Severe acidosis and subsequent neurologic status

Umbilical cord pH, blood gases, and lactate at birth: normal values, interpretation, and clinical utility

Normal birth is a eustress reaction, a beneficial hedonic stress with extremely high catecholamines that protects us from intrauterine hypoxia and assists in the rapid shift to extrauterine life. Occasionally the cellular O2 requirement becomes critical and an O2 deficit in blood (hypoxemia) may evolve to a tissue deficit (hypoxia) and finally a risk of organ damage (asphyxia). An increase in H+ concentration is reflected in a decrease in pH, which together with increased base deficit is a proxy for the level of fetal O2 deficit. Base deficit (or its negative value, base excess) was introduced to reflect the metabolic component of a low pH and to distinguish from the respiratory cause of a low pH, which is a high CO2 concentration. Base deficit is a theoretical estimate and not a measured parameter, calculated by the blood gas analyzer from values of pH, the partial pressure of CO2, and hemoglobin. Different brands of analyzers use different calculation equations, and base deficit values can thus differ by multiples. This could influence the diagnosis of metabolic acidosis, which is commonly defined as a pH <7.00 combined with a base deficit ≥12.0 mmol/L in umbilical cord arterial blood. Base deficit can be calculated as base deficit in blood (or actual base deficit) or base deficit in extracellular fluid (or standard base deficit). The extracellular fluid compartment represents the blood volume diluted with the interstitial fluid. Base deficit in extracellular fluid is advocated for fetal blood because a high partial pressure of CO2 (hypercapnia) is common in newborns without concomitant hypoxia, and hypercapnia has a strong influence on the pH value, then termed respiratory acidosis. An increase in partial pressure of CO2 causes less increase in base deficit in extracellular fluid than in base deficit in blood, thus base deficit in extracellular fluid better represents the metabolic component of acidosis. The different types of base deficit for defining metabolic acidosis in cord blood have unfortunately not been noticed by many obstetrical experts and organizations. In addition to an increase in H+ concentration, the lactate production is accelerated during hypoxia and anaerobic metabolism. There is no global consensus on definitions of normal cord blood gases and lactate, and different cutoff values for abnormality are used. At a pH <7.20, 7% to 9% of newborns are deemed academic; at <7.10, 1% to 3%; and at <7.00, 0.26% to 1.3%. From numerous studies of different eras and sizes, it can firmly be concluded that in the cord artery, the statistically defined lower pH limit (mean -2 standard deviations) is 7.10. Given that the pH for optimal enzyme activity differs between different cell types and organs, it seems difficult to establish a general biologically critical pH limit. The blood gases and lactate in cord blood change with the progression of pregnancy toward a mixed metabolic and respiratory acidemia because of increased metabolism and CO2 production in the growing fetus. Gestational age-adjusted normal reference values have accordingly been published for pH and lactate, and they associate with Apgar score slightly better than stationary cutoffs, but they are not widely used in clinical practice. On the basis of good-quality data, it is reasonable to set a cord artery lactate cutoff (mean +2 standard deviations) at 10 mmol/L at 39 to 40 weeks' gestation. For base deficit, it is not possible to establish statistically defined reference values because base deficit is calculated with different equations, and there is no consensus on which to use. Arterial cord blood represents the fetus better than venous blood, and samples from both vessels are needed to validate the arterial origin. A venoarterial pH gradient of <0.02 is commonly used to differentiate arterial from venous samples. Reference values for pH in cord venous blood have been determined, but venous blood comes from the placenta after clearance of a surplus of arterial CO2, and base deficit in venous blood then overestimates the metabolic component of fetal acidosis. The ambition to increase neonatal hemoglobin and iron depots by delaying cord clamping after birth results in falsely acidic blood gas and lactate values if the blood sampling is also delayed. Within seconds after birth, sour metabolites accumulated in peripheral tissues and organs will flood into the central circulation and further to the cord arteries when the newborn starts to breathe, move, and cry. This influence of "hidden acidosis" can be avoided by needle puncture of unclamped cord vessels and blood collection immediately after birth. Because of a continuing anaerobic glycolysis in the collected blood, it should be analyzed within 5 minutes to not result in a falsely high lactate value. If the syringe is placed in ice slurry, the time limit is 20 minutes. For pH, it is reasonable to wait no longer than 15 minutes if not in ice. Routine analyses of cord blood gases enable perinatal audits to gain the wisdom of hindsight, to maintain quality assurance at a maternity unit over years by following the rate of neonatal acidosis, to compare results between hospitals on regional or national bases, and to obtain an objective outcome measure in clinical research. Given that the intrapartum cardiotocogram is an uncertain proxy for fetal hypoxia, and there is no strong correlation between pathologic cardiotocograms and fetal acidosis, a cord artery pH may help rather than hurt a staff person subjected to a malpractice suit based on undesirable cardiotocogram patterns. Contrary to common beliefs and assumptions, up to 90% of cases of cerebral palsy do not originate from intrapartum events. Future research will elucidate whether cell injury markers with point-of-care analysis will become valuable in improving the dating of perinatal injuries and differentiating hypoxic from nonhypoxic injuries.

Umbilical cord blood acid-base analysis at birth and long-term neurodevelopmental outcomes in children: a systematic review and meta-analysis

BACKGROUND

Umbilical cord blood acid-base sampling is routinely performed at many hospitals. Recent studies have questioned this practice and the association of acidosis with cerebral palsy.

OBJECTIVE

To investigate the associations between the results of umbilical cord blood acid-base analysis at birth and long-term neurodevelopmental outcomes and mortality in children.

SEARCH STRATEGY

We searched six databases using the search strategy: umbilical cord AND outcomes.

SELECTION CRITERIA

Randomised controlled trials, cohorts and case-control studies from high-income countries that investigated the association between umbilical cord blood analysis and neurodevelopmental outcomes and mortality from 1 year after birth in children born at term.

DATA COLLECTION AND ANALYSIS

We critically assessed the included studies, extracted data and conducted meta-analyses comparing adverse outcomes between children with and without acidosis, and the mean proportions of adverse outcomes. The certainty of evidence was assessed using the Grading of Recommendations, Assessment, Development and Evaluations approach.

MAIN RESULTS

We have very low confidence in the following findings: acidosis was associated with higher cognitive development scores compared with non-acidosis (mean difference 5.18, 95% CI 0.84-9.52; n = two studies). Children with acidosis also showed a tendency towards higher risk of death (relative risk [RR] 5.72, 95% CI 0.90-36.27; n = four studies) and CP (RR 3.40, 95% CI 0.86-13.39; n = four studies), although this was not statistically significant. The proportion of children with CP was 2.39/1000 across the studies, assessed as high certainty evidence.

CONCLUSION

Due to low certainty of evidence, the associations between umbilical cord blood gas analysis at delivery and long-term neurodevelopmental outcomes in children remains unclear.

A predictive model for prognosis in very low birth weight infants with late-onset sepsis

OBJECTIVES

This study aims to develop a predictive model to assess the probability of poor prognosis in very low birth weight infants (VLBWI) with late-onset sepsis (LOS).

METHODS

A total of 309 eligible VLBWI with LOS were included in the study. Logistic regression was used to determine prognostic factors for VLBWI with LOS. A nomogram incorporating these factors was created to predict the probability of poor prognosis. Poor prognosis includes death and survival with severe complications.

RESULTS

In the developmental cohort, the incidence of poor prognosis was 59.5% (147/247). Forward stepwise logistic regression analysis showed that HCO3, albumin (ALB), ionized calcium (iCa), blood urea nitrogen (BUN), gestational age (GA), and birth weight (BW) were independent predictors of poor prognosis in VLBWI with LOS. The predictive model showed good discrimination and calibration. In the developmental cohort, the prediction model had a sensitivity of 83.7%, a specificity of 74.0%, and a C-index of 0.845 (95% confidence interval: 0.795-0.894).

