Use of a Mechanical Ventilator with Respiratory Function Monitoring Provides More Consistent Ventilation during Simulated Neonatal Resuscitation

INTRODUCTION

Positive pressure ventilation (PPV) with T-Piece and self-inflating bag (SIB) during neonatal resuscitation after birth is associated with variability in ventilation. The use of a ventilator with respiratory function monitoring (RFM) for PPV, however, has not been evaluated.

OBJECTIVE

To determine if ventilator + RFM can reduce ventilation variability compared to T-Piece and SIB in a preterm manikin at different combinations of target tidal volume (VT) and lung compliance (CL).

METHODS

Twenty clinicians provided PPV via mask and endotracheal tube (ETT) using SIB, T-Piece, T-Piece + RFM and Ventilator + RFM to a manikin with adjustable lung CL. Three combinations of CL and target VT: Low CL-Low VT, Low CL-High VT and High CL-Low VT were used in a random order.

RESULTS

The use of ventilator + RFM for PPV via ETT during High CL-Low VT period reduced the proportion of breaths with expiratory VT above target when compared to the other 3 devices (56 ± 35%, 85 ± 20%, 90 ± 25%, 92 ± 12% for ventilator + RFM, T-Piece + RFM, T-Piece, SIB, respectively; p < 0.05). During PPV via both mask and ETT, ventilator + RFM maintained the set Ti and rate, whereas SIB and T-Piece use resulted in higher rates, and T-Piece in higher proportion of breaths with prolonged Ti. During PPV via mask, ventilator + RFM reduced gas leakage compared to other devices.

CONCLUSION

In this simulation study, use of a mechanical ventilator with RFM led to an overall improvement in volume targeting at different settings of CL and reduced the gas leak during mask ventilation. The efficacy and safety of using this strategy to neonatal resuscitation in the delivery room needs to be evaluated.

Early Caffeine and Weaning from Mechanical Ventilation in Preterm Infants: A Randomized, Placebo-Controlled Trial

OBJECTIVE

To evaluate in a randomized, double-blind, placebo-controlled trial the effect of early caffeine on the age of first successful extubation in preterm infants.

STUDY DESIGN

Preterm infants born at 23-30 weeks of gestation requiring mechanical ventilation in the first 5 postnatal days were randomized to receive a 20 mg/kg loading dose followed by 5 mg/kg/day of caffeine or placebo until considered ready for extubation. The placebo group received a blinded loading dose of caffeine before extubation.

RESULTS

Infants were randomized to receive caffeine (n = 41) or placebo (n = 42). Age at first successful extubation did not differ between early caffeine (median, 24 days; IQR, 10-41 days) and control groups (median, 20 days; IQR, 9-43 days; P = .7). An interim analysis at 75% enrollment showed a trend toward higher mortality in 1 of the groups and the data safety and monitoring board recommended stopping the trial. Unblinded analysis revealed mortality did not differ significantly between the early caffeine (9 [22%]) and control groups (5 [12%]; P = .22).

CONCLUSIONS

Early initiation of caffeine in this group of premature infants did not reduce the age of first successful extubation. A nonsignificant trend toward higher mortality in the early caffeine group led to a cautious decision to stop the trial. These findings suggest caution with early use of caffeine in mechanically ventilated preterm infants until more efficacy and safety data become available.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01751724.

Hypoxemia Episodes during Day and Night and Their Impact on Oxygen Saturation Targeting in Mechanically Ventilated Preterm Infants

BACKGROUND

Hypoxemia episodes (HE) occur frequently in ventilated preterm infants and hinder the achievement of arterial oxygen saturation (SpO2) targets. These episodes may increase the risk for retinopathy of prematurity and neurodevelopmental disability. There are no data on the variation in HE and SpO2 targeting between day and night.

OBJECTIVE

The aim of this study was to evaluate the difference between day and night on the frequency and severity of HE and achievement of SpO2 targets.

METHODS

Twenty-four mechanically ventilated preterm infants with ≥4 episodes of SpO2 <75% over an 8-h period were enrolled. The fraction of inspired oxygen (FiO2), SpO2, and ventilator parameters were recorded over 24 h. Data from the day (9 a.m. to 5 p.m.) were compared to the night (9 p.m. to 5 a.m.) for the frequency of HE and proportion of time within and outside the target SpO2 range (90-95%).

