Cardiology

Hands-on defibrillation with safety drapes: Analysis of compressions and an alternate current pathway

a b s t r a c t

Background: Hands-on defibrillation (HOD) could theoretically improve the efficacy of cardiopulmonary resusci- tation (CPR) though a few mechanisms. Polyethylene drapes could potentially facilitate safe HOD, but questions remain about the effects of CPR on polyethylene’s conductance and the magnitude of current looping through rescuers’ arms in contact with patients.

Methods: This study measured the leakage current through 2 mil (0.002 in.) polyethylene through two different current pathways before and after 30 min of continuous compressions on a CPR mannequin. The two pathways analyzed were the standardized IEC (International Electrotechnical Commission) leakage current analysis and a setup analyzing a current pathway looping through a rescuer’s arms and returning to the patient. First, ten mea- surements involving the two pathways were obtained on a single polyethylene drape. 30 min of continuous com- pressions were applied to the drape on a CPR mannequin after which the ten measurements were repeated.

Results: Twenty patients undergoing elective cardioversion for atrial fibrillation (18/20) or atrial flutter (2/20) at Emory University Hospital underwent analysis all receiving 200 J shocks (age 38-101, 35% female). Through the IEC measurement method the peak leakage current mean was 0.70 +/- 0.02 mA before compressions and 0.59

+/- 0.19 mA after compressions. Only three of the ten measurements assessing current passing through a rescuer’s arms had detectable current and each was of low magnitude. All measurements were well below the maximum IEC recommendations of 3.5 mA RMS and 5.0 mA peak.

Conclusions: Polyethylene may facilitate safe HOD even after long durations of compressions. Current looping through a rescuer’s arms is likely of insignificant magnitude.

(C) 2021

  1. Introduction

Minimizing interruptions in compressions in cardiopulmonary re- suscitation (CPR) has been shown to reduce morbidity and mortality [1-5]. Studies have demonstrated a relationship between the success rate of defibrillation and the amount of time delay between the cessa- tion of compressions and shock delivery [6-9]. As a result, delays and interruptions in chest compressions have become focal points in recent CPR guidelines [10-12]. The traditional requirement that rescuers stand clear of the patient while delivering shocks contributes to a significant amount of “hands-off” time in the critical periods leading up to shock delivery which would otherwise be used for more chest compressions [13,14]. Given these observations, some have hypothesized that CPR could be improved by continuing compressions through shock delivery

* Corresponding author at: Emory University School of Medicine, 49 Jesse Hill Dr. SE Suite 491, Atlanta, GA 30303, USA.

E-mail address: [email protected] (J.A. Wight).

with hands-on defibrillation (HOD) [15]. While the instance of injury to rescuers in CPR is very rare, the concept of HOD has some important and unexplored Safety concerns [16,17].

Polyethylene clinical exam gloves facilitate safe contact with patients during shocks, but follow-up investigations found that most commonly used nitrile gloves could not withstand the stresses of long durations of compressions and multiple shocks [18-21]. Additionally, requiring each compressor to use specific gloves could be cumbersome in crowded and fast moving CPR situations.

Alternatives to facilitate HOD include a safety barrier with high physical and electrical resistance between the patient and compressor. Polyethylene is of particular interest given its common use in electrical high voltage electrical insulation, physical strength, affordability, and frequent use in the medical arena [22,23]. Thin 2 mil polyethylene drapes were shown to reduce leakage current to rescuers during elec- tive cardioversions for atrial fibrillation or atrial flutter [24].

Questions remain regarding whether polyethylene barriers could

withstand long durations of compressions and if alternative current

https://doi.org/10.1016/j.ajem.2021.11.044

0735-6757/(C) 2021

pathways are of importance including the electrical pathway ascending a rescuers arm and descending the opposite arm back to the patient [15]. This study assessed 1) the impact of 30 min of chest compressions on the leakage current through polyethylene drapes before and after chest compressions and 2) the leakage current through a current path- way mimicking current ascending and descending through a rescuer’s arms. We hypothesized that there would not be a significant change in the leakage current after compressions and that the alternate current pathway through a rescuers’ arms would have lower current magni- tude.

