Breathing In Infants Research Articles

Variables Associated with the Early Failure of Nasal CPAP in Very Low Birth Weight Infants

To identify risk factors and neonatal outcomes associated with the early failure of "bubble" nasal continuous positive airway pressure (CPAP) in very low birth weight (VLBW) infants with respiratory distress syndrome (RDS). Following resuscitation and stabilization at delivery, a cohort of 261 consecutively inborn infants (birth weight < or = 1250 g) was divided into three groups based on the initial respiratory support modality and outcome at 72 hours of age: "ventilator-started" group, "CPAP-failure" group, and "CPAP-success" group. CPAP was successful in 76% of infants < or = 1250 g birth weight and 50% of infants < or = 750 g birth weight. In analyses adjusted for postmenstrual age (PMA) and small for gestational age (SGA), CPAP failure was associated with need for positive pressure ventilation (PPV) at delivery, alveolar-arterial oxygen tension gradient (A-a DO2) >180 mmHg on the first arterial blood gas (ABG), and severe RDS on the initial chest x-ray (adjusted odds ratio [95% CI] = 2.37 [1.02, 5.52], 2.91 [1.30, 6.55] and 6.42 [2.75, 15.0], respectively). The positive predictive value of these variables ranged from 43% to 55%. In analyses adjusted for PMA and severe RDS, rates of mortality and common premature morbidities were higher in the CPAP-failure group than in the CPAP-success group. Although several variables available near birth were strongly associated with early CPAP failure, they proved weak predictors of failure. A prospective controlled trial is needed to determine if extremely premature spontaneously breathing infants are better served by initial management with CPAP or mechanical ventilation.

Index of Suspicion in the Nursery

Index of Suspicion in the Nursery

185 Treatment of RDS Using Aerosolized Kl4 Lung Surfactant in Combination with NCPAP

The leading treatments for premature infants suffering from respiratory distress syndrome (RDS) include 1) intratracheal instillation of lung surfactants, and 2) nasal continuous positive air pressure (nCPAP). Both approaches have shown clinical promise. An ideal therapy would combine the benefits of lung surfactant treatment and nCPAP (i.e., no intubation). Previous attempts to deliver aerosolized lung surfactants yielded discouraging results, largely due to inefficient delivery of the aerosol. Therefore, a patient interface was engineered to efficiently direct aerosolized KL4 lung surfactant to the lungs of neonates in conjunction with nCPAP. Two custom components were designed which linked the aerosol generator to the nasal prongs: 1) an aerosol Conditioning System (CS) to modulate the aerosol and control deposition, and 2) a Prong Adapter (PA) to integrate the CS with ventilator circuits and nasal prongs. These components were cGMP produced by injection molding. An Aeroneb Professional Nebulizer System (Aerogen Inc.) and cGMP produced KL4 lung surfactant at 20mg/ml total phospholipid were the aerosol generator and lung surfactant studied, respectively. The interface components were evaluated in vitro using an InfantStar ventilator. A Harvard Ventilator was used to simulate infant breathing. This novel interface was able to direct 17 +/-2 mg/min of lung surfactant (0.4 mg-total phospholipids per minute) aerosolized by the Aeroneb Pro to the infant-simulator. In contrast, only 8 mg/min was delivered to the simulated infant using an aerosol generator in-line with the CPAP circuit for the same operating conditions (p<0.005). Ventilator gas flow rates, temperature, and nasal prong size were all examined and not found to have a significant impact on the efficiency of aerosol delivery to the simulated infant. In short, this system holds promise to combine the life saving benefits of lung surfactant replacement with nCPAP therapies for infants with RDS and is currently undergoing clinical testing.

