Thomas H. Shaffer

Improved oxygenation and lung compliance withprone positioning of neonates

Fourteen intubated infants recovering from neonatal respiratory disease had arterial blood gases and lung mechanics measured in the supine position and in two variants of the prone position. Prone positioning resulted in significant increases in mean (+/- SEM) arterial oxygen tension (Pa(o2 70.4 +/- 2.5 to 81.1 +/- 4.4mm Hg), dynamic lung compliance (1.7 +/- 0.24 to 2.55 +/- 0.37 ml/cm H2O),and tidal volume (8.6 +/- 1.0 to 10.5 +/- 1.2 ml) when all prone values were compared to supine values. Prone positioning with the abdomen protruding freely, when compared to all supine values, was associated with significantly increased dynamic lung compliance and tidal volume. Values for prone-abdomen free were not significantly different from values for prone-abdomen restricted. This suggests that there are clinical benefits from prone positioning in neonates recovering from respiratory disease.

Pulmonary physiotherapy in neonates:Physiologic changes and respiratory management

To investigate physiologic alterations in respiratory function associated with chest physiotherapy, arterial blood gases, respiratory patterns, lung mechanics, and functional residual capacity were measured in 13 neonates (weights 1.25 to 3.20 kg) during the control period, after vibration of the chest and suctioning, after hyperventilation, and two hours after suctioning. Compared to control values, mean PO2decreased significantly after suctioning to 43 mm Hg and increased significantly after hyperventilation to 78 mm Hg. There was a significant decrease in inspiratory resistance and a trend toward decrease in expiratory resistance after suctioning, with return to control levels after hyperventilation. Respiratory rate increased significantly after suctioning. Functional residual capacity, dynamic lung compliance, and tidal volume, as well as PCO2 and base excess, were not changed appreciably throughout the protocol. Because of potentially severe hypoxemia, this study suggests that suctioning and hyperventilation are not warranted on a routine basis in infants recovering from respiratory diseases.

Positive End Expiratory Pressure: Effects on Lung Mechanics of Premature Lambs

Pulmonary mechanics were determined at 0, 3, 6, and 10 cm H2O positive and expiratory pressure (PEEP) in premature lambs at a mean gestational age of 134 days. Functional residual capacity increased (p less than 0.005) by 7% (1.6 ml/kg) per cm H2O PEEP. Dynamic lung compliance and specific compliance significantly decreased by 10% (0.11 ml/cm H2O/kg) and 9% (0.0051 l/cm H2O) per cm H2O PEEP, respectively, for PEEP above 3 cm H2O level. Inspiratory lung resistance increased significantly (p less than 0.05) only between 0 and 6 cm H2O PEEP while expiratory lung resistance increased (p less than 0.05) between 0 cm H2O PEEP and all higher levels. The data suggest that PEEP in excess of 3 cm H2O produces undesirable effects on lung mechanics in premature lambs. These results may be important in predicting contraindications and potential complications of positive pressure breathing in the newborn.

A Method for Measuring Functional Residual Capacity in Neonates with Endotracheal Tubes

This study evaluates a new 60-s closed circuit helium (He) dilution technique for determination of functional residual capacity (FRC) in intubated neonates independent of snall gas leaks present around uncuffed endotracheal (ET) tubes. By analyticaly relating the fall in He concentration due to mixing with that due to leakage it is possible to predict the final equflibration concentration of He and, therefore, correct for ET tube leaks. The system (120 ml) contains an air pump, He meter, breathing bag in cylinder, a strip chart readout, and solenoid value. Continuous positive airway pressure (CPAP) or ventilator pressure can be applied during testing. One hundred in vitro measurements of FRC ranging from 5-100 cc in both leak and nonleak models were performed and were accurate to within ±7.8% standard deviation. Functional residual capacity measurements were also performed in 30 infants (weight 600-4400 gm).

An Electromechanical Demand Regulated Liquid Breathing System

The process of breathing liquid requires consideration of several problems not typical in gas respiration. These problems stem from the physical properties of liquid such as density, viscosity, and low diffusivity of gases which increase respiratory work. The objective of this study was to develop and study the feasibility of a demand controlled system for providing mechanical assistance and ameliorating respiratory work during liquid breathing.

Effect of external inspiratory loading on ventilation of premature infants.

Summary: 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 < 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 < 0.001) sustained increase in inspiratory time resulting in an increase in the ratio of inspiratory time/total respiratory time.

The effect of external expiratory resistance on lung volume and pulmonary function in the neonate

To investigate the acute physiologic effects of external expiratory resistance on lung function in extubated neonates recovering from respiratory disease, lung mechanics, respiratory patterns, and function residual capacity were measured in ten neonates during a control period and immediately after application of an external expiratory resistance of 30 cm H 2 O/l/second via a face mask. Following application of EER, mean FRC increased by 40.8% ( P

Alterations in Pulmonary Function of Premature Lambs Due to Positive End-Expiratory Pressure

These studies compare lung mechanics and volumes of premature lambs delivered at 139 days of gestation by cesarean section and ventilated by either intermittent positive pressure (IPP) or positive end-expiratory pressure (PEEP). During the first few hours of life, sequential determinations of lung compliance, specific lung compliance; lung resistance, specific lung conductance and functional residual capacity were made at half-hour intervals. Measurements in 5 lambs ventilated with PEEP demonstrated that lung compliance (p less than 0.005), specific lung compliance (p less than 0.001) and specific lung conductance (p less than 0.005) decreased; while lung resistance (p less than 0.10) and functional residual capacity (p less than 0.02) increased as compared to 7 lambs ventilated with IPP.

Limitations of Frequency Dependence as a Measure of Airway Obstruction

The purpose of this study is to develop a pulmonary model and determine the frequency response sensitivity of mechanical parameters such as impedance, dynamic compliance, and dynamic resistance as a function of individual airway properties. Computer simulations of a three compartment model of various physiological cases were used to determine lung parameters as a function of frequency, peripheral airway contribution to total airway resistance, and relative percent obstruction of the peripheral airways. Provided our present concepts of the lung are valid and adequately incorporated into the present model, our results indicate the utility of frequency dependence as a measure of airway obstruction.

Computer Assisted Evaluation and Computation of Pulmonary Function in the Critically Ill Neonate

At the Infant Intensive Care Unit of The Children’s Hospital of Philadelphia, approximately 500 newborn infants are admitted each year with various forms of respiratory disease, such as Respiratory Distress Syndrome, Meconium Aspiration Syndrome, and Neonatal Apnea. In these situations, when oxygen and carbon dioxide gas exchange is significantly compromised, it becomes necessary to apply respiratory support such as mechanical ventilation, continuous positive airway pressure (CPAP) and/or increased inspired oxygen concentration (FiO2) to maintain adequate vital signs.