Pilbeams Chapter 13 Flashcards
Improving the ventilatory status in a patient with Hypercapnic RF
-Reducing the partial pressure of PaCO2
-Reducing physiological dead space
-Reducing CO2 production
Improving oxygenation
-Administer O2
-Apply PEEP or CPAP
-Patient positioning
Hypoxemic hypoxia treatment
Occurs when a person breathes rarefied (high altitudes)
Hypoxemic hypoxia can be reversed by having a patient breathe an enriched oxygen mixture.
Hypoventilation induced hypoxia
Increase the minute ventilation
Anemia
Blood transfusion to improve the O2 carrying capacity of the hemoglobin.
Circulatory hypoxia
When the patient’s cardiac output is reduced
-Treatment would involve fluid resuscitation and pharmacological to normalize the CO. (drugs that increase contractility or decrease vascular resistance. Therefore, increasing O2 delivery to the tissues.
Histotoxic hypoxia
The body is unable to utilize oxygen for cellular respiration
Parameters used to assess oxygenation
FIO2, SPO2, PaO2, ABG’s, Hb, A-a gradient, PF ratio
-ABG’s should be measured within 15 to 30 minutes
-Every attempt should be made to keep FIO2 below 60% while keeping PaO2 between 60 to 90
Normal PaO2
80-100
Normal PvO2
40 mmHg
Normal PAO2
100-673 (FIO2 range: 21-100)
Normal A-a gradient
5-10 (on room air 21%)
30-60 (on 100%)
Normal P/F ratio
380-475
Normal PaO2/PAO2
80-100
Normal oxygen consumption (VO2)
250 mL/min
Normal oxygen delivery (DO2)
1000 mL/min
Normal oxygen content of mixed venous blood (CVO2)
15 vol%
Normal oxygen content of arterial blood (CaO2)
20 vol%
Normal saturation of mixed venous oxygen (SVO2)
75%
Normal saturation of arterial oxygen
97%
Adjusting the FIO2
The ABG obtained after MV is initiated is compared to the delivered FIO2. A linear relationship should exist between the 2.
-The known PaO2 and the known FIO2 can be used to obtain the desired FIO2.
-PaO2 (Desired) x FIO2 (Known)/ PaO2 (Known)
This equation is useful in making appropriate changes to the FIO2 to achieve the desired PaO2.
Selection of FIO2
-Maintaining a FIO2 above 60 can cause O2 toxicity
-Breathing 100% O2 can lead to absorption atelectasis and increase intrapulmonary shunting.
-FIO2 should be kept as low as possible.
If the PaO2 remains very low while the patient is breathing a high FIO2, what may be ocurring?
Significant shunting, V/Q mismatch, diffusion abnormalities
-In these cases, other methods beside increasing the FIO2 should be considered.
-Increase the Paw (as the Paw increases the PaO2 increases)
-As the PEEP increases, the Paw increases
-HFOV and APRV can increase the Paw
The use of PEEP
Increasing the PEEP to increase the Paw is used most frequently.
-The goal of PEEP is to recruit collapsed alveoli while avoiding overdistention of already open alveoli,
Goals of PEEP/ CPAP Therapy
-Maintain a PaO2 of 60 or greater SpO2 of 90%
-Recruit alveoli and maintain them in an aerated state
-Restore FRC
-Enhance tissue oxygenation
Definition of PEEP
A patient receiving MV, the baseline pressure at the end of expiration is above zero.
Application of CPAP and PEEP
Can be applied to a patient’s airway with a mask, nasal prongs, or an ET tube or a tracheostomy tube.
Mask CPAP
Patient’s receiving a CPAP with a mask should have a PF ratio greater than 200 and have a stable cardiovascular status.
-The hazards and complications of CPAP are vomiting, aspiration, skin necrosis or discomfort from the mask, CO2 retention, increased WOB and cerebral hemorrhage.
Nasal CPAP
Most commonly used in infants because they are mouth breathers.
-CPAP pressures of up to 15 can be used with this device
-Problems with Nasal CPAP include gastric distention, pressure necrosis, swelling of nasal mucosa, and abrasion of posterior pharynx.
Endotracheal Tube or Tracheostomy tube CPAP
May be used for patients who do not meet the requirement for nasal CPAP or mask CPAP.
Flow and threshold resistors
The more rapidly a device responds to patient effort, the less WOB that is required.
Flow resistor
A flow resistor achieves expiratory pressure by creating a resistance to gas flow through an orifice.
-As the diameter of the orifice decreases in size, the pressure level applied increases.
-As the diameter of the orifice increases, the pressure level applied decreases
Threshold resistor
A constant pressure is applied throughout expiration regardless of the rate of gas flow.
-The expiratory valve on most ventilators behave as threshold resistors.
Freestanding CPAP and CPAP on mechanical ventilators
Ventilator mode: CPAP/Spontaneous Mode-Adjust the
PEEP to the desired pressure level.
Freestanding CPAP or EPAP systems
(not used often at all, most hospitals use CPAP/Spontaneous mode)
Continuous flow-Closed system
Demand flow- Open system
On both systems, the patient must be able to comfortably maintain a near normal PaCO2.
What are the 2 levels of PEEP?
Physiological PEEP and therapeutic PEEP
Minimum or low PEEP
A minimum level of PEEP (3-5) should be used to help preserve a patient’s normal FRC.
Therapeutic PEEP
Therapeutic PEEP is 5 cm or greater, it is used in the treatment of refractory hypoxemia caused by intrapulmonary shunting and V/Q mismatching.
-High levels of PEEP are beneficial for a small number of patients with ARDS.
-High levels of PEEP are associated with Cardiopulmonary complications so their response to PEEP must be monitored carefully.
Optimal PEEP
The level at which the maximum beneficial effects of PEEP occur.
-Not associated with cardiopulmonary side effects.
-The PEEP at which static compliance is at its highest as PEEP is decreased after a recruitment maneuver.
Indications for PEEP and CPAP
-Patient’s with ARDS do not benefit from mechanical ventilatory support without PEEP.
-Patient’s with ARDS benefit from PEEP because it helps prevent collapse of the small airways and alveoli and aids in recruiting closed lung units.
Indications of PEEP therapy
-Bilateral infiltrates
-Recruitment of atelectasis with low FRC
-Reduced lung compliance
-PaO2 below 60 on an FIO2 greater than 50%
P/F ratio below 300 for ARDS
CPAP vs PEEP
-The patient provides all of the WOB at all times during CPAP.
-If a patient is able to breathe spontaneously and maintain an adequate PaCO2 CPAP is appropriate.
PEEP allows for the reduction of FIO2 because it improves oxygenation and helps avoid the complications of a high FIO2 in certain disorders.
What disorders may benefit from the use of
PEEP?
-ARDS
-Cardiogenic Pulmonary edema
-Bilateral diffuse pneumonia.
