Carbon dioxide—a complex gas in a complex circulation: Its effects on systemic hemodynamics and oxygen transport, cerebral, and splanchnic circulation in neonates after the Norwood procedure

Postnatal Cerebral Hemodynamics and Placental Vascular Malperfusion Lesions in Neonates With Congenital Heart Disease

BACKGROUND

Neonates with congenital heart disease (CHD) have smaller brain volume at birth. High rates of placental vascular malperfusion lesions may play a role in disrupted brain development.

METHODS

This is a single-center retrospective cohort study of infants born between 2010 and 2019 who were diagnosed with a major cardiac defect requiring surgery in the first year of life. Doppler ultrasound RI of the middle cerebral artery (MCA) and anterior cerebral artery were calculated within the first 72 hours of life. Placentas were evaluated using a standardized approach.

RESULTS

Over the study period, there were 52 patients with hypoplastic left heart syndrome (HLHS), 22 with single-ventricle right ventricular outflow tract obstruction (SV-RVOTO), 75 with a two-ventricle cardiac defect (2V), and 25 with transposition of the great arteries (TGA). MCA Doppler RI were significantly higher for all subgroups of CHD compared with control subjects (0.68 ± 0.11 in control subjects compared with 0.78 ± 0.13 in HLHS, P = 0.03; 0.77 ± 0.10 in SV-RVOTO, P = 0.002; 0.78 ± 0.13 in 2V, P = 0.03; and 0.80 ± 0.14 in TGA; P = 0.001) with the highest average MCA RI in the TGA group. In subgroup analyses, placental fetal vascular malperfusion in the 2V group was associated with higher MCA RI, but this relationship was not present in other subgroups, nor in regards to maternal vascular malperfusion.

CONCLUSIONS

Major forms of CHD are associated with significantly higher cerebral artery RI postnatally, but placental vascular malperfusion lesions may not contribute to this hemodynamic adaptation.

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.

Postnatal cerebral hemodynamics in infants with severe congenital heart disease: a scoping review

Patients with severe congenital heart disease (CHD) are at risk for impaired neurodevelopment. Cerebral blood supply may be diminished by congenital anomalies of cardiovascular anatomy and myocardial function. The aim of this scoping review was to summarize the current knowledge on cerebral hemodynamics in infants with severe CHD. A scoping review was performed. Five databases were searched for articles published from 01/1990 to 02/2022 containing information on cerebral hemodynamics assessed by neuroimaging methods in patients with severe CHD within their first year of life. A total of 1488 publications were identified, of which 26 were included. Half of the studies used Doppler ultrasound, and half used magnetic resonance imaging techniques. Studies focused on preoperative findings of cerebral hemodynamics, effects of surgical and conservative interventions, as well as on associations between cerebral hemodynamics and brain morphology or neurodevelopment. Cerebral perfusion was most severely affected in patients with single ventricle and other cyanotic disease. Neuroimaging methods provide a large variety of information on cerebral hemodynamics. Nevertheless, small and heterogeneous cohorts complicate this field of research. Further studies are needed to improve our understanding of the link between CHD and altered cerebral hemodynamics to optimize neuroprotection strategies. IMPACT: Postnatal cerebral hemodynamics are altered in infants with congenital heart disease (CHD) as compared to healthy controls, especially in most severe types such as single ventricle or other cyanotic CHD. Associations of these alterations with brain volume and maturation reveal their clinical relevance. Research in this area is limited due to the rarity and heterogeneity of diagnoses. Furthermore, longitudinal studies have rarely been conducted. Further effort is needed to better understand the deviation from physiological cerebral perfusion and its consequences in patients with CHD to optimize neuroprotection strategies.

