Pediatric Pulmonology 8:254-258 (1990)
Therapeutic and Diagnostic Methods Neonatal Gastric Intubation: Differential Respiratory Effects Between Nasogastric and Orogastric Tubes Jay S. Greenspan, MD,’ Marla R. Wolfson, PhD,3 William J. Holt, RRT,’ and Thomas H. Shaffer,pm3 Summary. The acute effects of nasogastric (NG) and orogastric (OG) tube placement on pulmonary function of neonates was assessed as a function of infant weight. Lung function was obtained on 14 healthy infants weighing less than 2 kg and 10 infants heavier than 2 kg with an NG and an OG tube in place. Additionally, 15 infants were studied for a third time without gastric intubation. Lung function was determined with an esophageal balloon and by pneumotachography (PeDSTM)via the least mean square analysis technique. Neither the below-2 kg infants nor the above-2 kg infants had apparent clinical compromise with NG and OG tube placement. Infants weighing less than 2 kg, however, demonstrated diminished minute ventilation and respiratory rate and had increased pulmonary resistance, resistive work of breathing, and peak transpulmonary pressure change with NG tube, as compared to OG tube, placement. The above-2 kg infants demonstrated no change in pulmonary function with NG vs. OG tube placement. These data indicate that small neonates demonstrate significant pulmonary compromise with NG placement that may not be clinically apparent. Pediatr Pulmonol 1990; 8:254-258. Key words: Healthy infants, 2 kg weight; dynamic compliance; total lung resistance; resistive work of breathing; minute ventilation; respiratory rate.
INTRODUCTION
Continuous gastric intubation is frequently required to nurture low birthweight neonates. The use of nasogastric (NG) vs. orogastric (OG) tube placement in these infants is dependent upon nursery staff style. NG tubes result in an increased nasal resistance, and, therefore, NG placement has been associated with increased airway resistance. I It has also been shown that the removal of NG tubes in some infants who are near-obligate nose breathers can diminish the incidence of apnea.2 However, since NG tubes are easier to secure, in some nurseries this mode is routinely utilized for small healthy neonates. Factors that could affect the degree of pulmonary compromise caused by NG placement include the infant’s size relative to the size of the feeding tube, as well as the infant’s ability to compensate for this added resistance. Larger infants, or infants with larger nostrils, would be expected to have less change in nasal resistance with NG tube placement.’ Because there are limited data on the effect of gastric tube placement on neonatal lung mechanics as well as breathing patterns, we sought to study
the effect of NG and OG placement on the pulmonary status of neonates. Additionally, to determine how healthy infants of different sizes are affected by the route of gastric tube placement, we evaluated the pulmonary function of small (less than 2 kg), and larger (heavier than 2 kg) neonates after nasal and oral intubation. We chose the value of 2 kg body weight because this value differentiates low birthweight neonates in our nursery. These data should provide practical guidelines for the clinical management of healthy neonates requiring gastric tubes.
334
0 1990 Wiley-Liss, Inc.
From the Newborn Services’, Neonatal Respiratory Therapy’, Temple University Hospital and Departments of Physiology and Pediatrics, Temple University School of Medicine and St. Christopher’s Hospital for Children3, Philadelphia, Pennsylvania. Received August 4, 1989; (revision) accepted for publication November 1, 1989. Address correspondence and reprint requests to Dr. J. S . Greenspan, Section of Neonatology, Temple University Hospital, 3401 N. Broad Street, Philadelphia, PA 19140.
