Oxygenation, Respiratory & Circulatory Function – Exam Notes
Physiology of Oxygenation
Four sequential steps for effective oxygenation
Ventilation: The mechanical process of moving air in and out of the lungs. It is regulated by respiratory centers in the pons and medulla oblongata, which respond primarily to changes in blood (pH) and levels. An increase in or (acidosis) stimulates an increased rate and depth of breathing.
Alveolar gas exchange (external respiration): The diffusion of from the alveoli into the pulmonary capillaries and the diffusion of from the blood into the alveoli. This process is governed by partial pressure gradients and the properties of the alveolar-capillary membrane.
transport & delivery: The process by which oxygen is carried from the lungs to the body tissues. This is influenced by:
Dissolved in plasma: A small amount of oxygen (approximately 3%) is transported dissolved in the plasma.
Hemoglobin (Hgb) concentration: The primary mechanism for transport (97%) is by binding to hemoglobin in red blood cells. A decreased Hgb level reduces the blood's oxygen-carrying capacity.
Hgb– affinity: The ease with which hemoglobin binds and releases oxygen. Factors like pH, concentration, temperature, and 2,3-bisphosphoglycerate (2,3-BPG) influence this affinity (e.g., a right shift of the oxyhemoglobin dissociation curve means Hgb gives up more readily to tissues).
Cellular (internal) respiration: The diffusion of from the capillaries into the tissue cells and the utilization of by the mitochondria for ATP production via oxidative phosphorylation. Concurrently, diffuses from the cells into the capillaries.
Key blood measurements in oxygenation assessment
(Partial pressure of arterial oxygen): Normal range is . Indicates the amount of oxygen dissolved in arterial blood.
(Oxygen saturation): Normal range is . Represents the percentage of hemoglobin binding sites occupied by oxygen.
Cardiac cycle's role: The heart's efficient pumping (e.g., ) is essential for circulating oxygenated blood to all tissues and returning deoxygenated blood to the lungs.
Factors Affecting Oxygenation
Age:
Older adults: Experience decreased chest wall compliance, weakening of respiratory muscles, and reduced elastic recoil of the lungs, leading to less efficient gas exchange. They also have a diminished cough reflex and ciliary function, increasing the risk of respiratory infections and aspiration.
Infants/Young children: Have smaller airways, less developed immune systems, and higher metabolic rates, making them more susceptible to respiratory distress and infections.
Environment/Lifestyle:
Tobacco smoke: Causes vasoconstriction, impairs ciliary function, increases mucus production, and destroys alveolar-capillary membranes, leading to chronic obstructive pulmonary disease (COPD) and increased cancer risk.
Air pollutants and allergens: Exposure can trigger bronchospasm, inflammation, and exacerbate respiratory conditions like asthma.
Occupational dust/chemicals: Chronic exposure (e.g., asbestos, silica, coal dust) can lead to pneumoconiosis, fibrosis, and restrictive lung diseases.
Disease processes:
Obstructive lung diseases: Characterized by airflow limitation due to narrowed airways, leading to air trapping and increased residual volume.
Asthma: Reversible airway inflammation and hyperresponsiveness, resulting in bronchospasm, edema, and mucus production.
Emphysema: Destruction of alveolar walls, leading to large, non-elastic airspaces and reduced surface area for gas exchange.
Chronic bronchitis: Chronic inflammation and excessive mucus production in the bronchi, resulting in persistent cough and airway obstruction.
Restrictive lung diseases: Involve reduced lung expansion due to stiffness of the lung tissue itself or the chest wall, affecting total lung capacity.
Pneumonia: Infection leading to inflammation and fluid accumulation in the alveoli, impairing gas exchange.
Pulmonary fibrosis: Scarring and thickening of lung tissue, making lungs stiff and difficult to expand.
Pleural conditions/Trauma: Conditions affecting the pleura or structural integrity of the chest wall.
Pleural defects: Conditions affecting the pleura (membranes surrounding the lungs) or the space between them (pleural space).
Pleural effusion: Accumulation of excess fluid in the pleural space, compressing the lung.
Hemothorax: Presence of blood in the pleural space, often due to trauma.
Pneumothorax: Presence of air in the pleural space, causing lung collapse. Can be spontaneous or traumatic.
Tension pneumothorax: A life-threatening condition where air enters the pleural space but cannot exit, leading to increasing pressure, lung collapse, mediastinal shift, and impaired cardiac output.
