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 Table of Contents  
ORIGINAL RESEARCH REPORT
Year : 2020  |  Volume : 17  |  Issue : 4  |  Page : 145-149

Base excess and pH as predictors of outcomes in secondary peritonitis in a resource limited setting - A prospective study


1 Department of Surgery, UCH, College of Medicine UI, Ibadan, Oyo State, Nigeria
2 Department of Surgery, UCH, Ibadan, Oyo State, Nigeria

Date of Submission06-Mar-2020
Date of Acceptance21-Jul-2020
Date of Web Publication19-Oct-2020

Correspondence Address:
Dr. O Oludolapo Afuwape
Department of Surgery, College of Medicine UI/UCH, P.M.B 5116, Ibadan, Oyo State
Nigeria
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcls.jcls_18_20

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  Abstract 


Background: Estimation of the serum pH and base excess as determinants of the adequacy of resuscitation may predict the patient outcome in peritonitis. Materials, Patients and Methods: This was a prospective study conducted in University College Hospital, Ibadan, on patients from 18 years and above with diagnosis of secondary peritonitis who had exploratory laparotomy over a 4-month period (January to April 2017). The patients' biodata, pulse rate, blood pressure, and clinical diagnosis were documented. At presentation, the patients were resuscitated with intravenous normal saline and broad-spectrum antibiotics. Each patient had measurements of acid-base status, and pH analyzed at presentation and in the immediate postoperative period (within 1 h) using the I-STAT point of care device. They were followed up for 48 h after the surgery. The changes in base excess and serum pH in survivors and nonsurvivors were described at 48 h after surgery. This was statistically compared using SPSS version 20 (Chicago, IL, USA). Results: A total of 45 patients were recruited comprising 37 males and 8 female patients. The mean age was 40.86 ± 15.45 years. The mean admission base excess was −4.76 ± 5.41. The mean admission pH was 7.41 ± 0.07. There were 28 (62%) survivors and 17 (38%) mortalities. The pH on admission and base excess values and after surgery demonstrated statistical significance in survivors and nonsurvivors. Conclusion: Changes in base excess and serum pH values are plausible outcome markers in patients with peritonitis resuscitated with early goal-directed therapy.

Keywords: Acidosis, outcome, peritonitis


How to cite this article:
Afuwape O O, Ayandipo O, Aroso S. Base excess and pH as predictors of outcomes in secondary peritonitis in a resource limited setting - A prospective study. J Clin Sci 2020;17:145-9

How to cite this URL:
Afuwape O O, Ayandipo O, Aroso S. Base excess and pH as predictors of outcomes in secondary peritonitis in a resource limited setting - A prospective study. J Clin Sci [serial online] 2020 [cited 2020 Nov 29];17:145-9. Available from: https://www.jcsjournal.org/text.asp?2020/17/4/145/298451




  Introduction Top


Many surgical conditions, including secondary peritonitis requiring emergency surgery, are associated with varying degrees of altered fluid distribution with varying degrees of tissue hypoperfusion and acidosis.[1] Generalized peritonitis remains a severe condition despite improvements in surgical techniques. Patients with peritonitis often require varying degrees of resuscitation. Strict adherence to surgical principles has reduced mortality rates in peritonitis. In spite of the global reduction in peritonitis-associated mortality in developed countries, the mortality rates are still relatively higher in developing countries.[2] Physiologic parameters often measured during patient resuscitation include the blood pressure, pulse characteristics, and urinary output. These parameters are readily obtained in hospitals in developing countries. However, despite achieving normal values of these parameters at resuscitation, there may still be inadequate organ perfusion in some patients.[3],[4] This is the concept of occult tissue hypoperfusion, which is a situation when clinical parameters may appear normal despite the fact that the actual tissue perfusion is suboptimal.[5] The most commonly used serum parameters in assessing the adequacy of resuscitation are pH (a measure of acidity or hydrogen ion concentration) and base excess.[6],[7] Both parameters are indicators of relative acidosis in patients. Acidosis is a marker of severity in critically ill patients, and as such, it is a tool in assessing critically ill patients.[8] In the absence of equipment such as blood gas analyzers, base excess is a measurement of metabolic component of acid-base disorders. It has been a predictor of mortality in various studies.[8],[9] It is calculated from the pH and partial pressure of oxygen (pO2[a]) and carbon dioxide (pCO2[a]) in arterial blood.[10] The normal human blood pH is 7.35–7.45, while the normal base excess value for humans is 0 mEq/L (range is −2–+2 mEq/L). A base excess above +2 mEq/L indicates metabolic alkalosis, whereas a value of <−2 mEq/L (base deficit) reflects metabolic acidosis. The extent of deviation from normal values indicates the severity of the metabolic response. This may, therefore, be helpful in predicting morbidity and mortality in emergency surgery.[11] Emergency surgical conditions are associated with varying forms of deranged acid-base equilibrium ranging from occult hypoperfusion to shock.

