Keywords

1 Introduction

In Japan, the increase in the number of elderly persons needing long-term care has become a serious problem.

According to the Annual Report on the Aging Society in Japan [1], at the end of FY2014, the number of people aged 65 and over who were certified as requiring long-term care was 5.918 million, 1.39 times more than at the end of FY2006; and the ratio of elderly people certified as care level 4 or 5, to the total number of those certified, was 21.9%. (Under the Japanese long-term care insurance system, nursing care level is classified between 1 and 5 based on assessment of care requirements, where level 5 is the highest.)

More than half of those certified as requiring long-term care, who are living at home, are living with their families, who are also their main caregivers. According to a governmental survey [1], more than half of the main caregivers of those certified as care level 4 or 5 spend “almost the entire day” taking care of them, which means that the care of such people is a severe burden; and excretion care is one of the most demanding tasks for caregivers.

The Japan Science and Technology Agency (JST) is funding the Impulsing Paradigm Change through Disruptive Technologies (ImPACT) Program. One of the R&D projects in the ImPACT Program is the Innovative Cybernic System for a ZERO Intensive Nursing-care Society project [2]. This project aims to develop an innovative cybernic system that combines the human brain-nerve-muscular system with robots and other devices. Cybernics is an interdisciplinary research field established by Sankai [3]. The developed system will improve, extend, amplify, and assist the residual functions of human beings. As part of this project, technologies for safety testing of defecation assist devices, as well as such devices themselves, are being studied.

In this study, based on a bibliographic survey, we investigated safety criteria which may be used to develop safety testing technologies for defecation assist devices. In addition, we developed a rectal model sheet for use in safety testing.

2 Target Care Task

We focused on excretion care as our target care task, and investigated in detail the difficulties experienced in this form of care.

Gallagher and O’Mahony summarized relevant statistics, etiology, complications, evaluation criteria, and treatment of constipation in the elderly [4]. According to this study, 30–40% of elderly people living in their communities, and over 50% of the residents of nursing homes, experience chronic constipation. The study also indicated that fecal impaction following constipation causes complications such as diarrhea, intestinal obstruction, stercoral ulcers, etc.

Knight et al. noted that constipation is a critical problem for bedridden patients, and that chronic constipation is a potential cause of intestinal diverticulitis [5].

Efforts for the prevention or relief of constipation in everyday life include dietary modification and physical exercise. Laxatives are also used to relieve constipation [4].

In some cases, mechanical intervention methods are required to remove fecal impaction. Popular methods include enemas and manual disimpaction, but both are burdensome tasks for caregivers.

Several devices have been developed to assist defecation. Coloplast, Ltd. offers the Peristeen® anal irrigation system [6], which introduces water into the bowel through a rectal catheter, using a manual pump. The water stimulates the bowel and encourages defecation.

Centurion Medical Products Corporation offers the DisImpactor® [7], which penetrates fecal impactions and makes them easier to remove.

Several Japanese researchers have also studied defecation assist devices. Yagata et al. proposed an “evacuation care system” [8], which is inserted into the rectum, crushes a fecal impaction using ultrasound, and suctions out the impaction with water. Nakamura et al. proposed a “feces suctioning catheter”, with two different types of design [9].

In spite of such efforts to develop useful devices, defecation assist devices are not popular in Japan, one possible reason for which is that no methods have yet been established for testing and evaluating the safety of such devices.

Therefore, we have been investigating safety tests and evaluation of defecation assist devices.

3 Identification of Safety Hazards

3.1 Incidents in Excretion Care

Safety incidents in excretion care, especially those involving the use of enemas, have been reported by several researchers.

Paran et al. reported cases of perforation of the rectum and/or sigmoid colon caused by irrigation enemas [10]. Thirteen patients with perforation of the rectum and/or sigmoid colon, caused by irrigation enemas, were admitted to the surgical department of their hospital over a three-year period, and three of these patients died of sepsis and multi-organ failure.

