Saturday, 27 April 2013

What I've been reading

Image of the book cover

The Boy Who Could See Demons
by Carolyn Jess-Cooke
"Alex Broccoli is ten years old, likes onions on toast, and can balance on the back legs of his chair for fourteen minutes. His best friend is a 9000-year-old demon called Ruen. When his depressive mother attempts suicide yet again, Alex meets child psychiatrist Anya."
This book was number six of my 12 Books of Christmas, and the first one I've read that was both a good book and didn't have any sex in it. It kept me reading - I finished it when I should have been in bed - but reflecting afterwards, I found a lot of inconsistency. The demons were both real (because they revealed knowledge that the boy could not have had) and not real (because they were a feature of the boy's illness), and I don't like it when the author just leaves paradoxes lying there, no matter how gripping the story.

Image of the book cover

by Mary Roach
"Eating is the most pleasurable, gross, necessary, unspeakable biological process we humans undertake. But very few of us realise what strange wet miracles of science operate inside us after every meal - let alone have pondered the results of the research."
The sort of book that I like: interesting facts about the digestive system, told in an amusing and irreverent way. Nothing earth-shattering or particularly unexpected, but enough to keep me well entertained with a few  proper laughs thrown in. I'm going to look out for her other books, especially the one about space travel.

Image of the book cover

by Anya Seton

narrated by Diana Bishop
"Katherine comes to the court of Edward III at the age of 15. The naïve convent-educated orphan of a penniless knight is dazzled by the jousts and the entertainments of court. Katherine is beautiful, and she turns the head of the King's favourite son John of Gaunt. But he is married, and she is soon to be betrothed."
I knew very little about this book except that it's on one of my reading lists. Another reason I chose it was because it's very long, and my audio book subscription is not keeping up with the length of journeys that I now undertake. But it was definitely worth it: a beautifully written story, read perfectly, and paced to perfection. Lots of period detail that I'm prepared to believe is well-researched, and very satisfying all round. Best book of the year so far (although that's not saying much, I've had some dodgy selections recently!)

Image of the book cover

When You Are Engulfed in Flames
by David Sedaris

narrated by David Sedaris
"Sedaris proceeds from bizarre conundrums of daily life - the etiquette of having a lozenge fall from your mouth into the lap of a fellow passenger or how to soundproof your windows with LP covers against neurotic songbirds - to the most deeply resonant human truths."
I bought and read this book a year ago - for some reason I didn't include it on the blog back then - and enjoyed it so much that I felt moved to read it again. It's a series of short stories read by the author, who has a dry American humour and a very characteristic style. Sister D once gave me one of his books more than 10 years ago, and I disliked it a great deal - I wonder why? At the time, I remember thinking that his writing was cruel, but it doesn't seem that way now. Anyway, I'm re-reading it because I ran out of audio book subscription with more than 10 days to go before the next monthly credit, and I have pretty much decided to increase my subscription to two books a month while I'm spending so much time in the car.

Tuesday, 23 April 2013

Carbohydrate reference tables

Daffodils not yet blooming in the park
Leamington Spa, March 2013
People with diabetes who take insulin can do so in a number of different ways. The most common regimens are either a twice-daily injection, a fixed basal-bolus schedule of four injections, or basal-bolus with 'carb-counting'.

The twice-daily injection is 'mixed' insulin, where a proportion of the shot is long-acting and the rest is short-acting insulin. The amount is fixed, so with this regimen it is important to eat regular amounts at regular times, because if you skip a meal or a snack or don't consume enough carbohydrate, you can experience low blood glucose - a 'hypo'.

The fixed basal-bolus regimen consists of a daily shot of long-acting insulin, and three fixed injections of rapid acting insulin, one with each main meal. This is a little bit more flexible than using the mixed insulin, because you can tweak it a little by adding in or omitting some extra rapid-acting insulin as a 'correction' to pre-meal blood glucose levels that are too high or too low. It is still necessary to eat regular and consistent amounts of carbohydrate.

