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Ross M Ungerleider

Publications and source records attributed to Ross M Ungerleider.

At least 19 recordsLinked to original sources
PubMed2006

Hypothermic low-flow cardiopulmonary bypass impairs pulmonary and right ventricular function more than circulatory arrest.

BACKGROUND: Hypothermic circulatory arrest (HCA) is used during surgical treatment of certain congenital heart defects. The possibility of ischemic neurologic injury associated with HCA has led some surgeons to use low-flow cardiopulmonary bypass (CPB) during the hypothermic interval (hypothermic low flow [HLF]). This study investigates the inflammatory response to HCA and HLF, and reports the consequences of this response on pulmonary and right ventricular function. METHODS: Piglets (3.1 to 6.6 kg) were cooled to 16 degrees to 18 degrees C using CPB, and randomized: HCA for 60 minutes (n = 7), or HLF (50 cc.kg(-1).min(-1)) for 60 minutes (n = 6). The piglets were rewarmed to 36 degrees C and weaned from CPB. Serum tumor necrosis factor-alpha (TNF-alpha) concentration, percent lung water, and pulmonary and cardiac function were measured before and after CPB. RESULTS: Tumor necrosis factor-alpha was higher after HLF (2,990.5 +/- 884.5 pg/mL), compared with HCA (347.6 +/- 89.2 pg/mL; p = 0.03). The percent lung water was higher after HLF (84.8% +/- 0.3%) than HCA (82.0% +/- 0.4%; p < 0.001). The alveolar to arterial oxygen gradient was worse after HLF (457 +/- 42 mm Hg) than HCA (285.8 +/- 45 mm Hg; p = 0.02). Pulmonary vascular resistance was greater after HLF (36.08 +/- 8.28 mm Hg.mL(-1).m(-2).min(-1)) than HCA (14.55 +/- 3.46 mm Hg. mL(-1).m(-2).min(-1); p = 0.049). The right ventricular pressure waveform peak derivative, corrected for systolic pulmonary artery pressure, was lower after HLF (14.1 +/- 1.4 sec(-1)), than HCA (23.8 +/- 2.7 sec(-1); p = 0.01). CONCLUSIONS: Hypothermic low flow extends exposure to CPB, and is associated with an increased inflammatory response compared with HCA. The greater inflammatory response after HLF may result in substantial nonneurologic morbidity in the postoperative period, demonstrated by pulmonary and right ventricular dysfunction. Interventions that attenuate the inflammatory response to CPB may prevent pulmonary and right ventricular dysfunction after HLF.

Animals↗
PubMed2006

Cardiac output augmentation during hypoxemia improves cerebral metabolism after hypothermic cardiopulmonary bypass.

BACKGROUND: Hypothermic circulatory arrest (HCA) impairs cerebral oxygen delivery (CDO2) and cerebral oxygen consumption (CMRO2), which are further reduced by perioperative hypoxemia. This study investigates if continuous hypothermic low-flow cardiopulmonary bypass (HLF) or intermittent hypothermic low-flow cardiopulmonary bypass (IHLF) can prevent reductions in CDO2 and CMRO2 during hypoxemia. METHODS: Eighteen neonatal piglets, cooled to 16 degrees to 18 degrees C with cardiopulmonary bypass (CPB), were randomly assigned into three groups: HCA, HLF (50 cc.kg(-1).min(-1)), or IHLF (1 minute of HLF for every 15 minutes of HCA). After 60 minutes of hypothermia, normothermic CPB (100 cc.kg(-1).min(-1)) was established and cerebral perfusion data measured at hyperoxemia (PaO2 150 to 250 mm Hg), hypoxemia (PaO2 50 to 60 mm Hg), and severe hypoxemia (PaO2 30 to 40 mm Hg), and with increased CPB flow (200 cc.kg(-1).min(-1)) during severe hypoxemia. RESULTS: The CMRO2 (in mL O2.100 g(-1).min(-1)) was lower after HCA (2.5 +/- 0.3), compared with HLF (4.1 +/- 0.5, p = 0.02) and IHLF (6.2 +/- 0.8, p = 0.002). Within groups, the change from hyperoxemia to severe hypoxemia resulted in decreased CMRO2: HCA (1.3 +/- 0.2, p = 0.004), HLF (3.0 +/- 0.5, p = 0.01), and IHLF (2.9 +/- 0.5, p = 0.01). During severe hypoxemia, increasing CPB flow (from 100 cc.kg(-1).min(-1) to 200 cc.kg(-1).min(-1)) improved CMRO2: HCA (1.9 +/- 0.5, p = 0.05), HLF (4.2 +/- 0.5, p = 0.05), and IHLF (7.4 +/- 0.5, p = 0.04). CONCLUSIONS: Hypoxemia reduces CDO2 and CMRO2 despite the method of hypothermic CPB. Increased CPB flow during hypoxemia can restore both CDO2 and CMRO2 to values found with hyperoxemia and slower CPB flows. Augmenting cardiac output during periods of perioperative hypoxemia may prevent cerebral injury after exposure to hypothermic cardiopulmonary bypass.