  1. Methods

The study protocol was approved by the Institutional Review Board. Written informed consent was obtained from all patients. Patient’s undergoing elective cardioversion for atrial fibrillation or flutter were recruited for this study. In summary, the amount of current leaking through a single polyethylene drape atop patients undergoing cardioversions was quantified, the drape was then stressed with 30 min of chest compressions on a CPR mannequin before the same cur- rent leak measurements were repeated from additional cardioversions on the same drape.

Patients underwent cardioversion with an initial shock of 200 J based upon the preference of the electrophysiology department to avoid exposing patients to repeat shocks in the event a lower joule shock failed. Patients who failed a 200 J shock would then receive up a 360 J shock based upon the clinical determination of the treating electrophysiologist. The external defibrillator used was a Lifepac 15 (Medtronic Corp, Minnesota), which delivers a biphasic waveform. The defibrillator power source was a grounded standard mains outlet. The shocking electrodes were self-adhesive pads placed in the anteroposterior position for all patients. The same 2 mil (0.002 in.) low density polyethylene drape was used in each measurement. The polyethylene was 1 square meter in area and made by TRM manufactur- ing (Corona, CA).

Two current leak pathways were analyzed in this study. A schematic of the patient, polyethylene drape and current measurement apparatus schematic used to measure the standardized IEC leakage current is shown in Fig. 1. To assess the current flow from the drape, a conductive grounding pad with adhesive conductive gel was applied to the drape over the approximate location of contact in CPR. The wire from the grounding pad was connected to the IEC 60990 startle-reaction weighted touch current circuit terminal A in Fig. 2 [25].

The IEC 60990 startle reaction circuit is a well-established model of human electrical impedance and is used in this standardized electrical safety testing setup to evaluate current exposure to potentially affected people. This circuit which mimics humans’ electrical resistance proper- ties allows for safe estimation of current exposure to people in any

Image of Fig. 2

Fig. 2. IEC 60990 Startle-Reaction Weighted Touch Current Circuit. Voltage changes were measured across U2 in this figure. Currents were then calculated across utilizing Ohm’s law [25].

situation without actually involving people for testing. In standardized electrical safety testing, current runs from the high voltage source though the circuit and to electric ground allowing measuring of current magnitude and associated risk. In Fig. 2 showing the human impedance model circuit, Rs and Cs represent human skin resistance and capacitance, respectively. Rb represents internal human body resistance [26]. R1 and C1 adjust for the dependence of human body impedance upon frequency [27]. During the cardioversion shock, a laptop oscillo- scope (Picoscope 2202) and a voltage probe (Tektronix P2220) were used to capture the voltage changes U2 across the 500 Ohm resistor as described in IEC 60990 and subsequently calculate the current in con- junction with Ohm’s Law [25]. To simulate pressure in a CPR situation and ensure good electrical contact, approximately 20 lbs. of downward force was applied to a towel over the drape and grounding pad during shock delivery.

The second current pathway we analyzed was intended to assess the amount of current that could pass up a rescuers arm and back down to the patient. A schematic of this apparatus is shown in Fig. 3. To assess current flow off the drape, two EKG electrodes with adhesive conduc- tive gel were applied to the drape 8 cm apart over the approximate location contact in CPR. One electrode was connected to IEC 60990 ter- minal A, and the other electrode was connected to IEC 60990 terminal B. The data collection process was the same in this setup otherwise.

During data collection, first the amount of current leak involving the two pathways through a single polyethylene drape atop patients undergoing cardioversion was measured a total of 10 times including 5 measurements with both pathways. After 10 measurements, 30 min of continuous compressions were applied to the drape on a CPR manne- quin after which the same measurements were repeated on the same drape from 10 additional cardioversions. The CPR mannequin was

Image of Fig. 1

Fig. 1. Patient – Measurement Apparatus Setup. The 3’x3′ polyethylene drape was placed over the patient’s anterior chest. A grounding pad was attached to the drape in the approximate location of chest compressions. The wire from the grounding pad was attached to terminal A in the IEC 60990 circuit and terminal B was connected to electric ground.

