The effect of hypothermic cardiopulmonary bypass and total circulatory arrest on cerebral metabolism in neonates, infants, and children

Early Impairment of Cerebral Bioenergetics After Cardiopulmonary Bypass in Neonatal Swine

Objectives: We previously demonstrated cerebral mitochondrial dysfunction in neonatal swine immediately following a period of full-flow cardiopulmonary bypass (CPB). The extent to which this dysfunction persists in the postoperative period and its correlation with other markers of cerebral bioenergetic failure and injury is unknown. We utilized a neonatal swine model to investigate the early evolution of mitochondrial function and cerebral bioenergetic failure after CPB. Methods: Twenty piglets (mean weight 4.4 ± 0.5 kg) underwent 3 h of CPB at 34 °C via cervical cannulation and were followed for 8, 12, 18, or 24 h (n = 5 per group). Markers of brain tissue damage (glycerol) and bioenergetic dysfunction (lactate to pyruvate ratio) were continuously measured in cerebral microdialysate samples. Control animals (n = 3, mean weight 4.1 ± 1.2 kg) did not undergo cannulation or CPB. Brain tissue was extracted immediately after euthanasia to obtain ex-vivo cortical mitochondrial respiration and frequency of cortical microglial nodules (indicative of cerebral microinfarctions) via neuropathology. Results: Both the lactate to pyruvate ratio (P < .0001) and glycerol levels (P = .01) increased in cerebral microdialysate within 8 h after CPB. At 24 h post-CPB, cortical mitochondrial respiration was significantly decreased compared with controls (P = .046). The presence of microglial nodules increased throughout the study period (24 h) (P = .01, R2 = 0.9). Conclusion: CPB results in impaired cerebral bioenergetics that persist for at least 24 h. During this period of bioenergetic impairment, there may be increased susceptibility to secondary injury related to alterations in metabolic delivery or demand, such as hypoglycemia, seizures, and decreased cerebral blood flow.

Distinct profiles of cerebral oxygenation in focal vs. secondarily generalized EEG seizures in children undergoing cardiac surgery

Objectives

Seizures are common in children undergoing cardiopulmonary bypass (CPB). Cerebral oxygen saturation (ScO2) by near-infrared spectroscopy is routinely monitored in many centers, but the relations between the levels and changes of ScO2 and brain injuries remain incompletely understood. We aimed to analyze the postoperative profiles of ScO2 and cerebral blood flow velocity in different types of EEG seizures in relation to brain injuries on MRI.

Methods

We monitored continuous EEG and ScO2 in 337 children during the first 48 h after CPB, which were analyzed in 3 h periods. Cerebral blood flow peak systolic velocity (PSV) in the middle cerebral artery was measured daily by transcranial Doppler. Postoperative cerebral MRI was performed before hospital discharge.

Results

Based on the occurrence and spreading types of seizures, patients were divided into three groups as patients without seizures (Group N; n = 309), those with focal seizures (Group F; n = 13), or with secondarily generalized seizures (Group G; n = 15). There were no significant differences in the onset time and duration of seizures and incidence of status epilepticus between the two seizures groups (Ps ≥ 0.27). ScO2 increased significantly faster across Group N, Group G, and Group F during the 48 h (p < 0.0001) but its overall levels were not significantly different among the three groups (p = 0.30). PSV was significantly lower (p = 0.003) but increased significantly faster (p = 0.0003) across Group N, Group G, and Group F. Group F had the most severe brain injuries and the highest incidence of white matter injuries on MRI among the three groups (Ps ≤ 0.002).

Conclusion

Postoperative cerebral oxygenation showed distinct profiles in secondarily generalized and particularly focal types of EEG seizures in children after CPB. A state of 'overshooting' ScO2 with persistently low PSV was more frequently seen in those with focal seizures and more severe brain injury. Information from this study may have important clinical implications in detecting brain injuries when monitoring cerebral oxygenation in this vulnerable group of children after CPB.

The incidence, risk factors and outcomes of impaired cerebral autoregulation in aortic arch surgery: a single-center, retrospective cohort study

BACKGROUND

Impairment of cerebral autoregulation (CA) has been observed in patients undergoing cardiopulmonary bypass (CPB), but little is known about its risks and associations with outcomes. The cerebral oximetry index (COx), which is a moving linear correlation coefficient between regional cerebral oxygen saturation (rScO2) and mean blood pressure (MAP), may reflect CA function. When COx approaches 1, it implies that CA is damaged, whereas the CA is functional when the COx value approaches 0. The objective of this study was to analyze the incidence and risks of impaired CA, based on COx assessment, in patients undergoing total aortic arch replacement under systemic moderate hypothermia and circulatory arrest of the lower body (MHCA). We also evaluated the association between impaired CA and patient outcomes.

METHODS

One hundred and fifty-four adult patients who underwent total aortic arch replacement with stented elephant trunk implantation under MHCA at our hospital were retrospectively analyzed. Patients were defined as having new-onset impaired CA if pre-CPB COx < 0.3 and post-CPB COx > 0.3. Pre- and intraoperative factors were tested for independent association with impaired CA. Postoperative outcomes were compared between patients with normal and impaired CA.

RESULTS

In our 154 patients, 46(29.9%) developed new-onset impaired CA after CPB. Multivariable analysis revealed a prolonged low rScO2 (rScO2 < 55%) independently associated with onset of impaired CA, and receiver operating charactoristic curve showed a cutoff value at 40 min (sensitivity, 89.5%; specificity, 68.0%). Compared with normal CA patients, those with impaired CA showed a significantly higher rates of in-hospital mortality and postoperative complications.

CONCLUSIONS

Prolonged low rScO2 (rScO2 < 55%) during aortic arch surgery was closely related to onset of impaired CA. Impaired CA remained associated with the increased rates of postoperative complications and in-hospital mortality.

TRIAL REGISTRATION

ChiCTR1800014545 with registered date 20/01/2018.

Depth of anesthesia, temperature, and postoperative delirium in children and adolescents undergoing cardiac surgery

BACKGROUND

After pediatric cardiosurgical interventions, postoperative delirium can occur, which can be associated with undesirable consequences during and after the hospital stay. It is therefore important to avoid any factors causing delirium as far as possible. Electroencephalogram (EEG) monitoring can be used during anesthesia to individually adjust dosages of hypnotically acting drugs. It is necessary to gain knowledge about the relationship between intraoperative EEG and postoperative delirium in children.

METHODS

In a dataset comprising 89 children (53 male, 36 female; median age: 0.99 (interquartile range: 0.51, 4.89) years) undergoing cardiac surgery involving use of a heart-lung machine, relationships between depth of anesthesia as measured by EEG (EEG index: Narcotrend Index (NI)), sevoflurane dosage, and body temperature were analyzed. A Cornell Assessment of Pediatric Delirium (CAP-D) score ≥ 9 indicated delirium.

