The Indian Journal of Pediatrics February 2015, Volume 82, Issue 2, pp 131-135. Ind J Pediatr. 2014 Sep 4. [Epub ahead of print] PMID: 25186564
INTRA GASTRIC PRESSURES IN NEONATES RECEIVING BUBBLE CPAP
Prashant Tyagi1, Neeraj Gupta1, Akanksha Jain1,Jacob Puliyel1, Pramod Upadhyay 2
(1) Department of Paediatrics and Neonatology, St. Stephen’s Hospital, New Delhi.
(2) National Institute of Immunology, New Delhi.
Address for communication
C/O Jacob Puliyel
Deptt. of Paediatrics
St Stephens Hospital
Objectives of the study: To study intra-gastric pressures in neonates receiving bubble CPAP (BCPAP) by nasopharyngeal prong.
Methods: 27 neonates were recruited for the study. BCPAP pressure of 6 cm water was used in all the neonates. A pressure sensor attached to orogastric tube, measured the intra gastric pressure prior to starting BCPAP and again between 30 and 90 minutes of BCPAP. The clinical variables like Downe’s score, oxygen saturation, venous blood gas pH, pCO2 and abdominal girth were recorded alongside with pressure readings.
Results: BCPAP resulted in improvement (p<0.05) in parameters of respiratory distress such as Downe’s score (DS), oxygen saturation (SpO2) and venous blood gas parameters (pH, pCO2). There was no statistical significant increase in intragastric pressures (p= 0.834). There were no gastrointestinal complications; abdominal distention, necrotising enterocolitis or gastric perforation during the study.
Conclusion: Nasopharyngeal BCPAP at 6 cm of water pressure is an effective modality of treating babies with respiratory distress and our study shows that it was not associated with a significant rise in intra gastric pressures.
Early use of continuous positive airway pressure (CPAP) in newborns is associated with lower incidence of chronic lung disease.1 This has led to an increase in the use of CPAP as an alternative to intubation and ventilation, in some units.2,3
CPAP has also been established as an effective method for weaning from mechanical ventilation, in preventing extubation failure and is used in the management of apnea of prematurity.4,5
Although bubble CPAP (BCPAP) is seen to be superior to continuous steady pressure CPAP,6-11 its pressure delivery system can be highly variable and unpredictable as reported by Kahn et al 12.
CPAP has been associated with gastrointestinal adverse effects – although rarely. In 1992 Jailey et al13 published a case and coined the term CPAP belly syndrome. They used this term to denote the gaseous bowel-distension in infants treated with nasal CPAP. These infants do not have abdominal distension at birth, but after treatment with nasal CPAP for a short period develops soft, strikingly distended abdomens and visibly dilated loops. The continuous flow of air in the nasopharynx causes an increase in swallowing of air. The distended abdomen causes increase in pressure on the diaphragm, which may result in a compromised respiratory state. 14
Rare case reports of gastric insufflations potentially leading to aspiration, abdominal distention and perforation in neonates on CPAP have been reported. 15,16 Reporting of 2 deaths in the BCPAP study group of Gupta et al 17 due to necrotizing enterocolitis (NEC) are disconcerting and raises question marks on serious gastrointestinal side effects of BCPAP and safety of this potentially good, cost effective intervention for saving newborn lives.
There are no studies that have looked at intra gastric pressures during CPAP. The pressures transmitted from oropharynx to stomach during BCPAP are not known.
This study was designed to measure and to look for any change in the intra gastric pressures after starting BCPAP. We also looked out for gastrointestinal complications such as increased abdominal distention, CPAP Belly Syndrome, NEC or gastric perforation in babies receiving nasopharyngeal BCPAP.
MATEIRIAL AND METHODS
A prospective study to measure intra gastric pressures in neonates requiring BCPAP was done from July 2011 to July 2012 at Neonatal Intensive Care Unit (NICU) of St. Stephen’s hospital, New Delhi. This study was approved by St. Stephen’s hospital ethical committee in June 2011.
