The most common site of airway obstruction is the hypopharynx (1,2). During coma due to any cause in humans (but not in dogs), when the head is in the flexed or midposition, the relaxed tongue and neck muscles fail to lift the base of the tongue and epiglottis from the posterior pharyngeal wall (Fig. 1.2). The nasal passage is sometimes obstructed by congestion, blood, mucus, or a valvelike behavior of the soft palate that blocks exhalation, regardless of whether the patient is in the lateral, supine, or prone position. Other causes of airway obstruction include foreign matter, laryngospasm, bronchospasm, bronchial secretions, mucosal edema, aspiration of gastric contents or foreign matter, and inflammatory processes.
Thus, emergency airway control (Fig. 1.2 step A) should start with stretching the anterior neck structures by tilting the head backward, using chin support, and, if necessary, adding forward displacement of the mandible and opening of the mouth (the triple airway maneuver) (Fig. 1.16). An unconscious patient should be placed supine and horizontal, with the head tilted backward and aligned with the neck and chest. The legs may be elevated to centralize the blood volume. The prone
position makes the face inaccessible. When an unconscious patient is breathing spontaneously and adequately and the rescuer cannot keep holding the head, the stable side position is preferred, with the head maintained tilted backward. The next step should be an attempt at positive-pressure inflation of the lungs.
thrusts, chest thrusts, finger sweep) remains controversial (9). Abdominal thrusts produce a weak cough effect. Back blows produce higher airway pressures than thrusts when the airway is closed, but they may either loosen the object or further impact it in a standing or sitting victim. Back blows are not recommended by the American Heart Association, but they are recommended abroad (7,8 and 9).
Devices for airway control may be considered for use in BLS and ALS. Nasopharyngeal and oropharyngeal tubes still require backward tilt of the head. Use of the esophageal orbturator and esophageal gastric tube airway has been accompanied by an increased risk of complications ( 3,7). The pharyngotracheal lumen airway is inserted blindly into the oropharynx and can result in either esophageal or tracheal placement. The use of pharyngotracheal lumen airway, the esophageal-tracheal tube, and the laryngeal mask needs further evaluation (3,4,5,6 and 7).
Endotracheal Intubation
Endotracheal intubation with a cuffed tube is preferred to control the airway. Patients who tolerate an intubation attempt need an endotracheal tube. Details of intubation techniques should be studied and practiced (7), including equipment needed, orotracheal versus nasotracheal intubation, rapid-sequence intubation (see inside cover), intubating the awake patient, difficulties encountered during intubation attempts, tactile orotracheal intubation, transillumination orotracheal intubation, use of the lighted stylet, fiberoptic laryngoscopic intubation, special considerations for the intubation of infants and small children, extubation, and complications. A gastric tube should be inserted as soon as feasible. An alternative to endotracheal intubation is cricothyrotomy, performed by trained personnel ( 2). Tracheotomy (below the cricoid cartilage) should be an elective procedure, although in extreme emergency can be done quickly.
Clearing the pharyngeal airway and the tracheobronchial tree may require strong suction. In massive aspiration of solid foreign matter, ventilation bronchoscopy using a large bare, rigid ventilation bronchoscope rather than the popular flexible, small-bore fiberoptic bronchoscope, can be a lifesaving resuscitative measure (see
Chapter 9-6 Asphyxiation Regarding Pediatric Foreign Bodies). Bronchodilation and bronchial clearing are important maneuvers in the management of status asthmaticus, severe bronchitis, near-drowning, and aspiration. Tension pneumothorax can asphyxiate a patient rapidly by lung collapse and bronchial kinking and compression due to mediastinal displacement. In suspected tension pneumothorax, confirmation by needle puncture (in the anterior upper thorax) and insertion of a large-bore chest tube (open or closed technique) should not be delayed until confirmation by radiography ( 2).
Breathing Support
Currently recommended methods of artificial ventilation are based on intermittent inflation of the lungs with positive pressure applied to the airway, followed by
passive exhalation at atmospheric pressure (2). If direct mouth-to-mouth ventilation is impossible, one should try mouth-to-nose ventilation (2). During ventilation via mask, which closes the mouth, nasal obstruction can be overcome with use of the triple airway maneuver (Fig. 1.16) or insertion of an oropharyngeal or
nasopharyngeal tube under the mask. Pressing the cricoid cartilage backward can counteract gastric insufflation and passive regurgitation. When high inflation pressures are needed, endotracheal intubation is preferable.
Infection Risk from CPR
The chance that a rescuer might become infected during direct mouth-to-mouth ventilation (with hepatitis or the human immunodeficiency virus) is minimal. No such transmission has been documented (2,7,9). Although transmission of human immunodeficiency virus via blood is a real possibility, such transmission via saliva has not been documented. Laypersons should carry a saliva filter, facemask, or face shield. Health professionals should carry a valved exhaled air ventilation device that directs the victim's exhaled air away from the operator. Adjuncts should include an adapter for optional oxygen enrichment.
Use of Bag-Valve Units and Transport Ventilators
The self-refilling bag-valve unit, when attached to an oronasal facemask, is difficult to use, but when it is attached to a tracheal tube it is easy to use and highly effective. For a nonintubated patient, mouth-valve-mask ventilation with oxygen is recommended, because both of the rescuer's hands are free to provide mask fit, head tilt, and jaw thrust.
