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|NI FEATURE: TIMELESS REVERBERATIONS - COMMENTARY
|Year : 2019 | Volume
| Issue : 3 | Page : 635-638
The saga of the 'Chhabra' shunt
Devendra K Chhabra
Department of Neurosurgery, King George Medical College; Department of Neurosurgery, Sanjay Gandhi Postgraduate Institute of Medical Sciences; Department of Neurosurgery, Vivekanand Institute of Medical Sciences, Lucknow, Uttar Pradesh, India
|Date of Web Publication||23-Jul-2019|
Dr. Devendra K Chhabra
Department of Neurosurgery, Vivekanand Institute of Medical Sciences, Lucknow, Uttar Pradesh
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Chhabra DK. The saga of the 'Chhabra' shunt. Neurol India 2019;67:635-8
This narration is written to highlight the two major themes it is based on:
A. 'Necessity is the mother of invention'
In the 1960s and 1970s, post tuberculous hydrocephalus was rampant in Indian children. Every neurosurgeon of India at that time was worried regarding the non-availability of shunts in the country. Even congenital hydrocephalus did not have a viable recourse. One of my own cousins, who was suffering from tuberculous meningitis with hydrocephalus, had to be shifted to Christian Medical College, Vellore, at that time to undergo a ventriculoperitoneal cerebrospinal fluid diversion procedure. Highlighting the endemicity and the malaise of post-tuberculous hydrocephalus, in a computed tomographic scan based study done in the year 2009, it was found that only three of 60 children and adults with tuberculous meningitis were found to have normal ventricles, giving an incidence of 95%. Significantly, 87% of the children in this study had severe hydrocephalus. Robert H. Pudenz, a renowned neurosurgeon in the United States, had invented the shunt valve and is credited with the starting of ventriculoatrial shunt surgery. In 1955, he had demonstrated that a venous catheter worked optimally when in the right atrium. The slit valve, responsible for the regulated drainage of cerebrospinal fluid, therefore, had to be located at the most distal portion of the shunt system to prevent retrograde filling and thrombosis. The Pudenz shunt devised by him had to be imported to India. The procedure was cumbersome and the cost was prohibitive. The import licence was difficult to obtain and there was a single dealer in Delhi, J Mitra and Sons, who had the sole responsibility of making the Pudenz shunt available to Indian patients. In sheer desperation, occasionally, even a Ryle's tube was used as a ventriculoperitoneal shunt system in India in those trying times.
Professor Purushottam Upadhyaya, the former Chief of Paediatric Surgery, All India Institute of Medical Sciences (AIIMS) New Delhi, India, invented the “Upadhyaya Valve”, the first indigenous shunt valve for hydrocephalus, which was based on the concept of the Holter shunt system., This, too, was difficult to obtain because it was manufactured in small volumes only. The material that was used to make the shunt system was also not very flexible, making it difficult to install the shunt with ease. Although the principles of various ventriculoperitoneal shunt systems were well-known and the designs of the ventricular and peritoneal ends were freely available, the material for manufacturing the shunt system was only available from the United States. The silastic (a combination of silicone and plastic) tubing material, being biological inert, biocompatible, and flexible, was very suitable as an appropriate material for shunt tubing. These silicone elastomers, silicone tubing and some cross-linked polydimethylsiloxane materials were only manufactured by the Dow Corning company, the owner of the global trademark of the product.
