W4 Oxygen Delivery (not tested) Flashcards
Giving oxygen
The power of added oxygen: Has the capacity to increase the arterial PaO2 by 10x from 100 mmHg to 600 mmHg
All forms of hypoxemia respond to added oxygen (hypoventilation, diffusion impairment, ventilation-perfusion mismatch) except SHUNTING. The reason being the blood that bypasses the ventilated alveoli (shunt) does not “see” the added oxygen, and being low in oxygen concentration, depresses the arterial PO2. There are useful gains of dissolved oxygen.
Other FACTORS in OXYGEN DELIVERY: hemoglobin concentration, cardiac output, and local blood flow
Oxygen — methods of delivery
Low flow
High flow
Divided into LOW FLOW and HIGH FLOW systems
LOW FLOW:
a. Provide lower oxygen flow than actual inspiratory flow
b. With inspiration, the oxygen is DILUTED with room air
c. The degree of dilution depends on inspiratory flow (therefore they do not allow for an accurate calculation of the inspiratory oxygen fraction FiO2)
d. Each liter of supplemental oxygen supplies 3-4% of additional O2
HIGH FLOW:
a. Provide higher flow than the inspiratory flow
b. The FiO2 is stable and not affected by breathing
Oxygen — methods of delivery
Low flow — nasal cannula
a.Most common and used for mild hypoxia
b.Can deliver 1-6 liters/min (increase up to 24-45% from 21% room air)
c.The higher the patient’s inspiratory flow rate, the lower the resulting concentration
d.When higher flow rates are used, it is often humidified to prevent patient discomfort and crusting of secretions on the mucosa
e.Advantages are the patient can talk and eat
f.Disadvantages are the low maximum inspired concentration of oxygen available and the unpredictability of the concentration
Oxygen — methods of delivery
Low flow — simple face mask
a.Can deliver between 5-15 liters/min (~60% FiO2) and utilized when a moderate amount of oxygen is indicated
b.Fits over the nose/mouth and has side exhalation ports through which CO2 is exhaled to avoid retention
c.Add humidification to avoid mucosal dryness
d.Limited by how well the mask fits, is confining to claustrophobic patients, and can not eat/drink
Oxygen — methods of delivery
Low flow — non-rebreather max
a.Adds a reservoir bag (1L) to deliver a higher concentration of oxygen
b.A one way valve between the mask and the reservoir bag prevents the patient from inhaling expired air
c.Set to deliver 10-15 liters/min; anything < 10 liters will cause the bag to collapse during inspiration
d.Oxygen concentrations can increase to 80-100% as the patient uses the additional oxygen enriched air from the reservoir
e.Exhaled air escapes via one way valves on the side of the mask
f.USeful in hypoxic patients that are VENTILATING well; risks include carbon dioxide retention and aspiration from vomiting
Oxygen — methods of delivery
High flow — Venturi max
VENTURI MASK
a.Allows for precise measurement of the delivered FiO2
b.Uses different sized ports to change the FiO2 delivered; oxygen enters the mask through a narrow jet and combines with air entering through surrounding holes. The diameter of the holes can be adjusted to achieve the desired O2 concentration (smaller diabetes, less ambient air and higher O2 concentration)
c.Can deliver 24-50% oxygen concentrations
d.Useful for COPD patients where precise oxygen delivery is important
e. Confining; can not eat
Oxygen — methods of delivery
High flow — high flow cannula
HIGH FLOW NASAL CANNULA
a.Can provide up to 60 liters/minute with an FiO2 of 100%
b.Humidified
c.Limits the entrainment of air that leads to unpredictability of inspired oxygen concentrations
d.Additional benefit of flushing the deap space in the upper airway and generating some positive end expiratory pressure (PEEP)
Positive pressure ventilation
Form of respiratory therapy that delivers air or a combination of air combined with oxygen by positive pressure/mechanical ventilation into the lungs. As gas enters the lungs, the alveoli pressure increases until a change in pressure is detected by the machine delivering the air/O2. Expiration happens passively.
Positive End Expiratory Pressure (PEEP) is used in conjunction with mechanical ventilation. At the end of mechanical or spontaneous exhalation, PEEP maintains the patient’s airway pressure above atmospheric level by exerting pressure that opposes passive emptying of the lung. Counteracts atelectasis that can occur when the patient is ventilated in the supine position.
