Acid Base

ACID BASE BALANCE&FLUID BALANCE&ABG IINTERPRETATION : ACID BASE BALANCE&FLUID BALANCE&ABG IINTERPRETATION ©2009 , Dr Tanmay Mehta

Slide 2 : Delicate balance of fluid and electrolytes and acids and bases required to maintain good health?

Slide 3 : Homeostasis

Slide 4 : Fluid within cells of body is known as?

Slide 5 : ICF

Slide 6 : Major cation of ICF?

Slide 7 : K+

Slide 8 : Fluid located outside of cell is known as?

Slide 9 : ECF

Slide 10 : Major cation of ECF?

Slide 11 : Na+

Slide 12 : Movement of H2O across cell membranes from less concentrated to more concentrated?

Slide 13 : Osmosis

Slide 14 : Substances dissolved in a liquid are known as?

Slide 15 : Solutes

Slide 16 : The concentration within a fluid is known as?

Slide 17 : Osmolality

Slide 18 : Movement of molecules in liquids from an area of higher concentration to an area of lower concentration is known as?

Slide 19 : Diffusion

Slide 20 : Fluid and solute move together across a membrane from an area of psi to an area of lower psi?

Slide 21 : Filtration

Slide 22 : Substance moves across cell membranes from less concentrated solution to more concentrated solution – requires a carrier?

Slide 23 : Active transport

Slide 24 : List some routes of fluid loss?

Slide 25 : Urine Insensible fluid loss Feces Perspiration

Slide 26 : List major electrolytes?

Slide 27 : Sodium Potassium Chloride Phosphate Magnesium Calcium Bicarbonate

Slide 28 : Acid base balance is the regulation of ____ ions?

Slide 29 : Hydrogen

Slide 30 : The acidity or alkalinity of a solution is measured as ____?

Slide 31 : pH

Slide 32 : The more ____ a solution the lower the pH?

Slide 33 : Acidic

Slide 34 : The more ____ the solution the higher the pH?

Slide 35 : Alkaline

Slide 36 : H2O has a pH of ____ and is neutral?

Slide 37 : 7

Slide 38 : The ____ hydrogen ions, the more acidic the solution and the lower the pH?

Slide 39 : More

Slide 40 : The lower the hydrogen concentration, the more ____ the solution and the higher the pH?

Slide 41 : Alkaline

Slide 42 : Most important buffer system?

Slide 43 : Bicarbonate-carbonic acid buffer system?

Slide 44 : Lungs help regulate acid-base balance by eliminating or retaining ____?

Slide 45 : Carbon dioxide

Slide 46 : Normal CO2 level?

Slide 47 : 35-45

Slide 48 : Kidneys are the ____ regulators of acid base balance?

Slide 49 : Long-term

Slide 50 : Kidneys maintain pH balance by excreting or conserving ____ and ____ ions?

Slide 51 : Bicarbonate, hydrogen

Slide 52 : Normal bicarbonate levels?

Slide 53 : 22-26

Slide 54 : Factors affecting homeostasis?

Slide 55 : Age Gender Body size Environment Lifestyles

Slide 56 : List the acid base imbalances?

Slide 57 : Respiratory acidosis Respiratory alkalosis Metabolic acidosis Metabolic alkalosis

Slide 58 : Signs and symptoms of respiratory acidosis?

Slide 59 : Dyspnea Disorientation Coma Dysrythmias Ph <7.35 PaCo2 >45 Hypokalemia Hyporemia

Slide 60 : Treatment for respiratory acidosis?

Slide 61 : Treat underlying cause Support ventilation Correct electrolyte imbalance IV sodium bicarbonate

Slide 62 : Causes/etiology of respiratory acidosis?

Slide 63 : COPD Neuromuscular disease Respiratory center depression Late ARDS Inadequate mechanical ventilation Sepsis Burns Excess bicarb intake

Slide 64 : Respiratory alkalosis may be caused by hyperventilation due to?

Slide 65 : Anxiety Pain Increased body temp Overventilation with ventilator Hypoxia ASA overdose Hypoxemia CNS trauma/tumor Emphysema Pneumonia

Slide 66 : Signs and symptoms of respiratory alkalosis?

Slide 67 : Tachycardia SOB CP Syncope Coma Seizures Numbness/tingling of extremities Blurred vision pH >7.45 CO2 < 35

Slide 68 : Treatment for respiratory alkalosis?

