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Intubation/RSI

General Indications

  • Respiratory failure: No strict cutoffs for hypoxemia or hypercarbia but overall clinical judgment taking into account degree of respiratory distress, degree of impairment in gas exchange, as well as anticipated trajectory with other treatments
    • Parenchymal: i.e. ARDS, pneumonia, aspiration
    • Upper Airway obstruction: i.e. severe croup, subglottic stenosis, etc. not responsive to other treatments
    • Neuromuscuar weakness: i.e. NIF <20 cmH20 in Guillain Barre, muscular dystrophy, spinal muscular atrophy, botulism
    • Failure of respiratory drive
  • Airway protection due to insufficient airway protective reflexes: i.e. severe brain injury, GCS <8 in trauma patients, lack of sufficient cough or gag
  • Hemodynamic instability: i.e. shock, CPR
  • Therapeutic control of ventilation: i.e. Intracranial hypertension, pulmonary hypertension, metabolic acidosis with insufficient compensation
  • Pulmonary Toilet: i.e airway clearance, inability to handle secretions

Physiology of Intubation

  • Noxious stimuli that raises blood pressure and heart rate initially
  • Vagal nerve reflex that can lead to significant bradycardia (particularly in younger patients like infants)
  • Positive pressure breaths impede venous return by increasing intrathoracic pressure, thereby potentially leading to life threatening hypotension, particularly in hypovolemic or preload dependent conditions (ie cardiac tamponade, septic shock, etc)
  • Positive pressure ventilation also reduces LV afterload, and therefore may be beneficial in patients with dysfunction in cardiac contractility 
  • Laryngoscopy can stimulate laryngospasm and bronchospasm
  • Patients are prone to hypoxemia, particularly pediatric patients as they have reduced FRC as higher basal metabolic rates (thus higher oxygen consumption)
  • Increase in ICP with laryngoscopy

The Difficult Airway

  • Risk factors include:
    • History of difficult intubation
    • History of upper airway obstruction or OSA
    • Recent airway surgery (i.e. tonsillectomy, cleft repair)
    • Facial trauma
    • Mandibular hypoplasia, micrognathia, midface hypoplasia, or large tongues
    • Genetic syndromes such as Treacher Collins, Godlenhar, Down Syndrome, Pierre Robin Sequence, etc
    • Obesity
    • Limited cervical spine mobility (ie atlantoaxial instability in Trisomy 21 patients or trauma patients with potential cervical injuries)
  • Mallampati Classification (B in figure below) based on maximal mouth opening and what structures can be visualized
  • Cormack-Lehane Classification (A in figure below) describes what can be seen during intubation and ranges from I (full view of cords) to IV (neither glottis nor epiglottis visualized)

Figure 1: Cormack Lehane Grading (above) and Mallampati Class (below)

ASA Difficult Airway Algorithm


Figure 2: ASA Difficult Airway Algorithm


Intubation Procedure

Equipment

  • MSOAP mnemonic: Monitors/Medications, Suction (ie Yankauer suction), Oxygen (O2 source, bag and mask), Airway equipment (ie blades, tubes, stylet, CO2 detector, Personnel (physician, respiratory therapist, nursing, etc)
  • Blade selection: 
    • Miller blades (straight blade) generally used in younger children. Action is to actually lift the epiglottis. Miller 0 used in small neonates, Miller 1 used in infants, and Miller 2 generally used in those >2-3 yrs of age
    • Macintosh blades (curved blade) generally used in older children. Positioned in the vallecula thereby lifting the epiglottis up and exposing the glottis
Image from Irwin and Rippe's Intensive Care Medicine, 7th Edition

Figure 3: MacIntosh and Miller Blades proper positioning for endotracheal intubation


  • Tube Selection:
    • Tube size formulas include: 4 + age/4 with a half size down for a cuffed tube (While previously thought to lead to increased rates of subglottic stenosis, cuffed tubes can be used in all ages). Other teaching is that the tube should be the same diamater as the 5th finger of the patient
  • Tube depth
    • Generally 3X the inner diameter of the tube and then adjusted based on radiography (i.e. 4.0 tube inserted to a depth of 12 cm at the teeth)

