Impact of trauma centre capacity and volume on the mortality risk of incoming new admissions.

INTRODUCTION: Trauma centre capacity and surge volume may affect decisions on where to transport a critically injured patient and whether to bypass the closest facility. Our hypothesis was that overcrowding and high patient acuity would contribute to increase the mortality risk for incoming admissions. METHODS: For a 6-year period, we merged and cross-correlated our institutional trauma registry with a database on Trauma Resuscitation Unit (TRU) patient admissions, movement and discharges, with average capacity of 12 trauma bays. The outcomes of overall hospital and 24 hours mortality for new trauma admissions (NEW) were assessed by multivariate logistic regression. RESULTS: There were 42 003 (mean=7000/year) admissions having complete data sets, with 36 354 (87%) patients who were primary trauma admissions, age ≥18 and survival ≥15 min. In the logistic regression model for the entire cohort, NEW admission hospital mortality was only associated with NEW admission age and prehospital Glasgow Coma Scale (GCS) and Shock Index (SI) (all p<0.05). When TRU occupancy reached ≥16 patients, the factors associated with increased NEW admission hospital mortality were existing patients (TRU >1 hour) with SI ≥0.9, recent admissions (TRU ≤1 hour) with age ≥65, NEW admission age and prehospital GCS and SI (all p<0.05). CONCLUSION: The mortality of incoming patients is not impacted by routine trauma centre overcapacity. In conditions of severe overcrowding, the number of admitted patients with shock physiology and a recent surge of elderly/debilitated patients may influence the mortality risk of a new trauma admission.

Lung and chest wall impedances in the dog: effects of frequency and tidal volume.

Dependences of the mechanical properties of the respiratory system on frequency (f) and tidal volume (VT) in the normal ranges of breathing are not clear. We measured, simultaneously and in vivo, resistance and elastance of the total respiratory system (Rrs and Ers), lungs (RL and EL), and chest wall (Rcw and Ecw) of five healthy anesthetized paralyzed dogs during sinusoidal volume oscillations at the trachea (50-300 ml, 0.2-2 Hz) delivered at a constant mean lung volume. Each dog showed the same f and VT dependences. The Ers and Ecw increased with increasing f to 1 Hz and decreased with increasing VT up to 200 ml. Although EL increased slightly with increasing f, it was independent of VT. The Rcw decreased from 0.2 to 2 Hz at all VT and decreased with increasing VT. Although the RL decreased from 0.2 to 0.6 Hz and was independent of VT, at higher f RL tended to increase with increasing f and VT (i.e., as peak flow increased). Finally, the f and VT dependences of Rrs were similar to those of Rcw below 0.6 Hz but mirrored RL at higher f. These data capture the competing influences of airflow nonlinearities vs. tissue nonlinearities on f and VT dependence of the lung, chest wall, and total respiratory system. More specifically, we conclude that 1) VT dependences in Ers and Rrs below 0.6 Hz are due to nonlinearities in chest wall properties, 2) above 0.6 Hz, the flow dependence of airways resistance dominates RL and Rrs, and 3) lung tissue behavior is linear in the normal range of breathing.

Effects of cardiac oscillations and lung volume on acinar gas mixing during apnea.

We evaluated the importance of cardiogenic gas mixing in the acini of 13 dogs during 2 min of apnea. 133Xe (1-2 mCi in 4 ml of saline) was injected into an alveolar region through an occluded pulmonary artery branch, and washout was measured by gamma scintillation scanning during continued occlusion or with blood flow reinstated. The monoexponential rate constant for Xe washout (XeW) was -0.4 +/- 0.08 (SE) min-1 at functional residual capacity (FRC) with no blood flow in the injected region. It decreased by more than half at lung volumes 500 ml above and 392 ml below FRC. With intact pulmonary blood flow, XeW was -1.0 +/- 0.08 (SE) min-1 at FRC, and it increased with decreasing lung volume. However, if calculated Xe uptake by the blood was subtracted from the XeW measured with blood flow intact, resulting values at FRC and at FRC + 500 ml were not different from XeW with no blood flow. Reasonable calculation of Xe blood uptake at 392 ml below FRC was not possible because airway closure, increased shunt, and other factors affect XeW. After death, no significant XeW could be measured, which suggests that XeW caused by molecular diffusion was small. We conclude that 1) the effect of heart motion on the lung parenchyma increases acinar gas mixing during apnea, 2) this effect diminishes above or below FRC, and 3) there is probably no direct effect of pulmonary vascular pulsatility on acinar gas mixing.

