Intra-abdominal hypertension in pediatrics
How common is IAH and ACS in pediatrics:
Some pediatric intensivists still believe that IAH and ACS are uncommon in children. This belief may come from early literature on the topic that suggested the problem occurred in less than 1% of critically ill children.[1, 2] However, entry criteria for measuring IAP in these studies required a distended abdomen before measurement was obtained. Since abdominal girth is not predictive of IAP, this entry criteria is known to miss many patients suffering from the illness – likely resulting in significant underestimation of disease prevalence. However, the authors of the study did note that progression to ACS carried a 40-60% mortality rate, that abdominal compartment syndrome occurred at intra-abdominal pressures as low as 15 mm Hg, and that the syndrome existed in a broad array of medical and surgical patients, not just trauma patients so they did manage to note this was a problem in a broad cross section of critically ill children. In contrast to the Beck and Diaz data, a more recent prospective study suggests a dramatically higher incidence of ACS even though these authors also did not screen every patients via bladder pressure.[3] Ejike et al found ACS to be present in 17.6% of ventilated PICU patients (they were only able to consent 1/3 of patients to enter the study, but even those who they had no clinical suspicion carried a 22% incidence of IAH and 7% of them progressed to ACS). Those with ACS had a significantly higher mortality (33.3%) and length of stay (13 d) than those without ACS (2.4% mortality, 6 day LOS). Both of these studies as well as numerous other case series demonstrate this syndrome is not confined to trauma patients. It is ubiquitous to critically ill patients and occurs in children with many conditions including sepsis, Wilms tumor, perforated bowel, necrotizing enterocolitis, intussusception, meningococcemia and gastroschisis.[1, 4-7]
What intra-abdominal pressure is of concern in children?
Although the definition for IAH and ACS in adults requires pressures of 12 mm Hg and 20 mm Hg respectively, these are really just guidelines and the individual patients organ function must be considered. It is especially important in children to not just look at a number, but look at the patient since their underlying mean arterial pressure is lower than adults and this varies with age. The point - due to lower baseline MAP, the splanchnic perfusion of a small child will be more impacted at a lower abdominal pressure. (click here to read more about the concept of splanchnic or abdominal perfusion pressure) In fact – neonates can have a compartment syndrome at levels of IAP in the range of 9-13 mm Hg.[8] As mentioned above, Beck found a pressure of 15 mm Hg high enough to cause compartment syndrome.[1] Baroncini investigated hemodynamic function in children of various ages undergoing laparoscopic procedures.[9] These authors found substantial impacts on cardiopulmonary function at very low levels in neonates and at slightly higher levels in older children. They recommend a maximal pressure of 6 mm Hg during laparoscopy in neonates and of 12 mm Hg in older children. Ejike prospectively evaluated IAP in a broad cohort of critically ill children and concluded that pressures of >10 mm Hg were potentially dangerous.[10] Neonatal pressures in the 10 mm Hg range are thought be several authors to be suggestive of abdominal compartment syndrome if organ dysfunction is present.[10,17,18,19]
Special issues in Neonates
Already discussed above is the concept of
splanchnic perfusion pressure (or abdominal perfusion pressure -
click here for
information on this concept) and
how the low MAP seen in neonates can result in very low gut
perfusion even at relatively moderate increases of IAP. Gerstmann
found many sick neonates to have IAP levels exceeding their CVP
raising the concern for reduced or obstructed venous return.[11] Sukhotnik believes that this pathophysiology is at least partly the
cause of necrotizing enterocolitis.[8] This belief is confirmed in a
small study by Bonnard where they correlated higher IAP (in the
level of 9 mm Hg) with worsening bowel ischemia and death in
children with NEC.[17] Based on these findings Bonnard believes IAP
measurements are likely useful for predicting which baby with NEC is
appropriate for surgical intervention. Another clinical setting
where IAP is quite important is in children with congenital
abdominal wall defects. In this setting IAP values are useful to
direct rate of silo compression and safety of abdominal wall defect
closure.[12-14]
How much saline should be infused into a child’s bladder to obtain an adequate pressure measurement?
