Evolution of mechanical ventilation of the newborn infant

Artificial ventilation of the newborn infant is the foundation of neonatology. Early practitioners included pediatricians, anesthesiologists, cardiologists, respiratory therapists, and engineers. The discovery of surfactant, followed by the death of Patrick Kennedy, jump-started the new area, with investment and research rapidly expanding. The ever more complex design of mechanical ventilators necessitated a more thorough understanding of newborn pulmonary physiology in order to provide support with minimal associated injury. This piece briefly reviews and highlights this history.

Laryngeal Mask Airway for Surfactant Administration in Neonates: A Randomized, Controlled Trial

OBJECTIVE

To determine if preterm infants with moderate respiratory distress syndrome on continuous positive airway pressure (CPAP) who received surfactant via a laryngeal mask airway (LMA) would have a decreased rate of intubation and mechanical ventilation compared with those on CPAP who did not receive surfactant.

STUDY DESIGN

In this prospective, multicenter, randomized controlled trial, 103 premature infants 28^0/7-35^6/7 weeks gestation, ≥1250 g and ≤36 hours old on CPAP requiring fraction of inspired oxygen 0.30-0.40 were assigned to receive surfactant administered through an LMA then placed back on CPAP (LMA group) or maintained on CPAP with no surfactant administered (control group). The primary outcome was treatment failure necessitating intubation and mechanical ventilation in the first 7 days of life.

RESULTS

Surfactant administration through an LMA (n = 50) significantly decreased the rate of intubation and mechanical ventilation compared with controls (n = 53): 38% vs 64%, respectively, OR 0.30 (95% CI 0.13, 0.70), P = .006, number needed to treat: 4). There were no serious adverse events associated with placement of the LMA or surfactant administration.

CONCLUSIONS

In premature neonates with moderate respiratory distress syndrome, surfactant administered through an LMA decreased the rate of intubation and mechanical ventilation. This intervention may have significant impact on clinical care in both high and low resource settings.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01116921.

The Randomized, Controlled Trial of Late Surfactant: Effects on Respiratory Outcomes at 1-Year Corrected Age

OBJECTIVE

To determine the effects of late surfactant on respiratory outcomes determined at 1-year corrected age in the Trial of Late Surfactant (TOLSURF), which randomized newborns of extremely low gestational age (≤28 weeks' gestational age) ventilated at 7-14 days to late surfactant and inhaled nitric oxide vs inhaled nitric oxide-alone (control).

STUDY DESIGN

Caregivers were surveyed in a double-blinded manner at 3, 6, 9, and 12 months' corrected age to collect information on respiratory resource use (infant medication use, home support, and hospitalization). Infants were classified for composite outcomes of pulmonary morbidity (no PM, determined in infants with no reported respiratory resource use) and persistent PM (determined in infants with any resource use in ≥3 surveys).

RESULTS

Infants (n = 450, late surfactant n = 217, control n = 233) were 25.3 ± 1.2 weeks' gestation and 713 ± 164 g at birth. In the late surfactant group, fewer infants received home respiratory support than in the control group (35.8% vs 52.9%, relative benefit [RB] 1.28 [95% CI 1.07-1.55]). There was no benefit of late surfactant for No PM vs PM (RB 1.27; 95% CI 0.89-1.81) or no persistent PM vs persistent PM (RB 1.01; 95% CI 0.87-1.17). After adjustment for imbalances in baseline characteristics, relative benefit of late surfactant treatment increased: RB 1.40 (95% CI 0.89-1.80) for no PM and RB 1.24 (95% CI 1.08-1.42) for no persistent PM.

CONCLUSION

Treatment of newborns of extremely low gestational age with late surfactant in combination with inhaled nitric oxide decreased use of home respiratory support and may decrease persistent pulmonary morbidity.

TRIAL REGISTRATION

ClinicalTrials.gov: NCT01022580.

Real-time pulmonary graphics

Real-time pulmonary graphics now enable clinicians to view lung mechanics and patient-ventilator interactions on a breath-to-breath basis. Displays of pressure, volume, and flow waveforms, pressure-volume and flow-volume loops, and trend screens enable clinicians to customize ventilator settings based on the underlying pathophysiology and responses of the individual patient. This article reviews the basic concepts of pulmonary graphics and demonstrates how they contribute to our understanding of respiratory physiology and the management of neonatal respiratory failure.

Inhaled nitric oxide increases urinary nitric oxide metabolites and cyclic guanosine monophosphate in premature infants: relationship to pulmonary outcome

OBJECTIVE

Inhaled nitric oxide (iNO) has been tested to prevent bronchopulmonary dysplasia (BPD) in premature infants, however, the role of cyclic guanosine monophosphate (cGMP) is not known. We hypothesized that levels of NO metabolites (NOx) and cGMP in urine, as a noninvasive source for biospecimen collection, would reflect the dose of iNO and relate to pulmonary outcome.

STUDY DESIGN

Studies were performed on 125 infants who required mechanical ventilation at 7 to 14 days and received 24 days of iNO at 20-2 ppm. A control group of 19 infants did not receive iNO.

RESULTS

In NO-treated infants there was a dose-dependent increase of both NOx and cGMP per creatinine (maximal 3.1- and 2-fold, respectively, at 10-20 ppm iNO) compared with off iNO. NOx and cGMP concentrations at both 2 ppm and off iNO were inversely related to severity of lung disease during the 1st month, and the NOx levels were lower in infants who died or developed BPD at term. NOx was higher in Caucasian compared with other infants at all iNO doses.

CONCLUSION

Urinary NOx and cGMP are biomarkers of endogenous NO production and lung uptake of iNO, and some levels reflect the severity of lung disease. These results support a role of the NO-cGMP pathway in lung development.

Bi-level CPAP does not improve gas exchange when compared with conventional CPAP for the treatment of neonates recovering from respiratory distress syndrome

AIM

We hypothesised that short-term application of bi-level nasal continuous positive airway pressure CPAP (SiPAP) compared with conventional nasal CPAP (nCPAP) at the same mean airway pressure in infants with persistent oxygen need recovering from respiratory distress syndrome would improve CO2 removal with no change in oxygen requirement.

DESIGN

Non-blinded, randomised, observational four-period crossover study.

SETTING/POPULATION

Level III NICU; low-birthweight infants requiring CPAP and oxygen while recovering from respiratory distress syndrome.

METHODS

Infants requiring nasal CPAP for >24 h prior to study enrolment, and fraction of inspired oxygen requirement (FiO2) of 0.25-0.5, were randomised to either nCPAP or SiPAP. A crossover design with four 1 h treatment periods was used such that each infant received both treatments twice. Oxygen saturations (SaO2), transcutaneous CO2 (tcCO2) and vital signs were monitored continuously. Polysomnographic recordings were analysed for apnoea, bradycardia and oxygen desaturation.

RESULTS

Twenty low-birthweight infants receiving 0.3±0.04% supplemental oxygen on CPAP of 6 cm H2O were studied at an average of 33 days of age (±23 days, SD). There were no differences in tcCO2 or other physiological parameters except mean blood pressure, which was lower during nCPAP (52.3±8.3 vs 54.4±9.1 mm Hg; ±SD; p<0.01). No differences in short or prolonged apnoea, bradycardia or significant desaturation events were observed.

CONCLUSIONS

At similar mean airway pressures, SiPAP does not improve CO2 removal, oxygenation or other studied physiological parameters with the exception of mean blood pressure, which was not clinically significant.

TRIAL REGISTRATION NUMBER

NCT01053455.

Aerosolized KL4 surfactant improves short-term survival and gas exchange in spontaneously breathing newborn pigs with hydrochloric acid-induced acute lung injury

BACKGROUND

Surfactant therapy may be beneficial in acute lung injury (ALI). In spontaneously breathing newborn pigs with ALI supported with continuous positive airway pressure (CPAP), we evaluated the hypothesis that aerosolized KL4 surfactant (AERO KL4 S) would provide a similar therapeutic effect as intratracheal KL4 surfactant (ETT KL4 S) when compared to controls.

