Point-of-care ultrasound in pediatric anesthesiology and critical care medicine
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Ultrasound has increasingly become a clinical asset in the hands of the anesthesiologist and intensivist who cares for children. Though many applications for ultrasound parallel adult modalities, children as always are not simply small adults and benefit from the application of ultrasound to their management in various ways. Body composition and size are important factors that affect ultrasound performance in the child, as are the pathologies that may uniquely afflict children and aspects of procedures unique to this patient population. Ultrasound simplifies vascular access and other procedures by visualizing structures smaller than those in adults. Maturation of the thoracic cage presents challenges for the clinician performing pulmonary ultrasound though a greater proportion of the thorax can be seen. Moreover, ultrasound may provide unique solutions to sizing the airway and assessing it for cricothyroidotomy. Though cardiac ultrasound and neurosonology have historically been performed by well-developed diagnostic imaging services, emerging literature stresses the utility of clinician ultrasound in screening for pathology and providing serial observations for monitoring clinical status. Use of ultrasound is growing in clinical areas where time and diagnostic accuracy are crucial. Implementation of ultrasound at the bedside will require institutional support of education and credentialing. It is only natural that the pediatric anesthesiologist and intensivist will lead the incorporation of ultrasound in the future practice of these specialties.
Échographie au point d’intervention en anesthésiologie et soins intensifs pédiatriques
L’échographie est devenue de plus en plus un outil clinique dans les mains des anesthésiologistes et des intensivistes qui prennent soin d’enfants. Bien que de nombreuses applications échographiques suivent le modèle des modalités pour adultes, les enfants ne sont pas simplement de petits adultes et bénéficient d’applications échographiques propres à la gestion de leur situation. La composition et la taille de leur corps sont des facteurs importants qui affectent la performance de l’échographie, de même que les maladies des enfants ainsi que les procédures qui sont uniques à cette population. L’échographie simplifie l’accès vasculaire et d’autres procédures en visualisant des structures qui sont plus petites que celle des adultes. La maturation de la cage thoracique présente des défis pour le clinicien effectuant une échographie pulmonaire bien qu’il puisse voir une plus grande proportion du thorax. De plus, l’échographie peut fournir des réponses uniques aux dimensions des voies respiratoires et à leur évaluation en vue d’une cricothyroïdotomie. Historiquement, les échographies cardiaques et neurologiques ont été réalisées par des services d’imagerie diagnostique bien développés, mais des publications de plus en plus nombreuses soulignent la pertinence de la pratique de l’échographie par des cliniciens pour dépister des troubles et fournir des observations répétées dans le cadre d’une surveillance clinique. L’utilisation de l’échographie est en progression dans des domaines cliniques où le temps et l’exactitude diagnostique sont essentiels. La mise en œuvre de l’échographie au point d’intervention nécessitera un soutien institutionnel en matière de formation et de reconnaissance des compétences. Il est tout à fait naturel que les anesthésiologistes et Intensivistes pédiatriques soient à la tête de l’incorporation de l’échographie dans la pratique future de ces spécialités.
Suggestions for probe selection in various pediatric point-of-care applications
Linear 2.5 cm in length, shorter recommended
Linear 2.5 cm in length or shorter
Any linear, curvilinear, microconvex
Any linear, curvilinear
Any linear, curvilinear
Phased array, microconvex
Phased array, microconvex, curvilinear
Phased array, curvilinear
Phased array 6-12 MHz
Phased array 1-5 MHz, 2-6 MHz
Phased array 1-5 MHz
Vascular (venous and arterial) access and procedural
Linear 12 MHz and higher (>18 MHz if possible)
Linear 4 cm length recommended
Phased array, microconvex
Any sector probe
Any sector probe
Microconvex, TCD through fontanelles or phased array 1-5 MHz through temporal windows
Phased array 1-5 MHz (TCD)
Phased array 1-5 MHz (TCD)
Linear 12 MHz and higher (>18 MHz if possible)
Linear 12 MHz and higher (>18 MHz if possible)
Linear 12 MHz and higher (>18 MHz if possible)
The purpose of this narrative review is to summarize the use of ultrasound for vascular access, assessment of the airway, lungs, and circulation in children. Imaging of the abdominal cavity, gastric contents, and the central nervous system will also be discussed. This review will conclude with a brief discussion of training and certification issues unique to providers caring for children.
