Test 8 Flashcards
Positive Pressure improves
Alveolar Recruitment and Oxygenation, excessive pressures may damage the lung tissue
-May also result in other potentially serious unwanted effects, such as reduced venous return of blood to the heart
Inspiratory limb and expiratory limb
Inspiratory- facilitates breath delivery
Expiratory- which directs exhaled gases toward the expiratory port on the vent for measurement
The circuit is comprised of large bore corrugated tubing, which much like the lungs has
Compliance and Elastance
Tube compliance, combined with positive pressure generated during breath delivery, causes
the circuit to bulge or stretch, resulting in reduced gas delivery to the pt.
- This amount is an estimated 3-5ml of volume per cmH2O pressure. Thus at a PIP of 25cmH2O about 100ml are lost to the compressible circuit
- Most modern vents measure and compensate for this compressible vol.
Ve and Va
Minute ventilation and alveolar ventilation, the main factors that facilitate the rate of removal of Carbon Dioxide from the blood
Alveolar Ventilation
determines the true amount of gas that reaches the alveoli to participate in gas exchange. It also controls for the amount lost through factors such as dead space and , if mechanically ventilated, the amount of compressible volume
Deadspace is defined as
areas of ventilation where there is no perfusion of blood to promote gas exchange.
-An example of this is the volume of air that remains in the conducted airways that never reaches the alveoli for gas exchange
Anatomical deadspace, and VA
Anatomical deadspace is estimated as 1ml/ilb of predicted body weight
- Va can be estimated as: (Vt- deadspace volume) x RR
- Excessive tubing or various adapters that are added to the vent circuit further increase the deadspace volume, impacting the Va
A 200-lb PBW male patient is being mechanically ventilated in volume control ventilation. His RR is 20 bpm, and his Vt is 550 mL, resulting in a PIP of 25 cm H2O.
What is the patient’s estimated alveolar ventilation?
Also recall that 25 cm H2O equals roughly 100 mL of compressible volume retained in the circuit. A 200-lb PBW patient has an anatomic dead space of 200 mL (1 mL/lb).V̇a = (550 – 300) x 20. V̇a = 5000 mL or 5.0 L.
Hypoxemia
Low levels of O2 in the arterial blood
-is most commonly assessed through examination of ABG results and interpretation of the partial pressure of arterial oxygen (PaO2)
Normal PaO2
80-100mmHg
Primary factors that impact oxygenation during MV include
- FiO2
- Mean Airway Pressure (Paw), which itself is influenced by PEEP and I:E ratio
- Lung function
The primary determinants of PaCO2 are
the production of carbon dioxide (VCO2) by the body and alveolar ventilation
While we cannot directly control the amount of carbon dioxide the body produces, we can impact Va by manipulating various MV settings that increase the Ve such as
Vt
RR
I-time
E-time
Pulse oximeters provide an estimated
percentage of hemoglobin saturated with oxygen
For normal healthy pts ETCO2 correlates well with PaCO2, but as
deadspace to Vt ratio (Vd/Vt) increases, the correlation becomes less accurate and inconsistent
Normal spontaneous breathing is the result of
a negative pressure gradient between the intrathoracic cavity and the atmosphere, created by the contraction of the diaphragm
-MV is the opposite: positive pressure
VILI
is the result of overdistention of the alveoli
Commonly measured pressures in lungs include
PIP
Pplat
PEEP
AutoPEEP
Compliance
- Elastance of the lung
- Obstructive diseases such as Emphysema increases the cl
- Restrictive diseases such as pulmonary fibrosis decreases it
During volume control ventilation
- There is an inverse relationship between Cl and airway pressures such as PIP and Pplat
- there is a direct relationship between Raw and PIP
During Pressure control ventilation
- There is an inverse relationship between Cl and delivered volumes
- There is an inverse relationship between Raw and Vt
Increases in Raw are commonly due to
secretions in the airway or bronchospasm of the smooth muscle lining the airway
Air trapping
in the lungs can be caused by an obstructive disease process or inadequate vent settings
AutoPEEP
additional pressure above the PEEP set on the MV, and the combination of the two represents total PEEP
-Increases the WOB and reduces venous return and cardiac output
following will occur in volume control ventilation during a decrease in compliance?
