V/Q Mismatch

VQ Mismatch

  1. Introduction
    1. Ventilation and Perfusion ratios are important to understand in daily pt care. To understand this subject and the pathological changes that cause abnormalities is very important.
  2. Foundation
    1. We have to refresh the basic knowledge of the cardiovascular and respiratory system and the important factors that go along.


  1. Right Side of the heart
    1. With the right side of the heart the deoxygenated blood is going to enter into the Right Atrium (RA) through the Tricuspid Valve into the Right Ventricle (RV).
    2. The RV will then pump the blood through the Pulmonary Valve into the Pulmonary Trunk. The blood is then going to separate into the right and left Pulmonary Arteries.
    3. The pressure inside the vasculature is systolic force of 25mmHg with a diastolic pressure of 8mmHg.
  2. Pulmonary Circulation to the Right Lung (Source 6)
    1. In the right lung the Right Pulmonary Artery is going to separate into the Superior Lobar Artery and the Middle Lobar Artery.
      1. The Superior Lobar Artery is going to bring the deoxygenated blood into the upper right lobe.
      2. The Middle Lobar artery is going to branch into the Inferior Lobar Artery. The Middle Lobar Artery is going to bring deoxygenated blood to the middle lobe.
      3. The Inferior Lobar artery will deliver the deoxygenated blood into the lower right lobe.
  3. Pulmonary Circulation to the Left Lung (Source 6)
    1. The left lung is much more complex with far more variants. Unlike the right lung vasculature the Left Pulmonary Artery is going to give off several Superior Lobar arteries to the upper lobe before finally branching off into a variable number of Inferior Lobar Arteries to supply the lower Lobe.
  4. Pulmonary Arteries and Capillary Beds
    1. The pulmonary arteries are going to continue to branch off until eventually reaching the pulmonary capillary beds.
    2. The pulmonary capillary beds are going to surround Alveoli (6).
    3. The capillary beds are where we see diffusion take place. This area inside the body is known as the Alveolar Capillary Membrane. This area is a single cell layer thick.
    4. The Alveolar Capillary Membrane has a large enough surface area to allow for adequate area for diffusion.
      1. This membrane also has a significant strength to resist mechanical failure in the event of increased forces that can help with diffusion of Carbon Dioxide (CO2) and Oxygen (O2) (4).
    5. The overall capillary pressure of blood is about 7 mmHg.
  5. Pulmonary Veins (6)
    1. The Alveolar Capillary beds are going to join back together into the Pulmonary Venules and Veins.
    2. The Pulmonary Veins are going to exit the lungs and deliver the oxygenated blood to the Left Atrium (LA).
    3. There are to Pulmonary Veins from each side to
  6. Other factors
    1. Significantly shorter than the systemic circulation.
    2. Includes Arterial Lumens that are larger due to being thin with distensible walls.
      1. This allows them to stretch to maintain blood flow when the body is experiencing low Cardiac Output (CO).
      2. This also prevents rupture of the micro vessels.

Respiratory- Concentrating on the topic of the lower respiratory system and volumes related to the topic.

  1. Respiratory Pathways (6)
    1. Trachea brings in air from the environment to participate in gas exchange. The Trachea is from the Larynx to the level of the Carina.
    2. At the Caina the Trachea is going to separate into the Main Bronchi.
    3. The Main Bronchi the airway path will continue to divide into the Lobar Bronchi that supply each lobe of the lungs.
      1. Right has 3 Lobar Bronchi.
      2. Left has 2 Lobar Bronchi.
    4. The Lobar Bronchi will continue to divide into smaller and smaller air pathways.
    5. These divisions will eventually reach the Alveolar Ducts that contain the Alveolar Sacs.
    6. In the Alveoli is where gas exchange will take place.
  2. Lung Volumes
    1. In the adult with average sized lungs there is about 480 Million Alveoli. Depending on the size of your lungs, this can affect the overall alveolar count. In turn can affect what is considered appropriate for your respiratory volumes. (3)
    2. Lung Volumes are important aspect of diagnosis, treatment, and maintaining adequate homeostasis. (7)
      1. Tidal Volume (TV)- the amount of air that is moved into or out of the lungs during a single breath. About 500mL.
      2. Total Lung Capacity- the substantial amount of air that can be moved within the respiratory system. About 6,000mL in the adult male, ⅓ less in adult females due to the smaller lung size.
      3. Inspiratory Reserve Volume- the deepest breath you can take after normal breathing. About 3,000mL.
      4. Expiratory Reserve Volume- the maximum amount of air that you can forcibly breath out after normal breathing. About 1,200mL.
      5. Residual volume- the amount of gas that remains in your lungs to keep your lungs for collapsing. About 1,200mL. This volume of gas does not move during ventilation.
  3. Dead Space (5)
    1. Dead Space is the area inside the respiratory system that does not participate in gas exchange.
    2. We lose a part of the ventilated air to the dead space. About 30% of our TV is lost. Meaning that we lose about 150mL of TV.
    3. Our Physiologic Dead Space in the lungs can increase how much ventilatory volume is lost due to some lung disease states that affect the alveoli. Preventing them from functioning properly.

