Original article / research
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2024 |
Month :
January
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Volume :
13 |
Issue :
1 |
Page :
BO18 - BO21 |
Full Version
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Application of Compensation Rules in the Four-quadrant Graphical Tool for Arterial Blood Gas Interpretation: A Cross-sectional Study
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T Rajini Samuel
1. Associate Professor, Department of Biochemistry, Shri Sathya Sai Medical College and Research Institute, Sri Balaji Vidyapeeth (Deemed to be University), Chennai, Tamil Nadu, India.
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Correspondence
Address :
T Rajini Samuel,
Dr. T Rajini Samuel,
Associate Professor, Department of Biochemistry, Shri Sathya Sai Medical College and Research Institute, Sri Balaji Vidyapeeth (Deemed to be University), Guduvancherry-Thiruporur Main Road, Ammapettai, Chengalpet District-603108, Tamil Nadu, India.
E-mail: samuel.biochemistry@gmail.com
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| | | ABSTRACT |  | : Introduction: Arterial Blood Gas (ABG) interpretation plays an indispensable role in emergency medicine and the care of intensive care patients, yet it remains a challenging task. Although several graphical methods exist for ABG interpretation, they are not commonly used at the bedside. The existing graphs are complicated, difficult to understand, and unable to diagnose many disorders. In previous research articles, the current author developed and published a four-quadrant graphical tool for ABG interpretation. The tool incorporates compensation rules, which are crucial for identifying changes resulting from compensations or the presence of a second primary acid-base disorder.
Aim: To develop a method for applying compensation rules in a four-quadrant graphical tool to interpret ABG reports for complex acid-base disorders in clinical practice.
Materials and Methods: This cross-sectional study was conducted at Shri Sathya Sai Medical College and Research Institute, Chennai, Tamil Nadu, India, from November 2022 to April 2023. A total of 232 ABG samples were utilised, and the values of pH, pCO2, HCO3, Standard HCO3, and Standard Base Excess (SBE) were recorded. These values were classified according to different acid-base disorders. Three derived ratios were calculated using the values of pCO3, bicarbonate, and standard bicarbonate, as these ratios change in various acid-base disorders and provide clues for differentiating between different acid-base disturbances. A four-quadrant graph method was constructed using the values of SBE, pCO3, and these ratios. Subsequently, compensation rules were applied to this graph method.
Results: The four-quadrant method facilitated the easy identification of different acid-base disorders, and the application of compensation rules further simplified the identification of mixed or compensatory acid-base disorders.
Conclusion: The application of compensation rules in this four-quadrant graphical tool for ABG interpretation distinguishes this tool as a unique method among existing approaches. This tool offers an optimal and simplified approach for interpreting ABG results for complex acid-base disturbances, making it highly suitable for clinical practice at the bedside. |
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| Keywords
: Acid-base disturbances, Graphical interpretation, Mixed disorder |
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| DOI and Others
: DOI: 10.7860/NJLM/2024/66448.2818
Date of Submission: Jul 09, 2023
Date of Peer Review: Sep 30, 2023
Date of Acceptance: Nov 28, 2023
Date of Publishing: Jan 01, 2024
AUTHOR DECLARATION:
• Financial or Other Competing Interests: None
• Was Ethics Committee Approval obtained for this study? Yes
• Was informed consent obtained from the subjects involved in the study? No
• For any images presented appropriate consent has been obtained from the subjects. NA
PLAGIARISM CHECKING METHODS:
• Plagiarism X-checker: Jul 12, 2023
• Manual Googling: Nov 17, 2023
• iThenticate Software: Nov 27, 2023 (10%)
Etymology: Author Origin
Emendations : 8 |
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INTRODUCTION |
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ABG interpretation plays an indispensable role in emergency medicine and the care of intensive care patients, yet its interpretation is challenging. Only a few graphical methods exist for ABG interpretation, such as the Siggaard-Andersen chart (S-A chart), Davenport or Bicarbonate-pH diagram, and Grogono diagram. However, these methods are not commonly utilised in clinical practice. The S-A chart has some flaws in diagnosing acid-base disorders with various combinations of pH-pCO2 values. The Davenport or Bicarbonate-pH diagram is complicated and difficult to understand. The Grogono diagram, a two-axis diagram using pCO2 on the horizontal axis and SBE on the vertical axis, is considered superior to the S-A chart but fails to provide accurate interpretation in atleast 25% of cases (1),(2),(3),(4),(5). Therefore, a newer graphical method utilising the four-quadrant approach was developed by the current author and published in previous research articles (6),(7).
