Foundations of Critical Care Nursing (FCCN) Level 1 - Mayo Clinic Study Guide

PaO2 definition and value

Partial pressure of oxygen in the blood, normal value is 70 to 100.

SaO2 definition and value

Oxygen saturation, the amount of oxygen carried by the red blood cells, normal value is 92% to 100%

pH definition and value

Overall reflection of acid-base balance in the body, normal value is 7.35 to 7.45.

PaCO2 definition and value

Acid by-product of cell metabolism that drives and reflects ventilation, normal value is 35 to 45.

HCO3 definition and value

Base that assists in removing excess acids, normal value is 22 to 26.

What are the indications to draw an ABG?

- somnolence or change in level of consciousness

- respiratory decompensation

- metabolic imbalances

- evaluation of changes to respiratory status or monitoring ventilator settings

What are the lab values indicating acidosis?

- pH less than 7.35

- PaCO2 greater than 45

- HCO3 less than 22

What are the lab values indicating alkalosis?

- pH greater than 7.45

- PaCO2 less than 35

- HCO3 greater than 26

What values indicate hypoxemia?

- PaO2 of less than 70

- SaO2 of less than 92%

What value indicates excessive oxygen therapy?

PaO2 greater than 100

What is compensation?

The body tries to return pH to normal when CO2 or HCO3 levels cause an imbalance

What lab value shows full compensation?

A normal pH

What indicates partial compensation?

When the pH is not fully normalized

How do we decide what type of imbalance it is if the body is fully compensated?

Decide if the pH value is closer to the acidotic or alkalotic value

Causes, assessment, and treatment of respiratory acidosis

- caused by retaining CO2 from hypoventilation

- presents as a headache, tachycardia, confusion, or restlessness

- treated by improving ventilation

How does the body compensate for respiratory acidosis?

The kidneys work slowly to retain HCO3

Causes, assessment, and treatment of respiratory alkalosis

- caused by blowing off too much CO2 during hyperventilation

- presents as headache, tachycardia, confusion, or restlessness

- treated by decreasing tidal volume, relieving anxiety, controlling pain, and correcting hypoxia

How does the body compensate for respiratory alkalosis?

The kidneys work slowly to excrete HCO3

Causes, assessment, and treatment of metabolic acidosis

- caused by abnormal metabolism, increased acid retention, and decreased HCO3

- presents as Kussmaul respirations, tachycardia, headache, weakness, nausea/vomiting, or abdominal pain

- treated by correcting renal failure, HCO3 replacement, control diarrhea, and improving perfusion

How does the body compensate for metabolic acidosis?

The lungs work quickly to blow of excess CO2 with hyperventilation

Causes, assessment, and treatment of metabolic alkalosis

- caused by losing acid by vomiting or NG suction, K+ or Cl- loss resulting in retaining bases, and increased HCO3

- presents as confusion, muscle cramps, or shallow respirations

- treated by restoring fluids and electrolytes and limiting alkaline intake

How does the body compensate for metabolic alkalosis?

The lungs work to hold onto CO2 by causing hypoventilation

What are the consequences of a low pH?

Cardiac contractions decrease and so does the vascular response to catecholamines and drugs in the body

What are the consequences of a high pH?

Impairs the oxygenation of tissues and neuromuscular function

What conditions cause respiratory alkalosis?

- anxiety attacks

- use of stimulants

- high levels of pain

- iatrogenic causes

- hypoxemia

- fever

- sepsis

- salicylate poisoning

- pregnancy

- pulmonary edema

- pulmonary vascular disease

What conditions cause metabolic acidosis?

- DKA

- starvation

- shock

- lactic acidosis

- renal failure

- salicylate toxicity

- diarrhea

- pancreatic or intestinal fistula

- Cl- retention from TPN

What conditions cause respiratory acidosis?

- CNS depression

- analgesics and sedatives

- pneumonia

- COPD

- neuromuscular disease

- pneumothorax

- pulmonary embolism

- obesity

- kyphoscoliosis

What are the steps to interpreting ABGs?

1. look at the pH value

2. check the PaCO2

3. check the HCO3

4. match the primary imbalance

How do you match the primary imbalances with ABGs?

- match the pH to the value of PaCO2 (respiratory) and HCO3 (metabolic)

What are the ways to improve ventilation?

- cough and deep breathe

- tripod position

- bag mask

- BiPAP

- increase tidal volume

In what lead should bundle branch blocks be monitored?

Lead V1

What are the causes of a right bundle branch block?

- coronary artery disease

- myocardial infarction

- cardiac structural problems

- congenital heart defects

- myocarditis

- advanced COPD

- pulmonary hypertension

- pulmonary embolism

How does a right bundle branch block present on an ECG?

Wide QRS in V1 with two R waves (bunny ears)

What are the causes of a left bundle branch block?

- myocardial infarction

- cardiomyopathy

- severe hypertensive heart disease

- myocarditis

- advanced aortic stenosis

How does a left bundle branch block present on an ECG?

Negative deflection wide QRS and opposite T wave deflection (carrot), may have small R wave followed by S wave

What are the causes of prolonged QTc?

- antiarrythmics

- antimicrobials

- antidepressants

- antipsychotics

What QTc value means that is is prolonged?

QTc greater than 500

How much oxygen can be used in a nasal cannula?

