Management of postcardiotomy hypertension by microcomputer-controlled administration of sodium nitroprusside.

Manual administration of sodium nitroprusside in patients who have undergone cardiac operations can be associated with wide swings in mean systemic arterial pressure. Moreover, it is necessary for constant attention to be paid in order to minimize these potentially catastrophic arterial pressure changes. A microcomputer-based controller was constructed in the belief that it might improve the accuracy of systemic arterial pressure control as well as relieve the clinical staff of a time-consuming task. Comparison was made of the effectiveness of manual control versus computer control of sodium nitroprusside infusion in two groups of patients with similar clinical characteristics. In the manual control group the mean systemic arterial pressure could be maintained within 5 mm Hg of the target pressure only half (52%) of the time. In the computer-controlled group the mean systemic arterial pressure was maintained within 5 mm Hg of the target pressure 94% of the time (p less than 0.005). Thus, computerized control of sodium nitroprusside infusion eliminated the need for an intensive care unit nurse to be "locked into" the task of making frequent adjustments of infusion rate. Of even greater importance, control of mean systemic arterial pressure was more precise.

The natural history of thoracic aortic aneurysms.

Because improved understanding of the natural history of thoracic aneurysms would enhance our ability to determine in which cases the risk of surgical treatment is justified, the rate of enlargement of thoracic aneurysms and thoracoabdominal aneurysms was studied in 67 patients by means of serial computer-generated three-dimensional reconstructions of computed tomographic scans. Patients were followed for a mean of 1.5 +/- 0.15 years (0.2 to 5.35 years) with an average interval between examinations of 0.9 +/- 0.1 year (0.2 to 5.0 years). Thirty-nine patients continue to be followed; 7 were lost to follow-up; 14 died during follow-up (4 after aneurysm rupture), and 10 underwent an operation. Indications for operation included the presence of pain, an absolute aortic diameter larger than 8 cm, an increase in aortic diameter of more than 1 cm per year, or marked irregularity of aneurysm contour. Aortic diameter and volume data were generated from the aortic silhouette obtained by tracing each computed tomographic slice with a translucent digitizing tablet. Estimated change in aortic diameter after 1 year was 0.43 cm; estimated change in aortic volume was 88.1 ml. The impact of possible risk factors on the enlargement of aneurysms was examined by analysis of variance (p < 0.05). A significantly higher rate of aneurysm expansion was found in patients with a larger aortic diameter (> 5 cm) at diagnosis (change in diameter = 0.17 cm versus 0.79 cm; change in volume = 40 ml versus 141.8 ml), and in smokers (change in diameter = 0.35 cm versus 0.70 cm; change in volume = 78.3 ml versus 120.8 ml). Changes in diameter and volume for aneurysms of different initial diameters and volumes was predicted by exponential regression by the equations: change in diameter = 0.0167 (initial aortic diameter)2.1; change in volume = 0.0356 (initial aortic volume)1.322. No correlation was noted between the rate of enlargement and age, sex, or the presence of dissection. A history of hypertension correlated with a greater aortic diameter at diagnosis but did not significantly affect the rate of enlargement.(ABSTRACT TRUNCATED AT 250 WORDS)

Prospective study of the natural history of thoracic aortic aneurysms.

BACKGROUND: The decision whether or not to recommend resection of moderately large descending thoracic and thoracoabdominal aneurysms requires weighing the relatively high mortality and significant risk of paraplegia associated with operation against the likelihood that the aneurysm will rupture spontaneously, with an almost invariably fatal outcome. To better define the risk of aneurysm rupture, we undertook a prospective study of patients who had not had operation on their moderately large descending thoracic and thoracoabdominal aneurysms. METHODS: Patients were enrolled at the time of their second computed tomographic scans: three-dimensional computer-generated reconstructions allowed determination of several dimensional parameters for each study, including diameters and cross-sectional areas at the site of maximal dilatation in the descending aorta and in the abdomen as well as total thoracoabdominal surface area. Comparisons of serial studies permitted calculation of yearly rates of change in these dimensions. RESULTS: Of 114 patients, 8 died of causes unrelated to the aneurysm, 26 died of rupture, 20 met previously determined criteria for operation, and 60 survived without operation or rupture. Multivariate regression analysis identified maximal diameter in the descending and in the abdominal aorta as independent risk factors for rupture, as well as older age, the presence of even uncharacteristic pain, and a history of chronic obstructive pulmonary disease. A piecewise exponential model enabled construction of an equation allowing calculation of rate of rupture in patients in whom the values of the risk factors are known, and also of the probability of rupture in a given individual over a specified time interval. CONCLUSIONS: Because using this equation--based on easily determined risk factors (age, pain, chronic obstructive pulmonary disease, maximal thoracic and maximal abdominal aortic diameter)--allows the risk of aneurysm rupture within a given interval to be estimated fairly accurately for each individual patient, it is our current practice to recommend operation when the calculated risk of rupture within 1 year exceeds the anticipated mortality of elective operation, rather than relying on general operative guidelines based almost exclusively on aneurysm size.

