Jeremy W. Cannon

Real-Time Three-Dimensional Ultrasound for Guiding Surgical Tasks

Objective: As a stand-alone imaging modality, two-dimensional (2D) ultrasound (US) can only guide basic interventional tasks due to the limited spatial orientation information contained in these images. High-resolution real-time three-dimensional (3D) US can potentially overcome this limitation, thereby expanding the applications for US-guided procedures to include intracardiac surgery and fetal surgery, while potentially improving results of solid organ interventions such as image-guided breast, liver or prostate procedures. The following study examines the benefits of real-time 3D US for performing both basic and complex image-guided surgical tasks. Materials and Methods: Seven surgical trainees performed three tasks in an acoustic testing tank simulating an image-guided surgical environment using 2D US, biplanar 2D US, and 3D US for guidance. Surgeon-controlled US imaging was also tested. The evaluation tasks were (1) bead-in-hole navigation; (2) bead-to-bead navigation; and (3) clip fixation. Performance measures included completion time, tool tip trajectory, and error rates, with endoscope-guided performance serving as a gold-standard reference measure for each subject. Results: Compared to 2D US guidance, completion times decreased significantly with 3D US for both bead-in-hole navigation (50%, p = 0.046) and bead-to-bead navigation (77%, p = 0.009). Furthermore, tool-tip tracking for bead-to-bead navigation demonstrated improved navigational accuracy using 3D US versus 2D US (46%, p = 0.040). Biplanar 2D imaging and surgeon-controlled 2D US did not significantly improve performance as compared to conventional 2D US. In real-time 3D mode, surgeon-controlled imaging and changes in 3D image presentation made by adjusting the perspective of the 3D image did not diminish performance. For clip fixation, completion times proved excessive with 2D US guidance (< 240 s). However, with real-time 3D US imaging, completion times and error rates were comparable to endoscope-guided performance. Conclusions: Real-time 3D US can guide basic surgical tasks more efficiently and accurately than 2D US imaging. Real-time 3D US can also guide more complex surgical tasks which may prove useful for procedures where optical imaging is suboptimal, as in fetal surgery or intracardiac interventions.

Port placement planning in robot-assisted coronary artery bypass

Properly selected port sites for robot-assisted coronary artery bypass graft (CABG) improve the efficiency and quality of these procedures. In clinical practice, surgeons select port locations using external anatomic landmarks to estimate a patients internal anatomy. This paper proposes an automated approach to port selection based on a preoperative image of the patient, thus avoiding the need to estimate internal anatomy. Using this image as input, port sites are chosen from a grid of surgeon-approved options by defining a performance measure for each possible port triad. This measure seeks to minimize the weighted squared deviation of the instrument and endoscope angles from their optimal orientations at each internal surgical site. This performance measure proves insensitive to perturbations in both its weighting factors and moderate intraoperative displacements of the patients internal anatomy. A validation study of this port site selection was performed. cardiac algorithm also Six surgeons dissected model vessels using the port triad selected by this algorithm with performance compared to dissection using a surgeon-selected port triad and a port triad template described by Tabaie et al., 1999. With the algorithm-selected ports, dissection speed increased by up to 43% (p = 0.046) with less overall vessel trauma. Thus, this algorithmic approach to port site selection has important clinical implications for robot-assisted CABG which warrant further investigation.

Tool Localization in 3D Ultrasound Images

Real-time three-dimensional ultrasound has been demonstrated as a viable tool for guiding surgical procedures [1]. This visualization technique may enable a range of new minimally invasive techniques in cardiac and fetal surgery. It is becoming increasingly clear, however, that instruments such as endoscopic graspers when immersed in liquids display artifacts and irregularities that make it difficult to determine the tool’s location, orientation, and geometry (Figure 1a). In addition, the instrument’s shape can appear incomplete due to its orientation or obstacles in the field. Since the geometry and properties of these instruments are known a priori, it is feasible to combine this information with the ultrasound image data to locate and render an enhanced representation of the instrument. This paper introduces a preliminary study of enhancing tool display in three-dimensional ultrasound, focusing on the relationship between the tissue and instrument.

