Simple Algorithm of Arterial Blood Gas Analysis to Ensure Consistent, Correct and Quick Responses!

Journal of Anesthesia & Critical Care: Open Access

Abstract Review Article

Background: Arterial blood gas (ABG) analysis is an essential part of diagnosing Volume 5 Issue 5 - 2016 and managing a patient’s oxygenation, ventilation status as well as acid-base balance. The usefulness of this diagnostic tool is dependent on being able to correctly interpret the results. The body operates efficiently within a fairly Classified Specialist/Associate Prof Anesthesiology & Intensive narrow range of blood pH (acid-base balance). Even relatively small changes can Care, Combined Military Hospital, Bangladesh be detrimental to cellular function. Disorders of acid-base balance can create complications in many disease states, and occasionally the abnormality may be so *Corresponding author: Lt Colonel Abul Kalam Azad, severe so as to become a life-threatening risk factor. A thorough understanding of acid-base balance is mandatory for physicians, intensivists, and anesthesiologists Intensive Care, Combined Military Hospital, Post Code-1206, are not exception! We must always interpret them in light of the patient’s history, DhakaClassified Cantonment, Specialist/Associate Dhaka, Bangladesh Prof Anesthesiology & clinical presentation and laboratory information’s. Tel: 008801715010956; Email:

Objectives: ABG is not merely a tracing paper! So many variables right at the Received: July 11, 2016 | Published: August 30, 2016 tracing paper as well as clinical variables of the patients hatch fearfulness among young physicians. So the effort was to make ABG EASY and to develop an algorithm which will conduct navigating diagnosis!

Conclusion: Arterial blood gases help assess three vital physiologic processes in the critically ill patient: acid-base balance, ventilation and oxygenation. Initial blood gas analysis helps diagnose underlying disease processes as well as guide therapeutic interventions. Serial measurements can be utilized to assess proper response to therapy. Blood gas analysis takes a step-by-step approach and practice. Blood gas data should always be integrated in light of the full clinical and laboratory information.

Keywords: Oxygenation; Ventilation; Acid-base; Metabolic; Saturation; Bicarbonate

Introduction Basic terminology [6-8] Arterial blood gas (ABG) analysis is a crucial part of diagnosing a) PH H is inversely and managing a patient’s state of oxygenation, ventilation as well related to H+ ion concentration. as acid-base balance. The practicability of this diagnostic tool : signifies free hydrogen ion concentration. P Acid: a substance that can donate H+ ion, i.e. lowers PH. is dependent on being able to correctly interpret the results. b) Disorders of acid-base balance can create complications in many c) Base: a substance that can accept H+ ion, i.e. raises PH. disease processes, and occasionally underlying disorders may be so severe that might cause life-threatening risk. So, thorough d) Anion: an ion with negative charge. understanding of acid-base balance is vital for any physician, e) Cation: an ion with positive charge. intensivist, and anesthesiologists are not exception. f) Acidemia: blood PH< 7.35 with increased H+ concentration. ABG analysis is a diagnostic tool that allows the objective evaluation of a patient’s oxygenation, ventilation and acid- g) Alkalemia: blood PH>7.45 with decreased H+ concentration. base balance. The results from an ABG will indicate not only h) Acidosis: Abnormal process or disease which reduces PH due patient’s respiratory status but also indicate how well a patient’s to increase in acid or decrease in alkali. kidneys and other internal organs (metabolic system) are functioning. Although all of the data in an ABG analysis can be i) Alkalosis: Abnormal process or disease which increases PH useful, it is possible to interpret the results without all variables. due to decrease in acid or increase in alkali. Essentials of interpreting ABG need maximum of six values: Requirement of acid-base balance [7,8] - Oxygen concentration (PO2), - Oxygen saturation (SaO2), - Bicarbonate ion concentration (HCO3-), - Base excess, - Carbon Acid-base balance is important for metabolic activity of the dioxide concentration (PCO2); - Hydrogen ion concentration (PH) body: [1-5]. PH of arterial blood = 7.35 – 7.45.

