1 Department of Intensive Care Medicine and 2 Resuscitation Training Department, Birmingham Heartlands Hospital, Bordesley Green East, Birmingham B9 5SS, UK *Corresponding author
Accepted for publication: April 20, 2002
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Abstract |
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Methods. Sixty Advanced Life Support (ALS) course directors, selected at random, were questioned to establish their current practice. Twenty ALS providers received 5 min revision in the three techniques for the initial monitoring of a collapsed patient and were then randomly tested to measure the time from confirmation of arrest to the first shock.
Results. Forty-two directors indicated their preferred methods for initial monitoring as 74% leads, 21% paddles and 5% hands-free adhesive pads. Before testing, 10 providers preferred paddles and 10 preferred leads. Monitoring through leads 54 (range 4965) s was significantly slower than paddles 28 (2431) s, P<0.01 and adhesive pads 23 (1927) s, P<0.01. There was no significant difference in the time taken between paddles and adhesive pads.
Conclusion. The current practice of monitoring through leads delays the time to deliver the first shock. We recommend that initial monitoring through leads be discontinued in favour of hands-free adhesive pads or defibrillator paddles/gel pads.
Br J Anaesth 2002; 89: 4058
Keywords: complications, cardiac arrest; equipment, defibrillators; monitoring, electrocardiography
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Introduction |
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In 1999 the medical devices agency issued a safety notice warning that spurious asystole might be diagnosed in error after attempted defibrillation using paddles and gel pads.6 A further report was published shortly afterwards in the British Medical Journal of a similar episode at a district general hospital in England,7 when a patient was monitored using gel pads with defibrillator paddles. After delivering a shock, a period of apparent asystole was noted on the defibrillator monitor (shown as a continuous or broken line); however, simultaneous electrocardiographic (ECG) lead monitoring with independent electrodes showed that the patient remained in VF. Without additional monitoring with ECG leads, a delay in the delivery of further shocks would have resulted. Despite the limited number of reports of spurious asystole in the literature,68 the wide publicity these reports have received may have changed practice from the rapid paddles/gel pad technique to monitoring initially through standard ECG leads.
We set out to determine current preferences for the initial monitoring of the collapsed patient and to measure the difference in time taken to deliver the first shock with the following three monitoring techniques: defibrillator paddles and gel pads, ECG leads, and hands-free adhesive pads.
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Methods |
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In the second part of the study, 20 doctors or nurses were recruited without prior warning to perform a defibrillation test. All subjects had undertaken the Resuscitation Council UK Advanced Life Support Provider Course and were working at Birmingham Heartlands Hospital. The subjects preference for initial monitoring was recorded before testing. Five minutes of revision time was given in a standardized manner, covering the three different techniques for initial monitoring that were to be tested. These three techniques were: (i) defibrillator paddles and gel pads, where gel pads (defib-pads; 3M, Germany) and defibrillator paddles are placed on the patients chest; (ii) ECG leads, where three standard ECG (3M-red-dot; 3M, Germany) electrodes are used for monitoring and gel pads/paddles are used for defibrillation; and (iii) hands-free adhesive pads (Multi-function Adult electrode pads; Hewlett Packard, UK), which are adhesive electrode pads used for monitoring and defibrillation. All tests were undertaken on a Laerdal adult ALS manikin skill trainer using a Heartsim 200 rhythm simulator (Laerdal Medical, Norway). The Codemaster XL (Hewlett Packard) defibrillator was used for all tests, with default monitoring set to paddles for monitoring through paddles/gel pads, and leads (lead II) for ECG leads and hands-free adhesive pad tests. There was no significant difference in charge time between the defibrillators used (2.4 (range 2.42.4) s for defibrillator 1 compared to 2.3 (2.32.4) s for defibrillator 2 during 10 successive shocks P>0.05). The training manikin is designed to have the ECG leads attached directly onto the chest wall and therefore it was not possible to obtain reliable ECG signals by attaching the ECG electrode dots to the ECG monitoring points. To reflect clinical practice, subjects actually attached leads and electrodes to the manikins chest, but the ECG signal was fed directly to the defibrillator after the third lead had been attached correctly.
The subjects were then presented with three simulated defibrillation tests in a randomized order (block randomization). The manikin was stated to be in cardiac arrest and the subject was required to establish initial monitoring, determine the underlying rhythm and deliver the first shock. The time taken from the start of each test until the defibrillator was charged to 200 J (as indicated by the defibrillator audible warning bleep) was recorded.
