Decreased activity and oxygen desaturation in prone ventilated preterm infants during the first postnatal week

ISSUES IN PULMONARY NURSING

Decreased activity and oxygen desaturation in prone ventilated preterm infants during the first postnatal week Ying-Ju Chang, PhD, RN,a Gene Cranston Anderson, PhD, FAAN,b Donna Dowling, PhD, MN,b and Chyi-Her Lin, MD,b Tainan, Taiwan, Republic of China, and Cleveland, Ohio. OBJECTIVE: To compare the effects of supine and prone positions on oxygen saturation (SpO2), desaturation episodes (SpO2 < 90% and ≥ 20 seconds), and motor activity in ventilated preterm infants during their first postnatal week. DESIGN: With use of a crossover design, we randomly assigned infants to a supine/prone or prone/supine position sequence. Infants were placed in each position for 2 hours. A stabilization period of 10 minutes before observation of each position was allowed. During the protocol, care procedures were kept minimal and ventilator settings remained unchanged. SETTING: Neonatal intensive care units at 2 tertiary care centers in Taiwan. SAMPLE: The sample consisted of 28 infants receiving mechanical ventilation who were 25 to 36 weeks’ gestation, without known congenital abnormalities, within 7 postnatal days of birth, and were not receiving sedation. RESULTS: When prone, infants had higher SpO2, fewer episodes of oxygen desaturation, and less motor activity than when supine. No significant differences in duration of SpO2 less than 90%, 85%, and 80% were found between the 2 positions. Seventy-four percent of desaturation episodes were associated with vigorous motor activity and crying. CONCLUSION: The prone position results in less motor activity and may stabilize oxygenation for ventilated preterm infants. This may conserve energy and decrease complications of hypoxia for sick preterm infants. (Heart Lung® 2002;31:34-42.)

P

reterm infants who require assisted ventilation are susceptible to oxygen desaturation because of physiologic instability and vulnerability to handling and stimulation. Stress induced

From the Department of Nursing, Department of Pediatrics, College of Medicine of National Cheng Kung University, Tainan, Taiwan, Republic of China,a and Frances Payne Bolton School of Nursing, Case Western Reserve University, Cleveland, Ohio.b This study was supported by the National Science Council and College of Medicine Fund of National Cheng Kung University of Taiwan, Republic of China. Reprint requests: Ying-Ju Chang, PhD, RN, Department of Nursing, College of Medicine, National Cheng Kung University, No. 1 Ta-Hsueh Road, Tainan, Taiwan, 701, Republic of China. Copyright © 2002 by Mosby, Inc. 0147-9563/2002/$35.00 + 0 2/1/120241 doi:10.1067/mh1.2002.120241

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by intensive care increases oxygen consumption in sick infants.1-3 Therefore, efforts to decrease oxygen demand are essential for this high-risk population. Positioning is an important factor related to ventilation.4,5 Appropriate positions for neonates have been broadly discussed and investigated. The American Academy of Pediatrics6-7 recommended that the prone position may be appropriate for sick preterm infants because oxygenation is better during prone placement. In addition, infants placed prone are less active when awake and in more optimal sleep states.8-10 The beneficial effect of the prone position on oxygenation might be associated with different pulmonary mechanisms. Compared with the supine position, the prone position decreased the