METHODS

We randomized pigs with HCl-induced ALI to: (1) 175 mg/kg KL4 surfactant via endotracheal tube (ETT); (2) AERO KL4 S (22.5 mg/min phospholipid) for 60 min via continuous positive airway pressure (CPAP); or (3) sham procedure on CPAP. We obtained physiologic data and arterial blood gases throughout the 3-hr study. At study end, lungs were excised for analysis of interleukin-8 (IL-8), myeloperoxidase (MPO) levels and histomorphometric data.

RESULTS

Pigs treated with ETT KL4 S and AERO KL4 S had improved survival and sustained pO2 compared to controls. The AERO KL4 S group had higher pH compared to controls. Lung IL-8 levels were lower in the AERO KL4 S group compared to controls. Histomorphometric analysis showed less hemorrhage in the ETT and AERO KL4 S groups compared to controls. The AERO KL4 S group had more open lung units per fixed-field than the ETT KL4 S or controls.

CONCLUSIONS

AERO KL4 S produced similar improvements in survival, physiology, inflammatory markers, and morphology as ETT KL4 S in an ALI model.

Tracheostomy for infants requiring prolonged mechanical ventilation: 10 years' experience

BACKGROUND

Despite advances in care of critically ill neonates, extended mechanical ventilation and tracheostomy are sometimes required. Few studies focus on complications and clinical outcomes. Our aim was to provide long-term outcomes for a cohort of infants who required tracheostomy.

METHODS

This study is a retrospective review of 165 infants born between January 1, 2000 and December 31, 2010 who required tracheostomy and ventilator support. Children with complex congenital heart disease were excluded.

RESULTS

Median gestational age was 27 weeks (range 22-43), and birth weight was 820 g (range 360-4860). The number of male (53.9%) and female (46.1%) infants was similar (P = .312). Infants were divided into 2 groups based on birth weight ≤1000 g (A) and >1000 g (B). Group A: 87 (57.6%) infants; group B 64 (42.4%). Overall tracheostomy rate was 6.9% (87/1345) for group A versus 0.9% (64/6818) for B (P <.001). Group A had a longer time from intubation to positive pressure ventilation independence, 505 days (range 62-1287) vs 372 days (range 15-1270; P = .011). Infants who had >1 reason for tracheostomy comprised 78.8% of the sample; 69.1% of infants were discharged on ventilators. Birth weight did not affect time from tracheostomy to decannulation (P = .323). More group A infants were decannulated (P = .023). laryngotracheal reconstruction rate was 35.8%. Five-year survival was 89%. Group B had higher mortality (P = .033). 64.2% of infants had developmental delays; 74.2% had ≥2 comorbidities.

CONCLUSIONS

Tracheostomy rates were higher for extremely low birth weight infants than previously reported rates for all infants. Decannulation rates and laryngotracheal reconstruction rates were consistent with previous studies. Survival rates were high, but developmental delay and comorbidities were frequent.

Laryngeal mask airway for surfactant administration in a newborn animal model

Premature infants are subjected to adverse effects of intubation to benefit from surfactant. We hypothesized that administration of surfactant through a laryngeal mask airway (LMA) is as effective as administration through an endotracheal tube (ETT) and that time and physiologic changes during instrumentation will be less in the LMA group. This study is a randomized, controlled trial using newborn pigs. Lung injury was induced via surfactant washout. Animals were randomized into groups: 1) LMA placed, no surfactant administered (control; n = 8); 2) surfactant via an LMA (LMA group; n = 8); and 3) surfactant via an ETT (ETT group; n = 8). We demonstrated that partial pressure of oxygen in arterial blood (Pao2) levels of the LMA and ETT groups were not statistically different. Time for successful placement of LMA was 19 ± 1 s versus ETT 123 ± 35 s (mean ± SEM); number of attempts for successful LMA placement was 1.1 (1-2) versus ETT 1.9 (1-7) [mean (range)]. Administration of surfactant via an LMA compared with an ETT resulted in similar improvements in oxygenation. Placement of the device required less time and fewer attempts. These data suggest that further study in human neonates is justified. If proven effective, some infants with respiratory distress may be able to receive surfactant while avoiding intubation.

Improved gas exchange and survival after KL-4 surfactant in newborn pigs with severe acute lung injury

OBJECTIVE

To determine the effectiveness of artificial surfactant therapy using KL-4 surfactant in newborn pigs with hydrochloric acid (HCl)-induced acute lung injury (ALI).

DESIGN

After induction of ALI via intratracheal HCl instillation, pigs were randomized to receive 5.8 ml/kg KL-4 surfactant or no surfactant prior to extubation to bubble CPAP.

SETTING

Clinical laboratory.

SUBJECTS

Spontaneously breathing newborn pigs (<1 week of age).

INTERVENTIONS

Treatment with KL-4 surfactant on bubble CPAP with PEEP of 6 cmH(2)O for 3.5 hr after extubation compared with controls.

MEASUREMENTS

Physiologic parameters and arterial blood gases were measured every 15 min. At the conclusion of the study, the lungs were excised for the analysis of histopathology and morphometric data.

MAIN RESULTS

Pigs treated with KL-4 surfactant had arterial blood gases with less acidosis (P < 0.001), higher P(a)O(2) levels (P < 0.001), and lower P(a)CO(2) levels (P < 0.001). Pigs treated with KL-4 surfactant had improved survival compared with controls (6/12 KL-4, 2/12 control, P < 0.05). Postmortem morphometric data demonstrated that pigs treated with KL-4 surfactant had larger (P < 0.05) exchange units in the caudal-dorsal lung as compared to relatively atelectatic region in the control animals.

CONCLUSIONS

In newborn pigs with severe HCl-induced ALI, treatment with KL-4 surfactant resulted in improved respiratory parameters, less dependent atelectasis, and improved short-term survival.

Observational study of humidified high-flow nasal cannula compared with nasal continuous positive airway pressure

OBJECTIVES

To conduct an in vitro evaluation of a humidified high-flow nasal cannula (HFNC) system at different flows, cannula sizes, and air leaks and also an in vivo analysis of mean end-expiratory esophageal pressure (EEEP) from nasal continuous positive airway pressure at 6 cm H(2)O (NCPAP+6) versus HFNC.

STUDY DESIGN

In the in vitro study, we measured HFNC system pressure and flow, with varying degrees of leak and with and without the use of a pressure-limiting valve. In the in vivo study, we measured EEEP in 15 newborns on NCPAP+6 and then on HFNC at 6 L/minute, with flow decreased by 1 L/minute every 30 minutes. Heart rate, respiratory rate, fraction of inspired oxygen, arterial oxygen saturation, respiratory distress syndrome score, and EEEP were recorded for each intervention. Data analysis was done using repeated-measures analysis of variance and linear regression.

RESULTS

In the in vitro study, in the absence of leaks, the pressures were limited by the pressure-limiting valve only at flows > or = 2 L/minute. With leaks of 30% and 50%, delivered pressures were always < 3 cm H(2)O. In the in vivo study, respiratory rate increased from baseline (NCPAP+6) as flow decreased (P < .02). Intrapatient and interpatient coefficients of variation were always high.

CONCLUSIONS

A pressure-limiting valve is necessary in a HFNC system. Although mean EEEP levels were similar in NCPAP+6 and HFNC, tachypnea developed as flow diminished. This system apparently cannot predict EEEP, because of interpatient and intrapatient variation.

Growth and neurodevelopmental outcomes after early low-dose hydrocortisone treatment in extremely low birth weight infants

BACKGROUND

Low cortisol concentrations in premature infants have been correlated with increased severity of illness, hypotension, mortality, and development of bronchopulmonary dysplasia. A total of 360 mechanically ventilated infants with a birth weight of 500 to 999 g were enrolled in a randomized, multicenter trial of prophylaxis of early adrenal insufficiency to prevent bronchopulmonary dysplasia. Mortality and bronchopulmonary dysplasia were decreased in the hydrocortisone-treated patients exposed to chorioamnionitis. We now report outcomes at 18 to 22 months' corrected age.

