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INTRODUCTION 3 METHODS………………………………………………………………………………………………………………………………………………3 CORRELATION BETWEEN ABG AND VBG IN CABG 4 PAIN SCORE USING 23G AND 25G NEEDLES IN ABG ANALYSIS 4 COMPARING ABG AND VBG AMONG ICU PATIENTS 5 COMPARING ARTERIAL AND VENOUS LACTASE AMONG CHILDREN WITH SEPSIS 6 EFFECTS OF HEPARIN IN ABG ANALYSIS 6 COMPARISON BETWEEN ARTERIAL AND CAPILLARY SAMPLING IN ED 7 EFFECT OF STORAGE TEMPERATURE IN ABG ANALYSIS 8 COMPARING ETCO2 AND ABG IN ICU PATIENTS 8 ABG IN COPD OVER LONG TERM……………………………………………………………………………………………………………..9 ABG VS VBG DIFFERENCES DURING HEMORRHAGIC SHOCK…………………………………………………………………….9 SUMMARY 10 REFERENCES 11

The effectiveness of a blood gas test depends on various clinical conditions. Though basic, a blood gas test is an essential procedure in the diagnosis of underlying disease among critical patients. Given the importance and the frequent clinical use of a blood gas test in diagnostic processes, one may think that the applicability and situational effectiveness of a blood gas test is straightforward among respiratory therapists. Contrary to that assumption, there are many situations such as the acceptable temperature of the sample, time frame to analysis, and the type of syringes used that are still unknown to many respiratory therapists. On the other hand, there are clinical situations where venous blood gas testing becomes effective as opposed to the standard arterial blood gas tests. Evidently, there is a knowledge gap among respiratory therapists when it comes to clinical situations and the appropriateness of the blood gas test in diagnosis particularly among the critically ill patients.

METHODS

The literature review was done using the following criteria. The database search was through PubMed. Keywords used were arterial blood gas, venous blood gas, and human blood gas. The years searched were limited to 2013 to 2018. Only English Language, peer-reviewed research articles were chosen.

CORRELATION BETWEEN ABG AND VBG IN CABG

One important aspect of a blood gas test is the collection of blood particularly in the treatment of acute diseases. Although arterial blood sampling is assumed to be the standard , there has been increasing interest in the effectiveness of venous blood sample in gas testing. Because of its effectiveness in estimating common blood parameters such as bicarbonate, PCO2 and PO2, the ABG has been routinely applied in the diagnosis of patients undergoing elective Coronary Artery Bypass Graft (CABG) surgery.1 However, the arterial procedure of collecting blood is invasive and painful to many patients. There is also the risk of complications including embolism, hematoma and thrombosis besides the infections. As a result venous blood gas testing has been suggested as an alternative method of collecting blood for testing in CABG. According to clinical studies conducted by Esmaeilivand, et al. venous blood gas (VBG) analysis is not an effective replacement for ABG for measuring important blood parameters for such as PO2 status1.The VBG is preferable particularly in patients who have been hospitalized for lengthy durations and have a central venous catheter, a common occurrence among patients undergoing CABG. The advantages associated with VBG include the limited risk of thrombosis and embolism. It is also easier for the medical staff to perform unlike the ABG which involves needle-stick injuries and potential infections

In conducting blood gas tests, inherent risks have been raised about the painful experiences and the risk of hepatitis when ABG is preferred. Attempts have been made in clinical conditions to evaluate whether the size and type of the needle used contribute to the pain experienced by the patients. According to Yee et al., ABG analysis is critical in the evaluation of acid-base among patients in emergency department. The greater risk associated with inserting needles deeper into the skin in ABG is a drawback. However, the researchers established that regardless of the size of the needle used in drawing blood from the arterial sources, the resulting differences in the pain felt whether using size 23G or 25G was negligible. Similarly their ease or difficulty of use associated with the either needle size on the part of the healthcare provider was also negligible. However, size 23G needles were more prominent in causing injuries and hematoma of the puncture site.2