Submit Manuscript | http://medcraveonline.com J Anesth Crit Care Open Access 2016, 5(5): 00199 Simple Algorithm of Arterial Blood Gas Analysis to Ensure Consistent, Correct and Quick Copyright: 2/9 Responses! ©2016 Kalam

Alteration of pH value out of the range 7.35-7.45 will have effects on normal cell function. PH< 6.8 or > 8.0 death occurs.

Changes in excitability of nerve and muscle cells

↓PCan→ lead depresses to loss ofthe consciousness. CNS H

↑PTingling → over-excitability sensations, nervousness, of CNS muscle twitches.

Alteration of enzymatic activity: PH change out of normal range can alter the shape of the enzyme rendering it non-functional.

PH change

Alteration of K+ levels

Acid-base state of ECF influence:

Citation: Kalam LCAA (2016) Simple Algorithm of Arterial Blood Gas Analysis to Ensure Consistent, Correct and Quick Responses!. J Anesth Crit Care Open Access 5(5): 00199. DOI: 10.15406/jaccoa.2016.05.00199 Simple Algorithm of Arterial Blood Gas Analysis to Ensure Consistent, Correct and Quick Copyright: 3/9 Responses! ©2016 Kalam

K+ distribution in ECF and ICF Renal excretion of K+ Acid-base disturbance or imbalance I. Acid-base balance: the process maintaining PH value in a normal range

Acid-base balance: the process maintaining PH value in a normal range

Many conditions can alter body PH: Many conditions can alter body PH:

• Acidic or basic food • Acidic or basic food

• Metabolic intermediate by- • Metabolic intermediate by- products products

• Some disease processes • Some disease processes

Acid-base disturbance or imbalance Acid-base disturbances: i. Secondary alterations to some diseases or pathologic processes ii. Can aggravate and complicate the original disease iii. Concept of acids and bases: iv. Acids are molecules that can release H+ in solution. (H+ donors) v. Bases are molecules that can accept H+ or give up OH- in solution. (H+ acceptors) vi. Acids and bases can be: a. Strong – dissociate completely in solution

b. Weak HCl, – dissociate NaOH only partially in solution Lactic acid, carbonic acid Regulation of acid-base balance a. Blood buffering React very rapidly (less than a second) b. Respiratory regulation Reacts rapidly (seconds to minutes)

c. Ion exchange between intracellular and extracellular compartment and intracellular buffering Reacts slowly (2~4 hours) d. Renal regulation Reacts very slowly (12~24 hours)

- - - Respiratory regulation HCO3 /H2CO3 3 2CO3 3 ]/[H2CO3] tend +] can stimulate peripheral chemoreceptor The lung regulates the ratio of [HCO -]/[H CO ] to approach 3 2 3 → ↓ [HCO ] and ↑ [H ] → [HCO 20/1 by controlling the alveolar ventilation and further 2 to decrease, while ↑[H -] / [H CO H is elimination of CO , so as to maintain constant PH value. 2 3 2 3 2 maintained.→respiratory center exciting →↑alveolar ventilation →↑CO Regulation of alveolar ventilation (V ) elimination →↓PaCO → [HCO ] tends to 20/1 → P A Renal regulation

a. VA is controlled by respiratory center (at medulla oblongata). - The kidney regulates [HCO3 ] through changing acid excretion - b. Respiratory center senses stimulus coming from: and bicarbonate conservation, so that the ratio of [HCO3 ]/[H2CO3] approach 20/1 and PH value is constant. Central chemoreceptor (located at medulla oblongata) Bicarbonate conservation c. Alteration of [H+ a. Bicarbonate regeneration by distal tubule and collecting duct. + ] in Cerebrospinal fluid b. Bicarbonate reclamation by proximal tubule. A ↑[H ] in Cerebrospinal fluid→ respiratory center exciting→ d. Alteration of PaCO How does the renal regulation maintain the constant PH ↑V 2 value? PaCO2 A increase 10 times +