Animals↗
PubMed2006

Effects of circuit miniaturization in reducing inflammatory response to infant cardiopulmonary bypass by elimination of allogeneic blood products.

Conventional neonatal cardiopulmonary bypass requires the use of large volumes of allogeneic blood to prevent unacceptable hemodilution. Evidence is accumulating to suggest that the use of blood products during cardiopulmonary bypass has a negative effect on clinical recovery through inflammatory side effects. This would suggest an advantage for eliminating blood use in infant cardiopulmonary bypass through circuit miniaturization. In this article, we review the data supporting this rationale and provide the results from studies in our laboratory that emphasize the benefits of circuit miniaturization.

Age Factors↗
PubMed2006

Recognition and management of heparin-induced thrombocytopenia in pediatric cardiopulmonary bypass patients.

Repeated exposure to unfractionated heparin is the rule in many congenital heart disease patients. Heparin-induced thrombocytopenia occurs in 1% to 3% of adult cardiac surgeries, and carries high thrombotic morbidity (38% to 81%) and mortality (approximately 28%). Although heparin-induced thrombocytopenia appears to be infrequent in pediatric patients, particularly neonates, our evolving experience suggests postcardiopulmonary bypass congenital heart disease patients may be at increased risk. Diagnostic and therapeutic challenges include frequency of thrombocytopenia after cardiopulmonary bypass, imperfect laboratory testing, lack of established dosing of alternative anticoagulants (such as argatroban and lepirudin), and increased anticoagulant-related bleeding in young children.

Adolescent↗
PubMed2006

Current assessment of mortality rates in congenital cardiac surgery.

BACKGROUND: The purpose of this study is to evaluate whether published and widely quoted mortality rates for pediatric cardiac surgery accurately reflect current expectations. Our hypotheses are that (1) mortality rates at high-quality pediatric cardiac programs are lower than published national results despite (2) a change in case mix with a shift away from low complexity operations. METHODS: We requested data for all pediatric cardiac surgical procedures performed between 2001 and 2004 at 29 Congenital Heart Surgeon's Society (CHSS) member institutions (using CHSS as a surrogate for recognized high quality). Procedures were categorized by Risk Adjustment for Congenital Heart Surgery, version 1 (RACHS-1) category. In-hospital mortality rates for each category were calculated and compared with those in the 2002 manuscript of Jenkins and colleagues. RESULTS: We received data for 16,805 procedures from 11 institutions. In all, 12,672 operations (76%) could be placed into RACHS-1 categories. Overall in-hospital mortality for categorized operations was 2.9% and was most related to case mix. There was a significant decrease in the percentage of category 1 operations, and there were significant increases in category 2, 4, and 6 operations. There were significant decreases in category 2, 3, 4, and 6 mortality rates (Jenkins 2002 [CHSS]): (1) 0.4% [0.7%], (2) 3.8% [0.9%], (3) 8.5% [2.7%], (4) 19.4% [7.7%], (5) not applicable, and (6) 47.7% [17.2%]. There was no significant association between hospital surgical volume and mortality. CONCLUSIONS: This outcomes "footprint" suggests that we could hold ourselves accountable to higher benchmarks than those reflected by some published standards. Mortality rates declined, despite an increase in case mix complexity. The lack of association between hospital surgical volume and mortality suggests that other factors determine outcomes at high-quality institutions. In addition to continually validating our expectations for treatment, future research needs to identify these factors by understanding the system of care and identifying process measures that influence outcomes.