Image of Fig. 3Fig. 3. Arm loop measurement apparatus. The electrodes were attached to the polyethylene about 8 cm apart and connected to terminals A and B of the startle- reaction weighted touch current circuit.

equipped to provide visual feedback on the pressure and timing of com- pressions to ensure the drape was subjected to adequate stress. The mannequin is used in BLS certification assessments and was lent to

Table 1

Mean peak current leak and mean RMS current leak through polyethylene drape before and after compressions through the IEC measurement method (n = 10)

our investigators for the purposes of this study. Three investigators preformed continuous compressions in rotation at 2 min intervals to prevent rescuer fatigue during compressions. Depth and speed of

Before Compressions (n = 5)

After Compressions (n = 5)

Maximum IEC Recommendations

compressions were adjusted based upon the mannequin’s feedback.

The location of the measurement pad over the drape was marked to en-

RMS Current Leak Mean (mA)

0.05 +/- 0.01 0.04 +/- 0.03 3.5

sure compressions were applied to the same area of the drape where all

RMS Range 0.04-0.07 0.01-0.06 3.5

measurements occurred. After 30 min of compressions, the same 10 measurements including 5 of both pathways were repeated on the same drape from 10 additional cardioversions.

Peak Current Leak Mean (mA)

Peak Current Leak Range

0.70 +/- 0.02 0.59 +/- 0.19 5.0

0.67-0.73 0.21-0.75 5.0

The leakage current was assessed through the same drape a total of 20 times to assess if the physical stress of CPR and sequential shocks im- pacted the ability of polyethylene to act as an electrical insulator. Im- pedance values corresponding with shocks were also recorded.

  1. Results

Abbreviations: RMS (root mean square); mA (milliampere).

Table 2

Average peak current leak and average RMS current leak through polyethylene drape be- fore and after compressions as measured through a rescuer’s arms (n = 10)

Data was gathered from a total of 20 patients undergoing elective

?Before Compressions (n = 5)

?After Compressions (n = 5)

Maximum IEC Recommendations

cardioversion for atrial fibrillation (18/20) or flutter (2/20) all receiving

200 J shocks (age 38-101, 35% female). All patients had successful res-

RMS Current Leak Mean (mA)

0.02 +/- 0.02 0.0060 3.5

toration of sinus rhythm after the initial 200 J shock with none requiring

RMS Range 0.0082-0.032 n/a 3.5

a repeat 200 J or 360 J shock. Of the 20 shocks, 10 shocks were evaluated through the International Electrotechnical Commission (IEC) method with 5 before and 5 after compressions. An additional 10 shocks were evaluated via Fig. 3 to assess current passing through a rescuer’s arms

Peak Current Leak Mean (mA)

Peak Current Leak Range

0.06 +/- 0.002 0.19 5.0

0.060-0.063 n/a 5.0

with 5 before and 5 after compressions. The peak leakage current was significantly higher than the root mean square (RMS) and the shock waveforms showed peaks around the onset and offset of each phase of the shock sequence Fig. 4.

Through the standardized IEC method the mean RMS leakage cur- rent was 0.05 +/- 0.01 mA and mean peak leakage current was 0.70

+/- 0.02 mA before compressions with corresponding values of mean RMS of 0.04 +/- 0.03 mA and mean peak of 0.59 +/- 0.19 mA after compressions Table 1. The total charge, which equals the integral of current over time, associated with the shock in Fig. 4 from the IEC standard measurement technique was 0.71 uC and was reflective of the charge in other shocks with the IEC measurement technique. Through the arm current pathway, only 3 of the 10 total measurements assessing current had detectable current and each value was very low in magnitude Table 2. The mean impedance of the patients evaluated through the standard IEC startle-reaction weighted touch current method was similar before and after compressions at 71 Ohms and 68 Ohms respectively. All measurements through both methods were below the general maximum IEC recommendations of 3.5 RMS and

5.0 mA peak. The peak values were in the vicinity of the maximum rec- ommended values for handheld equipment and medical equipment of

1.06 mA peak (?2 * 0.75 mA RMS) and 0.71 mA peak (.?2*0.50 mA RMS) respectively [28,29].

