The mechanism of lung volume change during mechanical ventilation.

To understand ventilator-induced lung injury (VILI) during positive pressure ventilation, mechanisms of normal alveolar mechanics must first be established. Isotropic "balloonlike" alveolar volume (VA) change has been viewed as the prevailing mechanism of normal lung volume (VL) changes. We hypothesized that change in VL is predominantly caused by alveolar recruitment-derecruitment (R/D). Fifteen mongrel dogs were anesthetized and intubated with a tracheal divider. Through a thoracotomy incision, in vivo microscopy of subpleural alveoli was performed as the degassed lung was inflated to 80% TLC, and then deflated to residual volume (RV). Still photomicrographs were evaluated to determine if change in VL is due to change in VA or R/D of alveoli. We noted a steady, significant increase in alveolar recruitment as VL increased to 80% TLC (p < 0.05). However, VA increased significantly, but only to 20% TLC (p < 0.05). Once recruited, alveoli did not demonstrate any further volume change, whereas the lung as a whole maintained a normal pressure/volume relationship. In our model, changes in VL predominantly are caused by R/D.

Carotid endarterectomy after NASCET and ACAS: a statewide study. North American Symptomatic Carotid Endarterectomy Trial. Asymptomatic Carotid Artery Stenosis Study.

PURPOSE: Since the North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Artery Stenosis Study (ACAS) established the efficacy of carotid endarterectomy at large academic centers, there have been two community-based studies of outcomes after this operation. The purpose of this study was to perform a statewide survey to evaluate postoperative morbidity and mortality after carotid endarterectomy among patients throughout Maine. METHODS: A statewide registry was established to collect prospective data on carotid operations from January 1 to December 31, 1995. All surgeons and hospitals in the state were solicited to participate. All carotid endarterectomies were intended to be included; the only exclusion criterion was out-of-state residence. Comorbidities, preoperative studies, surgical indications, operative technique, and postoperative outcomes were analyzed. State administrative data were used to assess registry coverage. RESULTS: Ten of 17 hospitals participated, and 58% of all carotid endarterectomies performed in the state were included. Three hundred sixty-four operations were entered into the registry. Forty-four percent of the operations were performed for transient ischemic attack, 37% for asymptomatic stenosis, and 19% for stroke. The postoperative stroke rate was 2.5% with a total neurologic complication rate of 4.7% (transient ischemic attack and stroke). There was one postoperative death (mortality rate 0.3%). Patients with symptoms had a higher incidence of postoperative stroke (4.0% vs 0% asymptomatic; p < 0.05) and transient ischemic attacks (3.8% vs 0.8% asymptomatic). Hospital stroke rates varied from 0% to 7%. Stroke rate did not differ significantly between low-volume hospitals (2 to 28 patients/year, 3.3%) and high-volume hospitals (29 to 101 patients/year, 2.3%) or between low-volume surgeons (fewer than 11 operations/year, 1.7%) and high-volume surgeons (more than 12 operations/year, 2.4%). Among 26 reporting surgeons, stroke rate varied from 0% to 10%; the absolute number of strokes per surgeon varied between zero and two. CONCLUSION: The statewide registry showed a postoperative stroke plus death rate of 2.8%, comparable with the NASCET and ACAS findings. Although this study had inherent limitations, the results from one state, including a variety of community practices, achieved results comparable with those of landmark trials.

Monitoring hospital trauma mortality using statistical process control methods.

