AT - Induction techniques in infants and children

patient preparation

A variety of premeds can be used to reduce pt anxiety prior to induction. These are detailed in "Peds Lecture 6: Methods of Distraction and Premedication in Infants and Children," but include midazolam, ketamine, and dexmedetomidine, among others. In select cases, parental presence can be useful. You can distract the pt during induction by telling a story. Other distraction techniques include counting, watching a video, or playing a game. The goal is to put the child at ease and make this experience as stress-free as possible. A low-sensory envt (dimmed lights, classical music, no one interacts w/ the pt except the anesthesiologist) has been shown to reduce anxiety during induction, as have clown doctors. Hypnosis and virtual reality have also been used successfully; a large randomized controlled trial evaluating virtual reality is ongoing

RSI

Aspiration of gastric contents is a feared complication of anesthesia. However, incidence in kids is incredibly rare. Studies performed on hundreds of thousands of kids in the US/UK have shown the incidence to be btwn 2-4 aspirations per 10,000 pts undergoing anesthesia, w/ no pts experiencing mortality. This is a similar incidence to that seen in adults (~1 in 3000). The incidence of aspiration is higher in emergency surgeries - in kids, risk may be as high as 1/400, in adults its at least 1/1,000. Factors associated w/ aspiration include a full stomach, delayed gastric emptying or other pathologic abdominal processes, and insufficient anesthesia, coughing, and/or straining during induction or intubation. Despite its rarity, the standard of care for school-age kids at risk for aspiration (including those w/ a full stomach and NPO times <4 hrs) is a RSI. This includes preoxygenation prior to IV induction of anesthesia. Preoxygenation should not upset the child - consider IV premed to reduce anxiety and allow the child to tolerate the mask. Preoxygenation is important bc mask ventilation is typically avoided so as not to distend the stomach and increase risk of regurgitation/aspiration. Likewise, elevating the head of the bed and/or suctioning the stomach prior to induction may be helpful and necessary in some cases to reduce risk of aspiration (ex pyloric stenosis in infants). After adequate preoxygenation, an IV induction agent such as propofol, ketamine, etc. is given to induce. At this time, cricoid pressure is held (in adults a force of 44 Newtons is applied) w/ the goal of closing the esophageal lumen and preventing passive regurgitation of gastric contents. In standard RSI, immediately after the induction agent is given, a rapid-onset neuromuscular blocking drug is given - succinylcholine 2 mg/kg is the standard, though rocuronium 1.2 mg/kg can also be given while cricoid pressure is held. When using succinylcholine, consider giving atropine 0.02 mg/kg prior to induction to blunt the bradycardic reflex induced by this drug (particularly in young kids). A brief amount of time is allowed for the NMB to act (~60 sec or less) and the pt is then intubated. The biggest risk of RSI is the hypoxia that ensues btwn induction and intubation since no ventilation is given during this time. Note that evidence for cricoid pressure is lacking and one study in awake adults showed that cricoid pressure displaced the esophagus laterally 90% of the time, rather than compressing it as desired. A survey of ped anesthesiologists suggested that only a~1/2 use cricoid pressure when indicated - concerns about cricoid pressure include anatomical distortion of the airway, decreased LES tone, confusion about how much pressure to apply, and lack of evidence that it improves outcomes. Indeed, the most recent Pediatric Advanced Life Support Guidelines state "Theres insufficient evidence to recommend routine cricoid pressure application to prevent aspiration during intubation in kids. . . Dont continue cricoid pressure if it interferes w/ ventilation or the speed or ease of intubation." Cricoid pressure should be avoided when CI'ed. CI's include: active vomiting (cricoid pressure could lead to esophageal rupture), unstable c spine, difficult intubation/ventilation where rapid securement of the airway and/or ability to ventilate is unlikely or impossible, esophageal issues such as Zenker diverticulum, presence of a sharp foreign body, and injury in the vicinity of the airway, esophagus, and/or neck.

goals of induction

Goals of anesthesia induction include a smooth, safe, comfortable transition from the awake to the anesthetized state. Avoidance of hypoxia, hemodynamic instability, aspiration, hypothermia, and traumatic injury are paramount.