Image of Fig. 4

Fig. 4. Representative shock waveform from standardized IEC measurement technique. The peaks appear at the beginning and end of each phase of the shock sequence. Current leak was calculated with the voltage from the waveforms and Ohms law.

Abbreviations: RMS (root mean square); mA (milliampere).

* 2 measurements for RMS current leak and peak current leak reached the threshold for detectable values before compressions and 1 measurement reached that threshold for af- ter compressions, hence no range for the latter.

  1. Discussion

This study assessed 1) the effect of chest compressions on the insu- lation properties of the drape and 2) the potential current exposure res- cuers might be exposed to in an alternate current pathway in which current ascents one arm and descends the other arm to the patient. After 30 min of compressions on the drape with CPR mannequin, there was no apparent increase in the current leakage through both measurement techniques. The current looping through the arms path- way was found to be of very low magnitude and was not detectable in some of the measurements.

Our analysis has some drawbacks worth consideration. The pads in all cases of our analysis were in the anterior-posterior configuration. The sternum-apex pad configuration, typically used in CPR, notably in- volves a different vector field. The orientation of the sternum-apex vec- tor field could potentially increase the amount of current leakage to a rescuer that our analysis did not account for. The anterior-posterior con- figuration used in the study reflects institutional protocol preference for atrial fibrillation cardioversion as is some suggestion of advantage of this configuration [30]. Also, the entire study was performed on only a single polyethylene drape and whether the section of polyethylene we used happened to be more or less durable than average, the results could be unrepresentative. Given the nature of the data collection, leak- age values could not be compared on the same patient before and after compressions, and the sample size was reasonably small. Compressions were performed for only 30 min, which is surely shorter than the longest code situations. Additionally, while the CPR mannequin gave feedback on the compressions to ensure they were of adequate depth, compres- sions in an actual code situation might be of greater force. Another draw- back is that our design did not account for the case of wet contact with the patient and drape which could increase current leak. The electrodes with conductive adhesive gel atop the polyethylene drape are a reason- able model for wet contact between the rescuer and drape. Electrodes

Declaration of interests”>have similar conductance to human body tissue and given their small size would likely contribute orders of magnitude less to the impedance of the apparatus compared to the high total body impedance [31-33].

Our model also assumes that rescuers’ bare hands are in contact with the polyethylene while typically in CPR rescuers wear some kind of medical examination glove. Gloves would provide an additional layer of safety to further reduce current leak affecting rescuers and conse- quently our study likely significantly overestimates current leak if gloves are used concurrently with the polyethylene drape. Studies have demonstrated that common medical examination gloves can be ef- fective in reducing perception of shocks and current leak [18,34].

In our model of alternate current pathways, the electrodes repre- senting the points of contact of rescuers’ hands with the drape were not overlapping but instead about 8 cm apart whereas rescuers’ hands are typically overlapping in CPR. Theoretically, in a real life situation with overlapping hands there would be some degree of current flow be- tween the rescuers’ hands which did not travel up their arms and through their chest. Consequently this model may overestimate the cur- rent exposure through this pathway. This is logical as the standardized touch current measurement apparatus is connected to electric ground and in a far lower resistance pathway so it is unsurprising that our measurements assessing current looping through rescuers’ arms were of significantly lower magnitude. We choose to use two separated electrodes as this represents a worst case scenario where a potential dif- ference could cause a current exposure to the rescuer. If both terminals of the circuit were connected to the same electrode, there would be no electrical potential difference to drive current. Our authors with signifi- cant expertise in electrical engineering and current leak safety agree with this design and analysis. Despite the imperfect approximation, current flow through a rescuer’s arms is likely of very low and insignif- icant magnitude.

