Occlusion Pressures of Tactical Pneumatic Tourniquet 2".

BACKGROUND: The Tactical Pneumatic Tournqiuet 2" (TPT2, 5.1cm-wide deflated) allows total average applied pressure measurement, which should be useful toward development of emergency-use limb tourniquet certification devices. METHODS: The TPT2 hand bulb was replaced with stopcocks and syringes, allowing filling with continuous pressure measurement. Forearm and mid-thigh applications involved two sets of five Doppler-based pulse gone/return pairs. Second set pulse gones were chosen a priori for occlusion pressures (preliminary work indicated greater consistency in second sets). RESULTS: All 68 forearms occluded (30 female, 38 male, median circumference 17.8cm, range 14.6-23.5cm; median second set of pulse gone tourniquet pressures 176mmHg, range 128-282mmHg). Fifty-five thighs occluded (median circumference 54.3cm, range 41.6-62.4cm; median systolic pressure 126mmHg, range 102-142mmHg; median second set of pulse gone pressures 574mmHg, range 274-1158mmHg). Thirteen thigh applications were stopped without occlusion because of concerning pressures combined with no indication of imminent occlusion and difficulties forcing more air into the TPT2 (3 female, 10 male, peak pressures from 958-1377mmHg, median 1220mmHg, p<.0001 versus occluded thighs; median circumference 63.3cm, range 55.0-72.9cm, p<.0001 versus occluded thighs; median systolic pressure 126mmHg, range 120-173mmHg, p<.019 versus occluded thighs). Thigh TPT2 impression widths on five subjects after occlusion were as follows: 3.5cm, occlusion 274mmHg; 2.8cm, occlusion 348mmHg; 2.9cm, occlusion 500mmHg; 2.8cm, occlusion 782mmHg; 2.7cm, occlusion 1114mmHg. CONCLUSIONS: Though probably useful to tourniquet certification, the required pressures for thigh occlusion make the TPT2 undesirable for any clinical use, emergency or otherwise.

Effects of Tourniquet Features on Application Processes.

BACKGROUND: We investigated emergency-use limb tourniquet design features effects on application processes (this paper) and times to complete those processes (companion paper). METHODS: Sixty-four appliers watched training videos and then each applied all eight tourniquets: Combat Application Tourniquet Generation 7 (CAT7), SOF™ Tactical Tourniquet-Wide Generation 3 (SOFTTW3), SOF™ Tactical Tourniquet-Wide Generation 5 (SOFTTW5), Tactical Mechanical Tourniquet (TMT), OMNA Marine Tourniquet (OMT), X8T tourniquet (X8T), Tactical Ratcheting Medical Tourniquet (Tac RMT), and RapidStop™ Tourniquet (RST). Application processes were scored from videos. RESULTS: Thirty-three appliers had no prior tourniquet experience. All 512 applications were placed proximal to the recipient's simulated distal thigh injury. Thirty-one appliers (13 with no experience) had 66 problem-free applications (18 by no experience appliers). Tightening-system mechanical problems were more frequent with windlass rod systems (26 losing hold of the rod, 27 redoing rod turns, and 58 struggling to secure the rod) versus ratchet systems (3 tooth skips and 16 advance failures). Thirty-five appliers (21 with no experience) had 68 applications (45 by no experience appliers) with an audible Doppler pulse when stating "Done"; causes involved premature stopping (53), inadequate strap pull (1 SOFTTW3, 1 RST), strap/redirect understanding problem (1 SOFTTW5, 1 X8T, 4 Tac RMT, 1 RST), tightening-system understanding problem (2 CAT7, 1 SOFTTW3, 1 TMT, 1 RST), and physical inability to secure (1 SOFTTW3). Fifty-three appliers (32 no experience) had 109 applications (64 by no experience appliers) not correctly secured. Six involved strap/redirect understanding problems: 4 Tac RMT, 1 X8T, 1 SOFTTW5; 103 involved improper securing of non-self-securing design features: 47 CAT7 (8 strap, 45 rod), 31 TMT (17 strap, 19 rod), 22 OMT (strap), and 3 SOFTTW3 (rod). CONCLUSION: Self-securing systems have process advantages. Because most emergent tourniquet recipients require transport, we believe tourniquet security is a critical design aspect. Decisions regarding tourniquet choices may become very different when both occlusion and tourniquet security are considered.

Effects of Tourniquet Features on Application Processes Times.

