Anaesthesia Product News

Nobody believes in the infallible God-like nature of clinicians any more. This is a good thing, as physicians should be held to account and not simply allowed to bury their mistakes. But who holds the account?

Constant scrutiny is mainly provided by the general public and the media. Unfortunately, Government policy is shaped by the uninformed and emotive views of these two large and powerful groups. Expensive and unproven advances in medicine that may improve the lives of small but vocal groups drown out the needs of the many.

Government seems powerless to wrench itself away from media-driven hysteria, and hard-earned tax money pours in the wrong direction. The establishment of the National Institute for Clinical Excellence (NICE) was supposed to overcome these problems, but has itself become overwhelmed by public pressure and a Government desperate to appear pro-active in the eyes of the media. Rational allocation of appropriate medical therapy, the primary aim of NICE, has been hijacked, to the detriment of us all. For example, if vascular biologists and cardiologists received the same degree of research funding and media interest as breast cancer, hypertension would probably be a thing of the past. However, 70-year-olds with strokes bore the public and don’t photograph well, so do not excite media interest. Consequently, healthcare provision in the United Kingdom is so chaotic that no-one is happy.

Why has NICE faltered so badly? In my view, the problem lies in the way medicine has developed as a speciality. The public genuinely believes that doctors are constantly engaged in frontline research. The man in the street imagines clinicians stepping from the wards straight into the laboratory, looking for the next big advance. In other words, the public and the media regard medicine as a scientific endeavour.

Of course, in reality, nothing could be further from the truth. In the United Kingdom, the practise of medicine is mainly by anecdote, rote learning and post-graduate experience. The majority of my own speciality (anaesthesia) regard basic science as irrelevant to patient care. In many Universities, the modern medical curriculum relegates pure science to a secondary role, in favour of a more ‘patient-orientated’ approach. The theory is that the perceived loftiness and arrogance of doctors compromises their ability to practise medicine, and should be replaced by a more ‘touchy feely’ approach.

I fully agree that a good bedside manner and the ability to listen are crucial. However, I also contend that a doctor’s ability to practise medicine is dangerously compromised if the clinician does not understand the physiology and pathophysiology of the disease he or she is treating. If a knowledge of pharmacology is lacking, the hapless doctor cannot decide the veracity of claims made by pharmaceutical companies. Without an understanding of research techniques, clinicians cannot make informed judgements about original articles published in medical journals, let alone perform the research themselves, even assuming the Government were able to make the funding available.

One of the principle reasons for public hysteria when medical mistakes occur is that it is assumed that medicine is practised according to sound scientific principles. According to this logic a failure to treat a disease must therefore represent incompetence rather than ignorance. The truth is that with the exception of some vocal middle-class individuals, the average person cares more about being cured than sympathetic hand-holding.

The desire of the individual to have his disease adequately treated or cured cannot be reconciled with the anecdotal approach to medicine that is practised in the UK. Hence the rise of NICE and that most pernicious ‘validation tool’, evidence-based medicine. The laudable concept of evidence-based practice is that treatment of a disease is based on research published in the medical literature. The flaw, as we have seen, is that very little original research is actually carried out. This leaves NICE with very little to go on. Where then to obtain the evidence? The answer seized upon has been to trawl the medical literature for other people’s research on a particular topic, pool it together, and then try to weight it to provide a consensus. This is the technique of meta-analysis - a technique much loved in British medical academia because it is impossible to perform any real research in UK universities, owing to a combination of lack of funding and daunting Ethics Committee requirements.

Meta-analysis requires only a computer and an appropriate software program. Does meta-analysis provide accurate conclusions? A recent study showed that the quality of meta-analyses on Critical Care topics was poor. The most common mistakes noted by these authors were the lack of a proper literature search, avoidance of bias (i.e. selecting some studies for inclusion in the meta-analysis and not others) and most alarmingly, failing to check the validity of the study and therefore its relevance to the overall meta-analysis.

Examinations of meta-analyses carried out in other specialities have led to similar conclusions. You might want to think about this the next time you base your practice on a meta-analysis or accept a study from a pharmaceutical company based on this methodology. You could be practising junk medicine.

Nevertheless, because of a lack of basic research at the fundamental level, and lack of proper randomised controlled trials at the sharp end, this is all you, me and NICE have to go on.

