Sleeping position and responses to a carbon dioxide challenge in convalescent prematurely born infants studied post-term.

OBJECTIVES: To test the hypothesis that the ventilatory response to a carbon dioxide (CO2) challenge would be lower in the prone compared to the supine position in prematurely born infants studied post-term. To determine whether there were postural-related differences in respiratory drive, respiratory muscle strength, thoracoabdominal synchrony and/or lung volume. DESIGN: Prospective cohort study. SETTING: Tertiary neonatal unit. PATIENTS: Eighteen infants (median gestational age 31 (range 22-32) weeks) were studied at a median of 5 (range 2-11) weeks post-term. INTERVENTIONS: The ventilatory responses to three added carbon dioxide (CO2) levels (0% baseline, 2% and 4%) were assessed in the prone and supine positions. MAIN OUTCOME MEASURES: The airway pressure change after the first 100 ms of an occluded inspiration (P0.1) (respiratory drive) and the maximum inspiratory pressure during crying with an occluded airway (Pimax) (respiratory muscle strength) were measured. The P0.1/Pimax ratio at each CO2 level and slope of the P0.1/Pimax response were calculated. RESULTS: The mean P0.1 (p<0.05) and P0.1/Pimax (p<0.05) were higher and the functional residual capacity (p=0.031) lower in the supine compared to the prone position. The mean P0.1 and P0.1/Pimax increased independently of position as the percentage CO2 increased (p<0.001). There was no tendency for the differences in P0.1 and P0.1/Pimax between the prone and supine position to vary by CO2 level. CONCLUSIONS: Convalescent, prematurely born infants studied post-term have a reduced respiratory drive, but not a lower ventilatory response to a CO2 challenge, in the prone compared to the supine position.

Ventilatory response to added dead space and position in preterm infants at high risk age for SIDS.

OBJECTIVE: The vulnerability of prematurely born infants to sudden infant death syndrome (SIDS) in the prone position might be explained by a reduced ability to respond to a stress, such as hypercarbia, in that position; our objective, therefore, was to further explore the influence of position on the response to a stress. WORKING HYPOTHESIS: The ability of prematurely born infants to respond to added dead space in the prone compared to the supine position would be impaired at the high risk age for SIDS. PATIENTS: Twenty infants, median gestational age of 30 (range 24-32) weeks were studied at a median postmenstrual age (PMA) of 45 weeks. In addition, comparisons were made to the results of 25 infants studied at 36 weeks PMA. METHODOLOGY: Infants were studied supine and prone. Breath by breath minute volume was measured at baseline and after a dead space was incorporated into the breathing circuit; the time constant of the response was calculated. The pressure generated in the first 100 msec of an occlusion (P0.1 ), the maximum inspiratory pressure during an airway occlusion and functional residual capacity (FRC) were also measured in both positions. RESULTS: The median time constant was longer (38 (range 15-85) vs. 26 (range 2-40) sec (P = 0.002)). P0.1 lower (P = 0.003) and FRC higher (P = 0.031) in the prone compared to the supine position. In the prone position, the time constant correlated with PMA (P = 0.047), that is, the rate of response to added dead space was significantly damped with increasing postnatal age up to the critical age for SIDS. CONCLUSIONS: The dampened rate of response to added dead space in the prone compared to the supine position lends support to the hypothesis that a poorer response to a stress may contribute to prematurely born infants increased risk of SIDS in the prone position.

The effects of sleeping position on ventilatory responses to carbon dioxide in premature infants.

BACKGROUND: The prone sleeping position, particularly in prematurely born infants, is associated with an increased risk of sudden infant death syndrome. A possible mechanism is an impaired ability to respond to respiratory compromise. The hypothesis that the ventilatory response to a carbon dioxide (CO(2)) challenge in convalescent, prematurely born infants would be lower in the prone compared with the supine position was therefore tested. METHODS: In each position, ventilatory responses to increasing levels of inspired CO(2) were assessed. The airway pressure change after the first 100 ms of an occluded inspiration (P(0.1)) and the maximum inspiratory pressure with an occluded airway during crying (P(imax)) were measured; the ratio of the P(0.1) to the P(imax) at each inspired CO(2) level and the slope of the P(0.1)/P(imax) response were calculated. Chest and abdominal wall asynchrony was assessed using inductance plethysmography and functional residual capacity (FRC) measured using a helium gas dilution technique. RESULTS: Eighteen infants with a median postmenstrual age of 35 (range 35-37) weeks were studied. In the prone versus the supine position, the mean P(0.1) (p=0.002), the mean P(imax) (p=0.006), the increase in P(0.1) with increasing CO(2) (p=0.007) and the P(0.1)/P(imax) response slope (p=0.007) were smaller. Thoracoabdominal asynchrony was not significantly influenced by position or inspired CO(2). FRC was higher in the prone position (p=0.019). CONCLUSIONS: Convalescent, prematurely born infants have a reduced ventilatory response to CO(2) challenge in the prone position, suggesting they may have an impaired ability to respond to respiratory compromise in that position.

