Replace the chloride and potassium – supplement normal saline (one of the few times 0.9% saline is my fluid of choice) with potassium chloride.
If the cat is on a maintenance fluid rate at this point (it’s been in the hospital for several days and does not have any reported ongoing losses) you could supplement using the potassium chart that is referenced in every textbook and journal article out there, or you can calculate your desired rate of supplementation and mix that into a more customized bag of fluids. If you are using the chart and the cat was on a higher fluid rate, you would want to calculate the rate of potassium supplementation and be sure that you stay at or below 0.5mEq/kg of potassium per hour – but don’t be afraid to be aggressive (as long as you are monitoring and checking the potassium every 4-6 hours) to get the potassium up to normal and keep it there. Remember your patient’s alkalosis isn’t going to get better until you correct the hypokalemia.
The same table is presented in pretty much every textbook and journal article in veterinary medicine. Here’s a link to it in the Merck Manual (just because it’s open access): Guideline for Potassium Supplementation in Dogs and Cats (scroll down to the potassium section).
Normal saline (NS) has 154mEq/L of chloride (to go along with it’s 154mEq/L of sodium), plus the additional chloride you will add with your KCl. Using NS for your maintenance fluid for this patient should take care of the chloride deficit. If the patient was hypovolemic or volume contracted I would also use NS for replacement until the chloride returns to normal (then switch to a more balanced crystalloid).
The down-side to the NS is the cat is already mildly hypernatremic (although I question if this sample is possibly reported with canine reference ranges for the sodium, or if the machine that the sample was run on really does have a normal sodium range this low for cats… for the sake of discussion we will say the cat is mildly hypernatremic) it would be nice to give her something with a little less sodium (more free water). The high sodium also suggests a degree of contraction alkalosis. You could take a bag of Plasmalyte A or Normosol R and supplement with potassium – but you won’t get correction of the chloride very quickly this way. On the other hand just getting her some volume with an isotonic fluid (NS is technically isotonic to her) might give her kidneys the ability to fix this without any other help from us. It’s a trade-off, and in this case I would probably go for the NS with added KCl and then adjust as needed at the 4-6h mark based on recheck electrolytes.
Notice that the cat’s lactate is 12… that should prompt a look for reasons why, and near the top of the list (after is the cat breathing/oxygenating/ventilating) would be is the volume status adequate? The cat has been in the ICU for several days according to the history, with no reported ongoing losses. I would expect that severe of a volume deficit to have been corrected by now. But her blood pressure is a little soft (technically not low, but also not normal) so this warrants a look/assessment early on as part of the hyperlactatemia work-up. I would probably give her a small bolus with plain NS before supplementing her bag with potassium and see what that does for her pressures and mentation, then decide on a fluid rate and pick my potassium supplementation based on that.
The cat is hypoventilating (pCO2 of 58), which looks like it is compensation for the severe metabolic alkalosis. BUT with the cat’s mentation, high lactate, etc I would want to know if it is oxygenating okay or if it is failing to oxygenate due to hypoventilation. You could start with a pulse-ox reading if the cat has good pulsatile flow, but if it isn’t working well or it’s low she needs an arterial blood gas to check her paO2 (and calculate her A-a gradient).
Remember that the alkalosis makes her prone to hypoventilating (as compensation for the metabolic alkalosis), that the alkalosis shifts the oxygen-hemoglobin dissociation curve left (hemoglobin holds on to oxygen tighter/doesn’t deliver oxygen to tissues as well as it would under normal conditions), and that the hypokalemia and hypocalcemia make her further prone to hypoventilation due to muscle weakness. All of these things add up to a strong potential for hypoxia to occur at the tissue level. Depending on the severity you might be able to overcome this with oxygen supplementation, or she might need assisted (mechanical) ventilation until we ‘fix’ enough of her problems for her to take back over herself.
What about the calcium?
I think a reasonable argument could be made for calcium supplementation since both the hypocalcemia and metabolic alkalosis are significant. Ileus is a common complication of hypocalcemia, and since this cat’s ileus is probably part of the generating process for her metabolic alkalosis (and the metabolic alkalosis is making the hypocalcemia worse, in a horrible vicious circle…) improving her ionized calcium is probably a good choice.
Other stuff…
Finally don’t forget that we need to continue to treat her underlying disease (GI lymphoma, remember she was just diagnosed a few days ago and we are trying to see if the steroids will make her feel better with a good quality of life again) and it’s associated complications (vomiting, ileus) symptomatically, etc. We also need to keep up with her other nursing care needs – mobilization activities, hygiene, monitoring, etc.
