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76 Cards in this Set
- Front
- Back
What is acute respiratory failure?
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PAO2<60 and / Or PaCO2 >50 with pH < 7.25
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What are the two types of respiratory failure?
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Type 1: Acute Hypoxic Respiratory Failure (Low O2)
Type 2: Acute Hypercapnic Respiratory Failure (High CO2) |
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Primary causes of Acute Hypoxic RF
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V/Q mismatch
Shunt alveolar hypoventilation diffusion impairment decreased inspired O2 |
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V/Q Mismatch
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Normally lungs have more perfusion at the basis than at the apices because of gravity. Mismatches occur when normally perfused areas become unventilated due to such things as bronchospasm, mucus plugging, airway inflammation, etc.
V/Q mismatches will respond to supplemental O2 V/Q mismatch VS Shunt - Shunts don’t contact the capillary beds |
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V/Q Mismatch: Clinical Presentation
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Hypoxemia
dypsnea tachycardia tachypnea use of accessory muscles nasal flaring cyanosis abnormal BS - wheezing, diminished, unilateral abnormalities whiteout or blackout of CXR |
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Alveolar hypoventilation
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This form of hypoxemia exists when a patient goes into resp failure and the PCO2 rises significantly enough to displace the alveolar PAO2, thereby causing hypoxemia.
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Diffusion Impairment
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Most common causes with patients with interstitial lung diseases (Fibrosis, Asbestosis, Silicosis) where the interstitial wall is abnormally thickened which increases the time needed for gas to diffuse.
also caused by the alveolar destruction common to emphysema, and patients with abnormal pulm vasculature, or anemia, pulm hypertension and PE. Clinical Presentation: No real clinical presentation for diffusion impairment itself-usually patient will show symptoms of the underlying causative disease. Silicosis, anemia, emphysema, etc. Also the CXR will reflect the disease that is the cause of the impairment. |
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Decreased inspired Oxygen
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May occur at high altitudes (mountain climbing, airplane)
Pb decreases which lowers the PaO2 -O2 becoming disconnected - cylinder empties, etc |
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What is the primary purpose of PEEP?
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It increases FRC
(NBRC question) |
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Acute Hypercapnic R.F.
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Also called ventilatory failure.
Elevated CO2=uncompensated respiratory acidosis pH<7.25 PCO2>50 HCO3 wnl Because elevated CO2 levels eventually displace alveolar O2-Hypoxemia will usually accompany ventilatory failure. |
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3 Major disorders responsible for hypercapnic resp. failure:
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Decreased ventilatory drive
respiratory muscle fatigue or failure increased WOB |
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Decreased Ventilatory Drive
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Anything that interferes or disrupts the CNS breathing mechanisms such as the spinal cord, phrenic nerves, and central and peripheral chemoreceptors
Drugs Brainstem lesions hypothyroidism morbid obesity sleep apnea most causes are reversible |
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Clinical Presentation of Decreased Ventilatory Drive
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Bradypnea
Apnea Adult RR < 12 bpm is ABNORMAL May be obtunded, comatose Obese may have sleep apnea |
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Respiratory Muscle Fatigue / Failure
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Caused by neuromuscular disease such as ALS, Myasthenia gravis, Guillain barre syndrome, polio, and Muscular Dystrophy
May be irreversible and terminal (ALS) or reversible and self limiting (GB-MG) |
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Respiratory Muscle Fatigue / Failure: Presentation
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Drooling, weakness, respiratory fatigue
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Increased WOB
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May be caused by COPD, asthma exacerbations, pneumothorax, rib fxs, pleural effusions, extensive burns
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Acute Hypercapnic RF
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Hypercapnic respiratory failure occurs when ventilation is impaired due to
decreased ventilatory drive, muscle fatigue, or increased WOB |
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Complications of Acute Respiratory Failure
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Psychosis
GI complications Multi Organ Failure Renal Failure Cardiac Failure Death |
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Standard Criteria for Mechanical Ventilation
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Apnea
Acute RF Impending RF Hypoxemic RF with increased WOB |
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In order to assess a patient's need for vent support we have to evaluate 3 main factors:
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Ventilatory mechanics - Is he strong enough to breathe?