Normal VQ Ratio

  1. Volumes for VQ (7)
    1. Resting Minute Ventilation Volume
      1. About 6L/min
      2. About ⅓ of this minute volume is lost to dead space. Meaning that the volume is reduce to about 4L/min.
    2. Pulmonary Blood Flow
      1. About 5L/min of blood flow that is circulated through the lungs by the heart.
    3. Making the overall ratio of Ventilation (V) to Perfusion (Q) 4:5 or 0.8 L/min.
      1. Once simple way to understand this is to divide the lungs into three sections to understand what normal VQ ratios are. The V and Q throughout the lungs differs.
  2. Zone 1- Also known as the Apex (8)
    1. The VQ ratio here is naturally higher.
    2. Blood flow will be lower to the area
    3. Ventilation coming to the apex is not going to be fully able to be involved due to the lower perfusion.
    4. Due to its location above the heart the alveolar size is going to be larger giving you a larger surface area for gas exchange.
    5. Less Pulmonary Intravascular pressure as well due to less blood flow.
    6. Basically you have poor V with pretty bad Q.
  3. Zone 2- The Middle (8)
    1. The VQ ratio here is naturally neutral.
    2. We have equal levels of V and Q.
    3. Making an appropriate ratio.
  4. Zone 3-The Base (8)
    1. The VQ ratio here is naturally lower.
    2. There is a higher level of blood flow to this area.
    3. The alveolar size is going to decrease as you move superior to inferior throughout the lung tissue. This is also partially due to the difference in intrapleural pressure.
    4. The alveoli are able to expand and play more of an active role in gas exchange but are still not quite enough for equal V and Q ratio.
    5. Basically we have good V and great Q.
  5. Factors that affect VQ (8)
    1. Gravity plays a significant role in how much blood flow the different sections of the lungs will receive.
    2. Variations in pressures, respiratory volumes, cardiac functioning and output, positioning, altitude and individuals overall health will affect the overall VQ ratios.

Intrapulmonary Shunting

  1. What it is (1)
    1. Where you have blood flow without appropriate aeration. Where the amount of O2 going into the respiratory system is not involved in gas exchange. Resulting in a decreased Minute Ventilation form the 4L/min.
    2. As CO2 comes to the alveolar capillary membrane it is not able to diffuse properly out from the red blood cells into the alveoli to be breathed off. At the same time you are not getting the appropriate O2 brought into the alveoli to diffuse into the bloodstream.
    3. The CO2 will either stay in the bloodstream or move back into the bloodstream. Being returned to the left side of the heart. In the same situation where the alveoli are completely occluded the O2 will never be able to diffuse into the bloodstream and be exhaled out.
  2. Causes (1)
    1. Pneumonia, Pulmonary Edema, Asthma, and COPD can result in a disturbance of the cellular metabolism.
    2. Decreasing the surface area of the alveoli by damaging the alveoli or by leading to an accumulation of fluid in the lungs.
    3. Creating a state where the alveoli are nonfunctional, stopping or reducing gas exchange.
    4. Pneumothorax along with atelectasis can also cause this to occur by the collapsing of the alveoli reducing the overall surface area available for diffusion to take place.
  3. Important information (2)
    1. This shift of nonfunctional alveoli increases the overall pulmonary dead space.
    2. Causing the low VQ mismatch.
    3. Decreasing the PAO2 of the functional alveoli.
    4. Casing overall increased hypoxia.

