Positive end-expiratory pressure modulates perfluorochemical evaporation from the lungs

To study the effects of positive end-expiratory pressure (PEEP) level on perfluorochemical (PFC) elimination profiles (E(L)), 6 ml/kg of perflubron were instilled into healthy anesthetized rabbits. The ventilation strategy was to maintain constant minute ventilation (300 ml/kg/min) and mean airway pressure (7-8 cm H(2)O) while randomly changing the PEEP levels from 5 to 0, 1, 3, and 10 cm H(2)O, each for a period of 15 min. The PFC content in the expired gas was measured and the E(L) was calculated. There was a significant reduction in the E(L) when decreasing the PEEP levels from 5 to 0 cm H(2)O, but no differences were seen when the PEEP was increased from 5 to 10 cm H(2)O. The results indicate that PEEP levels influence PFC elimination profiles; therefore, the measurement of the E(L) and PEEP levels should be considered when optimizing supplemental PFCs during partial liquid ventilation.

Role of ventilation strategy on perfluorochemical evaporation from the lungs

To study the effect of ventilation strategy on perfluorochemical (PFC) elimination profile (evaporative loss profile; E(L)), 6 ml/kg of perflubron were instilled into anesthetized normal rabbits. The strategy was to maintain minute ventilation (VE, in ml/min) in three groups: VE(L) (low-range VE, 208 +/- 2), VE(M) (midrange VE, 250 +/- 9), and VE(H) (high-range VE, 293 +/- 1) over 4 h. In three other groups, respiratory rate (RR, breaths/min) was controlled at 20, 30, or 50 with a constant VE and adjusted tidal volume. PFC content in the expired gas was measured, and E(L) was calculated. There was a significant VE- and time-dependent effect on E(L.) Initially, percent PFC saturation and loss rate decreased in the VE(H) > VE(M) > VE(L) groups, but by 3 h the lower percent PFC saturation resulted in a loss rate such that VE(H) < VE(M) < VE(L) at 4 h. For the groups at constant VE, there was a significant time effect on E(L) but no RR effect. In conclusion, E(L) profile is dependent on VE with little effect of the RR-tidal volume combination. Thus measurement of E(L) and VE should be considered for the replacement dosing schemes during partial liquid ventilation.

Perfluorochemical elimination from the lungs: effect of initial dose

Liquid-assisted ventilation with perfluorochemical (PFC) has been beneficial in a variety of respiratory diseases in animals and humans. Although PFC evaporation from the lungs is in part dependent on ventilation strategy and positioning, guidelines for initial and replacement dosing are unclear. We hypothesized that PFC evaporative loss over time is dependent on the size of the initial dose. Juvenile rabbits (n = 18) were ventilated using constant animal position and ventilator strategy. PFC (perflubron: LiquiVent ) was instilled endotracheally, using four groups with initial doses of 2, 6, 12, and 17 mL/kg. A previously described thermal detector that measures PFC in expired gas was used to calculate loss rate, residual perflubron in the lung, and volume loss as a % of initial fill volume. There was a significant dose, time, and dose-time interaction such that evaporative loss was dependent on initial PFC volume and time after fill (P < 0.05). Evaporative loss rate decreased earlier at lower doses. The percentage of initial volume lost to evaporation over time was inversely related to dose and could not be predicted by decreasing % PFC saturations, independent of dose. Evaporative loss should be considered to optimize both the application of PFC to the lung and replacement dosing during partial liquid ventilation.

On-line techniques for perfluorochemical vapor sampling and measurement

The authors developed a compact gas sampling and perfluorochemical (PFC) measuring system for use in total and partial liquid ventilation systems, based on a precision two-thermistor thermal detector (TD). They describe the sensitivity and linearity of their on-line method for PFC analysis of expired gases and show how it may be used in partial liquid ventilation studies for determining PFC saturation and loss. Gas is sampled for a short time from a breathing circuit through a heated tube at a selectable point in the breathing cycle. Inspiration is sensed by a pressure transducer. The sample of gas is pulled into the heated (48 degrees C) thermistor chamber by suction and held there while the cooling effect of the vapor changes the thermistor temperature. Dry air in another chamber affects a second thermistor, and the difference of these responses is amplified. The raw signal is corrected for the effects of varying O2 levels by a fuel cell. This signal is sampled and held and displayed on a front panel display. Calibration is performed in percentage saturation at 37 degrees C using the PFC in use at that temperature, or another standard such as O2. In-vitro testing showed a linear response in the thermal detector device (R2 = 0.99) over the range of vapor pressures tested (0-14) mmHg) and was reproducible to within 3%. When electronically corrected for changes in O2 concentration, there was less than a 2% change in PFC saturation. The TD responses to CO2 (R2 = 0.99) and water vapor (R2 = 1.0) were linear and approximately equal and opposite over the normal operating ranges of expired gases. In-vivo results in rabbits showed a significant (R2 = 0.73; p < 0.01) correlation between the auto-sampler and manual collection modes for determination of PFC in expired gas.

Current status of liquid ventilation

Perfluorochemical liquid has been used experimentally to enhance mechanical ventilation for the past 30 years. Liquid ventilation is one of the most extensively studied revolutionary medical therapies being considered for use in practice. Since 1989, when the first human neonates were treated with perfluorochemical liquid, more than 500 human patients--neonate, pediatric, and adult--have been treated with liquid ventilation as part of clinical trials. However, most of the clinically relevant information known to the medical field about liquid ventilation still comes from the laboratory. This paper seeks to briefly present current information available from studies involving liquid ventilation, both laboratory-based and clinical trials, as well as to inform the reader on patient management. In addition, we attempt to elucidate future directions.

Pulmonary administration of gentamicin during liquid ventilation in a newborn lamb lung injury model

OBJECTIVES

Newborns with pulmonary infection frequently present with acute lung injury leading to ventilation/perfusion abnormalities in which intravenous delivery of antibiotics to the lung can be suboptimal. Tidal liquid ventilation (TLV) has been shown to be an effective means for delivering drugs directly to the pulmonary system. The objective of this study was to compare, with lung injury, antibiotic delivery achieved by conventional techniques (gas ventilation and intravenous gentamicin) with that using pulmonary administration of drug (PAD) during TLV.