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respiratory rate in preterm infants with respiratory distress syndrome (RDS) immediately after extubation11 but not in preterm infants with a physically stable condition.5,8 For ventilated preterm infants with RDS and greater than 2 weeks postnatal age, decreased respiratory resistance when prone was reported.12 Increased tidal volume during prone placement was found in preterm infants in stable condition13 and in mechanically ventilated infants only when the abdominal movement was not restricted.14 Nevertheless, a later study showed no significant change in tidal volume between supine and prone positions in preterm infants who had RDS and required assisted ventilation.15 Wagaman et al14 indicated that the prone position increased lung compliance by 39% in the intubated preterm infant when the abdomen was allowed to protrude. However, other studies showed no significant change in lung compliance between prone and supine positions in preterm infants in stable condition13 and intubated preterm infants with chronic pulmonary disease.15 Dean4 proposed that the prone position could increase oxygenation by the change of gravitational force on the lung and thus increase the ventilation and perfusion ratio. Although this mechanism has been supported by studies for adult patients, only 1 study examined this factor for full-term infants and demonstrated no significant difference in pulmonary blood flow between prone and supine positions.16 Increased arterial oxygenation in prone position was associated with an increased synchrony of the chest-wall movement during breathing.8,17 Synchronous chest-wall movement is described as all anterior parts of the rib cage expanding together in relation to diaphragmatic contraction during inspiration.8,18 In preterm infants with postconceptional ages of 32 to 36 weeks’ gestation who were in stable condition, a significant increase in chest-wall synchrony with an increased arterial oxygenation during the prone position was found in either the quiet-sleep or active-sleep state.8 In the supine position, there was an increased asynchronous movement of the intercostal muscles in relation to diaphragmatic contraction, both resulting in rib-cage distortion.5,8 A distorted chest wall will reduce functional residual capacity and pulmonary oxygen reserves and thus induce respiratory depression. Furthermore, a compensatory increase of diaphragmatic movements during asynchronous breathing will induce diaphragmatic fatigue, which might result in apnea and oxygen desaturation.19 Most studies on the effects of the prone position focus on nonventilated preterm infants8,9,11 and

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ventilated preterm infants more than 2 weeks postnatal age or with chronic lung disease.10,12,15,20 Whether ventilated preterm infants can benefit from prone positioning at an earlier postnatal age is unknown. The purpose of this study was to compare effects of prone and supine positions on oxygen saturation (SpO2), desaturation episodes, and motor activity in ventilated preterm infants during the first week postbirth.

METHOD Design A 2-period crossover design was used. Each subject was placed supine or prone for 2 hours, followed by the other position for 2 more hours in a consecutive period. Infants were randomly assigned to position sequence: supine/prone (S/P) or prone/supine (P/S), with a 10-minute stabilization period preceding observation in each position. To achieve an equal distribution of S/P and P/S position sequence, permuted block randomization was performed by a third person who selected balanced combinations of position consequence from a block with even size at random and then put the arrangement for each identification number in a sealed envelope. During the study protocol, only minimal care procedures were allowed and no adjustments of ventilator settings were made.

Setting and samples A convenience sample of 28 preterm infants at 2 tertiary care centers in Taiwan was recruited. Infants were eligible for the study if they met the following criteria: (a) gestational age of 25 to 36 weeks, determined by maternal menstruation history; (b) postnatal age of 7 or fewer days; (c) mechanically ventilated with intermittent mandatory ventilation; and (d) relatively stable condition, defined as no need for frequent change of ventilator settings. Infants who were treated with sedatives or had known congenital anomalies were excluded. This protocol was approved by the Institutional Review Board of each hospital. Written parental informed consent was obtained before the study.

Study protocol Throughout the protocol, infants stayed in the same servocontrolled incubator or radiant warmer. When supine, the infant’s head was in the midline or slightly turned to one side to adapt to the ventilator tubing. A small roll of cloth was put under the knees to promote flexion. When prone, the infant’s head was turned to one side. If the infant had

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umbilical catheters, cautious handling was provided to prevent kinking and/or shifting of the catheter. Flexion of extremities was maintained by bringing the arms close to the body and the hands close to the head and putting a small roll of cloth under the hips. In both positions, the extremities were contained by surrounding the infant’s body with a soft roll of cloth.21

chronological log. An electric timer that was synchronized with the clock of the computer data acquisition system was used to monitor the time interval so that the period of measurement for movement could be compared to the SpO2. The inter-rater agreement between the investigator and a trained research assistant was 89%.