PATIENTS AND METHODS

Surviving infants were evaluated with standardized neurologic examination and Bayley Scales of Infant Development-II. Neurodevelopmental impairment was defined as a Mental Developmental Index or Psychomotor Developmental Index of <70, cerebral palsy, blindness or deafness.

RESULTS

A total of 252 (87%) of 291 survivors were evaluated. Cerebral palsy was diagnosed in 13% of hydrocortisone-treated versus 14% of placebo-treated infants. Fewer hydrocortisone-treated infants had a Mental Development Index <70, and more of the hydrocortisone-treated infants showed evidence of awareness of object permanence. Incidence of neurodevelopmental impairment was not different (39% [hydrocortisone] vs 44% [placebo]). There were no differences in physical growth measures. Chorioamnionitis-exposed infants treated with hydrocortisone were shorter and weighed less than controls but had no evidence of neurodevelopmental impairment. Among infants not exposed to chorioamnionitis, hydrocortisone-treated patients were less likely to have a Mental Development Index of <70 or to be receiving glucocorticoids at follow-up.

CONCLUSIONS

Early, low-dose hydrocortisone treatment was not associated with increased cerebral palsy. Treated infants had indicators of improved developmental outcome. Together with the short-term benefit previously reported, these data support additional studies of hydrocortisone treatment of adrenal insufficiency in extremely premature infants.

The role of high-frequency ventilation in neonates: evidence-based recommendations

High-frequency ventilation (HFV) uses small tidal volumes and extremely rapid ventilator rates. Despite the wealth of laboratory and clinical research on HFV, there are no established guidelines for prioritizing the use of HFV versus conventional mechanical ventilation (CMV) in neonatal respiratory failure. Examination of the currently available randomized controlled trials and meta-analysis of HFV versus CMV does not demonstrate any clear benefit of HFV either as a primary mode or as a "rescue" mode of ventilation in neonates who have respiratory insufficiency. The current literature does support the preferential use of HFV over CMV in conjunction with inhaled nitric oxide to maximize oxygenation in hypoxemic respiratory failure, in particular, as a result of persistent pulmonary hypertension.

Decreased lung injury after surfactant in piglets treated with continuous positive airway pressure or synchronized intermittent mandatory ventilation

BACKGROUND

Treatment with surfactant (S) decreases lung injury in paralyzed, mechanically ventilated animals. The use of nasal continuous positive airway pressure (CPAP) as an alternative to mechanical ventilation may further improve acute pulmonary outcomes.

OBJECTIVES

To evaluate the effect of surfactant (+S, -S) and synchronized intermittent mandatory ventilation (SIMV) on lung morphology and inflammatory markers in 24 spontaneously breathing piglets treated with CPAP or SIMV after saline lavage-induced lung injury.

METHODS

After induction of lung injury, animals were randomized to CPAP-S, CPAP+S or SIMV+S and treated for 4 h. Physiologic parameters were continuously monitored. After treatment, animals were euthanized and lungs fixed. Bronchoalveolar lavage (BAL) samples were collected for neutrophil count and H(2)O(2).

RESULTS

No physiologic differences were noted. BAL fluid from CPAP-S animals contained more neutrophils and more neutrophil H(2)O(2) than fluid from the SIMV+S or CPAP+S groups (p < 0.05 or greater). Pathologic injury scores were higher in dependent lung regions from CPAP groups (p < 0.05). Injury pattern scores showed greater dependent alveolar inflammation in all (p < 0.02), with more dependent atelectasis in the CPAP groups (p < 0.01). Morphometrics showed less total open alveolar air space in nondependent regions of the SIMV+S group compared to CPAP groups (p < 0.001). Dependent regions showed less total open alveolar air space compared to nondependent regions in the CPAP groups (p < 0.001).

CONCLUSIONS

Animals treated with surfactant prior to CPAP or SIMV had less acute lung injury. SIMV+S animals had less open air space in nondependent regions. This suggests, during early ventilatory support, surfactant administration may modulate pulmonary inflammation. CPAP alone without surfactant may not provide optimal pulmonary protection. The addition of mechanical breaths may alter and add to injury.

Early inhaled nitric oxide therapy in premature newborns with respiratory failure

BACKGROUND

The safety and efficacy of early, low-dose, prolonged therapy with inhaled nitric oxide in premature newborns with respiratory failure are uncertain.

METHODS

We performed a multicenter, randomized trial involving 793 newborns who were 34 weeks of gestational age or less and had respiratory failure requiring mechanical ventilation. Newborns were randomly assigned to receive either inhaled nitric oxide (5 ppm) or placebo gas for 21 days or until extubation, with stratification according to birth weight (500 to 749 g, 750 to 999 g, or 1000 to 1250 g). The primary efficacy outcome was a composite of death or bronchopulmonary dysplasia at 36 weeks of postmenstrual age. Secondary safety outcomes included severe intracranial hemorrhage, periventricular leukomalacia, and ventriculomegaly.

RESULTS

Overall, there was no significant difference in the incidence of death or bronchopulmonary dysplasia between patients receiving inhaled nitric oxide and those receiving placebo (71.6 percent vs. 75.3 percent, P=0.24). However, for infants with a birth weight between 1000 and 1250 g, as compared with placebo, inhaled nitric oxide therapy reduced the incidence of bronchopulmonary dysplasia (29.8 percent vs. 59.6 percent); for the cohort overall, such treatment reduced the combined end point of intracranial hemorrhage, periventricular leukomalacia, or ventriculomegaly (17.5 percent vs. 23.9 percent, P=0.03) and of periventricular leukomalacia alone (5.2 percent vs. 9.0 percent, P=0.048). Inhaled nitric oxide therapy did not increase the incidence of pulmonary hemorrhage or other adverse events.

CONCLUSIONS

Among premature newborns with respiratory failure, low-dose inhaled nitric oxide did not reduce the overall incidence of bronchopulmonary dysplasia, except among infants with a birth weight of at least 1000 g, but it did reduce the overall risk of brain injury. (ClinicalTrials.gov number, NCT00006401 [ClinicalTrials.gov].).

Effect of dose on response to adrenocorticotropin in extremely low birth weight infants

CONTEXT

Various cosyntropin doses are used to test adrenal function in premature infants, without consensus on appropriate dose or adequate response.

OBJECTIVE

The objective of this study was to test the cortisol response of extremely low birth weight infants to different cosyntropin doses and evaluate whether these doses differentiate between groups of infants with clinical conditions previously associated with differential response to cosyntropin.

DESIGN

The design was a prospective, nested study conducted within a randomized clinical trial of low-dose hydrocortisone from November 1, 2001, to April 30, 2003.

SETTING

The setting was nine newborn intensive care units.

PATIENTS

The patients included infants with 500-999 g birth weight.

INTERVENTION

The drug used was cosyntropin, at 1.0 or 0.1 microg/kg, given between 18 and 28 d of birth.

MAIN OUTCOME MEASURE

We measured the cortisol response to cosyntropin.

RESULTS

Two hundred seventy-six infants were tested. Previous hydrocortisone treatment did not suppress basal or stimulated cortisol values. Cosyntropin, at 1.0 vs. 0.1 microg/kg, yielded higher cortisol values (P < 0.001) and fewer negative responses (2 vs. 21%). The higher dose, but not the lower dose, showed different responses for girls vs. boys (P = 0.02), infants receiving enteral nutrition vs. not (P < 0.001), infants exposed to chorioamnionitis vs. not (P = 0.04), and those receiving mechanical ventilation vs. not (P = 0.02), as well as a positive correlation with fetal growth (P = 0.03). A response curve for the 1.0-microg/kg dose for infants receiving enteral nutrition (proxy for clinically well infants) showed a 10th percentile of 16.96 microg/dl. Infants with responses less than the 10th percentile had more bronchopulmonary dysplasia and longer length of stay.

CONCLUSIONS

A cosyntropin dose of 0.1 microg/kg did not differentiate between groups of infants with clinical conditions that affect response. We recommend 1.0 microg/kg cosyntropin to test adrenal function in these infants.