Cardiac Surgical Procedures↗
PubMed2005

Matching procedure to morphology improves outcomes in neonates with tricuspid atresia.

OBJECTIVE: This study was undertaken to characterize morphologic substrate of tricuspid atresia with ventriculoarterial concordance and discriminate management strategies that lead to successful definitive repair. METHODS: From 1999 to 2004, a total of 150 babies with type I tricuspid atresia were enrolled from first diagnosis at 26 institutions. Antegrade pulmonary blood flow was absent in 19%, restricted in 54%, and unrestricted in 28%. Competing-risk methodology determined the time-related prevalence and risk factors for death versus cavopulmonary anastomosis and subsequent death versus Fontan completion. RESULTS: Overall 5-year survival was 86%. Initial palliation included systemic-pulmonary arterial shunt in 64%, pulmonary artery banding in 11%, and cavopulmonary anastomosis in 24%. Median age at cavopulmonary anastomosis was 6 months, with 83% undergoing bidirectional Glenn shunt and 17% undergoing hemi-Fontan procedure. By the age of 2 years, 89% had cavopulmonary anastomosis, 6% were dead, and 4% remained alive without cavopulmonary anastomosis. Risk factors for death without cavopulmonary anastomosis included presence of mitral regurgitation (P = .03) and palliation with systemic-pulmonary arterial shunts not originating from the innominate artery (P = .04). Factors associated with decreased transition rate to cavopulmonary connection included patient variables (younger admission age to a participating institution, noncardiac anomalies) and procedural variables (larger systemic-pulmonary arterial shunt diameter, previous palliation). Of patients undergoing cavopulmonary anastomosis, 75% had undergone a Fontan operation within 3 years. CONCLUSION: Smaller shunt size and decreased pulmonary blood flow decrease mortality after initial palliation and increase the rate of successful transition to cavopulmonary anastomosis. Outcomes can be improved by placing smaller shunts from the innominate artery, especially in patients with any mitral regurgitation.

Cardiac Surgical Procedures↗
PubMed2005

Acute hemodynamic effects of pacing in patients with Fontan physiology: a prospective study.

OBJECTIVES: The purpose of this research was to assess the hemodynamic response to atrial, ventricular, and dual-chamber pacing in patients with Fontan physiology. BACKGROUND: Bradycardia, due to sinus node dysfunction or atrioventricular (AV) block, with need for pacing, is common after the Fontan operation. The optimal pacing mode for Fontan patients is unknown, but is critical, as hemodynamic aberrancies may cause severe clinical deterioration. We hypothesized that AV synchrony is vital for maximizing Fontan hemodynamics. METHODS: A cross-over trial was conducted with 21 patients (age 2 to 18 years, median 4 years; male patients = 13) in the intensive care unit after a Fontan operation. Hemodynamic parameters, including mean left atrial pressure (LAP, in mm Hg), mean pulmonary artery pressure (PAP, in mm Hg), mean arterial blood pressure (MAP, in mm Hg), and indexed cardiac output via Fick (Qs, in l/min/m2) were measured with atrial, ventricular, and dual-chamber pacing. Measurements were made after pacing for 10 min in each mode, and a 10-min rest was given between each pacing maneuver. RESULTS: Asynchronous ventricular (VOO) pacing resulted in significantly worse hemodynamics when compared to dual-chamber (DOO) and atrial (AOO) pacing with a higher LAP (9.4 VOO; 6.8 DOO; 5.4 AOO) and PAP (15.2 VOO; 13.5 DOO; 12.7 AOO) and lower Qs (3.0 VOO; 3.5 DOO; 3.9 AOO) and MAP (60.1 VOO; 66.5 DOO; 67.2 AOO). CONCLUSIONS: Asynchronous ventricular pacing, after the Fontan procedure, has acute, adverse hemodynamic consequences (elevated LAP and PAP and decreased Qs and MAP).

