Abstract
The priorities of airway management during cardiopulmonary resuscitation are to minimise interruptions in chest compressions, to optimise blood flow and oxygen delivery to vital organs and to minimise delays in defibrillation if the initial rhythm is shockable. Thus, during the initial treatment of cardiac arrest, unusually, the circulation takes priority over the airway. Maintaining a patent airway will enable ventilation and oxygenation of the lungs, which becomes increasingly important after the first 3–4 minutes of sudden primary cardiac arrest (i.e. of cardiac cause). The optimal airway management strategy during cardiac arrest is uncertain. Many cardiac arrest patients are treated with multiple airway devices and this stepwise approach to airway management is difficult to study in controlled trials. The results of three recent randomised clinical trials suggest tracheal intubation should only be used in those settings with a high intubation success rate. While early oxygenation and ventilation are logically more important after asphyxial cardiac arrest existing resuscitation guidelines recommend the same sequence of actions regardless.
Objectives of Airway Management during Cardiac Arrest
The priorities of airway management during cardiopulmonary resuscitation (CPR) are to minimise interruptions in chest compressions, to optimise blood flow and oxygen delivery to vital organs and to minimise delays in defibrillation if the initial rhythm is shockable. Thus, during the initial treatment of cardiac arrest, unusually, the circulation takes priority over the airway. Maintaining a patent airway will enable ventilation and oxygenation of the lungs, which becomes increasingly important after the first 3–4 minutes of sudden primary cardiac arrest (i.e. of cardiac cause). Early oxygenation and ventilation are important after asphyxial cardiac arrest although existing resuscitation guidelines recommend the same sequence of actions regardless of cause.
Stepwise Approach to Airway Management during Cardiac Arrest
Airway management during cardiac arrest is undertaken by a range of individuals with widely varying skills, from laypeople to highly skilled anaesthetists. On witnessing an out-of-hospital cardiac arrest (OHCA) and calling the emergency medical services (EMS), untrained bystanders are usually instructed by the dispatcher to provide compression-only CPR. Bystanders trained in CPR may attempt a chin lift manoeuvre to restore airway patency and attempt mouth-to-mouth rescue breathing. An EMS technician will be trained to use an oropharyngeal airway (OPA) and bag-mask device, while a paramedic is likely to be trained to use a supraglottic airway (SGA) and, in many cases, a tracheal tube. Thus, during resuscitation following OHCA, there is often a progression in complexity of airway management, from no intervention (compression-only CPR), mouth-to-mouth, and bag-mask ventilation, through to SGA devices and tracheal intubation. The best airway management technique is likely to vary with patient factors, the cause of cardiac arrest, the stage of resuscitation and the skills of the attending rescuers. The ideal airway management strategy during CPR remains unclear and this typical stepwise approach makes it complicated to study (Figure 31.1).
The situation is not dissimilar following in-hospital cardiac arrest (IHCA). Depending on the location in hospital, the first responders are unlikely to have advanced airway skills and there is frequently a short period of compression-only CPR while resuscitation equipment is obtained. In the United Kingdom (UK), resuscitation teams will often not include a doctor trained in intubation and the resuscitation team may use an OPA and bag-mask and/or an SGA. Intubation is more likely if the resuscitation attempt is prolonged, if the airway cannot be maintained with an SGA, or after return of spontaneous circulation (ROSC) has been achieved.
Bag-Mask Ventilation
Oxygenating and ventilating the lungs with a self-inflating bag and face mask is considered to be basic airway management. Two breaths are given after every 30 chest compressions. Many studies show EMS personnel can ventilate the lungs of anaesthetised patients using a bag-mask, but few studies show if this is successfully achieved during CPR. Many OHCA observational studies show better outcomes when a bag-mask is used compared with advanced airway management (with an SGA or tracheal tube). A meta-analysis of 17 observational studies included nearly 400,000 patients and reported that use of an advanced airway was associated with reduced long-term survival (odds ratio (OR) 0.49 (95% confidence interval (CI) 0.37–0.65)). These results are clearly biased by confounders such as the fact that those who achieve ROSC very rapidly may not then need an advanced airway (‘resuscitation time bias’). Even though many observational studies use statistical techniques, such as propensity analysis, in an attempt to eliminate confounders, it is possible that unaccounted for factors remain responsible for the better outcome associated with basic compared with advanced airway management.
Tracheal Intubation
Once the trachea has been intubated, chest compressions can continue uninterrupted while the lungs are ventilated at 10 breaths min−1 – even if inspiration coincides with a chest compression, lung inflation will still be achieved and gastric inflation prevented. Regurgitation is common after cardiac arrest and tracheal intubation will prevent subsequent aspiration of gastric contents. However, in OHCA studies two thirds of those cardiac arrest victims who regurgitate do so before arrival of EMS personnel.
Limitations of tracheal intubation during resuscitation are that the procedure may interrupt chest compressions; with less experienced intubators this may be for long periods. A United States study of 100 pre-hospital paramedic intubations documented median intubation-related interruptions to CPR of 110 (inter-quartile range (IQR) 54–198) seconds, exceeding 3 minutes in a quarter of cases. Current European guidelines recommend compression pauses for < 5 seconds for tracheal tube insertion.
Several studies have documented rates of unrecognised oesophageal intubation after OHCA of 2–6%. Tracheal intubation would have to offer very significant advantages over other forms of airway management to offset this complication. Use of waveform capnography during advanced life support, regardless of location, is now mandated by international guidelines and should reduce the risk of unrecognised oesophageal intubation; it also has several other functions during CPR (Figure 31.2).