Niv et al. conducted a two-phase study [11], the first phase of which was a retrospective study, based on which they formulated guidelines that governed patient treatments in the study’s second phase. In the first phase, they studied 269 patients referred to the Emergency Department of their hospital because of severe constipation, over a one-year period. They reviewed the medical records of the patients, and monitored return visits within one week, as well as 30-day mortality. Of the 269 patients, 207 (76.9%) were treated with a cleansing enema, and three (1.4%) suffered colorectal perforation. The authors suggested that the rigid tip of the enema device was a possible cause of the perforations.

Christensen et al. evaluated the long-term outcome of transanal irrigation for constipation and fecal incontinence [12]. Over a ten-year period, 348 patients suffering from defecation disturbances, and with differing background pathologies, were treated with transanal irrigation, and two suffered bowel perforations as a result of the treatment.

The prevalence of enema-related perforation varies among the studies; however, perforation is one of the serious concerns associated with enema device use, as well as with the use of other transanal defecation assist devices.

3.2 Safety Hazards for Prospective Defecation Assist Devices

As a specific target method, we focused on transanal bowel irrigation; and as prospective target devices, we focused on those that are inserted into the rectum and assist defecation in a fully-automated manner, to alleviate some of the caregiver’s burden through the use of robotic technology. Moreover, the prospective devices must achieve a high level of safety, which requires appropriate testing methods. Therefore, we conducted a bibliographic survey to develop methods and device specifications required for effective safety testing.

First, through brainstorming, we explored potential safety hazards associated with use of the prospective automated transanal bowel irrigation devices. Five mechanical hazards were identified: (1) perforation of the rectum by jet flow, (2) laceration of the rectum by suction, (3) rupture of the rectum by hydraulic pressure, (4) perforation of the rectum by contact between the defecation assist device and the rectal wall, (5) laceration due to the repetitive insertion or removal of the device.

We then estimated the pressure range within which the human rectum may be harmed, for each of these five hazards, based on a bibliographic survey.

Below is a description of the various hazards.

  1. (1)

    Perforation of the rectum by jet flow. Here, the jet flow from the defecation assist device perforates the rectal wall. Since no reports of such perforation or ablation of rectal tissue by jet flow were found in the survey, we referred in this case to the literature on the strength of the relevant body tissues.

  2. (2)

    Laceration of the rectum by suction. Here, the device sucks and tears the rectal wall when it tries to remove feces from the rectum. The literature offers a possible case, in which the authors infer that colonic perforation was caused by the rapid transanal decompression and continuous suction of the device [13].

  3. (3)

    Rupture of the rectum by hydraulic pressure. Here, water from the defecation assist device increases the pressure in the rectum to the bursting point. The literature offers a case in which the rectum was perforated due to enemas or spouting hot water in a spa facility [14, 15].

  4. (4)

    Perforation of the rectum by contact between the device and the rectal wall. Here, the tip of the nozzle of the device strikes and perforates the rectal wall. Possible cases have been reported involving the use of endoscopes during inspection or surgery [16].

  5. (5)

    Laceration of the rectum due to the repetitive insertion or removal of the device. Here, the nozzle of the device comes into contact with and lacerates the rectal wall, possibly by the sharp tip or edge of the nozzle.

4 Bibliographic Survey

A promising method for evaluating the safety of defecation assist devices is simulation of the respective hazardous events: pressure caused by contact between the nozzle or water and the rectal wall is measured, and the pressure on the rectal wall is determined to be above or below a safe level with reference to pressure data from the literature.

4.1 Perforation of the Rectum by Jet Flow

A high-pressure water stream is used for incision and ablation in surgery [17]. According to [17], the biomedical effects of this stream in water jet surgery include: (1) perforating, (2) crushing and fracturing, (3) ablating, (4) cleansing and spraying or infusing a drug in tissue.

