Effects of phenylephrine on systemic and cerebral circulations in humans: a systematic review with mechanistic explanations.

We conducted a systematic review of the literature reporting phenylephrine-induced changes in blood pressure, cardiac output, cerebral blood flow and cerebral tissue oxygen saturation as measured by near-infrared spectroscopy in humans. We used the proportion change of the group mean values reported by the original studies in our analysis. Phenylephrine elevates blood pressure whilst concurrently inducing a reduction in cardiac output. Furthermore, despite increasing cerebral blood flow, it decreases cerebral tissue oxygen saturation. The extent of phenylephrine's influence on cardiac output (r = -0.54 and p = 0.09 in awake humans; r = -0.55 and p = 0.007 in anaesthetised humans), cerebral blood flow (r = 0.65 and p = 0.002 in awake humans; r = 0.80 and p = 0.003 in anaesthetised humans) and cerebral tissue oxygen saturation (r = -0.72 and p = 0.03 in awake humans; r = -0.24 and p = 0.48 in anaesthetised humans) appears closely linked to the magnitude of phenylephrine-induced blood pressure changes. When comparing the effects of phenylephrine in awake and anaesthetised humans, we found no evidence of a significant difference in cardiac output, cerebral blood flow or cerebral tissue oxygen saturation. There was also no evidence of a significant difference in effect on systemic and cerebral circulations whether phenylephrine was given by bolus or infusion. We explore the underlying mechanisms driving the phenylephrine-induced cardiac output reduction, cerebral blood flow increase and cerebral tissue oxygen saturation decrease. Individualised treatment approaches, close monitoring and consideration of potential risks and benefits remain vital to the safe and effective use of phenylephrine in acute care.

Changes in cerebral tissue oxygen saturation during anaesthetic-induced hypotension: an interpretation based on neurovascular coupling and cerebral autoregulation.

There is currently no consensus regarding how to intervene in anaesthetic-induced hypotension. Whether or not the balance between cerebral oxygen supply and demand is maintained lacks adequate elucidation. It is thus intriguing to explore how cerebral tissue oxygen saturation is affected by anaesthetic-induced hypotension. Thirty-three patients scheduled for elective non-neurosurgical procedures were included in this study. Physiological measurements were performed immediately before induction with propofol and fentanyl and after tracheal intubation. Mean (SD) Bispectral index decreased from 84.3 (9.3) to 24.4 (8.0) (p<0.001). Mean arterial pressure decreased from 84.4 (10.6) mmHg to 53.6 (11.4) mmHg (p<0.001). However, cerebral tissue oxygen saturation remained stable (67.0 (9.4) % vs 67.5 (7.8) %, p=0.6). These results imply that the fine balance between cerebral oxygen supply and demand is not disrupted by anaesthetic-induced hypotension. An interpretation based on neurovascular coupling and cerebral autoregulation is proposed.

A novel application for bolus remifentanil: blunting the hemodynamic response to Mayfield skull clamp placement.

OBJECTIVE: Neurosurgery often requires skull immobilization with a Mayfield clamp, which often causes brief intense nociceptive stimulation, hypertension and tachycardia. Blunting this response may help prevent increased intracranial pressure, cerebral aneurysm or vascular malformation rupture, and/or myocardial stress. While various interventions have been described to blunt this response, no reports have compared administration of a propofol versus a remifentanil bolus. METHODS: We retrospectively analyzed the hemodynamic response to Mayfield placement in over 800 patients who received a prior propofol or remifentanil bolus from 2004 to 2010. RESULTS: Patients who received remifentanil experienced a 55% smaller increase in heart rate (p < 0.0001) and a 40% smaller increase in systolic blood pressure (p < 0.0001) after Mayfield placement than patients who received propofol. These data were retrospectively obtained from patients who were not randomized to receive remifentanil versus propofol, and hence these data could be subject to possible confounding. Nonetheless, these differences remained significant after multivariate analysis for possible confounding variables. CONCLUSIONS: Thus, a remifentanil bolus is more effective than a propofol bolus in blunting hemodynamic responses to Mayfield placement, and possibly for other short, intense nociceptive stimuli.

Effect of surgical clipping versus endovascular coiling on recovery from oculomotor nerve palsy in patients with posterior communicating artery aneurysms: A retrospective comparative study and meta-analysis.

BACKGROUND: Oculomotor nerve palsy (OMNP) is a well-recognized complication of posterior communicating artery (PCOM) aneurysms. Only a few comparative studies have assessed the effect of clipping versus coiling on recovery from OMNP in PCOM aneurysms. A retrospective review and meta-analysis was conducted to assess the relationship between PCOM aneurysm treatment and OMNP. MATERIALS AND METHODS: Medical records of all patients presenting between January 2000 and February 2013 with intracranial aneurysm were searched. All patients with OMNP secondary to PCOM aneurysm were included for analysis. Patients undergoing surgical clipping or endovascular coiling were compared with respect to complete resolution of OMNP after aneurysm surgery (i.e., primary outcome). A meta-analysis of published studies of OMNP associated with PCOM aneurysm was performed after a MEDLINE search. RESULTS: Seventeen patients with OMNP secondary to PCOM aneurysms met the inclusion criteria. Surgical clipping (seven of eight patients, or 87.5%) resulted in greater complete resolution of OMNP compared with endovascular coiling (four of nine patients, or 44.4%), P = 0.13. A meta-analysis of similar studies revealed that complete resolution of OMNP was more commonly associated with surgical clipping (36 of 43 patients, or 83.7%) than with endovascular coiling (29 of 55 patients, or 52.7%), yielding an adjusted odds ratio (OR) of 6.04 [confidence interval (CI) =1.88-19.45, P = 0.003]. Multivariate analysis found that the degree of pre-operative OMNP (OR = 0.07, CI = 0.02-0.28, P = 0.001) and surgical clipping (OR = 6.37, CI = 1.73-23.42, P = 0.005) were significant factors that affected the complete recovery of OMNP. CONCLUSION: Complete recovery of OMNP with PCOM aneurysms is more commonly associated with surgical clipping than with endovascular coiling. Also, the degree of pre-operative OMNP and the treatment modality are significant factors that affect the complete recovery of OMNP.