Diffusion defects: Impaired gas transfer across the alveolar-capillary membrane.
Thickening of the membrane (e.g., fibrosis, acute respiratory distress syndrome [ARDS]).
Decreased surface area (e.g., emphysema, pneumonectomy).
Circulatory Influences
Ventilation–Perfusion (V/Q) mismatch: An imbalance between the amount of air reaching the alveoli (V) and the amount of blood flowing through the pulmonary capillaries (Q). This is the most common cause of hypoxemia.
Dead space: Areas of the lung that are ventilated but poorly perfused (e.g., pulmonary embolism, severe emphysema). Air enters, but little to no gas exchange occurs.
Shunt: Areas of the lung that are perfused but poorly ventilated (e.g., pneumonia, atelectasis, ARDS). Blood bypasses well-oxygenated alveoli, leading to deoxygenated blood returning to the systemic circulation.
Atherosclerosis: The hardening and narrowing of arteries due to plaque buildup. This reduces blood flow (ischemia) to organs, leading to conditions like:
Myocardial Infarction (MI): Heart attack due to blocked coronary arteries, impairing the heart's pumping ability.
Cerebrovascular Accident (CVA): Stroke due to blocked or ruptured cerebral arteries, affecting brain function, including respiratory control.
Heart failure & Hypovolemia: Conditions that lead to inadequate cardiac output (CO), meaning the heart cannot pump enough blood to meet the body's metabolic demands.
Heart failure: The heart's inability to pump blood effectively, leading to fluid backup in the lungs (pulmonary edema) and systemic circulation, impairing tissue perfusion and gas exchange.
Hypovolemia: Decreased circulating blood volume (e.g., hemorrhage, dehydration) leads to reduced venous return and thus reduced cardiac output and oxygen delivery to tissues.
Blood factors:
Low Hemoglobin (Hgb): Conditions like anemia (due to iron deficiency, blood loss, chronic disease) reduce the number of red blood cells or the amount of Hgb available, significantly decreasing the blood's oxygen-carrying capacity.
Impaired cellular uptake of : Even with adequate delivery, cells may be unable to utilize oxygen effectively.
Cyanide poisoning: Disrupts cellular oxidative phosphorylation, preventing cells from using oxygen.
Sepsis: Systemic inflammatory response can lead to microcirculatory dysfunction, hindering oxygen extraction by tissues.
Physiological Responses to Reduced Oxygenation
Increased oxygen extraction & Anaerobic metabolism: When oxygen supply is insufficient for aerobic metabolism, cells switch to anaerobic metabolism (without ) to produce ATP. This is less efficient and produces lactic acid as a byproduct.
Lactic acidosis: Accumulation of lactic acid lowers blood pH, leading to metabolic acidosis, which can impair enzyme function and cellular processes throughout the body and further compromise organ function.
High altitude:
Acute response: The immediate response to lower atmospheric partial pressure of oxygen at high altitude is an increase in ventilation (hyperventilation/tachypnea) to try and maintain . Peripheral chemoreceptors are stimulated.
Chronic adaptation: Over time, the kidneys release erythropoietin, stimulating red blood cell production (polycythemia) to increase oxygen-carrying capacity. There can also be some degree of decreased cellular demand or increased efficiency of oxygen utilization at the tissue level.
transport and acid–base balance: is primarily transported as bicarbonate (). Its levels in the blood are critical for maintaining pH.
Hypercapnia: Elevated arterial () usually indicates hypoventilation. This leads to respiratory acidosis (decreased pH), as combines with water to form carbonic acid.
Tachypnea: Rapid breathing, often a compensatory mechanism for acidosis or hypoxemia, can lead to increased excretion (if effective ventilation is achieved) or, if non-effective, may indicate respiratory distress and worsening hypercapnia.
Assessment & Diagnostics
History (COLDSPA): A systematic approach to symptom gathering.
Cough: Onset, frequency, character (dry, productive).
Sputum: Color (clear, white, yellow, green, rust, bloody), consistency, amount. Color helps indicate pathology (e.g., green/yellow suggests bacterial infection).
Shortness of Breath (SOB)/Dyspnea: Onset, severity (at rest, with exertion), alleviating/aggravating factors, orthopnea, paroxysmal nocturnal dyspnea.
Pain: Chest pain (location, character, pleuritic vs. cardiac).
Associated symptoms: Fever, chills, fatigue, wheezing.