BACKGROUND: We investigated emergency-use limb tourniquet design features effects on application processes (companion paper) and times to complete those processes (this paper). METHODS: Sixty-four appliers watched training videos then each applied all eight tourniquets: Combat Application Tour- niquet Generation 7 (CAT7), SOF™ Tactical Tourniquet-Wide Generation 3 (SOFTTW3), SOF™ Tactical Tourniquet-Wide Generation 5 (SOFTTW5), Tactical Mechanical Tourniquet (TMT), OMNA Marine Tourniquet (OMT), X8T-Tourniquet (X8T), Tactical Ratcheting Medical Tourniquet (Tac RMT), and RapidStop Tourniquet (RST). Application processes times were captured from videos. RESULTS: From "Go" to "touch tightening system" was fastest with clips and self-securing redirect buckles and without strap/redirect application process problems (n, median seconds: CAT7 n=23, 26.89; SOFTTW3 n=11, 20.95; SOFTTW5 n=16, 20.53; TMT n=5, 26.61; OMT n=12, 25.94; X8T n=3, 18.44; Tac RMT n=15, 30.59; RST n=7, 22.80). From "touch tightening system" to "last occlusion" was fastest with windlass rod systems when there were no tightening system understanding or mechanical problems (seconds: CAT7 n=48, 4.21; SOFTTW3 n=47, 5.99; SOFTTW5 n=44, 4.65; TMT n=38, 6.21; OMT n=51, 6.22; X8T n=48, 7.59; Tac RMT n=52, 8.44; RST n=40, 8.02). For occluded, tightening system secure applications, from "touch tightening system" to "Done" was fastest with self-securing tightening systems tightening from a tight strap (occluded, secure time in seconds from a tight strap: CAT7 n=17, 14.47; SOFTTW3 n=22, 10.91; SOFTTW5 n=38, 9.19; TMT n=14, 11.42; OMT n=44, 7.01; X8T n=12 9.82; Tac RMT n=20, 6.45; RST n=23, 8.64). CONCLUSIONS: Suboptimal processes in- crease application times. Optimal design features for fast, occlusive, secure tourniquet applications are self-securing strap/ redirect systems with an easily identified and easily used clip and self-securing tightening systems.

Clothing Effects on Limb Tourniquet Application.

BACKGROUND: Sometimes tourniquets are applied over clothing. This study explored clothing effects on pressures and application process. METHODS: Generation 7 Combat Application Tourniquets (C-A-T7), Generation 3 SOF® Tactical Tourniquets-Wide (SOFTTW), Tactical Ratcheting Medical Tourniquets (Tac RMT), and Stretch Wrap And Tuck Tourniquets (SWATT) were used with different clothing conditions (Bare, Scrubs, Uniform, Tights) mid-thigh and on models (ballistic gel and yoga mats). RESULTS: Clothing affected pressure responses to controlled force applications (weight hangs, n=5 thighs and models, nonlinear curve fitting, p < .05). On models, clothing affected secured pressures by altering surface interactions (medians: Gel Bare C-A-T7 247mmHg, SOFTTW 99mmHg, Tac RMT 101mmHg versus Gel Clothing C-A-T7 331mmHg, SOFTTW 170mmHg, Tac RMT 148mmHg; Mats Bare C-A-T7 246mmHg, SOFTTW 121mmHg, Tac RMT 99mmHg versus Mats Clothing C-A-T7 278mmHg, SOFTTW 145mmHg, Tac RMT 138mmHg). On thighs, clothing did not significantly influence secured pressures (n=15 kneeling appliers, n=15 standing appliers) or occlusion and completion pressures (n=15). Eleven of 15 appliers reported securing on clothing as most difficult. Fourteen of 15 reported complete applications on clothing as most difficult. CONCLUSIONS: Clothing will not necessarily affect tourniquet pressures. Surface to tourniquet interactions affect the ease of strap sliding, so concern should still exist as to whether applications over clothing are dislodged in a distal direction more easily than applications on skin.

Driving with undiagnosed obstructive sleep apnea (OSA): High prevalence of OSA risk in drivers who experienced a motor vehicle crash.

