Complex acute pain treatment in German hospitals: retrospective analysis of regional differences

Complex acute pain therapy is a therapeutic measure for special pain therapy and symptom control in patients with severe acute pain conditions. This severe acute pain can occur, for example, after operations, accidents or even with severe, exacerbated tumors. The complex acute pain therapy is coded using the operation and procedure code (OPS) 8-919 (DIMDI, 2023). In 2021, there were a total of over 16.6 million hospital cases in Germany, and complex acute pain treatment was prescribed for more than 200,000 patients of these cases (InEK, 2023). Based on hospital diagnoses, it is known that there are regional differences in Germany for osteoporotic fractures as well as hospital deaths after femoral fractures and heart failure (Möckel, 2022; Möckel et al., 2020, 2023; Wachter et al., 2015). A study by Hoffmann et al. (2020) was also able to show that there are regional differences in the prescription of the painkiller metamizole in Germany. In this analysis, the usage prevalence was lowest in Saxony with 7.0% and highest in Schleswig-Holstein with 11.1% (Hoffmann et al., 2020). It should also be noted that between 1998 and 2008–2011 the use of painkillers in Germany increased from 19% to 21%. This increase is primarily due to over-the-counter painkillers (10.0% to 12.2%), whereas the use of prescription painkillers remained constant (Sarganas et al., 2015). In the study by Sarganas et al. (2015) showed that females, increasing age, obese people and smokers had a higher chance of taking prescription painkillers. In contrast, higher socioeconomic status and more physical activity per week were associated with lower odds (Sarganas et al., 2015).

>> Since, to our knowledge, there is currently no current data on possible regional differences in complex acute pain treatments in Germany, the aims of this study were: (i) to analyze the number of cases of complex acute pain treatment from German hospitals in order to identify possible federal state differences and (ii) To examine correlations between the age-standardized rate of complex acute pain treatment and socioeconomic/health factors as well as the main diagnoses behind complex acute pain treatment in the federal states.
methods
Study design and data sources
This study is a retrospective analysis of case numbers from German hospitals. The number of cases for the implementation of complex acute pain treatment (OPS 8-919), the number of all hospital cases for Germany as a whole and for the individual federal states in 2021 were taken from the InEK data browser (InEK, 2023).
The information on the total population in Germany in 2011 and 2021, the age-standardized rates for the ICD codes M17.1, M75.1, M16.1, M75.4, C20, C64, C67.8, S83.*, S42 .2, T36.*-T50.* and Z38.0 in the individual federal states in 2021 were taken from the federal health reporting information system (GBE database) (Federal Health Reporting, 2023a, 2023b). Information on the proportion of social assistance recipients and the foreign population, the unemployment rate of all civilian workers, the gross monthly income, the proportion of residents per km2, the proportion of adults who smoke, life expectancy from the age of 0 and on health expenditure per resident: in for the individual federal states were taken from the Destatis/Genesis database, from the Federal Agency for Civic Education, the federal and state statistical offices and from Statista (Federal Agency for Civic Education, 2023; Destatis, 2023c, 2023a, 2023b, 2023d; Statista, 2023; Federal and State Statistical Offices, 2023; Federal Statistical Office, 2023). Since this study is a retrospective analysis of published data, an ethics approval was not necessary for its implementation.

statistical evaluation
Based on the case numbers of complex acute pain treatment and all hospital cases, age-specific case number rates of complex acute pain treatment (<18 years, 18–39 years, 40–59 years, 60–74 years, ≥75 years) as well as the gender-specific rate per 100,000 hospital cases (all diagnoses , procedures, etc.) with the associated 95% confidence intervals (95% CI) are calculated for Germany as a whole and for the individual federal states. Age-standardized case number rates (ASR) for complex acute pain treatment per 100,000 hospital cases and 95% CIs were then calculated for Germany as a whole and for the individual federal states (ASRBL). To identify significant differences in ASRs across states, Standardized Rate Ratio (SRR) and associated 95% CIs were calculated using the following formulas (Boyle & Parkin, nd):