CONCLUSION

Our study identified independent predictors of poor prognosis in VLBWI with LOS and used them to construct a predictive model. This model can help clinicians to identify high-risk groups with poor prognosis early and provide important clinical reference information.

IMPACT

This article highlights the development of a predictive model to assess the probability of poor prognosis in very low birth weight infants with late-onset sepsis (LOS). The model constructed in this manuscript was the first model to predict the poor prognosis of VLBWI with LOS. We mean a poor prognosis that includes death and some severe complications that may lead to long-term disability. Clinicians can use the model's scoring results to assess a patient's condition and accurately identify the occurrence of poor prognosis.

Is there a role for therapeutic hypothermia administration in term infants with mild neonatal encephalopathy?

OBJECTIVE

Identifying term infants presenting with early mild neonatal encephalopathy (NE) as candidates for therapeutic hypothermia (TH) remains unclear. Study objectives were to characterize the neonatal clinical, magnetic resonance imaging (MRI), and longer-term outcome in infants with mild NE treated with TH.

STUDY DESIGN

Retrospective cohort study of infants admitted with mild or moderate NE treated with TH. Enrollment criteria included a sentinel event, severe acidosis, DR interventions, and low Apgar scores.

RESULTS

Infants with mild (n = 11) and moderate NE (n = 37) received TH. Mild NE findings included hyperalertness (64%), hypotonia (73%), high level sensory response (91%); 64% progressed to moderate NE. Infants with mild vs. moderate NE had less severe MRI changes (0 vs. 16%) and no cerebral palsy (CP) (0 vs. 13%).

CONCLUSIONS

Outcomes were favorable with mild NE whereas four infants with moderate NE developed CP. A potential role for TH in this population requires further study.

Threshold of metabolic acidosis associated with newborn cerebral palsy: medical legal implications

Obstetricians and gynecologists belong to 1 of the medical specialties with the highest rate of litigation claims. Among birth injury cases, those cases with cerebral palsy outcomes account for litigation settlements or judgments often in the millions of dollars. In cases of potential perinatal asphyxia, a threshold level of metabolic acidosis (base deficit ≥12 mmol/L) is necessary to attribute neonatal encephalopathy to an intrapartum hypoxic event. With increasing duration or severity of a hypoxic stress resulting in metabolic acidosis, newborn infant umbilical artery base deficit increases. It may be alleged that, as base deficit levels increase beyond 12 mmol/L, there is an increased likelihood and severity of cerebral palsy. As a corollary, it may be claimed that an earlier delivery (by minutes) would reduce the base deficit and prevent or reduce the severity of cerebral palsy. This issue is of relevance to obstetricians as defendants, because retrospective "expert" analysis of cases may suggest that optimal management decisions would have resulted in an earlier delivery. In addressing the association of metabolic acidosis and cerebral palsy, base deficit should be measured as the extracellular component (base deficit_{extracellular fluid}) rather than the commonly used base deficit_blood. Studies suggest that, beyond the base deficit threshold of 12 mmol/L, the incidence and severity of cerebral palsy does not significantly increase (until ≥20 mmol/L), although the risk of neonatal death rises markedly. Thus, among most infants with hypoxia-associated neonatal encephalopathy, the occurrence of cerebral palsy is unlikely to be impacted by delivery time variation of few minutes, and this argument should not serve as the basis for medical legal claims.

A Global View of Neonatal Asphyxia and Resuscitation

Birth asphyxia (BA), assumed to be related to intrapartum related hypoxia-ischemia, accounts for one million neonatal deaths annually. In the low resource setting BA is usually defined as a failure to initiate or sustain spontaneous breathing at birth. In the resource replete setting BA is a biochemical definition related to impaired gas exchange, due to interruption of placental blood flow (PBF). An umbilical arterial pH <7.00 referred to as severe fetal acidemia, reflects a degree of acidosis, where potential risk of adverse neurologic sequelae is increased. However, even with this degree of acidemia, the likelihood of mortality or adverse neurologic sequelae remains low. The aim is to focus on the definition of BA in the low resource setting, and compare it to the diagnosis in the resource replete setting, highlighting the importance of interruption of placental blood flow as it relates to morbidity and mortality. With asphyxia, the fetus aims to redistribute cardiac output to protect more vital organs e.g., brain, myocardium, and adrenal gland at the expense of decreased flow to organs such as kidney or intestine. In an experimental newborn model, animals subjected to asphyxia immediately develop primary apnea with bradycardia sustained blood pressure and normal pH. Recovery of respirations follows basic interventions, i.e. stimulation coupled with reversal of asphyxia. However, if asphyxia is sustained, secondary apnea manifests with bradycardia, hypotension, and pH <7.00. More intensive resuscitation including bag mask ventilation ± intubation ± cardio-pulmonary resuscitation may be necessary for correction upon reversal of asphyxia. Identification of a severely acidemic state (cord arterial pH < 7.00) in the newborn, may help to differentiate the truly asphyxiated intrapartum related cases that result in mortality, from those cases where mortality is related to delay in or ineffective basic resuscitation.

Re-examining the arterial cord blood gas pH screening criteria in neonatal encephalopathy

OBJECTIVE

Screening criteria for neonatal encephalopathy remain a complex combination of subjective and objective criteria. We examine the utility of universal cord blood gas testing and mandatory encephalopathy evaluation for infants with pH ≤7.10 on umbilical cord arterial blood gas (cABG) as a single screening measure for timely identification of moderate/severe encephalopathy.

DESIGN, SETTING, PATIENTS

Infants born at a single centre between 2008 and 2015, who were ≥36 weeks, had no congenital anomalies and had a cABG pH ≤7.10 were identified for a retrospective cohort study. Maternal/perinatal and patient factors were collected.

RESULTS

27 028 infants were born during the study period; 412 met all inclusion criteria. Of those, 35/85 infants with pH <7.00 and 34/327 infants with pH between 7.00 and 7.10 had moderate/severe encephalopathy. Encephalopathy was identified on the basis of pH and examination alone (no other perinatal criteria present) in 5/35 and 13/34 infants in the two pH groups, respectively.A cABG pH threshold of ≤7.10 was associated with a sensitivity of 74.2% and a specificity of 98.7% for detection of moderate/severe encephalopathy. Based on these data, 25 infants with cABG pH between 7.00 and 7.10 will need to be screened to identify one neonate with moderate/severe encephalopathy, who might have otherwise been missed using conventional screening, a 15% increase in appropriate selection and treatment over current methods.

CONCLUSION

Universal cord blood gas screening with a pH threshold ≤7.10 and mandatory encephalopathy examination results in greater detection of infants with moderate/severe encephalopathy and timely initiation of therapeutic hypothermia.

Pathophysiology of Birth Asphyxia

The pathophysiology of asphyxia generally results from interruption of placental blood flow with resultant fetal hypoxia, hypercarbia, and acidosis. Circulatory and noncirculatory adaptive mechanisms exist that allow the fetus to cope with asphyxia and preserve vital organ function. With severe and/or prolonged insults, these compensatory mechanisms fail, resulting in hypoxic ischemic injury, leading to cell death via necrosis and apoptosis. Permanent brain injury is the most severe long-term consequence of perinatal asphyxia. The severity and location of injury is influenced by the mechanisms of injury, including degree and duration, as well as the developmental maturity of the brain.

Outcomes of extremely low birthweight infants with acidosis at birth

OBJECTIVES

To test the hypothesis that acidosis at birth is associated with the combined primary outcome of death or neurodevelopmental impairment (NDI) in extremely low birthweight (ELBW) infants, and to develop a predictive model of death/NDI exploring perinatal acidosis as a predictor variable.