PaCO2 - - - > 60mmHg→ V HCO3 /H2CO3 3 2CO3 3 ]/[H2CO3] tend to Peripheral chemoreceptor (carotid and aortic body) ↑[H ] in Blood→+ ] rapidly can stimulate buffered the by activity buffer of system CA, H +-ATPase such as > 80mmHg→ respiratory center inhibited → ↓ [HCO ] and ↑ [H + ] → [HCO e. +] decrease,- while ↑[H- H 2 2 of HCO3 3 ] / [H2CO3 is maintained. and glutaminase→↑secretion of H and ammonia, ↑reabsorption ↓PaO or2 ↑PaCO or ↑[H A → [HCO ] tends to 20/1 → P intracellular buffering: ↓PaO2< 60mmHg→ respiratory center exciting→ ↑V Ion exchange between intra- and extracellular compartment & A. Intracellular buffer system How does ↓PaO alteration< 30mmHg→ of alveolar respiratory ventilation center regulate inhibited pH value? 2- 4- + a. Phosphate buffer system (HPO4 /H2PO )

↑[H ] in Blood→ rapidly buffered by buffer system such as

b. Hemoglobin (Hb-/HHb) and oxyhemoglobin buffer system iii. ECF as a percent of body weight varies with age and fat - (HbO2 /HHbO2) content. B. Ion exchange between intra- and extracellular compartment In general, however, recommendations for bicarbonate therapy are in the range of 0.1 to 0.2 mEq times the body weight times the + + shift into cells and K+ shift base excess (ignoring the minus sign). out of cells i.e. ↑Extracellular [H ] → H Bicarb = 0.1 x (-B.E.) x Wt in Kg a. Tips for determining primary and mixed acid base disorder b. acidosis→ hyperkalemia [11,12] Base excess & basealkalosis→ deficit [9,10]hypokalemia Tip-1: Only a process of acidosis can make the PH acidic and only a In human physiology base excess and base deficit refer to an process of alkalosis can make PH alkaline Tip-2: In primary disorder PH blood. The value is usually reported as a concentration in units of acidosis, when compensation is complete excess or deficit, respectively, in the amount of base present in the mEq/L, with positive numbers indicating an excess of base and 7.35 ─ 7.40 is indicative of primary Tip-3: In primary disorder PH to +2 mEq/L. Comparison of the base excess with the reference alkalosis, when compensation is complete rangenegative assists a deficit. in determining A typical reference whether range an acid/base for base excessdisturbance is −2 7.40 ─ 7.45 is indicative of primary Tip-4: Keeps in mind that three states of compensation are is caused by a respiratory, metabolic, or mixed metabolic/ possible: respiratory problem. a) 3- The base excess of blood does not truly indicate the base excess H b) Non-compensation-Partial-compensation- alteration When ofall only three PCO2 variables or HCO like P , content and the absence of hemoglobin, ECF has a different PaCO and HCO - are abnormal. of the total extracellular fluid (ECF). Because of different protein 2 3 H c) Complete-compensation- P is normal but both PaCO2 HCO - are abnormal. clinicalbuffering determination capacity. What’s of the more,amount each of bicarbonate extracellular required fluid (for for 3 & treatmentexample CSF of vssevere interstitial acidosis fluid) is usually has a different based on buffer the base status. excess The Tip-5: Don’t interpret any blood gas data without examining of the blood. There is an unavoidable inaccuracy, however, due to corresponding serum electrolytes. several factors: H Tip-6: Truly normal P with distinctly abnormal HCO3- and PaCO2 i. The time course of the acidosis makes the blood acid poorly invariably suggests two or more disorders.