Effects of Arterial Carbon Dioxide Tension on Cerebral and Somatic Regional Tissue Oxygenation and Blood Flow in Neonates After the Norwood Procedure With Deep Hypothermic Cardiopulmonary Bypass

Neonates undergoing the Norwood procedure for hypoplastic left heart syndrome are at higher risk of impaired systemic oxygen delivery with resultant brain, kidney, and intestinal ischemic injury, shock, and death. Complex developmental, anatomic, and treatment-related influences on cerebral and renal-somatic circulations make individualized treatment strategies physiologically attractive. Monitoring cerebral and renal circulations with near infrared spectroscopy can help drive rational therapeutic interventions. The primary aim of this study was to describe the differential effects of carbon dioxide tension on cerebral and renal circulations in neonates after the Norwood procedure. Using a prospectively-maintained database of postoperative physiologic and hemodynamic parameters, we analyzed the relationship between postoperative arterial carbon dioxide tension and tissue oxygen saturation and arteriovenous saturation difference in cerebral and renal regions, applying univariate and multivariate multilevel mixed regression techniques. Results were available from 7,644 h of data in 178 patients. Increases in arterial carbon dioxide tension were associated with increased cerebral and decreased renal oxygen saturation. Differential changes in arteriovenous saturation difference explained these effects. The cerebral circulation showed more carbon dioxide sensitivity in the early postoperative period, while sensitivity in the renal circulation increased over time. Multivariate models supported the univariate findings and defined complex time-dependent interactions presented graphically. The cerebral and renal circulations may compete for blood flow with critical limitations of cardiac output. The cerebral and renal-somatic beds have different circulatory control mechanisms that can be manipulated to change the distribution of cardiac output by altering the arterial carbon dioxide tension. Monitoring cerebral and renal circulations with near infrared spectroscopy can provide rational physiologic targets for individualized treatment.

Clinical applications of transcranial Doppler in non-trauma critically ill children: a scoping review

BACKGROUND

Many applications of transcranial Doppler (TCD) as a diagnosis or monitoring tool have raised interest in the last decades. It is important that clinicians know when and how to perform TCD in this population, what parameter to assess and monitor and how to interpret it.

OBJECTIVE

This review aims to describe the emerging clinical applications of TCD in critically ill children excluding those suffering from trauma.

METHODS

Databases Web of Science, Cochrane and PubMed were searched in May 2020. We considered all publications since the year 2000 addressing the use of TCD as a prognostic, diagnostic or follow-up tool in children aged 0 to 15 years admitted to intensive care or emergency units, excluding neonatology and traumatic brain injury. Two independent reviewers selected 82 abstracts and full-text articles from the 2011 unique citations identified at the outset.

RESULTS

TCD provides crucial additional information at bedside about cerebrovascular hemodynamics. Many clinical applications include the diagnosis and management of various medical and surgical neurologic conditions (central nervous system infections, arterial ischemic stroke, subarachnoid hemorrhage and vasospasm, brain death, seizures, metabolic disease, hydrocephalus) as well as monitoring the impact systemic conditions on brain perfusion (hemodynamic instability, circulatory assistance).

CONCLUSION

To conclude, TCD has become an invaluable asset for non-invasive neuromonitoring in critically ill children excluding those suffering from trauma. However, the scope of TCD remains unclearly defined yet and reference values in critically ill children are still lacking.

The perinatal transition and early neonatal period in hypoplastic left heart syndrome is associated with reduced systemic and cerebral perfusion

BACKGROUND

The impact of the striking perinatal circulatory changes on blood flow distribution have not to date been well-examined in hypoplastic left heart syndrome (HLHS). This study aims to document perinatal redistribution of cardiac output in HLHS compared to healthy controls, to further understand the impact of perinatal transition on cerebral and systemic blood flow.

METHODS

Prospectively recruited HLHS cases (n=31) and healthy controls (n=19) underwent serial echocardiography from late fetal stages to 96 hours after birth. Combined cardiac output (CCO), systemic, pulmonary, cerebrovascular and splanchnic flow data were compared between HLHS neonates and controls, and the impact of vasoactive support and positive pressure ventilation (PPV) in HLHS patients examined.

