Paul E. Watkins

Contamination of ballistic fractures: an in vitro model

This study allowed the development of an in vitro model of a high-energy ballistic fracture. Direct fractures are more heavily contaminated than indirect fractures, and the spread of contamination is more extensive than examination of the wounds, particularly the entry wounds, would suggest. The major spread of contamination is along tissue planes, and we would recommend that these are thoroughly lavaged in the management of the fracture. The fracture site is heavily contaminated, with endosteal spread in direct fractures. However, there appears to be relatively little bony contamination beyond the fracture site.

Spread of infection, in an animal model, after intramedullary nailing of an infected external fixator pin track.

Implant sepsis, due to previous external fixator pin track infection, is the most common complication of secondary intramedullary (IM) nailing of the tibia. We have developed an animal model, which allows different treatment methods to be studied. Using an established ovine model of a pin track infection, Staphylococcus aureus was used to infect the external fixator pins, two weeks prior to reamed IM nailing. In the control group, the animals were killed at a mean of 10.5 days following nailing, when widespread infection was evident, with septic arthritis, abscess formation, and infection of the entire length of the tibia in all six animals. In the treatment group, before IM nailing, the pin sites were débrided, and both local and systemic antibiotics were administered. All surgical wounds healed without evidence of infection, 4 of the 6 animals survived for 28 days, and bacteria were only isolated from 1 of the 6 implants. Treatment was successful at reducing, but not eliminating, infection after secondary nailing.

Fluid accumulation and the rapid spread of bacteria in the pathogenesis of external fixator pin track infection

An animal model was used to study the pathogenesis of pin track infection. The roles of fluid accumulation around the pin/bone interface and mechanical loosening of the pin were specifically studied. In addition, the spread of bacteria in relation to the clinical appearance of the pin track was assessed. This study demonstrated that fluid accumulation around the interface is an important factor in the spread of infection from the superficial wound track to the medulla of the bone. Spread occurs despite the absence of mechanical pin loosening, and can occur before any clinical features of infection are apparent.

Early intramedullary nailing in an animal model of a heavily contaminated fracture of the tibia

An ovine model was developed to study the outcome following intramedullary nailing of a heavily contaminated fracture. Animals in the control group received no treatment directed at controlling infection, whereas those in the treatment group received wound debridement, lavage and the use of appropriate systemic antibiotics. Despite this, infection developed at the osteotomy site and along the entire length of the implant in all animals in both groups. It was felt that standard methods of wound management might be inadequate when applied at the time of intramedullary nailing since the spread of contamination following the use of reamers was demonstrated in all animals. Results from this study support the clinical impression that heavily contaminated fractures should not be treated by primary intramedullary nailing.

a Porcine Model Of Sepsis Resulting From The Combined Insults Of Hemorrhage And Peritonitis

ABSTRACT The physiological responses to either hemorrhage or sepsis have been well documented, however, their simultaneous delivery, as often seen in penetrating trauma, has not been extensively studied. A terminally‐anesthetized porcine model of fixed‐volume hemorrhage combined with intraperitoneal sepsis was developed. Large White pigs (45–60 kg) were bled 40% of blood volume and peritonitis was induced using an E. coli (O18:K1:H7) culture. Three groups of animals were sequentially studied. Group A (n = 8) received 108 bacteria, and Groups B (n = 4) and C (n = 5) received 1010 organisms. All animals were maintained on a 2.5 mL/kg/h infusion of 0.9% saline. Group C was autotransfused at 1 h. Animals were monitored for up to 24 h. Cardiovascular features of hypovolemia were recorded in all animals. Animals in Group A improved clinically with little microbiological evidence of systemic sepsis. Group B showed rapid cardiovascular collapse, early E. coli‐positive blood cultures, and an early rise in serum TNF‐&agr; levels. Autotransfusion of Group C significantly improved cardiopulmonary parameters, acid‐base status, and survival. A reproducible model of hemorrhage and peritonitis, appropriate for abdominal trauma, which allows investigation of resuscitative and pharmacological interventions has been characterized.

Fibrinogen-impregnated collagen as a combined haemostatic agent and antibiotic delivery system in a porcine model of splenic trauma.

