1 Ω at 1.5 s ( p = 0.028), and 0.95 Ω at 2.0 s ( p = 0.096). Time to recharge our clinical defibrillators to standard biphasic shock dose was 2.80 ± 0.05 s. Conclusions During cardiac arrests in children ≥8 yrs, TTI decreased after biphasic shocks, but the limited magnitude and duration of TTI changes suggest that stacked-shocks would not improve defibrillation success.

The effect of transport on quality of cardiopulmonary resuscitation in out-of-hospital cardiac arrest

Introduction Most manikin and clinical studies have found decreased quality of CPR during transport to hospital. We wanted to study quality of CPR before and during transport for out-of-hospital cardiac arrest patients and also whether quality of CPR before initiation of transport was different from the quality in patients only receiving CPR on scene. Materials and methods Quality of CPR was prospectively registered with a modified defibrillator for consecutive cases of out-of-hospital cardiac arrest in three ambulance services during 2002–2005. Ventilations were registered via changes in transthoracic impedance and chest compressions were measured with an extra chest compression pad placed on the patients’ sternum. Paired t-tests were used to analyse quality of CPR before vs. during transport with ongoing CPR. Unpaired t-tests were used to compare CPR quality prior to transport to CPR quality in patients with CPR terminated on site. Results Quality of CPR did not deteriorate during transport, but as previously reported overall quality of CPR was substandard. Quality of CPR performed on site was significantly better when transport was not initiated with ongoing CPR compared to episodes with initiation of transport during CPR: fraction of time without chest compressions was 0.45 and 0.53 ( p < 0.001), compression depth 37 mm and 34 mm ( p = 0.04), and number of chest compressions per minute 61 and 56 ( p = 0.01), respectively. Conclusion CPR quality was sub-standard both before and during transport. Early decision to transport might have negatively affected CPR quality from the early stages of resuscitation.

Effect of implementation of new resuscitation guidelines on quality of cardiopulmonary resuscitation and survival

Background During cardiopulmonary resuscitation (CPR), advanced life support (ALS) providers have been shown to deliver inadequate CPR with long intervals without chest compressions. Several changes made to the 2005 CPR Guidelines were intended to reduce unnecessary interruptions. We have evaluated if quality of CPR performed by the Oslo Emergency Medical System (EMS) improved after implementation of the modified 2005 CPR Guidelines, and if any such improvement would result in increased survival. Materials and methods Retrospective, observational study of all consecutive adult cardiac arrest patients treated during a 2-year period before (May 2003–April 2005), and after (January 2006–December 2007) implementation of the modified 2005 CPR Guidelines. CPR quality was assessed from continuous electronic recordings from LIFEPACK 12 defibrillators where ventilations and chest compressions were identified from transthoracic impedance changes. Ambulance run sheets, Utstein forms and hospital records were collected and outcome evaluated. Results Resuscitation was attempted in 435 patients before and 481 patients after implementation of the modified 2005 CPR Guidelines. ECGs usable for CPR quality evaluation were obtained in 64% and 76% of the cases, respectively. Pre-shock pauses decreased from median (interquartile range) 17 s (11, 22) to 5 s (2, 17) ( p = 0.000), overall hands-off ratios from 0.23 ± 0.13 to 0.14 ± 0.09 ( p = 0.000), compression rates from 120 ± 9 to 115 ± 10 ( p = 0.000) and ventilation rates from 12 ± 4 to 10 ± 4 ( p = 0.000). Overall survival to hospital discharge was 11% and 13% ( p = 0.287), respectively. Conclusion Quality of CPR improved after implementation of the modified 2005 Guidelines with only a weak trend towards improved survival to hospital discharge.