METHODS

Twelve newborn lambs with an acid lung injury were randomized to receive gentamicin either intravenously during gas ventilation or via PAD during TLV using LiquiVent (Alliance Pharmaceutical Corporation, San Diego, CA, and Hoechst-Marion Roussel, Bridgewater, NJ) perfluorochemical. Gentamicin (5 mg/kg) was administered over 1 minute, and serum levels were obtained at 15-minute intervals. Arterial blood gases and pulmonary mechanics were measured. Ventilation efficiency index and arterial/alveolar oxygen ratio were calculated. Lung-tissue gentamicin levels were measured 4 hours after administration and corrected to dry weight.

RESULTS

Serum gentamicin levels were similar in both groups. Lung gentamicin levels (micrograms/g) were significantly higher for TLV. Also, TLV resulted in significantly more of the total delivered dose in the lung after 4 hours. Ventilation efficiency index and arterial/alveolar oxygen ratios were significantly higher for TLV.

CONCLUSIONS

In this lung injury model, both methods achieved equivalent serum gentamicin levels with higher lung levels using PAD during TLV. This study suggests that TLV may provide an effective vehicle for gentamicin delivery in infants with severe pulmonary infection and ventilation/perfusion abnormalities.

Comparison of perfluorochemical fluids used for liquid ventilation: effect of endotracheal tube flow resistance

Neonatal endotracheal tubes with small inner diameters are associated with increased resistance regardless of the medium used for assisted ventilation. During liquid ventilation (LV) reduced interfacial tension and pressure drop along the airways result in lower alveolar inflation pressure compared with gas ventilation (GV). This is possible by optimizing liquid ventilation strategies to overcome the resistive forces associated with liquid density (rho) and viscosity (mu) of these fluids. Knowledge of the effect of rho, mu, and endotracheal tube (ETT) size on resistance is essential to optimize LV strategies. To evaluate these physical properties, three perfluorochemical (PFC) fluids with a range of kinematic viscosities (FC-75 = 0.82, LiquiVent = 1.10, APF-140 = 2.90) and four different neonatal ETT tubes (Mallincrokdt Hi-Lo Jet ID 2.5, 3.0, 3.5, and 4.0 mm) were studied. Under steady-state flow, flow and pressure drop across the ETTs were measured simultaneously. Resistance was calculated by dividing pressure drop by flow, and both pressure-flow and resistance-flow relationships were plotted. Also, pressure drop and resistance were each plotted as a function of kinematic viscosity at flows of 0.01 L.s-1 for all four ETT sizes. Data demonstrated a quadratic relationship with respect to pressure drop versus flow, and a linear relationship with resistance versus flow: both were significantly correlated (R = 0.92; P < 0.01) and were inversely related to ETT size. Additionally, there was a significant correlation between pressure drop or resistance and kinematic viscosity (R = 0.99; P < 0.01). For LV in neonates these data can be used to select the optimum ETT size and PFC liquid depending OR the chosen ventilation strategy.

Enhanced distribution of adenovirus-mediated gene transfer to lung parenchyma by perfluorochemical liquid

Although gene therapy holds great promise for the treatment of inherited and acquired diseases of the lung, a number of issues including efficient delivery and distribution of genes to pulmonary target cells must still be addressed. In this study we evaluated the use of perfluorochemical (PFC) liquid as a vehicle for delivery of recombinant adenovirus (AdCBlacZ) to lungs of juvenile rabbits. Virus was instilled into trachea of rabbits, and 4 days later the lungs were removed, cut into multiple pieces, and assayed for beta-galactosidase (beta-Gal) activity. Total lung expression of the beta-Gal reporter gene was increased two- to three-fold by instillation of the virus (10(11) particles/kg body weight) in saline (1.5 ml/kg) simultaneously with perflubron liquid (15 ml/kg) compared to virus+saline alone (control). Uniformity of beta-Gal activity between lobes was significantly improved by the PFC liquid. In perflubron-treated lungs approximately 45% of the lung pieces had beta-Gal-specific activity values within 50-150% of the mean specific activity for the total lung, compared to only approximately 15% of the pieces in control lungs. More of total lobar beta-Gal activity was recovered in the distal lung tissue (approximately two-fold greater than controls, p < 0.05). Morphological assessment of X-Gal-stained, fresh-frozen lung sections showed increased levels and more complete staining of alveolar wall cells in the PFC group. These data indicate that the PFC liquid perflubron enhances distribution of virus-mediated gene expression to the lung parenchyma in healthy rabbits. PFC liquid may be a useful treatment vehicle for accessing distal spaces of the damaged or diseased lung.

Partial liquid ventilation in critically ill infants receiving extracorporeal life support. Philadelphia Liquid Ventilation Consortium

OBJECTIVES

To demonstrate that a period of partial liquid ventilation (PLV) with perflubron improves pulmonary function, without adverse events, in a select group of critically ill infants receiving extracorporeal life support (ECLS) with a high likelihood of mortality.

METHODS

This was an open-label, noncontrolled, phase I and II trial of PLV in two infants with congenital diaphragmatic hernia and four infants with acute respiratory distress syndrome (ARDS) who were failing to improve while receiving ECLS. PLV was performed by instilling and maintaining a functional residual capacity of sterile perflubron for 4 to 96 hours.

RESULTS

Four infants were successfully weaned off ECLS for at least 3 days, and two infants (both with ARDS) are long-term survivors after PLV. All infants demonstrated lung recruitment and improved lung compliance, and there were no adverse events related to PLV.

CONCLUSIONS

The study suggests that perflubron PLV is safe, improves lung function, and recruits lung volume in critically ill infants receiving ECLS. PLV therapy for infants with ARDS seems to have a great deal of promise. Based on this and other phase I and II trials, studies of PLV on selected full-term infants before ECLS have been initiated.

Use of liquid ventilation with perflubron during extracorporeal membrane oxygenation: chest radiographic appearances

PURPOSE

To assess the effectiveness of performing liquid ventilation with perflubron in neonates with severe respiratory failure or pulmonary hypertension who receive extracorporeal membrane oxygenation (ECMO) life support.