Internal jugular vein catheterization
Use of ultrasound in improving first-attempt success and reduction in complications is well described in the anesthesiology and critical care literature. It has been well defined in a 2015 Cochrane Library review describing overall increased success in pediatric central venous catheter insertion in the internal jugular vein using dynamic ultrasound guidance.4 Transverse (or short-axis) active (or dynamic) visualization is the primary methodology for insertion in the vast majority of published literature. One consideration is that the majority of available literature on this topic studied trainees as the primary operator in central venous catheter insertion.5,6 This raises the question of whether or not clinicians experienced in landmark methods would necessarily benefit from ultrasound.7 Nevertheless, since trainees place many internal jugular central venous catheters in high-volume centres, the practical question of whether trainees perform better with ultrasound remains germane. Available evidence4 suggests that ultrasound is standard of practice for internal jugular catheterization in many pediatric environments. Anatomic issues unique to the pediatric patient including a shorter area of exposed neck, steeper angle of entry in the average patient, and closer proximity of other critical anatomic structures including the carotid artery, trachea, and spine could influence successful placement.
For the purposes of discussing the non-cardiac applications in this manuscript, indicator orientation for non-cardiac procedures and diagnostics will be towards the patient’s right or head (screen indicator to the left).
Femoral and subclavian vein catheterization
The use of ultrasound to assist peripheral and central arterial access has been described in the pediatric critical care13 and anesthesiology settings.14-16 Though the available evidence varies, the contemporary literature suggests an improvement in first pass success and number of attempts. Notably in a study by Kantor et al. use of ultrasound in arterial access improved success not only in trainees who used it primarily, but also among trainees who were experienced in landmark techniques.13 This study was performed in radial artery catheterization, and it is likely applicable to peripheral artery catheterization in other anatomic areas given the relative anatomical concerns of other vessels such as the ulnar, dorsalis pedis, and posterior tibial arteries.
Peripheral venous access
The use of ultrasound for peripheral venous access has seen increased adoption in the pediatric arena recently not only as a means to obtain access on difficult patients, but also to reduce patient discomfort and increase provider safety and satisfaction at the bedside. Using a high-frequency linear transducer, the authors have reported that use of ultrasound can reduce stick attempts to approximately 1.3 attempts per patient with an over 97% success rate in the critically ill child by a team of vascular access personnel in an academic pediatric intensive care unit.17 A major factor in this accuracy is the use of a transducer that can achieve a 20 MHz centre frequency or higher in the point-of-care ultrasound market, which is becoming increasingly available (L40-8/12 linear array, BK Ultrasound, Peabody, MA, USA; SL3116 linear array, Esaote North America, Fishers, IN, USA; L10-22 linear array, General Electric Healthcare, Chicago, IL, USA; UHF22, UHF48, UHF70 linear arrays, Fujifilm-VisualSonics, Toronto, ON, Canada; L20-5 linear array, Mindray North America, Mahwah, NJ, USA). Important considerations in ultrasound-guided peripheral vein catheterization include depth of insertion, as the technology permits visualization of veins a centimetre or deeper from the skin surface.18 At depths of 10 mm, insertion of a 25-mm long cannula at 30° to the skin may only leave less than 3 mm of catheter in the vessel. Extravasation at these depths is also problematic because it may be diffuse and difficult to palpate, delaying detection and increasing the potential for injury. For these reasons it is recommended that intravenous catheters placed at these depths be longer than 25 mm. Colour-flow Doppler has also been described as a means of confirming intravenous placement in children and is readily implemented.19
Airway and pulmonary
Multiple authors have described the utility of neck and lung ultrasound for confirmation of intubation in the pediatric operating room and intensive care unit (ICU).28 Akin to adult methods, the trachea is visualized in a manner identical to that described above for endotracheal tube sizing. Placing the probe in position during intubation permits visualization of the tube as it passes through the trachea causing a sudden reduction in air column width.29 Inadvertent esophageal intubation will be observed as passage of an air column through the esophagus instead of the trachea, posterior and slightly to the left of the patient’s trachea. It should be noted that cricoid pressure cannot be readily performed in this situation as the ultrasound probe in the subglottic area and the skin will likely have gel on it.
Similar to this technique, movement of the diaphragm can also be assessed by clinicians in pediatric patients at risk for failure of extubation and has been extensively described in the cardiac ICU setting. This technique in the hands of intensivists has also been found valid compared with fluoroscopy35 and electromyography.36 It is potentially useful in the management of the patient with potential diaphragm or phrenic injury or with muscle weakness, whether congenital or acquired.
