Steven C Dronen

Effect of blood pressure on hemorrhage volume and survival in a near-fatal hemorrhage model incorporating a vascular injury

STUDY HYPOTHESISnIn a model of near-fatal hemorrhage that incorporates a vascular injury, stepwise increases in blood pressure associated with aggressive crystalloid resuscitation will result in increased hemorrhage volume and mortality.nnnDESIGNnThis study used a swine model of potentially lethal hemorrhage in the presence of a vascular lesion to compare the effects of resuscitation with mean arterial pressures of 40, 60, and 80 mm Hg. Twenty-seven fully instrumented immature swine (14.8 to 20 kg), each with a surgical-steel aortotomy wire in place, were bled continuously from a femoral artery catheter to a mean arterial pressure of 30 mm Hg. At that point the aortotomy wire was pulled, producing a 4-mm aortic tear and uncontrolled intraperitoneal hemorrhage. When the animals pulse pressure reached 5 mm Hg, the femoral artery hemorrhage was discontinued and resuscitation was begun.nnnINTERVENTIONSnSaline infusion was begun at 6 mL/kg/min and continued as needed to maintain the following desired endpoints: group 1 (nine) to a mean arterial pressure of 40 mm Hg, group 2 (nine) to a mean arterial pressure of 60 mm Hg, and group 3 (nine) to a mean arterial pressure of 80 mm Hg. After 30 minutes or a total saline infusion of 90 mL/kg, the resuscitation fluid was changed to shed blood infused at 2 mL/kg/min as needed to maintain the desired mean arterial pressure or to a maximum volume of 24 mL/kg. Animals were observed for 60 minutes or until death.nnnMEASUREMENTS AND MAIN RESULTSnData were compared using repeated-measures analysis of variance with a post hoc Tukey-Kramer, Fishers exact test, and Kruskal-Wallis. Mortality was significantly greater in group 3 (78%) compared with either group 1 (11%; P = .008) or group 2 (22%; P = .028). Mean survival times were significantly shorter in group 3 (44 +/- 12 minutes) compared with either group 1 (58 +/- 6 minutes; P = .007) or group 2 (59 +/- 3 minutes; P = .006). The average intraperitoneal hemorrhage volumes were 13 +/- 14 mL/kg, 20 +/- 25 mL/kg, and 46 +/- 11 mL/kg for groups 1, 2, and 3, respectively (group 1 versus 2, P = .425; group 1 versus 3, P < .001; group 2 versus 3, P = .014). Group 2 animals demonstrated significantly greater oxygen deliveries compared with groups 1 and 3.nnnCONCLUSIONnIn a model of near-fatal hemorrhage with a vascular injury, attempts to restore blood pressure with crystalloid result in increased hemorrhage volume and markedly higher mortality.

Succinylcholine-assisted intubations in prehospital care

Although endotracheal intubation is considered the optimal technique for airway management in critically ill patients, performance of this task in the prehospital setting is at times difficult due to increased masseter muscle tone, vocal cord spasm, or patient combativeness. Use of short-acting paralyzing agents by paramedics to facilitate intubation in these situations is an uncommon practice. We report the recent experience of an emergency medical service system that has used succinylcholine (SUX) for more than ten years. We reviewed prehospital patient intubations for two years; 215 patients were intubated by paramedics without the use of SUX and 95 patients were intubated with the use of SUX. The patient group intubated with SUX was characterized by a greater percentage of women (48% vs 35%; P less than .05), a higher mean Glasgow Coma Scale score (8.6 vs 3.4), fewer intubations for cardiac arrest (3% vs 81%), and more hospital survivors (58% vs 24%; P less than .005). The groups were not different with respect to mean age or frequency of trauma. Paramedics chose to use SUX in 69% of nonarrested patients requiring intubation. SUX-assisted intubation was used most often for the indications of airway protection and respiratory distress. Review of hospital records showed no difference between the groups for frequency of either aspiration pneumonia or mechanical ventilation in patients surviving to hospital admission. No patient receiving SUX required emergency cricothyrotomy, nor was esophageal intubation noted in either group. Succinylcholine-assisted intubation was used safely and selectively by the paramedics in this EMS system to permit airway control and ventilation of patients with more difficult intubations.

Prehospital use of neuromuscular blocking agents in a helicopter ambulance program

We prospectively studied the use of succinylcholine chloride and pancuronium bromide by the physician/nurse flight team of our hospital-based helicopter ambulance service. Patients who received these agents at the scene of an accident (prehospital group, n = 39) were compared with patients who were paralyzed by the flight team in the emergency department of transferring hospitals (control group, n = 35). By protocol, succinylcholine was used primarily for endotracheal intubation and pancuronium for prolonged paralysis after endotracheal intubation. Seventy-four patients received one or both agents. Overall, 61 of 74 patients had intracranial pathology as their primary diagnosis (82%). Endotracheal intubation was the primary indication for paralysis in the majority of patients (67 of 74), although intracranial pressure control, ventilation, agitation control, and seizure control were frequent secondary indications. Prior intubation attempts had failed in 40 of 74 patients (54%). After paralysis, intubation was successful in 68 of 71 patients (96%). Serious complications (ie, dysrhythmia requiring drug therapy) occurred in three patients but resolved with appropriate therapy in each case. Minor complications (ie, dysrhythmia not requiring drug therapy, histamine flush, infiltrated IV line) occurred in 18 patients. There was no significant difference in successful intubation or complication rate between the prehospital and control group. Paralysis allowed airway stabilization in a significant number of critically ill patients who could not otherwise be endotracheally intubated, with a lower incidence of complications than has been previously reported for ED patients. These results suggest that neuromuscular blocking agents can be used safely and effectively at accident scenes by a physician/nurse team.