STUDY DESIGN

The study population consisted of ELBW infants born between 2002 and 2007 at National Institute of Child Health and Development (NICHD) Neonatal Research Network hospitals. Infants with cord blood gas data and documentation of either mortality prior to discharge or 18-22 month neurodevelopmental outcomes were included. Multiple logistic regression analysis was used to determine the contribution of perinatal acidosis, defined as a cord blood gas with a pH<7 or base excess (BE) <-12, to death/NDI in ELBW infants. In addition, a multivariable model predicting death/NDI was developed.

RESULTS

3979 patients were identified of whom 249 had a cord gas pH<7 or BE<-12 mEq/L. 2124 patients (53%) had the primary outcome of death/NDI. After adjustment for confounding variables, pH<7 and BE<-12 mEq/L were each significantly associated with death/NDI (OR=2.5 (1.6, 4.2) and OR=1.5 (1.1, 2.0), respectively). However, inclusion of pH or BE did not improve the ability of the multivariable model to predict death/NDI.

CONCLUSIONS

Perinatal acidosis is significantly associated with death/NDI in ELBW infants. Perinatal acidosis is infrequent in ELBW infants, however, and other factors are more important in predicting death/NDI.

Maternal and fetal Acid-base chemistry: a major determinant of perinatal outcome

Very small changes in pH may significantly affect the function of various fetal organ systems, such as the central nervous system, and the cardiovascular system with associated fetal distress and poor Apgar score. Review of existing data on maternal-fetal acid-base balance in pregnancy highlight the factors that are associated with derangements of the acid-base status and the impact of the derangements on fetal outcome. Extensive search of electronic databases and manual search of journals for relevant literature on maternal and fetal acid chemistry, clinical studies and case studies were undertaken. There is a substantial reduction in the partial pressure of carbon dioxide (pCO2) in pregnancy. Adequate buffering prevents significant changes in maternal arterial pH. Normal fetal metabolism results in the production of acids which are buffered to maintain extracellular pH within a critical range. Fetal hypoxia can occur when maternal oxygenation is compromised, maternal perfusion of the placenta is reduced, or delivery of oxygenated blood from the placenta to the fetus is impeded. When adequate fetal oxygenation does not occur, metabolisms proceed along with an anaerobic pathway with production of organic acids, such as lactic acid. Accumulation of lactic acid can deplete the buffer system and result in metabolic acidosis with associated low fetal pH, fetal distress and poor Apgar score. There is a significant reduction in pCO2 in pregnancy. This change, however, does not result in a corresponding significant reduction in maternal arterial pH, because of adequate buffering. Very small changes in pH may cause significant derangement in fetal function and outcome.

Application of 256-slice computed tomography with low radiation doses in neonates with hypoxic-ischemic encephalopathy

Hypoxic-ischemic encephalopathy (HIE), an injury or disease with lack of oxygen in the brain, may occur at any stage in childhood but the exact mechanisms that cause HIE remain unknown. In this study, 150 newborns suspected of having neonatal HIE and scheduled for a brain CT scan were randomly assigned to three equally sized groups as follows: standard dose group (120 kV, 250 mAsec), low dose group 1 (120 kV, 150 mAsec) and low dose group 2 (120 kV, 50 mAsec). All other acquisition parameters were the same in all groups. The CT dose index (CTDI), dose length product (DLP) and the image noise were compared among the three groups. The image quality was evaluated by blinded readers. The DLP of low dose group 2 was 19.3% of that of the standard dose group without a significant difference (P>0.05). The image noise of the low dose group 1 was greater than that of the standard dose group with a significant difference (P<0.01). Low dose scanning is feasible in the screening of HIE in neonates and is beneficial in protecting newborns against unnecessary radiation damage.

Developmental outcome at 6.5 years after acidosis in term newborns: a population-based study

OBJECTIVES

Infants who develop encephalopathy after perinatal asphyxia have an increased risk of death and adverse neurologic outcome. Conflicting results exist concerning outcome in healthy infants with metabolic acidosis at birth. The aim of the current study was to evaluate whether metabolic acidosis at birth in term infants who appear healthy is associated with long-term developmental abnormalities.

METHODS

From a population-based cohort (14,687 deliveries), 78 infants were prospectively identified as having metabolic acidosis (umbilical artery pH < 7.05 and base deficit in the extracellular fluid >12.0 mmol/L). Two matched controls per case were selected. The child health and school health care records were scrutinized for developmental abnormalities.

RESULTS

Outcome measures at 6.5 years of age for 227 of 234 children (97%) were obtained. No differences were found concerning neurologic or behavioral problems in need of referral action or neurodevelopmental diagnosis in comparison of control children with acidotic children who had appeared healthy at birth, ie, had not required special neonatal care or had no signs of encephalopathy.

CONCLUSIONS

Infants born with cord metabolic acidosis and who appear well do not have an increased risk for neurologic or behavioral problems in need of referral actions or special teaching approaches at the age of 6.5 years.

[Cerebral palsy and perinatal asphyxia (II--Medicolegal implications and prevention)]

Obstetric litigation is a growing problem in developed countries and its escalating cost together with increasing medical insurance premiums is a major concern for maternity service providers, leading to obstetric practice cessation by many practitioners. Fifty-four to 74 % of claims are based on cardiotocographic (CTG) abnormalities and their interpretation followed by inappropriate or delayed reactions. A critical analysis is performed about the nine criteria identified by the American College of Obstetricians and Gynecologists and the American Academy of Pediatrics in their task force on Neonatal Encephalopathy and Cerebral Palsy: four essential criteria defining neonatal asphyxia and five other suggesting an acute intrapartum event sufficient to cause cerebral palsy in term newborns. The importance of placental histologic examination is emphasized in order to confirm sudden catastrophic events occurring before or during labor or to detect occult thrombotic processes affecting the fetal circulation, patterns of decreased placenta reserve and adaptative responses to chronic hypoxia. It may also exclude intrapartum hypoxia by revealing some histologic patterns typical of acute chorioamnionitis and fetal inflammatory response or compatible with metabolic diseases. Magnetic resonance imaging (MRI) of the infant's damaged brain is very contributive to elucidate the mechanism and timing of asphyxia in conjunction with the clinical picture, by locating cerebral injuries predominantly in white or grey matter. Intrapartum asphyxia is sometimes preventable by delivering weak fetuses by cesarean sections before birth, by avoiding some "sentinel" events, and essentially by responding appropriately to CTG anomalies and performing an efficient neonatal resuscitation. During litigation procedures, it is necessary to have access to a readable CTG, a well-documented partogram, a complete analysis of umbilical cord gases, a placental pathology and an extensive clinical work-up of the newborn infant including cerebral MRI. Malpractice litigation in obstetric care can be reduced by permanent CTG education, respect of national CTG guidelines, use of adjuncts such as fetal blood sampling for pH or lactates, regular review of adverse events in Clinical Risk Management (CRM) groups and periodic audits about low arterial cord pH in newborns, admission to neonatal unit, the need for assisted ventilation and the decision-to-delivery interval for emergency operative deliveries. Considering the fast occurrence of fetal cerebral hypoxic injuries, and thus despite an adequate management, many intrapartum asphyxias will not be preventable. Conversely, well-documented hypoxic-ischemic brain insults during the antenatal period do not automatically exclude intrapartum suboptimal obstetric care.

