Remember when Domino's had the 30-minute delivery guarantee, and then when they retracted it ostensibly because their drivers were getting into too many accidents? EMS agencies are often required to arrive at the scene of a request for service within 8 minutes, at least 90% of the time, as part of their contract with the communities that they serve. And not surprisingly, ambulances are [1] most frequently involved in crashes while in emergency (red lights and sirens) mode, trying to make the 8 minute standard. The [2] ambulance crash log at EMSN has virtually daily reports of collisions involving ambulances.

However, a new study concluded that response times of 8 minutes or less were not associated with increased survival in most instances:

Results: Of 34,111 calls involving emergency response, 11,078 patients (32%) were transported to the study institution and 10,382 (94%) had response time data available. Of these, 9,559 patients (92%) had data available to categorize them into groups based on their level of illness severity and were thus included in the study. A survival benefit was identified for response times 4 minutes (odds ratio [OR], 0.70; 95% confidence interval [CI] = 0.52 to 0.95). No survival benefit was identified when response time was modeled as a continuous variable (OR, 1.01; 95% CI = 0.98 to 1.04) or when dichotomized at 8 minutes (OR, 1.06; 95% CI = 0.80 to 1.42).

Conclusions: A paramedic response time within 8 minutes was not associated with improved survival to hospital discharge after controlling for several important confounders, including level of illness severity. However, a survival benefit was identified when the response time was within 4 minutes for patients with intermediate or high risk of mortality. Adherence to the 8-minute response time guideline in most patients who access out-of-hospital emergency services is not supported by these results.

[3] EMS House of Defrance, unable to find original journal.

An earlier study by the same author also found no correlation between survival of trauma patients and the 8 minute response time standard:

Emergency Medical Services (EMS) agencies are increasingly being held to an ambulance response time (RT) criterion of responding to a medical emergency within 8 min for at least 90% of calls. This recommendation resulted from one study of outcome after nontraumatic cardiac arrest and has never been studied for any other emergency. This retrospective study evaluates the effect of exceeding the 8 min RT guideline on patient survival for victims of traumatic injury treated by an urban paramedic ambulance EMS system and transported to a single Level I trauma center. Of 3576 patients identified by the hospital trauma registry, 3490 (97.6%) had complete records available. Patients were grouped according to ambulance RT: < or = 8 min (n = 2450) or > 8 min (n = 1040). After controlling for other significant predictors, there was no difference in survival after traumatic injury when the 8 min ambulance RT criteria was exceeded (mortality odds ratio 0.81, 95% CI 0.43-1.52). There was also no significant difference in survival when patients were stratified by injury severity score group. Exceeding the ambulance industry response time criterion of 8 min does not affect patient survival after traumatic injury.

[4] J Emerg Med. 2002 Jul;23(1):43-8 via PubMed.

Many ambulances still respond emergency to every request for service, or at least a great majority of them. My county uses Medical Priority Dispatching, which has reduced the problem somewhat. However, we still respond emergency to the scene about 75% of time, yet only about 5% of the patients are deemed to have enough of a life threat to justify driving to the hospital with the red lights and sirens activated. The studies above that reducing response time to the "standard" of 8 minutes or less does not decrease mortality, so I propose making the criteria for an emergency response to the scene more stringent. Patients in extremis, where the first study showed a response time of 4 minutes or less correlated with a survival benefit, should obviously get an emergency response. (Though my district at home is 80 sq. miles containing suburban and rural areas, so it can take over 10 minutes just to drive to the scene, but that's another story.) Examples include respiratory/cardiac arrest, ineffective breathing, airway obstructions, etc. (Basically 1-Echo's, some 1-Delta's, and possibly some 1-Charlie's.) But why should we risk the lives of the crew and to the general public by driving emergency to a patient at a doctor's office, a patient that has been having "trouble breathing" or chest pain for two days, or a patient with an isolated extremity sprain rule out fracture. None of these patients will experience any increased morbidity or mortality in the 1-2 extra minutes it would take for a non-emergency response, but the risk of an ambulance accident is greatly increased. Despite this, Medical Priority Dispatching sends ambulances to all these cases in emergency mode.

Let's use some common sense, and by reducing the number of emergency runs, we will reduce the number of ambulance collisions, and mitigate the risk to the crew, and to the general public.

(You never thought you'd hear me advocating for less lights and sirens use, did you? Must be the heat. )