Airway anatomy

Bag Mask Ventilation

• See Shock section in CV for more on oxygen delivery vs demand

Causes of Hypoxemia

1. Decreased Inhaled O2

   1. At high elevations above sea level, atmospheric pressure drops. (260mmHg on top of Mt. Everest) - decreased PaO2

2. Hypoventilation

   1. CNS depression (sedatives, GBS, ALS)

   2. Obesity

   3. Neuromuscular disease

   4. Rib fractures, Scoliosis

3. Diffusion limitation

   1. Alveolar fibrosis

   2. Will increase A-a gradient as alveoli can see high O2 but cannot get into blood stream

4. V/Q mismatch

5. Right to left shunt

   1. Physiologic R-L shunt includes bronchial veins that drain into the pulmonary veins and Thebesian veins which drain coronary venous return into the LV

   2. Extreme V/Q mismatch where there is no ventilation and only perfusion.

   3. Shunts do not respond to O2

   4. Usually does not affect CO2 clearance until > 50% shunt

   5. Pathologic shunt can come from pneumonia, ARDS etc

Respiratory Distress/Failure

Two types: 

1. Type 1 respiratory failure- failure to oxygenate

2. Type 2 respiratory failure – failure to ventilate/remove CO2 failure hypercapnia

-   It is generally a clinical (and billing) diagnosis, defined by a patient requiring a higher level of respiratory support from baseline (any form of O2)

Signs & Symptoms: 

Increased work of breathing, tachypnea, grunting, nasal flaring, and retractions

• Signs of increased work of breathing are blunted in those with neuromuscular disorders and these patients instead present with tachypnea and shallow breathing without retractions. 

Blood Gases

• What’s on a blood gas?

●      pH, pCO2, pO2, a calculated bicarbonate value, and base deficit/excess

●      Electrolytes (Na, K, Cl: not as accurate as an RFP but still helpful to trend; iCa and glucose: much more accurate and safer to intervene on)

●      Lactate, mixed venous saturation (SvO2), and hemoglobin and hematocrit (much more accurate on a CBC, but still sometimes helpful to trend)

• Can get an arterial sample (ABG) or a venous sample (VBG)

• Mixed venous saturation (SvO2)

●      A measure of the body’s oxygen consumption and is most accurately measured if sampled from the right atrium (RA)

●      Normal SvO2 should be 75%, assuming the patient has normal lungs from which blood in the pulmonary veins that is sent out to the body via the aorta is 100% saturated, and knowing the body uses about 25% of the O2 it is supplied under normal conditions.

●      A lower SvO2 may indicate increased oxygen consumption or demand (i.e. sepsis, anemia, fever)

A higher SvO2 may indicate increased oxygen delivery, decreased oxygen demand (i.e. if the patient is receiving 100% FiO2 or is currently sedated), or decreased oxygen extraction ability 

Non-Invasive Modalities

Includes Low Flow and High Flow Oxygen Delivery Devices as well as Non-Invasive Positive Pressure Devices (CPAP, BiPAP)

Invasive Mechanical Ventilation (MV)

• Indications

  • • • Respiratory failure not improved with non-invasive methods

      • Airway protection

      • Decrease overall metabolic demand in states of shock

• 4 Phases of IMV Breath

  • • • Trigger - initiation of the breath. This can be time (set by ventilator) or detection of air flow change within the ventilator circuit (patient effort sets this)

      • Limit - what tells the ventilator to stop the inhalation part of the breath. This is flow, pressure or volume limited

      • Cycling - what tells the ventilator to switch to exhalation. This is time, flow, pressure or volume cyled. 

      • PEEP- the amount of pressure in the aveoli at the end of exhalation - at "baseline" prior to next breath. 

      • Nice description here by Deranged Physiology 

With invasive mechanial ventilation, you are converting the patient from NEGATIVE pressure ventilation  to POSITVE pressure ventilation. 

The effects of this on your cardiac and respiratory physiology is known as cardiopulmonary interactions. This will be explained in the section below on this page.

