TO VENTILATE OR NOT TO VENTILATE: MECHANICAL VENTILATION 101

Transcription

1 TO VENTILATE OR NOT TO VENTILATE: MECHANICAL VENTILATION 101 Deborah Silverstein, DVM, DACVECC Introduction Garret Pachtinger, VMD, DACVECC COO, VETgirl With special thanks to Drs. L. King, L. Waddell and K. Beer Introduction Justine A. Lee, DVM, DACVECC, DABT CEO, VETgirl VETgirl On-The-Run The tech-savvy way to get online veterinary CE! A subscription-based podcast and webinar service offering veterinary RACE-approved CE VETgirl ELITE Up to 5 members: $599/year Up to 10 members: $999/year podcasts/year plus 30+ hours of webinars! $199/year 40+ hours of RACE-CE > 10 members: Ping us 1

2 Video Archives! New and improved video! Download our itunes podcasts free! Social media and our blog! Logistics: CE Certificates n n n n n Type in questions ed to you 48 hours after the webinar Active participation = no quiz Watching video later, must complete quiz n ELITE members only / contact with ANY questions n garret@vetgirlontherun.com n justine@vetgirlontherun.com 2

3 Introduction Deborah Silverstein, DVM, DACVECC Associate Professor Department of Clinical Studies University of Pennsylvania School of Veterinary Medicine Outline What is mechanical ventilation? Indications Hypoventilation Differentials! Hypoxemia Differentials! Concern for fatigue/exhaustion Types and modes of ventilation Pressure vs. volume limited A/C, SIMV, PEEP Complications Prognosis What is the veterinary evidence? What is mechanical ventilation? Iron Lungà negative pressure ventilation Using a machine to perform some or all of the work of breathing PPV: Positive Pressure Ventilation Machine provides an increase in airway pressure to move gas into the lungs Mandy Jo 4 yo FS American Staffordshire terrier Found acutely paralyzed at the bottom of the stairs No motor function x 4 Hyper-reflexive x 4 Intact pain sensation Respiration mainly diaphragmatic, little intercostal movement What are your differentials? What would you recommend to the owners? Mandy Jo : Diagnostics Suspect spinal cord injury Myelogram shows compression at C2/C3 Impairment of respiration due to failure of impulse generation in the phrenic and intercostal nerves 3

4 Mandy Jo : Post-op Dorsal laminectomy C2/C3/C4 Post-op admit to ICU: No chest wall movement, cyanotic ph 7.01 PaO 2 54 mmhg (FiO 2 21%) PaCO 2 80 mmhg HCO 3 25 mmol/l What is your diagnosis? Calculating the A-a gradient Useful in determining lung function Is the dog just hypoventilating or is there a pulmonary parenchymal problem? The simplified version: P A O 2 = x [PaCO 2 ] A-a gradient = P A O 2 PaO 2 Normal = 5-15 mmhg The REALLY simplified version: PaO 2 + PaCO 2 > 120 = NORMAL A-a gradient On room air only! Ways to deliver oxygen Mandy Jo ABG following oxygen supplementation: ph PaO mmhg (mask) PaCO 2 91 mmhg HCO mmol/l What do you think now? What would you like to do? Indications for PPV Hypoventilation PaCO 2 > 60 mmhg Hypoxemia PaO 2 < 60 mmhg despite O 2 supplementation Impending fatigue PaCO 2 increasing PaO 2 decreasing and non-responsive to increased FiO 2 If you re staring at your patient in the oxygen cage and wondering if you should initiate PPV, the answer is probably yes Other situations Causes of hypoventilation Think about it anatomically! 4

5 Mandy Jo The decision to ventilate Mandy Jo : Goals of PPV in an animal with ventilatory failure Plan: Use the ventilator to provide respiratory support while the spinal cord heals Decision: How should we do this? To increase tidal volume towards normal (Vt=10-15 ml/kg) To improve minute ventilation to allow: Elimination of CO 2 Resolution of respiratory acidosis Resolution of distress (Normal minute ventilation Ve= ml/kg/min) Modes of Ventilation Controlled ventilation Modes of Ventilation Ventilator does all of the work Patient can trigger ventilator Assisted ventilation Patient can initiate breaths and ventilator assists Synchronized intermittent mandatory ventilation Combination of mandatory (controlled) breaths and spontaneous breaths Pressure-controlled ventilation (PC) Gas is delivered to a chosen airway pressure, regardless of the tidal volume Appropriate for animals with lung disease Volume-controlled ventilation (VC) A pre-determined tidal volume is given regardless of the airway pressure generated Appropriate for animals with normal lungs and some with lung disease Trigger, Cycle and Limit Variable Inspiratory trigger variableà time, flow or pressure necessary to cause the machine to start inspiration Positive End Expiratory Pressure (PEEP) Positive pressure applied at the end of each breath Purpose: Recruit alveoli and hold them open for use in gas exchange + prevent repetitive collapse and opening of the alveoli If the animal attempts to breathe and generates the preset negative flow or pressure, the ventilator will synchronize or assist the breath Cycle variableà causes inspiration to end (flow or time) Limit variableà preset limits that will not terminate a breath, but cannot be exceeded 5