Prophylaxis of early adrenal insufficiency to prevent bronchopulmonary dysplasia: a multicenter trial

BACKGROUND

Infants developing bronchopulmonary dysplasia (BPD) show decreased cortisol response to adrenocorticotropic hormone. A pilot study of low-dose hydrocortisone therapy for prophylaxis of early adrenal insufficiency showed improved survival without BPD at 36 weeks' postmenstrual age, particularly in infants exposed to histologic chorioamnionitis.

METHODS

Mechanically ventilated infants with birth weights of 500 to 999 g were enrolled into this multicenter, randomized, masked trial between 12 and 48 hours of life. Patients received placebo or hydrocortisone, 1 mg/kg per day for 12 days, then 0.5 mg/kg per day for 3 days. BPD at 36 weeks' postmenstrual age was defined clinically (receiving supplemental oxygen) and physiologically (supplemental oxygen required for O2 saturation > or =90%).

RESULTS

Patient enrollment was stopped at 360 patients because of an increase in spontaneous gastrointestinal perforation in the hydrocortisone-treated group. Survival without BPD was similar, defined clinically or physiologically, as were mortality, head circumference, and weight at 36 weeks. For patients exposed to histologic chorioamnionitis (n = 149), hydrocortisone treatment significantly decreased mortality and increased survival without BPD, defined clinically or physiologically. After treatment, cortisol values and response to adrenocorticotropic hormone were similar between groups. Hydrocortisone-treated infants receiving indomethacin had more gastrointestinal perforations than placebo-treated infants receiving indomethacin, suggesting an interactive effect.

CONCLUSIONS

Prophylaxis of early adrenal insufficiency did not improve survival without BPD in the overall study population; however, treatment of chorioamnionitis-exposed infants significantly decreased mortality and improved survival without BPD. Low-dose hydrocortisone therapy did not suppress adrenal function or compromise short-term growth. The combination of indomethacin and hydrocortisone should be avoided.

Standardized lung recruitment during high frequency and conventional ventilation: similar pathophysiologic and inflammatory responses in an animal model of respiratory distress syndrome

OBJECTIVE

To evaluate standardized lung recruitment strategy during both high frequency oscillation (HFO) and volume-targeted conventional ventilation (CV+V) in spontaneously breathing piglets with surfactant washout on pathophysiologic and inflammatory responses.

DESIGN

Prospective animal study.

SETTING

Research laboratory.

SUBJECTS

Twenty-four newborn piglets.

INTERVENTIONS

We compared pressure support and synchronized intermittent mandatory ventilation, both with targeted tidal volumes, (PSV+V, SIMV+V) to HFO. Animals underwent saline lavage to produce lung injury, received artificial surfactant and were randomized to one of the three treatment groups (each n=8). After injury and surfactant replacement, lung volumes were recruited in all groups using a standard protocol. Ventilation continued for 6 h.

MEASUREMENTS AND MAIN RESULTS

Arterial and central venous pressures, heart rates, blood pressure and arterial blood gases were continuously monitored. At baseline, post lung injury and 6 h we collected serum and bronchoalveolar lavage samples for proinflammatory cytokines: IL 6, IL 8 and TNF-alpha, and performed static pressure-volume (P/V) curves. Lungs were fixed for morphometrics and histopathologic analysis. No physiologic differences were found. Analysis of P/V curves showed higher opening pressures after lung injury in the HFO group compared to the SIMV+V group ( p<0.05); no differences persisted after treatment. We saw no differences in change in proinflammatory cytokine levels. Histopathology and morphometrics were similar. Mean airway pressure (P(aw)) was highest in the HFO group compared to SIMV+V ( p<0.002).

CONCLUSIONS

Using a standardized lung recruitment strategy in spontaneously breathing animals, CV+V produced equivalent pathophysiologic outcomes without an increase in proinflammatory cytokines when compared to HFO.

Clinical validation of a continuous intravascular neonatal blood gas sensor introduced through an umbilical artery catheter

INTRODUCTION

Arterial blood gas (ABG) values are a necessary diagnostic measurement in the management of critically ill neonates. We hypothesized that a fiberoptic intravascular blood gas sensor, adapted for use through an umbilical artery catheter, would produce blood gas results with clinically acceptable bias and precision, in comparison to laboratory values, but with no blood loss.

METHODS

We evaluated a fiberoptic intravascular blood gas sensor (Neotrend) in 23 consecutive neonates suffering respiratory failure. The sensor was inserted into the descending aorta via a 4.0 or 4.5 French umbilical artery catheter and extended 20 mm beyond the catheter tip. Arterial blood samples were drawn as clinically indicated and analyzed using a standard laboratory analyzer. Sensor measurements were recorded at the time of arterial blood sampling. Additionally, we recorded and evaluated data related to umbilical artery catheter placement (low position [L3-L4] vs high position [T8-T10]), duration of sensor functioning and use, and sensor bias and precision compared to the laboratory analyzer (using Bland-Altman technique and linear regression analysis of pH, P(aCO2), and P(aO2)).

RESULTS

Duration of sensor use ranged from 1 to 304 hours (3-304 h in high position and 1-91 h in low position). Nine sensors were used for > 72 h (1 in low position and 8 in high position). Nine sensors were placed in low position, with a placement success rate of 56%. Eighteen sensors were placed in high position, with a placement success rate of 89%. The sensor values for pH, P(aCO2), and P(aO2) were strongly correlated (p < 0.0001) with the laboratory-determined values. Bias and precision for all values met standards for discrete analyzers for laboratory use.

CONCLUSIONS

The Neotrend device was accurate and reliable in the neonatal setting, allowing blood gas assessment with no iatrogenic blood loss. Catheter placement in high position may increase the likelihood of successful sensor placement and sensor duration of function.

Muscle proteolysis and weight loss in a neonatal rat model of sepsis syndrome

Our hypothesis is that nitrogen loss in septic neonates is caused by increased muscle proteolysis. Sprague-Dawley rat pups (P7) were injected intraperitoneally with NaCl or 4 mg/kg/BW lipopolysaccharide (LPS) and then sacrificed at 2, 4, 24, and 48 hr. Sepsis syndrome was confirmed by elevated serum tumor necrosis factor (24.6 ng/mL +/- 18.4 [LPS] and < 1.0 ng/mL [controls]; p < .05). Proteolysis in gastrocnemius/soleus muscle was analyzed by quantitation of tissue tyrosine loss. The neonatal rats injected with LPS had significant media tyrosine release at 24 hr compared to the controls (0.39 +/- 0.14 versus 0.25 +/- 0.11 micromol tyrosine/g muscle; p < .05). At 48 hr, LPS-induced muscle tyrosine release ceased (0.24 +/- 0.04 [control] versus 0.23 +/- 0.03 micromol tyrosine/g muscle [LPS]). After 48 hr, gastrocnemius/soleus weight was less in the LPS-injected rats (50.5 +/- 4.8 to 31.2 +/- 4.0 g; p < .0001). Similar changes were not seen in the extensor digitorum longus, suggesting that some muscles were relatively preserved. Also, LPS resulted in significant weight loss. We conclude that selective muscle proteolysis contributes to nitrogen loss in neonatal sepsis. Although proteolysis abates by 48 hr, short-term injury results in significant muscle-mass deficit.