Modes of Mechanical Ventilation

• Two main forms of ventilation: 

  • • • Pressure Control (PC) - you guessed it, you tell the ventilator what PRESSURES you want. Volume is variable since you are only controlling the pressure. Pressure is maintained for the duration of the inspiratory phase. 

• • • • Volume Control (VC) - you guessed it, you tell the ventilator what VOLUME you want. Pressures needed to generate this volume vary. Set the volume, and once that is reached in the breath, then the ventilator cycles to exhalation

• Typically two ways the ventilator supports each breath: SIMV (synchronized intermittent mandatory ventilation) and Assist Control (AC)

• • • • SIMV - the ventilator synchronizes mandatory breaths with patient’s spontaneous breaths

        • • Ventilator will not give a breath while patient is trying to exhale or immediately after the patient has just taken a breath. The patient's spontaneous breaths are only supported with additional pressure support, but no guaranteed tidal volume or rate

      • AC - every breath, whether mechanical or spontaneous (by the patient) is fully supported

Ventilator modes combine SIMV/AC with PC or VC. Visualizations of these are below. 

Common modes of ventilation 

• SIMV - Pressure Regulated Volume Guaranteed/Volume Control (PRVG/PRVC)

  • • • The most commonly used ventilator mode used in the PICU

      • Ventilator will adjust pressure needed to provide desired tidal volume

      • Benefit of having the "decelerating flow" pattern of PC, but able to manipulate a patient's minute ventilation. 

      • Also lower overall PIP when compared to traditional VC modes. Will need to monitor PIP though as not setting pressure to achieve volumes.

      • Patient will get set PS when taking spontaneous breaths above the set rate

      • Each breath stops (cycles off) when the airflow reaches 30% of maximal flow 

      • Set: Rate, PEEP, Tidal Volume, Pressure Support, FiO2, iT, max PIP

• SIMV - Pressure Control Ventilation (PCV)

  • • • Ventilator gives each breath with a pressure above the PEEP (the pressure control, PC)

      • PIP will be PEEP + PC for mandatory breaths

      • Tidal volume will be variable as you are no longer dictating a tidal volume. Report tidal volumes patient pulls

      • Each breath stops (cycled off) by the set inspiratory time 

      • Set: Rate, PEEP, PC, FiO2, iT

• SIMV - Volume Control Ventilation (VCV)

  • • • Ventilator will deliver a set volume using whatever pressure is required - must monitor PIP as will change with each breath

      • Set: Rate, PEEP, Tidal Volume, FiO2, iT, PIP max

• Pressure Support Ventilation (PSV)

  • • • All breaths are patient generated and supported with extra pressure support. Weaning ventilator support. 

      • Monitor patient’s RR, tidal volumes, work of breathing, SpO2 while on the pressure support trial to assess patient distress. 

      • Set: PEEP, PS, back-up rate, FiO2

• Airway Pressure Release Ventilation (APRV) 

  • • • Continuous postive airwya pressure (CPAP) with intermittent release phase

      • Have a CPAP (P high) for a set amount of time (T high) to maintaine FRC and alveolar recruitment

      • Then have time-cylced release phase at a low pressure (P low) for a short period of time (T low) where ventilation/CO2 removal occurs 

      • Set: Phigh, Plow, Thigh, Tlow, FiO2

Special Considerations in Cardiac/SMA Patient Populations and Use of Oxygen in Non-Invasive/Invasive Ventilation 

• Cardiac: 

  • • • Remember oxygen is a vasodilator and giving O2 to a cardiac patient with lesions that unbalanced pulmonary to systemic circulation (e.g HLHS) can result in increased pulmonary blood flow and decreased systemic flow. 

• SMA: 

  • • • Due to neuromuscular weakness, will not clinically display increase in work of breathing even when ill

      • Administering oxygen without optimizing ventilation may mask hypercarbia/worsening hypercarbic respiratory failure

      • Optimize airway clearance and ventilation strategies prior to increasing FiO2 in hypoxemic SMA patients

Extubation Readiness

Patients are assessed daily via an Extubation Readniess Protocol to see patient is on low amounts of mechanical ventilation and thus qualify for a trial of PSV. 