Prone Positioning Improves Oxygenation in Adult Burn Patients with Severe Acute Respiratory Distress Syndrome

BACKGROUND Prone positioning (PP) improves oxygenation and may provide a benefit in patients with acute respiratory distress syndrome (ARDS). This approach adds significant challenges to patients in intensive care by limiting access to the endotracheal or tracheostomy tube and vascular access. PP also significantly complicates burn care by making skin protection and wound care more difficult. We hypothesize that PP improves oxygenation and can be performed safely in burn patients with ARDS. METHODS PP was implemented in a burn intensive care unit for 18 patients with severe refractory ARDS. The characteristics of these patients were retrospectively reviewed to evaluate the impact of PP on Pao2:FiO2 ratio (PFR) during the first 48 hours of therapy. Each patient was considered his or her own control before initiation of PP, and trends in PFR were evaluated with one-way analysis of variance. Secondary measures of complications and mortality were also evaluated. RESULTS Mean PFR before PP was 87 (±38) with a mean sequential organ failure assessment score of 11 (±4). PFR improved during 48 hours in 12 of 14 survivors (p < 0.05). Mean PFR was 133 (±77) immediately after PP, 165 (±118) at 6 hours, 170 (±115) at 12 hours, 214 (±126) at 24 hours, 236 (±137) at 36 hours, and 210 (±97) at 48 hours. At each measured time interval except the last, PFR significantly improved. There were no unintended extubations. Facial pressure ulcers developed in four patients (22%). Overall, 14 survived 48 hours (78%), 12 survived 28 days (67%), and six survived to hospital discharge (33%). CONCLUSIONS PP improves oxygenation in burn patients with severe ARDS and was safely implemented in a burn intensive care unit. Mortality in this population remains high, warranting investigation into additional complementary rescue therapies. LEVEL OF EVIDENCE Therapeutic study, level IV.

Clearly defining pediatric massive transfusion: cutting through the fog and friction with combat data.

BACKGROUND Massive transfusion (MT) in pediatric patients remains poorly defined. Using the largest existing registry of transfused pediatric trauma patients, we sought a data-driven MT threshold. METHODS The Department of Defense Trauma Registry was queried from 2001 to 2013 for pediatric trauma patients (<18 years). Burns, drowning, isolated head injury, and missing Injury Severity Score (ISS) were excluded. MT was evaluated as a weight-based volume of all blood products transfused in the first 24 hours. Mortality at 24 hours and in the hospital was calculated for increasing transfusion volumes. Sensitivity and specificity curves for predicting mortality were used to identify an optimal MT threshold. Patients above and below this threshold (MT+ and MT−, respectively) were compared. RESULTS The Department of Defense Trauma Registry yielded 4,990 combat-injured pediatric trauma patients, of whom 1,113 were transfused and constituted the study cohort. Sensitivity and specificity for 24-hour and in-hospital mortality were optimal at 40.1-mL/kg and 38.6-mL/kg total blood products in the first 24 hours, respectively. With the use of a pragmatic threshold of 40 mL/kg, patients were divided into MT+ (n = 443) and MT− (n = 670). MT+ patients were more often in shock (68.1% vs. 47.0%, p < 0.001), hypothermic (13.0% vs. 3.4%, p < 0.001), coagulopathic (45.0% vs. 29.6%, p < 0.001), and thrombocytopenic (10.6% vs. 5.0%, p = 0.002) on presentation. MT+ patients had a higher ISS, more mechanical ventilator days, and longer intensive care unit and hospital stay. MT+ was independently associated with an increased 24-hour mortality (odds ratio, 2.50; 95% confidence interval, 1.28–4.88; p = 0.007) and in-hospital mortality (odds ratio, 2.58; 95% confidence interval, 1.70–3.92; p < 0.001). CONCLUSION Based on this large cohort of transfused combat-injured pediatric patients, a threshold of 40 mL/kg of all blood products given at any time in the first 24 hours reliably identifies critically injured children at high risk for early and in-hospital death. This evidence-based definition will provide a consistent framework for future research and protocol development in pediatric resuscitation. LEVEL OF EVIDENCE Diagnostic study, level II. Prognostic/epidemiologic study, level III.

Acute respiratory distress syndrome in wartime military burns: application of the Berlin criteria.

