principles of mechanical ventilation and blood gas interpretation
DESCRIPTION
PRINCIPLES OF MECHANICAL VENTILATION and BLOOD GAS INTERPRETATION. Definitions. Tidal Volume (TV): volume of each breath. Rate: breaths per minute. Minute Ventilation (MV): total ventilation per minute. MV = TV x Rate. Flow: volume of gas per time. - PowerPoint PPT PresentationTRANSCRIPT
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PRINCIPLES OF MECHANICAL PRINCIPLES OF MECHANICAL VENTILATION andVENTILATION and
BLOOD GAS INTERPRETATIONBLOOD GAS INTERPRETATION
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DefinitionsDefinitions• Tidal Volume (TV):Tidal Volume (TV): volume of each breath. volume of each breath.• Rate:Rate: breaths per minute. breaths per minute.• Minute Ventilation (MV):Minute Ventilation (MV): total ventilation total ventilation
per minute. MV = TV x Rate.per minute. MV = TV x Rate.• Flow:Flow: volume of gas per time. volume of gas per time.• Compliance:Compliance: the distensibility of a system. the distensibility of a system.
The higher the compliance, the easier it is The higher the compliance, the easier it is to inflate the lungs.to inflate the lungs.
• Resistance:Resistance: impediment to airflow. impediment to airflow.• SIMVSIMV: patient breathes spontaneously : patient breathes spontaneously
between ventilator breaths. Allows between ventilator breaths. Allows patient-ventilator synchrony, making for a patient-ventilator synchrony, making for a more comfortable experience.more comfortable experience.
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DefinitionsDefinitions
• PIP:PIP: maximum pressure measured by the maximum pressure measured by the ventilator during inspiration. ventilator during inspiration.
• PEEP:PEEP: pressure present in the airways at the end pressure present in the airways at the end of expiration.of expiration.
• CPAP:CPAP: amount of pressure applied to the airway amount of pressure applied to the airway during all phases of the respiratory cycle.during all phases of the respiratory cycle.
• PS:PS: amount of pressure applied to the airway amount of pressure applied to the airway during spontaneous inspiration by the patient.during spontaneous inspiration by the patient.
• I-time:I-time: amount of time delegated to inspiration. amount of time delegated to inspiration.
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Types of VentilationTypes of Ventilation
• Volume ControlVolume Control• Pressure ControlPressure Control• Pressure Support-CPAPPressure Support-CPAP• Pressure-Regulated Volume ControlPressure-Regulated Volume Control
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Volume ControlVolume Control
• The patient is given a specific volume of air during The patient is given a specific volume of air during inspiration.inspiration.
• The ventilator uses a set flow for a set period of time The ventilator uses a set flow for a set period of time to deliver the volume: TV (cc) = Flow (cc/sec) x i-time to deliver the volume: TV (cc) = Flow (cc/sec) x i-time (sec)(sec)
• The PIP observed is a product of the lung compliance, The PIP observed is a product of the lung compliance, airway resistance and flow rate. The ventilator does airway resistance and flow rate. The ventilator does not react to the PIP unless the alarm limits are not react to the PIP unless the alarm limits are violated.violated.
• The PIP tends to be higher than during pressure The PIP tends to be higher than during pressure control ventilation to deliver the same volume of air.control ventilation to deliver the same volume of air.
• With SIMV, the patient can breath spontaneously With SIMV, the patient can breath spontaneously between vent breaths. This mode is often combined between vent breaths. This mode is often combined with PS.with PS.
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Triggering the VentilatorTriggering the Ventilator
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Pressure ControlPressure Control
• Patient receives a breath at a fixed airway pressure.Patient receives a breath at a fixed airway pressure.• The ventilator adjusts the flow to maintain the pressure.The ventilator adjusts the flow to maintain the pressure.• Flow decreases throughout the inspiratory cycle.Flow decreases throughout the inspiratory cycle.• The pressure is constant throughout inspiration.The pressure is constant throughout inspiration.• Volume delivered depends upon the inspiratory Volume delivered depends upon the inspiratory
pressure, I-time, pulmonary compliance and airway pressure, I-time, pulmonary compliance and airway resistance.resistance.