Bicarbonate is calculated using the Modified Henderson equation. Standard bicarbonate represents the concentration of bicarbonate in the plasma from blood equilibrated with a normal PaCO2 (40 mmHg) and a normal pO2 (over 100 mmHg) at a normal temperature (37°C). Under normal ventilation, the actual bicarbonate and standard bicarbonate concentrations are approximately equal. However, in abnormal respiration (either hypoventilation or hyperventilation), the two values change and deviate from each other based on variations in pCO2 concentration (6),(8),(9).
Simple acid-base disorders are relatively easy to interpret, but in clinical practice, most ABG results are complex, involving compensations or mixed disorders, which are challenging to understand and interpret (3),(6). Compensation rules play a significant role in identifying changes resulting from compensations or the presence of a second primary acid-base disorder. The aim of the current study was to apply the developed concept of compensation rules in this four-quadrant graphical tool for ABG interpretation.
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Material and Methods |
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This cross-sectional study was conducted from November 2022 to April 2023 at Shri Sathya Sai Medical College and Research Institute, Chennai, Tamil Nadu, India. Ethical clearance was obtained (IEC No: 2016/272), and this study serves as an extension of author’s previous research (6),(7),(8). A total of 232 ABG samples were collected from ICU patients for analysis. The consistency of the ABG reports was assessed using the Modified Henderson Equation, and consistent results were included while inconsistent results were excluded (3),(6). At a pCO2 of 40 mmHg, the H2CO3 concentration is 1.2 mmol/L (H2CO3=0.03×pCO2). The calculation of SBE and the novel-derived ratios are detailed below (6),(7),(10).
Standard Base Excess (SBE)=cHCO3-24.8+16.2×(pH-7.40)
Ratio 1=HCO3/Std HCO3
Ratio 2=(HCO3/H2CO3)- (Std HCO3/H2CO3) OR
Ratio 2=(HCO3-Std HCO3)/H2CO3
Modified Ratio 2=(Std HCO3/1.2)-(HCO3/H2CO3)
Modified Ratio 2 (modified version of Ratio 2) was used as it is logical to correlate Std bicarbonate with an H2CO3 concentration of 1.2 mmol/L.
Compensation bedside rules: The Boston Method (6 rules) using bicarbonate or the Copenhagen Method (4 rules) using SBE can be applied to assess compensation, but the six bicarbonate-based bedside rules are more commonly utilised in clinical practice (11),(12),(13).
Six bicarbonate-based bedside rules:
Rule for acute respiratory acidosis:
Expected (HCO3)=24+{(Actual pCO2-40)/10}
Rule for chronic respiratory acidosis:
Expected (HCO3)=24+4 {(Actual pCO2-40)/10}
Rule for acute respiratory alkalosis:
Expected (HCO3)=24-2 {(40-Actual pCO2)/10}
Rule for chronic respiratory alkalosis:
Expected (HCO3)=24-5 {(40-Actual pCO2)/10} (range:±2)
Rule for a metabolic acidosis:
Expected pCO2=1.5×(HCO3)+8 (range: ±2)
Rule for a metabolic alkalosis:
Expected pCO2=0.7×(HCO3)+20 (range: ±5)
Four SBE-based bedside rules:
Acute respiratory acidosis or alkalosis:
An acute deviation in pCO2 will not alter the SBE. If SBE changes then it denotes metabolic disturbances only (11),(12),(13).