Vt will remain the same, PIP will increase
Pressure Volume Curve
used to aid in ventilator parameter selection, minimizing the physiologic impact of auto-PEEP and high airway pressure
- Can be examined using the inspiratory curve of the pressure-volume loop
- Normally football shaped in the healthy lung
“bird beak” in pressure volume curve idicates
alveolar overdistension
Two points that can assist in setting PEEP and targeting a Pplat threshold level that maintains alveolar recruitment while avoiding overdistension
- the lower inflection point (LIP)
- The upper inflection point (UIP)
LIP
lower inflection point (LIP)- represents the pressure at which a large number of alveoli are recruited. Setting the PEEP at this level helps improve oxygenation and prevents alveolar collapse
UIP
Upper inflection point (UIP)- represents the point at which a large number of alveoli are overdistended. Using volume or pressure control strategies that maintain Pplat below this threshold helps prevent alveolar overdistension and VILI
Stress index method
evaluates the level of PEEP to avoid overdistension and underrecruitment of alveoli
-Used during constant flow tidal volume delivery (square flow waveform)
An upwardy concave sloping pressure-time curve suggests
Improved Cl and is scored as a stress index of less than 1, indicating additional potential for recruitment and increase levels of PEEP
A pressure-time curve lacking concavity is scored as
a stress index equal to 1 , meaning the amount of pressure and volume is ideal to minimize overdistension and maximize recruitment of alveoli
A downwardly concave sloping pressure-time curve is scored as
a stress index of greater than 1, representing alveolar overdistension and the need to decrease PEEP and/or tidal volume
Respiratory Muscle load represents
the amount of work required to meet the pts physiologic needs. This load can be increased due to a variety of different factors
- Minute ventialtion
- Increased Resistive load
- Increased elastic load
What increases minute ventilation in respiratory muscle load? Resistive load? Elastic load?
- Minute ventilation: Pain and anxiety, Sepsis, Increased deadspace, excessive feeding
- Increased Resistive Load: Bronchospasm, Secretions, Small artificial airways
- Increased Elastic Load: Low lung compliance, Low chest wall compliance, AutoPEEP
Respiratory Muscle Capacity represents
the ability of the respiratory muscles to perform the work needed to meet or exceed the respiratory muscle load.
Things that impair the capacity of the respiratory muscles to meet a given resp muscle load
- Depressed Respiratory drive: sedative medications, Brainstem Lesions
- Neuromuscular conditions: Cervical spine injury, Phrenic nerve injury, Critical illness polyneuropathy, Prolonged neuromuscular blockade, Hyperinflation, Malnutrition, Electrolyte disturbance, primary neuromuscular disease
Which of the following options that may be be encountered during mechanical ventilation can potentially increase the respiratory muscle load?
Excessive secretions, Increased Ve, Low CL
Multiple organ dysfunction syndrome (MODS)
Can occur secondary to VILI due to the increase in systemic inflammatory cytokines, which can have a neg impact on other organ systems
Hemodynamics
Regers to the movement of blood within the body and the various pressures created by this movement include:
- Arterial Blood Pressure (ABP)
- Central Venous Pressure (CVP)
- Pulmonary Arterial Pressure (PAP)
- Renal function decreases= fluid retention= increase paco2
Which of the following interventions are often needed during mechanical ventilation to compensate for changes in a patient’s hemodynamic status?
Vasopressors, Inotropic Meds, Fluid Administration
All of the following are not true hemodynamic parameters, but at a minimum, mechanically ventilated patients are continuously monitored for:
Heart rate/rhythm
Blood pressure (BP)
Respiratory rate (RR)
Arterial oxygen saturation (Spo2)
Norm BP range
Systolic = 90–140 mm Hg Diastolic = 60–90 mm Hg
Normal MAP
65-105
Normal PAP
Pulmonary Artery Pressure
Systolic = 15–30 mm Hg
Diastolic = 4–12 mm Hg
Normal CVP
Central venous Pressure
0-8
Pulmonary Artery Wedge Pressure (PAWP)
2-12
The normal range for cardiac index (CI)
2.5-3.5l/min/m
CVP represents
Central venous pressure (CVP) represents the filling pressure or preload of the right atrium and requires the placement of an invasive line.
-measures are most useful for patients in a volume-depleted state and can help guide fluid and blood volume replacement.
Swan-Ganz Catheter
Pulmonary artery catheter (commonly called PA catheters), or Swan-Ganz catheters, are invasive multiport lines capable of measuring pressures and sampling blood from the right atrium, the right ventricle, and the pulmonary artery. In addition, PA catheters allow the clinician to estimate the left atrial pressure using PAWP and they allow direct measurement of CO.