Repici et al. studied the efficacy and safety of colorectal endoscopic submucosal dissection (ESD) using a device called a HybridKnife [18], which combines a water jet and an electrocautery needle. The maximum pressure of the water jet is 80 bars (8 MPa).

If the flow pressure from a defecation assist device is too high, using a water jet device such as this, perforation may result.

Work-related abdominal perforation by the high-pressure water jet gun has been repeatedly reported [19, 20]. In these cases, patients failed to handle a water jet gun properly in cutting or cleaning tasks, and struck their abdomen with the jet from outside. In each case, the pressure of the water jet was 40 MPa or more.

Repici et al. specified the maximum water jet pressure of the device, but the pressure actually used in ESD is not available, and our survey found no other report on perforation or laceration of the rectum by such water jets. Thus, the safety threshold was determined based on the literature on the mechanical properties of the related human body tissue.

Yamada and Evans reported the results of various material tests on various organs from fresh cadavers [21]. For the expansive properties test, specimens from 75 individuals were used. Before the experiments, the test materials were soaked in a saline solution overnight for stabilization. Then the specimens were cut into 15 mm × 15 mm squares, attached to a Mullen tester with a test hole of 7 mm, and subjected to pressure. The mean value of the ultimate expansion strength of rectal specimens from those between the age of 70 and 89 was 6.1 kg/cm2 (0.598 MPa). As the mean value of ultimate expansion strength declines with age (except for those under 10 years of age), the safety threshold for expansive strength should be determined based on the value of those between the age of 70 and 89.

4.2 Laceration of the Rectum by Suction

Here, the device sucks the rectal wall when it suctions feces.

Hyodo et al. reported a case possibly involving a similar mechanism [13]. In this case, a transverse colon cancer patient required intestinal tract decompression using a transanal decompression tube. The applied pressure of continuous suction was 10 cm H2O (0.98 kPa). Four days after insertion of the tube, it was observed that it had penetrated into the mesentery in the area containing the tumor. A possible cause of the perforation was thought to be the continuous suction by the tip of the tube in contact with the intestinal tract.

Tracheal suction would appear to be another medical practice involving such a hazard. According to the “Tracheal aspiration guidelines 2013” published by Japan Society of Respiratory Care Medicine [22], the intensity of negative pressure for tracheal suctioning should be limited to 20 kPa.

The case described in Hyodo et al. suggests that far less suction pressure than is used in tracheal suction may cause tissue damage, though the damaged area in this case was not intact but affected by cancer.

4.3 Rupture of the Rectum by Hydraulic Pressure

Here the water spouting from the device accumulates in the rectum, which increases the intrarectal pressure, and finally causes a rupture of the rectum due to hydraulic pressure. This kind of accident, involving a similar mechanism, is often reported. Choi, for example, reported two cases of rectosigmoid colon perforation caused by the hydrostatic pressure of tap water during unauthorized anal irrigation or enemas [14], and Takei et al. reported a case of rectal perforation due to spouting hot water in a spa [15]. Many cases have also been reported involving watercraft accidents.

Burt investigated the pressure necessary for the intestinal tract to be ruptured [23]. He prepared specimens of the gastrointestinal tract, from the rectum to the esophagus, of 18 cadavers, attached these to an accumulator and a manometer, and subjected them to pressure sufficient to rupture them. Among the results, we focused on the rectal data for three adults: a 21-year-old female, a 45-year-old female, and a 78-year-old male, for whom the pressure at which perforation of the mucosa occurred was 4.94 psi (34.1 kPa), 2.09 psi (14.4 kPa), and 3.80 psi (26.2 kPa), respectively.

Either the mean or the minimum value of the above results could mark the safety threshold for the risk of rupture by pressure.

4.4 Perforation of the Rectum by Contact Between the Device and the Rectal Wall

Here, the tip of the nozzle of the device makes contact with and perforates the intestinal wall when inserting the nozzle into the rectum. Niwa noted that the intestinal canal can be perforated when using an endoscope for inspection or surgery [16]. According to his survey, 68 cases of perforation were reported among 54463 cases of colonoscopy inspection.