RESULTS

The frequency of severe HE (SpO2 <75, ≥20 s) and prolonged severe HE (SpO2 <75, ≥60 s) was lower during the night compared to the day (1.6 ± 1.0 vs. 2.4 ± 1.3 episodes/h, p = 0.008, and 0.53 ± 0.35 vs. 0.90 ± 0.54 episodes/h, p = 0.018). There was no difference in mean episode duration. The frequency and duration of mild HE (SpO2 <85, ≥20 s) were lower during the night compared to the day (5.9 ± 2.7 vs. 7.1 ± 2.5 episodes/h, p = 0.003, and 72 ± 15 vs. 87 ± 25 s, p = 0.01, respectively). The proportion of time in severe hypoxemia (SpO2 <75%) was smaller, whereas time in hyperoxemia (SpO2 >95%) was greater, during the night compared to the day. The mean FiO2 did not differ between day and night.

CONCLUSION

In this group of infants with frequent HE, nighttime was associated with fewer episodes when compared to daytime. This is likely due to less handling and sensory stimulation during the night. The increase in time spent with hyperoxemia during the night is likely to be due to more tolerance of high SpO2 with less proactive weaning of FiO2.

Volume Guarantee Ventilation: Effect on Preterm Infants with Frequent Hypoxemia Episodes

BACKGROUND

Preterm infants on mechanical ventilation have spontaneous hypoxemia episodes (HE) triggered by decreases in lung volume and tidal volume (VT). Volume guarantee (VG) is a mode where the ventilator peak pressure is adjusted to keep the exhaled VT at a target level. The effect of VG on HE under routine clinical conditions has not been fully evaluated.

OBJECTIVE

To evaluate the effect of VG on HE in preterm infants in comparison to pressure control (PC) ventilation under routine clinical conditions.

METHODS

Twenty-four mechanically ventilated preterm infants with ≥4 HE of arterial oxygen saturation (SpO2) <75% over 8 h were enrolled. They were studied over 2 consecutive 24-hour periods of VG and PC, in random order.

RESULTS

While the frequency of HE (SpO2 <85% for ≥20 s) did not differ, their duration was reduced during VG. The frequency or duration of severe HE (SpO2 <75% for ≥20 s) did not differ between PC and VG. The proportion of time in severe hypoxemia (SpO2 <75%) during VG did not differ from PC [median: 4.4 (IQR 2.9-5.0) vs. 5.0% (IQR 3.9-6.9), p = 0.44]. The fraction of inspired oxygen (FiO2) was lower during VG compared to PC.

CONCLUSION

The use of VG during routine clinical conditions resulted in a modest reduction in the duration of HE (SpO2 <85%) and FiO2 compared to PC. The use of VG did not reduce the more severe HE.

A randomized controlled trial of two nasal continuous positive airway pressure levels after extubation in preterm infants

OBJECTIVE

To compare extubation failure rate with two ranges of nasal continuous positive airway pressure (NCPAP) in oxygen dependent preterm infants.

STUDY DESIGN

Preterm infants of birth weight 500-1000 g and gestational age 23-30 weeks, extubated for the first time during the first 6 weeks while requiring fraction of inspired oxygen ≥ 0.25, were randomly assigned to a NCPAP range of 4-6 (low NCPAP) or 7-9 (high NCPAP) cmH2O.

RESULTS

Infants were randomized to low (n = 47) or high NCPAP (n = 46) at day 16.3 ± 14.7 and 15.5 ± 12.4, respectively. Rates of extubation failure per criteria (24% vs 43%, P = .04, OR and 95% CI: 0.39 [0.16-0.96]) and re-intubation (17% vs 38%, P = .023, 0.33 [0.016-0.85]) within 96 hours were significantly lower in the high- compared with the low NCPAP group. This was mainly due to a strikingly lower failure rate in the 500-750 g birth weight strata. Duration of ventilation, bronchopulmonary dysplasia, or severe bronchopulmonary dysplasia did not differ significantly. No infant developed pneumothorax during 96 hours post-extubation.

CONCLUSIONS

Extubation failure in preterm infants with residual lung disease was lower with NCPAP range of 7-9 compared with 4-6 cmH2O. These findings suggest the need for higher distending pressure post-extubation in the more immature infants who are still oxygen dependent.