Adolescent↗
PubMed2005

The use of live three-dimensional Doppler echocardiography in the measurement of cardiac output: an in vivo animal study.

OBJECTIVES: The purpose of this study was to investigate whether cardiac output (CO) could be accurately computed from live three-dimensional (3-D) Doppler echocardiographic data in an acute open-chested animal preparation. BACKGROUND: The accurate measurement of CO is important in both patient management and research. Current methods use invasive pulmonary artery catheters or two-dimensional (2-D) echocardiography or esophageal aortic Doppler measures, with the inherent risks and inaccuracies of these techniques. METHODS: Seventeen juvenile, open-chested pigs were studied before undergoing a separate cardiopulmonary bypass procedure. Live 3-D Doppler echocardiography images of the left ventricular outflow tract and aortic valve were obtained by epicardial scanning, using a Philips Medical Systems (Andover, Massachusetts) Sonos 7500 Live 3-D Echo system with a 2.5-MHz probe. Simultaneous CO measurements were obtained from an ultrasonic flow probe placed around the aortic root. Subsequent offline processing using custom software computed the CO from the digital 3-D Doppler DICOM data, and this was compared to the gold standard of the aortic flow probe measurements. RESULTS: One hundred forty-three individual CO measurements were taken from 16 pigs, one being excluded because of severe aortic regurgitation. There was good correlation between the 3-D Doppler and flow probe methods of CO measurement (y = 1.1x - 9.82, R(2) = 0.93). CONCLUSIONS: In this acute animal preparation, live 3-D Doppler echocardiographic data allowed for accurate assessment of CO as compared to the ultrasonic flow probe measurement.

Animals↗
PubMed2005

Using a miniaturized circuit and an asanguineous prime to reduce neutrophil-mediated organ dysfunction following infant cardiopulmonary bypass.

BACKGROUND: Contemporary infant cardiopulmonary bypass circuits require a blood prime. Blood, especially when stored, generates an inflammatory response, and may contribute to organ dysfunction following cardiopulmonary bypass. We determined whether using a miniaturized circuit and an asanguineous prime attenuated the post-bypass inflammatory response, and improved right ventricular and pulmonary function. METHODS: Sixteen infant piglets were placed into 3 groups based on prime components: group I (fresh blood), group II (stored blood), and group III (miniaturized circuit and asanguineous prime). Piglets were placed on cardiopulmonary bypass (100 mL.kg(-1).min(-1)), cooled to 18 degrees C, and underwent continuous perfusion (50 mL.kg(-1).min(-1)) for 30 minutes. They were rewarmed and separated from bypass. Serum tumor necrosis factor-alpha, right ventricular function, and pulmonary function were measured before and 30 minutes after bypass. Neutrophil priming activity in fresh and stored donor blood was also assessed. RESULTS: Animals in group III had significantly improved cardiopulmonary function than the groups receiving blood (right ventricular cardiac index [mL.kg(-1).min(-1)]: group I [18.8 +/- 4.8], group II [21.5 +/- 6.2], and group III [81.2 +/- 11.4], p < 0.001; and pulmonary vascular resistance index [dynes.mL(-1).kg(-1)]: group I [1169 +/- 409], group II [1610 +/- 486], and group III [214 +/- 63], p = 0.03). Tumor necrosis factor-alpha (pg.mL(-1)) was lower in group III (1465 +/- 39) than in the groups receiving blood (3940 +/- 777), p = 0.002. Neutrophil priming activity (nmol.min(-1)) was also higher in stored blood (3.7 +/- 6) than in fresh blood (1.9 +/- 0.2), p = 0.02. CONCLUSIONS: We have devised a unique miniaturized circuit that allows an asanguineous prime without hemodilution in an infant swine model. The employment of this circuit attenuates the post-bypass inflammatory response and has salutary effects on cardiopulmonary function.

