Cats with urethral obstruction ("blocked cats") can present in a state of shock with moderate-to-severe hypoperfusion and should receive adequate fluid resuscitation with bolus therapy as needed using an isotonic crystalloid solution before worrying about relieving the obstruction. Blocked cats may have clinically significant hyperkalaemia and can also be severely acidaemic. With this in mind, does it matter whether we use 0.9% sodium chloride or a more balanced solution such as Hartmann's solution (buffered lactated Ringer's solution, compound sodium lactate), Normosol-R or Plasmalyte 148? This is discussed in detail in this podcast and a paper from the veterinary literature presented.
A summary of the podcast including the reference for the paper discussed can be found on the Veterinary ECC Small Talk website HERE.
If you are interested in taking a presentation and acquiring some course notes describing in detail an approach to the overall management of blocked cats, please visit the website HERE.