DALLAS-- In their new guidelines for cardiopulmonary resuscitation and emergency cardiovascular care, the American Heart Association and the International Liaison Committee on Resuscitation have made major changes to the recommendations for advanced cardiovascular life support (ACLS).[1] One important change: Practitioners must now confirm tracheal tube position by using both primary (clinical examination) and secondary (technologic) methods of confirmation.

To many ACLS experts, this change is long overdue because physical examination alone is often insufficient to confirm tracheal tube position. "Recent studies have found higher-than-expected rates of tube misplacement or dislodgment with this method," John Field, MD, the ACLS Editor for the guidelines, told RESPIRATORY REVIEWS. Secondary confirmation, such as the use of end-tidal carbon dioxide (CO2) monitors, is therefore also recommended for confirming tube position.

Other key features of the new ACLS recommendations include updated approaches to the evaluation and management of tachycardia and tachyarrhythmias. Also, several notable alterations have been made to adult basic life support (see sidebar).

New Approaches to Adult Basic Life Support

Upon encountering an unresponsive adult, the lone lay rescuer should call 911 first, then start cardiopulmonary resuscitation (CPR), according to new guidelines. This recommendation is intended to decrease the time from cardiac arrest to defibrillation, since survival drops 7% to 10% for each minute without defibrillation. The recommendation to call 911 first does not apply, however, to adult drowning, trauma, or drug-intoxication victims, who should still get CPR for about a minute before the lone rescuer phones 911. Of course, when two rescuers are available, one should call for help and get an automated external defibrillator (if appropriate and available) while the other starts CPR. Because lay rescuers take too long to check a pulse and often cannot do it accurately, they will no longer be taught or expected to perform a pulse check when learning adult basic life support. For these rescuers, the absence of signs of circulation--normal breathing, coughing, or movement--is the signal to perform chest compressions and attach an automated external defibrillator. However, health care providers should continue to do a pulse check and assess for signs of circulation. As part of the effort to simplify adult basic life support, laypeople will no longer be taught the complex sequence for managing a foreign-body airway obstruction in unresponsive adults. If such an obstruction is suspected, lay rescuers should perform CPR, looking for and removing a foreign body in the mouth, if present, each time they administer rescue breathing. Health care providers should continue to perform the sequence for managing a foreign-body airway obstruction in unresponsive adults. --Timothy Begany

CONFIRMING TUBE POSITION

A tracheal tube's position should be confirmed immediately after insertion. According to the new ACLS recommendations, the primary way to do this is through physical examination. This typically involves auscultation over the epigastrium and lung fields and, if necessary, use of a laryngoscope to see if the tube has passed through the vocal cords.

A variety of devices are available to provide secondary confirmation. The ACLS recommendations focus on two: end-tidal CO2 and esophageal detectors. The evidence to support use of these devices is rated class IIa (good to very good) and IIb (fair to good), respectively.

End-tidal CO2 detectors quantify the amount of exhaled carbon dioxide, which is a sign of proper tube placement. These devices are especially reliable after three to six breaths in patients with perfusing rhythms. With the continuous and quantitative varieties, confirming tube position usually takes only a few seconds. These CO2 detectors can also detect low CO2 levels when tube dislodgment occurs.

However, end-tidal CO2 detectors are not perfect. False-positive readings (ie, the detector shows a low CO2 level consistent with esophageal placement even when the tube is in the trachea) may occur in patients with cardiac arrest as well as in those in whom exhaled carbon dioxide is low or absent because of poor lung perfusion. Unnecessary extubation may result. There have also been reports of false-negative results (ie, the device suggests tracheal placement when the tube is in the esophagus) in patients who drank carbonated liquids before arrest.

Esophageal detectors, which require the user to pull back a plunger or compress a flexible bulb, create suction from the near end of the tracheal tube. If the tube is in the esophagus, the suction will pull the esophageal mucosa against the detector's distal end and prevent the plunger from moving or the bulb from reexpanding. Use of an esophageal detector is recommended in patients with cardiac arrest because their exhaled CO2 is normally low; results obtained with an end-tidal CO2 detector will reflect low pulmonary blood flow rather than tube misplacement.