Surfactant and partial liquid ventilation via conventional and high-frequency techniques in an animal model of respiratory distress syndrome

OBJECTIVE: To compare the physiologic and pathologic effects of conventional ventilation (CV) and high-frequency ventilation (HFV) during partial liquid ventilation (PLV) with perflubron after surfactant treatment with the results of HFV plus surfactant in an animal lung-injury model created by saline lavage. We also studied the dose effects of perflubron during HFV. DESIGN: Randomized experimental study. SETTING: Research animal laboratory. SUBJECTS: A total of 32 newborn piglets. INTERVENTIONS: After lung injury was induced, the animals were randomized to one of four groups: a) CV + surfactant + perflubron to functional residual capacity (FRC); b) HFV + surfactant + perflubron to FRC; c) HFV + surfactant + 10 mL/kg perflubron; and d) HFV + surfactant. All then received intratracheal surfactant. After 30 mins, perflubron was administered to the PLV groups. The animals underwent ventilation for 20 hrs. MEASUREMENTS AND MAIN RESULTS: Arterial blood gases and hemodynamic variables were continuously monitored. Pulmonary histologic and morphometric analyses were performed after death or euthanasia at 20 hrs. All animals had sustained improvements in arterial/alveolar oxygen ratios, and no differences were observed among groups. All HFV groups required higher mean airway pressures to maintain oxygenation (p <.05). Hemodynamics did not differ among groups. Pathologic analysis demonstrated decreased lung injury in both cranial-dorsal (nondependent) and caudal-ventral (dependent) lobes of all animals treated with PLV when compared with those treated with HFV + surfactant (p <.05). CONCLUSIONS: After surfactant treatment, physiologic support over 20 hrs was similar during HFV with or without perflubron and CV with perflubron. All PLV modalities improved lung pathologic factors uniformly to a greater degree than did HFV + surfactant. A lower treatment volume of perflubron during HFV produced physiologic and pathologic results similar to those produced by perflubron with respect to FRC during either CV or HFV.

Effect of sepsis syndrome on neonatal protein and energy metabolism

OBJECTIVE

It was our hypothesis that septic illness would alter both protein and energy metabolism in neonates, with elevations of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6), and interleukin-1 beta (IL-1 beta) serving as markers for these effects.

STUDY DESIGN

A total of 31 infants with suspected sepsis were enrolled into four groups: septic, sick-nonseptic, healthy-nonseptic, and recovered septic infants. Degree of illness, oxygen consumption, nitrogen balance, urine 3-methylhistidine/creatinine (MeH/Cr), and TNF-alpha, IL-6, IL-1 beta, and C-reactive protein (CRP) were measured.

RESULTS

Oxygen consumption increased, while nitrogen balance decreased and MeH/Cr increased with increasing degree of illness. Nitrogen balance improved on recovery from sepsis. IL-6 and CRP levels were elevated in septic infants compared with sick-nonseptic and healthy infants.

CONCLUSION

Neonates experience a hypermetabolic response with increased nitrogen loss during septic illness, proportional to the degree of illness. Increased delivery of protein substrate may be nutritionally advantageous to the septic neonate.

Variations in end-expiratory pressure during partial liquid ventilation: impact on gas exchange, lung compliance, and end-expiratory lung volume

STUDY OBJECTIVES

To determine the effects of different levels of positive end-expiratory pressure (PEEP) during partial liquid ventilation (PLV) on gas exchange, lung compliance, and end-expiratory lung volume (EELV).

DESIGN

Prospective animal study.

SETTING

Animal physiology research laboratory.

SUBJECTS

Nine piglets.

INTERVENTIONS

Animals underwent saline solution lavage to produce lung injury. Perflubron was instilled via the endotracheal tube in a volume estimated to represent functional residual capacity. The initial PEEP setting was 4 cm H(2)O, and stepwise changes in PEEP were made. At 30-min intervals, the PEEP was increased to 8, then 12, then decreased back down to 8, then 4 cm H(2)O.

MEASUREMENTS AND RESULTS

After 30 min at each level of PEEP, arterial blood gases, aortic and central venous pressures, heart rates, dynamic lung compliance, and changes in EELV were recorded. Paired t tests with Bonferroni correction were used to evaluate the data. There were no differences in heart rate or mean BP at the different PEEP levels. CO(2) elimination and oxygenation improved directly with the PEEP level and mean airway pressure (Paw). Compliance did not change with increasing PEEP, but did increase when PEEP was lowered. EELV changes correlated directly with the level of PEEP.

CONCLUSIONS

As previously reported during gas ventilation, oxygenation and CO(2) elimination vary directly with PEEP and proximal Paw during PLV. EELV also varies directly with PEEP. Dynamic lung compliance, however, improved only when PEEP was lowered, suggesting an alteration in the distribution of perflubron due to changes in pressure-volume relationships.

Randomized controlled trial of volume-targeted synchronized ventilation and conventional intermittent mandatory ventilation following initial exogenous surfactant therapy

We set out to evaluate the impact of volume-targeted synchronized ventilation and conventional intermittent mandatory ventilation (IMV) on the early physiologic response to surfactant replacement therapy in neonates with respiratory distress syndrome (RDS). We hypothesized that volume-targeted, patient-triggered synchronized ventilation would stabilize minute ventilation at a lower respiratory rate than that seen during volume-targeted IMV, and that synchronization would improve oxygenation and decrease variation in measured tidal volume (V(t)). This was a prospective, randomized study of 30 hospitalized neonates with RDS. Infants were randomly assigned to volume-targeted ventilation using IMV (n = 10), synchronized IMV (SIMV; n = 10), or assist/control ventilation (A/C; n = 10) after meeting eligibility requirements and before initial surfactant treatment. Following measurements of arterial blood gases and cardiovascular and respiratory parameters, infants received surfactant. Infants were studied for 6 hr following surfactant treatment. Infants assigned to each mode of ventilation had similar birth weight, gestational age, and Apgar scores at birth, and similar oxygenation indices at randomization. Three patients were eliminated from final data analysis because of exclusionary conditions unknown at randomization. Oxygenation improved significantly following surfactant therapy in all groups by 1 hr after surfactant treatment (P < 0.05). No further improvements occurred with time. Total respiratory rate was lowest (P < 0.05) and variation in tidal volume (V(t)) was least in the A/C group (P < 0. 05). Minute ventilation (V(')(E)), delivered airway pressures, respiratory system mechanics, and hemodynamic parameters were similar in all groups. We conclude that volume-targeted A/C ventilation resulted in more consistent tidal volumes at lower total respiratory rates than IMV or SIMV. Oxygenation and lung mechanics were not altered by synchronization, possibly due to the volume-targeting strategy. Of the modes studied, A/C, a fully-synchronized mode, may be the most efficient method of mechanical ventilator support in neonates receiving surfactant for treatment of RDS.

Perfluorocarbon priming and surfactant: physiologic and pathologic effects

OBJECTIVE

To test the hypothesis that perfluorocarbon (PFC) priming before surfactant administration improves gas exchange and lung compliance, and also decreases lung injury, more than surfactant alone.

DESIGN

Prospective, randomized animal study.

SETTING

Animal research laboratory of Children's Hospital of St. Paul.

SUBJECTS

Thirty-two newborn piglets, weighing 1.55 +/- 0.18 kg.

INTERVENTIONS

We studied four groups of eight animals randomized after anesthesia, paralysis, tracheostomy, and establishment of lung injury using saline washout to receive one of the following treatments: a) surfactant alone (n = 8); b) priming with the PFC perflubron alone (n = 8); c) priming with perflubron followed by surfactant (n = 8); and d) no treatment (control; n = 8). Perflubron priming was achieved by instilling perflubron via the endotracheal tube in an amount estimated to represent the functional residual capacity, ventilating the animal for 30 mins, and then removing perflubron by suctioning. After all treatments were given, animals were mechanically ventilated for 4 hrs.

MEASUREMENTS AND MAIN RESULTS

We evaluated oxygenation, airway pressures, respiratory system compliance, and hemodynamics at baseline, after induction of lung injury, and at 30-min intervals for 4 hrs. Histopathologic evaluation was carried out using a semiquantitative scoring system and by computer-assisted morphometric analysis. After all treatments, animals had decreased oxygenation indices (p < .001) and increased respiratory system compliance (p < .05). Animals in PFC groups had similar physiologic responses to treatments as animals treated with surfactant only; both the PFC-treated groups and the surfactant-treated animals required lower mean airway pressures throughout the experiment (p < .001) and had higher pH levels at 90 and 120 mins (p < .05) compared with the control group. Pathologic analysis demonstrated decreased lung injury in surfactant-treated animals compared with animals treated with PFC or the controls (p < .02).

