Transcript GRAPHS
Acid-Base Disorders
Sharon Anderson, M.D.
Division of Nephrology and Hypertension May 2003
General Acid-Base Relationships
Henderson-Hasselbach equation: pH = pK + log HCO 3 _ /pCO 2 H + = 24 x pCO 2 /HCO 3 _
0.1 pH unit =
10 nm/L H +
Approach to Acid-Base Disorders
1. Consider the clinical setting!
2. Is the patient acidemic or alkalemic?
3. Is the primary process metabolic or respiratory?
4. If metabolic acidosis, gap or non-gap?
5. Is compensation appropriate?
6. Is more than one disorder present?
Simple Acid-Base Disorders Disorder Metabolic acidosis Metabolic alkalosis Respiratory acidosis Respiratory alkalosis pH H + Primary Compensatory Disorder Response HCO 3 _ pCO 2 HCO 3 _ pCO 2 pCO pCO 2 2 HCO 3 _ HCO 3 _
Metabolic Acidosis Etiology: Inability of the kidney to excrete the dietary H + load, or increase in the generation of H + (due to addition of H+ or loss of HCO 3 )
Metabolic Acidosis: Elevated Anion Gap
AG = Na + - (Cl + HCO 3 ) = 12 ± 2 [Note: Diagnostic utility is best when AG > 25] Causes: Ketoacidosis Lactic acidosis Intoxications Renal failure Rhabdomyolysis
Anion Gap in Hypoalbuminemia The true anion gap is underestimated in hypoalbuminemia (= fall in unmeasured anions); AG must be adjusted Formulas for adjusted AG: – –
For every 1.0 fall in albumin, increase AG by 2.5
Consider the patient’s “normal” AG to be (2 x alb) + (0.5 x phosphate) – Adjusted AG = Observed AG + (2.5 x [normal alb adjusted alb]
Ketosis
Diabetes Starvation Alcoholic Isopropyl alcohol* * Ketosis with normal AG and HCO 3 _
Ketosis: Points to Remember -- Normal AG and HCO 3 _ = isopropyl alcohol -- Beta-hydroxbutyrate not seen by ketotest -- Acetoacetate spuriously Cr -- False positive ketotest: paraldehyde, disulfiram, captopril
Lactic Acidosis Type A: Type B: Hypoxic Lactate:pyruvate > 10:1 Glycolytic Lactate:pyruvate = 10:1
Intoxications Causing High AG Acidosis
Aspirin - [high salicylate level; also primary respiratory alkalosis]
Methanol - [optic papillitis]
Ethylene Glycol - [calcium oxalate crystals]
Paraldehyde
Use of venous vs. arterial pH
As compared with arterial blood gasses: pH pCO 2 HCO 3 0.03-0.04
7-8 mmHg 2 mEq/L
The Delta/Delta: AG/ HC0 3 Rationale: For each unit INCREASE in AG (above normal), HC0 3 should DECREASE one unit (below normal) “Normal” values: AG = 12, HC0 3 = 24
Use of the Delta/Delta: Examples AG HCO3 Diagnosis 18 ( 18 ( 6) 6) 18 ( 6) 18 ( 22 ( 12 ( 6) 2) Appropriate; pure AG acidosis HCO 3 has less than predicted, so HCO 3 is too high; mixed AG acidosis AND met alk 12) HCO3 has more than predicted, so HCO 3 is too low; mixed AG AND non-AG acidosis
Causes of Low Anion Gap Etiology: Fall in unmeasured anions or rise in unmeasured cations Hyperkalemia Lithium intoxication Hypercalcemia Hypermagnesemia Multiple myeloma Artefactual: hypernatremia, bromide, hyperlipidemia
Osmolar Gap Measured serum osmolality > calculated serum osmolality by > 10 mOsm Calc Sosm = (2 x Na) + BUN/2.8 + Glu/18
