METHODS

Non-transported cases were defined as those cases where a 999 call was made, an ambulance from any one of the 12 East Midlands ambulance stations in Nottinghamshire attended the scene, but the patient was not conveyed to hospital. Cases where the patient was dead before the arrival of the ambulance and those where the call was malicious were excluded. The computer databases that hold both the Command and Control data and information scanned routinely from patient report forms completed by the ambulance crew¹⁴ were searched to find the first 500 non-transported cases starting from 1 March 2000. The sample size was determined to provide 95% confidence limits of ±5% for each variable with an allowance made for missing data. The patient report forms for these cases were further examined by manual inspection and data entered on a database using Microsoft Access 97. Clinical categories were attributed to each case after examination of the free text description of the incident recorded on the patient report form. Each case was categorised by three researchers (OA, TD, and PM) using a system devised by the authors. Where there was disagreement about categorisation the case was discussed and a consensus reached.

Data collected comprised age, sex, type of residence, the initial AMPDS code assigned by control, category A status, clinical category, whether patient had been drinking alcohol, and the reason the patient was not transported to hospital. The time each ambulance was committed was calculated from the ambulance control records. This was taken as the interval between the call being passed to the ambulance crew and the time when they became available to respond to another call.

Proportions, means, medians, and 95% confidence intervals were calculated using SPSS for Windows version 9.0.

RESULTS

Of the 500 cases where data were extracted from the patient report forms, two were excluded because they were the result of malicious calls, leaving 498 cases. The age distribution (fig 1) shows a distinct bimodal distribution with peaks in early adulthood and between the ages of 65 and 90 years. Men accounted for 46% of the cases studied.

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Figure 1

Age distribution of all non-transported patients.

Table 1 shows the clinical categories. Falls account for over a third of all non-transported calls and non-specific illnesses for one in ten. Alcohol intoxication was the primary diagnosis in 30 (6%) cases, and a further 18 (4%) were linked to alcohol.

Table 2 shows the reasons for non-transportation. In almost half the cases the reason is recorded as a refusal to travel, in a quarter no injuries were found, and in 13% a visit by the patient's general practitioner was arranged. Falls was the commonest clinical category for both the refusal to travel (30%) and no injuries (55%) groups, whilst general assistance (23%) was the largest category where the reason for non-conveyance was that a GP visit had been arranged.

AMPDS codes were available for 418 (84%) cases. Of those with codes available 108 (26%) were AMPDS code delta (the most urgent code) and 93 (22%) were from AMPDS codes that constitute category A calls. For all clinical categories there was close agreement between AMPDS code delta and category A classifications, except for road traffic accidents where of the 28 cases where AMPDS codes were available 13 were classified as AMPDS code delta (46%, 95% CI 30% to 64%) and only 1 as category A (4%, 95%CI 1% to 18%).

The mean time the ambulance was committed was 34 minutes and the median 33 minutes (standard deviation 17 minutes, interquartile range 24–43 minutes).

Falls

Falls accounted for 170 (34%) of the non-transported calls. The mean age of non-transported cases presenting with falls was 73 years (median 79 years, SD 20, interquartile range 68–86 years). The age distribution is shown in figure 2. Ninety two (59%) were female, 50 (33%) lived alone, and four (2%) lived in a nursing or residential home. Ten (6%) were linked to alcohol. Fifteen (10%) of fallers were classified as AMPDS code delta and 15 (10%) were category A while 89% of those aged over 70 were AMPDS code alpha or bravo.

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Figure 2

Age distribution of non-transported patients who had suffered a fall.

DISCUSSION

This is the first UK study to describe the epidemiology of non-transported 999 calls and link these data to the AMPDS code used to determine the priority of the ambulance service response. However, there are a number of limitations in the study design.

There was no independent validation of the clinical assessment made by the ambulance crew nor did this study follow up non-transported patients to establish the clinical outcome after the ambulance left the scene. In addition, few AMPDS codes were recorded by the crews after they had attended the patient so no comparison could be made with the initial code assigned by the call taker. Therefore, it was not possible to confirm from our data whether the decision not to transfer the patient to hospital was appropriate or to analyse whether the urgency assigned to the call by AMPDS was justified by the clinical need.

Clinical data on the nature of the incident could not be easily extracted from the routine computer database. Therefore the authors had to develop their own coding system to categorise the free text description of the incident on the patient report form and this limited comparisons between our survey and other published research. Manual inspection also introduced possible observer error into the study findings but this was minimised by three of the authors independently categorising each call.

The distinctive bimodal age distribution found in this study for non-transported calls is similar to a previous UK epidemiological survey of all 999 calls that also reported the highest prevalence of callers aged 15–39 and over 60.⁸ The largest clinical category was falls constituting over a third of the non-transported 999 calls in our series. However, accidents and other trauma have consistently been identified as the largest single reason for all 999 calls in previous UK studies.^8–11 This finding suggests that falls are more likely than other problems to result in non-transportation of 999 calls to hospital.

The finding that a large number of elderly people with falls were assigned low priority when the calls were received and subsequently not transported to hospital suggests that an alternative response may be appropriate. However, there is a need for caution, as the fact that some patients were left at home does not necessarily mean that this was the appropriate patient management. One study in the US¹⁵ found that between 3% and 11% of patients determined on scene not to need an ambulance had a critical event. A further US study¹⁶ found that 48% of patients who refused medical assistance from an ambulance crew sought further medical care within a week, with 7% being admitted to hospital. The current study found that falls was the commonest clinical group in those who were not transported because of a refusal to travel, but was unable to determine whether the opinion of the crew may have been a factor in the patient's decision to remain at home.

Previous research into the safety and reliability of the AMPDS priority dispatch system has reported its high sensitivity and the low risk of serious under prioritisation of emergency 999 calls.¹⁷ The current study has found that 26% of all non-transported calls are assigned the highest (delta) code when the ambulance is dispatched. This suggests this system may have a relatively low specificity for identifying life threatening calls but the factors associated with possible over prioritisation using AMPDS have not been explored. Furthermore, we were unable to evaluate other possible explanations for the unexpectedly high proportion of non-transported calls being assigned the highest priority AMPDS code. These might have included correctly prioritised life threatening conditions that could be effectively managed by the crew at the scene without hospital care (such as diabetic hypoglycaemia), a failure of ambulance crews in some cases to adequately assess a serious condition that did require hospital transfer and, finally, an improvement in the patients clinical status between the call being made and the arrival of the vehicle.

The demand for the emergency ambulance service in the UK has been rising steadily⁴ and attention has become increasingly focused on the management of less serious, non-life threatening category C calls. In 2000 there were 10 158 non-transported calls in Nottinghamshire, committing ambulances for almost 6000 hours. There are potentially major gains if some of these calls could be safely triaged by AMPDS to an alternative response, both in terms of increasing the ability of the ambulance service to respond more effectively to clinically urgent 999 calls and cost savings for the health service. Further research is needed to explore whether a group of non-transported 999 calls can be identified at the time the call is received and more appropriately managed without the dispatch of an emergency ambulance.