In this retrospective observational study of point-of-care testing in OHCA patients, we found frequent abnormalities in acid-base balance and electrolyte concentrations. Therapeutic measures were regularly carried as a result yet on-site treatment time was not extended significantly. An improved survival probability in OHCA patients who undergo POCT was observed.
Data acquisition
Since all of the emergency medical service units (with emergency physicians) in this study region were operated by the same organisation and all of the vehicles were equipped with identical POCT equipment, there was no bias due to lack of equipment availability nor were there differences in measurements due to differences in training or differences between devices. Furthermore, since all patients in the study region are transported to the only available cardiac arrest centre, every patient in this study received similar hospital treatment and we were able to collect a complete set of data covering the entire course of treatment.
Interpretation of the results
Abnormal pre-hospital POCT results can determine the choice of treatment. Given that such abnormal results occured so frequently in this study, it seems to be important and useful to determine them as early as possible. In some cases, however, it must also be determined whether such values really do indicate subsequent treatment. In general, the more unfavourable a patient’s prognosis (due to a long period without resuscitation measures, for example), the further outside the reference range that patient’s POCT results are likely to be. In such cases, these early test results could be seen as an indicator of the prognosis rather than as a trigger for therapeutic measures.
The available evidence for administering buffer substances to resuscitation patients, for instance, is inconsistent. There are also no exact pH value limits to trigger buffering and the subject is controversial 13–18. On the one hand, with increasing acidosis, the oxygen-haemoglobin dissociation curve shifts favourably within a certain range and oxygen release to peripheral tissues increases. On the other hand, acidosis reduces myocardial contractility, the threshold for possible ventricular fibrillation and the effectiveness of catecholamines 17,19. What is clear, however, is that alkalosis is harmful to resuscitation patients 20,21. What is more, buffering has the side effect of decreasing serum potassium concentration 22.
In this study, many patients had metabolic acidosis that required treatment. Patients who had collapsed unobserved and had an initial non-shockable rhythm on ECG were also often found to have pH and potassium levels indicative of acidosis and hyperkalaemia, respectively. These observations could potentially be interpreted as a basis for further treatment options if no POCT analyser is available. Taking such treatment measures without previously recorded baseline values could result in incorrect treatment, however.
There was no significant difference between venous and arterial samples in terms of the parameters that are relevant for buffering (pH, BE). Venous sampling thus seems sufficient.
While the need for buffering is controversially discussed, electrolyte imbalances should always be treated and there are clear relevant recommendations 10. The frequency of hyperkalaemia found in this study as well as the deficit in terms of its treatment even when diagnosed early both suggest a lack of awareness of the issue, at least in the cases included in our study. The precise reasons for the deficit in treatment could not be determined in this study due to its design without questionnaires.
However, irrespective of these findings, for any measure taken in an emergency situation, the time and effort required must be weighed against the benefit. We found that treatment at the scene of the emergency was not delayed to any relevant extent by performing POCT. This was likely due to the common practice of taking a blood sample when placing an intravenous catheter, which does not require additional training on the part of the emergency medical team members and can thus easily be delegated. Venous sampling also happens to be more suitable for determining acid-base status 23,24.
The results of our study suggest that patients who undergo POCT have better prognosis in overall outcomes.
Limitations
The retrospective design of this study without patient randomisation leaves some uncertainties when it comes to interpreting the results. Because the emergency medical service teams were not interviewed, their reasons for performing or, as the case may be, not performing POCT remain unclear. We compared the patient groups with and without pre-hospital point-of-care testing for a first overview of the topic even though these patient groups arose only by chance. Our assessment of the differences between these two groups is limited by these factors and any interpretations of our results must be cautious.
Because resuscitation patients are generally older and have acute pathologies, their prognosis is generally poor. Treatment for OHCA (including resuscitation) is a complex, multimodal process that is performed in a wide range of settings with many different influencing variables. All of these factors make it difficult to assess the effect of any individual measure, which, combined with the lack of proper patient randomisation in our study, means that our observations and evaluations must be interpreted with caution. However, we believe this makes it all the more important to optimise the treatment process wherever possible and appropriate.
Perspectives
Whether POCT is globally applicable is open to debate. Germany has a comprehensive emergency medical service system with emergency physicians. We can assume therefore that emergency medical service teams in Germany have the specialist skills required to interpret the results of point-of-care testing and incorporate them into their response. Indeed, this additional measure appears to be primarily carried out by emergency medical service teams with advanced skills and training, which in itself presumably has a favourable effect on the patient’s overall prognosis. In general, we recommend using POCT at least in cases of suspected metabolic or electrolyte imbalances in the peri-arrest period. Further research should determine whether POCT can be used as part of the treatment process without negative consequences (or potentially even to the benefit of the patient) if the necessary training for emergency medical service teams is provided and standard procedures for its use as a diagnostic tool and the consequent complex treatment are established.