BACKGROUND: We sought to develop a simple and effective way to monitor trends in trauma mortality, using objective clinical categories and methods of statistical process control. STUDY DESIGN: Control charts and Pareto analysis were applied to trauma mortality data at the Maine Medical Center. We collected data prospectively on patients who died in our hospital after acute injury during 1985-1996 (and retrospectively for 1975-1984) to identify cases requiring medical quality review. We excluded from this study patients older than 80 years, those whose Glasgow Coma Scale motor component was never > 3 at any time after admission, and those with pathologic fractures, carcinomatosis, high quadriplegia, or severe burns. The remaining deaths were classified as resulting from inability to resuscitate (mostly hemorrhage), neurologic deterioration, or organ failure. The annual numbers in each of these categories were evaluated under the hypothesis of stationary Poisson processes with mean values equal to those seen from 1975-1984. RESULTS: After the exclusions, annual mortality from trauma has remained within control limits consistent with the Poisson model. Death from neurologic deterioration has shown a trend consistent with significant improvement in the process mean. Transient peaks in the other categories did not exceed control limits, but Pareto analysis prompted detailed studies of aortic and liver trauma. CONCLUSIONS: Process control methodology is easy to apply and potentially useful in monitoring hospital trauma mortality.

Variation in carotid endarterectomy mortality in the Medicare population: trial hospitals, volume, and patient characteristics.

CONTEXT: The North American Symptomatic Carotid Endarterectomy Trial (NASCET) and the Asymptomatic Carotid Atherosclerosis Study (ACAS) demonstrated the efficacy of carotid endarterectomy (CEA) in reducing the risk of stroke and death in selected patients when surgery was performed in institutions whose participation depended on demonstrated excellence. Thirty-day mortality rates in the trials were very low: 0.6% in NASCET and 0.1% in ACAS. OBJECTIVE: To assess perioperative mortality among Medicare patients undergoing CEA in all nonfederal institutional settings. DESIGN: Retrospective national cohort study. SETTING AND PATIENTS: All 113300 Medicare patients undergoing CEA during 1992 and 1993 in "trial hospitals" (those participating in NASCET and ACAS, n=86) and "nontrial hospitals" (all other nonfederal institutions performing CEAs, n=2613). Nontrial hospitals were stratified into terciles based on volume of CEAs performed. MAIN OUTCOME MEASURES: Crude and adjusted perioperative (30 day) mortality rates. RESULTS: The perioperative mortality rate was 1.4% (95% confidence interval [CI], 1.2%-1.7%) at trial hospitals; mortality in nontrial hospitals was higher: 1.7% (95% CI, 1.6%-1.8%) (high volume); 1.9% (95% CI, 1.7%-2.1 %) (average volume); 2.5% (95% CI, 2.0%-2.9%) (low volume); (P for trend, <.001). In multivariate modeling, patients undergoing their procedures at trial hospitals had a mortality risk reduction of 15% (95% CI, 0%-31%) compared with high-volume nontrial hospitals, 25% (95% CI, 7%-40%) compared with average-volume hospitals, and 43% (95% CI, 25%-56%) compared with low-volume hospitals (P for trend, <.001). CONCLUSION: Medicare patients' perioperative mortality following CEA is substantially higher than that reported in the trials, even in those institutions that participated in the randomized studies. Caution is advised in translating the efficacy of carefully controlled studies of CEA to effectiveness in everyday practice.

Vascular endothelial growth factor increases the mitogenic response to fibroblast growth factor-2 in vascular smooth muscle cells in vivo via expression of fms-like tyrosine kinase-1.

Vascular endothelial growth factor (VEGF) has traditionally been considered an endothelial cell-specific factor inducing angiogenesis and vascular permeability in vivo. In the present study, expression of VEGF and its receptors, fetal liver kinase-1 (flk-1) and fms-like tyrosine kinase-1 (flt-1), was examined in rat carotid arteries after balloon injury. Although VEGF and flk-1 were not detectable, high levels of flt-1 mRNA and protein were expressed by smooth muscle cells (SMCs) in the neointima, as demonstrated by en face in situ hybridization and Western blotting. Intimal SMC proliferation in chronically denuded rat carotid arteries was unaffected by intraluminal infusion of VEGF, whereas fibroblast growth factor (FGF)-2 increased the number of replicating SMCs 4-fold. Pretreatment with VEGF doubled the mitogenic response to infused FGF-2 by increasing SMC replication in deeper layers of the intima. VEGF increased the permeability of chronically denuded vessels to plasma proteins but had no effect on the uptake of locally infused biotinylated FGF-2. These findings demonstrate that vascular SMCs express functional flt-1 receptors after arterial injury and that VEGF has synergistic effects with FGF-2 on SMC proliferation. These effects are likely to be mediated by a VEGF-mediated increase in permeability as well as a direct interaction between the VEGF and FGF signaling pathways.

