Steven Mayfield

The Apgar score revisited: Influence of gestational age

We tested the hypothesis that Apgar scores are in part related to the newborn infants level of maturity. Seventy-three pregnant women with normal fetuses of gestational age 22 to 42 weeks were studied. Fetal well-being was documented by a prospectively designed recording of pregnancy history, labor complications, and birth outcome, including cord blood pH and base deficit measurements. The 1- and 5-minute Apgar scores were directly related to gestational age. Respiratory efforts, muscle tone, and reflex were the major determinants for a decreasing Apgar score with declining gestational age. We conclude that the 1- and 5-minute Apgar scores are influenced by the infants level of maturity and that our data may be useful in evaluating the true value of Apgar scores in assessing the fetal and neonatal condition of low birth weight infants.

Temperature measurement in term and preterm neonates

Body temperatures of 99 term and 44 preterm infants were measured at four sites: core (5 cm beyond the anus, with an electronic telethermometer), rectum (2 cm, with a mercury-in-glass thermometer), axilla, and between the skin and mattress. Temperatures measured at the four sites agreed closely in this group of largely normothermic infants. However, five of seven term infants with abnormal core temperature (greater than 1.5 SD below or above the mean) would have been judged to be normothermic by each of the three other measurements. The temperatures in preterm infants were lower and varied less with the site of measurement, indicating a smaller core-surface temperature gradient because of their relative lack of thermal insulation by body fat. Axillary temperature was as reliable as rectal temperature measured in the usual way with a mercury-in-glass thermometer. Measurement of the temperature between the skin and mattress was nearly as accurate as the other more frequently used methods. Ninety percent of temperatures were within 0.1 degree C of their final stabilization readings by 5 minutes for each type of thermometer and measurement site.

Neurologic and developmental status related to the evolution of visual-motor abnormalities from birth to 2 years of age in preterm infants with intraventricular hemorrhage**

We prospectively and longitudinally evaluated neurologic status, cognitive status, and visual-evoked responses in 63 premature infants with cerebral intraventricular hemorrhage, 27 premature infants without hemorrhage, and 22 full-term normal infants. We hypothesized that severe intraventricular hemorrhage (grades III and IV) is associated with impaired visual-motor function, in part because of compression-related injury of the periventricular white matter by ventricular dilation. Infants with grade III or IV hemorrhage had significantly more neurologic sequelae at term and at 3, 7, 12, and 24 months; lower Bayley mental and motor scores at 3, 7, and 12 months; more abnormality on Kohen-Raz subscales for eye-hand coordination, object manipulation, and object relations at 3, 7, and 12 months; and lower Mullen vision-receptive and vision-expressive coordination scores at 24 months. The 12-month visual-evoked response correlated with the 24-month vision-receptive and vision-expressive organization scores for infants with grade III or IV intraventricular hemorrhage (r = -0.49, p less than 0.01, and r = -0.40, p less than 0.05, respectively). The data confirm our hypotheses of increased cognitive and neurologic sequelae, and increased abnormality of visual-motor coordination, during the first 2 years of life in infants with severe (grade III or IV) intraventricular hemorrhage.

Postprandial gastrointestinal blood flow and oxygen consumption: effects of hypoxemia in neonatal piglets.

ABSTRACT: The effects of feeding on gastrointestinal (GI) perfusion and oxygen transport in hypoxemic neonates is unknown. We evaluated these effects in unanesthetized, spontaneously breathing newborn piglets by comparing three experimental groups: nine hypoxemic piglets (mean PaO2 26 torr) which were fed with formula, six hypoxemic piglets (mean PaO2 27 torr) which were not fed, and four normoxemic piglets (mean PaO2 79 torr) which were fed and served as controls. The control-fed group exhibited an increase in stomach and small intestinal mucosal-submucosal blood flow within 30 min following feeding which was significantly greater than that observed in the hypoxemic fed piglets. GI O2 delivery and O2 uptake rose significantly (p<0.05) following a meal secondary to increases in total GI blood flow. Oxygen extraction was unchanged postprandially in the control group. In the hypoxemic nonfed piglets, total and regional GI blood flow was unaltered during hypoxemia. Reductions in arterial O2 content led to significant decreases in GI O2 delivery. Gastrointestinal oxygen uptake remained stable with a compensatory increase in GI O2 extraction. In the hypoxemic-fed piglets, hypoxia significantly decreased stomach blood flow and led to unchanged blood flow in the remainder of the GI tract. Significant reductions in arterial O2 content and GI O2 delivery were observed, accompanied by significant increases in O2 extraction. Hypoxemic fed animals did not exhibit the expected increase in O2 uptake to meet postprandial metabolic demands. When the hypoxemic insult was terminated, fed piglets demonstrated significant total and regional GI hyperemia leading to increased GI O2 uptake when compared with hypoxemic nonfed piglets. We conclude that in the presence of hypoxemia, the newborn piglets GI tract is subject to decreased oxygen availability. In contrast to the fasted GI tract, the fed GI tract exhibits a significant hyperemia following a limited period of severe hypoxemia and an ability to increase oxygen uptake in an attempt to meet the demands of nutrient absorption. Oxygen uptake is not increased to the same extent as in normoxemic fed animals, thus the efficiency of these mechanisms in satisfying the postprandial O2 demand remains to be determined.