Transthoracic impedance used to evaluate performance of cardiopulmonary resuscitation during out of hospital cardiac arrest

There is a need to measure cardiopulmonary resuscitation (CPR) in order to document whether ambulance personnel follow CPR guidelines. Our goal was to do this using defibrillator technology based on changes in transthoracic impedance (TTI) produced by chest compressions and ventilations. 122 incidents of out-of-hospital cardiac arrest between May 2003 and February 2004 were analysed based on data recorded from defibrillators in Oslo EMS. New software was used to analyze chest compressions and ventilations based on changes in thoracic impedance between the defibrillator pads, as well as ECG and other event data. In total, 25+/-14% (varying from 76% to 3%) of the time chest compressions were not performed on patients without spontaneous circulation (NFR=No Flow Ratio). When adjusting for time spent on analysis of ECG, pulse check and defibrillation, NFR was 20+/-13% (varying from 70% to 3%). Mean compressions delivered per minute was 87+/-16 and the compression rate during active compressions was 117+/-9min(-1). Individual variation was 31-117min(-1) (mean) and 95-144min(-1) (active periods). A mean of 14+/-3ventilations/min was recorded, varying from 8 to 26min(-1). Compared with the rest of the episode, the first 5min had a significantly higher proportion of time without chest compressions; 30+/-17% (p<0.001) and significantly lower mean compression and ventilation rates; 80+/-19min(-1) and 12+/-4min(-1), respectively (p<0.001 in both cases). Core CPR values can be measured from TTI signals by using a standard defibrillator and new software. NFR was 25% (20% adjusted) with great rescuer variability.

Changes in transthoracic impedance during sequential biphasic defibrillation

Sequential monophasic defibrillation reduces transthoracic impedance (TTI) and progressively increases current flow for any given energy level. The effect of sequential biphasic shocks on TTI is unknown. We therefore studied patients undergoing elective cardioversion using a biphasic waveform to establish whether this is a phenomenon seen in the clinical setting. Adults undergoing elective DC cardioversion for atrial flutter or fibrillation received sequential transthoracic shocks using an escalating protocol (70J, 100J, 150J, 200J, and 300J) with a truncated exponential biphasic waveform. TTI was calculated through the defibrillator circuit and recorded electronically. Successful cardioversion terminated further defibrillation shocks. A total of 58 patients underwent elective cardioversion. Cardioversion was successful in 93.1% patients. First shock TTI was 92.2 [52.0-126.0]Omega (n=58) and decreased significantly with each sequential shock. Mean TTI in patients receiving five shocks (n=5) was 85.0Omega. Sequential biphasic defibrillation decreases TTI in a similar manner to that seen with monophasic waveforms. The effect is likely during defibrillation during cardiac arrest by the quick succession in which shocks are delivered and the lack of cutaneous blood flow which limits the inflammatory response. The ability of biphasic defibrillators to adjust their waveform according to TTI is likely to minimise any effect of these findings on defibrillation efficacy.

Alteration in transthoracic impedance following cardiac surgery

Haemodynamically significant ventricular tachyarrhythmias are a frequent complication in the immediate post-operative period after cardiac surgery. Successful cardioversion depends on delivery of sufficient current, which in turn is dependent on transthoracic impedance (TTI). However, it is uncertain if there is a change in TTI immediately following cardiac surgery using cardiopulmonary bypass (CPB). TTI was measured on 40 patients undergoing first time isolated cardiac surgery using CPB. TTI was recorded at 30 kHz using Bodystat Multiscan 5000 equipment before operation (with and without a positive end-expiratory pressure (PEEP) of 5 cm of H(2)O) and then at 1, 4 and 24 h after the operation. Data was analyzed to determine the relationship between pre- and post-operative variables and TTI values. Mean pre-operative TTI was 54.5+/-10.55 ohms without PEEP and 61.8+/-15.4 ohms on a PEEP of 5 cm of H(2)O. TTI dropped significantly (p<0.001) after the operation to 47.2+/-10.6 ohms at 1 h, 42.6+/-10.2 ohms at 4 h and 41.8+/-10.4 ohms at 24 h. A positive correlation was noted between duration of operation and TTI change at 1 h (r=0.38; p=0.016). There was no significant correlation between the duration of bypass and change in TTI. TTI decreases by more than 30% in the immediate post-operative period following cardiac surgery. This state may favour defibrillation at lower energy levels.

