A Sense of Touch in Laparoscopy

Abstract

Laparoscopy is Minimally Invasive Surgery (MIS) that is conducted in the belly alcove and which enables instruments, which enter the body through small incisions, to manipulate tissue. The possible complications arising during laparoscopic surgery are partly caused by improper grasp control on the part of the surgeons using the graspers. This is mainly caused by a reduction in the perception of haptic information (combination of tactile and kinaesthetic information) from the grasped tissue as a result of indirect grasping. The experiments presented in this thesis focus on the improvement of laparoscopic grasp control and the related learning aspects, to see if the former might be improved by means of augmented feedback received on haptic information. The aim of this thesis is to answer the following main research question: “Can augmented feedback on haptic information enhance the surgeon’s control of laparoscopic grasp force?” To understand natural haptics and perception, the parts of the human motion control system involved in grasping are discussed in Chapter 2. The discussion includes barehanded human grasp control and a description is given of the sensory systems involved. A literature review describes the current situation surrounding haptics in MIS, the factors that influence the amount of grasp force applied to the tissue and precisely what sensory information is at present available during the use of laparoscopic graspers. Questionnaire results show the importance of this topic from a surgeon’s point of view. Surgeons need haptic feedback as that is reduced when traditional MIS instruments are used and it is completely absent in Robotic assisted Minimally Invasive Surgery (RMIS). At the start of this PhD project it was not clear which factors control the application of laparoscopic grasp force to tissue. Experiments, presented in Chapter 3, were done in which tasks that were carried out barehanded were compared to tasks that were carried out laparoscopically via instruments with various force transmission ratios. These experiments provided insight into how accurately a human can sense forces and tactile information through a laparoscopic instrument during tissue-grasping tasks. The results of experiments show that in order to successfully control the force applied to the tissue, tactile feedback is essential. The question is whether humans can learn to control their grasp without such tactile feedback but with the help of augmented feedback that compensates for the missing haptic information. The principals of human grasp control discussed in the opening chapters show that both haptics and vision are important in the controlling of hand forces. These principals are the same as those required for the safe control of instruments in MIS. However, the instruments cause a disturbance in visual and kinaesthetic feedback and they cannot provide tactile information at all. The numbers of consequential and inconsequential errors that are being made due to insufficient grasp force control indicate that there is a need to enhance the currently available combination of visual and haptic feedback. The matter of whether augmented feedback can help performance in laparoscopic grasping is tested and discussed in chapter 4. Several augmented feedback modalities are considered (visual, tactile, illusionary and combinations thereof). Experiments, show that having augmented tactile feedback on grasp forces is a good way to help in laparoscopic grasp control. Surgeons at all levels of experience benefit to control their grasp forces with the aid of augmented haptic feedback. With the help of augmented feedback they learn more quickly to control their laparoscopic grasp force and apply reduced overall grasp forces. In addition to receiving augmented haptic feedback all the time during tool usage the question raised if it is possible to train the surgeons to cope with the distorted intrinsic feedback provided by the current graspers by means of only training with augmented feedback. This is supported by the fact that it is known that augmented feedback during the learning process can aid performance in several tasks other than grasping. The advantage of learning to cope with distorted intrinsic feedback is that there is no need for the development of new and expensive instruments in the operating room as the normal instruments can still be used. The results of experiments presented in Chapter 4 show that the majority of surgeons do not become dependent on the augmented signal. This implies that when the augmented feedback is removed they continue to perform with the same improved force control and thus learned to deal with the intrinsic feedback available. Furthermore, experiments showed that performance was still enhanced when the participant’s attention was distracted by introducing an additional aiming-task (with the second hand), while the task whereby controlling grasp forces was needed continued with the other hand. To optimise the augmented haptic feedback signal used in the experiments presented in Chapter 4, a design for a new grasper handle was developed. This new laparoscopic grasper handle with integrated augmented tactile feedback actuators is presented in Chapter 5. To see if people are able to learn grasp control with two hands simultaneously, two of these new handles were used in experiments. The results show that learning with two hands simultaneously is indeed possible and that people do not get confused as a result. From the research done during this PhD project it can be concluded that augmented tactile feedback on grasp forces can aid laparoscopic grasp control even if it is only provided during a training period. Furthermore, the research conducted resulted in the development of a working prototype of a laparoscopic grasper containing augmented tactile feedback on grasp forces together with guidelines for training devices containing augmented haptic feedback.