where Zα/2 = 1.96 and X is defined as

and SE (ASR) represents the standard error of the age-standardized rates (Boyle & Parkin, nd). When calculating the SRR, the federal state whose ASR was most comparable to that for Germany as a whole (Baden-Württemberg) was used as the reference (ASRRef).
Correlations were determined using Pearson correlation, calculating the correlation factor r and the associated 95% CIs. The statistical analysis was carried out using the JASP program (JASP Team, 2022).
Results
Characteristics of hospital cases and age-specific rates
There were a total of 221,287 cases of complex acute pain treatment in the InEK database for 2021. The proportion of female patients was 54.79% and for male patients it was 45.21% (Table 1). The 60–74 year old age group was most frequently represented with 33,25%, followed by 40–59 year olds (27,22%) and ≥75 year olds (21,57%). The most common diagnosis in patients with complex acute pain treatment was other primary gonarthrosis (9,20%). In total (all diagnoses, procedures, etc.) there were 16.6 million cases in the InEK database, with 52,21% of the patients being female and the age group of ≥75 years (29,33%) being most frequently affected by the intervention was (Table 1) (InEK, 2023).
With one exception, both were in Germany as a whole
(Men 1260.8 [95% CI: 1253.1; 1268.6] and women 1398.6 [95% CI: 1390.8; 1406.5] per 100,000 hospital treatments) as well as the non-age-standardized rates in the individual federal states complex acute pain treatment in men was numerically lower or comparable to the rates in women (Fig. 1A). Only in Saarland was the complex acute pain treatment rate per 100,000 hospital treatments significantly higher for men (1414.1 [95% CI: 1345.9; 1482.4]) than for women (989.4 [95% CI: 934.3; 1044, 6]).
The age-specific number of cases of complex acute pain treatment per 100,000 hospital treatments in Germany among ≤18 year olds was 295.4 (95% CI: 287.5; 303.2) with federal state variations between 61.7 (95% CI: 38.4; 84. 9; Thuringia) and 604.8 (95% CI: 545.5; 664.1; Hamburg) (Fig. 1B). Among 18-39 year olds and 40-59 year olds, the rates for Germany were 1378.1 (95% CI: 1363.6; 1392.5) and 1846.2 (95% CI: 1831.6; 1860.8) per 100,000 hospital cases. There were fluctuations between the federal states between 531.2 (95% CI: 448.3; 614.1; Bremen) and 2191.4 (95% CI: 2062.9; 2319.9; Brandenburg) among 18–39 year olds and 859.7 (95% CI: 800.2; 919.2; Thuringia) and 2527.4 (95% CI: 2419.5; 2635.4; Brandenburg) among 40–59 year olds. In the two oldest age groups, the case number rates for complex acute pain treatment were 1778.3 (95% CI: 1765.6; 1791.0; 60–74 year olds) and 980.2 (95% CI: 971.4; 988.9; ≥ 75-year-olds) per 100,000 hospital treatments for Germany. In the federal states, the rate among 60-74 year olds fluctuated between 1024.4 (95% CI: 971.9; 1076.9; Thuringia) and 2555.5 (95% CI: 2467.6; 2643.5; Brandenburg) as well in ≥75 year olds between 563.8 (95% CI: 538.6; 589.1; Hesse) and 1649.9 (95% CI: 1586.8; 1713.0; Brandenburg) per 100,000 hospital treatments (Fig. 1B) .

Age-standardized caseload rates and standardized rate ratios
The age-standardized case number rate (ASR) for complex acute pain treatment for Germany as a whole was calculated as 1376.8 (95% CI 1370.3; 1383.3) cases per 100,000 hospital cases (Fig. 2). The highest age-standardized rate per 100,000 hospital cases was for the state of Brandenburg (1994.2 [95% CI: 1943.6; 2044.9]) and the lowest for Thuringia (698.7 [95% CI: 671.1; 726.3] ) can be determined (Fig. 2).
In comparison to the reference federal state of Baden-Württemberg, the standardized rate ratios (SRR) of the ASRs of complex acute pain treatment in the federal states of Berlin, Bremen, Hesse, Lower Saxony, Rhineland-Palatinate, Saarland, Saxony-Anhalt and especially Thuringia (SRR: 0, 51 [95% CI: 0.49, 0.52]) (Fig. 3) significantly lower. Significantly higher SRRs occurred in the federal states of Bavaria, Mecklenburg-Western Pomerania, North Rhine-Westphalia and especially in Brandenburg (SRR: 1.44 [95% CI: 1.40; 1.49]).
Only the ASR of the S83.* coded dislocation, sprain and strain of the knee joint and ligaments of the knee joint was significantly correlated with the ASRs of the complex acute pain treatment (r: 0.61 [95% CI: 0.16; 0.85]; p= 0.012) (Table 2). Other ICD-10 codes and socioeconomic factors in the states showed no significant correlations with the ASRs of complex acute pain treatment.

