Obstructive Diuresis: This condition occurs when there is a sudden relief of urinary obstruction, leading to a rapid increase in urine production. The patient's history of chronic urinary retention followed by a significant increase in urinary output (2 liters followed by 600ml in 1.5 hours) supports this diagnosis. The body's response to the relief of obstruction can lead to an initial period of increased diuresis.

Diuretic Effect: If the patient has recently started or increased diuretic medication, this could explain the sudden increase in urine output.
Infection or Sepsis: A urinary tract infection or sepsis could potentially cause an increase in urine output, although this would typically be accompanied by other symptoms such as fever, dysuria, or systemic signs of infection.
Fluid Overload: Patients with fluid overload conditions (e.g., heart failure, renal failure) might experience increased urine output once the underlying condition is managed or if they receive diuretics.

Post-Renal Acute Kidney Injury (AKI): Although less likely, any condition causing a sudden obstruction and subsequent relief could potentially lead to AKI. Monitoring renal function is crucial.
Sepsis: As mentioned, sepsis could be a cause of increased urine output and is critical not to miss due to its high mortality rate if not promptly treated.
Diabetic Ketoacidosis: Though less directly related to urinary retention, DKA can cause osmotic diuresis leading to high urine output. It's a life-threatening condition that requires immediate diagnosis and treatment.

Nephrogenic Diabetes Insipidus: A condition where the kidneys are unable to concentrate urine, leading to excessive urine production. This could be a rare cause of the patient's symptoms but would typically have a more chronic presentation.
Psychogenic Polydipsia: Excessive water drinking can lead to high urine output. However, this diagnosis would be less likely in the context of chronic urinary retention and the specific pattern of urine output described.

To confirm obstructive diuresis, monitor the patient's urine output, fluid status, and renal function closely. Management involves:

Fluid Replacement: To prevent dehydration, especially in the initial phases of diuresis.
Monitoring Electrolytes: To correct any imbalances that may occur due to the loss of electrolytes in the urine.
Assessment of Renal Function: Through serum creatinine and urine output to ensure that the kidneys are recovering from the obstruction.
Addressing the Underlying Cause: Of the urinary retention, whether it be a prostate issue, neurological problem, or other cause, to prevent recurrence.