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79 Cards in this Set
- Front
- Back
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Normal pH?
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7.35-7.45
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Three systems that regulate acid-base balance?
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Buffering
Resp Renal |
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Modified Henderson equation?
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H = 24 X pCO2/HCO3
should = ~40 |
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Usefulness of modified henderson equation and acid-base disorders?
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change in numerator (pCO2) leads to resp acidosis/alkalosis
change in denominator leads to metabolic acidosis/alkalosis |
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How do secondary responses to primary A-B disorders change?
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always change in the same direction, i.e. if HCO3 goes up, pCO2 will go up as a result
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Who provides immediate defense against A-B changes?
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Buffering System
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Who are the Buffering System players
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Bicarb/Carbon Dioxide
Proteins Phosphate ions Bone Hemoglobin |
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Who is the next line of defense?
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Resp Regulation
altered alveolar ventilation |
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Who then is the ultimate defense?
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RENAL!
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2 components of Renal Regulation?
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Reclaim Filtered HCO3
Generate HCO3 consumed by net acid production (excretion of nonvolatile acid) |
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Where is the majority of bicarb reabsorbed?
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PCT (90%)
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What is required for bicarb reabsorption?
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H in the lumen
Luminal Carbonic Anhydrase |
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Example of carbonic anhydrase inhibitor and what does it lead to?
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Acetazolamide
leads to bicarb wasting |
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Where is the remaining bicarb reabsorbed?
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Distal Nephron (10%)
no more luminal carbonic anhydrase, so acid gets excreted after buffering w/ NH3 |
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What has to get excreted w/ NH4?
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Cl
based on law of electrical neutrality |
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What is one of the main sources of ammonia for buffering?
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Glutamine
Creates new bicarb and H's |
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Equation for Compensation?
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Compensation = (Bicarb X 1.5) + 8
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3 general mechanisms for Metabolic Acidosis?
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Loss of Bicarb (diarrhea)
Addition of Acid (diabetic KA) Failure of kidney to excrete acid (RF) |
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CV effects of acidosis?
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Dec contractility
Central Venous Vasoconstriction Dec Arterial Blood Pressure |
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Resp effects of acidosis?
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Inc Minute Ventilation
Deep, regular, sighing respirations (Kussmaul) |
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Equation for AG?
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Na - (Cl + HCO3)
should equal around 12 |
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What's the point of the AG?
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to account for unmeasured anions
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who is the main unmeasured anion?
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Albumin
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Causes of Normal AG Met. Acidosis?
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GI Loss of HCO3 (diarrhea)
Renal Loss of HCO3 Ingestion of Cl acids |
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Causes of renal loss of HCO3?
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RTA
Carbonic Anhydrase Inhibitors |
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Hallmarks of RTA?
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Inability to excrete H
Inappropriate reabsorption of HCO3 |
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Types of RTA?
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1
2 4 |
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Defect in RTA 1 vs 2 vs 4
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1: Deficiency in H secretion by alpha intercalated cells
2: Defect in Prox Tubule Bicarb reabsorption 4: Aldo def or resistance (hyporenin hypoaldo) |
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pH in RTA 1 vs 2?
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1: usually > 5.5
2: initially > 7, but in steady state < 5.5 |
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Kickers for RTA 1?
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pH > 5.5
usually HypoK Urinary NH4 is decreased UAG is positive Nephrocalcinosis and Nephrolithiasis |
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Causes for RTA Type I?
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Familial
Auto Dom Disease (sjorgen's, SLE) AmphoB Toulene Tubulointerstitial Disease |
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Kickers for RTA Type II?
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Defective PCT bicarb reabsorption--> inc distal bicarb delivery
pH ends up < 5.5. HypoK UAG positive |
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what is Fanconi's Syndrome?
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Causes RTA Type II
decrease reabsorption of most solutes in PCT HCO3, AA's, Glucose, Phophates, and uric acid |
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Causes of Type II RTA?
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Isolated Defect (carbonic anhydrase inhibitors/def)
Generalized Defect (fanconi's) |
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Causes of Generalized Defect leading to Type II RTA?
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Multiple Myeloma
Wilson's Disease Drugs (ifosfamide, cidofovir) |
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Kickers for Type IV RTA?
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Hyporenin, Hypoaldo
Defect is aldo def or resistance Impairs Na reabsorption and H and K secretion HyperK UAG positive |
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Causes of Type IV RTA?
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DM
Tubulointerstitial Disease AIDS HTN nephrosclerosis |
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What's the point of UAG?
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Indirect measure of NH4 excretion
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How to calculate UAG?
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Na + K - Cl (in pee)
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Normal UAG?
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0-30 (i.e. positive)
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When is UAG negative?
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GI loss of bicarb
usually -20 to -50 |
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Causes of High AG Metabolic Acidosis?
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Inc Endogenous Acid (LA or KA)
Ingestion of Toxic Substances (methanol, ethylene glycol, salicylate) Failure to excrete Acid (RF) |
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Hallmark of High AG Metabolic Acidosis?
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Dec HCO3 w/ Normal Cl
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for the common conditions leading to High AG Metabolic Acidosis, what are the unmeasured anions?