Time used for ventilation in two-rescuer CPR with a bag-valve-mask device during out-of-hospital cardiac arrest

Professional rescuers only deliver chest compressions 39% of the available time before intubation during out-of-hospital cardiac arrest. In manikin-studies lay rescuers need approximately 15s to deliver two ventilations. It is not known how much time professional rescuers use for two ventilations and we hypothesised that the time used for two ventilations with a bag-valve-mask device before tracheal intubation is longer than recommended and that the extended time contributes to the high no flow time. Quality of CPR was available for analysis in 628 cases of out-of-hospital cardiac arrest in the ambulance service in Oslo, Akershus, London, and Stockholm from 2002 to 2005. The 2000 Guidelines were used as the reference. Ventilations were registered from changes in transthoracic impedance as measured through the standard defibrillation pads. We included episodes only with CPR with a 15:2 pattern for at least 1 min and identified all pauses between chest compressions before intubation. In the remaining 172 episodes we identified 3097 chest compression pauses. In 1587 (51%) of the pauses we identified two ventilations and a mean pause length for each episode was calculated. The median of these means was 5.5s (IQR; 4.5, 7). These pauses comprised a median 9% (IQR; 4%, 15%) of the time before intubation in these episodes. In 892 (29%) of the pauses we identified a different number of ventilations, or other interventions in addition to ventilation. In the remaining 618 pauses (20%) no ventilations were registered. Professional rescuers delivered two bag-valve-mask ventilations within the 5-6s as indicated in the 2000 Guidelines, slightly longer than the 3-4s recommended in the 2005 Guidelines. However, only half the pauses were used for two ventilations, and the total time for two ventilations accounted for only 27% of the time without chest compressions. Excessive time for ventilation cannot explain the high no-flow time during CPR by professional rescuers before intubation.

Abstract 1804: Is CPR Quality Improving? A Retrospective Study Of Out-of-hospital Cardiac Arrest

Aim of the study: To evaluate 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: 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 ± SD 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 short arrest time (&lt;1 min). 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±3 per minute respectively in 2003 to 111±10 and 12±3 in 2006 (p&lt;0.0001 and p=0.001). In 2003–4 10% were discharged alive vs. 16 % in 2005–6 (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. Quality of CPR from May 2003 to 2006.

Transthoracic impedance changes as a tool to detect malpositioned tracheal tubes

Undetected malpositioned or dislodged ventilation tubes during cardiac arrest have fatal consequences, and no single method can detect the tube position reliably during such low-flow states. We wanted to test the ability of impedance changes as measured across the chest via the standard defibrillation pads to distinguish between oesophageal and tracheal ventilations in non-circulated patients. After the end of futile resuscitation transthoracic impedance was measured with a prototype defibrillator, and ventilation variables were collected with a spirometer-capnography unit during tracheal ventilations and after repositioning of the tube; during oesophageal ventilations for paired comparisons. We registered 123 oesophageal and 178 tracheal ventilations in nine patients. Transthoracic impedance changes associated with ventilations were always larger during tracheal than oesophageal ventilations (mean difference 1.3 ohms (95% CI 1.0, 1.5), P<0.001), and all such changes above 1.2 ohms were associated with tracheal ventilations, while changes below 0.4 ohms always were associated with oesophageal ventilations. By subtracting 0.5 ohms from the individual mean transthoracic change associated with tracheal ventilations, tube position was predicted with sensitivity 0.99 and specificity 0.97. Transthoracic impedance changes may be used to detect malpositioned and dislodged tubes also during situations without spontaneous circulation. Our predictive values must be retested in another population.

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

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. 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. 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). 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.