Effect of positive end-expiratory pressure on ductal shunting and systemic blood flow in preterm infants with patent ductus arteriosus

BACKGROUND

Left to right (L-R) shunting through a patent ductus arteriosus (PDA) can reduce systemic and cerebral blood flow in preterm infants. To minimize this, the positive end-expiratory pressure (PEEP) is often raised to increase pulmonary vascular resistance and reduce L-R shunting. The effects of this maneuver on systemic and cerebral hemodynamics and oxygenation are not well documented.

OBJECTIVE

To compare the effects of different PEEP on the left ventricular output (LVO), superior vena cava (SVC) flow, LVO/SVC flow ratio, cerebral oxygenation (CrSO2) and gas exchange in mechanically ventilated preterm infants with PDA.

METHODS

Sixteen mechanically ventilated infants of 23-30 weeks' gestational age with L-R shunting through the PDA were studied. Ultrasound measurements of LVO and SVC flow, CrSO2, arterial oxygen saturation and transcutaneous CO2 tension (TcPCO2) obtained at PEEP of 2 and 8 cm H2O were compared with baseline values at 5 cm H2O.

RESULTS

There was a small but significant reduction in LVO and the LVO/SVC flow ratio at PEEP of 8 compared to 5 cm H2O. SVC flow and CrSO2 did not differ significantly.

CONCLUSIONS

Increasing PEEP to 8 cm H2O in ventilated preterm infants with a PDA produced a modest decrease in L-R ductal shunting as indicated by a lower LVO/SVC flow ratio. The higher PEEP did not have a significant effect on cerebral perfusion or oxygenation.

Multicenter crossover study of automated control of inspired oxygen in ventilated preterm infants

OBJECTIVE

To determine the efficacy and safety of automated adjustment of the fraction of inspired oxygen (Fio(2)) adjustment in maintaining arterial oxygen saturation (Spo(2)) within an intended range for mechanically ventilated preterm infants with frequent episodes of decreased Spo(2).

METHODS

Thirty-two infants (gestational age [median and interquartile range]: 25 weeks [24-27 weeks]; age: 27 days [17-36 days]) were studied during 2 consecutive 24-hour periods, one with Fio(2) adjusted by clinical staff members (manual) and the other by an automated system (automated), in random sequence.

RESULTS

Time with Spo(2) within the intended range (87%-93%) increased significantly during the automated period, compared with the manual period (40% ± 14% vs 32% ± 13% [mean ± SD]). Times with Spo(2) of >93% or >98% were significantly reduced during the automated period (21% ± 20% vs 37% ± 12% and 0.7% vs 5.6% [interquartile ranges: 0.1%-7.2% and 2.7%-11.2%], respectively). Time with Spo(2) of <87% increased significantly during the automated period (32% ± 12% vs 23% ± 9%), with more-frequent episodes with Spo(2) between 80% and 86%, whereas times with Spo(2) of <80% or <75% did not differ between periods. Hourly median Fio(2) values throughout the automated period were lower and there were substantially fewer manual Fio(2) changes (10 ± 9 vs 112 ± 59 changes per 24 hours; P < .001), compared with the manual period.

CONCLUSIONS

In infants with fluctuations in Spo(2), automated Fio(2) adjustment improved maintenance of the intended Spo(2) range led to reduced time with high Spo(2) and more-frequent episodes with Spo(2) between 80% and 86%.

Effects of instrumental dead space reduction during weaning from synchronized ventilation in preterm infants

OBJECTIVE

A majority of the modalities of synchronized ventilation in preterm infants require the use of flow sensors that can increase dead space and may adversely affect ventilator weaning. The objective of this study was to assess the effects of flow sensor dead space during synchronized intermittent mandatory ventilation (SIMV) weaning in preterm infants.

STUDY DESIGN

Twelve preterm infants (gestational age 25+/-2 weeks, birth weight 705+/-158 g, age: 31+/-186 days, SIMV rate: 25+/-8 breaths min(-1), peak inspiratory pressure 18+/-2 cm H(2)O, positive end-expiratory pressure: 5+/-0.5 cm H(2)O, pressure support: 9+/-3 cm H(2)O, fraction of inspired oxygen: 34+/-6%) underwent two 2.5-h weaning periods during which SIMV rate was reduced twice by 5 breaths min(-1) at 30-min intervals as tolerated, with and without reduction of flow sensor dead space, in random sequence. A 30-min baseline was obtained before each weaning period. Dead space was reduced by flushing the flow sensor with a continuous gas leak flow in the endotracheal tube connector.