Effects of NG Placement on Pulmonary Function
MATERIALS AND METHODS
Fourteen appropriate-for-gestational-age infants weighing less than 2 kg at time of study (X & SD birthweight, 1.38 & 0.4 kg; gestational age, 32 & 3 wks; study weight, 1.42 & 0.3 kg) and 10 appropriate-forgestational-age infants heavier than 2 kg (X SD birth0.8 kg; gestational age, 36 4 weeks; weight, 2.31 study weight, 2.46 ? 0.6 kg) were enrolled after parental consent was obtained. Infants were not on ventilatory support, were breathing room air and were in no respiratory distress at time of study. All infants were black, were on advancing or full gastric feeds, and were without abdominal distension. Some of the infants had recovered from lung disease, and all were considered stable by an attending neonatologist. Infants with gastrointestinal or nasal abnormalities were excluded. Each infant was sequentially evaluated with either an NG or an OG tube in place. A 5 French Accumark feeding tube (Concord Laboratories, Inc., Keene, NH) was positioned at least 10 minutes prior to each study. To study the effect of a gastric tube on the esophageal balloon, 15 infants (7 below 2 kg, 8 over 2 kg) were studied a third time without a gastric tube. The order of testing (NG vs. OG vs. no feeding tube) was randomized. To eliminate the possible effects of feeding per se, the infant’s feeds were held for at least 30 minutes prior to and during t e ~ t i n g .Infants ~ were monitored for heart and respiratory rate and oxygen saturation throughout the study.
*
* *
Data Collection
The infants were studied unsedated in the supine position. As previously simultaneous signals of air flow and transpulmonary pressure were related to a software program for data analysis (PeDSTM, MAS Inc., Hatfield, PA). An airfilled balloon (Mallinckrodt, 8 French, St. Louis) was placed orally into the distal esophagus and was attached to a differential pressure transducer (Model P7D Celesco Transducer Products, Inc., Canoga Park, CA). The balloon position was checked by observing the on-line pressure tracing. Since all infants were asymptomatic with respect to lung disease, no chestwall distortion was observed; thus, concerns regarding the accuracy of pleural pressure estimates using an esophageal balloon catheter were obviated.* The transpulmonary pressure change was measured as the difference between the airway and the esophageal pressure. Air flow was measured with a heated pneumotachometer (Fleisch Model 00, OEM Medical, Richmond, VA) and a differential pressure transducer (Model MP45, Validyne Engineering Corp., Northridge, CA). This was attached to a face mask with a low-volume adapter (Vital Signs, Totowa, NJ). A tube from the sideport of this
255
adapter was attached to the Celesco differential pressure transducer to measure airway pressure. The resistance and dead space of this assembly is 13.2 cmH,O/L/sec and 1.7 mL, respectively.6 The face mask was gently placed on the infant’s face, and the infant was comforted until a prolonged period of quiet sleep was observed. Sampling of pressure and flow signals occurred during 60 seconds of quiet sleep. Data Analysis
The pulmonary function was evaluated by analysis of flow, volume, and transpulmonary pressure signals. The mechanics and energetics of breathing were determined by the least mean square analysis technique.6 Statistical differences in mechanics, energetics, and ventilation of the infants were evaluated as a function of gastric tube placement and infant weight, with an analysis of variance and post-hoc testing (Stats Plus, Human Systems Dynamics, Northridge, CA). RESULTS
The infants tolerated gastric tube placement and pulmonary function testing well and had no clinical evidence of respiratory distress or chest wall distortion during the testing period. The coefficient of variation was less than 15% for all measured parameters in each infant. Heart rate and transcutaneous oxygen saturation remained stable showing no effect of NG vs. OG placement. The studies performed with OG placement demonstrated near-normal pulmonary function profiles for neonates. Typical scalar tracings of the pressure, flow, and volume signals for a less than 2 kg infant with an OG and an NG tube in place are shown in Figure 1. With NG placement, the infant demonstrated an increased pulmonary resistance and had diminished peak flow, particularly on expiration. The infants had increased transpulmonary pressure changes and diminished respiratory rates while maintaining a similar tidal volume. Therefore, minute ventilation was reduced. Such changes were not seen in the heavier than 2 kg infants (Fig. 1). Figure 2 demonstrates the individual effects of gastric tube placement on pulmonary resistance in infants weighing less than and more than 2 kg. As shown, pulmonary resistance was consistently increased in the smaller infants with NG placement, regardless of the baseline value. In contrast, only a few of the heavier infants demonstrated an increase in pulmonary resistance with NG placement. The mean percent increase in pulmonary resistance from OG to NG placement was 66% for the smaller infants, significantly greater than the 8% increase found in the larger infants (P 2 kg NG
OG
62?5* 6624 387 -+ 20* 354 2 35 1.6 ? 0.2 1.3 & 0.2 86 +- 18* 66 k 14 24?5* 2124 6.9 5 0.8* 7.3 t 1.0 1.6t0.2* 2.4t0.2
NG 6525 376 f 59 1.4 -+ 0.2 65 zk 14 23k4 6.6 +- 1.1 2.5zk0.3
*NG vs. OG significantly different P < 0.05.