• The delivered volume can vary from breath-to-breath The delivered volume can vary from breath-to-breath depending upon the above factors. MV not assured.depending upon the above factors. MV not assured.
• Good mode to use if patient has large air leak, because Good mode to use if patient has large air leak, because the ventilator will increase the flow to compensate it.the ventilator will increase the flow to compensate it.
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Volume vs. PressureVolume vs. Pressure
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Changes in ARDSChanges in ARDS
Volume Control Pressure Control Volume Control Pressure Control
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CPAP-Pressure SupportCPAP-Pressure Support
• No mandatory breathsNo mandatory breaths• Patient sets the rate, I-time, and respiratory Patient sets the rate, I-time, and respiratory
effort.effort.• CPAP performs the same function as PEEP, except CPAP performs the same function as PEEP, except
that it is constant throughout the inspiratory and that it is constant throughout the inspiratory and expiratory cycle.expiratory cycle.
• Pressure Support (PS) helps to overcome airway Pressure Support (PS) helps to overcome airway resistance and inadequate pulmonary effort and resistance and inadequate pulmonary effort and is added on top of the CPAP during inspiration.is added on top of the CPAP during inspiration.
• The ventilator increases the flow during The ventilator increases the flow during inspiration to reach the target pressure and make inspiration to reach the target pressure and make it easier for the patient to take a breath.it easier for the patient to take a breath.
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SIMV + PSSIMV + PS
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Volume ControlVolume Control• In this mode, a target minute ventilation is set. In this mode, a target minute ventilation is set. • The ventilator will adjust the flow to deliver the The ventilator will adjust the flow to deliver the
volume without exceeding a target inspiratory volume without exceeding a target inspiratory pressure. pressure.
• Decelerating flow pattern.Decelerating flow pattern.• No change in minute ventilation if pulmonary No change in minute ventilation if pulmonary
conditions change.conditions change.• Can ventilate at a lower PIP than in regular volume Can ventilate at a lower PIP than in regular volume
control.control.• Hard to use on a spontaneously breathing patient Hard to use on a spontaneously breathing patient
or one with a large air leak.or one with a large air leak.• Not a “weaning” mode.Not a “weaning” mode.
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Initial Ventilator SettingsInitial Ventilator Settings
• Rate: 20-24 for infants and preschoolersRate: 20-24 for infants and preschoolers 16-20 for grade school kids 16-20 for grade school kids
12-16 for adolescents 12-16 for adolescents• TV: 10-15ml/kgTV: 10-15ml/kg
• PEEP: 3-5cm HPEEP: 3-5cm H22OO
• FiOFiO22: 100%: 100%
• I-time: 0.7 sec for higher rates, 1sec for lower I-time: 0.7 sec for higher rates, 1sec for lower ratesrates
• PIP (for pressure control): about 24cm HPIP (for pressure control): about 24cm H22O. O.
• Pressure Support: 5-10cm HPressure Support: 5-10cm H22O.O.
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Adjusting The VentilatorAdjusting The Ventilator
• pCOpCO22 too high too high
• pCOpCO22 too low too low
• pOpO22 too high too high
• pOpO22 too low too low
• PIP too highPIP too high
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pCOpCO22 Too High Too High
• Patient’s minute ventilation is too low.Patient’s minute ventilation is too low.• Increase rate or TV or both.Increase rate or TV or both.• If using PC ventilation, increase PIP.If using PC ventilation, increase PIP.• If PIP too high, increase the rate instead.If PIP too high, increase the rate instead.• If air-trapping is occurring, decrease the If air-trapping is occurring, decrease the
rate and the I-time and increase the TV to rate and the I-time and increase the TV to allow complete exhalation.allow complete exhalation.
• Sometimes, you have to live with the high Sometimes, you have to live with the high pCOpCO22, so use THAM or bicarbonate to , so use THAM or bicarbonate to increase the pH to >7.20.increase the pH to >7.20.