inhalation induction risks

Inhalational induction isnt w/o risks. W/ no IV access, the anesthesiologist is unable to tx complications w/ IV drugs - instead, IM meds must be given until IV access can be established. IM drugs take longer to act than IV drugs. Thus, the IV should be placed as soon as possible once the pt has LOC. Induction of anesthesia via inhaled gas is esp precarious since pts must pass thru "Stage II" to reach the deeper levels of anesthesia. In transitioning from the awake to the asleep state under anesthetic gas, pts pass through various stages. These stages were 1st described by John Snow in the 1800s, though the categories we use today were developed by Arthur Guedel in 1937. Stage II is an excitatory phase in which the pt is no longer conscious but doesnt have a stable respiratory pattern. It may be characterized by the following: pupillary dilation and/or divergence, drooling, coughing, breath holding, irregular respirations, emotional lability, delirium, restless or erratic movements or jerking, vomiting, and laryngospasm. Stage II is considered the most dangerous stage of anesthesia and should be traversed quickly to avoid the above effects. Complete laryngospasm (closure of vocal cords) is the most concerning possibility during inhalational induction, particularly since pts falling asleep via mask induction dont have secure airways. Additionally, w/o IV access, laryngospasm cant be tx'ed quickly. Laryngospasm can lead to hypoxemia and hemodynamic instability. Tx of laryngospasm includes continuous positive airway pressure (CPAP) w/ 100% o2 to break the spasm, and either deepening (e.g. w/ medication thru the IV) or lightening the pt to get them out of Stage II - jaw thrust and/or stimulation at the base of the mandible near the mastoid process may also help break laryngospasm. If these measures fail, succinylcholine is the definitive tx. A dose as low as 0.1 mg/kg succinylcholine IV can relax the vocal cords enough to allow deepening w/ inhaled anesthetic. An intubating dose of 1-2 mg/kg IV or 4 mg/kg IM may be necessary if laryngospasm or hypoxemia is severe. W/ the muscle relaxation induced by inhaled anesthetic gases, many pts can also develop upper airway obstruction. If not tx'ed, this can result in similar sequelae as laryngospasm - hypoxemia and hemodynamic instability. Upper airway obstruction is best tx'ed w/ CPAP. An oral airway may also prove useful, so long as its not inserted during Stage II, which may trigger laryngospasm. In addition to the above risks, holding a mask on a child's face can be traumatic. This is particularly true for toddlers, who are old enough to remember the experience but too young to understand why its happening. Thus, careful pt eval and prep are important prior to any mask induction.

Patient preparation

For children who are old enough to understand, its important to prepare them for what to expect during induction. Explain what will happen, from what the bed/pillow will look like to how you want them to breathe once the mask is on. You can make certain aspects of the process into a game. For ex, you can explain that for each big breath they take to blow up the balloon (bag), they will see a mountain on the screen (ETCO2 waveform), and points greater than 35 will get them a popsicle of their choice (assuming this is true) when they wake up. Give the pt control over certain things. Just be careful not to give them a choice about something if one of the choices is not an option - for ex, dont ask the patient, "Are you ready to go to sleep now?" or "Can I place the mask on your face now?" If they say "No," you may be in a difficult predicament. Reasonable options for giving the pt control include: asking them if they want to come back alone or w/ a parent (if you think its appropriate); and allowing them to choose whether to hold the mask on their own face, or whether you or the parent holds the mask. You can also bring a mask to the preop area and let them smell the scents and pick a flavor of candy air for the mask. They can decorate the mask with stickers to personalize it and become more comfortable with it. They can also bring stuffed animals or toys to the OR that bring them comfort, in concordance w/ OR policy.

IM induction

IM injection is not ideal but is necessary in rare cases. For combative older kids or teenagers who refuse oral, IV, or intranasal premed, and refuse to participate in an inhalational induction, IM medication may be required. Current practice involves dosing IM medication as sedation/premedication and then proceeding w/ inhalational induction once the pt is sedate and agreeable, although induction dose IM meds can also be given. Other possible indications for IM induction include: pts at risk for MH who will not tolerate IV placement, and pts w/ incredibly poor venous access in whom an inhalational induction is CI'ed; for ex, congenital heart dz pts who cant tolerate the drop in BP associated w/ inhalational induction may do better w/ an IM ketamine induction