PA catheters allow measurement of several hemodynamic parameters, including:
CVP PAP PAWP CO Mixed venous oxygen saturation
PA catheters also provide information used to estimate the systemic vascular resistance (SVR) and pulmonary vascular resistance (PVR). The indicators for use of a PA catheter include the need to:
Measure CO
Assess pulmonary hypertension and intravascular volume
Differentiate shock states
Differentiate diffuse pulmonary infiltrates
Assess severity of valvular heart disease or cardiomyopathy
Define intracardiac shunts
Which of the following are true regarding CVP lines?
- May have an improved safety profile in comparison to PA catheters
- Positioned in the superior vena cava
- Allow for assessment of the patient’s fluid status
Different pharmacologic agents are used to control anxiety and eliminate the discomfort associated with mechanical ventilation, including:
Analgesics (narcotics) to treat pain
Sedatives (benzodiazepines) to minimize anxiety
Paralytics to suppress spontaneous movement
-If short-term sedation is required to improve synchrony between the patient and ventilator, propofol is commonly used.
Physical signs observed during patient and ventilator assessment may indicate the need for additional sedation.
Patient–ventilator asynchrony Excessive sweating (diaphoresis) Tachypnea Tachycardia Restlessness
It is important to remember that medications given for pain or anxiety can
suppress the patient’s spontaneous respiratory drive.
-
ICU delirium
combination of cognitive defects, including agitation, changes in arousal patterns, confusion, hallucinations, and delusions, among others
- associated with many negative factors, such as an increased length of hospital stay, increased time on a ventilator, increased mortality, and increased cost of stay.
- sedatives such as benzodiazepines are associated with more delirium than alternative medications.
Positive pressure applied intrathoracically during mechanical ventilation can impact
renal function and fluid balance.
- Mechanical ventilation has been shown to reduce the blood supply to the renal system, resulting in increased levels of antidiuretic hormone (ADH) and decreased atrial natriuretic peptide (ANP).
- The changes in these fluid-regulating hormones reduce urine output and promote fluid retention.
Normal urine output is estimated at
1 mL/kg/hr of predicted body weight (PBW).
can help determine if reductions in cardiac output and changes in fluid balance are due to mechanical ventilation.
PA catheter
Which of the following changes associated with mechanical ventilation may lead to increased fluid retention and a decrease in urine output?
Decreased ANP, Cardiac output, Increased ADH
Which of the following are ways to assess a patient’s fluid balance?
Daily Weight, Hemodynamic Monitoring, comparison of fluid input and output
Laryngeal edema
is a common occurrence after intubation and mechanical ventilation.
-It is caused by an inflammatory response to the irritation of the larynx during intubation or after extubation. Laryngeal swelling can result in significant airway resistance, making it difficult to breathe.
Tracheal mucosal trauma is a complication associated
with intubation and tracheal suctioning, both of which are required during mechanical ventilation.
-Physical injury may be caused due to contact between the endotracheal tube, an overinflated cuff, or the suction catheter and the tracheal wall. The tracheal mucosal trauma can range in presentation from minor bleeding to more serious injuries, such as tracheoesophageal fistula.
Airway Complications
Laryngeal Edema
Tracheal Mucosal Trauma
Contamination of the lower resp tract
loss of upper airway humidification
Potential pulmonary complications include:
Ventilator-induced lung injury (VILI) Barotrauma Oxygen toxicity Atelectasis Ventilator-acquired pneumonia Inflammation Auto-PEEP Asynchrony
Which of the following are associated with accidental disconnection from the ventilator circuit?
Potential induction of infectious agent into the lower airway
Increased WOB
Loss of alveolar recruitment
Due to the relationship between and close proximity of the lungs and heart, mechanical ventilation can have a negative impact on cardiovascular function. Such as:
Reduced Venous return-drop in BP
Reduced cardiac output-Drop in stroke vol/ cardiac contraction= reduced CO
Hypotension= low BP
Gastrointestinal bleeding
thought to be a result of a reduction in tissue perfusion and excessive gastric acids, ulceration and gastrointestinal bleeding are a concern during mechanical ventilation.
Nutritional status is an important mediator in preventing complications not directly related to the gastrointestinal tract.
Malnourished patients are at a higher risk for developing respiratory muscle weakness, which in turn can lead to difficulty weaning off the mechanical ventilator.
- increase risk for pneumonia
- Conversely, excessive caloric intake can increase carbon dioxide production, which in turn can increase ventilatory requirements.
Hormonal imbalance
The intravascular pressure changes associated with low blood pressure, reduced venous return, and reduced cardiac output cause an increase in antidiuretic hormone (ADH) and a decreased secretion of atrial natriuretic peptide (ANP).