Objective: Obstructive sleep apnea (OSA) is a risk factor for motor vehicle crashes (MVC), and patients with diagnosed OSA have a higher likelihood of being involved in a traffic accident. OSA, however, is often underdiagnosed in the general population. The purpose of this study was to assess the risk of undiagnosed OSA among hospitalized patients involved in MVCs.Methods: This is a prospective, observational pilot study of adult trauma patients admitted to a Level 1 trauma center after being the driver in a MVC. Patients were administered the STOP-Bang to assess risk of OSA and were asked questions about the circumstances of the MVC. Patients with a STOP-Bang score 5-8 were considered to be at high risk for OSA. Differences between variables were assessed using independent t-tests and chi-square.Results: Eighty patients participated in the study, and 26% (n = 21) were considered to be at high risk for OSA based on the STOP-Bang score. Compared to patients at low and intermediate risk, patients at high risk for OSA were significantly older (p < .001), had longer hospitalization (p = .06), and were less likely to discharge home from the hospital (p = .01). Patients at moderate and high risk had higher rates of hospital readmission within 1 year of discharge, when compared to the low risk group. Eighty-four percent of all crashes involved a single occupant (driver) in the vehicle, 58% involved only a single vehicle, and 40% occurred on a rural road. There were no significant differences between risk groups for number of vehicles involved in the accident, location of the accident, or number of vehicle occupants.Conclusions: Results of this pilot study suggest that more than one-quarter of drivers hospitalized after motor vehicle crashes were at high risk for OSA. Diagnosed or undiagnosed OSA is a significant public health concern and an established risk factor for motor vehicle accidents. Standardized screening for risk of sleep apnea should be considered by primary care physicians when guiding patients on health and behavior decisions, particularly in regards to driving and road safety.

Potentially inappropriate medication prescribing in the elderly: Is the Beers Criteria relevant in the Emergency Department today?

STUDY OBJECTIVE: To investigate the frequency of Beers Criteria (BC) medication and opioid use in patients age 65 years and older arriving in the Emergency Department. METHODS: We performed a retrospective observational study of a convenience sample of 400 patients, age 65 years and older, arriving to and discharged solely from the Emergency Department. We examined 400 sequential patient charts with visit dates April-July 2017, for the presence of a Beers Criteria medication or opioid prescription. We also examined each chart for nine specific chief complaints, including return visits and subsequent admissions. RESULTS: Of the 400 patients included in this study, 304 patients (76%; 95% confidence interval [CI] 72% to 80%) had at least 1 prescription at the index ED visit for an "avoid" or "use with caution" Beers Criteria medication. Of these patients, 194 (64%; 95% CI 58% to 69%) had ≥2 Beers medication prescriptions and 122 patients (40%; 95% CI 35% to 46%) had ≥3 Beers medication prescriptions. We found no difference in the number of patients with a chief complaint of interest between the BC medication list (28%) and lacking a BC medication (29%) (p-value = 1). No patients returned in the next 7 days for a medication-related complaint. CONCLUSION: The results of this study call into question the routine application of lists without high-quality evidence to critique the prescribing of certain medications. Further patient-oriented study of the relevance of the Beers Criteria list, especially in light of the changed face of medication profiles and populations, is called for.

Best Tourniquet Holding and Strap Pulling Technique.

BACKGROUND: Appropriate strap pressure before tightening-system use is an important aspect of nonelastic, limb tourniquet application. METHODS: Using different two-handed techniques, the strap of the Generation 7 Combat Application Tourniquet (C-A-T7), Tactical Ratcheting Medical Tourniquet (Tac RMT), Tactical Mechanical Tourniquet (TMT), Parabelt, and Generation 3 SOF® Tactical Tourniquet-Wide (SOFTTW) was secured mid-thigh by 20 appliers blinded to pressure data and around a thigh-sized ballistic gel cylinder by gravity and 23.06kg. RESULTS: Pulling only outward (90° to strap entering buckle) achieved the lowest secured pressures on thighs and gel. For appliers, the best holding location was above the buckle, and the best strap-pulling direction was tangential to the thigh or gel (0° to strap entering buckle). Preceding tangential pulling with outward pulling resulted in higher secured pressures on the gel but did not aid appliers. Appliers generally did not reach secured pressures achievable for their strength. Of 80 thigh applications per tourniquet, 77 C-A-T7, 41 Tac RMT, 35 TMT, 16 Parabelt, and 10 SOFTTW applications had secured pressures greater than 100mmHg. CONCLUSIONS: The default for best tourniquet strap-application technique is to hold above the buckle and pull the strap tangential to the limb at the buckle. Additionally, neither strength nor experience guarantees desirable strap pressures in the absence of pressure knowledge.

Masimo Perfusion Index Versus Doppler for Tourniquet Effectiveness Monitoring.