Marked variation in oxycodone pharmacokinetics in infants

The pharmacokinetics of oxycodone (13-hydroxy-7,8-dihydrocodeinone) has been studied in adults and in children who are older than 6 months but there is no information on the disposition of oxycodone in neonates and young infants. The aim of this study was to study the pharmacokinetics of oxycodone in infants varying in age from 0 to 6 months. Twenty-two infants undergoing surgery were given postoperatively an intravenous bolus of 0.1 mg.kg(-1) of oxycodone hydrochloride. Ten of the patients were younger than 1 week (group 1), six from 1 week to 2 months (group 2) and six from 2 to 6 months (group 3). Plasma samples were collected for the analysis of oxycodone concentrations up to 24 h. Pharmacokinetics were characterized by noncompartmental methods. The median (range) values for the clearance (Cl) were 9.9 (2.3-17.2), 20.1 (3.7-40.4) and 15.4 (14.8-80.2) ml.min(-1).kg(-1) in the above three groups. The values for volume of distribution at steady-state were 3.3 (1.9-4.7), 5.6 (1.3-8.5) and 3.2 (1.8-6.0) l.kg(-1) and for elimination half-life (t(1/2)) 4.4 (2.4-14.1), 3.6 (1.6-11.6) and 2.0 (0.8-3.9) h, respectively. Both Cl (r = 0.46) and half-life (r = -0.46) were correlated to the age of the patient (P < 0.05). There were 13 patients who were on mechanical ventilation at the time of oxycodone administration. None of the spontaneously breathing infants had hypoventilation which required assistance during the study. The values for Cl and t(1/2) varied greatly between the subjects. This variability was most pronounced in the two youngest groups. Routine dosing of oxycodone in young infants may be dangerous. The dose of oxycodone must be titrated individually.

Numerical Simulation of Air Flow and Medical-Aerosol Distribution in an Innovative Nebulizer Hood

The use of a hood to administer therapeutic aerosols to wheezy infants has many advantages and was found as efficient as administration using a mask. The aim of the present study is to investigate numerically the airflow induced drug dispersion inside the hood. Drug droplet dispersion is examined with respect to three breathing phases: inspiration, expiration, and apnea. The governing equations describing the airflow and the trajectories of drug droplets were solved using the FLUENT 6.1 Computational Fluid Dynamics (CFD) software package. The geometry and mesh were generated with the GAMBIT package. The velocity field of the air and the trajectories of drug droplets inside the funnel--the tube that delivers the drug from the nebulizer to the infant's mouth--and close to its exit are robust and do not show any appreciable differences among the three breathing phases studied. However, in other parts of the hood, air velocity, and particle motion largely depend on the infant's breathing and physiological state. The efficiency of drug delivery to the mouth during inspiration is found to be as high as 84%, whereas it is much smaller in the other two (common) breathing phases examined. Our results may be utilized to improve the hood design and to increase its efficacy for administration of aerosolized medications to infants.

Effect of propofol and CPAP on airway size and configuration in infants

INTRODUCTION General anesthetics attenuate upper airway muscle activity, rendering the airway vulnerable to obstruction. Infants are more susceptible to anesthesia-induced airway obstruction than older children and adults. Continuous positive airway pressure (CPAP) can prevent or treat airway obstruction during anesthesia. Using spin echo magnetic resonance imaging (MRI) to obtain high-resolution images of airway structures, we studied the interaction of propofol and CPAP on upper airway size and configuration in spontaneously breathing infants.

Volume guarantee ventilation, interrupted expiration, and expiratory braking

Background: In volume guarantee ventilation with the Dräger Babylog 8000 ventilator, inspiratory and expiratory flows are monitored and the expiratory tidal volume calculated following each inflation. The pressure for the...

Morphine, Hypotension, and Intraventricular Hemorrhage in the Ventilated Premature Infant

The article in this issue of Pediatrics entitled “Morphine, Hypotension, and Adverse Outcomes Among Preterm Neonates: Who’s to Blame?” is a reanalysis of a data set recently published.1,2 Before attributing blame and passing judgment, it is important to briefly review the data. Thus, the genesis of the study was based on pilot observations that suggest that morphine infusions decrease the frequency of early neurologic injury in ventilated infants.3 The authors extended these initial observations and conducted a multicenter, blinded, randomized trial to test the hypothesis that preemptive morphine, compared with a placebo group, would significantly reduce the frequency of early neurologic injury in ventilated preterm neonates. The primary outcome was neonatal death, severe intraventricular hemorrhage (IVH) (grade III/IV), or periventricular leukomalacia (PVL) defined as cystic echolucency adjacent to the lateral ventricles on cranial sonography obtained at 4 to 7 days and at 28 to 35 days of postnatal life. Ventilated infants were stratified by gestational age (GA) at birth as follows: 23 to 26, 27 to 29, and 30 to 32 weeks. The principal findings were that both groups had similar rates of composite outcome, severe IVH, and PVL. Because open-labeled morphine was an option for both groups, when the data were reanalyzed the morphine as well as the placebo group of infants, who received open-labeled morphine, had significantly worse rates of severe IVH or composite outcome, respectively.2 Regarding adverse effects, infants in the group receiving morphine had an increased incidence of hypotension (defined as the need for vasopressor support or intravenous fluid boluses ≥20 mL/kg), particularly during the … Address correspondence to Jeffrey M. Perlman, MB, ChB, Department of Pediatrics, Weill Cornell Medical Center, New York, NY 10021. E-mail: jmp2007{at}med.cornell.edu