Other things to consider when determining if you patient is ready for the ETT to be removed are:

Bronchial Hygiene

• Very important for PICU patients to treat atelectasis and mobilize/clear secretions

• Typically contraindicated in severe TBI patients &  after some surgeries

• Not effective for asthma or bronchiolitis

• Try to time BH with nebulizer treatments and in between feeds, if able

Types of Bronchial Hygiene:

1. PDs: Manual chest percussion to help loosen up secretions

2. Vibes: A vibrating tool that works similar to PDs

3. High Frequency Chest Wall Oscillation (Vest): A device that is wrapped around the patient’s chest and vibrates at a high frequency in 5 min intervals to help loosen up secretions

4. EZPAP: Positive pressure is provided while the patient breathes spontaneously to improve/prevent atelectasis.

5. Cough Assist: Used on patients who have a poor/weak cough -- provides alternating positive and negative pressure to mimic coughing and loosen/mobilize secretions.

6. IPV (intrapulmonary percussive ventilator): Used on intubated patients; provides rapid low volume breaths to help with mucus clearance. Should not be used on patients at risk for PTX/obstructive processes (eg. asthma)

7. Bag Lavage Suction: Small amount of saline is bagged into the patient’s lungs followed by suctioning. Can help clear out thicker, copious secretions. Used on intubated/trached patients.

Common Pediatric Respiratory Diseases

PARDS Management 

• Main goals: reversal/treatment of the underlying cause, support of organ function, and mechanical ventilation until patient improves

• Overall ventilator concept is lung protective

• Tolerate hypercarbia (pH >7.2), hypoxemia (>88%) to help prevent toxic ventilator settings

• Consider prone positioning in severe cases

• Avoid/treat fluid overload, use NMB if needed (especially early on)

• Corticosteroids, iNO, surfactant, etc. are generally not recommended. Corticosteroids and iNO are sometimes considered in cases of severe pARDS

• ECMO is useful for severe ARDS (OI > 40)

Asthma (Critical Asthma) 

Definition: an extreme form of asthma exacerbation characterized by hypoxemia, hypercarbia, and secondary respiratory failure. All patients with bronchial asthma are at risk of developing this

• ~ 190-200 deaths/per in US

• 6.2% of children in US have asthma 

• > 1 million ER visits a year 

Clinical Presentation:

• Tachypnea, increased work of breathing with retractions, forced exhalation, unable to speak, wheezing (or "silent chest" due to lack of air flow), tachycardia, hypoxemia, encephalopathy 

• on CXR, will see hyperinflation of the bilateral lung fields with flattened diaphragms 

• May also see pulsus paradoxus on pulse oximetry 

  • • • • Decrease in SBP by > 10 mmHg with inspiration (can also see in cardiac tamponade)

        • Due to large intrathoracic negative pressure, increased preload, bowing of the interventricular septum into the LV, reducing LV preload 

        • Also large intrathoracic negative pressure increased LV afterload and thus decreaed SBP

Goals of Treatment: 

• reverse bronchospasm

• reduce inflammation

• improve work of breathing

• improve ventilation and oxygenation 

These goals are achieved with bronchodilators, systemic steroids, non-invasive ventilation, and …TIME.

In the RBC PICU we have a protocol for patients with asthma, called the Asthma Care Path in the PICU (almost all Children’s Hospitals have similar protocols). Our Respiratory Therapists score patients and administer medications in the PICU. 

Initial treatment: 

• First line treatment: Albuterol, systemic steroids, +/- Magnesium sulfate, ipratropium, isotonic fluid resusciatation 

  • • • IV fluid can help augment cardiac output due to elevated PVR, dehydration, improve V/Q mismatch

• Second line treatment: BiPaP -great if patient has worsening work of breathing 

  • • can receive continuous albuterol through BiPaP mask 

• Third line treatment: terbutaline/aminophylline, Heliox, ketamine 

• Fourth line treatment (severe cases): invasive mechanical ventilation, inhaled anesthetics, ECMO

A note on IMV (i.e. intubation)- only performed in extreme circumstances because patients are at incredibly high risk for cardiopulmonary arrest. It is also  incredibly challenging to ventilate asthma patients on a ventilator because can't mimic the rate and large tidal volumes they were taking prior to being in extremis. Absolute indications for invasive ventilation in asthma include apnea, cardiopulmonary arrest, and acute encephalopathy. 

