Recently there has been an increased awareness in the need for adequate sedation and pain control for Pediatric Intensive Care Unit (ICU) patients. Fentanyl is an opioid commonly used in Pediatric ICU patients to decrease pain and increase sedation. Although opioids (e.g. morphine and fentanyl) provide excellent pain relief, they have many side effects including dependence, tolerance and withdrawal. These side effects lead to increased doses in order to maintain pain control and/or sedation. There have been a few adult studies pointing to some possible treatments. For example, giving low dose naloxone along with opioids. Adult studies show that this combination not only decreases the frequency of opioid side effects, but also improves pain control and prevents the development of tolerance. We propose that children who receive low dose naloxone infusions along with fentanyl infusions will demonstrate: 1) decreased total daily doses of Fentanyl, 2) decreased frequency of withdrawal and 3) increased pain and sedation control. In this randomized, blinded prospective trial we will enroll 168 Pediatric ICU patients. Patients will receive either low dose naloxone or placebo simultaneously with their fentanyl infusion. Pain and sedation will be assessed using the Modified Motor Activity Assessment Scale (MMAAS). The fentanyl infusion will be increased to provide adequate pain control and/or sedation. Naloxone infusion will not be adjusted. Approximately 48 hours prior to removal from the ventilator, patients will have their fentanyl infusions decreased while being monitored for withdrawal. Patients showing signs of withdrawal will receive methadone, an opioid taken by mouth. Once off fentanyl, naloxone will be stopped. Patients will continue to be monitored for withdrawal for 4 days or until ICU discharge. If this study works, patients who receive low dose naloxone along with opioid infusions will have less tolerance and dependence and demonstrate less withdrawal. This may cause shorter Intensive Care Unit stays.