Instruments

SpO2 and the duration and the lowest value of desaturation episodes were retrieved from the computer file for data analysis. Repeated-measures analysis of variance was used to examine the effects of prone and supine positions on motor activity, mean SpO2, mean standard deviation of SpO2, and mean frequency and durations of desaturation episodes. The chi-square test was used to examine the occurrence of desaturation episodes in relation to the lowest value. The alpha level of .05 (2-tailed) was set for the final decision of significance of overall statistical tests.

Oxygen saturation. SpO2 was measured with pulse oximetry (Biopac OXY100, Novametrix 515C mode; Biopac System Inc, Santa Barbara, Calif) from the same pulsatile arterial site of the infant’s foot. Data that contained motion artifacts were excluded during data analysis by evaluating the synchronized measure of pulse waveform from the oximeter and heart rate (HR) from an electrocardiogram (ECG) (Biopac ECG100A; Biopac System Inc). When the difference between pulse rate and HR was greater than 3, the SpO2 data were excluded.22 Pulse rate, pulse waveform, SpO2, and HR were continuously recorded by a computerized data acquisition system (Biopac MP100; Biopac System Inc). To produce accurate waves of ECG simultaneously, the sampling frame was set on 100 samples/second. A desaturation episode was defined as SpO2 less than 90% and lasting longer than 20 seconds.23,24 During the study period, 1 investigator stayed at the bedside to identify behavioral patterns and clinical events temporally related to desaturation episodes. To prevent severe hypoxia, the investigator would intervene with an increase in oxygen by 15% to 20% if the infant demonstrated a drop of SpO2 to less than 80% that lasted for 20 seconds. After SpO2 returned to 90%, oxygen was reduced to the initial level. Motor activity. Motor activity was measured with Woodson and Hamilton’s Motor Activity Scale (MAS).25 The MAS is an ordinal scale that includes 6 levels of motor activity with rating scales from zero to 5: zero = no motor activity other than respiratory movements; 1 = activity restricted to face or head, excluding sucking; 2 = activity involving neck or limited to 1 limb; 3 = simultaneous activity in 2 limbs; 4 = simultaneous activity in 3 or more limbs; and 5 = crying with generalized activity. The criterion validity of the MAS has been supported by concurrent measures of HR with a strongly positive correlation r = 0.92).25 Activity was observed for 30 seconds every 5 minutes during the study period, and the highest level observed was scored and recorded on a

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Statistical analysis

RESULTS Demographic information is shown in Table I. Fourteen infants were studied in the P/S sequence, and another 14 infants were studied in the S/P sequence. Eighteen infants had been treated with surfactant, and unintentionally the position sequence of these infants was equally distributed (9 P/S and 9 S/P). Furthermore, 10 infants (4 in prone position and 6 in supine position) did not complete the 4hour protocol because of the need for interventions, such as airway suctioning and immediate handling or clinical management for changes in condition. Therefore, equal duration of prone and supine positions with a conjunctive section for each infant was selected for data analysis. For example, when the infant was placed prone for 120 minutes and then turned to supine for only 90 minutes, only the last 90 minutes of prone position and the whole 90 minutes of supine position were used for analysis. The duration of prone and supine position for this study ranged from 60 to 120 minutes.

Motor activity Mean MAS was lower when infants were prone compared with supine, 1.1 versus 2.2, P < .001 (Table II). By paired t comparison time by time, significantly lower mean MAS in the prone placement across 6 consecutive 20-minute periods was found (Fig 1). With multiple comparisons, the trend of mean MAS change across the 6 time periods either in prone or supine position was not significant. When the sequences of P/S and S/P were com-

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Table I Characteristics of subjects (N = 28) Infant characteristics

Mean ± SD or n

Boy/girl Birth weight (g) Body weight at study (g) Gestational age (wk) Postnatal age at study (h) Apgar score at 1 min Apgar score at 5 min Spontaneous delivery/cesarean section Diagnosis of RDS/no RDS Treatment with surfactant Ventilator setting during protocol Fraction of oxygen used (%) Peak inspiratory pressure (cm H2O) Positive end-expiratory pressure (cm H2O) Mean airway pressure (cm H2O) Rate per min Ventilatory index during study (mean airway pressure × rate) Duration of each position (min)*