Chronic respiratory acidosis or alkalosis:
SBE=0.4×(pCO2-40)
Metabolic acidosis:
Expected CO2=40+SBE
Metabolic alkalosis:
Expected CO2=40+(0.6×SBE)
Statistical Analysis
These graphs were constructed using scatter plots with two variables in MS Excel 2019 version.
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Results |
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The total of 232 samples was classified into various acid-base disorders and is clearly depicted in (Table/Fig 1). The graphical relationship between pCO2 and ratio 1, ratio 2, and modified ratio 2 is clearly depicted in (Table/Fig 2),(Table/Fig 3),(Table/Fig 4), respectively.
A sample model of a four-quadrant graph using SBE and (pCO2-40 mmHg) parameters is shown in (Table/Fig 5), clearly illustrating the different areas of various acid-base disturbances. In (Table/Fig 6), a four-quadrant graph was constructed using SBE and modified ratio 2 for all the 232 cases. Similarly, in (Table/Fig 7), a four-quadrant graph was constructed using SBE and (pCO2-40 mmHg) for all the 232 cases. The application of compensation rules in the four-quadrant graph method, using the concept of a shift in the plotted point’s position, is demonstrated in (Table/Fig 8).
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Discussion |
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The actual bicarbonate and standard bicarbonate concentrations are approximately equal under normal ventilation. However, in hypoventilation and hyperventilation, these two values deviate from each other. At a pCO2 of 40 mmHg, both bicarbonate and standard bicarbonate values are equal, resulting in a difference of zero. The ratio 2 value is zero when the ratio 1 value is one. The ratio 1 (HCO3/Std HCO3) is greater than 1 for increased pCO2 and less than 1 for decreased pCO2. The ratio 2 is positive and greater for increased pCO2, and negative and greater for decreased pCO2 values (6),(7),(14).
Respiratory acid-base disorders and compensations in metabolic acid-base disorders due to respiratory mechanism changes affect the values of these ratios in different conditions. These derived ratios provide clues for differentiating various acid-base disturbances (6),(7),(14). Modified ratio 2 clearly distinguishes different pCO2 values. Both ratio 2 and modified ratio 2 are positive and greater for increased pCO2, and negative and greater for decreased pCO2 values. Modified ratio 2 is used because Std bicarbonate is measured at a pCO2 of 40 mmHg, and it seems logical to correlate Std bicarbonate with an H2CO3 concentration of 1.2 mmol/L (at a pCO2 of 40 mmHg).
SBE greater than +2 mmol/L indicates metabolic alkalosis, while SBE less than -2 mmol/L indicates metabolic acidosis. The normal range for pCO2 is 35 to 45 mmHg. Higher pCO2 values are observed in respiratory acidosis, while lower pCO2 values are seen in respiratory alkalosis (6),(7),(14). Modified ratio 2 is positive and greater for respiratory acidosis, and negative and greater for respiratory alkalosis.
A four-quadrant graph is constructed for ABG interpretation using SBE and modified ratio 2 values for all 232 cases. Another four-quadrant graph was constructed using SBE and the parameter (pCO2-40 mmHg). The modified ratio 2 is zero at a pCO2 of 40 mmHg, so the zero central point is common to all three parameters. A three-dimensional graph can be created by merging these two four-quadrant graphs since SBE is common to both of them on the x-axis (6),(7),(14).
The various acid-base disorders can be easily visualised in different regions of the four-quadrant graph, with normal levels occupying the central region. In the 1st quadrant (both the x and y axes are positive), metabolic alkalosis and respiratory acidosis are represented. In the 2nd quadrant (x-axis positive and y-axis negative value), metabolic alkalosis and respiratory alkalosis are represented. In the 3rd quadrant (both the x and y axes are negative), metabolic acidosis and respiratory alkalosis are represented. In the 4th quadrant (x-axis negative and y-axis positive), metabolic acidosis and respiratory acidosis are represented (6),[7,]1(4).