Alveolar Dead Space

  1. What it is (2)
    1. You still are getting an appropriate aeration without adequate blood flow.
    2. Blood flow is unable to get into the capillary beds.
    3. The oxygen being brought into the alveoli does not participate in diffusion.
    4. Increasing the overall TV that is lost to dead space.
    5. Causing a decrease in overall perfusion.
  2. Causes
    1. Pulmonary Arteriovenous Malformations (AVMS), Congenital heart defects, pulmonary embolisms, Cardiogenic shock, air emboli, and Hypoxic pulmonary vaso constriction. (1&2)
  3. Important information
    1. Decreasing the overall oxygenated blood and causes a buildup of CO2 (7).
    2. Causing Hypoxemia. (7)
    3. Leading to overall changes in pH.

Signs/Symptoms & Scenario

  1. S/S (1)
    1. Increase CO2 in the blood
    2. Decreased EtCO2 readings
    3. Remember that CO2 bond to hemoglobin is stronger than O2.
    4. Due to the potential cause of VQ mismatch being variable, the symptoms for identification and recognition is vital.
    5. The signs and symptoms of the pathology is going very and drive treatment.
    6. As you progress further into critical care, lab values, blood gasses, imaging, ect… will become an important tool for identification and understanding the degree of mismatch.
  2. Scenario
    1. Dispatched for a 38 year old female pt.
    2. Dispatch sends you to a local hotel.
    3. Upon arrival you see a young female clasping her chest in a tripod position.
    4. Vitals
      1. HR: 136
      2. BP: 176/86 (116)
      3. RR: 26
      4. SpO2: 74% on Room Air
    5. Assessment
      1. Airway is patent.
      2. Breathing is labored, tachypnea, and with excessive volumes
      3. Circulation  is strong, regular, and rapid.
      4. Chest
        1. Bilateral lungs have wheezing in the bases and clear in the middle to upper lobes.
        2. Retractions noted to the subclavicular area.
      5. Abdomen is WNL.
      6. Skin is pale with cyanosis to the lips.
      7. Pt is able to speak in 3-5 words at a time.
    6. Subjective
      1. Pt relays that she has had worsening SOB over the last 2 hours. Pt relays that she woke up from sleep feeling like an elephant was sitting on her chest. Pt relays that it hurts to breathe and she feels like there is glass in her chest. Pt relays that even her heart beating it is so painful. Pt relays that the pain is 10/10. Pt relays that she just got into town. Pt relays that she flew in on a 6 hour flight. Pt relays that she felt a little shaky and dizzy after the flight and thought it would get better after a little bit of rest. Pt relays that she does have Asthma, but has never had an issue like this before. Pt relays that she used her Albuterol MDI about 30 minutes prior to your arrival, but it did not help. Pt relays that she has a 3 week old new born at home with her husband. Pt relays that she had a healthy pregnancy but her OBGYN relayed that she had some abnormal labs a week ago at her last follow up appointment. Pt relays that she does have a list of medications, but it is getting harder to breathe.
    7. PMH, Medications, Allergies
      1. PMH: Asthma
      2. Medications: Albuterol, Vitamin D3, Vitamin C, and an oral contraceptive.
      3. Allergies: Penicillin and Solumedrol.
    8. Treatments:
      1. Albuterol & Ipratropium Nebulizer
      2. IV Access
      3. 12-lead EKG
        1. Shows no ST elevation, but a shift in R axes deviation
      4. EtCO2 Monitoring
    9. Follow up vitals.
      1. HR: 140
      2. BP: 182/96 (124)
      3. RR: 28
      4. SpO2: 98% on the nebulizer treatment
      5. EtCO2: 16
      6. Skin has improved to pale with no signs of cyanosis
    10. Upon reassessment you note that the pts starting to be able to breathe easier, the subclavicular retractions have cleared. Bilateral lung sounds are clear upon reassessment after the pt completed the nebulizer treatment. However after taking the pt off the nebulizer you note that her room air SpO2 is only 92%
    11. You load the pt up into the unit. During transport you continue delivering oxygen via NC at 4 Lpm and are able to keep the pts SpO2 at 94%.
    12. Vitals
      1. HR: 136
      2. BP: 158/88 (111)
      3. RR: 24
      4. SpO2: 94% on O2 at 4 Lpm via NC
      5. EtCO2: 20
      6. Skin is PWD.

Content Creator: Carli Wymore
CAPCE Course Number: 22-EMTP-F3-3306
Total CE Hours: 1.0
Level: Advanced
EMT-CE uses the NEMSES guidelines as the foundation for every course outline.