Range

15/13 1378 ± 522 1335 ± 514 29.5 ± 3.5 38 ± 31 4.6 ± 1.9 7.0 ± 1.0 16/12 20/8 18 35 18.2 4.3 7.4 19.7 151 104

± ± ± ± ± ± ±

687-2650 656-2550 25-36 5-120 2-8 4-9

11 3.9 0.5 1.8 8.2 84 17

21-55 12-25 4-5 5-11 6-40 48-400 60-120

*Durations for prone and supine positions were equal for each infant.

pared, no significant differences were found for total mean MAS and MAS in 6 consecutive 20minute periods. Further examination on whether the mean MAS between prone and supine positions would be different in infants who had and had not been treated with surfactant. Although mean MAS was lower in both groups when prone, a significant difference between the 2 positions was only found in the surfactant group (see Table II).

Oxygen saturation Significantly higher mean SpO2 was observed when infants were prone compared with supine, 96.5% versus 95.7%, P = .003 (see Table II). A consistently higher SpO2 was demonstrated during each of 6 consecutive 20-minute periods of prone placement (Fig 2). By paired t comparison time by time, whereas, significant differences were only found in the third and fifth 20-minute periods. By multiple comparisons, the trend of SpO2 change across 6 time periods either in prone or supine position was not significant. In addition, a significantly lower mean SD of SpO2 was found when infants were prone, indicating less fluctuation of

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SpO2 (1.3 vs 1.9, P = .006). No significant differences were found for a total mean SpO2, SpO2 of 6 consecutive 20-minute periods, or mean SD of SpO2 when the sequences of P/S and S/P were compared. Further examination on whether the mean SpO2 and mean SD of SpO2 between prone and supine positions would be different in infants who received or did not receive surfactant. Similarly, although mean SpO2 was higher and SD of SpO2 was lower in both groups when prone, significant differences between the 2 positions were only found in the surfactant group (see Table II).

Oxygen desaturation Desaturation occurred in 14 of the 28 infants; 14 experienced desaturation in supine compared with 5 of them in prone. Durations of prone and supine placement in these 14 infants ranged from 82 to 120 minutes (107 ± 14 minutes). Among these 14 infants significantly fewer desaturation episodes occurred when the infants were in the prone position (0.9 vs 4.9, P = .003; see Table II). No significant difference was found in the frequency of desaturation in relation to the lowest values of 89% to 85%, 84% to 80%, and 79% to 70% between the prone and supine

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Table II Comparisons of SpO2, oxygen desaturation, and motor activity by position Outcomes

Level of motor activity Total sample (n = 28)† Surfactant group (n = 18) Nonsurfactant group (n = 10) SpO2 Total sample (n = 28) Surfactant group (n = 18) Nonsurfactant group (n = 10) SD of SpO2 Total sample (n = 28) Surfactant group (n =18) Nonsurfactant group (n = 10) Desaturation (n = 14)‡ Number of episodes Frequency of desaturation in relation to lowest value 89%-85% 84%-80% 79%-70% Total Duration of desaturation(s) <90% <85% <80%

Supine

Prone

F

P value*

2.2 ± 0.7 2.3 ± 0.7 1.9 ± 0.7

1.1 ± 0.8 1.0 ± 0.6 1.36 ± 1.0

42.7 130.3 2.1

<.001 <.001 .182

95.7 ± 2.1 95.8 ± 2.3 95.5 ± 2.0

96.5 ± 1.9 96.7 ± 1.8 95.9 ± 2.0

10.6 15.7 0.7

.003 <.001 .423

1.9 ± 1.5 2.1 ± 1.5 1.5 ± 1.4

1.3 ± 1.0 1.3 ± 0.8 1.3 ± 1.4

8.9 11.7 0.3

.006 .003 .599

4.9 ± 3.9

0.9 ± 1.7

14.1 4.2

.003 .123§

3.9 2.8

.072 .200

50 9 9 68

(73.6) (13.2) (13.2) (100)