After identifying the primary disorder of the acid-base disturbances, compensation rules are applied to help identify the presence of compensations or a mixed acid-base disorder. If the measured pCO2 is higher than the expected pCO2, it indicates the presence of respiratory acidosis, and if it is lower, it indicates the presence of respiratory alkalosis. If the measured (HCO3-) value is higher than the expected (HCO3-), it denotes the presence of metabolic alkalosis, and if it is lower, it denotes the presence of metabolic acidosis. The difference between the measured and the expected level {either pCO2 or (HCO3-)} indicates the magnitude of the severity. These steps are routinely performed in ABG interpretation, but it can be an arduous task (11),(12),(15),(16).
These concepts are applied in the graphical tool to facilitate easier interpretation and overcome the challenges of the task. After applying the compensation rules in the four-quadrant graph method, if no major shift (within acceptable limits) is observed in the plotted point’s position, it indicates only compensations without the presence of a second acid-base disorder. The combined acid-base disturbances resulting from compensations or mixed acid-base disorders can be easily identified and located using the concept of a shift in the plotted point’s position on the four-quadrant graph. An upward positive shift signifies respiratory acidosis, a downward negative shift indicates respiratory alkalosis, a right positive shift represents metabolic alkalosis, and a left negative shift signifies metabolic acidosis. The compensation rules that are commonly used with bicarbonate can also be applied here because the SBE parameter plotted on the X-axis is calculated using bicarbonate values. Therefore, changes in expected bicarbonate values will be reflected when SBE values are calculated using the expected bicarbonate value. Hence, there is no compulsion to use the compensation rules solely based on SBE.
Limitation(s)
The calculation of the anion gap and delta gap, which helps in identifying hidden metabolic acid-base disorders, cannot be displayed in the graphical tool. This limitation exists in the study; however, it can be calculated separately and correlated with the clinical history.
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Conclusion |
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The interpretation of ABG results holds significant clinical value; however, understanding complex acid-base disorders can be challenging. Few graphical methods are available, but they are not practically convenient for clinical practice. The proposed application of compensation rules using the shift concept in the four-quadrant graph method appears to be simpler and easier, addressing the difficulties associated with complex acid-base disorders involving various compensations and mixed disorders. The inclusion of modified ratio two, standard bicarbonate, and compensation rules in this graph method makes it a unique diagnostic tool compared to other existing methods. The incorporation of these parameters, along with the simplified approach of the four-quadrant graph, may make this diagnostic graphical tool a suitable for ABG interpretation, especially for junior staff. However, further confirmation by other researchers working with intensive care unit patients is required for widespread acceptance and adoption of this graphical tool in clinical practice. When used in conjunction with other ABG parameters and proper clinical correlation, this diagnostic ABG tool may aid in better understanding and interpretation of ABG reports, particularly for junior doctors and staff nurses.
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| | 1. | Barnette L, Kautz DD. Creative ways to teach arterial blood gas interpretation. Dimens Crit Care Nurs. 2013;32(2):84-87. ?doi?https://doi.org/10.1097/DCC.0b013e31826bc732#doi#?pmid?23388867#pmid#
[ Google Scholar] [ CrossRef] [ PubMed] | | 2. | Doig AK, Albert RW, Syroid ND, Moon S, Agutter JA. Graphical arterial blood gas visualization tool supports rapid and accurate data interpretation. Comput Inform Nurs. 2011;29(4 Suppl):TC53-60. ?doi?https://doi.org/10.1097/NCN.0b013e31821ef636#doi#?pmid?21562382#pmid#
[ Google Scholar] [ CrossRef] [ PubMed] | | 3. | Sood P, Paul G, Puri S. Interpretation of arterial blood gas. Indian J Crit Care Med. 2010;14(2):57-64. ?doi?https://doi.org/10.4103/0972-5229.68215#doi#?pmid?20859488#pmid#
[ Google Scholar] [ CrossRef] [ PubMed] | | 4. | Behrakis P, Vasileiou M, Anastasios L, Nikolaos T. Latest developments in graphic diagnostic approach of arterial blood gases disturbances. Pneumon. 2004;17(2):150-58.
