OBJECTIVE To document the incidence of transient episodes of bradycardia in a group of healthy term and preterm infants during the first 1 to 6 months of life. DESIGN Longitudinal polysomnographic study. SETTING Sleep laboratory in a university-affiliated urban medical center. PARTICIPANTS Fourteen healthy term-born infants, nine preterm infants with apnea in the nursery, and 10 preterm infants without apnea. Infants with neonatal morbidity except apnea were excluded. MEASUREMENTS Transient episodes of bradycardia (< or = 100 beats per minute) were identified in 2- to 4-hour early evening polysomnographic tracings. The relationship with apnea, transcutaneous oxygen levels, and sleep state was determined. RESULTS Transient episodes of bradycardia to 60 to 70 beats per minute were common, but there were no drops below 50 beats per minute. The incidence of transient episodes of bradycardia was inversely related to heart rate. Results for apneic and nonapneic premature infants were similar. CONCLUSIONS Transient episodes of bradycardia are considered normal reflex responses and are not related to risk for sudden infant death syndrome. These results have implications for the setting of monitor alarms.

ABSTRACT: Repetitive polysomnograms were recorded from a total of 33 infants, 19 healthy preterm infants, and 14 term controls between 40 wk postconceptional age and 6 mo of age. These nighttime recordings lasted 2—4 h, except at 52 wk in preterm infants and at 3 mo of age in term infants when an overnight 12-h recording was performed. Minute by minute values of transcutaneous Po. (Ptco2) and transcutaneous PCO2 (PtcCO2) levels and variability during the awake state, active sleep, and quiet sleep were obtained through computer analyses of the polygraphic data. The results from preterm infants at corrected postconceptional age could not be differentiated from those of control infants. PtcO2 levels rose between 40 wk and 3 mo, and PtcCO2 levels declined. Sleep states modulated only the variability of PtcO2, not the level; in contrast, state modulation was seen in both variability and level of PtcCO2 throughout the age span studied. During sleep the number of transient declines in PtcO2 > 2.03 kPa (15 mm Hg) decreased with advancing age. Hypercapnic PtcCO2 values decreased with age as well, but their prevalence in healthy, young infants suggests the need for revaluation of criteria for hypercapnia based on transcutaneous measurements. The data demonstrate that ventilatory regulation continues to undergo changes between 1 and 3 mo, the age of highest risk for sudden infant death syndrome.

Nine of nineteen infants in this study exhibited two or more central apnea greater than or equal to 20 seconds when they were older than one week and between 32-36 weeks postconceptional age (PCA). We focused on the sequelae of these apneas. Apnea was separated from other morbidity associated with immaturity by the selection of consistently healthy infants. Following discharge, polygraphic tracings were obtained at 40, 44 and 52 weeks PCA in these non-apneic and previously apneic infants. Sleep states, minute by minute values for heart and respiratory rate, skin temperature and transcutaneous O2 (PtcO2) and CO2 (PtcCO2), apnea and transient decreases in PtcO2 were determined. Polygraphic measurements did not differentiate preterm infants with late apnea in the nursery from non-apneic ones. However, the apneic group exhibited a transient decrease in awakenings at 44 weeks PCA.

Sequential hemodynamic and biochemical changes were studied in 24 infants with sepsis due to beta-hemolytic streptococcus to define the temporal patterns of physiologic events and to compare them in surviving (n = 11) and nonsurviving (n = 13) infants. Septicemia was documented by positive blood culture in all. Biophysical and biochemical measurements were obtained before and hourly, for 11 h after antibiotic therapy was initiated. Surviving infants had significantly higher Hct and systolic and mean arterial pressures than nonsurvivors. In nonsurvivors, low BP was associated with a concomitant rise in CVP and severe metabolic acidosis refractory to therapy. Although there were no differences in PaO2 or PaCO2 between survivors and nonsurvivors, arterial-alveolar oxygen gradients were significantly greater in nonsurviving infants. These data show cardiorespiratory and metabolic alterations that differentiate surviving and nonsurviving infants with beta-hemolytic streptococcal septicemia.

We studied obstructive sleep apnea > 3 seconds in 16 preterm and 14 term infants at 44 weeks postconceptional age (PCA). Seven preterm infants had experienced prolonged central apnea between 32 and 36 weeks. In two thirds of the pauses the presence of movements precluded clear categorization. Obstructive and mixed apnea were typically brief and the majority were associated with a HR acceleration. Preterm infants with and without previous apnea exhibited similar amounts of obstructive pauses. Term infants exhibited slightly fewer obstructive pauses with and without HR drops below 100 beats per minute (BPM). The brevity of obstructive pauses and the nature of the HR changes suggest that these phenomena are usually benign.