Prospective evaluation of the scapular manipulation technique in reducing anterior shoulder dislocations.

STUDY OBJECTIVEnTo evaluate the speed, efficacy, and safety of the scapular manipulation technique in reducing acute anterior shoulder dislocations.nnnDESIGNnProspective study.nnnSETTINGnUrban emergency department with an annual census of 65,000 patients.nnnPARTICIPANTSnForty-eight adult patients with acute anterior shoulder dislocation.nnnINTERVENTIONSnPatients had an initial neurovascular and radiographic evaluation performed. They were sedated with IV fentanyl and midazolam. The shoulder was reduced using the scapular manipulation technique. The patient was re-evaluated for any evidence of complication. The total dose of analgesic required and time to reduction were recorded.nnnRESULTSnThe scapular manipulation technique was successful in 46 of 48 (96%) cases. The average time to reduction was 6.05 minutes, and no complications were detected. Average doses of 1.83 mg midazolam and 204 micrograms fentanyl were required for reduction.nnnCONCLUSIONnThe scapular manipulation technique is a very fast, effective, safe method of reducing anterior shoulder dislocations in the ED. [Kothari RU, Dronen SC: Prospective evaluation of the scapular manipulation technique in reducing anterior shoulder dislocations.

Aeromedical transport of patients with post-traumatic cardiac arrest

Patients experiencing cardiac arrest secondary to trauma make up 8% to 15% of air ambulance scene flights in reported series. Our study examined the role of aggressive physician intervention at the accident scene in conjunction with rapid air transport to a trauma center in reducing the mortality after post-traumatic cardiac arrest. We retrospectively studied 67 patients who experienced cardiac arrest before the arrival of the flight team. Fifty-eight patients were victims of blunt trauma, and nine sustained penetrating trauma. Forty-seven patients were transported to the base hospital; 20 were pronounced dead at the scene after resuscitation attempts were made. Six patients developed a pulse and blood pressure and were hospitalized; none survived to hospital discharge. Review of autopsy data revealed that the majority of patients had head or thoracoabdominal injuries or both that were incompatible with life. We conclude that physician intervention at the scene and rapid aeromedical transport are not likely to improve mortality after traumatic cardiac arrest.

Improved outcome with early blood administration in a near-fatal model of porcine hemorrhagic shock

Current recommendations for the preoperative management of hemorrhagic shock include the initial infusion of 2 L of isotonic crystalloid regardless of the severity of hemorrhage. While this approach may be adequate for patients who experience only mild to moderate hemorrhagic insults, it has never been tested in a clinically relevant model of severe life-threatening hemorrhage. The authors used a porcine model of rapidly fatal hemorrhage with a reproducible and relevant physiologic end-point, the absence of vital signs, to test the hypothesis that even brief delays in blood replacement may result in higher mortality rates and worsen hemodynamic and metabolic responses to hemorrhage. Twenty-four immature swine (11-17 kg) were bled continuously at a decelerating rate until the following criteria were met: (1) respiratory arrest, (2) a pulse pressure of 0 and, (3) a slowing of cardiac electrical activity of 15% or more. Resuscitation was begun 1 minute later. The animals were randomly assigned to one of three resuscitation regimens. Group A (n = 8) received shed blood at a rate of 3 mL/kg/min for 10 minutes followed by normal saline (NS) at a rate of 3 mL/kg/min for 10 minutes. Group B (n = 8) received NS at a rate of 3 mL/kg/min for 10 minutes followed by shed blood at a rate of 3 mL/kg/min for 10 minutes. Group C, controls, (n = 8) received NS at a rate of 3 mL/kg/min for 20 minutes. Animals were observed for 30 minutes after resuscitation or until death. Mortality was 25%, 37.5%, and 100% for groups A, B, and C, respectively (P < .05 for group C versus group A or B).(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dichloroacetate in spinal stroke in the rabbit

