The Out-of-Hospital Validation of the Canadian C-Spine Rule by Paramedics

Background 

North American emergency medical services (EMS) annually transport more than 1 million trauma patients with a suspected cervical spine injury.1 Approximately 2% of these patients have a cervical spine fracture, and less than 1% develop neurologic deficits.2 Because of the potential for spinal cord injury, out-of-hospital trauma guidelines usually recommend that paramedics protect the cervical spine of trauma patients during ambulance transport, which is usually achieved by such measures as a backboard, a cervical spine collar, and head immobilization.3 This general protocol is often followed regardless of whether the patient is fully alert and stable and regardless of whether the patient was ambulatory at the scene. This practice is not evidence based, but rather the result of region-specific protocols developed by EMS medical directors. A Cochrane Review found no evidence that spinal immobilization lessens mortality or neurologic injury or improves spinal stability during transport.4

Importance 

Cervical spine immobilization in the field is often unnecessary, is time intensive for paramedics in the field, and is very uncomfortable for patients. The potential for multiple clinical and system adverse effects and discomfort with immobilization have been well documented. Chest straps used in immobilization have a marked pulmonary restrictive effect, even in healthy nonsmokers.5 Immobilization on a board leads to progressively worse pain in the head, neck, and back area, often resulting in the necessity to radiograph the spine in the emergency department (ED).6 Immobilized patients consume valuable ED space, require immediate attention from physicians, nurses, and radiology technicians, and aggravate the problem of ED crowding.7, 8

Goal of This Investigation 

Clinical decision rules attempt to reduce the uncertainty of medical decisionmaking by standardizing the collection and interpretation of clinical data.9 We designed the Canadian C-Spine Rule to allow physicians to clear the cervical spine in a few minutes by means of simple questions and assessment. This rule is based on 3 high-risk criteria, 5 low-risk criteria, and the ability of patients to rotate their neck. We derived and validated the Canadian C-Spine Rule in 2 large multicenter studies involving a total of 17,207 alert and stable ED trauma patients.2, 10 Several investigators have used other decision rules to evaluate the potential for paramedics to clear the cervical spine in the field and avoid immobilization,11, 12, 13 but all resulted in missed cervical spine injuries. The goal of this study is to prospectively assess the performance characteristics, reliability, and clinical sensibility of the Canadian C-Spine Rule for alert, stable, and cooperative trauma patients when used by paramedics in the out-of-hospital setting.

Study Design 

We conducted a prospective multicenter cohort study to evaluate a convenience sample of trauma patients assessed in the field by advanced and basic care paramedics using the Canadian C-Spine Rule.

Setting 

This national study took place between 2002 and 2006 in 7 locations, with populations ranging from 70,876 to 935,106, distributed in 3 Canadian provinces: Ontario (Ottawa, Windsor, Halton, Sarnia, and Niagara Falls), Alberta (Calgary), and Nova Scotia (Industrial Cape Breton, Kentville, Truro, and Bridgewater). All sites have sophisticated EMS services, with first-responding firefighters and second-tier basic care and advanced care paramedics. The Ontario communities share a central computerized ambulance response information system and a common ambulance call report. Nova Scotia also benefits from a uniform response information system and a common ambulance call report used throughout the province. Participation of paramedics in this study was voluntary.

Selection of Participants 

We enrolled a convenience sample of alert, stable, and cooperative patients transported by ambulance to local hospitals after sustaining acute blunt trauma with potential injury to the neck. These are patients for whom standard EMS protocols require immobilization. We defined “alert” as a Glasgow Coma Scale14 score of 15 (converses, fully oriented, and follows commands). “Stable” refers to normal vital signs as defined by the Revised Trauma Score3 (systolic blood pressure 90 mm Hg or greater and respiratory rate between 10 and 24 breaths/min on arrival). “Cooperative” indicates that the patient willingly follows commands and is not agitated. “Acute” refers to injury within the past 8 hours. “Trauma with potential injury to the neck” included patients with either posterior neck pain with any blunt mechanism of injury, or no neck pain but some visible injury above the clavicles. Patients were ineligible if they were younger than 16 years, had a penetrating trauma to the neck, were acutely paralyzed (paraplegia, quadriplegia), or had known vertebral disease (ankylosing spondylitis, rheumatoid arthritis, spinal stenosis, or previous cervical spine surgery). The research ethics board at each participating institution approved the study and waived the requirement for written informed consent, with the exception of Nova Scotia, where written consent was necessary before enrollment.