Thus, the circumstances were opportune for the introduction of a better Indian substitute for facilitating the treatment of hydrocephalus. I was an Assistant Professor at King George Medical College working under the tutelage of Professor VS Dave, the Head of the Department of Neurosurgery. In 1978, I asked one of my resident house officers, Dr. G.D. Agarwal, who had an engineering frame of mind and a business background, “GD, can you do something about this dire need?” He took up the challenge of designing the new shunt system and has devoted his life-time to it. The inert, silastic tubing was initially imported from the parent company in the United States. A manufacturing unit was assembled in King George Medical College and we all got to work conceptualising the design for an indigenous low cost shunt system for India. Prof. VS Dave wholeheartedly supported our venture and we are grateful to him for his magnanimity and mentorship. The shunt was tested in King George Medical College, Lucknow, and the clinical results of the shunt procedures were presented at various conferences across the country. The simple tubing with a slit valve often resulted in overdrainage of cerebrospinal fluid and, therefore, a new design of the shunt chamber (the Z flow shunt) that prevented overdrainage was conceptualised. Dr. GD Agarwal placed a stellar role in executing the design and in procuring the biomaterial for the indigenous shunt system that we were designing. This shunt chamber was based upon the principle of gravity dependent overdrainage prevention system [Figure 1]. When the patient was standing upright, with maximum chances of overdrainage of the cerebrospinal fluid from the ventricular system to the peritoneum, one, two, or three (depending on performance level) stainless steel weighting spheres pressed on a sapphire ball which closed the cerebrospinal fluid flow aperture. This increased the shunt's opening pressure and prevented overdrainage of cerebrospinal fluid. In the lying down position of the patient, the stainless steel spheres moved away from the sapphire ball, and the opening pressure of the valve becomes nearly zero mm Hg, thus opening the shunt aperture and facilitating the cerebrospinal fluid drainage. One of my neurosurgical residents, who subsequently became a long-standing colleague and friend, Dr Piyush Mittal, published a paper in Acta Neurochirurgica regarding this Z flow hydrocephalus shunt system, which closely resembled the working of the gravitational shunts prevalent at those times, like the Cordis horizontal-vertical LP valve shunt system. However, our subsequent experience showed that this shunt drained erratically and occasionally, a particulate matter in the cerebrospinal fluid, like blood product or minute brain matter, resulted in shunt obstruction. Therefore, the need for adopting a new shunt design arose.
|Figure 1: The Z flow shunt (a) When the patient is standing upright, with chances of overdrainage of the cerebrospinal fluid, the stainless steel weighting spheres press on a sapphire ball, which closes the cerebrospinal fluid flow aperture. This increases the shunt's opening pressure and prevents overdrainage of cerebrospinal fluid. (b) In the lying down position of the patient, the stainless steel spheres moved away from the sapphire ball, and the opening pressure of the valve becomes nearly zero mm Hg, thus opening the shunt aperture and facilitating the cerebrospinal fluid drainage. (c) The actual photograph of the shunt valve of the Z flow shunt|
Click here to view
This new design resulted in the 'slit and spring valve' shunt [Figure 2]. The shunt system had two slit valves. Experience had shown that a simple slit valve was prone to malfunction unless a spring was used to support the slit through which the cerebrospinal fluid drained. The proximal slit valve in the shunt chamber was, therefore, girdled by a stainless steel spring, which protected as well as supported the slit valve and helped in maintaining the opening pressure. Thus, when the pressure differential between the ventricular system and the peritoneal cavity was high, as in the standing posture of the patient, the spring over the valve prevented the valve from overstretching, thus preventing overdrainage of cerebrospinal fluid. In recumbent position of the patient, the spring maintained an optimum pressure on the valve and kept its open, thus facilitating cerebrospinal fluid drainage even at a minimum pressure differential. The distal slit valve was at the distal part of the peritoneal end that further prevented overdrainage, spontaneously opening when there was cerebrospinal fluid pressure head encountered, and partially closing when there was no pressure differential. This simple but highly efficient design further ensured against leakage and backflow. Its valve did not suffer from deformation or overstretching. Thus, even under conditions of a high cerebrospinal fluid pressure head, the valve maintained its optimum functional capability. This shunt system was more efficient, and was compatible with computed tomographic and magnetic resonance imaging, without producing any artefacts. Three pressure models of the shunt system have been introduced, with the medium pressure system allowing for a flow rate of cerebrospinal fluid of 20 ml/hr at a pressure gradient of 10 cm of water. This is the physiological rate of cerebrospinal formation and absorption. The most important precaution before the implantation of the shunt has been that the whole system must be flushed with distilled water or saline to ensure that the slit valves open up to their normal size before the shunt is implanted.
|Figure 2: (a) The schematic diagram; and, (b) the actual photograph of the slit and spring valve shunt. The proximal slit valve in the shunt chamber is girdled by a stainless steel spring, which helps in maintaining the opening pressure. Thus, when the pressure differential is high, as in the standing posture of the patient, the spring over the valve prevents the valve from overstretching, thus preventing overdrainage of cerebrospinal fluid. In recumbent position of the patient, the spring maintains an optimum pressure on the valve and keeps its open, thus facilitating cerebrospinal fluid drainage even at a minimum pressure differential. The distal slit valve at the distal end of the peritoneal end further prevents overdrainage|
Click here to view
In 1982-83, Dr. Agarwal set up a factory in Shajahanpur to devote himself full-time to the manufacturing of various low cost medical devices. He also worked hard to bring the manufacturing to international standards in terms of the materials used, maintaining its strength, flexibility and longevity, ensuring a proper gamma sterilization that the shunt undergoes to render it bacteria-free, and its optimized packing to facilitate its use while maintaining the international sterilization standards. In 1985, this design received the Indian Patent No. 162530. I refused to be a co-signatory of the patent as I did not want to accept any royalty from the device or its subsequent modifications. Both Dr. Agarwal and myself were intensely aware that we wanted to keep this a low-cost device (the current cost is approximately Indian rupees five thousand) so that it could be afforded by the vast majority of patients. Dr. Agarwal, in his graciousness, named the initial device and its subsequent modifications, the “Chhabra shunt.”
