Transport to Hospital Times and Survival: The Case of Snake Bite

High-income countries have well developed ambulance services. However, investment in acquiring and maintaining effective systems of transport for sick and injured patients does not seem to have been a priority for many low- and middle-income countries (LMICs).  In some settings, for example post conflict states, lack of ambulance services is understandable; what is the point of transferring people to non-functioning or non-existent hospitals? But most LMICs do have a network of hospitals providing emergency care. The point must be reached where the opportunity costs of further improvements in fixed facilities is less than those of providing transport to reach the facilities in the first place.

There are many types of transport: motorised ambulance, motorbike ambulance, bicycle ambulance, and private vehicles. These different types of transport operate with or without trained clinical staff to accompany the patient. Moreover, there are many different types of clinical scenario where rapid transport may be required, from a very sick child to major trauma. There are also many different settings, rural vs. urban for example. The cost-effectiveness of different forms of transport will vary considerably between these different types of vehicle, different staff configurations, different clinical scenarios, and different geographical settings. Thus, the cost-effectiveness of a given type of transport, staffed in a given way and dealing with a particular clinical scenario, may have different effects and costs in different geographic and social contexts.

However, there is one unifying variable that underpins all cost-effectiveness calculations: this is the function that relates marginal changes in transport times in reaching a facility to the contingent marginal changes in outcome. In many circumstances death is the primary outcome of interest. Then, given an estimate of the relationship between time delay and survival, a local decision-maker can populate a cost-effectiveness model with context specific data. In this way it is possible to calibrate the anticipated benefit of a proposed transport system through its effect on reducing time to treatment.

In a forthcoming paper we will develop the model that relates transfer time to survival, taking into account costs, baseline survival rates, and whether or not treatment is administered in association with transport. To illustrate the model we will populate it with data for one particular scenario: snake bite. We use snake bite as the example, not only for its (considerable) intrinsic interest, but also because the best data we can find for transport time vs. survival rates, relates to snake bite. Our purpose is to illustrate the methodology so that it can be applied more generally. The case for ambulance services, of any particular type and in any setting, turns on its use across all emergency conditions. The investment case certainly could not be made on the basis of just one condition, least of all an uncommon scenario such as snake bite. Nevertheless, the model we propose could be used across a range of common scenarios to build up a case for a particular type of transport in a particular context.

— Richard Lilford, CLAHRC WM Director

Snake Bites, a Much More Serious Problem Than you Thought

I hate snakes. It turns out that I hate them with due cause! Snake bites are responsible for 50,000 deaths per year in India alone and that is thought to be a considerable underestimate.[1] Most snakes bite in the day or early evening and most cause considerable pain at the location of the bite. Not so the common krait (Bungarus caeruleus).[2] The krait hunts by night and most of its bites occur after midnight. The poison is ten times more potent than that of the cobra. Fully one-third of krait bites are fatal. People are often bitten while sleeping on the ground. The krait’s teeth are like small needles, so the victim often does not know that they have been bitten. The victim will soon present with abdominal pain and descending paralysis, and may even become ‘locked in’.

Access to care is a big problem following snake bites, since every hour counts. However, mis-diagnosis, lack of anti-venom, and lack of ventilators all contribute to the high mortality rate from snake bites. The biggest problem is probably access, and thousands of people die through neglect. This is just one of many diseases that could be more successfully tackled if access to places of care was improved, a topic I am pursuing as part of Dion Morton’s NIHR Unit on Global Surgery.

— Richard Lilford, CLAHRC WM Director

References:

1. Mohapatra B, Warrell DA, Suraweera W, et al. Snakebite mortality in India: a nationally representative mortality survey. PLoS Negl Trop Dis. 2011; 5: e1018.
2. Bawaskar HS, Bawaskar PH, Bawaskar PH. Snake bite in India: a neglected disease of poverty. Lancet. 2017; 390: 1947-8.

The Most Dangerous Animal

It is very difficult to know which animal is the most dangerous (human beings aside). The mosquito would be a good answer, while game rangers are fond of surprising tourists by saying that it is the hippopotamus. The latter is almost certainly wrong and you can surprise the game ranger by asking him or her for evidence. There is none. But the snake is undoubtedly a very dangerous creature. Cobras and mambas are lethal, but apparently the greatest number of animal deaths worldwide is from a small, but agile viper, called the saw-scaled viper. This is a viper that likes to bite and it is ubiquitous in areas lacking modern medical facilities.

The problem, recently discovered, is that the anti-venom for this snake tends to be specific to the area in which the viper is found.[1] Small geographical differences in the structure of the protein toxin that causes blood to clot in the vessels accounts for this spatial specificity. This means that anti-venoms must be made locally.

The real problem with snake bite treatment is that anti-venoms are not available when needed or they become damaged during transit and storage. Snakes are very important for local ecologies. A campaign of extermination would probably do humans more harm than good. So the battle between person and snake, which started all those years ago in the Garden of Eden, is set to continue.

— Richard Lilford, CLAHRC WM Director

Reference:

1. Rogalski A, SOerensen C, op den Brouw B, Lister C, Dashevsky D, Arbuckle K, Gloria A, Zdenek CN, Casewell NR, Gutiérrez JM, Wüster W, Ali SA, Masci P, Rowley P, Frank N, Fry BG. Differential procoagulant effects of saw-scaled viper (Serpentes: Viperidae: Echis) snake venoms on human plasma and the narrow taxonomic ranges of antivenom efficacies. Toxicol Lett. 2017; 280: 159-70.