Test 1 Flashcards
“iron lung” is referring to what?
negative pressure ventilation
mechanisms of positive pressure ventilation
pressure at mouth inc, air flows into lungs and diaphragms flatten, machine cycles off and mouth pressure returns, alveoli recoil and air flows out of lungs, and then a pause happens
Cycle definition
transition from inhalation to exhalation
What are some desired physiological effects of + pressure ventilation
dec. WOB, normalize blood gas, inc min.ventilation, inc alveolar ventilation, improved distribution of gases
What are some effects on circulation during normal ventilation (spontaneous)
inc. venous return, sends blood to heart, inc preload, inc stroke volume, inc CO
effects on circulation during + pressure ventilation
dec. venous return, dec preload, dec. stroke volume, and dec CO, BP might drop
complications of mechanical ventilation
dec. CO, barotrauma (pneumomediastinum, subcutaneous emphysema, pneumo, damage to pulm. capillaries, renal malfunction, CNS malfunction, stress ulcers, psychological trauma, deep vein thrombosis, dec hepatic blood flow, deconditioning of respiratory musc. and infections
What is a simple pneumo
collection of air in the space around the lungs, may need to be treated (look at BP)
What is a tension pneumo
collection of air in the thoracic cavity which builds up air and puts pressure on the lung so it cannot expand normally, this MUST be treated
equation for MAP
systolic +2(diastolic)/3
VAP bundle definition
a pneumonia infection that must have developed more than 48 hours after the patient was intubated
What is the leading cause of death among hospital acquired infections?
VAP
What are some things you can do to prevent VAP
elevate HOB 30 degrees, daily sedation vacations, assessment of readiness to wean, peptic ulcer prophylaxis, use non invasive forms when possible, oral hygiene, closed system suction, rotate ETT every 24 hours,
Compliance definition
stiffness or stretchiness of resp. system
High compliance
stretches easily, not very elastic
Low compliance
difficult to stretch, very elastic
Is static or dynamic compliance more accurate?
static
State compliance equation
Delta V/Pplat-PEEP
On vent how do you calculate static compliance
VT/Pplat-PEEP
Normal range for static compliance during spontaneous breathing
50-100 mL/cm H2O, acceptable >25
Equation for dynamic compliance
Delta VT/(PIP-PEEP)
Resistance (Raw) definition
the drag of friction on gas flow in the airways
Raw equation
Pmax-Pplast/VI (VI needs to be in L/sec)
Time constant definition
amount of time needed to inflate a lung region to 60% of capacity
Time constant equation
Raw X CL
What will inc. time constant?
resistance, compliance
An increased time constant is associated with what?
Auto PEEP
Assisted spontaneous breaths definition
a breath during which some or all flow is generate by the vent doing work for the patient, patient effort still beings and ends breath and determines tidal volume
continuous mandatory ventilation (CMV) definition
all breaths are mandatory
Continuous spontaneous ventilation (CSV) definition
all breaths are spontaneous
Intermittent Mandatory Ventilation (IVM) definition
breaths can be mandatory or spontaneous
During CMV all breaths are either what?