According to Kim, ABG testing is commonly used in clinical tests to evaluate the acid-base and respiratory conditions of patients in critical situations. Like other researchers, Kim established that ABG analysis is fraught with complications such as reflex sympathetic dystrophy and formation of aneurysm. The researchers established that VBG may eventually take over from the ABG as the standard procedure in testing for common parameters of blood gas among patients admitted in critical care. Contrary to previous studies that questioned the reliability of VBG test values, the more recent experiments have confirmed concurrence of values adduced using either method in testing particularly for testing acidosis or base component of the blood. The effectiveness of the VBG extended to all common parameters including bicarbonate and PCO2 among patients in the ICU exhibiting varied pathologies. While ABG analysis is effective in testing common parameters, the venous procedure posse lower risks and is equally effective among patients in the intensive care unit.3

Early blood gas testing is a critical aspect in the treatment of sepsis among the children. The disease is characterized by additional demand for oxygen in the body tissues. Any imbalance between the demand and supply of oxygen to the blood tissues leads to hypoxia and eventually the production of lactase. Such a critical situation brings about alteration of homeostasis which has the potential for multiple organ injury. Blood gas testing helps to detect the development of sepsis so that appropriate therapeutic intervention can be administered. Given the difficulty in drawing arterial blood among the pediatric patients, there is a need to seek an alternative method of assessing the pathological status of the child. According to Fernández Sarmiento, there is a strong correlation between central venous lactate and arterial lactate among children suffering from sepsis. Furthermore, the study indicated that there were no significant statistical differences between the two approaches regarding weight, age and diagnosis.4

Heparin plays an important role in arriving at accurate results when conducting a blood gas test, using heparin prevents blood clotting. Heparin added in syringes when conducting an ABG is central to determining the accurate status of common parameters among patients experiencing cardiopulmonary compromise. Although there are several pre-analytical factors such as sample temperature, air in the syringe and the skill of the attending respiratory therapist, excessive heparin is central in influencing the accuracy of blood gas tests by as much as 75%. The type of heparin used, whether liquid or dry balanced, and the amount used in preparing the sample, as well as the manner it is mixed with the sample blood, is crucial in assessing correctly the various blood parameters during the test. Although many syringes are preloaded with the right amount and type of heparin, there are many areas where for one or more reasons such preloaded syringes are unavailable. Studies indicate that the amount of heparin to be used in an ABG sample should not exceed 0.1cc. Alternatively, flushing the syringe with heparin is sufficient.5

Another important aspect of blood gas testing is the comparison between capillary and arterial blood sampling. Unlike arterial, capillary blood sampling presents reduced risks such as ischemia and possible formation of fistula. The relevance of collecting capillary blood samples is most significant among patients in an emergency department. Other than the procedure being easy to administer and less painful, studies also indicate similarity in test outcomes when compared with ABG under similar clinical conditions. Measures of blood gas parameters such as pH, PO2, and HCO3 returned negligible statistical differences between capillary and arterial blood samples (p =0.001). The close correlation between capillary and arterial blood samples is most significant for blood collected from the capillaries at the fingertip and the arterial sources.6

EFFECT OF STORAGE TEMPERATURE IN ABG ANALYSIS

The reliability of a blood gas test is dependent on the storage of the blood sample and time delay between collection and testing of the sample. Blood gas parameters including pH and bicarbonate are determined to a large extent by the storage temperatures. While the importance of an ABG is unquestioned among critically ill patients, pre-analytical determinants can alter the accuracy of the test outcome. Studies indicate that a delay in the analysis of the collected sample can reduce PaO2 and at the same time increase PaCO2 as a result of the metabolism of the cell. It is therefore advisable to keep the sample on ice if the sample testing will take more than 30 minutes. Conversely, it is not worthwhile to preserve the sample on ice if the time between collection and blood analysis does not exceed 30 minutes. Furthermore, where there is a delay in carrying out the test, the respiratory therapist should be aware of changes in gas patterns particularly where the blood samples are taken in plastic syringes. However, when the samples are stored in glass syringes, it is recommended to cool the blood sample purposely to reduce the rate of metabolism of leukocytes. This is due to the low permeability associated withO2 molecules. On the other hand, the respiratory therapist should be aware of the risk of overestimation of PaO2.7

