Setting the Bolus Rate for a Dehydrated Beagle
Pepper is a 6.5 kg spayed female Beagle, 3 years old, with two days of vomiting and small-bowel diarrhea. She is quiet but responsive; heart rate 140, temperature 39.1 degrees C, skin tent persists about 2 seconds, mucous membranes are tacky, and the veterinarian estimates 7% dehydration. PCV is 54% and total solids 7.8 g/dL. The veterinarian orders a 180 mL bolus of 0.9% sodium chloride over 30 minutes, then 60 mL/hr for 6 hours, and asks you to place the catheter and start fluids. The only IV pole on the treatment floor is occupied, so you plan to hang the bag on the cage-top hook. The shelf holds 10 gtt/mL macro-drip sets, 60 gtt/mL micro-drip sets, 22 g and 24 g over-the-needle catheters, and one volumetric infusion pump that is charging in the back. Pepper has never had an IV catheter and is shivering.
1. Calculate the bolus and maintenance rates in mL/hr and drops per minute for both drip sets, and state which set and delivery method you choose and why.
Read the worked answer
Bolus: 180 mL over 30 minutes = 6 mL/min = 360 mL/hr.
- 10 gtt/mL macro-drip: 360 mL/hr x 10 / 60 = 60 gtt/min = 1 drop per second. Countable and deliverable by gravity.
- 60 gtt/mL micro-drip: 360 mL/hr x 60 / 60 = 360 gtt/min = 6 drops per second. Not countable, and the micro set is wasted on a rate this high.
Choice for the bolus: the 10 gtt/mL macro-drip set, run at 1 drop per second, if the pump is not ready in time. If the pump is charged, use the pump - it is more accurate and it alarms.
Maintenance: 60 mL/hr = 1 mL/min.
- Macro-drip: 10 gtt/min = 1 drop every 6 seconds - easy to drift off, and small counting errors become large volume errors over 6 hours.
- Micro-drip: 60 gtt/min = 1 drop per second - countable, but a pump is still better.
Choice for maintenance: the volumetric pump for accuracy over 6 hours; if unavailable, the micro-drip set at 1 drop per second with an hourly recount.
Also plan the bag: at 60 mL/hr a 500 mL bag lasts about 4 hours of maintenance, so have a second bag ready, label the bag with rate and start time, and time the bolus with a clock rather than by eye.
2. Which catheter do you select and where do you place it? What is your rule if you miss twice?
Read the worked answer
Size: a 22 g over-the-needle catheter is the default for a 6.5 kg dog. It delivers roughly 30 mL/min by gravity, comfortably above the 6 mL/min the bolus requires, and is less traumatic than a 20 g. A 24 g is the fallback if the cephalic vein is very small, but it makes a gravity bolus slow, so it would need a pump or a pressure bag.
Site: cephalic vein. Clip a wide area, perform aseptic skin prep with chlorhexidine scrub alternating with alcohol for three back-and-forth passes, let it dry, and wear gloves. Secure with tape and a light bandage, cap with a T-port, flush with saline, and aspirate to confirm blood return before connecting fluids.
Two-strike rule: after two unsuccessful attempts, stop. Release the tourniquet, hold pressure for 2–3 minutes, and reassess. Then try the other cephalic, and then the lateral saphenous. Warm the limb, have a second person hold the head and body calmly, and ask a more experienced colleague rather than continuing to poke. Repeated blind stabs create hematoma, which makes every later attempt harder and damages the vein. Document the number and sites of attempts.
Dehydration flattens veins. If access is critical and unobtainable, tell the veterinarian - intraosseous access is the next option and is their decision.
3. What do you check before leaving the patient, and what would make you stop or slow the bolus mid-infusion?
Read the worked answer
Before walking away:
- Count drops for 15 seconds and multiply by 4 to confirm the rate.
- Inspect the catheter site for swelling, coolness, or resistance - any of those means the catheter has slipped or blown; stop, remove, and replace.
- Check the line for kinks, the bag for remaining volume, and the connections for security.
- Set a timer for the end of the bolus and record the start time on the cage card.
During the 30-minute bolus (stay nearby, do not leave it running unattended):
- Site: recheck for swelling each pass. A blown catheter in a dehydrated dog wastes the access you just obtained.
- Respiratory rate and effort: a new cough, serous nasal discharge, or increased effort suggests overload. It is unlikely at 180 mL in a 7% dehydrated dog, but this is exactly why a bolus is never hung and abandoned.
- Vomiting: slow the rate, note the volume, and tell the veterinarian - ongoing losses change the fluid plan.
- Perfusion: CRT, gum color, heart rate. A falling heart rate with a rising PCV warrants reassessing.
- Temperature: she is shivering, which could be fever, pain, or hypothermia. Take a temperature rather than assuming.
- Mentation: a dog that becomes duller during a bolus needs the veterinarian, not a faster rate.
At the end of the bolus, recheck skin tent and mucous membranes and report the change, along with urine output if she voids.