Abstract
This chapter, reviews the basics of monitoring in children. The author provides a discussion on the utility of a host of invasive and non-invasive monitoring techniques from non-invasive blood pressure measurements to placement of umbilical lines. Most importantly, the chapter highlight the limitations of these monitoring devices in small children.
A three-day-old, 3 kg female infant with transposition of the great arteries presents for an arterial switch operation. Transthoracic echo revealed an L-type transposition with an unrestrictive atrial shunt. The patient has been stable since birth in the neonatal intensive care unit receiving an alprostadil infusion.
Prior to the procedure, vitals include: temperature 37.20C, BP 63/42, HR 130 bpm, SpO2 88% on room air.
What Are the American Society of Anesthesiologists (ASA) Standard Monitors?
The goals of monitoring are to have consistent feedback on the patient’s oxygenation, ventilation, circulation, and body temperature. This is most commonly achieved with the ASA basic monitors: 3-lead electrocardiogram, pulse oximetry, non-invasive blood pressure, capnography, temperature probe for cases lasting longer than 30 minutes or shorter cases with expected temperature changes, and oxygen/inspired gas monitoring.
What Other Monitors May Be Useful for This Case?
Neonates undergoing congenital cardiac surgery require additional monitoring beyond the ASA basic monitors. At minimum, an arterial line will be needed for continuous blood pressure monitoring on bypass as well as to facilitate blood sampling. Many centers will also assess brain oxygenation with near-infrared spectroscopy (NIRS), central/right atrial pressures with a central venous catheter, and post-surgical anatomy and function with transesophageal echocardiography (TEE).
What Is Near-Infrared Spectroscopy and What Does It Monitor?
NIRS is a monitor of oxygenation in the cerebral vessels. Using technology similar to pulse oximetry, a probe is placed on the forehead which emits light in the near-infrared spectrum. The probe then subsequently analyzes scattering and absorption to assess oxyhemoglobin and deoxyhemoglobin saturations in the cerebral vasculature. During cardiac and other procedures, sudden changes in NIRS serve to alert the anesthesiologist to decreases in cerebral oxygenation or perfusion.
How Is NIRS Different from Pulse Oximetry?
Whereas pulse oximetry takes advantage of pulsatility to distinguish between arterial and venous blood, giving a reading that reflects arterial saturation, NIRS does not incorporate pulsatility and measures both venous and arterial hemoglobin saturations. Therefore, a normal NIRS saturation will be much lower than a pulse oximeter reading, often in the 70s or 80s when the arterial saturation is 100%. Thresholds for abnormal NIRS values are thus defined by a change greater than 20% or an absolute reading of <50%.
How Should a Noninvasive Blood Pressure Cuff Be Sized?
Choosing an appropriately sized cuff is important; a small cuff tends to overestimate blood pressure while an oversized cuff tends to underestimate it. Ideally a cuff should be 2/3rds to 3/4ths the width of the upper arm.
What Is the Normal Blood Pressure in Children?
A crude estimate according to PALS may be obtained by the following formula:
What Arteries Can Be Used for Invasive Blood Pressure Monitoring?
The most common arteries for arterial line placement include the radial, ulnar, femoral, dorsalis pedis, and posterior tibial arteries. In addition, in the newborn the umbilical arteries can be used for cannulation; these are most easily placed at birth, but can occasionally still be placed in the first several days of life.
What Techniques Can Be Used to Identify an Artery for Line Placement, and What Are the Limitations of Each?
Palpation is the simplest method of locating an artery for cannulation; however, numerous studies have demonstrated improved success with ultrasound utilization. Surgical cut-down allows for the direct visualization of the artery, but requires tissue dissection and may result in vessel laceration or hemorrhage.
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