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ORIGINAL CONTRIBUTIONS

Received: December 22^nd 2014

Judged: March 4^th 2015

Intra-abdominal pressure as a surgery predictor in patients with acute abdominal pain

Manuel Alejandro Campos-Muñoz,^a Enrique Villarreal-Ríos,^b Mariano Chimal-Torres,^c Josué Atila Pozas-Medina^c

^aServicio de Urgencias, Hospital General de Zona 89, Delegación Jalisco, Guadalajara, Jalisco

^bUnidad de Investigación Epidemiológica y en Servicios de Salud, Santiago de Querétaro, Querétaro

^cServicio de Urgencias, Hospital General Regional 1, Delegación Querétaro, Santiago de Querétaro, Querétaro

Instituto Mexicano del Seguro Social, México

Communication with: Manuel Alejandro Campos-Muñoz

Telephone: 33 3646 3486

Email: campos_alejandro@hotmail.com

Background: Intra-abdominal pressure is the pressure’s state of balance within the abdominal cavity when a patient is at rest. This pressure may vary during mechanical ventilation or spontaneous breathing. The objective was to establish the intra-abdominal pressure as a surgery predictor in patients with acute abdominal pain.
Methods: From April to December, 2013, it was carried out a nested case-control study on patients with acute abdominal pain in the emergency room of a second level hospital. Thirty-seven patients fit the inclusion criteria; they all underwent surgery with a previous measurement of the intra-abdominal pressure. Based on the results of the anatomopathological study, we divided the patients into two groups: those with evidence of acute abdominal inflammatory process (n = 28) (case group), and patients without evidence of acute abdominal inflammatory process (n = 9) (control group).
Results: In the case group, 100 % of patients shown high intra-abdominal pressure with a p = 0.01 (OR = 5 [95 % CI = 2.578-9.699]. In the case group, the mean intra-abdominal pressure was 11.46, and in the control group 9.2 (p = 0.183).
Conclusions: Abdominal pain requiring surgical intervention is directly related to intra-abdominal pressure > 5 mmHg.

Keywords: Abdominal pain; Surgery; Diagnosis

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Intraabdominal pressure (IAP) is the steady state of pressure of the abdominal cavity at rest. It can present changes during mechanical or spontaneous ventilation, and increase during inspiration or decrease during expiration.^1,2

The abdomen is considered an incompressible compartment of limited distensibility that responds to Pascal’s law, i.e., the pressure measured at one point can be assumed to represent the pressure in the whole compartment. Because of this, IAP can be measured virtually anywhere in the abdomen: intraperitoneal, bladder, uterus, rectum, stomach, or inferior vena cava.^1,3,4

The method for measuring intra-abdominal pressure recommended by the consensus guidelines of the World Society of Abdominal Compartment Syndrome (WSACS) is via the bladder; this because of its easy implementation and low cost.^1,5,6

In healthy patients, IAP varies in a range from 0 to 5 mmHg.⁶ In some physiological conditions such as pregnancy and obesity, pressures reach 10 to 15 mmHg, and in the critically ill patient numbers may be 5 to 7 mmHg.^1,3,6

IAP monitoring is a procedure used for the diagnosis of intra-abdominal hypertension and abdominal compartment syndrome in surgical patients.⁷ It is used as a prognostic marker in patients with closed abdomen trauma, and in post-surgery patients it indicates the need for intervention or reoperation. Abdominal compartment syndrome in these patients is usually a severe complication that threatens life;^1,8,9 increased IAP has also been associated with increased frequency of complications, so monitoring is used to improve prognostics and identify complications early following surgery.^8,10-12

The interest of this work is to evaluate the behavior of IAP in patients with suspected atraumatic surgical pathology. It is believed that the inflammatory or occupying process or a process that decreases the elasticity of the abdominal wall is susceptible to raising intraabdominal pressure,^1,13 and that these changes are part of the pathophysiology of emergency surgical conditions, commonly presented as visceral edema and free intraperitoneal fluid.^8,14 This suggests that surgical pathology in patients in the emergency department may cause increased intra-abdominal pressure.

