Tissue oxygen saturation measurement in prehospital trauma patients: a pilot, feasibility study
- 1London's Air Ambulance & Emergency Medicine Research Group Edinburgh (EMERGE), Royal London Hospital, London, UK
- 2London's Air Ambulance, Royal London Hospital, London, UK
- Correspondence to Dr Richard M Lyon, Pre-hospital Care, London's Air Ambulance & Emergency Medicine Research Group Edinburgh (EMERGE), The Helipad, Royal London Hospital, Whitechapel Road, London E1 1BB, UK;
Contributors DJL conceived the study. DJL and JT coordinated the running of the study. RML was responsible for data analysis and writing the manuscript. All authors read and approved the final manuscript.
- Accepted 24 June 2012
- Published Online First 25 July 2012
Background This study evaluated the feasibility of prehospital tissue oxygen saturation (StO2) in major trauma patients.
Methods A prospective, pilot feasibility study carried out in a physician based prehospital trauma service.
Results Prehospital StO2 was recorded on 13 patients. Continuous StO2 monitoring was achieved on all patients, despite intermittent failure of pulse oximetry and non-invasive blood pressure monitoring in six patients. No adverse outcomes of StO2 monitoring were reported. The specific equipment used was reported to be inconveniently bulky and heavy for use in the prehospital setting.
Conclusions Prehospital measurement and monitoring of StO2 is feasible in trauma patients undergoing prehospital anaesthesia and may be useful in the early identification of shock, triggering of transfusion protocols and guiding fluid resuscitation.
Major trauma is a leading cause of mortality and serious morbidity across the world. Patients who survive an initial traumatic insult often die as a result of haemorrhage.1 Despite recent advances in the clinical care of haemorrhagic shock secondary to trauma, mortality still exceeds 50%.2 Optimal methods of detecting shock, the timing of fluid resuscitation and appropriate end points for resuscitation in trauma patients remain unknown.
Identifying trauma patients who will subsequently require a massive transfusion is difficult, particularly in the prehospital setting. Routine clinical variables such as pulse and blood pressure have not been shown to reflect poor tissue perfusion, particularly occult hypo-perfusion.3 ,4 The optimal device for using as an end point of resuscitation would be non-invasive to allow use in the prehospital environment, providing an objective parameter to measure tissue perfusion and oxygenation. Tissue oxygen saturation (StO2) has been described as a means of assessing perfusion status.5–7 The use of StO2 monitoring in the prehospital setting has yet to be fully evaluated.
We conducted a pilot, feasibility study of using prehospital StO2 monitoring in trauma patients undergoing prehospital anaesthesia by the London's Air Ambulance prehospital team.
We prospectively sought to enrol at least 10 patients to undergo StO2 monitoring prior to induction of prehospital anaesthesia and have monitoring continued during transport to hospital. Inclusion criteria were any major trauma patient undergoing prehospital anaesthesia in whom the team were able to site an StO2 monitor without compromising clinical care. Pulse, non-invasive blood pressure (NIBP) and pulse oximetry were measured in all patients.
The study was conducted over a 6-month period. Patients were followed up to the point of hospital admission. Initial injuries, CT results and activation of major transfusion protocols were recorded. The study was registered with the Barts and the London Hospital Trust as an evaluation of service improvement.
Thirteen patients had prehospital StO2 recorded during the study period. Eleven patients were male and two female. The age of the patients ranged from 16 to 82 (mean=47). All patients underwent prehospital anaesthesia and all had StO2 monitoring commenced prior to induction. A summary of patients in whom prehospital StO2 was measured is shown in table 1.
Prehospital StO2 monitoring
Continuous monitoring of StO2 was achieved in all cases. Placement of the thenar eminence probe was fast and reliable with a single size fitting left or right hands of all patients. The monitoring unit was found by all members of the prehospital team to be heavy (4 kg) and large for easy use in the prehospital setting.
Two patients were thought to be suffering from major traumatic haemorrhage on initial assessment by the prehospital team. Both patients subsequently received massive transfusions in hospital.
The StO2 trace of patient 2 is shown in figure 1. Peripheral SaO2 monitoring was lost at an early stage. Heart rate and NIBP measurements were inconsistent and several spurious, high readings were noted. The StO2 trace can clearly be seen to be declining in a consistent manner after induction of anaesthesia, in keeping with ongoing haemorrhage. The patient went on to receive a massive transfusion inhospital for intraabdominal injuries with major haemorrhage.
The StO2 trace of patient 8 is shown in figure 2. Despite early normalisation of systolic blood pressure after initial intravenous fluid resuscitation, the StO2 trace continued to decline, possibly due to ongoing haemorrhage. Heart rate, SaO2 and NIBP monitoring are all interrupted during the prehospital phase and readings are not consistent.
In six patients, NIBP or pulse oximetry readings failed during the prehospital phase either as a result of a poor pulse oximetry pickup or spurious NIBP readings. StO2 reading was available in all patients without technical difficulty.
Tissue hypo-perfusion is a recognised pathophysiological process in traumatic haemorrhage leading to multiple organ dysfunction and death. We found the use of a simple, non-invasive monitoring technique to measure peripheral tissue oxygenation in prehospital trauma patients undergoing emergency anaesthesia to be feasible and early indications suggest StO2 levels rapidly fall in patients with ongoing haemorrhage undergoing prehospital anaesthesia.
We specifically found heart rate, NIBP and SaO2 monitoring to either be technically challenging or to provide inconsistent, varying results in the prehospital setting. StO2 monitoring was continuous in all cases.
We found StO2 a feasible option for prehospital emergency medical personnel to non-invasively assess hypo-perfusion. However, taking the equipment from the helicopter or response car was noted to be restricted by the weight and size of the monitoring equipment. We specifically evaluated the use of StO2 monitoring in patients undergoing prehospital anaesthesia and found it to be feasible in this context.
Prehospital measurement and monitoring of StO2 are feasible in trauma patients undergoing prehospital anaesthesia and may be useful in the early identification of shock. StO2 monitoring appears to be possible when other routine parameters such as NIBP and SaO2 are inconsistent or not possible to measure. StO2 monitoring equipment will need to become small and lighter to be used routinely in prehospital practice. Further research is warranted to assess the clinical benefit of prehospital StO2 monitoring.
The authors wish to thank Mrs Elizabeth Foster for her assistance with data collection and the doctors and paramedics of London's Air Ambulance for their assistance with the study.
Funding The InSpectra StO2 monitor was loaned to the study team by Hutchison Technology Inc (Hutchinson, Minnesota, USA).
Competing interests None.
Ethics approval This study was registered with Barts and the London Hospital Trust to conduct the study as an evaluation of service improvement.
Provenance and peer review Not commissioned; externally peer reviewed.