Slide 69 : Treat underlying cause Assist client to breathe more slowly Breath in paper bag Sedation

Slide 70 : Conditions that may lead to metabolic acidosis?

Slide 71 : Renal failure DKA Starvation Lactic acidosis

Slide 72 : ____ diarrhea may lead to metabolic acidosis?

Slide 73 : Prolonged

Slide 74 : Signs and symptoms of metabolic acidosis?

Slide 75 : Kussmal’s respirations Lethargy HA Weakness N/V pH <7.35 Bicarb <22 CO2 >38

Slide 76 : Acid loss due to vomiting and gastric suction may lead to ____ alkalosis?

Slide 77 : Metabolic

Slide 78 : Overuse of ____ may lead to metabolic alkalosis?

Slide 79 : Antacids

Slide 80 : Signs and symptoms of metabolic alkalosis?

Slide 81 : Hyperventilation Dysrhythmias Dizziness Hypertonic muscle tetany pH >7.45 Bicarb >26 Hypokalemia hypocalcemia

Slide 82 : Treatment metabolic alkalosis?

Slide 83 : Give K+ Treat underlying cause

Slide 84 : List the normal values for Ph PaCO2 HCO3 PaO2 O2 sat

Slide 85 : 7.35-7.45 35-45 22-26 80-100 95-98%

Slide 86 : ROME stands for?

Slide 87 : R – respiratory O – opposite M – metabolic E – equal (arrows go same direction as pH arrow)

ABG INTERPRETATION : ABG INTERPRETATION

Objectives : Objectives What’s an ABG? Understanding Acid/Base Relationship General approach to ABG Interpretation Clinical causes Abnormal ABG’s Case studies Take home

What is an ABG : What is an ABG Arterial Blood Gas Drawn from artery- radial, brachial, femoral It is an invasive procedure. Caution must be taken with patient on anticoagulants. Helps differentiate oxygen deficiencies from primary ventilatory deficiencies from primary metabolic acid-base abnormalities

What Is An ABG? : What Is An ABG? pH [H+] PCO2 Partial pressure CO2 PO2 Partial pressure O2 HCO3 Bicarbonate BE Base excess SaO2 Oxygen Saturation

Acid/Base Relationship : Acid/Base Relationship This relationship is critical for homeostasis Significant deviations from normal pH ranges are poorly tolerated and may be life threatening Achieved by Respiratory and Renal systems

Case Study No. 1 : Case Study No. 1 60 y/o male comes ER c/o SOB. Tachypneic, tachycardic, diaphoretic and Cyanotic. Dx acute resp. failure and ABG’s Show PaCO2 well below nl, pH above nl, PaO2 is very low. The blood gas document Resp. failure due to primary O2 problem.

Case Study No. 2 : Case Study No. 2 60 y/o male comes ER c/o SOB. Tachypneic, tachycardic, diaphoretic and Cyanotic. Dx acute resp. failure and ABG’s Show PaCO2 very high, low pH and PaO2 is moderately low. The blood gas document Resp. failure due to primarily ventilatory insufficiency.

Buffers : There are two buffers that work in pairs H2CO3 NaHCO3Carbonic acid base bicarbonate These buffers are linked to the respiratory and renal compensatory system Buffers

Respiratory Component : Respiratory Component function of the lungs Carbonic acid H2CO3 Approximately 98% normal metabolites are in the form of CO2 CO2 + H2O ? H2CO3 excess CO2 exhaled by the lungs

Metabolic Component : Metabolic Component Function of the kidneys base bicarbonate Na HCO3 Process of kidneys excreting H+ into the urine and reabsorbing HCO3- into the blood from the renal tubules 1) active exchange Na+ for H+ between the tubular cells and glomerular filtrate 2) carbonic anhydrase is an enzyme that accelerates hydration/dehydration CO2 in renal epithelial cells

Acid/Base Relationship : H2O + CO2 ? H2CO3 ? HCO3 + H+ Acid/Base Relationship

Normal ABG values : Normal ABG values pH 7.35 – 7.45 PCO2 35 – 45 mmHg PO2 80 – 100 mmHg HCO3 22 – 26 mmol/L BE -2 - +2 SaO2 >95%

Acidosis Alkalosis : Acidosis Alkalosis pH < 7.35 PCO2 > 45 HCO3 < 22 pH > 7.45 PCO2 < 35 HCO3 > 26

