Principles of Mechanical Ventilation

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     1  Principles of Mechanical Ventilation RET 2284 Module 4.0 Ventilator Management - Initial Assessment
     2  Assessment and Documentation of MV This module will review the assessment and documentation of the patient-ventilator interaction in the initial stages
     3  Assessment and Documentation of MV Verify the physician’s order Some orders are specific Mode, rate, Vt, FiO2, PEEP Some orders are flexible Desired range of PaCO2 and PaO2 Initial settings: Mode, rate, Vt, FiO2, PEEP which can be manipulated to achieve the desired blood gas results
     4  Assessment and Documentation of MV Verify that the ventilator has passed OVP OVP – Operational Verification Procedure Usually an automated self-test Usually includes a system-leak test to check the integrity of the ventilator circuit, humidifier and related equipment Done before placing a patient on the ventilator for the first time and before reconnecting the patient to a ventilator if the circuit has been changed or disassembled for any reason Must be documented
     5  Assessment and Documentation of MV Place the patient on the ventilator Set parameters on ventilator in accordance with the physicians orders Connect the patient to the ventilator Listen to breath sounds to confirm adequate volume delivery and proper placement of ET Tube
     6  Assessment and Documentation of MV Check patient’s vital signs – especially heart rate and blood pressure because these may be affected by mechanical ventilation Note: Positive pressure ventilation can reduce venous return to the heart, cardiac output, and blood pressure
     7  Assessment and Documentation of MV Activate alarms (e.g., apnea, low pressure, low Vt, and high pressure limits) Obtain ABG about 15 minutes after ventilation Evaluates effectiveness of ventilation and oxygenation
     8  Assessment and Documentation of MV Chest x-ray – Verify ET tube placement If the patient’s clinic presentation indicates a need, other determinations my be include: CBC Glucose, sodium, potassium, chloride, CO2, blood urea nitrogen, creatinine, phosphate, magnesium PT, PTT, platelet count Blood, sputum, urine culture
     9  Assessment and Documentation of MV Documentation of the PT-Vent System AKA – “Vent Check” Patient information and ventilator settings should be documented regularly when a patient is receiving ventilator support; every 1 – 4 hours depending on the institutions policy Documentation is done on a ventilator flow sheet – electronic or paper record
     10  Assessment and Documentation of MV Documentation of the PT-Vent System AARC Recommendations Data relevant to the patient-ventilator system check are recorded on the appropriate hospital form and become part of the patient’s medical record The patient-ventilatory system check includes patient information and observations of ventilator settings at the time of the check
     11  Assessment and Documentation of MV Documentation of the PT-Vent System AARC Recommendations The record should include the physician’s order for mechanical ventilator settings The patient-ventilatory system check includes a brief narrative of the clinical observations of the patient’s response to mechanical ventilation at the time of the check