Physical exam:
Inspection: Observe respiratory rate, rhythm, depth, effort (use of accessory muscles), cyanosis (central/peripheral), clubbing of fingers, chest shape (barrel chest).
Palpation: Assess for tracheal deviation, fremitus (tactile vibratory thrills, increased with consolidation, decreased with fluid/air), tenderness.
Percussion: Evaluate lung density. Resonance over normal lung tissue, dullness over consolidation or fluid, hyperresonance over air trapping (emphysema, pneumothorax).
Auscultation: Listen for breath sounds (vesicular, bronchial, bronchovesicular), presence of adventitious sounds (crackles/rales, wheezes, rhonchi, pleural rubs), and their location.
Ventilation studies:
Spirometry: Measures lung volumes and airflow rates (e.g., Forced Vital Capacity [FVC], Forced Expiratory Volume in 1 second []). Used to diagnose and monitor obstructive and restrictive lung diseases.
Peak Flow Spectroscopy (PFS): Measures the maximum speed of expiration, indicating large airway function, commonly used in asthma management.
Sputum analysis: Microscopic examination and culture of sputum to identify pathogens (bacteria, fungi, viruses) and guide antimicrobial therapy. Cytology can detect abnormal cells (e.g., cancer).
Hematology:
Lactate: Elevated levels ({>2 \;mmol/L}) indicate tissue hypoperfusion or anaerobic metabolism, suggesting severe hypoxia or shock.
Hgb/Hct: Hemoglobin and hematocrit levels assess the oxygen-carrying capacity of the blood. Low levels indicate anemia.
Venous blood gases (VBG): Provide information on venous pH, , and bicarbonate, often used to screen for acid-base imbalances when ABG is not immediately available.
Enzymes:
Creatine Phosphokinase (CPK): Elevated levels, particularly isoenzymes like CK-MB, indicate myocardial muscle damage.
Lactate Dehydrogenase (LDH) isoenzymes: Can indicate tissue injury in various organs, including the lungs and heart.
Lipid panel: Measures cholesterol (total, LDL, HDL) and triglycerides. High levels are a significant risk factor for cardiovascular disease (CVD), which directly impacts circulatory oxygenation.
Arterial Blood Gas (ABG) normals: Provide a snapshot of oxygenation, ventilation, and acid-base status.
(acidity/alkalinity of blood)
(respiratory component)
(metabolic component/bicarbonate)
Imaging and endoscopic procedures:
Pulse oximetry: Non-invasive measurement of arterial oxygen saturation (), providing continuous monitoring of oxygenation effectiveness.
Chest X-ray (CXR): Provides images of lungs, heart, and chest wall. Used to detect pneumonia, pulmonary edema, effusions, pneumothorax, tumors, and fractures.
Bronchoscopy: Direct visualization of the tracheobronchial tree using a flexible scope. Allows for biopsy, lavage (BAL), and removal of foreign bodies or mucus plugs.
Thoracentesis: A procedure to remove fluid or air from the pleural space for diagnostic or therapeutic purposes.
Common Nursing Problems
Ineffective airway clearance: Inability to clear secretions or obstructions from the respiratory tract to maintain a patent airway (e.g., due to excessive mucus, weak cough).
Ineffective breathing pattern: Inspiration and/or expiration that does not provide adequate ventilation (e.g., tachypnea, bradypnea, dyspnea, use of accessory muscles).
Impaired gas exchange (V/Q mismatch): Excess or deficit in oxygenation and/or carbon dioxide elimination at the alveolar-capillary membrane.
Decreased cardiac output → ineffective tissue perfusion: Inadequate blood pumped by the heart to meet metabolic demands, leading to insufficient oxygen and nutrient delivery to tissues.
Activity intolerance: Insufficient physiological or psychological energy to endure or complete required or desired daily activities, often due to hypoxia.
Anxiety: A state of apprehension or uneasiness often triggered by dyspnea or fear of not being able to breathe.
Interventions
Promote Airway Clearance
Teach effective cough/huffing: Instructions on controlled cough techniques (e.g., deep breath, hold, then two or three short, forced exhalations with open glottis) to mobilize secretions. Huffing is less strenuous for patients with COPD.
Postural drainage & Chest Physical Therapy (CPT): Techniques to use gravity and manual percussion/vibration to loosen and mobilize secretions from specific lung segments, followed by coughing or suctioning. Requires specific positioning for different lobes.