RESULTS

In late gestation, CCO was similar between HLHS and controls, whereas middle cerebral artery (MCA) pulsatility index (PI) in HLHS was consistent with low cerebral vascular resistance. In the 96 hours after birth, CCO and pulmonary blood flow progressively increased in HLHS compared to controls (p<0.001), and CCO was further increased in HLHS neonates receiving vasoactive support (p=0.01). HLHS neonates had reduced systemic and 6-24hr superior vena cava (SVC) flow when compared to controls (p<0.001). Low systemic flow was further suggested by increased MCA and celiac artery PI at 6 - 48 hours in HLHS neonates (p<0.001). Systemic and SVC flow did not differ between those with and without vasoactive support.

CONCLUSION

We provide quantitative echocardiographic evidence associating impaired cerebral and systemic blood flow with perinatal hemodynamic changes in the preoperative HLHS neonate.

Effects of different ventilation on cerebral oxygen saturation and cerebral blood flow before and after modified ultrafiltration in infants during ventricular septal defect repair

OBJECTIVE

To analyse the changes of different ventilation on regional cerebral oxygen saturation and cerebral blood flow in infants during ventricular septal defect repair.

METHODS

Ninety-two infants younger than 1 year were enrolled in the study. End-expiratory tidal pressure of carbon dioxide was maintained at 40-45 and 35-39 mmHg in relative low and high ventilation groups. Regional cerebral oxygen saturation and flow velocity of the middle cerebral artery were recorded after anaesthesia (T0), cut pericardium (T1), separation from cardiopulmonary bypass (T2), the end of modified ultrafiltration, (T3) and at the end of operation (T4).

RESULTS

The relative low ventilation group exhibited a significantly high regional cerebral oxygen saturation at each time point except for T2 (T0:77 ± 4, T1:76 ± 5, T3:76 ± 8, T4:76 ± 8, respectively, p < 0.001). Flow velocity of the middle cerebral artery in the relative low ventilation group was higher compared to the relative high ventilation group at each time point except for T2 (T0:53 ± 14, T1:54 ± 15, T3:53 ± 17, T4:52 ± 16, respectively, p < 0.001). Between the two groups, T2 showed the lowest middle cerebral artery flow velocity (relative low ventilation: 39 ± 15, relative high ventilation: 39 ± 11, p < 0.001).

CONCLUSION

The infants' regional cerebral oxygen saturation and middle cerebral artery flow velocity performed better in the range of 40-45 mmHg end-expiratory tidal pressure of carbon dioxide during CHD surgery. Modified ultrafiltration increased cerebral oxygen saturation. It was important to regulate ventilation in order to balance cerebral oxygen in infants.

Effects of hypercarbia on arterial oxygenation during one-lung ventilation: prospective randomized crossover study

Background

This study aimed to evaluate the effects of hypercarbia on arterial oxygenation during one-lung ventilation (OLV).

Methods

Fifty adult patients undergoing elective video-assisted thoracoscopic lobectomy or pneumonectomy were enrolled. Group I patients (n = 25) were first maintained at normocarbia (PaCO₂: 38–42 mmHg) for 30 min and then at hypercarbia (45–50 mmHg). In Group II patients (n = 25), PaCO₂ was maintained in the reverse order. Arterial oxygen partial pressure (PaO₂), respiratory variables, hemodynamic variables, and hemoglobin concentration were compared during normocarbia and hypercarbia. Arterial O₂ content and O₂ delivery were calculated.

Results

PaO₂ values during normocarbia and hypercarbia were 66.5 ± 10.6 and 79.7 ± 17.3 mmHg, respectively (mean difference: 13.2 mmHg, 95% CI for difference of means: 17.0 to 9.3, P < 0.001). SaO₂ values during normocarbia and hypercarbia were 92.5 ± 4.8% and 94.3 ± 3.1% (P = 0.009), respectively. Static compliance of the lung (33.0 ± 5.4 vs. 30.4 ± 5.3 ml/cmH₂O, P < 0.001), arterial O₂ content (15.4 ± 1.4 vs. 14.9 ± 1.5 ml/dl, P < 0.001) and O₂ delivery (69.9 ± 18.4 vs. 65.1 ± 18.1 ml/min, P < 0.001) were significantly higher during hypercarbia than during normocarbia.

