Now that the airway is open (previous step), you can assess if the person is breathing or not. How? By the look listen and feel technique. If they are breathing, you should evaluate if they are breathing at a rate sufficient to sustain life i.e. 12-18 breaths per minute. This is based on the following formula:

Where MV is minute ventilation, TD tidal volume and RR respiratory rate or breaths per minute. Normal values would render the equation as follows:

If they are breathing at a sufficient rate, then remember to keep the airway open and wait for help. Victims with significant breathing difficulties should be evaluated by a healthcare professional. If they are not, then proceed to give breaths.

The physiology underlying respiration and respiratory problems is interesting. The chain of command starts at the respiratory center in the medulla which fires automatically but receives inputs from the central and peripheral chemoreceptors which can stimulate or inhibit it. The central chemoreceptors comprise 60% of the chemoreceptors and are found in the CSF fluid. They are sensitive only to CO2 not to O2 because O2 cannot cross the blood brain barrier. The peripheral ones are located in the aortic and carotid bodies and are O2 sensitive. The electric signal is then sent down via the phrenic nerve IX to the respiratory muscles. These muscles are the diaphragm first and foremost and the extrinsic intercostals. Recall that these control inspiration whereas expiration is primarily a passive process.

Problems can occur anywhere along this chain. A change in the external environment, stroke, heart attack, tumor, trauma, blood loss, toxins (narcotics, sedatives), can all disrupt the natural homeostasis and deregulate the respiratory center's firing pattern. On another level, a spinal fracture below C4 can cut or impinge on the phrenic nerve because it comes out there. A problem at the nerve-muscle junction or with the muscle itself can also affect the respiratory process.

In any case, by giving breaths, the rescuer is doing the work for the victim. Actively pushing in his/her own expired air. The question the arises, does expired air contain enough oxygen to satisfy the victim's body's basic demand? The answer is yes. Expired air contains 16-17% O2 (known as the FiO2), whereas fresh air contains 21% - only a small difference.

how well do you know your stuff?