A systematic review of the role of intrapartum hypoxia-ischemia in the causation of neonatal encephalopathy

The object of this review was to determine the incidence, morbidity, and mortality of an umbilical arterial pH < 7.0; the incidence of hypoxic-ischemic encephalopathy; and the proportion of cerebral palsy associated with intrapartum hypoxia-ischemia in nonanomalous term infants. A systematic review of the English language literature on the association between intrapartum hypoxia-ischemia and neonatal encephalopathy was conducted by using Pubmed and Embase. For nonanomalous term infants, the incidence of an umbilical arterial pH < 7.0 at birth is 3.7 of 1000, of which 51 of 297 (17.2%) survived with neonatal neurologic morbidity, 45 of 276 (16.3%) had seizures, and 24 of 407 (5.9%) died during the neonatal period. The incidence of neonatal neurologic morbidity and mortality for term infants born with cord pH < 7.0 was 23.1%. The incidence of hypoxic-ischemic encephalopathy is 2.5 of 1000 live births. The proportion of cerebral palsy associated with intrapartum hypoxia-ischemia is 14.5%. The vast majority of cases of cerebral palsy in nonanomalous term infants are not associated with intrapartum hypoxia-ischemia.

INTRAPARTUM ST ANALYSIS

The last century has seen dramatic developments in medical care as technological advances have been applied to both diagnosis and treatment. Some areas of obstetrics have been slow to benefit from these advances – and none more so than the care of the fetus in labour.

Effects of acute acidemia on the fetal cardiovascular defense to acute hypoxemia

In complicated pregnancy, fetal hypoxemia rarely occurs in isolation but is often accompanied by fetal acidemia. There is growing clinical concern about the combined effects of fetal hypoxemia and fetal acidemia on neonatal outcome. However, the effects on the fetal defense responses to acute hypoxemia during fetal acidemia are not well understood. This study tested the hypothesis that fetal acidemia affects the fetal defense responses to acute hypoxemia. The hypothesis was tested by investigating, in the late-gestation sheep fetus surgically prepared for long-term recording, the in vivo effects of acute fetal acidemia on 1) the fetal cardiovascular responses to acute hypoxemia and 2) the neural and endocrine mechanisms mediating these responses. Under general anesthesia, five sheep fetuses at 0.8 gestation were instrumented with catheters and Transonic flow probes around the femoral and umbilical arteries. After 5 days, animals were subjected to an acute hypoxemia protocol during intravenous infusion of saline or treatment with acidified saline. Treatment with acidified saline reduced fetal basal pH from 7.35 +/- 0.01 to 7.29 +/- 0.01 but did not alter basal cardiovascular variables, blood glucose, or plasma concentrations of catecholamines, ACTH, and cortisol. During hypoxemia, treatment with acidified saline increased the magnitude of the fetal bradycardia and femoral vasoconstriction and concomitantly increased chemoreflex function and enhanced the increments in plasma concentrations of catecholamines, ACTH, and cortisol. Acidemia also reversed the increase in umbilical vascular conductance during hypoxemia to vasoconstriction. In conclusion, the data support our hypothesis and show that acute acidemia markedly alters fetal hemodynamic, metabolic, and endocrine responses to acute hypoxemia.

Compensatory rebound of body movements during sleep, after asphyxia in neonatal rats

PURPOSE: The usefulness of body movements that occur during sleep when assessing perinatal asphyxia and predicting its long-term consequences is contradictory. This study investigated whether neonatal rats manifest these movements in compensatory rebound after asphyxia, and if these alterations play an important role in its pathogenesis. METHODS: Eight neonatal rats (aged 6-48h) were implanted with small EMG and EKG electrodes and sleep movements were recorded over a 30-minute control period. Recordings were continued during asphyxia caused by the enclosure of the animal in a polyvinyl sheet for 60 minutes, followed by a 30-minute recovery period. RESULTS: Heart rate was lowered to bradycardic level during asphyxia causing behavioral agitation and increased waking time during the initial phase (30 minutes). Sleep-related movements were also significantly reduced from 12.5 ± 0.5 (median ± SE/2min) to 9.0 ± 0.44 in the final half of the period (Anova, p<0.05). Movement frequency increased in the recovery period to 15.0 ± 0.49 (Anova, p<0.05). CONCLUSION: These data show that newborn rats present compensatory rebound of body movements during sleep which may help in the diagnosis of asphyxia and other problems related to sleep parameters.

Use of umbilical cord blood gas analysis in the assessment of the newborn

Analysis of paired arterial and venous specimens can give insights into the aetiology of acidosis in the newborn

Intrapartum asphyxia and cerebral palsy: is there a link?

Perinatal hypoxic-ischemic cerebral injury, secondary to interruption of placental blood flow that results in cerebral palsy (CP), is a rare event. The ability to link an intrapartum event to subsequent CP should include a history of a sentinel event during labor, followed by the delivery of a depressed acidemic infant, and the subsequent evolution of neonatal encephalopathy, systemic organ injury, and acute neuroimaging abnormalities.

Combination of early perinatal factors to identify near-term and term neonates for neuroprotection

OBJECTIVE

To determine early predictors of abnormal outcome at > or =24 months' age in neonates at risk for hypoxic-ischemic brain injury.

STUDY DESIGN

A prospective cohort study with developmental follow-up of > or =24 months. Infants were selected based on risk factors, and neurologic outcome was determined. Variables affecting the outcome were evaluated with univariate and multivariate methods, and a scoring system was devised to predict adverse outcome.

RESULTS

A total of 41 infants born > or =35 weeks' gestational age with possibility of hypoxic-ischemic insult were enrolled. In all, 39 (95%) had known outcomes, of whom 17 (48%) had an abnormal neurologic outcome, including five deaths. The variables within the first hour of life correlating with the adverse outcome were 1- and 5-minute Apgar scores, intubation in the delivery room and cord/initial base-deficit > or =20 mmol/l. A scoring system was derived based on significant variables, and a score > or =5 had a 90% positive predictive value for abnormal outcome. Seizures, multiorgan failure and abnormal imaging studies were also significantly associated with abnormal outcome.

CONCLUSIONS

The proposed scoring system, being highly predictive of outcome at 24 months' age, may be potentially useful in selecting subjects for preventive or therapeutic interventions to prevent or minimize neurologic morbidity due to hypoxic brain injury.

Birth asphyxia and cerebral palsy

There has been a societal presumption that most, if not all, cases of hypoxic ischemic encephalopathy-induced cerebral palsy occur during the 3 hours that are related to the events of labor and delivery; society has tended to overlook the remaining 7000 hours of the pregnancy. As a result of this societal perspective, often times the obstetrician has been targeted unfairly as the person who is responsible for a given child's neurologic injuries. Rather, the entire pregnancy, labor, delivery, and well beyond birth require examination to understand fully the pathophysiologic mechanisms that are responsible for an infant's brain injuries, and their long-term impact on the child.

Severe umbilical cord acidemia and neurological outcome in preterm and full-term neonates

BACKGROUND

Severe intrauterine hypoxia-ischemia and acidemia may lead to a disturbed neurodevelopment.

OBJECTIVES

To study the effects of acidemia at birth on neurodevelopment in preterm and full-term neonates.

SUBJECTS AND METHODS

Short- and long-term outcome were studied retrospectively in 44 inborn preterms and 95 full-terms with severe acidemia at birth defined as a pH of the umbilical artery <7.00. Outcome was compared with 67 preterm and 90 full-term non-acidemic neonates (pH>7.15). Intraventricular hemorrhage (preterms) or seizures (both preterms and full-terms) were considered an adverse short-term outcome. Neonatal death, cerebral palsy or neurodevelopmental delay were considered an adverse long-term outcome.

RESULTS

Severe intraventricular hemorrhage (IVH) occurred in 5 of the 44 (11%) acidemic preterms and in none of the 67 (0%) non-acidemic preterms (p<0.01). Seizures were observed in 9 of the 44 (20%) and 11 of the 95 (12%) acidemic preterms and full-terms, respectively, and in none of the 67 (0%) and 1 of the 90 (1%) non-acidemic preterms and full-terms, respectively (p<0.001 for preterms, p<0.01 for full-terms). Nine preterms (6 acidemic, 3 non-acidemic) and 2 full-terms (both acidemic) died in the neonatal period. Adverse long-term outcome occurred in 32% of the acidemic preterms, in 21% of the non-acidemic preterms, in 7% of the acidemic full-terms and in 7% of the non-acidemic full-terms.