Causes of High Osmolar Gap Isotonic hyponatremia Hyperlipidemia Hyperproteinemia Mannitol Glycine infusion Chronic renal failure Ingestions Ethanol, isopropyl alcohol, ethylene glycol, mannitol Contrast Media
Relationship between AG and Osmolar Gap AG Ethylene glycol Methanol
+ +
Renal failure
+
Isopropyl alcohol
-
Ethanol Lipids, proteins
-
Osm gap
+ + + + + +
Comments * Double gap * Double gap * Double gap
Causes of Normal AG (Hyperchloremic) Metabolic Acidosis
High K + Low K + Adrenal insufficiency Interstitial nephritis NH 4 Cl, Arg HCl Diarrhea RTA Ureteral diversion
Use of the Urine Anion Gap (UAG) in Normal AG Acidosis Batlle et al. NEJM 318:594, 1988 Urine AG = (Na + K) - Cl Negative UAG = Normal, or GI loss of HCO 3 Positive UAG = altered distal renal acidification Caveats: Less accurate in patients with volume depletion (low urinary Na); and in patients with increased excretion of unmeasured anions (e.g. ketoacidosis), where there is increased excretion of Na and K to maintain electroneutrality)
Use of the Urinary AG in Normal Gap Acidosis Batlle et al. NEJM 318:594, 1988
Plasma K Normal Normal-low High High Normal-low UAG + + + U pH < 5.5
> 5.5
< 5.5
> 5.5
> 5.5
Diagnosis Normal GI HCO 3 loss Aldo deficiency Distal RTA Proximal RTA
Use of the Urine Osmolal Gap When UAG is positive, and it is unclear if increased cation excretion is responsible, urine NH can be estimated from urine osmolal gap 4 concentration Calc Uosm = (2 x [Na+K]) + urea nitrogen/2.8 + glu/18 The gap between the calculated and measured Uosm = mostly ammonium In patients with metabolic acidosis, urine ammonium should be > 20 mEq/L. Lower value = impaired acidification
Renal Tubular Acidosis
Type 1 (distal) Type 2 (proximal) Type 4 Defect HCO 3 Urine pH Plasma K Response to HCO 3 Rx distal acid. May be < 10 prox HCO 3 12-20 reab aldo > 17 > 5.3
Variable < 5.3
Usually low Good Usually low Poor High Fair
Calculation of Bicarbonate Deficit Bicarb deficit = HCO 3 space x HCO 3 deficit/liter HCO 3 space =
0.4
x lean body wt (kg) HCO 3 deficit/liter = [desired HCO 3 ] - [measured HCO 3 ]
Approach to Metabolic Acidosis Osmolar Gap High Anion Gap Normal Normal Uremia Lactate Ketoacids Salicylate Increased Ethylene glycol Methanol GI Fluid Loss?
Diarrhea Ileostomy Enteric fistula Yes Distal RTA (Type 1) No > 5.5
Urine pH < 5.5
Serum K High Low Proximal RTA (Type 2) Type 4 RTA
Metabolic Alkalosis Etiology: Requires both generation of metabolic alkalosis (loss of H + through GI tract or kidneys) and maintenance of alkalosis (impairment in renal HCO 3 Causes of metabolic alkalosis excretion) Loss of hydrogen Retention of bicarbonate Contraction alkalosis Maintenance factors: Decrease in GFR, increase in HCO 3 reabsorption
Use of Spot Urine Cl and K Urine Chloride Very Low (< 10 mEq/L) Vomiting, NG suction Postdiuretic, posthypercapneic Villous adenoma, congenital chloridorrhea, post- alkali > 20 mEq/L Urine Potassium > 30 mEq/L Low (< 20 mEq/L) Laxative abuse Other profound K depletion Diuretic phase of diuretic Rx, Bartter’s, Gitelman’s, primary aldo, Cushings, Liddle’s, secondary aldosteronism
Treatment of Metabolic Alkalosis 1. Remove offending culprits.