chanics from studies performed with OG placement in the same infants. The mean & SEM pulmonary resistance was 60 2 10 cmH,O/L/sec and compliance 1.5 0.2 mL/cmH,O/kg with no gastric tube and 59 k 9 cmH,O/L/sec and 1.5 ? 0.3 mL/cmH,O/kg, respectively, with an OG tube in place. The on-line scalar tracings for studies without a gastric tube were similar to those with OG placement (Fig. 1).
*
DISCUSSION
The necessity for gastric decompression and initiation of enteral alimentation requires gastric intubation in neonates. This can be achieved with either OG or an NG intubation. However, for infants with no clinically apparent pulmonary compromise, the NG route is frequently chosen because tubes passed this way are easier to secure and less likely to elicit a gag or become reg~rgitated.'.~In our intensive care nursery a majority of healthy neonates are nurtured with NG tubes. In the present study, all infants were considered to be without pulmonary compromise and, hence, candidates for NG placement. The infants were breathing comfortably without supplemental oxygen or ventilatory support and had clinically recovered from previous pulmonary dysfunction. Although intrapatient variability in pulmonary mechanics was minimal, differences between infants of the same size were noted. This interpatient variability is consistent with previous findings in infants with little or no lung disease.637The infants tolerated gastric tube placement and pulmonary function testing well. The tests performed with an OG tube were similar to those performed without gastric intubation, demonstrating that the gastric tube did not interfere with lung function determinations. The infants demonstrated no apparent clinical compromise associated with OG vs. NG placement. Infants weighing less than 2 kg, however, demonstrated significant hypoventilation, resulting primarily from a decreased respiratory rate with no change in inspiratory to expiratory timing ratios. The increased pulmonary resis-
tance and resistive work of breathing as well as diminished peak expiratory tidal flow in the less than 2 kg infants suggest significant airway compromise from the NG tube secondary to partial nasal obstruction in this population of near-obligate nose breathers .9 Similar changes have been reported for animals and human neonates. Previous studies have demonstrated that some infants may adapt to added resistance by altering breathing strategies or lowering oxygen consumption to maintain normal energy e x p e d i t ~ r e . ~ ~The ' ~ ~ long-term '' outcome of these strategies, however, remains unclear. In this study the smaller infants demonstrated a diminished minute ventilation despite an increase in peak transpulmonary pressure change and resistive work of breathing (increased energy expenditure). Therefore, these findings are suggestive of an ineffectual strategy to overcome the additional resistive load. Although increased pulmonary resistance and resistive work of breathing due to NG placement may not be clinically apparent in infants, these changes could present long-term problems with respect to respiratory muscle fatigue and weight gain. l4 Nasogastric tube placement has been shown to increase nasal resistance and, in some cases, increase airway resistance in low birthweight neonates.' In the present study we looked at the effect of NG placement on the overall pulmonary function profile and found that only infants who weighed less than 2 kg had a significant response to NG vs. OG placement. Further analysis of data failed to define a linear correlation between infant size and changes in pulmonary function. The observed changes in pulmonary mechanics and energetics were presumably due to the smaller nasal-to-catheter size ratio in the less than 2 kg group. The heavier than 2 kg group had a variable response to NG placement, and, therefore, no significant changes in mean pulmonary mechanics were found (Figs. 2, 3). It is particularly noteworthy that several of these infants demonstrated a decreased pulmonary resistance with NG tube placement. This was probably secondary to an altered breathing strategy such as partial oral breathing, in response to the NG placement.'