Conclusions

Hypercarbia increases PaO₂ and O₂ carrying capacity and improves pulmonary mechanics during OLV, suggesting that it may help manage oxygenation during OLV. Therefore, permissive hypercarbia may be a simple and valuable modality to manage arterial oxygenation during OLV.

The effects of ventilation on left-to-right shunt and regional cerebral oxygen saturation: a self-controlled trial

BACKGROUND

Increase of pulmonary vascular resistance (PVR) is an efficient method of modulating pulmonary and systemic blood flows (Qp/Qs) for patients with left-to-right (L-R) shunt, and is also closely associated with insufficient oxygen exchange for pulmonary hypoperfusion. So that it might be a preferred regime of maintaining arterial partial pressure of carbon dioxide tension (PaCO₂) within an optimal boundary via ventilation management in congenital heart disease (CHD) patients for the inconvenient measure of the PVR and Qp/Qs. However, the appropriate range of PaCO₂ and patient-specific mechanical ventilation settings remain controversial for CHD children with L-R shunt.

METHODS

Thirty-one pediatric patients with L-R shunt, 1-6 yr of age, were included in this observation study. Patients were ventilated with tidal volume (V_T) of 10, 8 and 6 ml/kg in sequence, and 15 min stabilization period for individual V_T. The velocity time integral (VTI) of L-R shunt, pulmonary artery (PA) and descending aorta (DA) were measured with transesophageal echocardiography (TEE) after an initial 15 min stabilization period for each V_T, with arterial blood gas analysis. Near-infrared spectroscopy sensor were positioned on the surface of the bilateral temporal artery to monitor the change in regional cerebral oxygen saturation (rScO₂).

RESULTS

PaCO₂ was 31.51 ± 0.65 mmHg at V_T 10 ml/kg vs. 37.15 ± 0.75 mmHg at V_T 8 ml/kg (P < 0.03), with 44.24 ± 0.99 mmHg at V_T 6 ml/kg significantly higher than 37.15 ± 0.75 mmHg at V_T 8 ml/kg. However, PaO₂ at a V_T of 6 ml/kg was lower than that at a V_T of 10 ml/kg (P = 0.05). Meanwhile, 72% (22/31) patients had PaCO₂ in the range of 40-50 mmHg at V_T 6 ml/kg. VTI of L-R shunt and PA at V_T 6 ml/kg were lower than that at V_T of 8 and 10 ml/kg (P < 0.05). rScO₂ at a V_T of 6 ml/kg was higher than that at a V_T of 8 and 10 ml/kg (P < 0.05), with a significantly correlation between rScO₂ and PaCO₂ (r = 0.53). VTI of PA in patients with defect diameter > 10 mm was higher that that in patients with defect diameter ≤ 10 mm.

CONCLUSIONS

Maintaining PaCO₂ in the boundary of 40-50 mmHg with V_T 6 ml/kg might be a feasible ventilation regime to achieve better oxygenation for patients with L-R shunt. Continue raising PaCO₂ should be careful.

TRAIL REGISTRATION

Clinical Trial Registry of China (http://www.chictr.org.cn) identifier: ChiCTR-OOC-17011338 , prospectively registered on May 9, 2017.

