Effects of body size on operative, intermediate, and long-term outcomes after coronary artery bypass operation.

BACKGROUND: To investigate the role of body size, if any, on operative and longer term outcomes following coronary artery surgery. METHODS: A total of 3,560 consecutive patients undergoing coronary artery bypass grafting from 1991 to 1997, including 2,401 (67%) males and a mean +/- SD age of 63 +/- 10 years were ranked based on their body mass index (BMI). The association in these patients of preoperative, long-term, and economic data with variations in BMI were studied using regression analyses. Long-term survival was studied using 5-year Kaplan-Meier survival analysis. RESULTS: Operative mortality, myocardial infarction, cerebrovascular accidents, blood transfusions, and length of hospital stay were all increased in the smallest patients (BMI < or = 24 kg/m2). Obesity did not increase adverse operative outcomes except for a greater rate of sternal wound infections occurring with increasing severity of obesity. Direct variable costs were lowest in patients clustered around normal BMI, with cost increasing similarly at low and high extremes. This effect was correlated with similar BMI effects on ventilatory and intensive care requirements. Excluding operative mortality, 5-year survival trends were similarly worse for the smallest (BMI < or = 24) and most severely obese (BMI > 34) patients. Mild obesity (BMI > or = 30 to BMI < 34) did not affect long-term survival. CONCLUSIONS: Among study patients, immediate operative outcomes were adversely affected by small body size, which reflected older age (66 +/- 10 years) and an exaggerated adverse impact of cardiopulmonary bypass. Younger age and smaller effects of cardiopulmonary bypass lead to better operative outcomes in the obese. Long-term outcomes were, however, suboptimal in severely obese patients although that group was the youngest (60 +/- 10 years). In addition to their large body habitus, other factors, including substantial prevalence of diabetes, insulin dependence and hypertension, probably played a significant role in the poor long-term outcome in the severely obese.

Predictors of gastrointestinal complications in cardiac surgery.

Gastrointestinal problems are infrequent but serious complications of cardiac surgery, with high rates of morbidity and mortality. Predictors of these complications are not well developed, and the role of fundamental variables remains controversial. In a retrospective review of our cardiac surgery experience from July 1991 through December 1997 we found that postoperative gastrointestinal complications were diagnosed in 86 of 4,463 consecutive patients (1.9%). We categorized these 86 patients into 2 groups--Surgical and Medical--according to the method of treatment used for their complications. In the Medical group, 9 of 52 patients (17%) died; in the Surgical group, 17 of 34 (50%) died. By logistic multivariate analysis, we identified 8 parameters that predicted gastrointestinal complications: age greater than 70 years, duration of cardiopulmonary bypass, need for blood transfusions, reoperation, triple-vessel disease, New York Heart Association functional class IV, peripheral vascular disease, and congestive heart failure. Postoperative re-exploration for bleeding was a predictor specific to the Surgical group. Use of an intraaortic balloon pump was markedly higher in the Gastrointestinal group than in the Control group (30% vs 10%, respectively), as was the use of inotropic support in the immediate postoperative period (27% vs 5.6%). Our results suggest that intra-abdominal ischemic injury is a likely contributing factor in most gastrointestinal complications. In turn, the ischemia is probably caused by hypoperfusion due to low cardiac output, hypotension due to blood loss, and intra-abdominal atheroemboli. The derived models are useful for identifying patients whose risk of gastrointestinal complications after cardiac surgery may be reduced by clinical measures designed to counter these mechanisms.

Resource utilization in coronary artery bypass operation: does surgical risk predict cost?