-These hormonal changes result in water and sodium retention during mechanical ventilation.
Reduced Urine Output
Partially influenced by the hormonal changes in ADH and ANP, reduced urine output during mechanical ventilation can also be the result of blood flow redistribution in the kidneys due to systemic cardiovascular pressure changes.
There are several neurologic complications associated with mechanical ventilation and the medications used to facilitate patient tolerance.
Sleep Distrubance
Increased ICP
Critical illness weakness
Normal alveolar stretching limits are reached in the range of
30 to 35 cm H2O; transpulmonary pressures in excess of this value can result in VILI.
-Repetitive tidal volume stretch with volumes greater than 9 mL/kg of PBW without maximum airway pressure exceeding 30 cm H2O may also contribute to VILI.
repeated alveolar collapse and recruitment occurring with each inhalation and exhalation.
This cyclical atelectasis can result in the pressure between an open and closed alveolar unit exceeding 100 cm H2O
-Can also cause VILI
Subcutaneous emphysema
is air trapped in the subcutaneous layer of the skin.
-Usually appearing in the chest, neck, and face, subcutaneous emphysema is not as severe as the underlying condition that created it, such as pneumothorax.
Pneumothorax
is air in the pleural space that accumulates after alveolar rupture or other injury to the lung such as in puncture wounds.
Biotrauma
is an increased number of inflammatory cytokines in the lungs. It is caused by VILI.
Which of the following conditions are classified as pulmonary barotrauma?
Subcutaneous Emphysema
Pneumothorax
pneumomediastinum
Due to the incidence of VAP and related increases in morbidity, mortality, and cost of care, institutions have developed a series of prevention strategies, sometimes referred to as a VAP bundle.
Hand Hygiene, Elevated head of bed, Specific antibiotic regimen, oral care, Specialized artificial airways, Limited circuit changes
Positive pressure can impact the following body systems
Cardiovascular
Renal
Gastrointestinal
Pulmonary
PIP is the
pressure in the lungs at the end of inspiration
Pplat is
positive pressure in the lungs during inhalation and is measured during a period of zero gas flow, such as during an inspiratory pause
PEEP is the
amount of pressure in lungs at the end of expiration
Resistance in the lungs can be increased by
secretions and bronchospasm
During volume control ventilation, decreases in
compliance and increases in resistance result in increased airway pressure for the volume constant.
During pressure control ventilation, decreases in
compliance and increases in resistance result in decreases in delivered volume for the pressure constant.
A recruitment maneuver is an
intentional momentary increase in transpulmonary pressure to try to reopen collapsed alveoli.
Such as
-Sustained high-pressure inflation: PEEP setting to 30-50cmH2o for 20-40 sec
-intermittent sigh: increase in Vt reach Pplat of 45
-extended sigh: stepwise increase of PEEP by 5 with stepwise reduction in Vt, every 2 min until CPAP=30 for 30 seconds
-intermittent PEEP increase: Set baseline to higher level
-Pressure control + PEEP: pressure control ventilation set at 10 to 15 cm H2O with a PEEP of 25 to 30 cm H2O, to reach a PIP of 40 to 45 cm H2O for 2 minutes.
potential results of performing a recruitment maneuver?
Reversal of atelectasis
over-distention of alveoli
A need to increase the set PEEP level
VILI
VAP criteria include:
The aforementioned new infiltrate on a chest x-ray
Fever
Increased white blood cell count
Purulent tracheal secretions
Assuming the infiltrate developed after several days on the ventilator, what diagnostic tests could be ordered to confirm a diagnosis of VAP?
Evaluate pts temp
Evaluation of pts tracheal secretions
White blood cell count
The CPIS score is based on a number of factors, including
emperature, white blood cell count, tracheal secretions, oxygenation status, chest x-ray, and status of the pulmonary infiltrate. Higher scores indicate a more severe infection and guide antibiotic therapy.
Peptic ulcer disease prophylaxis
Administration of antacids and proton pump inhibitors help reduce gastrointestinal complications associated with mechanical ventilation. A reduction in gastric acid reduces the amount of material that can lead to potential aspiration.
Deep vein thrombosis prophylaxis
While not directly contributing to VAP prevention, deep vein thrombosis prophylaxis is used to prevent possible pulmonary embolism, which may extend ventilator days and place the patient at increased risk for VAP.
Comprehensive oral care includes several components, such as:
Use of antiseptic mouth rinses such as chlorhexadine
Physical cleaning of the teeth, gums, and tongue
Frequent supraglottic suctioning of the oropharynx
