Physiologic Monitoring

The monitoring used for any specific patient should depend on the child's condition and the magnitude of the planned surgical procedure. The perioperative monitoring techniques available are listed in Table 51-5 . Noninvasive monitoring is placed prior to induction of anesthesia. In the crying pediatric patient, the anesthesiologist may elect to defer application of monitoring devices until immediately after the induction of anesthesia. Standard monitoring includes an electrocardiographic system, pulse oximetry, capnography, precordial stethoscope, and an appropriate-sized blood pressure cuff (either oscillometric or Doppler). Additional monitoring includes an indwelling arterial catheter, temperature probes, and an esophageal stethoscope. Foley catheters are generally employed when surgical intervention entails CPB or might produce renal ischemia, or when the anesthetic management includes a regional technique associated with urinary retention. Some centers routinely employ central venous pressure (CVP) monitoring for major cardiovascular surgery. Alternatively, the authors typically use directly placed transthoracic atrial lines to obtain that information for separation from CPB and the postoperative period. In that setting, the benefits of the information or access provided by percutaneous CVP catheters in the pre-bypass period must be weighed against the risks they pose.

Continuous monitoring of arterial pressure is only possible through an indwelling intra-arterial catheter.

TABLE 51-5 -- Monitoring of organ systems

Cardiopulmonary system

Esophageal stethoscope

Electrocardiogram

Standard seven-lead system, ST-T wave analysis, esophageal electrocardiographic lead

Pulse oximetry

Automated oscillatory blood pressure

Capnograph

Ventilator parameters

Indwelling arterial catheter

Central venous pressure catheter

Pulmonary artery catheter

Transthoracic pressure catheter

Left or right atrium, pulmonary artery

Echocardiography with Doppler color flow imaging

Epicardial or transesophageal

Central nervous system

Peripheral nerve stimulator

Processed electroencephalography

Specialized

Cerebral blood flow—xenon clearance methodology

Cerebral metabolism—near-infrared spectroscopy, oxygen consumption measurements

Transcranial Doppler

Jugular venous bulb saturations

Temperature

Nasopharyngeal, rectal, esophageal, tympanic

Renal function

Foley catheter

2017

Myocardial and cerebral preservation is principally maintained through hypothermia; therefore, the accurate and continuous monitoring of body temperature is crucial. Rectal and nasopharyngeal temperatures are monitored, as they reflect core temperature and brain temperature, respectively. Monitoring of esophageal temperature is a good reflection of cardiac and thoracic temperature. Tympanic probes, although a useful reflection of cerebral temperature, can cause tympanic membrane rupture.

Pulse oximetry and capnography provide instantaneous feedback concerning adequacy of ventilation and oxygenation. They are useful guides in ventilatory and hemodynamic adjustments to optimize p:s before and after surgically created shunts and pulmonary artery bands. Peripheral vasoconstriction in patients undergoing deep hypothermia and circulatory arrest renders digital oxygen saturation probes less reliable. In the newborn, the use of a tongue sensor has been advocated to provide a more central measure of oxygen saturation, with less temperature-related variability.^[42]

The use of transthoracic (in the right or left atrium, pulmonary artery) or transvenous pulmonary artery catheters is determined on an individual basis based on the disease process, physiologic state, and surgical intervention. For example, in children undergoing a Fontan procedure for tricuspid atresia or univentricular heart, catheters in the Fontan pathway and the pulmonary venous atrium are especially useful. Following a Fontan operation, PBF must occur without benefit of a ventricular pumping chamber. Subtle changes in preload, PVR, and pulmonary venous pressure will influence PBF and thus systemic cardiac output. Data derived from systemic venous pressure and left atrial pressure (LAP) help distinguish the relative importance of intravascular volume (CVP), PVR (CVP-LAP gradient), or ventricular compliance (LAP), each of which requires a different therapeutic approach.

As a general guideline, a transvenous pulmonary artery catheter (PAC) may be placed using the internal jugular approach in children weighing more than 7 kg. A 5.0 Fr PAC is used for children weighing between 7 and 25 kg, and a 7.0 Fr PAC for children weighing greater than 25 kg. For infants weighing less than 7.0 kg, percutaneous placement of a PAC can be performed from the femoral vein. Occasionally, the latter technique will require fluoroscopy. The use of intraoperative transthoracic monitoring lines and echo-Doppler limits the need for transvenous pulmonary artery catheters in most cases.