The occurrence of central apnea of 15 seconds or longer, transient episodes of bradycardia (TEB), and periodic breathing were studied in 66 healthy premature infants when at least 1 week old and between 32 and 36 weeks postconceptual age. Eight-hour cardiorespiratory recordings were visually scanned for the presence of these patterns. Central apnea of 15 seconds or longer was seen in almost half of the infants. The TEB were numerous, and the majority were not associated with central apnea; however, all but five of the apneic episodes that lasted 15 seconds or longer were accompanied by a TEB. Infants spent as much as 40% of their time in periodic breathing. The frequency with which these patterns are seen in healthy premature infants strongly suggests that they are normal findings. Our results do not support the opinion that brief periods of apnea are abnormal when accompanied by a TEB.

Changes in pulmonary resistance, dynamic compliance, tidal volume, and transcutaneous PO2 and PCO2 after nebulized administration of metaproterenol were evaluated in eight newborn infants (birth weight 650 to 1060 g, gestational age 25 to 28 weeks) with chronic lung disease receiving mechanical ventilation. The infants were monitored continuously before and for 15 minutes after nebulization of metaproterenol during 3 consecutive days at mean age 34 days. There were significant increases in compliance, tidal volume, and tcPO2, and significant decreases in pulmonary resistance and tcPCO2. These data show that bronchospasm contributes significantly to the high pulmonary resistance in preterm infants with chronic lung disease and that metaproterenol is beneficial in the therapy of infants with chronic lung disease requiring mechanical ventilation.

Although endotracheal (ET) suctioning is performed frequently in sick newborn infants, its effects on cardiorespiratory variables and intracranial pressure (ICP) have not been thoroughly documented in neonates greater than 24 h who were not paralyzed while receiving mechanical ventilation. This study evaluates these changes in preterm infants who required ventilatory assistance. We measured transcutaneous PO2 and PCO2 (PtcO2 and PtcCO2, respectively), intra-arterial BP, heart rate, ICP, and cerebral perfusion pressure (CPP) before, during, and for at least 5 min after ET suctioning in 15 low birth weight infants less than 1500 g and less than or equal to 30 days of age. One infant was studied twice. A suction adaptor was used to avoid disconnecting the patient from the ventilator and to attempt to minimize hypoxemia and hypercapnia during suctioning. The patients were studied in the supine position and muscle relaxants were not used. PtcO2 decreased 12.1% while PtcCO2 increased 4.7% 1 min after suctioning; however, greater increases in mean BP (33%) and ICP (117%) were observed during suctioning. CPP also increased during the procedure. ICP returned to baseline almost immediately, whereas BP remained slightly elevated 1 min after suctioning. Our findings demonstrate that ET suctioning significantly increases BP, ICP, and CPP in preterm infants on assisted ventilation in the first month of life. These changes appear to be independent of changes observed in oxygenation and ventilation.

Several newly developed methods of monitoring hemodynamic variables in the low birth weight infant are reviewed. Among those values included are the neonatal heart rate, arterial blood pressure, and transcutaneous O2 and CO2.

Naloxone (N) reduces the decrease in ventilation induced by hypoxia in healthy term infants. In addition, N by blocking endogenous opiates has a potential role in the therapy of hypotensive patients with septic shock and may allow the release of catechol-amines. However, serial measurements of the cardiopulmonary effects of N in normotensive infants are not available. During active sleep we studied 8 term infants (mean age 1.9 days) and 8 preterm infants (mean gestational age 34 wks, age 2.1 days) who had recovered from transient respiratory distress, prior to removal of their umbilical arterial line. Heart rate (HR), aortic blood pressure (BP), transcutaneous PO2 (PtcO2), transcutaneous PCO2 and respiratory frequency (RR) were measured before and 5, 10, 15, 20, 25 and 30 minutes after administration of N (0.1 mg/kg IV) or placebo. A Dinamap BP monitor was used in 3 preterm infants. Plasma levels of epinephrine (E) and norepinephrine (NE) were also determined before and 10 and 20 minutes after N administration. Interestingly, 5 preterm infants increased their PtcO2 and RR after N. However, there was no significant change in any cardiac or respiratory parameter measured in both groups of infants and levels of E and NE did not appreciably change following administration of N. There were no changes following placebo. Our findings indicate that in normotensive infants: 1)N does not have a major influence on BP, HR, oxygenation and ventilation; 2)levels of E and NE remain within normal range following administration of N.