RESULT

Transcutaneous CO(2) tension during SIMV weaning periods without and with reduced dead space did not differ from baseline, whereas total minute ventilation and tidal volume were lower during the SIMV weaning period with reduced dead space. Three infants did not tolerate SIMV weaning without while one infant did not tolerate weaning with reduced dead space.

CONCLUSION

SIMV weaning elicited a compensatory rise in spontaneous ventilation. When flow sensor dead space was reduced during SIMV weaning, gas exchange was maintained with lower minute ventilation. Instrumental dead space imposes a ventilatory burden during SIMV weaning in small preterm infants.

Automated adjustment of inspired oxygen in preterm infants with frequent fluctuations in oxygenation: a pilot clinical trial

OBJECTIVE

To assess the efficacy of a system for automated fraction of inspired oxygen (FiO(2)) adjustment in maintaining oxygen saturation (SpO(2)) within an intended range in preterm infants with spontaneous fluctuations in SpO(2).

STUDY DESIGN

Sixteen infants (gestational age, 24.9 +/- 1.4 weeks; birth weight, 678 +/- 144 g; age, 33 +/- 15 days) with frequent hypoxemia episodes underwent two 4-hour periods of FiO(2) adjustment by clinical personnel (routine) and the automated system (automated).

RESULTS

Compared with the routine period, the percent time within intended SpO(2) range (88%-95%) increased during the automated period (58% +/- 10% versus 42% +/- 9%; P < .001), whereas the percent time with SpO(2) higher than the intended range and >or=98% were reduced (9% +/- 10% versus 31% +/- 8% [P < .001] and 3% +/- 5% versus 16% +/- 9% [P < .001], respectively). Percent time with SpO(2) < 88% increased during the automated period (33% +/- 7% versus 27% +/- 9%; P = .003) because of more frequent episodes, whereas the time with SpO(2) < 75% did not differ. The 4-hour median FiO(2) was lower during the automated period (29% +/- 4% versus 34% +/- 5%; P < .001).

CONCLUSION

Automated FiO(2) adjustment improved maintenance of SpO(2) within the intended range and reduced hyperoxemia and FiO(2). These findings should be examined in longer periods with standard clinical conditions and, eventually, in the context of randomized trials powered to detect clinically important effects on outcome.

Targeted minute ventilation and tidal volume in an animal model of acute changes in lung mechanics and episodes of hypoxemia

BACKGROUND

Acute episodes of hypoxemia in ventilated preterm infants are triggered by changes in ventilation, lung volume (LV) and respiratory system compliance (C(RS)) that are not prevented by conventional synchronized intermittent mandatory ventilation (SIMV).

OBJECTIVE

To assess in a rabbit model of episodic hypoxemia the individual and combined efficacy of targeted tidal volume (V(T)) and minute ventilation (V'(E)) by automatic adjustment of peak inspiratory pressure (PIP) and ventilator rate, respectively.

METHODS

Six young New Zealand white rabbits were ventilated with SIMV, targeted V(T), targeted V'(E), and combined targeted V'(E) + V(T) in random sequence. Hypoxemia episodes were induced by apnea alone or by apnea combined with a reduction in LV and C(RS). Apnea was induced by a bolus of propofol. The reduction in LV and C(RS) was induced by chest compression with a cuff. PaO(2) and PaCO(2) were measured continuously by an indwelling arterial electrode.

RESULTS

During SIMV, apnea caused a decrease in ventilation and PaO(2). This was attenuated during targeted V'(E) and targeted V'(E) + V(T). Apnea plus a reduction in LV and C(RS) caused a greater decrease in ventilation and PaO(2) during SIMV. These changes were attenuated during targeted V(T) and targeted V'(E). The attenuation was more pronounced during targeted V'(E) + V(T).

CONCLUSION

In this animal model, targeted V'(E) was effective in reducing hypoxemia caused by apnea. When apnea was accompanied by a reduction in LV and C(RS), the combined adjustment of PIP and ventilator rate was more effective than each individually. This combined strategy may be effective in ameliorating acute episodes of hypoxemia in preterm infants but this remains to be proven.

