Breeding Emergency Kit
I recommend three things in a gerbil breedeing emergency kit:
A Clamp Lamp, Kitten Milk Replacement, and Ornacycline.

1) Clamp Lamp and 40 watt grow light (and thermometer) to warm up one corner of the tank to 80 degrees if pups are cold to the touch or have respiratory infection.  Purchase at a petstore, hardware store or walmart.

2) Kitten Milk Replacement. Buy the powdered and mix one teaspoon up at a time.  Mix 1 part powder with 2 parts room temperature water (according to instructions for a kitten).  Stir with your finger and microwave for 7 seconds.  Use an infant medicine dispensor.  Tilt the pup back slightly and put the dropper to the side of the pup's lip.  Feed one tiny drop at a time until the pup figures out this is food and laps it up.  This milk dries like cement so try not to get it on the pup's fur and wipe excess with a warm, moist paper towel.  Use the milk for runts, if the mother's milk is unavailable, or for severe respiratory infection.  This is usually used to supplement the gerbil mother's milk or in the final stages of weaning for a pup whose growth stagnates. Purchase in the cat section of a pet store.  Available at pet stores, vet's office and (cheapest at) Walmart superstores - pet section.

3) Ornacycline for respiratory infection (clicking) in gerbil pups - typically would occur at three weeks.  Ornacyline can be found in the bird section of your pet store.  Mix up the dosage for a small bird.  (1/4 tablet to 2 oz water) place in the water bottle for the parents and pups to drink. Replace the medicated water every day. Place a few drops of medicated water directly on the lips of the effected pups a few times a day for 10 days.  For severe respiratory infection (see pictures below) where gerbil has puffy fur, glazed eyes, scrawny tail and the stops growing or loses weight, treat with Ornacycline and supplement feed with Kitten Milk Replacement.
Shown below are 4 week old pups with severe respiratory infection.  Treat aggressively with Ornacycline and supplemental Kitten Milk Replacement feedings - and they should pull through.