oxygen 2

• Oxygen can be prescribed or ordered in Liters per minute (Lpm)
• Patient Refusal: when the patient does not consent to receiving oxygen therapy
• 1. a gradient:

  • Measures the Alveolar arterial gradient
  • Helps in diagnosing hypoxemia and narrowing down the diagnosis
• V/Q mismatch:

  • Shunt defect (impaired ventilation; preserved perfusion, e.g., Lobar Pneumonia)
  • Dead space (impaired perfusion; preserved ventilation, e.g., Pulmonary embolism)
• Alveolar Hypoventilation – Type 2:

  • Ventilatory failure or pump failure
  • Inability to eliminate CO2 effectively
• Low ambient pressure:

  • Refers to going to high altitudes
  • Above sea level, the barometric pressure tends to decrease, causing a decrease in PAO2
• Hypoxia:

  • A deficiency of oxygen at the tissue level
  • Remember that CaO2 is 98% in hemoglobin and 2% in plasma
• Hypoxic Hypoxia:

  • PaO2 problem, reduced oxygen tension
  • Examples include high altitude, equipment error, and drug overdose
• Anemic Hypoxia:

  • PaO2 is normal but the amount of hemoglobin that can carry oxygen is reduced
  • Problem in oxygen in the blood, examples include Anemia, carboxyhemoglobin, and Methemoglobinemia
• Stagnant Hypoxia:

  • Normal CaO2, but blood flow in tissues is reduced, leading to reduced oxygen delivery
• Histotoxic Hypoxia:

  • Problem in the tissue, e.g., Cyanide poisoning
  • Classified as Anemic because carbon monoxide binds to Hb
• CaO2:

  • Computes oxygen content of hemoglobin (mL) + oxygen content in the plasma
  • If PaO2 is less than 60, it triggers Peripheral chemoreceptors
• Oxygen index:

  • Added during COVID-19
  • A-a ratio is the most reliable because it's not easily affected by changes in supplemental O2
• Diffusion Disorder:

  • Pulmonary fibrosis
• Shunting:

  • Perfusion with no ventilation (collapsed alveoli)
  • Mnemonic: Strip clip hard
• Pulmonary vasoconstriction:

  • Pulmonary Vascular Resistance increases due to hypoxic vasoconstriction
  • Caused by low inspired PO2
• Cyanosis:

  • Indicates a shortage of O2 in the blood
• Cor pulmonale:

  • Right heart failure
  • Pulmonary hypertension leads to increased afterload
• Lung cancer mostly causes clubbing
• Alveolar capillary membrane:

  • Anatomically is 5, and physiologically is 3 due to the fusion of interstitial space (basement membrane and capillary endothelium)
• Haldane:

  • Dissociation occurs in the lungs
  • Oxygen causes the unbinding of CO2 and Hb
• Bohr:

  • In the tissues
  • CO2 causes oxyhemoglobin to unbind
• COPD patients:

  • Compensated respiratory acidosis with high PCO2 levels and decreased pH
  • They are not driven by CO2 for breathing, oxygen becomes the main drive
• Administration of high flow O2 with COPD patients:

  • Low flow is recommended because they are used to low O2 and high CO2 levels
  • Peripheral chemoreceptors respond to high PO2 rather than central
• ROS formation:

  • Occurs when Free O2 reacts with free electrons
• Administration of 100% Oxygen to a patient with myocardial infarction:

  • Not recommended, administer anticoagulant until stable before giving oxygen
• Increase in capillary permeability leads to edema and eventually to thickened membranes and pulmonary fibrosis
• Premature:

  • Refers to 34 weeks of gestation, avoid giving 100% O2 to prevent vascular proliferation
• High concentration of O2 can cause atelectasis
• Nitrogen:

  • Prevents alveolus collapse and is absorbed more slowly
• Denitrogenation:

  • Refers to the absence of nitrogen when there is 100% O2
• Humidity Therapy


  • Addition of water vapor to inspired gas
• Humidification


  • Method to artificially condition the gas used in respiration of a patient as a therapeutic modality
  • Primary goal: Maintain normal physiologic conditions in the lower airways
• Physiology


  • Heat and moisture exchange is a primary function of the URT
  • Nasal mucosal lining is kept moist by secretions from mucus glands, goblet cells, transudation of fluid through cell walls, and condensation of external humidity
  • Inhale - saturate, Exhale - unsaturated (air cools- condensation)
  • Vibrissae - Nose Hair for Filter
  • Ultimate goal of respiratory system: Gas Exchange to give adequate O2 and remove CO2
  • The mouth is less effective at heat and moisture exchange than the nose because: Less warm & moist surface area than the nose, Less vascular epithelium than the nose
  • Nostril conditions the air during inspiration (turbinates and concha- warm, filter, humidify) unlike breathing through mouth
  • Dry air can damage respiratory lining
  • Increase humidity carrying capacity, more water vapor it can hold
  • As inspired gas travels through the lungs, it achieves BTPS conditions: Body temperature (37°C), Barometric pressure (760 mmHg), Saturation with water vapor (100% relative humidity @ 37°C)
  • Isothermic saturation boundary - located 5cm below the Carina
• Respiratory System


  • When the temperature is at 37°C, absolute humidity at 44mg/L, relative humidity of 100% is an ideal condition for the cilia to work efficiently
  • Goblet Cells + Submucosal Glands maintain the mucus layer
  • Pseudostratified ciliated columnar epithelium (in Nasopharynx) serves as Trap for pathogen and as interface for humidity exchange
  • Turns to simple humoidal type: Terminal Bronchioles with scars of submucosal gland and goblet cells
  • Gel and Sol Layer
  • Capacity of Lower Airways to humidify air is less/limited than Upper
  • Above ISB, temperature & relative humidity decrease during inspiration & increase during exhalation
  • Below ISB, temperature & relative humidity remain constant
  • ISB shift DISTALLY when: Person breathes through the mouth, Person breathes dry air, cold air, Breathing is bypassed
• ET Tube


  • Upper airway loses capacity to give heat and moisture exchange
  • ISB is shifted down to Respiratory tract
  • Increase burden in respiratory tract
  • Damage respiratory epithelium
  • Minute ventilation higher than normal: MV= Vt x RR, 1:2 34:15
• Basic Properties of Humidity Therapy

  • Humidity is essentially the water vapor in a gas
  • Water in gaseous form: Water vapor or Molecular Water
  • Alveoli - Absolute humidity regardless of Humidity of inspired air
• A patient on a T-tube flow-by

  Inspiring air from a
• NOTE!!!: The warmer the air the more water it can hold
• Absolute Humidity: The actual content of water vapor in a gas measured in mg/L