Mechanical Ventilation Review Chapter 16
Five bodily functions that PPV can significantly alter:
The physiological effects of PPV on the cardiovascular system depend on what two factors?
Amount of pressure applied and patients cardiopulmonary status
How does spontaneous inspiration facilitate venous return to the right heart?
The fall in intrapleural pressure that draws air into the lungs during inspiration also draws blood into the major thoracic vessels and heart. Resulting in increased right ventricular SV
During part part of a spontaneous breath is right ventricular preload increased?
spontaneous inspiration, due to increased return of blood to the right side of the heart and the stretching and enlargement of the right heart volume. The right ventricular preload increases.
During what part of a spontaneous breath is left ventricular preload decreased?
Spontaneous expiration, due to rising intrapleural pressure causing a reduction in venous return and right ventricular SV.
An increase in CVP will do what to the pressure gradient between systemic veins and the right heart?
Reduces the pressure gradient
What effects does overdistention have on the pulmonary capillaries and the right ventricular afterload?
Increased resistance to blood flow through the pulmonary circulation.
This increases right ventricular afterload. Increased PVR and resting volume of the right ventricle.
What conditions need to exist for the interventricular septum to move to the left during PPV?
Dilation of the right ventricle. Mean airway pressure >15 cmH20 (blood volume is depleted)
How can PPV cause myocardial ischemia?
Increases in intrathoracic pressure during PPV can decrease coronary perfusion
List the compensatory mechanisms responsible for maintaining systemic BP during ventilation of normal individuals?
Increased Sympathetic tone
Increased peripheral venous pressure from arterial and venous constriction
Peripheral shunting of blood away from the kidneys and lower extremities
List four factors that can block the body's compensatory mechanisms for maintaining arterial BP while a patient is receiving PPV?
Moderate level of general anesthesia
Spinal cord transection
How can a respiratory therapist check that normal vascular reflexes are intact when PPV is being initiated?
Measure blood pressure soon after
Normovolemic patients may experience decreases in CO when peep levels of _________ cmH20 are used.
List the three factors that can influence CO during PPV?
Lung & chest wall compliance and Raw
Duration and magnitude of PPV
Explain how PPV can benefit the cardiac function of a patient with left ventricular dysfunction?
PPV can reduce venous return and thus preload to the heart. This improves length-tension relationships within the heart and improves SV
What pressure exerts the most influence on the extent of harmful effects caused by PPV?
Mean airway pressure
What is the formula for calculating Mean airway pressure?
1/2 ( PIP - peep ) x ( Ti / TCT ) + peep
Note: If there is an inspiratory hold you add it to Ti
How do you calculate TCT?
60 sec / RR
What happens to the mean airway pressure when an inspiratory hold is added?
It will increase
What type of inspiratory flow produces uneven ventilation?
High inspiratory flow rates
List an I:E ratio that is most likely to cause air trapping and significant hemodynamic complications?
1: 1 , and 2:1
What type of TE allows for better alveolar emptying and less chance of developing intrinsic peep?
The amount of mean airway pressure required to achieve a certain level of oxygenation may indicate?
The severity of a patients lung disease
List five factors that influence mean airway pressure during mechanical ventilation?
I:E ratio ( 1:1, 2:1)
Explain why rapid inspiratory flow rates may produce lower mean airway pressures in patients with normal conducting airways?
allows delivery of the desired VT in a shorter time, which in turn produces lower mean airway pressure
For peep levels to affect CO, what circumstances have to exist?
Peep must transmit its pressure to the intrathoracic space and intrathoracic vessels, thus decreasing CO
In what circumstances would high levels of peep NOT cause a decrease in CO?
Reduced lung compliance (stiff lung)
What is the formula for calculating cerebral perfusion pressure?
MABP - ICP
How can an increased ICP be observed clinically?
Jugular vein distention (JVD)
What effect does hyperventilation have on cerebral vessels?
Hyperventilation lowers PaCO2, which temporarily constricts cerebral vessels
List three ways renal function can be altered by PPV?