RESULTS

The EEG could be used in patients of all age groups for patient monitoring during anesthesia. In the context of induced hypothermia, EEG monitoring supported individually adjusted sevoflurane dosing. The NI was significantly correlated with the body temperature; decreasing temperature was accompanied by a decreasing NI. A CAP-D score ≥ 9 was documented in 61 patients (68.5%); 28 patients (31.5%) had a CAP-D < 9. Delirious patients with an intubation time ≤ 24 h showed a moderate negative correlation between minimum NI (NImin) and CAP-D (rho = -0.41, 95% CI: -0.70 - -0.01, p = 0.046), i.e., CAP-D decreased with increasing NImin. In the analysis of all patients' data, NImin and CAP-D showed a weak negative correlation (rho = -0.21, 95% CI: -0.40 - 0.01, p = 0.064). On average, the youngest patients had the highest CAP-D scores (p = 0.002). Patients with burst suppression / suppression EEG had a longer median intubation time in the intensive care unit than patients without such EEG (p = 0.023). There was no relationship between minimum temperature and CAP-D score.

CONCLUSIONS

The EEG can be used to individually adjust sevoflurane dosing during hypothermia. Of the patients extubated within 24 h and classified as delirious, patients with deeper levels of anesthesia had more severe delirium symptoms than patients with lighter levels of anesthesia.

Normothermic Versus Hypothermic Norwood Procedure

BACKGROUND

Either deep hypothermia with circulatory arrest or hypothermic perfusion with antegrade selective cerebral perfusion is used during the Norwood procedure for hypoplastic left heart syndrome. Normothermic perfusion has been described for pediatric patients. The aim of this study was to compare the early outcomes of patients undergoing the Norwood procedure with antegrade selective cerebral perfusion under hypothermia with the procedure under normothermia.

METHODS

From 2005 to 2020, 117 consecutive patients with hypoplastic left heart syndrome underwent the Norwood procedure: 68 (58.2%) under hypothermia and 49 (41.8%) under normothermia. Antegrade selective cerebral perfusion flow was adjusted to maintain right radial arterial pressure above 50 mm Hg, and a flow rate of 40 to 50 mL kg^-1 min^-1. Baseline characteristics, operative data, and postoperative outcomes including lactate recovery time were compared.

RESULTS

The baseline characteristics and cardiovascular diagnosis were similar in both groups. The normothermic group had a significantly shorter bypass time (in minutes) of 90.31 (±31.60) versus 123.63 (±25.33), a cross-clamp time of 45.24 (±16.35) versus 81.93 (±16.34), and an antegrade selective cerebral perfusion time of 25.61 (±13.84) versus 47.30 (±14.35) (P < .001). There were no statistically significant differences in the immediate postoperative course, or in terms of in-hospital mortality, which totaled 9 (18.4%) in the normothermic group, and 10 (14.9%) in the hypothermic group (P = .81).

CONCLUSION

The normothermic Norwood procedure with selective cerebral perfusion is feasible and safe in terms of in-hospital mortality and short-term outcomes. It is comparable to the standard hypothermic Norwood with selective cerebral perfusion.

Association of Ongoing Cerebral Oxygen Extraction During Deep Hypothermic Circulatory Arrest With Postoperative Brain Injury

Cardiac surgery utilizing circulatory arrest is most commonly performed under deep hypothermia (∼18°C) to suppress tissue oxygen demand and provide neuroprotection during operative circulatory arrest. Studies investigating the effects of deep hypothermic circulatory arrest (DHCA) on neurodevelopmental outcomes of patients with congenital heart disease give conflicting results. Here, we address these issues by quantifying changes in cerebral oxygen saturation, blood flow, and oxygen metabolism in neonates during DHCA and investigating the association of these changes with postoperative brain injury. Neonates with critical congenital heart disease undergoing DHCA were recruited for continuous intraoperative monitoring of cerebral oxygen saturation (ScO₂) and an index of cerebral blood flow (CBF_i) using 2 noninvasive optical techniques, diffuse optical spectroscopy (DOS) and diffuse correlation spectroscopy (DCS). Pre- and postoperative brain magnetic resonance imaging (MRI) was performed to detect white matter injury (WMI). Fifteen neonates were studied, and 11/15 underwent brain MRI. During DHCA, ScO₂ decreased exponentially in time with a median decay rate of -0.04 min^-1. This decay rate was highly variable between subjects. Subjects who had larger decreases in ScO₂ during DHCA were more likely to have postoperative WMI (P = 0.02). Cerebral oxygen extraction persists during DHCA and varies widely from patient-to-patient. Patients with a higher degree of oxygen extraction during DHCA were more likely to show new WMI in postoperative MRI. These findings suggest cerebral oxygen extraction should be monitored during DHCA to identify patients at risk for hypoxic-ischemic injury, and that current commercial cerebral oximeters may underestimate cerebral oxygen extraction.

Neuromonitoring and Neurocognitive Outcomes in Cardiac Surgery: A Narrative Review

Neurocognitive dysfunction after cardiac surgery can present with diverse clinical phenotypes, which include postoperative delirium, postoperative cognitive dysfunction, and stroke, and it presents a significant healthcare burden for both patients and providers. Neurologic monitoring during cardiac surgery includes several modalities assessing cerebral perfusion and oxygenation (near-infrared spectroscopy, transcranial Doppler and jugular venous bulb saturation monitoring) and those that measure cerebral function (processed and unprocessed electroencephalogram), reflecting an absence of a single, definitive neuromonitor. This narrative review briefly describes the technologic basis of these neuromonitoring modalities, before exploring their use in clinical practice, both as tools to predict neurocognitive dysfunction, and with a bundle of interventions designed to optimize cerebral oxygen supply, with the aim of reducing postoperative delirium and cognitive dysfunction following cardiac surgery.

Avoiding use of total circulatory arrest in the practice of congenital heart surgery

Deep hypothermic circulatory arrest (DHCA) technique has been an important armamentarium in the correction of congenital heart diseases. There have been many controversies and concerns associated with DHCA, particularly neurological damage. Selective ante grade cerebral perfusion (SACP) was introduced as an adjunct to DHCA with the objective of limiting the neurologic injury during aortic arch repairs. Over the past two decades, various aspects of cardiopulmonary bypass and DHCA have been studied and modified such as optimisation of flows, anti-inflammatory interventions, haematocrit, and temperature to improve neurologic outcomes. With the changes in practice of DHCA, outcomes have significantly improved but SACP intuitively appears attractive to offer better neuroprotection. The strategy of conduct of SACP is evolving and needs to be standardised for comparing outcomes. In this review we have discussed the various physiological and technical factors involved in conduct of SACP in paediatric cardiac surgery and outcomes with SACP.

Lower limit of adequate oxygen delivery for the maintenance of aerobic metabolism during cardiopulmonary bypass in neonates

BACKGROUND

The objective of cardiopulmonary bypass (CPB) is to maintain an adequate balance between oxygen delivery (Ḋo2) and consumption. The critical Ḋo2 is that at which consumption becomes supply dependent. This study aimed to identify the critical Ḋo2 in neonates, who have higher metabolic rates than adults.

