Pathophysiology of Acid-Base Disturbances Part II Wanda Lovitz, ARNP

Objectives  Review acid-base concepts discussed last class period Primary acid-base disorders  Causes  Clinical manifestations  ABG interpretation  Treatment  Further discuss compensatory mechanisms in acid-base imbalances Types and levels of compensation  Perform practice exercises

Acid-Base/pH Balance

Primary Vs. Compensatory Mechanisms:  Primary event: The problem that initiates the acid-base imbalance (hypo/hyperventilation; anything causing increase acid in the blood, aka diarrhea; anything causing increase base in the blood, aka ingestion of Tums, vomiting)  Primary disorder: What results from the primary event (resp acidosis or alkalosis; metabolic acidosis or alkalosis)  Compensatory mechanisms: Physiologic activities that adjust the pH toward a more normal level without correcting the underlying cause of the disorder

Interpreting ABG’s: Step 1 1. Look at the pH & determine if it is  (acidosis)  (alkalosis), or normal. Consider 7.0 Neutral *If 7.40 – label “alkalosis” Examples: 7.26 __________ 7.49 __________ 7.38 __________

Interpreting ABG’s: STEP 1 Look at the pH & determine if it is  (acidosis)  (alkalosis), or normal. *If < 7.40, label “acidosis” or “A” *If > 7.40 – label “alkalosis” or “B” for base Examples: 7.26  A “acidosis” 7.49  B “alkalosis” 7.38 normal but more_  A “ACIDOSIS”

Interpreting ABG’s: STEP 2 2. Look at the pCO ² - Is it  (A/acid),  ( B/alkaline), or normal? (If abnormal here…CO2 → RESPIRATORY problem – inverse relationship {  }) ROME = Respiratory Opposite Examples: pH  - pCO²  __________ pH  - pCO²  __________

Interpreting ABG’s: STEP 3 3. Look at the HCO³ - Is it  ( B /alkaline) OR  (A /acid), or normal? (If abnormal here…HCO3, METABOLIC problem – direct relationship { or  }) ROME = Metabolic Equivalent Examples: pH  - HCO³  _________ pH  - HCO³  _________

Remember…pH Points The Way  Which One Matches? pCO²?  or HCO³?  /

Example:  pH 7.52 (  B /alkaline)  pCO ² 37(  normal)  HCO³ 28(  B/ alkaline)  Label this imbalance: metabolic alkalosis

Example  pH 7.29 (  A /acid)  pCO ² 55 (  A /acid)  HCO³ 23(  normal)  Label this imbalance: respiratory acidosis

Now, let’s talk ‘compensation’…

Compensation: 4 Levels  Uncompensated pH abnormal; acid OR base component abnormal  Partially compensated pH abnormal; acid AND base component abnormal  Compensated pH WNL; acid or base imbalance is neutralized, but not corrected; acid or base components are abnormal, but balanced  Corrected pH WNL; all acid or base parameters are returned to WNL after state of imbalance

Interpreting ABG’s: STEP 4 4. Check for compensation Is the body trying to restore normal pH by altering the buffer system which is NOT involved in the imbalance? If compensation has occurred, this value will move in SAME direction as the other component

Apply All 4 Steps…Let’s Try One pH 7.30  A/ acid pCO ² 52  A/acid HCO³ 29  B/alkaline Interpretation: respiratory acidosis, partial compensation Hint : PH points the way.... which value “matches” the PH? Here it is the PCO2 the respiratory indicator, (both are “acid ) so the problem is respiratory acidosis. The kidneys are compensating by retaining bicarbonate (note the compensating mechanism is moving in the SAME direction as the causative component, in this case “increasing”)

Interpreting ABGs….. Another one  PH 7.52  PCO2 48  HCO3 39

Another one… pH 7.52  B /alkaline pCO ² 48  A /acid HCO³ 39  B /alkaline Interpretation: metabolic alkalosis, partial compensation Hint: PH points the way to metabolic problem. BOTH the PH and the bicarb component are on the alkaline side ( the  HCO3 means more base), metaboic alkalosis. The compensatory component is the lungs and the value is moving in the same direction (increasing).

And Another: Mrs. Neace, a 72 year old female with COPD in hospital with URI pH 7.39 pCO² 60 HCO³ 37

And Another: 72 year old female with COPD in hospital with URI pH 7.39  A /more acid pCO² 60  A /acid HCO³ 37  B /alkaline Interpretation: compensated respiratory acidosis Hint: PH is normal, but on the acidic side. The pCO2 is high also indicating acidity (more hydrogen ions). Remember pCO2 combines with H2O to form carbonic acid H2CO3, respiratory acidosis. We know full compensation occurred because the PH is NORMAL.

