Now that it is clear that biphasic defibrillators are superior to monophasic ones and hospitals and paramedic units have spent millions “upgrading” their defibrillators based on the recommendations of the American Heart Association, it's time for the data. Ready! Fire! Aim!
Unfortunately, like so many other things in medicine, we tend to go off a little half cocked, especially when there is aggressive marketing driving change. It appears this may be the case when it comes to defibrillators.
Sure, biphasic defibrillators theoretically may be better than monophasics, and maybe in a series of cases defibrillation may be more successful with the newer units than the older versions, but the bottom line must remain the same: Are we getting more survivors with good neurologic function?
The following study from the home of the best prehospital cardiac arrests results in the country, Seattle, randomized patients to be shocked with monophasic and biphasic defibrillators who had prehospital ventricular fibrillation. There were no statistically significant differences in first shock success rates, rates of sustained return of spontaneous circulation, rates of survival to hospital admission, survival to discharge, or neurologic outcome.
Given the extraordinarily good results traditionally achieved in Seattle prehospital cardiac arrest studies (and, again, achieved in the current study), it would seem that this would be the best environment to demonstrate the superiority of one form of defibrillation over another. But this was not the case. What could be expected in cities with more customary results of prehospital arrest, typically three to five percent survival-to-discharge rates? It would seem in these more typical cities that it would be extraordinarily difficult to demonstrate superiority of one modality over another given the overall abysmal save rates.
Transthoracic Incremental Monophasic vs. Biphasic Defibrillation by Emergency Responders (TIMBER)
Kudenchuk PJ, et al, Circulation 2006; 114:2010
BACKGROUND: The results of studies reporting that biphasic waveform defibrillation requires less energy than monophasic waveform defibrillation in resuscitation from cardiac arrest are likely to foster efforts to replace monophasic with more costly biphasic defibrillators.
METHODS: In this study from the University of Washington, prehospital provider units were randomized to use a monophasic or biphasic defibrillator (provided by Medtronic). Outcomes were prospectively analyzed in adults with prehospital ventricular fibrillation (VF) as the initial recorded rhythm of arrest, who were managed with a monophasic or biphasic defibrillator. Care was most often initially provided by EMTs equipped with an automatic external defibrillator (AED), followed by paramedics equipped with a manual defibrillator.
RESULTS: In 165 patients, VF was terminated with the first shock in 82 percent of patients receiving a monophasic shock and 88 percent of those receiving a biphasic shock, and rates of sustained return of spontaneous circulation (ROSC) were 20 percent and 24 percent, respectively (p=NS). Among 148 patients completely managed with either monophasic or biphasic shocks by similarly equipped EMT and paramedic units, rates of survival to hospital admission were 73 percent in the monophasic shock group and 76 percent in the biphasic shock group. Rates of survival to discharge were 34 percent and 41 percent respectively, and discharge to home was documented for 23 percent and 24 percent, respectively.
CONCLUSIONS: Biphasic defibrillation was not more effective than monophasic defibrillation for the prehospital management of cardiac arrest in adults with an initial rhythm of VF.
Ventilate or Not?
And what about the quality of CPR? Every few years the American Heart Association comes out with updated recommendations on the most effective ways to perform CPR: compression rates, interposed ventilation, ventilation rates, two-rescuer rates as opposed to one-rescuer rates. How can anyone remember these guidelines?
The next paper suggests that some fundamental assumptions about CPR may be mistaken. More specifically, is it important to perform ventilation at all when doing chest compressions? Radical.
This well designed study found that CPR done with chest compressions only, and without ventilations, was as effective as that performed with ventilations when patient outcomes were the gold standard. When the data were teased a bit, some classes of patients were noted to actually do better with chest compression only (although this may be a little post hoc data dredging). Bottom line: It seems like more people would be willing to do a modified form of CPR using chest compressions only if they knew that this was an option.
BACKGROUND: It has been reported that bystander CPR is attempted for less than one-third of prehospital cardiac arrest patients. Reluctance to perform mouth-to-mouth ventilation and the complexity of the technique might be barriers to undertaking conventional CPR. At least one study reported that compression-only CPR yielded better outcomes than conventional CPR.