BACKGROUND Acute respiratory distress syndrome (ARDS) prevalence and related outcomes in burned military casualties from Iraq and Afghanistan have not been described previously. The objective of this article was to report ARDS prevalence and its associated in-hospital mortality in military burn patients. METHODS Demographic and physiologic data were collected retrospectively on mechanically ventilated military casualties admitted to our burn intensive care unit from January 2003 to December 2011. Patients with ARDS were identified in accordance with the new Berlin definition of ARDS. Subjects were categorized as having mild, moderate, or severe ARDS. Multivariate logistic regression identified independent risk factors for developing moderate-to-severe ARDS. The main outcome measure was the prevalence of ARDS in a cohort of patients burned as a result of recent combat operations. RESULTS A total of 876 burned military casualties presented during the study period, of whom 291 (33.2%) required mechanical ventilation. Prevalence of ARDS in this cohort was 32.6%, with a crude overall mortality of 16.5%. Mortality increased significantly with ARDS severity: mild (11.1%), moderate (36.1%), and severe (43.8%) compared with no ARDS (8.7%) (p < 0.001). Predictors for the development of moderate or severe ARDS were inhalation injury (odds ratio [OR], 1.90; 95% confidence interval [CI], 1.01–3.54; p = 0.046), Injury Severity Score (ISS) (OR, 1.04; 95% CI, 1.01–1.07; p = 0.0021), pneumonia (OR, 198; 95% CI, 1.07–3.66; p = 0.03), and transfusion of fresh frozen plasma (OR, 1.32; 95% CI, 1.01–1.72; p = 0.04). Size of burn was associated with moderate or severe ARDS by univariate analysis but was not an independent predictor of ARDS by multivariate logistic regression (p > 0.05). Age, size of burn, and moderate or severe ARDS were independent predictors of mortality. CONCLUSION In this cohort of military casualties with thermal injuries, nearly a third required mechanical ventilation; of those, nearly one third developed ARDS, and nearly one third of patients with ARDS did not survive. Moderate and severe ARDS increased the odds of death by more than fourfold and ninefold, respectively. LEVEL OF EVIDENCE Epidemiologic/prognostic study, level III.

A porcine model for evaluating the management of noncompressible torso hemorrhage.

BACKGROUNDnNoncompressible hemorrhage from central vascular injuries remains the leading cause of preventable death in modern combat. This report introduces a large animal model of noncompressible torso hemorrhage, which permits assessment of the various approaches to this problem.nnnMETHODSnYorkshire swine were anesthetized and monitoring devices for central aortic pressure, carotid flow, and intracerebral and transcutaneous brain oximetry were applied. Class IV hemorrhagic shock was induced through an iliac arterial injury and animals were subjected to different vascular control methods including thoracic aortic clamping, supraceliac aortic clamping, direct vascular control, and proximal endovascular balloon occlusion. After vascular control, the injury was shunted, and damage control resuscitation was continued. Serum markers, intravenous fluid volumes, and vasopressor requirements were tracked over a subsequent resuscitation period. Postmortem tissue analysis was performed to compare levels of acute ischemic injury between groups.nnnRESULTSnThe protocol for animal preparation, hemorrhage volume, open surgical technique, and posthemorrhage resuscitation was developed using four animals. The endovascular approach was developed using two additional animals. After model development, treatment animals subsequently underwent noncompressible hemorrhage with thoracic aortic clamping, supraceliac aortic clamping, direct vascular control, and endovascular aortic occlusion. Premature death occurred in one animal in the direct vascular control group.nnnCONCLUSIONnThis study presents a large animal model of class IV hemorrhagic shock from noncompressible hemorrhage, which permits comparison of various vascular control methods to address this challenging problem. Future studies using this model as the standard will allow further development of strategies for the management of noncompressible hemorrhage.

Extracorporeal Gas Exchange and Spontaneous Breathing for the Treatment of Acute Respiratory Distress Syndrome: An Alternative to Mechanical Ventilation?

Objectives:Venovenous extracorporeal gas exchange is increasingly used in awake, spontaneously breathing patients as a bridge to lung transplantation. Limited data are available on a similar use of extracorporeal gas exchange in patients with acute respiratory distress syndrome. The aim of this study was to investigate the use of extracorporeal gas exchange in awake, spontaneously breathing sheep with healthy lungs and with acute respiratory distress syndrome and describe the interactions between the native lung (healthy and diseased) and the artificial lung (extracorporeal gas exchange) in this setting. Design:Laboratory investigation. Setting:Animal ICU of a governmental laboratory. Subjects:Eleven awake, spontaneously breathing sheep on extracorporeal gas exchange. Interventions:Sheep were studied before (healthy lungs) and after the induction of acute respiratory distress syndrome via IV injection of oleic acid. Six gas flow settings (1–10 L/min), resulting in different amounts of extracorporeal CO2 removal (20–100% of total CO2 production), were tested in each animal before and after the injury. Measurements and Main Results:Respiratory variables and gas exchange were measured for every gas flow setting. Both healthy and injured sheep reduced minute ventilation according to the amount of extracorporeal CO2 removal, up to complete apnea. However, compared with healthy sheep, sheep with acute respiratory distress syndrome presented significantly increased esophageal pressure variations (25 ± 9 vs 6 ± 3 cm H2O; p < 0.001), which could be reduced only with very high amounts of CO2 removal (> 80% of total CO2 production). Conclusions:Spontaneous ventilation of both healthy sheep and sheep with acute respiratory distress syndrome can be controlled via extracorporeal gas exchange. If this holds true in humans, extracorporeal gas exchange could be used in awake, spontaneously breathing patients with acute respiratory distress syndrome to support gas exchange. A deeper understanding of the pathophysiology of spontaneous breathing during acute respiratory distress syndrome is however warranted in order to be able to propose extracorporeal gas exchange as a safe and valuable alternative to mechanical ventilation for the treatment of patients with acute respiratory distress syndrome.