Mechanisms of hypoxemia episodes in spontaneously breathing preterm infants after mechanical ventilation

BACKGROUND

Preterm infants often present with recurrent episodes of hypoxemia after mechanical ventilation.

OBJECTIVE

To evaluate the role of abdominal muscle activity and central apnea on the frequency and severity of hypoxemia episodes (HEs) in preterm infants with a history of mechanical ventilation.

METHODS

Continuous recordings of arterial oxygen saturation (SpO(2)), gastric pressure, respiratory inductance plethysmography and abdominal surface electromyography were obtained during 4 h from spontaneously breathing preterm infants who had recently been extubated and presented with frequent HEs.

RESULTS

Ten infants (gestational age 26.4 +/- 1.1 weeks, body weight 816 +/- 128 g, age 44 +/- 21 days, FiO2 0.31 +/- 0.09, mechanically ventilated for 33 +/- 37 days) were studied 12 +/- 7 (mean +/- SD) days after extubation. These infants presented with 10.2 +/- 9.3 HEs/h (SpO2 <88%, > or =10 s). Of these, 8.2 +/- 6.2 HEs/h were associated with abdominal muscle contraction while only 2.0 +/- 4.5 HEs/h were associated with > or =10 s apnea (p < 0.05). Of the more severe HEs (SpO(2) <75%, > or =10 s), 2.7 +/- 3.1 HEs/h were associated with abdominal contraction and only 0.7 +/- 2.1 HEs/h with apnea (p < 0.05). Resting lung volume decreased by 69 +/- 16% of tidal volume in HEs associated with abdominal contraction.

CONCLUSIONS

In this group of premature infants who presented with frequent HEs after mechanical ventilation, most HEs were associated with abdominal muscles contraction and a loss in lung volume. These findings provide an alternate mechanism to explain these episodes in spontaneously breathing preterm infants with a history of mechanical ventilation.

Effects of non-invasive pressure support ventilation (NI-PSV) on ventilation and respiratory effort in very low birth weight infants

BACKGROUND

Nasal continuous positive airway pressure (NCPAP) is used to provide support to non-intubated infants, but it often fails. Pressure support ventilation (PSV) is a mode of synchronized ventilation that can supplement the spontaneous breathing effort, but it is unknown if it is effective in non-intubated very low birth weight (VLBW) infants.

OBJECTIVES

To compare the acute physiological effects of non-invasive PSV (NI-PSV) versus NCPAP on tidal volume (V(T)), minute ventilation (V(E)), gas exchange, breathing effort, and chest wall distortion in VLBW infants.

METHODS

Stable preterm infants of birth weight less 1,250 g were studied during consecutive 2 hr periods of NCPAP and NI-PSV in random sequence. VT, V(E), and thoraco-abdominal synchrony were measured using respiratory inductance plethysmography. Breathing effort was measured by esophageal manometry. Gas exchange was measured by pulse oximetry and transcutaneous PCO2.

RESULTS

Fifteen infants of birth weight (mean +/- SD) 808 +/- 201 g and 25.9 +/- 1.8 weeks gestational age were studied while on NCPAP 5.3 +/- 0.6 cm H2O and on NI-PSV with 7.9 +/- 1.3 cm H2O above NCPAP of pressure support. There were no differences in VT, V(E), PCO2 or hypoxemia episodes. Peak and minute inspiratory effort were significantly reduced in NI-PSV mode as compared to NCPAP. There was a significant reduction in indices of chest wall asynchrony in NI-PSV mode.

CONCLUSION

When compared to NCPAP, NI-PSV did not increase minute ventilation, but it effectively unloaded the patient's respiratory pump as indicated by a lower inspiratory effort and reduced chest wall distortion.

Role of abdominal muscles activity on duration and severity of hypoxemia episodes in mechanically ventilated preterm infants

BACKGROUND

Episodes of hypoxemia are often observed in ventilated preterm infants. The factors that determine their duration, severity and the failure of the mechanical breaths to maintain ventilation have not been fully defined.

OBJECTIVE

To determine the relation between activity of the abdominal muscles and the duration and severity of hypoxemia episodes in ventilated preterm infants.