Idiopathic apnea in preterm infants, more than 30 weeks of gestation, after the first week of life is uncommon and poorly understood. To study ventilatory control in these infants we measured minute ventilation, respiratory frequency, tidal volume, end-tidal oxygen pressure and carbon dioxide pressure, and transcutaneous oxygen pressure before and during the fifth minute of breathing 4% carbon dioxide in air. Nine healthy preterm infants and eight infants with three or more episodes of apnea (greater than or equal to 20 s) in 24 hours were studied during active sleep. We found that infants with apnea had a significantly increased alveolar carbon dioxide pressure while respiratory frequency, minute ventilation, and slope were significantly decreased. Alveolar-transcutaneous oxygen gradients were essentially unchanged. These preterm infants with apnea have a decreased carbon dioxide sensitivity. They have a decreased minute ventilation primarily as a result of decreased respiratory frequency and their alveolar-transcutaneous oxygen gradient is normal. Our findings suggest that the major deficit in these infants is a central disturbance in the regulation of breathing.

The use of bronchodilators in newborn infants is common clinical practice; however, their effects on gas exchange and on the cardiovascular system have not been evaluated. The purpose of this study was to investigate the effects of Isoetharine (I) nebulization, given during the first 3 days of life, on trans-cutaneous PO2 (PtcO2) and PCO2 (PtoCO2), heart rate (HR) and blood pressure (BP) of 12 preterm infants with severe HMD treated with ventilator; BW 1570±537gm, GA 30±3wks. 2ml of I 0.08% were nebulized while connected to the ventilator at the same baseline mean airway pressure each day. Data obtained before (baseline) and 15 min after I were compared. There were no cardiac arrhythmias found during the study. HR, BP, and PtcO2 were not significantly different 15 min after I nebulization, however, PtcCO2 reduced from mean values of 45 to 43 mmHg in day 1(p<.05) from 48 to 44 mmHg in day 2(p<.05) and from 47 to 42 mmHg in day 3(p<.05). The absence of cardiovascular effects after I are explained by its selective action on B2 receptors. The decrease in PtcCO2 suggests that I nebulization, given at constant mean airway pressure, improves ventilation either by relieving bronchoconstrictioh with an increase in minute ventilation or improvement in ventilation-perfusion matching. We conclude that I is an effective drug to improve ventilation without significant cardiovascular side effects in infants with severe HMD.

Prolapse of the umbilical cord (PUC) has been considered a cause of stillbirth and neonatal hypovolemic shock. Traditional theory held that, during labor, a significant portion of blood volume leaves the fetus between contractions, while placental blood does not reach the fetus because of cord compression. This theory antedated modern management of PUC. The objectives of this study were to determine the impact of current management of PUC with tocolysis, maternal position changes, cord reposition and prompt C-section, on fetal/neonatal mortality and on incidence of neonatal hypovolemic shock. 38,585 deliveries occuring during 2½ yrs. were reviewed, and there were 103 (0.37%) cases of PUC identified. Hypovolemia was evaluated by clinical signs of hypoperfusion, heart rate, blood pressure and Hct changes during the first 5 hours of life. Stillbirth rate in PUC was 8 times that without PUC. Infants born after PUC did not have low Apgar scores. There were no neonates with clinical evidence of hypovolemia or shock. Heart rate, blood pressure, and Hct from those born with PUC were not significantly different from normal. This study shows: a)high incidence of stillbirths associated with PUC, b)virtual absence of cardiovascular and clinical signs of hypovolemia in neonates born after PUC. We conclude that with current perinatal management, PUC is not a cause of neonatal hypovolemic shock; however, further early diagnostic efforts are required if the high incidence of stillbirths associated with PUC is to be reduced.

Normative values of intra-arterial blood pressure (ABP) in newborns were obtained using a strain gauge connected to an umbilical artery catheter without interposition of continuous infusion devices. Currently values on which treatment decisions are based, are obtained while systems for continuous infusion of fluids - (intraflow-IF), even though ABP values from these different techniques have not been compared. We evaluated 170 pairs of direct umbilical ABP measurements obtained, with and without IF systems, from 16 infants, BW range 730-4790 gm, during the first week of life. Mean systolic blood pressures were 4 and diastolic 4.2 mmHg lower while using IF systems than without (p<.001). The size of the infant and the infusion capacity through the IF system influence the magnitude of the observed differences. The smaller the infant-with lower blood pressure-and the greater the capacity of the IF system, the lower will be the ABP values obtained. Under these conditions hypotension will be overdiagnosed, leading to overtreatment especially of the very immature infant. In order to avoid iatrogenic disease in these infants, if IF systems are used, ABP values should be obtained with and without IF before therapy for hypotension is initiated.