Respiratory Acidosis : Respiratory Acidosis Think of CO2 as an acid failure of the lungs to exhale adequate CO2 pH < 7.35 PCO2 > 45 CO2 + H2CO3 ? ? pH

Causes of Respiratory Acidosis : Causes of Respiratory Acidosis emphysema drug overdose narcosis respiratory arrest airway obstruction

Metabolic Acidosis : Metabolic Acidosis failure of kidney function ? blood HCO3 which results in ? availability of renal tubular HCO3 for H+ excretion pH < 7.35 HCO3 < 22

Causes of Metabolic Acidosis : Causes of Metabolic Acidosis renal failure diabetic ketoacidosis lactic acidosis excessive diarrhea cardiac arrest

Respiratory Alkalosis : Respiratory Alkalosis too much CO2 exhaled (hyperventilation) ? PCO2, H2CO3 insufficiency = ? pH pH > 7.45 PCO2 < 35

Causes of Respiratory Alkalosis : Causes of Respiratory Alkalosis hyperventilation panic d/o pain pregnancy acute anemia salicylate overdose

Metabolic Alkalosis : Metabolic Alkalosis ? plasma bicarbonate pH > 7.45 HCO3 > 26

Causes of Metabolic Alkalosis : Causes of Metabolic Alkalosis ? loss acid from stomach or kidney hypokalemia excessive alkali intake

How to Analyze an ABG : How to Analyze an ABG PO2 NL = 80 – 100 mmHg 2. pH NL = 7.35 – 7.45 Acidotic <7.35 Alkalotic >7.45 PCO2 NL = 35 – 45 mmHg Acidotic >45 Alkalotic <35 HCO3 NL = 22 – 26 mmol/L Acidotic < 22 Alkalotic > 26

Four-step ABG Interpretation : Four-step ABG Interpretation Step 1: Examine PaO2 & SaO2 Determine oxygen status Low PaO2 (<80 mmHg) & SaO2 means hypoxia NL/elevated oxygen means adequate oxygenation

Four-step ABG Interpretation : Step 2: pH acidosis <7.35 alkalosis >7.45 Four-step ABG Interpretation

Four-step ABG Interpretation : Step 3: study PaCO2 & HCO 3 respiratory irregularity if PaCO2 abnl & HCO3 NL metabolic irregularity if HCO3 abnl & PaCO2 NL Four-step ABG Interpretation

Four-step ABG Interpretation : Step 4: Determine if there is a compensatory mechanism working to try to correct the pH. ie: if have primary respiratory acidosis will have increased PaCO2 and decreased pH. Compensation occurs when the kidneys retain HCO3. Four-step ABG Interpretation

~ PaCO2 – pH Relationship : ~ PaCO2 – pH Relationship 80 7.2060 7.3040 7.4030 7.5020 7.60

ABG Interpretation : Compensated Respiratory Acidosis CO2 More Abnormal Respiratory Acidosis CO2 Expected Mixed Respiratory Metabolic Acidosis CO2 Less Abnormal CO2 Change c/w Abnormality Metabolic Metabolic Acidosis CO2 Normal Compensated Metabolic Acidosis CO2 Change opposes Abnormality Acidosis ABG Interpretation

ABG Interpretation : Compensated Respiratory Alkalosis CO2 More Abnormal Respiratory Alkalosis CO2 Expected Mixed Respiratory Metabolic Alkalosis CO2 Less Abnormal CO2 Change c/w Abnormality Metabolic Alkalosis CO2 Normal Compensated Metabolic Alkalosis CO2 Change opposes Abnormality Alkalosis ABG Interpretation

Respiratory Acidosis : Respiratory Acidosis pH 7.30 PaCO2 60 HCO3 26

Respiratory Alkalosis : Respiratory Alkalosis pH 7.50 PaCO2 30 HCO3 22

Metabolic Acidosis : Metabolic Acidosis pH 7.30 PaCO2 40 HCO3 15

Metabolic Alkalosis : Metabolic Alkalosis pH 7.50 PCO2 40 HCO3 30

What are the compensations? : What are the compensations? Respiratory acidosis ? metabolic alkalosis Respiratory alkalosis ? metabolic acidosis In respiratory conditions, therefore, the kidneys will attempt to compensate and visa versa. In chronic respiratory acidosis (COPD) the kidneys increase the elimination of H+ and absorb more HCO3. The ABG will Show NL pH, ?CO2 and ?HCO3. Buffers kick in within minutes. Respiratory compensation is rapid and starts within minutes and complete within 24 hours. Kidney compensation takes hours and up to 5 days.