Pleural effusions in pediatric patients can be visualized using a linear array transducer in a manner similar to adults. Additionally, the size of the pediatric thorax permits identification of effusion from the subcostal position. A phased array or curvilinear probe placed transversely in the subxiphoid region and aimed up into the thorax can image pleural effusions behind the liver. This view permits a wide field view of an effusion that may capture the trajectory of thoracostomy drains and any complexity to the effusion better than is possible with the narrower field of a linear array.
For the purposes of this cardiac discussion, view orientation will be discussed in the cardiac convention where the indicator appears to the right of the screen and is oriented towards either the patient’s head or left. Though pediatric cardiology echocardiography often inverts the probe position to the bottom of the screen for subcostal or apical imaging, this discussion will maintain probe position for these views at the top of the screen as it facilitates ease of use among providers in the ICU setting. Views are obtained analogous to those described in the review of cardiac applications in this journal issue. Inferior vena cava views of the heart can be obtained from the subxiphoid position similar to those seen in adults. Given that hypovolemic shock is common in children, the calibre of the IVC in a dehydrated child can be narrow and difficult to detect.
Intravascular volume status
As in adults, pericardial effusion is readily identified in the subcostal view with the patient resting with the head inclined to 15° or more. Similarly, in the presence of shock and vital sign abnormalities such as pulsus parodoxus and tachycardia, identification of RV collapse in early diastole, collapse of the right atrium in mid systole, IVC plethora, and alteration in mitral valve inflow velocity of more than 25% through the respiratory cycle as determined using pulsed wave Doppler are indicative of tamponade physiology.50
Pericardiocentesis in pediatric patients can be assisted using cardiac ultrasound by placing the transducer in the region of the percutaneous needle insertion and identifying its track with the transducer to determine the depth of insertion to effusion. Usually this is performed in the subxiphoid position but can also be performed in the apical position depending on the insertion position. Monitoring the procedure performed with puncture at the subcostal position from the apical position is also possible; however, direct visualization of the needle on insertion is difficult and rare. Rather, confirmation of pericardial puncture can be determined by visualization of a Seldinger wire, injection of agitated saline or contrast, or watching drainage of the effusion though crude. Recently methods for pericardiocentesis have been described using a linear transducer placed longitudinally over the needle in the subxiphoid position.2 With this arrangement the advancement of the needle into the effusion is dynamically monitored under direct visualization and the authors describe no complications of the technique.
Use of ultrasound in the determination of reversible causes of cardiac arrest has been described in the medical literature, though infrequently.51 The use of focused cardiac ultrasound is limited by practical constraints of attempting views within the ten seconds allotted for pulse checks. It is arguable that the greatest utility of the technique is early in an arrest when determination of a reversible cause could have the greatest impact on outcome. Potential reversible causes of arrest ultrasound could help identify include pericardial tamponade, hypovolemia, cardiogenic shock, RV failure, and pneumothorax. Aside from pneumothorax, the remaining four causes require cardiac views in between compression cycles. During a cardiac arrest it is important that ultrasound gel is wiped from the patient in between uses because of the potential for it to conduct electricity. At the authors’ institution52 cardiac arrest ultrasound is performed by a dedicated operator not responsible for other aspects of the code and focuses on image acquisition and recording during a ten-second pulse check clearly requested during the process of the arrest. The operator or team leader clearly counts down the amount of time hands are off of the chest for compressions, and if the operator cannot get the image or ten seconds are reached compressions are reinstated and the gel is wiped off. During compressions the data are reviewed and shared with the code team. By and large, only a single subcostal view is usually used because of the presence of defibrillator pads obstructing the parasternal and apical views. It is only in the cases of hypovolemia and pneumothorax that ultrasound is used to titrate therapies, as tamponade is remedied in cardiac arrest with pericardial drainage and therapies for RV or LV failure do not necessarily lead to rapid changes in cardiac ultrasound unless the loading conditions of the heart change significantly. A sonographic finding of an akinetic heart, known as cardiac standstill in the adult-focused cardiac ultrasound literature, has been associated with failure to achieve return of spontaneous circulation. Though in adults in some populations this has been implemented as an indicator to cease resuscitative efforts, the experience at the authors’ institution has been that if patients are otherwise potential candidates for veno-arterial extracorporeal membranous oxygenation therapy, cardiac function can recover on this support.53
Imaging of the stomach for gastric contents can be performed in a manner analogous to that seen in adults.54,55 Use of ultrasound to identify peritoneal fluid has been described in pediatric abdominal trauma. Accuracy is affected by operator skill and some series describe dismal performance of focused assessment with sonography for trauma (FAST) in identifying bleeding in the trauma setting.56 The presence of free fluid is suspicious for intraabdominal blood loss; however, lack of an anechoic fluid-filled area does not necessarily exclude injury. In a large-scale prospective evaluation of the efficacy of the FAST examination in the emergency room setting it was not found to improve outcomes or resource utilization.57 Its effect in the OR and ICU in terms of detection of free abdominal fluid of non-trauma etiologies is undetermined however. Techniques described for abdominal ultrasound in trauma can also be used in patients with ascites in the evaluation of pathology and planning for paracentesis. Though Morison’s pouch and the retrovesical space are common areas where fluid is seen in trauma, it is important to consider that the patient is typically flat in this setting similar to the OR. In the inpatient setting, the inclined inpatient may show fluid pooling in the lower abdominal quadrants instead.