Statistical analysis
Data were entered into Excel 97 (Microsoft, NY, USA) and analysed using SPSS 10.0 for windows (SPSS Inc., Chicago, IL, USA). Monitoring preferences from all subjects were analysed using 2 and Fishers exact tests. Defibrillation test data were analysed for normality and found to be in a non-normal distribution. Friedmans repeated measures analysis of variance (ANOVA) on ranks with Dunnetts test was used for multiple comparisons between the three monitoring techniques. Data were expressed as medians (interquartile range). A P value <0.05 was considered statistically significant.
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Results |
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Discussion |
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A potential limitation of our findings from the questionnaire survey to ALS course directors is the moderate response rate. However, the clear preference (74%) for monitoring initially through ECG leads amongst the respondents suggests that this teaching practice is widespread. The second part of this study consisted of a simulated cardiac arrest using a resuscitation manikin and has several inherent limitations. First, the prior revision and controlled environment of the laboratory test is likely to have shortened the time to first shock for all tests, as the equipment was immediately available and defibrillator operators were probably more relaxed than during a genuine cardiac arrest. Secondly, the signal quality obtained through the resuscitation manikin may be different from that seen in clinical practice, although our experience is that it is similar irrespective of which monitoring technique is used. The poor quality signals seen when attaching ECG leads and electrodes to the manikin may have artificially increased the time taken to deliver the first shock with this technique. However, this was identified in a pilot study and overcome by feeding the electrical signal directly from the rhythm simulator to the defibrillator during the actual study. Despite these limitations, the findings of this study can probably reasonably be extrapolated to the clinical environment.
After the early reports of spurious asystole, Bradbury and colleagues conducted an in vitro study to investigate this phenomenon.10 Using a low (50 ) and high impedance (1050
) defibrillator test model they measured the time delay in the return of a test signal following defibrillation through gel pads and hands-free adhesive pads. They found significant delays (up to 61 s) in the return of the test signal with the gel pad/paddle combination using the high impedance test model after several shocks. This was caused by retention of the electrical charge by the gel pads. However, no such delays in the return of the test signal occurred with the low impedance system or when hands-free adhesive pads were used with either system. As the low impedance test model is closer to the reported mean transthoracic impedance of patients in cardiac arrest,11 they concluded that the results supported their clinical observations that spurious asystole is relatively rare in practice. In addition spurious asystole occurs only after several successive shocks so this should not influence the choice of initial monitoring. If after two or three shocks the rare phenomenon of spurious asystole is seen on the monitor, then ECG lead monitoring should be rapidly established.
Whilst our experience and that of others7 10 suggests that spurious asystole occurs only rarely, no prospective studies have formally investigated this phenomenon. A recent study examining the recurrence of VF following defibrillation with automated external defibrillators (and hands-free adhesive pads) in the pre-hospital environment reported delays in the recurrence of VF of >30 s in half of all the patients studied.12 To our knowledge there have been no reported cases of spurious asystole occurring with the hands-free adhesive pads. The work by Bradbury and colleagues10 suggests that it is unlikely to occur with this device. However, only simultaneous ECG lead monitoring can determine if some of these delays could be attributable to spurious asystole, and further prospective studies are required.
The choice of initial monitoring technique in cardiac arrest is considered an important issue in resuscitation training. We have recently reported that in a group of 25 ALS instructors, five considered that initial monitoring with defibrillator paddles and gel pads without simultaneous ECG lead monitoring constituted unacceptable performance,13 although current guidelines recommend the defibrillator paddles and gel pads technique for initial monitoring.9 At present we are aware of only a handful of high profile case reports reporting the phenomena of spurious asystole.68 14 Monitoring though ECG leads may delay defibrillation by on average 30 s. Early defibrillation improves survival from cardiac arrest,24 11 16 and extrapolating the data presented in the modified Larsen model for survival from cardiac arrest5 17 it can be anticipated that delays in defibrillation of this order may reduce survival by 3.55%.
In the absence of convincing data that spurious asystole is common, we recommend that in the unmonitored collapsed patient, initial monitoring through leads should not be used, and hands-free adhesive pads or defibrillator paddles and gel pads should be; however, if asystole or apparent loss of signal occurs after defibrillation with defibrillator paddles and gel pads then monitoring with ECG leads should be established as soon as possible. After the first three shocks are given, the ECG leads can then be attached if appropriate while basic life support is initiated. This recommendation is consistent with the advice recently published in the Resuscitation Council UK Instructor Bulletin.
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References |
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