METHODS

Clinically stable ventilated preterm infants weighing between 500 and 1,000 g at birth, who presented with frequent episodes of hypoxemia, were studied. Recordings of arterial oxygen saturation (SpO(2)), tidal volume and abdominal surface electromyography were obtained during 4 h to assess the temporal relationship between activation of abdominal musculature with the onset, duration and severity of hypoxemia episodes.

RESULTS

In 15 infants, GA (mean +/- SD) 25 +/- 1.5 weeks, BW 697 +/- 141 g, age 37 +/- 14 days, synchronized intermittent mandatory ventilation rate 17 +/- 6 breaths/min, peak inspiratory pressure 18 +/- 1.9 cm H(2)O, positive end-expiratory pressure 4.8 +/- 0.6 cm H(2)O, and fraction of inspired oxygen (FiO(2)) 0.4 +/- 0.1 were studied. These infants presented with 7.2 +/- 4.4 episodes of hypoxemia (SpO(2) <88%) per hour. The number of abdominal muscle contractions per episode correlated with the duration and severity of the episodes of hypoxemia. The episode duration increased by 14 +/- 18 s per abdominal muscle contraction. The lowest SpO(2) reached during an episode of hypoxemia decreased by 1.7 +/- 1.4% for every abdominal muscle contraction.

CONCLUSIONS

These data document a relationship between abdominal muscles contraction and the duration and severity of hypoxemia episodes in ventilated preterm infants. These findings can explain the failure of mechanical ventilation to prevent their occurrence or decrease their severity.

Randomized, controlled trial comparing synchronized intermittent mandatory ventilation and synchronized intermittent mandatory ventilation plus pressure support in preterm infants

BACKGROUND

Prolonged mechanical ventilation is associated with lung injury in preterm infants. In these infants, weaning from synchronized intermittent mandatory ventilation may be delayed by their inability to cope with increased respiratory loads. The addition of pressure support to synchronized intermittent mandatory ventilation can offset these loads and may facilitate weaning.

OBJECTIVE

The purpose of this work was to compare synchronized intermittent mandatory ventilation and synchronized intermittent mandatory ventilation plus pressure support in weaning from mechanical ventilation and the duration of supplemental oxygen dependency in preterm infants with respiratory failure.

METHODS

Preterm infants weighing 500 to 1000 g at birth who required mechanical ventilation during the first postnatal week were randomly assigned to synchronized intermittent mandatory ventilation or synchronized intermittent mandatory ventilation plus pressure support. In both groups, weaning followed a set protocol during the first 28 days. Outcomes were assessed during the first 28 days and until discharge or death.

RESULTS

There were 107 infants enrolled (53 synchronized intermittent mandatory ventilation plus pressure support and 54 synchronized intermittent mandatory ventilation). Demographic and perinatal data, mortality, and morbidity did not differ between groups. During the first 28 days, infants in the synchronized intermittent mandatory ventilation plus pressure support group reached minimal ventilator settings and were extubated earlier than infants in the synchronized intermittent mandatory ventilation group. Total duration of mechanical ventilation, duration of oxygen dependency, and oxygen need at 36 weeks' postmenstrual age alone or combined with death did not differ between groups. However, infants in synchronized intermittent mandatory ventilation plus pressure support within the 700- to 1000-g birth weight strata had a shorter oxygen dependency.

CONCLUSIONS

The results of this study suggest that the addition of pressure support as a supplement to synchronized intermittent mandatory ventilation during the first 28 days may play a role in reducing the duration of mechanical ventilation in extremely low birth-weight infants, and it may lead to a reduced oxygen dependency in the 700- to 1000-g birth weight strata.

Acute effects of PEEP on tidal volume and respiratory center output during synchronized ventilation in preterm infants

BACKGROUND

Positive end expiratory pressure (PEEP) is routinely used in mechanically ventilated preterm infants to maintain lung volume. An acute increase in PEEP can affect lung mechanics and tidal volume, but it is unknown if these effects elicit compensatory changes in respiratory center output.

OBJECTIVES

To investigate the acute effects of changes in PEEP on tidal volume (V(T)), lung compliance (C(L)), and respiratory center output (RCO) during synchronized intermittent mandatory ventilation (SIMV) in preterm infants at different levels of basal respiratory drive.