METHODS: This prospective observational Japanese study compared 30-day outcomes in 4,068 adult survivors of bystander-witnessed prehospital cardiac arrest who received compression-only or conventional CPR or no bystander CPR and were transported to one of 58 EDs after initial resuscitation.
RESULTS: Most of the patients (71%) received no bystander CPR; 11 percent received compression-only CPR, and 18 percent received conventional bystander CPR. Favorable neurologic outcomes at 30 days were more frequent in patients receiving bystander CPR than in those receiving no bystander CPR (5% vs. 2%, p < 0.0001). There were no differences between the compression-only and conventional CPR groups in this outcome overall, but a favorable neurologic outcome was more common after compression-only CPR than conventional CPR in the subgroups with apnea on EMS arrival (6.2% vs. 3.1%), those with initial ventricular fibrillation or tachycardia (19% vs. 11%), and in those having resuscitation initiated within four minutes of collapse (10.1% vs. 5.9%). There were no differences in 30-day survival in patients receiving compression-only or conventional CPR.
CONCLUSIONS: This study suggests that there is no evidence of a superiority of conventional bystander CPR over compression-only CPR in adults with witnessed prehospital cardiac arrest.
Tox Testing Irrelevant to Care
I rarely order toxicology panels on patients or blood alcohol levels (except perhaps to determine which staff member is able to most accurately estimate the level). I find that they're not clinically useful. Most toxicology care is focused on treating the patient's symptoms: Fix the blood pressure and pulse and treat the end-organ manifestations of toxicity. In most cases, there is some history available to guide decision-making regarding etiology. With few exceptions, if patients haven't manifested significant symptoms within six hours, they aren't going to. The one notable exception is acetaminophen, and many would advise a low threshold for measuring this drug.
Unfortunately, many EDs are burdened by psychiatrists who want toxicology clearance for patients being admitted to their service despite the fact that the patient may be fully awake without evidence of any organ dysfunction.
The next paper addresses the use of bedside immunoassay testing for drugs of abuse or poisoning and clearly demonstrates how unreliable these tests can be. Considering that they are not quantitative or particularly accurate, it really doesn't matter that much because routine toxicology testing is largely irrelevant to patient care. The good part is that they are quickly performed.
Comparison of Urinary On Site Immunoassay Screening and Gas Chromatograph-Mass Spectrometry Results of 111 Patients with Suspected Poisoning Presenting at an Emergency Department
von Mach MA, et al
Ther Drug Monit 2007;29(1):27
BACKGROUND: Opinions conflict regarding the utility of urine drug screening in ED patients. In some circumstances, accurate drug test results could have considerable medicolegal importance in addition to clinical relevance. In the ED setting, immunoassay-based (IA) tests that have rapid turnaround times are most commonly used, but correct interpretation of these tests requires considerable knowledge concerning the analytes that are covered and the possibility of cross-reactions.
METHODS: This German study compared the results of the Triage 8 on-site urine drug screening device (Biosite) and laboratory-based gas chromatography-mass spectrometry (GC-MS) in 111 ED patients with suspected intoxication and/or poisoning.
RESULTS: Isolated alcohol intoxication not detectable with the Triage 8 was documented in eight patients. GC-MS identified toxicologically relevant substances not detectable with the Triage 8 in 17 patients (15.3%) with Triage 8 results positive for 28 substances (and confirmed on GC-MS) and in 23 patients (20.7%) with negative Triage 8 results. The Triage 8 and GC-MS results were in disagreement in 21 patients (18.9%), including 15 Triage 8 false-positives and eight Triage 8 false-negatives involving substances reportedly detectable with the Triage 8.
CONCLUSIONS: Use of the Triage 8 or other IA-based on-site drug screening tests appears to be problematic in patients presenting to the ED with possible intoxication and/or poisoning. Half of the patients in this study had ingested substances not detectable with the Triage 8, and one-fifth of the patients had discordant Triage 8 and CG-MS findings.