Journal of the New Zealand Medical Association, 10-September-2004, Vol 117 No 1201
Co-morbidities in trauma patients: common and significant
Chuan-Ping Tan, Alex Ng, Ian Civil
Trauma is a heterogeneous ‘disease’ that affects all age groups with varying degrees of severity. Factors that affect trauma outcome include the severity of the injury, pre-existing health status, time to definitive care, and the quality of care.
While injury severity, time to definitive care, and the quality of care in trauma patients can be easily quantified, it has been a lot more difficult to quantify pre-existing health status (or ‘host factors’) in trauma patients and relate these to trauma outcome.
The trauma literature gives little credence to co-morbidities seen in trauma patients. In most trauma outcome analyses, the surrogate of age is used to represent co-morbidity. In the most commonly used trauma outcome analyses, age >551 is used as a single co-morbid surrogate.
In an earlier analysis of co-morbidity in trauma patients admitted to Auckland Hospital,2 co-morbidities were seen in patients aged as young as 40 years of age.
As part of a larger study designed to establish a single abbreviated injury scale (AIS)-like’ grade for co-morbidity (where the clinical severity of the patient’s co-morbidity is graded like the AIS),3 the authors evaluated the incidence of all major and minor co-morbidity in a cohort of trauma patients aged ≥40 years admitted to Auckland Hospital.
Study type—A prospective study of the incidence of co-morbidities in trauma patients aged ≥40 years who were admitted to the Auckland hospital was undertaken.
Study population and period—Between 1 January 2003 and 3 March 2003, data was collected on all trauma patients admitted to Auckland Hospital. The primary inclusion criterion for the study were patients who had suffered a significant traumatic event that required a period of hospitalisation under the trauma team. The second inclusion criterion was that the population to be studied had to be 40 years of age or greater.
Data collected—The data was collected using a customised trauma registry available to the Auckland Hospital trauma team.4 We also recorded major and minor co-morbidities from these patients. The APACHE 2 PIC (pre-injury conditions) system 6 was used to define our criteria for major co-morbidities, whereas minor co-morbidity was any other ongoing condition recorded in the patient clinical record or noted by the first author.
Data collection method—Patients were identified by checking Auckland Hospital’s Trauma Registry daily. The first author then reviewed the case notes; and if the case notes were unclear, the patient would then be interviewed. A simple questionnaire with the data points stated above was used to facilitate data collection. Data was also collected from the Auckland Hospital Discharge Database.
During the study period (1 January 2003 to 3 March 2003), 105 patients who fitted the above study criteria were reviewed. Of these 105 patients, 57 were males and 48 were females. Their demographics, co-morbidities, ISS (injury severity score), and outcome data are broken down into the various age groups as seen in Table 1.
Table 1. Demographics table
ISS=injury severity score; SNF=specialised nursing facility; LOS=length of stay
Co-morbidities were seen in all age groups in both genders. Overall, 71% of the population had pre-existing co-morbid conditions; 23% of the study population had major co-morbidity described in the APACHE 2 PIC6 system (Table 2).
Table 2. APACHE 2 Pre-injury criteria (PIC)
CAPD=chronic ambulatory peritoneal dialysis.
Examples of the minor co-morbidities are shown in Table 3.
Table 3. Minor co-morbidities
An ISS of >15 is classified as major trauma. Injury severity in patients admitted to Auckland Hospital was found to decrease as age increases.
The mortality rate in this study population was 4.7%. All deaths were due to unsurvivable head injury.
The mean length of stay for the cohort of study patients was 8 days (range 1–61 days), and there was an association between major co-morbidities and the length of stay.
When we compared the length of stay between those with and without co-morbidities, their length of stay in hospital was 11 days (range 1–61 days) vs 6.8 days (range 2–35 days).
Twenty-one percent of the patients were discharged to a specialised nursing facility (ie, other hospitals, nursing homes, or rehabilitation facility). Of these 21% who were discharged to a specialised nursing facility, 33% had an ISS of >15.
The results of this study showed that co-morbidities are very common in trauma patients admitted to Auckland Hospital. The prevalence of co-morbidities in the various age groups seen in this study is similar to that seen by Mittal et al in their study.2 They noted that 53.3% of patients aged ≥60 years had co-morbidities compared with our study where we found that 58% of patients aged ≥65 years had co-morbidities.