8 4 0 12

110 ± 105 (68)¶ 60 ± 77 (23) 35 ± 69 (9)

(66.7) (33.3) (0) (100)

152 ± 129 (12) 67 ± 64 (6)

*Group differences were evaluated with repeated-measures analysis of variance †Mean ± SD. ‡Durations of prone and supine placement ranged from 82 to 120 minutes (107 ± 14 minutes). §Group differences were evaluated with the χ2 test. ❘❘No. (%). ¶No. of desaturation episodes.

positions. However, 13% of the desaturation episodes that occurred in the supine position were less than 80%; this did not occur in the prone position. Among these severe desaturation episodes with SpO2 less than 80% (n = 9), 4 episodes lasted longer than 20 seconds and were intervened with an increase in oxygen for a mean duration of 11 minutes with a range of 8 to 17 minutes. Furthermore, the durations of desaturation less than 90% and less than 85% between prone and supine positions were not statistically significant. Finally, 74% of the desaturation episodes were associated with crying and movement (Table III). However, no significant differences were found for the frequencies of those associated events between the prone and supine positions.

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DISCUSSION This study demonstrated that prone placement had a beneficial influence on oxygenation in ventilated preterm infants during their first postnatal week. This result is consistent with previous reports that studied arterial oxygen saturation and tension in nonventilated preterm infants8,11,26 and ventilated preterm infants later in their clinical course.10,12,14,20,27 During the study, prone placement resulted in consistently lower motor activity, a finding that has not been reported before. The mechanism underlying higher SpO2 and fewer desaturation episodes during prone placement might be temporally inter-related to lower motor activity. Motor activity affects oxygenation by influencing chest-wall movement and respiratory pat-

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Fig 1 Change of motor activity by time and position. Data are expressed as mean and 1 standard error at 20, 40, 60, 80, 100, and 120 minutes. P values of paired t comparisons between supine and prone positions at 6 time points are, respectively, .002 (n = 28), .004 (n = 28), .044 (n = 28), < .001 (n = 27), < .001 (n = 25), and .002 (n = 17).

Fig 2 Change of SpO2 by time and position. Data are expressed as mean and 1 standard error at baseline (zero), 20, 40, 60, 80, 100, and 120 minutes. P values of paired t comparisons between supine and prone positions at 7 time points are, respectively, .157 (n = 28), .156 (n = 28), .217 (n = 28), .017 (n = 28), .123 (n = 27), .047 (n = 25), and .067 (n = 17).

terns (pause and regularity). Crying and gross body movement have been associated with lower oxygenation and hypoxemic episodes11,28-34 and may have long-term sequelae.30 Dinwiddie et al30 state that changes of the blood pressure in crying

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preterm infants are similar to the Vasalva maneuver in adults and could decrease arterial oxygenation; they suggest that this could result from either rightto-left shunting because of increased right atrial filling after the preceding inspiration or from venti-

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Table III Associated events during oxygen desaturation Frequency No. (%) Events

Crying Movement and restlessness None Total

Total

21 38 21 80

(26.3) (47.4) (26.3) (100)

Supine

19 34 15 68

(27.9) (50.0) (22.1) (100)

Prone

2 4 6 12

(16.7) (33.3) (50.0) (100)

Group differences were evaluated with the chi-square test, χ2 = 4.12. P = .127.

