Mark Klimek NCLEX Review: Acid-Base Balance and Ventilators

Acid/Base Balance

To solve acid-base disorders, it is important to know the normal values for pH, CO2 and HCO3 (bicarbonate).

 

The first value to look at in an acid-base disorder is the pH

- If pH is <7.35, the acid-base imbalance is acidotic

- If pH is >7.45, the acid-base imbalance is alkalotic

 

Now, to determine if the imbalance is metabolic or respiratory, determine whether HCO3 goes in the same or opposite direction with pH

Rule of the Bs: If pH and Bicarb move both in the same direction, then the acid-base imbalance is metabolic … Otherwise, it is respiratory.

 

Example #1

- pH       7.3   Acidosis

- HCO3  20    Metabolic

- This is an example of metabolic acidosis

 

Example #2

- pH        7.58   Alkalotic

- HCO3   32      Metabolic

- This is an example of metabolic alkalosis

 

Example #3

- pH       7.22   Acidosis

- HCO3  35    Respiratory

- This is an example of respiratory acidosis

 

As the pH goes, so goes my patient, except for Potassium … That means

- If pH is low, everything is low, except potassium

- If pH is high, everything is high, except potassium

 

If pH goes over 7.45, this is alkalosis

Therefore, everything is UP: tachycardia, tachypnea, HTN, seizures, irritability, spastic, diarrhea, borborygmi (increase bowel sounds), hyperreflexia (3+, 4+)

However, potassium is low (opposite). Therefore, Hypokalemia

- What is the nursing intervention?

- Pt need suctioning because of seizures

 

If pH goes below 7.35, this is acidosis

Therefore, everything is DOWN: bradycardia, constipation, absent bowel sounds, flaccid, obtunded, lethargy, coma hyporeflexia (0, 1+), bradypnea, low BP.

However, potassium is high. Therefore, Hyperkalemia

- What is the nursing intervention?

- Patient needs to be ventilated with an Ambu bag—respiratory arrest

So, remember that “MAC Kussmaul” is the only acid-base imbalance to cause Metabolic ACidosis with Kussmaul respirations.

 

Causes of Acid/Base imbalance:

First ask yourself, “Is it LUNG? … If yes, then it is respiratory

Then ask yourself, “Are they overventilating or underventilating?

- If UNDERventilating, then pick acidosis—pH is under 7.35

- If OVERventilating, then it is alkalosis, pH is over 7.45

 

What type of acid-base derangement is present in the following condition?

In labor?

- Respiratory alkalosis … Overventilating—pH increases … Alkalosis

Drowning?

- Respiratory acidosis … Underventilating—pH decreases … Acidosis

Pt is on PCA (patient-controlled anesthesia) pump?

- Ventilation is down … Respiratory acidosis

 

If it is not LUNG, then it is metabolic. If the patient has prolonged gastric vomiting or suction (sucking out acid), pick alkalosis.

- For everything else that isn’t lung, pick metabolic acidosis

- So, when you don’t know what to pick, pick metabolic acidosis

 

Tip

- Set your default setting to Metabolic Acidosis

- Always pay attention to modifying phrase rather than original noun.

 

 Ventilator

 A ventilator is a machine designed to move breathable air into and out of the lungs, aids patients who are physically unable to breathe, or breathing insufficiently to breathe … A ventilator is equipped with a high and a low-pressure alarm.

 

High pressures alarms are always triggered by increased resistance to air flow. Look for obstructions:

- Kinks in tubing …Solution: unkink the tube

- Condensed water in the dependent tube …Solution: empty it

- Mucus plugs … Solution: Ask patient to turn, cough, deep breathe; or suction the tubing PRN

 

What is the appropriate order to address high pressure alarm in a mechanical ventilator?

(1) Unkink. (2) Empty water out of tubing. (3) turn pt, ask pt to cough or deeply breathe, and (4) suction

 

Low pressures alarms are always triggered by decrease in resistance. This can be caused by

- Main tubing disconnection

- O2 sensor tube disconnection

- In both cases, reconnect the disconnected tubing unless tube is on floor … Bag pt and call Respiratory Therapist

 

The ventilator may be set too high or too low

Setting is too high … Patient is over-ventilated

- Respiratory Alkalosis … Panting

Setting is too low … Patient is under-ventilated

- Respiratory Acidosis … Patient is retaining CO2

 

Question

The physician wants to wean patient off vent in the morning. At 6 am, the ABGs say respiratory acidosis. What would you do next?

Notify the physician that the patient is not ready to be weaned off the respirator

- Pt is in respiratory acidosis, which means that he is underventilated … Therefore, not ready to be weaned off the ventilator.

- If patient were in respiratory alkalosis (overventilated), he should be ready to be weaned off.