METHODS

In a retrospective cohort of neonates, Ḋo2 was calculated from CPB parameters recorded during aortic cross-clamping. High lactate concentration measured after aortic unclamping (lactOFF) was used to identify anaerobic metabolism. Data were analysed using mixed linear and proportional odds regression models. The relationship between Ḋo2 and temperature was analysed in a subgroup of patients with lactOFF <2.5 mM, thought to have had balanced oxygen delivery and consumption. The estimated regression coefficient was further used to adjust hypothetical Ḋo2 thresholds, and Ḋo2 excursions below the threshold were quantified as magnitude-durations. The lowest threshold that provided magnitude-durations and linked with an increase in lactOFF was used as the lowest suitable (critical) Ḋo2 at 37°C.

RESULTS

Overall, 22 896 time points were analysed in 180 neonates. In 40 patients with lactOFF <2.5 mM, Ḋo2 varied by 22.87 (0.70) ml min-1 m-2 °C-1. When varying the Ḋo2 threshold between 340 and 380 ml min-1 m-2, excursions below the threshold were linked with incremental lactOFF. A 100 ml m-2 excursion below the 340 ml min-1 m-2Ḋo2 threshold increased the risk of a 1 mM increment in lactOFF by 22% (odds ratio: 1.22; 95% confidence interval: 1.02-1.45).

CONCLUSIONS

It was found that 340 ml min-1 m-2 is likely to represent the lowest suitable Ḋo2 required in neonates to maintain aerobic metabolism during normothermic CPB.

Non-invasive optical neuromonitoring of the temperature-dependence of cerebral oxygen metabolism during deep hypothermic cardiopulmonary bypass in neonatal swine

Management of deep hypothermic (DH) cardiopulmonary bypass (CPB), a critical neuroprotective strategy, currently relies on non-invasive temperature to guide cerebral metabolic suppression during complex cardiac surgery in neonates. Considerable inter-subject variability in temperature response and residual metabolism may contribute to the persisting risk for postoperative neurological injury. To characterize and mitigate this variability, we assess the sufficiency of conventional nasopharyngeal temperature (NPT) guidance, and in the process, validate combined non-invasive frequency-domain diffuse optical spectroscopy (FD-DOS) and diffuse correlation spectroscopy (DCS) for direct measurement of cerebral metabolic rate of oxygen (CMRO₂). During CPB, n = 8 neonatal swine underwent cooling from normothermia to 18℃, sustained DH perfusion for 40 min, and then rewarming to simulate cardiac surgery. Continuous non-invasive and invasive measurements of intracranial temperature (ICT) and CMRO₂ were acquired. Significant hysteresis (p < 0.001) between cooling and rewarming periods in the NPT versus ICT and NPT versus CMRO₂ relationships were found. Resolution of this hysteresis in the ICT versus CMRO₂ relationship identified a crucial insufficiency of conventional NPT guidance. Non-invasive CMRO₂ temperature coefficients with respect to NPT (Q₁₀ = 2.0) and ICT (Q₁₀ = 2.5) are consistent with previous reports and provide further validation of FD-DOS/DCS CMRO₂ monitoring during DH CPB to optimize management.

Near-Infrared Spectroscopy in Pediatric Congenital Heart Disease

Near-infrared spectroscopy (NIRS) is widely used to monitor tissue oxygenation in the pediatric cardiac surgical population. Clinicians who use NIRS must understand the underlying measurement principles in order to interpret and use this monitoring modality appropriately. The aims of this narrative review are to provide a brief overview of NIRS technology, discuss the normative and critical values of cerebral and somatic tissue oxygen saturation and the interpretation of these values, present the clinical studies (and their limitations) of NIRS as a perioperative monitoring modality in the pediatric congenital heart disease population, and introduce the emerging and future applications of NIRS.

Impact of Regional Cerebral Perfusion on Outcomes Among Neonates Undergoing Norwood Operation

OBJECTIVES

To evaluate the impact of regional cerebral perfusion (RCP) during heart operation on outcomes in neonates undergoing Norwood operation.

METHODS

We performed a retrospective cohort study using data from the Single Ventricle Reconstruction trial data set. The adjusted effect of RCP use on each outcome was studied using a penalized logistic regression model with bootstrap validation.

RESULTS

Of 549 patients included in the study, 252 patients (45.9%) received RCP during their heart operation. In univariate comparisons, the majority of the baseline characteristics and preoperative risk factors were similar in the RCP and No RCP group. The total cardiopulmonary bypass (CPB) time and the total cross-clamp (CC) time were longer in the RCP group (RCP vs No RCP, median CPB time: 161 minutes vs 109 minutes; median CC time: 63 minutes vs 43 minutes). In adjusted models, the use of RCP was not associated with decreased mortality and/or need for heart transplant at hospital discharge (odds ratio [OR]: 0.73; 95% confidence interval [CI]: 0.43-1.25) or prolonged mechanical ventilation (OR: 1.20, 95% CI: 0.62-2.28) or prolonged hospital length of stay (OR: 1.30, 95% CI: 0.73-2.30). We demonstrated that use of RCP was associated with longer CPB times, increased use of ultrafiltration, and higher probability of open chest after Norwood operation.

CONCLUSIONS

This study did not demonstrate any impact of RCP on in-hospital mortality and/or heart transplantation, prolonged mechanical ventilation, and prolonged hospital length of stay among neonates undergoing Norwood operation.

Electroencephalographic Response to Deep Hypothermic Circulatory Arrest in Neonatal Swine and Humans

BACKGROUND

Piglets are used to study neurologic effects of deep hypothermic circulatory arrest (DHCA), but no studies have compared human and swine electroencephalogram (EEG) responses to DHCA. The importance of isoelectricity before circulatory arrest is not fully known in neonates. We compared the EEG response to DHCA in human neonates and piglets.

METHODS

We recorded 2 channel, left and right centroparietal, subdermal EEG in 10 neonatal patients undergoing operations involving DHCA and 10 neonatal piglets that were placed on cardiopulmonary bypass and underwent a simulated procedure using DHCA. EEG waveforms were analyzed for the presence and extent of burst suppression and isoelectricity by automated moving window analysis. The patients were monitored with 16-channel array EEG for 48 hours postoperatively and underwent postoperative brain magnetic resonance imaging.

RESULTS

After induction of anesthesia, humans and piglets both displayed slowing or brief suppression, then mild burst suppression, and then severe burst suppression during cooling. All piglets subsequently achieved isoelectricity at 22.4° ± 6.9°C, whereas only 1 human did at 20.2°C. Piglets and humans emerged from severe, mild, and then brief suppression patterns during rewarming. Among the patients, there were no seizures during postoperative monitoring and 1 instance of increased white matter injury on postoperative magnetic resonance imaging.

