Impedance threshold devices (ITDs) like the ResQPOD were popular class IIa recommendations in the 2005 ECC recommendations. After five years of research, their true benefit is being reconsidered. The theory behind ITDs is that they limit passive air entry during the decompression phase of CPR. Air can be pushed out of the lungs when the chest cavity is compressed, but, because of a valve, air is not allowed back in. This improves the negative pressure within the chest, which improves preload and blood return to the heart. To work properly, the ITD must have a sealed airway, whether it is a cuffed endotracheal tube or a face mask with a constant seal on the patient's face. Current research has demonstrated that the ITD improves patient survival during out-of-hospital cardiac arrest to hospital admission, and improves ROSC, but the ITD does not improve neurological function or long-term survival to hospital discharge. Because this latter research result is different than what was reported in the 2005 recommendations, for now, the ITD is only a class IIb recommendation.4
Advanced Cardiac Life Support
It is no secret that prehospital intubation has taken a lot of negative press lately. However, early intubation improves 24-hour survival for cardiac arrest patients. In the prehospital setting, this is within 12 minutes of arrest.5 The endotracheal tube is a class IIa LOE A airway alternative used during cardiac arrest. When performing intubation, the routine use of cricoid pressure is now a class III intervention because it is associated with increased intubation times. Additionally, intubations can be performed while chest compressions are performed; should compressions be paused, limit the pause to less than 10 seconds. Following successful intubation, the new gold standard for airway monitoring and confirmation is numerical and waveform capnography (Figure 2). Waveform capnography is a class I LOE A recommendation because it is 100% sensitive and specific for identifying tube placement.5
There is new emphasis in this year's recommendations on having a backup airway management strategy, and supraglottic airways are considered reasonable alternatives. Studies and recommendations were established for the Combitube, the King LT and the laryngeal mask airway (LMA). As a group they are class IIa LOE B alternatives, because, when properly placed, they can ventilate the patient just as effectively as an endotracheal tube.5 The Combitube is a class IIa alternative to intubation and, depending on the study, produces effective ventilation 62%-100% of the time.5 There is limited research for the King LT airway during cardiac arrest management, but, when placed properly, it has an 85% successful ventilation rate. During cardiac arrest, it is a class IIb LOE C alternative. The two most significant reasons for ineffective ventilations are cuff rupture during placement and aspiration. It is impossible to suction the trachea through a King LT. Even though LMAs do not prevent aspiration, they can provide ventilations equivalently to the endotracheal tube. It is noted to be particularly beneficial in confined spaces or when airway access is difficult. It is a class IIa LOE B alternative, but the AHA stresses having a backup available, because some patients are not able to be ventilated with the LMA.5
There are many reasons to provide continuous waveform capnography, also called end-tidal CO2 (EtCO2) monitoring, on all cardiac arrest patients. Even when an alternative airway is used, capnography still works; it is just not as effective. During a cardiac arrest, the CO2 waveform will be fairly flat and the CO2 levels relatively constant. However, once ROSC occurs, there will be a nearly immediate return of a normal capnography waveform.
Normal numerical capnography readings are 35-45 mmHg, but these won't be seen during a cardiac arrest. Any abrupt increase to near normal EtCO2 levels suggests ROSC. Good chest compressions will return CO2 to the lungs throughout the arrest state, but in a volume less than normal. If consistent chest compressions are performed, the CO2 level should be relatively consistent (the number will vary with each patient). Poor compressions result in low CO2 readings. Particularly when EtCO2 readings are less than 10 mmHg, try to improve the quality of chest compressions. Consistent EtCO2 readings below 10 mmHg are a predictor that ROSC is unlikely. The closer to normal the CO2 reading, the greater the chances of ROSC become.
Research no longer supports routine use of sodium bicarbonate during cardiac arrest management. It is a class III recommendation now because its administration compromises cerebral perfusion pressure, inhibits oxygen release, and worsens cerebral and myocardial acidosis. Its use is now limited to special circumstances, such as known metabolic acidosis, hyperkalemia and tricyclic antidepressant overdose.