Mechanical Ventilation in Infants and Children Proshad Efune, MD Iqbal

Mechanical Ventilation in Infants and Children Proshad Efune, MD Iqbal Ahmed, MBBS FRCA University of Texas Southwestern Medical Center Children’s Health System of Texas Dallas, Texas

Disclosures No relevant financial relationships

Learning Objectives Describe the physiology and indications for mechanical ventilation Distinguish anesthesia and ICU ventilators used for children Describe the most commonly used modes of mechanical ventilation Recognize strategies to avoid complications of mechanical ventilation

Controlled Ventilation: A Life Saving Innovation Negative Pressure Ventilation -The body’s “natural” way to ventilate -Historically used in polio epidemics: e.g., “Iron lung” Positive Pressure Ventilation (PPV): used in OR and ICU By Kuebi Armin Kübelbeck - Own work, CC BY 3.0, https://commons.wikimedia.org/w/index.php?curid 28965570

Physiology of PPV Positive pressure is used to actively inflate the lungs Prs Pelastic Presistance Prs Pawo Pmus j Where Prs Pressure supplied to the respiratory system Expiration is passive

Indications for Mechanical Ventilation Need for controlled or supported ventilation during anesthesia Hypoxemic or hypercarbic respiratory failure Neuromuscular weakness Decreased respiratory drive To decrease work of breathing in patients with shock To decrease afterload in patients with cardiac failure Neurologic impairment (Intubate for Airway protection)

Cardiovascular Effects of PPV Inspiration with positive pressure ventilation increases intrathoracic pressure RA pressure venous return RV stroke volume LV afterload: LV pumps against trans-mural pressure of the aorta Transmural pressure Intravascular pressure – intrathoracic pressure PEEP venous return cardiac output Positive pressure slightly decreases ventilation-perfusion (V-Q) matching

Simplest Ventilator: Manual Ventilation Components: - Breathing system: e. g. Ambu Bag - Fresh gas flow: oxygen source or air entrainment - Reservoir bag - Adjustable pressure limiting valve (APL) or an Ambu-type valve Can be delivered via face mask, LMA, ETT, or tracheostomy

Manual Ventilation Advantages Disadvantages Low cost/low tech Imprecise Ubiquitous availability Operator fatigue May be lifesaving in resource limited settings Single provider may be unable to perform other important tasks Practical for short periods

Problems with Older Anesthesia Machine Ventilators Unable to deliver small tidal volumes precisely Don’t function well at higher respiratory rates Offer little more than volumecontrolled mode Changes in fresh gas flows can change delivered tidal volumes

Ventilators on Older Anesthesia Machines Schematic of a traditional anesthesia machine design indicating gas flows during mechanical inspiration The set tidal volume enters the bellows compartment (1), but the tidal volume delivered to the patient (4) is altered because of circuit compliance and fresh gas flows (2) From “Feldman JM. Optimal Ventilation of the Anesthetized Pediatric Patient. Anesth Analg. 2015;120(1):165-175”

Ventilators on Older Anesthesia Machines circuit compliance inspiratory pressure set tidal volume inspiratory time Actual delivered tidal volume fresh gas flow

Newer Anesthesia Machine Ventilators Have multiple modes available: - Pressure Support - Pressure Control - Volume Control-SIMV - Pressure Regulated Volume Control (Auto-Flow or Volume Guarantee) Can more precisely deliver small tidal volumes and higher respiratory rates suitable for infants Can compensate for circuit compliance and leaks and separate delivered tidal volumes from fresh gas flows

Ventilators on Newer Anesthesia Machines Modern anesthesia ventilator capable of delivering the set tidal volume to the patient’s airway using compliance compensation and eliminating the interaction between fresh gas flow and tidal volume The ventilator delivers a larger volume to compensate for circuit compliance (1) so that the set volume is delivered to the airway (4) Fresh gas cannot enter the circuit during inspiration and influence tidal volume because of a valve between the fresh gas flow and the ventilator (2) From “Feldman JM. Optimal Ventilation of the Anesthetized Pediatric Patient. Anesth Analg. 2015;120(1):165-175”

Modern Anesthesia Workstation Vaporizers Volumes/pressureflow monitoring APL valve Reservoir bag CO2 Absorber Vent Modes

Regardless of how sophisticated the OR ventilator is, a backup manual system should always be ready in case of mechanical/electrical or gas supply failure

