Focused Cardiac Ultrasound in the Pediatric Perioperative Setting

Karen R. Boretsky, MD; David B. Kantor, MD, PhD; James A. DiNardo, MD; Achikam Oren-Grinberg, MD

Disclosures

Anesth Analg. 2019;129(4):925-932. 

In This Article

Calculations and Measurements

It is important to emphasize that extensive quantitative calculations are not a goal of FoCUS. While quantitative assessment is a basic component of comprehensive echocardiographic examinations, qualitative assessment is more fundamental to pediatric FoCUS. In adult and pediatric FoCUS studies, a good correlation between visually estimated (qualitative) and formally measured (quantitative) cardiac ejection fraction has been demonstrated.[29–31] When time and training allow, simple calculations can be performed. The RV:LV ratio, while visually estimated in all cardiac views, is best calculated using the RV to LV diameters in end systole in the PSAX view. An RV:LV ratio of >1 is pathologic. Neonates are an exception and may have a slightly dominant RV immediately after birth.

While the PSAX is considered to be the best view for qualitative assessment of LV function,[32] it is important to use several windows to assess the LV as no single view can provide a comprehensive picture of contractility.

Clinical Application of FoCUS

Although a FoCUS examination may be less likely to detect abnormalities than a comprehensive echocardiographic examination, it does provide valuable data to supplement physiologic data and physical examination findings.[6,33–35] For the pediatric patient, the most relevant parameters assessed by the FoCUS examination are LV and RV size and contractility which are essential for the differentiation of causes of hypotension and shock. Children can develop sudden and severe hypotension for which a definitive cause is not immediately certain. The typical differential diagnosis includes air embolus, anaphylaxis, hypovolemia, pericardial tamponade, and respiratory insufficiency. The absolute amount of air necessary to induce hemodynamic instability from air embolus and the quantity of blood loss causing hypotension are smaller in children. For example, the approximate LV end-diastolic volume of a 5 kg child is 10–15 mL and the estimated blood volume is 350–400 mL. Detection of hypovolemia in children is complicated by the fact that hypotension is a late sign of hypovolemia in children compared to adults. As a result of heart rate increases and robust vasoconstrictive reflexes, children can remain normotensive until intravascular losses of 30%–40% have occurred.[12,36,37] The ability of FoCUS to accurately detect a state of low cardiac preload and to facilitate rapid, goal-directed fluid resuscitation has been demonstrated in children.[12,38] A compilation of relevant clinical cases from our 12-month experience after the introduction of FoCUS in our anesthesia department at Boston Children's Hospital are shown in Table 2. These are examples of the emerging role of FoCUS for the pediatric anesthesiologist.

FoCUS shortens the time to make a definitive diagnosis and institute appropriate therapy after the onset of symptoms in pediatric emergency departments and intensive care units (ICUs).[12,37,39] Rapid diagnosis and treatment of hypotension has been shown to improve outcomes in pediatric shock.[38] Serial FoCUS examinations can be used to monitor an intervention and confirm resolution of pathology in real time.[12,40,41] Our experience suggests that FoCUS is also advantageous for healthy children who develop hemodynamic instability in the operating room setting; most of the patients (4/7) in our 1-year experience were classified as American Society of Anesthesiologists (ASA) I and II patients.

In conjunction with chest auscultation and examination of the breathing circuit, a primary respiratory problem and a respiratory event occurring as the result of a primary cardiac event can be differentiated with FoCUS.[24,25,42] Adverse respiratory events are common in infants and children in the perioperative period and can rapidly produce hemodynamic instability with up to 40% of intraoperative cardiac arrests in children occurring from a respiratory etiology.[42]

While a comprehensive review of ultrasound imaging of the lung and airway is beyond the scope of this article, the addition of ultrasound imaging of the airway and lungs can be useful in diagnosing endotracheal tube (ETT) malposition and select lung pathologies in children contributing to hemodynamic instability. While successful tracheal intubation is typically confirmed by the presence of end-tidal carbon dioxide (ETCO2) and confirmation of bilateral breath sounds, ETCO2 may not be detectable in the presence of poor cardiac output, poor lung compliance, and severe bronchospasm. A transversely oriented high-frequency linear transducer placed over the midneck just above the sternal notch can visualize both the trachea and the esophagus.[43] During intubation, observation of an empty esophagus and widening subglottis indicates successful tracheal intubation, while the appearance of the ETT in the esophagus indicates esophageal intubation. This approach yields a sensitivity and specificity of 98.5%–100% and 75%–100%, respectively, in both adult and pediatric patients.[43–46] Endobronchial intubation can be ruled out by observing bilateral pleural sliding using a sagittal transducer in a midaxillary view. Accurate identification of tracheal versus bronchial intubation is 95%–100% utilizing ultrasound as compared to 62% using auscultation.[47,48] Pneumothorax can be ruled out by observing the characteristic ultrasound imaging of pleural sliding, and a large pleural effusion can be directly observed.[48–51]

Insufficient evidence exists to recommend for or against the routine use of FoCUS during adult or pediatric cardiac arrest,[53] as evidence is limited to case reports and small series.[23,53–56] There are, however, potential advantages, and FoCUS may be considered when appropriately skilled personnel are available to identify reversible causes of cardiac arrest such as pericardial tamponade, hypovolemia, and pulmonary and air embolus.[14,23,53–57] Due to the unreliability of palpating pulses in unconscious children, even by experienced health care providers,[58,59] FoCUS has been shown to assist in demonstrating presence or absence of cardiac pulse.[54] Extracorporeal membrane oxygenation as a rescue strategy when prolonged conventional cardiopulmonary resuscitation (CPR) cannot restore spontaneous circulation, referred to as extracorporeal membrane oxygenation for cardiopulmonary resuscitation (E-CPR), is increasingly used in children.[60] E-CPR for pediatric patients with in-hospital cardiac arrest requiring ≥10 minutes of CPR is associated with improved survival and favorable neurological outcome at discharge compared with CPR alone.[60] Rapid determination of myocardial standstill using FoCUS may promote more expedient initiation of E-CPR with the opportunity to shorten periods of CPR and improve outcomes. As with adults, the S4CH view is the recommended imaging window in the settings of cardiac arrest and CPR.[55,56,58] This view is least disruptive of chest compressions and easier to obtain. The time allowed for an emergent examination is strictly limited to 10 seconds to minimize interruption of chest compressions. The transducer can be positioned before the pulse check, and the acquired video clip can be reviewed after resumption of CPR. With adequate training, images can be acquired during the 10-second pauses allotted for pulse checks.[57] If S4CH images are of insufficient quality to be useful, A4CH or PSAX views may be attempted. On return of spontaneous circulation after cardiac arrest, FoCUS has been used to qualitatively assess LV systolic recovery over time. Given the ease with which a portable ultrasound device can be brought to the patient bedside, a FoCUS examination should be considered as part of the code response.

It is sometimes challenging to decide how to proceed when unexpected findings are discovered on FoCUS examinations. Patients and their families should be made aware of general concerns but should be reassured that concerning findings will be delineated with a cardiology consult and an expertly performed comprehensive echocardiogram as indicated. At our pediatric institution, we developed guidelines to direct follow-through for incidental findings on FoCUS ultrasound examinations[61] based on hemodynamic stability, severity of abnormality and symptoms, and perceived acuity of the finding. Individual institutions will need to establish guidelines that work within the context of their system.

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