Regional chest wall impedance during nonrespiratory maneuvers.

To assess changes in total and regional chest wall properties during nonrespiratory maneuvers, we measured electromyographic activity of various chest wall muscles, esophageal pressure, and rib cage and abdominal surface displacements in six subjects before and during various static tasks. Subjects were seated at functional residual capacity, and quasi-sinusoidal forcing at the mouth (0.4 Hz, 500 ml) was imposed during the maneuver in the absence of active breathing. Magnitude of total chest wall impedance (magnitude of Zw) increased with effort during all maneuvers; changes in phase were small. Maneuvers involving primarily muscles of the neck and rib cage--holding a 10-kg weight, 10 kg of isometric tension between the arms, and isometric neck flexion--roughly doubled the magnitude of rib cage impedance (magnitude of Zrc) and, to a lesser degree, increased magnitude of diaphragm-abdomen impedance (magnitude of Zd-a). Unilateral and bilateral leg lifts, in addition to increasing magnitude of Zd-a, increased magnitude of Zrc. Passive 90 degrees rotation of the torso caused approximately 25% increases in magnitude of Zrc and magnitude of Zd-a; if the rotation was actively maintained by the trunk muscles, both regional impedances increased over 100%. Increases in magnitude of regional impedance were correlated to increases in regional electromyographic activity; changes in phase were small. Passive restriction of rib cage displacement by strapping increased magnitude of Zrc and magnitude of Zw but not magnitude of Zd-a, whereas abdominal strapping increased magnitude of Zd-a but did not affect magnitude of Zrc or magnitude of Zw.(ABSTRACT TRUNCATED AT 250 WORDS)

Respiratory impedances and acinar gas transfer in a canine model for emphysema.

We examined how the changes in the acini caused by emphysema affected gas transfer out of the acinus (Taci) and lung and chest wall mechanical properties. Measurements were taken from five dogs before and 3 mo after induction of severe bilateral emphysema by exposure to papain aerosol (170-350 mg/dose) for 4 consecutive wk. With the dogs anesthetized, paralyzed, and mechanically ventilated at 0.2 Hz and 20 ml/kg, we measured Taci by the rate of washout of 133Xe from an area of the lung with occluded blood flow. Measurements were repeated at positive end-expiratory pressures (PEEP) of 10, 5, 15, 0, and 20 cmH2O. We also measured dynamic elastances and resistances of the lungs (EL and RL, respectively) and chest wall at the different PEEP and during sinusoidal forcing in the normal range of breathing frequency and tidal volume. After final measurements, tissue sections from five randomly selected areas of the lung each showed indications of emphysema. Taci during emphysema was similar to that in control dogs. EL decreased by approximately 50% during emphysema (P < 0.05) but did not change its dependence on frequency or tidal volume. RL did not change (P > 0.05) at the lowest frequency studied (0.2 Hz), but in some dogs it increased compared with control at the higher frequencies. Chest wall properties were not changed by emphysema (P > 0.05). We suggest that although large changes in acinar structure and EL occur during uncomplicated bilateral emphysema, secondary complications must be present to cause several of the characteristic dysfunctions seen in patients with emphysema.

Effect of pulmonary edema on transfer of gas from acinus to airways.