0.25L to 6L

How much oxygen can be used in a oxymask?

5L to 10L

How much oxygen can be used in an aerosol mask?

10L

How much oxygen can be used in a non-rebreather mask?

> 10L

What is perfusion?

The forward flow of blood carrying oxygen to the cells and tissues

What are the requirements of perfusion?

- oxygen carrying capacity

- ability of oxygen to attach to the red blood cells

- cardiac output

- blood pressure

What is oxygenation?

The process of attaching O2 to the red blood cells

What is ventilation?

Physically moving air in and out of the lungs

What is systolic blood pressure?

Pressure on the arterial walls during ventricular contraction

What is diastolic blood pressure?

Pressure during ventricular relaxation

What is the equation for mean arterial pressure (MAP)?

[(2 x DBP) + SBP] / 3

What is the equation for cardiac output?

Stroke volume x HR

How do we assess perfusion?

- oxygenation and ventilation

- pulses

- blood pressure

- skin

- kidneys

-sensorium

What skin findings indicate perfusion status?

- flushed skin means the vessels are dilated

- pale skin means the vessels are constricted

- ash skin means poor oxygenation

How do we assess oxygenation?

SpO2 and PaO2

How do we assess ventilation?

Respiratory rate and pattern and PaCO2

What is preload?

The amount of fluid filling the heart

How do you assess preload?

- HR

- urine output

- skin

- pulses

- passive leg raise

- ultrasound

How does dilation of vessels impact preload?

Veins dilate and lower preload

How does constriction of vessels impact preload?

Veins constrict and increase preload

What is the cause of low preload?

Hypovolemia

What is the cause of high preload?

Hypervolemia

How is preload measured?

- central venous pressure

- pulmonary wedge pressure

- veins and volume status

What is the Franklin-Starling principle?

Giving fluids does improve the cardiac output but too many fluids can decrease the cardiac output

What is afterload?

The amount of resistance the heart must pump against when ejecting blood

How is afterload assessed?

- blood pressure

- skin

- pulses

- pulmonary vascular resistance

- systemic vascular resistance

How does dilation of the vessels impact afterload?

Decreased pressure makes it easier for the blood to eject, causing increased forward flow

How does constriction of vessels impact afterload?

Increased pressure makes it harder for the blood to eject, caused decreased forward flow

What is systemic vascular resistance?

Resistance to flow from the peripheral vasculature

What is pulmonary vascular resistance?

Resistance to flow from the pulmonary vasculature

How does high afterload present?

- high blood pressure

- pale and cool skin

- weak pulses

How does low afterload present?

- low blood pressure

- warm and pink skin

- strong pulses

What is contractility?

The force of contraction of the heart muscle, measured in stroke volume

How is contractility assessed?

- ECG that looks at stroke volume

- cardiac output or cardiac index

- delivery and consumption of oxygen

How does dilation of the vessels impact contractility?

When vessels are dilated it takes less effort for the heart to overcome, increasing the stroke volume

How does constriction of the vessels impact contractility?

When vessels are constricted it takes more effect for the heart to overcome, decreasing the stroke volume

What conditions impact contractility?

- poor preload

- hypertension

- cardiac ischemia

- cardiac injury

- myocarditis

- cardiomyopathy

- cardiac tamponade

- sepsis

- COVID

- electrolyte imbalances

- structural problems of the heart

What parts of the heart does the right coronary artery supply?

The right side of the heart and the SA/AV nodes

What parts of the heart does the left main coronary artery supply?

The LAD (anterior septum) and left circumflex (lateral wall of the left ventricle)

What do the ECG limb leads view?

Looks across the chest

What do the ECG precordial leads view?

Looks directly into the chest

What is lead V1 used for?

Viewing arrhythmias

What is lead V3 used for?

Ischemic changes

What is lead III used for?

Monitoring

What is lead II used for?

P waves

What is the impact of atrial fibrillation on cardiac output?

Decreased preload and lower cardiac output

What is the impact of tachycardia on cardiac output?

The heart doesn't fill completely which decreases preload and lowers the cardiac output and blood pressure, unable to deliver oxygenated blood

What is the impact of complete heart block on cardiac output?

Lowers the cardiac output and impacts ventricular filling

What is the impact of bradycardia on cardiac output?

Directly impacts cardiac output, unable to deliver oxygenated blood

How does ischemia present on an ECG?

Flipped T waves and ST depression

How does cardiac injury present on an ECG?

ST elevation

How does infarction present on an ECG?

Q waves that form after 24 hours

What is the J point on an ECG?

Junction where the QRS meets the ST

What is the isoelectric line on an ECG?

The area with absence of electrical activity

What is stable angina?

The imbalance of oxygen delivery and demand

How does stable angina present?

Chest pain with activity that goes away with rest

What is unstable angina?

Plaque rupture and thrombus formation

How does unstable angina present?

Chest pain at rest, no infarction, and normal troponins

What is an NSTEMI?

Thrombus is intermittently occlusive, non-full thickness infarction

How does an NSTEMI present?

Chest pain with infarction and elevated troponin levels

What is a STEMI?

Occlusive thrombus that causes full-thickness infarction

How does a STEMI present?

Chest pain with infarction and ST elevation

What are troponins?

The release of protein found in the heart muscle