Alkalosis respiratorik

dr. Rohmania Setiarini

Terms

• Acid– Any substance that can yield a hydrogen ion

(H+) or hydronium ion when dissolved in water– Release of proton or H+

• Base– Substance that can yield hydroxyl ions (OH-)– Accept protons or H+

Terms

• Acidosis– pH less than 7.35

• Alkalosis– pH greater than 7.45

• Note: Normal pH is 7.35-7.45

The Acid-Base Balance

• Balance of H conc. In ECF . • To Achieve Homeostasis .• Balance Between :

The H Intake or Production

The H Removal

NORMAL VALUE

• Arterial blood = 7.35 – 7.45

Can be explained as follows;

Normal value of H+ ion conc. is about 40nEq/lit.

40 nEq/lit = 0.00000004 Eq/lit.

Therefore pH = - log [0.00000004]

= 7.4

pH and H+ ion concentration

pH• 6.0• 7.0• 8.0• 9.0

H+ ion in nmol/lit• 1000• 100• 10• 1.0

Note : one point drop in pH results in a ten fold decrease in H+ ion conc.

Scale of pH measurement

• The pH scale is between 0 – 14.

At 7 (neutral e.g. water) where the amount of H+ and Hydroxyl ion are equal at 23o

8

Maintenance of blood pH

• Three lines of defense to regulate the

body’s acid-base balance

– Blood buffers

– Respiratory mechanism

– Renal mechanism

9

Buffer systems

• Take up H+ or release H+ as conditions change

• Buffer pairs – weak acid and a base• Exchange a strong acid or base for a

weak one• Results in a much smaller pH change

The body maintains ECF physiologic pH by buffers

• Bicarbonate buffer HCO3- : CO2 (53%)

• Hemoglobin (Hb) – in ery (35%)• Plasma proteins (mainly albumin) (7%)• Phosphate buffer HPO4

2- / H2PO4- (3%)

NH3/NH4+ and HPO4

2-/H2PO4- are the most important

urinary buffer systems.

11

Respiratory mechanisms

• Exhalation of CO2

• Rapid, powerful, but only works with volatile acids

• H+ + HCO3- ↔ H2CO3 ↔ CO2 + H20

• Doesn’t affect fixed acids like lactic acid• Body pH can be adjusted by changing rate

and depth of breathing

CO2 CO2

12

Kidney excretion

• Most effective regulator of pH• The pH of urine is normally acidic • H+ ions generated in the body are eliminated by acidified

urine.

• Can eliminate large amounts of acid

• Reabsorption of bicarbonate (HCO3-)

• Excretion of ammonium ions(NH4+)

• If kidneys fail, pH balance fails

13

Respiratory Alkalosis

• Carbonic acid deficit↓• pCO2 less than 35 mm Hg (hypocapnea)

• Most common acid-base imbalance

Respiratory Alkalosis

Etiology– Hyperventilation due to Conditions that stimulate

respiratory center» extreme anxiety, stress, or pain» Fever» overventilation with ventilator» hypoxia» salicylate overdose» hypoxemia (emphysema or pneumonia)» CNS trauma or tumor

Respiratory Alkalosis

• Symptoms– Tachypnea or Hyperpnea– Complaints of chest pain– Light-headedness, syncope, coma, seizures– Numbness and tingling of extremities– Difficult concentrating, tremors, blurred vision– Weakness, paresthesias, tetany

– Lab findings– pH above 7.45– CO2 less than 35

16

Compensation of Respiratory Alkalosis

• Kidneys conserve hydrogen ion

• Excrete bicarbonate ion

Respiratory Alkalosis

• Treatment• Monitor VS and ABGs• Treat underlying disease• Assist patient to breathe more slowly, breathe in a

paper bag or apply rebreather mask• IV Chloride containing solution – Cl- ions replace

lost bicarbonate ions• Sedation

Compensations for Respiratory Alkalosis

• Acute respiratory alkalosis–HCO3 decreases by 2 for every 10 mm

decrease in pCO2

• Chronic respiratory alkalosis–HCO3 decreases by 4 for every 10 mm

decrease in pCO2

Respiratory alkalosis

• Compensation• The compensatory response to a respiratory alkalosis is

initially a release of hydrogen from extracellular and intracellular buffers.

• This is followed by reduced hydrogen excretion by the kidneys.

• This results in decreased plasma bicarbonates. • In chronic respiratory alkalosis, compensation can lead

to pH returning to normal.

20

1) Effects on the central nervous system

(a) Excitability is increased. • Manifestations are more severe than

those of metabolic alkalosis.

21

The reasons :

• (a) Hyperventilation leads to low [CO2] in plasma and cerebral vasoconstriction, the oxygen supply to the brain is decreased.

• (b) The left-shift of oxygen-hemoglobin dissociation curve leads to brain hypoxia.

22

Glutamic acid

Glutamate decarboxylase

r-GABA, r-aminobutyric acid

r-GABA transminase

Succinic acid

Kreb’s cycle

(c) The production of GABA (gama aminobutyric acid, a inhibitory transmitter), is decreased due to the activity of enzyme for the production is reduced in alkalosis.

Diagnosis of Acid-Base Imbalances1. Look at the pH

• is the primary problem acidosis (low) or alkalosis (high)

2. Check the CO2 (respiratory indicator)• is it less than 35 (alkalosis) or more than 45 (acidosis)

3. Check the HCO3- (metabolic indicator)• is it less than 22 (acidosis) or more than 26 (alkalosis)

4. Which is primary disorder (Resp. or Metabolic)?

• If the pH is low (acidosis), then look to see if CO2 or HCO3- is acidosis (which ever is acidosis will be primary).

• If the pH is high (alkalosis), then look to see if CO2 or HCO3- is alkalosis (which ever is alkalosis is the primary).

• The one that matches the pH (acidosis or alkalosis), is the primary disorder.

25

5. Look at the value that doesn’t correspond to the observed pH change. If it is inside the normal range, there is no compensation occurring. If it is outside the normal range, the body is partially compensating for the problem.