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pCOpCO22 Too Low Too Low
• Minute ventilation is too high.Minute ventilation is too high.• Lower either the rate or TV.Lower either the rate or TV.• Don’t need to lower the TV if the PIP is <20.Don’t need to lower the TV if the PIP is <20.• PIP <24 is fine unless delivered TV is still PIP <24 is fine unless delivered TV is still
>15ml/kg.>15ml/kg.• TV needs to be 8ml/kg or higher to prevent TV needs to be 8ml/kg or higher to prevent
progressive atelectasisprogressive atelectasis• If patient is spontaneously breathing, If patient is spontaneously breathing,
consider lowering the pressure support if consider lowering the pressure support if spontaneous TV >7ml/kg.spontaneous TV >7ml/kg.
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pOpO22 Too High Too High
• Decrease the FiODecrease the FiO22. .
• When FiOWhen FiO22 is less than 40%, decrease the is less than 40%, decrease the PEEP to 3-5 cm HPEEP to 3-5 cm H22O.O.
• Wean the PEEP no faster than about 1 Wean the PEEP no faster than about 1 every 8-12 hours.every 8-12 hours.
• While patient is on ventilator, don’t wean While patient is on ventilator, don’t wean FiOFiO22 to <25% to give the patient a margin to <25% to give the patient a margin of safety in case the ventilator quits.of safety in case the ventilator quits.
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pOpO22 Too Low Too Low
• Increase either the FiOIncrease either the FiO22 or the mean airway or the mean airway pressure (MAP).pressure (MAP).
• Try to avoid FiOTry to avoid FiO22 >70%. >70%.• Increasing the PEEP is the most efficient way of Increasing the PEEP is the most efficient way of
increasing the MAP in the PICU.increasing the MAP in the PICU.• Can also increase the I-time to increase the MAP Can also increase the I-time to increase the MAP
(PC).(PC).• Can increase the PIP in Pressure Control to Can increase the PIP in Pressure Control to
increase the MAP, but this generally doesn’t increase the MAP, but this generally doesn’t add much at rates <30bpm.add much at rates <30bpm.
• May need to increase the PEEP to over 10, but May need to increase the PEEP to over 10, but try to stay <15 if possible.try to stay <15 if possible.
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PIP Too HighPIP Too High
• Decrease the PIP (PC) or the TV (VC).Decrease the PIP (PC) or the TV (VC).• Increase the I-time (VC).Increase the I-time (VC).• Change to another mode of ventilation. Change to another mode of ventilation.
Generally, pressure control achieves the Generally, pressure control achieves the same TV at a lower PIP than volume control.same TV at a lower PIP than volume control.
• If the high PIP is due to high airway If the high PIP is due to high airway resistance, generally the lung is protected resistance, generally the lung is protected from barotrauma unless air-trapping occurs.from barotrauma unless air-trapping occurs.
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Weaning PrioritiesWeaning Priorities
• Wean PIP to <35cm HWean PIP to <35cm H22OO
• Wean FiOWean FiO22 to <60% to <60%
• Wean I-time to <50%Wean I-time to <50%
• Wean PEEP to <8cm HWean PEEP to <8cm H22OO
• Wean FiOWean FiO22 to <40% to <40%
• Wean PEEP, PIP, I-time, and rate towards Wean PEEP, PIP, I-time, and rate towards extubation settings.extubation settings.
• Can consider changing to volume control Can consider changing to volume control ventilation when PIP <35cm Hventilation when PIP <35cm H22O.O.