MATERIALS AND METHODS

We studied an infant (aged 1 month) and a neonate with respiratory failure who underwent ECMO and liquid ventilation with perflubron, which was slowly instilled via an endotracheal tube (in the infant, 40 mL for more than 1 hour; in the neonate, 28 mL within 1 hour).

RESULTS

The infant survived termination of ECMO support and has been breathing room air since 6 months of age. The neonate died soon after ECMO support was withdrawn.

CONCLUSION

A minority of neonates or infants with severe respiratory failure or pulmonary hypertension do not respond adequately to treatment with ECMO and are almost certain to die with termination of ECMO support. Liquid ventilation with perflubron offers a potential salvage therapy in this patient population. In addition, perflubron is a good contrast agent to use in the evaluation of neonatal pulmonary abnormalities.

Neonatal endotracheal tubes: variation in airway resistance with different perfluorochemical liquids

To evaluate the effect of the physical properties of density and viscosity on airway resistance, three perfluorochemical fluids (PFCs) were used: FC-75, Liquivent, and APF-140. Using two different endotracheal tubes (ETT) (3.0mm ID and 4.0mm internal diameter (ID)), the three fluids were studied at steady state flow conditions over a range that approximated peak flow required for liquid ventilation of neonatal lambs (0.005-0.02 l/sec). The slope of airway resistance (Raw)-flow curves and absolute values of Raw for the 3 PFC liquids were higher for the 3.0 ETT compared to the 4.0 ETT. The 3.0 ETT demonstrated resistance changes that were dependent on flow, density and viscosity. The 4.0 ETT showed a resistance-flow relationship that was relatively less dependent on flow, density and viscosity.

Effect of enteral gavage feeding rate on pulmonary functions of very low birth weight infants

To compare the effects of intermittent and continuous feedings on pulmonary function, we studied 24 very low birth weight neonates (mean +/- SD: birth weight, 1.2 +/- 0.3 kg; gestational age, 30.5 +/- 1.1 weeks) at 2 to 4 weeks of age. All infants had a previous diagnosis of respiratory distress syndrome but no subsequent diagnosis of bronchopulmonary dysplasia. Pulmonary mechanics were measured before the beginning of intermittent or continuous feedings and 10 minutes after each meal was completed. Twelve infants were randomly assigned to intermittent and 12 to continuous feedings. These infants had similar birth weight, gestational age, study age, and baseline lung function. After intermittent feedings, there was a significant decrease in tidal volume (38%), minute ventilation (44%), and dynamic compliance (28%), whereas pulmonary resistance increased significantly (100%). In comparison, the pulmonary function data remained unchanged after continuous feedings. These data demonstrate that intermittent feeding of very low birth weight infants can lead to airflow and respiratory instability. These adverse effects appear to be dependent on the rate that feedings are administered. A slower pace of feeding may be more advantageous for infants prone to respiratory instability.

Multichannel polysomnographic recording for evaluation of infant apnea

The preceding discussion has consisted of a review of the technical and clinical aspects of pediatric multichannel recordings, which have become a widely used procedure in the clinical evaluation of infants with various apnea syndromes. It has been shown that multichannel recordings are superior to two-channel pneumocardiograms. Multichannel recordings should therefore be considered in all infants with unexplained episodes of apnea, bradycardia or cyanosis, in order to clarify the type of apnea and to rule out underlying conditions such as gastroesophageal reflux or seizures. The role of multichannel recording in predicting the risk of further apnea and SIDS, however, remains questionable. The clinical introduction of documented monitoring in the home setting with integrated pulse oximetry and a method for monitoring respiratory airflow might help to identify those infants at risk for apnea and SIDS in the future (see article by Weese-Mayer and Silvestri). Nevertheless, multichannel recordings in the hospital have provided a useful tool in the initial evaluation of many infants with infant apnea, and, for SIDS research, they have been useful for evaluating the complex autonomic control mechanisms during sleep and wakefulness.

Pseudoreflux syndrome-increased periodic breathing during the neonatal period presenting as feeding-related difficulties

Sixteen infants who presented with symptoms suggestive of gastroesophageal reflux (GER)-associated apnea were evaluated at the Breathing Disorder Center of the Children's Hospital of Philadelphia. These neonates had a history of occasional emesis and an apparent life-threatening event (ALTE) that occurred while awake which was similar to the presentation of a group of infants previously described. Evaluation of the present group of infants however, revealed increased periodic breathing (12.1 +/- 1.8 SEM% of total sleep time) as opposed to the obstructive apnea that was typically seen with GER. Pathologic gastroesophageal reflux could not be diagnosed in relationship to apneic events. Infants who present during the first month of life with symptoms suggestive of GER-associated apnea should have careful evaluation of reflux and respiratory patterns to confirm the correct diagnosis. Because of the similarities of these infants to the GER group, we have called their disorder pseudoreflux.

Pneumograms in premature infants: a study of longitudinal data

In order to define longitudinal data in premature infants, impedance pneumograms were performed weekly on 23 healthy premature infants. Studies were performed while infants remained hospitalized and at the discretion of the attending physician following discharge. A total of 97 studies were obtained on the study group. The recordings were analyzed for percentage of sleep time spent in periodic breathing, apnea density, and duration of longest apneic pause. Infants in this study demonstrated decreased percent of periodic breathing and decreased apnea density with increased maturation; longest pause per recording was independent of postconceptional age. Results from this study provide data to assist in the evaluation of pneumograms in the premature infant.