Cardiopulmonary Resuscitation in Infants and Children With Cardiac Disease: A Scientific Statement From the American Heart Association

Cardiac arrest occurs at a higher rate in children with heart disease than in healthy children. Pediatric basic life support and advanced life support guidelines focus on delivering high-quality resuscitation in children with normal hearts. The complexity and variability in pediatric heart disease pose unique challenges during resuscitation. A writing group appointed by the American Heart Association reviewed the literature addressing resuscitation in children with heart disease. MEDLINE and Google Scholar databases were searched from 1966 to 2015, cross-referencing pediatric heart disease with pertinent resuscitation search terms. The American College of Cardiology/American Heart Association classification of recommendations and levels of evidence for practice guidelines were used. The recommendations in this statement concur with the critical components of the 2015 American Heart Association pediatric basic life support and pediatric advanced life support guidelines and are meant to serve as a resuscitation supplement. This statement is meant for caregivers of children with heart disease in the prehospital and in-hospital settings. Understanding the anatomy and physiology of the high-risk pediatric cardiac population will promote early recognition and treatment of decompensation to prevent cardiac arrest, increase survival from cardiac arrest by providing high-quality resuscitations, and improve outcomes with postresuscitation care.

Evolution of the concept of oxygen transport in the critically ill, with a focus on children after cardiopulmonary bypass

The concept of oxygen transport, defined as the relation between oxygen consumption (VO2) and delivery (DO2), is of fundamental importance in critically ill patients. The past 200 years have witnessed a stepwise progressive improvement in the understanding of pathophysiological disturbances in the balance of DO2 and VO2 in critically ill patients including those after cardiopulmonary bypass surgery. Intermittent spectacular technological achievements have accelerated the rate of progress. Therapeutic advances have been particularly impressive during the recent decades. Examination of the relation between DO2 and VO2 provides a useful framework around which the care of the critically ill may be developed. Until now, only a few groups have used this framework to examine children after cardiopulmonary bypass. The key topics that will be covered in this review article are the evolution of the concept from its early development to its present, increasingly sophisticated, role in the management of critically ill patients, with a focus on children after cardiopulmonary bypass surgery.

Effects of Hypercapnia on Acute Cellular Rejection after Lung Transplantation in Rats

BACKGROUND

Hypercapnia alleviates pulmonary ischemia-reperfusion injury, regulates T lymphocytes, and inhibits immune reaction. This study aimed to evaluate the effect of hypercapnia on acute cellular rejection in a rat lung transplantation model.

METHODS

Recipient rats in sham-operated (Wistar), isograft (Wistar to Wistar), and allograft (Sprague-Dawley to Wistar) groups were ventilated with 50% oxygen, whereas rats in the hypercapnia (Sprague-Dawley to Wistar) group were administered 50% oxygen and 8% carbon dioxide for 90 min during reperfusion (n = 8). Recipients were euthanized 7 days after transplantation.

RESULTS

The hypercapnia group showed a higher oxygenation index (413 ± 78 vs. 223 ± 24), lower wet weight-to-dry weight ratio (4.23 ± 0.54 vs. 7.04 ± 0.80), lower rejection scores (2 ± 1 vs. 4 ± 1), and lower apoptosis index (31 ± 6 vs. 57 ± 4) as compared with the allograft group. The hypercapnia group showed lower CD8 (17 ± 4 vs. 31 ± 3) and CD68 (24 ± 3 vs. 43 ± 2), lower CD8 T cells (12 ± 2 vs. 35 ± 6), and higher CD4/CD8 ratio (2.2 ± 0.6 vs. 1.1 ± 0.4) compared to the allograft group. Tumor necrosis factor-α (208 ± 40 vs. 292 ± 49), interleukin-2 (30.6 ± 6.7 vs. 52.7 ± 8.3), and interferon-γ (28.1 ± 4.9 vs. 62.7 ± 10.1) levels in the hypercapnia group were lower than those in allograft group. CD4, CD4 T cells, and interleukin-10 levels were similar between groups.

CONCLUSIONS

Hypercapnia ameliorated acute cellular rejection in a rat lung transplantation model.

Extubation Failure Is Associated With Increased Mortality Following First Stage Single Ventricle Reconstruction Operation

OBJECTIVES

To identify the prevalence, causes, risk factors, and outcomes associated with extubation failure following first stage single ventricle reconstruction surgery.

DESIGN

Retrospective cohort analysis of neonates who underwent a first stage single ventricle reconstruction operation. Extubation failure was defined as endotracheal reintubation within 48 hours of first extubation attempt.

