FINAL EXAM REVIEW

Final Exam Overview and Breakdown

• Total Number of Questions: Approximately $111$ to $115$ questions.

• New Material Coverage: Approximately $44$ questions covering Chest X-rays, Fluid and Electrolytes, Control of Ventilation, and $V/Q$ matching.

• Topic Specific Question Counts:

  • Electrolytes and Fluid Balance: $15$ questions.

  • Chest X-ray: $11$ questions.

  • $V/Q$ Relationships: Approximately $13$ questions (subject to minor reduction).

  • Control of Ventilation: $5$ questions.

  • PFTs: $5$ questions.

  • Diffusion: $11$ questions.

  • ABG Interpretation: $3$ to $4$ questions where the interpretation must be typed in directly.

• Non-Graded Essay: A final section asking for feedback on the course (what worked, what could be improved). This should be saved for the end of the exam.

Fluid and Electrolytes

• Respiratory Connections: Understand specific connections between electrolytes and respiratory diseases, specifically the relationship between Chloride ($Cl^-$) and Cystic Fibrosis.

• Normal Electrolyte Ranges (Brain Dump): These must be memorized based on the values presented in class, even though clinical lab ranges may vary slightly.

  • Sodium ($Na^+$): $135\text{ to }145\,mEq/L$.

  • Chloride ($Cl^-$): $96\text{ to }105\,mEq/L$ (or $98\text{ to }105\,mEq/L$).

  • Calcium ($Ca^{2+}$): Only total calcium needs to be known for this exam.

• RAAS System (Renin-Angiotensin-Aldosterone System):

  • Understand the process and why it occurs.

  • The RAAS is critical for the lungs, kidneys, and heart regarding fluid balance.

• Sodium and Fluid Balance: Sodium plays the major role in regulating fluid balance.

• Albumin: Highlighted as an extremely important factor in fluid and oncotic pressure.

• Major Fluid Imbalances: Understand the signs, symptoms, and causes for the four major fluid imbalances.

• Electrolyte Compartmentalization: Know which electrolytes are abundant in specific compartments:

  • Intracellular Fluid (ICF).

  • Extracellular Fluid (ECF).

Control of Ventilation

• Central Chemoreceptors:

  • Know where they are located.

  • Understand what stimulates them (primarily changes in $H^+$ concentration/$pH$ in the CSF).

  • Identify the specific fluid they are in contact with (Cerebrospinal Fluid).

• Reflexes: Understand the specific reflex triggered by tidal volume and stretch receptors (Hering-Breuer reflex).

• Chronic $CO_2$ Retainers: Understand the specific "Hypoxic Drive" to breathe utilized by these patients.

• Dorsal Respiratory Group (DRG): Understand what impulses from the DRG cause in the respiratory cycle.

• Intracranial Pressure (ICP): Understand methods used to help decrease high ICP, such as therapeutic hyperventilation.

Anatomy and Physiology of the Heart

• Resistance Vessels: Arterioles are considered the main resistance vessels in systemic circulation.

• Preload and Afterload:

  • Define both terms.

  • Identify factors that increase or decrease preload.

• Circulation Characteristics:

  • Systemic Circulation: High pressure, high resistance.

  • Pulmonary Circulation: Low pressure, low resistance.

• Coronary Artery Perfusion: Occurs during diastole. When blood sits back down on the aortic valve, it enters the coronary artery openings.

• Heart Chambers and Oxygenation:

  • Identify which parts of the heart carry deoxygenated blood (Right side).

  • Identify which parts of the heart carry oxygenated blood (Left side).

• Circulation Path: Review the specific path of blood flow through the heart chambers, valves, and major vessels.

Anatomy and Physiology of the Respiratory System

• Mechanics of Breathing:

  • Inspiration: An active process. The primary muscle of inspiration is the diaphragm.

  • Expiration: Primarily a passive process due to elastic recoil; there is no single "main" muscle of expiration in normal breathing.