6 Traditional recommendations for PPV settings Tidal volume ml/kg RR bpm Peak Inspiratory Pressure mmhg PEEP 0-2 cm H 2 0 Emphasis on maintaining adequate values for PaO 2 and PaCO 2 Mandy Jo 20kg Pre-ventilation Initial settings RR Vt (mls) Ve (mls/kg/min) FiO2 0.4 (mask) 0.5 Pressure 7 PEEP 2 PaO2 253 PaCO2 91 Mandy Jo 20kg Mandy Jo 20kg Pre-ventilation Initial settings RR Vt (mls) Ve (mls/kg/min) FiO2 0.4 (mask) 0.5 Pressure 7 PEEP 2 PaO PaCO Initial settings RR 12 Vt 125 Ve 75 FiO2 0.5 Pressure 7 PEEP 2 PaO2 136 PaCO2 87 New settings Mandy Jo 20kg Mandy Jo 20kg Initial settings New settings RR Vt Ve FiO Pressure 7 12 PEEP 2 2 PaO2 136 PaCO2 87 Initial settings New settings RR Vt Ve FiO Pressure 7 12 PEEP 2 2 PaO PaCO

7 Airway management in ventilator patients Low pressure high volume endotracheal tubes Heated humidifiers always added to circuit Suction airway secretions as needed Maintain sterile airway as much as possible Immunosuppression and invasive airway tubes increase risk of ventilator acquired pneumonia Mandy Jo Volume controlled ventilation Tracheostomy tube Nutritional support The benefits of tracheostomy Modes of Ventilation Synchronized intermittent mandatory ventilation (SIMV) Ventilator is set to deliver a minimum desired number of breaths per minute Patient can breathe spontaneously between ventilator breaths Some work of breathing is assumed by the patient Useful for weaning, preventing muscle atrophy Mandy Jo : Progression Ventilator outcomes in dogs with cervical spinal cord injury (Beal MW, et al. JAVMA 2001) Gradual improvement in respiratory muscle activity Weaned from ventilator after 5 days Walking after 4 weeks Objectives Describe ventilator management, clinical course, and outcome in dogs with ventilatory failure secondary to cervical spinal cord disease or injury Identify risk factors for perioperative ventilation in surgically managed cases of cervical spinal cord disease/injury 7

8 Results 268 dogs with cervical spinal cord surgeries 13 required perioperative PPV 4.9% incidence in surgical patients 1 non-surgical cervical injury included (FCE?) No significant relationship between the need for perioperative PPV and Breed Age Underlying disease process Results: Outcome 10 of 14 dogs weaned from ventilator (71%) 4/14 euthanized Multiple organ failure (n=2) No improvement in ventilation after 10 days (n=1) Owner elected euthanasia (n=1) Results Duration of ventilation Mean (n=14) = 4.5 days Mean (survivors) = 4.5 days Range = ( days) Neurologic outcome in survivors 9/10 dogs were ambulatory with bladder and bowel function 1/10 non-ambulatory Mean time to return to function = 53.4 days (n=7) Sasha 30 kg FS Golden Retriever Hit by car 1 hour prior to presentation Heart rate 200 bpm, weak pulses and pale mucous membranes Distended abdomen, possible fluid wave Respiration rate 48 bpm, significantly increased respiratory effort Diffuse crackles on lung auscultation PCV 34% TS 4.2 g/dl Sasha : Thoracic radiographs at admission Pulmonary contusion Hemorrhage from multiple capillaries into the pulmonary parenchyma and alveoli Can progress over hours following initial trauma Ongoing hemorrhage Pulmonary edema following fluid therapy Respiratory distress often worsens before it improves 8

