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Emerg Med J doi:10.1136/emermed-2012-201578
  • Original article

Prehospital non-drug assisted intubation for adult trauma patients with a Glasgow Coma Score less than 9

  1. William Pickett1
  1. 1Department of Emergency Medicine, Queen's University, Kingston General Hospital and Hotel Dieu Hospital, Kingston, Ontario, Canada
  2. 2Department of Emergency Medicine, University of Ottawa, Ottawa, Ontario, Canada
  1. Correspondence to Dr Christopher Charles Douglas Evans, Department of Emergency Medicine, Queen's University Kingston General Hospital and Hotel Dieu Hospital, c/o 76 Stuart Street, Kingston, ON, Canada K7L 2V7; c.evans{at}queensu.ca
  • Accepted 30 September 2012
  • Published Online First 10 November 2012

Abstract

Objectives Prehospital airway management for adult trauma patients remains controversial. We sought to review the frequency that paramedic non-drug assisted intubation or attempted intubation is performed for trauma patients in Ontario, Canada, and determine its association with mortality.

Methods We conducted a retrospective cohort study using the Ontario Trauma Registry's Comprehensive Data Set for 2002–2009. Eligible patients were greater than 16 years of age, had an initial Glasgow Coma Score of less than 9 and were cared for by ground-based non-critical care paramedics. The primary outcome was mortality. Outcomes were compared between patients undergoing prehospital intubation versus basic airway management. Logistic regression analyses were used to quantify the association between prehospital intubation and mortality.

Results Of the 2229 patients included in the analysis, 671 (30.1%) underwent prehospital intubation. Annual rates of prehospital intubation declined from 33.7% to 14.0% (ptrend<0.0001) over the study period. Unadjusted death rates were 66.0% versus 34.8% in the intubation and basic airway groups, respectively (p<0.0001). Intubation in the prehospital setting was associated with a heightened risk of mortality (adjusted OR 2.8, 95% CI 1.1 to 7.6).

Conclusions Prehospital non-drug assisted intubation for trauma is being performed less frequently in Ontario, Canada. Within our study population, paramedic non-drug assisted intubation or attempted intubation was associated with a heightened risk of mortality.

Introduction

In Canada, and most parts of the world, injuries are the leading cause of death and severe disability in the first 4 decades of life.1 Patients with a decreased level of consciousness secondary to traumatic brain injury (defined as a Glasgow Coma Score less than 9) are at risk for aspiration, hypoventilation and hypoxia. Early airway management is critical for the survival of these patients and, as such, advanced life support (ALS) training, including prehospital intubation, has been widely integrated into many prehospital care systems.2–5 Despite widespread practice, prehospital non-drug assisted intubation remains controversial, as several studies have suggested either no benefit2 ,4 or an increased risk of mortality to patients.5 ,6

The province of Ontario, Canada, has a population of approximately nearly 13 million persons distributed over more than 900 000 km2 of land.7 The provincial trauma system is organised around 11 designated regional trauma centres. Prehospital trauma care is provided by three levels of paramedic: (1) primary care paramedics, who provide basic life support including the use of a bag-mask ventilation device for airway management; (2) advanced care paramedics with ALS training including the ability to perform non-drug assisted intubations; and (3) critical care paramedics, who work with the provincial air ambulance programme and can perform rapid sequence intubations using sedative and paralytic medications. Advanced care paramedics were introduced into the Ontario prehospital system on a widespread basis in 1998 and since that time the effectiveness of ALS care on outcomes from cardiac arrest, respiratory distress and trauma has been evaluated in several landmark studies.6 ,8–10 Within the Ontario system, ALS care was studied over the time period of 1998–2002 and found to confer no beneficial effect on overall death rates for major trauma patients, and was associated with a heightened risk of mortality for patients with a prehospital Glasgow Coma Score of 8 or less.6

Despite the lack of evidence of effectiveness, trauma patients in Ontario continue to undergo prehospital non-drug assisted intubation by advanced care paramedics (hereafter, ‘prehospital intubation’). We sought to revisit the relationship between prehospital intubation and outcome in patients injured over the years 2002–2009 in Ontario, as experience with ALS care increased. Our specific objectives were to: (1) describe the annual frequency of prehospital intubation for trauma during the period 2002–2009; (2) determine the association between prehospital intubation and subsequent outcome; and (3) compare outcomes between patients undergoing intubation in the prehospital versus trauma centre settings.