Aspirin enhances platelet-derived growth factor-induced vascular smooth muscle cell proliferation.

PURPOSE: Aspirin is frequently used after vascular reconstruction to pharmacologically prevent graft occlusion and to suppress the development of myointimal hyperplasia in vascular surgery, but its efficacy is controversial. The purpose of this study was to examine the direct effects of aspirin on platelet-derived growth factor (PDGF)-induced vascular smooth muscle cell (SMC) proliferation. METHODS: Human aortic SMCs were grown to confluence in 96 well plates. 3 x 10(-5) mol/L aspirin was added 24 hours previously and PDGF 10 ng/ml at the beginning of each experiment. Cell proliferation at 48 hours was determined using tritiated thymidine uptake. Supernatant 12-L-hydroxy 5,8,10,14-eicosatetraenoic acid (12-HETE) and prostaglandin E2 (PGE2) were measured by competitive enzyme immunoassay. RESULTS: Aspirin did not change vascular SMC proliferation rates relative to controls (4665 +/- 181 counts per minute [CPM] vs 4749 +/- 155 CPM). However, aspirin pretreatment of PDGF-stimulated vascular SMCs increased proliferation (9408 +/- 237 CPM vs 7283 +/- 283 CPM; p < 0.001). 5,8,10,14-eicosatriynoic acid, a 12-lipoxygenase inhibitor, decreased basal (2037 +/- 181 CPM vs 2306 +/- 158 CPM; p < 0.05) and PDGF-stimulated vascular SMC proliferation (4909 +/- 1089 CPM vs 4310 +/- 1022 CPM; p < 0.001). Aspirin increased supernatant 12-HETE levels and decreased PGE2 levels in both basal and PDGF-stimulated cell cultures. CONCLUSIONS: Aspirin enhances PDGF-stimulated vascular SMC proliferation. The effects of aspirin on vascular SMC proliferation may be mediated by changes in vascular SMC arachidonic acid metabolism.

Abdominal vascular catastrophes.

Abdominal vascular catastrophes are due to rupture of arterial aneurysms or arterial occlusion leading to end organ ischemia. In this article, we will discuss rupture of abdominal aortic aneurysms and visceral artery aneurysms. Arterial occlusion secondary to embolism, thrombosis and dissection will be presented. Mesenteric ischemia secondary to low flow states, venous thrombosis and other conditions will also be covered. These uncommon, but frequently fatal pathological processes, are of interest to both general and vascular surgeons.

Percutaneous dilatational tracheostomy. A safe, cost-effective bedside procedure.

OBJECTIVE: To evaluate the safety and cost-effectiveness of percutaneous dilatational tracheostomy performed in the intensive care unit. DESIGN: Retrospective review of 65 patients with cost-effectiveness analysis. SETTING: University-affiliated tertiary care teaching hospital with a 34-bed combined medical-surgical intensive care unit. PATIENTS: All patients who underwent percutaneous dilatational tracheostomy under the supervision of a single general surgeon during a 19-month period. Cost analysis was based on comparison with standard operative tracheostomies performed during the same period. RESULTS: Percutaneous dilatational tracheostomy was completed in all patients in whom it was attempted, regardless of airway anatomy, body habitus, and ventilator settings. The mean duration of the procedure performed in the intensive care unit was 13.6 minutes (95% confidence interval, 11.7 to 15.5 minutes). Intraoperative complications occurred in 14 patients (22%), most of which were minor technical difficulties, and none resulted in serious morbidity. Postoperative complications occurred in six patients (9%), including one death secondary to premature decannulation, three bleeding complications, one episode of subcutaneous emphysema, and one air leak. Two long-term airway complications after percutaneous dilatational tracheostomy were documented during a mean 7.5-month follow-up of 28 patients. Mean patient charges for the procedure performed in the intensive care unit by a surgeon, nurse, and respiratory therapist were $997 (95% confidence interval, $975 to $1018) compared with $2642 (95% confidence interval, $2513 to $2772) for standard tracheostomy (P<.001). This represented a savings of $1645 (95% confidence interval, $1492 to $1798) per tracheostomy. CONCLUSIONS: Percutaneous dilatational tracheostomy is a safe, rapid, cost-effective alternative to standard open tracheostomy. It can be performed at the bedside, obviating the need to transport critically ill patients from their optimal intensive care unit environment.