Even worse than all of this is the curse of expert opinion. Here again, the public perception is that expert opinion is based on that expert’s personal research and a clear appraisal of a supposedly wide body of medical literature. When this perception is shown to be untrue, patient and media indignation follow, sometimes with disastrous results for the expert, never mind the patient.

Recent well-publicised events revolving around an expert witness and a failure to understand statistics is a good example of this. Expert opinions are just that, an opinion. With luck it is based on original published research, but in practice opinion is frequently the result of experience and bias. Most experts don’t have the time or money to do the original research. In our chaotic medical world, where there are few hard facts to go on, panels of well-intentioned experts are convened to provide a consensus on the management of individual diseases. These consensus reports filter down to the rest of us as guidelines and protocols, often through bodies such as the Royal Colleges and NICE.

Consensus is a bunch of people having the same opinion, e.g. a political party. It is not science. Junk medicine again. Anyone who wishes to delve further into the difference between consensus and science is referred to the seminal lecture on the topic by the author Michael Crichton. The great danger here is that not only are we being made to practise according to what is essentially untested opinion, but that the judicial system has a touching faith in the validity of these protocols, and it is becoming increasingly difficult to deviate from them without being accused of malpractice, even if original properly conducted research is available to refute these protocols.

What is worse, neither the expert panels nor the protocol generating bodies can be held accountable if the recommended therapy is ineffective or even harmful. This is a very dangerous state of affairs for doctors and patients alike. How can we extract ourselves from the practise of junk medicine?

The situation at present is so bad that it will take many years to change. The faults that have led to junk medicine are endemic and need to be corrected at grass-roots level. This means a radical change in the teaching of medical students. The first step is that basic science must be re-added to the medical curriculum. It must be taught in such a way that the relevance of science to treating patients is clear. At the moment such relevance is utterly lacking in UK medical curricula. These changes need to translate into a fresh approach to basic science at the level of Royal College examinations. The Colleges need to consider the inclusion of research modules as an integral part of post-graduate medical training. Only a few clinicians will wish to make a career out of research, but we all owe it to our patients to be able to understand and criticise the research carried out by others. We need to be able to shine a harsh light on the poor meta-analyses and the government (NICE) generated protocols that hold us and our patients to ransom. Only then can we restore public faith in medical science.

References

Delaney A. et al: A Systematic Evaluation of the Quality of Meta-Analyses in the Critical Care Literature. Critical Care 2005; R575-R582.
Crichton M.: Aliens Cause Global Warming. Caltech Michelin Lecture January 17th 2003. www.sepp.org/NewSEPP/GW-Aliens-Crichton.html

Artificial Respiration has a long and distinguished history. Mouth-to-mouth resuscitation is mentioned several times in the Old Testament. By the 18th Century, people were looking for a more ‘scientific’ way to provide artificial respiration. The Royal Humane Society of England, the 18th Century equivalent of the Resuscitation Council, advocated the use of bellows to inflate the patient’s lungs. Although the lives of some drowning victims (and other forms of trauma) were saved by this technique, this early mechanical device suffered all the disadvantages of positive pressure ventilation with none of the advantages. The obvious disadvantages were fixed respiratory frequency and force, which were entirely dependent on the bellows’ operator. Furthermore, no adjustments could be made for patient size or lung compliance. The unfortunate result of this was barotrauma, even to the extent of burst lungs - a disastrous outcome.

By the mid-19th Century the bellows technique had fallen into disuse because of these problems. Unfortunately, mouth-to-mouth resuscitation was not re-instituted, because, in a staggering mis-appliance of science, it was thought that expired air did not contain enough oxygen to support bodily functions. It was at this time that the various manual techniques of ventilation, which mainly involved turning the patient prone and pumping either their arms or their back, were introduced. These formed the mainstay of resuscitation practice until the middle of the 20th Century.

Royal Humane Society Resuscitation Set from 1774. Photograph reproduced with the kind permission of the Association of Anaesthetists of Great Britain and Ireland.

Mouth-to-mouth resuscitation was not re-introduced until the 1960s, when proper studies demonstrated that prone methods of resuscitation not only produced a small tidal volume in comparison to mouth-to-mouth ventilation, but only worked if the patient’s airway was not obstructed - a point that had been previously overlooked. For these reasons the principles of Airway, Breathing and Circulation were introduced at this time.