258
Greenspan et al.
The changes observed in our infants may, in part, be related to the population studied. Our less than 2 kg infants had low baseline pulmonary resistance, and any change in resistance would, therefore, be readily detectable. Furthermore, all infants were black and may, therefore, have had a different baseline nasal resistance and degree of occlusion with an NG tube than other racial
group^.','^ This study indicates that the increased airway resistance experienced with 5 French nasogastric tube placement is most consistent in the less than 2 kg neonates. The NG placement in these infants causes acute pulmonary compromise for which they are unable to fully compensate. These data suggest that, regardless of pulmonary status, the OG route should be preferred to NG placement in low birthweight infants until they reach 2 kg body weight.
5.
6.
7.
8. 9. 10.
I I.
REFERENCES 12. Stocks J. Effect of nasogastric tubes on nasal resistance during infancy. Arch Dis Child. 1980; 5517-21. Van Someren V, Linnett SJ, Stothers JK, Sullivan PG. An investigation into the benefits of resiting nasoenteric feeding tubes. Pediatrics. 1984; 74:379-383. Ostertag SC, LaGamma EF, Reisen CE, Ferrantino FC. Early feeding does not affect the incidence of necrotizing enterocololitis. Peditarics. 1986; 77:275-280. Rothbarth BS, Pedigo C. High risk infants on families. In: Scipien GM, Barnard MU, Chard MA, Howe J, Phillips PJ, eds.
13.
14.
15.
Comprehensive Pediatric Nursing, 3rd Edition. New York: McGraw-Hill, 1986:584. Pate1 BD, Dinwiddie R, Kumar SP, Fox WW. The effects of feeding on arterial blood gases and lung mechanics in newborn infants recovering from respiratory disease. J Pediatr. 1977; 90: 435-438. Bhutani VK, Sivieri EM, Abbasi S , Shaffer TH. Evaluation of neonatal pulmonary mechanics: Two factor least mean square analysis technique. Pediatr Pulmonol. 1988; 4: 150-158. Greenspan JS, Abbasi S, Bhutani VK. Sequential changes in pulmonary mechanics in the very low birth weight ( 51000 grams) infant. J Pediatr. 1988; 113:732-737. Lesouef PN, Lopes JM, England SJ, Bryan MH, Bryan AC. Influence of chest wall distortion on esophageal pressure. J Appl Physiol. 1983; 55:353-358. Miller MJ, Martin RJ, Carlo WA, Fouke JM, Strohl KP, Fanaroff AA. Oral breathing in newborn infants. J Pediatr. 1985; 107;465. Harding R, Wood GA, Thorburn GD. Control of oral breathing in the newborn. In: Jones CT, ed. Research in Perinatal Medicine (VII), Fetal and Neonatal Development. Ithaca, NY: Perinatology Press, 1988:373-377. Martin RJ, Miller MJ, Siner B, Difiore JM, Carlo WA. Effect of unilateral nasal occlusion on ventilation and pulmonary resistance in preterm infants. Pediatr Res. 1989; 25:223A. Boychuk BB, Seshia MMK, Rigatto H. The immediate ventilatory response to added inspiratory elastic and resistive loads in preterm infants. Pediatr Res. 1977; I1:276-279. Duara S, Gerhardt T, Net0 GS, Tamayo M, Suguihara C, Bancalari E. Changes in oxygen consumption with hypoventilation in preterm infants. Pediatr Res. 1989; 23:307A. Wolfson MR, Bhutani VK, Shaffer TH, Bowen FW. Mechanics and energetics of breathing helium in infants with bronchopulmonary dysplasia. J Pediatr. 1984; 104:752-757. Polgar G, Kong GP. The nasal resistance of newborn infants. J Pediatr. 1965; 67557-567.