Tip-7: Whenever the PCO2 and [HCO3] are abnormal in opposite ii. reflect the total body acid burden in many cases. directions, ie, one above normal while the other is reduced, a varies. mixed respiratory and metabolic acid-base disorder exists. Depending on the state of hydration, body fluid distribution

Facts about Acid-Base balance…… [13]

… A respiratory component …. A respiratory acid …. Moves opposite to the direction of PH. ROME … A metabolic component ….. It is a base (Metabolic) …. Moves in the same direction of PH. Compensation of primary & mixed disorder

Compensation for simple acid-base disturbances always drives the compensating parameter (ie, the PCO2, or [HCO3-]) in the same direction as the primary abnormal parameter (ie, the [HCO3-] or PCO2 parameters in the opposite direction as the primary abnormal parameters. ) & compensation for mixed disorder always drives compensating

Moves in same direction If the ratio is between 0.4-1 then it is due to Mixed ... Primary disorder … Moves in opposite direction (HAGMA+NAGMA)Bedside Rules for disorserAssessment of Compensation [14] Rule 1: The 1 for 10 Rule for Acute Respiratory Acidosis … Mixed disorder

The [HCO3] will increase by 1 mmol/l for every 10 mmHg

elevation in pCO2 above 40 mmHg. Description of superscripts inside algorithm box [15-29] Expected [HCO3] = 24 + {(Actual pCO2 - 40) / 10} a. Increase or decrease of PH in relation with HCO - indicate 3 Rule 2: The 4 for 10 Rule for Chronic Respiratory Acidosis metabolic disorder The [HCO ] will increase by 4 mmol/l for every 10 mmHg b. Increase or decrease of PH in relation with PCO indicate 3 2 elevation in pCO above 40mmHg. respiratory disorder 2 Expected [HCO ] = 24 + 4 {(Actual pCO - 40) / 10} c. Step to look at compensation, noncompensation means 3 2

alteration of only PCO2 or HCO3- Rule 3: The 2 for 10 Rule for Acute Respiratory Alkalosis d. Partial compensation means PH, PCO and HCO - all variables 2 3 The [HCO3] will decrease by 2 mmol/l for every 10 mmHg are abnormal decrease in pCO2 below 40 mmHg. e. Full compensation means only PH is normal but PCO and 2 Expected [HCO3] = 24 - 2 {(40 - Actual pCO2) / 10} HCO - are abnormal 3 Rule 4: The 5 for 10 Rule for a Chronic Respiratory Alkalosis f. unmeasured anions in the plasma which primarily includes The [HCO3] will decrease by 5 mmol/l for every 10 mmHg Sulphate,Anion Gap Organic (AG) acids, = Na+ Albumin -( Cl and + Phosphate HCO3-), it (SOAP). represents The decrease in pCO2 below 40 mmHg. normal value of AG is 12 ± 4, an increase AG almost always Expected [HCO3] = 24 - 5 {(40 - Actual pCO2) / 10} ( range: indicates metabolic acidosis +/- 2) g. HAGMA(High Anion Gap Metabolic Acidosis)- Increase anion gap means an acid has been added to the blood, causes are KULT means Ketoacidosis,Uraemia,Lactic acidosis, Toxins RuleThe expected 5: The One pCO &2 a(in Half mmHg) plus 8 is Rule calculated - for a Metabolic from the followingAcidosis formula: h. Expected pCO = 1.5 x [HCO3] + 8 (range: +/- 2) HCO3 is lost to maintain electroneutrality Cl is conserved by 2 NAGMA( Normal Anion Gap Metabolic Acidosis)- when Kidney’s, so anion gap is normal, causes are DURHAM means Rule 6: The Point Seven plus Twenty Rule - for a Metabolic Alkalosis Acetazolamide, Misc Diarrhoea, Ureterosigmoid fistula, RTA, hyperalimentation, The expected pCO2 (in mmHg) is calculated from the following i. 3 formula: DeltaDelta ratio Gap=∆AG/∆HCO is a formula that can be used to assess elevated Expected pCO = 0.7 [HCO ] + 20 (range: +/- 5) anion gap metabolic acidosis and to evaluate whether mixed acid 2 3 base disorder is present. Conclusion [30] In High anion gap metabolic acidosis (HAGMA) Delta ratio will be 1-2 to identify the causes of acid base and oxygenation disturbances. ForThe accuracy Analysis arterial of arterial blood bloodgases gasshould values never have be significantinterpreted role by If the ratio is greater than 2 in a HAGMA it is due to concurrent themselves, it must always interpret them in light of the patient’s metabolic alkalosis. history and clinical presentation. It also has great impact on bedside patient management as well. be =0.4 In Nonanion gap metabolic acidosis (NAGMA) delta ratio will