Ventilation - Can his body eliminate CO2? ABG? Oxygenation - Can his lungs deliver O2 to the tissues? |
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Tests to determine if patient is strong enough to breath:
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Some tests to determine:
MIF/NIF = (>-20) VC = > 15 ml/kg VT = >5 ml/lg RR = <30 VE = <10 lpm |
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Evaluate Oxygenation - Are tissues being oxygenated?
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PaO2 - from ABG
PaO2/FIO2 ratio |
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PaO2
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measured off the ABG. Reflects the pressure of oxygen in the arterial blood (plasma)
Normal = 80 to 100 MMHG (varies with age) critical < 60 |
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PaO2/FIO2 ratio
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calculate normal range on RA
100 mmhg/.21 = 476 critical values are <300 (ALI) <200 (ARDS) |
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Indications for mechanical ventilation
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Apnea - absence of breathing
acute respiratory failure impending respiratory failure Hypoxemic respiratory failure with increased WOB or ineffective breathing pattern |
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Mechanical ventilation - Definition
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Using a machine to effectively protect the airway and manage ventilation and or oxygenation for patients unable to do so normally.
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Philip Drinker
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The first modern and practical respirator nicknamed the “iron lung: was invented by Harvard medical researchers Philip Drinker and Louis Agassiz Shaw in 1927.
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Control Ventilation
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The ventilator delivers a pre-determined Vt (volume or pressure targeted) at a preset frequency (patient controls nothing)
Advantages - Guaranteed minute ventilation or peak pressure Disadvantages - No patient interaction. The patient cannot initiate a breath |
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Maximum plateau pressure
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plateau pressure should not be allowed to exceed 30/CMH20
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Barotrauma
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PEEP > 10 cmH20
MAP> 30 cmH20 PIP >50 cmH20 Plat > 20 |
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Assist/Control Ventilation (AC)
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The ventilator delivers a pre-determined VT with each inspiratory effort generated by the patient. A back-up frequency is set to insure a minimum VE
Advantages - Patient can increase VE by increasing respiratory rate Disadvantages - Dys-synchrony Respiratory alkalosis Dynamic hyperinflation (auto peep / intrinsic peep) |
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Synchronized Intermittent Mandatory Ventilation (SIMV)
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The ventilator delivers a pre-determined VT at a preset frequency and allows the patient to take spontaneous breaths between ventilator breaths. Spontaneous breaths may be augmented with pressure support
Advantages Decreased mean airway pressure Improved venous return Disadvantages increased oxygen consumption increased work of breathing |
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Pressure Control Ventilation (PCV)
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The practitioner sets the maximal pressure obtained by the ventilator (preset pressure), frequency and time the pressure is sustained (inspiratory time). Inspiratory time is set as a percent of the total cycle or absolute time in seconds.
Advantages Tidal volume variable with constant peak airway pressure Full ventilatory support Decreased mean airway pressure Control frequency Disadvantages Ventilation does not change in response to clinical changing needs. http://www.ccmtutorials.com/rs/mv/page10.htm |
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Pressure Support Ventilation (PSV)
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The ventilator delivers a predetermined level of positive pressure each time the patient initiates a breath. A plateau pressure is maintained until inspiratory flow rate decreases to a specified level (e.g. 25% of the peak flow value).