Behavioral characteristics and early temperament of premature infants with intracranial hemorrhage

Behavioral characteristics of 12 full-term and 44 premature infants with and without intracranial hemorrhage (ICH) were studied. Cranial ultrasonography prospectively documented Grade I-II ICH in 14, Grade III-IV in 19 and no ICH in 11 premature infants. Examination at corrected age of 40 +/- 2 weeks using the Neonatal Behavioral Assessment Scale showed that infants in the ICH groups had lower levels of arousal and more abnormal reflexes than full-terms. Infants with ICH III-IV displayed less optimal motor responses than full-term infants and diminished orientation responses, especially to visual stimuli. Thus, lower level of arousal, immature motoric processes, and poor visual orientation differentiated premature with ICH from full-term infants, although premature infants without these sequelae, did not differ significantly from full-term infants. The above may represent early manifestations of visual-perceptual and motor problems noted in the follow-up of ICH infants. Further, neonatal behavior was found to affect parent ratings of infant temperament (via the Bates Infant Characteristics Questionnaire) at 3 months corrected age, and the relationships between neonatal behavior and parental ratings differed depending upon the infants gestational age and severity of hemorrhage. We conclude that neonatal behaviors are less optimal in premature infants, and least optimal in premature infants with severe intracranial hemorrhage when compared to fullterm infants.

Cardiovascular effects of hypoxia/hypercarbia and tension pneumothorax in newborn piglets.

ObjectivesTo test the hypothesis that, in newborn piglets, the presence of a tension pneumothorax modifies the cardiovascular responses to hypoxia/hypercarbia. DesignProspective laboratory study. SettingPerinatal cardiovascular research laboratory at a university school of medicine. SubjectsSeven newborn piglets. InterventionsWe sequentially exposed the piglets to a baseline (control I) measure, hypoxia/hypercarbia, tension pneumothorax with normoxia/normocarbia, and tension pneumothorax with hypoxia/hypercarbia added. Measurements and Main ResultsBrain and systemic blood pressures and blood flow (radionuclide-microspheres) were measured. Hypoxia/hypercarbia resulted in increased brain perfusion (207 ± 61% of control, mean ± SEM, p < .05) and heart perfusion (176 ± 58% of control, p < .05) and decreased gastrointestinal perfusion (-37 ± 9% of control, p < .05). Tension pneumothorax with normoxia/normocarbia reduced the cardiac output (-70 ± 8% of control, p < .05), which was redistributed toward the brain (p < .05) at the expense of the gastrointestinal tract (p < .05). Although this redistribution in cardiac output persisted during tension pneumothorax with hypoxia/hypercarbia added, sustained reductions in cardiac output (-57 ± 11%, of control, p < .01) were associated with smaller increases in perfusion to brain (55 ± 54 vs. 207 ± 61% of control, tension pneumothorax with hypoxia/hypercarbia added, and hypoxia/hypercarbia time periods, respectively, p < .05) and heart (65 ± 49 vs. 176 ± 58% of control, tension pneumothorax with hypoxia/hypercarbia added, and hypoxia/hypercarbia time periods, respectively, p < .05) and larger decreases in blood flow to gastrointestinal tract, pancreas, and kidneys (p < .05) than with hypoxia/hypercarbia alone. ConclusionsTension pneumothorax-induced reductions in cardiac output limit the hypoxia/hypercarbia-mediated increases in perfusion to brain and heart and accentuate the hypoxia/hypercarbia-related decreases in perfusion to kidneys and splanchnic organs. (Crit Care Med 1994; 22:1453–1460)

Anemia blunts the thermogenic response to environmental cold stress in newborn piglets