Acidosis may be associated with reduced tissue perfusion in intra-abdominal sepsis with inadequate oxygen delivery, resulting in tissue hypoxia and anaerobic glycolysis. Consequently, the citric acid cycle pathway is unable to rapidly metabolize lactate with resulting acidosis. Secondly, in peritonitis, endotoxins or exotoxins from Gram-negative bacteria or Gram-positive bacteria respectively cause the release of proinflammatory cytokines by macrophages, which initiate a systemic inflammatory response syndrome and multiple organ dysfunction syndromes ultimately which also worsens acidosis.[12] Acidosis is associated with reduced myocardial contractility, arterial vasodilation, and impaired catecholamine responsiveness, which may result in increased morbidity and mortality in ill patients. It has been postulated that survivors of severe sepsis and septic shock had better acidosis resolution than nonsurvivors.[13]

Few studies on predictive use of base excess have been carried out in the African population. This is a pilot study to evaluate the predictive value of serum pH and base excess on mortality of patients admitted with generalized secondary peritonitis in our local population. The objective of this study is to determine the pattern of acidosis and correlate this with the postoperative outcome in patients with secondary peritonitis in a resource-limited environment.


  Materials, Patients and Methods Top


This study was conducted in the emergency department and the general surgical wards of University College Hospital on patients with the clinical diagnosis of secondary peritonitis over a 4-month period (January to April 2017) with a follow-up period of 48 h. The patients studied included all consecutive consenting patients who fulfilled the inclusion criteria. Written informed consent was obtained from the patients or relatives of patients who were unable to give consent.

Inclusion criteria

All consenting patients from 18 years and above with the diagnosis of secondary peritonitis who ultimately had exploratory laparotomy for the surgical condition.

Exclusion criteria

Patients with primary peritonitis, trauma associated peritonitis, localized peritonitis, peritonism, or history of either chronic liver or kidney disease were excluded from the study. Similarly, patients who required laparotomy for trauma and patients who had exploratory laparotomy for an initial diagnosis of peritonitis but subsequently found to have a contrary diagnosis were excluded from the study. Patients whose physiological parameters remained sub-optimal (persistent hypotension) even with resuscitation were excluded because they subsequently had various staged and less invasive procedures and not immediate exploratory laparotomy.

The study was approved by the Oyo State Health Ministry Ethical Review Committee. At presentation, all the recruited patients had their bio-data documented. Other data obtained were the pulse rate; blood pressure and clinical diagnosis. The recruited patients were examined to confirm the diagnosis as well as to determine their physiologic parameters before appropriate intervention. Those who required resuscitation were resuscitated with intravenous normal saline and broad-spectrum antibiotics (ceftriaxone and metronidazole) given at appropriate doses and frequency during and after resuscitation. The goal of resuscitation was to achieve a minimum systolic blood pressure of 90 mmHg and adequate tissue perfusion characterized by a urinary output of not <50 ml per hour before surgery. The volume of administered fluid varied depending on the clinical parameters of the patient at presentation. The patients who did not have a physiologic fluid deficit at presentation had maintenance fluid admiration before surgery. Investigations at presentation included the complete blood count, urea, and electrolytes and glucose levels. Each patient had two measurements of acid-base status, and pH analyzed at presentation before resuscitation and in the immediate postoperative period (within 1 h of completion of surgery) using the I-STAT point of care device. They were followed up for 48 h after surgery.