[ Google Scholar] | | 5. | Theakos N, Loukos A, Vassiliou M, Moukas M, Zaka M, Behrakis PK. pH- logPaCO2 diagram for the diagnostic approach of simple acid-base disorders. 2nd Mediterranean Congress on Thoracic Diseases Athens, Greece 4-7 March 1998.
[ Google Scholar] | | 6. | Samuel R. A graphical tool for arterial blood gas interpretation using standard bicarbonate and base excess. Indian J Med Biochem. 2018;22(1):85-89. ?doi?https://doi.org/10.5005/jp-journals-10054-0061#doi#
[ Google Scholar] [ CrossRef] | | 7. | Samuel R. Revised graphical tool for ABG interpretation using modified bicarbonate/ standard bicarbonate ratio. Int J Clin Chem Lab Med. 2019;5(3):19-29. ?doi?https://doi.org/10.20431/2455-7153.0503003#doi#
[ Google Scholar] [ CrossRef] | | 8. | Samuel R. Application of standard bicarbonate/carbonic acid ratio in arterial blood gas analysis. Int J Clin Biochem Res. 2018;(2):314-20.
[ Google Scholar] | | 9. | Jørgensen K, Astrup P. Standard bicarbonate, its clinical significance, and a new method for its determination. Scand J Clin Lab Invest. 1957;9(2):122-32. ?doi?https://doi.org/10.3109/00365515709101210#doi#?pmid?13442565#pmid#
[ Google Scholar] [ CrossRef] [ PubMed] | | 10. | Rajini Samuel T, Vyshnavi R, Vanaja R, Ragashree CM, Rajagopalan B. Graphical analysis of arterial blood gas analysis using standard base excess. Int J Pharm Sci Rev Res. 2017;46(1):223-28.
[ Google Scholar] | | 11. | Joynt GM, Choi GYS. Chapter: Blood gas analysis in the critically ill Oxford Textbook of Critical Care (2 ed.) Publisher: Oxford University Press, 2016. Doi: 10.1093/med/9780199600830.003.0072. ?doi?https://doi.org/10.1093/med/9780199600830.003.0072#doi#?pmid?27438101#pmid#
[ Google Scholar] [ CrossRef] [ PubMed] | | 12. | Kerry Brandis.Chapter: Assessment of Acid-Base Disorders. Acid-base physiology. Open Education Resource LibreTexts Project (https://LibreTexts.org),2023.
[ Google Scholar] | | 13. | Schlichtig R, Grogono AW, Severinghaus JW. Human PaCO2 and standard base excess compensation for acid-base imbalance. Crit Care Med. 1998;26(7):1173-79. Doi: 10.1097/00003246-199807000-00015. ?doi?https://doi.org/10.1097/00003246-199807000-00015#doi#?pmid?9671365#pmid#
[ Google Scholar] [ CrossRef] [ PubMed] | | 14. | Rajini Samuel T. Who is balancing: Is it RBC or acid-base status? Intech Open Publisher. 2019:01-15. Doi: http://dx.doi.org/10.5772/intechopen.84768. ?doi?https://doi.org/10.5772/intechopen.84768#doi#
[ Google Scholar] [ CrossRef] | | 15. | Bruno CM, Valenti M. Acid-base disorders in patients with chronic obstructive pulmonary disease: A pathophysiological review. J Biomed Biotechnol. 2012;2012:915150. ?doi?https://doi.org/10.1155/2012/915150#doi#?pmid?22500110#pmid#
[ Google Scholar] [ CrossRef] [ PubMed] | | 16. | Oosthuizen NM. Approach to acid-base disorders- A clinical chemistry perspective. CME. 2012;30(7):230-34. [ Google Scholar]
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| TABLES AND FIGURES | |
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