inhalation induction variations

If a pt doesnt want the mask on his/her face, it can be removed and the end of the circuit can be placed btwn the fingers of a cupped hand, which can be moved progressively closer to the pt's face. While this technique leads to more OR pollution, it can be less traumatic for the pt and works bc nitrous and the halogenated anesthetics are denser than air, so will pool around the pt's face preferentially. Pts who are already asleep could be left asleep w/ the mask brought close to their face but not touching until they are deeper on a mixture of nitrous and O2. Once the mask is on the face, sevo can be titrated in. Thus the pt isnt even aware that he/she is being induced. This is called the "steal" technique. However, the benefits of this technique must be weighed against the risk of the child's surprise upon awakening in an unexpected envt. For kids who are old enough to follow instructions and cooperate and want to fall asleep quickly, a modified single breath technique can be performed. Pts are coached to take as big a breath as possible through their mouths and then blow all the air out of their lungs and hold. This is practiced several times including a run w just the mask on the face. Once the pt is comfortable w/ this plan and has exhaled all the air from his/her lungs, the mask is connected to a circuit that has been primed w/ o2, nitrous, and sevo and is immediately placed on the pt's face. The pt is then instructed to take a giant breath of this concentrated gas mixture and hold it in before exhaling. This allows for a rapid inhalational induction.

"Controlled" or Modified RSI

In neonates, infants, and toddlers, in particular, high metabolism and rate of o2 uptake can result in rapid desat w/o ventilation. In these pts, the risk of aspiration must be carefully weighed against the risk of hypoxia and the ensuing complications that can occur from the period of apnea during RSI. Some practitioners avoid standard RSI in this population bc the risk of hypoxia, cardiorespiratory compromise, and traumatic rushed intubation are more likely and detrimental than the small risk for aspiration. Remember that aspiration tends to occur when inadequate depth of anesthesia and insufficient muscle paralysis are present at the time of induction and intubation. A retrospective study performed in the US on >1000 kids undergoing standard RSI showed that 2.6% developed hypoxemia (SpO2 <90%) and 1.3% developed hemodynamic instability (bradycardia or hypotension). One pt experienced emesis but had no evidence of aspiration. Difficult intubation occurred in 1.7% of pts. Pts <20 kg had a significantly higher incidence of severe hypoxemia (SpO2 <80%) compared to older, larger kids. Note that the rates of these complications are higher than the 0.03% rate of aspiration in this population. A study in Switzerland evaluated a modified "controlled" RSI and intubation technique in >1000 kids at risk for aspiration. They utilized a protocol in which gentle bag mask ventilation (w/ a max of 10-12 cm H2O PIP) was allowed after induction. Cricoid pressure was avoided and backwards, upwards, rightwards pressure (BURP) was allowed only after adequate paralysis and depth of anesthesia were achieved (zero twitches on TOF monitor). In this study, hypoxemia (SpO2 <90%) occurred in <1% and none of the pts developed hemodynamic instability. A single case of gastric regurg occurred (0.1%), but no pulmonary aspiration was detected. So you should think twice before performing standard RSI in young kids <20 kg. Rather, a modified or "controlled" RSI allowing gentle ventilation and avoidance of cricoid pressure should be considered in neonates, infants, and toddlers <20 kg at risk for aspiration

Rectal Induction Meds

In studies, rectal ketamine was given in conjunction w/ benzodiazepines for induction - this may improve efficacy. Rectal midazolam is effective as a premed but does not consistently produce unconsciousness at doses ranging from 0.5-5 mg/kg. Rectal thiopental has also been studied and used extensively as a premed. However, doses up to 40 mg/kg may be successful for induction of anesthesia.