The kidneys respond to hemodynamic changes resulting from high intrathoracic pressures
Humoral responses occur including antidiuretic hormone (ADH), atrial natriuretic factor, and renin-angiotensin-aldosterone changes
Abnormal pH, PaCO2, and PaO2 abnormalities affect the kidney
At what glomerular capillary pressure will urinary output become severely reduced?
What happens to kidney function when blood flow to the outer cortex and outer medullary tissue increases?
less urine, creatinine, and sodium are excreted
List the three hormones that are involved in fluid and electrolyte balance during PPV and what effects does each of them exert?
(ADH) antidiuretic hormone, BP changes caused by PPV precipitate release of ADH, resulting in oliguria
(ANF) atrial natriuretic factor, PPV, and peep can reduce the filling pressure by reducing atrial stretch leading to decreased secretion of ANF causing water and sodium retention
renin-angiotensin-aldosterone, plasma renin activity is increased during PPV, which activates the renin-angiotensin-aldosterone cascade resulting in the retention of both sodium and water.
Describe the effects of abnormal ABGs on renal function?
PaO2 <40 mmHg (severe hypoxemia) interferes with normal renal function
Acute Hypercapnia PaCO2 >65 mmHg can also severly impair renal function
What effects does PPV have on the pharmacokinetics of certain drugs?
Many drugs (sedatives, Neuromuscular blocking agents, etc) and their metabolites are excreted by the kidneys. The altered renal function caused by PPV can prolong the effects of these drugs and affect patient care
How can PPV and peep affect liver function?
PPV and peep cause an elevation in serum bilirubin (>2.5 mg/100mL) even when no evidence of preexisting liver disease is present.
Drop in CO, an increased diaphragmatic force against the liver, a decrease in portal venous flow, or an increase in splanchnic resistance. Any of these changes lead to hepatic ischemia and impaired liver function.
What causes gastric distention in patients receiving PPV and how can it be reduced?
can result from swallowing air that leaks around the ET cuff. A gastric tube can be used to remove the air and decompress the stomach
Why are medical and surgical patients subject to malnutrition during serious illness?
because of inadequate food intake and increased metabolic rate associated with fever and wound healing
List three deleterious effects that nutritional depletion can have on mechanically ventilated patients?
Reduced response to hypoxia and hypercapnia
Muscle atrophy from prolonged bed rest and lack of use
Muscle wasting including respiratory muscles from lack of nutrition
Respiratory tract infections from impaired cell immunity
Decreased surfactant production and development of atelectasis
Lower serum albumin levels which affect colloid oncotic pressures and can contribute to pulmonary edema
What effects can overfeeding have on a mechanically ventilated patient?
Can lead to increased oxygen consumption, increased carbon dioxide production, and the need for increased minute ventilation, resulting in increased WOB.
List five ways of assessing a patient's nutritional status?
Actual versus predicted IBW
Serum albumin < 3.5 g/dL
Transferrin >300 mg
How can some of the complications associated with mechanical ventilation be reduced?
Through early recognition of signs and symptoms of the problems associated with PPV, followed by appropriate intervention
What effects does the normal thoracic pump mechanism have on cardiac output?
Improves CO in healthy individuals
During PPV with peep, which of the following is true regarding the thoracic pump mechanism?
CO is decreased and venous return is decreased
A patient's inability to compensate for a diminished CO during PPV will result in which of the following?
For which of the following reasons are patient's with ARDS are less likely to experience hemodynamic changes during PPV, even with high pressures?
Pressure is not transmitted to the pleural space
Hazardous cardiovascular side effects in patients with severe bronchospasm are due to which of the following?
Presence of auto-peep
Methods of increasing mean airway pressure include?
Adding an inflation hold
The risk of cardiovascular complications is least with the use of which of the following ventilator modes?
CPAP with pressure support
The anticipated effects of PPV on the kidneys include which of the following?
Decreased urinary output