'Carbohydrate counting' is the most flexible option, where you still need the once- or twice-daily long-acting insulin, but you match the rapid-acting insulin to the amount of carbohydrate you eat. It allows you to skip meals, eat extra meals, eat early or late, and eat as much or as little carbohydrate as you want, but in return you have to do some work. In order to match carbs and insulin, you have to estimate how much carbohydrate is in your food, convert that to units of insulin, sometimes add in or take away a correction dose, and that's what you inject.

Estimating carbohydrate content of food can be done in a few ways. Food labels are the best estimate, as long as the food has a label and you can work out how much of it you ate. A whole margarita pizza is 337g and the label says it contains 29.1g carbohydrate per 100g, and you ate about a third of it with salad - call it 30g carbs. But if you cooked six handfuls of raw macaroni and added tomato and cheese and shared it with your partner who ate a bit more than half and there's some left over, and the macaroni packet says there's 73g of carbohydrate per 100g raw macaroni and the tin of tomatoes is 400g at 3g carbs per 100g, and then you had a medium apple, then how much carbohydrate did you have?

There are now pictorial guides and smartphone apps that will help you to estimate visually how much carbohydrate is in various foods, but they cost money, and many people don't have smartphones either. So we give patients carbohydrate reference tables that we have compiled ourselves.

For historical reasons, our hospital has two different carb reference booklets. Neither is particularly comprehensive, and I have some major concerns about their inconsistency. I don't much like either of them, so when it was suggested that I take over the project to bring them together in a single updated version, I thought that would be a great idea.

I have spent a lot of time on four different supermarket websites. They are great; nowadays you can find out all sorts of nutritional information without actually having to pick up a packet of food and look at the label. I am discovering some interesting things - for example, the carbohydrate content of sliced bread is a common starting point, and it's easy to remember that a thick slice is about 20g carbohydrate, a medium slice is about 15g and a thin slice is 10g. What I discovered in my 'research' is that supermarkets no longer offer thin sliced bread. Who knew!

I've also been using the pictorial guides, and the Bible for nutritional information: McCance and Widdowson's The Composition of Foods (Sixth Edition) which contains not only the carbohydrate content but a million other details of the nutritional composition of almost anything edible that you can think of. I must be about a third of the way through the job of revising the tables, and there are some interesting questions that I'll take to the team for a decision. For example, I think we've already decided that, unlike previous tables, we won't be rounding the figures to the nearest 5g. But how many different breakfast cereals should be included, given that cereals always have labels with nutritional information? Should we bother to include any cereals at all?

It's an interesting exercise, it's useful for me to focus on carb content of all sorts of foods, and a handy task to have when patients don't turn up for their appointments. I'm looking forward to having an agreed final version that we can all trust.

Wednesday, 17 April 2013

Low calorie sweeteners

Gilded sculptures of skeleton cutting thread of life for unfortunate mortal
Asamkirche, Munich, March 2013
We often recommend to people with diabetes that they limit their intake of sugar, but that artificial sweeteners can be used in their place. In fact, I discovered following a bit of research that there are more categories of sweeteners than I had thought, including fruit sugar (fructose), nutritive and non-nutritive sweeteners. And that the advice to avoid sugar may not actually be valid. I haven't yet got the complete picture and I certainly need to do more investigation to understand the claim (by Diabetes UK) that, if the same total amount of carbohydrate is consumed, then "sugar does not raise blood glucose levels any higher than starch."

Fructose is only slightly slower to be converted into blood glucose compared with sucrose, but usually comes neatly packaged inside fruit which has many obvious benefits. Granulated and refined fructose, however, is comparable with sucrose. Nutritive sweeteners are polyols (sugar alcohols), including sorbitol, maltitol, xylitol, isomalt and mannitol. They contain fewer calories than sugar and are better in terms of dental health, but are generally not absorbed consistently from the gut into the bloodstream. This has two consequences: firstly, it is more difficult to estimate their effect on blood glucose and therefore to administer the correct dose of insulin. Secondly, as they are not fully absorbed, then they pass on through the gut causing flatulence and producing a laxative effect.