Pulmonary mechanics in preterm neonates with respiratory failure treated with high-frequency oscillatory ventilation compared with conventional mechanical ventilation

Pulmonary mechanics were measured in 43 preterm neonates (mean +/- SD values of birth weight 1.2 +/- 0.3 kg, gestational age 30 +/- 2 weeks) with respiratory failure who were concurrently randomly assigned to receive conventional mechanical ventilation (n = 22) or high-frequency ventilation (n = 21). The incidence of bronchopulmonary dysplasia was comparable in the two groups (high-frequency ventilation 57%, conventional ventilation 50%). Pulmonary functions were determined at 0.5, 1.0, 2.0, and 4.0 weeks postnatal ages. Data were collected while subjects were in a nonsedated state during spontaneous breathing. These sequential data show similar patterns of change in pulmonary mechanics during high-frequency ventilation and conventional mechanical ventilation irrespective of gestational age, birth weight stratification, or bronchopulmonary dysplasia. There was no significant difference in the pulmonary functions with either mode of ventilation during the acute phase (less than or equal to 4 weeks) of respiratory disease. When evaluated by the clinical diagnosis of bronchopulmonary dysplasia, the pulmonary data suggested a less severe dysfunction in the high-frequency oscillatory ventilation-treated bronchopulmonary dysplasia group compared with the conventional mechanical ventilation-treated group. These results indicate that high-frequency oscillatory ventilation in preterm neonates does not reduce the risk of acute lung injury; however, the magnitude of the pulmonary dysfunction in the first 2 weeks of life merits a reevaluation.

A randomized placebo-controlled study to evaluate the effects of oral albuterol on pulmonary mechanics in ventilator-dependent infants at risk of developing BPD

Albuterol is a specific beta-2 agonist that has been reported to be effective in treating infants and children with bronchospastic pulmonary disease. The use of oral albuterol has not been investigated in patients with bronchopulmonary dysplasia (BPD). Thirty premature infants were randomized to receive oral albuterol (0.15 mg/kg/dose q8h) or a volume- and color-matched placebo (D5/W). Pulmonary functions were evaluated at baseline and at 48 and 96 hours after entry to the study. The study was also designed for crossover from placebo to albuterol or albuterol to caffeine in the event that the infant's total pulmonary resistance did not improve at the time of the 48 hour pulmonary function evaluation. Heart rate and respiratory rate showed a statistically significant but clinically unimportant increase in the albuterol-treated infants. There were no significant differences noted in systolic or diastolic blood pressure. Percent improvement in the pulmonary function indices were calculated from baseline to 48 hours and from baseline to 96 hours for the placebo and albuterol-treated groups. The results indicate that at 48 hours there were statistically significant improvements in total resistance (14.5%), inspiratory resistance (10.8%), and expiratory resistance (12.9%) in the albuterol-treated infants as compared to the spontaneous deterioration of the same values by 25%, 81%, and 11%, respectively, in the placebo-treated infants. In conclusion, oral albuterol therapy of 48 hours duration improved pulmonary resistance without major cardiovascular side effects in ventilator-dependent premature infants.

Ventilatory response to combined high frequency jet ventilation and conventional mechanical ventilation for the rescue treatment of severe neonatal lung disease

High frequency jet ventilation (HFJV) was used to treat 176 infants who were either failing to respond to conventional mechanical ventilation (CMV) or demonstrating pulmonary air leak. The median birthweight for infants treated with HFJV was 1530 g, median gestational age was 31 weeks. Median duration of therapy with HFJV was 3.0, with a range of 0.1 to 27 days. During the first 24 hours of treatment, mean airway pressure decreased from 16.2 +/- 0.3 (Mean +/- SEM) cmH2O to 12.2 +/- 0.3 cmH2O, while mean PaO2 increased from 65.3 +/- 3.0 torr to 93.3 +/- 3.0 torr during the same time period. Simultaneously, mean PaCO2 decreased from 46.4 +/- 1.5 torr to 36.6 +/- 1.0 torr, although peak inflating pressure decreased from 34.3 +/- 0.7 cmH2O to 30.1 +/- 0.8 cmH2O. Ninety-five (54%) infants treated with HFJV survived. Of 123 infants with RDS 75 (61%) survived. The rate of complications for HFJV patients was similar to that seen with CMV in our nursery. This study suggests that HFJV provides improved oxygenation and ventilation of infants at lower mean and peak pressures compared to conventional mechanical ventilation. HFJV combined with CMV may be a valuable adjunct to therapy in infants with severe lung disease.

Changes in pulmonary mechanics following caffeine administration in infants with bronchopulmonary dysplasia

The effects of caffeine upon pulmonary mechanics were measured in 16 infants with bronchopulmonary dysplasia (BPD). Pulmonary function tests were performed immediately prior to and 1 hour following a dose of 10 mg/kg of caffeine. A 37% increase in minute ventilation (mean +/- SEM; 436.6 +/- 26.3 to 580.8 +/- 30.7 ml/min/kg) was seen with caffeine administration (P less than 0.001), primarily from a 42% increase in tidal volume (6.2 +/- 0.4 to 8.5 +/- 0.4 ml/kg) (P less than 0.001). Total lung resistance decreased by 20% (134.6 + 24.2 to 105.3 +/- 20.1 cmH2O/L/sec) (P = 0.01), and total pulmonary compliance improved by 47% (0.642 +/- 0.104 to 0.908 +/- 0.190 ml/cmH2O/kg) (P less than 0.01). In five matched control infants with BPD, no effects of placebo upon pulmonary mechanics were detected. Since caffeine has a wide therapeutic index with few side effects, it may be an effective adjunct in the treatment of infants with BPD.

Continuous intracranial pressure monitoring and serial electroencephalographic recordings in severely asphyxiated term neonates

We report our observations from intensive intracranial pressure (ICP) monitoring and serial clinical neurologic and electroencephalographic examinations in ten asphyxiated full-term neonates, of whom five died and at least two survivors had multiple severe neurologic handicaps. Direct measurements of ICP were obtained by a newly developed infant subarachnoid bolt and/or a transfontanelle pressure transducer. Simultaneous ICPs were recorded and correlated when possible. We noted a dependence of transfontanelle ICP values on application technique and force. In infants with no bleeding diathesis, the subarachnoid bolt was safe and no complications were encountered. Only six infants experienced pathologic elevations of ICP following birth asphyxia, and of these infants only two had sustained, marked increases of ICP. We also noted abundant fluctuations of cerebral perfusion pressure (mean arterial blood pressure minus ICP), but the majority of fluctuations were accounted for by mean arterial pressure changes rather than ICP changes. We found no deterioration of clinical neurologic function as measured by serial mental status examinations and electroencephalogram samples at the time the maximum ICP was measured. We also noted very little change in ICP during most electrographic seizures. In these infants ICP did increase after birth but major ICP elevations were uncommon and did not appear to introduce any acute functional neurologic disturbances. Most changes in cerebral perfusion pressure were attributed to blood pressure rather than ICP changes. It appears unlikely that cerebral edema and elevated ICP play a major role in determining neurologic outcome in some asphyxiated term infants.

