Indications for Mechanical Ventilation. Mechanical Ventilation. Indications for Mechanical Ventilation. Modes. Modes: Volume cycled

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1 Mechanical Ventilation Eric A. Libré, MD VCU School of Medicine Inova Fairfax Hospital and VHC Indications for Mechanical Ventilation Inadequate ventilatory effort Rising pco2 with resp acidosis (7.25) COPD exacerbation Neuromuscular disease Adequate pco2 but high ventilatory load ARDS Inadequate ventilatory response to metabolic acidosis sepsis 1 2 Indications for Mechanical Ventilation Inadequate oxygenation po2 <60 on 100% non-rebreather pulmonary embolism sepsis pneumonia Airway protection trauma neurologically impaired patients Modes Nomenclature Trigger = what initiates the breath Limit = what controls gas delivery Cycle = what terminates the breath 3 4 Modes: Volume Modes: Volume Assist Control (AC) patient triggered, flow limited and volume patient gets a full breath every time he initiates a breath rate you set is simply a safety net in case he initiates less breaths than you set 5 Synchronized Intermittent Mandatory Ventilation (SIMV) time triggered, flow limited and volume pt. gets full support only for the number of breaths you set all other effort is on their own can be combined with pressure support to give assistance during spontaneous breaths 6 1

2 Modes: Pressure Support Pressure Support patient triggered, pressure limited and patient pt. starts the breath, he gets pressure to reduce his workload and as long as he keeps inhaling.. pressure keeps being applied he controls rate, time of inspiration and volume received. Pressure Control Pressure Control time triggered, pressure limited, time breath is time initiated, flow decelerates as pressure limit is approached flow continues ever so slowly so as not to exceed the pressure limit when time expires the breath is exhaled time is based on the rate and the I:E ratio 7 8 Pressure Regulated Volume Control Pt. triggered, pressure limited and volume hybrid between standard assist control and pressure control physician sets target volume vent attempts to use lowest necessary pressure target pressure based on compliance from last three breaths decelerating flow rate is used Assist Control good when pts. are not stable (allows pt. to dictate minute ventilation) pt. can overbreath if they are anxious, in pain or neurologically impaired remember: turning down the rate does nothing if they are breathing over the set rate 9 10 SIMV good when patients are stable (minute ventilation requirements aren t likely to increase) post surgical patient weaning quickly chronic stable vent patients can be uncomfortable Pressure Support good when patients are having trouble synchronizing to the vent. least work of breathing if done correctly most comfortable theoretical concern about apnea can t be used on a heavily sedated pt

3 Pressure Control Ventilation Least risk of barotrauma Isn t as uncomfortable as once believed Don t need to paralyze pts. unless using inverse ratio Need to be certain that they are getting adequate volumes at pressure you set Commonly adjusted variables FIO2: always start at 100% and back down Tidal Volume: Non-ARDS = 10 cc/kg of ideal body weight ARDS = 6-8 cc/kg of ideal body weight Rate: start at and adjust according to desired ph and pco2 PEEP: start at 5 and adjust upward if need to increase po2 (especially if FIO2 >60%) Less Commonly Adjusted Variables Inspiratory/Expiratory ratio can sometimes improve oxygenation by decreasing the ratio from 1:3 (standard) to 1:1 or even inversing recruits more alveoli and allows for better diffusion by letting gas dwell longer Less Commonly Adjusted Variables Flow rate standard is about L/min adjusting this is especially useful in AC or SIMV allows for reduction in peak pressures if you decrease it can reduce air-trapping (AUTO-PEEP) if you increase it Auto-PEEP occurs when there is incomplete emptying of one breath before the next breath is given primarily occurs in patients with airway obstruction leads to hypotension if severe (>10 cm pressure) alarms: high peak pressures in volume modes low volumes in pressure control mode Auto-PEEP Corrective Measures bronchodilators and steroids to reduce obstruction decrease tidal volume or rate increase flow rate to allow more time for exhalation if very severe (significant hypotension) disconnect vent temporarily

4 Weaning Brochard study favored pressure support Esteban study favored T-piece trials Frequency to tidal volume ratio (Yang and Tobin) <105 associated with reasonable possibility of weaning negative predictive value =.95 positive predictive value =.78 Weaning No specific method is vastly superior than others Most common CPAP (or T-piece) trials for 1 hr Pressure support wean until pt. tolerates PS= 5-8 IMV weaning (slowly backing down until pt. is on less than 5 breaths per minute) Proning can be used as last ditch effort to oxygenate very hypoxic patients allows perfusion to go to areas not flooded with fluid and debris improves V/Q matching no good data regarding reduction in longterm mortality switch position every 8-12 hrs Sedation Always consider some sedation narcotics and benzodiazepines propofol try to avoid paralyzing risk of longterm weakness steroids and aminoglycosides worsen risk Non-invasive Positive Face mask or nasal mask Biphasic Positive Airway Pressure (BiPAP) set inspiratory and expiratory pressures some machines let you set a rate some machines are volume (rare) Non-invasive Positive Best success in hypercapneic resp failure Temporizing measure while bronchodilators and steroids are taking effect inspiratory pressure affects volume iepco2 expiratory pressure affects oxygenation iepo

5 Non-invasive Positive Best if patients are oriented and can be coached Less likely to be useful if: high rates are needed lungs are poorly compliant Don t use if patients are unstable or condition is rapidly deteriorating 25 5

Basics of Mechanical Ventilation. Dr Shrikanth Srinivasan MD,DNB,FNB,EDIC Consultant, Critical Care Medicine Medanta, The Medicity

Basics of Mechanical Ventilation Dr Shrikanth Srinivasan MD,DNB,FNB,EDIC Consultant, Critical Care Medicine Medanta, The Medicity Overview of topics 1. Goals 2. Settings 3. Modes 4. Advantages and disadvantages