Andersons pediatric cardiology 1840

The pressure waveforms themselves are valuable sources of data In arterial tracings, the slope of the upstroke can be used to generally assess contractility A steep upstroke indicates adequate cardiac contractility, whereas a blunted upstroke may indicate poor contractility, aortic valve disease, or peripheral vasoconstriction from vasoactive drugs The position of the dicrotic notch of the ventricular end-systolic pressure is an important indicator of peripheral vascular resistance A low notch indicates low systemic vascular resistance (SVR) and can be a useful clinical indicator in a neonate with a patent arterial duct Significant respiratory variation in the arterial waveform may indicate hypovolemia Finally, one of the most important indications for placement of an invasive arterial catheter is the need for accurate assessment of the pulse width A wide pulse width in the preoperative neonate is an important indicator of diastolic runoff into the pulmonary circulation and may be an early indicator of inadequate systemic blood flow The reliability of these invasive data is improved by the use of a central arterial catheter as opposed to the noninvasive assessment of blood pressure Another advantage of an indwelling catheter is the ability to draw blood samples for serial laboratory monitoring This is particularly useful for patients in whom there is concern for an evolving deficiency in DO2 For example, the development of a metabolic acidosis or a rise in serum lactate levels may be an early indicator of inadequate DO2 In neonates requiring diuretic therapy, an indwelling catheter allows for the daily assessment of serum electrolytes and safer intravenous replacement of any derangements Indwelling central venous catheters also allow for the administration of parenteral nutrition Peripheral Vascular Line It is important to consider that the majority of preoperative neonates with a fUVH may be managed adequately with a peripheral intravenous line rather than an indwelling central venous catheter The peripheral catheter can be used to administer infusions of PGE1 and low-concentration glucose Peripheral intravenous catheters carry low insertion complication rates and minimize the risk for thromboembolism, vascular occlusion, and infection complications Pulse Oximetry Continuous pulse oximetry is utilized in all neonates with a fUVH The probe is often placed on the distal extremity In patients with fUVH with anatomic obstruction to systemic blood flow (see Chapter 69), a “preductal” and “postductal” saturation measurement is typically monitored by a probe on the right hand and either foot Near Infrared Spectroscopy A near infrared spectroscopy (NIRS) probe is used in many centers as a surrogate measure of the adequacy of DO2.31,32 The probe is attached with a noninvasive self-adhesive pad applied to the forehead, abdomen, and/or lumbar area.33 It emits light in the near infrared spectrum, which is then measured by sensors at specific distances from the light source Oxyhemoglobin and deoxyhemoglobin have unique peak absorption in the near infrared spectrum Total hemoglobin concentration is measured by the absorbance of light at 800 nm Analogous to the calculation of systemic saturation by the pulse oximeter, the NIRS monitor reports the ratio of oxyhemoglobin to total hemoglobin concentration This value is often used as a surrogate for “mixed venous” oxygen saturation Commercially available NIRS devices use proprietary algorithms to subtract oxygen saturation from overlying tissue such as bone It is also important to note that NIRS does not distinguish between arterial and venous blood Owing to these limitations, the NIRS monitor is used primarily as an adjunct to other indicators of cardiac output Novel Noninvasive Algorithms Based on High-Fidelity Continuous Physiologic Data Increasing numbers of centers now employ solutions to linearly display highfidelity continuous physiologic data at the patient's bedside These systems are capable of presenting in a single longitudinal view any continuous physiologic data stream connected to the bedside monitor Continuous data inputs include heart rate, respiratory rate, arterial and venous pressures, pulse oximetry, temperature, ventilator data, and medication infusion data These data are typically displayed at 5-second intervals Modern systems are also capable of overlaying serial pertinent laboratory data (including blood gas and lactate levels) on the physiologic data streams Longitudinal displays can be used to quickly visualize important clinical trends in pre- versus postductal oxygen saturations, blood pressures, and pulse width Continuous data streams have recently been used to develop complex mathematical algorithms to detect the risk for inadequate DO2 One such algorithm, the iDO2 index, approved by the US Food and Drug Administration, uses physiologic data streams to display the probability of the mixed venous saturation below 40% and thus inadequate DO2 This algorithm was validated in a large cohort of neonates with a fUVH and a multidistribution circulation A sustained period with an iDO2 index below 40% has been associated with an increased incidence of cardiac arrest and a protracted stay in the CICU Electroencephalography Continuous EEG monitoring may provide information on cortical brain activity In standard EEG monitoring, leads are placed over regions of the skull, and a cart with a CPU and video camera is placed at the foot of the bed Changes in the electrical tracings are correlated with abnormal movements or changes in vital signs Preoperative EEG monitoring is not routinely undertaken in most centers unless there is specific concern for a structural brain abnormality, genetic syndrome, or clinical seizure Physiology and Presentation of Shock in the Neonate With a Functionally Univentricular Heart Neonates with a fUVH and hypoplasia/atresia of the systemic AV valve and/or ventricle as well as hypoplasia/atresia of the aorta valve (see Chapter 69) may develop and grow adequately in utero; following birth, however, their systemic blood flow is dependent on a patent arterial duct and unobstructed systemic and pulmonary venous return (see Chapter 70) In the current era, with the advent of fetal echocardiography and the increasing prevalence of prenatal diagnosis, many neonates with a fUVH are delivered following a prenatal diagnosis with informed families, physiologic stability,34,35 and an expectant cardiovascular team However, there are still neonates who are not detected prenatally and, as the arterial duct constricts, there is systemic hypoperfusion with a relative increase in pulmonary blood flow.36 Clinically this presents as tachypnea and poor feeding, progressing to listlessness and finally cardiovascular shock The clinical presentation mimics sepsis and the onus on the clinician is to have a high index of suspicion for CHD.37 On laboratory testing there is profound metabolic acidosis with an elevated lactate and end-organ dysfunction with elevated hepatic enzymes and creatinine Shock occurs when oxygen demand exceeds systemic DO2 In this instance,