Methods

Study design

This was a formal analysis of data collected in the Ontario Trauma Registry (OTR) Comprehensive Data Set (fiscal years 01 April 2002 to 31 March 2009). The Ontario Trauma Registry is maintained by the Canadian Institute for Health Information which compiles data on severely injured trauma patients who present to Ontario's 11 trauma centres.1 Eligible registry patients are assigned an International Classification of Diseases (V.9 or 10 CA)11 external cause of injury code, have an Injury Severity Score >12 and have been assessed at one of the participating facilities. The study received ethics approval from the Queen's University Health Sciences and Affiliated Hospitals Research Ethics Board (Study code: EMED-143-10).

Study population

We included adult trauma patients (>16 years) with a recorded initial Glasgow Coma Score of 3–8 (either at the scene or at the emergency department (ED)) who were transported by advanced or basic life support paramedics by land ambulance to an Ontario ED. We therefore excluded: paediatric patients, those with missing ages, those where the Glasgow Coma Score was missing or inappropriate (eg, <3), patients treated by critical care paramedics and those with missing airway procedure information.

Patients treated by critical care paramedics were excluded because these providers are able to intubate patients using sedative-hypnotic and paralytic medications, both of which alter the physiological response to laryngoscopy, and may be associated with differential outcomes compared with patients intubated by ALS paramedics, who cannot provide such medications. Patients transported by helicopter or fixed wing aircraft were excluded because these patients are generally cared for by critical care paramedics.

Prehospital airway management

The primary clinical exposure of interest was intubation at the scene or en route to the hospital. We used Ontario Trauma Registry scene procedure codes to categorise patients into two cohorts: intubation or basic airway management. Patients in the intubation cohort were those where paramedics attempted endotracheal intubation, nasotracheal intubation or surgical airway. Patients not undergoing such procedures were considered to have received basic airway management (supplementary oxygen, oral or nasal airways, or assisted ventilation with a bag-mask device). It is not possible to ascertain from Ontario Trauma Registry data whether a procedure was completed successfully, only whether it was attempted by the paramedic. The Ontario Trauma Registry does not document paramedic use of supraglottic airway devices.

Additional patient, scene and hospital information

Additional information considered in this analysis included patient demographics, injury characteristics (mechanism, year and location), vital signs (at the scene, primary hospital ED and lead trauma hospital ED), performance of cardiopulmonary resuscitation by paramedics, Injury Severity Scores,11–13 Trauma Injury Severity Scores14 and Revised Trauma Score.15 ,16

Patient outcomes

The primary outcome was mortality at the trauma centre. Secondary outcomes were: (1) paramedic on-scene time in minutes; (2) total prehospital time in minutes; (3) special care (intensive care) unit length of stay in days; (4) total length of stay at the trauma centre in days; and (5) neurological disability upon discharge as measured by the Glasgow Outcome Score.17 Some of these outcomes were also considered as covariates in the analysis of airway management and its relationship to patient survival to hospital discharge.

Data analysis

Eligible cases with complete data constituted the base study population. We performed the following steps in our statistical analysis, based on precedent by the previous Ontario Prehospital Advanced Life Support Study trauma study (OPALS).6 First, percentages of eligible trauma cases who received prehospital intubation were described by study year. Second, the study population was described according to airway management status in the field (intubation vs basic airway techniques) and by patient and injury-related factors. Patient factors included demographics, year of injury and vital signs (heart rate, unassisted respiratory rate, blood pressure, Glasgow Coma Score) at the scene and upon arrival to the primary hospital or trauma centre. We also described whether cardiopulmonary resuscitation was performed, scene time, total prehospital time, and whether or not initial care was provided at a trauma centre. Additional injury factors included injury mechanisms, place of injury occurrence and indicators of injury severity as suggested by the Major Trauma Outcomes Study and the OPALS trauma study.6 ,8 ,18

Primary and secondary study outcomes were next described by airway management status in the field. For the primary outcome of mortality, the following ‘a priori’ subgroups were evaluated independently and as a part of the entire study population: year of study (2002–2009), patient age group (16–30, 31–50, 51–70, >70 years), observed hypotension at the trauma centre (systolic blood pressure <100 mm Hg) and initial hospital disposition (non-trauma centre vs trauma centre). A cut-off for systolic blood pressure of less than 100 mm Hg was based on the precedent set by the previous OPALS trauma study.6

To further control for baseline differences in injury severity between the prehospital intubation and basic airway management groups, we compared outcomes between patients who were intubated in the prehospital setting with three groups: (1) patients intubated at the trauma centre; (2) patients not intubated either by paramedics or at the trauma centre; and (3) patients whose records intubation occurred in the prehospital setting and at the trauma centre. Patients in the last group were included in the analysis because we felt that these patients were almost certainly intubated by paramedics (as it is very unlikely this procedure would have been recorded in the registry if it had not been performed) and then arrived in the ED with an endotracheal tube in place, leading data abstractors to indicate intubation also occurred in the ED. The purpose of these comparisons was to determine any relative benefit of intubation in the prehospital versus trauma centre setting.