discussion
This analysis shows significant federal state differences in the use of complex acute pain treatment in German hospitals, with the age-standardized case number rates being highest in Brandenburg, Bavaria and North Rhine-Westphalia. Only the age-standardized rate of ICD-10 S83.* coded dislocation, sprain and strain of the knee joint showed a significant correlation with the age-standardized rate of complex acute pain treatment.
Unlike the prescription of metamizole (Hoffmann et al., 2020), no obvious east-west gradient can be observed for complex acute pain treatment. Interestingly, the prevalence of metamizole use in federal states such as Brandenburg and Saxony is below the prevalence for Germany (Hoffmann et al., 2020), but above the rate for Germany for the acute pain treatment analyzed in this study. In contrast, the federal states of Mecklenburg-Western Pomerania and North Rhine-Westphalia show a higher rate or prevalence than Germany as a whole in both the present study and the study on metamizole.
With one exception, the correlations cannot identify any evidence of connections between the age-standardized acute pain treatment rate and specific diagnoses, which are often possible causes for the pain treatment. A vague indication of a possible reason for the regional differences can so far only be derived from the correlation between the case number rate for acute pain treatment and the age-standardized rate of the ICD-10 code S83.*. On a global level, however, it is known that the use of opioid analgesics is associated with the Human Development Index and the cancer-related death rate (excluding leukemias) (Ju et al., 2022). For Germany as a whole, associations were found, among other things, between the socio-
economic status, obesity and smoking status have been reported to be associated with the use of analgesics and/or opioid analgesics (Sarganas et al., 2015). However, a correlation of complex acute pain treatments with gross monthly salary, life expectancy from the age of 0 or the proportion of smoking adults in the federal states could not be identified in the present analysis (Table 2).
At this point in time, we are not aware of any other analyzes of complex acute pain treatment in German hospitals that address the causes of the regional differences. Accordingly, there is a need for further quantitative surveys that are able to explain the differences in the use of the OPS code 8-919 in Germany. Particularly against the background of possible dependence due to the use of pain-relieving medication, information appears to be sensible and important (Häuser et al., 2021). Painkiller addiction is currently a major problem in countries such as the USA or Great Britain (Kibaly et al., 2021; Roberts & Richards, 2023).
The results of the present analysis raise various questions that are related to the prescription of complex acute pain therapy and must be answered by subsequent, more detailed studies. It is therefore important to identify the cause of the regional differences in Germany. Reasons could be, for example, regionally different incidences of diseases, but also possibly differences in care and problems. Furthermore, it is relevant to determine how long the complex pain therapy is carried out in each individual case and which classes of active ingredients are used. In Germany, TÜV Rheinland awards the “Quality Management Acute Pain Therapy” certification, which allows clinics to call themselves pain-free clinics. The question of whether the number of prescriptions for complex acute pain therapy correlates with the number of clinics that have this certification could also be the subject of further research (Korczak et al., 2013)
This study has several limitations that have not yet been discussed. On the one hand, it is a correlation study (ecological study) that was carried out with aggregated data from patients in the individual federal states and not with individual data. On the other hand, the analysis cannot reveal any causes for the regional differences. It must also be noted that the identified correlation cannot provide a causal relationship. Lastly, it should be pointed out that only the data from 2021 was used, which was a Corona year.
Conclusion
Based on this analysis, it can be assumed that there are regional differences in the use of complex acute pain treatment in Germany. Since these differences can be an indication of regional differences in the disease process, but also of differences in care, further analyzes are necessary. These analyzes should ideally be carried out with more detailed data sets than those used in the present correlation study. In particular, this could also include supply
Aspects such as regional hospital density or waiting times for illnesses that are associated with severe pain are taken into account. <<