Pulmonary hypertension and persistent fetal circulation in the newborn

Despite these infants' very significant medical instabilities, which require vigorous therapeutic intervention, we have seen a population of infants with little in the way of persistent residual problems. Although many of their pulmonary complications persist after hospital discharge, most resolve within the first year of life. In addition, there are few neurodevelopmental disabilities encountered in such a high-risk population of children.

Predicting survival in infants with persistent pulmonary hypertension of the newborn

Since persistent pulmonary hypertension of the newborn (PPHN) often occurs as a life-threatening illness, it would be advantageous to identify the highest-risk infants within the first 24 hours of life so that transfer to centers with extracorporeal membrane oxygenation (ECMO) or high-frequency ventilation can be facilitated. Fifty-three infants with PPHN were evaluated retrospectively. A multivariate discriminant analysis of risk factors determined that lowest pH, critical PaCO2, highest inspiratory pressure (PI), maximum ventilator rate, and 5-minute Apgar score were significantly different between the 35 survivors (66%) and the 18 infants (34%) who had died when examined within the first 24 hours of life. A clinical scoring system was designed based on these five criteria, which predicted outcome accurately in 93% of infants. A logistic regression analysis was performed as a check on these results and found that lowest pH, critical PaCO2, and PI predicted outcome with great accuracy. These results suggest that the use of these scoring systems within the first 24 hours of age may help predict outcome in infants with PPHN.

Effect of early furosemide administration in neonates with respiratory distress syndrome

The effect of early furosemide-induced diuresis was prospectively evaluated in 39 neonates less than 24 hr of age with clinical respiratory distress syndrome (RDS) who received either four doses of furosemide (1 mg/kg) or no diuretic. Measurements of FiO2 alveolar-arterial oxygen gradient (P[A-a]O2), peak inspiratory pressure (PIP), and urine output as a fraction of intake (O/I) were averaged for every 8 hr. The furosemide group overall showed a significant decrease (P less than 0.01) in FiO2, P[A-a]O2, and PIP with an earlier (32 hr vs 52 hr) and more pronounced diuresis (35% greater O/I) when compared to the controls. This effect was accentuated in the subgroup with 1,000-1,500 g birth weight (significantly lower FiO2 and P(A-a)O2 from 16 to 48 hours), while no increase in urine output was observed for the infants weighing less than 1,000 g. A significant reduction in supplemental oxygen and need for ventilatory support at 96 hr of age was observed in the furosemide-treated, less than 1,500-g infants. The incidence of patent ductus arteriosus was not increased following furosemide therapy, and no significant difference in echocardiographic parameters was observed in 21 infants from both groups, who were followed daily during the first week of life. This study suggests that early furosemide-induced diuresis, particularly in infants weighing 1,000-1,500 g at birth, promotes improvement in pulmonary functions in RDS and leads to faster reduction in oxygen and ventilatory support.

Use of caffeine in infants unresponsive to theophylline in apnea of prematurity

Eleven premature infants with severe apnea unresponsive to therapeutic theophylline levels were studied to determine if caffeine is an effective treatment in such cases. Apnea was documented and quantitated with thermistor-pneumocardiograms measuring heart rate, thoracic impedance, and nasal air flow. Infants with prolonged central or mixed apnea were then treated with caffeine and restudied. Caffeine reduced the total number of apneic episodes of greater than 10 sec duration by 80% (P less than 0.01) and prolonged episodes of apnea (greater than 20 sec) by 88% (P less than 0.05). These data suggest that caffeine may be effective in the management of apnea of prematurity, particularly the prolonged type, unresponsive to theophylline.

Effect of high-frequency jet ventilation on preterm and rabbit tracheal mechanics

The effect of high-frequency jet ventilation (HFJV) on both tracheal dimensions and mechanics was evaluated in preterm and term rabbit airways. Seven tracheal segments were studied at 27 days (group I) and 31 days (group II) of gestation, respectively. Tracheal dimensions and segmental pressure-volume relationships were determined before and after 60 minutes of HFJV (peak pressure 20 cm H2O; mean airway pressure 6.7 to 6.8 cm H2O at 10 Hz). Both tracheal lengths and diameters increased significantly (p less than 0.01) in each group and resulted in increased tracheal volumes: 109% in group I (p less than 0.01) and 60% in group II (p less than 0.01). The mean specific tracheal compliance decreased in group I, from 0.036 cm H2O-1 to 0.015 cm H2O-1 (p less than 0.01), and in group II from 0.029 cm H2O-1 to 0.021 cm H2O-1 (p less than 0.01). Furthermore, the collapsing transmural pressure (the pressure required for total collapse of tracheal segments) decreased significantly (p less than 0.01) in both groups. These data demonstrate significant dimensional and mechanical deformation of tracheal segments after HFJV. An increased propensity toward collapsibility is also observed following HFJV. These changes are similar to those with tracheomalacia. The influence of such deformation on tracheal gas flow during HFJV needs to be further investigated.

Inductive plethysmography--a facilitated postural calibration technique for rapid and accurate tidal volume determination in low birth weight premature newborns

Inductive plethysmography is a noninvasive method of measuring lung volumes in infants. This technique, however, has had very limited use in premature newborns because of the difficulty of calibrating the device with regard to the small tidal volumes (VT) in such infants. The present study describes a facilitated calibration of the inductive plethysmograph in low birth weight infants. The technique depends on generating significantly different compartmentalization of VT into rib cage and abdominal components by changing the infant's position from supine to upright. Linear regression analyses were performed to compare VT measurements made in 9 premature infants with the inductive plethysmograph and the pneumotachygraph; an overall Z-transformed correlation of 501 breath-to-breath comparisons yielded an r value of 0.80; the mean VT (pneumotachygraph) was 13.9 +/- 4.7 ml SD; the mean VT (inductive plethysmograph) was 14.3 +/- 5.1 ml SD. It is concluded that inductive plethysmography is an accurate method to measure VT in small premature infants. Moreover, the ease of the two-position technique for calibration of the device gives the inductive plethysmograph greater utility as a clinical and research tool for measuring lung volumes in premature infants.