2. Chloride (saline) responsive alkalosis: Replete volume with NaCl.
3. Chloride non-responsive (saline resistant) alkalosis: Acetazolamide (CA inhibitor) Hydrochloric acid infusion Correct hypokalemia if present
Calculation of Bicarbonate Excess Bicarb excess = HCO 3 space x HCO 3 excess/liter HCO 3 space =
0.5
x lean body wt (kg) HCO 3 excess/liter = [measured HCO 3 ] - [desired HCO 3 ]
Respiratory Acidosis
Causes of Respiratory Acidosis Inhibition of medullary respiratory center Disorders of respiratory muscles and chest wall Upper airway obstruction Disorders affecting gas exchange across pulmonary capillaries Mechanical ventilation
Respiratory Alkalosis Causes of Respiratory Alkalosis Hypoxemia Pulmonary disease Stimulation of medullary respiratory center Mechanical ventilation
Mixed Acid-Base Disorders: Clues -- Degree of compensation for primary disorder is inappropriate -- Delta AG/delta HCO 3 _ = too high or too low -- Clinical history
Problem 1 A 30-yo man with DM presents with a week of polyuria, polydipsia, fever to 102, nausea, and abdominal pain. He is orthostatic on admission. 130
I
94
I
75
I
906 6.1
I
6
I
2.3
pH 7.14
pCO 2 18 pO 2 102
130
I
94
I
75
I
906 7.14/18/102 Problem 1, cont.
6.1
I
6
I
2.3
1. Anticipate the disorder DKA (with anion gap acidosis) 2. Acidemic or alkalemic? 3. Metabolic or respiratory?
pH = acidemic; must be metabolic (low HCO 3 , low pCO 2 ) 4. If metabolic acidosis: gap or non-gap?
AG = 30; + anion gap metabolic acidosis 5. Is compensation appropriate?
pCO2 should = last 2 digits of pH [18] or (1.5 x HCO 3 ) + 8 [17] 6. Mixed disorder?
AG = 30 ( 18); HCO 3 = 6 ( 18); thus simple AG met acidosis
Problem 2 A 30-yo man with DM presents with a week of polyuria, polydipsia, fever to 102, and vomiting for four days. 135
I
6.1
I
89
I
50
I
1181 10
I
2.3
pH 7.26
pCO 2 pO 2 23 88
135 I 89 I 50 I 1181 7.26/23/88
Problem 2, cont.
6.1 I 10 I 2.3
1. Anticipate the disorder DKA (AG acidosis); met alk from vomiting 2. Acidemic or alkalemic? 3. Metabolic or respiratory?
pH = acidemic; must be metabolic (low HCO 3 , low pCO 2 ) 4. If metabolic acidosis: gap or non-gap?
AG = 36; + anion gap metabolic acidosis 5. Is compensation appropriate?
pCO2 should = last 2 digits of pH [26] or (1.5 x HCO 3 ) + 8 [23] 6. Mixed disorder?
AG = 36 ( 24); HCO 3 = 10 ( 14); HCO 3 is too high; mixed AG metabolic acidosis and metabolic alkalosis
Problem 3 A 30-yo man with DM presents with a week of polyuria, polydipsia, fever to 102, and diarrhea.
138
I
111
I
49
I
650 5.5
I
8
I
1.4
pH 7.26
pCO 2 23 pO 2 88
138 I 111 I 49 I 650 7.26/23/88
Problem 3, cont.
1. Anticipate the disorder
5.51 I 8 I 1.4
DKA (AG acidosis); nongap met acidosis from diarrhea 2. Acidemic or alkalemic? 3. Metabolic or respiratory?
pH = acidemic; must be metabolic (low HCO 3 , low pCO 2 ) 4. If metabolic acidosis: gap or non-gap?
AG = 19; + anion gap metabolic acidosis 5. Is compensation appropriate?
pCO2 should = last 2 digits of pH [26] or (1.5 x HCO 3 ) + 8 [23] 6. Mixed disorder?
AG = 19 ( 7); HCO 3 = 8 ( 16); HCO 3 is too low; mixed AG metabolic acidosis and metabolic acidosis (nongap)
Problem 4 A 30-yo man with DM presents with a week of polyuria, polydipsia, fever, cough, and prurulent sputum.
140
I
104
I
75
I
1008 7.0
I
7
I
2.6
pH 6.95
pCO 2 33 pO 2 60
140 I 104 I 75 I 1008 6.95/33/60
Problem 4, cont.
