An endoscopic surgical method involves an advancement of an endoscope (20) to a target location within an anatomical region of a body and a generation of a plurality of endoscopic video frames (22) as the endoscope (20) is advanced to the target location with the endoscopic video frames (2) illustrating monocular endoscopic images of the anatomical region. For real-time estimation of a depth of an object within monocular endoscopic images (e.g., depth of a bronchial wall within an monocular endoscopic images of a bronchial tube), the method further involves (S41) a determination of an optical flow of one or more image points within a frame time series of the monocular endoscopic images of the anatomical region, and (S42) an estimation of a depth field indicative of a depth of the object within the monocular endoscopic images as a function of the optical flow of the image point(s).