Elderly woman comes in the ER in CHF.She is a 30 year smoker with a history of high blood pressure.Her initial abg is ph 7.31 co2 58 po2 68 hco3 32 on 4liters o2.She is given nitro,lasix and neb treatments.The next morning her blood gas is ph 7.42 co2 65 po2 65 hco3 41 on 2 liters.How did she over compensate?