pressure control or volume control, full vent support
What are the 3 types of triggering in CMV
control, assist, assist/control
Assist/Control definition
breaths can be time or patient triggered, patient can breathe more often than the set rate, provides backup if patient becomes apneic
IMV mechanisms
combo of spont. breaths with mandatory breaths
Advantages of IMV
dec. muscle atrophy, improve CO, and support can be withdrawn gradually
Disadvantages of IMV
inc WOB during spontaneous breaths, potential for breath stacking if mandatory breaths are sychronized with patient effort
SIMV definition
vent opens up a window of time to wait for patient effort
CSV mechanisms
all breaths are initiated and ended by the patient, used to wean
Bubble CPAP
uses blender, flowmeter, has water seal on exhalation limb, exhale against water level resistance which creates elevated pressure in chest. Used only in PEDS
Pressure Support Ventilation (PSV) definition
PS can be done with other modes like SIMV and VC, spontaneous breaths are supported with positive pressure, helps patients overcome WOB
Airway Pressure Release Ventilation
used with CPAP, pt breathes spontaneously at elevated baseline pressure, reduces MAP, typically regarded as a FULL SUPPORT MODE
Servo Controlled Modes
computer monitors patient volumes during pressure or spontaneous breaths, if volume falls below the minimum the vent provides assistance
Pressure Regulated Volume Control
full support, flow is delivered in a way to dec. PIP
PEEP mechanism
positive end expiratory pressure, elevated baseline, used to inc. FRC and O2, common starting point is 2-5 cmH2O
Benefits of PEEP
inc FRC, dec shunt, inc CL, dec WOB, inc PaO2
Bad effects of PEEP
inc incidence of baratrauma, dec. venous return, inc WOB if peep isnt at right level, inc PVR, inc ICP, dec renal blood flow, inc deadspace
Best level of PEEP is achieved at what?
best static compliance, best mixed venous O2
Inspiratory hold mechanism
improves distribution of gas, dec. atelectasis, inc. alveolar recruitment
Ventilator classification schemes
input power (power source), power conversion and transmission, control system
Pneumatic vents mechanisms
have moving parts, needles, venturi entrainers, flexible diaphragms, spring loaded valves and all are used to control flow, volume delivery, and inspiratory/expiratory function
Fluidic vents mechanisms
rely on special principles to control gas flow, not really used to ventilate in acute care setting
Power conversion definition
used to deliver gas under pressure to patient circuit
Drive mechanism definition
convert input power to output work, they determine characteristic flow and pressure patterns the vent produces
Compressors (Blowers) definition
reduce internal volumes within the ventilator to generate a positive pressure for gas delivery
Compressors may be what?
piston driven, rotating blades, moving diaphragms, bellows
Spring loaded bellows
adjustable spring at top of bellows applies force per unit area or pressure, contains pre blended gas
Linear Drive Piston
electrical motor connected by special gearing mechanism to piston rod or arm, may be seen in high frequency vents
Rotary drive piston
non linear drive, sine wave
flow control valves
newer vents have this, rapid flow time and greater flexibility for flow
proportional vavles
uses electrical plunger
most vents are what type of system
closed loop
What is the closed loop system
intelligent system because they compare set control variable to measure control variable this allows the vent to respond to changes in the patients condition
Control variables definition
parameter that can be manipulated by the vent
What are the 4 control variables
pressure, flow, volume, time (cant control all 4 at the same time)
What is the equation of motion
Pressure=(elastance X volume) + (Resistance X Flow)
When thinking about flow what other control variable should you think of?
volume
What is the the total time equation
Tt= TI + TE
What are the 4 phases of ventilation
begin inspiration (trigger), inspiration (limits), end insp/start exp (cycle), expiration (baseline)
what trigger is very common
negative. set 0.5-3 cm H2O below baseline pressure
What is a limit variable?
does not end on inspiration, only applies a limit to some parameters to not exceed a preset value during inspiration
Limits vs. Cycles
cycles shut off breath, and limits dont shut off breath
Tidal volume equation
VE/f
normal range for tidal volume
5-8 ml/kg
tidal volume definition
volm of air expired in one normal spontaneous respiratory cycle
Vital capacity definition
max vol of air that can be inhaled after a max inspiration
vital capacity range
65-75, acceptable >10
Minute ventilation equation
VE= f X VT
minute ventilation definition
volume of air breathed in one minute
Max voluntary ventilation definition
largest volume of air that can be breathed in 10-20 second period.