Therapeutic and Diagnostic Methods Neonatal Gastric Intubation: Differential Respiratory Effects Between Nasogastric and Orogastric Tubes Jay S. Greenspan, MD,’ Marla R. Wolfson, PhD,3 William J. Holt, RRT,’ and Thomas H. Shaffer,pm3 Summary. The acute effects of nasogastric (NG) and orogastric (OG) tube placement on pulmonary function of neonates was assessed as a function of infant weight. Lung function was obtained on 14 healthy infants weighing less than 2 kg and 10 infants heavier than 2 kg with an NG and an OG tube in place. Additionally, 15 infants were studied for a third time without gastric intubation. Lung function was determined with an esophageal balloon and by pneumotachography (PeDSTM)via the least mean square analysis technique. Neither the below-2 kg infants nor the above-2 kg infants had apparent clinical compromise with NG and OG tube placement. Infants weighing less than 2 kg, however, demonstrated diminished minute ventilation and respiratory rate and had increased pulmonary resistance, resistive work of breathing, and peak transpulmonary pressure change with NG tube, as compared to OG tube, placement. The above-2 kg infants demonstrated no change in pulmonary function with NG vs. OG tube placement. These data indicate that small neonates demonstrate significant pulmonary compromise with NG placement that may not be clinically apparent. Pediatr Pulmonol 1990; 8:254-258. Key words: Healthy infants, 2 kg weight; dynamic compliance; total lung resistance; resistive work of breathing; minute ventilation; respiratory rate.
INTRODUCTION
Continuous gastric intubation is frequently required to nurture low birthweight neonates. The use of nasogastric (NG) vs. orogastric (OG) tube placement in these infants is dependent upon nursery staff style. NG tubes result in an increased nasal resistance, and, therefore, NG placement has been associated with increased airway resistance. I It has also been shown that the removal of NG tubes in some infants who are near-obligate nose breathers can diminish the incidence of apnea.2 However, since NG tubes are easier to secure, in some nurseries this mode is routinely utilized for small healthy neonates. Factors that could affect the degree of pulmonary compromise caused by NG placement include the infant’s size relative to the size of the feeding tube, as well as the infant’s ability to compensate for this added resistance. Larger infants, or infants with larger nostrils, would be expected to have less change in nasal resistance with NG tube placement.’ Because there are limited data on the effect of gastric tube placement on neonatal lung mechanics as well as breathing patterns, we sought to study
the effect of NG and OG placement on the pulmonary status of neonates. Additionally, to determine how healthy infants of different sizes are affected by the route of gastric tube placement, we evaluated the pulmonary function of small (less than 2 kg), and larger (heavier than 2 kg) neonates after nasal and oral intubation. We chose the value of 2 kg body weight because this value differentiates low birthweight neonates in our nursery. These data should provide practical guidelines for the clinical management of healthy neonates requiring gastric tubes.
334
0 1990 Wiley-Liss, Inc.
From the Newborn Services’, Neonatal Respiratory Therapy’, Temple University Hospital and Departments of Physiology and Pediatrics, Temple University School of Medicine and St. Christopher’s Hospital for Children3, Philadelphia, Pennsylvania. Received August 4, 1989; (revision) accepted for publication November 1, 1989. Address correspondence and reprint requests to Dr. J. S . Greenspan, Section of Neonatology, Temple University Hospital, 3401 N. Broad Street, Philadelphia, PA 19140.