Finally, multiple logistic regression analyses were used to quantify the effect of prehospital intubation on the primary outcome of mortality, while controlling for other factors known to potentially affect patient survival or confound the relationship of interest.7 For both the comparisons between prehospital and trauma centre intubation and the logistic regression analyses, we excluded patients who received prehospital cardiopulmonary resuscitation and so were presumably dead (but for whom resuscitation attempts continued) in the prehospital setting.

Analyses were performed with IBM SPSS Statistics V.19 (IBM Corporation, Armonk, New York, USA, 2010).

Results

Patient population

After application of inclusion and exclusion criteria a final study population of 2229 patients was available for analysis (figure 1).

Table 1 describes the characteristics of the patients included in the analysis. The average patient age was 44.4 (SD: 20.8) years. The majority of patients were male (1625, 72.9%) and injured by blunt mechanisms (2033, 91.2%). A higher percentage of patients within the prehospital intubation group experienced penetrating injuries (95, 14.2%) compared with those in the basic airway management group (75, 4.8%). Most patients were injured on a street or highway (1153, 51.7%) or at home (579, 26.0%).

Table 1

Characteristics of the 2229 patients included in the study

Figure 1

Flow diagram of patients included in the final analysis. GCS: Glasgow Coma Score.

Patients in the prehospital intubation group were more critically injured than patients receiving basic airway management. In the prehospital setting, these patients were more likely to have a Glasgow Coma Score of 3 (405, 63.2% vs 499, 37.5%) or hypotension (193, 28.8% vs 238, 15.3%), and they also had lower respiratory (13.4±11.0 vs 18.7±8.6) and heart rates (73.9±44.8 vs 88.6±31.2) at the scene. Prehospital intubation patients were significantly more likely to concurrently receive cardiopulmonary resuscitation (26.4% vs 4.9%). Median Injury Severity Scores were higher in the intubation compared with basic airway management groups (31 vs 26). Although there were a large number of patients with missing data reported to the central data registry, the median Revised Trauma Score (4.1 vs 5.0) and Trauma Injury Severity Score (2 vs 4) also indicated that the intubation cohort was more severely injured than the basic airway management group.

On arrival at the trauma centre, consistent with the prehospital findings, the prehospital intubation group demonstrated less favourable median Glasgow Coma Scores (3 vs 6), mean systolic blood pressure (109.7±61.1 vs 131.7±39.6 mm Hg), mean respiratory (15±9.1 vs 18.6±7.3 breaths per minute) and mean heart rates (79.7±43.8 vs 91.6±30.2 beats per minute) than the basic airway management cohort (table 1).

Patient outcomes

Outcomes are summarised in table 2. Death rates were significantly higher in patients undergoing intubation compared with basic airway management (66.0% vs 34.8%, p<0.0001). Median total prehospital times (47 vs 45 min) and time spent at the scene of injury (18 vs 17 min) were also longer in the intubation group. Neurological disability at discharge was worse in the prehospital intubation cohort. The median lengths of stay at the lead trauma hospital and in the Special Care Unit/Intensive Care Unit (SCU/ICU) were both shorter in the prehospital intubation cohort (5.5 vs 12 days and 1 vs 8 days, respectively), as differentially higher numbers of prehospital intubation patients died in the time interval immediately following admission.

Table 2

Primary and secondary outcomes in trauma patients undergoing prehospital basic airway management or non-drug assisted intubation

Outcomes in clinically important patient subgroups were consistent with those of the entire patient cohort (table 3). Death rates were higher in the prehospital intubation cohort, irrespective of age group, hypotension at the scene or year of study. Overall, patients taken directly to a trauma centre had higher death rates than those initially transported to a non-trauma centre (49.2% vs 34.4%). The highest death rates (70.3%) were in patients undergoing prehospital intubation and then transported directly to a trauma centre.