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ComplicationsComplications
• PulmonaryPulmonary– BarotraumaBarotrauma– Ventilator-induced Ventilator-induced
lung injurylung injury– Nosocomial pneumoniaNosocomial pneumonia– Tracheal stenosisTracheal stenosis– TracheomalaciaTracheomalacia– PneumothoraxPneumothorax
• CardiacCardiac– Myocardial ischemiaMyocardial ischemia– Reduced cardiac Reduced cardiac
outputoutput
• GastrointestinalGastrointestinal– IleusIleus– HemorrhageHemorrhage– PneumoperiteneumPneumoperiteneum
• RenalRenal– Fluid retentionFluid retention
• NutritionalNutritional– MalnutritionMalnutrition– OverfeedingOverfeeding
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Acute DeteriorationAcute Deterioration
• DIFFERENTIAL DIAGNOSESDIFFERENTIAL DIAGNOSES– PneumothoraxPneumothorax– Right mainstem intubationRight mainstem intubation– PneumoniaPneumonia– Pulmonary edemaPulmonary edema– Loss of airwayLoss of airway– Airway occlusionAirway occlusion– Ventilator malfunctionVentilator malfunction– Mucus pluggingMucus plugging– Air leakAir leak
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Physical ExamPhysical Exam
• Tracheal shiftTracheal shift– PneumothoraxPneumothorax
• WheezingWheezing– BronchospasmBronchospasm– Mucus pluggingMucus plugging– Pulmonary edemaPulmonary edema– Pulmonary Pulmonary
thromboembolismthromboembolism
• Asymmetric breath Asymmetric breath soundssounds– PneumothoraxPneumothorax– Mainstem intubationMainstem intubation– Mucus plugging with Mucus plugging with
atelectasisatelectasis
• Decreased breath Decreased breath sounds bilaterallysounds bilaterally– Tube occlusionTube occlusion– Ventilator malfunctionVentilator malfunction– Loss of airwayLoss of airway
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Pressure PatternsPressure Patterns
• Elevated peak and Elevated peak and plateau pressuresplateau pressures– PneumoniaPneumonia– Pulmonary edemaPulmonary edema– PneumothoraxPneumothorax– AtelectasisAtelectasis– Right mainstem Right mainstem
intubationintubation
• Elevated peak Elevated peak pressure, normal pressure, normal plateau pressureplateau pressure– Airflow obstructionAirflow obstruction– Mucus pluggingMucus plugging– Partial tube occlusionPartial tube occlusion
• Reduced peak and Reduced peak and plateau pressureplateau pressure– Cuff leakCuff leak– Ventilator malfunctionVentilator malfunction– Large bronchopleural Large bronchopleural
fistulafistula
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Extubation CriteriaExtubation Criteria
• NeurologicNeurologic• CardiovascularCardiovascular• PulmonaryPulmonary
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NeurologicNeurologic
• Patient must be able to protect his airway, Patient must be able to protect his airway, e.g, have cough, gag, and swallow reflexes.e.g, have cough, gag, and swallow reflexes.
• Level of sedation should be low enough that Level of sedation should be low enough that the patient doesn’t become apneic once the the patient doesn’t become apneic once the ETT is removed.ETT is removed.
• No apnea on the ventilator.No apnea on the ventilator.• Must be strong enough to generate a Must be strong enough to generate a
spontaneous TV of 5-7ml/kg on 5-10 cm Hspontaneous TV of 5-7ml/kg on 5-10 cm H22O O PS or have a negative inspiratory force PS or have a negative inspiratory force (NIF) of 25cm H(NIF) of 25cm H22O or higher.O or higher.
• Being able to follow commands is preferred.Being able to follow commands is preferred.
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CardiovascularCardiovascular
• Patient must be able to increase cardiac Patient must be able to increase cardiac output to meet demands of work of output to meet demands of work of breathing.breathing.
• Patient should have evidence of adequate Patient should have evidence of adequate cardiac output without being on significant cardiac output without being on significant inotropic support.inotropic support.
• Patient must be hemodynamically stable.Patient must be hemodynamically stable.
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PulmonaryPulmonary
• Patient should have a patent airway.Patient should have a patent airway.• If no air leak, consider decadron and racemic If no air leak, consider decadron and racemic
epinephrine.epinephrine.• Pulmonary compliance and resistance should be Pulmonary compliance and resistance should be
near normal.near normal.• Patient should have normal blood gas and work-Patient should have normal blood gas and work-
of-breathing on the following settings:of-breathing on the following settings:– FiOFiO22 <40% <40%– PEEP 3-5cm HPEEP 3-5cm H22OO– Rate: 6bpm for infants, 2bpm for toddlers, CPAP/PS for Rate: 6bpm for infants, 2bpm for toddlers, CPAP/PS for
1hr for older children and adolescents1hr for older children and adolescents– PS 5-8cm HPS 5-8cm H22OO– Spontaneous TV of 5-7ml/kgSpontaneous TV of 5-7ml/kg
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Blood Gas InterpretationBlood Gas Interpretation
NORMAL VALUESNORMAL VALUES
ArterialArterial Venous Venous CapillaryCapillary
pH pH 7.4 (7.38-7.42) 7.4 (7.38-7.42) 7.36 (7.31-7.41)7.36 (7.31-7.41) 7.35-7.407.35-7.40
pOpO22 80-100 mm Hg80-100 mm Hg 35-40 mm Hg35-40 mm Hg 45-60 mm Hg45-60 mm Hg
pCOpCO22 35-45 mm Hg35-45 mm Hg 41-52 mm Hg41-52 mm Hg 40-45 mm Hg40-45 mm HgSatSat >95% on RA >95% on RA 60-80% on RA60-80% on RA >70%>70%
HCOHCO33 22-26 mEq/L22-26 mEq/L 22-26mEq/L22-26mEq/L 22-22-26mEq/L26mEq/L
BEBE -2 to +2 -2 to +2 -2 to +2-2 to +2 -2 to +2-2 to +2
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Rules Of InterpretationRules Of Interpretation
• ∆∆ in pCOin pCO22 of 10mm Hg should of 10mm Hg should ∆∆ pH by 0.08. pH by 0.08.
