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Invasive blood pressure (IBP) measurement and Point-of-care (POC) lab investigations are essential and quite common procedures for emergency and critical care, both in the emergency department and ICU. Intermittend non invasive (NIBP) and inaccurate blood pressure measurement is often misleading in prehospital setting. IBP measurements are considered to be the gold standard in critical care. Blood gas analysis as well as the results of haemoglobine and electrolytes may lead to live saving interventions.
We investigated the value of POC lab in a prehospital setting on scene in a physician staffed emergency medical service. The study was also performed to compare invasive blood pressure with non invasive blood pressure measurements using auscultatory or palpation methods.
Methods and Materials
With approval by local ethics commission critical ill or injured patients (NACA≥5) on scene required an intra-arterial line. IBP measurements were compared with non invasive blood pressure. Statistical analysis was conducted with the Bland-Altman method for comparisons of repeated measures.
Blood samples were drawn and POC lab was analyzed with the mobile Abbot I-Stat analyzer. The analysis included blood gas, haemoglobine and electrolytes. Outcome variables were the incidence of pathologic results, the correlation between PaCO2 and etCO2 in mechanically ventilated patients and emergency interventions based on POC lab results and IBP measurement.
45 patients were included with a total of 229 comparisons of IBP and NIBP. Error measurement was reported as mean ± standard deviation. A high standard deviation implies inaccuracy in noninvasive measurements. Sytolic IBP: 20,9±27,4mmHg, diastolic IBP: -0,3±20,2mmHg. In 46,6% IBP lead to an urgent medical intervention.
33 patients were included with a total of 58 POC lab investigations (up to 3/patient) resulting in 682 measurements. Out of these 307 (45%) showed pathologic values. In 22 (66,7%) patients the acid-base-state and in 16 (45,8%) patients haemoglobine disagreed with standard values, in 8 (24,2%) patients hypokalaemia and in 6 (18,8%) hyperkalaemia occured. In total 32 (97%) patients had at least one pathologic result. In 18 (54,5%) patients POC lab lead to an urgent medical intervention. The difference PaCO2-etCO2 in 21 mechanically ventilated patients was 17,2mmHg±12,9 (mean±SD) with a maximum of 42,9mmHg.
NIBP is unaccurate in critically ill or injured patients on scene in the emergency medical service and leads to incorrect interpretations of blood pressure. IBP is useful to lead to medical intervention.
Point-of-care lab investigations on scene is suited to provide essential additional information for emergency treatment before admission to the hospital. The high and unpredictable difference of PaCO2-etCO2 does not allow to adjust mechanical ventilation based on etCO2 in these patients.