CONCLUSIONS

Acidemia at birth increased the occurrence of severe IVH in preterm neonates and seizures in both preterm and full-term neonates. However, no significant effect of acidemia on long-term outcome could be demonstrated.

Severe fetal acidemia and subsequent neonatal encephalopathy in the larger premature infant

The contribution of intrapartum hypoxia-ischemia to neonatal encephalopathy in the larger preterm infant remains poorly defined. Such infants could become potential candidates for neuroprotective strategies. The objective of this study was to determine in preterm infants of gestation 31 to 36 weeks, with severe fetal acidemia (i.e., cord arterial pH < 7.00) the incidence of moderate to severe neonatal encephalopathy as well as the perinatal characteristics that may facilitate early identification. The data of 61 preterm infants of mean birth weight 1998 gm and mean gestation of 33.6 weeks were retrieved. Short-term abnormal neurologic outcome measures included evidence of encephalopathy with or without seizures or neuroimaging abnormalities. Eight (13%) of 61 infants developed an abnormal neonatal neurologic outcome. More infants with abnormal vs normal outcome had 1-minute Apgar of 0, i.e., 4/8 vs 3/53, 5-minute Apgar score </=5 (7/8 vs 17/53), required chest compressions (5/8 vs 6/53), cord pH (6.75 vs 6.90), and base deficit 20 vs 18 (P < 0.05). By multivariate analysis, only gestation was associated with abnormal outcome (P = 0.0003). We conclude that the larger depressed preterm infant is at increased risk for moderate to severe encephalopathy. Such infants could also be considered potential candidates for neuroprotective strategies.

Umbilical artery blood gas parameters in neonates with early onset seizures who die

OBJECTIVE

To relate umbilical artery blood gas parameters to mortality among neonates with hypoxic-ischaemic encephalopathy related to early onset seizures.

DESIGN

Population cohort study.

SETTING

British Columbia Women's Hospital.

POPULATION

Forty-seven infants at >or=32 weeks of gestation admitted to NICU with early onset seizures secondary to hypoxic-ischaemic encephalopathy with umbilical artery blood gases done at delivery.

METHODS

Patients were divided into two groups: (1) Infants with neonatal seizures who survived, and (2) infants with neonatal seizures who died related to hypoxic-ischaemic encephalopathy complications. Comparison of umbilical artery pH, PO(2), PCO(2), base deficit was done between the two groups with Student's t tests.

MAIN OUTCOME MEASURES

Umbilical artery pH, PO(2), PCO(2) and base deficit.

RESULTS

The PO(2) was significantly higher in the group that expired (18.36 +/- 9.15 vs 12.33 +/- 7.51). There were no significant differences in any other blood gas parameters between the groups.

CONCLUSION

Neither the umbilical artery pH nor base deficit is predictive of neonatal death in infants with hypoxic-ischaemic encephalopathy with seizures. The finding of a high PO(2) in neonates who died may indicate an inability of those infants to efficiently extract oxygen from blood.

Evidence of intrapartum hypoxia-ischemia is not present in the majority of cases of neonatal seizures

OBJECTIVE

To determine the extent to which neonatal seizures are associated with intrapartum hypoxia-ischemia.

METHODS

In this case-control study, all neonates diagnosed with seizures at a single institution from 1988 to 1999 were compared to a control group without seizures matched in a 2:1 fashion for gestational age at delivery, birth weight and mode of delivery. Data were abstracted from the maternal and neonatal charts. Parametric variables were compared using an independent samples t test, and non-parametric variables were compared using a Fisher exact test, with p < 0.05 being considered significant.

RESULTS

There were 13 cases of neonatal seizures identified, of which one was chromosomally abnormal and excluded from further analysis. For the cases, the mean gestational age at delivery was 34.8 +/- 6.9 weeks, with four preterm and eight term deliveries. The mean birth weight for the cases was 2684 +/- 1369 g (range 590-4350 g). For both cases and controls, 83% were delivered vaginally and 17% by Cesarean section. For term neonates with seizures, the mean length of stay was 11.6 +/- 5.0 days, as compared to 2.5 +/- 0.9 days in the control group (p < 0.001). A 1-min Apgar score of < 7 was found in six of 12 (50%) cases and seven of 24 (29%) controls, and a 5-min Apgar score of < 7 was found in four of 12 (33%) cases and four of 24 (17%) controls (non-significant). In the controls, the mean base excess was -2.8 +/- 2.6 mEq/l, and the mean umbilical arterial pH was 7.28 +/- 0.09. In the case group, two infants born at 24 weeks did not have an umbilical arterial blood gas obtained; in the remaining cases, the mean base excess was -7.6 +/- 6.9 mEq/l (p = 0.02), and the mean cord pH was 7.17 +/- 0.23 (p = 0.065), with only three of ten (30%) having a pH < 7.00 (p = 0.02).

CONCLUSION

Clinically significant acidosis was found in only 30% of neonates who developed seizures, and only one of 12 cases (8%) could possibly have met the criteria of the American College of Obstetricians and Gynecologists for neurological morbidity linked to intrapartum asphyxia. The majority of cases of neonatal seizures were not associated with evidence of intrapartum hypoxia-ischemia.

Umbilical cord blood gas analysis

Umbilical cord blood gas and pH values should always be obtained in the high-risk delivery and whenever newborn depression occurs. This practice is important because umbilical cord blood gas analysis may assist with clinical management and excludes the diagnosis of birth asphyxia in approximately 80% of depressed newborns at term. The most useful umbilical cord blood parameter is arterial pH. Sampling umbilical venous blood alone is not recommended because arterial blood is more representative of the fetal metabolic condition and because arterial acidemia may occur with a normal venous pH. A complete blood gas analysis may provide important information regarding the type and cause of acidemia and sampling the artery and vein may provide a more clear assessment. The sampling technique is simple and easily mastered by any treatment person in the delivery room. Preheparinized syringes ensure a consistent dose and amount of heparin. Depending on how normality is defined and on the population studied, normal ranges for umbilical cord blood gas values vary (see Table 1). In general, the lower range for normal arterial pH extends to at least 7.10 and that for venous pH to at least 7.20. Many different factors during pregnancy, labor, and delivery can affect cord blood gases. Umbilical blood sampling for acid-base status at all deliveries cannot be universally recommended because many facilities do not have the capabilities to support such a practice and in doing so may impose an excessive financial burden. Considering the costs, the accumulated published data, and the nonspecificity of electronic fetal monitoring in the evaluation of fetal oxygenation, it may be more rational to implement universal cord blood gas analysis. Care providers and institutions with the logistical capabilities in place should consider the cost efficacy of routine cord blood gas analysis because it is the gold standard assessment of uteroplacental function and fetal oxygenation/acid-base status at birth.

Clinical Implications of Perinatal Depression

The evaluation of the depressed newborn as a possible role in intrapartum asphyxia must be based on the objective findings of the fetal heart rate tracing, umbilical cord blood gas, and newborn neurologic function. Using these points as a basis for long-term followup, the following principles have been elucidated: Intrapartum asphyxia is an uncommon cause of childhood neurologic disfunction, the intrapartum insult necessary to cause long-term neurologic dysfunction is profound, and the child who does not manifest encephalopathy in the newborn period will not suffer long-term neurologic dysfunction that can be attributed to intrapartum asphyxia.

Association between umbilical blood gas parameters and neonatal morbidity and death in neonates with pathologic fetal acidemia

OBJECTIVE

Our purpose was to correlate umbilical artery blood gas parameters with neonatal death and indicators of morbidity in neonates with pathologic fetal acidemia (pH <7.0).