Misplaced and dislodged endotracheal tubes may be detected by the defibrillator during cardiopulmonary resuscitation

We present two cases of unrecognized endotracheal tube misplacements in out-of-hospital cardiopulmonary resuscitation recognized by the analysis of transthoracic impedance. In Case 1, ventilation-induced changes in transthoracic impedance disappeared after an intubation attempt corresponding to oesophageal intubation. This was clinically recognized after several minutes, the endotracheal tube was repositioned and alterations in transthoracic impedance resumed. In Case 2, the initial ventilation-induced signal change following endotracheal intubation weakened after a few minutes. At that time, the defibrillator gave vocal and visual feedback to the rescuers on ventilatory inactivity, a pharyngeal air leak was discovered simultaneously and the tube was found to be dislodged. Continuous monitoring of transthoracic impedance provided by the defibrillator during cardiopulmonary resuscitation may contribute to the early detection of an initially misplaced or later dislodged endotracheal tube.

Advanced cardiac life support before and after tracheal intubation—direct measurements of quality

Tracheal intubation should improve the quality of cardiopulmonary resuscitation (CPR) by enabling adequate ventilation without pauses in external chest compressions. Out-of-hospital cardiac arrests of all causes were sampled in this non-randomized, observational study of advanced cardiac life support in three ambulance services (Akershus, London and Stockholm). Prototype defibrillators (Heartstart 4000SP, Philips Medical Systems, Andover, MA, USA and Laerdal Medical AS, Stavanger, Norway) registered all chest compressions via an extra chest pad with an accelerometer mounted over the lower part of sternum and ventilations from changes in transthoracic impedance between the standard defibrillator pads. The quality of CPR was analyzed off-line for 119 episodes. Numbers and differences are given as mean +/- S.D. and differences as mean and 95% confidence intervals. Chest compressions were not given in cardiac arrest for 61 +/- 20% of the time before intubation compared to 41 +/- 18% after intubation (difference: 20% (16-24%)). Compressions and ventilations per minute increased from 47 +/- 25 to 71 +/- 23 (difference: 24 (19, 29)) and 5.6 +/- 3.7 to 14 +/- 5.0 (difference: 8.7 (7.6, 9.8)) respectively. Four cases of unrecognized oesophageal intubation (3%) were suspected from the disappearance of ventilation induced changes in thoracic impedance after intubation. The quality of CPR improved after tracheal intubation, but the fraction of time without blood flow was still high and not according to international guidelines. On-line analysis of thoracic impedance might be a practicable aid to avoid unrecognized oesophageal intubation, but this area needs further research.

Diagnosis of Sleep-Related Breathing Disorders by Visual Analysis of Transthoracic Impedance Signals in Pacemakers

Minute ventilation sensors of cardiac pacemakers measure ventilation by means of transthoracic impedance changes between the pacemaker case and the electrode tip. We investigated whether this technique might detect sleep-related breathing disorders. In 22 patients, analog waveforms of the transthoracic impedance signal measured by the pacemaker minute ventilation sensor over the course of a night were visualized, scored for apnea/hypopnea events, and compared with simultaneous polysomnography. Analysis of transthoracic impedance signals correctly identified the presence or absence of moderate to severe sleep apnea (apnea/hypopnea index, AHI >20 h(-1)) in all patients (receiver operating characteristics, ROC=1.0). The ROC for AHI scores of > or =5 h(-1) and > or =10 h(-1) showed an area under the curve of 0.95, P<0.005, and 0.97, P<0.0001, respectively. Accuracy over time assessed by comparing events per 5-minute epochs was high (Cronbach alpha reliability coefficient, 0.85; intraclass correlation, 0.73). Event-by-event comparison within +/-15 seconds revealed agreement in 81% (kappa, 0.77; P<0.001). Detection of apnea/hypopnea events by pacemaker minute ventilation sensors is feasible and accurate compared with laboratory polysomnography. This technique might be useful to screen and monitor sleep-related breathing disorders in pacemaker patients.