Ico

result in a pathologic accumulation of 1 ?• (greater than 26 mEq/L or mmol/L), urn a condition termed metabolic alkalosis, or it may result in the loss of bey ond normal (less than 22 mEq/L or mmol/L), a condition termed metabolic acidosis.

In contrast to the lungs' rapid effects on CO2, the kidneys change the 1 3 very slowly (hours to days).

Respiratory and metabolic derangements can occur in isolation or in combination. If a patient has an isolated primary acid-base disorder that is not accompanied by another primary acid-base disorder, a simple (uncomplicated) disorder is present. The most common clinical disturbances are simple acid-base disorders. If two or three primary acid-base disorders are simultaneously present, the patient has a mixed (complicated) disorder. More complex clinical situations lead to mixed acid-base disturbances. Because CO2 is a volatile acid, it can rapidly be changed by the respiratory system. If a respiratory acid-base disturbance is present for minutes to hours it is considered an acute disorder, while if it is present for days or longer it is considered a chronic disorder. By definition, the metabolic machinery that regulates 1 3 results in slow changes and all metabolic disorders are chronic.

Changes that follow the primary disorder and attempt to restore the blood pH to normal are referred to as compensatory changes. It should be stressed that compensation never normalizes the pH. Because all metabolic acid-base disorders are chronic and the normal respiratory system can quickly alter the PaCO2, essentially all meta-

bolic disorders are accompanied by some degree of respiratory compensation. ' Similarly, chronic respiratory acid-base disorders are typically accompanied by attempts at metabolic compensation.4,5 However, with acute respiratory acid-base disorders there is insufficient time for the metabolic pathways to compensate significantly.6 As such, acute respiratory derangements are essentially uncompensated.

The amount of compensation (metabolic or respiratory) can be reliably predicted based on the degree of derangement in the primary disorder. Table 28-1 outlines the simple acid-base disorders and provides formulas for calculating the expected com-

pensatory responses. Although it is not mandatory to memorize these formulas in order to interpret acid-base problems, they can be helpful tools. If the measured values tirnr differ markedly from the calculated values (the measured serum 1 3 is greater than 2 mEq/L [2 mmol/L] from the calculated value or the measured PaCO2 is more than 4 mm Hg [0.54 kPa] from the calculated value), a second acid-base disorder is present as outlined in Table 28-2.

Table 28-1 The Six Simple Acid-Base Disorders

Type of Disorder

pH

PaCO/

HCO;

1. Metabolic acidosis

;

Decreased** PaCO. = (IS x HCO.') + 8

Decreased^

2. Metabolic alkalosis

t

increased* PaCO, - (0.9 x 1 ) +

Increased'

Acute respiiatory acidosis

¿PaCO/

4. Chronic respiratory acidosis

;

Increased*

Increased* ¿HCO = 0.35 X ¿PaCOa

Acute respiratory alkalosis

T

Decreased

Approximately normal ¿HCQ2~ = 0.2 x ¿PaCO/

6. Chronic inspiratory alkalosis

T

Decreasedf

Decreased" A HCO. =■ 0.4 x A PaCO.^

"PaCO in nnm Hg.

^Respiratory compensation: if inappropriate, see Table 28 -2. ^Primary disorder,

''Metabolic compensation: i il nap propria re, see Table ~JB-J.

Table 28-2 Diagnosis of Concurrent Acid-Base Disturbances When Compensation Is Inappropriate

Primary Acid-Base Assessment of Concurrent Acid

Disturbance_Compensation Base Disturbance

Metabolic acidosis

PaGQ

.too

low

Respiratory alkalosis

PaOpj

too

high17

Respiratory acidosis

Metabolic alkalosis

PaCO

1:00

loW

Respiratory alkalosis

PaCO

, too

high*

Respiratory acidoses

Respiratory acidosis

HCO3

too

low*

Metabolic acidosis

HCO^

too

high6

Metabolic alkalosis

Respiratory alkalosis

HCO<

COO

low*

Metabolic acidosis

HCO,

too

high6

Metabolic alkalosis

Reducing Blood Pressure Naturally

Reducing Blood Pressure Naturally

Do You Suffer From High Blood Pressure? Do You Feel Like This Silent Killer Might Be Stalking You? Have you been diagnosed or pre-hypertension and hypertension? Then JOIN THE CROWD Nearly 1 in 3 adults in the United States suffer from High Blood Pressure and only 1 in 3 adults are actually aware that they have it.

Get My Free Ebook


Post a comment