CONCLUSIONS

Priming the lung with PFC neither improved the physiologic effects of exogenous surfactant nor improved lung pathology in this animal model.

Synchronized gas and partial liquid ventilation in lung-injured animals: improved gas exchange with decreased effort

We hypothesized that partial liquid ventilation (PLV) with perflubron in spontaneously breathing lung-injured animals would increase respiratory workload compared to animals treated with gas ventilation (GV), and that a fully synchronized mode, assist-control ventilation (AC), would reduce the piglets' effort when compared to intermittent mandatory ventilation (IMV) or synchronized IMV (SIMV) during both GV and PLV. Newborn piglets with saline lavage-induced lung injury were randomized to sequential 30-min periods of IMV --> SIMV --> AC (n = 5), or AC --> SIMV --> IMV (n = 5) during GV followed by PLV. Pulmonary mechanics measurements and an esophageal patient effort index (PEI, defined as the product of the area below baseline of the esophageal pressure-time curve and respiratory rate [RR]) were determined to estimate the patient's nonmechanical work of breathing, using a computer-assisted lung mechanics analyzer. GV to PLV comparisons showed no change in PEI (IMV, 57.8 vs. 49.7; SIMV, 52.3 vs. 46.8; AC, 15.7 vs. 13.7 cm H2O x s/min); intermode comparisons showed significantly decreased PEI in AC vs. IMV and SIMV during GV, and in AC vs. SIMV (AC vs. IMV, P = 0.06) during PLV. AC consistently resulted in the highest minute ventilation, lowest total respiratory rate, most physiologic pH, and least tidal volume variability. These observations suggest that synchronization with AC during GV and PLV may have substantial physiologic benefits.

Dynamics of spontaneous breathing during patient-triggered partial liquid ventilation

This study evaluates different ventilator strategies during gas (GV) and partial liquid ventilation (PLV) in spontaneously breathing animals. We hypothesized that during PLV, spontaneously breathing animals would self-regulate respiratory parameters by increasing respiratory rate (RR) and minute ventilation (V'E) when compared to animals mechanically ventilated with gas, and further that full synchronization of each animal's effort to the ventilator cycle would decrease RR at stable tidal volumes (V(T)). We studied 12 newborn piglets (1.54 +/- 0.24 kg) undergoing GV and PLV in 3 different modes: intermittent mandatory ventilation (IMV), synchronized IMV (SIMV), and assist control ventilation (AC). Modes occurred sequentially in random order during GV first, with the same order then repeated during PLV. Animals initially received continuous positive airway pressure (CPAP) and returned to CPAP during PLV at the end of the experiment. Pressure-limited, volume-targeted ventilation was used with a tidal volume goal of 13 cc/kg. Rate was set at 10/min during IMV and SIMV, with a back-up rate of 10/min during AC. RR, V'E, mechanical (V(T)) and spontaneous tidal volumes (sV(T)) were measured breath-to-breath using a computer-assisted lung mechanics analyzer; mean values were determined over 30-min periods. Data analysis used paired t-tests with Bonferroni correction as needed (P < 0.05). Blood gases were stable in all modes during GV and PLV. RR (min(-1)) and V'E (L x min(-1)/kg) increased in all modes from GV to PLV (RR: CPAP 71 vs. 128; IMV 69 vs. 112; SIMV 65 vs. 107; AC 33 vs. 47. V'E: CPAP 0.47 vs. 0.72; IMV 0.46 vs. 0.61; SIMV 0.45 vs. 0.61; AC 0.38 vs. 0.53; P < 0.05). Intermode comparisons during PLV showed a lower RR with AC (P < 0.02), and a higher V'E with CPAP (P < 0.05). V(T) and dynamic respiratory system compliance decreased from GV to PLV (V(T) P < 0.05; C(rs,dyn) P < 0.01); sV(T) remained unchanged. V(T) and sV(T) did not differ in intermode comparisons. We conclude that during PLV, spontaneously breathing piglets with normal lungs maintain physiologic blood gases by increasing V'E through increased RR. AC produced the most efficient respiratory pattern during PLV, with increased V'E achieved by a modest increase in RR.

High-frequency oscillation versus conventional ventilation following surfactant administration and partial liquid ventilation

Surfactant followed by partial liquid ventilation (PLV) with perfluorocarbon (PFC; LiquiVent) improves oxygenation, lung compliance, and lung pathology in lung-injured animals receiving conventional ventilation (CV). In this study, we hypothesize that high-frequency oscillation (HFO) and CV will provide equivalent oxygenation in lung-injured animals following surfactant repletion and PLV, once lung volume is optimized. After saline-lavage lung injury during CV, newborn piglets were randomized to either HFO (n = 10) or CV (n = 9). HFO animals were stabilized over 15 min without optimization of lung volume; CV animals continued treatment with time-cycled, pressure-limited, volume-targeted ventilation. All animals then received 100 mg/kg of surfactant (Survanta). Thirty minutes later, all received intratracheal PFC to approximate functional residual capacity. Thirty minutes after PLV began, mean airway pressure (MAP) in both groups was increased to improve oxygenation. MAP was directly adjusted during HFO; PEEP and PIP were adjusted during IMV, maintaining a pressure sufficient to deliver 15 mL/kg tidal volume. Animals were treated for 4 h. The CV group showed improved oxygenation following surfactant administration (OI: 26.79 +/- 1.98 vs. 8.59 +/- 6.29, P < 0.0004), with little further improvement following PFC administration or adjustments in MAP. Oxygenation in HFO-treated animals did not improve following surfactant, but did improve following PFC (0I: 27.78 +/- 6.84 vs. 15.86 +/- 5.53, P < 0.005) and adjustments in MAP (OI: 15.86 +/- 5.53 vs. 8.96 +/- 2.18, P < 0.03). After MAP adjustments, there were no significant intergroup differences in oxygenation. Animals in the CV group required lower MAP than animals in the HFO group to maintain similar oxygenation. We conclude that surfactant repletion followed by PLV improves oxygenation during both CV and HFO. The initial response to administration of surfactant and PFC was different for the conventional and high-frequency oscillation groups, likely reflecting the ventilation strategy used; animals in the CV group responded most to surfactant, whereas animals in the HFO group responded most after PFC instillation. The ultimately similar oxygenation of the two groups once lung volume had been optimized suggests that HFO may be used effectively during administration of, and treatment with, surfactant and perfluorocarbon.

Prolonged partial liquid ventilation using conventional and high-frequency ventilatory techniques: gas exchange and lung pathology in an animal model of respiratory distress syndrome

OBJECTIVE

To evaluate the effect of prolonged partial liquid ventilation with perflubron (partial liquid ventilation), using conventional and high-frequency ventilatory techniques, on gas exchange, hemodynamics, and lung pathology in an animal model of lung injury.

DESIGN

Prospective, randomized, controlled study.

SETTING

Animal laboratory of the Infant Pulmonary Research Center, Children's Health Care-St. Paul.

SUBJECTS

Thirty-six newborn piglets.

INTERVENTIONS

We studied newborn piglets with lung injury induced by saline lavage. Animals were randomized into one of five treatment groups: a) conventional gas ventilation (n = 8); b) partial liquid ventilation with conventional ventilation (n = 7); c) partial liquid ventilation with high-frequency jet ventilation (n = 7); d) partial liquid ventilation with high-frequency oscillation (n = 7); and e) partial liquid ventilation with high-frequency flow interruption (n = 7). After induction of lung injury, all partial liquid ventilation animals received intratracheal perflubron to approximate functional residual capacity. After 30 mins of stabilization, animals randomized to high-frequency ventilation were changed to their respective high-frequency modes. Hemodynamics and blood gases were measured before and after lung injury, after perflubron administration, and then every 4 hrs for 20 hrs. Histopathologic evaluation was carried out using semiquantitative scoring and computer-assisted morphometric analysis on pulmonary tissue from animals surviving at least 16 hrs.