BACKGROUND: Current healthcare trends may render financial risk of cardiac operation a key component of clinical decision making. It has been suggested, based on large cohorts of patients stratified by clinical risk, that the cost of operation can be predicted from models of clinical risk since length of stay (LOS) is highly correlated to clinical risk, and LOS is correlated to hospital costs and charges. Direct correlation of actual surgical costs with surgical risk are lacking. METHODS: Variable direct costs, LOS, and The Society of Thoracic Surgeons predicted mortality risk [STS risk (%)] were collected and analyzed in 628 consecutive patients undergoing coronary artery bypass grafting (CABG) at our institution in 1997. RESULTS: Cost of CABG had a near-normal distribution, and cost in 21 outlier patients (cost > two standard deviations above the mean) was an average 5.3 times normal (median cost). For individual patients, cost was well correlated to LOS (R2 = 0.48) but not with STS risk (R2 = 0.12). LOS was also poorly predicted by STS risk (R2 = 0.09). However, despite its poor prediction of cost, STS risk was an unbiased estimator over the entire population. A result manifested, when patients were grouped into similar risk (<1%, 1-2%, 2+ -3%, 3+ -5%, 5+ -10%, and >10%) cohorts, by high correlation between cost and STS risk (R2 = 0.99), cost and LOS risk (R2 = 0.99), and LOS and STS risk (R2 = 0.97). CONCLUSIONS: Our data demonstrated that, in large CABG cohorts, surgical risk models can accurately predict cost of CABG. However, despite a trend for increasing cost with increasing STS risk, surgical risk models based on preoperative data are poor predictors of cost in individual patients. Use of these models should be limited to analysis of cost trends in cardiac operation, but not for predicting financial risk in individual patients during clinical decision making.

Theoretical optimization of pulmonary-to-systemic flow ratio after a bidirectional cavopulmonary anastomosis.

A univentricle with parallel pulmonary and systemic circulations is inherently inefficient because mixing of pulmonary and systemic venous return occurs. Thus a cavopulmonary anastomosis is used as a staged palliative procedure to reduce volume overload in patients with cyanotic congenital heart disease. On the basis of oxygen uptake and consumption, an equation was derived that related cardiac output, pulmonary venous oxygen saturation, upper body oxygen consumption, and superior-to-inferior vena caval blood flow ratio (QSVC/QIVC) to oxygen delivery. The primary findings were as follows. 1) As QSVC/QIVC increases, total body oxygen delivery and arterial and superior vena caval oxygen saturations increase. 2) As QSVC/QIVC increases, lower body oxygen delivery and inferior vena caval oxygen saturation initially increase, then peak, and then decrease. 3) As the percentage of lower body oxygen consumption increases, oxygen delivery and saturation decrease. 4) A cavopulmonary anastomosis decreases the required cardiac output for a given oxygen delivery. Thus we concluded that a high systemic arterial oxygen saturation after cavopulmonary anastomosis requires a high percentage of upper body oxygen consumption and a high QSVC/QIVC and that the cavopulmonary anastomosis reduces the volume load on the single ventricle.

Monitoring systemic venous oxygen saturations in the hypoplastic left heart syndrome.

Although progress has been made in treating hypoplastic left heart syndrome, improvements in perioperative care may further decrease mortality. We present a case in which continuous monitoring of systemic venous oxygen saturation allowed stabilization and successful management of a critically ill infant. Systemic venous oxygen saturation may provide a more accurate representation of a child's clinical status, allowing more rapid intervention and better outcomes.

Animal model of the univentricular heart and single ventricular physiology.

The univentricular heart complexes are a fairly common and potentially lethal set of congenital cardiac anomalies. Progress in developing new therapeutics has been hampered by a lack of suitable animal models. The authors developed a stable, closed heart preparation to systematically examine potential interventions. Using neonatal piglets (3.5-6.0 kg), a 6-mm PTFE graft was anastomosed end to end to the innominate artery and end to side to the pulmonary artery. An atrial septostomy was made, using a Rashkind septostomy catheter passed transvenously. With the same catheter, the tricuspid valve was rendered incompetent. Occlusion of the right ventricular outflow tract completed a univentricular circuit. All cardiac output exited from the left ventricle, and pulmonary blood flow was maintained via the innominate artery-to-pulmonary artery shunt. Pressure transducers measured central venous (mid inferior vena cava), aortic, and pulmonary arterial pressures. Oximetric probes recorded systemic venous and arterial oxygen saturations. Transit-time flow probes measured total cardiac output and pulmonary flows. Systemic flow was calculated by subtracting pulmonary flow from total cardiac output. This model has been completed in 30 animals. Minimal pressure drops have been recorded across the innominate-to-pulmonary artery graft. Pulmonary flows up to 700 +/- 52 mL/min were seen. Total cardiac outputs are as high as 1370 +/- 88 mL/min. Mean ratios of pulmonary to systemic flow (Qp/Qs ratio) range from 1.29 +/- 0.08 to 0.41 +/- 0.09. The model allows for full continuous monitoring of systemic and pulmonary pressures and flows and for accurate characterization of the physiological effects of respiratory and pharmacological interventions. In addition, mechanical constriction of the graft may allow direct alteration of the Qp/Qs ratio, with determination of an optimum value for this ratio.