Using Older Anesthesia Machine Ventilators For Infants If pressure-controlled mode available, set initial pressure limit low ( 15 cm H2O) Set appropriate respiratory rate and fresh gas flow Watch chest excursion, auscultate, and monitor expired tidal volume and ETCO2 (if available) Slowly increase pressure limit, if necessary, to achieve desired results If available, use arterial blood gas to confirm adequacy of ventilation when ETCO2 is not available

Using Older Anesthesia Machine Ventilators For Infants If pressure-controlled mode not available, set inspiratory time and expiratory pause to obtain desired respiratory rate appropriate for age Set inspiratory flow rate low and slowly increase to achieve desired pressure limit on Paw dial If available, use arterial blood gas to confirm adequacy of ventilation when ETCO2 is not available

Using Older Anesthesia Machine Ventilators For Infants: Caution Vigilance is required when ventilating infants on older anesthesia machines Changes in airway compliance or lung/chest wall compliance can occur intraoperatively, increasing or decreasing the delivered tidal volume Using appropriately sized CUFFED endotracheal tubes will decrease the leak and increase the accuracy of delivering tidal volumes in infants

Fundamental Principles Minimize apparatus dead space for optimal gas Use the lowest airway pressure, FiO2 and tidal volume exchange (circuit design, ETTvigilance length, connectors, Take measures and practice to avoid necessary to obtain desired gas exchangelung valves) injury and ensure adequate ventilation

Apparatus Dead Space Y-piece of circle breathing system Redundant connector adding apparatus dead space Elbow connector Small increases in dead space can substantially increase the Vd/Vt ratio in children causing HYPOVENTILATION and HYPERCARBIA

Removal of Connector Reduces Dead Space Be diligent about minimizing apparatus dead space in children

OR vs ICU Ventilators OR Ventilators ICU Ventilators Short term ventilation (minutes to hours) Longer ventilation (days to weeks) Simple modes of ventilation suitable for anesthetized patients Many sophisticated modes for critically ill patients with severe lung disease Circle systems, CO2 absorbers and one-way valves popular in many countries Almost never used in ICU Designed for anesthetic delivery of inhalational anesthetic agents (IAA) Inhalational agents rarely used in ICU ventilators Scavenging systems in line for IAA Scavenging separate for inhaled NO Humidification through circuit HMEs or circle system Integrated heater/humidifier Adjustable pressure limiting valve (APL) integrated in system for manual mode No APL. Need separate manual backup system

Infant and Neonatal Ventilator Humidifier to prevent desiccation of respiratory tract on inspiratory limb Expiratory limb

ICU Transport Ventilator With Basic ICU Modes Can function adequately for most ICU patients Suitable for lower resource settings as a main ICU workhorse Needs electrical power to work. Older version works on compressed gas supplies without power

ICU Ventilators Modes Controlled Assist-control ventilation (ACV) Synchronized intermittent mandatory ventilation (SIMV) Pressure-controlled ventilation (PCV) Pressure support ventilation (PSV) Airway pressure release ventilation (APRV) Pressure regulated volume control (PRVC) Proportional assist ventilation (PAV) Neurally adjusted ventilatory assist (NAVA) Controls and settings

Controlled Ventilation Pressure-controlled: Time cycled, pressure-limited, decelerating flow, constant pressure waveform – Better for recruitment and maintaining lung volumes and preventing pressure injury, but tidal volume not guaranteed Volume-controlled: Time cycled, volume-limited, constant inspiratory flow, ascending pressure waveform – Higher peak pressures and pressure varies with lung compliance. Barotrauma can be prevented by setting pressure limit

Flow Pressure Pressure-Controlled Ventilation Time Time Target pressure is maintained throughout the duration of inspiratory time during which the flow decreases

Flow Pressure Volume-Controlled Ventilation Time Time Constant flow is maintained through the set inspiratory time and peak pressure is reached towards end inspiration

Pressure-Regulated, VolumeControlled (PRVC) Combines decelerating flow pattern with guaranteed tidal volume First breath delivered – volume limited, constant flow Measured plateau pressure then used to pressure limit the following breath Ventilator automatically adjusts the PIP required to deliver guaranteed TV for each subsequent breath Best of both worlds?