Physiologic effects of terbutaline on pulmonary function of infants with bronchopulmonary dysplasia

This study defines the physiologic changes in pulmonary mechanics induced by subcutaneous terbutaline administration in ventilator-dependent infants with severe bronchopulmonary dysplasia (BPD). Eight such infants (mean +/- SEM weight = 2.56 +/- 0.32 kg, postnatal age = 13.0 +/- 3.2 weeks) were chosen for the study. Pulmonary mechanics and arterial blood gases were measured in the control state and at 30 and 60 minutes following the subcutaneous injection of 5 micrograms/kg terbutaline. There was a significant (p less than 0.001) improvement in lung compliance from baseline values at 30 minutes and at 60 minutes (38%). A significant (p less than 0.05) decrease of 23% in the average pulmonary resistance at 30 minutes and a 26% decrease at 60 minutes from control values were observed. An increase in the I/E ratio occurred in all patients at 60 minutes (p less than 0.01). In addition, clinical improvement was noted in six of eight infants. Administration of terbutaline demonstrated a significant improvement in the pulmonary mechanics of infants with severe BPD.

Infant apnea

This review provides an understanding of current problems related to apnea of infancy. Methods for diagnosis, evaluation, and treatment of apnea are discussed.

Transition phase during hyperventilation therapy for persistent pulmonary hypertension of the neonate

It is important for the clinician who is hyperventilating infants with persistent pulmonary hypertension (PPHN) to recognize a transition phase during therapy when pulmonary hypertension is no longer the primary cause of hypoxemia, because infants who are hyperventilated develop parenchymal lung disease after 2 to 3 days. This study reports ten infants who showed PaO2 lability early in the course of PPHN, with an inverse relationship between PaO2 and PaCO2. At a mean age of 79 +/- 14 (SEM) there was a transition phase, after which PaO2 lability decreased and the infants did not require hyperventilation. The mean change in PaO2 per change in PaCO2 was significantly (p less than .05) higher pretransition (22.4 +/- 5.2) compared to during transition (5.1 +/- 1.4) or post-transition (1.9 +/- 1.2). Mean alveolar-arterial oxygen gradient was higher (p less than .05) pretransition (495 +/- 36) vs. post-transition (405 +/- 52) and was more labile relative to PaCO2 change pretransition (20.3 +/- 5.9) compared to post-transition (.3 +/- 2.4). When ventilator settings were reduced after the transition phase, PaCO2 rose by 12.2 torr.

Preterm infants: ventilation and P100 changes with CO2 and inspiratory resistive loading

The ventilatory effects of inspiratory flow-resistive loading and increased chemical drive were measured in ten neonates during progressive hypercapnia in control and loaded states. Hypercapnia (mean increase PCO2 = 15-20) resulted from inspiring 8% CO2 in room air and inspiratory loading by a flow-resistive load = 100 cmH2O X l-1) X s. Hypercapnia produced an increase in group minute ventilation secondary to increasing tidal volumes and breathing frequencies. Loading shifted the minute ventilation-CO2 response to the right, and slopes decreased significantly (P less than 0.05) consequent to a significant decrease in the frequency-CO2 slopes (P less than 0.05), which became negative in four of the ten subjects. Mouth pressure measured at 100 ms after onset of inspiratory effort (P100) occlusion pressure-CO2 slopes measured in five subjects showed no significant increase with load application. Resistive loading produced significant increases in inspiratory time (P less than 0.02) and the inspiratory time/total breath time ratio (P less than 0.01). Airway occlusion elicited the Hering-Breuer reflex, with a significant increase in inspiratory time-to-total breath time ratio (P less than 0.01). The results show that the inspiratory resistive load produced ventilatory compromise in newborns and insufficient compensatory augmentation of central drive.

A newly recognized profile in neonatal lung disease with maternal diabetes

A radiographic pattern associated with respiratory distress, distinct from hyaline membrane disease and transient tachypnea of the newborn, is described in eight infants of diabetic mothers. The radiographic findings demonstrate a regional distribution of reticulogranular densities accompanied by increased lung volumes. Clinical features were gestationally mature infants in moderate respiratory distress with tachypnea, hypercapnia, and hypoxemia requiring supplemental oxygen, with steady improvement and uneventful recovery within 2 weeks. There was no bacteriologic evidence of infection or radiographic evidence of delayed lung fluid absorption. The mothers had mild diabetes. These features characterize a newly recognized entity in diabetes-related idiopathic lung disease of the newborn. Possible causative factors are discussed.

Use of mechanical ventilation for clinical management of persistent pulmonary hypertension of the newborn

Following a discussion of arterial blood gas examinations for specific diagnosis of PPHN, the authors present guidelines for the management of these infants using mechanical ventilation.

Long-term follow-up of newborns with persistent pulmonary hypertension

Persistent pulmonary hypertension of the newborn (PPHN) is a syndrome associated with high morbidity and mortality. Mechanical ventilation attempts to maintain a PaCO2 less than 30 torr and a pH greater than 7.5 until pulmonary hypertension resolves. To assess whether the disease or its therapy adversely affects neurodevelopmental or cardiorespiratory outcome, 11 infants diagnosed and treated for PPHN were evaluated at a mean age of 31 months. Nine had normal developmental quotients (DQs) and 2 had mildly delayed DQs. Eight children were entirely normal neurologically, 2 had slightly increased lower-extremity tone, and 1 had unilateral hypertonia. All cardiac exams, echocardiograms, and ECGs were normal. Four children had chronic lung disease requiring either daily or intermittent bronchodilator therapy; however, their activity levels were unaffected. These results suggest that subsequent normal development with little significant medical compromise may be expected in this group of critically ill infants.