According to Taghizadieh et al., capnography might be used to determine the ETCO2 levels instead of ABG among patients with metabolic acidosis. In studies aimed at establishing the comparison between arterial blood bicarbonate and ETCO2 among patients with metabolic acidosis, experiments revealed that capnography is effective for primary diagnosis where patients are able to breathe spontaneously in the emergency wards. However, ABG should be considered as the gold standard in the analysis of the blood.8

ABG IN COPD OVER LONG TERM

Blood gas testing for patients with COPD must recognize the changes in blood gases over the long term. Given the high rate of mortality and morbidity arising from COPD, early diagnosis could prove pivotal in effective intervention strategies. In the studies conducted by Cukic, one common characteristic among patients with COPD is the decline of pH and PaO2 while PaCO2 shoots up as the disease advances. This is indicative of progressive limitation of the airflow. However, pertaining to the patients who are on consistent therapeutic treatment, the PaO2 and PaCO2 elements were judged to be significantly smaller when compared with not on therapy9.

ABG VS VBG DIFFERENCES DURING HEMORRHAGIC SHOCK

In other studies conducted on rabbits, it was revealed that hemorrhage shock leads to notable acidosis and base decline for both venous as well as arterial blood samples. Additionally, there was a difference in PCO2 dissimilarity between arterial hypocarbia and venous hypercarbia.10 These results seem to mirror previous studies that concluded that the dissimilarity between venous and arterial blood sample was evident in cases of severely hypoperfused states10.

SUMMARY

The suitability of the method to apply in testing blood gas is dependent on the nature of disease as well as the state of the patient. While ABG is the gold standard for blood gas analysis, there are instances where VBG is equally effective yet posing limited risks compared with ABG. Importantly, pre-analytical conditions such as temperatures and the storage of the blood sample are crucial in determining the accuracy of the test.

1. Esmaeilivand M, Khatony A, Moradi G, Najafi F, Abdi A. Agreement and correlation between arterial and central venous blood gas following coronary artery bypass graft surgery. J Clin Diagn Res. 2017 Mar;11(3):OC43–OC46.

2. Yee K, Shetty AL, Lai K. ABG needle study: a randomised control study comparing 23G versus 25G needle success and pain scores. Emerg Med J. 2014;7(3):254-287.

3. Kim BR, Park SJ, Shin HS, Jung YS, Rim H. Correlation between peripheral venous and arterial blood gas measurements in patients admitted to the intensive care unit: a single-center study. Kidney Res Clin Pract.2013;32(1):32-38.

4. Fernández Sarmiento J, Araque P, Yepes M, Mulett H, Tovar X, Rodriguez F. Correlation between arterial lactate and central venous lactate in children with sepsis. Crit Care Res Pract. 2016;4(2):26-31.

5. Kumar A, Kushwah S, Sahay S. Effect of extra amount of heparin in syringe and its effect on arterial blood gas analysis. Euro J Med. 2015;2(6): 290-293.

6. Heidari K, Hatamabadi H, Ansarian N, Alavi-Moghaddam M, Amini A, Safari S, Mazandarani PD, Vafaee A. Correlation between capillary and arterial blood gas parameters in an ED. Am J Emerg Med. 2013;1;31(2):326-329.

7. Mohammadhoseini E, Safavi E, Seifi S, Seifirad S, Firoozbakhsh S, Peiman S. Effect of sample storage temperature and time delay on blood gases, bicarbonate and pH in human arterial blood samples. Iran Red Crescent Med J. 2015;17(3):435-475.

8. Taghizadieh A, Pouraghaei M, Moharamzadeh P, Ala A, Rahmani F, Sofiani KB. Comparison of end-tidal carbon dioxide and arterial blood bicarbonate levels in patients with metabolic acidosis referred to emergency medicine. J Cardiovasc Thorac Res. 2016;8(3):98–101.