One of the limitations in our study was the small number of patients so we cannot draw any statistically significant conclusions—but when we analysed the data, we found that those patients with major co-morbidities tended to have a longer hospital stay [11 days (range 1–61 days)] compared to those without co-morbidities [6.8 days (range 2–35 days)].
Morris et al5 (in their study of the effect of pre-existing conditions on mortality in trauma patients) showed that 8.8% of all trauma patients admitted into all acute care hospitals in California in 1983 had co-morbidities. When they analysed their data by breaking the patients up into various age groups they found that 25% of all patients aged ≥65 years had co-morbidities compared to our study which is about 58%. One of the limitations of the study by Morris et al is that they depended on the discharge medical records for their study data, which could have grossly under-reported the incidence of co-morbidities in these patients.
A similar study by Milzman et al6 prospectively evaluated the effect of pre existing disease on the mortality of trauma patients, and found that 16% of their study population of 7798 patients had one or more co-morbidities. On further analysis of their results, they found that the mean age of patients with co-morbidities was 49.2 years, whereas the mean age for those without co-morbidities was 30.6 years. When they reanalysed their results according to age groups, they found that 48.8% of all co-morbidities occurred in the age group ≥65 years.
In Table 1, we also note that, as age progresses, the number of major co-morbidities increases—whereas that of the minor co-morbidities decreases. This trend is surprising as we would expect the number of minor co-morbidities to increase as well. This could be due to the fact that younger patients may have had fewer medical records to go through, hence data collection of co-morbidities would be easy.
In contrast, the older age group may have had extensive medical records and minor co-morbidities in this group might have been overlooked. The minor co-morbidities seen in this older age group are shown in Table 3. Some of the minor co-morbidities (such as atrial fibrillation and peripheral vascular disease) although not life threatening on their own, could contribute significantly to the patient’s morbidity and mortality when included in the trauma scenario.
Undoubtedly, severe co-morbidity in a young patient (<40) is likely to affect outcome, but the likelihood of such co-morbidities in this age group is low. Existing trauma scales (using age as a surrogate) effectively draws a line at 55 years of age and suggest that co-morbidity above 55 will affect the outcome of the patient—whereas below 55, co-morbidity is relatively uncommon.
Similarly we drew a line at the age of 40 (based on our previous pilot study), however we believe that analysis of specific co-morbidities, rather than age, will allow us to apply a ‘severity factor’ to any injured patient, regardless of age.
Some studies have investigated the effect of co-morbidities on a trauma patient outcome.5–7 All of these studies found that the presence of co-morbidities worsens the outcome of the trauma patient, but unfortunately they suffered from methodological problems, such as flaws in the classification of minor vs major co-morbidities (studies using ICD 9 classification versus the APACHE system) and over-reliance on medical records in collecting study data which could have significantly under-reported the incidence of co-morbidities in the study populations.
Richmond et al8 found that pre-existing medical conditions did not contribute to mortality risk but the authors noted that their finding was inconsistent with the current literature and they believed the reason for their study finding was due to their inability stratify the medical condition by severity (which may have led to the above finding). However these methodological flaws were implicated in the study by Morris et al4 which found that the presence of co-morbidities worsens the outcome of the trauma patient.
The same study by Richmond et al8 showed that whilst co-morbidities did not influence mortality they increase the odds of experiencing a complication, and these complications significantly increased the odds of death.
Because of the modest numbers patients in our study, we were unable to observe any statistically significant association between ‘pre-existing co-morbidities’ and ‘mortality and final destination at discharge’. Indeed, co-morbidities in trauma patients are complex and not well addressed by any of the existing injury scales.
Our study shows that co-morbidities are surprisingly common in trauma patients and likely to impact on the outcomes—both in terms of survival and complications/length of stay. The results also suggest that it is feasible to perform a larger scale study at Auckland Hospital to further evaluate the effect of co-morbidities on the outcome of trauma patients. An appealing possibility would be the development of a modifier to the current ISS system that incorporates a single ‘AIS–like’ co-morbidity score.
Author information: Chuan-Ping Tan, Surgical Registrar; Alex Ng, Trauma Surgeon and Associate Director; Ian Civil, Trauma Surgeon and Director, Trauma Services, Auckland City Hospital, Auckland
Correspondence: Dr C-P Tan, Room 43.105, Level 4, Auckland City Hospital, Park Road, Private Bag 92024, Grafton, Auckland. Fax: (09) 375 4357; email: email@example.com
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