Ventilator Management Michael Schmitz DO MS Emergency Medicine Internal

Ventilator Management Michael Schmitz, DO, MS Emergency Medicine/Internal Medicine October 10, 2007

Objectives: • To review differences in ventilator modes • To review how to interpret ventilator settings and readings • To discuss the protocol for assessing a ventilated patient who is in distress • To review the pathophysiology of the obstructive lung diseases • To discuss guidelines for ventilator settings for patients with obstructive lung disease

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Nomenclature A/C 600/14/50%/+5

Volume Cycled Ventilation • A/C Ventilation • SIMV

Pressure Cycled Ventilation • Pressure Support (PSV) • Airway Pressure Release (APRV)

Flow Rate / I: E Ratio • Flow Rate: a measure of the rate of delivery of oxygen through the system to the patient. (usually 60 liters per minute) • I: E Ratio: a measure of total inspiratory time to expiratory time. (1: 3) is ideal – Inspiratory time = Tidal Volume / Inspiratory flow – An increase in flow rate will shorten inspiratory time and decrease I: E – Insufficient flow rates contribute to patient dyspnea – Insufficient expiratory time increases mean airway pressure, the likelihood of barotrauma and auto-PEEP.

Trigger Mode/Sensitivity • Trigger Mode- (A/C) Most common is “pressure triggering”; the patient must generate a sufficient NET negative airway pressure in order to receive a breath • Sensitivity- the set negative pressure the patient must overcome to open the demand valve and trigger a breath

Flow Pattern • Constant (square) • Decelerating (ramp) -possibly better in COPD • Sinusoidal

PEAK VS. PLATEAU PRESSURES • Peak Pressure: Pressure at the end of inspiration. Determined by inflation volume, airway resistance and the elastic recoil of the lungs and chest wall • Plateau Pressure: Measured when airflow is stopped. It is directly proportional to the elasticity of the lungs and chest wall

PEAK VS. PLATEAU PRESSURES •

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Positive End-Expiratory Pressure • PEEP: an elevation in alveolar pressure above atmospheric pressure at the end of exhalation ACV without PEEP ACV with PEEP • Extrinsic PEEP (e. PEEP): applied through a mechanical ventilator

Positive End-Expiratory Pressure Physiologic: (3 -5 cm H 20) overcomes the decrease in functional residual capacity due to endotracheal intubation (glottis has been bypassed): – improves gas exchange by opening small airways in the dependent lung zones and distributing inspired gas homogeneously. – decreases expiratory flow limitation and dynamic hyperinflation. – decreases oxygen consumption

Positive End-Expiratory Pressure Supraphysiologic PEEP: (> 5 cm H 20) – Offsets auto-PEEP in patients with obstructive lung disease – Improves oxygenation in patients with hypoxemic respiratory failure – Improves oxygenation and cardiac performance in patients with cardiogenic pulmonary edema Caution in: focal lung disease, pulmonary embolism, hypotension, patients with increased ICP, hypovolemia, bronchopleural fistula

Positive End-Expiratory Pressure

Auto-PEEP • Intrinsic PEEP (i. PEEP, aka occult, ventassociated) occurs because of incomplete ventilation: Initiating a new breath prior to complete exhalation causes air-trapping

Auto-PEEP • Causes: high minute volume ventilation, expiratory flow limitation or increased expiratory resistance • Hypoxemia, hypotension and barotrauma can occur as a result

Auto-PEEP

PEEP • Applying PEEP can decrease the magnitude of negative pressure that the patient must generate to trigger the ventilator, which reduces work done by the muscles of inspiration

Consequences of MV • Positive pressure ventilation preferentially inflates the more compliant, non-dependent upper lung zones • Uneven gas distribution contributes to barotrauma and auto-PEEP, with a preference for damaging “normal” alveoli • Occurs in ARDS, asthma and chronic interstitial lung disease

Consequences of MV • Barotrauma causes damage to adjacent alveoli via stretching and shearing forces. • High peak airway pressures are directly correlated with barotrauma

Consequences of MV • Complications of alveolar rupture can be devastating: – Pulmonary interstitial emphysema – Pneumomediastinum – SQ Emphysema – Pneumothorax – Pneumoperitoneum

Ventilator Synchrony • Setting the ventilator to cycle with the patient’s respiratory rhythm – Requires close patient monitoring – Try to prevent ineffective triggering – Adjust oxygen flow rate in proportion to tidal volume * may increase peak airway pressure – Adequate sedation is critical – Any increased sense of effort (fatigue vs. forced exhalation) on the part of the patient contributes to sensation of dyspnea

Case Presentation • 65 year-old man BIBEMS c/o increasing dyspnea over 3 days associated with temperature of 100. 3 and increase in thickened, green sputum. He has a history of emphysema, is on home oxygen and has been using his inhalers without relief.

