SPA Annual Meeting Reviews

Hocus PoCUS in Pediatrics

Reviewed by Kamie Yang, MD
Assistant Professor, University of Michigan

Dr. Yang

Gastric Volume, Lung/Airway, Cardiac, Peds-only Application
Dr. Walid Alrayashi, MD

What can Point of Care Ultrasound (PoCUS) help us to accomplish in pediatric anesthesia?  Walid Alrayashi, MD (Clinical Instructor, Boston Children’s Hospital, Boston) sought to describe how PoCUS can be utilized to evaluate the gastric, airway, lung, and cardiac systems of pediatric patients.

He started his informative talk by highlighting how PoCUS can be utilized in pediatric anesthesia when issues of NPO uncertainties arise, where a simple ultrasound scan of the stomach can definitively illustrate when it is safe to do a mask induction.  Additionally, PoCUS has been shown to both decrease time to patient diagnosis while also decreasing the cost of patient evaluation (ex. patients with dyspnea in the ED).

GASTRIC ULTRASOUND
Performing gastric ultrasound is reliable, reproducible, and can be used in challenging situations when the fullness of the stomach is uncertain due to difficult or inconsistent patient histories.  It can also identify patients with slow gastric emptying due to underlying conditions like fractures, sepsis, and opiate use.  Unique to pediatrics, gastric ultrasound is especially useful when applied to infants with pyloric stenosis.  In can be used to evaluate the adequacy of gastric suctioning prior to induction and can help us make educated decisions about the best method of induction (rapid sequence induction (RSI), modified RSI, mask induction). 

How to perform gastric ultrasound:
Scan patient in two positions to locate antrum:

1. Supine
2. Right lateral decubitus (RLD) (fluid collects dependently at pylorus, which is on the right side, so this allows you to get highest estimate of volume)

Figure 1: Patient position for gastric ultrasound scanning.
In patients that are
<40kg: use linear probe.
>40kg: use curvilinear probe.

Figure 2: Gastric ultrasound scanning decision tree & volume equation

1. No content – negative for full stomach
2. Clear Fluid – “starry night” look, can be normal, if <1.5cc/kg in volume. Cross sectional area (CSA) is measured using a free tracing tool on the ultrasound machine and volume is estimated via the above equation.
3. Solid Content – indicates full stomach, is seen as heterogeneous bright white material with a “drop-off” underneath

Figure 3: Gastric ultrasound images
L = Liver
Ao= is a benchmark for measurements, should be seen when obtaining a standard view.

Image A: Empty stomach
Image B: Clear fluid = “starry night”
Image C: Full stomach

AIRWAY ULTRASOUND
Dr. Alrayashi then continued his excellent talk by discussing how airway ultrasound can be used in pediatric anesthesia to:

1. Reliably delineate neck landmarks in emergency airway situations. 
2. Size ETTs
3. Confirm ETT position & depth 

How to perform airway ultrasound:

Figure 4: Probe position for short and long axis airway ultrasound imaging
1. Short axis: place probe above sternal notch, scan cephalad.
2. Long axis

Airway Short Axis Images

Figure 5: Short axis airway image
* Low trachea – broad tracheal ring. Saline filled ETT can be used to identify cuff at the sternal notch to document proper ETT position, making daily CXRs unnecessary and allowing for less radiation exposure to patients.
* Cricoid cartilage – narrower and broader, with “drop-out” one each side. Yellow line indicates internal diameter of cricoid area and can be used to measure proper ETT size.
* Cricothyroid Membrane (CTM) – Dotted green line. Thin, flat bright band, with tissue–air interface seen and “drop-out” on each side.
* Thyroid cartilage: triangular, pointed structure, blue = vocal cords.

Airway Long Access Images

Figure 6: Long axis airway image
“Beads on a string” = tracheal rings (orange)
Cricothyroid Membrane (CTM) can be found between thyroid and cricoid cartilage.

LUNG ULTRASOUND
Interestingly, interpretation of lung ultrasounds is different because evaluation is based mostly on artifact interpretation rather than identifying anatomic structures.  This is because the lung is filled with air and ultrasound beams do not travel well through it.  Three well-known lung ultrasound artifacts are (1) Lung sliding, (2) A lines, and (3) B lines.

Lung Ultrasound Artifacts:

1. Lung Sliding:  Movement is seen when the visceral and parietal pleura slide against each other and create an artifactual bright line that shimmers.  “Drop-outs” on either side are due to the ribs. 