Multidisciplinary approach to pseudoaneurysms complicating pancreatic pseudocysts. Impact of pretreatment diagnosis.

OBJECTIVE: To determine the effectiveness of thin-section, dynamic-contrast computed tomography and angiography in detecting the presence of pancreatic pseudoaneurysms. DESIGN: This case series consisted of 57 patients who were being examined for endoscopic drainage of pancreatic pseudocysts. SETTING: All patients were examined in a tertiary care, teaching hospital. PATIENTS: Fifty-seven consecutive patients were examined for 2 years. Follow-up ranged from 6 months to 2 years. INTERVENTIONS: All patients underwent thin-section, high-speed, dynamic-contrast computed tomography. Those patients with findings that were consistent with the presence of a pseudoaneurysm underwent angiography. Embolization was attempted if a pseudoaneurysm was present. Endoscopic retrograde cholangiopancreatography was used to determine pancreatic ductal anatomy before operation. MAIN OUTCOME MEASURE: No undetected pseudoaneurysm has complicated this series of endoscopically drained pseudocysts. RESULTS: Five patients had findings that were consistent with a pancreatic pseudoaneurysm on computed tomography. Angiographic findings confirmed a pseudoaneurysm in four patients, and angiographic embolization was successful in three. Four patients underwent resection, while one was treated with embolization and endoscopic stenting of a compressed pancreatic duct. There were no mortalities. CONCLUSIONS: Before endoscopic drainage of a pancreatic pseudocyst, a thin-section, high-speed, dynamic-contrast computed tomographic scan is essential. If there are findings consistent with the development of a pseudoaneurysm, angiography must be performed. This allows delineation of the arterial anatomy, as well as the option of performing angiographic embolization. While patients with pseudoaneurysms in the body and tail of the pancreas underwent resection, angiographic embolization alone was an acceptable alternative when the lesion was located in the head of the pancreas.

Should percutaneous transluminal renal artery angioplasty be applied to ostial renal artery atherosclerosis?

PURPOSE: The purpose of this study was to review the results of percutaneous transluminal renal artery angioplasty (PTRA) in patients with atherosclerosis to assess safety, anatomic and functional outcome, and differences in outcome between ostial and nonostial lesions. METHODS: We used retrospective review of 52 consecutive patients who had undergone attempted PTRA for renal artery atherosclerosis during the calendar years 1987 to 1992. RESULTS: Fifty-two patients had 60 renal arteries on whom PTRA was attempted. The mean age was 68 years. Atherosclerosis was generalized in 81% of the patients. The indication for angioplasty was salvage of functioning renal parenchyma in 81% of patients. Eight patients were undergoing dialysis at the time of attempted PTRA. Five arteries (8%) could not be dilated. There were one cardiac death and two arterial complications requiring surgery within 30 days. Thirty-five percent of patients with available angiograms had an anatomic improvement above a threshold of one stenotic group (30% to 40% diameter improvement), with residual stenosis of less than 50%. Half of patients treated for hypertension had improvement in their hypertension. Overall, there was no change in creatinine levels before and after the procedure. Four of eight patients undergoing dialysis at the time of PTRA were able to discontinue dialysis during follow-up. Four patients (11%) required surgical bypass and five patients (14%) required chronic dialysis during follow-up. CONCLUSIONS: Modest success at low risk can be expected from PTRA in a group of patients with severe atherosclerosis. No significant difference in results between ostial and nonostial lesions was noted.