Advantages The flow rate, inspiratory time, and frequency are variable and determined by the patient Decreased inspiratory work enhanced muscle reconditioning Disadvantages Requires spontaneous respiratory effort Delivered volumes affected by changes in compliance http://www.ccmtutorials.com/rs/mv/psv.htm |
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PEEP
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PEEP is “Positive End Expiratory Pressure”
PEEP is not really a mode of its own, but is used in conjunction with other modes as a tool to improve oxygenation. PEEP is the application of positive pressure to change baseline variable during CMV, SIMV, IMV and PCV. PEEP is primarily used to improve oxygenation in patients with severe hypoxemia. |
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Advantages of PEEP
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Improves oxygenation by increasing FRC
Decreases physiological shunting Improved oxygenation will allow the FIO2 to be lowered (FIO2s of 60% and greater run risk of oxygen toxicity) Increased lung compliance |
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Disadvantages of PEEP
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Increased incidence of pulmonary barotrauma
Potential decrease in venous return Increased work of breathing (particularly auto peep) increased intracranial pressure |
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Indications for PEEP
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Refractory hypoxemia and intrapulmonary shunt
Decreased FRC and Lung compliance |
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Complications of PEEP Therapy
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Decreased venous return and cardiac output
Barotrauma Increased ICP Impaired renal function because of the decreased pressure gradient, the amount of blood delivered to the RA is decreased which in turn results in a decreased cardiac output and hypotension - That’s why any vented patient with a dangerously low BP Should have any PEEP DC’d ASAP. |
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Plateau Pressure (Pplat)
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To measure the Pplat on a Ventilated patient, you must perform an “Inspiratory hold” maneuver-usually 1-2 seconds.
Once you determine the Plateau pressure you can use it to calculate the patient’s static lung compliance. Pplat represents the actual pressure in the lungs minus Raw |
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Compliance Calculation
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Compliance = Vte/Plat (static) press - PEEP
500/15-5 = 50 ml/cmH20 |
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Airway Resistance Calculation
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Raw = (PIP- Plateau (static))/peak flow
Raw = (20-15)/1L/sec = 5cmH20/L/sec |
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decreasing lung compliance
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indicated by increasing plateau pressures as well as increasing peak pressures.
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What Respiratory Rate?
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Normal adult 8-12 bpm
COPD 8-12 bpm Asthma 12-24 Closed head injury (CHI)15-20 ARDS 15-25 |
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What Tidal volume?
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First find IBW
Formula to find IBW Males IBW in lbs = 106+[6x(height in inches - 60)] Females IBS in lbs = 105+[5 x (height in inches -60)] convert lbs to kgs by dividing lbs by 2.2 Normal lungs - 6-12 ml/kg COPD 8-10 Asthma 6-10 CHI 8-12 ARDS 4-8 |
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What FIO2 to start?
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start at 100% and titrate lower watching SATs or ABGs
weaned down to <60% ASAP as long as Sats allow to avoid O2 toxicity |
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Initial PEEP Settings
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Probably 95% of docs will order 5 CM PEEP initially. It is though 3-5cm PEEP is low enough to be safe and yet may help oxygenation.
PEEP may be titrated upwards if patient is still hypoxemic on FIO2’s greater than 40-50% |
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I Time or I:E Ratio
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Normal IE ratio is 1:2 - 1:3. In some cases it may be desirable to manipulate the IE ratio on Patients with air trapping or auto peep. They may benefit from a longer expiration than normal
COPD 1:3 or even 1:4 ARDS - inverse ratio - 2:1, 3:1....10:1 |
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Peak Flow
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Most adults require a peak flow of at least 40Lpm
increasing Peak flow will shorten I time |
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square wave
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Provides even, constant peak flow during insp. phase.
Usually results in higher peak pressures |
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Accelerating Flow
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Accelerating - increases flow throughout resp cycle, may improve distribution of ventilation in patients with partial airway obstruction
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Decelerating flow / tapered flow
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Produces high initial inspiratory pressure and then decelerates. Helps reduce peak pressure in COPD patients.
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What flow pattern to use?
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Most RTs set a tapered or decelerating flow pattern. Most of the newer vents calculate which flow pattern is most beneficial for that patient and will automatically use it.
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2 types of sensitivity
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pressure triggering
flow triggering Pressure set @ -1 to -2 cmH2O Flow set @ 1-10LPM below baseline Use flow triggering if given the choice |
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Ventilator alarm settings:
Low exhaled VT |
Set about 100 MLS lower than your set tidal volume. If volumes drop that low alarm will sound to warn of possible leak or circuit disconnect.