SETTING

The Royal Children's Hospital, Melbourne.

PATIENTS

Data were collected for all infants who underwent a Norwood or Damus-Kaye-Stansel procedure between 2005 and 2014 at our institution.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Extubation failure occurred in 23 of 137 neonates (16.8%; 95% CI, 11.0-24.1%) who underwent a trial of extubation. Overall, 42 patients (30.7%) were extubated to room air, 88 (64.2%) to nasal continuous positive airway pressure, and seven (5.1%) to high-flow nasal cannulae, though there was no major difference in extubation failure rates between these three groups (p = 0.37). The median time to reintubation was 16.7 hours (interquartile range, 3.2-35.2), and male infants failed extubation more frequently (63.2% vs 87.0%; p = 0.02), although age, gestation, weight, cardiac diagnosis (hypoplastic left heart syndrome vs other single ventricle conditions), shunt type (modified Blalock-Taussig vs right ventricle-pulmonary artery shunt), intraoperative perfusion times, preextubation mechanical ventilation duration, preextubation acid-base status, and postoperative fluid balance were not related to extubation outcome. Infants who failed extubation had a higher intensive care mortality (19.4% vs 3.5%; p = 0.03) and in-hospital mortality (30.4% vs 6.1%; p < 0.001).

CONCLUSIONS

There is a high prevalence of extubation failure following first stage single ventricle reconstruction, and this is associated with considerably worse patient outcomes. The high prevalence and also the wide variation in rates of extubation failure in reported literature provide with an opportunity for implementation of quality assurance activities to minimize this complication and improve outcomes.

Multisite Tissue Oxygenation Monitoring Indicates Organ-Specific Flow Distribution and Oxygen Delivery Related to Low Cardiac Output in Preterm Infants With Clinical Sepsis

OBJECTIVES

Cardiac output may be compromised in preterm infants with sepsis. Whether low cardiac output is associated with low tissue oxygen supply in these patients is unclear. The aim of the current study was to assess the association between cardiac output, assessed by echocardiography, and tissue oxygenation, measured with multisite near-infrared spectroscopy, in a cohort of preterm infants with clinical sepsis.

DESIGN

Prospective observational cohort study.

SETTING

Level III neonatal ICU.

PATIENTS

Twenty-four preterm infants (gestational age < 32 wk) with clinical sepsis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Clinical and echocardiographic assessment of hemodynamics was performed within 48 hours of sepsis workup and repeated at least 24 hours later. We measured cerebral, renal, and intestinal tissue oxygen saturation using near-infrared spectroscopy during an hour of stable measurements directly preceding or following echocardiography and calculated fractional tissue oxygen extraction in each tissue. We determined Spearman correlation coefficients between fractional tissue oxygen extraction and right ventricular output corrected for patent foramen ovale flow, left ventricular output corrected for ductus arteriosus flow, and superior vena cava flow. Right ventricular output corrected for patent foramen ovale and left ventricular output corrected for ductus arteriosus flow both correlated significantly with intestinal fractional tissue oxygen extraction (ρ, -0.700; p = 0.036 and ρ, -0.604; p = 0.029, respectively). In contrast, no significant correlations were found between cardiac output measurements and cerebral and renal fractional tissue oxygen extraction, respectively. Changes in cardiac output measurements were not associated with observed changes in fractional tissue oxygen extraction values.

CONCLUSIONS

Right ventricular output corrected for patent foramen ovale and left ventricular output corrected for ductus arteriosus flow, indicators of systemic blood flow in preterm infants with shunts, were negatively associated with intestinal fractional tissue oxygen extraction, but not with renal and cerebral fractional tissue oxygen extraction. These findings suggest that during low output states due to clinical sepsis intestinal perfusion is most at risk.