We used the simple circuit nasopharyngeal BCPAP that has been described earlier by Kaur et al 18 for our study. All babies with gestational age 28 weeks to 42 weeks requiring BCPAP for mild to moderate respiratory distress based on Downe’s score 19 ≥ 4, post extubation and apnea were included. A chest X ray was done in all cases to rule out congenital anomalies like diaphragmatic hernia, tracheoesophageal fistula or other causes of respiratory distress. Newborns requiring intubation at birth, respiratory distress secondary to birth asphyxia, congenital anomalies like cleft lip, cleft palate, choanal atresia and congenital heart disease diagnosed after starting of BCPAP were excluded from the study.
Written informed consent was obtained from parents to record pressures during BCPAP. Data recorded included anthropometry and post conceptual age. Downe’s score was used to monitor improvement in respiratory distress of babies every 30 minutes on BCPAP in all cases by principal investigator of this study.
Oxygen saturation was recorded by Phillips Avant TM 9600 pulse oximeter. Venous blood gas pH and pCO2 were recorded before starting CPAP and when the intra gastric pressures were re-measured. Downe’s score, oxygen saturation, and abdominal girth were recorded alongside. All observations were recorded in supine position.
All babies were kept nil per oral, before starting CPAP, for respiratory distress. Feeds were also held for post extubation and apnea cases. Babies were continued as fasting during entire duration of 90 minutes, for pressure recordings.
Flow was same as required to required to generate a pressure of 6 cm of H2O mixed (Air + Oxygen) BCPAP. Although flow can affect pressure, this has only a limited effect because of the blow off. Flow was maintained such that there was a continuous flow of bubbles from the blow-off valve but such that it did not agitate the water violently.
The pressure sensor probe by sensoromedic ® was attached to a 5V regulated power supply and the voltage drop across appropriate leads of the sensor, which was proportional to the pressure difference, was measured by a milli-voltmeter. This probe shows 1 mV of change in mili-voltmeter for a pressure difference of 2.91cm of H20. We could read up to the resolution of 0.01 mV by the pressure monitor, therefore, minimum sensitivity of the sensor was 0.291 mm or simply 0.3 mm of water height. For continuous monitoring of the data the serial port of the mill-voltmeter was logged to a computer by its RS 232 port. The software for the data logging was provided by the milli-voltmeter manufacturer - MECO® 81 K -TRMS. We routinely checked the calibration using the probe at different depths of water and found it accurate with an error of less than 2%.
In order to prevent dissipation of intragastric pressures through OG tube end and to get accurate pressure changes induced by BCPAP OG tube end was attached to pressure sensor probe which
was passed through oropharynx into stomach . The sensor probe was devised such that OG tube number 8 was best fit to the circuit, without any leaks, for the study. The mean of 10 readings was taken as the initial pressure(IG0). Without removing the sensor probe attached OG tube lying in stomach intragastric (IG1) readings were taken after 30 minutes but within 90 minutes of BCPAP.
Sample Size Calculations
In the absence of data of intra gastric pressure from neonates, accurate sample size calculations to avoid Type 2 errors could not be done and this study proposed to use a sample size of 25 neonates as a pilot to look at the variance in pressures which can allow accurate sample size calculations in the future.
A paired samples t test with 95% confidence limits was used to compare difference in pressures, and clinical variables before and after BCPAP .
Total 31 neonates were monitored for pressures; three neonates had to be excluded because of diagnosis of congenital heart disease and one due to diagnosis of diaphragmatic hernia which were made after starting of BCPAP. Results of the remaining 27 infants were analyzed.
BCPAP was used in 21 neonates with respiratory distress, in 6 neonates post-extubation and in 2 neonates with meconium aspiration and apnea respectively.
The mean post conceptual age at the time of measuring pressures was 35.2 weeks (SD 3.1) and a mean weight was 2084 grams (SD 773).
In our study there was statistical improvement (p<0.05) in parameters of respiratory distress like Downe’s score (DS), oxygen saturation (SpO2), venous blood gas parameters (pH, pCO2). Table 1 gives the details of change in clinical variables after BCPAP.