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Low Minute Volume Alarm
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Best to set at 1 liter below the current exhaled minute volume
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Low Inspiratory Pressure
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Set 10-15 below the PIP. (Not usually done in real life. Usually set much lower to avoid nuisance alarms)
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High Inspiratory Pressure Alarm
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Set 10-15 above PIP. (Once again usually set at 50-60) if alarms, might need Sxing, sedation, etc.
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Apnea alarm
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Apnea interval - usually set at 20”. If no breath occurs after 20” period, vent will alarm and go into backup anea mode. Set VT, RR, etc to match set parameters.
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High Respiratory Rate
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Set 10-15 above total RR.
Important if patient on CPAP. Shows if patient is tiring |
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High / Low FIO2
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Set 5-10% above the analyzed FIO2 and 5 to 10% below
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Pressure control Ventilation - PCV
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A preset pressure is set in the ventilator. Once it it reached, inspiration ends.
The delivered VT is unknown but varies with Raw and Cstat. pressure is constant-volume is variable when lung compliance decreases, delivered VT decreases. In other words, as the lungs become stiffer and harder to ventilate, the VT becomes smaller The pressure control can be used like the VT control. When Inspiratory pressure is increased, the VT will increase |
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Why use PCV instead of Volume control?
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In patients with ARDS that have lungs so stiff that conventional VCV is now ineffective.
Usually they will be on FIO2 of 1.0, PEEP 15, and have PIPs > 50cmH20 |
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PCV - Initial Settings
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Usually are close to these:
PIP set to about 50% of what it was on VCV (or may use Pplat from VCV) FIO2 100% to start Target VT 4-8ml/kg PEEP 50% of previous I/E 1:2 or 2:1 * with APRV mode Important to closely monitor exh VT |
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Reported benefits of PCV
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Improved gas exchange
increased PaO2 Lower PIP Lower PEEP Less CV effects Less Barotrauma |
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Volume Ventilation
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Volume delivery constant
inspiratory pressure varies inspiratory flow is constant Inspiratory time determined by set flow, Vt and rate |
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Pressure Ventilation
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Volume varies
inspiratory pressure is constant inspiratory flow varies Inspiratory time set by clinician |
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Pressure Control Ventilation - PCV
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The ventilator delivers a set pressure limit over a set inspiratory time
Classification: Pressure controlled, machine triggered, pressure limited and machine cycled. |
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Figure a required FIO2:
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[PaO2 (desired) * FIO2 (current)] / PaO2 (current)
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Figure a required RR
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[RR (current) * PCO2 (current)] / PCO2 (desired)
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Find a required VT
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[Vt (current) * PCO2 (current)] / PCO2 (desired)
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Advantages of Noninvasive ventilation
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Avoids complications related to artificial airway
Easier to start and stop ventilation Less sedation required Preserves airway defense, speech and swallowing No need for invasive monitoring |
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Disadvantages of Noninvasive ventilation
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Not for patients at risk of aspiration (mask)
Excess secretions May not be effective in patients with severe hypoxemia May irritate eyes, cause gastric distention, skin pressure lesions, dry nose, claustrophobia |
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CPAP
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Continuous Positive Airway Pressure
Improves oxygenation by opening and recruiting the airways and allowing more time for alveoli to exchange gases Increases FRC Usually set at low levels (2-10 cm). Pressures Higher than 10 will probably be ineffective as it will be too uncomfortable for the patient to tolerate. CPAP helps Oxygenation only (+PaO2) It has NO effect on Ventilation (PCO2) |
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When to initiate weaning
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When there is:
Adequate Oxygenation PaO2/FIO2> 250 Vent setting: Peep < 8 and FIO2 , 0.5 PH > 7.25 Hemodynamic stability Ability to initiate an Inspiratory effort Sedation (especially with resp-depressing drugs) has itself been weaned |
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Weaning Failure
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HR > 140 bpm or a sustained increase of > 20%
RR > 35 breaths/min for > 5 mins O2 Sats < 90% for >30 seconds HR with a sustained decrease of > 20% SBP > 180 for > 5 mins SBP < 90 for > 5 min Clinical features: Anxiety, agitation, diaphoresis |