• Seashore Sign: In M-mode view, there is no motion of the soft tissue, while there is still movement of the visceral pleura and parietal pleura.  Indicates normal lung.
• Barcode Sign: In M-mode view, there is no lung sliding and no motion is seen throughout lung.  Indicates there is no visceral/parietal movement. Abnormal lung.

2. A lines: Indicates, normal aerated lung. This appears as equidistant, horizontal bright lines that fade as you go from top to bottom.

3. B lines: Reverberation artifacts due to increased density in lung (ex. fluid, interstitial disease, ARDS). Looks like comet tails. Especially seen when scanning anterior portions of chest.

Figure 7: Images of lung artifacts: Lung sliding, A lines, & B lines

Other examples Dr. Alrayashi highlighted were how to use lung ultrasound to diagnose a pneumothorax or pleural effusion.  A pneumothorax can be nearly definitively diagnosed if you see the following three things on ultrasound: (1) No lung sliding, (2) No B lines, (3) + Lung point – tip of lung seen coming in and out of view.  Additionally, a pleural effusion can be diagnosed if the “spine sign” is seen, where the spine is visible posterior of the lung due to the pleural fluid creating an acoustic window.

Figure 8: Pleural effusion seen on lung ultrasound (+ spine sign)
Scanning along the posterior axillary line. Spine is usually not seen posterior to the lung, but due to the pleural fluid, you can see the spine.

L = Liver
K = Kidney
* = pleural effusion.

CARDIAC ULTRASOUND
The last application of PoCUS Dr. Alrayashi discussed was cardiac ultrasound.  To understand the conventions utilized in cardiac ultrasound, it is important to recognize that cardiac ultrasound is based on the cardiac axis, not the body axis.  Thus, the following is true when discussing cardiac ultrasound images:

• Long axis = long axis of heart
• 4 chamber view = orthogonal to above
• Short axis = orthogonal to 1 & 2 (aka “donut view”)

Tips he highlighted for getting the best cardiac ultrasound images included the following:

• Use a phased array probe for cardiac ultrasound because it has a small footprint and will allow you to sneak between ribs.  It also allows for better depth resolution.
• Always use the cardiac software preset on the ultrasound machine
• By convention, the orientation indicator should be at the right side of the screen. 

Dr. Alrayashi continued his talk by discussing the three basic transthoracic echocardiac windows: (1) Parasternal, (2) Apical, (3) Subcostal.   

Figure 9: The 3 basic cardiac ultrasound windows. Illustration of the cardiac axes.
1. Parasternal (next to sternum)
2. Apical (point of maximal impact)
3. Subcostal (subxiphoid)

Summary
To incorporate PoCUS into our practice, it is important to understand the barriers that currently exist to it’s widespread use.  The emergency medicine literature cites that the limitations to ultrasound use mostly include; (1) Lack of equipment and (2) Need for education.  Luckily, ultrasound equipment is quickly becoming cheaper and even more wireless and portable.  There are even some portable probes that you can connect to your phone.  Education is also becoming more widely available and Dr. Alrayashi encouraged us to explore these programs.

Using PoCUS in pediatrics is really a “match made in heaven”.  Children have more water content and their bones are less ossified.   Thus, we can truly see much more with ultrasound in children.   Today, ultrasound is being utilized to do everthing from diagnosing intraventicular hemorrhages to scanning a sacral dimple to decide whether or not to perform a caudal.  NG tube placement can even be confirmed with ultrasound to avoid unnecessary radiation exposure.  He highlighted numerous ways we can utilize PoCUS throughout the perioperative period and encouraged us to take the opportunity to scan patients with pathology to practice identifying their pathologies with ultrasound.   Also, currently, ED and ICU physicians are utilizing PoCUS more than anesthesia physicians and may prove to be a useful local resource.

He then ended his talk with a case where PoCUS proved to be life saving.  In this case, a 16-month-old presented to the operating room for a hip procedure.  After induction, a caudal was placed.  Fifteen minutes later, the patient became hypotensive, bradycardic, and the ETCO2 began to decrease.  An anesthesia stat was called and a large differential was considered.  Thoughts were given to local anesthetic toxicity, ETT dislodgement, problem with the caudal, to name a few.  Luckily, an ultrasound was available and a quick cardiac ultrasound demonstrated that the RV was filled with air, diagnosing a venous air embolism.  They were able to support the patient with ionotropes and fluid and watched the air dissipate over time.  