Development of chemoreceptor responses in infants

This paper is devoted to the field of chemoreception and its role in the control of breathing in infants. We use "chemoreception" to refer to the capacity to sense and process changes in P(O2) and P(CO2), and also to react to these changes by adjusting ventilation in order to maintain homeostasis. Functional chemoreceptors are not essential to commence or even to sustain breathing efforts immediately at or after birth; the intense brain activation, which occurs at birth, is sufficient. Over subsequent days to weeks, however, this "neurogenic" drive weakens and drive from the chemoreceptors becomes critical for generating and maintaining a normal breathing rhythm. Failure of the chemoreceptors to develop normally, consequently, becomes an important underlying cause of breathing dysfunction, particularly during sleep. The paper deals with the methods available to study chemoreception in newborn infants and provide an overview of the early postnatal changes and interactions, which influence breathing at rest and under stress. The latter may be described in terms of the threshold and strength as well as the delay/speed with which ventilation changes in response to chemical stimulation. We conclude with a survey of disorders associated with chemoreceptor deficits in infancy.

Neuromuscular paralysis for newborn infants receiving mechanical ventilation.

Ventilated newborn infants breathing in asynchrony with the ventilator are at risk for complications during mechanical ventilation, such as pneumothorax or intraventricular hemorrhage, and are exposed to more severe barotrauma, which consequently could impair their clinical outcome. Neuromuscular paralysis, which eliminates spontaneous breathing efforts of the infant, has potential advantages in this respect. However, a number of complications have been reported with muscle relaxation in infants, so that concerns exist regarding the safety of prolonged neuromuscular paralysis in newborn infants. To determine whether routine neuromuscular paralysis of newborn infants receiving mechanical ventilation compared with no routine paralysis results in clinically important benefits or harms. The Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2004), MEDLINE (from 1966 to April 2004) and EMBASE (from 1988 to April 2004) were searched. References of review articles were hand searched. Language restriction was not imposed. All trials using random or quasi-random patient allocation, in which the routine use of neuromuscular blocking agents during mechanical ventilation was compared to no paralysis or selective paralysis in newborn infants. Methodological quality was assessed blindly and independently by the two authors. Data were abstracted using standard methods of the Cochrane Collaboration and its Neonatal Review Group, with independent evaluation of trial quality, and abstraction and synthesis of data by both authors. Treatment effect was analysed using relative risk, risk difference and weighted mean difference. Ten possibly eligible trials were identified, of which six were included in the review. All the included trials studied preterm infants ventilated for respiratory distress syndrome, and used pancuronium as the neuromuscular blocking agent. In the analysis of the results of all trials, no significant difference was found in mortality, air leak or chronic lung disease, but there was a significant reduction in intraventricular hemorrhage and a trend towards less severe intraventricular hemorrhages. In the subgroup analysis of trials studying a selected population of ventilated infants with evidence of asynchronous respiratory efforts, a significant reduction in intraventricular hemorrhage (any grade and severe IVH) was found, and a trend towards less air leak. In the subgroup analysis of trials studying an unselected population of ventilated infants, no significant differences were found for any of the outcomes. For ventilated preterm infants with evidence of asynchronous respiratory efforts, neuromuscular paralysis with pancuronium seems to have a favourable effect on intraventricular hemorrhage and possibly on air leak. Uncertainty remains, however, regarding the long term pulmonary and neurologic effects, and regarding the safety of prolonged use of pancuronium in ventilated newborn infants. There is no evidence from randomized trials on the effects of neuromuscular blocking agents other than pancuronium. The routine use of pancuronium or any other neuromuscular blocking agent in ventilated newborn infants cannot be recommended based on current evidence.

