Trained health professionals have more limited use for AEDs than manual external defibrillators. Recent studies show that AEDs does not improve outcome in patients with in-hospital cardiac arrests. AEDs have set voltages and does not allow the operator to vary voltage according to need. AEDs may also delay delivery of effective CPR. For diagnosis of rhythm, AEDs often require the stopping of chest compressions and rescue breathing. For these reasons, certain bodies, such as the European Resuscitation Council, recommend using manual external defibrillators over AEDs if manual external defibrillators are readily available.