ABSTRACT.: We tested the hypothesis that isovolemic anemia blunts the thermogenic response to environmental cold stress in 3 to 4-day-old newborn piglets. Eight animals were studied in both thermoneutral (31.6-32.8° C) and cold (19.6-20.2° C) environments, before and after an isovolemic, partial volume exchange transfusion which reduced the hematocrit from 26 to 15 %. In the non anemic phase of study, deep rectal temperatures declined but had plateaued by 30 minutes after onset of cold stress and remained within normal limits for newborn piglets. In the anemic phase of study, deep rectal temperature declined continuously throughout cold stress with true body core hypothermia (< 38° C) observed at all measurement points beyond 15 min of cold stress. Baseline oxygen consumption did not differ between the two study phases (17.6 ± 1. 8 versus 16.7 ± 2.1 ml/kg−1min−1, mean ± SEM). However, during environmental cold stress, oxygen consumption increased by 64% over baseline in the nonanemic phase of study (p < 0.05) whereas 21% increase over baseline was observed in the anemic phase (p NS). We conclude that isovolemic anemia limited oxygen consumption and heat production during environmental cold stress, resulting in body core hypothermia.

1360 THE APGAR SCORE REVISITED: DEVELOPMENTAL PATTERNS IN “OPTIMAL” NEWBORNS

The five objective criteria used in the Apgar score to assess the newborn include four signs (tone, reflex irritability, color, respiratory drive) that depend upon developmental maturity. The immature infant, with typically flaccid muscle tone is penalized by the Apgar method for developmental immaturity. We hypothesized that in nonasphyxiated fetuses, Apgar scores should correlate directly with gestational age (lower scores with decreasing maturity). 62 parturients (gestation: 23-42 weeks) were prospectively enrolled. By objective documentation of pregnancy history, labor complications, fetal heart rate tracings, cord blood pH & BE, their fetuses were judged as normal at the time of delivery. Direct relationship between Apgar scores and gestational age following a linear regression (y=.34x-4.8 at 1′, r=0.82; y=.28x-1.6 at 5′, r=0.77) was observed. Analysis of the total score into components reveals heart rate to be least influenced by maturity. Respiratory effort and muscle tone increase with increasing maturity. Skin color improves with development at the 5′ score. Reflex irritability trends upward but with more variability at 1′ than 5′. These data suggest that 1) the standard Apgar score may not be appropriate for the assessment of fetal well-being in premature infants, 2) scores thought representative of asphyxia in more mature newborns may not represent asphyxia in immature infants, and 3) these normative data are useful in the assessment of fetal status at various levels of maturity.

1456 REGIONAL BLOOD FLOW (Q) DURING ENVIRONMENTAL COLD STRESS(ECS)

We studied regional Q and its regulation during ECS in seven 3-4 day old piglets by measuring cardiac output(CO), organ Q, arterial-mixed venous O2 content difference(A-VΔO2), O2 consumption(VO2), plasma epinephrine(E) and norepinephrine(NE), mean arterial pressure(MAP), and core (Tc) and ambient(Tamb) temperatures. A vascular resistance index(R) was calculated (MAP ÷ Q). Each animal was studied in a thermoneutral environment (CONTROL) and 30 min. after the nadir of ECS. Results (Mean±SEM):We conclude that ECS results in (1) ↑QSM(↑ heat production) due to ↓R (2) ↓QGI, QKI, and QAD due to ↑R (3)↑A-VΔO2 with unchanged E and NE. We speculate that changes in R result initially from metabolic autoregulation(↓R) followed by altered peripheral sympathetic tone(↑R).

1455 REGIONAL OXYGEN(O 2 ) DELIVERY DURING ENVIRONMENTAL COLD STRESS (ECS) IN ANEMIC PIGLETS

We studied regional O2 delivery (DO2) in 3, awake 3-day old piglets during CONTROL(HCT=25.6±0.8%) and ANEMIC(HCT=14.9±0.1%) periods. Measurements of blood flow(Q, radiolabeled microspheres) and arterial O2 content(CaO2) were made in a warm environment(W) and after 60 min.of ECS. DO2 was calculated from measured values (ml O2·100g−1·min−1). Preliminary results are below (Mean±SEM):We conclude that anemia with ECS: 1)blunts the normal increase in DO SM 2)augments the decrease in DO2 GI 3)has no effect on DO2BR due to increased QBR 4)decreases DO2KI and DO2AD when compared with the normal, steady state(W-CONTROL). We speculate that, unless associated with increased regional O2 extraction, anemia with ECS may compromise tissue oxygenation of less vital organs such as the kidneys, adrenals and/or gastrointestinal tract.