ACID –BASE DISTURBANCES Dr. A. Zolfaghari Assistant Professor of EM SSU

EVALUATION AND ANALYSIS OF ACID-BASE DISORDERS

Acid-Base Analysis, What do You Need?  Blood gas (pH, CO 2 )  Serum chemistry (Na, Cl, HCO 3 )  Calculator

Acid-Base Normals:  pH= 7.40 ( )  PCO 2 = 40 ( )  HCO 3 = 24 ( )

Henderson-Hasselbach Equation pH [H+]

 [H+]pH          

7.20 PCO2 60 HCO3 24  PH=log(H+)=24 × PCO2/HCO3  7.40 >>> 40=24 × 40/24  PH= 24× 60/24

Important concepts  -emia refers to a pH  -osis refers to an abnormal condition or process

Acidemic vs. Alkalemic  pH < 7.35 = Acidemic  pH > 7.45 = Alkalemic

 Respiratory Acidosis: Acute: 10 mm Hg  PCO2 >>>  1 mEq/L HCO3 Chronic (>5 days of hypercapnia): 10 mm Hg  PCO2 >>>  4 mEq/L HCO3  Respiratory Alkalosis: Acute: 10mmHg  in PCO 2 >>>  2 mEq/L HCO 3 Chronic: 10mmHg  in PCO 2 >>>  4 mEq/L HCO 3  Metabolic Acidosis: PCO 2 = 1.5(HCO 3 ) +8  2  Metabolic Alkalosis: PCO2 = 0.9 (HCO3) mEq/L  HCO3 >>> 0.6  PCO2

Rule 1  Look at the pH. Whichever side of 7.40 the pH is on, the process (CO 2, HCO 3 ) that caused it to shift that way is the primary abnormality. Principle: The body does not fully compensate for a primary acid-base disorder

Keep It Simple:  CO 2 = Acid   CO 2 =  pH (acidemia)   CO 2 =  pH (alkalemia)  HCO 3 = Base   HCO 3 =  pH (alkalemia)   HCO 3 =  pH (acidemia)

Four Primary Disorders:  PCO 2 < 35 = respiratory alkalosis  PCO 2 > 45 = respiratory acidosis  HCO 3 < 22 = metabolic acidosis  HCO 3 > 26 = metabolic alkalosis  Can have mixed pictures with compensation  Can have up to 3 abnormality simultaneously (1 respiratory + 2 metabolic)  The direction of the pH will tell you which is primary!

Example # 1: Blood gas: 7.50 / 29 / 22

 Alkalemic  Low PCO 2 is the primary (respiratory alkalosis)  Acute Respiratory Alkalosis

Acute Respiratory Alkalosis

Example # 2: Blood gas: 7.25 / 60 / 26

 Acidemic  Elevated CO 2 is primary (respiratory acidosis)  Acute Respiratory Acidosis

Acute Respiratory Acidosis

Example # 3: Blood gas: 7.34 / 60 / 31

 Acidemic  Elevated CO 2 is primary (respiratory acidosis)  Metabolic compensation has occurred = chronic process  Chronic Respiratory Acidosis * true metabolic compensation takes 3 days (72hrs)

Chronic Respiratory Acidosis with Metabolic Compensation

Example # 4: Blood gas: 7.50 / 48 / 36

 Alkalemic  Elevated HCO 3 is primary (metabolic alkalosis)  0.9*36+ 9=41  1  HCO3 >>> 0.6  CO2 (12* 0.6=7.2) 48  Metabolic Alkalosis with Respiratory Compensation* *Respiratory compensation takes only minutes

Metabolic Alkalosis with Respiratory Compensation

Example # 5: Blood gas: 7.20 / 21 / 8

 Acidemic  Low HCO 3 Is primary (metabolic acidosis)  Respiratory compensation is present  Metabolic Acidosis with Respiratory Compensation  PH=7.20 >>> PCO2=20

Anion Gap (AG):  The calculated difference between the positively charged (cations) and negatively charged (anions) electrolytes in the body: AG= Na + - (Cl - + HCO 3 - )  Normal AG = 12 ± 2 (10 – 14)

Rule 2  Calculate the anion gap. If the anion gap is  20, there is a primary metabolic acidosis regardless of pH or serum bicarbonate concentration Principle: The body does not generate a large anion gap to compensate for a primary disorder (anion gap must be primary)

Rule 3  Calculate the excess anion gap (total anion gap – normal anion gap) and add this value to the measured bicarbonate concentration:  if the sum is > than normal bicarbonate (> 30) there is an underlying metabolic alkalosis (MAL)  if the sum is less than normal bicarbonate (< 23) there is an underlying nonanion gap metabolic acidosis (NAGMA) 1.Excess AG = Total AG – Normal AG (12) 2.Excess AG + measured HCO 3 = > 30 or < 23?

