There's also the perverse incentives in the american medico-legal system: surgeons get sued for not performing surgery, or performing surgery badly, but they rarely get sued for performing 'unnecessary' surgery unless its completely egregious. If the patient has a history/examination which could indicate a need for surgery, and the patient has given informed consent, the surgeon is very unlikely to be succcessfully sued for operating. I'm not implying this is a consious decision on their part, rather a subconscious influence of their training, anecdotes from other surgeons etc.
The problem with that anecdote is that its all with the benefit of hindsight. Certainly, in this instance, non-operative management was appropriate. But the more important question is what on average happens to the entire 'population' of people presenting with Hadfield's symptoms and signs if they're managed operatively and non-operatively.
If we imagine a disease where non-operative management leads to a 50% mortality rate within a year. If we take 100 people with this disease and manage them non-operatively, at the end of a year we'll have 50 people saying how pleased they are to have avoided surgery and complaining about the aggressiveness of surgeons, and we'll have 50 dead people.
That's why the diagnosis and management of disease must be informed by high quality clinical studies, rather than anecdotes.
Look at the graph in figure 2 - the massive overlap in the interquartlie ranges suggests that any differene in the median values can be attributed to random variation within the samples, rather than a true difference in the populations.
Also its better to quote an absolute rather than relative reduction, so the difference is really 3.6%
There's a role for a human-machine hybrid, and indeed there are also quite complicated control systems in work in anaesthesia. As an example, syringe pumps which perform pharmacokinetic calculations: you enter the patient's height, weight, sex, and age, then set a target plasma drug concentration and the pump uses complex pharmacokinetic models to determine how much drug to deliver to acheive that goal and maintain it. I can imagine more elegant systems coming in the future - ie a pump that can adjust drug delivery rates to maintain a given blood pressure. But the overall process of safely delivering an anaesthetic, from pre-operative assessment to post-operative recovery and discharge, is far beyond automating at the moment.
A common comparison is drawn to flying a plane - its a proceduralised and mechanical process for a lot of the time, but occasionally unexpected things happen and you need knowledge and skills to react quickly and prevent serious injury and death. Its like flying a plane but if every plane was built differently with no instruction manual, some of the planes are badly broken before you take off, and someone's trying to repair the engines in mid air.
I'm currently revising for my anaesthetics exams. The things I'm meant to know include:
* The physics and mechanical principles of all the equipment I use, from the ventilator to the pulse oximiter - so that I can identify when and how it might fail and how to respond
* The pharmacokinetics, pharmacodynamics, and mechanism of all the drugs I might use - so I can understand their effects, side-effects, and interactions
* The physiology and function of the human body, including the respiratory, circulatory, neurological, renal, gastrointestinal, musculoskeletal, and immune systems - so I can understand how anaesthesia effects these systems, and how diseases and disorders of the systems will interact with the anaesthetic and how problems can be identified and treated
* The anatomy of the body, with particular focus on the head and neck anatomy to aide in intubation and airway procedures, and neuro-anatomy to aide in regional anaesthetic techniques
* The anatomical, phsiological, and pharmacological consequences of pregnancy, childhood, old-age, and a huge variety of acute and chronic diseases - so I can understand and adapt anaesthetics to these conditions
ICU ventilators are surprisingly complicated machines, we've just brought some HAMILTON-C6 machines at work if you want an idea of the top of the line. Ventilating sick COVID patients, or indeed anyone with ARDS, is one of the most challenging things we do in intensive care. Even with high end commercial ventilators, the mortality rate for intubated COVID patients is >70%.