Ventilator Strategies: Beyond the scope of this website, but in general large tidal volumes, generous pressure support, low PEEP or 0 PEEP, low respiratory rate. Need to monitor plateau pressures to be cognizant of barotrauma/risk of pneumothorax (PIPs not reliable/accurate of alveolar pressure)

Upper Airway Obstruction 

• caused by resistance to airflow in the non-conducting portions of the airway --> supraglottic, glottic, subglottic and tracheal 

• Causes: croup, vocal cord dysfunction, subglottic stenosis, tracheal/laryngomalacia, epiglottis, angioedema, anaphylaxis, burns, foreign body, post-operative edema from T+A, sedation, poor airway/muscle tone, laryngeal web/mass

• Symptoms: stridor, tripod positioning, drooling, suprasternal retractions, hypoxemia, snoring

• Treatment: racemic epinephrine, steroids (Decadron), Heliox, and ultimately intubation

What is helilox?

Heliox

• Mixture of helium and oxygen of various blends: 80% Helium/20% Oxygen or 70% Helium/30% Oxygen

  • • • • • Really requires > 70% helium to be beneficial, so may have limited use in hypoxemic patients requiring more than 30% FIO2

• Mechanism of Action: Helium is less dense than nitrogen and oxygen. Decreasing the density of the air flow helps promote laminar flow → less resistance → decreased work of breathing.

■   This reduces a patient’s Reynolds number --> the lower the number, the more laminiar the fluid/airflow is

Bronchiolitis 

• Definition:  typically viral infection causing inflammation of the lower respiratory tract in children < 2 years of age and can present with signs of symptoms of respiratory distress, ranging from mild to life-threatening

•  Pathophysiology: 

  • • Typical viruses: RSV (most common), rhinovirus, parainfluenza, human metapneumovirus, adenovirus 

    • Infects epithelial cells can causes cell death/edema leading to air trapping, increased mucous production, atelectasis, increased work of breathing and imparied ventiation

• Treatment: 

  • • Mostly supportive care (frequent nasal suctioning, IVF, fever/pain control, close monitoring)

    • SpO2 goals > 92% but < 97%

      • • Can be with low flow or high flow nasal cannula, as well as non invasive positive pressure (see earlier discussion on these on this page)

    • Can trial bronchodilators and steroids in select patients

    • For apneas, cardiopulmonary instability, or severe respiratory distress/acidosis, may warrant invasive mechanical ventilation 

    • New vaccines on the horizon!

***lots of work done by Intensivists in our own RBC Group. Check them out!***

1. Shein SL, Slain KN, Rotta AT, Milési C, Cambonie G. High-flow nasal cannula flow rate in young infants with severe viral bronchiolitis: the question is still open. Intensive Care Med. 2019 Jan;45(1):134-135. doi: 10.1007/s00134-018-5474-4. Epub 2018 Nov 27. PMID: 30483835.

2. Shein SL, Slain KN, Clayton JA, McKee B, Rotta AT, Wilson-Costello D. Neurologic and Functional Morbidity in Critically Ill Children With Bronchiolitis. Pediatr Crit Care Med. 2017 Dec;18(12):1106-1113. doi: 10.1097/PCC.0000000000001337. PMID: 28930814.

3. Clayton JA, Slain KN, Shein SL, Cheifetz IM. High flow nasal cannula in the pediatric intensive care unit. Expert Rev Respir Med. 2022 Apr;16(4):409-417. doi: 10.1080/17476348.2022.2049761. Epub 2022 Mar 7. PMID: 35240901.

4.  Shein SL, Kong M, McKee B, O'Riordan M, Toltzis P, Randolph AG. Antibiotic Prescription in Young Children With Respiratory Syncytial Virus-Associated Respiratory Failure and Associated Outcomes. Pediatr Crit Care Med. 2019 Feb;20(2):101-109.PMID: 30720644.