the epidural. Risks and complications In addition to blocking nerves which carry pain signals, local anesthetics may block nerves which carry other signals, though sensory nerve fibers are more sensitive to the effects of the local anesthetics than motor nerve fibers. For this reason, adequate pain control can usually be attained without blocking the motor neurons, which would cause a loss of muscle control if it occurred. Depending on the drug and dose administered, the effects may last only a few minutes or up to several hours. As such, an epidural can provide pain control without as much of an effect on muscle strength. For example, a woman in labor who is being administered continuous analgesia via an epidural may not have impairment to her ability to move. Larger doses of medication are more likely to result in side effects. Very large doses of some medications can cause paralysis of the intercostal muscles and thoracic diaphragm responsible for breathing, which may lead to respiratory depression or arrest. It may also result in loss of sympathetic nerve input to the heart, which may cause a significant decrease in heart rate and blood pressure. Obese people, those who have given birth prior, those with a history of opiate use, or those with cervical dilation of more than 7 cm are at a higher risk of inadequate pain control. If the dura is accidentally punctured during administration, it may cause cerebrospinal fluid to leak into the epidural space, causing a post-dural-puncture headache. This occurs in approximately 1 in 100 epidural procedures. Such a headache may be severe and last several days, or rarely weeks to months, and is caused by a reduction in CSF pressure. Mild post-dural-puncture headaches may be treated with caffeine and gabapentin, while severe headaches may be treated with an epidural blood patch, though most cases resolve spontaneously with time. Less common but more severe complications include subdural hematoma and cerebral venous thrombosis. The epidural catheter may also rarely be inadvertently placed in the subarachnoid space, which occurs in less than 1 in 1000 procedures. If this occurs, cerebrospinal fluid can be freely aspirated from the catheter, and this is used to detect misplacement. When this occurs, the catheter is withdrawn and replaced elsewhere, though occasionally no fluid may be aspirated despite a dural puncture. If dural puncture is not recognized, large doses of anesthetic may be delivered directly into