These nutritive sweeteners are often used in 'diabetic' products, which is why we generally advise people to steer clear of those. As an aside, Diabetes UK is now calling for an end to food labelling as 'Suitable for Diabetics,' saying that it is misleading, since a report from the European Commission in 2008 states that there is no role or benefit from the use of diabetic foods, and specifically:
  • There are no grounds for developing specific compositional requirements for foods intended for people with diabetes;
  • People with diabetes should be able to meet their dietary needs by appropriate selection from everyday foods; so
  • There are no grounds for especially formulated foods for people with diabetes to manage their condition.
But I digress.

There are now five different chemicals that are commonly found in artificial (non-nutritive) sweeteners: aspartame, sucralose, acesulfame K, saccharin and stevia. In the supermarket aisles, you will find Canderel, Splenda, Sweetex, Hermesetas, Sweet & Low and Truvia as well as Silver Spoon, Tate & Lyle and supermarket own brands. There are tablets and granulated sweeteners, types designed for baking, and 'half-and-half' sugar if the transition to sweetener is a step too far. It should be possible to find something palatable.

Sometimes there is suspicion: wasn't there a report about rats getting cancer? Are sweeteners really a suitable replacement for sugar? The European Food Safety Authority (EFSA) has been tasked with reviewing all food additives for safety by 2020.  They were asked to review aspartame as a priority; their report was published in January 2013 and can be found in full on the EFSA website (ref 2013-EN-399). The following highlights are quoted directly from that report.
  • Aspartame is classified as additive E 951. 
  • The molecular shape of aspartame stimulates our taste bud receptors in a similar way to sugar, so we perceive the taste as sweet, but in fact the molecule is broken down to aspartic acid, phenylalanine and methanol in the stomach and gut before absorption. So the actual aspartame molecule does not reach the bloodstream (oral bioavailability is zero).
  • No significant acute or subchronic toxicity has been observed in animal models even at the highest doses of aspartame which could reasonably be administered. 
  • Epidemiological studies have not identified any association between brain tumour incidence and use of aspartame.
  • It is suitable for pregnant women.
So aspartame was found to be safe. And, presumably in response to some other hypothesis, the EFSA review also states that "intervention studies have consistently failed to demonstrate that low calorie sweeteners promote weight gain."

Safe as it is, an Acceptable Daily Intake (ADI) still has to be specified. This has been set at 40 mg per kg body weight per day, which for a person weighing 70 kg (11 stone or 154 pounds) would equate to 140 level teaspoons of sugar. This daily amount would be equivalent to 12 x 330ml cans (4 litres) of diet soft drink containing the maximum permitted amount of aspartame, or 36 or more cans (12 litres) at the usual concentration in diet soft drinks on sale.

Of course, there is one significant proviso - people with the inherited metabolic disorder phenylketonuria need to restrict their intake of phenylalanine, so they should definitely avoid aspartame and aspartame-containing products. The rest of us can do as we wish.

Low calorie sweeteners: Their safety, role in the diet and route to the supermarket shelf, Complete Nutrition Vol. 13 No. 1, Feb/Mar 2013
Review of data on the food additive aspartame, EFSA, 8 Jan 2013 (2013-EN-399)
Position Statement on Sweeteners, Diabetes UK, July 2007
Position Statement on 'Diabetic Foods', Diabetes UK, March 2013

Wednesday, 10 April 2013

A morning in clinic

Garden view through wrought iron gate
Sissinghurst, June 2012
I have a patient booked at 9am. When I looked forward over the clinic list yesterday, he needs an interpreter. I am still new to these hospital systems, is one booked? I asked office admin to check. Office admin called back a bit later, asking "Which language?" The records say ‘patient attended with interpreter’ but don’t say what language. A bit of detective work and deduction and I come up with a theory, but this morning, office admin regret to tell me they couldn't arrange an interpreter. Plan B: do as much as possible with drawing and hand gestures and make a new appointment, with interpreter.