Current flow was mostly limited to short spikes around the onset

and offset of each part of the biphasic shock and did match closely the known waveform of the Lifepak. Capacitive coupling in the measure- ment apparatus between the patient and the measuring pad atop the drape is likely at play in causing the sharp spikes at the beginning and end of each portion of the shock sequence. The leakage currents were all of low magnitude and well below the general IEC recommendations of 3.5 mA RMS and 5 mA peak. The handheld and medical equipment thresholds of 1.06 mA peak (?2 * 0.75 mA RMS) and 0.71 mA peak (.?2*0.50 mA RMS), respectively, are significantly more stringent, and multiple shocks did exceed the medical peak current leak threshold slightly with the greatest magnitude of current leak being 0.75 mA. There are few studies investigating current leak, but our results are on similar in magnitude to past work including those with electrical insu- lating gloves [18,24,35]. Deakin et al. found significantly lower current leak at only 20 uA with electrical insulating gloves and a different mea- surement technique [35]. The low AC RMS current leakages are indica- tive of low total current leaks over the shock duration. 2mil polyethylene is exceedingly thin, and it would likely not be an issue to decrease the current leak below this stringent medical standard with thicker polyethylene.

As has been shown, the leakage current measured is of low magni- tude and would be on the lower border of the region AC-2 in IEC 60479-1, which is associated with a prickling sensation, but no harmful effects [36]. The amount of current required to cause ventricular fibrilla- tion for a current duration of about 10 ms according to IEC 60479-1 is around 500 mA for comparison with our highest value of 0.75 mA [36]. Although there are less defined standards for charge exposure, research has supported the concept that charge rather than current ex- posure has a greater bearing on shock risk [37]. Charge is equal to cur- rent integrated over time, and the net charge of our representative waveform of 0.71 uC is very low. This falls into the safe and impercepti- ble zone based upon IEC 6049-2 [38]. Ample historical data regarding electric fences safety indicate that charge values below 4mC are of safe magnitude, which is over 500 times greater than the charge we found

[39]. Overall the measured leakage current is of safe magnitude, but it does make sense to attempt to lessen the leakage current to the greatest extent possible and utilizing thicker polyethylene of 6-8mil might be advisable given the study limitations previously discussed. 2mil poly- ethylene is so thin that there should not be any practical issue in using thicker drapes in future experiments surrounding HOD. 2mil polyethyl- ene was chosen for evaluation here for consistency with previous study and originally chosen based upon the similar thickness to clinical exam gloves.

Polyethylene could be a good choice for a safety shield to facilitate HOD, though more data would be beneficial. While we have not ob- served any failure in polyethylene drapes, it will be important to charac- terize the leakage currents that rescuers could be exposed to if a drape did fail or was used improperly. It is far more likely that misuse of a drape would result in harm to a rescuer than the small magnitudes of leakage current through the polyethylene drape. Polyethylene has high electrical and physical resistance and is quite affordable compared to the automated compression devices available. If HOD is attempted, a logical CPR kit design might include a polyethylene drape attached to a shocking adhesive pad designated for the anterior chest. It is hard to know whether HOD could yield improvements in patient morbidity or mortality, but there is surely is enough data supporting minimal inter- ruption in compressions and the special value of the compressions lead- ing up to shock delivery to make it worth investigating carefully.

  1. Summary

Long durations of compressions on polyethylene do not appreciably affect the protective properties of a HOD safety drape. Alternate current pathways from two points of rescuer-patient contact also appear to be associated with low levels of leakage current to rescuers.

Declaration of interests

Dr. Lloyd has received Research Grants from Medtronic Corp, and has received honoraria from Boston Scientific Inc. and Medtronic Corp. The remaining authors report no conflicts of interest.

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