9 Sasha : Admission PCV 34% TS 4.2 g/dl ph 7.39 PaO 2 64 mmhg (room air) PaCO 2 23 mmhg HCO 3 13 mmol/l Lactate 4.2 mmol/l EKG: Sinus tachycardia Oscillometric BP: 95/42, mean 65 mmhg Causes of hypoxemia 1. Low FiO 2 or atmospheric partial pressure of oxygen 2. Hypoventilation 3. Ventilation:perfusion (V/Q) mismatch 4. Shunting 5. Diffusion impairment Causes of hypoxemia Sasha Initial overnight management Oxygen supplementation Isotonic crystalloid bolus 2 x 10 ml/kg over 30 minutes each Transfuse 2 units packed red blood cells Transfuse 2 units fresh frozen plasma Start vasopressor therapy Monitor Sasha : Day 2 Cardiovascular system improved Sasha Decision: Intubate and repeat radiographs Severe dyspnea, cyanotic mucous membranes, loud crackles diffusely ph 7.37 PaO 2 41 mmhg (60% oxygen) PaCO 2 35 mmhg HCO 3 18 mmol/l Lactate 2.2 mmol/l 9

10 Sasha The decision to ventilate Sasha : Goals of PPV for patients with failure of pulmonary gas exchange Plan: Use the ventilator to provide respiratory support while the lung parenchyma heals Decision: How should we do this? To improve tidal volume To improve gas exchange by opening recruitable alveoli To minimize the energy expenditure associated with increased work of breathing To resolve respiratory distress To minimize ventilator-induced lung injury by avoiding high airway distending pressures Long term anesthesia in ventilator patients Anesthesia is needed to facilitate maintenance of the endotracheal tube Injectable anesthetics and sedatives usually given by CRI Opioids Benzodiazepines Ketamine Dexmedetomidine Propofol Alfaxalone Neuromuscular blockade if needed Barotrauma and volutrauma in abnormal lungs Normal tidal volumes may Over-distend compliant alveoli Produce high airway pressures Some alveoli and terminal bronchioles may be collapsed at end expiration and expanded during inspiration: termed recruitable Cyclical expansion and collapse of recruitable alveoli may result in shear stress in these and adjacent alveoli Problems with PPV in abnormal lungs Over-distension alveolar epithelial and capillary endothelial injury in previously normal alveoli High airway pressures may contribute to barotrauma, resulting in: Interstitial emphysema Pneumomediastinum Pneumoperitoneum Subcutaneous emphysema Pneumothorax Pneumothorax in ventilated animals: What do our studies show? King et al. JAVMA 1994 Pneumothorax developed in 12 animals (29%) during PPV Mean PIP in pneumothorax dogs: cm H 2 O Mean PIP in those without pneumothorax: cm H 2 O P <

11 Pneumothorax in ventilated animals: What do our studies show? Lee et al. JAVMA 2005 Pneumothorax developed during PPV in 15/53 cats (28%) Pneumothorax developed in: PIP > 25 cm H 2 O: 7 of 16 cats PIP < 25 cm H 2 O: 8 of 20 cats No statistical significance Pneumothorax in ventilated animals: What do our studies show? Hopper et al. JAVMA 2007 Pneumothorax developed during PPV in 10/148 animals (7%) No variables tested were associated with development of pneumothorax Rutter et al. JVECC 2011 Dogs with LMN disease Pneumothorax in 4/14 dogs Hoareau et al. JVECC 2011 Brachycephalics Pneumothorax in 0/15 dogs More problems with PPV High FiO 2 values may exacerbate inflammation and oxidative injury Placement of an endotracheal or tracheostomy tube bypasses host defenses in already immunocompromised patients Hemodynamic compromise Inflammation associated with PPV in diseased lungs Pro-inflammatory cytokines produced as a result of: over-distension shear stress infection oxidative injury (high FiO 2 ) Cause progression of lung disease May be released into the circulation and contribute to or cause SIRS and multiple organ failure What about ALI/ARDS? Life-threatening complications of critical illness Inflammation and changes in the alveolar-capillary membrane lead to pulmonary edema alveolar flooding with protein-rich fluid and loss of lung volume ALI: acute lung injury ARDS: acute respiratory distress syndrome Diagnosed based on clinical signs and findings! Diagnosing ALI/ARDS 1. Acute onset (< 72 hours) of tachypnea and labored breathing 2. Known risk factors 3. Evidence of pulmonary capillary leak without increased pulmonary capillary pressure a. Bilateral pulmonary infiltrates on radiographs or CT b. High protein fluid in conducting airways 4. Evidence of inefficient gas exchange a. P:F < 300 for ALI, < 200 for ARDS b. Increased A-a gradient 5. Evidence of diffuse pulmonary inflammation 11