lation-perfusion imbalance during the expiratory phase of crying. Less motor activity in the prone position may occur for several reasons. First, the prone position simulates aspects of the intrauterine environment, eg, the natural fetal position that facilitates flexion, hand-to-mouth positions, and containment of extremities.21 Thus, infants in the prone position may have been less easily agitated by environmental stimulation. Second, these preterm infants may have had higher auditory thresholds, as reported in prone infants by Franco et al.35 Thus, prone placement could have advantages for preterm infants who are exposed to constant ambient noise in the intensive care unit. Furthermore, less occurrence of oxygen desaturation in the prone position might also have reduced the infant’s distressed motor responses.36,37 Prone placement might contribute to better SpO2 in other ways. In a crossover design with ventilated preterm infants with RDS, inspiratory resistance during ventilation was lower when the infants were prone.15 Similarly, ventilated preterm infants less than 1250 g and greater than 2 weeks postnatal age had decreased respiratory resistance when prone during quiet sleep.12 The investigators of both studies inferred that lower respiratory resistance and higher SpO2 might be attributed to a more stable rib cage in the prone position, a mechanism documented by Martin et al8 in 1979. These changes in pulmonary physiology might explain some desaturation episodes without observed causes such as crying or movement during supine placement in this study. On the basis of the fact that mean levels of SpO2 in supine and prone positions were all acceptable, increase in SpO2 during prone placement was small

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(< 1%) and not clinically significant. Previous studies showed a larger increase in SpO2 (2% to 2.7%) in prone ventilated preterm infants who had chronic lung disease20,26 or who were more than 2 weeks postnatal age.12,23 Two reasons merit consideration. First, although these infants were ventilated, their conditions were stable, an eligibility requirement for this research. The required fraction of oxygen in these infants was not high and the average SpO2 was greater than 95% in both positions. Second, the severity of respiratory functions of the subjects might be an important factor that affected the magnitude of change in SpO2. Although respiratory functions of the subjects were relatively stable, our study revealed that the prone position had a greater influence on SpO2 in infants who had RDS and were treated with surfactant before entering the trial. Respiratory functions of these infants might be more vulnerable than of those who had no need for surfactant. To improve oxygenation, it is worth future study to identify target groups by severity of respiratory function for application of the prone position. McEvory et al20 reported that durations of oxygen desaturation of less than 90%, 85%, and 80% were shorter when ventilated preterm infants with chronic lung disease were prone compared with when they were supine. In contrast, no significant difference in durations of oxygen desaturation between the prone and supine conditions was found in our study, which might be affected by the far fewer desaturation episodes that occurred when the infants were prone. In addition, the duration of desaturation with SpO2 less than 80% was minimized by increasing the inspired oxygen to protect the infants from severe hypoxia. Regardless of these factors, the better stability of oxygenation

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when prone can be inferred from the documented fewer frequencies of desaturation episodes, the fewer subjects who had hypoxemia, and the smaller SD of SpO2. Although the increase in SpO2 during the prone position was small, taken together with the finding that the infants had fewer desaturation episodes as well (0.9 vs 4.9 in 107 minutes), it suggests more stability for sick infants in prone than supine over time. We observed that 74% of the desaturation episodes were associated with vigorous body movement and crying. These findings are consistent with other reports that ventilated preterm infants with a mean postnatal age of 4 weeks had fewer desaturation episodes when prone compared with supine (0.3 vs 1.7 in 1 hour). In addition, 78% of hypoxemic episodes of that study were associated with body movement.23 This study was not designed to identify causal relationships; however, the findings warrant further investigation to determine whether there is any causal relationship between restlessness, especially straining and hard crying, and oxygen desaturation in ventilated preterm infants. Arterial oxygen desaturation is associated with abnormal cerebral blood volume and increased fragility of capillaries. Rapid changes in cerebral perfusion with fluctuation of blood pressure might cause cerebral injury.38-43 Therefore, prone placement sooner or even first after birth may prevent or minimize oxygen desaturation and thus may benefit the future health of ventilated preterm infants. The authors thank Dr Richard J. Martin for critical review on this manuscript and the staff of the Neonatal Intensive Care Unit at National Cheng Kung University Hospital and Sin-Lau Christian Hospital for their supports.