Near-infrared spectroscopy: exposing the dark (venous) side of the circulation

The safety of anesthesia has improved greatly in the past three decades. Standard perioperative monitoring, including pulse oximetry, has practically eliminated unrecognized arterial hypoxia as a cause for perioperative injury. However, most anesthesia-related cardiac arrests in children are now cardiovascular in origin, and standard monitoring is unable to detect many circulatory abnormalities. Near-infrared spectroscopy provides noninvasive continuous access to the venous side of regional circulations that can approximate organ-specific and global measures to facilitate the detection of circulatory abnormalities and drive goal-directed interventions to reduce end-organ ischemic injury.

Measurement of systemic oxygen consumption in patients during extracorporeal membrane oxygenation — description of a new method and the first clinical observations

Background:

Extracorporeal membrane oxygenation (ECMO) provides temporary life-saving support for patients with severe cardiac failure, but is associated with significant morbidity and mortality. While ECMO enables oxygen delivery (DO2), little is known about oxygen consumption (VO2), largely due to technical difficulties. We aimed to introduce the adaptation of respiratory mass spectrometry to measure VO2 in patients during ECMO and to use this unique model to determine the pathological dependency of VO2 on DO2 in humans.

Methods and Patients:

Respiratory mass spectrometry remains the ‘state-of-the-art’ method, allowing the highly sensitive and rapid measurement of VO2 in critically ill patients. The principle and design of the respiratory mass spectrometer are described, together with the setting up of this machine with the ECMO oxygenator and the native lungs of the patients. In two patients with severe dilated cardiomyopathy and little cardiac contraction, the decrease in pump flow and, hence, DO2 by 20% was associated with a decrease in VO2 by 5% and 8%, respectively, whereas the increase in pump flow was not associated with any significant change in VO2.

Conclusions:

The direct measurement of VO2 by respiratory mass spectrometry in ECMO patients provides a unique technique for clinical research on the metabolism and VO2-DO2 relationship in this special group of critically ill patients. Our pilot study is the first to demonstrate a pathological dependency of VO2 on DO2 in humans. Further studies are warranted with this technique to examine the changes and the factors affecting systemic oxygen transport in patients during ECMO.

pH effects on cardiac function and systemic vascular resistance in preterm infants

OBJECTIVE

To investigate the effect of pH on cardiac function and systemic vascular resistance (SVR) in preterm infants.

STUDY DESIGN

In this prospective observational study, we evaluated hemodynamically stable, ≤ 30 weeks' gestation preterm infants during the first 2 postnatal weeks. Cardiac function was assessed by echocardiography at the time of arterial blood draw for clinically indicated blood gas analysis. Data were separately analyzed for the transitional (days 1-3) and post-transitional (days 4-14) periods.

RESULTS

We evaluated 147 pairs of arterial blood gases and echocardiograms in 29 preterm neonates (gestational age = 26.2 ± 1.5 weeks). Arterial pH ranged from 7.02-7.46. There was no linear relationship between pH and shortening fraction or stress-velocity index in transitional or post-transitional periods. We found a weak negative linear relationship between pH and left ventricular output and a positive linear relationship between pH and SVR only during the post-transitional period. These relationships were maintained after adjustment for the degree of base deficit. Arterial CO2 had effects similar to pH on myocardial function.

CONCLUSIONS

Unlike adults, myocardial contractility remains relatively unaffected by acidosis even at pH values close to 7.00 in hemodynamically stable preterm neonates during the first 2 postnatal weeks. However, as in adults, worsening acidosis in preterm neonates after the immediate transitional period is associated with a decrease in SVR along with an increase in left ventricular output. Thus, although myocardial contractility remains unaffected in preterm neonates during the first 2 postnatal weeks, the vascular response to acidosis undergoes a relatively rapid postnatal maturational process.

