The hemodynamic response to incremental increases in negative intrathoracic pressure in healthy humans

Abstract

Negative intrathoracic pressure (nITP) generally augments venous return and left ventricular (LV) stroke volume (LVSV), though large increases in nITP, commonly seen in respiratory disease, attenuate LVSV. Despite this consistent finding, the degree of nITP required to reduce LVSV and the contributions of series and direct ventricular interaction (DVI) in mediating this response remain unclear. We hypothesized that nITP ≤−15 cmH₂0 would augment LVSV, while nITP ≥-20 cmH₂o would reduce LVSV via DVI and increased afterload.

Twenty-three healthy subjects were randomly given inspiratory loads during spontaneous breathing to generate −5, −10, −15, −20 and −25 cmH₂O. LV volumes, LV geometry, inferior vena cava collapsibility (cIVC) and LV meridional end-systolic wall-stress (LVESMWS) were assessed in the supine position using tri-plane echocardiography.

LVSV remained unchanged up to −15 cmH₂O, but was significantly reduced at nITP ≥−20 cmH₂O (−12 ± 8% and −15 ± 11% at −20 and −25 cmH2o, respectively, P < 0.05) due to significant reductions in LV end-diastolic volume (LVEDV), while end-systolic volume (LVESV) was unchanged. cIVC on inspiration was significantly increased at all levels of nITP, while LVESMWS only increased at −25cmH₂O (P < 0.05). DVI, as indicated by a significant increase in the radius of septal curvature, occurred at nITP ≥−10 cmH₂O.

In supine healthy humans, nITP ≤−15 cmH₂O does not significantly affect LV function, despite increased DVI. In contrast, nITP ≥−20 cmH₂O causes significant reductions in LVSV and LVEDV, which appear to be mediated by DVI and increased afterload at −25 cmH₂O. The impact of cIVC during nITP remains unclear.

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Sedation for magnetic resonance imaging using propofol with or without ketamine at induction in pediatrics—A prospective randomized double-blinded study

Summary

Introduction

Deep sedation using propofol has become a standard technique in children. This double-blinded randomized clinical trial aims to compare the clinical effects of propofol-mono-sedation vs a combination of propofol and ketamine at induction and a reduced propofol infusion rate for maintenance in children undergoing diagnostic magnetic resonance imaging.

Methods

Children aged from 3 months to 10 years scheduled as outpatients for elective magnetic resonance imaging with deep sedation were included. They were randomized into 2 groups, receiving either 1 mg/kg ketamine at induction, then a propofol infusion rate of 5 mg/kg/h or a propofol infusion rate of 10 mg/kg/h without prior ketamine. Time to full recovery (modified Aldrete score = 10) was the primary outcome. Further outcomes were quality of induction, immobilization during image acquisition, recovery, postoperative nausea and vomiting, emergence delirium using the Pediatric Anesthesia Emergence Delirium scale, vital signs and adverse cardiorespiratory events. All patients and parents as well as anesthetists, imaging technicians, and postsedation personnel were blinded. Data are given as median (range).

Results

In total, 347 children aged 4.0 (0.25-10.9) years, weighing 15.6 (5.3-54) kg, ASA classification I, II, or III (141/188/18) were included. The ketamine-propofol group showed significantly shorter recovery times (38 (22-65) vs 54 (37-77) minutes; median difference 14 (95% CI: 8, 20) minutes; P < .001), better quality of induction, and higher blood pressure, but higher incidence of movement requiring additional sedative drugs. There were no significant differences in respiratory side effects, cardiovascular compromise, emergence delirium, or postoperative nausea and vomiting.

Conclusion

Both sedation concepts proved to be reliable with a low incidence of side effects. Ketamine at induction with a reduced propofol infusion rate leads to faster postanesthetic recovery.

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Chronic intermittent hypoxia and renovascular hypertension: A case of one plus one equals one-half!

Abstract

The homeostatic regulation of blood pressure depends on an exquisite interplay between multimodal sensors, several brain regions and long-range control systems that serve to maintain and defend cardiovascular constancy.

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An Outbreak of NDM-1-Producing Klebsiella pneumoniae, Associated with OmpK35 and OmpK36 Porin Loss in Tunisia

Microbial Drug Resistance , Vol. 0, No. 0.


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Spread of Vancomycin-Resistant Enterococcus faecium Isolates Despite Validated Infection Control Measures in an Italian Hospital: Antibiotic Resistance and Genotypic Characterization of the Endemic Strain

Microbial Drug Resistance , Vol. 0, No. 0.


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Molecular Characterization and Clonal Diversity of Methicillin-Resistant and -Susceptible Staphylococcus aureus Isolates of Milk of Cows with Clinical Mastitis in Tunisia

Microbial Drug Resistance , Vol. 0, No. 0.


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Review: human placental oxygenation in late gestation: experimental and theoretical approaches

Abstract

The placenta is crucial for life. It is an ephemeral but complex organ acting as the barrier interface between maternal and fetal circulations, providing exchange of gases, nutrients, hormones, waste products and immunoglobulins. Many gaps exist in our understanding of the detailed placental structure and function, particularly in relation to oxygen handling and transfer in healthy and pathological states in utero.

Measurements to understand oxygen transfer in vivo in the human are limited, with no general agreement on the most appropriate methods. An invasive method for measuring partial pressure of oxygen in the intervillous space through needle electrode insertion at the time of Caesarean sections has been reported. This allows for direct measurements in vivo whilst maintaining near normal placental conditions, however there are practical and ethical implications in using this method for determination of placental oxygenation. Furthermore, oxygen levels are likely to be highly heterogeneous within the placenta.

Emerging non-invasive techniques, such as MRI, and ex vivo research are capable of enhancing and improving current imaging methodology for placental villous structure and increase the precision of oxygen measurement within placental compartments. These techniques, in combination with mathematical modelling have stimulated novel cross-disciplinary approaches that could advance our understanding of placental oxygenation and its metabolism in normal and pathological pregnancies, improving clinical treatment options and ultimately outcomes for the patient.

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