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LA: lactate
Diabetic KA: acetoacetate, **beta-hydroxybutyrate** RF: phosphates and sulfates MEthanol: formic acid Ethylene glycol: glycolic acid, oxalic acid |
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General causes of LA?
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Inc lactate production
Dec lactate clearance |
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More specific causes of LA?
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Type A: dec tissue perfusion
Type B: Impaired oxidative phosphorylation |
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Specific causes of Type A LA?
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Shock
CO poisoning Cyanide toxicity |
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Causes of Type B LA?
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Sepsis
Uncontrolled Diabetes Malignancy Thiamine def Ethanol or metformin toxicity |
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Types of KA?
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Diabetic
Starvation Alcoholic |
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Key for unmeasured anions in DKA?
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Beta-hydroxybutyrate is the most predominant, but we can only measure acetoacetate
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What is helpful in the diagnosis of Toxin induced High AG Metabolic Acidosis?
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Osmole Gap
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Substances w/ increased osmole gap?
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Ethylene Glycol**
Methanol** ethanol acetone isopropyl alcohol |
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how to figure out osmole gap?
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measured osmolarity - calculated osmolarity
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how do you calculate plasma osmolarity?
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(2 X Na) + (Glucose/18) + (BUN/2.8)
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Normal Osmole Gap =?
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< 10
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Unmeasured anions in Salicylate intoxication?
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Lactate
Salicylate |
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Effects of salicylate intoxication?
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Direct Stimulatory effect on Resp Center-->resp alkalosis
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Rx for salicylate intoxication?
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Inc pH
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mnemonic for High AG Metabolic Acidosis??
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MUDPILES
methanol uremia/RF DKA (or other KA) paraldehyde? isoniazid/iron LA ethylene glycol salicylate |
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Great flow chart for Metabolic Acidosis?
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1. you got Met Acidosis
2. Measure AG 3a. Normal AG, measure UAG 4a. Positive UAG = RTA, Neg UAG = Diarrhea 3b. High AG, measure osmole gap 4b. High Osmole Gap = Ethylene glycol or methanol. Normal Osmole Gap = LA, KA, Salicylate, Uremic acidosis |
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2 major pathogenic mechanisms to metabolic ALKALOSIS?
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Chloride/Saline responsive (most comon)
Cl/Saline resistant so check Urine Cl |
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What's up with the generation phase of Met Alk?
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H is lost in urine or GI--> Inc HCO3
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When will kidneys retain HCO3 and maintain alkalosis?
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1. Vol def + Cl def + K def + reduced GFR
2. HypoK from autonomous hyperaldosteronism |
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Why does dec Cl --> HCO3 retention?
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B/c Cl is necessary for HCO3/Cl exchanger in beta-intercalated cells
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Major Causes of Metabolic Alkalosis: Cl responsive?
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**Vomiting and Nasogastric suction**
Diuretics Exogenous alkali post-hypercapnic state |
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Key to Dx of Metabolic Alkalosis: Cl responsive?
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Low urine Cl ( < 10)
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Rx for Metabolic Alkalosis: Cl responsive??
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Correct Volume depletion
Discontinue diuretics PPI's for vomiting and nasogastric suction Correct K Pts w/ CHF: acetazolamide Rarely: dilute hyrdrochloric acid |
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Causes of Metabolic Alkalosis: Cl Resistant?
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Direct Stimulation of renal HCO3 reabsorption
Mineralcorticoid excess Apparent MC excess Bartter's, Gitelman's |
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Kicker for Dx of Metabolic Alkalosis: Cl Resistant??
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Urine Cl > 20
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Rx for Metabolic Alkalosis: Cl Resistant??
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Correct underlying problem
Correct for K |
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Causes of Acute Resp Acidosis?
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HYPOVENTILATION
Overdose of sedatives Anesthesia Cardiac Arrest Aspiration |
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Causes of Chronic Resp Acidosis?
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COPD
Primary Hypoventilation CNS disorders Myopathy |
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Clinical Manifestations of Resp Acidosis?
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Hypoxemia
NEURO anxiety/restlessness confusion myoclonus/asterixis/seizures inc ICP, HA CARDIOVASCULAR Dec CO and BP arrhythmias |
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What's interesting about Chronic Resp Alkalosis?
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it can return the pH to normal
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Causes of Resp Alkalosis
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HYPERVENTILATION
anxiety sepsis cirrhosis preggers Pulmonary Emobolus Salicylates CNS disorders |
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Clinical manifestations of Resp Alk?
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can be pretty benign
or just the neuro and cardio stuff you'd expect with an anxiety attack |
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What is the Delta Gap and why is it useful?
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Comparison of change in AG and change in HCO3...should be somewhat 1:1
Useful for detecting additional A-B disorders on top of High AG metabolic acidosis (met alk or normal gap met acid) |
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So what kind of delta gap is indicative of Met. Alk? normal gap met acid?
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Met Alk: if change in AG is big and change in HCO3 isn't
Normal AG Met Acid: HCO3 decreases a LOT more than AG inc |
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What is the Triple Ripple?
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High AG Met Acid
Resp Acidosis Met Alk Clinically: High AG Met Acid: Ethylene glycol Resp Acidosis: Aspiration Met Alk: Vomiting |