7.0 I 7 I 2.6
1. Anticipate the disorder DKA (AG acidosis); resp alk or resp acidosis from hypoxemia/pneumonia 2. Acidemic or alkalemic? 3. Metabolic or respiratory?
pH = acidemic; must be metabolic (low HCO 3 , low pCO 2 ) 4. If metabolic acidosis: gap or non-gap?
AG = 29; + anion gap metabolic acidosis
140 I 104 I 75 I 1008 6.95/33/60
Problem 4, cont.
7.0 I 7 I 2.6
5. Is compensation appropriate?
pCO 2 should = last 2 digits of pH [95!!] or (1.5 x HCO 3 ) + 8 [18]; pCO 2 is too high so he has a superimposed respiratory acidosis 6. Mixed disorder?
AG = 29 ( 17); HCO 3 = 7 ( 17); so metabolic acidosis is pure AG acidosis. Thus, mixed AG metabolic acidosis and respiratory acidosis
Problem 5 A 31-yo woman who is 33 weeks pregnant presents with a 2-day history of vomiting. 140
I
104
I
3.0
I
26
I
8 0.6
I
85 pH 7.64
pCO 2 25 pO 2 93
140 I 104 I 8 I 85 7.64/25/93
Problem 5, cont.
3.0 I 26 I 0.6
1. Anticipate the disorder Pregnancy: resp alk Vomiting: met alk 2. Acidemic or alkalemic? pH = alkalemic 3. Metabolic or respiratory?
If resp, HCO 3 should be low; if metabolic, then pCO 2 should be high; must have both 4. If metabolic acidosis: gap or non-gap? N/A; no acidosis; no AG
140 I 104 I 8 I 85 7.64/25/93
Problem 5, cont.
3.0 I 26 I 0.6
5. Is compensation appropriate?
NO (by eyeball, for reasons listed above) 6. Mixed disorder?
Yes, mixed metabolic and respiratory alkalosis. No acidosis component.
Problem 6 A 60-yo man has crushing chest pain, SOB and diaphoresis. He has HTN, for which he takes HCTZ. Exam shows BP 88/60, bilateral crackles, S3. EKG shows ischemia; CXR = pulmonary edema.
140
I
5.9
I
94
I
20
I
45
I
300 1.9
pH 7.14
pCO 2 60 pO 2 52
140 I 94 I 45 I 300 7.14/60/52
Problem 6, cont.
1. Anticipate the disorder
5.9 I 20 I 1.9
Pulm edema -> resp alk or resp acidosis; shock -> metabolic acidosis; HCTZ -> metabolic alkalosis 2. Acidemic or alkalemic? pH = acidemic 3. Metabolic or respiratory?
If resp, HCO 3 should be > 24 in compensation; if metabolic, then pCO 2 should < 40; must have both respiratory and metabolic acidoses 4. If metabolic acidosis: gap or non-gap? AG = 26; + anion gap metabolic acidosis
140 I 94 I 45 I 300 7.14/60/52
Problem 6, cont.
5.9 I 20 I 1.9
5. Is compensation appropriate?
NO (by eyeball, for reasons listed above) 6. Mixed disorder? Anything else?
AG = 26 ( 14); HCO 3 = 20 ( 4 ); so HCO 3 is too high; must have a superimposed metabolic alkalosis. Thus, triple disorder: respiratory acidosis, anion gap metabolic acidosis, and metabolic alkalosis
Problem 7 A 55-yo woman with a history of a CVA presents to clinic complaining of shortness of breath. 140
I
3.9
I
100
I
30
I
30 1.5
I
115 pH 7.36
pCO 2 38 pO 2 91
140 I 100 I 30 I 115 7.36/38/91
Problem 7, cont.
3.9 I 30 I 1.5
1. Anticipate the disorder Resp alk due to CNS disorder or acute pulmonary process 2. Acidemic or alkalemic? pH = acidemic 3. Metabolic or respiratory? 4. If metabolic acidosis: AG? HCO 3 is high (not metabolic acidosis); pCO 2 is < 40 (not respiratory acidosis); AG is normal (10), so what’s going on??
140 I 100 I 30 I 115 7.36/38/91
Problem 7, cont.
3.9 I 30 I 1.5
LAB ERROR!