Animals↗
PubMed2005

The influence of valve physiology on outcome following aortic valvotomy for congenital bicuspid valve in children: 30-year results from a single institution.

OBJECTIVE: Aortic valvotomy is widely used for the treatment of congenital aortic stenosis in children. We sought to evaluate whether the predominant post-valvotomy physiology, aortic insufficiency (AI) or aortic stenosis (AS) independently affected patient outcome. METHODS: From 1972-2002, 57 children with congenital aortic stenosis underwent valvotomy. We divided age-matched patients with residual lesions based on their predominant pathology into three groups: Group I (n=14), patients with moderate AI; Group II (n=14), patients with moderate AS, and Group III (n=14), patients with combined AI and AS. Fifteen patients with severe AI or mild residual lesions following valvotomy were excluded from analysis. RESULTS: mean freedom from aortic valve replacement (AVR) was 11.2+/-1.7 years in Group I and 21.5+/-3.9 years in Group II, P=0.05. AVR was required in 11 patients (79%) in Group I vs. only 5 (36%) in Group II, P=0.05. Group III was intermediate, with 9 (64%) requiring AVR. At the time of AVR, patients with aortic stenosis had significantly higher fractional shortening % than those with insufficiency or combined lesions, (Group 1: 38.2+/-7.9 vs. Group II: 46.3+/-5.5 vs. Group III: 39.2+/-3.7, P=0.007). Patients in Group II also had less severely dilated ventricles (mm) than those in the other groups, (Group 1: 50.2+/-12.5 vs. Group II: 39.5+/-8.3 vs. Group III: 49.0+/-8.1, P=0.030). CONCLUSIONS: patients with predominant AI following valvotomy are more likely to need AVR sooner than those with residual stenosis without AI. Therefore, cautious use of repeat valvotomy using maneuvers to avoid AI (small balloons), may prolong freedom from aortic valve replacement in those patients with significant residual AS.

Aortic Valve↗
PubMed2005

Oversizing pulmonary homograft conduits does not significantly decrease allograft failure in children.

OBJECTIVE: Placement of oversized pulmonary ventricle-pulmonary artery conduits is routinely performed to decrease conduit failure in children. However, this practice has recently been challenged as somatic outgrowth may not be the main determinant of allograft failure in children. Our objective was to determine whether placement of oversized homografts for extracardiac pulmonary ventricle (PV) outflow tract reconstruction improves longevity in young children. METHODS: We reviewed 102 consecutive PV-PA conduits inserted in 70 patients less than 18 years between 1984 and 2003. Conduits placed in an anatomic position (n=23) as part of a Ross operation, were excluded. Conduits were initially stratified into two age groups: Group 1, those placed in patients 10 years. Normalization of conduit size to patient's body surface area at the time of insertion (z-value) was then performed to divide the conduits into oversized (O/S) and non-oversized (NO/S) groups. Determinants of conduit failure and allograft longevity were then compared between groups. RESULTS: Seventy-nine extracardiac conduits were placed, and 57 of these were in patients under 10 years of age. The majority had a diagnosis of tetralogy of Fallot (n=38), truncus arteriosus (n=19), pulmonary atresia with ventricular septal defect (n=12), or D-TGA with pulmonary stenosis and ventricular septal defect (n=7). Thirty-seven conduits were oversized (O/S) based on z-value, and 42 were non-oversized (NO/S), and the mean age at initial homograft placement was 7.0+/-7.5 years. Overall, oversizing conferred no significant advantage with respect to actuarial freedom from homograft replacement at 1, 5, or 10 years (96, 79, and 21%, O/S vs 93, 60, and 24%, NO/S), P=0.44. Oversizing was more frequent in Group 1 than Group 2 (53 vs 32%), and conduit failure was also more frequent with 49% requiring reoperation during the study period vs 38% in Group 2. In the subset of patients <or=10 years, both homograft explantation rate (50% O/S vs 48% NO/S) and median interval to conduit failure were similar between the O/S and NO/S patients (7.1 vs 4.8 years), P=0.340. Risk factors for conduit failure identified in multivariable regression analysis included the presence of pulmonary artery branch stenosis, lack of previous definitive repair, a diagnosis of pulmonary atresia, the need for percutaneous intervention. CONCLUSIONS: There is no significant benefit to placement of an oversized PV-PA homograft in this series of patients from a single institution. Even in young patients with rapid somatic growth, normalizing extracardiac allografts to BSA provides excellent conduit longevity and outcomes.

