Gastric tonometry and intravesical pressure measurement were performed on eight babies born with gastroschisis for 72 hours after abdominal closure. Intravesical pressure was not high. The gastric mucosal pco2 and gastric mucosal pH remained stable and closely matched arterial values. Tonometry may be a useful technique to monitor these babies.
- abdominal compartment syndrome
- ACS, abdominal compartment syndrome
- IAH, intra-abdominal hypertension
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Mortality in gastroschisis is caused by intestinal atresia, or bowel or renal ischaemia.1 Because recognising intestinal ischaemia after abdominal closure is difficult, measurement of intragastric,2 or intravesical pressure3 have been proposed as monitoring techniques.
Gastric tonometry measures the mucosal concentration of CO2 in the stomach, which rises as perfusion falls. Thus it may provide a better method of monitoring than pressure techniques. Tonometry can predict the development of the abdominal compartment syndrome (ACS) after trauma or surgery.4 It is not known whether uncomplicated closure of the abdomen of a baby with gastroschisis causes changes in gastric perfusion. The aims of this study were to determine the values of gastric tonometry for 72 hours after repair of gastroschisis while measuring intra-abdominal pressure.
PATIENTS AND METHODS
Eight consecutive babies diagnosed antenatally with gastroschisis and delivered in one institution were recruited. Average gestation and birth weight were 37 weeks and 2.5 kg respectively. Surgery was performed under general anaesthesia with full muscle relaxation. Babies were ventilated for the duration of this study.
Tonometry was performed using a Datex TC-200 Tonocap monitor (Tonometrics Division, Instrumentarium Corp., Helsinki, Finland). Tonometry measures the CO2 concentration in the gastric lumen. It is assumed that this is in equilibrium with the CO2 concentration in the mucosa, termed the regional pco2 (prco2). It is further assumed that the mucosal concentration varies as a result of production (metabolism), or removal (blood flow); finally it is assumed that local metabolism is constant and therefore alterations in CO2 concentration reflect changes in blood flow. Knowing the variables of prco2 and arterial bicarbonate concentration allows the gastric intramucosal (intracellular, not intralumenal) pH (pHi) to be calculated from the Henderson Hasselbalch equation.5 The CO2 gap is the difference between gastric mucosal and arterial concentrations.
prco2, pHi, intravesical pressure, and arterial gas tensions were measured prior to fascial closure, after closure, and six hourly for 72 hours. The decision to close the abdomen primarily, or in stages, or to reopen the abdomen was made independently of this study.
Informed consent was obtained from parents, and the regional ethics committee approved the protocol.
Two cases were incomplete because of kinking of the catheter in one and loss of the arterial line in another. All had fascial closure within six hours of birth. None required re-exploration, and all had an uneventful subsequent course.
The mean intravesical pressure was 10.3 mm Hg (95% confidence interval (CI) 9.4 to 11.2). The highest pressure was 20 mm Hg.
The gastric mucosal pco2 and arterial pco2 were not significantly different (see fig 1). The mean gastric mucosal pco2 was 4.37 (95% CI 4.2 to 4.5). The mean arterial pco2 was 4.42 (95% CI 4.3 to 4.6). The mean pco2 gap was 0.067 (95% CI −0.06 to 0.19).
The mean pHi and arterial pH were identical at 7.37 (95% CI: gastric pH 7.35 to 7.39; arterial pH 7.35 to 7.38). There was no correlation between intravesical pressure and either gastric pco2 (r = −0.05) or gastric mucosal pH (r = 0.11).
Closure of the abdomen in babies with gastroschisis risks intestinal and renal ischaemia1 because of intra-abdominal hypertension (IAH), causing ACS. Tonometry is used to monitor for the development of ACS after trauma,4 and in severe sepsis where impaired splanchnic perfusion is significant.6
The absence of data regarding expected values of tonometry variables prevents its application to babies undergoing abdominal closure. We report a series without IAH. For tonometry to be of use, such cases should show close approximation between gastric pco2 and arterial pco2, and between gastric mucosal pH and arterial pH. It was unknown whether deterioration in mucosal perfusion could be expected. We have shown that where there is no rise in intra-abdominal pressure, there is very close approximation of gastric mucosal pco2 and arterial pco2, and between gastric mucosal pH and arterial pH.
Whether tonometry will prove more sensitive than clinical suspicion, or conventional pressure monitoring in detecting impaired gut or renal perfusion will require a larger study to recruit babies who show a rise in intra-abdominal pressure, or in whom the clinical concern is such that the question of staged closure or reopening the abdomen after primary closure occurs. This study provides data on babies who did not develop complications related to closure to allow such a large study.
The gastric tonometer and catheters were purchased with the financial support of the Newcastle University Hospitals Special Trustees. The authors acknowledge the support and cooperation of the staff of the neonatal surgical unit.
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