Methods of Measurement 

Every paramedic completed a 2-hour Web-based training session, followed by a practical demonstration using case scenarios to assess the Canadian C-Spine Rule uniformly. Paramedics subsequently assessed patients in the field by using the Canadian C-Spine Rule, recorded their findings, along with their interpretation of the decision rule itself, on a standard data collection form before arrival at the hospital, and proceeded to immobilize all patients before transport, as per their current protocol. Before the start of the trial, paramedics from Calgary and Nova Scotia could decide not to immobilize patients for transport, following local protocols; they continued to selectively immobilize patients as part of this study, but using the Canadian C-Spine Rule instead. EMS supervisors and study personnel were always available to answer questions, during and between patient evaluations.

We have slightly revised the Canadian C-Spine Rule for out-of-hospital use (Figure 1). We removed the low-risk criteria pertaining to “delayed onset of neck pain” because paramedics were going to assess patients before such a delay would occur. We asked paramedics to measure the clinical sensibility related to the interpretation and use of the Canadian C-Spine Rule by indicating whether cervical spine immobilization was indicated or not according to the decision rule and how comfortable they would be (5-point scale from “very comfortable” to “very uncomfortable”) if in fact following the rule's recommendation for each patient assessed. Time permitting, some patients were assessed independently by a second paramedic to determine interobserver agreement.

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Figure 1. The Canadian C-Spine Rule for alert (Glasgow Coma Scale score 15) and stable trauma patients for whom cervical spine injury is a concern, including patients with either posterior neck pain with any blunt mechanism of injury or no neck pain but some visible injury above the clavicles. MVC, Motor vehicle crash.

Outcome Measures 

The primary outcome, acute cervical spine injury, was defined as any fracture, dislocation, or ligamentous instability demonstrated by radiographic imaging. All injuries were considered clinically important unless radiography, including computed tomography (CT) and flexion-extension views, demonstrated one of the following isolated clinically unimportant cervical spine injuries: avulsion fracture of osteophyte, fracture of transverse process not involving facet joint, fracture of spinous process not involving lamina, or simple compression fracture less than 25% of vertebral body height. This definition of clinically important cervical spine injury was standardized according to the results of a formal survey of 129 neurosurgeons, spine surgeons, neuroradiologists, and emergency physicians at 8 Canadian academic centers.15 Emergency physicians at each receiving hospital determined whether patients required cervical spine imaging according to their clinical evaluation, which may have included using the Canadian C-Spine Rule. For those imaged, standard diagnostic imaging may have included plain radiography, oblique views, flexion-extension views, and CT at the discretion of the treating physician. Staff radiologists interpreting the radiographs were provided with routine clinical information but not the contents of the data form.

We asked a study nurse to contact all enrolled patients who did not have diagnostic imaging by telephone or mail within 14 days and classified them as having no acute cervical spine injury if they met all the following explicit criteria: (1) pain in neck is rated as none or mild, (2) restriction of movement of neck is rated as none or mild, (3) does not require use of a neck collar, and (4) neck injury has not prevented return to usual occupational activities (work, housework, or school). The nurse assessing these criteria was unaware of the patient's status for the Canadian C-Spine Rule. Patients who could not fulfill these criteria were recalled for clinical reassessment and cervical spine radiography. The validity of these criteria to exclude acute cervical spine injury was previously determined in a substudy in which the telephone follow-up questionnaire was applied to a random sample of study patients with and without cervical spine injury and who had all undergone radiography.16 The questionnaire proved to be 100% sensitive for identifying 66 abnormal cases among the 389 radiography patients reached by telephone.

Primary Data Analysis 

We measured the performance characteristics of the rule for identifying acute cervical spine injury, as well as the performance characteristics of the interpretation of the rule by the attending paramedics with 95% confidence intervals (CIs) for sensitivity, specificity, and negative predictive value. The final interpretation of the rule, ie, positive or negative for cervical spine injury, was made by the investigators according to the status of the patient for the component variables, as documented by the attending paramedic on their study data collection sheet or patient care reports. We assessed the reliability of the rule by using the κ coefficient for each variable and for the interpretation of the rule between paramedics. We estimated the clinical sensibility of the rule by reporting paramedics' theoretical comfort in using the rule and the potential of the rule for reducing the number of patients requiring immobilization if the rule had been applied. We performed all analyses with SAS statistical software, version 9.1 (SAS Institute, Inc., Cary, NC).