Methods

A prospective study of cases and controls nested in a cohort was done; it included all patients over 18 years old who were admitted to the emergency department of a secondary care hospital with suspected acute abdominal inflammatory process requiring surgery for resolution in the period between April and December 2013.

Thirty-seven patients met the inclusion criteria; these were patients admitted to the emergency department with suspected abdominal inflammatory process who were surgically treated to resolve the symptom and who accepted IAP measurement prior to surgery. The study was approved by the institutional ethics committee and patients' informed consent was obtained.

Groups were formed with the results of the pathological examination of the surgical specimen: patients with evidence of acute abdominal inflammatory process (n = 28) and patients without evidence of acute abdominal inflammatory process (n = 9). Patients in which no pathological specimen was found were removed from the study. The sample excluded patients with a history of trauma, gravid uterus, grade III obesity (defined as body mass index > 40 kg/m²SC),¹⁵ known abdominal tumor, mechanical ventilation, history of bladder, prostate, or urethra surgery, urethral stricture, neurogenic bladder, and peritoneal dialysis.

Doctors from different posts were trained in the correct measurement of intra-abdominal pressure with indirect technique via the bladder, and the proper conduct of the procedure was verified in random measurements by the principal investigator.

Other variables associated with surgical indication were taken into account: clinical manifestations and evolution time.

Statistical data analysis was done with Chi-squared test for nominal variables and Student’s t-test for comparison of two independent samples for discrete or continuous variables.

Results

Patients between 18 and 91 years old were included, with an average of 41.61 years. The variable of body mass index (BMI) was recorded; only 27% of the population had normal weight and 64.8% had some degree of overweight or obesity.

The case group had 18 women, which corresponded to 64.28%. The mean BMI was 27.24, ranging from 19.22 to 36.68.

The control group had six women, accounting for 66.66%, with p = 0.896 (Figure 1) and average BMI was 25.22, ranging from 18.5 to 29.9, with p = 0.251.

The most frequent preoperative diagnoses were acute appendicitis (15 patients) and acute gallstone cholecystitis (14 patients). The most common postoperative diagnosis was acute gallstone cholecystitis (15 patients).

Among the recorded clinical findings, in the case group respiratory rate had an average of 19.25, heart rate 81.46, and systolic blood pressure showed an average of 111.79, while diastolic blood pressure had an average of 66.82.

In the control group the average respiratory rate was 19.56 (p = 0.813) and heart rate 83.11 (p = 0.791). The average systolic blood pressure was 110 (p = 0.794) and diastolic blood pressure 67.78 (p = 0.802) (Table I).

Regarding intra-abdominal pressure, in the case group the average was 11.33 mmHg, ranging from 5.97 to 29.1. When analyzing this, taking normal pressure as < 5 mmHg​​ and high as > 5.1 mmHg, we found that 100% of cases were in the high range.

In the control group the mean was 8.57 mmHg, ranging from 4.48 to 11.19 (p = 0.056). We found only two patients with normal IAP and seven patients with high IAP, p = 0.01, with an odds ratio (OR) of 5 (95% CI: 2.578-9.699) (Figure 2).

A second analysis established three groups of IAP (normal, < 5 mmHg; abnormal, 5.1 to 11.9; and intra-abdominal hypertension, > 12 mmHg). In the case group no patients had normal IAP, 22 patients had abnormal IAP, and six patients had intra-abdominal hypertension. In the control group two patients had normal pressure, seven patients had abnormal IAP, and none were recorded as having intra-abdominal hypertension (p = 0.017) (Figure 3).

Of the clinical manifestations reported, among the cases, constipation was found in two patients and diarrhea in two patients. Five patients in this group had fever.