• pH ∆ of 0.15 is equal to ∆ in HCOpH ∆ of 0.15 is equal to ∆ in HCO33 of 10mEq/L. of 10mEq/L.
• Normal pCONormal pCO22 in the face of respiratory distress in the face of respiratory distress is a sign of impending respiratory failure.is a sign of impending respiratory failure.
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Acid-Base DiagramAcid-Base Diagram
From Goldberg, M., From Goldberg, M., Green, S.B., Moss, M.L., Green, S.B., Moss, M.L., et al.: JAMA 223:269-et al.: JAMA 223:269-275, 1973275, 1973
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Respiratory DisturbancesRespiratory Disturbances
• Acute respiratory acidosis occurs when COAcute respiratory acidosis occurs when CO22 is is retained acutely.retained acutely.
• Chronic respiratory acidosis occurs when the Chronic respiratory acidosis occurs when the retained COretained CO22 gets buffered by renal retention of gets buffered by renal retention of HCOHCO33. The pH is higher than in acute respiratory . The pH is higher than in acute respiratory acidosis, but it is still <7.4.acidosis, but it is still <7.4.
• Acute respiratory alkalosis occurs when COAcute respiratory alkalosis occurs when CO22 is is blown off acutely.blown off acutely.
• Chronic respiratory alkalosis occurs when the Chronic respiratory alkalosis occurs when the reduction of COreduction of CO22 is compensated for by the renal is compensated for by the renal excretion of HCOexcretion of HCO33. The pH is lower than in acute . The pH is lower than in acute respiratory alkalosis, but it is still >7.4.respiratory alkalosis, but it is still >7.4.
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t C
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lum
for
the P
ICU
Metabolic DisturbancesMetabolic Disturbances
• Acute metabolic acidosis gets compensated by Acute metabolic acidosis gets compensated by COCO22 reduction within 12-24 hours. The pH is reduction within 12-24 hours. The pH is still usually <7.4.still usually <7.4.
• Metabolic alkalosis is rare. Usual causes are Metabolic alkalosis is rare. Usual causes are pyloric stenosis, chronic diuretic use, and pyloric stenosis, chronic diuretic use, and bicarbonate infusions.bicarbonate infusions.
• Otherwise healthy people do not usually retain Otherwise healthy people do not usually retain COCO22 to compensate for metabolic alkalosis. to compensate for metabolic alkalosis.
• Patients who are severely dehydrated or have Patients who are severely dehydrated or have lung disease will retain COlung disease will retain CO22 to compensate for to compensate for metabolic alkalosis.metabolic alkalosis.
UTHSCSA
UTHSCSA
Ped
iatr
ic R
esid
en
t C
urr
icu
lum
for
the P
ICU
Ped
iatr
ic R
esid
en
t C
urr
icu
lum
for
the P
ICU
HypoxemiaHypoxemia
There are five reasons for hypoxemia:There are five reasons for hypoxemia:
• FiOFiO22 too low (high altitude) too low (high altitude)
• Global alveolar hypoventilationGlobal alveolar hypoventilation• Right-to-left shuntsRight-to-left shunts• V/Q mismatchV/Q mismatch• Incomplete diffusionIncomplete diffusion