• The Hilum: Also known as the lung root. It serves as the entry and exit point for the airways (bronchi) and the main vasculature (pulmonary arteries/veins).

• Lung Anatomy:

  • Know the number of lobes and segments in the right and left lungs.

  • Right Main Stem Bronchus: Deviates at a less steep angle than the left. This makes it a more common site for foreign body aspiration (coins, food) and unintentional right-mainstem intubation by ET tubes.

• Histology: Know the tissue types found throughout the majority of the respiratory tract (e.g., pseudostratified ciliated columnar epithelium).

• Medical Director: Dr. Varani (potential bonus question).

• Hypoxic Pulmonary Vasoconstriction (HPV): A shunting mechanism where the lungs detect low oxygen in a specific area and constrict local vessels to shunt blood to better-oxygenated areas to improve gas exchange.

Blood Cells and CO2 Transport

• Cell Types:

  • Eosinophils: Elevated in allergic reactions and asthma.

  • Erythrocytes (RBCs): Primary function is the transport of oxygen via hemoglobin.

  • Definitions: Know terms for high counts (e.g., polycythemia, leukocytosis) and low counts (e.g., anemia, leukopenia).

• Pulmonary Vascular Resistance (PVR): Review reasons why PVR may increase or decrease.

• $CO_2$ Transport Mechanisms:

  • Know the various ways $CO_2$ is carried in the blood: Dissolved in plasma, as bicarbonate ($HCO_3^-$), and carbaminohemoglobin.

  • Review the percentages associated with each transport method.

• Transport Effects:

  • Bohr Effect: The impact of $CO_2$ and $pH$ on the affinity of hemoglobin for oxygen.

  • Haldane Effect: The impact of oxygen on the affinity of hemoglobin for $CO_2$.

Diffusion of Gases

• Calculations Required:

  • Alveolar Oxygen Tension ($P_A O_2$).

  • The gradient between $P_A O_2$ and venous oxygen ($P_V O_2$).

  • The gradient between alveolar $CO_2$ ($P_A CO_2$) and arterial $CO_2$ ($P_a CO_2$).

• Barometric Pressure: Effects of high and low altitudes on pressure and diffusion gradients.

• Pathology: How specific diseases affect the diffusion of gases.

• Fick’s Law of Diffusion: Concepts including equilibrium, movement from high to low concentration, and factors affecting the rate of gas transfer.

• Capillary Transit Time: Understand the time required for diffusion to reach equilibrium at the alveolar-capillary (AC) membrane.

• AC Membrane Thickening: Patients with thickened AC membranes typically show impairment during exercise or when transit time is decreased.

Oxygen Transport and Hypoxia

• Calculations:

  • Arterial Oxygen Content: $C_a O_2 = (Hb \times 1.34 \times S_a O_2) + (P_a O_2 \times 0.003)$.

  • Understand that Hemoglobin ($Hb$) has the greatest effect on total oxygen content compared to dissolved oxygen in plasma.

• Definitions and Normal Values:

  • Oxygen Delivery ($DO_2$): The total amount of oxygen delivered to the tissues per minute.

  • Oxygen Consumption ($VO_2$): The amount of oxygen extracted and used by the tissues.

  • Oxygen Extraction Ratio ($OER$): Calculated as $\frac{VO_2}{DO_2}$.

• Oxyhemoglobin Dissociation Curve:

  • Right Shift: Caused by high $CO_2$, low $pH$ (acidosis), high temperature, and high $2,3-DPG$. Represents decreased affinity (easier unloading at tissues).

  • Left Shift: Caused by low $CO_2$, high $pH$ (alkalosis), low temperature, and low $2,3-DPG$. Represents increased affinity (stronger binding at lungs, harder unloading at tissues).

  • $P_{50}$: The partial pressure of oxygen at which hemoglobin is $50\%$ saturated. Understand what increases or decreases in $P_{50}$ signify.

