Oxygen Therapy

Goal of Oxygen

 

n      Maintain adequate tissue oxygenation while minimizing cardiopulmonary work.

 

Clinical Objectives

 

n      Correct documented or suspected acute hypoxemia.

n      Decrease the symptoms associated with chronic hypoxemia.

n      Decrease the workload hypoxemia imposes on the cardiopulmonary system.

 

Correcting Hypoxemia

 

n      Raise alveolar and blood levels of oxygen.

 

Decreasing the Symptoms of Hypoxemia

 

n      Relieves the symptoms associated with certain lung disorders( ex. COPD).

n      Improve mental function.

 

Minimizing Cardiopulmonary Workload

 

n      Decrease the demands and both the heart and lungs.

n       Hypoxemic patients breathing room air can achieve acceptable arterial oxygenation only by increasing ventilation®­ventilatory demand and work of breathing.

n       Acceptable tissue oxygenation can be maintained by ­cardiac output.

 

n        O2 therapy increase blood oxygen content®¯workload of the heart to meet tissue demand.

n       Important when the heart is stressed with disease ( ex. Myocardial infarction).

 

 

n      Hypoxemia causes pulmonary vasoconstriction and pulmonary hypertension.

n       ­Workload on the right heart.

n       This increase workload can lead to right ventricular failure (cor pulmonale).

 

Assessing the Need for Oxygen Therapy

 

n      Laboratory measures to document hypoxemia.

n      Clinical problem or condition.

n      Bedside assessment techniques.

 

 

n      Laboratory measures used to document hypoxemia include either Hb saturation or po2, as determined by either invasive or noninvasive means.

 

n       Clinical problems or disorders in which hypoxemia is common also need O2 therapy.

n        Post-op patients.

n        Carbon monoxide poisoning.

n        Cyanide poisoning.

n        Shock.

n        Trauma.

n        Myocardial infarction.

 

Bedside Physical Assessment Can Also Reveal a Need for O2 Therapy.

 

Precautions and Hazards of Supplemental Oxygen

 

n      Oxygen toxicity

n      Depression of ventilation

n      Retinopathy of prematurity

n      Absorption Atelectasis

 

Oxygen Toxicity

 

n      Affects the lungs and central nervous system.

n      Two primary factors determine oxygen’s harmful effects;

n       The PO2.

n       Exposure time.

 

 

 

n      CNS effects (including tremors, twitching, and convulsions) tend to occur only when a patient is breathing oxygen at  pressures greater than 1 atmosphere.

 

n      Patient’s exposed for prolonged periods show signs similar to bronchopneumonia.

n       Patchy infiltrates on chest x-ray, usually in the lower lung fields.

n       Major alveolar injury: capillary damage®interstitial edema®thickening of alveolar-capillary membrane ®type I alveolar cells are destroyed, type II cells proliferate.

 

n      An exudative phase follows, causing a low V/Q ratios, physiological shunting, and hypoxemia.

n      End stage® hyaline membranes form in alveolar region, followed by the development of pulmonary fibrosis and hypertension.

 

n      As the lung injury worsens, blood oxygenation deteriorates® additional oxygen®toxic effects worsen.

n      Oxygen toxicity is caused by overproduction of oxygen free radials.

n       Oxygen free radicals are byproducts of cellular metabolism.

 

n      In the presence of high PO2 free radicals can overwhelm the antioxidant systems and cause cell damage.

n      You should never withhold supplemental oxygen from a hypoxic patient.

 

Depression of Ventilation

 

n      When breathing moderate to high oxygen concentrations, COPD patients with chronic hypercapnia tend to ventilate less.

n       Suppression of the hypoxic drive.

n   Normal response to high PCO2 is blunted , with the primary stimulus to breathe being oxygen lack ( as sensed by the peripheral chemoreceptors).
n   Raising blood O2 levels in these patients suppresses the peripheral chemoreceptors, thereby depressing ventilatory drive and elevating the PCO2.

 

n         High levels of O2 may disrupt the normal V/Q balance, causing an increase in the VD/VT ratio and a rise in paco2.