BACKGROUND: In addition to a plethysmograph, Masimo pulse oximeters display a Perfusion Index (PI) value. This study investigated the possible usefulness of PI for monitoring limb tourniquet arterial occlusion. METHODS: Tactical Ratcheting Medical Tourniquets were applied to the thighs of 15 subjects. Tightening ended at one ratchet-tooth advance beyond Doppler- indicated occlusion. The times and pressures of Doppler and PI signal absences and returns were recorded. RESULTS: Intermittent PI signal error occurred in 149 of 450 runs (PI, 33% versus Doppler, 0%; p < .0001). PI signal loss lagged Doppler-indicated occlusion by 19 ± 15 seconds (mean ± standard deviation, p < .0001). PI Signal Return lagged tourniquet release by 13 ± 7 seconds (Doppler Signal Return took 1 ± 1 seconds following tourniquet release; p < .0001). PI failed to detect early Doppler audible pulse return in 30 of 39 occurrences. CONCLUSION: The PI available on Masimo pulse oximeters is not appropriate for monitoring limb tourniquet effectiveness.

Effects of Distance Between Paired Tourniquets.

BACKGROUND: In practice, the distance between paired tourniquets varies with unknown effects. METHODS: Ratcheting Medical Tourniquets were applied to both thighs of 15 subjects distally (fixed location) and proximally (0, 2, 4, 8, 12cm gap widths, randomized block). Applications were pair, single distal, single appropriate proximal. Tightening ended one-ratchet tooth advance past Doppler-indicated occlusion. Pairs had alternating tightening starting distal. RESULTS: Occlusion pressures were higher for: each single than respective individual pair tourniquet, each pair distal than respective pair proximal, and each single distal than respective single proximal (all p < .0001). Despite thigh circumference increasing proximally, occlusion pressures were lower with proximal tourniquet involvement (pair or single, p < .0001). Occlusion losses before 120 seconds occurred most frequently with pairs (0cm 4, 2cm 4, 4cm 6, 8cm 7, 12cm 5 for 26 of 150), in increasing frequency with increasingly proximal singles (0cm 0, 2cm 1, 4cm 1, 8cm 2, 12cm 6 for 10 of 150, p < .0001 for trend), and least with single distal (2 of 150, p < .0001). Paired tourniquets required fewer ratchet advances per tourniquet (pair distal 5 ± 1, pair proximal 4 ± 1, single distal 6 ± 1, single proximal 6 ± 1). Final ratchet tooth advancement pressure increases (mmHg) were greatest for singles (distal 61 ± 10, proximal 0cm 53 ± 7, 2cm 51 ± 9, 4cm 50 ± 7, 8cm 45 ± 7, 12cm 36 ± 7) and least in pairs (distal 41 ± 8, proximal 32 ± 7) with progressively less pair interaction as distance increased (pressure change for the pair tourniquet not directly advanced: 0cm 13 ± 4, 2cm 10 ± 4, 4cm 6 ± 3, 8cm 1 ± 2, 12cm -1 ± 2). CONCLUSIONS: Occlusion pressures are lower for paired than single tourniquets despite variable intertourniquet distances. Very proximal placement has a pressure advantage; however, pairs and very proximal locations may be less likely to maintain occlusion. Increasingly proximal placements also increase tissue at risk; therefore, distal placements and minimal intertourniquet distances should still be recommended.

Effectiveness of Pulse Oximetry Versus Doppler for Tourniquet Monitoring.

BACKGROUND: Pulse oximeters are common and include arterial pulse detection as part of their methodology. The authors investigated the possible usefulness of pulse oximeters for monitoring extremity tourniquet arterial occlusion. METHODS: Tactical Ratcheting Medical Tourniquets were tightened to the least Doppler-determined occluding pressure at mid-thigh or mid-arm locations on one limb at a time on all four limbs of 15 volunteers. A randomized block design was used to determine the placement locations of three pulse oximeter sensors on the relevant digits. The times and pressures of pulsatile signal absences and returns were recorded for 200 seconds, with the tourniquet being tightened only when the Doppler ultrasound and all three pulse oximeters had pulsatile signals present (pulsatile waveform traces for the pulse oximeters). RESULTS: From the first Doppler signal absence to tourniquet release, toe-located pulse oximeters missed Doppler signal presence 41% to 50% of the times (discrete 1-second intervals) and missed 39% to 49% of the pressure points (discrete 1mmHg intervals); fingerlocated pulse oximeters had miss rates of 11% to 15% of the times and 13% to 19% of the pressure points. On toes, the pulse oximeter ranges of sensitivity and specificity for Doppler pulse detection were 71% to 90% and 44% to 51%, and on fingers, the respective ranges were 65% to 77% and 78% to 83%. CONCLUSION: Use of a pulse oximeter to monitor limb tourniquet effectiveness will result in some instances of an undetected weak arterial pulse being present. If a pulse oximeter waveform is obtained from a location distal to a tourniquet, the tourniquet should be tightened. If a pulsatile waveform is not detected, vigilance should be maintained.