Effects of oxygen, positive end-expiratory pressure, and carbon dioxide on oxygen delivery in an animal model of the univentricular heart.

OBJECTIVE: Respiratory manipulations are a mainstay of therapy for infants with a univentricular heart, but until recently little experimental information has been available to guide their use. We used an animal model of a univentricular heart to characterize the physiologic effects of a number of commonly used ventilatory treatments, including altering inspired oxygen tension, adding positive end-expiratory pressure, and adding supplemental carbon dioxide to the ventilator circuit. RESULTS: Lowering inspired oxygen tension decreased the ratio of pulmonary to systemic flow. This ratio was 1.29 +/- 0.08 at an inspired oxygen tension of 100%, 0.61 +/- 0.09 at an inspired oxygen tension of 21%, and 0.42 +/- 0.09 at an inspired oxygen tension of 15% (p < 0.05 compared with an inspired oxygen tension of 100% and a positive end-expiratory pressure of 0 cm H2O). High-concentration supplemental carbon dioxide (carbon dioxide tension of 80 to 90 mm Hg) added to the ventilator circuit decreased inspired oxygen tension from 1.29 +/- 0.11 to 0.42 +/- 0.12 (p < 0.05 compared with baseline). A mixture of 95% oxygen and 5% carbon dioxide (carbon dioxide tension of 50 to 60 mm Hg) did not decrease the pulmonary/systemic flow ratio significantly. All three types of interventions influenced systemic oxygen delivery, which was a function of the pulmonary/systemic flow ratio. As the pulmonary/systemic flow ratio decreased from initially high levels (greater than 1), oxygen delivery first increased and reached an optimum at a flow ratio slightly less than 1. As the pulmonary/systemic flow ratio decreased further, below 0.7, oxygen delivery decreased. The ability of systemic arterial and venous oxygen saturations to predict the pulmonary/systemic flow ratio was examined. Venous oxygen saturation correlated well with both pulmonary/systemic flow ratio and systemic oxygen delivery, whereas arterial oxygen saturation did not accurately predict either pulmonary/systemic flow ratio or oxygen delivery. CONCLUSION: This model demonstrated the value of estimating the pulmonary/systemic flow ratio before initiating therapy. When the initial ratio was greater than about 0.7, interventions that decreased the ratio increased oxygen delivery and were beneficial. When the initial pulmonary/systemic flow ratio was below 0.7, interventions that decreased the ratio decreased oxygen delivery and were detrimental. We conclude by presenting a framework to guide therapy based on the combination of arterial and venous oxygen saturations and the estimate of the pulmonary/systemic flow ratio that they provide.

Inotropes in the hypoplastic left heart syndrome: effects in an animal model.

BACKGROUND: Despite substantial changes in the surgical treatment of children born with the hypoplastic left heart syndrome, overall mortality remains high. Although further improvements in outcomes appear to depend on more effective perioperative care, few experimental data exist to guide appropriate pharmacologic therapy in these infants. Because different inotropic agents may have different effects on the ratio of pulmonary to systemic flow (Qp/Qs), we hypothesize that they may not be equally effective at increasing oxygen delivery. METHODS: In neonatal piglets (n = 6; 3.5 to 6.5 kg), we placed an innominate artery-to-pulmonary artery shunt, created an atrial septal defect, and then occluded right ventricular outflow. We examined the effects of a number of commonly used inotropic agents, administering high and low concentrations of dopamine (5 and 15 micrograms.kg-1 .min-1), dobutamine (5 and 15 micrograms.kg-1.min-1), and epinephrine (0.05 and 0.1 microgram /min). RESULTS: Dobutamine at 15 micrograms.kg-1.min-1 increased the Qp/Qs ratio from 1.03 +/- 0.6 at baseline to 2.52 +/- 0.55 (p < 0.05) and decreased oxygen delivery from 50 +/- 4.3 to 36 +/- 1.7 mL/min (p < 0.1). The arterial-venous oxygen difference increased as oxygen delivery went down, going from 44% +/- 1% to 48% +/- 2% (p < 0.1). Epinephrine at 0.1 microgram.kg-1.min-1 decreased the Qp/Qs ratio from 1.23 +/- 0.21 to 0.82 +/- 0.08 (p < 0.05) and increased oxygen delivery from 40 +/- 9.7 to 56 +/- 1.7 mL/min (p < 0.05). Systemic venous oxygen saturation increased from 36% +/- 4.8% to 50% +/- 8.6% (p < 0.05). Although dopamine decreased the Qp/Qs ratio and increased oxygen delivery, these changes were not statistically significant. CONCLUSIONS: Dopamine, dobutamine, and epinephrine all increased cardiac output but had substantially different effects on the Qp/Qs ratio and on oxygen delivery, possibly due to differential effects on systemic and pulmonary vascular resistances. This suggests that inotropic agents may not be equally beneficial in the clinical setting. Systemic venous oxygen saturation and the arteriovenous oxygen difference may help determine if a given inotrope improves oxygen delivery.