     12  Assessment and Documentation of MV Documentation of the PT-Vent System Patient information
     13  Patient and ventilator parameters
     14  Patient and ventilator parameters Patient and ventilator parameters (cont.)
     15  Patient and ventilator parameters Patient and ventilator parameters (cont.)
     16  Patient and ventilator parameters Patient and ventilator parameters (cont.)
     17  Patient and ventilator parameters Patient and ventilator parameters (cont.)
     18  Patient and ventilator parameters Patient and ventilator parameters (cont.)
     19  Assessment and Documentation of MV Mode Institution determines the method for charting mode Sensitivity Check for autotriggering Assess the patient’s ability to trigger the vent Documentation Pressure triggered (e.g., - 2 cmH2O) Flow triggered (e.g., 2 L/min)
     20  Assessment and Documentation of MV Tidal Volume, Rate, Minute Ventilation Usually displayed digitally May be verified with respirometer Correcting Tubing Compliance Volume loss due to tubing compliance (compressible volume) Accounts for approximately 1.5 – 2.5 mL/cm H2O of lost volume Newer vents automatically compensate
     21  Assessment and Documentation of MV Determination of Circuit Compressible Volume Loss Set VT to 100-200 and PEEP to zero Set inspiratory pause at 2 seconds Select a minimum flow rate and maximum pressure limit Occlude Y-connection and initiate a mechanical breath Record the exhaled volume (ml) and peak inspiratory pressure (cm H2O) Divide exhaled volume by PIP (V/PIP) = circuit compression factor Multiply compression factor by the patient’s PIP (PIP minus PEEP if PEEP is used) Example Circuit compression factor = 150 ml / 50 cm H2O = 3 ml/cm H2O Circuit compression volume = 3 ml/cm H2O x (60 cm H2O PIP – 10 cm H2O PEEP) 3 ml/cm H2O x 50 cm H2O = 150 ml (circuit volume Loss)
     22  Assessment and Documentation of MV Alveolar Ventilation Because of the use of HMEs and other circuit adapters that add mechanical dead space to the ventilator circuit, a knowledge of the effect of dead space on alveolar volume delivery is important; especially in infants, children, small adults, and adults with ARDS treated with low tidal volumes
     23  Assessment and Documentation of MV Alveolar Ventilation Anatomical Dead Space Normal anatomical dead space (VDanat) is about 1 mL/lb IBW Note: Bypassing the upper airway with an artificial airway reduces VDanat by about one half
     24  Assessment and Documentation of MV Alveolar Ventilation Added Mechanical Deadspace (VDmech) Y-connectors, HMEs, and/or flex tubing all add mechanical deadspace To measure this volume, fill the device with water and empty into graduated container) When determining actual alveolar ventilation, the volume of these devices must be subtracted from the tidal volume Example: VT – VDanat – VDmech = Alveolar Ventilation
     25  Assessment and Documentation of MV Alveolar Ventilation Final Alveolar Ventilation VA = (VT – VDanat – VDmech) x f .
     26  Assessment and Documentation of MV Alveolar Ventilation - QUESTION A 36-year-old male patient with ARDS is ventilated with a VT of 400mL. The patient’s IBW is 176 lb (80 kg). The HME has a volume of 50 mL. What is the approximate alveolar volume for one breath for this patient? 350 mL 260 mL 400 mL 190 mL
     27  Assessment and Documentation of MV Alveolar Ventilation - ANSWER VDant is about 180 ml (80 kg IBW x 2.2 lb = 176). With an ET tube in place, the VDant is reduced to about half to 90 mL. The HME adds about 50 mL of mechanical dead space. VD is about 140 mL. VT – VD = VA 400 – 140 = 260 mL/breath VA = 260 mL
     28  Assessment and Documentation of MV Monitoring Airway Pressures Ensures that very high pressure limits are not exceeded Provide information about the patient’s conditions
     29  Assessment and Documentation of MV Monitoring Airway Pressures Peak Inspiratory Pressure (PIP or PPeak)
     30  Assessment and Documentation of MV Monitoring Airway Pressures Peak Inspiratory Pressure (PIP or PPeak) The highest pressure observed during inspiration Used to calculate dynamic compliance (CD) A constant VT with an ? PIP may indicate a ? in lung compliance (CL) or an ? in Raw A declining PIP may indicate a leak or may a sign of improvement in CL or Raw
     31  Assessment and Documentation of MV Monitoring Airway Pressures Plateau Pressure (PPlateau)
     32  Assessment and Documentation of MV Monitoring Airway Pressures Plateau Pressure (PPlateau) Obtained by using the ventilator’s inspiratory pause of 0.5 – 1.5 seconds Static pressure is read when no gas flow is occurring Reflects the elastic recoil of the alveolar walls and thoracic cage against the volume of air in the lungs Cannot be measured accurately if the patient makes active respiratory efforts
     33  Assessment and Documentation of MV Monitoring Airway Pressures Set Pressure The operator sets a target pressure to be delivered to the patient during PC-CMV, PC-SIMV and PSV Example 15 cm H2O 22 cm H2O