METHODS

Preterm infants were studied during SIMV at three levels of PEEP (2, 4, and 6 cm H(2)O for 2-3 min each) and at two levels of inspired CO(2). Peak inspiratory pressure (PIP) was adjusted to maintain the same delta pressure at the airway. RCO was assessed by measuring total diaphragmatic electrical activity. The level of inspired CO(2) was adjusted by modifying the instrumental dead space.

RESULTS

Sixteen preterm infants GA: 25 +/- 2 weeks, BW: 786 +/- 242 g, age: 18 +/- 15 days, SIMV: rate 14 +/- 3 b/min, Ti: 0.35 +/- 0.01 s, PIP: 16 +/- 1 cm H(2)O, and FiO(2): 0.31 +/- 0.06 were studied. At both levels of inspired CO(2), C(L), V(T), and V'(E) from spontaneous and mechanical breaths decreased significantly with higher PEEP. RCO did not change, but at lower respiratory drive, there was a trend towards an increase in RCO with higher PEEP.

CONCLUSION

Higher PEEP levels can have acute negative effects on lung mechanics and ventilation in preterm infants without a sufficient compensatory increase in RCO.

Effects of volume-targeted synchronized intermittent mandatory ventilation on spontaneous episodes of hypoxemia in preterm infants

BACKGROUND

Hypoxemic episodes in ventilated preterm infants are frequently caused by reduced ventilation due to a decrease in lung volume and acute worsening of respiratory mechanics.

OBJECTIVE

To compare the efficacy of conventional time-cycled, pressure-limited flow synchronized intermittent mandatory ventilation (SIMV) and volume-targeted SIMV (VT-SIMV) in reducing the frequency and severity of these episodes.

METHODS

SIMV and VT-SIMV were compared in preterm infants with frequent spontaneous episodes of hypoxemia. VT-SIMV was provided with the Draeger Babylog 8000plus ventilator in volume-guarantee mode.

RESULTS

In all, 32 infants (birth weight 668 +/- 126 g, gestational age 24.8 +/- 1.1 weeks, age 37.5 +/- 17.3 days) were studied during 2-hour periods of SIMV and VT-SIMV in random sequence. In an initial phase, a group of 12 infants was supported during VT-SIMV with a target tidal volume of 4.5 ml/kg (VT-SIMV 4.5). A planned interim analysis did not show differences in frequency and duration of hypoxemia between VT-SIMV 4.5 and SIMV, and the initial phase was stopped. In a second phase of the study, 20 infants were studied while supported with a target tidal volume of 6.0 ml/kg during VT-SIMV (VT-SIMV 6.0). In the second phase of the study, the frequency of the hypoxemic episodes did not change but the mean episode duration was shorter during VT-SIMV compared to SIMV. The proportion of mechanical breaths with small tidal volumes (< or =3 ml/kg) was reduced during VT-SIMV 6.0 versus SIMV, while the peak inspiratory pressure and mean airway pressure were increased.

CONCLUSION

VT-SIMV did not reduce the frequency of hypoxemic episodes, but VT-SIMV 6.0 was effective in reducing the duration of the hypoxemic episodes.

Effects of pressure support during an acute reduction of synchronized intermittent mandatory ventilation in preterm infants

BACKGROUND

During weaning of synchronized intermittent mandatory rate in preterm infants, the spontaneous breaths must overcome the resistance of the endotracheal tube and the disease-induced respiratory loads. Pressure Support (PS) can be used as an adjunct to synchronized intermittent mandatory ventilation (SIMV) to partially unload the spontaneous breaths.

OBJECTIVE

To evaluate the effects of two levels of PS as an adjunct to SIMV on gas exchange and breathing effort during an acute reduction in SIMV rate in preterm infants.

METHODS

In all, 15 infants (birth weight 793 +/- 217 g, gestational age 26.4 +/- 1.5 weeks, postnatal age 15 +/- 16 days). Ventilatory support consisted of SIMV with peak inspiratory pressure (PTP) 16.3 +/- 1.3 cmH(2)O, positive end-expiratory pressure (PEEP) 4.3 +/- 0.6 cmH(2)O, and fraction of inspired oxygen (FiO(2)) 0.26 +/- 0.06. Infants were studied during four 30-minute periods: Two baseline SIMV periods and two periods of SIMV plus PS, in random order. During SIMV + PS, SIMV rate was lowered by 10 breaths per minute (b/minute) and PS was set at 3 and 6 cmH(2)O (SIMV+PS3 and SIMV + PS6, respectively).