Prospective evaluation of factors associated with intraaortic balloon rupture.

The authors undertook a prospective analysis of all intraaortic balloon catheter (IAB) insertions at Hahnemann University Hospital during an 18 month period. Attention was directed to balloon rupture and factors associated with this complication. A total of 384 insertions were attempted in 363 patients: 19 patients (5.2%) experienced balloon rupture. The mean time to rupture was 2.1 +/- 3.3 days (range 0-15 days). All ruptured IAB catheters were removed percutaneously without subsequent complications. Ten balloons were subjected to leak testing and scanning electron microscopy. All but one rupture appeared to be the result of balloon abrasion against atherosclerotic plaque. The puncture site occurred at variable distances from the proximal end of the balloon at 9.4 +/- 8.3 cm. Comparison of patients with and without balloon rupture revealed several significant (p < 0.04) differences by univariate analysis (Table 1). No procedure related variables (IAB catheter size 9 versus 11 Fr, sheathless insertion, duration of counterpulsation) were associated with rupture. Stepwise logistic regression analysis revealed body surface area as the only independent predictor of balloon rupture (p = 0.007). Intraaortic balloon rupture with 40 cc balloons, is directly related to the size of the patient. Evaluation of smaller balloons in patients with body surface area < or = 1.8 m2 appears warranted to minimize IAB rupture.

Computer-generated 3D representations of the aorta: a new tool in the management of aortic aneurysm patients.

In order to facilitate care of patients with thoracic aortic aneurysms, we have developed a computer program which allows three dimensional (3D) reconstructions of the aorta from serial sections of CT scans. Each completed study, which can be displayed on a single data sheet, provides a 3D drawing of the aorta, the diameter of each aortic slice, the volume of each aortic segment, the total volume and surface area of the aorta, and a quantity we have called the tortuosity index. The method enables appreciation of transverse as well as longitudinal increases in aneurysm size, and eccentricities in aortic pathology can easily be recognized. The data are stored on floppy discs: this allows a second program to provide comparisons of the important findings from multiple and long-term serial CT studies.

Reduction of unexpected, life-threatening events in postoperative cardiac surgical patients; the role of computerized surveillance.

With increasing use of computerized surveillance (CS) in critical care, a key question is whether it favorably influences clinical outcome. Knowing that two intensive care unit beds would soon have CS capability, we embarked on an uninterrupted prospective study in which the incidence of sudden, unexpected life-threatening events (SULTE) was compared in post-open heart surgery patients whose subsystem performances were evaluated by conventional methods (CM) as opposed to those who would be followed by CS involving automatic acquisition and generation of 30 cardio-respiratory variables. We evaluated 211 patients, 91 with CM and 120 by CS. Since CS availability was limited, sicker patients were given priority for the two CS beds. Despite the obvious bias in favor of CM, there was a statistically significant reduction (P less than 0.001) in the incidence of SULTE in those patients followed by CS (1 of 120 patients: 0.8%; no SULTE-related deaths) in comparison to the CM patients (11 of 91 patients: 12%; two SULTE-related deaths.) The data suggest that computerized surveillance can play a role in reducing morbidity and possibly mortality in postoperative cardiac surgical patients.

Circulatory support with a left-heart assist device after intracardiac operation: design concepts and management techniques.

A simple left-heart assist device was developed to reduce left ventricular preload while simultaneously increasing total systemic blood flow. It consists of special cannulas connected to a simple extracorporeal tubing loop and roller pump, designed to permit bypass of as much as 5 liters of blood per minute from left atrium to ascending aorta. Employed in 15 patients with advanced heart disease who were in low cardiac output following repair, the system was proven effective. An asset of the device is the ability to subsequently separate the patient from the device without need to reenter the thorax or abdomen.