Table 3

Death rates (%) in clinically important subgroups of trauma patients undergoing prehospital basic airway management or non-drug assisted intubation

After excluding the 11.3% (251/2229) of patients who received prehospital cardiopulmonary resuscitation, we found that patients intubated in the prehospital setting were still significantly more physiologically deranged and more likely to die than patients receiving intubation at the trauma centre (table 4). Patients undergoing prehospital cardiopulmonary resuscitation had an 88.8% (222/251) death rate.

Table 4

Comparison of trauma patient outcomes among: (1) patients who did not undergo prehospital or trauma centre intubation; (2) patients undergoing prehospital intubation; (3) patients undergoing trauma centre intubation; and (4) patients whose records indicated intubation occurred in the prehospital and trauma centre settings

Adjusted ORs for the primary outcome of mortality derived from the multiple logistic regression analysis are presented in figure 2. Mortality was strongly associated with prehospital intubation (adjusted OR 2.8, 95% CI 1.1 to 7.6), trauma centre intubation (adjusted OR 2.6, 95% CI 1.3 to 5.6), hypotension (SBP<100 mm Hg, adjusted OR 2.4, 95% CI 1.1 to 5.3), age (adjusted OR 1.7 per 10-year interval, 95% CI 1.5 to 1.9 per 10-year interval), Injury Severity Score (adjusted OR 1.3 per 10 unit increase, 95% CI 1.1 to 1.7 per 10 unit increase) and Glasgow Coma Score (per unit, adjusted OR 0.8, 95% CI 0.7 to 0.8). A series of sensitivity analyses were conducted to examine these relationships with further adjustment for heart rate, respiratory rate, prehospital scene time, total prehospital time, Trauma Injury Severity Score and Revised Trauma Score; there were no discernible changes in the main effects that are summarised in figure 2 with the addition of the latter variables to the logistic models (data not shown).

Figure 2

Logistic regression analysis with adjusted OR (95% CI) of mortality for various parameters. Goodness-of-fit: p>0.20. ISS: Injury Severity Score; GCS: Glasgow Coma Score.

Trends in prehospital airway management

Over the 7-year study period, the percentage of patients undergoing prehospital intubation for trauma declined from 33.7% to 14.0% (ptrend<0.0001; figure 3). Among the 671 prehospital intubations with full data, 460 (68.6%) were endotracheal intubations, 209 (31.1%) were nasotracheal intubations and 2 (0.3%) were surgical airways.

Figure 3

Percentage of trauma patients undergoing prehospital intubation (grey) and mortality (black) by year in Ontario, Canada. χ2 Test for a declining linear trend in these prehospital intubation percentages, ptrend<0.0001, and for an increasing linear trend in mortality, ptrend=0.08, with no evidence of a statistically significant correlation between annual rates of prehospital intubation and mortality (Pearson r=0.26; p=0.53).

Discussion

Since the first evaluation of prehospital ALS care in Ontario in 2002, there has been a significant decline in the proportion of patients undergoing prehospital intubation for trauma. Over the same time period death rates have remained consistent, and the previously noted association between prehospital intubation and mortality has persisted. The decline in the performance of prehospital intubation may relate to the publication of the Stiell et al (2008) study,6 and more generally an increased sense of the limited benefit of this intervention in trauma patients.

The association between prehospital non-drug assisted intubation and mortality has at least two potential explanations. The first is that the relationship is a causal one, in which non-drug assisted intubation in the prehospital setting heightens the risk of mortality. Physiological explanations for this association have included: spikes in intracranial pressure related to laryngoscopy without rapid sequence induction,19 inadvertent hypoxaemia during intubation efforts20 or cerebral ischaemia due to hyperventilation.21 ,22 Prolonged scene times are unlikely to explain this association, as we and others6 have found that prehospital non-drug assisted intubation does not increase scene times by a clinically relevant extent.

An alternative explanation is the differential selection of sicker patients to receive intubation in the field. Critically ill trauma patients requiring early airway management face very high death rates,5 and existing injury severity measures may not provide an adequate means to adjust for injury severity in this population. Even after risk adjustment, patients undergoing prehospital intubation may still be more critically injured than those treated with basic airway management techniques.5

The association we have identified (OR 2.8, 95% CI 1.1 to 7.6) is consistent with other recent reports on the topic.2 ,5 ,6 In the original OPALS trauma study, the OR for mortality associated with prehospital intubation was 2.8 (95% CI 1.6 to 5.0), while in the more recent Davis et al (2011) study it was 2.91 (95% CI 2.13 to 3.98). Bakalos (2011) described an OR of 0.892 for survival (95% CI 0.775 to 2.026) based on a meta-analysis of nine trials.

