Supraglottic airways play an important part in the bundle of care for cardiac arrest. However, use of these airway adjuncts remain somewhat controversial.
It was recently reported that SGAs can improve outcomes vs. an ET tube in patients with a cardiac arrest,1 but another large study from the same time period in Great Britain found no difference when either adjunct was applied early in the treatment of cardiac arrest.2 Importantly, more than 90% of all patients treated in both studies still died from cardiac arrest, regardless of the type of airway adjunct deployed.1,2
We examined whether different SGAs behave the same way when used clinically. Our work builds on prior studies in pigs suggesting that not all SGAs function the same and that some may cause internal strangulation. Our current work also builds on recent studies that were performed using the human cadaver model to study the physiology of CPR.
This human cadaver model is particularly useful in that we can measure airway pressures as well as intracranial pressures. The airway and intracranial pressures and changes in those pressures are similar to what we’ve observed in animal models and cardiac arrest in humans. More specifically, we previously reported changes in airway pressures in human cadavers that were identical to what we have observed in humans in cardiac arrest.
Because of the importance of the SGA in the bundle of care, as well as the use of the impedance threshold device (ITD), a circulatory adjunct that attaches to the SGA, we assessed in human cadavers the ability of a variety of SGAs to maintain negative intrathoracic pressure during the recoil phase of CPR. Generation of negative intrathoracic pressure with the impedance threshold device is associated with superior outcomes.
We studied five different SGAs in seven cadavers, randomizing the order between the five SGAs and an endotracheal (ET) tube. We performed CPR manually, with the LUCAS mechanical chest compression device, and the ACD CPR device called the ResQPUMP, in both the supine position and in the head-up position.
We first identified that when CPR is performed supine with any of these methods of CPR, an ITD was essential to create a negative intrathoracic pressure. With mechanical CPR, there was no vacuum in the absence of the ITD. This is important for those using a mechanical chest compression device, as it shows that it doesn’t work nearly as well alone as with the ITD.
When looking at the generation of negative intrathoracic pressure with the five different airways, three of the SGAs (the LMA, i-gel and AirQ) and the ET tube resulted in the greatest negative intrathoracic pressure during the recoil phase of CPR, suggesting these airways should be used in an optimal bundle of care.
By contrast, the Combitube and King SGA failed to adequately seal the airway consistently during the decompression phase of CPR, and this resulted in an inferior vacuum compared to the other three SGAs.
These findings are similar to pig studies performed with SGAs.3 Our observations were similar during CPR in a supine position, with both automated CPR and ACD CPR, as well as head-up CPR with both automated CPR and ACD CPR. In all cases, the ITD was essential to generate negative intrathoracic pressure during the chest recoil phase.
In summary, SGAs and the ET tube play an important role in the treatment of cardiac arrest: both of them enable the rescuer to maintain an adequate seal so that an intrathoracic vacuum can be developed during CPR to enhance circulation, especially with the ACD+ITD combination.
But all SGAs aren’t equal. The King and Combitube should be avoided if the goal is to both maintain and allow for the generation of the negative intrathoracic pressure during the recoil phase of CPR.
This is more than an implementation issue, this is a question of what tools will help you to provide the best care for your patients and deliver the best clinical outcomes. We know that generation of a negative intrathoracic pressure is critical, and you’ll get less of this negative intrathoracic pressure that helps drive cardio-cerebral circulation during CPR by using the right SGA.
1. Wang HE, Schmicker RH, Daya MR, et al. Effect of a strategy of initial laryngeal tube insertion vs endotracheal intubation on 72-hour survival in adults with out-of-hospital cardiac arrest: A randomized clinical trial. JAMA. 2018;320(8):769–778.
2. Benger JR, Kirby K, Black S, et al. Effect of a strategy of a supraglottic airway device vs tracheal intubation during out-of-hospital cardiac arrest on functional outcome: The AIRWAYS-2 randomized clinical trial. JAMA. 2018;320(8):779–791.
3. Segal N, Yannopoulos D, Mahoney BD, et al. Impairment of carotid artery blood flow by supraglottic airway use in a swine model of cardiac arrest. Resuscitation. 2012;83(8):1025–1030.