Mechanical Ventilation Flashcards
Oxygen delivery equation
DO2= cardiac output x arterial O2 Content
Reasons for oxygen delivery failure
hypotension, acidosis, coagulopathy
oxygen use equation
VO2=Cardiac output x O2a-O2v
The normal oxygen extraction ratio is
about 25%
heart has very high demand
The anesthesia goal of oxygen therapy is
to maintain oxygenation and ventilation
The oxygen therapy goal is
prevention and correction of hypoxemia and tissue hypoxia
Surgical patients have an
increased risk of hypoxemia & hypoxia
Hypoxemia is
deficiency of O2 in blood
Hypoxia is
O2 delivery to tissues not sufficient to meet metabolic demand
Types of hypoxia include
hypoxic, circulatory, hemic, demand, and histotoxic
Hypoxia signs and symptoms include
vasodilation, tachycardia, tachypnea, cyanosis, confusion, and lactic acidosis
Improving oxygenation in mechanically ventilated patients includes
treatment tailored to cause
utilizing increase VE, increased cardiac output, increased O2 carrying capacity, optimize V/Q relationship, decrease O2 consumption, increase FiO2
The nasal cannula (flow rates)
flow rates 1-6 L/min
FiO2 increases about 4% per L/min
Simple face masks (FiO2)
minimum 6L flow required to prevent rebreathing
FiO2 40-60%
Face masks with reservoirs
FiO2 60-100%
Venturi masks
have more precise FiO2 of 24-50%
have to set flow rate
Based off of Bernoulli’s theory
Oxygen toxicity occurs from
high FiO2 over long periods which can be harmful to lung tissue and cause
decreased ciliary movement, alveolar epithelial damage, and interstitial fibrosis
Oxygen toxicity is dependent upon
FiO2, duration, patient susceptibility
Safe levels of oxygen to prevent oxygen toxicity is
100% O2 for up to 10-20 hours
Oxygen toxicity occurs from
50-60% O2 for more than 24-72 hours
Absorption atelectasis occurs when
nitrogen is replaced by oxygen
under-ventilated alveoli have decreased volume- due to greater uptake of oxygen
increases pulmonary shunting
Induced hypoventilation occurs due to
Chronic CO2 retainers rely on hypoxic drive
peripheral chemoreceptors are triggered by hypoxemia
Increased O2 can lead to hypoventilation
Fire hazards can occur because
O2 supports combustion
use extreme caution with head and neck cases
Retinopathy occurs
with O2 therapy in neonates; it can lead to vascular proliferation, fibrosis, retinal detachment, and blindness
Populations at risk of retinopathy include
<36 weeks gestational age
weight <1500 gm
up to 44 weeks gestational age are considered high risk
Safe O2 administration to prevent retinopathy is
PaO2 60-80 mmHg
Hypercapnia is
increased CO2 >45 mmHg
increased CO2 concentration or increased CO2 production
Hypercapnia is caused by
increased alveolar dead space- decreased alveolar perfusion, interruptions in pulmonary circulation, pulmonary disease
Decreased alveolar ventilation- can be central or peripheral defect, respiratory depression most common cause in immediate postoperative period
Clinical manifestations of hypercapnia include
directly produces vasodilation of peripheral vessels, indirectly increases HR after catecholamine release, produces effects due to an acidotic state
Non-specific signs of hypercapnia include
headache, nausea/vomiting, sweating, flushing, shivering, restlessness
Treatment for hypercapnia includes:
adjust treatment to the cause
increase minute ventilation
Considerations for hypercapnia (CNS, CV, and pulm)
CNS considerations: regulation of ventilatory drive, cerebral blood flow
cardiovascular considerations: depression of smooth muscle and cardiac muscle, increased catecholamine release, vasodilation versus vasoconstriction
Pulmonary considerations: increased respiratory rate, increased pulmonary vascular resistance
Hypocapnia is
CO2 <35 mmHg
Hypocapnia typically caused by
iatrogenic
Hypocapnia clinical manifestations include
CNS: decrease CBF
CV: decrease in CO, coronary constriction
Pulmonary: hypoxemia may result from hypoventilation
Treatment of hypocapnia includes
decreasing minute ventilation
Goals of mechanical ventilation is
to maintain homeostasis
Goals of mechanical ventilation in the OR is to
ensure adequate oxygenation and CO2 removal for safe and effective surgery
Goals of mechanical ventilation in the ICU is to
treat severe respiratory distress, provoke lungs with a “break” to rest and heal, decreases O2 consumption by providing rest for respiratory muscles
Peak inspiratory pressure (PiP) is
total pressure required to distend LUNGS and AIRWAYS
Pressure used to calculate DYNAMIC COMPLIANCE
Plateau pressure is
distending pressure to expand ONLY THE LUNGS
measures redistribution of air flow through lungs
plateau pressure is used to calculate STATIC COMPLIANCE
The variables we control include (control variables)
respiratory rate, tidal volume, pressure (PiP, Plat/ PAW)
I:E ratio (I:E)
Depending on the mode of ventilation selected you can control
either tidal volume or pressure delivered
In the total respiratory cycle, each breath has 4 parts:
- start of inspiration
- inspiration itself
- end of inspiration
- expiration
The trigger variable is
the start of inspiration
The limit variable is
maintenance of inspiration
The cycling variable is
transition to expiration
The baseline variable is
end expiration
The trigger variable represents
the start of inspiration
can be affected with or without patient inspiratory effort by either pressure, volume, flow, or time
Pressure as the trigger variable:
pressure decrease in circuit stimulates ventilator to deliver breath
Volume as the trigger variable:
volume change in circuit can stimulate ventilator to deliver breath
Flow as the trigger variable:
change of flow in circuit stimulates ventilator to deliver breath
Time as the trigger variable:
set time interval triggers ventilator to deliver breath
*** this occurs independent of patient effort
The limit variable
controls how an inspiratory breath is maintained, once threshold is reached variable will not exceed set limit
-this DOES NOT cause termination of inspiration
When pressure is set as the limit variable:
sets upper pressure limit that cannot be exceeded
When volume is set as limit variable:
sets upper volume limit that cannot be exceeded