Unilateral smoke inhalation increases pulmonary blood flow to the injured lung.

Smoke inhalation (SI) affects the homogeneity of lung perfusion possibly by increasing alveolar surface tension. Anesthetized dogs (n = 8) were ventilated with a tracheal divider and a dual ventilator. One lung (left or right) was exposed to 5 minutes of SI while the other remained on room air. Total pulmonary blood flow (cardiac output) was measured by thermal dilution and left lung blood flow was measured with an ultrasonic flow probe. Since SI is associated with elevation of alveolar surface tension (AST), we studied a second group of dogs (n = 6) in which AST was increased in one lung with aerosolized dioctyl sodium sulfosuccinate (OT). The OT elevates AST without otherwise damaging the lung. Unilateral SI resulted in systemic hypoxemia (Pao2 fell from 91 +/- 6 to 55 +/- 4 mm Hg) and increased venous admixture (9 +/- 2% to 29 +/- 4%) both of which remained different from baseline values (p < 0.05) for 2 hours. Blood flow to the smoke exposed lung increased gradually and became significantly larger than that to the contralateral normal lung 2 hours following inhalation (smoke lung = 64% +/- 6% and normal lung = 36% +/- 6% of total blood flow). Following smoke exposure, pulmonary vascular resistance (PVR) increased with time in the unexposed normal lung (baseline = 8.7 +/- 1.4; 2 hours post smoke = 22.6 +/- 7.9 mm Hg/L/min, p < 0.05); PVR did not change in the smoke injured lung.(ABSTRACT TRUNCATED AT 250 WORDS)

The neurovascular outcome of scapulothoracic dissociation.

PURPOSE: The purpose of this study was to define the role of acute revascularization in the management of scapulothoracic dissociation (SD), a rare injury of the upper extremity in which severe traction to the shoulder girdle results in combined arterial, brachial plexus, and musculoskeletal injury. METHODS: The results of a retrospective study of 11 patients with SD who were compared with 41 patients from the literature are presented. RESULTS: All 11 patients were involved in high-speed accidents. All patients had chest wall hematoma, absent radial pulse, and complete brachial plexus palsy. All patients had subclavian or axillary occlusion shown by angiography; one patient with simultaneous brachial artery injury had limb-threatening ischemia. No patient had active bleeding from the injured artery. Six limbs were revascularized, five were not. All five non-revascularized limbs remained viable. No patient had delayed hemorrhage. No patient had significant neurologic recovery; all limbs remained insensate and functionless. Two viable arms underwent late amputation because of neurologic dysfunction. CONCLUSION: The infrequent occurrence of delayed hemorrhage and limb-threatening ischemia and the dismal functional outcome of the brachial plexus injury suggest a conservative policy toward revascularization for the arterial injury in SD.

Changing patterns in surgery for chronic renal artery occlusive diseases.

We report 66 patients undergoing 69 operations for chronic renal artery occlusive diseases operated on at two institutions between January 1985 and June 1990. Etiology was atherosclerosis in 59 patients (90%); fibromuscular disease in four (6%), and three children with nonfibromuscular disease stenosis (4%). Atherosclerosis was local in 10 and generalized in 49 (83% of all patients). Fifty operations (72%) were for salvage of renal function. Average serum creatinine was 2.3 mg/dl and was elevated in 46 patients (70%). Donor arteries for reconstruction were aorta 20 (29%), aortic graft 16 (23%), and other abdominal arteries 33 (48%). Twenty-one patients had concomitant vascular procedures including 16 aortic replacements. The two operative deaths (3%) followed aortic replacements. Three grafts (4%) occluded before discharge from the hospital. Eighty-six percent of patients undergoing renal salvage avoided long-term dialysis. In past decades fibromuscular disease and localized atherosclerosis were the most frequent renal artery occlusive diseases undergoing surgery, hypertension was the predominant indication, and the most frequent operation was aortorenal bypass. As a result of improved pharmacologic management of hypertension and the development of percutaneous transluminal dilation, most patients in this series had far advanced generalized atherosclerosis, and renal salvage was the most frequent indication for operation. As a consequence of the severity of the atherosclerosis, 48% of operations avoided the aorta, 23% replaced the aorta, and aortorenal bypass was used in only 29%.