Effects of NG Placement on Pulmonary Function
MATERIALS AND METHODS
Fourteen appropriate-for-gestational-age infants weighing less than 2 kg at time of study (X & SD birthweight, 1.38 & 0.4 kg; gestational age, 32 & 3 wks; study weight, 1.42 & 0.3 kg) and 10 appropriate-forgestational-age infants heavier than 2 kg (X SD birth0.8 kg; gestational age, 36 4 weeks; weight, 2.31 study weight, 2.46 ? 0.6 kg) were enrolled after parental consent was obtained. Infants were not on ventilatory support, were breathing room air and were in no respiratory distress at time of study. All infants were black, were on advancing or full gastric feeds, and were without abdominal distension. Some of the infants had recovered from lung disease, and all were considered stable by an attending neonatologist. Infants with gastrointestinal or nasal abnormalities were excluded. Each infant was sequentially evaluated with either an NG or an OG tube in place. A 5 French Accumark feeding tube (Concord Laboratories, Inc., Keene, NH) was positioned at least 10 minutes prior to each study. To study the effect of a gastric tube on the esophageal balloon, 15 infants (7 below 2 kg, 8 over 2 kg) were studied a third time without a gastric tube. The order of testing (NG vs. OG vs. no feeding tube) was randomized. To eliminate the possible effects of feeding per se, the infant’s feeds were held for at least 30 minutes prior to and during t e ~ t i n g .Infants ~ were monitored for heart and respiratory rate and oxygen saturation throughout the study.
*
* *
Data Collection
The infants were studied unsedated in the supine position. As previously simultaneous signals of air flow and transpulmonary pressure were related to a software program for data analysis (PeDSTM, MAS Inc., Hatfield, PA). An airfilled balloon (Mallinckrodt, 8 French, St. Louis) was placed orally into the distal esophagus and was attached to a differential pressure transducer (Model P7D Celesco Transducer Products, Inc., Canoga Park, CA). The balloon position was checked by observing the on-line pressure tracing. Since all infants were asymptomatic with respect to lung disease, no chestwall distortion was observed; thus, concerns regarding the accuracy of pleural pressure estimates using an esophageal balloon catheter were obviated.* The transpulmonary pressure change was measured as the difference between the airway and the esophageal pressure. Air flow was measured with a heated pneumotachometer (Fleisch Model 00, OEM Medical, Richmond, VA) and a differential pressure transducer (Model MP45, Validyne Engineering Corp., Northridge, CA). This was attached to a face mask with a low-volume adapter (Vital Signs, Totowa, NJ). A tube from the sideport of this
255
adapter was attached to the Celesco differential pressure transducer to measure airway pressure. The resistance and dead space of this assembly is 13.2 cmH,O/L/sec and 1.7 mL, respectively.6 The face mask was gently placed on the infant’s face, and the infant was comforted until a prolonged period of quiet sleep was observed. Sampling of pressure and flow signals occurred during 60 seconds of quiet sleep. Data Analysis
The pulmonary function was evaluated by analysis of flow, volume, and transpulmonary pressure signals. The mechanics and energetics of breathing were determined by the least mean square analysis technique.6 Statistical differences in mechanics, energetics, and ventilation of the infants were evaluated as a function of gastric tube placement and infant weight, with an analysis of variance and post-hoc testing (Stats Plus, Human Systems Dynamics, Northridge, CA). RESULTS
The infants tolerated gastric tube placement and pulmonary function testing well and had no clinical evidence of respiratory distress or chest wall distortion during the testing period. The coefficient of variation was less than 15% for all measured parameters in each infant. Heart rate and transcutaneous oxygen saturation remained stable showing no effect of NG vs. OG placement. The studies performed with OG placement demonstrated near-normal pulmonary function profiles for neonates. Typical scalar tracings of the pressure, flow, and volume signals for a less than 2 kg infant with an OG and an NG tube in place are shown in Figure 1. With NG placement, the infant demonstrated an increased pulmonary resistance and had diminished peak flow, particularly on expiration. The infants had increased transpulmonary pressure changes and diminished respiratory rates while maintaining a similar tidal volume. Therefore, minute ventilation was reduced. Such changes were not seen in the heavier than 2 kg infants (Fig. 1). Figure 2 demonstrates the individual effects of gastric tube placement on pulmonary resistance in infants weighing less than and more than 2 kg. As shown, pulmonary resistance was consistently increased in the smaller infants with NG placement, regardless of the baseline value. In contrast, only a few of the heavier infants demonstrated an increase in pulmonary resistance with NG placement. The mean percent increase in pulmonary resistance from OG to NG placement was 66% for the smaller infants, significantly greater than the 8% increase found in the larger infants (P 2 kg NG
OG
62?5* 6624 387 -+ 20* 354 2 35 1.6 ? 0.2 1.3 & 0.2 86 +- 18* 66 k 14 24?5* 2124 6.9 5 0.8* 7.3 t 1.0 1.6t0.2* 2.4t0.2
NG 6525 376 f 59 1.4 -+ 0.2 65 zk 14 23k4 6.6 +- 1.1 2.5zk0.3
*NG vs. OG significantly different P < 0.05.