STUDY DESIGN

We reviewed maternal and neonatal charts of 93 neonates with an umbilical artery pH <7.0 who were delivered at 2 university-based centers. The relationships between umbilical artery pH, PO (2), PCO (2), bicarbonate, base deficit, and neonatal variables-death, need for intubation, cardiopulmonary resuscitation, seizures, hypoxic-ischemic encephalopathy, respiratory distress syndrome, intraventricular hemorrhage, meconium, sepsis, and intrauterine growth restriction-were determined with the Student t test, Mann-Whitney U test, and multiple logistic regression analysis. Data are presented as either median with 25th-75th percentiles or mean +/- SD.

RESULTS

The mean gestational age at delivery was 37.9 +/- 3. 6 weeks, and the mean birth weight was 3003 +/- 866 g. There was no relationship between neonatal death, respiratory distress syndrome, intraventricular hemorrhage, necrotizing enterocolitis, patent ductus arteriosus, meconium, sepsis, and any umbilical artery blood gas parameter. The PO (2) was not related to any of the variables studied. A lower umbilical artery pH was associated with hypoxic-ischemic encephalopathy (6.69 vs 6.93, P =.03), cardiopulmonary resuscitation (6.83 vs 6.93, P =.03), seizure (6.75 vs 6.93, P =.02), intubation (6.83 vs 6.94, P <.001), and intrauterine growth restriction (6.72 vs 6.93, P =.01). Greater mean base deficit was associated with seizure (20.6 vs 15, P =.01), intubation (18.0 vs 13.7, P <.001), cardiopulmonary resuscitation (18.5 vs 15.0, P =.03), intrauterine growth restriction (22.0 vs 14. 0, P =.02), and hypoxic-ischemic encephalopathy (24.0 vs 14.5, P =. 03). Arterial PCO (2) was higher only in infants with hypoxic-ischemic encephalopathy (138 vs 95.5, P =.048), intubation (106.0 vs 90.5, P =.003), and cardiopulmonary resuscitation (106.5 vs 93.0, P =.04). After control for birth weight and gestational age in the multivariate analysis, base deficit and bicarbonate were independently related to death or morbidity.

CONCLUSION

Our data suggest that "pathologic" fetal acidemia is indicated by an umbilical artery pH <7.00 with a metabolic component. The metabolic component of fetal acidemia (ie, base deficit and bicarbonate) is the most important variable in subsequent neonatal morbidity. As expected, the umbilical artery PO (2) has no apparent clinical utility. The ability to predict more accurately which newborn infants with fetal acidemia are at risk of having complications may lead to a more efficient implementation of preventive measures.

Obstetric evaluation of fetal acid-base balance

Several techniques may be used to evaluate fetal acid-base status during the ante- and intrapartum periods. Percutaneous blood sampling (cordocentesis) may be used to measure standard blood-gas parameters while the fetus is still in utero, but because of the risks associated with such procedures and the limited clinical utility of the results, this procedure is recommended for blood gas analysis only as part of a research protocol. Intrapartum blood specimens may be safely obtained via fetal scalp sampling, but the need for such sampling has been dramatically reduced by the use of other noninvasive tests such as fetal scalp stimulation or vibroacoustic stimulation. Finally, assay of blood obtained from a segment of umbilical cord collected at delivery indicates acid-base status at birth, but the range of normal values is wide, and only the most abnormal results have any prognostic significance.

The merit of routine cord blood pH measurement at birth

We searched the literature for mean values of arterial cord blood pH at birth and their lower limits of statistical normality. An arterial cord blood pH, correctly sampled, measured, validated, and interpreted, provides the most objective and sensitive index for fetal hypoxemia during labor. We advise to sample both artery and vein from a clamped segment of the cord within 30 minutes after birth. In accordance with physiological and statistical evidence, it is proposed to classify arterial cord blood pH in three categories: normal (when > 7.11), abnormal (when < 6.99), and borderline (7.00-7.11). An abnormal pH indicates that the fetus was in a state of biochemical decompensation at birth. Disadvantages of routine measurement include extra work load and the lack of a universally agreed definition of normal or abnormal pH. The major advantage of routine measurement is to provide care-givers with immediate feedback on their care during childbirth and an opportunity to learn from that feedback.

Neonatal tolerance to hypoxia: a comparative-physiological approach

Newborn mammals exhibit a number of physiological reactions which differ from normal adult physiology and are often regarded as signs of immaturity. However, when looked upon from a comparative point of view, it becomes obvious that some of these 'physiological peculiarities' bear striking similarity to adaptation mechanisms known from hypoxia-tolerant animals and may thus contribute to the well-established, yet poorly understood, phenomenon of neonatal hypoxia tolerance. As the mammalian fetus lives at oxygen partial pressures corresponding to 8000 m altitude, the first line of perinatal hypoxia defense consists of long-term adaptations to limited intrauterine oxygen supply: (1) improved O2 transport by fetal acclimatization to high altitude, (2) reduced metabolic rate by hibernation-like deviation from metabolic size allometry, (3) diminished cerebral vulnerability by functional analogies to diving turtle brain, and (4) enhanced metabolic flexibility by optional repartitioning of energy supply from growth to maintenance metabolism. In the case of birth asphyxia, these background mechanisms are complemented by short-term responses to acute oxygen lack: (1) reduction of body temperature as in natural torpor, (2) reduction of heart rate and redistribution of circulation as in diving mammals, (3) reduction of respiration rate typical of 'hypoxic hypometabolism', and (4) reduction of blood pH according to the concept of 'acidotic torpidity'. Although anaerobic metabolism is improved in neonatal mammals by increased glycogen stores, reduced metabolic demands, and sustained wash-out of acid metabolites, neonatal hypoxia tolerance seems to be primarily based on the ability to maintain tissue aerobiosis as long as possible. This is even reflected by isoenzyme patterns which do not consistently favour anaerobic glycolysis and, thus, are reminiscent of the 'lactate paradox' found in high altitude adaptation. Altogether, from a biological point of view, the perinatal period appears as a source of adaptive mechanisms that can be refound, in varying combinations, in many survival strategies. From a clinical point of view, the interplay of long- and short-term mechanisms offers a novel approach to estimation of the newborn's ability to withstand temporary oxygen lack. However, most of these mechanisms are not unambiguous and, above all, not unlimited in their protective effect so that they do not release obstetricians or neonatologists from their obligation to counteract fetal or neonatal hypoxia without delay.

Effects of obstetrician characteristics on cesarean delivery rates. A community hospital experience

OBJECTIVE

Despite a decrease in the overall cesarean delivery rate at Ravenswood Hospital Medical Center in Chicago, a wide range of variation existed among individual obstetricians' rates. This study evaluated obstetricians' characteristics to determine whether they affected cesarean delivery rates.

STUDY DESIGN

In 1994 members of my department adopted strategies to decrease the cesarean delivery rate. Data on women who were delivered at the obstetric unit from 1994-1997 and data on their neonates were studied. Certain characteristics of obstetricians were also analyzed. The data were grouped according to personal characteristics and obstetricians' cesarean delivery rates: group 1 had a low rate (</=15%) and group 2 had a high rate (>15%). Pearson chi2 analysis was used to evaluate the differences between the proportions. P <.05 was considered significant.

RESULTS

The departmental cesarean delivery rate decreased from 20.5% in 1994 to 15.5% in 1997 (P <.0001), whereas individual obstetricians' rates varied from 0% to 44.4%. Obstetricians in group 1 (average rate 12.2%) and group 2 (average rate 20.8%, P <.0001) served similar populations with similar outcomes. Compared with obstetricians in group 2, those in group 1 (low rate) performed more vaginal deliveries after cesarean birth and used epidural analgesia and the vacuum extractor more frequently. Young age of physician, graduation from a domestic medical school, group practice, and smaller volume of births were all significantly linked to lower cesarean delivery rates.