Accurate measurement of oxygen consumption in children undergoing cardiac catheterization

Oxygen consumption (VO(2) ) is an important part of hemodynamics using the direct Fick principle in children undergoing cardiac catheterization. Accurate measurement of VO(2) is vital. Obviously, any error in the measurement of VO(2) will translate directly into an equivalent percentage under- or overestimation of blood flows and vascular resistances. It remains common practice to estimate VO(2) values from published predictive equations. Among these, the LaFarge equation is the most commonly used equation and gives the closest estimation with the least bias and limits of agreement. However, considerable errors are introduced by the LaFarge equation, particularly in children younger than 3 years of age. Respiratory mass spectrometry remains the "state-of-the-art" method, allowing highly sensitive, rapid and simultaneous measurement of multiple gas fractions. The AMIS 2000 quadrupole respiratory mass spectrometer system has been adapted to measure VO(2) in children under mechanical ventilation with pediatric ventilators during cardiac catheterization. The small sampling rate, fast response time and long tubes make the equipment a unique and powerful tool for bedside continuous measurement of VO(2) in cardiac catheterization for both clinical and research purposes.

Systemic oxygen transport derived by using continuous measured oxygen consumption after the Norwood procedure-an interim review

The balance between systemic O(2)consumption (VO(2)) and O(2)delivery (DO(2)) is impaired in children after cardiopulmonary bypass surgery, with decreased DO(2)and increased VO(2). The major goal, and the major challenge, of postoperative management has been to match DO(2)to VO(2)in order to sustain cellular metabolism, particularly in neonates after the Norwood procedure. While much effort has been put into augmenting cardiac output and DO(2), VO(2)remains largely ignored. Respiratory mass spectrometry allows the precise and continuous measurement of VO(2). Measured VO(2), using the direct Fick principle, allows for the calculation of each element of systemic O(2)transport in the complex Norwood circulation. The actual measurements of O(2)transport have allowed us, in the past five years or so, to extensively investigate the Norwood physiology in terms of the VO(2)-DO(2)relationship and the factors affecting it in clinical treatments. Therefore, the first objective of this article is to introduce the technique of respiratory mass spectrometry and its adaption to measure VO(2)across paediatric ventilators with continuous flow. The second objective is to give an interim review of the main findings in our studies on systemic O(2)transport in 17 neonates in the first 72 h after the Norwood procedure. These findings include the profiles of systemic O(2)transport, the important contribution of VO(2)to the impaired balance of O(2)transport and the complex effects of some routine clinical treatments on the VO(2)-DO(2)relationship (including catecholamines, PaCO(2), Mg(2+)and hyperglycaemia, as well as patient-specific anatomical variations). The influence of systemic O(2)transport on cerebral oxygenation is also introduced. This information may help us to refine postoperative management in neonates after the Norwood procedure. Our initial studies mark the end of the beginning, but much is yet explored. Ultimately, the resultant improved systemic and regional O(2)transport in the early postoperative period may have an important impact on long-term outcomes, thereby improving the quality of life for these vulnerable children.

Should what we know about neurobehavioral development, complex congenital heart disease, and brain maturation affect the timing of corrective cardiac surgery?

Despite remarkable improvements in perioperative care, adverse neurobehavioral outcomes following neonatal and infant cardiac surgery are commonplace and are associated with substantial morbidity. It is becoming increasingly clear that complex congenital heart disease is associated with both abnormalities in neuroanatomic development and a delay in fetal brain maturation. Substantial cerebral ischemic/hypoxic injury has been detected in neonates with complex congenital heart disease both prior to and following corrective cardiac surgery. The brain of the neonate with complex congenital heart disease appears to be uniquely vulnerable to the types of ischemic/hypoxic injury associated with perioperative care. It remains to be determined whether delaying surgical correction to allow for brain maturation will be associated with improvements in neurobehavioral outcomes.

Advances in near-infrared spectroscopy to study the brain of the preterm and term neonate

This article reviews tissue oximetry and imaging to study the preterm and newborn infant brain by near-infrared spectroscopy. These two technologies are now advanced; nearly 100 reports on their use in newborn infants have been published, and commercial instruments are available. The precision of oximetry, however, is a limitation for its clinical use of assessing cerebral oxygenation. Imaging of brain function needs very well defined protocols for sensory stimulation as well as signal analysis to provide meaningful results.