An exemplary sensor includes a sensor pad having a first portion and a second portion separated by a waist portion. The waist portion is narrower than the first portion and the second portion. A light source that is disposed on the first portion is configured to generate near-infrared light and transmit the near-infrared light through part of a patient's body. A light detector that is disposed on the second portion is configured to detect near-infrared light that has traveled through the part of the patient's body. The near-infrared light detected indicates an amount of oxygen in the part of the patient's body through which the near-infrared light traveled.