 

Retinopathy of Prematurity

 

n      ROP: also Retrolental fibroplasis®is an abnormal eye condition that occurs in some premature or low-birth weight infants who receive supplemental oxygen.

n      Excessive blood oxygen levels cause retinal vasoconstriction, which leads to necrosis of the blood vessels.

 

n      In response, new vessels form and increase in number.

n      Hemorrhage of these new vessels causes scarring behind the eye’s retina.

n      Scarring leads to retinal detachment and blindness.

n      Mostly effects neonates up to one month of age.

 

n       Excessive oxygen is not the only factor associated with ROP.

n        Hypercapnia.

n        Hypocapnia.

n        Intraventricular hemorrhage.

n        Infection.

n        Anemia.

n        Hypocalcaemia.

n        Hypothermia.

 

 

n      The American academy of pediatrics recommends keeping an infants arterial po2 below 80 mmHg as the best way to minimize the risk of ROP.

 

Absorption Atelectasis

 

n       Fio2 > 0.50 increase the risk of a unique form of atelectasis (absorption atelectasis).

n        When breathing room air, the greatest content of this gas is nitrogen (~78%). It must be remembered that nitrogen is inert.

n        Nitrogen exerts a significant partial pressure within the alveolus – stinting the alveolus open.

n        If 100% oxygen is breathed, the nitrogen is washed out and when the oxygen is transferred across the alveolar capillary membrane, there is not enough pressure within the alveolus to hold it open.

n        Absorption atelectasis results.

 

Oxygen Delivery Systems

 

n      We categorize oxygen delivery devices by their design. Three basic designs exist:

n       Low-flow systems

n       Reservoir

n       High-flow systems

 

Low-Flow Systems

 

n      Provides supplemental oxygen directly to the airway at flows of 8 L/min or less.

n         Normal adult’s inspiratory flow exceeds 8 L/min, the oxygen provided by a low-flow device is always diluted with air, resulting in a low and variable FIO2.

 

Nasal Cannula

n       You can use a humidifier when the output exceeds 4 L/min.

n  Nasal drying.

n  Nose bleeds.

 

Nasal Catheter

 

n       You insert the catheter gently advancing it along the floor of either nasal passage, until you visualize it just behind and above the uvula.

n       If placed too deep , catheter can provoke gagging and swallowing of gas, causing aspiration.

n       Should be changed every eight hours.

 

Transtracheal Catheter

 

n      A physician surgically inserts this thin Teflon catheter into the trachea between the second and third rings.

 

 

Reservoir Systems

 

n      Incorporate a mechanism to gather and store oxygen between patient breaths.

n      Patients draw on this reserve supply whenever their inspiratory flow exceeds the oxygen device in the device.

n       Reservoir Cannula.

n       Pendant reservoir Cannula.

 

n      Reservoir masks

n       Simple mask

n       Partial Rebreathing mask

n       Nonrebreathing mask

 

Simple Mask

 

n      Input flow range is 5 to 12 L/min.

n       Flow less than 5 l/min, the mask volume acts as dead space and causes CO2 rebreathing.

n       Provides a variable FIO2.

n  Flow rate.

n  Patient breathing pattern.

n  Extent of air leakage.

n  Mask volume.

 

Partial Rebreathing Mask

 

n      A partial rebreathing mask has no valves.

n      During inspiration, source gas flows into the mask and passes directly to the patient.

n      During expiration, source gas enters the bag.

n      Some of the patient’s exhaled gas also enters the bag ( about the first third).

n      It contains mostly oxygen and little CO2.

 

n      As the bag fills with both oxygen and dead space gas, the last two thirds of exhalation (high in CO2) escapes out of the mask’s exhalation ports.

n      As long as the oxygen input flow keeps the bag from collapsing during inhalation.

Nonrebreathing Masks

n      Prevents rebreathing via one-way valves. An inspiratory valve sits atop the bag, while the the expiratory ports on the mask body.

n      During inspiration, a slight negative pressure mask pressure closes the expiratory valves, preventing air dilution.