Hydration monitoring: Encourage adequate fluid intake ( unless contraindicated) to thin secretions and facilitate their removal. Monitor intake and output (I&O) and signs of dehydration or fluid overload.
Medications:
Expectorants (e.g., Guaifenesin): Loosen bronchial secretions, making coughs more productive.
Mucolytics (e.g., Acetylcysteine): Breakdown the viscosity of mucus, improving clearance.
Bronchodilators: Relax bronchial smooth muscles, widening airways.
Beta-adrenergic agonists (e.g., Epinephrine, Albuterol, Salmeterol): Short-acting (rescue) or long-acting (maintenance) drugs that stimulate beta-2 receptors in the lungs, causing bronchodilation.
Corticosteroids (inhaled e.g., Fluticasone; systemic e.g., Prednisone): Reduce airway inflammation and hyperresponsiveness. Systemic corticosteroids are used for acute exacerbations.
Mast-cell stabilizers (e.g., Cromolyn): Prevent the release of inflammatory mediators from mast cells, used for asthma prophylaxis.
Methylxanthines (e.g., Theophylline): Cause bronchodilation and mild anti-inflammatory effects, but have a narrow therapeutic range and potential for toxicity.
Artificial airways: Endotracheal or tracheostomy tubes for patients unable to maintain a patent airway or who require mechanical ventilation. Proper care prevents complications.
Suction as needed: Mechanical removal of secretions from the trachea and bronchi in patients unable to clear their own airways (e.g., with artificial airways, impaired cough reflex). Aseptic technique is crucial.
Improve Uptake & Delivery
Administer supplemental : Provide oxygen through various delivery devices (nasal cannula, masks, non-rebreather, Venturi mask) to increase the inspired oxygen concentration, raise , and reduce work of breathing. Titrate based on and patient assessment.
Transfuse blood components:
Packed Red Blood Cells (PRBCs): For severe anemia or acute blood loss to increase oxygen-carrying capacity.
Volume expanders: For hypovolemia to improve circulating volume and tissue perfusion.
Enhance CO & Tissue Perfusion
Fluid/Na management: Careful management of fluid balance to optimize cardiac preload without causing fluid overload (in heart failure) or dehydration (in hypovolemia).
Daily weights, I&O: Essential for monitoring fluid status.
Activity & positioning:
Elevated head/torso (Fowler's position): Reduces abdominal pressure on the diaphragm, allowing for maximal lung expansion and easing work of breathing.
Activity: Gradual increase in activity to improve cardiovascular conditioning and oxygen utilization, while monitoring for signs of activity intolerance.
Medications:
Diuretics (e.g., Furosemide, Hydrochlorothiazide): Reduce circulating fluid volume, decreasing preload and alleviating pulmonary congestion in heart failure.
Cardiac glycosides (e.g., Digoxin): Positive inotropic effect (increase contractility) and negative chronotropic effect (slow heart rate), improving cardiac output.
Inotropes (e.g., Dobutamine, Milrinone): Directly increase myocardial contractility, used for acute heart failure or cardiogenic shock.
Antihypertensives:
ACE inhibitors (-prils): Reduce afterload and preload, prevent ventricular remodeling.
Beta-blockers (-olols): Reduce heart rate and contractility, improve myocardial oxygen supply-demand balance.
Calcium Channel Blockers (CCB: e.g., Amlodipine, Diltiazem): Cause vasodilation and can reduce heart rate, decreasing cardiac workload.
Vasodilators & Nitrates (e.g., Nitroglycerin, Hydralazine): Reduce preload and/or afterload by relaxing vascular smooth muscle, improving blood flow and reducing cardiac workload.
Emergencies
Clear airway obstruction: Immediate action is critical.
Upper airway obstruction: Heimlich maneuver (abdominal thrusts) for conscious adults, back blows and chest thrusts for infants.
Lower airway obstruction: Bronchodilators for bronchospasm, suctioning for secretions.
Initiate CPR when indicated: Cardiopulmonary resuscitation (chest compressions and rescue breaths) for cardiac arrest or respiratory arrest, maintaining cerebral and cardiac perfusion until advanced medical help arrives.
Key Laboratory / Diagnostic Ranges (Quick Recall)
Lipids:
Total Cholesterol (Chol) < 5.17\;mmol/L
Low-Density Lipoprotein (LDL) < 3.36\;mmol/L
High-Density Lipoprotein (HDL) > 1.03\;mmol/L
Triglycerides (TG) < 2.82\;mmol/L