chanics from studies performed with OG placement in the same infants. The mean & SEM pulmonary resistance was 60 2 10 cmH,O/L/sec and compliance 1.5 0.2 mL/cmH,O/kg with no gastric tube and 59 k 9 cmH,O/L/sec and 1.5 ? 0.3 mL/cmH,O/kg, respectively, with an OG tube in place. The on-line scalar tracings for studies without a gastric tube were similar to those with OG placement (Fig. 1).
*
DISCUSSION
The necessity for gastric decompression and initiation of enteral alimentation requires gastric intubation in neonates. This can be achieved with either OG or an NG intubation. However, for infants with no clinically apparent pulmonary compromise, the NG route is frequently chosen because tubes passed this way are easier to secure and less likely to elicit a gag or become reg~rgitated.'.~In our intensive care nursery a majority of healthy neonates are nurtured with NG tubes. In the present study, all infants were considered to be without pulmonary compromise and, hence, candidates for NG placement. The infants were breathing comfortably without supplemental oxygen or ventilatory support and had clinically recovered from previous pulmonary dysfunction. Although intrapatient variability in pulmonary mechanics was minimal, differences between infants of the same size were noted. This interpatient variability is consistent with previous findings in infants with little or no lung disease.637The infants tolerated gastric tube placement and pulmonary function testing well. The tests performed with an OG tube were similar to those performed without gastric intubation, demonstrating that the gastric tube did not interfere with lung function determinations. The infants demonstrated no apparent clinical compromise associated with OG vs. NG placement. Infants weighing less than 2 kg, however, demonstrated significant hypoventilation, resulting primarily from a decreased respiratory rate with no change in inspiratory to expiratory timing ratios. The increased pulmonary resis-
tance and resistive work of breathing as well as diminished peak expiratory tidal flow in the less than 2 kg infants suggest significant airway compromise from the NG tube secondary to partial nasal obstruction in this population of near-obligate nose breathers .9 Similar changes have been reported for animals and human neonates. Previous studies have demonstrated that some infants may adapt to added resistance by altering breathing strategies or lowering oxygen consumption to maintain normal energy e x p e d i t ~ r e . ~ ~The ' ~ ~ long-term '' outcome of these strategies, however, remains unclear. In this study the smaller infants demonstrated a diminished minute ventilation despite an increase in peak transpulmonary pressure change and resistive work of breathing (increased energy expenditure). Therefore, these findings are suggestive of an ineffectual strategy to overcome the additional resistive load. Although increased pulmonary resistance and resistive work of breathing due to NG placement may not be clinically apparent in infants, these changes could present long-term problems with respect to respiratory muscle fatigue and weight gain. l4 Nasogastric tube placement has been shown to increase nasal resistance and, in some cases, increase airway resistance in low birthweight neonates.' In the present study we looked at the effect of NG placement on the overall pulmonary function profile and found that only infants who weighed less than 2 kg had a significant response to NG vs. OG placement. Further analysis of data failed to define a linear correlation between infant size and changes in pulmonary function. The observed changes in pulmonary mechanics and energetics were presumably due to the smaller nasal-to-catheter size ratio in the less than 2 kg group. The heavier than 2 kg group had a variable response to NG placement, and, therefore, no significant changes in mean pulmonary mechanics were found (Figs. 2, 3). It is particularly noteworthy that several of these infants demonstrated a decreased pulmonary resistance with NG tube placement. This was probably secondary to an altered breathing strategy such as partial oral breathing, in response to the NG placement.'