 

n       At the same time, the inspiratory valve a top the bag opens, providing oxygen to the patient.

n       During exhalation, valve action reverses the direction of flow.

n       Because it is a closed system, a leak-free Nonrebreathing mask with competent valves and enough flow to prevent the bag from collapse during inspiration can deliver 100% gas source.

 

High Flow Systems

 

n      Supply a given oxygen concentration at flows equaling or exceeding the patient’s peak inspiratory flow ( provide at least 60 L/min total flow).

n       Air-entrainment.

n       Blending system.

 

n      All high flow systems mix air and oxygen to achieve a given FIO2.

n      Air-entrainment devices or blending systems are used to mix theses gases.

 

 

 

Air-entrainment Systems

 

n      Direct a high-pressure oxygen source through a small nozzle or jet surrounded by air-entrainment ports.

n      Amount of air entrained varies;

n       Size.

n       The velocity of oxygen at the jet.

n  Larger the intake ports and higher the gas velocity at the jet, more air is entrained.

 

n      Because entrainment devices dilute source oxygen with air, they always  provide less than 100% oxygen.

n      The more air they entrain, the higher their total output flow, but the lower the delivered FIO2.

n      Function as true high-flow system only at low FIO2.

 

n      The FIO2 provided by air-entrainment devices depends on:

n       The air-to-oxygen ratio.

n       Amount of flow resistance downstream from the mixing site.

 

“Magic Box”

 

n       Draw a square and place 20 at the top left corner and place a 100 at the bottom left corner.

n         Place the desired fio2in the middle of the box.

n       Subtract diagonally from lower left to upper right.

n       Subtract diagonally again from upper left to lower right.

 

n       Air-entrainment masks.

n        Venti-mask; Restricted orifice or jet through which oxygen flows at high velocity(.24-.40%).

n       Air-entrainment nebulizers.

n        Humidification and temperature control.

n   Aerosol mask.

n   Face tent.

n   Tracheostomy collar.

n   T-tube.

 

 

n       Assess whether an air-entrainment nebulizers flow rate meets the patient’s needs.

n        Visual inspection: observe the mist output at the expiratory side of the t-tube. As long as you can still mist escaping throughout inspiration.

n         Compare it with the patient’s peak inspiratory flow rate. (Three times his /her minute volume).

 

Blending Systems

 

n      You input separate pressurized air and oxygen sources, and then mix these gases either manually or by a blender.

n       Enclosures;

n  Oxygen tents.

n  Hoods.

n  Incubators.

 

What Oxygen Therapy Should I Use?

 

n      Purpose.

n      Patient.

n      Performance.

n       Match the match the performance characteristics of the equipment to both the objectives of the therapy and the patient’s special needs.

 

What Is Pulse Oximetry?

 

n      Principle of spectrophotometry® photoplethysmography.

n       Uses light to detect the tiny volume changes that occur in living tissue during pulsatile flow.

n       Uses two wavelength of light, one red and one infrared.

 

n      Measured by a photodetector on the right side. The resulting output signal is filtered and amplified by instrument electronics.

n      Accuracy falls between 3-5%.

 

Protocol-Based Oxygen therapy

 

Hyperbaric Oxygen

 

n      The therapeutic use of oxygen at pressure greater than 1 atmosphere.

n      Administered via:

n        A multiplace chamber(large tank capable of holding up to 12 people).

n       Monoplace chamber: transparent plexiglass cylinder for a single patient.

 

Other Medical Gases

 

n      Nitric Oxide (NO):

n       Pulmonary vasodilator

n  Relaxes capillary smooth muscle, inhalation reduces intrapulmonary shunting, improves arterial oxygenation, and lowers pulmonary vascular resistance and pulmonary artery pressure.

 

n      Helium.

n       Airway obstruction:

n  Manage large airway obstruction managing certain patients with COPD, acute upper airway obstruction of various origin, post-extubation stridor in pediatric trauma patients, and refractory viral croup.

Uses for Nitric Oxide

Complications