Mixed Acid-Base Abnormalities : Mixed Acid-Base Abnormalities Case Study No. 3: 56 yo ? ? neurologic dz required ventilator support for several weeks. She seemed most comfortable when hyperventilated to PaCO2 28-30 mmHg. She required daily doses of lasix to assure adequate urine output and received 40 mmol/L IV K+ each day. On 10th day of ICU her ABG on 24% oxygen & VS:

ABG Results : ABG Results pH 7.62 BP 115/80 mmHg PCO2 30 mmHg Pulse 88/min PO2 85 mmHg RR 10/min HCO3 30 mmol/L VT 1000ml BE 10 mmol/L MV 10L K+ 2.5 mmol/L Interpretation: Acute alveolar hyperventilation (resp. alkalosis) and metabolic alkalosis with corrected hypoxemia.

Case study No. 4 : Case study No. 4 27 yo retarded ? with insulin-dependent DM arrived at ER from the institution where he lived. On room air ABG & VS: pH 7.15 BP 180/110 mmHg PCO2 22 mmHg Pulse 130/min PO2 92 mmHg RR 40/min HCO3 9 mmol/L VT 800ml BE -30 mmol/L MV 32L Interpretation: Partly compensated metabolic acidosis.

Case study No. 5 : Case study No. 5 74 yo ? with hx chronic renal failure and chronic diuretic therapy was admitted to ICU comatose and severely dehydrated. On 40% oxygen her ABG & VS: pH 7.52 BP 130/90 mmHg PCO2 55 mmHg Pulse 120/min PO2 92 mmHg RR 25/min HCO3 42 mmol/L VT 150ml BE 17 mmol/L MV 3.75L Interpretation: Partly compensated metabolic alkalosis with corrected hypoxemia.

Case study No. 6 : Case study No. 6 43 yo ? arrives in ER 20 minutes after a MVA in which he injured his face on the dashboard. He is agitated, has mottled, cold and clammy skin and has obvious partial airway obstruction. An oxygen mask at 10 L is placed on his face. ABG & VS: pH 7.10 BP 150/110 mmHg PCO2 60 mmHg Pulse 150/min PO2 125 mmHg RR 45/min HCO3 18 mmol/L VT ? ml BE -15 mmol/L MV ? L . Interpretation: Acute ventilatory failure (resp. acidosis) and acute metabolic acidosis with corrected hypoxemia

Case study No. 7 : Case study No. 7 17 yo, 48 kg ? with known insulin-dependent DM came to ER with Kussmaul breathing and irregular pulse. Room air ABG & VS: pH 7.05 BP 140/90 mmHg PCO2 12 mmHg Pulse 118/min PO2 108 mmHg RR 40/min HCO3 5 mmol/L VT 1200ml BE -30 mmol/L MV 48L Interpretation: Severe partly compensated metabolic acidosis without hypoxemia.

Case No. 7 cont’d : Case No. 7 cont’d This patient is in diabetic ketoacidosis. IV glucose and insulin were immediately administered. A judgement was made that severe acidemia was adversely affecting CV function and bicarb was elected to restore pH to ? 7.20. Bicarb administration calculation: Base deficit X weight (kg) 4 30 X 48 = 360 mmol/L Admin 1/2 over 15 min & 4 repeat ABG

Case No. 7 cont’d : Case No. 7 cont’d ABG result after bicarb: pH 7.27 BP 130/80 mmHg PCO2 25 mmHg Pulse 100/min PO2 92 mmHg RR 22/min HCO3 11 mmol/L VT 600ml BE -14 mmol/L MV 13.2L

Case study No. 8 : Case study No. 8 47 yo ? was in PACU for 3 hours s/p cholecystectomy. She had been on 40% oxygen and ABG & VS: pH 7.44 BP 130/90 mmHg PCO2 32 mmHg Pulse 95/min, regular PO2 121 mmHg RR 20/min HCO3 22 mmol/L VT 350ml BE -2 mmol/L MV 7L SaO2 98% Hb 13 g/dL

Case No. 8 cont’d : Case No. 8 cont’d Oxygen was changed to 2L N/C. 1/2 hour pt. ready to be D/C to floor and ABG & VS: pH 7.41 BP 130/90 mmHg PCO2 10 mmHg Pulse 95/min, regular PO2 148 mmHg RR 20/min HCO3 6 mmol/L VT 350ml BE -17 mmol/L MV 7L SaO2 99% Hb 7 g/dL

Case No. 8 cont’d : Case No. 8 cont’d What is going on?