Characteristics of Study Subjects 

We enrolled 2,393 eligible patients in the study between May 2002 and June 2006 (Figure 2). One thousand one hundred twenty-six patients were not evaluated with cervical spine radiography and required telephone follow-up. We reached 788 (70.0%) of those patients, among which 682 were determined to not have sustained a cervical spine injury, according to our validated proxy assessment tool. A total of 1,949 enrolled patients had complete outcome assessments, and the characteristics of these study patients are presented in Table 1; 12 (0.6%) had a clinically important cervical spine injury. In 2 cases, the investigators could perform an independent assessment of the rule according to the paramedic care report but could not evaluate the paramedic assessment of the rule according to their study data collection sheet. The characteristics of the 444 patients without outcome assessments were similar to those with radiographic evaluation but were less likely to be admitted to the hospital (Table E1, available online at http://www.annemergmed.com).

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Figure 2. Flow of patients recruited in the study.

Table 1. Characteristics of the 1,949 enrolled study patients with complete outcome assessment.

	Characteristic	Value	Characteristic	Value
	Age, y		Characteristics of motor vehicle crash, No. (%)
	Median (interquartile range)	39.0(26–52)	Simple rear-end crash	336(17.2)
	Range	16, 103	Rollover	124(6.4)
	Female sex, No. (%)	990(50.8)	Head-on crash	49(2.5)
	Mechanism of injury, No. (%)		Ejection from vehicle	9(0.5)
	Motor vehicle crash	1,218(62.5)	Death of other(s) in same crash	4(0.2)
	Motorcycle crash	41(2.1)
	Crash involving other motorized vehicles	21(1.1)	Cervical-spine radiography performed, No. (%)	1,267(65.0)
	Bicycle struck	36(1.8)	Outcome by telephone follow-up, No. (%)	682(35.0)
	Bicycle crash	25(1.3)	Acute cervical-spine injury, No. (%)	18(0.9)
	Other bicycle accident	29(1.5)	Fracture	14(0.7)
	Pedestrian struck	44(2.3)	Dislocation	3(0.2)
	Pedestrian struck and thrown	30(1.5)	Ligamentous instability	7(0.4)
	Fall from elevation <3 ft (1 m) or down <5 stairs	209(10.7)	Clinically important cervical spine injury, No. (%)	12(0.6)
	Fall from elevation of 3–10 ft (1–3 m) or down 5–15 stairs	108(5.5)
	Fall from elevation >10 ft (3 m) or down >15 stairs	70(3.6)	Stabilizing treatments, No. (%)	6(0.3)
	Fall onto head (axial load)	1(0.1)	Internal fixation	5(0.3)
	Heavy object onto head (axial load)	9(0.5)	Halo	1(0.1)
	Contact sport (axial load)	16(0.8)	Brace	2(0.1)
	Diving	2(0.1)	Rigid collar	3(0.2)
	Other sport	21(1.1)
	Assault with fist or feet	33(1.7)	Admitted to hospital, No. (%)	210(10.8)
	Assault with a blunt object	14(0.7)
	Head struck by other object	11(0.6)
	Hit head on an object	5(0.3)
	Other	6(0.3)

We defined acute cervical spine injury as any fracture, dislocation, or ligamentous instability demonstrated by radiographic imaging. All injuries are considered clinically important unless radiography, including CT and flexion-extension views, demonstrates one of the following isolated clinically unimportant cervical spine injuries: avulsion fracture of osteophyte, fracture of transverse process not involving facet joint, fracture of spinous process not involving lamina, or simple compression fracture less than 25% of vertebral body height.

The distribution of various elements of the Canadian C-Spine Rule among the 1,947 patients assessed by paramedics is detailed in Table 2; 944 (48.5%) were believed to have at least 1 of the high-risk factors mandating immobilization. Among the remaining 1,003 participants, 927 (92.4%) had at least 1 low-risk factor, allowing for safe assessment of neck range of motion. Range of motion was evaluated in 761 (82.1%) of these 927 patients and was successful in 731.

Table 2. Distribution of various elements of the Canadian C-Spine Rule among 1,947 patients⁎ assessed by paramedics.