Underestimation of Pupil Size by Critical Care and Neurosurgical Nurses.

BACKGROUND: Early detection of pupillary changes in patients with head injuries can alert the care team to increasing intracranial pressure. Previous research has shown inconsistencies in pupil measurement that are most likely due to the subjective nature of measuring pupils without the assistance of technology. OBJECTIVES: To evaluate nurses' abilities to assess pupil diameter accurately and detect unequal pupils. METHODS: In a 3-part study, the accuracy of critical care and neurosurgical nurses' assessments of pupils was determined. The study included assessment of drawings of eyes with an iris and pupil, examination of photographs of human eyes, and bedside examination of patients with a head injury. RESULTS: Subjective assessments of pupil diameter and symmetry were not accurate. Across all phases of the study, pupil diameters were underestimated and the rate of error increased as pupil size increased. Nurses also failed to detect anisocoria and misidentified pupil reactivity. In addition, nearly all nurses relied on subjective estimation, even when tools were available. CONCLUSIONS: Critical care and neurosurgical nurses underestimated pupil size, were unable to detect anisocoria, and incorrectly assessed pupil reactivity. Standardized use of pupil assessment tools such as a pupillometer is necessary to increase accuracy and consistency in pupil measurement and to potentially contribute to earlier detection of subtle changes in pupils. If pupillary changes are identified early, diagnostic and treatment intervention can be delivered in a more timely and effective manner.

Implementation of a rib fracture triage protocol in elderly trauma patients.

Elderly patients are highly susceptible to rib fractures after trauma. The use of a clinical pathway to determine resource allocation for patients with rib fractures has resulted in positive treatment outcomes. This retrospective study assessed the efficacy of a triage protocol involving trauma services on hospital length of stay in elderly patients with fractured ribs. Patients who had 3 or more ribs fractured experienced a statistically significant reduction in hospital length of stay after protocol implementation. We conclude that elderly patients with 3 or more rib fractures should be systematically referred to a trauma specialist.

Assessment of the implementation of a protocol to reduce ventilator-associated pneumonia in intensive care unit trauma patients.

Ventilator-associated pneumonia (VAP) is the primary hospital-acquired infection contracted by critically ill patients who receive mechanical ventilation. This retrospective study evaluated the efficacy of a multifaceted VAP prevention protocol in an adult trauma population. Ventilator-associated pneumonia was defined according to the National Healthcare Safety Network (2009) criteria. The number of days to onset of VAP in the postprotocol period was longer than the preprotocol period despite a concomitant increase in the number of mechanical ventilation days.

The cumulative effect of multiple critical care protocols on length of stay in a geriatric trauma population.

The elderly individuals are the most rapidly growing cohort within the US population, and a corresponding increase is being seen in elderly trauma patients. Elderly patients are more likely to have a hospital length of stay (LOS) in excess of 10 days. They account for 60% of total ICU days. Length of stay is frequently used as a proxy measure for improvement in injury outcomes, changes in quality of care, and hospital outcomes. Patient care protocols are typically created from evidence-based guidelines that serve to reduce variation in care from patient to patient. Patient care protocols have been found to positively impact patient care with reduced duration of mechanical ventilation, shorter LOS in the ICU and shorter overall hospitalization time, reduced mortality, and reduced health care costs. The following study was designed to assess the impact of the implementation of 4 patient care protocols within an elderly trauma population. We hypothesized that the implementation of these protocols would have a beneficial impact on patient care that could be measured by a decrease in hospital LOS. An archival, retrospective pretest/posttest study was performed on elderly trauma patients. The new protocols helped guide practical changes in care that resulted in a 32% decrease in LOS for our elderly trauma patients which exceeds the 25% decrease found in other studies. Additionally, the "Other" category for each variable was less frequently used in the post-protocol phase than in the pre-protocol phase, suggesting a spillover effect on the level of detail recorded in the patient chart. With less variation in practices in the post-protocol phase, Injury Severity score, and admission systolic blood pressure emerged as significant predictors of LOS.

