10 IMPORTANT TERMS TIME Volume Pressure Flow I - Time: amount of time spent in inspirationE - Time: amount of time spent in expirationVolumeAmount of tidal volume that a patient receivesPressureMeasure of impedance to gas flow rateFlowMeasure of rate at which gas is delivered
11 A Few More Terms PEEP = positive end expiratory pressure Pressure maintained in the airways at the end of exhalationKeeps Alveoli from collapsingPIP = peak inspiratory pressurePoint of maximal airway pressureDelta P = the difference between PIP – PEEPMAP = mean airway pressure
16 Volume Ventilation Preset Ventilator Determines Advantages Volume PEEP RateI-timeFiO2Ventilator DeterminesPressure requiredAdvantagesGuaranteed minute ventilationMore comfortable for patientDraw-backsLarge ETT leakNot optimal for poorly compliant lungs
17 Pressure Ventilation Preset Vent determines Advantages Draw back PIP PEEPRateI-timeFiO2Vent determinesTidal volume givenAdvantagesProvides more support at lower PIP for poorly compliant lungsDraw backMinute ventilation not guaranteed
20 MODES OF VENTILATION Controlled Mechanical Ventilation (CMV) Assist Control (AC)Continuous Positive Airway Pressure (CPAP)Intermittent Mandatory Ventilation (IMV)Synchronized Intermittent Mandatory Ventilation (SIMV)Pressure SupportVolume SupportPressure Regulated Volume Control (PRVC)
21 Assist Control Volume or Pressure control mode Parameters to set: RateI – timeFiO2
22 Assist Control Machine breaths: Patient’s spontaneous breath: Delivers the set volume or pressurePatient’s spontaneous breath:Ventilator delivers full set volume or pressure & I-timeMode of ventilation provides the most support
23 SIMV Synchronized intermittent mandatory ventilation Volume or Pressure modeParameters set:Volume or pressureRespiratory rateI – timeFiO2Pressure support
24 SIMV Synchronized intermittent mandatory ventilation Machine breaths: dDelivers the set volume or pressurePatient’s spontaneous breath:Set pressure support deliveredMode of ventilation provides moderate amount of supportWorks well as weaning mode
25 Pressure Support Parameters set: Machine breaths: none ***** FiO2Machine breaths: none *****Patient’s spontaneous breaths: set pressure support deliveredPurposes:Final step prior to extubationRe-train muscle strength
26 Continuous Positive Airway Pressure (CPAP) Positive airway pressure maintained throughout respiratory cycle: during inspiratory and expiratory phasesCan be administered via ETT or nasal prongs
29 HypoxiaHypoventilation: decreased alveolar ventilation, i.e. CNS depressionDiffusion impairment: abnormality at pulmonary capillary bedShunt: blood flow without gas exchangeIntra-pulmonaryIntra-cardiacVentilation-perfusion mismatch: Both dead space and shunt abnormalities
30 Treating Hypoxia Increase FiO2: >60% toxic to lung parenchyma Increase mean airway pressurePEEP : not too much, not too littlePIPI-time
31 Hypercarbia Decreased minute ventilation Treatment: Respiratory rate Tidal volumeTreatment:Increase respiratory rate: assure I-time not too short as rate increasedIncrease tidal volumeAllow permissive hypercarbia
32 Pulmonary Disease: Obstructive Airway obstruction causing increase resistance to airflow: e.g. asthmaOptimize expiratory time by minimizing minute ventilationBag slowly after intubationDon’t increase ventilator rate for increased CO2
35 HIFI - Theory Resonant frequency phenomena: Lungs have a natural resonant frequencyOutside force used to overcome airway resistanceUse of high velocity inspiratory gas flow: reduction of effective dead spaceIncreased bulk flow: secondary to active expiration
38 HIFI - Gas Transport Conventional bulk flow Coaxial flow: different flow directions in central and peripheral air columnsTaylor dispersion: gas molecules disperse beyond the bulk flow front
39 HIFI - Gas Transport Molecular diffusion: gas mixing within alveoli Pendelluft phenomenon: inter-alveolar gas mixing due to impedance differences
40 HIFI - Advantages Advantages: Disadvantages: Decreased barotrauma / volutrauma: reduced swings in pressure and volumeImprove V/Q matching: secondary to different flow delivery characteristicsDisadvantages:Greater potential of air trappingHemodynamic compromisePhysical airway damage: necrotizing tracheobronchitisDifficult to suctionOften require paralysis
41 HIFI – Clinical Application Adjustable ParametersMean Airway Pressure: usually set 2-4 higher than MAP on conventional ventilatorAmplitude: monitor chest riseHertz: number of cycles per secondFiO2I-time: usually set at 33%
43 Scenario #1The following blood gas is presented to you for a 4yr patient that is now 3hours post-op from an OLT.7.52 / 24 / 250 / 20 / -4The ventilator settings are SIMV PC/PS PEEP – 4, Delta P-28, FiO2 – 50%, RR – 12.
44 Scenario #2A 8yr female with ALL s/p chemo presents to the PICU with fever and neutropenia 1day prior. She is found with positive blood cultures this AM and got intubated secondary to respiratory failure. It is now 4am and the morning labs show the following ABG:7.23 / 60 / 58 / 22 / -2The ventilator settings are SIMV TV - 10cc/Kg, PEEP – 5, PIP – 38, PS – 14, FiO2 – 70%, RR – 20, I-time – 0.7You go to examine the patient and she is agitated, hypertensive, and with a respiratory rate of 40.
45 Scenario #3There is a 6 month old patient that presents with RSV bronchiolitis that progresses to severe disease and the patient is now on a HIFI ventilator. The patient’s ABG is as follows:7.24 / 58 / 75 / 21 / -3The ventilator settings are as follows: HIFI with MAP – 20, Amp – 28, Hz – 8, FiO2 – 40%.As you are looking at the chest X-ray, the nurse mentions the patient looks more edematous this evening compared to last night.
46 References http://www.ccmtutorials.com/rs/mv/ Editors: Rogers MC & Nichols DG. Textbook of Pediatric Intensive Care. Baltimore, Willimams & Wilkins, 1996.Cairo JM & Pilbeam SP. Mosby’s Respiratory Care Equipment. St. Louis, Mosby, 1999.Evita 4 Intensive Care ventilator, Operating instructions, 2001.West JB. Pulmonary Pathophysiology. Baltimore, Willims & Wilkins, 1992.
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