CONCLUSIONS

Cesarean delivery rates can safely be reduced. Certain individual obstetrician characteristics influence cesarean delivery rates. Obstetricians' commitment facilitates lowering of cesarean delivery rates.

Acute fetal asphyxia and permanent brain injury: a retrospective analysis of current indicators

OBJECTIVE

To determine whether a term neonate who has had sufficient intrapartum asphyxia to produce persistent brain injury will manifest the following four criteria: profound acidemia (arterial pH <7.00), an APGAR score < or =3 for 5 min or longer, seizures within 24 h of birth, and multiorgan system dysfunction.

METHODS

Singleton, liveborn, neurologically impaired neonates > or =37 weeks gestation who lived at least 6 days and had sufficient documentation of current intrapartum asphyxia criteria were retrospectively analyzed. Of these infants, solely neonates with acute fetal asphyxia due to a sudden prolonged FHR deceleration that lasted until delivery from a catastrophic event, e.g., uterine rupture, cord prolapse, were included. Organ system dysfunction was defined by separate criteria for each organ system. Dysfunction in one or more was defined as multiorgan system dysfunction.

RESULTS

Of the 292 eligible infants in the registry, 47 satisfied the entry criteria. In these 47 neonates, 10 (21%) satisfied all 4 criteria for intrapartum asphyxia.

CONCLUSIONS

Our retrospective study suggests that currently used indicators to define permanent fetal brain injury are not valid.

Newborn assessment and long-term adverse outcome: a systematic review

The medical literature was searched for publications between 1966 and September 1997 for data on the association of Apgar score, umbilical blood pH, or Sarnat grading of encephalopathy with long-term adverse outcome. Odds ratios for these associations were combined to calculate common odds ratios with 95% confidence intervals. Our search identified abstracts of 1312 studies and 81 articles with sufficient numeric data to formulate contingency tables. Forty-two of these qualified for inclusion in our meta-analysis. The strongest associations in the prediction of neonatal death were found by comparing umbilical artery pH <7 with pH >/=7 (common odds ratio 43; 95% confidence interval 15-124) and by comparing Sarnat grade III with grade II (common odds ratio 24; 95% confidence interval 13-45). In the prediction of cerebral palsy, the strongest associations were found for Sarnat grade III versus grade II (common odds ratio 20; 95% confidence interval 6-70) and for 20-minute Apgar score 0 to 3 versus 4 to 6 (common odds ratio 15; 95% confidence interval 5-50).

Does the onset of neonatal seizures correlate with the timing of fetal neurologic injury?

The onset of seizures after birth has been considered evidence of an intrapartum asphyxial event. The present study was undertaken to determine whether the timing of neonatal seizures after birth correlated with the timing of a fetal asphyxial event. Thus, singleton term infants diagnosed with hypoxic ischemic encephalopathy and permanent brain injury had a mean birth to seizure onset interval of 9.8 +/- 17.7 (range 1-90) hours. When these infants were categorized according to their fetal heart rate (FHR) patterns, the acute group (normal FHR followed by a sudden prolonged FHR deceleration that continued until delivery) tended to have earlier seizures than infants did within the tachycardia group (normal FHR followed by tachycardia, repetitive decelerations, and diminished variability) and the preadmission group (persistent nonreactive FHR pattern intrapartum). These seizure intervals were as follows: acute, 6.6 +/- 18.0 (range 1-90) hours; tachycardia, 11.1 +/- 17.1 (range 1-61) hours; and preadmission, 11.8 +/- 17.9 (range 1-79) hours (p < 0.05). But the range varied widely and no group was categorically distinct. In conclusion, the onset of neonatal seizures after birth does not, in and of itself, appear to be a reliable indicator of the timing of fetal neurologic injury.

Predictive value of plasma and cerebrospinal fluid tumour necrosis factor-alpha and interleukin-1 beta concentrations on outcome of full term infants with hypoxic-ischaemic encephalopathy

AIM

To determine the predictive value of plasma and cerebrospinal fluid (CSF) tumour necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) concentrations on the outcome of hypoxic-ischaemic encephalopathy (HIE) in full term infants.

METHODS

Thirty term infants with HIE were included in the study. HIE was classified according to the criteria of Sarnat and Sarnat. Blood and CSF were obtained within the first 24 hours of life and stored until assay. Five infants died soon after hypoxic insult. Neurological examinations and Denver Developmental Screening Test (DDST) were performed at 12 months in the survivors.

RESULTS

At the age of 12 months neurological examination and DDST showed that 11 infants were normal; 14 had abnormal neurological findings and/or an abnormal DDST result. Eleven normal infants were classified as group 1 and 19 infants (14 with abnormal neurological findings and/or an abnormal DDST and five who died) as group 2. CSF IL-1 beta and TNF-alpha concentrations in group 2 were significantly higher than those in group 1. Plasma IL-1 beta and TNF-alpha concentrations were not significantly different between the two groups. IL-1 beta, but not TNF-alpha concentrations, in group 2 were even higher than those in group 1, although non-survivors were excluded from group 2. When the patients were evaluated according to the stages of Sarnat, the difference in the three groups was again significant. Patients whose CSF samples were taken within 6 hours of the hypoxic insult had higher IL-1 beta and TNF-alpha concentrations than the patients whose samples were taken after 6 hours.

CONCLUSIONS

Both cytokines probably contribute to the damage sustained by the central nervous system after hypoxic insult. IL-1 beta seems to be a better predictor of HIE than TNF-alpha.

Intrapartum fetal hypoxia and biochemical markers: a review

Intrapartum fetal hypoxia is a rare event, although fetal intrapartum surveillance is discussed as a subject of major importance. This is mainly because of consequences of fetal hypoxia that may lead to cerebral palsy. A fetus suffering from hypoxia initially compensates by producing energy through anaerobic metabolism. At some stage, the fetus becomes decompensated and basic cellular functions fail, with risks of permanent morbidity or mortality. How long a fetus can survive on anaerobic metabolism differs because metabolic reserves differ, i.e., growth-restricted fetuses might deteriorate at an earlier stage. An increasing body of evidence has clarified brain-damaging mechanisms. Neuronal loss occurs in two phases: during the primary hypoxic event and later during the reperfusion/reoxygenation phase. Animal studies have suggested the possibility of prophylactic treatment to prevent neuronal loss after the hypoxic event. Intrapartum diagnostic tools should aim for detecting fetal hypoxemia/hypoxia when the fetus is still compensated. This may be achieved by assessment of biochemical data such as pH, lactate, and oxygen saturation, with the aim of prophylactic intervention before the fetus becomes decompensated. The measurement of cord blood levels of oxygen free radicals and excitatory amino acids at the time of birth may prove to be helpful in determining the risk of brain damage and evaluating the effect of prophylactic treatments to prevent or ameliorate brain injury from hypoxia.

The effect of profound umbilical artery acidemia in term neonates admitted to a newborn nursery

OBJECTIVE

To determine whether there were immediate adverse effects of an umbilical artery pH < or = 7.0 in term and near-term infants.

STUDY DESIGN

All infants triaged to the newborn nursery with an umbilical artery pH < or = 7.0 from May 1993 through April 1994 (n = 37) were prospectively identified; 35 of the 37 infants were enrolled and matched with nonacidemic control infants (n = 35). Organ system dysfunction (neurologic, renal, hepatic, gastrointestinal) was evaluated either clinically or biochemically with selected blood and urine parameters.