Medications

  • Oxygen as a premedication. Preoxygenation functions to denitrogenate (air is 21% oxygen and essentially 79% nitrogen) the functional residual capacity, providing a resevoir of oxygen which can oxygenate the pulmonary blood flow despite apnea during laryngoscopy
  • Bag mask ventilation can be provided, although in rapid sequence intubation, BMV is avoided to avoid distending the stomach and potentially contributing to emesis in someone who may have a full stomach
  • Premedications: 
    • Atropine (0.02 mg/kg) or glycopyrrolate (0.01 mg/kg) provide anticholinergic effects, preventing bradycardia and potentially decreasing secretions. They are generally recommended in young infants
    • Lidocaine (1 mg/kg IV), although controversial in its efficacy, is used to blunt increased intrancranial pressure with laryngoscopy
  • Sedatives/Analgesics:
    • Fentanyl (1-2 mcg/kg slow push): Synthetic opioid designed to avoid hemodynamic compromise, can cause rigid chest syndrome if pushed quickly. 
    • Midazolam (0.1 mg/kg IV): Short acting benzodiazepene providing anxiolysis, sedation, and amnesia. Can cause transient hypotension
    • Etomidate (0.3 mg/kg IV): short acting anesthetic providing rapid loss of consciousness, no significant hypotension, does cause respiratory depression. Inhibits 11 beta hydroxlyase and thus can lead to adrenal suppression and is thus generally contraindicated in patients with septic shock. No analgesic activity
    • Ketamine: Analgesic and dissociative anesthetic that preserves respiratory drive and also leads to catecholamine release, thereby increasing blood pressure and heart rate. Can lead to myocardial depression in the setting of catecholamine depletion. Excellent agent for procedural sedation that may include noxious stimuli. Does lead to bronchorrea and thus can provoke laryngospasm. Can also lead to emergence delerium, particularly in young adults/adolescents. This may be attenuated with benzodiazepene use. May be associated with spike in ICP
    • Propofol: ultra short acting anesthetic with no analgesic properties. Can cause profound hypotension as well as respiratory depression/apnea. Prolonged infusion, particularly at high doses, can lead to propofol infusion syndrome (mitochondrial toxicity leading to bradycardia/lactic acidosis/cardiovascular collapse)
    • Morphine and Lorazepam generally not utilized as fentanyl and midazolam provide the same effects with a more rapid onset and shorter duration of action. In addition, morphine is associated with histamine release which can lead to hypotension
  • Neuromuscular blockade:
    • Rocuronium: Most commonly used in the PICU. A dose of 1 mg/kg IV provides neuromuscular blockade in approximately 45 seconds. It is metabolized by the liver
    • Succinylcholine: Depolarizing neuromuscular blockade with rapid onset of action (30-45 seconds). Useful as duration of action is short (5-10 minutes). Dose: 1-2 mg/kg. Numerous contraindications including hyperkalemia, crush injury, muscular disorder, increase intracranial pressure, spinal cord injury, burns, etc. Can lead to significant hyperkalemia (as a result of activation of Ach receptors that may be upregulated in some of these conditions). Can also trigger malignant hyperthermia.
    • A defasciculating dose of neuromucular blockade (1/10 of the usual dose) can be given prior to succinylcholine to prevent the fasciculations that otherwise occur with succinylcholine administration
  • Specific Patient Populations:
    • General PICU patient: Fentanyl/midazolam/rocuronium is a generally safe choice in most patients
    • Increased intracranial pressure: avoid ketamine and succinylcholine, use lidocaine for premedication
    • Septic shock or hypotension: Consider ketamine, avoid etomidate (with the caveat that in primary cardiac failure, ketamine does have direct myocardial depressant effects and thus may not be the best choice for that population)
    • Status epilepticus: Any is probably ok but may want to avoid ketamine
    • Anterior mediastinal mass: These patients might be easily intubated but the anterior mediastinal mass may compress intrathoracic airway structures distal to where you can get an endotracheal tube. Hence, in the process of giving them sedation, they lose their muscle tone and can acutely collapse their airway, leading to arrest and death. Avoid sedation and intubation if at all possible (often try for diagnostics via LN biopsy or other more easily obtainable method, empiric chemotherapy/radiation if needed). Can prone the patient to try and relieve compression. Additionally, if planning to intubate, should have backup (ie ECMO) readily available
    • Diabetic Ketoacidosis: Patients often hyperventilate to compensate for severe metabolic acidosis. Hence, their PCO2 may be as low as 7-8 mmHg. These patients with severe DKA are often at higher risk for cerebral edema, the most dangerous complciation of DKA. If you intubate them, it is almost impossible to bag or mechanically ventilate them to the same low PCO2. Hence, their PCO2 inevitably rises, and with it, cerebral blood flow and thus ICP increase. This can potentially precipitate herniation and death. Hence, we try to avoid intubating DKA patients unless absolutely necessary (ie even if their GCS is 7, if they are ventilating adequately and not frankly aspirating, it may be worthwhile to hold off intubation). We tend to intubate these patients when their PCO2 begins to rise or they demonstrate significant obtundation and clear compromise of their airway. 
    • Asthma: Can be very difficult to ventilate after converting to mechanical ventilation and positive pressure ventilation. Also at high risk for futhter air trapping, barotrauma, and air leak. Hence, we generally try to avoid intubating asthmatics if possible 

Intubation

Figure 4: View of vocal cords with tube passing through
  • Make sure everything is ready:  MSOAP: Monitors/Meds, Suction, Oxygen, Airway equipment (blades, ETT's, Mapelson anesthesia bag, etc), Personnel (RT, nursing, physician) 
  • Patient placed supine in "sniffing" position
  • Shoulder roll sometimes helpful 
  • Head extended to align oral, pharyngeal, and laryngeal axes
  • Cricoid pressure may avoid gastric distension during BMV (evidence is not clear)
  • Laryngoscope advanced via left hand into the right side of the airway, sweeping the tongue to the right. 
  • Handle is lifted along the line of the handle to avoid torque and trauma to the lips/teeth/alveolar ridge
  • When glottis is visualized, tube is handed to the operator's right hand, who places it in the right side of the mouth through the glottis
  • Tube is advanced to approximately 3X the diameter of the tube
  • Bagged breaths are given through the ETT with the ETCO2 detector in place, looking for color change (purple to yellow) to indicate CO2 is detected
  • CXR is done to verify tube placement and adjustments are made as needed to position the tube generally about T2-T3 or midway between the thoracic inlet and the carina

References

1) G.H. Bledsoe, S.M. Schexnayder: Pediatric rapid sequence intubation: a review. Pediatr Emerg Care.20:339-344 2004 15123910

2) J.D. McAllister, K.A. Gnauck: Rapid sequence intubationof the pediatric patient. Fundamentals of practice. Pediatr Clin North Am. 46:1249-1284 1999 10629684