Remember the Rules 1. Look at the pH: ( 7.40?) whichever caused the shift (CO 2 or HCO 3 ) is the primary disorder 2. Calculate the anion gap: if AG  20 there is a primary metabolic acidosis (regardless of pH or HCO 3 ) 3. Calculate the excess anion gap, add it to HCO 3 : Excess AG = Total AG – Normal AG (12) Excess AG + HCO 3 = ? If sum > 30 there is an underlying metabolic alkalosis If sum < 23 there is an underlying nonanion gap metabolic acidosis

GAP=(calculated AG-12)-(24- measured HCO3)  Values greater than +6 equate to either simultaneous metabolic alkalosis or respiratory acidosis. # Values less than −6 imply a greater loss of HCO3 −, suggesting concurrent respiratory alkalosis or rarely a low-AG state.

Example # 1 Blood gas: 7.50 / 20 / 15 Na= 140,Cl = 103

 Alkalemic  Low CO 2 is primary (respiratory alkalosis)  Partial metabolic compensation for chronic condition?  AG = 22 (primary metabolic acidosis)  Excess AG (AG – 12) + HCO 3 = 25 (no other primary abnormalities)  Respiratory Alkalosis and Metabolic Acidosis The patient ingested a large quantity of ASA and had both centrally mediated resp. alkalosis and anion gap met. Acidosis associated with salicylate overdose

Example # 2 Blood gas: 7.40 / 40 / 24 Na= 145, Cl= 100

 pH normal  AG = 21 (primary metabolic acidosis)  Excess AG (AG – 12) + HCO 3 = 33 ( underlying metabolic alkalosis)  Metabolic Acidosis and Metabolic Alkalosis This patient had chronic renal failure (met. acidosis) and began vomiting (met. alkalosis) as his uremia worsened. The acute alkalosis of vomiting offset the chronic acidosis of renal failure = normal pH

Example # 3 Blood gas 7.50 / 20 / 15 Na= 145, Cl = 100

 Alkalemic  Low CO 2 is primary (respiratory alkalosis)  AG = 30 (primary metabolic acidosis)  Excess AG (AG – 12) + HCO 3 = 33 (underlying metabolic alkalosis)  Respiratory alkalosis & Metabolic Acidosis and Metabolic Alkalosis This patient had a history of vomiting (met. alkalosis), poor oral intake (met. acidosis) and tachypnea secondary to bacterial pneumonia (resp. alkalosis)

How Many Primary Abnormalities Can Exist in One Patient?  Three primary abnormalities is the max because a person cannot simultaneously hyper and hypoventilate  One patient can have both a metabolic acidosis and a metabolic alkalosis – usually one chronic and one acute

Example # 4 Blood gas: 7.10 / 50 / 15 Na= 145, Cl= 100

 Acidemic  High CO 2 and low HCO 3 - both primary (respiratory acidosis and metabolic acidosis)  AG = 30 (metabolic acidosis is anion gap type)  Excess AG + HCO 3 = 33 (underlying metabolic alkalosis)  Respiratory Acidosis, AG Metabolic Acidosis and Metabolic Alkalosis This is an obtunded patient (resp. acidosis) with a history of emesis (metabolic alkalosis) and lab findings c/w diabetic ketoacidosis (metabolic acidosis w/ gap)

Example # 5 Blood gas: 7.15 / 15 / 5 Na= 140, Cl= 110

 Acidemic  Low HCO 3 - primary (metabolic acidosis)  AG= 25 (metabolic acidosis is anion gap type)  Excess AG + HCO 3 = 18 (underlying nonanion gap metabolic acidosis)  Anion Gap and Nonanion gap Metabolic Acidosis Diabetic ketoacidosis was present (anion gap met. acidosis). Patient also had a hyperchloremic nonanion gap met. acidosis secondary to failure to regenerate bicarbonate from ketoacids lost in the urine.