High levels of brain lactate may contribute to cellular death and dysfunction in acute cerebral ischemia. Although sodium dichloroacetate (DCA) has been shown to lower brain lactate in incomplete cerebral ischemia, functional outcome has not been assessed with DCA. We examined the effects of DCA treatment on functional neurologic outcome using a previously developed model for spinal stroke in the rabbit. Thirty male New Zealand white rabbits weighing 1.3-2.8 kg were studied. After anesthesia with 15-40 mg/kg pentobarbital IV, a laparotomy was performed and the aorta exposed. A metal clamp was placed on the aorta just distal to the left renal artery for 20 minutes and then removed. The abdominal wound was closed in two layers. Animals then received either 2cc normal saline (n = 15) or 300 mg/kg DCA in 2cc normal saline (n = 15) over 10 minutes. The animals were returned to their cages when awake and were examined at 24 hours, 48 hours, and 72 hours for neurologic assessment. The exams were performed by a blinded examiner who was unaware of the treatment given. A three point ambulatory score (0 = cant walk, 1 = walk but not hop, 2 = hopping) and a two point activity score (0 = inactive, 1 = active) were used. At 24 hours, 67% of the DCA-treated animals were actively moving about compared to only 27% of the controls (P = 0.03; Fisher Exact Test). Ten of fifteen control animals were unable to walk, while only five of fifteen DCA-treated animals were unable to walk (P = 0.07). Sixty percent of the DCA animals were able to hop compared to 27% of controls (P = 0.06). These results suggest that DCA can reduce morbidity from spinal cord ischemia in the rabbit.

Intravenous fluid therapy in the prehospital management of hemorrhagic shock: improved outcome with hypertonic saline?6% dextran 70 in a swine model

The small quantities of 7.5% hypertonic saline (HTS) in 6% Dextran 70 (DEX 70; Travenol Laboratories, Deerfield, IL) required to produce marked improvement in tissue perfusion may make it an ideal solution for the prehospital management of hypotensive trauma patients. This study shows that the initial treatment of porcine hemorrhagic shock with 7.5% HTS/6% DEX 70 results in significantly improved hemodynamics and higher survival rates than those seen in animals treated with normal saline. These results are very encouraging and dictate the need for evaluation in human trials.

Lack of efficacy of naloxone in a fixed-volume hemorrhage model

Animal studies using a reservoir model of hemorrhagic shock have shown the narcotic antagonist naloxone to be of value in reversing the hemodynamic effects of severe hemorrhage. We conducted a study to evaluate the ability of naloxone to limit the deleterious effects of a fixed-volume hemorrhage. Fifteen mongrel dogs were bled 50% of their estimated blood volumes during one hour. This was followed by a one-hour stabilization period; reinfusion during a 30-minute period; and finally, an additional one-hour monitoring period. Eight dogs received 2 mg/kg IV naloxone 30 minutes prior to hemorrhage and 2 mg/kg/hr for the duration of the study. Seven control dogs received an equivalent volume of saline without naloxone. Pulmonary capillary wedge pressure, central venous pressure, cardiac output, heart rate, blood pressure, arterial and mixed venous blood gases, and serum lactate were measured at 19 intervals throughout the study period. Mean arterial pressure, cardiac index, and systemic vascular resistance were calculated for each sampling period. With the exception of serum lactates, which were higher in the naloxone group, there were no significant differences between the groups in the mean values calculated for each sampling interval (P less than .05, two-tailed independent t test). Furthermore, the changes in hemodynamic parameters observed during the hemorrhage, stabilization, reinfusion, and monitoring periods were not significantly different. We conclude that in this fixed-volume hemorrhage model, naloxone does not prevent or reverse hemodynamic deterioration.

Transcutaneous oxygen tension measurements during graded hemorrhage and reinfusion

Measurement of transcutaneous oxygen tension (PtCO2) has been suggested as a useful monitoring tool in the hypovolemic patient. Our study was undertaken to evaluate changes in PtCO2 that occur during graded hemorrhage and reinfusion, and to compare PtCO2 values to standard cardiorespiratory and biochemical parameters during hypovolemia. Seven mongrel dogs were bled 50% of their estimated blood volume (44 mL/kg) over one hour. This was followed by a one-hour monitoring period, a 30-minute reinfusion period, and an additional one-hour monitoring period. Pulmonary capillary wedge pressure (PCWP), central venous pressure (CVP), cardiac output (CO), mean arterial pressure (MAP), mixed venous oxygen tension (MvO2), arterial blood gases, and PtCO2 were measured serially throughout the study period. Cardiac index (CI), peripheral vascular resistance (PVR), O2 consumption, delivery, and percentage of extraction were calculated for each sampling period. A statistically significant fall in CI, MvO2 and PCWP occurred following the first 10% of blood loss; PtCO2 and MAP fell significantly after 20% hemorrhage; CVP fell after 30% hemorrhage. PtCO2 rose significantly after the first 10% of reinfusion, and it continued to rise during the entire reinfusion period, as did MvO2, CO, MAP, CVP, and PCWP. In contrast to the other measured variables, the elevations in PtCO2, and MvO2 were more pronounced early in the reinfusion period. During postreinfusion monitoring, PtCO2, MvO2, CO, and PCWP fell significantly despite maintenance of prehemorrhage MAP and CVP. Overall PtCO2 correlated well with MvO2 and the O2 extraction ratio, and to a lesser extent with CI, MAP, and O2 delivery.(ABSTRACT TRUNCATED AT 250 WORDS)