Further investigation revealed that the venous air embolism was caused by a technical error - the resident neglected to flush the hotline and accidently delivered 20cc of air to the patient.  In this situation, the correct diagnosis would have been very difficult to obtain in such as timely manner if PoCUS was not available.

Dr. Alrayashi closed his talk by stating that PoCUS can really help save lives.  In pediatrics, the great acoustic windows make it well worth your effort to learn how to use this tool.   In the end, it will make your job easier by helping you to more accurately perform procedures and more quickly narrow differentials.  He believes you will find it easy to learn and incorporate into your practice.  He ended his useful lecture with the quote: “llusions are common in clinical medicine.  Let’s not be fooled”.

Hot Topics In Regional Anesthesia 

Dr. Aysha Hasan, MD

Aysha Hasan, MD (Division Chief of Acute Pain and Regional Anesthesiology, St. Christopher's Hospital for Children, Philadelphia) opened her talk by asking why we should perform regional anesthesia in pediatrics.  She cited how utilizing regional anesthesia techniques can shorten hospital discharge times, curb risks for opiate drug addiction, and improve postoperative pain management.  In her talk, she discussed (1) regional anesthesia adjuncts and (2) select pediatric regional anesthesia techniques. 

REGIONAL ANESTHESIA ADJUNCTS
1.   Buprenorphine:   Buprenorphine is a partial mu receptor agonist that inhibits potassium channels and accentuates calcium channels.  Interestingly, given perineurally, it yields a 100% increase in duration of analgesia.  It demonstrates the best efficacy when placed in the brachial plexus, femoral nerve, and sciatic nerve.  Typical dose = 0.3mg/kg.  This drug has been given perineurally to adults, but its efficacy in pediatric patients has yet to be determined. 

2.   Tramadol: Tramadol is a weak opiate agonist that stimulates serotonin release, inhibits norepinephrine reuptake, and blocks potassium channels.  When given systemically, tramadol can cause significant side effects, including headache and nausea.  However, when given perineurally (doses of 50-200mg), side effects are very low.  It also prolongs block duration and shortens block onset. 

3.   Clonidine:  Clonidine is an alpha 2 agonist with alpha 1 stimulatory effects.  Efficacy studies have shown mixed results for this adjunct, with the most compelling data demonstrating that it increases the duration of action of short acting local anesthetics only.  Typical dose = 1.5mcg/kg.  No benefit has been seen in block quality and the addition of clonidine to continuous catheter blocks has not been shown to be beneficial.  

4.   Dexmedetomidine. Dexmedetomidine is an alpha 2 receptor activator that inhibits norepinephrine through the activation of locus coerulus, thus inhibiting the propagation of pain.  In adults, it causes significant side effects when given at doses of 2mcg/kg, including hypotension, bradycardia, and sedation.  In the pediatric population, Dr. Hasan has added much smaller doses (4-8mcg) to a 20cc block syringe and has seen an increase in analgesia duration by 24-48 hours.  However, due to the prolonged numbness and motor weakness that can result, patients can become very alarmed.  Thus, it is important to carefully select which patients receive this adjunct.  She currently uses this adjunct for 23-hour stay patients and has transitioned many catheter patients to single shot techniques by using this adjunct.

5.   Dexamethasone – Dexamethasone is a very controversial adjunct.  Initial studies showed that perineural administration of dexamethasone prolonged local anesthetic duration.  However, more recent studies have shown contrary results, where equal benefits were seen with intravenous and perineural administration.  The Cochran database suggests low to moderate efficacy.  Since intravenous dexamethasone is given routinely at her institution as PONV treatment, Dr. Hasan does not routinely use dexamethasone perineurally. 

Adjuncts that are not beneficial include NMDA antagonists such as ketamine and magnesium.  Magnesium cannot cross the blood brain barrier, thus intrathecal and epidural routes may be favorable.  However, though it results in mild side effects, no significant improvement in block duration has been seen with addition of this adjunct, so Dr. Hasan does not use magnesium in her practice.  There are also no extensive studies of ketamine given perineurally or in the epidural space and she also does not use ketamine as an adjunct.  Additionally, Dr. Hasan does not use neostigmine, opiates, or ketorolac perineurally.  Interestingly, intravenous neostigmine has been shown to help alleviate postdural puncture headache (PDPH) after wet taps and may prove useful during conservative PDPH treatment.