We directly measured the effect of progressive pulmonary edema on gas transfer from the acinus by injecting 133Xe dissolved in saline through a pulmonary artery catheter into an acinar region with occluded blood flow and measuring 133Xe washout by gamma scintillation scanning. We measured washout in six anesthetized paralyzed dogs during mechanical ventilation with O2 before and after injection of 0.6 mg/kg of oleic acid into the right atrium, which induces severe pulmonary edema within 2 h. Changes in the elastance and resistance of the lung were also calculated from measurements of airway flow, airway pressure, and esophageal pressure. Before injection of oleic acid, the monoexponential rate constant for 133Xe washout was 3.6 +/- 1.4 (SE) min-1; from this we estimated that the rate of gas transfer of 133Xe from the acini was 1.0 l/min. The rate constant decreased gradually after the injection and was correlated with increases in elastance and resistance (r = -0.66) and decreases in alveolar PO2 (r = 0.71). At 2 h after injection, the rate constant (1.2 +/- 0.8 min-1) was lower than control (P < 0.01), and the rate of gas transfer of 133Xe from the acini was < 0.32 l/min. We conclude that resistance in the acini is increased during pulmonary edema and that it is correlated, in the oleic acid model, with changes in overall lung mechanical properties.

Experimental repair of ventricular septal defects using autologous right ventricular muscle flaps: preliminary report.

Survival after repair of postinfarction ventricular septal defects remains poor, often due to extensive loss of contractile muscle in the septum or left ventricle. We evaluated whether a contractile flap of right ventricular muscle could be used to repair a similar ventricular septal defect to augment left ventricular performance in 7 fully instrumented mongrel dogs (weight, 23 to 28 kg). By using hypothermic bypass and cold fibrillatory arrest, a trapezoidal right ventricle flap was fashioned from the free wall of the mid to lower right ventricle, basing its widest portion anteriorly on the septum and left ventricle. A large, 2-cm-diameter core of septum was excised beneath this flap to simulate a postinfarct ventricular septal defect. The right ventricular flap was then invaginated through the defect and sewn to the left ventricular side of the septum with pledgeted sutures taken full thickness through the flap and septum in a "vest-over-pants" fashion. Contraction of the right ventricular flap was confirmed visually and by postbypass multiple gated acquisition scans. The right ventricular defect was closed with fascia lata. All dogs were weaned from bypass without inotropes. Precardiac and postcardiac outputs of 2.5 +/- 0.5 versus 2.3 +/- 0.4 L/min and left ventricular end-diastolic pressures of 4 +/- 2 versus 4 +/- 3 mm Hg were identical. No shunts were detected by oxygen saturation. Autopsies confirmed the integrity of the repair. We conclude that septal defects can be repaired by using contractile right ventricular muscle, thus preserving left ventricular function. This technique offers promise for repair of postinfarction ventricular septal defects by using autologous, already conditioned to contract, cardiac muscle, but its application in humans must await long-term testing.

Video techniques and data compared with observation in emergency trauma care.

Video recording is underused in improving patient safety and understanding performance shaping factors in patient care. We report our experience of using video recording techniques in a trauma centre, including how to gain cooperation of clinicians for video recording of their workplace performance, identify strengths of video compared with observation, and suggest processes for consent and maintenance of confidentiality of video records. Video records are a rich source of data for documenting clinician performance which reveal safety and systems issues not identified by observation. Emergency procedures and video records of critical events identified patient safety, clinical, quality assurance, systems failures, and ergonomic issues. Video recording is a powerful feedback and training tool and provides a reusable record of events that can be repeatedly reviewed and used as research data. It allows expanded analyses of time critical events, trauma resuscitation, anaesthesia, and surgical tasks. To overcome some of the key obstacles in deploying video recording techniques, researchers should (1) develop trust with video recorded subjects, (2) obtain clinician participation for introduction of a new protocol or line of investigation, (3) report aggregated video recorded data and use clinician reviews for feedback on covert processes and cognitive analyses, and (4) involve multidisciplinary experts in medicine and nursing.

Venous air embolism, hypotension, and end-tidal nitrogen.