Oximetría de pulso en la asistencia neonatal en 2005. Revisión de los conocimientos actuales

INTRODUCTION Oxygen saturation monitors or pulse oximeters (SpO2) were entered into practice in the 1980s not only without randomized trials but also, and probably more importantly, without education of neonatal bedside care providers around the world (i. e.: nursing staff, respiratory therapists and also physicians). Education about some known physiological principles, such as the changing relation between O2 and hemoglobin, PaO2 and O2 saturation (O2Sat), did not accompany the routine implementation of SpO2 monitors. Preterm infants of all gestational ages and postnatal ages receiving supplemental oxygen have been treated in many places using targets of O2Sat seen in normal healthy infants breathing room air (i. e.: “physiological” or “normal” values). This was accepted and entered into practice in many cases without full understanding of the meaning of what O2Sat really is and without considering the changing relationship between PaO2 and O2Sat and the differences in SpO2 monitors used. In the past few years, the findings in a number of studies have shown that the long-accepted “physiological” targets of O2Sat by many may in fact be too high. However a “comfort zone” exists in routine clinical practice and it is assumed that if the O2Sat is “high” and the baby appears pink, the preterm baby is “doing well”. On the other hand, in many units, based on understanding of known and proven concepts, the targets of O2Sat were never 97-100 % for preterm infants receiving supplemental oxygen early in life. Oximetry monitors have become commonplace in acute healthcare setting over the last 10-12 years. It has been said blood oxygen can now be considered a “fifth vital sign”. By 1989 there were 29 manufacturers producing 45 different models of oximeters1. There are currently less manufacturers producing over 20 different models and recent technological advances have changed some important aspects of SpO2 performance. All SpO2 monitors have some variability between the measurements with the actual arterial O2Sat value measured by a cooximeter, but true new generation SpO2 monitors are much better than all others. As importantly, monitors are affected by noise, but the different SpO2 monitors handle noise in different ways, leading to differences in real measurements, speed in which a problem is detected, alarms and false alarms, and the presence or not of “holding periods”. In addition, newer technology offers measurements of perfusion index. It is our objective to describe all these factors and others in relation to SpO2 monitoring for neonates. The reliability, accuracy and therefore clinical utility of pulse oximetry remain problematic in some types of infants under certain conditions. As it will be described in this manuscript, improved signal processing technology has substantially improved the ability of some oximeters to work reliably under conditions of poor perfusion, motion artifact and noise from other sources such as bilirubin lights. Historically it was common teaching that if clinicians or bedside care providers were confronted with questionable oxygen saturation values, they should estimate the reliability of the monitor by correlating the pulse rate measured by the oximeter with the heart rate obtained by an electrocardiogram (ECG) monitor used simultaneously. As it will be shown later, accuracy in the recording of pulse rates is also a problem of many monitors.

Therapeutic Benefits of Helium-Oxygen Delivery to Infants via Nasal Cannula

The benefits of helium-oxygen (heliox) administration for pediatric upper and lower respiratory disorders have been well described. However, while most studies advocate delivery via a sealed or semisealed facemask system, such systems may not be tolerated in the young child. This report describes the successful and efficacious delivery of heliox via nasal cannula to 5 infants. A mixture of 80% helium/20% oxygen was blended with 100% oxygen from a wall source and delivered via nasal cannula to 5 spontaneously breathing infants with respiratory distress at flow rates of 2 to 3 liters per minute. Treatment efficacy was retrospectively extracted from nursing, respiratory therapist, and physician entries in the medical record, specifically focusing on changes in respiratory rate, work of breathing, and oxygenation and/or ventilation parameters. All 5 infants tolerated the nasal cannula well. In 2, nasal cannulae were used after attempts to use a facemask system were not tolerated. All patients demonstrated rapid improvements in respiratory parameters including a decreased work of breathing (n = 5), respiratory rate (n = 4), transcutaneous CO2 (n = 2), and stridor (n = 2), or improved oxygenation (n = 1). In 1 patient, the recurrence of distress shortly after discontinuing heliox was rapidly reversed with heliox reinstitution. In infants with respiratory distress who do not tolerate a facemask, the use of nasal cannula represents a viable and efficacious alternative for heliox delivery.

The pediatric airway

Good airway management technique is an essential skill for physicians in most specialties. This article begins with a review of basic airway anatomy and the physiology of the uninstrumented airway. This subject is of particular importance given the increasing use of procedural sedation and the increased recognition of sleep-disordered breathing in infants and children. A discussion of the various artificial airways and their advantages and disadvantages follows. The difficult airway is an important contributor to both patient morbidity and mortality. It is important to have a planned management approach available for the anticipated and, more importantly, the unanticipated difficult airway. The recommendations of the American Society of Anesthesiologists Taskforce on the Management of the Difficult Airway have good application for this important problem. The fetus with the prenatal diagnosis of a lesion that predicts a difficult airway presents a particular challenge. The utilization of an ex-utero intrapartum treatment method is presented as an important approach for the delivery and airway management of these infants. This section closes with a discussion of the prehospital airway management of the pediatric patient.