Adolescent↗
PubMed2005

Reducing risk in infant cardiopulmonary bypass: the use of a miniaturized circuit and a crystalloid prime improves cardiopulmonary function and increases cerebral blood flow.

Advances in perfusion strategies have played an important role in improving outcomes following repair of complex congenital heart defects. The influence of cooling strategy, temperature, duration of circulatory arrest, and specific method of cerebral perfusion on neurologic morbidity have been extensively characterized. Similarly, the ability of pharmacologic agents to modulate the post-cardiopulmonary bypass (CPB) inflammatory response has been previously elucidated in both the laboratory and clinical arena. However, modification of the circuit and priming components have received comparably less attention. We recently showed that employment of a miniaturized circuit and a bloodless prime reduce inflammation and have salutary effects on cardiopulmonary function following hypothermic low-flow perfusion (HLF), and that this circuit may also improve cerebral protection following both deep hypothermic circulatory arrest and HLF. The current report, therefore, reviews current strategies utilized to minimize post-CPB inflammation and highlights the empirical evidence from our laboratory demonstrating the beneficial role of a miniaturized extracorporeal circuit in this context.

Animals↗
PubMed2005

Interrupted aortic arch: surgical decision making.

Interrupted aortic arch (IAA) is defined as the loss of luminal continuity between the ascending and descending aorta. It is associated with a multitude of lesions ranging from isolated ventricular septal defects to complex ones. Although results have improved in the modern era, repair of IAA is associated with a significant mortality and morbidity. In recent years, the move to a one-stage repair has become well established, and the optimal technique for aortic repair seems to be partial direct anastomosis with patch augmentation. Left ventricular outflow tract obstruction (LVOTO) continues to be an important factor affecting survival and re-intervention rates after IAA repair. Great variability exists with regard to definition and diagnosis of LVOTO. To guide the decision for left ventricular outflow tract (LVOT) intervention and which type to use, we propose a simple formula based on the baby's weight. We advocate a conservative approach when the LVOT diameter is greater than the baby's weight + 2 mm and a LVOT bypass procedure (Yasui or Norwood) if the LVOT diameter is less than the baby's weight in millimeters. If the LVOT diameter falls in between, no definitive recommendation can be made, and the surgical approach is based on the surgeon's experience and overall philosophy.

Aorta, Thoracic↗
PubMed2005

Advances in congenital heart surgery.

PURPOSE OF REVIEW: We provide an overview of the past year's literature on congenital heart surgery. RECENT FINDINGS: This review focuses on selected disease entities, operative techniques, perioperative management strategies, and quality of care. SUMMARY: Congenital heart surgery is an evolving field.

Cardiac Catheterization↗
PubMed2005

Impact of a transfer center on interhospital referrals and transfers to a tertiary care center.

