Background
Management strategies for preoperative infants with hypoplastic left heart syndrome (HLHS) include increased inspired nitrogen (hypoxia) and increased inspired carbon dioxide (hypercarbia). There are no studies directly comparing these 2 therapies in humans. This study compares the impact of hypoxia versus hypercarbia on oxygen delivery, under conditions of fixed minute ventilation.
Methods and Results
Ten anesthetized and paralyzed preoperative infants with HLHS were evaluated in a prospective, randomized, crossover trial comparing hypoxia (17% F
io
2
) with hypercarbia (2.7% F
ico
2
). Each patient was treated in a random order (10 minutes per condition) with a recovery period (15 to 20 minutes) in room air. Arterial (Sa
o
2
) and superior vena caval (Sv
o
2
) co-oximetry and cerebral oxygen saturation (Sc
o
2
) measurements were made at the end of each condition and recovery period. Sc
o
2
was measured by near infrared spectroscopy. Hypoxia significantly decreased both Sa
o
2
(−5.2±1.1%,
P
=0.0014) and Sv
o
2
(−5.6±1.7%,
P
=0.009) compared with baseline, but arteriovenous oxygen saturation (AV
o
2
) difference (Sa
o
2
−Sv
o
2
) and Sc
o
2
remained unchanged. Hypercarbia decreased Sa
o
2
(−2.6±0.6%,
P
=0.002) compared with baseline but increased both Sc
o
2
(9.6±1.8%,
P
=0.0001) and Sv
o
2
(6±2.2%,
P
=0.022) and narrowed the AV
o
2
difference (−8.5±2.3%,
P
=0.005). Both hypoxia and hypercarbia decreased the balance between pulmonary and systemic blood flow (Qp:Qs) compared with baseline.
Conclusions
In preoperative infants with HLHS, under conditions of anesthesia and paralysis, although Qp:Qs falls in both conditions, oxygen delivery is unchanged during hypoxia and increased during hypercarbia. These data cannot differentiate cerebral from systemic oxygen delivery.
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