While all this was going on, more sensible individuals were attempting to develop a true artificial respiration device. Several 19th Century workers developed variants of a box, which encased the patient’s body and had a rubber seal around the neck. The pressure within the box was then varied by the use of a pump, which was turned by hand, by steam or by electricity depending on chronology. Of course these were all forerunners of the gold standard, the Iron Lung - developed by a Chemical Engineer, Dr Phillip Drinker, and a Paediatrician, Dr Louis Agassiz Shaw, at Harvard University. Interestingly, their work was funded by the Consolidated Gas Company, who saw the funding of this research as a way to improve safety standards for their employees. Unlike its predecessors, the iron lung or Drinker Respirator was a negative pressure ventilator. Air was pumped out of the sealed chamber to create a negative pressure around the patient’s chest and abdomen, thus inducing passive inspiration. Expiration was provided by passive recoil.

The iron lung saved many lives in the polio epidemics of the early to mid-20th Century. Unlike the bellows technique of 100 years earlier, the iron lung could accommodate many different sizes of patient - from child to adult. In addition, the pump rate and pressure changes could be altered to some extent to tailor the device to the needs of the individual patient. As it was electrically driven it could provide long-term ventilation for those left with chronic respiratory paralysis post-polio. Many people survived for several years in this manner.

Nevertheless, there were many practical problems with the iron lung. They were large, heavy and noisy devices. Access to the patient to provide basic nursing care was difficult, and although portholes allowed some patient contact, bedsores were an intractable problem. A potential life-threatening complication of whole-body negative pressure ventilation was so-called ‘tank shock’. This phenomenon was caused by venous pooling in the abdomen as a result of the application of negative pressure, leading to reduced cardiac filling and severe hypotension.

Several companies attempted to overcome these difficulties, essentially by shrinking the iron lung down to a metal shell, which covered only the anterior chest wall. The pumping system remained the same as the iron lung, simply generating pressure over a smaller area. The metal shell was referred to colloquially as a cuirass, in recognition of its similarity to the breast plate of a suit of armour. The non-invasive negative pressure cuirass ventilator allowed a more normal existence for the patient, but it was still a bulky and noisy device. Additionally, the tidal volume that could be generated by the cuirass was smaller than that of the iron lung, and so this machine could only be used in the more chronic phase of the polio disease process.

During the early part of the 20th Century, the use of volatile anaesthetics for surgical anaesthesia was coming into its own. Of course, the use of substances such as chloroform and ether resulted in loss of laryngeal reflexes and an increase in airway secretions, not to mention the risk of larnygospasm in a lightly anaesthetised patient, making a general anaesthetic a bit of an adventure for all concerned.

Endotracheal intubation and intermittent positive pressure ventilation (IPPV) were developed during this time. There is no room to delve into their history in this article, but the point is that by the time of the Scandanavian polio epidemic in 1952, techniques of intubation and positive pressure ventilation were making their way out of the theatre suite and into the long-term care of polio victims. Studies performed at this time demonstrated that IPPV produced a higher tidal volume and better secretion clearance than the iron lung, not to mention greater ease of nursing care. The reader can see here the development of that most controversial and expensive of healthcare options, the Intensive Care Unit.

If IPPV is so good, why reconsider its use? The problem lies in large part with the way in which ITU has developed as a speciality. The early polio victims were generally young and had no primary lung disease. Crucial issues in modern Intensive Care, such as use of high oxygen fractions and high tidal volumes, mattered less in these individuals. In any case, ventilator-associated problems probably went undetected because the patient had so many neurological problems associated with his polio that distracted attention from his lung condition. As development of ITU has progressed over the last 40 years, the type of patient that is treated has changed completely, and is more likely to be an elderly individual with either a primary lung problem (eg pneumonia) or a secondary insult related to generalised sepsis, for example. In addition there may be more than one organ failure. We are a long, long way from the polio epidemics of yore.

The support of respiration via positive pressure ventilation leads to well-recognised problems of its own. The most serious pathologies are ventilator-associated pneumonia and ventilator induced lung injury. These complications are related firstly to the fact that even sticking a large suction cather? down an endotracheal tube will not clear secretions if positive pressure ventilation is pushing them further in, and secondly continual alveolar distension by positive pressure causes alveolar damage and augments any inflammatory process already going on in the lung.


