2006 OPEN FORUM Abstracts
Improved Oxygenation with Low-Dose Phenylephrine Infusion: Preliminary Findings in Patients with Traumatic Brain Injury (TBI)
Rosenthal
G, Siobal MS, Tang JF, Hemphill JC, Manley GT. Departments of
Anesthesia, Neurology, and Neurosurgery, San Francisco General Hospital, UCSF
Background: Intact
cerebral autoregulation (CA) has been associated with improved prognosis in TBI
patients 1. The integrity of CA may be assessed by elevating mean
arterial pressure (MAP) and observing the effect on intracranial pressure and
cerebral blood flow. Assessments of CA in TBI patients are conducted as part of
clinical care in our institution by continuous infusion of low-dose phenylephrine
to elevate MAP by 10 mmHg. Pulmonary complications and acute lung injury are
common in patients with severe TBI and may worsen outcome 2. Phenylephrine
infusion may improve oxygenation through enhanced hypoxic pulmonary
vasoconstriction (HPV) and improved ventilation-perfusion matching in patients
with pulmonary pathology 3. We examined the effect of low-dose
phenylephrine infusion on PaO2 to FiO2 ratio (P/F) in
patients with severe TBI.
Method: Thirty-five
oxygen challenges (increase in FiO2 to 1.0) and MAP challenges
(increase in MAP by phenylephrine infusion) were analyzed in 17 patients with severe
TBI. MAP, PaO2, and P/F, were
recorded at baseline and during oxygen and MAP challenges.
Results: Baseline
P/F was 297 ± 106. MAP at baseline and during oxygen challenge was 91 ± 9 and 93
± 9 mmHg respectively, increasing to 103 ± 10 mmHg (p < 0.0001) during MAP
challenge. Mean P/F with oxygen
challenge was 403 ± 124 increasing to 448 ± 104 (p < 0.0001) with MAP
challenge. We found an inverse correlation between baseline P/F and percent
change in PaO2 with MAP challenge (r = -0.56, p=0.0005), suggesting
that patients with a low P/F may have a greater rise in PaO2 in
response to phenylephrine infusion. Patients with a P/F < 300 had a 24% increase
in PaO2 with MAP challenge compared to an increase of 6% in those with a P/F > 300 (p <
0.0001).
Conclusion: In
severe TBI patients low-dose phenylephrine infusion may be associated with improved
oxygenation. The observed rise in PaO2 with phenylephrine infusion appears to correlate inversely with baseline P/F. The
potential benefit of phenylephrine infusion to improve oxygenation in patients
with low P/F refractory to standard therapies warrants further investigation.
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2. Holland MC,
Mackersie RC,
Morabito D,
Campbell AR,
Kivett VA,
Patel R,
Erickson VR,
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The development of acute lung injury is associated with worse neurologic
outcome in patients with severe traumatic brain injury. J Trauma.
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3.
Marshall
BE. Improvement in oxygenation by phenylephrine and nitric oxide in patients
with ARDS. Anesthesiology 1997;87(1):18‑25.