The most sensitive method of venous air embolism (VAE) detection in clinical use is the precordial Doppler detector. Because the Doppler detector may provide false-positive and false-negative data, many clinicians rely on end-tidal gas measurements for verification of VAE in the operating room. End-tidal nitrogen (ETN2) increases soon after experimental VAE are small enough to cause minimal changes in blood pressure; however, decreases in end-tidal CO2 (ETCO2) are more sensitive. A large VAE causes hemodynamic instability, and the effect of low cardiac output on ETN2 has not been evaluated. This study was done to compare the changes in ETN2 and ETCO2 during large bolus and infusion VAE. Five mongrel dogs were anesthetized, intubated, and ventilated (FIO2 1.0, PaCO2 38 +/- 4 (SD) mm Hg). The animals were studied in the supine position; anesthesia and paralysis were maintained with a constant infusion of thiamylal and pancuronium. Maintenance fluids were administered at 5 ml kg-1 h-1. Mean arterial and pulmonary arterial pressures (PAP) and ETN2 and ETCO2 were displayed on a strip chart recorder. The dogs underwent both bolus and infusion VAE in separate experiments 10 to 14 days apart. The air emboli were given in random order by automated syringe over 1 minute (infusion) (1 to 2.5 ml kg-1 min-1) or by hand injection over 5 seconds (bolus) (1 to 2.5 ml kg-1). Changes in precordial Doppler sounds occurred in all animals at all doses. The peak increase in PAP and decrease in ETCO2 were significant after all air doses. ETN2 changes were biphasic. The peak increase was significant after all air doses; the peak decrease was significant in 37 of 40 bolus and infusion VAE episodes, occurred within 1 to 3 minutes, and lasted 20 to 30 minutes.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of cardiac and respiratory function during surgery on patients with acute quadriplegia.

Cardiorespiratory function was assessed in 22 mechanically ventilated patients who underwent surgery within an average of 4.8 days following traumatic spinal cord injury at C3-7. A fluid challenge technique was used to derive right and left ventricular function curves and to assist in choice of therapy from four possible outcome responses. Both right and left ventricular stroke work increased but left ventricular stroke work was still lower than normal in six (27%) of 22 patients despite elevation of cardiac filling pressures. Pulmonary vascular resistance fell, but systemic vascular resistance was unchanged following fluid challenge. Respiratory function, including intrapulmonary shunt, lung/thorax compliance, dead space, and arterial pO2 and pCO2, were unchanged by fluid administration averaging 520 ml of plasma protein fraction in 12 minutes. The Bainbridge reflex was inoperative. There was no correlation between anesthetic agent, level or type of neurological deficit, and cardiorespiratory function. Left ventricular function was impaired so the use of peripheral vasoconstrictors that elevate systemic vascular resistance should be avoided in the management of spinal shock. Instead, myocardial depressants should be reduced and fluid replacement used to optimize cardiac function. Elevation of central venous or pulmonary capillary wedge pressures to 18 mm Hg should be used to reverse hypotension, acidosis, low venous pO2, or oliguria before institution of centrally acting inotropic therapy in the management of acute spinal cord injury.

Tetrodotoxin infusion: nonventilatory effects and role in toxicity models.