Conclusions:  To do accurate acid-base evaluations you need both blood gas and serum chemistry  Use a systematic approach  Remember the 3 rules  “normal” blood gases may not be normal  It is important to identify all the underlying acid-base in order to appropriately treat the patient

Example # 6  44 yo M 2 weeks post-op from total proctocolectomy for ulcerative colitis.  Na+ 134, K+ 2.9, Cl- 108, HCO3- 16, BUN 31, Cr 1.5 PH=7.31 PCO2=33

Answer 6  Primary Metabolic acidosis 1.5*16+8=30  AG= 132- (108+16)= 10 >>> NL AG  E. GAP= -2+16= 14 >>> NAGMA

Example # 7  9 yo M presents with N/V.  Na 132, Cl 93, HCO3- 11  PH=7.27 PCO2=23

Answer 7  Primary M.Ac. 1.5*11+8=24.5  AG= 132-(11+93)= 28 >>> H AG MAc  E. GAP = 16+11= 27

Example # 8  35 yo M involved in crush injury, boulder vs body.  Na 135, K 5.0, Cl 98, HCO3- 15 BUN 38, Cr 1.7, CK 42,346  BG: 7.30/32/96/15/-4

Answer 8  Primary M.Ac. 1.5*15+8=30.5  AG= 132-(98+15)= 22 >>> H AG MAc  E.GAP= 10+15=25

ABG Examples of Alkalosis Metabolic, Resp., and Mixed NormalSimple Metabolic Resp.Mixed Severe Mixed Mild Na K Cl HCO AG pCO pH

 بورد 86 سوال 7 بيمار 40 ساله ‌ اي به دنبال اسهال دو هفته ‌ اي با ضعف شديد عضلاني به ‌ اورژانس آورده ‌ مي ‌ شود. يافته ‌ هاي آزمايشگاهي به شرح زير است :  Na=140 /k=1.3 / Cl=117 / HCO3=10 / PH=7.26 / PCO2=23 / Ca=6.3 / Alb=6.3  محتمل ‌ ترين اختلال اسيد - باز كدام است؟  الف ) اسيدوز متابوليك خالص با آنيون گپ بالا  ب ) اسيدوز متابوليك خالص با آنيون گپ نرمال  ج ) مخلوط اسيدوز متابوليك با آنيون گپ نرمال و اسيدوز متابوليك با آنيون گپ بالا  د ) اسيدوز متابوليك به هماره ‌ الكالوز متابوليك

جج

  سوال 35 بورد 1385)  - خانم 52 ساله ‌ ي سیگاری برای چک آپ، آزمایش ‌ هایی را از نمونه خون وریدی انجام داده که ذیلاً آمده ‌ اند :  PH=7.3 Na ๋ = 136/mEq/L  PCO 2 =69 mmHg K ๋ = 3.8 mEq/L  HCO 3 =35 mEq/L CL - = 92mEq/L  کدام نتیجه ‌ از نظر وضعیت اسید - باز صحیح است؟  الف - اسیدوز تنفسی  ب - آلکالوز متابولیک به همراه اسیدوز تنفسی  ج - اسیدوز متابولیک به همراه اسیدوز تنفسی  د - اختلال اسید - باز در نمونه وریدی قابل قضاوت نیست

 ج و الف

  سوال 31 بورد 1385)  - در خانم جوانی که بعلت کتواسیدوز دیابتی در اورژانس تحت درمان با انفوزیون نرمال سالین و انسولین قرار دارد، سه ساعت بعد از شروع درمان یافته ‌ های آزمایشگاهی به شرح ذیل است :  Na=140 mEq/L Hco3=14 mEq/L  K=4/1 mEq/L BS=190 mg/dL  C1=106 mEq/L  مناسب ‌ ترین اقدام درمانی کدام است؟  الف - قطع انفوزیون وریدی انسولین و شروع درمان با انسولین زیر جلدی  ب - قطع انفوزیون وریدی انسولین و شروع انفوزیون با محلول دکستروز 5 % در نرمال سالین  ج - قطع انفوزیون نرمال سالین و شروع انفوزیون با محلول دکستروز 5 % در نرمال سالین  د - اندازه ‌ گیری مجدد کتون سرم و سپس تصمیم ‌ گیری نحوه ‌ ي انسولین و مایع داخل وریدی بر اساس نتیجه ‌ ي آن

جج

Example # 2: Blood gas: 7.25 / 60 / 26  Acidemic  Elevated CO 2 is primary (respiratory acidosis)  Acute Respiratory Acidosis  PH=7.25 >>> H+= 56 deltaH=16  PCO2=60 >>> deltaPCO2=20  16/20= 0.8

Example # 1: Blood gas: 7.50 / 29 / 22  Alkalemic  Low PCO 2 is the primary (respiratory alkalosis)  Acute Respiratory Alkalosis  PH=7.50 >>> H+=32 deltaH+=8  PCO2=29 >>> deltaPCO2= 11  8/11=0.73

DELTA GAP= (calculated AG- 12)- (24- measured HCO3) Delta GAP < -6:  mixed high anion gap & non anion gap metabolic acidosis OR  high anion gap metabolic acidosis & chronic respiratory alkalosis & a compesating hyperchloremic acidosis

Delta GAP > 6:  high anion gap metabolic acidosis & primary metabolic alkalosis