inhalational induction

Inhalational induction is the MC induction technique in peds pts. Inhalational induction precludes the need to place an IV in an awake child and the stresses that come w/ it. Nonpungent halogenated anesthetics are used for inhalation induction bc theyre less irritating to the airway. Thus, des and iso are avoided until after pt is asleep. A scented mask (strawberry, orange, etc.) is often used to make the mask more pleasant and agreeable to the child, and to hide the unique smell of the halogenated gas. If a pt is cooperative, then a scented mask is typically placed on the face w/ a mixture of nitrous oxide and O2 at a ratio ranging from 50:50 to 70:30 w/ total fresh gas flows of about 6-10 liters/min (LPM). Neither nitrous nor O2 has much smell and the nitrous starts to relax the pt in <1 minute. Once the pt is more relaxed, the conc of a nonpungent gas such as halothane or sevo is slowly increased until the pt is asleep. For sevo, the MC used inhalational anesthetic agent, the inhaled conc is increased by approx 1-2% every 2-5 breaths to the maximum dialed conc of 8% until the pt has loss of eyelash reflex. Pts breathing sevo w/ this technique typically lose consciousness in <1-2 min. Just be sure to decrease the gas conc shortly after the pt is asleep to avoid hypotension, bradycardia, apnea, and overdose of anesthetic - after the pt has lost consciousness, sevo is often decreased to 4-5% (2 MAC) until the IV is placed. Pts will typically maintain spontaneous ventilation such that bag mask ventilation is not necessary. If a pt is uncooperative and a premed is CI, then the circuit can be primed w/ a mixture of 70% nitrous, 30% O2, and the max dialed conc of halogenated gas to expedite the induction process. Priming of the circuit must be performed in advance. Fresh flows of gas at 6-10 LPM are run through the circuit for a couple of min (minimum time to prime 30 seconds, max time 5 min) w/ the end of the circuit occluded and excess gas captured via the machine's scavenging system. The bag is squeezed to empty it of air, allowing it to fill w/ the nitrous/O2/halogenated gas mixture. After this process, the occluded circuit is full of anesthetic gas and the pt will fall asleep faster once they breathe this mixture thru the mask. This technique of circuit priming is particularly useful in uncooperative and/or anxious pts bc of speed of onset. In these situations, time is of the essence - the faster the pt falls asleep, the less time they have to become more scared and agitated. In the worst case scenario, an anesthesiologist may have to hold the mask on the face of a struggling child. Additional techniques for dealing w/ an uncooperative pt include positioning the pt in such a way that they cant pull the mask off their face and delay induction. For ex, if a parent is present, they can give the patient a big hug, with their arms securely across the pt's arms. Likewise, the pt's arms and torso can be bundled in a blanket (i.e. a makeshift papoose) to prevent the pt from removing the mask. Its often helpful to stand behind the pt and cup the mask inlet btwn the thumb and first finger, while stabilizing the base of the hand against the pt's face to keep the mask from slipping. Placing the other hand on the back of the child's head can also help stabilize the pt and keep the mask secure until they're asleep. Factors that can slow inhalational induction include poor face-mask seal, low MV, and inducing at reduced dialed conc of anesthetic gas (i.e. < than the max dialed conc).

pre-induction preparation

Pre-induction pt preparation is very important. Every effort should be made to reduce pt anxiety prior to induction, as increased preop anxiety has been associated w/ emergence delirium in PACU and negative behavioral problems postop, including separation anxiety, eating disturbances, trouble sleeping, and aggression. The pt factors listed should all be considered when developing an induction strategy. For ex, if the pt is 4mo old, theres little pt preparation to do since the pt is too young to understand. Likewise, the pt hasnt yet developed stranger anxiety so bringing a parent back for induction wont provide any benefit to the pt, and a premed will not be necessary. However, if the pt is older (e.g. 6yo), developmentally normal, and hasn't had any prior traumatic experiences w/ anesthesia in the past, it would make sense to explain to him/her what to expect and what you expect out of them. You can adjust your plan based on the pt's level of understanding, maturity, and anxiety level. A premed should be considered if the patient is anxious. Just be sure to inquire about allergies, PMH, fasting time, and determine the pt's ideal body weight before administering any meds.