12 ARDS Lung Normal Lung ARDS Network, N Eng J Med 2000 Ventilation with lower tidal volumes as compared with traditional tidal volumes for ALI and ARDS Methods People with ALI or ARDS on PPV Randomly assigned to receive traditional tidal volumes (TTV) or low tidal volumes (LTV) Volume limited assist/control ventilation Used predicted rather than actual BW All patients followed day 0 - day 28 ARDS Network, N Eng J Med 2000 Ventilation with lower tidal volumes as compared with traditional tidal volumes for ALI and ARDS Results Trial terminated after 861 patients because interim analysis showed that LTV resulted in 22% decrease in mortality (P=0.005) Mortality in TTV group 39.8% Mortality in LTV group 31.0% Recommendations for PPV settings Traditional VT10-15 ml/kg PEEP as required to maintain oxygenation Emphasis on maintaining adequate values for PaO2 and PaCO2 Lung protective strategies VT 6-8 ml/kg PIP < 30 cmh2o PEEP > 5 cmh2o Permissive hypercapnia Pre-ventilation Initial settings RR Vt (mls) Ve (mls/kg/min) FiO Pressure 18 PEEP 2 PaO2 41 PaCO

13 Pre-ventilation Initial settings RR Vt (mls) Ve (mls/kg/min) FiO Pressure 18 PEEP 2 PaO PaCO Positive End Expiratory Pressure (PEEP) Improves oxygenation in the hypoxemic patient Positive airway pressure prevents complete exhalation, resulting in Increased FRC Increased alveolar recruitment Prevention of early airway closure Improved oxygenation on lower FiO2 But.. Decreases venous return Increases airway pressures Initial settings New settings RR Vt (mls) Ve (mls/kg/min) FiO Pressure PEEP 2 5 PaO2 75 PaCO2 39 Initial settings New settings RR Vt (mls) Ve (mls/kg/min) FiO Pressure PEEP 2 5 PaO PaCO New settings #1 New settings #2 RR Vt (mls) Ve (mls/kg/min) FiO Pressure PEEP 5 8 PaO2 183 PaCO2 41 New settings #1 New settings #2 RR Vt (mls) Ve (mls/kg/min) FiO Pressure PEEP 5 8 PaO PaCO

14 New settings #2 New settings #3 RR Vt (mls) Ve (mls/kg/min) FiO Pressure PEEP 8 8 PaO2 257 PaCO2 40 New settings #2 New settings #3 RR Vt (mls) Ve (mls/kg/min) FiO Pressure PEEP 8 8 PaO PaCO Sasha day 4 Progressive improvement in lung function over 48 hours Weaned from ventilator day 4 Discharged from hospital day 7 When to Wean? General guidelines: Improvement in primary disease process ABG (or SpO2 and PvCO2) WNL and FiO 2 40% and RR 20 bpm with normal TV PEEP <4 cm H 2 0 Cardiovascular stability Outcomes in dogs ventilated to treat pulmonary contusion following trauma Campbell VL, et al. JAVMA 2000 Objectives To assess pulmonary function, ventilator management and outcome in dogs that required PPV for acute pulmonary contusion following trauma (10 cases): Results: Patient population 10 dogs eligible for study 8 female, 2 male Type of trauma Hit by car (n=8) Dragged by car (n=1) Fell from deck (n=1) Mean body weight = /- 16 kg Range 5-50 kg 14

15 Results: Outcome Group A Survival to discharge (n=3) Improved lung function but died in hospital (n=2) Group B Died or euthanized because of progressive lung dysfunction (n=5) Published outcomes: Dogs and cats ventilated to manage Pulmonary Gas Exchange Failure Penn data (King and Hendricks) 20 patients : 4 survived (20%) JAVMA 1994, 204 (7): Davis data (Drellich) 45 patients over 7 years: 9 survived (20%), 5 discharged alive (11%) VCNA 2002, 32: Penn data Cats only (Lee) 5 cats out of 36 survived (14%) JAVMA 2005; 226(6): Davis data (Hopper) 73 patients: 26 weaned and 16 survived to discharge (22%) JAVMA 2007; 230: Conclusion QUESTIONS? Positive pressure ventilation can be used for short-term support of respiratory function in small animal patients This material is copyrighted by VETgirl, LLC. None of the materials provided may be used, reproduced or transmitted, in whole or in part, in any form or by any means, electronic or otherwise, including photocopying, recording or the use of any information storage and retrieval system, without the consent of VETgirl, LLC. Unless expressly stated otherwise, the findings, interpretations and conclusions expressed do not necessarily represent the views of VETgirl, LLC. Medical information here should be references by the practitioner prior to use. Under no circumstances shall VETgirl, LLC. be liable for any loss, damage, liability or expense incrred or suffered that is claimed to have resulted from the use of the information provided including, without limitation, any fault, error, omission, interruption or delay with respect thereto. If you have any questions regarding the information provided, please contact info@vetgirlontherun.com 15