Evaluation of the long-term effectiveness of extraluminal and intraluminal vasodilators in an in vitro porcine model of arterial graft spasm.

OBJECTIVE: Postoperative graft spasm is a concern when arterial conduits are used because there may be insufficient arterial graft flow. Intraoperatively, vasodilators are used to increase flow and prevent spasm, but little is known about their duration of effectiveness. METHODS: To examine this we attached porcine gastroepiploic and internal thoracic arteries (GEA, n = 48; ITA, n = 24, 10-12 cm long) to a computer-controlled perfusion system (constant inflow pressure 80 mm Hg) with a fixed outflow resistance. Norepinephrine (10(-9)-10(-5) M) was incrementally added to the perfusate at baseline (B), then immediately (h+0) and 2 h (h+2) after the vessels were treated with 30 min of extraluminal or intraluminal nitroglycerin, nitroprusside, verapamil or papaverine. RESULTS: At (B), norepinephrine caused a dose-dependent decrease in flow in both the ITAs and GEAs. In the ITAs, at (h+0), both extraluminal and intraluminal papaverine and, to a lesser extent nitroprusside, increased initial flow and decreased graft sensitivity to norepinephrine. At (h+2), only extraluminal papaverine sustained this maximal effect (ED50 for extraluminal papaverine at (B) 2.6 E(-7) vs. (h+2) 1.3 E(-6), P = 0.01). For the GEAs, at (h+0), both extraluminal and intraluminal verapamil, papaverine, nitroprusside and nitroglycerin attenuated flow reduction due to norepinephrine. At (h+2), only extraluminal papaverine, extraluminal verapamil and intraluminal verapamil were effective in preventing norepinephrine-induced spasm (ED50 for extraluminal papaverine at (B) 1.0 E(-7) vs. (h+2) 6.4 E(-6) (P = 0.004); extraluminal verapamil at (B) 1.2 E(-7) vs. (h+2) 4.0 E(-6); intraluminal verapamil at (B) 5.8 E(-7) vs. (h+2) 5.7 E(-6), P = 0.005). CONCLUSION: Verapamil-and papaverine-treated arteries have a greater duration of efficacy in resisting spasm than arteries treated with nitroglycerin and nitroprusside. In the ITA, extraluminal administration of papaverine is most efficacious, possibly due to the prolonged exposure afforded by this route of administration. The effects of verapamil and papaverine are more prolonged in the GEA when administered extraluminally, potentially due to absorption in the perivascular fat-pad and subsequent slow release. The results of this study suggest that extraluminally administered verapamil and papaverine appear to be the preferred vasodilators for preventing arterial graft spasm in the postoperative period. This may be especially important when multiple arterial grafts are used.

Control of vocal-tract length in speech.

Essential for the correct production of vowels is the accurate control of vocal-tract length. Perkell [Psychology of Speech Production (MIT, Cambridge, MA, 1969)] has suggested that two important determinants of vocal-tract length are vertical larynx position and lip spreading/protrusion, often acting together. The present study was designed to determine whether constraining lip spreading/protrusion induces compensatory vertical larynx displacements, particularly on rounded vowels. Upper lip and larynx movement were monitored photoelectrically while French and Mandarin native speakers produced the vowels /i,y,u/ first under normal-speech conditions and then with lip activity constrained. Significant differences were found in upper-lip protrusion and larynx position depending on the vowel uttered. Moreover, the generally low-larynx position of rounded vowels became even lower when lip protrusion was constrained. These results imply that compensatory articulations contribute to a contrast-preserving strategy in speech production.