BACKGROUND: The partnership of faculty physicians and senior clinical hospital administrators in the decision to accept interhospital transfers has not been fully studied. Transfers to academic medical centers on the basis of economics have been of particular concern. OBJECTIVES: To evaluate the impact of joint decision making on transfer acceptance, and to evaluate the basis for decisions to transfer patients to an academic medical center. METHODS: This was a database study of requested adult interhospital transfers, excluding psychiatric transfers, occurring between January 1, 2003, and December 31, 2003, by using data from a computerized patient-tracking system. Where possible, comparisons with the prior calendar year (i.e., prior to implementation of the administrative review process) were made. Incidence of refusal to accept requested transfers and payer mix of transfer patients were the main outcomes of interest. RESULTS: More than 90% of the adult patients were transferred for conditions that required tertiary care or met Emergency Medical Treatment and Labor Act (EMTALA) requirements. The patient conditions that did not meet tertiary care needs included obstetric patients who did not have prenatal care, patients who had hand and facial trauma, and patients who weighed more than 300 pounds. The payer mix of transfer patients remained stable when using the administrator and physician team to determine acceptance of transfers. During the evaluation period, approximately 91,500 patients statewide lost some level of Medicaid coverage. CONCLUSIONS: The value of an administrator and physician team as partners in the interhospital transfer process was demonstrated. Active management of interhospital transfers supports transfer of patients who require tertiary care or who meet EMTALA criteria, thus conserving limited bed capacity and ensuring financial equity, while caring for the uninsured and underinsured patients throughout the state.

Adult↗
PubMed2004

Postoperative hypoxemia exacerbates potential brain injury after deep hypothermic circulatory arrest.

BACKGROUND: Deep hypothermic circulatory arrest (DHCA) is often used in infants undergoing the Norwood procedure. These infants are hypoxic after surgery. Previous investigations into the cerebral metabolic response and oxygen utilization after DHCA examined animals with normal arterial oxygenation. This study reports the cerebral metabolic consequences if hypoxemic conditions are present after DHCA. METHODS: Eighteen neonatal piglets were randomly assigned to three groups. The control group was ventilated; the cardiopulmonary bypass group underwent 60 minutes of normothermic cardiopulmonary bypass, and the DHCA group underwent cardiopulmonary bypass and 60 minutes of DHCA (16 degrees to 18 degrees C) followed by rewarming. Hemodynamic and cerebral perfusion data were measured at an arterial partial pressure of oxygen (PaO2) of 150 to 250 mm Hg, and then at moderate hypoxemia (PaO2, 50 to 60 mm Hg) and severe hypoxemia (PaO2, 25 to 35 mm Hg). RESULTS: Cerebral oxygen delivery decreased by 44% from PaO2 150 to 250 mm Hg to severe hypoxemia (p < 0.001). Cerebral oxygen extraction increased from moderate hypoxemia to severe hypoxemia in the control (57.9% +/- 3.7% to 71.8% +/- 3.8%; p = 0.002) and cardiopulmonary bypass groups (61.2% +/- 2.6% to 70.6% +/- 1.2%; p = 0.035); however, the cerebral oxygen extraction of the DHCA group did not increase under these conditions (82.8% +/- 1.8% to 77.9% +/- 4.3%; p = 0.32). The cerebral metabolic rate of oxygen consumption of the DHCA group decreased from PaO2 150 to 250 mm Hg to severe hypoxemia (1.86 +/- 0.20 to 0.99 +/- 0.24 mL O2 x 100 g(-1) x min(-1); p = 0.02), whereas the cerebral metabolic rate of oxygen consumption did not change under these conditions in the control and cardiopulmonary bypass groups. CONCLUSIONS: Under hypoxemic conditions cerebral metabolic rate of oxygen consumption deteriorates after DHCA. Infants exposed to DHCA may be at greater risk of brain injury when postoperative hypoxemia is present. Because maximal cerebral oxygen extraction after DHCA occurs at moderate hypoxemia, techniques that increase cerebral oxygen delivery may reduce the risk of hypoxic brain injury.

Animals↗