Ultimately, the patients were divided into two groups, namely those who died and survivors at 48 h after the surgery. This was based on a study which indicated base deficit to be one of the independent predictors of early mortality within 48 h in critically ill patients.[14] In these two groups, preoperative and postoperative pH and base excess were statistically compared in other to note whether there were any statistically significant associations.

The collected data were analyzed using SPSS version 20 (Chicago, IL, USA).


  Results Top


A total of 45 patients were recruited during the study period. This consisted of 37 males and 8 females with a male:female ratio of 4.6:1. The mean age was 40.86 ± 15.45 years. The mean admission base excess was −4.76 ± 5.41, whereas the mean admission pH was 7.41±0.07. Twenty-eight (62%) of the patients survived while seventeen (38%) patients died [Table 1]. The distribution of intraoperative etiology peritonitis is shown in [Table 2]. A comparison of mean values of acid-base variables at presentation and immediate postoperative values of survivors and nonsurvivors is shown in [Table 3] while [Figure 1] and [Figure 2] show patterns of variation in values of pH and base excess in survivors and nonsurvivors, respectively. The median test demonstrated no statistical significance in the differences between the survivors and nonsurvivors [Table 4].
Table 1: Case demographics

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Table 2: Distribution of Post-operative diagnoses of aetiology of peritonitis

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Table 3: Comparison of admission and post-operative treatment acid-base variables in survivors and non-survivors

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Figure 1: Pattern of pH changes between admission values and postoperative values in survivors and nonsurvivors

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Figure 2: Pattern of base excess changes between admission values and postoperative values in survivors and nonsurvivors

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Table 4: Median test: Comparison of pre and post treatment acid.base variables in survivors and non survivors

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Further analysis of the four measured parameters (admission base and postoperative base excess values; admission and postoperative pH values) revealed a significant correlation between the admission base excess and the postoperative pH (P = 0.005 and 0.005, respectively) within the population of survivors.


  Discussion Top


Hemodynamic changes accompanying peritonitis is associated with lactic acidosis and reduced lactate clearance. Metabolic acidosis is associated with increased morbidity and mortality.[15] Intravenous fluid administration at resuscitation improves oxygen delivery to the tissues and corrects acidosis. Acidosis may persist despite adequate fluid administration in some patients with peritonitis due to regional blood flow redistribution and metabolic compartmentalization such that increased effective intravascular volume may not translate to sufficient oxygen delivery to all tissues.[16] Acidosis is associated with different immune/inflammatory pathways, which subsequently could predispose patients to follow a complicated clinical course.[16] Consequently, there is an alteration in the function of organs, which usually correct acidosis, such as the liver and the kidneys, with a global reduction in cellular function.[17]

In the 45 patients recruited in this pilot study, there were 17 (37.7%) postoperative mortalities within 48 h of surgery. We observed variable patterns of pH and base excess changes, both the survivors and the nonsurvivors. These changes may have been modulated further by a milieu of conditions such as the pathogenicity of the bacteria, intravenous fluid administration (hyperchloremic acidosis)[18] associated co-morbidity in the patients and improved tissue perfusion with CO2 washout from the tissues. Interestingly we found that patients with secondary peritonitis frequently had high anion gap metabolic acidosis. There were differences in the mean preoperative and postoperative acid base derangement of the survivors and nonsurvivors [Table 3]. The pH and base excess values revealed more severe acidosis in nonsurvivors compared to the survivors, but this was not statistically significant. All the patients who died had higher levels of acidosis at presentation with marginal changes after surgery, compared to survivors, while a significant proportion of the survivors demonstrated a significant (positive) shift in the pH and base excess values toward the normal ranges. A review of the pattern of change acid-base values among the two subpopulations [Figure 1] and [Figure 2] reveals that within the survivors 53.6% (15 patients) demonstrated increased base excess while 75% (21 patients) demonstrated an increase in pH both reflecting reduction in acidosis. On the other hand, the nonsurvivors demonstrated such a reversal of values in 47% (8 patients) and 35% (6 patients), respectively. Further analysis of the results demonstrated that there was a significant statistical relationship between the pH values preoperatively and survival (P = 0.035). We found that patients who died had relatively lower pH and base excess values preoperatively than the patients who survived [Figure 1] and [Figure 2].

