Bicarbonate is the main base used to buffer acids in the blood. When its level falls below about 22 mEq/L, it points to metabolic acidosis—the body has an excess of acid or a loss of base, so the pH drops. In metabolic acidosis, you expect low HCO3- with a low pH, and the respiratory system will compensate by increasing ventilation to blow off CO2 (lower PaCO2). If bicarbonate were high, that would suggest metabolic alkalosis. Respiratory disorders center on CO2; they may cause compensatory changes in bicarbonate, but a low bicarbonate is best explained by a metabolic acidosis.

CPAP and BiPAP are two forms of noninvasive positive airway pressure support. The defining feature of CPAP is a constant, single pressure maintained throughout the entire breathing cycle, which helps keep airways open and reduces the work of breathing without actively driving ventilation. That single-level pressure best describes CPAP. BiPAP, on the other hand, uses two pressure levels: a higher pressure during inhalation to aid ventilation and a lower pressure during exhalation to make exhale easier. This two-pressure setup supports both oxygenation and ventilation when needed, such as in certain respiratory failures or COPD exacerbations. So, the statement that CPAP delivers continuous positive air pressure at a single level is the best description. The other options misstate BiPAP’s two-pressure nature, or imply no pressure during exhalation, which isn’t correct since an expiratory pressure is still maintained.

The thing being tested is how much oxygen is actually delivered to a patient when using a ventilation device without an oxygen source. A pocket mask, with no supplemental oxygen, doesn’t provide an oxygen reservoir or concentrate the air you’re delivering. The patient ends up breathing a mix of room air and the rescuer’s exhaled breath, and that exhaled breath has a lower oxygen content (roughly around 15–16%). The result is an inspired O2 concentration of about 16–17%. By comparison, supplying oxygen with a mask or reservoir can raise FiO2 substantially—roughly 40–60% with a bag-valve mask with a reservoir, or up toward 90% or more with a nonrebreather mask. Ambient room air is about 21%, but without an oxygen source, a pocket mask doesn’t keep that value; it sits around the mid-teens.

Small bulges or pouches in the intestinal lining are diverticula, and when these sacs form in the colon the condition is diverticulosis. The phrase “may become inflamed” points to the potential complication diverticulitis, but the description itself directly matches diverticulosis—the presence of diverticula. The other terms refer to different conditions: gastritis is inflammation of the stomach lining, colitis is inflammation of the colon lining, and irritable bowel syndrome is a functional disorder with pain and altered bowel habits but without actual pouches.