The Decision To Intubate • Initiation of mechanical ventilation in COPD patients is associated with high patient mortality and poor potential for weaning • Indications: (E. B. M. vs. clinical gestalt) – – – Patient failed conservative management Severe, persistent acidosis Continued arterial hypoxemia despite initial therapy Patient fatigue Altered mental status Additional major illness (pulmonary embolism, AMI)

The usual vent settings are applied Some time passes………….

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Respiratory Distress in MV • Ventilator: Malfunction or Circuit Leak • Ventilator: Inadequate ventilator settings: – Inadequate Tidal volume, Fi. O 2, Flow rate, Positive end expiratory pressure (PEEP) or over/undersensitivity • Airway: (increased Ppeak-Pplat) – ENDOTRACHEAL TUBE MIGRATION, patient biting tube, balloon cuff leak, deflation or rupture – Bronchospasm, increased airway resistance imposed by heat and moisture exchanger, obstruction by secretions, blood or foreign object

Respiratory Distress in MV • Lungs: (Ppeak-Pplat unchanged or decreased): pneumonia, atelectasis, pulmonary edema, aspiration of gastric contents, pneumothorax, pleural effusion, pulmonary embolus, ENDOTRACHEAL TUBE MIGRATION! • Extrapulmonary: Abdominal distension, delerium, anxiety, pain, stroke, seizure

Respiratory Distress in MV

What to Do? • Protocol

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Goals for COPD patients • Adequate patient monitoring • Optimize ventilator settings to minimize excessive work of breathing • Assure Synchrony • Detect auto-PEEP and prevent barotrauma • Prevent further respiratory muscle atrophy • Intubate using the widest diameter ET tube possible (R = 8 nl / πr 4)

Obstructive Lung Diseases • • Asthma Chronic bronchitis Emphysema Congenital bullous lung disease

Pathophys COPD

Pathophys Emphysema

Vent Guidelines • Emphasis on assisted modes of ventilation (patient initiated), institution preference for A/C vs. IMV with PSV (to overcome ET tube) • SIMV: probably causes excess work, b/c of high resistance circuit but debatable; requires close patient monitoring

Vent Guidelines

VENT Guidelines Higher flow rates are highly beneficial

Vent Guidelines

Vent Guidelines • • • Tidal Volume: 5 -7 ml/kg Set Rate: 4 less than spontaneous rate Fi. O 2: adjust to Pa. O 2 of at least 60 mm. Hg Triggering: -1 to -2 cm H 2 O Prevent Auto-PEEP with sufficient PEEP Flow rate: Increase to provide increased expiratory time (70 -90 lpm) • Continue inhaled medications: requires sufficient tidal volume and inspiratory time

Pathophys Asthma • Airway narrowing caused by smooth muscle contraction, wall thickening and increased secretions combine to reduce air flow rates • Primarily a disease of the AIRWAYS with decreased elastic recoil of the lungs during attack • ABG for Pa. CO 2 to identify respiratory failure

Pathophys Asthma

Vent Settings Asthma • Respiratory rate 10 to 14 breaths/min (allows more time for exhalation) • Tidal volume less than 8 m. L/kg • Minute ventilation less than 115 m. L/kg • Inspiratory flow of 80 to 100 L/min • Extrinsic postive end-expiratory pressure less than 80 percent of the intrinsic PEEP • Continue inhaled medications and steroids

Vent Settings Asthma

Vent Settings Asthma • Intubate with largest diameter tube possible! (8. 0 mm and up) • First priority is to minimize auto-PEEP and keep plateau pressures low! • Lower respiratory rate and tidal volume may be necessary causing Pa. CO 2 to increase (permissive hypercapnia) • Sedation, then paralysis to force synchrony • Heliox

Osteopathic Considerations • Findings reflect anatomical changes related to increased lung volumes and impaired ventilation – Thoracic Vertebral Dysfunction – Rib Dysfunction (stuck in exhalation) – Diaphram Dysfunction (stuck down) • Law of La. Place T = Pr – Lymphatic obstruction: lymphatic drainage impaired by positive pressure

Summary • The need to initiate mechanical ventilation in patients with obstructive lung disease in the emergency department is associated with a higher inpatient mortality • Patients with obstructive lung disease require close monitoring of all physiologic parameters to prevent complications associated with positive pressure ventilation • Assessing a distressed ventilator dependent patient requires an organized approach • In general: low tidal volumes, higher flow rates and application of a conservative amount of PEEP are appropriate initial settings for patients with obstructive lung disease

References • • “The ICU Book” Marino PL, 2 nd Edition “Respiratory Physiology” West JB, 5 th Edition “Pulmonary Pathophysiology” Grippi MA “Textbook of Medical Physiology” Guyton and Hall 9 th Edition • “Chest Radiology Companion” Stern EJ, White CS • Harrison’s Principles of Internal Medicine 16 th Edition

References www. utdol. com : “principles of mechanical ventilation”, “alternate modes of mechanical ventilation”, “positive end expiratory pressure”, “pathophysiologic consequences of positive pressure ventilation”, “mechanical ventilation in acute respiratory failure complicating COPD”, “mechanical ventilation in adults w/ status asthmaticus”