CONCLUSIONS

Our data suggest that current cooling strategies may not be sufficient to eliminate all EEG activity before circulatory arrest in humans but are sufficient in swine. This important difference between the swine and human response to DHCA should be considered when using this model.

Comparison of Early Outcomes for Normothermic and Hypothermic Cardiopulmonary Bypass in Children Undergoing Congenital Heart Surgery

Objective: Comparison of early outcomes of normothermic cardiopulmonary bypass (N-CPB, ≥35°C) with hypothermic cardiopulmonary bypass (H-CPB, 28-34°C) for congenital heart defects. Methods: Data from 99 patients <2 years operated with N-CPB (n = 48) or H-CPB (n = 51) were retrospectively reviewed: aortic X-clamping and CPB duration, vasoactive inotropic score (VIS), arterial lactate, pH and base excess, urine output, extubation, PICU stay, transfusion requirements, chest drain losses, costs of transfusions, and costs of PICU stay. Results: The two groups were homogeneous for diagnosis, risk factors, surgery and demographic variables: N-CPB age 7.7 ± 6.1 months, weight 6.2 ± 2.4 kg, and H-CPB age 6.6 ± 6.5 months, weight 6.1 ± 2.4 kg. There were no hospital deaths in either group. VIS in N-CPB was lower than H-CPB on PICU arrival (9.7 ± 5.9 vs. 13.4 ± 7.9, P < 0.005), after 4 h (7.0 ± 5.2 vs. 11.1 ± 7.3, P < 0.001) and 24 h (2.8 ± 3.6 vs. 5.6 ± 5.6, P < 0.003); arterial pH was better at PICU arrival (7.33 ± 0.09 vs. 7.30 ± 0.09, P = 0.046) after 4 h (7.35 ± 0.07 vs. 7.32 ± 0.07, P = 0.022) and after 24 h (7.37 ± 0.05 vs. 7.35 ± 0.05, P = 0.01). Extubation was earlier in N-CPB than in H-CPB (22 ± 27 vs. 48 ± 57 h, P = 0.003) as PICU discharge (61 ± 46 h vs. 87 ± 69 h, P = 0.021). Transfusion requirements in operating room were lower in N-CPB vs. H-CPB for RBC, FFP, cryoprecipitate, and platelets, while during the first 24 h in PICU were lower only for cryoprecipitate and platelets. Chest drain losses (mL/kg) on PICU arrival, after 4 and 24 h were lower with N-CPB vs. H-CPB (respectively 1.5 ± 1.4 vs. 2.5 ± 2.7, P = 0.013, 7.8 ± 6.0 vs. 10.9 ± 8.7, P = 0.025, and 23.0 ± 12.0 vs. 27.9 ± 15.2, P = 0.043). Tranexamic acid infusion was required in 7/48 (14.6%) patients with N-CPB vs. 18/51(= 35.3%) in H-CPB (P = 0.009). The average total costs/patient of blood and blood products (RBC, FFP, cryoprecipitate, platelets) were lower in N-CPB vs. H-CPB for both the first 24 h after surgery (£204 ± 169 vs. £306 ± 254, P = 0.011) as well as during the total duration of PICU stay (£239 ± 193 vs. £427 ± 337, P = 0.001). The average cost/patient/day of stay in PICU was lower in N-CPB than in H-CPB (£4,067 ± 3,067 vs. £5,800 ± 4,600, P = 0.021). Conclusions: N-CPB may reduce inotropic and respiratory support, shorten PICU stay, and decrease peri-operative transfusion requirements, with subsequent costs reduction, compared to H-CPB. Future studies are needed to validate and support wider use of N-CPB.

Changes in Near-Infrared Spectroscopy After Congenital Cyanotic Heart Surgery

BACKGROUND

Since oxygen saturation from pulse oximetry (SpO₂) and partial pressure of arterial oxygen (PaO₂) are observed to improve immediately after surgical correction of cyanotic congenital heart disease (CHD), we postulate that cerebral (CrO₂) and somatic (SrO₂) oximetry also improves immediately post-correction. We aim to prospectively examine CrO₂ and SrO₂, before, during, and after surgical correction as well as on hospital discharge in children with cyanotic CHD to determine if and when these variables increase.

METHODS

This is a prospective observational trial. Eligibility criteria included children below 18 years of age with cyanotic CHD who required any cardiac surgical procedure. CrO₂ and SrO₂ measurements were summarized at six time-points for comparison: (1) pre-cardiopulmonary bypass (CPB); (2) during CPB; (3) post-CPB; (4) Day 1 in the pediatric intensive care unit (PICU); (5) Day 2 PICU; and (6) discharge. Categorical and continuous variables are presented as counts (percentages) and median (interquartile range), respectively.

RESULTS

Twenty-one patients were analyzed. 15 (71.4%) and 6 (28.6%) patients underwent corrective and palliative surgeries, respectively. In the corrective surgery group, SpO₂ increased immediately post-CPB compared to pre-CPB [99 (98, 100) vs. 86% (79, 90); p < 0.001] and remained in the normal range through to hospital discharge. Post-CPB CrO₂ did not change from pre-CPB [72.8 (58.8, 79.0) vs. 72.1% (63.0, 78.3); p = 0.761] and even decreased on hospital discharge [60.5 (53.6, 62.9) vs. 72.1% (63.0, 78.3); p = 0.005]. Post-CPB SrO₂ increased compared to pre-CPB [87.3 (77.2, 89.5) vs. 72.7% (65.6, 77.3); p = 0.001] but progressively decreased during PICU stay to a value lower than baseline at hospital discharge [66.9 (57.3, 76.9) vs. 72.7% (65.6, 77.3); p = 0.048].

CONCLUSION

CrO₂ and SrO₂ did not increase after corrective surgery of cyanotic CHD even up to hospital discharge. Future larger studies are required to validate these findings. (This study is registered with ClinicalTrials.gov ID: NCT02417259.).

Mid-Term Outcomes of Repair of Coarctation of Aorta With Hypoplastic Arch: Extended End-to-side Anastomosis Technique

The optimal surgical repair technique for coarctation associated with aortic arch hypoplasia (CoA-AAH) in neonates and infants is controversial. This study evaluates our current strategy using extended end-to-side anastomosis under selective cerebral and myocardial perfusion in treating this group of patients. Through a retrospective review, we analyzed the outcome of 87 infants who underwent surgical repair of CoA-AAH from January 2004 to December 2015. Patients with functional single ventricle were excluded. There were no early mortalities, and 4 patients (4.6%) experienced early complications. Eighty-five patients (97.7%) were followed up during a mean duration of 6.1 ± 3.53 years. There were 2 late mortalities (2.3%) and 3 reintervention (3.5%) of the aortic arch. Ten-year overall survival and freedom from reintervention for the entire cohort was 97.7% and 96.3%, respectively. At last follow-up, 4 patients (4.5%) showed a peak velocity greater than 2.5 m/s across the repair site. Seven patients (8.2%) were hypertensive. Our strategy with extended end-to-side anastomosis under selective cerebral and myocardial perfusion is safe and effective for repairing CoA-AAH in neonates and infants. Concomitant repair of associated cardiac anomalies can be done without added risk. Mid-term results are excellent with low rates of mortality, reintervention, and late hypertension.