Algorithm for interpreting arterial blood gas analysis: (Annexure-1)

References 15. Johnetta McCullough (2012) ABG interpretation. 1. Edward M (2007) Interpreting arterial blood gases. PCCSU Article 16. CP Dokwal (2009) Interpretation of arterial blood gases. Recent 21. Advance 3(1). 2. Canham EM (2003) Interpretation of arterial blood gases. In: 17. Parsons PE, et al., Critical Care Secrets. (3rd edn). Hanley and Belfus, Inc., Philadelphia, USA, 21-24. Adrouge HJ, Madias NE (1998) Management of life threatening acid 18. baseAsghar disorders. R (2007) N Use Engl of J the Med Delta 338(2): ratio 107-111. in the diagnosis of mixed acid 3. West JB (2003) Pulmonary pathophysiology; The essentials. (6th edn), Philadelphia, USA, 22-24. 19. base disorders. Ja Am SocNephrol 18(9): 2429-2431. 4. Hansen JE (1980) Should blood gas measurements be corrected for 56(1): 38-54. Emmett M, Narins R (1977) Clinical use of anion gap. Medicine 20. Figge J, Jabor A, Kazda A, Fencl V (1998) Anion gap and hypoalbuminemia. Crit Care med 26(11): 1807-1810. 5. theSeveringhaus patients temperature? JW, Astrup P,New Murray Engl JournalJF (1998) Med Blood 303-341. gas analysis and critical care medicine. Am J Respir Crit Care Med 157(4 Pt 2): 21. S114-S122. 22. Hodgkin JE, Soeprono EF, Chan DM (1980) Incidence of metabolic 6. Vishal Golay (2011) Interpretation of the arterial blood gas analysis. Galla JH (2000) Metabolic alkalosis. Ja Am SocNephrol 11: 369-375. alkalemia in hospitalized patients. Crit Care Med 8(12): 725-732. 23. Javaheri S, Kazemi H (1987) Metabolic alkalosis and hypoventilation 7. Yu-Hong Jian (2008) Acid base balance and disturbance. Path IPGME&R 2011. in humans. Am Rev Resp Dis 136(4): 1101-1116. physiology. 24. 8. Mansoor Aquil (2010) Blood gas analysis. composition in normal humans. Kidney Intl 24(5): 670-680. 9. Kurtz I, Mehar T, Hulter HN (1983) Effect of diet on plasma acid base 25. 43-53. Reily RF, Perazella MA (2007) Acid base fluid and electrolyte. Lange 10. Laffey JG, Kavanagh BP (2009) Hypocapnia. N Engl J Med 347(1): instant access 2007 McGraw Hill, New York, USA. 26. Willatts SM (1983) Lecture notes on fluid and electrolytes balance. 27. Adam Cooper. Arterial Blood gas interpretation. Nursing Education. 11. BlackwellLawrence ScientificMartin (1999) Publication, Arterial Oxford, blood UK. gas interpretation. All nd edn), 28. Drmanishasahay. ABC’s of ABG. National Nephrology Journal. Lippincott, Williams, Wilkins, USA, pp. 117-120. evaluation of mixed metabolic acid base disorder. Oman Med J You Need To Know About Arterial Blood Gas Analysis. (2 28(1):Mykola 73-74. V, Tsapenko (2013) Modified delta gap equation for quick 12. Sam Anaerson (1990) Six easy steps to interpreting blood gases. Am 29. Timur Graham (2006) Dr Steven Angus. Stepwise approach to interpreting the arterial blood gas. Acid Base on-line Tutorial. 13. JVishram Nurs 90(8): Buche 42-45. (2009) Arterial blood gases-a systemic approach. 30. doc 14. WorkshopKeary Brandis. module The of six advanced bedside rules.ventilation Anaestheia in Neocon. Education website www.carta.ca/contentFiles/file/pandemic...... /ABGinterpretation. 203.