Early surfactant administration with brief ventilation vs selective surfactant and continued mechanical ventilation for preterm infants with or at risk for respiratory distress syndrome.

Both prophylactic and early surfactant replacement therapy, compared with later selective surfactant administration, reduce mortality and pulmonary complications in ventilated infants with respiratory distress syndrome (RDS). However, continued post-surfactant intubation and ventilation are risk factors for chronic lung disease. Whether prophylactic or early surfactant administration followed by prompt extubation, compared with later, selective use of surfactant followed by continued mechanical ventilation reduces the need for mechanical ventilation and the incidence of chronic lung disease is unknown. To compare two treatment strategies in preterm infants with, or at risk for, RDS: early surfactant administration with brief mechanical ventilation (less than one hour) followed by extubation, vs later, selective surfactant administration, continued mechanical ventilation and extubation from low respiratory support. Two populations of infants receiving early surfactant were considered: spontaneously breathing infants with signs of RDS (surfactant administration during evolution of RDS prior to requiring intubation for respiratory failure) and infants at high risk for RDS (prophylactic surfactant administration within 15 minutes after birth). Searches were made of the Oxford Database of Perinatal trials, MEDLINE (1966-December 2003), CINAHL (1982-December 2003), EMBASE (1980-December 2003), Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2004), Pediatric Research (1990-2003), abstracts, expert informants and hand searching. No language restrictions were applied. Randomized or quasi-randomized controlled clinical trials comparing early surfactant administration with planned brief mechanical ventilation (less than one hour) followed by extubation, vs selective surfactant administration, continued mechanical ventilation and extubation from low respiratory support. Data were sought regarding effects on incidence of mechanical ventilation (ventilation continued or initiated beyond one hour after surfactant administration), incidence of bronchopulmonary dysplasia (BPD), chronic lung disease (CLD), mortality, duration of mechanical ventilation, duration of hospitalization, time in oxygen, duration of respiratory support (including CPAP and nasal cannula), number of patients receiving surfactant, number of surfactant doses administered per patient, incidence of air leak syndromes (pulmonary interstitial emphysema, pneumothorax), patent ductus arteriosus requiring treatment, pulmonary hemorrhage, and other complications of prematurity. Treatment effect was expressed as relative risk (RR) and risk difference (RD) for categorical variables, and weighted mean difference (WMD) for continuous variables. Four randomized controlled clinical trials met selection criteria and were included in this review. In these studies of infants with signs of RDS, intubation and early surfactant therapy followed by extubation to nasal CPAP (NCPAP) compared with later selective surfactant administration was associated with a lower incidence of mechanical ventilation [typical RR 0.70, 95% CI 0.59, 0.84]. None of the trials reported a significant difference in the incidence of BPD or CLD; however, meta-analysis for this outcome cannot yet be performed because the primary data from three of the trials have not yet been published in full. A larger proportion of infants in the early surfactant group received surfactant than in the selective surfactant group [typical RR 1.59, 95% CI 1.35, 1.88]. The number of surfactant doses per patient was significantly greater among patients randomized to the early surfactant group [WMD 0.51 doses per patient, 95% CI 0.36, 0.65]. Trends towards a decreased incidence of air leak syndromes (two studies) and a higher incidence of patent ductus arteriosus requiring treatment (one study) were seen in the early surfactant group. There was no evidence of effect on time in oxygen or duration of mechanical ventilation. Early surfactant replacement therapy with extubation to NCPAP compared with later, selective surfactant replacement and continued mechanical ventilation with extubation from low ventilator support is associated with a reduced need for mechanical ventilation and increased utilization of exogenous surfactant therapy. There is insufficient evidence at present to reliably evaluate effect on BPD or CLD.

Effect of sighs on breathing memory and dynamics in healthy infants.