Modified Augmented Renal Clearance Score Predicts Rapid Piperacillin and Tazobactam Clearance in Critically Ill Surgery and Trauma Patients

BACKGROUND Recent evidence suggests that current antimicrobial dosing may be inadequate for some critically ill patients. A major contributor in patients with unimpaired renal function may be Augmented Renal Clearance (ARC), wherein urinary creatinine clearance exceeds that predicted by serum creatinine concentration. We used pharmacokinetic data to evaluate the diagnostic accuracy of a recently proposed ARC score. METHODS Pharmacokinetic data from trauma/surgical intensive care unit patients receiving piperacillin/tazobactam were evaluated. We combined intermediate scores (4–6 points) into a single low score (⩽6) group and compared pharmacokinetic parameters against the high (≥7) ARC score group. Diagnostic performance was evaluated using median clearance and volume of distribution, area under the antibiotic time-concentration curve (AUC), and achievement of free concentrations greater than a minimum inhibitory concentration (MIC) of 16 &mgr;g/mL for at least 50% of the dose interval (fT > MIC ≥ 50%). Alternative dosing strategies were explored in silico. RESULTS The ARC score was 100% sensitive and 71.4% specific for detecting increased clearance, increased volume of distribution, decreased AUC, and fT > MIC < 50% at an MIC of 16 &mgr;g/mL. The area under the receiver operating characteristic curve was 0.86 for each, reflecting a high degree of diagnostic accuracy for the ARC score. Serum creatinine less than 0.6 mg/dL had comparable specificity (71.4%) but was less sensitive (66.7%) and accurate (area under the receiver operating characteristic curve, 0.69) for detecting higher clearance rates. Monte Carlo pharmacokinetic simulations demonstrated increased time at therapeutic drug levels with extended infusion dosing at a drug cost savings of up to 66.7% over multiple intermittent dosing regimens. CONCLUSION Given its ability to predict antimicrobial clearance above population medians, which could compromise therapy, the ARC score should be considered as a means to identify patients at risk for subtherapeutic antibiotic levels. Adequately powered studies should prospectively confirm the utility of the ARC score and the role of antimicrobial therapeutic drug monitoring in such patients. LEVEL OF EVIDENCE Diagnostic tests, level III.

Application of robotics in congenital cardiac surgery.

Over the past 5 years, robotic systems that combine advanced endoscopic imaging with computer-enhanced instrument control have been used for both coronary revascularization and intracardiac procedures in adults. In addition, endoscope positioning systems and articulated instruments with a robotic wrist mechanism have further expanded the potential applications for robotics in cardiac surgery. In pediatric cardiac surgery, potential applications can be divided into simple scope manipulation versus the use of 3-dimensional imaging and a robotic wrist for dissection and reconstruction. A voice-controlled robotic arm for scope manipulation can facilitate current pediatric thoracoscopic procedures such as ligation of patent ductus arteriosus and division of vascular rings. By using an advanced imaging system along with a robotic wrist, more complex extracardiac and even intracardiac procedures can be performed in children. Examples include coarctation repair, septal defect repair, and mitral or tricuspid valvuloplasty. Furthermore, with adequate intracardiac imaging, a robot-assisted off-pump approach to intracardiac pathology is conceivable. New real-time 3-dimensional echocardiography now offers sufficient resolution to enable such procedures, while the addition of instrument tracking, haptic feedback, and novel tissue fixation devices can facilitate safe and reliable intracardiac repair without extracorporeal circulation.