OBJECTIVE To assess the effect of rifampicin on the haemostatic function of a fibrinogen-impregnated collagen fleece. DESIGN Laboratory experiment. SETTING Government research establishment, UK. MATERIAL Six Large White pigs. INTERVENTIONS Four 5 cm incisions were made in the spleen of each animal. Three of the wounds were each covered with a sheet of either dry, saline-soaked or rifampicin-soaked fibrinogen-impregnated collagen. MAIN OUTCOME MEASURES The bleeding time and blood loss from each wound was recorded. Systemic serum rifampicin concentrations were measured using a Staphylococcus aureus inhibition assay. RESULTS Dry fibrinogen-impregnated collagen resulted in significantly less blood loss (112 (21) compared with 39 (13)ml, p < 0.05) and shorter bleeding time (16 (2) compared with 9 (1) min, p < 0.01) than in untreated control wounds. Pre-soaking in saline or rifampicin solution had no significant effect on its haemostatic function. Rifampicin concentrations above the minimum inhibitory concentration were recorded in the systemic circulation 45 minutes after injury and persisted for the duration of the experiment. CONCLUSIONS Fibrinogen-impregnated collagen is an effective haemostatic agent in splenic trauma that may be of use for both the local and systemic delivery of antibiotics.

The role of laser Doppler flowmetry in assessing the viability of bone fragments in an open fracture

The management of open fractures requires excision of all devitalised tissues, both bony and soft tissue, and failure to do so is likely to increase the risk of infection. This study evaluated the applicability of laser Doppler flowmetry for the objective evaluation of fracture fragment viability in an experimental open ballistic fracture over a period of 12 h. The results indicate that this technique could not be used to distinguish between vascularised and non-vascularised fragments at any time, and did not aid the surgeon in their decision making at the time of wound excision. Subjective evaluation, based upon the degree of soft tissue attachment of fragments, was a far better indicator of fragment vascularity, although it had a relatively low specificity. There remains the need for education and training for trauma surgeons in the evaluation of fragment viability to ensure adequate wound excision as part of fracture management.

The effects of repeated dosing with 7.5% sodium chloride/6% dextran following uncontrolled intra-abdominal hemorrhage.

The use of hypertonic saline Dextran (HSD) for resuscitation following trauma has many potential benefits, especially for the treatment of military casualties, but there is very limited data on the responses following multiple dosing with this fluid. The effects of a second dose of hypertonic saline dextran for resuscitation of uncontrolled intra-abdominal haemorrhage were studied in an experimental model. Under general anaesthesia, 17 large white pigs (weight range, 48–67 kg) were subjected to uncontrolled hemorrhage produced by a tear in the common iliac artery. This resulted in a significant (P < 0.01) reduction of both mean arterial pressure (MAP) and cardiac index. One hour after injury, animals were assigned to one of three groups, receiving either no resuscitation (Group A), or two doses of HSD (at a dose rate of 4 mL/kg), administered either 1 and 4 h after injury (Group B) or 1 and 7 h after injury (Group C). Animals were monitored for 12 h post-injury. A second infusion of HSD caused a significant hypernatremia and diuresis (P < 0.01) in both Groups B and C. There was a non-significant rise in MAP in both treatment groups, and in Group B only, there was a significant increase in cardiac index (P = 0.014). It is concluded that repeat administration of HSD for the resuscitation of uncontrolled hemorrhage results in limited cardiovascular improvements, but that the metabolic sequelae are potentially detrimental to survival.

Should Colon-Penetrating Small Missiles Be Removed? An Experimental Study of Retrocolic Wound Tracks

Small-fragment injury to the colon may occur in approximately 5% of battlefield casualties. The surgical management aims to reduce the risk of retrocolic infection and provide optimal conditions for colonic wound healing. This study aimed to quantify the risk of retrocolic infection. Steel fragments were fired through exteriorized porcine colon and caught in 20% gelatin. The fragments, and resultant tracks, were extracted and subjected to quantitative bacteriological examination to determine the extent of contamination. The median bacterial count for complete tracks was 1.2 x 10(4) CFU/g (interquartile range 1.8 x 10(3) to 2.7 x 10(4)). Counts were highest in the initial 1 cm of the track and reduced along its length. This study does not support wound track excision or missile fragment removal in cases of retrocolic trauma following penetrating colonic injury. Either or both procedures will increase local trauma and are likely to prejudice colonic wound repair.