Non-invasive: deliver positive pressure using a tight fitting mask around the patient’s nose and mouth
a.CPAP
b.BiPAP
c.Effective for short duration of ventilatory support in patients with pulmonary edema, COPD, or obesity hypoventilation syndrome; generally not effective for PNA or ARDS
d.Avoid in patients who can’t protect their airway, have excessive secretions, or are a risk to aspirate (diminished mentation)
Mechanical Ventilation:
a ventilator is connected to the upper airway via an endotracheal tube or less commonly, a tracheostomy tube
a. Tracheostomy is placed if a patient has been endotracheally intubated for an extended period of time (several weeks) or if the upper airway is compromised
b. Lungs are inflated by delivering positive pressure
CPAP (Continuous Positive Airway Pressure)
CPAP (Continuous Positive Airway Pressure)
a.Consists of a pump with a tube that is attached to a mask that goes over the patient’s face
b.Delivers constant PEEP (normally 5-12 cm H2O)
c.Maintains the upper and lower airways throughout inhalation and exhalation thereby preventing atelectasis and by increasing the functional residual capacity (FRC); therefore allows for increased gas exchange
d.Useful for OSA and patient’s can have a home device
e.Useful to wean patient off ventilator
BiPAP (Biphasic Positive Airway Pressure)
BiPAP (Biphasic Positive Airway Pressure)
a.Most commonly used noninvasive form of positive pressure ventilation
b.Similar to a CPAP, it delivers constant PEEP but with the added benefit of positive INSPIRATORY pressure (usually 5-25 mmHg) when the patient initiates a breath.
c.Settings: IPAP (inspiratory positive airway pressure) increases tidal volume and EPAP (expiratory positive airway pressure) which is the PEEP; an increase in EPAP increases FRC and gas exchange
d.Useful for type I and II respiratory failure including COPD and PNA as well as to prevent intubation or assist with extubation
Cardiac performance and positive pressure
Positive pressure can influence both ventricular filling and emptying
1. VENTRICULAR FILLING: positive pressure reduces filling by
a.Positive intrathoracic pressure impedes venous return by reducing the pressure gradient for venous inflow into the thorax
b.Positive pressure exerted on the outer surface of the heart reduces cardiac distensibility and decreases ventricular filling during diastole
2. VENTRICULAR EMPTYING:
a.Positive intrathoracic pressure can facilitate ventricular emptying by reducing the transmural pressure that must be developed by the ventricle to eject the stroke volume (acts like a hand to squeeze the ventricle)
Depending on ventricular filling or emptying, the cardiac output will be affected
In conditions where the intrathoracic pressure exceeds the central venous pressure (CVP), such as dehydration, the predominant effect of mechanical ventilation is to reduce ventricular filling and decrease cardiac output
When ventricular filling is adequate, the predominant effect of mechanical ventilation is to enhance ventricular emptying and increase stroke volume
Hazards of Oxygen Therapy
Hazards of Oxygen Therapy
CARBON DIOXIDE RETENTION
a.Important for COPD and obesity hypoventilation patients where hypoxic stimulation is needed; if this drive is removed then the level of ventilation can decrease and result in CO2 retention
b.Goal is to achieve a SaO2 of 88-94% with monitoring of ventilation using end tidal CO2 or ABGs
OXYGEN TOXICITY
c.High concentrations of O2 over an extended period of time can affect the capillary endothelium -> alveolar edema. The alveolar epithelium also affected -> fibrosis
d.Studies in monkeys show earliest changes occur with 100% oxygen over 2 days
ATELECTASIS
a.Normally, the area of the lung behind an airway blockage undergoes ABSORPTION ATELECTASIS where the sum of the partial pressures on the venous blood < atmospheric pressure with the result is the trapped air gets absorbed.
b.If the patient is getting a high O2 concentration, the rate of absorption is accelerated and the alveoli collapses
c.Seen in patients with respiratory failure from excessive secretions or debris in airways
Miscellaneous Hazards of Mechanical Ventilation
Mechanical problems: kinking of tubes, broken connections
Pneumothorax: especially if the PEEP or tidal volume are large
Interstitial Emphysema: air escapes rupture alveoli and tracks along the perivascular and peribronchial interstitium; possibly can enter the subcutaneous tissue of the neck and chest wall
Ventilator Induced Lung Injury: from excessive tidal volumes
Ventilator associated pneumonia
GI Bleeding
Arrhythmias: induced by pH changes and hypoxia