Infant apnea. An approach to management

Apnea of infancy represents a problem that is commonly encountered by the practicing pediatrician; yet, few publications have outlined a practical approach to the care of such infants. In addition, the somewhat controversial aspects of infant apnea and sudden infant death syndrome (SIDS) have resulted in the belief on the part of many physicians that the care of children with apnea or "near-miss" SIDS is either very difficult or of little value. This article, which is based upon the program at The Children's Hospital of Philadelphia, describes an effective management plan for identifying children at risk, lists appropriate evaluation studies, and presents a series of protocols for treating infants with apnea. The initiation of this program has helped to demystify the care of children with apnea and has been very well received by both parents and physicians.

Awake apnea associated with gastroesophageal reflux: a specific clinical syndrome

Fifteen infants with a specific clinical history including awake apnea were evaluated and compared with a control group of infants, using 24-hour studies of esophageal pH, nasal thermistor, impedance pneumography, and heart rate. Thirteen of the 15 children with awake apnea had clearly documented episodes of airway obstruction in associated with gastroesophageal reflux occurring at least twice during the study (mean 3.9 +/- 0.7, range 2 to 9). The control group did not show similar findings. All 15 children with awake apnea had frequent episodes of gastroesophageal reflux. Treatment with home monitoring and reflux precautions was successful in 10 of 15. Five children received therapy with urecholine hydrochloride because of continuing episodes of reflux-associated apnea. Two children subsequently required Nissen fundoplication, primarily for symptoms of severe esophagitis. Our data suggest that in children with awake apnea, the apnea is associated with gastroesophageal reflux. Medical management is usually successful, but fundoplication may be needed in refractory cases.

Effect of external inspiratory loading on ventilation of premature infants

The ventilatory response of 11 growing premature infants to external inspiratory resistive loads was evaluated. Air flow, tidal volume, minute ventilation, inspiratory duration and total breath duration were measured before and after application of a flow resistive load. A significant (P less than 0.001) immediate decrease in minute ventilation and tidal volume was observed in all infants after load application. Minute ventilation and tidal volume remained decreased throughout the 10-min study period. Minute ventilation and tidal volume for the group decreased to 48 and 50% of control mean value, respectively. In addition, there was a significant (P less than 0.001) sustained increase in inspiratory time resulting in an increase in the ratio of inspiratory time/total respiratory time.

Persistent pulmonary hypertension in the neonate: diagnosis and management

PPHN should be recognized as a clinical condition associated with a number of pulmonary and systemic diseases. Present therapy has resulted in increased survival, but the aggressive methods required to produce improvement necessitate a clear understanding of the underlying pathophysiology in order to minimize sequelae.

Episodic airway obstruction in premature infants

Seventy-six premature infants with clinical apnea, bradycardia, or cyanosis were studied with polygraph recordings of heart rate, nasal thermistor detection of airflow, and impedance pneumography. Pathologic apnea was defined by cessation of breathing for greater than 20 s or less than 20 s with bradycardia (heart rate, less than 100 beats per minute). Apnea was classified as central, obstructive, or mixed. Four hundred thirty-three apnea episodes were demonstrated: 238 (55.0%) were central, 53 (12.2%) showed obstructive apnea, and 142 (32.8%) were mixed. Fifty-two infants (68.5%) demonstrated some degree of obstructive apnea, while 24 infants (31.5%) had central apnea only. Bradycardia did not occur in any patient unless preceded by apnea. In premature infants, a significant percentage of apnea was associated with airway obstruction.

Effect of increased radiant warmer power output on state of hydration in the critically ill neonate

To correlate radiant warmer bed power output with state of hydration in the critically ill infant, warmer power input was measured by a wattmeter and recorded by an on-line computer every 5 sec for 2 periods of 8-24 h each in 11 newborns with respiratory distress syndrome (mean birth weight 1.42 kg, mean gestational age 31.4 weeks). The 2 periods were compared to define a high and a low radiant power period. Fluid intake and urine output, urine and serum osmolalities, serum electrolytes, and free water clearance during each study period (high vs low radiant power) were also compared. Mean radiant power density received during periods of high radiant power output (8.93 mw/cm2) was significantly greater than during periods of low radiant power output (7.85 mw/cm2, p less than 0.001). Mean urine osmolality and fluid intake to output ratio were also significantly increased during periods of high radiant power density. There was a trend toward increased serum osmolality and decreased free water clearance during periods of high radiant power; however, these differences were not significant. This study suggests that prospective measurement of radiant power density delivered to critically ill newborns may be clinically significant in predicting an infant's state of hydration.

Changes in pulmonary function during the diuretic phase of respiratory distress syndrome

To evaluate the relationship between improvement in pulmonary function and spontaneous diuresis in respiratory distress syndrome, nine premature infants requiring mechanical ventilation for RDS were studied at a mean age of 11.9 hours prior to the onset of diuresis, at onset of diuresis, at maximum urine output (mean age 44.9 hours), and at 24 hours after maximum urine output. Prior to diuresis functional residual capacity decreased from mean +/- SEM of 16.2 +/- 2 to 13.3 +/- 1.2 ml/kg, and dynamic lung compliance decreased from 2.5 +/- 0.3 to 1.8 +/- 0.3 ml/cm H2O (P less than 0.05), indicating that the respiratory disease was worsening. There was no significant change in alveolar-arterial oxygen gradient, peak inflating pressure, or rate of intermittent mandatory ventilation over this period. At the time of maximum urine output, however, FRC had increased 36% (P less than 0.05). CL had increased by 60% to 2.8 +/- 0.4 ml/cm H2O (P less than 0.025), AaDO2 had decreased from 246 +/- 27 to 184 +/- 30 torr (P less than 0.005), and PIP had decreased from 14.9 +/- 2.2 to 11.3 +/- 2.1 cm/H2O (P less than 0.05). On follow-up study 24 hours after maximum urine output, there was no further significant improvement in FRC, CL or PIP, but IMV rate and AaDO2 continued to decrease. These data show that the pulmonary function in RDS deteriorates until the onset of diuresis, after which it rapidly improves. This diuresis may represent the removal of excess lung liquid and seems necessary for improvement in RDS.