Deep inspirations (sighs) play a significant role in altering lung mechanical and airway wall function; however, their role in respiratory control remains unclear. We examined whether sighs act via a resetting mechanism to improve control of the respiratory regulatory system. Effects of sighs on system variability, short- and long-range memory, and stability were assessed in 25 healthy full-term infants at 1 mo of age [mean 36 (range 28-57) days] during quiet sleep. Variability was examined using moving-window coefficient of variation, short-range memory using autocorrelation function, and long-range memory using detrended fluctuation analysis. Stability was examined by studying the behavior of the attractor with use of phase-space plots. Variability of tidal volume (VT) and minute ventilation (VE) increased during the initial 15 breaths after a sigh. Short-range memory of VT decreased during the 50 breaths preceding a sigh, becoming uncorrelated (random) during the 10-breath presigh window. Short-range memory increased after a sigh for the entire 50 breaths compared with the randomized data set and for 20 breaths compared with the presigh window. Similar, but shorter duration, changes were noted in VE. No change in long-range memory was seen after a sigh. Coefficient of variation and range of points located within a defined attractor segment increased after a sigh. Thus control of breathing in healthy infants shows long-range stability and improvement in short-range memory and variability after a sigh. These results add new evidence that the role of sighs is not purely mechanical.

Tests of Respiratory Muscle Strength In Neonates

After completing this article, readers should be able to: 1. Describe the underlying cause of respiratory failure in about 50% of preterm infants who require intubation and mechanical ventilation. 2. Compare compliance characteristics of the chest wall in infants, older children, and adults. 3. List some of the conditions seen in neonates that can adversely affect respiratory muscle function. 4. List noninvasive tests for assessing respiratory muscle strength in neonates. Chest wall mechanics of neonates and infants play an essential role in ventilation that frequently is underappreciated. Dysfunction of the respiratory muscles can cause both a disease process and an inability of the patient to compensate for it. As an example, respiratory muscle failure may be the underlying cause in about 50% of preterm infants who have ventilatory failure. (1) In this article, we detail the current understanding of the physiology of the respiratory muscles in neonates and discuss a number of tests designed to assess their function. Mechanically, the respiratory system can be thought of as being composed of two components. The first includes the respiratory muscles, the rib cage, and the anterior abdominal wall, which together make up the “pump,” whose function is to move air in and out of the lungs. The second includes the airways and lung parenchyma through which gas exchange occurs and can be referred to as the “load” on which the pump must act. For ventilation to occur, the respiratory pump must overcome both the frictional (eg, airway resistance) and tissue elastic forces (eg, lung and chest wall compliance) that create the load. The balance between the capabilities of the pump and the magnitude of the load can influence whether respiratory “success” or “failure” occurs. The chest wall, which contains muscles and skeletal structures, undergoes dramatic maturational changes over the first several years of life. In addition …

Infant Pulmonary Mechanics During Tidal Breathing

After completing this article, readers should be able to: 1. Define what compliance and resistance represent when used to describe the respiratory system. 2. Calculate dynamic pulmonary compliance and resistance. 3. Characterize passive mechanics and how they are invoked. 4. Describe the single-compartment series elastic-resistive model of the lung. Tests of infant pulmonary function continue to evolve, broadening our understanding of normal growth and development of infant lungs and airways and providing diagnostic and therapeutic approaches for management of respiratory disease. Traditionally, measurements made during tidal breathing in infants have provided valuable information about lung mechanics, namely, compliance and resistance. In this article, we discuss the physiology on which these measurements are made and briefly describe how several tests are performed in infants to calculate tidal mechanics. Both clinical applications and limitations of the various techniques also are reviewed. Compliance describes the change in volume for a given change in pressure (ΔV/ΔP). When used to describe the respiratory system, compliance represents the elastic properties of the airways, pulmonary parenchyma, and chest wall. Resistance is defined as the amount of pressure required for a given flow rate (ΔP/V) and describes the nonelastic or frictional properties of the respiratory system, including resistance to airflow and tissue resistance. Because pressure change (ΔP=P1-P2), is a common factor in both compliance and resistance measurements, the choice of where P1 and P2 are measured defines the system or structures described by these mechanics. Thus, if pressures are measured at the proximal and distal ends of an airway, compliance and resistance of the airway can be calculated. If pressures are measured at the airway opening and in the pleural space (transpulmonary pressure), the airways, alveoli, and lung parenchyma are included, and lung compliance and resistance can be calculated. If pressures are measured at the airway opening …

