The Science Journal of the American Association for Respiratory Care

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.

1.     Mascia L, Andrews PJ, McKeating EG, Souter MJ, Merrick MV, Piper IR.  Cerebral blood flow and metabolism in severe brain injury: the role of pressure autoregulation during cerebral perfusion pressure management.  Intensive Care Med. 2000 Feb;26(2):202-5.

2.     Holland MC, Mackersie RC, Morabito D, Campbell AR, Kivett VA, Patel R, Erickson VR, Pittet JF. The development of acute lung injury is associated with worse neurologic outcome in patients with severe traumatic brain injury.  J Trauma. 2003 Jul;55(1):106-11.

3.     Marshall BE. Improvement in oxygenation by phenylephrine and nitric oxide in patients with ARDS. Anesthesiology 1997;87(1):18‑25.

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