Physiologic implications of two different heat shields for infants under radiant warmers

To study the effects of two different heat shields commonly used under radiant warmers (thin plastic blanket vs a plastic body hood) on premature newborn infants, eight neonates were studied to measure insensible water loss and radiant power density at the skin under control and two shielded conditions. The body hood was found to diminish transmission of radiant heat to the infant's skin by 80%, absorbing heat and becoming warm (P less than 0.001). The plastic blanket absorbed only 15% of radiant warmer heat output (P less than 0.01). Insensible water loss was significantly less under the plastic blanket (1.88 +/- 0.4) ml/kg/hour) than under control (2.70 +/- 0.50 ml/kg/hour, P less than 0.01) and hood (2.86 +/- 0.32 ml/kg/hour, P less than 0.05) conditions. There was no decrease in insensible water loss under the hood compared to controls. This study demonstrates that a thin plastic blanket is the more effective shield against insensible water loss under a radiant warmer. Caution should be exercised with any shielding device to prevent interference with radiant heat delivery.

Fluid, electrolyte, and glucose maintenance in the very low birth weight infant

The low birth weight premature newborn, less than 1000 gm, represents a difficult problem in the management of parenteral fluid, electrolyte, and glucose maintenance. To assess this problem, six infants (mean weight 720 gm, range 575-835 gm; mean gestation 26.5 +/- 0.4 SEM wk) nursed under radiant warmers were evaluated during the first three days of life to determine volume of fluid intake, sodium and dextrose intakes, and urine output. Insensible water loss (IWL) was measured on a metabolic scale. In accordance with current recommendations, infant received fluid volumes of 111 +/- 10, 152 +/- 16, and 191 +/- 27 ml/kg/day on days 1, 2, and 3, respectively. Sodium intake (usually as 0.2% saline) ranges 0-8.5 mEq/kg/day. Dextrose infusions (as 10% solution) ran from 3.3 to 13.7 mg/kg/min. Insensible water loss measured 159 +/- 15 ml/kg/day. Despite increasing fluid intake, serum sodium concentration increased from 141 +/- 3 mEq/l on day 1 to 155 +/- 7 mEq/l on day 3 (p less than 0.05). None of the infants became oliguric and only two urine specimens had specific gravity greater than 1.015. These data demonstrate a larger insensible water loss than reported previously in small infants, but increasing the administration of standard 10% dextrose and 0.2% saline solution to balance insensible losses may result in sodium and glucose overload. Recommendations are made for adjusting parenteral fluid therapy for birth weight groups 600-800, 801-1000, 1001-1500, and 1501-2000 grams and for environmental conditions or radiant warmer or incubator, with or without plastic shielding or phototherapy.

Improvement in lung mechanics as a function of age in the infant with severe bronchopulmonary dysplasia

Pulmonary function tests were performed in two groups of infants with bronchopulmonary dysplasia; a group less than 7 months of age with severe ventilator-dependent respiratory failure (Group A), and a group 7-22 months of age during resolution of their disease (Group B). Group A patients had significantly elevated minute volume, low specific compliance, elevated inspiratory and expiratory pulmonary resistance, and low functional residual capacity. Group B patients also demonstrated elevated minute volume, whereas specific compliance, inspiratory pulmonary resistance and functional residual capacity were within normal limits, and expiratory pulmonary resistance was only slightly above normal. With the exception of minute volume, the differences between the groups were significant (P less than 0.05). Sequential studies of resistance and compliance over 4-5 months in two patients in the younger group demonstrated values that approached or achieved normal range. It is concluded that pulmonary mechanics improve with age in the infant with severe bronchopulmonary dysplasia.

Radiant warmer power and body size as determinants of insensible water loss in the critically ill neonate

Twelve critically ill neonates mechanically ventilated for respiratory failure (mean weight 1.33 kg, mean gestation 31 wk) were studied to quantitate the effects of radiant power from a radiant warming device, body weight, and body surface area on insensible water loss. Radiant power density (Mw/cm2) was measured using a wattmeter and thermopile transducer. Insensible water loss was measured using a Potter Baby Scale. Weight correlated inversely with insensible water loss, (r = -0.86, P less than 0.001). Radiant power density correlated inversely to weight, (r = -0.71, P less than 0.001). There was a significant increase in insensible water loss as radiant power density increased, (r = 0.54, P less than 0.05). Net radiant power received (W/kg) by infants over their exposed surface area, correlated directly to insensible water loss, (r = 0.67, P less than 0.01) irrespective of body weight. Critically ill neonates ventilated for respiratory failure and nursed under radiant warmers incurred greater insensible water losses than previously reported for well infants. The magnitude of this increased insensible water loss is inversely related to body size and is determined directly by the radiant power density required to maintain body temperature.

Successful extubation of neonates: clinical and physiological factors

Arterial blood gases, pulmonary mechanics, lung volume measurements and clinical profiles were determined pre and postextubation in 19 infants recovering from respiratory disease. This study evaluated clinical and physiological factors which may be valuable in predicting successful extubation in neonates. Of the 19 patients, 4 required reintubation within 72 h. In this group of patients, the combined profile of low birth weight (1050 g), low gestational age (31 weeks), and high pulmonary resistance (inspiratory 278 cm H2O/L X sec, expiratory 309 cm H2O/L X sec) was significantly different from the 15 patients who were successfully extubated. In addition, lower pHa after extubation was also characteristic of those infants requiring reintubation.

Effect of heat shielding on convective and evaporative heat losses and on radiant heat transfer in the premature infant

Ten premature infants nursed on servocontrolled radiant warmer beds were studied in three environments designed to alter one or more factors affecting heat transfer (convection, evaporation, and radiation). In the control environment, infants were nursed supine on an open warmer bed. The second environment (walled chamber) was designed to reduce convection and evaporation by placing plastic walls circumferentially around the bed. In the third environment convection and evaporation were minimized by covering infants with a plastic blanket. Air turbulence, insensible water loss, and radiant warmer power were measured in each environment. There was a significant reduction in mean air velocity in the walled chamber and under the plastic blanket when compared to the control environment. A parallel decrease in insensible water loss occurred. In contrast, radiant power demand was the same for control and walled environments, but decreased significantly when infants were covered by the plastic blanket. This study suggests that convection is an important factor influencing evaporation in neonates nursed under radiant warmers. The thin plastic blanket was the most effective shield, significantly reducing radiant power demand.