Bronchodilators, the active ingredients in asthma inhalers, while probably increase the amount of oxygen that your lungs take in by a marginal amount, as I'm guessing that you're not asthmatic. Some stimulants can increase your respiratory rate but that simply adds to the risk of something bad happen, due to all of the dangers inherent to poly-drug abuse. If you really feel that you can't stop cold turkey, post how much codeine you have left, what dosages you have used it at, how frequently, and I will work out a plan for you to taper off it.