The unit started operating last month and is open 24 hours a day, seven days a week for the four month trial.
Ms Chittenden said the unit was to cater for stable medical direct admissions from GPs, those who were expected to stay less than 24 hours or those who needed closer monitoring by a trained medical nurse after hours.
"In the past, the patients who go into MAPU would normally have required admission to the medical unit or would sit in ED for a long time.
"The aim for [the unit] is to reduce admissions and to provide a focused medical nursing service to medical patients close to the ED point of entry."
Ms Chittenden said so far it had helped lift achievement against the Ministry of Health's shorter stays in emergency departments target.
"The expectation is that this lift in achievement against the health target will continue, with refinements to the operation of MAPU."
She said the new unit was one of a series of initiatives which would help the health board cope with the pressures the winter months posed for emergency department presentations and patients needing to be admitted to hospital.
"With one month of operation, the MAPU has significantly improved the process of decision-making in regards to medical admissions."
She said a review would be carried out after the trial looking at the unit's effectiveness in terms of patient care as well as the flow of patients through the emergency department.
It had also made a good contribution to the quality of care delivered to patients from experienced nurses, she said.
An example was that nurses with a good understanding of chronic conditions were able to intervene more effectively at an earlier stage.
A decision on whether to continue with the unit would be made in November or December.