A patient presents with acute gastroenteritis in a dehydrated state. Which of the following conditions is highly suggestive of pre-renal renal failure?
Urinary sodium > 40 m mol; Urine osmolality <350m osm/L
Urinary sodium > 40 m mol; Urine osmolality > 500m osm/L
Urinary sodium < 20 m mol; Urine osmolality > 500m osm/L
Urinary sodium < 20 m mol; Urine osmolality < 350m osm/L