MECHANICAL VENTILATION KENNEY WEINMEISTER M.D.

INDICATIONS FOR MV Hypoxemia Acute respiratory acidosis Reverse ventilatory muscle fatigue Permit sedation and/or neuromuscular blockade Decrease systemic or myocardial oxygen consumption

INDICATIONS CONTINUED Reduce intracranial pressure through controlled hyperventilation Stabilize the chest wall Protect airway Neurologic impairment airway obstruction

TYPES OF CONVENTIONAL MV Timed cycled Home ventilators Pressure cycled Pressure controlled Volume cycled Flow cycled Pressure support

VOLUME VENTILATION Controlled mechanical ventilation CMV Assist-control AC Synchronized intermittent mandatory ventilation SIMV Which mode?

VENTILATOR SETTINGS Tidal volume Respiratory rate 10 to 15 mL/kg Respiratory rate 10 to 20 breaths/minute normal minute ventilation 4 to 6 L/min Fraction of inspired oxygen Flow rate and I:E ratio

PRESSURE SUPPORT VENTILATION Flow cycled preset pressure sustained until inspiratory flow tapers to 25% of maximal value Comfortable Used mainly as a weaning mode Wean pressure until equivalent to air way resistance peak - plateau pressure

PRESSURE CONTROLED VENTILATION Pressure cycled Volume varies with lung mechanics Minute ventilation is not assured Improves oxygenation recruitment of alveoli Lessens volutrauma?

SETTINGS FOR PRESSURE CONTROL VENTILATION Inspiratory pressure I:E ratio 1:2, 1:1, 2:1, 3:1 Rate FIO2 Peep

PRESSURE REGULATED VOLUME CONTROLLED Ventilate with pressure control Preset volume Inspiratory pressure is adjusted breath to breath Minute ventilation is maintained

INDICATIONS FOR PEEP ARDS Stabilize chest wall Physiologic peep Decrease Auto-peep?

CONTRAINDICATIONS FOR PEEP Increased intracranial pressure Unilateral pneumonia Bronchoplueral fistulae

PEEP Increases FRC Recruits alveoli Improves oxygenation Best Peep based on lower inflection of pressure volume curve

TROUBLE SHOOTING VOLUME VENTILATION High pressure alarm Breath sounds CXR Low tidal volume disconnected Desaturation

TROUBLE SHOOTING PRESSURE VENTILATION Low tidal volumes or minute ventilation Desaturation Breath sounds Patient agitation CXR

Sedation in Mechanically Ventilated Patients Benzodiazepines Opioids Neuroleptics Propofol Ketamine Dexmedetomidine

Benzodiazepines Lorazepam Midazolam Half-life 12 to 15 hours Major metabolite inactive Midazolam Half-life 1-4 hours, increased in cirrhosis, CHF, obesity, elderly Active metabolite

Opioid Morphine Fentanyl Hydromorphone

Neuroleptics Haloperidol Side Effects Mild agitation .5mg to 2mg Moderate agitation 2 to 5 mg Severe 10 to 20 mg Side Effects Acute dystonic reactions Polymorphic VT Neuroleptic malignant syndrome

Propofol Side Effect Anticonvulsant Expensive Use short term Hypotension Bradycardia Anticonvulsant Expensive Use short term

Ketamine Dissociative anesthetic state Direct cardiovascular stimulant Brochodilator Side Effects Dysphoric reactions increased ICP

Dexmedetomidine Centrally acting alpha 2 agonist Approved for 24 hours or less Side Effects Hypotension Bradycardia Atrial fibrillation

Maintenance of Sedation Titrate dose to ordered scale Motor Activity Assessment Scale MAAS Sedation-Agitation Scale SAS Ramsay Rebolus prior to all increases in the maintenance infusion Daily interruption of sedation

NEUROMUSCULAR BLOCKING AGENTS Difficult to asses adequacy of sedation Polyneuropathy of the critically ill Use if unable to ventilate patient after patient adequately sedated Have no sedative or analgesic properties

Neuromuscular Blocking Agents Depolarizing Bind to cholinergic receptors on the motor endplate Nondepolarizing Competitively inhibit Ach receptor on the motor endplate

Depolarizing NMBA Succinylcholine Rapid onset less than 1 minute Duration of action is 7-8 minutes Pseudocholinesterase deficiency 1 in 3200 Side Effects Hyperthermia, Hyperkalemia, arrhythmias Increased ICP

Nondepolarizing Agents Pancuronium Drug of choice for normal hepatic and renal function Atracurium or Cisatracurium Use in patients with hepatic and/or renal insufficiency Vecuronium Drug of choice for cardiovascular instability

No bubble is so iridescent or floats longer than that blown by the successful teacher. Sir William Osler

MV IN OBTRUCTIVE AIRWAY DISEASE Decrease barotrauma related to mean airway pressure Increase I:E decrease TV and/or increase flow Minimize auto-peep auto-peep shown to cause most barotrauma Permissive hypercapnea

ARDS Set peep to pressure shown at lower inflection point of pressure volume curve Tidal volumes set below upper inflection point of pressure volume curve Use pressure control ventilation early Minimize volutrauma

Ventilation With Lower Tidal Volumes Tidal volume: 6 ml/kg Male 50 + 0.91(centimeters of height-152.4) Female 45.5+0.91(centimeters of ht - 152.4) Decrease or Increase TV by 1ml/kg to maintain plateau pressure 25 to 30. Minimum TV 4ml/kg PaO2 55 - 88 mm Hg. Sats 88 to 95% pH 7.3 to 7.45

CASE EXAMPLE 34 y/o female admitted with status asthmaticus and respiratory failure You are called to see patient for inability to ventilate Tidal volume 800 cc, FIO2 100%, AC 12 Peep 5 cm PAP 70, returned TV 200 cc

Case example continued Examine patient CXR Sedate Assess auto-peep Increase I:E Lower PAP and MAP Reverse bronchospasm & elect. Hypovent.

CONCLUSION Three options for ventilation Peep, know when to say no volume, pressure, flow Peep, know when to say no Always assess to prevent barotrauma ventilate below upper inflection point assess static compliance daily monitor for auto-peep