One strength of our study is the focus on a specific patient population: trauma patients with an initial Glasgow Coma Score less than 9. We chose this inclusion criterion because it is the major one paramedics use in making the decision to proceed with an intubation attempt. Although some of these patients were likely comatose for other reasons we felt that the application of this inclusion criterion would lead to more generalisable results.

An additional strength of our study is that we have provided a comparison of death rates between patients undergoing intubation in the prehospital setting versus the ED of the trauma centre. The intent of this comparison was to determine whether there was any incremental mortality risk associated with prehospital intubation. We found that intubation at the trauma centre was also associated with increased mortality. Thus, it seems that the need for intubation early in a trauma patient's course portends a heightened risk of mortality, regardless of the location the procedure occurs.

The most significant limitation to our study is the quantity of missing data we encountered in the Ontario Trauma Registry. For instance, after excluding paediatric patients and those with a Glasgow Coma Score greater than 8, there were 11 132 (43.0%) of patients with either a missing or inappropriate Glasgow Coma Scores in either the prehospital or hospital settings. Presumably, the limited availability of injury scores (Revised Trauma core and Trauma Injury Severity Score) was due to the large volume of missing data on vital signs. This in turn limited our analyses for accurate risk adjustment. Future studies using Ontario Trauma Registry data would benefit from greater data completeness.

An additional limitation of the study is that the Ontario Trauma Registry does not track the use of supraglottic airway devices by prehospital providers. Devices such as the Laryngeal Mask Airway (LMA North America Inc., San Diego, California, USA), King Laryngeal tube airway (Kingsystems, Noblesville, Indiana, USA) and Combitube (Tyco Healthcare, Mansfield, Massachusetts, USA) are widely used in many prehospital care systems, particularly in the setting of cardiac arrest, and have proven to be easily placed, safe and effective for ventilation.22–26 A single case series study has also reported high rates of procedural success and infrequent complications when physicians and paramedics used the Laryngeal Tube Suction Device (VBM Medizintechnik, Sulz, Germany) for prehospital trauma airway management.26 Further investigation of the role of supraglottic devices in prehospital trauma care should be encouraged.

Our analysis is also subject to several common types of bias that are typical of observational designs. First, our case selection was based upon the subsample of GCS<9 cases who were admitted to hospital and were subsequently registered in the OTR system with an Injury Severity Score that met or exceeded the minimum for trauma. This necessarily excluded cases who died prior to hospital arrival, ambulatory or other cases where paramedic services were not employed, and some cases taken to out-of-province institutions, If selection was associated with mortality and the likelihood of paramedic administered non-drug assisted intubation, then some selection bias is possible. Attrition bias is also possible due to the fact that our analysis was based on the subset of cases who were enrolled in the OTR and had complete data on the primary exposures, outcomes and covariates of interest. Finally, random misclassification of exposures and covariates is always a possibility, and such errors were likely to bias effect estimates towards the null.

The primary implication of our study is that prehospital non-drug assisted intubation remains of unproven benefit and is potentially a source of harm in trauma patients. Existing data do not allow us to determine whether there is a causal relationship between prehospital non-drug assisted intubation and mortality, or whether patients undergoing prehospital intubation simply represent a selected group of critically ill patients. We acknowledge that some patient populations including those in rural areas, facing prolonged transport times, those cared for by Critical Care Paramedics or with specific causes of airway compromise may benefit from prehospital intubation. The effectiveness of prehospital intubation in these settings remains open to further study.

Conclusions

Prehospital intubation for trauma is being performed less frequently in Ontario, Canada. Within our study population, prehospital non-drug assisted intubation or attempted intubation was associated with a heightened risk of mortality. Existing data do not allow us to determine whether this association represents a causal relationship or is due to the differential selection of sicker trauma patients to receive intubation in the field.

Acknowledgments

We wish to thank Dr Andrew Reed, Associate Medical Director, Regional Paramedic Program for Eastern Ontario and Ontario Provincial Police Physician, for his comments and feedback on this manuscript.

Footnotes

  • Contributors All of the authors contributed to this work. CCDE and WP developed the study design, performed data analysis and contributed in writing the manuscript. RB, IGS, and DH contributed to the study design and analysis and provided feedback and revisions to the manuscript. CCDE is the guarantor for the study.

  • Competing interests None.

  • Ethics approval Queen's University Health Sciences and Affiliated Hospitals Research Ethics Board (Study code: EMED-143-10).

  • Provenance and peer review Not commissioned; externally peer reviewed.

References


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