I would consider the following a bare-minimum feature set for a COVID patient ventilator, any less and it would do more harm than good:
- cycle between an inspiratory and expiratory phase
- during the inspiratory phase, deliver an adjustable volume of gas (in the region of 6 ml per kg of patient's body weight) using as little pressure as possible, with an adjustable upper limit of pressure (in the region of 30 cmH2O)
- during the expiratory phase provide an adjustable pressure against exhalation (in the region of 0-30 cmH2O)
- allow blending of air and oxygen to deliver an adjustable inspired oxygen fraction
- allow the timing of the inspiratory and expiratory phases to be independently varied, thereby allowing the respiratory rate and the ratio of inspiration to expiration time to be controlled. Permit respiratory rates in the range of 8-60 breaths per minute
- measure and display the pressures and volumes within the respiratory system
- allow adjustable alarm-limits for pressures and volumes, and provide clear audible and visual alarms if these values are exceeded
For added patient safety and benefit, the following would be helpful
- measure inspired and expired oxygen and carbon dioxide content, and display both on a continuous waveform graph
- allow the patient to initiate the inspiratory phase by sensing patient inspiratory effort and providing pressure support for inhalation; ie sense when the patient inhales and deliver 10-15 cmH2O pressure for 0.5 seconds to augment inhalation
Doesn't seem to be very helpful - In a multicenter cohort of 302 patients with MERS coronavirus, 92% of patients treated with BiPAP failed this modality and required intubation (Alraddadi 2019)
ICU ventilators are surprisingly complicated machines, we've just brought some HAMILTON-C6 machines at work if you want an idea of the top of the line
I would consider the following a bare-minimum feature set for a COVID patient ventilator, any less and it would do more harm than good:
- cycle between an inspiratory and expiratory phase
- during the inspiratory phase, deliver an adjustable volume of gas (in the region of 6 ml per kg of patient's body weight) using as little pressure as possible, with an adjustable upper limit of pressure (in the region of 30 cmH2O)
- during the expiratory phase provide an adjustable pressure against exhalation (in the region of 0-30 cmH2O)
- allow blending of air and oxygen to deliver an adjustable inspired oxygen fraction
- allow the timing of the inspiratory and expiratory phases to be independently varied, thereby allowing the respiratory rate and the ratio of inspiration to expiration time to be controlled. Permit respiratory rates in the range of 8-60 breaths per minute
- measure and display the pressures and volumes within the respiratory system
- allow adjustable alarm-limits for pressures and volumes, and provide clear audible and visual alarms if these values are exceeded
For added patient safety and benefit, the following would be helpful
- measure inspired and expired oxygen and carbon dioxide content, and display both on a continuous waveform graph
- allow the patient to initiate the inspiratory phase by sensing patient inspiratory effort and providing pressure support for inhalation; ie sense when the patient inhales and deliver 10-15 cmH2O pressure for 0.5 seconds to augment inhalation
I'm an anaesthetics and intensive care trainee, so I know something about ventilation. The reason COVID-19 patients need to get ventilated is due to a failure of oxygenation - the infection causes direct lung injury (ARDS) which impairs oxygen absorption in the lung tissue. Normally we breathe room air, which is 21% oxygen, this drops to around 10% oxygen in the arterial blood due to inefficiencies in the absorption in the lungs. In a normal healthy patient breathing 100% Oxygen, their arterial oxygen content would be around 90%. ARDS significantly impairs oxygen uptake by the lungs, in severe cases patients breathing 100% oxygen may have arterial oxygen concentrations of just 8-10%.
The purpose of ventilation in these severe ARDS patients is to augment oxygenation of the blood, using a combination of techniques including end-expiatory positive pressure and inverse-ratio ventilation, among others, and support the fatiguing respiratory muscles. Because the lungs of COVID-19 patients are already injured by the infection, they are very prone to further ventilator-associated injury. Modern intensive care ventilators have complicated computer-controlled 'modes', which allow precise regulation of ventilatory volumes, pressures, rates, timing, and gas blending. The ARDSnet trials in the early 2000s demonstrated the importance of carefully managed 'lung protective' ventilation, poor quality ventilation is likely to cause further lung injury and make the patient worse, not better. Therefore amateur ventilators are unlikely to be beneficial in COVID-19 unless they can provide similar lung protective ventilation, which would make them quite complicated.
Additionally, ventilation is just one component of the management of sick COVID-19 patients. First you need to pass a breathing tube into their trachea, which is a challenging and risky procedure when performed by a skilled operative in a otherwise well patient, let alone someone on the brink of respiratory failure. Once intubated you will need to keep them deeply sedated, otherwise they will strain against the ventilator and make effective ventilatory care impossible. This requires equipment, drugs, and skilled staff, all of which are going to be in short supply.
I work in the NHS, this is the current user experience
1. Type in user name and password onto computer
2. Logs in to windows, normally taking ~60 seconds, unless you've got the computer where the WiFi signal is poor (yes, WiFi on desktops!) and you get a 'no log in servers'
3. Windows finally loads, click the icon for the software for viewing blood test results
4. An internet explorer window opens, then closes, then after 10 seconds the software opens
5. Type in your username and password, wait 10 seconds
6. Now I want to prescribe some medications, close the first software (computer can't cope with two things open at once), click the logo for the prescribing software
7. A Google Chrome window opens, slowly loads the prescribing software website
8. Type in username and password
9. Navigate through the slow and unintuitive prescribing software
10. Oh wait, I can't prescribe this particular drug without checking a blood test result, close the prescribing software and go to step 4
11. Some alarm goes off, so I have to lock the computer and run. Return from dealing with the alarm, go back to step 1
That wouldn't be able to detect a heart attack, its to look for atrial fibrillation (AF), which is a long-term abnormality of heart rhythm associated with increased stroke risk
To properly rule out a heart attack you would need
a) A twelve-lead EKG - which requires twelve wires to be connected to specific locations on your body
and
b) Blood tests
Therefore for a consumer-grade device to properly rule out a heart attack it would need to be a large EKG machine with multiple connectors as well as a blood test analysis machine. And that's not even considering that proper analysis of an EKG trace requires a trained medical professional, as the automated traces are notoriously unreliable
A pulse oximiter measures the oxygen content of arterial blood in the peripheries. A heart attack is caused by a localised blockage of the arteries to the heart, causing reduced oxygen and nutrient delivery to an area of heart muscle. A heart attack alone would not affect peripheral oxygen content unless it was severe enough for a complication such as heart failure to develop, but by that stage it's much too late.