Volume Flow Pressure PRVC Time Time Set tidal volume Time

Pressure Support Ventilation Only spontaneous breaths are augmented Work of breathing imposed on the patient is reduced Respiratory rate, inspiratory time, and tidal volume controlled by patient A minimum negative inspiratory effort that exceeds the preset sensitivity (based on either pressure or flow) is necessary to trigger the ventilator

Can Intubation Be Avoided? Supplemental O2 by nasal cannula, Venti-mask, or non-rebreather High flow nasal cannula – heated, humidified O2 (HHFNC) Non-invasive positive pressure ventilation: BiPAP, CPAP (including bubble CPAP) HHFNC and non-invasive ventilation may decrease the need for intubation High flow nasal cannula setup

Monitoring Ventilation in the OR A trained anesthesia provider provides continuous vigilance Continuous pulse oximetry: The LIFEBOX project aims to supply low cost oximeters to low resource settings Oxygen analyzer to prevent delivery of hypoxic mixture Continuous end tidal CO2 monitoring (precordial stethoscope recommended if end tidal CO2 not available)

Monitoring Mechanically Ventilated Children in the ICU Continuous pulse oximetry is necessary; continuous end tidal CO2 monitoring is ideal Tidal volume, minute volume, airway pressures Arterial blood gases at suitable intervals Hemodynamic monitoring for cardiovascular changes Trained respiratory therapists and ICU nursing staff Technical support to operate and service ventilators Sufficient bedside nursing staff

Complications During Mechanical ventilation Ventilator-induced lung injury: barotrauma Ventilatorassociated respiratory infections New infiltrates on chest X-Ray Purulent endotracheal secretions Fever/leukocytosis Atelectasis Utilize PEEP and recruitment maneuvers Change patient position and chest physiotherapy

Lung Protective Strategies Limit tidal volumes to 4-6 Limit tidal volume to 7 ml/kg in the ICU, particularly ml/kg in the OR with ARDS Well established in adults, but limited data in children Prevent atelectasis by utilizing Use as low an FiO2 as possible to prevent oxygen toxicity at least 5 cm H2O PEEP

Ventilator Bundles Strict implementation of simple, inexpensive interventions in care of mechanically ventilated children can significantly decrease ventilator associated pneumonia (VAP) even in resource-limited settings Elevate head of bed to 30 Hand hygiene Oral care with chlorhexidine Stress ulcer prophylaxis Daily sedation interruptions Daily extubation readiness testing Haque A, Riaz Q and Ali SA. Implementation of ventilator bundle in pediatric intensive care unit of a developing country. Journal of the College of Physicians and Surgeons Pakistan 2017; 27(5):316-318.

Management Strategies for Mechanically Ventilated Children Utilize a minimum PEEP of 5 cm H2O Extubate patients when ready with sufficient staff available if reintubation is required

Facilitating Patient Extubation If appropriate, perform daily spontaneous breathing trials If no endotracheal tube cuff leak Consider a course of dexamethasone (0.5mg/kg q6h x 24 hours) starting at least 6 hours prior to extubation Upper airway obstruction accounts for 37% of failed extubations (Kurachek 2003)

Reducing Usage of Medical Gas Supplies Utilize oxygen concentrators if available Require electricity Can only provide 5 - 6 L/m Maximum FiO2 is 2 approximately 90% Wean respiratory support as quickly as feasible Limit flow rates when applicable

Sedation Strategies During ICU Mechanical Ventilation Drugs: Opioids, benzodiazepines, dexmedetomidine or clonidine - Routes of administration: IV, IM, PO/NG, SQ, PR - Continuous IV infusion provides best route of administration but requires a medication pump Sedation scoring should be regularly performed to avoid under and over-sedating Weaning of sedative agents should be performed to avoid withdrawal if greater than 5-7 days of exposure

Conclusions Lung protective ventilation strategies benefit intubated children Newer anesthesia machine ventilators approach the capabilities of ICU ventilators; older anesthesia machine ventilators are more limited

References: 1. Feldman JM. Optimal Ventilation of the Anesthetized Pediatric Patient. Anesth Analg. 2015;120(1):165-175. 2. Kurachek SC, Newth CJ, Quasney MW, et al. Extubation failure in pediatric intensive care: A multiple-center study of risk factors and outcomes. Crit Care Med 2003; 31:2657-2664. 3. Haque A, Riaz Q and Ali SA. Implementation of ventilator bundle in pediatric intensive care unit of a developing country. Journal of the College of Physicians and Surgeons Pakistan 2017; 27(5):316-318.