Does hypothermia impair cerebrovascular autoregulation in neonates during cardiopulmonary bypass?

BACKGROUND

Autoregulation monitoring has been proposed as a means to identify optimal arterial blood pressure goals during cardiopulmonary bypass, but it has been observed that cerebral blood flow is pressure passive during hypothermic bypass. When neonates cooled during cardiopulmonary bypass are managed with vasodilators and controlled hypotension, it is not clear whether hypothermia or hypotension were the cause of impaired autoregulation.

AIM

We sought to measure the effect of both arterial blood pressure and hypothermia on autoregulation in a cohort of infants cooled for bypass, hypothesizing a collinear relationship between hypothermia, hypotension, and dysautoregulation.

METHODS

Cardiopulmonary bypass was performed on 72 infants at Texas Children's Hospital during 2015 and 2016 with automated physiologic data capture, including arterial blood pressure, nasopharyngeal temperature, cerebral oximetry, and a cerebral blood volume index derived from near infrared spectroscopy. Cooling to 18°C, 24°C, and 30°C was performed on 33, 12, and 22 subjects, respectively. The hemoglobin volume index was calculated as a moving correlation coefficient between mean arterial blood pressure and the cerebral blood volume index. Positive values of the hemoglobin volume index indicate impaired autoregulation. Relationships between variables were assessed utilizing a generalized estimating equation approach.

RESULTS

Hypothermia was associated with hypotension, dysautoregulation, and increased cerebral oximetry. Comparing the baseline temperature of 36°C with 18°C, arterial blood pressure was 44 mm Hg (39-52) vs 25 mm Hg (21-31); the hemoglobin volume index was 0.0 (-0.02 to 0.004) vs 0.5 (0.4-0.7) and cerebral oximetry was 59% (57-61) vs 88% (80-92) (Median, 95% CI of median; P<.0001 for all three associations by linear regression with generalized estimation of equations with data from all temperatures measured).

CONCLUSIONS

Arterial blood pressure, temperature, and cerebral autoregulation were collinear in this cohort. The conclusion that hypothermia causes impaired autoregulation is thus confounded. The effect of temperature on autoregulation should be delineated before clinical deployment of autoregulation monitors to prevent erroneous determination of optimal arterial blood pressure. Showing the effect of temperature on autoregulation will require a normotensive hypothermic model.

Static cerebrovascular pressure autoregulation remains intact during deep hypothermia

BACKGROUND

Clinical studies measuring cerebral blood flow in infants during deep hypothermia have demonstrated diminished cerebrovascular pressure autoregulation. The coexistence of hypotension in these cohorts confounds the conclusion that deep hypothermia impairs cerebrovascular pressure autoregulation.

AIM

We sought to compare the lower limit of autoregulation and the static rate of autoregulation between normothermic and hypothermic piglets.

METHODS

Twenty anesthetized neonatal piglets (5-7 days old; 10 normothermic and 10 hypothermic to 20°C) had continuous measurements of cortical red cell flux using laser Doppler flowmetry, while hemorrhagic hypotension was induced without cardiopulmonary bypass. Lower limit of autoregulation was determined for each subject using piecewise regression and SRoR was determined above and below each lower limit of autoregulation as (%change cerebrovascular resistance/%change cerebral perfusion pressure).

RESULTS

The estimated difference in lower limit of autoregulation was 1.4 mm Hg (lower in the hypothermic piglets; 95% C.I. -10 to 14 mm Hg; P=0.6). The median lower limit of autoregulation in the normothermic group was 39 mm Hg [IQR 38-51] vs 35 mm Hg [31-50] in the hypothermic group. Intact steady-state pressure autoregulation was defined as static rate of autoregulation >0.5 and was demonstrated in all normothermic subjects (static rate of autoregulation=0.72 [0.65-0.87]) and in 9/10 of the hypothermic subjects (static rate of autoregulation=0.65 [0.52-0.87]). This difference in static rate of autoregulation of 0.06 (95% C.I. -0.3 to 0.1) was not significant (P=0.4).

CONCLUSION

Intact steady-state cerebrovascular pressure autoregulation is demonstrated in a swine model of profound hypothermia. Lower limit of autoregulation and static rate of autoregulation were similar in hypothermic and normothermic subjects.

Severe Aortic Stenosis and Severe Coarctation of the Aorta: A Hybrid Approach to Treatment

Hybrid surgery is becoming more popular in the treatment of children with congenital heart disease, particularly small infants and neonates. We report a case of a patient with aortic stenosis (AS) and coarctation of the aorta (CoA). Case: a 1-month-old baby presented with severe AS and CoA. The decision was made to perform a hybrid surgical procedure. The patient underwent a lateral thoracotomy for repair of the CoA and carotid cutdown for aortic balloon valvuloplasty (AoVP).

Non-invasive Assessment of Cerebral Blood Flow and Oxygen Metabolism in Neonates during Hypothermic Cardiopulmonary Bypass: Feasibility and Clinical Implications

The neonatal brain is extremely vulnerable to injury during periods of hypoxia and/or ischemia. Risk of brain injury is increased during neonatal cardiac surgery, where pre-existing hemodynamic instability and metabolic abnormalities are combined with long periods of low cerebral blood flow and/or circulatory arrest. Our understanding of events associated with cerebral hypoxia-ischemia during cardiopulmonary bypass (CPB) remains limited, largely due to inadequate tools to quantify cerebral oxygen delivery and consumption non-invasively and in real-time. This pilot study aims to evaluate cerebral blood flow (CBF) and oxygen metabolism (CMRO₂) intraoperatively in neonates by combining two novel non-invasive optical techniques: frequency-domain near-infrared spectroscopy (FD-NIRS) and diffuse correlation spectroscopy (DCS). CBF and CMRO₂ were quantified before, during and after deep hypothermic cardiopulmonary bypass (CPB) in nine neonates. Our results show significantly decreased CBF and CMRO₂ during hypothermic CPB. More interestingly, a change of coupling between both variables is observed during deep hypothermic CPB in all subjects. Our results are consistent with previous studies using invasive techniques, supporting the concept of FD-NIRS/DCS as a promising technology to monitor cerebral physiology in neonates providing the potential for individual optimization of surgical management.

Optimal Temperature Management During Cardiopulmonary Bypass: Warm, Cold, or Tepid?