MEASUREMENTS AND MAIN RESULTS

All animals developed acidosis and hypoxemia after lung injury. Oxygenation significantly (p < .001) improved after perflubron administration in all partial liquid ventilation groups. After 4 hrs, oxygenation was similar in all ventilator groups. The partial liquid ventilation-jet ventilation group had the highest pH; intergroup differences were seen at 16 and 20 hrs (p < .05). The partial liquid ventilation-oscillation group required higher mean airway pressure; intergroup differences were significant at 4 and 8 hrs (p < .05). Aortic pressures, central venous pressures, and heart rates were not different at any time point. Survival rate was significantly lower in the partial liquid ventilation-flow interruption group (p < .05). All partial liquid ventilation-treated animals had less lung injury compared with gas-ventilated animals by both histologic and morphometric analysis (p < .05). The lower lobes of all partial liquid ventilation-treated animals demonstrated less damage than the upper lobes, although scores reached significance (p < .05) only in the partial liquid ventilation-conventional ventilation animals.

CONCLUSIONS

In this animal model, partial liquid ventilation using conventional or high-frequency ventilation provided rapid and sustained improvements in oxygenation without adverse hemodynamic consequences. Animals treated with partial liquid ventilation-flow interruption had a significantly decreased survival rate vs. animals treated with the other studied techniques. Histopathologic and morphometric analysis showed significantly less injury in the lower lobes of lungs from animals treated with partial liquid ventilation. High-frequency ventilation techniques did not further improve pathologic outcome.

Exogenous surfactant and partial liquid ventilation: physiologic and pathologic effects

We compared the effects of surfactant and partial liquid ventilation (PLV), and the impact of administration order, on oxygenation, respiratory system compliance (Crs), hemodynamics, and lung pathology in an animal lung injury model. We studied four groups: surfactant alone (S; n = 8); partial liquid ventilation alone (PLV-only; n = 8); surfactant followed by partial liquid ventilation (S-PLV; n = 8); and partial liquid ventilation-followed by surfactant (PLV-S; n = 8). Following treatments, all animals had improved oxygenation index (OI) and Crs. Animals in PLV groups showed continued improvement over 2 h (% change OI: PLV-S -83% versus S -47%, p < 0.05; % change Crs: S-PLV 73% versus S 13%, p < 0.05). We also saw administration-order effects: surfactant before PLV improved Crs (0.92 ml/cm H2O after surfactant versus 1.13 ml/cm H2O after PLV, p < 0.02) without changing OI, whereas surfactant after PLV did not change Crs and OI increased (5.01 after PLV versus 8.92 after surfactant, p < 0.03). Hemodynamics were not different between groups. Pathologic analysis demonstrated decreased lung injury in dependent lobes of all PLV-treated animals, and in all lobes of S-PLV animals, when compared with the lobes of the S animals (p < 0.05). We conclude that surfactant therapy in combination with PLV improved oxygenation, respiratory system mechanics, and lung pathology to a greater degree than surfactant therapy alone. Administration order affected initial physiologic response and ultimate pathology: surfactant given before PLV produced the greatest improvements in pathologic outcomes.

Suspected betamethasone-induced leukemoid reaction in a premature infant

The use of antenatal corticosteroids in threatened pregnancies of less than 34 weeks' duration is a valuable tool for assisting fetal lung maturation. Although this practice has existed for over 20 years, little is known about a rare extreme elevation of the newborn's white blood cell count, called a leukemoid reaction. A case of leukemoid reaction is discussed to assist the clinician with the current thought processes and diagnostic differential behind this benign condition.

Partial liquid ventilation: a comparison using conventional and high-frequency techniques in an animal model of acute respiratory failure

OBJECTIVE

To test the hypothesis that high-frequency ventilation (HFV), when compared with conventional techniques, enhances respiratory gas exchange during partial liquid ventilation (PLV).

DESIGN

A four-period crossover design.

SETTING

Animal research laboratory of Children's Health Care-St. Paul.

SUBJECTS

Thirty-two newborn piglets, weighing 1.40 +/- 0.39 kg.

INTERVENTIONS

Animals were divided into four groups of eight animals: a) PLV with high-frequency jet ventilation; b) PLV with jet ventilation using a background intermittent mandatory ventilation (IMV) rate; c) PLV with high-frequency oscillation; or d) PLV with high-frequency flow interruption using a background IMV rate. After anesthesia, paralysis, and tracheotomy, a normal saline wash procedure produced lung injury. Perfluorocarbon was then instilled via the endotracheal tube in an amount estimated to represent functional residual capacity. Animals received randomly either PLV using conventional techniques or PLV using the selected HFV technique as initial treatment. Then, animals were crossed over to the alternative treatment at equal mean airway pressure, as measured at the endotracheal tube tip. This sequence was repeated for a total of four crossover periods, such that all animals were treated twice with PLV using conventional techniques and twice with PLV using HFV.

MEASUREMENTS AND MAIN RESULTS

We measured airway pressures at the endotracheal tube tip, aortic and central venous blood pressures, arterial blood gases, and respiratory system mechanics at baseline, after induction of lung injury, and at specified intervals throughout the experiment. Measurements were made before and 15 mins after crossovers, then ventilators were adjusted to normalize gas exchange. Measurements were again made 30 mins later, at the end of the treatment period. All types of PLV provided adequate gas exchange. Only PLV using jet ventilation with IMV produced gas exchange equal to that seen during PLV using conventional techniques at equivalent mean airway pressure. By the end of the treatment periods, only PLV using high-frequency oscillation continued to require higher airway pressure than PLV using conventional techniques for equivalent gas exchange.

CONCLUSIONS

Gas exchange was not enhanced during PLV-HFV. Application of HFV with PLV provides no clear acute physiologic advantages to PLV using more conventional techniques.

Lower respiratory rates without decreases in oxygen consumption during neonatal synchronized intermittent mandatory ventilation

OBJECTIVE

We tested the hypothesis that synchronization to patient effort during intermittent mandatory ventilation (SIMV), when compared to conventional unsynchronized intermittent mandatory ventilation (IMV), will decrease energy expenditure, as reflected by decreased oxygen consumption (VO2).

DESIGN

We used a four-period crossover design. Each patient was studied over four 30-min continuous time intervals. Patients were randomized to receive initially IMV or SIMV, then crossed over such that each patient was treated twice with each modality. Data were analyzed using an analysis of variance technique.

SETTING

Patients were receiving treatment in the newborn intensive care unit of Children's Hospital, St. Paul.

PATIENTS

We studied 17 patients, who ranged from 23 to 37 weeks gestation, were < or = 14 days old, and had study weights from 623 to 3015 g. All were mechanically ventilated for hyaline membrane disease.

MEASUREMENTS AND RESULTS

We measured and compared VO2, carbon dioxide consumption (VCO2), minute ventilation (VE), total respiratory rate, heart rate, arterial blood pressure, and arterial oxygen saturation (SaO2) values during IMV and SIMV. Total respiratory rate fell significantly during SIMV (73 +/- 26 during IMV, 57 +/- 17 during SIMV, p < 0.01) in spite of no significant change in VO2 (0.6 +/- 0.16% fall in VO2 during SIMV) or VCO2 (4.2 +/- 0.19% increase in VCO2 during SIMV) values. Moreover, there were no significant differences in heart rate, blood pressure, VE, or SaO2 values with either form of therapy.

CONCLUSIONS

Though total respiratory rate fell, these data do not support the hypothesis that SIMV significantly reduces respiratory rate by decreasing oxygen consumption and carbon dioxide production during infant mechanical ventilation. Rather, the marked fall in respiratory rate may be due to a more efficient respiratory pattern.

Mechanical ventilation of the newborn. An overview

Mechanical ventilation of the newborn infant is an ever-changing area. Its evolution has been hampered and stimulated by problems of small size, inadequate technology, unexpected complications, and changing expectations. With synchronized ventilation, a new technique in the neonatal ICU, clinicians again are reassessing their assumptions. HFV, a "new" technique for 15 years, has found a niche in the treatment of infants failing CV. Its use as an initial therapy for RDS, advocated by some, remains controversial. Monitoring gas flow patterns, tidal and minute volumes, and lung mechanics has become a part of the CV, but complications still occur. The only thing certain is that change will continue.

