A schematized capnogram from a normal patient is illustrated in Figure 1. During inspiration, PCO2 is zero. At the beginning of expiration, PCO2 remains zero as gas from anatomic dead space leaves the airway (phase I). PCO2 then sharply rises as alveolar gas mixes with dead space gas (phase II). During most of expiration, the curve levels and forms a plateau (phase III). This represents gas from alveoli and is called the alveolar plateau. PCO2 at the end of the alveolar plateau is called end-tidal PCO2 (PetCO2). The shape of the capnogram is abnormal in patients with abnormal lung function. PetCO2 presumably represents alveolar PCO2 (PACO2). PACO2 is determined by the ventilation-perfusion ratio (V / Q). With a normal V / Q, PACO2 approximates PaCO2. If V / Q decreases, PACO2 rises towards mixed venous PCO2 (PV CO2). With a high V / Q (ie, dead space), PACO2 approaches the inspired PCO2. PetCO2 can be as low as the inspired PCO2 (zero) or as high as the P V CO2. There is no more need to hesitate and you can start your treatment very soon, having spent several times less money. All you need at this point is to puchase ampicillin and be sure you will be given all the best quality stuff at the reliable pharmacy of your choice.