Case No. 8 cont’d : Case No. 8 cont’d If the picture doesn’t fit, repeat ABG!! pH 7. 45 BP 130/90 mmHg PCO2 31 mmHg Pulse 95/min PO2 87 mmHg RR 20/min HCO3 22 mmol/L VT 350ml BE -2 mmol/L MV 7L SaO2 96% Hb 13 g/dL Technical error was presumed.

Case study No. 9 : Case study No. 9 67 yo ? who had closed reduction of leg fx without incident. Four days later she experienced a sudden onset of severe chest pain and SOB. Room air ABG & VS: pH 7.36 BP 130/90 mmHg PCO2 33 mmHg Pulse 100/min PO2 55 mmHg RR 25/min HCO3 18 mmol/L BE -5 mmol/L MV 18L SaO2 88% Interpretation: Compensated metabolic acidosis with moderate hypoxemia. Dx: PE

Case study No. 10 : Case study No. 10 76 yo ? with documented chronic hypercapnia secondary to severe COPD has been in ICU for 3 days while being tx for pneumonia. She had been stable for past 24 hours and was transferred to general floor. Pt was on 2L oxygen & ABG &VS: pH 7.44 BP 135/95 mmHg PCO2 63 mmHg Pulse 110/min PO2 52 mmHg RR 22/min HCO3 42 mmol/L BE +16 mmol/L MV 10L SaO2 86% . Interpretation: Chronic ventilatory failure (resp. acidosis) with uncorrected hypoxemia

Case No. 10 cont’d : Case No. 10 cont’d She was placed on 3L and monitored for next hour. She remained alert, oriented and comfortable. ABG was repeated: pH 7.36 BP 140/100 mmHg PCO2 75 mmHg Pulse 105/min PO2 65 mmHg RR 24/min HCO3 42 mmol/L BE +16 mmol/L MV 4.8L SaO2 92% . Pt’s ventilatory pattern has changed to more rapid and shallow breathing. Although still acceptable the pH and CO2 are trending in the wrong direction. High-flow oxygen may be better for this pt to prevent intubation

Take Home Message: : Take Home Message: Valuable information can be gained from an ABG as to the patients physiologic condition Remember that ABG analysis if only part of the patient assessment. Be systematic with your analysis, start with ABC’s as always and look for hypoxia (which you can usually treat quickly), then follow the four steps. A quick assessment of patient oxygenation can be achieved with a pulse oximeter which measures SaO2.

It’s not magic understanding ABG’s, it just takes a little practice! : It’s not magic understanding ABG’s, it just takes a little practice!

Practice ABG’s : Practice ABG’s PaO2 90 SaO2 95 pH 7.48 PaCO2 32 HCO3 24 PaO2 60 SaO2 90 pH 7.32 PaCO2 48 HCO3 25 PaO2 95 SaO2 100 pH 7.30 PaCO2 40 HCO3 18 PaO2 87 SaO2 94 pH 7.38 PaCO2 48 HCO3 28 PaO2 94 SaO2 99 pH 7.49 PaCO2 40 HCO3 30 6. PaO2 62 SaO2 91 pH 7.35 PaCO2 48 HCO3 27 PaO2 93 SaO2 97 pH 7.45 PaCO2 47 HCO3 29 PaO2 95 SaO2 99 pH 7.31 PaCO2 38 HCO3 15 PaO2 65 SaO2 89 pH 7.30 PaCO2 50 HCO3 24 10. PaO2 110 SaO2 100 pH 7.48 PaCO2 40 HCO3 30

Answers to Practice ABG’s : Answers to Practice ABG’s Respiratory alkalosis Respiratory acidosis Metabolic acidosis Compensated Respiratory acidosis Metabolic alkalosis Compensated Respiratory acidosis Compensated Metabolic alkalosis Metabolic acidosis Respiratory acidosis Metabolic alkalosis