Nitric oxide synthase inhibition in healthy adults reduces regional and total cerebral macrovascular blood flow and microvascular perfusion.

The importance of nitric oxide (NO) in regulating cerebral blood flow (CBF) remains unresolved, due in part to methodological approaches, which lack a comprehensive assessment of both global and regional effects. Importantly, NO synthase (NOS) expression and activity appear greater in some anterior brain regions, suggesting region-specific NOS influence on CBF. We hypothesized that NO contributes to basal CBF in healthy adults, in a regionally distinct pattern that predominates in the anterior circulation. Fourteen healthy adults (7 females; 24 ± 5 years) underwent two magnetic resonance imaging (MRI) study visits with saline (placebo) or the NOS inhibitor, L-NMMA, administered in a randomized, single-blind approach. 4D flow MRI quantified total and regional macrovascular CBF, whereas arterial spin labelling (ASL) MRI quantified total and regional microvascular perfusion. L-NMMA (or volume-matched saline) was infused intravenously for 5 min prior to imaging. L-NMMA reduced CBF (L-NMMA: 722 ± 100 vs. placebo: 771 ± 121 ml/min, P = 0.01) with similar relative reductions (5-7%) in anterior and posterior cerebral circulations, due in part to the reduced cross-sectional area of 9 of 11 large cerebral arteries. Global microvascular perfusion (ASL) was reduced by L-NMMA (L-NMMA: 42 ± 7 vs. placebo: 47 ± 8 ml/100g/min, P = 0.02), with 7-11% reductions in both hemispheres of the frontal, parietal and temporal lobes, and in the left occipital lobe. We conclude that NO contributes to macrovascular and microvascular regulation including larger artery resting diameter. Contrary to our hypothesis, the influence of NO on cerebral perfusion appears regionally uniform in healthy young adults. KEY POINTS: Cerebral blood flow (CBF) is vital for brain health, but the signals that are key to regulating CBF remain unclear. Nitric oxide (NO) is produced in the brain, but its importance in regulating CBF remains controversial since prior studies have not studied all regions of the brain simultaneously. Using modern MRI approaches, a drug that inhibits the enzymes that make NO (L-NMMA) reduced CBF by up to 11% in different brain regions. NO helps maintain proper CBF in healthy adults. These data will help us understand whether the reductions in CBF that occur during ageing or cardiovascular disease are related to shifts in NO signalling.

Considerations in treating obese patients in office-based anesthesia.

The rise in obesity prevalence worldwide has presented problems for practitioners treating patients in the ambulatory setting. As more procedures are being performed in office-based suites, anesthesiologists are being asked to provide more anesthesia services for obese patients that may compromise safety. Conventional wisdom associates a higher body-mass index (BMI) with the potential for more adverse outcomes. When combined with the limited resources available in office-based anesthesia (OBA) locations, this prompts anesthesiologists to consider placing limits on BMI. However, not every OBA location is similar, thus contributing to the difficulty in establishing consensus BMI limits. Here, we review literature addressing obesity in ambulatory surgery and point out concerns that anesthesiologists should consider when treating obese patients in an OBA setting.

Transverse morphology of the sacroiliac joint: effect of angulation and implications for fluoroscopically guided sacroiliac joint injection.

OBJECTIVE: Effects of angulation of computed tomography (CT) reconstruction plane on sacroiliac (SI) joint morphology were studied, and factors influencing the approach to fluoroscopically guided SI joint injection were assessed. DESIGN AND PATIENTS: CT scans of pelvises were reformatted on 41 subjects, aged 51.7 (+/-15.1) years. Transverse images were reconstructed at the caudal 3 cm of the SI joint tilting plane of reconstruction from -30 degrees to +30 degrees at 15 degrees increments. Anteroposterior diameter of joint (depth), angle from sagittal plane (orientation angle), and distance from skin were measured. Joint contour was classified, and presence of bone blocking access to the joint was recorded. Comparison between angles were analysed by t-test. Relationships between variables were assessed by a Pearson correlation test. RESULTS: Depth was shorter with angulation in the inferior direction (P<0.01). Orientation angle increased with superior angulation (P<0.01). Distance from skin increased (P<0.01) with angulation in either direction. Joint contour was significantly different from baseline at each angle (P<0.001) but highly variable. Inferior angulation resulted in interposition of ilium between skin and SI joint, and superior angulation caused bone block due to the lower sacrum. None of these features was identified without tilting of the reconstruction plane, and effects were more pronounced with steeper angulation. CONCLUSION: Angulation of the reconstruction plane considerably affects the appearance of the sacroiliac joints. By shortening joint depth, an inferiorly directed approach to SI joint injection may make fluoroscopic guidance easier, although associated bony interposition can prevent access to the synovial compartment. A superiorly directed approach is more likely to have adverse effects.