MONITORING OF CRITICALLY SICK CHILD

Continuous monitoring is an essential component of care for a critically sick child in PICU, which includes periodic clinical and laboratory assessment of physiological parameters, as well as real-time monitoring with electronic equipments.

Although all systems deserve close monitoring in a sick child, five major areas of concern are—

(a) hemodynamic imbalance, (b) respiratory insufficiency,

(c) neurological damage, (d) renal damage, and (e) metabolic or electrolyte disturbances.

A. Respiratory monitoring aims to assess the state of gaseous exchange in lungs and includes: (a) clinical monitoring of respiratory rate, depth, efforts, cyanosis and air entry on auscultation, (b) periodic arterial blood gas analysis (Ch 7.6), and (c) non-invasive monitoring of ventilatory functions, e.g. pulse oximetry or capnography.

Pulse oximetry is a simple non-invasive method to monitor percentage of hemoglobin saturated with oxygen (SaO₂), with an accuracy of + 2%. However, Pulse oximeters are unreliable once the SaO₂ drops gt;70%. False values may also be obtained due to: (a) low capillary perfusion, e.g. shock, (b) presence of abnormal hemoglobin, e.g. methemoglobin or carboxyhemoglobin, (c) optic interference with external light source, e.g. phototherapy or warmers.

Capnography is a non-invasive method to monitor CO₂ changes in expired air during critical care or anesthesia, as a measure of—(a) altered CO₂ production,

(b) altered pulmonary perfusion or cardiac output,

(c) altered ventilatory system. It is continuously measured by an optical beach connected to patient's airway via T-tube and expressed as a wave-form on digital monitor. Important EtCO₂ abnormalities are:

• Sudden drop in EtCO₂ indicates airway block, ventilator malfunction/extubation or pulmonary hypoperfusion, e.g.

• Slow and sustained drop indicates combined cardio­respiratory failure.

• Sudden, exponential rise in EtCO₂ indicates acute deli­very of CO₂ in pulmonary circulation, e.g. bicarbonate injection,

• Gradual rise in EtCO₂ indicates alveolar hypoventilation or partial airway obstruction

B. Hemodynamic monitoring aims to assess the state of circulatory sufficiency at tissue levels and includes-

(a) clinical monitoring of heart rate and rhythm, pulse volume, capillary filling time and blood pressure,

(b) invasive central venous pressure monitoring (Ch 27.3), and (c) non-invasive BP monitoring.

Non-invasive BP monitoring (NIBP) is the standard of care in PICUs, which may be periodic or continuous.

Periodic NIBP involves use of automated oscillometric method, using a special double air-bladder cuff, tied over a peripheral artery. Proximal bladder is periodically inflated to occlude arterial flow, while distal one records oscillations during cardiac cycle and transmits them as digital signals to depict systolic, diastolic and mean BP.

Continuous NIBP is based on the principle of quot;force balance technologyquot;, i.e. the force exerted by systolic BP and the counter force required to counteract it. A finger cuff/probe is inflated and deflated in rapid sequence automatically via a servo system, while a light-emitting electrode on one clip transilluminates the capillary bed. Photo-iodide cell on the opposite clip measures the change in light intensity during various phases of cardiac cycle and produces equal counteracting pressure to occlude it, which is measured digitally.

C. Neurological monitoring is critically sick children generally include frequent clinical assessment of: (a) level of sensorium, (b) pupillary responses, (c) signs of raised intracranial pressure, apart from periodic evaluation of motor and other neurological signs. Glasgow coma scale is commonly used to monitor the level of sensorium in critically sick children (Ch 18.3).

D. Renal monitoring involves: (a) clinical assessment of urinary output for oliguria, and (b) periodic renal function tests, e.g. blood urea nitrogen, serum creatinine, etc. Urine output of lt;0.5 ml/kg/hour indicates poor renal perfusion, intrinsic renal dysfunction or excess ADH secretion (SIADH) that needs modifications in fluid therapy.

E. Metabolic monitoring is the most crucial component of monitoring in critically sick children after hemodynamic and respiratory assessments. Some extent of metabolic derangements due to endogenous events or exogenous

fluid/electrolyte/drug therapy is inevitable in most children under PICU care, which need careful correction. Common parameters for metabolic monitoring include: (a) blood glucose, (b) serum electrolytes, e.g. Na⁺, K⁺ and Ca⁺⁺, (c) acid-base status (Ch 7.6), (d) serum lactate and ammonia levels, apart from renal/hepatic function tests.

27.4.5