Normal MVV
120-180 LPM, acceptable >20
Negative inspiratory force definition
amount of negative pressure generated by the patients inspiratory effort
NIF range
-80-100 cm H2O or less, acceptable -20 or less
Max Expiratory Pressure defintion
highest pressure achieved during max expiration
Normal range for MEP
60-100, acceptable 40
Rapid shallow breathing index equation
f/Vt
rapid shallow breathing definition
number of breaths per minute divided by average spontaneous tidal volume in liters
What is the best single indicator of weaning success
rapid shallow breathing index
Normal range for rapid shallow breathing
<100 breaths/min/L
Airway occlusion pressure definition
inspiratory pressure measures at 100 milliseconds after airway occlusion
Number that correlates with lack of weaning success
<-6 cm H2O
Vd/Vt ratio definition
indicated the percentage of the patients tidal vol that is not participating in gas exchange
normal range for Vd/Vt
20-40% spontaneous breathing, 40-60% ventilated pts
Equation for Vd/Vt
PaCO2- PeCO2/PaCO2
Capnography/end tidal CO2 definition
the amount of carbon dioxide in the patients expired gases
Normal end tidal CO2
35-43 mmHg, acceptable 35-55
Arterial Oxygen tension gradient definition
difference b/w alveolar and arterial oxygen pressures, changes with FIO2
normal tension gradient
5-10 on RA, 25-65 on O2, acceptable 66-300
alveolar air equation tension gradient equation
(Pb-47)FiO2-(PaCO2 X 1.25)-PaO2
a/A ratio definition
percentage of oxygen that passes from alveolar gas to arterial blood
normal range for a/A ratio
75-95%, acceptable >60
PaO2/FiO2 ratio definition
used in determining whether or not a patient has acute lung injury or ARDS
normal range PaO2/FiO2
<200 ARDS normal is 380
Mixed venous O2 (SvO2) normal
75% acceptable >60%
how do you determine mixed venous
BP or catheter
Shunt definition
measures the percentage of CO not participating in gas exchange
Normal shunt
healthy <20%
shunt equation
(PAO2-PaO2) X 0.003/(CaO2-CvO2)+(PAO2-PaO2) X 0.003
Goals of noninvasive ventilation
inc. FRC, dec shunt, inc lung compliance, dec WOB, inc PaO2
what are some common uses for CPAP
obstructive sleep apnea, reverse atelectasis, respiratory distress in infants, adults with acute lung injury
hazzards and complications due to inc pressure
barotraume, dec CO/venous return, inc PVR, inc ICP, gastric distention, dec. renal/portal blood flow
Potential contraindications to NIV
patients unable to tolerate inc WOB, ICP >20, hemodynamic instability, acute sinisitis, recent facial surgery/trauma, epitaxis, esophageal surgery, nausea, middle ear issures, active hemoptysis
Typical CPAP blower units
common in HC, continuous flow, hard to exhale, filters air, can add humidity
Typical critical care vents
very expensive, extra alarms, may not work well with masks that leak,
general guidelines to NIV
needs spont. breathing pts, may require N-G tube, usually used at moderate levels, not appropriate for acute resp. failure
noninvasive positive pressure ventilation (NPPV)
blows off CO2, good for COPD patients, IPAP/EPAP
common uses for NPPV
copd exacerbations, asthma, pulmonary edema, community acquired pneumonia, respiratory failure, immunocompromised, no not intubate order, post operative status, difficulty weaning
Selection criteria for NPPV
use of accessory muscles, paradoxial breathing, resp rate >25, SOB, PaCO2.45 with pH <200
minimal leak allowed for masks during NPPV
<15 LPM max of 30 LPM
During CPAP what do you set
set only EPAP in using a BiPAP capable machine
what is Cflex
optional seting, gives a drop in pressure during exhaltion to reduce effort required
volume control is good for what patients
good when lungs are easy to open
pressure control is good for what patients
for inflammation/fibrotic lungs (ARDS, severe pulm edema)
how do you find Pplat
inc peak pressure and inspiratory hold, if >30 want to dec peak pressure
trigger sensitivity during initial vent settings
flow trigger 1-3 LPM below base flow
What is the formula for adjusting FiO2
Know FiO2/Known PaO2 = Desired FiO2/Desired PaO2
if PaCO2 is too low for vent settings what should you change?
dec RR, dec Vt
Formula for adjusting PaCO2
Known Vt X Known PaCO2= Desired Vt X Desired PaCO2