The Spearman rank correlation coefficient of admission/postoperative acid-base variables demonstrates a positive significant correlation between and preoperative base excess and preoperative pH (P = 0.005) as well as the postoperative base excess and postoperative pH (P = 0.003) in survivors [Table 5]. Contrary to a previous study,[19] acidosis and base excess was found to be associated with mortality. The survivors had less acidosis. However, this may also be explained by the concept of hyperchloremic acidosis, which may occur when large volumes of normal saline are administered at resuscitation.
Table 5: Spearman rank-correlation coefficients of admission/post treatment acid-base variables

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Inadequate prehospital care was also highlighted in this study. The patients did not have adequate intravenous fluid administration before the referral to the University College Hospital Emergency Department. They had varying suboptimal physiologic indices at the presentation in the emergency department. This may affect the duration and severity of tissue hypoperfusion in the absence of appropriate early resuscitation.


  Conclusion Top


Metabolic acidosis characterized by a reduction in pH and the increased base deficit is common in peritonitis. Changes in base excess and serum pH values are plausible outcome markers in patients with peritonitis resuscitated to the point of seemingly normal physiological parameters and urinary output. However, further studies need to be performed to determine the effect of chloride and other immeasurable anions in administered intravenous fluids on acidosis in these patients.

Limitation

The relatively small number of the study is a limitation. This serves as a pilot for future studies.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

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Santi M, McAnulty G, Grounds M. Base excess and lactate as prognostic indicators for patients admitted to intensive care-15 years later. Intensive Care Med Exp 2015;3(Suppl 1):A341.  Back to cited text no. 8
    
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Smith I, Kumar P, Molloy S, Rhodes A, Newman PJ, Grounds RM, et al. Base excess and lactate as prognostic indicators for patients admitted to intensive care. Intensive Care Med 2001;27:74-83.  Back to cited text no. 9
    
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Cortés-Samacá CA, Meléndez-Flórez HJ, Álvarez Robles S, Meléndez-Gómez EA, Puche-Cogollo CA, Mayorga-Anaya HJ. Base deficit, lactate clearance, and shock index as predictors of morbidity and mortality in multiple-trauma patients. Revista Colomb Anestesiol 2018;46:208-15.  Back to cited text no. 11
    
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Pavlidis TE. Cellular changes in association with defense mechanisms in intra-abdominal sepsis. Minerva Chir 2003;58:777-81.  Back to cited text no. 12
    
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Noritomi DT, Soriano FG, Kellum JA, Cappi SB, Biselli PJ, Libório AB, et al. Metabolic acidosis in patients with severe sepsis and septic shock: A longitudinal quantitative study. Crit Care Med 2009;37:2733-9.  Back to cited text no. 13
    
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Wigger O, Bloechlinger S, Berger D, Häner J, Zanchin T, Windecker S, et al. Baseline serum bicarbonate levels independently predict short-term mortality in critically ill patients with ischaemic cardiogenic shock. Eur Heart J Acute Cardiovasc Care 2018;7:45-52.  Back to cited text no. 14
    
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Abdul-Malak O, Vodovotz Y, Zaaqoq A, Guardado J, Almahmoud K, Yin J, et al. Elevated admission base deficit is associated with a complex dynamic network of systemic inflammation which drives clinical trajectories in blunt trauma patients. Mediators Inflamm 2016;: doi: 10.1155/2016/7950374.  Back to cited text no. 17
    
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    Figures

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