Hypothermia permitted the advent of cardiac surgery and is considered by many the mainstay of cerebral protection during cardiopulmonary bypass (CPB). How ever, some clinicians have questioned the importance of reduced temperatures during CPB and advocate "normo thermic" heart surgery. Hypothermia (mild, moderate, and profound) provides protection during periods of inadequate oxygen delivery by at least two mecha nisms. First, metabolic rate is directly related to tempera ture ; therefore, reduced temperatures increase toler ance to inadequate oxygen delivery. Q10 values (the ratio of metabolic rates at temperature X°C and tempera ture X°C - 10°C) are controversial and are reported as varying between 2.0 and 5.0. During profound hypother mia (temperature = 17°C), metabolic requirements are 10% to 15% of normothermic values. Second, reduced temperatures (even minimal reductions [34°C to 35°C]) attenuate the release of glutamate and other excitatory amines from ischemic neuronal cells. This phenomenon is thought to play an important role in hypothermic cerebral protection. Many investigators have assessed the impact of normothermic temperatures on cerebral outcomes in cardiac surgery patients. Although seem ingly conflicting conclusions are reported, this much is clear: cerebral temperatures in excess of 37°C exacer bate ischemic injury and even mild hypothermia re duces central nervous system damage in the ischemic brain.

The Postoperative Care of Adult Patients Exposed to Deep Hypothermic Circulatory Arrest

Deep hypothermic circulatory arrest with cardiopulmonary bypass is indicated for complex surgical operations in adult patients involving the aortic arch, thoracoabdominal aorta, cerebral vasculature, and tumors extending into the vena cava and heart. Understanding the principles of ischemic-reperfusion injury and the effects of hypothermia in attenuating this process is fundamental to the delivery of effective postoperative care. Neurologic injury is the most troublesome adverse effect after the use of deep hypothermic circulatory arrest and cardiopulmonary bypass, presenting as either a transient neurologic deficit (5.9% to 28.1%) or an irreversible neurologic injury (1.8% to 13.6%). In patients with neurological injury, early postoperative mortality is markedly increased (18.2%), and for those patients that survive, long-term cognitive disability is still evident 6 months later. Early postoperative support of organ function, along with timely diagnosis and treatment of organ injury, is essential in minimizing perioperative morbidity, particularly neurologic morbidity. Meticulous management of fluids, maintaining stable cardiovascular hemodynamics with particular attention to systolic blood pressure, optimizing oxygen delivery, limiting ventilatorassociated lung injury, intensive insulin therapy for control of blood glucose levels, and avoidance of hyperthermia are essential in limiting organ injury and reducing perioperative morbidity and mortality.

Cerebral injury during paediatric heart surgery: perfusion issues

Suboptimal neurodevelopmental outcome is common in children who have congenital heart disease. Its aetiology is often multifactorial. This review focuses on the role of cardiopulmonary bypass. Hypothermia is the mainstay of cerebral protection. Low flow and regional low flow are preferred to deep hypothermic circulatory arrest in many situations. Cooling and rewarming, aortopulmonary collaterals, pH, air emboli, the systemic inflammatory response, haematocrit, oxygenation, glucose and ultrafiltration can influence neurodevelopmental outcome. Although no pharmacological agents have been shown to have a beneficial effect on neurodevelopmental outcome in clinical practice in children, animal work on the use of steroids several hours before surgery is encouraging.

Perioperative cerebral hemodynamics and oxygen metabolism in neonates with single-ventricle physiology

Congenital heart disease (CHD) patients are at risk for neurodevelopmental delay. The etiology of these delays is unclear, but abnormal prenatal cerebral maturation and postoperative hemodynamic instability likely play a role. A better understanding of these factors is needed to improve neurodevelopmental outcome. In this study, we used bedside frequency-domain near infrared spectroscopy (FDNIRS) and diffuse correlation spectroscopy (DCS) to assess cerebral hemodynamics and oxygen metabolism in neonates with single-ventricle (SV) CHD undergoing surgery and compared them to controls. Our goals were 1) to compare cerebral hemodynamics between unanesthetized SV and healthy neonates, and 2) to determine if FDNIRS-DCS could detect alterations in cerebral hemodynamics beyond cerebral hemoglobin oxygen saturation (SO 2). Eleven SV neonates were recruited and compared to 13 controls. Preoperatively, SV patients showed decreased cerebral blood flow (CBFi ), cerebral oxygen metabolism (CMRO 2i ) and SO 2; and increased oxygen extraction fraction (OEF) compared to controls. Compared to preoperative values, unstable postoperative SV patients had decreased CMRO 2i and CBFi , which returned to baseline when stable. However, SO 2 showed no difference between unstable and stable states. Preoperative SV neonates are flow-limited and show signs of impaired cerebral development compared to controls. FDNIRS-DCS shows potential to improve assessment of cerebral development and postoperative hemodynamics compared to SO 2 alone.

Cold-inducible RNA-binding protein inhibits neuron apoptosis through the suppression of mitochondrial apoptosis

Cold-inducible RNA-binding protein (CIRP) is induced by mild hypothermia in several mammals, but the precise mechanism by which CIRP mediates hypothermia-induced neuroprotection remains unknown. We aimed to investigate the molecular mechanisms by which CIRP protects the nervous system during mild hypothermia. Rat cortical neurons were isolated and cultured in vitro under mild hypothermia (32°C). Apoptosis was measured by annexin V and propidium iodide staining, visualized by flow cytometry. Neuron ultrastructure was visualized by transmission electron microscopy. CIRP overexpression and knockdown were achieved via infection with pL/IRES/GFP-CIRP and pL/shRNA/F-CIRP-A lentivirus. RT(2) Profiler PCR Array Pathway Analysis and western blotting were used to evaluate the effects of CIRP overexpresion/knockdown on the neurons׳ transcriptome. Neuron late apoptosis was significantly reduced at day 7 of culture by 12h hypothermia, but neuron ultrastructure remained relatively intact. RT(2) Profiler PCR Array Pathway Analysis of 84 apoptosis pathway-associated factors revealed that mild hypothermia and CIRP overexpression induce similar gene expression profiles, specifically alterations of genes implicated in the mitochondrial apoptosis pathway. Mild hypothermia-treated neurons up-regulated 12 and down-regulated 38 apoptosis pathway-associated genes. CIRP-overexpressing neurons up-regulated 15 and down-regulated 46 genes. CIRP-knocked-down hypothermia-treated cells up-regulated 9 and down-regulated 40 genes. Similar results were obtained at the protein level. In conclusion, CIRP may inhibit neuron apoptosis through the suppression of the mitochondria apoptosis pathway during mild hypothermia.