Accurate pressure transduction requires a small pocket of fluid within a cavity connected via a continuous column of fluid to the transducer. (See “Volume of infusion” discussion and diagram on this web site). The size of this pocket can be small as long as that fluid pocket is equilibrated with the pressure in the cavity being measured. For example, when measuring arterial line or CVP pressure very little fluid is infused (3 mm/hour) simply to keep the hydrostatic coupling intact. When using the bladder to reflect pressure within the abdomen there needs to be some fluid to passively transmit intra-abdominal pressure, but not too much fluid. If the bladder is overdistended, the bladder wall begins to stretch and pressure measurements will rise to reflect bladder wall compliance, not intra-abdominal pressure. Three investigators have conducted research in pediatric ICU’s to determine the optimal volume of infusion to accurately transduce intra-abdominal pressure – all finding that volumes of about 1 ml/kg of less are optimal, while much higher volumes provide erroneous data.[10, 15, 16] Davis et al compared intra-abdominal pressure measured via a peritoneal dialysis catheter (gold standard) against IAP measured via the stomach and via the bladder using infusion volumes of 0, 1, 3 and 5 ml/kg. He found 1 ml/kg infused into the bladder to be the most accurate, while smaller or larger volumes were less accurate as was any volume infused when measuring gastric pressure.[15] Souminen found essentially identical results.[16] Ejike measured bladder compliance curves in children by infusing increasing volumes and measuring each pressure obtained with that volume.[10] She found that optimal volumes ranged from 6 ml to 25 ml in children between 3 kg and 50 kg. She concluded that 6 ml was enough in all situations and one never needed more than 20-25 ml in any child to obtain accurate IAP transduction via the bladder. Therefor, these studies suggest that one can either use 1 ml/kg (not ever needing more than 20-25 ml) or just use 6 ml infusion volume in pediatric patients to obtain accurate pressure transduction.
References:
1.
Beck, R., et al., Abdominal compartment syndrome in children. Pediatr Crit Care Med,
2001. 2(1): p. 51-6.
2.
Diaz, F.J., A. Fernandez Sein, and F. Gotay,
Identification and management
of Abdominal Compartment Syndrome in the Pediatric Intensive Care
Unit. P R Health Sci J, 2006.
25(1): p. 17-22.
3.
Ejike, J.C., et al.,
Outcomes of children with abdominal compartment syndrome. Acta
Clin Belg Suppl, 2007(1): p. 141-8.
4.
Ng, E., et al., Life threatening tension pneumoperitoneum from intestinal perforation
during air reduction of intussusception. Paediatr Anaesth, 2002.
12(9): p. 798-800.
5.
DeCou, J.M., et al.,
Abdominal compartment syndrome in children: experience with three
cases. J Pediatr Surg, 2000.
35(6): p. 840-2.
6.
Kidd, J.N., Jr., et al.,
Evolution of staged versus
primary closure of gastroschisis. Ann Surg, 2003.
237(6): p. 759-64;
discussion 764-5.
7.
Pearson, E.G., et al.,
Decompressive laparotomy for abdominal compartment syndrome in
children: before it is too late. J Pediatr Surg, 2010.
45(6): p. 1324-9.
8.
Sukhotnik, I., et al.,
Possible importance of increased intra-abdominal pressure for the
development of necrotizing enterocolitis. Eur J Pediatr Surg,
2009. 19(5): p. 307-10.
9.
Baroncini, S., et al.,
Anaesthesia for laparoscopic surgery in paediatrics. Minerva
Anestesiol, 2002. 68(5):
p. 406-13.
10.
Ejike, J.C., K. Bahjri, and M. Mathur,
What is the normal
intra-abdominal pressure in critically ill children and how should
we measure it? Crit Care Med, 2008.
36(7): p. 2157-62.
11.
Gertzmann, D.R. and D.M. Null,
Intra abdominal hypertension
and bladder pressure measurements in sick neonates. 2009 PAS
Annual Meeting, 2009: p. File number 450076.
12.
Allotey, J., et al.,
Benefit of preformed silos in the management of gastroschisis.
Pediatr Surg Int, 2007.
13.
Banieghbal, B., M. Gouws, and M.R. Davies,
Respiratory pressure
monitoring as an indirect method of intra-abdominal pressure
measurement in gastroschisis closure. Eur J Pediatr Surg, 2006.
16(2): p. 79-83.
14.
Olesevich, M., et al.,
Gastroschisis revisited: role of intraoperative measurement of
abdominal pressure. J Pediatr Surg, 2005.
40(5): p. 789-92.
15.
Davis, et al., Comparison of indirect methods of measuring intra-abdominal pressure in
children. Intensive Care Med, 2005.
31(3): p. 471-475.
16.
Suominen, P.K., et al.,
Comparison of direct and intravesical measurement of intraabdominal
pressure in children. J Pediatr Surg, 2006.
41(8): p. 1381-5.