     34  Assessment and Documentation of MV Monitoring Airway Pressures Peak Pressure Minus Plateau Pressure The difference between PIP and PPlateau is the transairway pressure (PTA); this is the amount of pressure required to overcome Raw (Raw = PTA/Flow)
     35  Assessment and Documentation of MV Monitoring Airway Pressures Peak Pressure Minus Plateau Pressure A higher than expected difference between PIP and PPlateau usually indicates increased Raw Raw increases with secretions, mucosal edema, bronchospasm, kinked ET tube or patient biting on ET tube, partly occluded HME (moisture or secretions)
     36  Assessment and Documentation of MV Monitoring Airway Pressures End-Expiratory Pressure (EEP) The lowest pressure measured in the expiratory phase
     37  Assessment and Documentation of MV Monitoring Airway Pressures End-Expiratory Pressure (EEP) The lowest pressure measured in the expiratory phase PEEP – Positive End Expiratory Pressure CPAP – Continuous Positive End Expiratory Pressure Auto-PEEP
     38  Assessment and Documentation of MV Monitoring Airway Pressures End-Expiratory Pressure (EEP) Auto-PEEP; air trapping during positive pressure ventilation – AKA: Air trapping Breath stacking Inadvertent PEEP Dynamic hyperinflation Occult PEEP Intrinsic PEEP
     39  Assessment and Documentation of MV Increased Raw Airway collapse on expiration Bronchospasm COPD Mucosal edema Secretions Short TE Long TI Slow peak flow rate High rate High VE High I:E ratio Increase Raw from ET Tube, expiratory valve, PEEP valve Monitoring Airway Pressures Causes of Auto-PEEP
     40  Assessment and Documentation of MV Accessory muscle use Decreased breath sounds Decreased chest wall movement Dyspnea Increased resonant percussion Increased radiolucency on CXR Inspiratory efforts do not trigger ventilator Patient still exhaling when vent delivers next breath Patient’s respiratory rate greater than ventilator’s response (assuming sensitivity is set correct) Monitoring Airway Pressures Auto-PEEP Suspected
     41  Assessment and Documentation of MV Monitoring Airway Pressures Auto-PEEP Suspected
     42  Assessment and Documentation of MV Monitoring Airway Pressures Measuring Auto-PEEP Exhalation valve is occluded for 1-2 seconds just prior to inspiration “Expiratory Pause” control on newer ventilators Level of auto-PEEP is reflected on the pressure gauge during the pause Reading is accurate only if the patient is not actively breathing Auto-PEEP = Total PEEP – set PEEP
     43  Assessment and Documentation of MV Increase TE Decrease respiratory rate (? TE ) Decrease VT (? TI) Decrease TI Increase peak flow rate (? TI) Brochodilators / suction Steroids Allow more spontaneous breathing (SIMV, PS, CPAP) Larger ET Tube Apply PEEP (up to 80% of auto-PEEP) Monitoring Airway Pressures Methods to reduce Auto-PEEP
     44  Assessment and Documentation of MV Monitoring Airway Pressures Mean Airway Pressure Closely parallels the mean alveolar pressure Newer vents calculate and display mean airway pressure Affected by: PIP EEP TI/Total cycle time f Inspiratory flow patterns and modes Important to tissue oxygenation!!! Affects lung volumes and cardiac output
     45  Assessment and Documentation of MV Monitoring Airway Pressures Pressure Limit Usually set 10 – 15 cm H2O above PIP Audible and visual alarms are activated if PIP exceeds a set limit Activation of high pressure limit alarm ends inspiration Often activated by coughing High peak pressures may indicate ? Raw or ? CL
     46  Assessment and Documentation of MV Monitoring Airway Pressures Low Pressure Alarm Visual or audible alarm is activated when pressure within the vent circuit has fallen significantly Leak or disconnect Usually set 10 cm H2O below PIP Note: If the leak is not obvious, the patient must be manually ventilated until the cause of the leak is determined
     47  Assessment and Documentation of MV Vital Signs Observing and recording the patient’s blood pressure (BP), heart rate (HR), temperature (T), respiratory rate (f), oxygen saturation (SpO2), and color every few hours help staff members evaluate possible changes in the patient’s overall condition Moderate changes in vital signs should alert the practitioner to the possibility of hypoxemia, impending cardiovascular collapse, or infection
     48  Assessment and Documentation of MV Vital Signs Heart Rate All patient on ventilatory support must be continuously monitored with a three-lead ECG Provides maximum/minimum HR alarms ECG electrode disconnection Vent disconnection - (hypoxemia, hypercapnia) Myocardium infarction (MI) Anxiety Pain Stress
     49  Assessment and Documentation of MV Vital Signs Temperature Hyperthermia Infection Tissue necrosis Metabolic states, e.g., hyperthyroidism Atelectasis Accidental or surgical trauma
     50  Assessment and Documentation of MV Vital Signs Temperature Hypothermia Metabolic disease CNS disorders Drugs Alcohol, heroin, carbon monoxide