Regional anesthesia and lumbar puncture
The practice of regional anesthesia in children is affected by the frequent need for sedation to accommodate the procedure. Developmental age is also relevant to determine adequacy of the block and whether any sensory or motor deficits persist after the block. Otherwise techniques are largely analogous for specific blocks.
Optic nerve sheath diameter
Education, credentialing, and certification
Limited literature is available regarding the education of anesthesiologists and intensivists on pediatric point-of-care ultrasound. The pathway for education leading to credentialing has typically taken a two-pronged approach similar to that used in adult emergency medicine.69 Experienced practitioners who have completed training are asked to participate in a brief dedicated course and then complete a program of image acquisition and review with a mentor. Trainees are asked to participate in a system of residency or fellowship didactics and practical experiences. Conlon et al. described feasibility in the pediatric ICU setting in a 2015 article detailing the construction of the program at the Children’s Hospital of Philadelphia,70 and ongoing curriculum development is occurring in various institutions worldwide as equipment becomes increasingly approachable and economical. Recommendations also exist in neonatology for the practice of targeted neonatal echocardiography with somewhat more extensive criteria given the increased potential for undiagnosed congenital heart disease.71 At the present time ultrasound education and practice in the pediatric anesthesia setting are lacking and would benefit greatly from ongoing development of airway and regional anesthesia methods such that the impact of ultrasound’s diagnostic and procedural performance in these areas is better understood.
Certification for practitioners to perform ultrasound independently in the pediatric setting has been largely limited to fellowship experiences in diagnostic specialties, with the exception of ultrasound fellowships in pediatric emergency medicine. One route for certification through testing is pursuit of a pediatric registered diagnostic sonographer certificate in a practitioner’s country of practice. In Canada, this is administered by Sonography Canada (Échocardiographie Canada) and in the United States this is the American Registry of Diagnostic Medical Sonographers. Others have pursued the board examinations of the National Board of Echocardiography (NBE) in the United States; however, there are no pediatric certificates offered by this organization. In 2019, it is anticipated that the NBE will offer an examination of Critical Care Echocardiography for clinicians of all specialties to seek certification in clinical applications of ultrasound largely focusing on the heart and lungs.72 Though this will be targeted at adult providers, it is anticipated that the substance of the examination will have broad applicability to the pediatric setting.73
In summary, ultrasound has seen broad and meaningful inroads into clinical practice for the anesthesiologist and intensivist who cares for infants and children. An ongoing interest in its application has yielded meaningful advancements in procedural performance and the assessment and management of pulmonary and hemodynamic conditions among others in the intra- and perioperative settings. That said, much remains to be elucidated in terms of the technology’s performance in its expanding role in the pediatric setting. One must be wary of extrapolating evidence regarding adult modalities to their use in children. These issues will be clarified if anesthesiologists and intensivists who care for children pursue evaluation of point-of-care ultrasound with the same enthusiasm that surrounds the use of this technology at the bedside.
Conflicts of interest
Dr. Erik Su has a research project on catheter associated thrombosis supported with loaned ultrasound equipment by General Electric Corporation.
This submission was handled by Dr. Gregory L. Bryson, Deputy Editor-in-Chief, Canadian Journal of Anesthesia.
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