The arterial blood gas is the most effective way to determine acid-base
balance and oxygenation in the clinical setting. It can reveal the severity of
hypoxemia and hypoperfusion. Normal pH values range from 7.34-7.45, with
PaO 2 and PaCO 2 values ranging from 80-100 mm Hg and 35-40 mm Hg,
respectively. The base deficit, which normally ranges from -2 to 2 mmol/L,
reflects the degree of metabolic acidosis present at the peripheral tissue level.
Values > -5 mmol/L correlate with impaired oxygenation and tissue perfusion,
metabolic acidosis, and impaired end organ function. The serum lactate level is
also a marker of tissue oxygenation, delivery and extraction. Lactate is produced
when oxygen delivery is inadequate or the tissues are unable to extract it
appropriately. In the latter situation, the cells turn to anaerobic respiration leading
to the production of lactate. Normal lactate levels are generally less than 2.5
mmol/L. The liver and kidneys clear lactate and thus hepatic or renal insufficiency
can contribute to elevated levels. A lactate >4 mmol/L or increasing levels on
serial measurement are predictive of morbidity and mortality. Lactate levels will
generally improve within 60 minutes of interventions used to improve tissue
perfusion.
IV. Management of Shock and Low Cardiac Output States
(^) Any patient suspected of developing LCO or shock needs to be placed in
a monitored environment that allows for active clinical surveillance. Fluid
resuscitation is always the first step of management in order to improve left
ventricular preload and DO 2. Most children can tolerate up to 60 mL/kg of