RESULTS

SIMV rate was reduced during SIMV + PS from 21.4 +/- 6.6 to 11.4 +/- 6.6 b/minute. Arterial oxygen saturation, transcutaneous carbon dioxide tension and FiO(2) remained unchanged. Minute ventilation, total respiratory rate and mean airway pressure were higher during SIMV + PS. Per-breath inspiratory effort was lower during SIMV + PS and this was more striking during SIMV + PS6. Spontaneous inspiratory effort per minute increased during SIMV + PS3, but this increase was averted during SIMV + PS6.

CONCLUSION

Assistance of the spontaneous breaths with pressure support maintained gas exchange. PS of 6 cm H(2)O prevented an increase in breathing effort during an acute 50% reduction in SIMV rate.

Acute effects of inhaled nitric oxide on pulmonary and cardiac function in preterm infants with evolving bronchopulmonary dysplasia

BACKGROUND

Inhaled nitric oxide (iNO) reduces pulmonary vascular resistance by preferential vasodilation in ventilated lung units. In experimental animals, iNO also reduces airway resistance by smooth muscle relaxation. Hence, there may be a therapeutic role for iNO in evolving bronchopulmonary dysplasia (BPD).

OBJECTIVE

To evaluate the acute effects of low-dose iNO on lung mechanics, ventilation distribution, oxygenation, and cardiac function in preterm infants with evolving BPD.

METHODS

Measurements of lung compliance (C(L)), airway resistance (R(L)), ventilation-distribution (N(2) clearance in multiple-breath washout), oxygenation (SpO(2)), left ventricular ejection fraction (LVEF) and right ventricular shortening fraction were obtained before and during 2 hours of iNO (10 ppm) in a group of ventilated preterm infants with evolving BPD.

RESULTS

A total of 13 preterm infants with (mean+/-SD) BW: 663.8+/-116 g, GA: 24.9+/-1.2 weeks, age: 32+/-14 days, mean airway pressure: 6.7+/-0.9 cmH(2)O and fraction of inspired oxygen: 0.35+/-0.06 were studied. iNO did not affect C(L), R(L) or N(2) clearance. There was a small increase in LVEF. Mean SpO(2) remained unchanged, but the duration of spontaneous hypoxemic episodes increased during iNO.

CONCLUSION

Low-dose iNO had no acute effects on lung function, cardiac function and oxygenation in evolving BPD.

Elimination of ventilator dead space during synchronized ventilation in premature infants

BACKGROUND

Mainstream airflow sensors used in neonatal ventilators to synchronize mechanical breaths with spontaneous inspiration and measure ventilation increase dead space and may impair carbon dioxide (CO(2)) elimination.

OBJECTIVE

To evaluate a technique consisting of a continuous gas leakage at the endotracheal tube (ETT) adapter to wash out the airflow sensor for synchronization and ventilation monitoring without CO(2) rebreathing in preterm infants.

DESIGN

Minute ventilation (V'(E)) by respiratory inductance plethysmography, end-inspiratory and end-expiratory CO(2) by side-stream microcapnography, and transcutaneous CO(2) tension (TcPCO(2)) were measured in 10 infants (body weight, 835+/-244 g; gestational age, 26+/-2 weeks; age, 19+/-9 days; weight, 856+/-206 g; ventilator rate, 21+/-6 beats/min; PIP, 16+/-1 centimeters of water (cmH(2)O); PEEP, 4.2+/-0.4 cmH(2)O; fraction of inspired oxygen (FIo(2)), 0.26+/-0.6). The measurements were made during four 30-minute periods in random order: IMV (without airflow sensor), IMV+Sensor, SIMV (with airflow sensor), and SIMV+Leak (ETT adapter continuous leakage).

RESULTS

Airflow sensor presence during SIMV and IMV+Sensor periods resulted in higher end-inspiratory and end-expiratory CO(2), Tcpco(2), and spontaneous V'(E) compared with IMV. These effects were not observed during SIMV+Leak.

CONCLUSIONS

The significant physiologic effects of airflow sensor dead space during synchronized ventilation in preterm infants can be effectively prevented by the ETT adapter continuous leakage technique.