BASIC LIFE SUPPORT

It is well accepted that effective CPR results in the artificial delivery of oxygenated blood to systemic circulatory beds at rates sufficient for preserving vital organ function and physiologic substrates until spontaneous circulation is reestablished. The mechanisms for provision of adequate blood flow have undergone intensive scrutiny, and the result has been both insightful and controversial. Ventilation, perfusion, CPR assessment, and automated external defibrillation (now included as a BLS intervention) will be reviewed in light of current understanding.

Airway Control and Ventilation

Anesthesiologists know well that ventilation is critical for restoration of spontaneous circulation and organ preservation in cardiac arrest (see Chapter 39 ). The AHA ACLS training program has effectively conveyed this treatment priority.^[8] The techniques used are obviously dependent

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When rescue breathing is indicated for a nonintubated patient, two breaths are delivered slowly (1.5 to 2.0 seconds) after the 15th compression during both one- and two-person CPR until the airway is secured.^[8] Emphasis is placed on the slow delivery of rescue breaths during a deliberate pause in chest compressions to minimize high airway pressure. Low airway pressure reduces the likelihood of excessive esophageal opening pressure contributing to gastric inflation ^[14] and its consequences.^{[15] [16]}

Because anesthesiologists use advanced life support procedures and devices early in resuscitation, whether in the operating room or elsewhere, these procedures are reviewed here within the context of early control of the airway and ventilation. In the traditional BLS/ACLS format, these procedures are all considered ACLS techniques and adjuncts.

Endotracheal intubation is the usual and expected standard of airway control in the critical care setting.^[17] Alternative airways that may be useful in gaining rapid control of the airway and ventilation while reducing the risk for pulmonary aspiration of gastric contents in situations where tracheal intubation is not possible include the laryngeal mask airway (LMA) and the esophageal-tracheal Combitube.^{[18] [19] [20]} These devices are classified in the Guidelines 2000 as acceptable and possibly helpful, especially when the rescuer is inexperienced in placing tracheal tubes.^[21] Although they may be helpful as temporizing devices, endotracheal intubation remains the optimal technique for controlling the airway and ventilating the lungs during CPR.

Confirmation of proper placement of an endotracheal tube can be difficult in a patient who has undergone cardiac arrest. Observation of the rise and fall of the thorax and auscultation of lung fields in this situation can be misleading. Likewise, because of the very low pulmonary blood flow during CPR, end-tidal carbon dioxide pressure (PETCO₂ ) detection devices may not readily distinguish tracheal from esophageal intubation. For these reasons, esophageal detector devices based on the description by Wee^[22] have been introduced and advocated for use in emergency situations such as cardiac arrest. Both a syringe and a self-inflating bulb have been used. The efficacy of these devices in distinguishing esophageal from tracheal intubation is based on the principle that the trachea remains patent during aspiration of air whereas the esophagus collapses because of its fibromuscular structure. The effectiveness of the self-inflating bulb in distinguishing esophageal from tracheal tube position^{[23] [24] [25]} and in confirming proper position of the esophageal-tracheal tube has been documented.^[26] In an emergency patient population, an esophageal detector device as described by Wee was observed to be more accurate than PETCO₂ detection because of its greater accuracy in patients in cardiorespiratory arrest. ^[27] False-negative results with the self-inflating bulb occur more frequently in emergency intubations than reported in anesthetized patients undergoing elective procedures. Causes include partial tube obstruction with secretions, atelectasis, bronchospasm, and endobronchial intubation.^[28] A high incidence of false-negative results was observed in morbidly obese patients. ^[29] In these patients, reduced functional reserve capacity and large-airway collapse secondary to invagination of the membranous posterior tracheal wall after the application of subatmospheric pressure with the self-inflating bulb were identified as the cause of the false-negative results.^[29] With these limitations in mind, the self-inflating bulb or syringe-type esophageal detector is useful in emergency situations such as cardiac arrest, particularly when used in combination with PETCO₂ detection.

Despite extensive experience with the LMA in fasted patients undergoing general anesthesia, its role during CPR remains somewhat controversial.^{[30] [31] [32] [33] [34]} In anesthetized patients, positive-pressure ventilation with the LMA has been observed to be safe and effective, but concern was expressed that gastric inflation could be a problem in the presence of increased inflation pressure.^[35] This problem, of course, is common in patients who sustain cardiorespiratory arrest because these patients typically have a full stomach and frequently require high inflation pressure during ventilation. The LMA has been used successfully in arrested patients who have no evidence of regurgitation or aspiration.^[36] In patients in whom endotracheal intubation is not possible, the LMA is more secure than a facemask and offers an alternative to control the airway and ventilate the patient.^{[32] [37]}

The esophageal-tracheal Combitube is an acceptable alternative airway device for use in cardiac arrest. The Combitube is a double-lumen device with proximal pharyngeal and distal inflatable cuffs that is introduced blindly into the airway. One lumen of the device has a closed distal lumen and ventilation holes at the level of the hypopharynx. The second lumen is open ended with a balloon cuff at its distal end. Both lumens of the airway can accommodate ventilation. Once inserted and followed by inflation of the pharyngeal and distal cuffs, confirmation of the proper ventilation port is mandatory. Auscultation and PETCO₂ detection must demonstrate that tracheal rather than esophageal ventilation is present. ^[38] When the esophageal-tracheal Combitube is placed properly, the airway is isolated and the risk of gastric aspiration is reduced.

If these devices and techniques are unsuccessful in securing an airway, an immediate cricothyroidotomy may be necessary. A 12-, 13-, or 14-guage catheter-over-needle device can be inserted quickly into the trachea through the cricothyroid membrane. Equipment permitting transtracheal jet ventilation from a 50-psi oxygen source through such a catheter should be available in the operating room and the ICU.^{[39] [40]} Benumof and Scheller^[40] provided specific guidelines for acceptable transtracheal

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