Reply To: Furosemide cri’s for acute congestive heart failure
The dose is a good question – generally we consider patients (dogs only, cats it is thought to be lower at 5-8mg/kg/day) have diuretic resistance at doses around 12mg/kg/day when given orally. However, it is an interesting finding that despite having tolerance to oral doses at this level that patients will still respond to IV furosemide. So, for example, the dog that has been on 10-12 mg/kg/day and is ‘rescued’ by a change in diuretic to, for example, torasemide will still respond to IV furosemide if they are re-admitted for decompensation. Oral furosemide will have a lower dose at which tolerance occurs for many reasons, but one of the main points will be the fact that bioavailability is notoriously difficult to predict with figures between 10 and 100%. IV furosemide on the other hand obviously does not have this issue.
I have tried to find some literature on the max dose of furosemide in dogs when it is given via CRI but I haven’t been able to. Most references use between 0.5-1mg/kg/day but you can go higher than this too. You can tailor it to the severity of CHF.
In terms of why switch to intermittent boluses before oral meds – there was a study in horses that showed a CRI gave better diuresis for the first 8 hours of administration, thereafter intermittent boluses gave better results. That is one rationale, but was obviously performed in healthy horses and so may not be the same in dogs. You could switch straight to oral meds if you think that the patient is dry, the only other good thing about intermittent boluses is that you then have a better idea of how much furosemide to send them home with i.e. if you have used 6mg/kg over a 24 hour period IV then you might opt to discharge them on a similar amount orally. The routes of admin aren’t like for like and so you do need to be a bit careful with this, but it can be helpful.
I’ve not encountered precipitation either. However, there must be some fluids with which you combine furosemide and crystals form so the IV route can’t be used. The study that I mentioned in my previous reply showed that, at least visually, those fluids did not cause crystals to form and were safe to administer IV with furosemide (for a maximum of 8 hours at least).
I would say in general my use of CRI depends where I am working and on the patient. I would use it for fulminant heart failure where they are being monitored relatively closely (in theory monitoring may be less intense with a CRI vs boluses as you give boluses depending on RR and so more decisions are needed). A protocol that I might use would be:
Patient in O2 with B-lines/ severe oedema on rads
Give 2mg/kg IV furosemide (or IM if placing an IV line is too stressful – you can use butorphanol IM if they are very anxious, just remember to wait long enough for this to take effect before attempting an IV)
Start a CRI of 0.5-1mg/kg/hr
Monitor RR hourly and when RR is 40 or less stop the CRI
At this point decide if the patient can go on to oral meds or if you prefer intermittent boluses
If using boluses I would go for q4-6 hours IV initially, still monitoring RR and giving additional 1mg/kg boluses IV if RR >40 at these checks (as long as this is believable, which can be an issue)
Once happy that the RR is consistently <40 and the effort is normal swap on to oral meds - If severe HF I would usually discharge on around 2mg/kg TID and then taper that down to the lowest effective dose at home with owner monitoring RR.
Monitor renal parameters and electrolytes at least q24 hours and one week after discharge
If you don't use a CRI I would use an initial bolus at 2mg/kg then 1mg/kg q1-2 hours until RR is <40 then increase the time between administration, give additional 1mg/kg boluses if RR>40 at any check. Once happy that they are stable change to oral meds.
This was a great topic and made me think I will do the next journal club on the use of CRIs in dogs going through the evidence that we have to date (which is a bit mixed for its use).
Thanks for making me think 🙂