RESULTS

Acidemic and control groups were similar for pregnancy complications before labor, but acidemic infants were more often delivered by cesarean section (20/35 vs 6/35, p = 0.001). No differences existed between acidemic and control infants in gestational age, birth weight, neurologic evaluations, hearing deficits, feeding tolerance, and hepatic function. The acidemic group had a higher mean serum creatinine than control infants on day 2 of life (0.90 +/- 0.34 vs 0.71 +/- 0.12 mg/dl, p = 0.005) and a greater number of infants with a urine Chemstrip positive for heme (14/35 vs 3/35, p = 0.005). No differences existed between groups in time to first void, urine specific gravity, and number of infants with microscopic hematuria.

CONCLUSION

Term and near-term infants born with an umbilical artery pH < or = 7.0 and triaged to the newborn nursery on the basis of a stable appearance in the delivery room do not have clinical manifestations of hypoxia-ischemia in the 48 hours after birth. The higher mean serum creatinine for acidemic compared with control groups is presumably prerenal in origin and results from processes responsible for profound fetal acidemia. Infants with an umbilical artery pH < or = 7.0 and assessed to be clinically well can be treated similar to nonacidemic infants.

Reliability of individual umbilical artery pH measurements

To examine the reliability of umbilical artery pH measurements, two study designs were employed: (1) contemporaneous measurement of two adjoining segments of umbilical cords at birth (n = 40) and (2) repeat measurements at < 5, 15, 30, 45 and 60 minutes after birth in separate sections of the same cords (n = 40). The cord sections were left at room temperature. Limits of agreement of the contemporaneous pH measurements were from -0.066 to +0.066. Mean umbilical artery blood pH declined only slightly with time. Limits of agreement for delayed measurements were -0.061 to +0.031 at 15 minutes, -0.087 to +0.033 at 30 minutes, -0.090 to +0.046 at 45 minutes and -0.091 to +0.049 at 60 minutes. We therefore conclude that in both contemporaneous and interval sampling the accuracy of umbilical artery pH measurements is subject to biological variation. The 95% confidence interval for an individual umbilical artery pH measurement typically lies between -0.066 and +0.066 of the measured value.

Predicting the outcome of postasphyxial hypoxic-ischemic encephalopathy within 4 hours of birth

OBJECTIVE

To build models that predict severe adverse outcome within 4 hours of birth in patients with postasphyxial hypoxic-ischemic encephalopathy. The goal was to develop models for selecting patients for therapeutic trials of neuroprotective medications.

STUDY DESIGN

Retrospective cohort study with follow-up to a minimum age of 12 months of 164 "outborn" term infants admitted to a tertiary neonatal intensive care unit, and 14 "inborn" term infants in the two tertiary perinatal centers in a regionalized setting. After performing univariate screening tests, multivariate models of association between risk factors and "severe adverse outcome" (death or major neurosensory impairment) were constructed.

RESULTS

Of 178 infants with postasphyxial hypoxic-ischemic encephalopathy of defined severity admitted consecutively between 1985 and 1992, 48 died, 40 survived with major neurosensory impairment, and 13 were lost to follow-up. The important predictors of severe adverse outcome in the first 4 hours were delayed onset of breathing, administration of chest compressions, and seizures. At 60 minutes of age, based on predicted probabilities of > 0.50, the sensitivity of the predictive model was 85% and specificity 68%. The parameter estimates of the predictive models are reported.

CONCLUSIONS

Age of onset of breathing, administration of chest compressions, and age of onset of seizures were the most important variables predictive of adverse outcome in this study. Although fairly sensitive and specific, these predictive models should be applied with caution. To build more accurate models, a template for the conduct of a large, multicenter prospective study is provided.

Long term outcome after umbilical artery acidaemia at term birth: influence of gender and duration of fetal heart rate abnormalities

OBJECTIVE

To study the outcome after acidaemia at term birth, and the relation to gender and duration of pathological fetal heart rate changes.

DESIGN

Population based study of 154 infants with umbilical artery pH < 7.05 at term birth. Neonatal outcome and the result of developmental screening at age four years were compared with a control group with pH > 7.10. Fetal heart rate traces in infants with acidaemia were reviewed, and the relation between duration of fetal heart rate changes and outcome was analysed.

RESULTS

Of the 154 newborns with acidaemia at birth, 10 had encephalopathy, of which two died and two developed cerebral palsy. Nine of these 10 infants were boys, and eight had pH < 7.00. Male newborns (n = 39) more often had pronounced acidaemia (pH < 7.00) than females (n = 22). Although few infants had severe impairment, infants born with acidaemia significantly more often had speech problems at follow up than controls (19/102 versus 8/98; P = 0.03). In infants with acidaemia, duration of abnormal fetal heart rate changes was significantly associated with neonatal encephalopathy and speech problems at age four years.

CONCLUSIONS

Acidaemia at term birth was associated with neonatal encephalopathy and with speech problems at four years of age. Boys had more often pronounced acidaemia and a complicated course. A protracted abnormal fetal heart rate trace was associated with poor outcome.

A study on the complexes between human erythrocyte enzymes participating in the conversions of 1,3-diphosphoglycerate

The ability of D-glyceraldehyde-3-phosphate dehydrogenase (GAPDH) catalyzing the reaction of 1,3-diphosphoglycerate synthesis in human erythrocytes to form complexes with enzymes which use this metabolite as substrate (3-phosphoglycerate kinase (3-PGK) or 2,3-diphosphoglycerate mutase (2,3-DPGM)) was studied. It was found that highly active 2,3-DPGM can be extracted from human erythrocyte hemolysates in a complex with GAPDH adsorbed on Sepharose-bound anti-GAPDH antibodies at pH 6.5, the molar ratio being one 2,3-GPGM subunit per subunit of GAPDH. No complexation was, however, detected at pH 8.0. The opposite was true for the interaction between GAPDH and 3-PGK, which could be observed at pH 8.0. In experiments carried out at pH 7.4, both GAPDH x 2,3-DPGM and GAPGH x 3-PGK complexes were detected. The Kd values of the complexes determined with purified enzyme preparations were in the range 2.40-2.48 microM for both the GAPDH x 2,3-DPGM and GAPGH x 3-PGK enzyme pairs, when titrations of GAPDH covalently bound to CNBr-activated Sepharose were performed by the soluble 2,3-DPGM or 3-PGK. If, however, GAPDH adsorbed on the specific antibodies covalently bound to Sepharose was used in the titration experiments, the Kd for the GAPDH x 2,3-DPGM complex was found to be 0.54 microM, and the Kd for the GAPDH x 3-PGK complex was 0.49 microM. The concentration of 2,3-diphosphoglycerate determined after 1 h of incubation of erythrocytes in the presence of glucose was found to increase 1.5-fold if the incubation was carried out at pH 6.5, but did not change upon incubation at pH 8.0. On the other hand, the concentration of 3-phosphoglycerate after incubation at pH 8.0 was twice as large as that found after incubation at pH 6.5. The results are interpreted on the hypothesis that specific protein-protein interactions between GAPDH and 2,3-DPGM or between GAPDH and 3-PGK may play a role in determining the fate of 1,3-diphosphoglycerate produced in the GAPDH-catalyzed reaction.

Umbilical cord blood gas analysis at the time of delivery

AIMS

it is now recommended that cord blood acid-base measurement is performed routinely at time of delivery in the UK as a measure of fetal response to labour. However, there remains some uncertainty about the value of this procedure. In this paper our experience of cord blood analysis is described and the literature is reviewed to: (1) provide an overview of the physiological basis of cord blood acid-base assessment; (2) describe the appropriate methodology and identify issues which have contributed to confusion and undermined the value of cord blood sampling; and (3) address the practical issues of cord blood sampling.

CONCLUSIONS

cord blood acid-base measurement has a sound physiological basis. It provides objective information which is a useful adjunct to subjective methods of newborn assessment, enables babies at risk of neonatal morbidity to be identified, can be helpful in litigation cases and is a prerequisite for clinical audit. However, to be of benefit the information must be correct and correctly interpreted.