**4. Airway, oxygenation, and ventilation**

Oxygen supplementation during CPR has been an acceptable practice. But the concentration of oxygen delivery during CPR can benefit or harm the overall survival depending on the clinical situations. Similarly, various devices have been used in various clinical settings for securing the airway. Ventilation strategies during CPR have been also proposed by various guidelines but the optimal ventilation protocol remains uncertain.

#### **4.1 Oxygen dose during CPR**

The optimum tissue and blood oxygenation during CPR are unknown and no study has been done to define the oxygenation goals during CPR. The common practice of giving 100% oxygen during CPR has been challenged in some clinical situations. Most of the current guidelines suggest the use of maximal possible oxygen concentration during CPR. There are numerous limitations to these recommendations. Lack of current clinical evidence to suggest optimal tissue/ blood oxygenation during CPR and unavailability of techniques measuring tissue oxygenation during CPR are important limitations in deciding optimum dosing of oxygen.

#### **4.2 Airway management during CPR**

Airway management during CPR includes basic airway management by the bag and mask ventilation with or without oropharyngeal airways and advanced airway management like supraglottic airway devices (SAD) and endotracheal intubation. The optimal management of airway during CPR is an unclear and traditional belief of superiority of advanced airway over basic airway management has been challenged by some of the recent observational studies. Most of the studies comparing various advanced airway devices like an endotracheal tube, combitube, supraglottic airway devices and bag and mask device during CPR were observational studies and were done in OHCA patients. The data were extrapolated for IHCA settings. Most of the newer guidelines in developing and low resource countries also recommend the use of any advanced airway or bag and mask to secure airway to achieve adequate ventilation. Type of airway device in use depends on the skills of rescuer [49]. Tracheal intubation mandates training of health care provider and may be

unsuccessful in emergencies with high chances of unrecognized-esophageal intubation. Comparatively, insertion of supraglottic devices is easier. A stepwise approach to airway management including bag and mask, supraglottic devices, and the endotracheal tube is commonly followed during CPR. This stepwise approach has never been validated in any human studies or RCT.

One of the serious complication in airway management during CPR is unrecognized esophageal intubation. There are few methods of confirming the correct placement of endotracheal tube which have been applied and tested in various settings. Waveform capnography is the most reliable method used to ensure the correct placement of an advanced airway device. This non-invasive monitoring has high sensitivity and specificity with very low false-positive rates [50]. Waveform capnography is an indicator of pulmonary blood flow and guides the quality of CPR. The use of esophageal detection devices and airway ultrasound during CPR is limited due to the lack of RCT and have considered inferior to waveform capnography.