Indeed the vast majority of patients with an acute heart attack would have completely normal pulse oximetry findings, the only way to properly diagnose a heart attack is with an electrocardiogram (EKG) and/or blood tests to look for markers of heart muscle damage
If inputs > outputs, there is net energy storage (as fat or protein)
If inputs < outputs, there is net energy deficit (lost from fat and protein)
Inputs = food and drink consumed
Outputs = Basal metabolic rate (BMR) + energy used for activity + energy lost in urine and faeces
Faeces caloric content varies between 50-350 kcal / day, urine 91–117 kcal / day [1]
Basal metabolic rate is primarily decided by fat-free mass, mass, and age, 26% of BMR is not defined by these parameters. Mean BMR is 1500 kcal/day, and 26% of this represents a variability of 1305-1695 kcal per day.[2]
(350-50) + (117-91) + (1695-1305) = 716 kcal
Therefore two people of identical age, fat-free mass and mass who consume identical caloric intake and perform identical exercise will have, at most, a variance of 716 kcal / day in their energy expenditure from the variance in urinary and faecal caloric loss and BMR
[1]: Rose C, Parker A, Jefferson B, Cartmell E. The Characterization of Feces and Urine: A Review of the Literature to Inform Advanced Treatment Technology. Critical Reviews in Environmental Science and Technology. 2015;45(17):1827-1879. doi:10.1080/10643389.2014.1000761. Section 3.2.5 and Section 3.6.4
[2] Factors influencing variation in basal metabolic rate include fat-free mass, fat mass, age, and circulating thyroxine but not sex, circulating leptin, or triiodothyronine. Johnstone AM, Murison SD, Duncan JS, Rance KA, Speakman JR. Am J Clin Nutr. 2005 Nov;82(5):941-8.
That robot performs sedation, not general anaesthesia. Sedation provides a slight depression in awareness and pain sensation, and is much easier than full general anaesthesia, in which the patient is completely paralysed, unconscious, and insensate. General Anaesthesia generally requires intubation, a complex practical procedure which can go wrong very quickly, and kill people very quickly. It requires close monitoring of numerous parameters, some of which are digital measures (blood pressure, heart rate, etc) but others are quite subjective, such as the patient's appearance and the current stage of the surgical procedure.
The claim that this device is a replacement for an anaesthatist is similar to claiming that an automated wheel balancing machine will one day replace car mechanics. Certainly it can perform one specific component of one kind of anaesthesia, but it is far cry from the full skill set of an anaesthatist.
I saw an asthmatic woman in A+E today, all her blood tests were in the 'normal' range, does that mean she's well?
No, she was very unwell. However the test results would either be normal in someone regardless of the severity of their asthma, or would be expected to be 'abnormal' in someone with mild asthma, and 'normal' in someone with severe asthma. The ability to interpret those test results, and take a history and examine the patient is important.
Similarly, we used the latest evidence-based guidelines to assess the patient's asthma severity, and based on several objective criteria (breathing rate, oxygenation of blood, peak flow, etc) the guidelines determined she had moderate-severe asthma
However we called the ICU doctors to see her. The ICU consultant, with many decades of experience managing acutely unwell asthmatics, simply looked at the patient for two minutes, observing how her chest moved during breathing, and the sounds and respiratory effort she was making, and decided to take her to ICU. This was a good decision as she ended up deteriorating and requiring very aggressive treatment. Whilst guidelines can make a suggestion based on the interpretation of some objective data points, the ability to assess a patient as a whole, based on history and examination, is still an important skill, and one which it is hard to automate
There are certainly handoff errors, but the vast majority of these can be avoided with a well structured handoff with safety-checks built in. The problems that make handoff bad include:
1) Handoff being done at the end of a long shift, so the doctors handing off their patients are tired, sick of working, and desperate to go home
2) Handoffs being interrupted by sick patients (understandably so) - I was once in a handoff that was abandoned half way through because of a cardiac arrest that half the team had to run off to
3) Rubbish handover systems - most hospitals use hand written notes on scraps of paper carried round by doctors; these can be lost, misread, or accidentally forgotten. There are some technological solutions being developed, but few hospitals have employed them so far