Brain temperature and its fundamental properties: a review for clinical neuroscientists

Brain temperature, as an independent therapeutic target variable, has received increasingly intense clinical attention. To date, brain hypothermia represents the most potent neuroprotectant in laboratory studies. Although the impact of brain temperature is prevalent in a number of common human diseases including: head trauma, stroke, multiple sclerosis, epilepsy, mood disorders, headaches, and neurodegenerative disorders, it is evident and well recognized that the therapeutic application of induced hypothermia is limited to a few highly selected clinical conditions such as cardiac arrest and hypoxic ischemic neonatal encephalopathy. Efforts to understand the fundamental aspects of brain temperature regulation are therefore critical for the development of safe, effective, and pragmatic clinical treatments for patients with brain injuries. Although centrally-mediated mechanisms to maintain a stable body temperature are relatively well established, very little is clinically known about brain temperature's spatial and temporal distribution, its physiological and pathological fluctuations, and the mechanism underlying brain thermal homeostasis. The human brain, a metabolically "expensive" organ with intense heat production, is sensitive to fluctuations in temperature with regards to its functional activity and energy efficiency. In this review, we discuss several critical aspects concerning the fundamental properties of brain temperature from a clinical perspective.

Modelling survival and mortality risk to 15 years of age for a national cohort of children with serious congenital heart defects diagnosed in infancy

BACKGROUND

Congenital heart defects (CHDs) are a significant cause of death in infancy. Although contemporary management ensures that 80% of affected children reach adulthood, post-infant mortality and factors associated with death during childhood are not well-characterised. Using data from a UK-wide multicentre birth cohort of children with serious CHDs, we observed survival and investigated independent predictors of mortality up to age 15 years.

METHODS

Data were extracted retrospectively from hospital records and death certificates of 3,897 children (57% boys) in a prospectively identified cohort, born 1992-1995 with CHDs requiring intervention or resulting in death before age one year. A discrete-time survival model accounted for time-varying predictors; hazards ratios were estimated for mortality. Incomplete data were addressed through multilevel multiple imputation.

FINDINGS

By age 15 years, 932 children had died; 144 died without any procedure. Survival to one year was 79.8% (95% confidence intervals [CI] 78.5, 81.1%) and to 15 years was 71.7% (63.9, 73.4%), with variation by cardiac diagnosis. Importantly, 20% of cohort deaths occurred after age one year. Models using imputed data (including all children from birth) demonstrated higher mortality risk as independently associated with cardiac diagnosis, female sex, preterm birth, having additional cardiac defects or non-cardiac malformations. In models excluding children who had no procedure, additional predictors of higher mortality were younger age at first procedure, lower weight or height, longer cardiopulmonary bypass or circulatory arrest duration, and peri-procedural complications; non-cardiac malformations were no longer significant.

INTERPRETATION

We confirm the high mortality risk associated with CHDs in the first year of life and demonstrate an important persisting risk of death throughout childhood. Late mortality may be underestimated by procedure-based audit focusing on shorter-term surgical outcomes. National monitoring systems should emphasise the importance of routinely capturing longer-term survival and exploring the mechanisms of mortality risk in children with serious CHDs.

Cerebral oxygen metabolism in neonatal hypoxic ischemic encephalopathy during and after therapeutic hypothermia

Pathophysiologic mechanisms involved in neonatal hypoxic ischemic encephalopathy (HIE) are associated with complex changes of blood flow and metabolism. Therapeutic hypothermia (TH) is effective in reducing the extent of brain injury, but it remains uncertain how TH affects cerebral blood flow (CBF) and metabolism. Ten neonates undergoing TH for HIE and seventeen healthy controls were recruited from the NICU and the well baby nursery, respectively. A combination of frequency domain near infrared spectroscopy (FDNIRS) and diffuse correlation spectroscopy (DCS) systems was used to non-invasively measure cerebral hemodynamic and metabolic variables at the bedside. Results showed that cerebral oxygen metabolism (CMRO2i) and CBF indices (CBFi) in neonates with HIE during TH were significantly lower than post-TH and age-matched control values. Also, cerebral blood volume (CBV) and hemoglobin oxygen saturation (SO2) were significantly higher in neonates with HIE during TH compared with age-matched control neonates. Post-TH CBV was significantly decreased compared with values during TH whereas SO2 remained unchanged after the therapy. Thus, FDNIRS-DCS can provide information complimentary to SO2 and can assess individual cerebral metabolic responses to TH. Combined FDNIRS-DCS parameters improve the understanding of the underlying physiology and have the potential to serve as bedside biomarkers of treatment response and optimization.

Single-stage correction of interrupted aortic arch in an adolescent patient

Interrupted aortic arch (IAA) is a rare condition that generally requires surgical correction in the newborn. We report a case of delayed presentation of type A interrupted aortic arch with ventricular septal defect in a 13-year-old female. Single-stage correction without circulatory arrest was accomplished via midline sternotomy approach. Tissue-to-tissue anastomosis was performed without the use of prosthetic material in order to optimize chances for future growth. This simplified technique avoids additional procedures, reduces ischemic time, and prevents problems related to circulatory arrest.

Anesthetic Considerations in Infants With Hypoplastic Left Heart Syndrome

Hypoplasia of the left ventricle is a congenital cardiac lesion that is almost universally fatal if left untreated. Six decades of improved diagnostic modalities, greater understanding of single ventricle physiology, and earlier surgical and palliative options have given many of these patients an opportunity of surviving well into adulthood. This review will summarize these advances and focus on the anesthetic implications of this challenging disease from diagnosis to beyond the first palliative surgery.

Early postoperative changes in cerebral oxygen metabolism following neonatal cardiac surgery: effects of surgical duration

OBJECTIVE

The early postoperative period following neonatal cardiac surgery is a time of increased risk for brain injury, yet the mechanisms underlying this risk are unknown. To understand these risks more completely, we quantified changes in postoperative cerebral metabolic rate of oxygen (CMRO(2)), oxygen extraction fraction (OEF), and cerebral blood flow (CBF) compared with preoperative levels by using noninvasive optical modalities.

METHODS

Diffuse optical spectroscopy and diffuse correlation spectroscopy were used concurrently to derive cerebral blood flow and oxygen utilization postoperatively for 12 hours. Relative changes in CMRO(2), OEF, and CBF were quantified with reference to preoperative data. A mixed-effect model was used to investigate the influence of total support time and deep hypothermic circulatory arrest duration on relative changes in CMRO(2), OEF, and CBF.

RESULTS

Relative changes in CMRO(2), OEF, and CBF were assessed in 36 patients, 21 with single-ventricle defects and 15 with 2-ventricle defects. Among patients with single-ventricle lesions, deep hypothermic circulatory arrest duration did not affect relative changes in CMRO(2), CBF, or OEF (P > .05). Among 2-ventricle patients, total support time was not a significant predictor of relative changes in CMRO(2) or CBF (P > .05), although longer total support time was associated significantly with greater increases in relative change of postoperative OEF (P = .008).

CONCLUSIONS

Noninvasive diffuse optical techniques were used to quantify postoperative relative changes in CMRO(2), CBF, and OEF for the first time in this observational pilot study. Pilot data suggest that surgical duration does not account for observed variability in the relative change in CMRO(2), and that more comprehensive clinical studies using the new technology are feasible and warranted to elucidate these issues further.