OBJECTIVES: To determine the cardiovascular, autonomic, and neuromuscular effects of an IV infusion of tetrodotoxin (TTX) when ventilation is supported. METHODS: TTX was infused in 18 anesthetized beagles during conventional mechanical ventilation. TTX infusion continued at a rate of 9.3 micrograms/kg/hr until apnea occurred with 1 minute of ventilator disconnection. Measurements included intravascular pressures, heart rate (HR), cardiac output, blood gases, displacements of the rib cage and abdomen, O2 delivery, and responses to train-of-four and tetanic peripheral nerve stimulation. Results are expressed as mean +/- SD. RESULTS: During TTX infusion, all the dogs had discoordinate movements of the rib cage, abdomen, and limbs. Vomiting, urination, defecation, and increased salivation occurred. Nicotinic and muscarinic effects, neuromuscular blockade, and cardiovascular depression were produced by TTX. Apnea occurred in 72.0 +/- 17.0 minutes when a total of 119.0 +/- 17.4 micrograms of TTX was infused. At apnea, decreases in arterial pressure, cardiac index, HR, O2 delivery, and systemic vascular resistance occurred, while pulmonary artery pressure and pulmonary vascular resistance increased. Loss of response to tetanic stimulation was closely correlated with the dose of TTX that produced apnea. CONCLUSION: The clinical symptoms and signs of TTX poisoning are similar to those of anticholinesterase poisons, and TTX dosing as described by this model may serve as a surrogate for organophosphorus poisoning. The model may be useful to determine optimum therapies for TTX poisoning and, since TTX prevents sodium influx into cells, to investigate enhanced survival in animals suffering from ischemia.

Changing patterns of posttraumatic acute renal failure.

ARF will continue to occur as more severely traumatized patients survive with better resuscitation. The incidence of ARF, however, appears to be steadily decreasing and ARF occurs only in patients with severe injury and multiple organ failure. ARF developing for the past three years in MIEMS was a nonoliguric variety in the majority of patients. Management of ORF with dialysis has been disappointing. Prevention of oliguria in ARF appears possible and may be one of the most important steps to decrease the morbidity and fatality rate. Further investigation is required to find the cause and optimum management of NORF.

Two-year mortality in 760 patients transported by helicopter direct from the road accident scene.

Of 760 direct admissions to a specialized trauma center, 173 (22.7%) victims of motor vehicle accidents died. Excluding patients dead on arrival, the mortality rate was 14.5%. Autopsy reports were reviewed and showed that the major cause of death was head injury (49.7%). Uncontrollable hemorrhage from massive trauma was the next most common problem and usually proved fatal in the first 24 hours after admission. The incidence of sepsis and renal failure increased with prolongation of CCRU stay. Following admission, respiratory failure was not a common cause of death (3%). Because of direct helicopter rather than ambulance transport from the scene of the motor vehicle accident, earlier attention was paid to diagnosis of trauma and treatment of respiratory insufficiency with mechanical ventilation. Because of the early initiation of therapy, there was rapid restoration of circulating volume and tissue perfusion. This may account for the low mortality.

Pleural decompression and drainage during trauma reception and resuscitation.

This review examines pleural decompression and drainage during initial hospital adult trauma reception and resuscitation, when it is indicated for haemodynamically unstable patients with signs of pneumothorax or haemothorax. The relevant historical background, techniques, complications and current controversies are highlighted. Key findings of this review are that: 1. Needle thoracocentesis is an unreliable means of decompressing the chest of an unstable patient and should only be used as a technique of last resort. 2. Blunt dissection and digital decompression through the pleura is the essential first step for pleural decompression, as decompression of the pleural space is a primary goal during reception of the haemodynamically unstable patient with a haemothorax or pneumothorax. Drainage and insertion of a chest tube is a secondary priority. 3. Techniques to prevent tube thoracostomy (TT) complications include aseptic technique, avoidance of trocars, digital exploration of the insertion site and guidance of the tube posteriorly and superiorly during insertion. 4. Whenever possible, blunt thoracic trauma patients should undergo definitive CT imaging after TT to check for appropriate tube position.

Cardiorespiratory function before and after chest physiotherapy in mechanically ventilated patients with post-traumatic respiratory failure.

Chest physiotherapy (CPT) is used frequently in the ICU, but there is little available information that quantitates its effect on cardiac or respiratory function. Nineteen mechanically ventilated patients with post-traumatic respiratory failure were studied before, immediately after, and 2 h after CPT was used to manage secretion retention. Cardiac index was unchanged, but there was an immediate decrease in intrapulmonary shunt, followed 2 h later by an increase in lung/thorax compliance. We did not find the reduced cardiac output reported by others. The reasons for this may include use of different CPT techniques, a young patient population (mean age 32.4 yr), and mechanical ventilation with positive end-expiratory pressure. CPT did not produce the deleterious cardiopulmonary changes associated with bronchoscopy, and it reduced retained lung secretions without producing hypoxemia. Intrapulmonary shunt and lung/thorax compliance were significantly improved, but the long-term clinical effect of these changes is unknown.