The Oxford Inflating Bellows, 1953. This type of bellow was saw a lot of use in the treating of polio sufferers. Designed by Richard Salt at the Nuffield Dept in Oxford, the version shown is the resuscitation version, not having the magnet for disabling the expiratory valve. Reproduced by kind permission of the Sheffield Museum of Anaesthesia, Sheffield Teaching Hospitals NHS Foundation Trust.		A KIFA cuiras, c. 1952. This cuirass can be seen in the Sheffield Museum of Anaesthesia. Reproduced by kind permission of the Sheffield Museum of Anaesthesia, Sheffield Teaching Hospitals NHS Foundation Trust.

By the 1980s, an alternative to intubation and IPPV was already being sought. Non-invasive positive pressure ventilation had been used to treat pulmonary oedema in the immediate post-war period, but technical difficulties resulted in the technique falling into disuse within about 20 years. The breakthrough was the development of the nasal continuous positive airway pressure (CPAP) mask in the early 1980s. This device was initially developed for use in chronic respiratory problems such as muscular dystrophy and sleep apnoea. Improvements in blood gas measurements and reduced work of breathing were soon noted, and to cut a long story short, CPAP has found its way into ITU and High Dependency Management as either a method of assisting weaning from mechanical ventilation, or even avoiding mechanical ventilation in the first place. Modern variants, such as bi-level positive pressure ventilation (Bi-PAP) have further improved patient outcome, and definitely reduce the rate of intubation.

But all forms of non-invasive positive pressure ventilation have distinct disadvantages. They all depend on a facial seal of some sort, whether that be a facial or nasal mask or a helmet. Patients and even healthy controls report feelings of isolation and frustration, which leads to poor patient compliance (between 15% and 50% non-compliance for this reason alone, depending on the study). Many patients with respiratory failure already feel claustrophobic, and the application of a tight-fitting mask can exacerbate this sensation. Facial and corneal abrasions can occur as a result of the tight-fitting mask and the relatively high flow of oxygen. From a nursing point of view, air leaks are a common and tiresome complication, made worse by the fact that the mask or helmet has to be removed to allow communication, eating, and oral hygiene. From a medical standpoint, some patients such as those with chronic obstructive airways disease and emphysema, may develop air trapping and secretion retention.

So, where next? Curiously, not far from where we started out, a new device on the market is using the old cuirass style ventilator in a different way to provide support in respiratory failure. This is the RTX Respirator (Deminax Medical Instruments Ltd). The RTX Respirator is a non-invasive biphasic cuirass ventilator. By biphasic, it is meant that the machine develops a negative pressure within the cuirass to assist inspiration, and a positive pressure to assist expiration. Thus both components of the respiratory cycle can be provided. The Respirator consists of a plastic cuirass, which fits over the patient’s chest, using a foam seal. A plastic tube leads to a power unit, which generates negative (inspiratory) and positive (expiratory) pressures within the cuirass. A separate sensor detects intra-thoracic pressures, and the pump software can be set to trigger pressure changes in parallel with the patient’s own respiratory effort. The patient’s respiratory cycle determines the respiratory rate, although default settings allow the software to generate a breath if no inspiratory activity occurs within a certain period of time. These features overcome the problems of fixed frequency and tidal volume inherent in the old cuirass systems of the early 20th Century. The positive expiratory pressure, combined with a ‘cough and sigh’ mode, help to improve secretion clearance. Further, a physiotherapy secretion clearance facility uses high frequency oscillation to loosen mucous plugs and decrease their viscosity. The current author has found this technique useful in the clearance of intractable secretions in post-operative patients.

In summary, the new biphasic cuirass ventilator not only seeks to avoid intubating the patient, but to do so in a way that overcomes all the problems described above. There is a great deal of anecdotal evidence to suggest that the RTX Respirator fulfils these requirements. The problem is that at present, there are no randomised controlled trials demonstrating its efficacy over other techniques, and this information is desperately required. The current author hopes to construct such trial in the near future, but to obtain an accurate answer, a great many patients will be required, and a multi-centre trial conducted. Watch this space. . .

References

Chari S, King J, Rajesh PB, Stuart-Smith K: J Cardiothorac Vasc Anesth 2004; 18 482-485.

RTX Respirator is a registered trademark of Deminax Medical Instruments Ltd.
Dr Karen Stuart-Smith has undertaken and published research using an RTX Respirator provided free of charge for research purposes by Deminax Medical Instruments Ltd.