Devices for ventilation may be considered for use in BLS and ALS. Oxygen-powered, pressure-cycled ventilators and resuscitator-inhalators are obsolete. A manually triggered, oxygen-powered resuscitator should provide 100% oxygen at less than 40 L/min and should have an inflation pressure-relief valve that opens at
approximately 60 cm H2O and, for spontaneously breathing victims, an oxygen demand system that requires no additional breathing effort. Automatic “transport
ventilators” may be used effectively in lieu of bag-valve-tracheal tube devices during and after CPR ( 2,7,9). Expiratory retardation is used to prevent intrapulmonary airway collapse during exhalation in cases of asthma and emphysema. Ventilation-perfusion mismatching calls for an increased inhaled oxygen concentration and positive end expiratory pressure, which should be titrated according to arterial and mixed venous oxygen values. Spontaneous breathing of oxygen with positive airway pressure, without the use of a mechanical ventilator, can be effective in increasing the partial pressure of arterial oxygen in hypoxemic patients, even without the use of an endotracheal tube.
Circulation Support
Cardiac arrest is “the clinical picture of sudden cessation of circulation in a patient who was not expected to die at the time” ( 2). Cardiac arrest is recognized when all the following are present: unconsciousness, apnea or gasping, deathlike appearance, and no pulse in the carotid and femoral arteries. Primary cardiac arrest results from either ventricular fibrillation (VF), which may be preceded by ventricular tachycardia (VT) or asystole, for example, due to heartblock or drug overdose.
Secondary cardiac arrest results from asphyxia or exsanguination, usually in mechanical asystole (pulselessness) with ECG complexes continuing in the form of pulseless electric activity or electromechanical dissociation. This is relatively easy to reverse. However, defibrillation may change VF to secondary electromechanical dissociation, which may be difficult to reverse. If primary VF remains untreated, it weakens and becomes electric asystole; but with reperfusion, VF resumes.
Pulselessness is determined by palpating the carotid artery (Fig. 1.2). In cardiac arrest, emergency artificial circulation is most readily produced by intermittent external chest compressions (Fig. 1.2). The blood flow produced by standard external CPR is unpredictably low—between 0 and 32% of normal ( 2,3,4,5,6 and 7). Because pressing on the sternum creates right atrial pressure peaks almost as high as arterial pressure peaks, perfusion pressures are low as well. Blood flow can be optimized by a 50:50 compression:relaxation ratio and is little influenced by compression rates between 40 and 120 per minute. In adults, a rate of about 80
compressions per minute (one to two compressions per second) is recommended . The currently recommended rates and ratios of ventilations to sternal compressions
(2:15 for nonintubated patients and 1:5 for intubated patients) are a compromise. During CPR, the trachea should be intubated as soon as possible, without
interrupting chest compressions for more than 15 seconds at a time. Once the endotracheal tube has been inserted, lung inflations during CPR need not be
synchronized with chest compressions. If performed optimally, standard external CPR is sometimes capable of preserving cerebral and myocardial viability in dogs and patients for more than 30 minutes, even after cardiac arrest (no blood flow) times of 5 to 10 minutes (2,3,7,18).
Blood flow seems to be generated by variable combinations of heart-pump and chest-pump mechanisms. Coronary and cerebral perfusion pressures generated by
external CPR can be augmented by epinephrine. Attempts to augment blood flow with simultaneous ventilation-compression CPR did not lead to improved outcome in
dogs (2) or human patients (22). These techniques to increase airway pressure are not considered to be BLS, because they require an endotracheal tube and mechanical devices. Administration of CPR via an inflatable vest to take advantage of fluctuation in overall intrathoracic pressure does not require an endotracheal tube, but application of the vest device is limited to ambulance personnel (21). Improving blood flow during BLS with intermittent abdominal compression CPR (23) or active compression-decompression CPR (25,26) appears promising, but these methods have yet to undergo controlled clinical trials.
Guidelines call for performing steps A, B, and C in this sequence (Fig. 1.2). In witnessed VF (i.e., VF that occurs in the presence of a trained bystander), coached vigorous coughing, if the patient is still conscious, can maintain consciousness for a few minutes. Performing steps C, A, and B in that sequence is physiologically sound advise (2) in witnessed sudden cardiac arrest, because the aortic blood retains oxygen without ventilation until recirculation begins ( 27). Even sudden cardiac arrest, however, is often preceded by hypoxemia, requiring steps A and B to be performed first. Moreover, laypersons should not be confused with two sequences. During CPR with steps A, B, and C, the earliest possible attempts at electric defibrillation should be made. Epinephrine should be given intravenously or
intratracheally, and CPR should be continued until a strong spontaneous pulse is restored. In asphyxial cardiac arrest (mechanical asystole), a spontaneous pulse may return after a few minutes of effective CPR, without the need for countershock; or CPR can provoke secondary VF (10).
Repetitive thumping (once per second) and sternal compressions (as for artificial circulation), however, are effective methods of mechanical pacing ( 7).
Cardiac Arrest in Trauma
In cases of trauma, circulation support goes beyond external cardiac resuscitation (which in itself has little to offer in an exsanguinated victim). Measures that may be needed in trauma include manual control of external hemorrhage, airway control, artificial ventilation, primary and secondary survey, extrication, positioning for shock, intravenous fluid resuscitation to prevent cardiac arrest from blood loss (not necessarily to restore normotension, which might provoke renewed bleeding), use of a tourniquet, control of internal hemorrhage below the diaphragm with the use of military antishock trousers, and resuscitative surgery.