In the control group, constipation was found in four patients (p = 0.008) with an OR of 0.096 (95% CI: 0.014 to 0.675) and diarrhea in five patients with p = 0.001, OR = 0.062 (IC 95 %: 0.009-0.432). Three patients had fever with p = 0.327, OR = 0.432 (95% CI: 0.08 to 2.356).

All patients were registered between 12 and 240 hours of onset of symptoms.

Patients who presented intra-abdominal hypertension had an average of 90 hours of evolution, while patients with normal IAP had an average of 40 hours of evolution (p = 0.019).

Discussion

Acute abdominal pain is a frequent complaint in the emergency room and it affects at least 10% of visits.^16,17 Differentiating between surgical and non-surgical conditions is particularly relevant when considering costs, waiting time, and the development of complications. The proposed model reduces hospital stay for patients whose medical decisions are pending diagnostic tests.¹⁸

The most common preoperative diagnosis in this study was appendicitis, which coincided with the literature.¹⁹ In the postsurgical results, the number one cause of surgery was acute gallstone cholecystitis, so there was a relationship with reports from studies in 2007.²⁰

The nutritional status of the sample coincided with that reported by the Encuesta Nacional en Salud y Nutrición 2012, which states that in Mexico 73% of women and 69.4% of men are overweight or obese.^15,21 The nutritional status of the case and control groups is considered statistically similar, as there is an average for BMI of 27.24 for cases and 25.²² for controls, which also agrees with the findings of other studies whose population had a mean BMI of 27.6.²²

As in other works, no association was found between symptoms and the presence of high intra-abdominal pressure.²² We can establish that the presence of diarrhea or constipation suggests a nonsurgical outcome of the disease, since they are the only two clinical manifestations that showed significant difference between the groups with an OR of < 1.

This study disagrees with the work of Filgueiras et al. (2001),²² in which they claim that patients with IAP < 11 mmHg (15 cm H₂O) have no intra-abdominal complications. In this study there were 22 patients with IAP between 5 and 12 mmHg who required surgery; therefore, we agree that a figure of > 11 mmHg requires the clinician to search for some intra-abdominal process.²³

In the present study we found statistically significant differences between normal and high intra-abdominal pressure, unlike what was reported by Kron in 1948 (which establishes an IAP of 25 mmHg as a criterion for surgical exploration); therefore, we can conclude that clinical suspicion coupled with nontraumatic abdominal pressure > 5 mmHg (OR = 5) in patients with abdominal pain may serve as a criterion for surgical intervention.²⁴

The average IAP between groups showed no statistically significant differences and it can be inferred that this is a type II error (beta error) due to the sample size.

Only one patient in the case group, with an IAP of 9.7 mmHg, died, which is related to what was reported in a study in which 13% of the population died because they had an IAP between 9.8 and 13.9 mmHg. Increased mortality in this work was associated with IAP > 25 mmHg; the study reported no deaths in patients with an IAP < 9.8 mmHg.¹²

No significant differences were found in the time of evolution between the groups, which ensures that this variable did not influence the results of the study. In both groups, the largest increase in intra-abdominal pressure was between 70 and 100 hours, which coincides with another study that reported that on the third day of illness patients had intra-abdominal hypertension. Unlike that study, we did find significant difference in the time of evolution among patients with intra-abdominal hypertension and patients with IAP (< 11.9), so we consider that IAP itself is related to the time of evolution of the illness.²⁵ All patients registered in the case group showed an IAP > 10.5 mmHg at 24 hours, while the controls measured in the first 24 hours showed an IAP < 8.5.

Conclusion

The most reliable IAP results must be taken within the first 24 hours (Figure 4). This should serve as a basis for deciding whether the patient should undergo surgery or not.

Acknowledgments

To Doctors Salvador Malfavón Prado and Gabriel García Soto, respectively medical director and emergency department chief of Hospital General Regional 1 of Querétaro, who supported us during the study period. We also want to thank the staff of the Querétaro Unidad de Investigación Epidemiológica y en Servicios de Salud of the Instituto Mexicano del Seguro Social. Their support is invaluable.

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