Medical personnel who use Pulmanex Manual resuscitators are being asked to return the devices because of a defect that in some cases could be fatal to patients. The Food and Drug Administration said Life Design Systems Inc. of Carrollton, Texas, is voluntarily recalling resuscitators with model numbers beginning with 90, 91, 95 or 96 and ending with a 0, 1, 2 or 3 after the hyphen. The recalled models have lot numbers 9321 through 9361 and were made from Nov. 17 through Dec. 27 last year. In five previous recalls, Life Designs Systems has recalled other models of the resuscitator for various reasons, the FDA said. The agency said it did not know of any deaths that have resulted from any of the faulty resuscitators. The resuscitator subject to the latest recall comes in adult, pediatric and neonatal sizes. It consists of a mask that is placed over the patient's mouth and nose and is attached to a plastic bag. Squeezing the plastic bag forces air into the patient's lungs. In faulty resuscitators, the rear valves can become dislodged and prevent air from reaching the person being resuscitated, the FDA said. If the problem is not recognized in time, the patient could die.