258
Greenspan et al.
The changes observed in our infants may, in part, be related to the population studied. Our less than 2 kg infants had low baseline pulmonary resistance, and any change in resistance would, therefore, be readily detectable. Furthermore, all infants were black and may, therefore, have had a different baseline nasal resistance and degree of occlusion with an NG tube than other racial
group^.','^ This study indicates that the increased airway resistance experienced with 5 French nasogastric tube placement is most consistent in the less than 2 kg neonates. The NG placement in these infants causes acute pulmonary compromise for which they are unable to fully compensate. These data suggest that, regardless of pulmonary status, the OG route should be preferred to NG placement in low birthweight infants until they reach 2 kg body weight.
5.
6.
7.
8. 9. 10.
I I.
REFERENCES 12. Stocks J. Effect of nasogastric tubes on nasal resistance during infancy. Arch Dis Child. 1980; 5517-21. Van Someren V, Linnett SJ, Stothers JK, Sullivan PG. An investigation into the benefits of resiting nasoenteric feeding tubes. Pediatrics. 1984; 74:379-383. Ostertag SC, LaGamma EF, Reisen CE, Ferrantino FC. Early feeding does not affect the incidence of necrotizing enterocololitis. Peditarics. 1986; 77:275-280. Rothbarth BS, Pedigo C. High risk infants on families. In: Scipien GM, Barnard MU, Chard MA, Howe J, Phillips PJ, eds.
13.
14.
15.
Comprehensive Pediatric Nursing, 3rd Edition. New York: McGraw-Hill, 1986:584. Pate1 BD, Dinwiddie R, Kumar SP, Fox WW. The effects of feeding on arterial blood gases and lung mechanics in newborn infants recovering from respiratory disease. J Pediatr. 1977; 90: 435-438. Bhutani VK, Sivieri EM, Abbasi S , Shaffer TH. Evaluation of neonatal pulmonary mechanics: Two factor least mean square analysis technique. Pediatr Pulmonol. 1988; 4: 150-158. Greenspan JS, Abbasi S, Bhutani VK. Sequential changes in pulmonary mechanics in the very low birth weight ( 51000 grams) infant. J Pediatr. 1988; 113:732-737. Lesouef PN, Lopes JM, England SJ, Bryan MH, Bryan AC. Influence of chest wall distortion on esophageal pressure. J Appl Physiol. 1983; 55:353-358. Miller MJ, Martin RJ, Carlo WA, Fouke JM, Strohl KP, Fanaroff AA. Oral breathing in newborn infants. J Pediatr. 1985; 107;465. Harding R, Wood GA, Thorburn GD. Control of oral breathing in the newborn. In: Jones CT, ed. Research in Perinatal Medicine (VII), Fetal and Neonatal Development. Ithaca, NY: Perinatology Press, 1988:373-377. Martin RJ, Miller MJ, Siner B, Difiore JM, Carlo WA. Effect of unilateral nasal occlusion on ventilation and pulmonary resistance in preterm infants. Pediatr Res. 1989; 25:223A. Boychuk BB, Seshia MMK, Rigatto H. The immediate ventilatory response to added inspiratory elastic and resistive loads in preterm infants. Pediatr Res. 1977; I1:276-279. Duara S, Gerhardt T, Net0 GS, Tamayo M, Suguihara C, Bancalari E. Changes in oxygen consumption with hypoventilation in preterm infants. Pediatr Res. 1989; 23:307A. Wolfson MR, Bhutani VK, Shaffer TH, Bowen FW. Mechanics and energetics of breathing helium in infants with bronchopulmonary dysplasia. J Pediatr. 1984; 104:752-757. Polgar G, Kong GP. The nasal resistance of newborn infants. J Pediatr. 1965; 67557-567.