SELECT PEDIATRIC REGIONAL TECHNIQUES

1. Erector Spinae Block (ESB): The ESB is a paraspinal fascial plane block, where the needle is placed between erector spinae muscle and thoracic transverse process to block the dorsal and ventral rami of spinal nerves.   It provides five dermatomes of coverage as a single shot block (usually two up and three down) and can be used to block sensation to the anterior, posterior, and lateral thoracic and abdominal walls.  This block will not cross midline and volume improves block efficacy.  Interestingly, Dr. Hasan has noticed that when utilizing a catheter ESB, giving boluses every hour provides better pain control than a simple continuous infusion.  She utilizes this block for procedures like thoracotomies, chest tubes, NUSS, tethered cord repairs, percutaneous nephrolithotomies, choleycystectomies, ventral hernia repairs, and lumbar fusions.  It is a useful procedure to use when coagulation status is not ideal and is useful for minor procedures for chronic pain patients.
2. Paraveterbral Block:  The paravertebral block covers the same areas at the ESB and can be used for the same procedures.  However, this block is placed slightly closer to epidural space and communicates directly with the epidural space, so has additional risks.  Like the ESB, it is a volume block.  The paravertebral block target is also located deeper in the body, so it may prove better for catheter techniques because it provides extra mechanical stability. 
3. Lumbar Plexus Block (LPB):  The lumbar plexus block can be used for one-sided blocks and has efficacy similar to an epidural without the side effects of an epidural.  It is known to be a “pre-fixed plexus” block, thus while it will block the femoral, genitofemoral, LCF, and obturator nerves, it might miss the ilioinguinal and iliohypogastric nerves because they come off on the upper parts of the lumber plexus.  Therefore, the LPB may not provide analgesia to the inguinal crease and a quadratus lumborum block should also be performed to adequately cover this area.  This block is deep and often requires a curvelinear probe to visualize.  You can also identify the lumbar plexus by using stimulation and looking for a patellar twitch.  It is also important to know that the aorta, IVC, and kidney are in the area of this block.  This block does not cover below the knee and is used for procedures of the anterior thigh.
4. Fascia Iliacus Block: This block is performed on the anterior portion of the iliacus muscle in the fascial plane below the fascia lata and above the iliacus muscle.  The nerves blocked include the femoral, lateral femoral cutaneous (LFC), and obturator nerves.  This block can be used in place of the LPB block with similar results.  However, it is a technically savvy block that does not have an easily discernable goal, unlike the LPB and the patellar twitch.  Therefore, block failures are more common.     
5. Sciatic Nerve Block: The sciatic nerve is the biggest nerve in the body and can be blocked at many locations.  Dr. Hasan especially described blocking the sciatic nerve anteriorly because you do not need to reposition the patient when also performing an adductor canal block (a.k.a“speedy block”).  She recommended use of nerve stimulation with these blocks.
6. Quadratus Lumborum Block (QLB): The quadratus lumborum muscle is the most posterior muscle of abdomen and includes the iliohypogastric and ilioinguinal nerves and the thoracolumbar nerves.  The QLB is better than the TAP block because it blocks the iliohypogastric and ilioinguinal nerves more posteriorly.  Thus, less nerve branching has occurred at this block location and the block will be more reliable.  This block covers dermatomes T7-L2 and is good for lower abdominal  surgeries. 
7. Pterygopalantine Fossa Block:  This block is used to block the maxillary V2 nerve.  Dr. Hasan explained a suprazygomatic approach, which involves inserting the needle into a fossa lateral to the eyebrow in the sphenoid bone and directing it caudally.  The needle will enter the pterygopalantine fossa and will block the lower eyelid, upper lip, lateral nose, cheek, roof of mouth, sinus of maxilla, and palate.  This block can be used for cleft palate repairs. 

Dr. Hasan closed her talk by highlighting a few additional benefits of performing pediatric regional anesthesia.  Especially in the era of COVID, regional anesthesia may prove useful as the primary block for procedures in sick children.  A successful block paired with IV sedation and spontaneous ventiliation may be more favorable during these times.  Regional anesthesia is also useful in children prone to addictive behaviors or recovering addicts.  It is also helpful in patients with a history of extreme PONV.

Bilateral Ultrasound Guided Thoracic erector Spinae Plane blocks using a programmed intermittent bolus improve opioid-sparing postoperative analgesia in pediatric patients after open cardiac surgery: a randomized, double block, placebo-controlled trial. RAPM. 2020 Aug 19.