Creatinine clearance of early detection of posttraumatic renal dysfunction.

Acute renal failure develops insidiously in the presence of normal urine output and vital signs. A prospective study was carried out to find whether renal impairment can be detected in the immediate postoperative period and to determine the renal function test best predicting the development of renal dysfunction. Forty patients with multiple trauma who required more than 10 units of blood and had a systolic blood pressure less than 80 mmHg on admission were studied. Creatinine clearance (Ccr), free-water clearance (CH2O), fractional excretion of Na+, blood urea nitrogen (BUN), urine flow rate, and vital signs were measured and compared in seven patients who developed renal dysfunction within a week of trauma (Group 1) and 33 patients who maintained normal renal function (Group 2). In all Group 1 patients Ccr remained less than 25 ml/min and CH2O greater than -15 ml/h for 6 h following surgery. None of the Group 2 patients had Ccr less than 25 ml/min for longer than 4 h following surgery. However, CH2O values were greater than -15 ml/h in 15 of the 33 Group 2 patients during the first 24 postoperative hours. Ccr values less than 25 ml/min were present, despite normal urine flow rate and blood pressure, in patients who subsequently developed renal dysfunction. Patients who have Ccr values less than 25 ml/min within 6 h following trauma and surgery may develop renal dysfunction, and some of them may proceed to acute renal failure. CH2O was not as good a predictor of development of renal dysfunction as Ccr.

An audio-video system for automated data acquisition in the clinical environment. LOTAS Group.

OBJECTIVE: Our objective was to develop an audiovideo data acquisition system that facilitates studying the activities of anesthesia care providers in the clinical environment. METHOD: Ceiling-mounted miniature video cameras, vital sign monitors, and videocassette recorders (VCRs) were interfaced to digital computers in two patient admitting areas and two operating rooms of a trauma center. This video data acquisition system network (VASNET) is simple to operate. Insertion of a videotape activates the system and begins video overlay of updated vital signs onto the video image every 5 sec. Recorded data is passed via a local area network, allowing remote monitoring of the data acquisition process. To facilitate analysis of the video at a later time, the image, soundtrack, and vital signs data are stamped with the same time code. Each tape is initialized by recording the data file name and wall clock time for 30 sec at the start of taping. This initialization enables comparison of the video recordings with anesthesia, surgical, and nursing records. RESULTS: During 2 years of operation, VASNET was used to record over 100 cases of acute trauma management. Vital signs overlaid onto the video image identified when patient monitors were in use and providing data. Participants found videotape review useful in assessing their own performance. VASNET was nonintrusive and acquired data with minimum user interaction. In one operating room, separate from the trauma center, VASNET was installed to function as a remote monitor, with the option of videotaping. Although users were aware of when videotaping occurred, once patient management was underway, the activities of the anesthesia care providers did not appear to be influenced by the videocassette recording. Equipment maintenance was not excessive. The most frequent problems were changes to the VCR control settings and disconnection of the power supply or interface connections. CONCLUSIONS: Videotapes of the process of anesthetizing and resuscitating trauma patients provided a record of the activities of anesthesia care providers. Video vignettes may be useful training tools. Excerpts from real scenarios can be incorporated into anesthesia stimulators. The soundtrack and timing of real events from such video acquisition may be useful in the development of multimedia simulations of trauma patient resuscitation. The data collection may be useful for research into human performance, ergonomics, training techniques, quality assurance, and certification of anesthesia care providers in trauma patient management. Potential additional applications of VASNET include remote monitoring of patients in the operating room, in the intensive care unit, during transportation, in hazardous environments, and in the field. Such VASNET telemetry may facilitate the availability of expert opinions during medical and other consultations.