The mean intragastric pressure before starting BCPAP was 12.422 cm H2O, (95 % CI 8.65 to 16.18) and during BCPAP it was 12.88 cm H2O (95 % CI 10.48 to 15.29). The intragastric pressure always remained positive and the overall change in intragastric pressure recordings (paired t test) was 0.464 cm H2O (95 % CI -5.11 to + 4.18,) (p = 0.838). Table 2 shows the intragastric pressures monitored.
Out of total 27 neonates 2 babies did not improved on BCPAP and required mechanical ventilation due to recurrent apnea of prematurity. There was no increase in abdominal girth, gastric distention leading to aspiration pneumonia, incidence of NEC or any other abdominal complications during nasopharyngeal BCPAP during the study.
In our study we found that intragastric pressures changed only marginally by 0.464 cm H20 which was statistically insignificant (p = 0.834).Omari Ti et al 20 suggested that the tone at upper end of esophagus and at gastro esophageal junction is higher than CPAP pressures administered routinely to premature babies so the air goes preferentially to the airways rather than the esophagus. However he noted that ‘CPAP belly’ can occur occasionally. He suggested the babies on CPAP, should have an orogastric (OG) tube left in situ with the outer end open to atmosphere. We routinely take this precaution in babies on BCPAP but during the duration of study we had the upper end of the OG tube closed so as to measure the pressures generated by CPAP.
Jackson et al 21 have observed that excessive abdominal distension usually occurred with use of incorrect nasopharyngeal prong position and after switching to shorter nasopharyngeal tube the incidence of abdominal distention was reduced remarkably. In our study we have used soft single nasopharyngeal tube to deliver BCPAP. 18 None of neonates in our study developed abdominal complication, increase in abdominal girth or NEC.
In a study by Ellina et al 22 BCPAP was associated with greater breathing asynchrony and increased work of breathing compared to ventilator derived CPAP in preterm infants with mild respiratory distress. The results of our study showed decrease in work of breathing and improvement in Downe’s score (p-0.0001) which further upholds the results by Prashanth et al 10 in which 80% of newborns with RDS given BCPAP had marked improvement in Downe’s score..
Strengths of the Study
Arguably our study is the first attempt to measure intra gastric pressures, while monitoring for gastrointestinal complications in babies receiving nasopharyngeal BCPAP. Our study has good internal validity as pressures were measured and compared in same neonate, individually such that each child acts as its own control.
Weakness of this Study
We measured pressures after 30 to 90 minutes post BCPAP; it is not clear whether monitoring continuous pressure for 24 hours would have altered the findings. However we felt it would be unethical to monitor the child with the orogastric tube closed for such a long time.
In our study, we used nasopharyngeal tube as the interface, other side effects such as pneumonia and infections were not studied and comparison arm was not present. Also it would be difficult to conclusively comment on efficacy or safety with a short duration single centered study.
Our study relatively had stable near term and term newborns. We perhaps cannot generalize these findings on very preterm babies with RDS and co morbidities. Finally our sample size was perhaps too small to pick up rare cases of intra abdominal complications following BCPAP.
We found that nasopharyngeal BCPAP at pressure of 6 cm water, decreased work of breathing, improved gas exchange and improved Downe’s score. We found no significant increase in intra gastric pressures and gastrointestinal complications such as abdominal distention, NEC, perforation during our study.
Further multi centric studies with larger number of cases, are required for predicting accurate changes in intragastric pressures.
WHAT THIS PAPER ADDS?
Nasopharyngeal Bubble CPAP does not increases intragastric pressures significantly in the majority of neonates. It is safe and an effective mode of delivering CPAP.
JP ,PU and NG conceived the project.
PU designed the interface for recording pressure.
PT and AJ did the measurements. All authors contributed to the Manuscript preparation
PU, PT and JP will be guarantor
Funding: None. Competing interests: None stated.
Dr Jacob M Puliyel –firstname.lastname@example.org
Dr.Prashant Tyagi- email@example.com
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