Another Example: Ally, a seven year old semi-comatose diabetic with Kussmaul breathing pH 7.05 pCO² 12 HCO³ 5

Another Example: 17 year old semi-comatose diabetic with Kussmaul breathing pH 7.05  A /acid pCO² 12  B/alkaline HCO³ 5  A /acid Interpretation: metabolic acidosis, partial compensation Hint: PH points toward acidiosis. Low bicarb (HCO3) indicates low levels of base, so acidotic. PH and HCO3 match so problem is metabolic in nature, metabolic acidosis. Lungs are attempting to compensate by decreasing CO2 (lower hydrogen). The compensating component is moving in the SAME direction.

Another Example: Megan, a 26 year old visibly anxious and hyperventilating pH 7.50 pCO ² 25 HCO³ 25

Another Example: 26 year old visibly anxious and hyperventilating pH 7.50  B/alkaline pCO ² 25  B/alkaline HCO³ 25  Normal Interpretation: respiratory alkalosis, uncompensated Hint: PH pointing toward alkalosis Matching component is pCO2 (low levels so also alkalotic). Therefore, we have respiratoy alkalosis. Bicarb (HCO3 is normal, so no compensation.

Levels Of Compensation: Respiratory Acidosis UncompensatedPartially compensated CompensatedCorrected pH  pCO ²  HCO³  With acidosis we need MORE base to compens ate  With acidosis we need MORE base to compensate

Levels Of Compensation: Respiratory Alkalosis UncompensatedPartially compensated CompensatedCorrected pH  pCO ²   HCO³  with alkalosis we need LESS base to compensate  with alkalosis we need LESS base to compensate

Levels Of Compensation: Metabolic Acidosis UncompensatedPartially compensated CompensatedCorrected pH  pCO ²  With acidosis we need less acid (hydrogen) to compensate  With acidosis we need less acid (hydrogen) to compensate HCO³  

Levels Of Compensation: Metabolic Alkalosis UncompensatedPartially compensated CompensatedCorrected pH   pCO ²   With alkalosis we need MORE acid (hydrogen) to compensate  With alkalosis we need MORE acid (hydrogen) to compensate HCO³ 

Primary Acid-Base Disorders  Respiratory Acidosis Mr. Abner  Respiratory Alkalosis Mrs. Beasley  Metabolic Acidosis Mr. Couch  Metabolic Alkalosis Ms. Dunn

Night Shift In The ER… Primary Acid-Base Disturbance  Causes WHAT IS THE PRIMARY EVENT? WHAT IS THE PRIMARY DISORDER?  Clinical manifestations WHAT DOES THIS PATIENT LOOK LIKE?  Interpret ABG’s WHAT ARE HIS/HER ABG’S? IS THERE ANY COMPENSATION TAKING PLACE YET?  Treatment HOW DO YOU TREAT THIS PATIENT?

Mr. Abner: Respiratory Acidosis  PH 7.25 A ↓  PCO2 67 A ↑  HCO3 24 N ↔  Causes: 58 y/o painter who smokes 1 ppd.  H/O COPD with home oxygen at HS. Became increasingly SOA over the last couple of days. DX: acute exacerbation COPD  Clinical Manifestations: SOA, productive cough of thick green sputum, T 101; RR 26/min; Pulse Ox 89% on RA  Interpretation: Resp Acidosis, uncompensated  Treatment: IV abx, O2 per venturi mask, elevate HOB, Solu Medrol IV

Mrs. Beasley: Respiratory Alkalosis  PH 7.57  B  CO2 30   HCO3 18   Causes: 27 y/o female with acute anxiety attack after hearing her friend was injured in Boston Marathon  Clinical Manifestations: c /o chest pain and numbness in hands. RR 36/min SOA  Interpretation: Resp alkalosis, partial compensation  Treatment: Xanax po, reassurance, O2, breathe into paper bag to increase CO2 levels

Mr. Couch: Metabolic Acidosis  PH 7.36 Normal but more A ↔  PCO2 30 B   HCO3 19 A   Causes: 23 y/o college student with Type I DM. Patient developed diarrhea after eating sushi in the Blue Deli yesterday.  Clinical Manifestations: Liquid stools in the last 24 hours. 5 lb weight loss. Weak. R32/min. Fruity smell to breath. FSBS 412  Interpretation: Metabolic Acidosis, full compensation  Treatment: NPO, IVF, IV Regular insulin

Ms. Dunn: Metabolic Alkalosis  PH 7.52 B   PCO2 38 ↔  HCO3 50 B   Causes: 20 y/o female who began vomiting after drinking at at Keenland on Sat. Roommate found her listless and barely responsive this morning.  Clinical Manifestations: lethargic, poor skin turgor, FC with concentrated urine.  Interpretation: Metabolic Alkalosis, uncompensated  Treatment: IVF, NPO, Phenergan supp