Acid and Base Disturbance
* pH Review
H+ is a proton
pH Range is from 0 - 14
If [H+] is high, the solution is acidic; pH < 7
If [H+] is low, the solution is basic or alkaline ; pH > 7
* The Body and pH
Homeostasis of pH is tightly controlledExtracellular fluid = 7.4Blood = 7.35 – 7.45 (7.40)< 6.8 or > 8.0 death occursAcidosis (acidemia) below 7.35Alkalosis (alkalemia) above 7.45Normal Serum HCO3- is 21-29 mmol/L*
* Small changes in pH can produce major disturbances
Most enzymes function only with narrow pH rangesAcid-base balance can also affect electrolytes (Na+, K+, Cl-)
* The body produces more acids than bases
Acids take in with foodsCellular metabolism produces CO2.CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-Slightly Alkaline plasma of 7.40(H+ : 40 nmol/L) is maintained by kidney capacity to produce an Acidic Urine(PH typically 5-6)in which the excess of metabolic acid can be excreted.* Renal Control of Acid-Base balance
Kidneys are Most effective regulator of pHIf kidneys fail, pH balance fails
Collecting ducts cells, Can eliminate large amounts of acid (Acid is secreted into the lumen by H+_ATPas )
Can also excrete base
Can conserve and produce bicarb ions Renal compensatory mechanisms may take hours to days OR EVEN WEEKS
* Respiratory mechanisms
Exhalation of carbon dioxide CO2CO2 + H20 ↔ H2CO3 ↔ H+ + HCO3-Body pH can be adjusted by changing rate and depth of breathingRespiratory mechanisms (hypo or hyperventilation) take several minutes to hours* Urinary Buffers
Bicarbonate: some 85% of the filtered Bicarbonate reabsorbed in the Proximal tubule phosphate: Maintain a 20:1 ratio HCO3- : H2CO Ammonia : Major intracellular buffer H+ + HPO42- ↔ H2PO4-*
*
* Compensation to Acid-Base Imbalances
If underlying problem is metabolic, hyperventilation or hypoventilation can help : respiratory compensation.If problem is respiratory, renal mechanisms can bring about metabolic compensation.
* Acidosis
Principal effect of acidosis is depression of the CNS through ↓ in synaptic transmission.Generalized weaknessDeranged CNS function the greatest threatSevere acidosis causes Disorientationcoma death* Alkalosis
Alkalosis causes over excitability of the central and peripheral nervous systems.Numbness
Lightheadedness
It can cause :
Nervousness
muscle spasms or tetany
Convulsions
Loss of consciousness
Death
Simple Acid-Base Disorders
Primary Compensatory Disorder pH H+ Disorder ResponseMetabolic acidosis HCO3_ pCO2Metabolic alkalosis HCO3_ pCO2Respiratory acidosis pCO2 HCO3_ Respiratory alkalosis pCO2 HCO3_*
* Respiratory Acidosis
Carbonic acid excess caused by blood levels of CO2 above 45 mm Hg(= PCO2 5.33 kpa). Hypercapnia – high levels of CO2 in blood causesChronic conditions:Depression of respiratory center in brain that controls breathing rateby drugs or head traumaParalysis of respiratory or chest muscles _EmphysemaAcute conditons:Adult Respiratory Distress SyndromePulmonary edemaPneumothorax* Compensation: Kidneys eliminate hydrogen ion and retain bicarbonate ion* Signs and Symptoms of Respiratory Acidosis
BreathlessnessRestlessness
Lethargy and disorientation
Tremors, convulsions, coma
Respiratory rate rapid, then gradually depressed
Skin warm and flushed due to vasodilation caused by excess CO2
Treatment Restore ventilation
Treat underlying dysfunction or disease
* Respiratory Alkalosis
cause is sustained hyperventilationCarbonic acid deficit..washing of CO2pCO2 less than 35 mm Hg (hypocapnea),Most common acid-base imbalance causeshigh altitudes (Oxygen deficiency) HyperventilationPul embolisim,Acute anxiety….HYS,Fever, anemiaEarly salicylate intoxication..stim brain stem resp.center&Cirrhosis chronic liver diseaseCl/p: perioaral & digital tingling ,Tetany (due to decrease ionised Ca++ caused by increase binding of Ca++ to Albumen in Alkalosis Treatment :Treat underlying causerebreathe into a paper bag* Metabolic Acidosis
characterized HCO3- less than 24,Caused by:Loss of bicarbonate through diarrhea or renal dysfunction
Accumulation of acids (lactic acid or ketones)
Failure of kidneys to excrete H+
Causes of Normal AG (Hyperchloremic) Metabolic Acidosis
High K+ Low K+Adrenal insufficiency Diarrhea
Interstitial nephritis RTA proximal,Distal
Ureteral diversion
AG = (Na+ + K+) - (Cl- + HCO3-) = 15
Metabolic Acidosis: Elevated Anion Gap
AG = (Na+ + K+) - (Cl- + HCO3-) = 15[Note: Diagnostic utility is best when AG > 25]
Causes Ketoacidosis
Lactic acidosis
Intoxications(salicylate ,Methanol poisoning)
Renal failure
Rhabdomyolysis
* Compensation for Metabolic Acidosis
Increased ventilationRenal excretion of hydrogen ions if possible
K+ exchanges with excess H+ in ECF
( H+ into cells, K+ out of cells)
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