Cochlear Dysfunction in Children following Cardiac Bypass Surgery

Background. Sensorineural hearing loss after procedures including extracorporeal circulation and hypothermia is greater than general population. Mild hypothermia has a protective role on cochlea; however, deep hypothermia may result in cochlear injury. This research aimed at assessing auditory function in children after open heart surgery in relation to different hypothermic techniques. Subjects and Methods. Forty children with acyanotic heart diseases who underwent open heart surgery were included: group I: twenty patients subjected to mild hypothermia (33° to 37°C), group II: twenty patients subjected to moderate hypothermia (28° to 32°C). Audiological assessment included basic evaluation and otoacoustic emissions. Results. Both groups had distortion-product otoacoustic emissions (DPOAEs) amplitude >3 dB SPL at all frequencies. However, group II showed lower amplitude at overall and at high frequencies (4.416–8.837 KHz) than group I. Transient evoked otoacoustic emissions (TEOAEs) showed partial pass in three patients of group I (15%) and in 15 patients of group II (75%). Moreover, group II showed statistical significant reduction in overall TEOAEs amplitude as well as at high frequencies (2–4 KHz). Conclusions. Patients exposed to moderate hypothermic technique had subtle cochlear dysfunction. Otoacoustic emissions should be used for early detection of subtle cochlear dysfunction in operated cardiac children.

Concomitant aortic valve and ascending aorta replacement with moderate hypothermic circulatory arrest to treat an aortic bicuspid valve with post-stenotic dilatation

We recommend concomitant surgery for aortic valve replacement (AVR) and ascending aortic replacement using moderate hypothermic circulatory arrest (CA) for post-stenotic dilatation complicated by an aortic bicuspid valve. Cardiopulmonary bypass (CPB) was established from the right atrium to the dilated ascending aorta. As soon as the rectal temperature decreased to 28 °C, CA was commenced and the open distal anastomosis of a polyester prosthesis, without any cerebral perfusion, was completed. AVR was then carried out during rapid re-warming with CPB using a side arm of the prosthesis. This procedure exhibited safe and satisfactory results. There are many benefits of carrying out the procedure in this way; it avoids the requirement for cannulation to a calcified aortic arch, provides a good operative field, for an easier distal anastomosis and suturing at the valve site, and reduces the risk of further dilatation or dissection of the residual ascending aorta in the later phase.

SjO2/SvO2 correlation during pediatric cardiac surgery with cardiopulmonary bypass

OBJECTIVES

To compare the SjO2 (cerebral oxygenation indicator) and SvO2 (cardiac output indicator) during pediatric cardiac surgery with cardiopulmonary bypass (CPB).

METHODS

Retrospective study. Data of SjO2 and SvO2 measured simultaneously at critical time periods during cardiac surgery with CPB were analyzed by the Spearman correlation test and Bland- Altman plot.

RESULTS

Regression analysis of the pooled data showed poor correlation between SjO2 and SvO2 (r²=0.14, P=0.03) and Bland- Altman plot had a high bias (-7.9), indicating independency of the two variables. SjO2<50% (indicative of cerebral ischemia-hypoxia) were observed in 50% of the measurements after rewarming during hypothermic CPB.

CONCLUSIONS

SvO2 is not a good predictor of SjO2 during pediatric cardiac surgery with CPB, and low SjO2 can be undetected measuring SvO2 only.

BRAIN TEMPERATURE DISTRIBUTION DURING DEEP HYPOTHERMIC CIRCULATORY ARREST IN HUMANS

This paper analyzes the effect of different cooling and rewarming strategies on the brain temperature distribution before and after circulatory arrest in adults and children. The temperature variations during systemic cooling, circulatory arrest, and rewarming are calculated using a thermal model that incorporates physiological parameters. The calculations presented here explain why sometimes hypothermia does not show the expected neuroprotective effect.

This work shows the importance of departing from a steady temperature distribution when using deep hypothermic circulatory arrest. In the calculations, the external cooling conditions of the head are varied, and it is observed that hypothermic cardiopulmonary bypass (CPB) together with external head cooling help reduce the temperature gradients within the head during periods of reduced blood flow, and reduces the temperature increase in the deep tissue produced by the residual cerebral metabolic activity. The results presented here agree with previous experimental observations1–3regarding the duration of systemic cooling using CPB.

BRAIN TEMPERATURE CALCULATIONS FOR SWINE USING EXPERIMENTAL MEASUREMENTS OF CEREBRAL BLOOD FLOW

In this study, numerical simulations are performed to analyze the brain temperature reduction in swine during selective head cooling, whole body cooling or while the animals experience ischemia. Brain temperature is calculated using a time dependent thermal model that incorporates available experimental measurements of the rectal temperature, the cerebral blood flow and the cerebral metabolic rate of oxygen consumption.

The calculated temperature distribution is validated against the in vivo temperature measurements recorded during the different experiments. These comparisons help to better understand the relations between brain temperature, blood flow and metabolic activity, which are essential to successfully apply hypothermia in the treatment of brain injury.

The calculations presented here reproduce the temperature behavior observed in all the experiments considered. It is observed that the arterial temperature and the cerebral metabolic rate are important parameters that affect the deep tissue temperature. It is also concluded that the accurate knowledge of parameters such as the skin and bone thermal conductivity are necessary for effective modeling.

Recommendations for haemodynamic and neurological monitoring in repair of acute type a aortic dissection

During treatment of acute type A aortic dissection there is potential for both pre- and intra-operative malperfusion. There are a number of monitoring strategies that may allow for earlier detection of potentially catastrophic malperfusion (particularly cerebral malperfusion) phenomena available for the anaesthetist and surgeon. This review article sets out to discuss the benefits of the current standard monitoring techniques available as well as desirable/experimental techniques which may serve as adjuncts in the monitoring of these complex patients.

Warm pediatric cardiac surgery: European experience

Cold pediatric cardiac surgery has been a dogma for 50 years. However, the beneficial effects of cold perfusion are counterbalanced by the drawbacks of hypothermia. Thus, we propose a major paradigm shift from hypothermic surgery to warm perfusion and intermittent warm blood cardioplegia. This approach gives satisfactory results even with prolonged aortic crossclamp times. The major advantages are reduced time to extubation and shorter intensive care unit stay. Warm pediatric surgery is an anecdotal phenomenon no more; over 10,000 procedures have been carried out in Europe. All types of cardiopathy have been treated, including arterial switch, total pulmonary anomalous venous return, interruption of the aortic arch, and hypoplastic left heart syndrome. Once surgeons decide to shift from hypothermia to normothermia, they never decide to shift back to hypothermia. This fact is evidence of the satisfactory clinical outcome obtained with this technique. The technique and the composition of microplegia is identical in all European centers, the only variable factor being the interval between microplegia injections, which varies from 10 to 25 min. We hope that the increasing interest in pediatric warm surgery will hearten new candidates.