Any new concept is met with a natural resistance. Our device ushered in intense scepticism and resistance from the Indian medical fraternity. Most neurosurgeons were reluctant to use the device on their patients. Our numerous presentations in conferences regarding the benefits of its utilization based upon our experience in Lucknow only generated more questions regarding its 'safety' and 'lack of adequate experience in its usage'. In the 1983 Annual Conference of the Neurological Society of India at Madurai, after a presentation on the experience with this shunt system, one neurosurgeon got up to state, “Is this actually being used in patients?” One of the initial neurosurgeons, who did accept the shunt system in its initial stages and started using it on his patients, was Prof. SN Bhagwati, the founder of Indian Society of Pediatric Neurosurgery. Gradually, more neurosurgeons from India started using the device. Yet, its usage at that time was far below our expectations, that were generated based upon the intense need for it in the Indian patients.
B. 'If you take care of the small things, the big things take care of themselves'
This prophetic remark by Emily Dickinson (1830-86), the famous American poet, subsequently worked in our favour too. This shunt system had started being regularly used in India. Dr. Benjamin C. Warf, currently Professor of Neurosurgery, Harvard Medical School and Boston's Children Hospital, was from 2000 to 2006, serving as Chief of Surgery and founding Medical Director at CURE Children's Hospital of Uganda, the only paediatric neurosurgery hospital in sub-Saharan Africa. He felt the need for a low-cost shunt system for his extremely poor patients in Uganda and decided to perform a randomised trial, that was published in 2005, of patients with the Chhabra shunt ($35 US dollars) [that was being widely used in East Africa], with those using the Codman-Hakim Micro Precision Valve shunt ($650) and assessed the one-year outcome. He stated in his conclusions, “Ventriculoperitoneal shunt insertion for treatment of hydrocephalus can be performed in a developing country with results similar to those reported in developed countries. No difference in outcome was noted between the two shunt types. No advantage was found in using a shunt system that, in this setting, is prohibitively expensive.” This study has been cited around 100 times in the medical literature. This trial prompted the International Society for Pediatric Neurosurgery to send one of its founding members and President, the Professor of Neurosurgery at the University of Marseille, Prof. Maurice Choux, to visit the production unit of the firm in Shahjahanpur in 2009, to ensure that it met European and world standards. Following his endorsement and that of the International Society for Pediatric Neurosurgery of the device, the shunt system became extremely popular and is now being used in nearly 50 countries. A very recent randomized controlled trial from the year 2019 by the same group of doctors from Uganda has found no significant difference in the infection rate between an antibiotic impregnated shunt and the Chhabra ventricular shunt. In India, it is being used in nearly every hospital and institute and still maintains its low cost so that it is beneficial to the poorest of patients also. What started as a small idea that was being initially executed in a small corner of a state medical college in 1978, has grown into an unimaginable project in 2019 and has benefited innumerable patients.
Comfort ushers in complacency. I am very concerned about the fact that among today's neurosurgeons, the ease of procuring the shunt system and its in vivo installation has relegated this life-saving procedure to an emergency, low priority procedure, to be performed by the doctor who is the lowest in the hierarchy of the department, who still does not have the foresight to understand the implications of his handy-work, and who has still not developed the innate skills and responsibility required for the long-term successful placement of the shunt system. This perhaps is responsible for the numerous iatrogenic complications encountered, which have often created the erroneous impression that it is the shunt system rather than the operator's technique that is responsible for the shunt failures. The practice of a shunt placement indeed needs an intense scrutiny by the current set of consultants-in-charge. Perhaps the establishment of a central data base in the country, where the placement of every shunt system, the name of the operating surgeon, and the ultimate outcome of the procedure is meticulously recorded and is mandated by law, will again usher in the required seriousness and responsibility in carrying out the cerebrospinal fluid diversion procedure.
I consider myself extremely lucky and blessed. It is not often that one enjoys the fruits of one's labours in one's own lifetime.
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[Figure 1], [Figure 2]