I am expecting a busy morning. The nurse in charge says hello, and tells me that one of her colleagues was exhibiting symptoms of diabetes, they persuaded her to check her blood glucose, it turned out to be higher than it should be. A diabetes consultant happened to be in the clinic at the time, he agreed to see her, and now he's writing to her GP. Her blood glucose this morning was too high again, so it's looking likely that she has diabetes. I offered to talk to her after clinic about her diet.

RSB drops in to say hello. He’s officially off work on holiday today, but has some work to do towards a diploma and is more likely to get it done if he’s sitting in an office rather than at home. He admires my new purchase – a door wedge, Robert Dyas, £1.69 (I won’t bore you with the annoyance of small crowded rooms with spring-loaded doors propped open with bins and chairs). I resolve to treat him to a doorstop of his own. He offers to help with a difficult patient later on, and for the interpreter patient he suggests Language Line, which is a service where the interpreter is on the phone to both the therapist and the patient.

The nurse in charge says the receptionists have all the Language Line instructions and equipment. The receptionists fish it out of a drawer and say it’s fairly straightforward to set up, they will come and help when the patient arrives. They also mention that the difficult patient has rearranged his appointment – this is good, the slot with the interpreter was only 30 minutes which would be tough to manage, and now there will be less pressure. I reminisce about clinics at my previous job, where 30 mins would have been luxurious – most consultations had to start winding up at 10 mins. Now I can have a roomy 60 minutes if I need it.

I call up to RSB to let him know he won’t be needed for the difficult patient. The patient needing the interpreter is now 15 mins late – looks like he’s not coming. This is a huge relief, although I always feel slightly guilty about feeling glad when someone doesn’t come. Now I only have two more patients to see this morning, plus the possible new diabetic colleague. I talk to reception about re-booking the interpreter patient, and they are surprised he hasn’t come, because they have seen him a number of times before and say that he always attends his appointments. We look a bit harder at the systems, and it looks as though his appointment was changed from two days ago. If the change was made very recently and he was sent a letter with the new appointment rather than being contacted by phone, the letter would probably not have arrived in time.

Next patient – looks like another DNA. I dig a bit deeper, and it looks as though three out of the four patients this morning were switched from two days ago (the fourth is the difficult patient, who we already know won’t be coming). I am now not expecting a busy morning. I ask office admin when the appointments were changed. It was back in January, so that’s not it. I now have time to talk to my nursing colleague about what would be best to eat, and then the last patient does actually turn up - one out of four.

P.S. RSB was delighted with his door wedge.

Friday, 5 April 2013

Pumping insulin

Squashes of all sizes and shapes
October 2012
In the early days of insulin-treated diabetes, people with Type 1 diabetes used to draw up insulin from a vial and inject using a hypodermic syringe. Nowadays, most people use 'pen' devices. These have a pre-filled insulin cartridge, a way of 'dialling' the number of units of insulin you want to inject, and a very tiny thin needle, which can be as little as 4 mm long. [Note: the linked website made me chuckle with its description of one of the insulin pens as "designed for people who don't like needles and children."]

However, today's blog is about one of the newer developments in insulin delivery, the insulin pump. This consists of an insulin reservoir containing rapid-acting insulin that provides continuous subcutaneous insulin infusion, 24 hours a day, via a cannula inserted into the skin. Most insulin pumps have a tube between the reservoir and the cannula, but there are tubeless types as well. The cannula can stay in place for two to three days. You can safely disconnect for about an hour, for showering, sports, trying on clothes etc.

For those of us who don't have Type 1 diabetes, our insulin level is adjusted minute by minute in response to all sorts of hormonal signals, such as levels of adrenaline, cortisol and growth hormones as well as the amount of blood-borne glucose. To imitate the insulin-secreting action of the normal pancreas, people on multiple daily injections (MDI) inject two types of insulin: long-acting once or twice a day, which is designed to release slowly into the circulation over a period of around 24 hours, and quick-acting insulin that lasts about 4 hours, injected at mealtimes to deal with the glucose entering the circulation from the carbohydrates that are eaten.