REFERENCES 1. Evans JC. Incidence of hypoxemia associated with caregiving in premature infants. Neonatal Network 1991;10(2):17-24. 2. Long JG, Philip AGS, Lucey JF. Excessive handling as a cause of hypoxemia. Pediatrics 1980;65:203-7. 3. Peters KL. Does routine nursing care complicate the physiologic status of the premature neonate with respiratory distress syndrome? J Perinat Neonat Nurs 1992;6(2):67-84. 4. Dean E. Effect of body position on pulmonary function. Phys Ther 1985;65:613-18. 5. Heimler R, Langlois J, Hodel DJ, Nelin LD, Sasidharan P. Effect of positioning on the breathing pattern of preterm infants. Arch Dis Child 1992;67:312-14. 6. American Academy of Pediatrics Task Force on Infant Positioning and SIDS. Positioning and sudden infant death syndrome (SIDS): update. Pediatrics 1996;98:1216-18. 7. American Academy of Pediatrics Task Force on Infant Sleep Position and SIDS. Changing concepts of sudden infant death syndrome: implication for infant sleeping environment and sleep position. Pediatrics 2000;105:650-6.

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8. Martin RJ, Herrell N, Rubin D, Fanaroff A. Effect of supine and prone positions on arterial oxygen tension in the preterm infant. Pediatrics 1979;63:528-31. 9. Masterson J, Zucker C, Schulze K. Prone and supine positioning effects on energy expenditure and behavior of low birth weight neonates. Pediatrics 1987;80:689-92. 10. Baird TM, Paton JB, Fisher DE. Improved oxygenation with prone positioning in neonates: stability of increased transcutaneous PO2. J Perinatol 1991;11:315-17. 11. Lioy J, Manginello FP. A comparison of prone and supine positioning in the immediate postextubation period of neonates. J Pediatr 1988;112:982-4. 12. Bowling S, McEvory C, Gozum E. Prone position improves functional residual capacity (FRC), respiratory compliance (CRS), and oxygenation in intubated preterm infants less than 1259 grams. Am J Respir Crit Care Med 1998;157:A373. 13. Hutchison AA, Ross KR, Russell G. The effect of posture on ventilation and lung mechanism in preterm and light-for-date infants. Pediatrics 1979;64:429-32. 14. Wagaman MJ, Shutack JG, Moomjian AS, Schwartz JG, Shaffer TH, Fox WW. Improved oxygenation and lung compliance with prone positioning of neonates. J Pediatr 1979;94:787-91. 15. Mendoza JC, Roberts JL, Cook LN. Postural effects on pulmonary function and heart rate of preterm infants with lung disease. J Pediatr 1991;118:445-8. 16. Aiton NR, Fox GF, Alexander J, Ingram DM, Milner AD. The influence of sleeping position on functional residual capacity and effective pulmonary blood flow in healthy neonates. Pediatr Pulmonol 1996;22:342-7. 17. Martin RJ, DiFiore JM, Randal KH, Miller MJ, Brooks LJ. Vulnerability of respiratory control in healthy preterm infants placed supine. J Pediatr 1995;127:609-14. 18. Miller HC, Behrle FC. Changing patterns of respiration in newborn infants. Pediatrics 1953;12:141-50. 19. Martin RJ, Miller MJ, Carlo WA. Pathogenesis of apnea in preterm infants. J Pediatr 1986;109:733-41. 20. McEvory C, Mendoza ME, Bowling S, Hewlett V, Sardesai S, Durand M. Prone positioning decreases episodes of hypoxemia in extremely low birth weight infants (1000 grams or less) with chronic lung disease. J Pediatr 1997;130:305-9. 21. Als H. A synactive model of neonatal behavioral organization: framework for the assessment of neurobehavioral development in the premature infant and for support of infants and parents in the neonatal intensive care environment. Part 1: theoretical framework. Phys Occup Ther Pediatr 1986;3/4(6):3-55. 22. Ramanathan R, Durand M, Larrazabal C. Pulse oximetry in very low birth weight infants with acute and chronic lung disease. Pediatrics 1987;79:612-17. 23. Dimaguila MAVT, Di Fiore JM, Martin RJ, Miller MJ. Characteristics of hypoxemic episodes in very low birth weight infants on ventilatory support. J Pediatr 1997;130:577-83. 24. Singer L, Martin RJ, Hawkins SW, Benson-Szekely LJ, Yamashita TS, Carlo WA. Oxygen desaturation complicates feeding in infants with bronchopulmonary dysplasia after discharge. Pediatrics 1992;90:380-4. 25. Woodson R, Hamilton C. Heart rate estimates of motor activity in preterm infants. Infant Behav Dev 1986;9:283-90. 26. Mizuno K, Itabashi K, Okuyama K. Effect of body position on the blood gases and ventilation volume of infants with chronic lung disease before and after feeding. Am J Perinatol 1995;12:275-7. 27. Fox MD, Molesky MG. The effect of prone and supine positioning on arterial oxygen pressure. Neonatal Network 1990;8(4):25-9. 28. Abu-Osba YK, Brouillette RT, Wilson SL, Thach BT. Breathing pattern and transcutaneous oxygen tension during motor activity in preterm infants. Am Rev Respir Dis 1982;125:382-7. 29. Dinwiddie R, Patel BD, Kumar SP, Fox WW. The effects of crying on arterial oxygen tension in infants recovering from respiratory distress. Crit Care Med 1979;7:50-3. 30. Dinwiddie R, Pitcher-Wilmott R, Schwartz JG, Shaffer TH, Fox WW. Cardiopulmonary changes in the crying neonates. Pediatr Res 1979;13:900-3.