ASSESSING TACHYCARDIA

Like the previous ACLS recommendations, the new guidelines recommend that the initial workup of tachycardia focus on a quick assessment of the patient's stability. A patient is deemed unstable if there are serious signs or symptoms related to the tachycardia and the ventricular rate is above 150 beats per minute. "Any instability in an arrhythmia calls for immediate electrical cardioversion," said Dr. Field, who is also an Associate Professor of Medicine at Pennsylvania State University in Hershey.

For tachycardic patients who do not require immediate cardioversion, the new recommendations more strongly emphasize the need to recognize impaired cardiac function, because it will have a major influence on choice of therapy. The guidelines also stress the importance of making a specific diagnosis rather than taking an overly simplistic approach. Currently, for example, many physicians administer adenosine when the heart monitor shows a tachycardia. This practice arose from the erroneous assumption that most of these arrhythmias are supraventricular tachycardias (SVT) with aberrancy, when, in fact, they are often wide-complex ventricular tachycardias (VT).

Initial electrocardiographic evaluation usually identifies one of the following four types of tachycardia:

• Atrial fibrillation/atrial flutter.
• Narrow-complex tachycardias.
• Stable wide-complex tachycardia of unknown origin.
• Stable monomorphic VT and/or polymorphic VT.

To facilitate treatment of these conditions and to minimize the risk of complications, especially drug-induced arrhythmias (called proarrhythmias), the ACLS recommendations now contain three detailed algorithms and a table (the previous guidelines contained just one algorithm). These new tools guide clinicians through diagnosis and treatment, reminding them to ask important questions, such as "How long has the arrhythmia persisted?" This question is especially important in patients with atrial fibrillation/atrial flutter, for example, because treatment varies depending on whether the duration of the arrhythmia is more or less than 48 hours. With narrow-complex SVT, knowing the ejection fraction is essential; a value below 40% suggests that cardiac function is compromised enough to alter therapy.

NEW TREATMENT STRATEGIES

The most important new concept in tachycardia therapy is to not give more than one type of antiarrhythmic unless absolutely necessary and a rhythm diagnosis is certain.

"We realize that many antiarrhythmics are also proarrhythmic," said Mary Fran Hazinski, RN, MSN, a Senior Science Editor in the Emergency Cardiovascular Care Program at the American Heart Association. Thus, the goal of the new recommendations is to avoid inducing arrhythmias, an adverse event that is more likely when patients with significant cardiac impairment receive two or more types of antiarrhythmic therapy. Typically, electrical cardioversion is preferable to a second antiarrhythmic drug when the first one fails.

Because of its broad spectrum of activity and relatively small negative inotropic effect when standard loading doses are given, amiodarone is an important alternative to other antiarrhythmics in the management of tachycardia and tachyarrhythmias. In fact, the ACLS recommendations now include it as an alternative to lidocaine and procainamide in the initial treatment of shock-refractory ventricular fibrillation.

Amiodarone is also effective for, among other things, controlling hemodynamically stable VT, polymorphic VT, and wide-complex tachycardia of unknown origin. "There is a growing body of evidence [showing] that it is effective for recurrent tachyarrhythmias, particularly atrial tachycardias, and for ventricular tachyarrhythmias," added Ms. Hazinski, who is also a Clinical Nurse Specialist in the Division of Trauma at Vanderbilt University Medical Center in Nashville.

In another important shift, a single 40-U dose of intravenous vasopressin can be used as an alternative to epinephrine for the management of ventricular fibrillation /pulseless VT. This change is based on limited but reasonably persuasive evidence that vasopressin is an effective vasoconstrictor and has a good safety profile; it is unlikely to cause ß-stimulation and or postarrest adrenergic storm. However, epinephrine also remains acceptable.

--Timothy Begany

Reference
1. The American Heart Association and the International Liaison Committee on Resuscitation (ILCOR). Guidelines 2000 for cardiopulmonary resuscitation and emergency cardiovascular care. An international consensus on science. Circulation. 2000;102(suppl 1):1-384.