Neuromodulation of the Perinatal Respiratory Network

Breathing movements are initiated and controlled by a neuronal network within the lower brainstem that is influenced by peripheral and suprapontine inputs. To provide adaptation of breathing to vocalisation, exercise or hypoxia, rhythmogenic neurons of the ventral respiratory group (VRG) within the ventrolateral medulla (VLM) are controlled by numerous neuromodulators. Underlying cellular mechanisms are currently analysed in respiratory active medulla preparations from perinatal rodents. This reveals properties of the perinatal respiratory network pivotal for understanding spontaneous or drug-induced perturbation of breathing in preterm and term infants. Already at birth, ligand-gated anion channels can inhibit VLM-VRG neurons. But impairment of Cl- extrusion by hormones or growth factors may interfere with respiratory functions. During severe hypoxia, resulting in anoxia of the VLM-VRG, perinatal respiratory activity persists for more than twenty minutes, although at a greatly reduced frequency. This frequency depression, associated with a hyperpolarisation of rhythmogenic VLM-VRG neurons, is reversed by K+ channel blockers, thyrotropin-releasing hormone or substance-P, for example. This response may represent an adaptive mechanism for energy conservation during oxygen depletion. Endogenous frequency depression of the normoxic perinatal respiratory rhythm, possibly mediated by endorphins or prostaglandins, may serve to dampen excessive respiratory activity in utero. Opiates and prostaglandins, known to impair breathing in infants during clinical administration, likely act directly to depress rhythmogenic VLM-VRG neurons. Based upon such findings in perinatal rodent models on synaptic inhibition and responses to hypoxia-anoxia or clinically-applicable drugs, novel pharmacological strategies are discussed that aim to stabilise infant breathing by targeting rhythmogenic respiratory neurons.

Use of Nasopharyngoscopy in the Evaluation of Children With Noisy Breathing

To evaluate the practice of using nasopharyngoscopy without routine fiberoptic bronchoscopy for children presenting to a pediatric pulmonary practice with nonspecific noisy breathing. Retrospective chart review. Records of patients who underwent nasopharyngoscopy between January 1, 1990, and December 31, 1999, were reviewed. Follow-up was obtained by office records and direct contact with the patient's family and/or primary care physician. Academic, tertiary care facility. Eighty-one children who underwent upper airway endoscopy to evaluate noisy breathing consistent with extrathoracic lesions were identified. One child had two evaluations separated by years for differing complaints, making a total of 82 procedures. Stridor was the chief complaint in three fourths of the children. Half of the children with stridor were found to have laryngomalacia. Long-term follow-up was available for 75 of 81 children, with median follow-up of 6 years (range, 1 to 13 years). No medical problems related to missed airway lesions developed in any infants initially evaluated using nasopharyngoscopy. Nasopharyngoscopy without lower airway endoscopy can be used safely for the initial evaluation of noisy breathing in infants and children provided excellent follow-up is available.

Effect of body temperature on the pattern of spontaneous breathing in extremely low birth weight infants supported by proportional assist ventilation.

The optimum body temperature for infants <1000 g is unknown. We investigated body temperature effects on spontaneous breathing using proportional assist ventilation (PAV), because this mode supports spontaneous breathing such that all breathing pattern variables remain controlled by the infant. Minute volume (MV), respiratory rate (RR), tidal volume (Vt), incidence and duration of respiratory pauses, arterial oxygen desaturations <85%, and arterial Pco2 levels will remain unaffected by targeting core body temperature to 36.1-36.5 degrees C (low normal range) versus 37.7-37.9 degrees C (upper normal). Twenty infants (mean +/- SD: birth weight, 696 +/- 155 g; gestational age, 25 +/- 1 wk; age, 5 +/- 3 d) who were supported by PAV were exposed to each target temperature range on 2 consecutive days in four 2-h intervals for a total of 8 h with the sequence of the temperature ranges randomized. Core body temperature was 36.5 +/- 0.2 degrees C and 37.9 +/- 0.2 degrees C in the two conditions. MV was 291 and 314 mL. min-1. kg-1, respectively (7% difference; p < 0.001) as a result of a difference in RR (8%; p < 0.001). The infants maintained their blood CO2 levels and Vt (5.25 +/- 0.6 versus 5.19 +/- 0.6 mL/kg). Incidence and duration of respiratory pauses were not different between conditions. Extremely immature infants who are supported by PAV modify their spontaneous breathing in response to changes in thermal environment such that Pco2 levels are appropriately maintained early in postnatal life. This response pattern occurred consistently and is currently of uncertain clinical significance.