Like the human pancreas, an insulin pump only has one type of insulin, but two separate ways that it is delivered. There is a background or 'basal' rate that delivers the constant low-level drip of insulin day and night. At mealtimes, the pump user still has to decide how much 'bolus' insulin to give and at what rate - the pump doesn't remove the need to test blood glucose and calculate the carbohydrate content of food, and the injected insulin still doesn't act as quickly as insulin secreted by the pancreas directly into the blood circulation. But there are advantages to having more control over the amount of insulin going in.

For example, the basal rate can be adjusted on an hourly basis, and some pump manufacturers set up their pumps with a variable basal rate to match the general circadian pattern found in most people. A pump can also be of great benefit when exercising or drinking alcohol, because both of these activities tend to lower blood glucose, and it can be frustrating to have to take extra carbohydrate in order to avoid a hypo, especially if you're trying to lose weight. With a pump, a temporary lower basal rate can be set. [Note: exercise with diabetes is a fascinating physiological puzzle that I've been trying to figure out for the past few weeks, and I'm sure a blog post will appear on that subject very soon.] If you're on a once-daily injection of background insulin, then you can only adjust the background rate over a period of days.

There's lots of flexibility with the bolus insulin too (which could almost be done with MDI if you were prepared to give several extra injections). Many people find particular foods take ages to digest, especially if there is a lot of fat mixed with the carbohydrate (pizza is a typical example). If they inject just before or just after the meal, the rapid-acting insulin deals with the first surge of glucose but then its period of action is over before the food is fully digested, and their blood glucose level drifts upwards. With a pump, you can program the meal bolus to be delivered either in multiple bursts (just after the meal and then 30/60 minutes after or whatever) or at a constant rate over a period of time. This also works for really long meals, like a posh dinner with big gaps between courses, or for buffets and parties where you might be grazing over a long period of time.

Other advantages with the pump: it can help you with the sums, so you can be more accurate with your insulin dosage. For example, if you have calculated that your meal contains 48 grammes of carbohydrate and your ratio is 1.8 units of insulin per 10 grammes of carbs, the pump can do the calculation without blinking and deliver fractions of a unit (8.64 units in this case). On MDI, everything would be rounded off because we don't hold 1.8 times tables in our heads, and most pens can only deliver whole units of insulin (50 g carbs at 2 units/10g = 10 units of insulin). The ratio of insulin to carbs may change through a day (many people are more insulin resistant in the morning) and that can be programmed in to the pump software. And if you tell it your blood glucose reading, it can also suggest a correction dose, which can even take account of 'insulin on board', i.e. any insulin previously injected that may still be having an effect.

Of course there are disadvantages, not least the cost of the pump, which is available on the NHS only for those who meet the funding criteria. There's the inconvenience of wearing the pump at all times, which can place limits on clothing: at the beach, or on special occasions (e.g. with a party dress). The most worrying to me, based on what I've seen of patient care for diabetes in hospital, is that with a pump you have no long-acting insulin on board, and if your pump is disconnected for any reason your blood glucose level will start to rise after just an hour or two. If this happens at home, perhaps because of a blocked tube or kinked cannula, you should spot it and be able to deal with it. In hospital, the general awareness of diabetes is fairly minimal, and knowledge of insulin pumps is non-existent. There might be a risk of not being given insulin because it is assumed that you will have some level of background insulin on board, and that could have serious consequences.

Where I work, there are special clinics for pump patients, and I attended one of the monthly education sessions where pumpers can drop in to catch up on particular aspects of treatment. My colleague RSB is covering the pump clinic at the moment, so I don't yet have much contact with this group of patients, except for Mr M, who is a pump user, and who is always happy to enhance my knowledge of the issues.

[Update: Mr M informs me that contrary to my assumption, the first wearable insulin infusion pump was invented by Dean Kamen in 1970, while the first insulin injection pen device was introduced and marketed by Novo Nordisk in 1985. Thank you, Mr M!]

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