Blunt trauma to the carotid arteries.

Blunt carotid artery trauma is an uncommon but potentially dangerous clinical entity. We report eight patients from a 10-year interval who sustained blunt injuries to the carotid arteries. Six of eight patients suffered a hyperextension injury or had a cervical spine fracture or both. Arteriography revealed four arterial dissections and four thrombotic occlusions. Two asymptomatic common carotid artery occlusions and one dissection with transient ischemic attacks had successful arterial reconstructions. Five patients were treated nonoperatively: three internal carotid artery dissections with minor or no neurologic deficit; one asymptomatic thrombosis; and one internal carotid artery thrombosis with a major fixed neurologic deficit that did not improve. No patient died, and seven of eight made a complete neurologic recovery or remained asymptomatic. The diagnosis of blunt carotid artery injuries should be suspected in patients with neck hyperextension injuries or with cervical spine fractures as well as in patients with neurologic deficits not explained by intracranial trauma. Duplex scanning may be a useful noninvasive study. Surgery is indicated for selected patients with accessible lesions who have minor or no neurologic deficits. Asymptomatic patients with small intimal flaps or dissections may be successfully treated nonoperatively.

High alveolar surface tension increases clearance of technetium 99m diethylenetriamine-pentaacetic acid.

The effect of high alveolar surface tension on alveolar epithelial permeability was studied in anesthetized closed-chest mongrel dogs. Alveolar surface tension was elevated by displacement of pulmonary surfactant from the alveolar hypophase by the aerosolized detergent dioctyl sodium sulfosuccinate (OT). After measurement of baseline hemodynamics, arterial blood gases, and airway pressure, the dogs were separated into groups: Group I inhaled a 1% solution of OT (15 mg/kg) in a vehicle of equal parts saline and ethanol; group II inhaled the same volume of vehicle without OT. The pulmonary clearance of technetium 99m diethylenetriamine-pentaacetic acid (99mTc-DTPA) (half-time in minutes) was studied immediately after aerosol (OT and vehicle) delivery and compared with that of historical control values. No change was seen in arterial blood gases and airway pressure after vehicle inhalation, whereas OT caused a marked fall in arterial oxygen tension and increase in airway pressure. Vehicle inhalation effected only a slight increase in DTPA clearance, whereas OT significantly reduced half-time over control and group II. These data suggest that high alveolar surface tension increases alveolar epithelial permeability.

Graft geometry and venous intimal-medial hyperplasia in arteriovenous loop grafts.

This study explores graft geometry and hemodynamics in a reproducible canine arteriovenous loop graft model of intimal-medial hyperplasia. Untapered 6 mm diameter polytetrafluoroethylene grafts (n = 10) were paired with 4 to 7 mm taper (n = 5) or 7 to 4 mm taper (n = 5) grafts for a 12-week period. Several hemodynamic variables were assessed at multiple locations, and venous intimal-medial thickness was measured at locations corresponding to the hemodynamic measurements. Color Doppler imaging demonstrated energy transfer out of the vessel in the form of perivascular tissue vibration. This was quantitated by the distance required for Doppler signal attenuation or volume of the detected vibration signal. Differences among graft types were noted for pressure, flow velocity, tissue vibration, and venous intimal-medial thickness. Hyperplasia was significantly decreased in 4 to 7 mm taper grafts. Stepwise deletion regression indicated volume of the vibration signal had a better correlation with venous intimal-medial thickness than any other variable (r 0.9, p less than 0.001). We conclude that graft geometry can have a significant impact on hemodynamic factors and venous intimal-medial hyperplasia in arteriovenous loop grafts. Flow disturbances appear to cause energy transfer through the vessel wall and into perivascular tissue. Kinetic energy transfer in the form of perivascular tissue vibration was quantitated in vivo and correlates strongly with venous intimal-medial thickness.