     51  Assessment and Documentation of MV Vital Signs Systemic Arterial Blood Pressure Monitored intermittently Stethoscope/sphygmomanometer Automatic BP cuff Monitored continuously Invasive intravascular arterial catheters “A-Line” Radial A-Line
     52  Assessment and Documentation of MV Vital Signs Central Venous Line (CVP) Placed in the superior vena cava or right atrium Provide valuable information regarding: Right heart function Fluid status Hypervolemia Hypovolemia
     53  Assessment and Documentation of MV Vital Signs Pulmonary Artery Pressure Monitored continuously Swan-Ganz catheter AKA: Balloon-tip, flow-directed, pulmonary artery catheter (BTFDC) Used in patients with severe cardiopulmonary complications
     54  Assessment and Documentation of MV Physical Examination of Chest Inspection Accessory muscles usage - ? WOB Paradoxical breathing - ? WOB Abdominal distention Gas, air swallowing, bleeding, ascites Impairs ventilation Palpation Percussion Auscultation
     55  Assessment and Documentation of MV ET and Tracheostomy Tube Cuffs Cuff Pressure Measurement Checked once per shift Pressures not to exceed: 27 – 34 cm H2O (20 – 25 mm Hg) Excessive pressures my cause tracheal damage if cuff pressures are greater than tracheal perfusion pressures
     56  Assessment and Documentation of MV ET and Tracheostomy Tube Cuffs High Cuff Pressure Overinflation of tube cuff Necessary to maintain minimum occlusion Artificial airway may have moved up into the larynx of pharynx Check depth of tube or chest x-ray ET tube may be too small
     57  Assessment and Documentation of MV ET and Tracheostomy Tube Cuffs No or Low Cuff Pressure Cuff not properly inflated Cuff leak Check: inflate cuff and clamp pilot tube Resolution: change cuff Pilot balloon leak Check: inflate cuff and place stopcock in pilot balloon in off position Resolution: clamp pilot tube Pilot tube leak Resolution: syringe with blunt-tipped needle
     58  Assessment and Documentation of MV Tube and Mouth Care Reposition ET tube every shift (Pilbeam) and retape if necessary Most facilities do this every 24 hours Prevents pressure injury to gums, mouth, lips Usually a two-man procedure Mouth care should be performed every shift Helps prevents ventilator-acquired pneumonia (VAP)
     59  JADA Continuing Education Pneumonia in nonambulatory patients The role of oral bacteria and oral hygiene Frank A. Scannapieco, DMD, PhD Background. Considerable evidence exists to support a relationship between poor oral health, the oral microflora and bacterial pneumonia, especially ventilator-associated pneumonia in institutionalized patients. Teeth or dentures have nonshedding surfaces on which oral biofilms (that is, dental plaque) form that are susceptible to colonization by respiratory pathogens. Subsequent aspiration of respiratory pathogens shed from oral biofilms into the lower airway increases the risk of developing a lung infection. In addition, patients may aspirate inflammatory products from inflamed periodontal tissues into the lower airway, contributing to lung insult.
     60  Assessment and Documentation of MV Mouth Care Kit for MV Patients
     61  Assessment and Documentation of MV Monitoring CL and Raw Static Compliance (Cs) Normal: 70 – 100 mL/cm H2O (Cs = VT/[Pplat – PEEP]) Changes in Cs over time is usually considered a result of change in the patient’s alveolar elastic recoil (can be affected by chest wall compliance) Causes for ? Cs Air trapping PE Atelectasis Consolidation Pneumonia Pneumothorx Hemothorax Pleural effusion
     62  Assessment and Documentation of MV Monitoring CL and Raw Static Compliance (Cs) Chest wall compliance reduced in the following Flail chest Chest wall muscle tension Pneumonmediastinum Abdominal distention
     63  Assessment and Documentation of MV Monitoring CL and Raw Static Compliance (Cs) Pressure Ventilation (PV) Reduced CS Set pressure remains constant while delivered VT decreases Increased CS Set pressure remains constant while delivered VT increases
     64  Assessment and Documentation of MV Monitoring CL and Raw Static Compliance (Cs) Volume Ventilation (VV) Reduction in CS Delivered VT remains constant while pressure increases Increases in CS Delivered VT remains constant while pressure decreases
     65  Assessment and Documentation of MV Monitoring CL and Raw Dynamic Compliance (CD) Normal: 40 – 70 mL/cm H2O (CD = VT/[PIP-PEEP]) Includes compliance and resistance components Lung and chest wall elastic recoil Airway resistance Decreases when: CS decreases Raw increases
     66  Assessment and Documentation of MV Monitoring CL and Raw Differentiating between lung and airway resistance problems Volume Ventilation ? PIP and ? Pplat (constant PTA) = ? CS ? PIP and Pplat constant (? PTA) = ? Raw
     67  Assessment and Documentation of MV Monitoring CL and Raw Airway Resistance (Raw) Normal Raw: 0.6 – 2.4 cm H2O/L/sec Approximately 6 cm H2O/L/sec or higher in intubated patients Can be estimated by PTA/Flow (L/sec) Use constant flow (square wave)