Monosomy 9p24-->pter and trisomy 5q31-->qter: case report and review of two cases

Partial deletion of the short arm of chromosome 9 (p24-->pter) and partial duplication of the long arm of chromosome 5 (q32-->qter) were observed in an abnormal boy who died at age 8 weeks of a complex cyanotic cardiac defect. He also had minor anomalies, sagittal craniosynostosis, triphalangeal thumbs, hypospadias, and a bifid scrotum. Two other infants with similar cytogenetic abnormalities were described previously. These patients had severe congenital heart defect, genitourinary anomalies, broad nasal bridge, low hairline, apparently low-set ears, short neck, and triphalangeal thumbs, in common with our patient. We suggest that combined monosomy 9p23,24-->pter and trisomy 5q31,32-->qter may constitute a clinically recognizable syndrome.

Synthetic surfactant for rescue treatment of respiratory distress syndrome in premature infants weighing from 700 to 1350 grams: impact on hospital resource use and charges

To determine the impact of the use of synthetic surfactant on hospital resource use and charges, we analyzed the economic data from a multicenter, randomized, placebo-controlled clinical trial of synthetic surfactant in infants with neonatal respiratory distress syndrome and birth weights between 700 and 1350 gm. Two 5 ml/kg doses of a synthetic surfactant (Exosurf Neonatal) or air placebo were administered to 419 infants who were receiving mechanical ventilation and had an arterial/alveolar oxygen tension ratio < 0.22. In addition to the clinical endpoints for safety and efficacy, data were collected on length of hospital stay, days in the neonatal intensive care unit, days of mechanical ventilation, days of oxygen supplementation, and hospital charges until the infant reached 1 year adjusted age. Growth and development of infants who received synthetic surfactant therapy in the study and survived to 1 year adjusted age were equivalent to those of the survivors in the air placebo group. For 1-year survivors, synthetic surfactant reduced the average length of stay at the different levels of care needed during the hospitalization such as neonatal intensive care unit days, days of mechanical ventilation, and days of oxygen supplementation. For nonsurvivors, synthetic surfactant increased the average length of stay, especially at more intense levels of care. Total hospital charges for the initial hospitalization and through 1 year adjusted age for a hypothetic cohort of 100 infants treated with synthetic surfactant were, on average, the same as those for a comparable cohort of infants in the air placebo group. These results indicate that rescue therapy with synthetic surfactant in infants with respiratory distress syndrome and birth weights from 700 to 1350 gm can result in significantly improved survival without significant increases in hospital charges.

Metabolic response of preterm infants to variable degrees of respiratory illness

In older children and adults, physiologic instability associated with severe illness causes increased cellular oxygen consumption (VO2), increased serum lactate and cortisol levels, and more negative nitrogen balance. To determine the metabolic response of preterm infants to severity of respiratory illness, we analyzed VO2, nitrogen balance, urinary 3-methyl-histidine and norepinephrine concentrations, and serum levels of lactate and cortisol as a function of ventilatory index (VI). Twelve 2-day-old premature infants who were appropriate in size for gestational age (mean +/- SEM birth weight: 1460 +/- 251 gm) and who required mechanical ventilation for respiratory distress syndrome had VO2 and carbon dioxide production measured by indirect calorimetry and blood and urine samples obtained concurrently. All infants received amino acids, 1.0 gm/kg per day, and a mean energy intake of 27 +/- 3 kcal/kg per day, provided as a parenteral dextrose solution. The resting energy expenditure exceeded energy intake in all infants. The VO2 value ranged from 5.5 to 9.2 ml/kg per minute and was directly correlated with VI (r = 0.79; p = 0.002). Nitrogen balance ranged from -160 to 53 mg/kg per day (mean: -33 +/- 21 mg/kg per day) but was not dependent on VI (r = 0.04) or VO2 (r = 0.01). The serum lactate level correlated directly with VI (r = 0.82; p = 0.002) and VO2 (r = 0.60; p = 0.05), but cortisol and urinary norepinephrine levels did not. We conclude that preterm infants with respiratory distress syndrome have increased VO2 rates and serum lactate concentrations directly related to the degree of respiratory illness. They are generally in a state of mildly negative nitrogen balance, the degree of which is not related to severity of illness. Although these infants may require increased energy delivery during illness, they do not appear to require excessive amounts of amino acids.

The effects of bedside pulmonary mechanics testing during infant mechanical ventilation: a retrospective analysis

We examined the effects of regular bedside testing of pulmonary mechanics (PM) on the outcome of 468 acutely ill, mechanically ventilated neonates. During the first of two 18-month study periods, 217 infants were mechanically ventilated without the assistance of PM measurements. During the second 18-month period, 251 infants were ventilated with the assistance of at least daily PM measurements. Using data obtained from the PM tests, we adjusted the infants' ventilators to maintain tidal volume, inspiratory time, and pressure-volume loops within predetermined limits. With the exception of the PM measurements, given the limitations of retrospective analyses, both groups of infants received identical medical and nursing care. The infants ventilated with the assistance of PM testing developed fewer pneumothoraces (4.0%; 10/251) vs. no PM testing, 10.1% (22/217); P < 0.05 by Chi-square analysis]. Infants weighing less than 1,500 g ventilated with the assistance of PM measurements had less intraventricular hemorrhage (IVH) overall, most notably, less grades I and II IVH (total IVH-PM testing, 39.1% vs. no PM testing, 65.7%; P < 0.01; Grades I-II IVH-PM testing, 30.4% vs. no PM testing, 54.9%; P < 0.01). IVH incidence was decreased independent of pneumothorax occurrence. Survival rates, incidences of bronchopulmonary dysplasia, and durations of mechanical ventilation and hospitalization were similar. This retrospective analysis suggests that PM testing during infant mechanical ventilation reduces common acute ventilator-associated complications.

Alterations in feline tracheal permeability after mechanical ventilation

OBJECTIVES

Previous investigations of ventilator-induced airway injury focused on histopathologic changes associated with various ventilators and strategies for their use. We hypothesized that mechanical ventilation is associated with alterations in tracheal epithelial permeability, and designed a study using an animal model to evaluate changes in tracheal epithelial permeability after administering different types of mechanical ventilation to test this hypothesis.

DESIGN

Prospective, multiple-group, controlled trial. Five groups of animals were studied and compared. Eight animals were studied without intubation or mechanical ventilation. A total of 28 animals (seven in each group) were studied after conventional mechanical ventilation, high-frequency positive-pressure ventilation, high-frequency jet ventilation, or high-frequency flow interruption at respiratory rates of 20, 150, 400, and 900 breaths/min, respectively. Comparison of data for each group was done using the Kruskall-Wallis analysis of variance. Between-group comparisons were made using standard error of the mean comparisons. For airway pressures and other physiologic data, one-way analysis of variance was performed. Between-group comparisons were made using the Student-Newman-Keuls' test.

SETTING

Small animal physiology laboratory.

SUBJECTS

Thirty-six adult cats.

INTERVENTIONS

Mechanically ventilated animals were treated for 8 hrs and then killed. Inspired oxygen concentration, BP, and mean airway pressures were comparable in mechanically ventilated animals. Spontaneously breathing control animals were killed without endotracheal intubation or exposure to mechanical ventilation.

MEASUREMENTS AND MAIN RESULTS

Permeability values in isolated tracheal segments were calculated for 14C-sucrose, 3H-inulin, and fluorescein isothiocyanate-dextran-20. Tracheal epithelial permeability to all studied molecules increased after exposure to mechanical ventilators. These different mechanical ventilators increased epithelial permeability in a progressive manner that paralleled ventilatory frequency. The changes were greatest after ventilation at the highest frequency. These observed changes in tracheal permeability are consistent with previously observed alterations in tracheal histopathology after exposure to mechanical ventilation.

CONCLUSIONS

Mechanical ventilation was associated with increases in tracheal permeability to large and small nonionic molecules. These changes occurred with all studied ventilators, used as they are clinically. Permeability changes paralleled ventilatory rate changes.