Available on all models of the 2002 and 2000 is the option of having an adjustable I:E Ratio control. Normally, without this option, the I:E Ratio is fixed at 1:2, that is, 1/3 of the period of each breath is inspiration and 2/3 of each breath is exhalation. Regardless of the respiratory rate, the patient will always have 2/3 of the cycle to exhale. This fixed I:E ratio can be fixed at a value other than 1:2 at no extra charge. The adjustable range is from 1:1.5 to 1:4. The pros and cons are that this option affords the operator more flexibility in dealing with animals that have compromised lung function. But during anesthesia most patients are lung healthy and the addition of this control can add to the complexity of setting the ventilator. For example consider that you have a hypocapnic patient. To bring that patients CO2 level to a more normal range you must decrease the overall gas exchange, the Minute Volume (MV). Without this option, only one knob controls the MV, that is the Volume control. With this option; however, increasing the I:E ratio would also cause a reduction in MV.