Costs associated with helmet use in motorcycle crashes: the cost of not wearing a helmet.

OBJECTIVE: The relationship between injuries sustained in a motorcycle crash (MCC) by unhelmeted motorcyclists and the multitude of costs associated with those injuries has been a decades-long debate. Results from research addressing injuries and mortality due to helmet use in MCCs demonstrates that unhelmeted motorcyclists experience more severe injuries, resulting in higher health care costs and an increased likelihood of requiring care beyond the hospital in other facilities. However, a link between injury severity and hospital costs has not been established with its spillover effect onto health insurance providers. This retrospective study was designed to delineate the health care and insurance costs of adult trauma patients admitted to a Level 1 trauma center due to an MCC. METHODS: The study included adult trauma patients 18 years of age or older admitted to a Level 1 trauma center due to an MCC between January 1, 2005, and December 31, 2010. The center is a receiving hospital for the central third of a Midwestern state, serving a medium-sized city as well as rural and isolated population areas. Patients were stratified into 2 groups based on helmet use. Patient variables included mechanism of injury, clinical characteristics, total units of blood used, intensive care unit (ICU) length of stay (LOS), hospital LOS, days on a ventilator, mortality, number of procedures during hospital stay, primary payor, discharge location, and total hospital charges. A linear regression model was used to predict the charges associated with the severity of injuries. RESULTS: A significant difference was found for total hospital charges. The mean total hospital charge for helmeted patients was $4184.26 compared to $7383.31 for unhelmeted patients. The prediction model was statistically significant, indicating that not wearing a helmet starts the patient at a cost of $3199.06. The cost of treatment for patients who wore helmets was $256.93 for each incremental increase in Injury Severity Score (ISS) compared to $537.57 for unhelmeted patients. ICU LOS, hospital LOS, and vent days were statistically significant, with durations longer for unhelmeted patients. Helmeted patients also required more units of blood. The total number of procedures for each patient approached significance, with the unhelmeted group requiring more procedures. CONCLUSIONS: The goal of the study was to delineate the medical costs associated with helmet use and nonuse in motorcyclists. The results demonstrate that medical costs due to an MCC for an unhelmeted motorcyclist were significantly higher than for a helmeted motorcyclist. These costs were paid by providers of health insurance, mainly Civilian Health and Medical Program of the Uniformed Services (CHAMPUS), Medicaid, and commercial insurance.

Diurnal variation and injury due to motor vehicle crashes in older trauma patients.

OBJECTIVE: By 2030 it is expected the elderly will comprise 25 percent of the drivers in the United States. It is also estimated that currently in the United States alone, 500 older adults are injured each day in motor vehicle crashes (MVCs). Current research has not been able to consistently produce a direct connection between MVCs and specific age-related changes. It is speculated that crash rates are more likely linked to an interaction between driver characteristics and driving conditions as well as the driving environment. Sundowner's syndrome occurs in older drivers starting in the late afternoon through early evening (generally between 3:00 pm and 8:00 pm) and involves behaviors such as confusion, disorientation, and restlessness. The following retrospective study was designed to assess the frequency of older drivers admitted to a trauma service due to an MVC based on the time of day of the MVC compared to younger and middle-aged drivers. METHODS: The study included all adult trauma patients ≥ 21 years of age admitted to a Level 1 trauma center due to a, MVC, in which they were the driver of the vehicle, between January 1, 2005, and December 31, 2010. RESULTS: A 3 (Injury Time Period) × 7 (Age Category) chi-square was performed to assess whether there was a disproportionate number of patients admitted as a function of time of injury and age. The overall chi-square was statistically significant. Consequently, a 3 × 7 analysis of variance (ANOVA) was performed on injury severity score (ISS). Tukey's posttest revealed that ISS was highest during the early evening time period. CONCLUSIONS: The evidence of the early evening time period having a differential impact on older drivers is through a demonstration of an Injury Time Period × Age Category interaction. This interaction was found to substantiate the hypothesis that older drivers have a disproportionately higher rate of injury due to an MVC during the early evening time period than younger and middle-aged drivers. In identifying the early evening's time period as a time in which older drivers are more likely to experience injury from an MVC than younger and middle-aged drivers, we believe that our research adds insight into why age restrictions have not been successful in reducing crash rates in the older driver population. It is the compound effect of age-related changes and environmental conditions that contributes to the higher proportion of MVCs. Age restrictions alone do not take into account environmental conditions.