Neonatal abstinence syndrome--postnatal ward versus neonatal unit management.

AIM: The aim of this cohort study was to test the hypothesis that caring for infants with neonatal abstinence syndrome (NAS) with their mothers on the postnatal ward rather than admit them to the neonatal unit would reduce treatment duration and length of hospital stay. RESULTS: The outcomes of infants with NAS cared for in 2002-2005 (Group A, n = 42) and 2006-2007 (Group B, n = 18) were compared. Group A infants were admitted to the neonatal unit for assessment and treatment as necessary, but Group B infants remained on the postnatal ward with their mother. Sixty infants (median gestational age 39, range 26-42 weeks) were included in the study. The proportion of infants in Group B compared to Group A requiring treatment for NAS was lower (45% versus 11%, p = 0.012) and the durations of treatment (mean 12.7 versus 7.3 days, p = 0.05) and hospital stay (mean 19.8 versus 15.9 days, p = 0.012) were shorter in Group B. No infant in either group was readmitted within the next 2 months. CONCLUSIONS: These results suggest caring for infants with NAS on the postnatal ward rather than the neonatal unit reduces the need for treatment and duration of hospital stay.

Position and ventilatory response to added dead space in prematurely born infants.

OBJECTIVES: Prematurely born infants are at increased risk of sudden infant death syndrome (SIDS) if slept prone. WORKING HYPOTHESIS: Prematurely born infants would have an impaired response to an added dead space and lower respiratory muscle strength in the prone compared to the supine position. STUDY DESIGN: Prospective study. PATIENT-SUBJECT SELECTION: Twenty-five infants, median gestational age of 30 (range 26-32) weeks. METHODOLOGY: The infants were studied supine and prone at a median of 36 weeks postmenstrual age. Breath by breath minute volume was measured at baseline and after a dead space was incorporated into the breathing circuit; the time constant of the response was calculated. The maximum inspiratory occlusion pressure generated (MIOP) and the pressure generated over the first 100 msec (P(0.1)) during airway occlusion were assessed. RESULTS: The median time constant was longer (26 (range 8-106) sec vs. 22 (range 6-92) sec (P = 0.045)) and the median MIOP (P = 0.001) and P(0.1) (P = 0.003) were lower in the prone compared to the supine position. CONCLUSION: Prematurely born infants have a dampened response to tube breathing and reduced respiratory muscle strength in the prone compared to the supine position, which may contribute to their increased vulnerability to SIDS in the prone position.

Hering-Breuer reflex, lung volume and position in prematurely born infants.

OBJECTIVES: To investigate the effect of position on the strength of the Hering-Breuer reflex in prematurely born infants and determine whether any differences seen were related to differences in lung or tidal volume between positions. WORKING HYPOTHESIS: Position related differences in the strength of the Hering-Breuer reflex relate to differences in lung or tidal volume. STUDY DESIGN: Prospective observational study. PATIENT/SUBJECT SELECTION: Eighteen infants, median gestational age 30 (range 25-32) weeks were studied. METHODOLOGY: Infants were examined in the supine and prone position, each position was maintained for 2 hr. At the end of each 2-hr period, the strength of the Hering-Breuer reflex was assessed by determining the prolongation of expiration following an end inspiratory occlusion. In addition, tidal volume and functional residual capacity (FRC) were assessed in each position. RESULTS: The strength of the Hering-Breuer reflex was greater (P = 0.01) and the mean FRC was higher (P < 0.0001) in the prone compared to the supine position. The position related differences in the strength of the reflex correlated significantly with position related differences in FRC (P = 0.05). CONCLUSIONS: The Hering-Breuer reflex is stronger in the prone compared to the supine position. Our results suggest this is explained by position related differences in lung volume.