Uno evaluated the contact force generated by a large intestine endoscope, using a model [24]. He assumed three types of mechanism for perforation of the large intestine by the endoscope; and based on the results reported by Yamada [25], he determined that the threshold pressure likely to cause perforation was 3–4 kg/cm2 (294–392 kPa). In Uno’s study, various regions of the large intestine were considered in determining this threshold.

4.5 Laceration of the Rectum by the Repetitive Insertion or Removal of the Device

Here, the nozzle of the defecation assist device lacerates the intestinal wall as it is inserted or removed from the intestine. As the sharp tip or edge of the nozzle is possible source of this harm, safety evaluation will be done based on stress concentration as well as the pressure applied on the intestinal wall. Since the sharp edges or protruding parts should be avoided at the design stage, no report was found concerning the cases involving a similar mechanism.

5 Development of the Rectal Model Sheet

We aim to develop safety testing technologies for defecation assist devices, in which physical interaction between the device and the rectum is evaluated. Though ideal samples used in safety tests will be tissues from human or animals, they are not easily available because of deviation in properties, difficulty in handling and issues in bio-ethics. Therefore, the model which reflects the properties of tissues are required to conduct safety tests. In order to conduct safety evaluation tests for the hazards described in Sect. 4, we developed a rectal model sheet. The properties of the sheet, such as the Young’s modulus and thickness, were determined based on the literature.

5.1 Young’s Modulus of the Rectal Wall

Riken and the Industrial Research Institute of Shizuoka Prefecture offer “the body tissue physical properties value database” for computational biomechanics [26]. Based on this database, we determined the relevant value of Young’s modulus to be 0.5 MPa, which corresponds to Young’s modulus for the large intestine in the circular direction.

5.2 Thickness of the Rectal Wall

Tsuga et al. evaluated the colorectal wall in normal subjects and patients with ulcerative colitis, using an ultrasonic catheter probe [27].

In order to determine the proper thickness of the rectal model sheet, we focused on the data on the study’s 36 normal subjects (25 men and 11 women), and determined that the mean value of total rectal wall thickness was 2.14 mm.

5.3 Specifications of the Rectal Model Sheet

Figure 1 shows the developed rectal model sheet. The sheet is made of silicone rubber, with a Young’s modulus of 0.5 MPa and thickness of 2.15 mm as target specifications, based on 5.1 and 5.2.

Fig. 1.
figure 1

Photo of the developed rectal model sheet

Full size image

The model is a single-layered, smooth, fringeless, square (200 mm × 200 mm) sheet. The sheet can be cut into pieces for use in strength testing. We will examine the validity of the developed model through experimentation.

Currently, we are planning tensile tests using the developed rectal model sheet to validate it. In the future, safety testing methods will be established corresponding to the hazards identified in Sect. 3, the safety tests using the rectum model sheet will be conducted, and the safety test results will be evaluated based on the criteria investigated in Sect. 4.

6 Conclusion

We conducted a bibliographic survey to investigate safety criteria for the development of safety test methods, and safety test device specifications, for defecation assist devices.

Prior to a bibliographic survey, the target devices were assumed as the defecation assist devices to be inserted into the rectum, and a primitive inspection of expected harms was conducted. Five mechanical hazards such as (1) perforation of the rectum by jet flow, (2) laceration of the rectum by suction, (3) rupture of the rectum by hydraulic pressure, (4) perforation of the rectum by contact between the defecation assist device and the rectal wall, (5) laceration of the rectum by the repetitive insertion or removal of the device were assumed.

Aiming to be used for safety evaluation test, we have developed a rectum model sheet. Properties of the rectum model sheet were determined with reference to the properties of human rectum.

For future work, we will establish safety testing method and conduct the safety tests using the rectum model sheet, and then evaluate the safety test results based on the criteria investigated in this study.