	Canadian C-Spine Rule Elements	Number of Patients†
	Assessed for high-risk factor (n=1,947)
	Age 65 y or older	205
	Dangerous mechanism	670
	Paresthesias in extremities	192
	Assessed for low-risk factor (n=1,003)
	Simple rear-end motor vehicle crash	261
	Ambulatory at any time at scene	602
	No neck pain at scene	422
	Absence of midline cervical spine tenderness	371
	Assessment of neck rotation possible (n=927)
	Patient able to actively rotate neck	731
	Paramedics did not attempt to evaluate neck rotation	166

⁎ In 2 cases, we could not evaluate the paramedic assessment of the rule according to their study data collection sheet. We omitted these 2 cases from the paramedic assessment analysis. † A patient can have more than 1 element of the decision rule.

Paramedics conservatively misinterpreted the rule in 320 patients (16.4%), including 154 cases (7.9%) in which “dangerous mechanism” was overcalled and 166 cases (8.5%) in which paramedics did not evaluate neck rotation as required by the Canadian C-Spine Rule. The Canadian C-Spine Rule assessment for these patients was later categorized by the investigators as “indeterminate.” Patient characteristics for these 320 patients were similar to those for which the rule was followed accurately, with the exception that none of the 320 patients had a cervical spine injury (Table E2, available online at http://www.annemergmed.com). Paramedics did not attempt to evaluate neck rotation in any of the 12 patients with a clinically important injury.

Main Results 

The performance characteristics of the Canadian C-Spine Rule as assessed by the investigators and by the paramedics are compared in Table 3. The sensitivity of the rule was 100% (95% CI 74% to 100%), regardless of whether the assessment was performed by the investigators or the paramedics. The specificity of the rule was 42.9% (95% CI% 40 to 45%) when assessed by investigators compared with 37.7% (95% CI 36% to 40%) when assessed by paramedics. The negative predictive value of the rule was 100% (95% CI 99% to 100%) for both investigators and paramedics.

Table 3. Sensitivity, specificity, and negative predictive value of the Canadian C-Spine Rule for 12 cases of clinically important injury among 1,629 patients⁎ assessed by the study investigators and 1,947 patients† assessed by the participating paramedics.

	Result of Assessment	Investigators (95% CI)		Paramedics (95% CI)
		Injury	No Injury	Injury	No Injury
	Positive, No.	12	924	12	1,204
	Negative, No.	0	693	0	731
	Sensitivity, %	100(74–100)		100(74–100)
	Specificity, %	42.9(40–45)		37.7(36–40)
	Negative predictive value, %	100(99–100)		100(99–100)

⁎ In 320 cases, the investigators could not perform an independent assessment of the rule according to the documentation provided by paramedics (including 166 cases in which neck rotation was not attempted, as required by the rule). We classified these cases as indeterminate for the rule and omitted them for this analysis. † In 2 cases, the investigators could perform an independent assessment of the rule according to the paramedic care report but could not evaluate the paramedic assessment of the rule according to their study data collection sheet. We omitted these 2 cases from the paramedic assessment analysis.

We performed secondary analyses involving all 1,949 patients to determine the potential effect of indeterminate cases when the rule was assessed by paramedics. When the rule was assumed to be positive for all indeterminate cases, the specificity was 32.4% (95% CI 31% to 34%), and when the rule was assumed to be negative for all indeterminate cases, the specificity was 46.6% (95% CI 45% to 49%). The sensitivity and negative predictive value remained the same because there were no cervical spine injuries among the indeterminate cases.

We assessed the reliability of paramedic interpretation of the rule by measuring the κ coefficient for interobserver agreement for each element of the rule (Table 4). The κ value for the overall interpretation of the rule was 0.93 (95% CI 0.87 to 0.99). A value greater than 0.80 is generally considered to reflect almost perfect agreement.17

Table 4. κ values for individual clinical variables in the Canadian C-Spine Rule among 155 interobserver paramedics.

We assessed the clinical sensibility of the rule in 2 ways. First, we measured the acceptability of the rule by using a 5-point Likert scale, ranging from “very uncomfortable” to “very comfortable.” Paramedics were “very uncomfortable” or “uncomfortable” applying the Canadian C-Spine Rule in 9.5% of cases; they were “comfortable” or “very comfortable” in 81.7% of cases. We also evaluated the potential effect of the rule on the number of necessary immobilizations. If paramedics were allowed to use the rule, 62.2% (95% CI 60% to 64%) of recruited patients would have required immobilization in the field compared with the actual immobilization rate of 100%.