• Hypoxia: Know definitions for different types (Hypoxic, Anemic, Circulatory, Histotoxic).

Pulmonary Function Testing (PFT)

• Disease Patterns: Differentiate between obstructive and restrictive diseases.

• Measurement Methods: Identify which lung volumes/capacities can be measured directly (Spirometry) vs. indirectly (e.g., Residual Volume via Plethysmography or Helium Dilution).

• Values and Indices:

  • Understand the importance of the $FEV_1/FVC$ ratio.

  • Define all lung volumes ($VT, IRV, ERV, RV$) and capacities ($VC, FRC, TLC, IC$).

  • Know which is the smallest volume and which is the largest capacity.

$V/Q$ Relationships

• $V/Q$ Ratios:

  • High $V/Q$: Ventilation exceeds perfusion (Dead space). Associated with high $P_a O_2$ and low $P_a CO_2$ in the affected unit.

  • Low $V/Q$: Perfusion exceeds ventilation (Shunt). Associated with low $P_a O_2$ and high $P_a CO_2$ in the affected unit.

• Lung Zones:

  • Zone 1: Highest $V/Q$ ratio, highest oxygen tension, lowest perfusion.

  • Zone 3: Lowest $V/Q$ ratio, lowest oxygen tension, highest perfusion.

• Calculations:

  • $P/F$ Ratio ($P_a O_2 / F_i O_2$): Normal ranges and clinical significance.

  • $A-a$ Gradient: $P_A O_2 - P_a O_2$.

  • Respiratory Quotient ($RQ$): Know the components used to calculate it.

  • Shunt Fraction ($Q_S/Q_T$): Know the different ranges and clinical interpretations (good, bad, or severe).

• Clinical Application: Patient positioning for optimal matching (e.g., putting the "good lung down").

Ventilation Principles

• Compliance ($C$):

  • Formula: $C = \frac{\Delta V}{\Delta P}$.

  • Know normal values for lung compliance, chest wall compliance, and total system compliance.

  • Elastance: The inverse of compliance ($E = 1/C$).

• Physical Tendencies: The lungs naturally want to recoil/collapse inward, while the chest wall naturally wants to expand outward.

• Dead Space:

  • Anatomic Dead Space Calculation: $1\,mL$ per pound of ideal body weight ($IBW$).

  • Identify conditions contributing to alveolar dead space.

• Alveolar Ventilation ($V_A$): Takes dead space into account. $V_A = (V_T - V_D) \times f$.

• Gas Movement Mechanics:

  • Gas moves from areas of high pressure to low pressure.

  • If there is no pressure gradient, there is no flow (equilibrium).

• Airway Resistance ($R_{aw}$):

  • Decreasing the radius of a tube increases resistance.

  • If the radius is decreased by half, the flow resistance increases by $16$ times (Poiseuille's Law).

• Boyle’s Law: Understand its relationship to the mechanism of ventilation.

Chest X-Ray (CXR)

• Anatomical Landmarks:

  • Carina: The bifurcation of the trachea; know its spinal level.

  • Diaphragm: Identify normal findings (e.g., right side slightly higher than left due to the liver).

  • Cardiothoracic Index: Used to evaluate heart size and potential cardiomegaly.

• Film Quality:

  • Overexposed: Looks very dark; lung tissue details are lost.

  • Underexposed: Looks very white; difficult to see through the heart.

  • In a good quality film, you should be able to see the thoracic vertebrae through the heart shadow.

• Pathology Identification:

  • Pleural Effusion: Look for blunting of costophrenic angles.

  • Atelectasis: Look for volume loss and shifting of structures toward the affected area.

  • Pneumothorax: Look for absence of lung markings and shifting of structures away from the affected area (in Tension Pneumothorax).

• Obstructions: Identify the radiographic differences between partial and complete airway obstructions.