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Decreased activity and oxygen desaturation in prone ventilated preterm infants 31. Henderson-Smart DJ, Read JC. Reduced lung volume during behavioral active sleep in the newborn. J Appl Physiol 1979;46:1081-5. 32. Holditch-Davis D, Edwards LJ, Wigger MC. Pathologic apnea and brief respiratory pauses in preterm infants: relation to sleep state. Nurs Res 1994;43:293-300. 33. Prechtl HFR, Fargel JW, Weinmann HM, Bakker HH. Postures, motility, and respiration of low-risk preterm infants. Med Child Neurol 1979;21:3-27. 34. Anderson GC. Risk in mother infant separation postbirth. Image J Nurs Sch 1989;21:196-9. 35. Franco P, Pardou A, Hassis S, Lurguin P, Groswasser J, Kahn A. Auditory arousal thresholds are higher when infants sleep in the prone position. J Pediatr 1998;132:240-3. 36. Gordin PC. Assessing and managing agitation in a critically ill infant. Matern Child Nurs 1990;15:26-32. 37. Ward SLD, Bautista DB, Keens TG. Hypoxic arousal responses in normal infants. Pediatrics 1992;89:860-4.

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38. Brazy JE. Effects of crying on cerebral blood volume and cytochromeaa3. J Pediatr 1988;112:457-61. 39. Jenni OG, Wolf M, Hengartner M, Siebenthal KV, Keel M, Bucher H-U. Impact of cerebral, obstructive and mixed apnea on cerebral hemodynamics in premature infants. Biol Neonate 1996;70:91-100. 40. Livera LN, Spencer SA, Thorniley MS, Wickramasinghe YABD, Rolfe P. Effects of hypoxaemia and bradycardia on neonatal cerebral haemodynamics. Arch Dis Child 1991;66:376-80. 41. Volpe JJ. Intraventricular hemorrhage and brain injury in the premature infant. Neonatal Neurol 1989;16:387-411. 42. Volpe JJ. Brain injury in the premature infant: current concepts of pathogenesis and prevention. Biol Neonate 1992;62:231-42. 43. Volpe JJ. Brain injury in the premature infant: overview of clinical aspects, neuropathology, and pathogenesis. Semin Pediatr Neurol 1998;5:135-51.

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