OBJECTIVES

I. To explain the principles of blood gas and acid-base analysis. II. To interpret blood gas analysis and diagnose various acid base disorders. III. Describe causes of acid base disorders. IV. Understand use of acid base nomograms.

. PCO2= 35-45 mmHg If the problem in the PCO2, it is respiratory acidosis or alkalosis. Compensation: The body . HCO3- = 22-26 mEq/L response to acid-base If the problem in the HCO3, it is metabolic acidosis or alkalosis. imbalance

Depending on the underlying problem the Complete compensation mechanisms differ : compensation: if the PH back into the

Respiratory problem Metabolic problem normal limits.

Kidney can brings Respiratory Partial compensation compensation: if the Metabolic (hypo/hyperventilation) PH still outside the compensation + normal range. Buffer system

ACID-BASE IMBALANCE: ACIDOSIS

Causes Compensation

A- Respiratory: . CNS depression (anaesthesia). Carbonic Kidneys acid excess eliminate Kidney also . Resp muscle paralysis/ diaphragm caused by hydrogen ion generates paralysis, rib fractures, etc.. blood levels and retain new . Obstructive lung diseases e.g. of CO2 above bicarbonate bicarbonate. Emphysema. 45 mm Hg. ion. . Pulmonary edema.

B- Metabolic: K+ exchanges Bicarbonate deficit: blood conc. of Renal with excess HCO3- drops below 22mEq/L. excretion of H+ in ECF Increased . Diabetic ketoacidosis. hydrogen ( H+ into ventilation. . Severe diarrahea.(loss of HCO3). ions if cells, K+ out . Hypoaldosteronism. possible. of cells). . Acute renal failure (fail to excrete H+). . Accumulation of acids.

ACID-BASE IMBALANCE: ALKALOSIS

Causes compensation A- Respiratory: Carbonic acid deficit: pCO is <35mmHg 2 Conditions that (hypocapnea). stimulate Most common acid-base imbalance. respiratory Kidneys Excrete . Hyperventilation: center and wash conserve bicarbonate out CO2 hydrogen ion. ion. . High altitude (Oxygen deficiency). (Hyperventilatio . Hysterical. n): . Anorexia nervosa. . Early salicylate intoxication.

B. Metabolic: Respiratory Blood conc. Of HCO3 is > 26mEq/L. compensation . Severe vomiting = loss of stomach acid Kidney excretes difficult or heavy ingestion of antacids. alkaline urine and (hypoventilation . Severe dehydration. retain H+. . Excess antacids & alkaline drugs. limited by . Hyperaldosteronism.(endocrine hypoxia). disorders).

Compensation

Respiratory Acidosis Respiratory Alkalosis

• Kidneys eliminate hydrogen ion and retain bicarbonate ion. Kidneys conserve hydrogen ion • Kidney also generates new Excrete bicarbonate ion bicarbonate.

Metabolic Acidosis Metabolic Alkalosis

• Increased ventilation • Kidney excretes alkaline urine and • Renal excretion of hydrogen ions if retain H+ possible • Respiratory compensation difficult – • K+exchanges with excess H+ in ECF hypoventilation limited by hypoxia • ( H+ into cells, K+ out of cells) Effects of acidosis Effects of alkalosis • Principal effect of acidosis: • Alkalosis causes over excitability of the central and peripheral nervous systems. - depression of the CNS through ↓ of - Numbness. synaptic transmission. - Lightheadedness. - Generalized weakness. - Deranged CNS function the greatest - It can cause : threat. . Nervousness. . muscle spasms or tetany . * Severe acidosis causes: . Convulsions . . Disorientation. . Loss of consciousness. . Coma. . Death. . Death.

RESPIRATORY: ALKALOSIS AND ACIDOSIS

Contact us: [email protected] METABOLIC: ACIDOSIS AND ALKALOSIS

Contact us: [email protected] Diagnosis of Acid-Base Imbalances : 1) Note whether the pH is low (acidosis) or high (alkalosis) - 2) Decide which value, pCO2 or HCO3 , is outside the normal range and could be the cause of the problem.

If the cause is a change in pCO2, the problem is respiratory. - If the cause is HCO3 the problem is metabolic.

The change in PH : The difference between If pH is normal (between 7.35-7.45) Compenstaed diarrhea and vomiting : If pH is abnormal (<7.35 or >7.45) uncompenstated. In diarrhea : cause metabolic Is the cause Respiratory or metabolic? acidosis due to loss of bicarbonate from intestine so If PCO2>45 = Respiratory acidosis the PH will decrease. If PCO2<35= Respiratory alkalosis In vomiting : cause metabolic If HCO3-< 22= Metabolic acidosis. alkalosis due to loss of HCL so If HCO3-> 26 = metabolic alkalosis. the PH will increase .

Example 1: A patient is in intensive care because he suffered a severe myocardial infarction 3 days ago. The lab reports the following values from an arterial blood sample: pH =7.21, PCO2= 42, HCO3- = 12: To answer it List the condition First : : acidosis or alkalosis, Second :metabolic or respiratory Third : compensated or uncompensated? The answer : Metabolic acidosis, uncompensated

Example 1: A 50 year-old man with history of type 2 diabetes was admitted to the emergency department with history of polyuria. On examination he had rapid and deep breathing. Blood analysis showed glucose level of 400 mg/dl. The following is the arterial blood analysis report of this patient: pH = 7.1, PCO2 = 40 mmHg and HCO3- = 18 mmol/L The answer : Metabolic acidosis, uncompensated

Example 2 : pH = 7.36, PCO2= 54, HCO3- = 32: the answer : respiratory, acidosis, compensated

Example 3: pH =7.38, PCO2= 38, HCO3- = 25: The answer : normal Summary How to diagnosis?

PH

Lower 7.4 Above 7.4 Acidosis alkalosis

Pco Hco3

If PCO2>45 If PCO2<35 If HCO3-< 22= If HCO3-> 26 = Respiratory Acidosis Respiratory alkalosis Metabolic acidosis. metabolic alkalosis.

(between 7.35-7.45) (<7.35 or >7.45) Compenstaed Uncompenstated

Ans Q1.which of the following cause acidosis? Q3. A patient is seen in the emergency

A. Hyperaldosteronism department with following blood value B. Sever vomiting PH=7.8,HCO3- =29,PCO2 =38 what is the acid-base :

C. Hyperventilation disorder? 1

D. Sever diarrhea A. Respiratory Acidosis .D

B. Respiratory Alkalosis C. Metabolic Acidosis

D. Metabolic Alkalosis 2 .A .A

Q2.How the kidney compensate alkalosis ? Q4.In the conversion from acute to

A. The kidney conserves H+ And excretes CHO- chronic respiratory alkalosis, what happen to 3 B. K+ exchanges with excess H+ in ECF blood PH ? .D C. Hyperventilation A. Increase D. A+C B. Decrease to normal C. Severe decreasing 4 .B D. Constant

Q1.How does the kidney compensate of Q3.What is “ Anorexia nervosa” ? respiratory acidosis? An emotional disorder characterized by an Kidney will eliminate H+ ions and retain HCO3- obsessive desire to loose weight by refusing to ions , also generates new HCO3- eat , so it will cause alkalosis. Q2.what is the difference between vomiting and Q4.a patient is in ER because she travels to high diarrhea an acid-base imbalance ? Altitude for 5hrs . The report as following . Vomiting : is combined with excessive loose of PH=7.49 acid . PCO2=25 Diarrhea : is combined with low absorption of PHCO3=21 HCO3- due to high flow fluid go out . What is the diagnosis ? Respiratory alkalosis uncompensated