By Henderson-Hasselbach H+ = 24 x pCO 2 /HCO 3 = 24 x (38/30) = 30 pH should be 7.50
Problem 8 You are in the ER, and are aware that the lab has been having intermittent problems with the chemistry autoanalyzer. A 30-yo diabetic man, well known to you from previous visits, comes in with severe nausea and vomiting. His blood alcohol level is very high. The ER attending advises you to check his labs and send him home if they are OK.
140
I
84
I
28
I
160 3.0
I
24
I
1.3
pH 7.40
pCO 2 pO 2 40 88
Problem 8, cont.
140 I 84 I 28 I 160 7.40/40/88 3.0 I 24 I 1.3
1. Anticipate the disorder Vomiting -> met alk; if unconscious, resp acidosis 2. Acidemic or alkalemic? 3. Metabolic or respiratory?
pH, pCO 2 disorder and HC0 3 are all normal --> no apparent 4. Lab error? Check H-H equations.
H+ = 24 x (pCO 2 /HCO 3 ) = 24 x (40/24) = 40, so pH = 7.40
5. Do you send him home?
Problem 8, cont.
140 I 84 I 28 I 160 7.40/40/88 3.0 I 24 I 1.3
5. Do you send him home?
AG = 32; + anion gap acidosis AG = 32 ( 20); HCO 3 = 24 ( 0); so HCO 3 have a superimposed metabolic alkalosis. is too high; must Thus, mixed AG acidosis and metabolic alkalosis
Problem 9 A 58-yo man with cirrhosis and Type 2 DM presents with fever, abdominal pain, SOB, and vomiting.
159
I
112
I
55
I
160 3.3
I
12
I
2.8
pH 7.31
pCO 2 19 pO 2 77
159 I 112 I 55 I 160 7.31/19/77
Problem 9, cont.
3.3 I 12 I 2.8
1. Anticipate the disorder Renal dis --> acidosis; dead gut --> lactic acidosis; vomiting --> met alk; pain --> resp alk; liver disease --> resp alk 2. Acidemic or alkalemic? 3. Metabolic or respiratory?
pH = acidemic; must be metabolic (low HCO 3 , low pCO 2 ) 4. If metabolic acidosis: gap or non-gap?
AG = 35; + anion gap metabolic acidosis
159 I 112 I 55 I 160 7.31/19/77
Problem 9, cont.
3.3 I 12 I 2.8
5. Is compensation appropriate?
pCO 2 should = last 2 digits of pH [31; not] or (1.5 x HCO 3 ) + 8 [26]; pCO 2 is too low so he has a superimposed respiratory alkalosis 6. Mixed disorder?
AG = 35 ( 23); HCO 3 = 12 ( 12); so HCO 3 is too high, so there must be a metabolic alkalosis.
Thus, triple disorder: AG metabolic acidosis, respiratory alkalosis, and metabolic alkalosis
Problem 10 A 70-yo man presents with vomiting and abdominal pain, for which he has been taking Rolaids. He is hypotensive and has a tender abdomen.
140
I
3.4
I
69
I
40
I
118 40
I
1.5
pH 7.74
pCO 2 30 pO 2 105
140 I 69 I 40 I 118 7.74/30/105
Problem 10, cont.
3.4 I 40 I 1.5
1. Anticipate the disorder Dead gut --> lactic acidosis; vomiting or Rolaids --> met alk; pain --> resp alk 2. Acidemic or alkalemic? 3. Metabolic or respiratory?
pH = alkalemic; must be both metabolic (high HCO 3 ) and respiratory (low pCO 2 ) 4. If metabolic acidosis: gap or non-gap?
AG = 31; + anion gap metabolic acidosis
140 I 69 I 40 I 118 7.74/30/105
Problem 10, cont.
3.4 I 40 I 1.5
5. Is compensation appropriate?
Cannot compute, too many disorders 6. Mixed disorder?
AG = 31 ( 19); HCO 3 = 40, not down; so HCO 3 high, so there must be a metabolic alkalosis.
is too Thus, triple disorder: AG metabolic acidosis, respiratory alkalosis, and metabolic alkalosis