Accidental cold-related injury leading to hospitalization in northern Sweden: an eight-year retrospective analysis

Accidental cold injuries, including hypothermia, frostbite and cold-water drowning, are important causes of injury and hospitalization in subarctic regions [1‐5]. Interest in these types of accidental injuries has increased after several cold-weather mass casualty events, [6, 7] where immersion and submersion in cold water has led to life-threatening hypothermia and cold-water drowning. Incidences and outcomes of cold injury have been reported for some regions [8] or nations [9] and in military populations [10, 11]. Accidental cold-related injury is a potentially life-threatening condition that can lead to significant morbidity and life-long effects. Populations in cold climate regions, without proper safeguards and preparation when outdoors, are always at risk for cold injury. Based on previously published material, it is recognized that the occurrence of cold-related injury is often multifactorial [12‐16]. Factors contributing to fatal hypothermia have been recently described [17]. It is not known if cold injury hospitalization and in-hospital survival is increasing over time, since presumably there is steady progress in prevention and treatment.

The aim of this study was to identify the incidence of cold-related patient injuries, and describe the rescue-activities, pre- and in-hospital treatment, and injury panorama in Northern Sweden during an 8-year study period from 2000 to 2007. Additionally, we wanted to estimate the association between cold-related injuries and ethanol/drug use, psychiatric illness or dementia, and accidents.

The main finding is an estimated recent incidence (3.4/100 000) for hypothermia with hospitalization which is higher than previously reported (1.1/100 000) from a similar region [9]. The findings for frostbite were confirmatory concerning annual incidence [24‐26]. In our cohort, there were more male victims, while female victims had a more advanced age. The age and gender results could support the idea that older females may be more affected while having chronic illness, and that younger males may be more often victims of exposure due to daytime outdoor activities. Frostbite occurred at a higher rate among males, and could be related to more common outdoor occupational or leisure-time activities [26]. In-hospital mortality for hypothermia (6%) in this cohort was relatively low compared to a Dutch report [9].

Another notable finding was the increase in hypothermia incidence over the study period. This may be due to attitudes where community members under-appreciate the risks, and overestimate their own abilities and equipment. A second factor may be an increased number of community members at advanced age and with chronic illness, who are more vulnerable for cold injury. A possible confounding factor may be bias related to changes in physician awareness and increased reporting. There has been an active educational process in the region (and nationally, in Sweden) concerning cold injury during the study period, sponsored by the Swedish National Board of Health and Welfare [5].

A small number of the hypothermia cases occurred indoors, [17] and typically these occur where there is an open door, or in an indoor site which is not heated or poorly heated. An explanation may be that there are demographic changes, more elderly and medically debilitated in the population living at home, and often alone, which may explain a higher relative risk in the regional population [27, 28]. Without earlier reports of cold-related injury incidences from the same region, it is not possible to determine if cold related injury incidences are changing, but a higher incidence of hypothermia than reported elsewhere suggests that it is possible.

Concerning pre-injury activities, the majority of victims had no specific activity identified in their patient journal. Possible explanations include that some of these victims were intoxicated (approximately 40% of total cases). Intoxication impairs the ability of an individual to assess and judge risks. It is also well recognized that many individuals combine intoxication with leisure outdoor activities such as snowmobile driving or fishing.

For a small subset of patients admitted with the diagnosis hypothermia, the only recorded temperature measurement was one that was over 35°C. There are several possible interpretations of this finding. One is that the clinicians simply failed to record a lower measured temperature. Another is that they measured a body core temperature correctly and the temperature was actually above 35°C at hospital admission. These types of patients, with mild cold injury are probably quite common, even though they usually are not identified with a formal hypothermia diagnosis in the national patient diagnosis registry.

A large portion of the hypothermia victims were diagnosed presumptively at the accident site, though a core temperature measurement was not recorded for this in the hospital records. One possible explanation of this is that the personnel had an opportunity to measure temperature, but did not prioritize doing this (and recording their measurements). Another possible explanation is that they did not have the means to measure core temperature. Once in the hospital, temperature was measured more systematically, although it was infrequently recorded which body area, and with which device. The optimal way to measure core temperature is in the esophagus, and this can be performed even in awake patients [29, 30]. Other minimally invasive means of assessing include urinary bladder (catheter) probes, or rectally. Measuring temperature in the ear by infrared methods is widely regarded as inaccurate, though a closed ear canal temperature measurement performed correctly is considered reliable even in a cold environment [31]. It is important that both site and time of measurement are recorded [32] so that a time course of rewarming can be reviewed and assessed. Furthermore, documentation in the hospital record according to an international standard for on-site evaluation and treatment, including level of consciousness and presence or absence of shivering, along with field treatment should be performed [33, 34].

External, non-invasive warming methods such as forced-air warming have become a favored method, even for moderate and severe hypothermia victims [35‐37]. Other more invasive rewarming methods persist, though in these observations at a very low incidence. There were very few cardiac arrest and extracorporeal rewarming events observed in this cohort. This may be due to very long transport distances to a single centralized thoracic surgery resource for the whole region. There is no clear evidence in our findings to suggest that less invasive methods are less effective.

Limitations of this retrospective chart review study design include primarily the risk for not being able to identify and collect all the relevant patient information from the four phases of care for cold injury victims. While ambulance and hospital records were reviewed, it is possible that not all relevant information was recorded in these journals, or that in the paper chart review process, some relevant information was recorded but not identified and abstracted. There were clear limitations concerning documentation of measurement of core temperature, and the time course of rewarming. Also, this type of relatively small sample size with retrospective analysis cannot be used to make precise estimates of risk. Prospective structured data collection and a formalized effective data capture in a registry will be needed in order to allow more precise and less bias analysis of cold injury and associated or contributing factors.

The incidence of accidental hypothermia seems to be increasing in this studied sub-arctic region. Likely associated factors are recognized (ethanol intake, dementia, and psychiatric diagnosis). We have not been able to evaluate if the regional health care system that was examined has been optimally effective with treatment, since limitations in hospital patient documentation restricted analysis of this.