IV induction meds

Propofol is the MC used IV induction agent in kids. Advantages = rapid onset, early redistribution half-life, and reduced incidence of airway issues and PONV. Disadvantages = pain at injxn site and hypotension/hemodynamic instability. IV lidocaine or an opioid can be given prior to propofol to attenuate pain at injxn site. Ketamine is useful for maintaining CV stability during induction, though pts in catecholamine-depleted states can still experience hypotension 2/2 myocardial depression. Negative effects include sialorrhea, nightmares and hallucinations, and PONV. Midazolam can attenuate hallucinations while glycopyrrolate can reduce sialorrhea. Etomidate is also very useful for maintaining hemodynamic stability. Side effects = adrenal suppression, pain at injxn site, and myoclonic movements. Methohexital is a barbiturate that can be used for induction in kids. It has a faster recovery time than thiopental. Disadvantages = myoclonic movements, hiccups, and pain at injection site. While midazolam can also be used as an induction agent in kids (0.15-0.5 mg/kg), its time to max effect is slower than propofol and its not as reliable at consistently achieving anesthesia when used as the sole induction agent (wide inter-individual variability). Its effects are potentiated, however, when used in w/ other drugs. Midazolam causes amnesia and tends to cause more psychomotor impairment upon awakening than other induction agents. Its MC used as a premed to reduce anxiety than as an anesthesia induction agent. Thiopental is a barbiturate that was historically used for induction in kids (5-8 mg/kg). It may have a prolonged effect in neonates and is no longer available in the US.

rectal induction

Rectal medication can be used if pt/families refuse other routes of premed such as oral or IM. Similar to oral and IM drugs, rectal drugs can be given in premed doses to relax the pt enough to tolerate inhalational induction. However, drugs can also be dosed rectally to induce general anesthesia. Rectal admin avoids the anxiety associated w/ mask induction, needles, and parental separation. However, rectal admin may be associated w/ emotional consequences in older kids. Therefore, its typically used in younger kids and/or developmentally delayed pts who are <20 kg (d/t dosing constraints). W/ rectal admin theres risk for failed and/or delayed time to induction - pts may defecate the drug, or it may not be readily absorbed and/or bioavailability may be low. In contrast, delayed emergence and/or respiratory compromise can occur d/t high and/or rapid uptake/bioavailability of drug. Delayed emergence may be attenuated by rectal aspiration of drug through a catheter after induction has occurred.

More on Pre-induction Prep

There are many things to consider outside of pt factors. For ex, if a parent is very anxious, they will likely not be helpful to the pt and could upset the pt further if they come back for induction. Indeed, studies have typically not supported parental presence at induction for reducing pt anxiety, though parents tend to be more satisfied when they can be present for induction. Debate is still ongoing regarding parental presence in the OR and infection risk. While reducing the #of people entering the OR/opening of OR doors has been shown to reduce bacterial contamination and surgical site infection (SSI) when instituted as part of a bundle, a recent study in pediatric neurosurgical pts evaluating parental presence at induction showed no difference in SSI when parents were present vs. absent. However, this study included only 41 pts/parents - there were 2 cases of SSI when parents were present (9%) vs. no cases of SSI when parents were absent. If the surgery is going to be long, and the pt is anxious, consider premed if theres no CIs. If the pt is presenting for ear tubes and is otherwise healthy and will go home immediately after surgery, a premed may outlast the surgery itself and may prolong the pt's recovery time. While the pt's comfort is paramount, risk and benefits of premed must be considered in the given context.

IV induction

When IV placement is easily tolerated and/or IV access is available, IV induction is often preferred. The presence of an IV allows for easy admin of premed, rapid induction of anesthesia, the ability to administer emergency meds in a timely fashion, minimization and/or avoidance of many of the risks associated w/ inhalational induction, and avoidance of the trauma that may ensue from holding a mask over a child's face. Indeed, a recent randomized controlled trial showed that IV induction is safer than inhalational induction in pts at high risk for periop respiratory complications. IV induction is commonly used in older kids who are capable of holding still for IV placement. Some pts may have negative associations w/ the mask from prior anesthetics and may request an IV. Local anesthetic (e.g. EMLA cream, lidocaine) is often used to numb the skin prior to IV placement. IV induction is performed when pts have indwelling lines - inpatients will often already have IVs in place and pts receiving chemo will often have central lines that can be used for induction. IV induction is indicated in pts who require a RSI, such as those considered to have a full stomach. Inhalational induction shouldnt be performed on pts w/ a full stomach as it takes too long to induce anesthesia and administer paralytic - the airway cannot be secured quickly and thus the pt is exposed to unnecessary aspiration risk. When performing an IV induction, pts should ideally be preoxygenated w/ 100% o2 via mask, or at least via a circuit connected to a cupped hand, in order to improve safety.