Intubation in burns patients: a 5-year review of the Manchester regional burns centre experience.

Despite criteria to guide intubation from the American Burn Association (ABA), concerns remain regarding over-intubation of burns patients. The purpose of this study was to review appropriateness of intubation at a UK regional burns centre over a 5-year period. A 5-year retrospective review of adult patients admitted to the Manchester Burns Centre who underwent intubation at or prior to admission was performed. Intubations for non-burn indications or burns >40%TBSA were excluded. Patient demographic and burn characteristics data were extracted from medical records. Indications for intubation were compared to ABA and Denver criteria. 47 patients were identified, of which 40 met inclusion criteria for analysis. 72.5% and 95% of these patients met ABA or Denver criteria respectively. 30.8% of patients were extubated within 48 h. 50% patients extubated within 48 h had ≤1 indication for intubation or negative laryngoscopy. Complications related to intubation and ventilation were noted in 37.5% of patients, with ventilation associated pneumonia (VAP) being the most common occurring in 27.5%. 95% of patients fulfilled recognised criteria for intubation. However, 30% were extubated within 48 h, suggesting potentially avoidable intubation. This study suggests current intubation criteria may over-estimate risk of airway compromise and supports results from non-UK studies that a proportion of patients may be suitable for close observation rather than early intubation.

Non-identifiability of parameters for a class of shear-thinning rheological models, with implications for haematological fluid dynamics.

Choosing a suitable model and determining its associated parameters from fitting to experimental data is fundamental for many problems in biomechanics. Models of shear-thinning complex fluids, dating from the work of Bird, Carreau, Cross and Yasuda, have been applied in highly-cited computational studies of hemodynamics for several decades. In this manuscript we revisit these models, first to highlight a degree of uncertainty in the naming conventions in the literature, but more importantly to address the problem of inferring model parameters by fitting to rheology experiments. By refitting published data, and also by simulation, we find large, flat regions in likelihood surfaces that yield families of parameter sets which fit the data equally well. Despite having almost indistinguishable fits to experimental data these varying parameter sets can predict very different flow profiles, and as such these parameters cannot be used to draw conclusions about physical properties of the fluids, such as zero-shear viscosity or relaxation time of the fluid, or indeed flow behaviours. We verify that these features are not a consequence of the experimental data sets through simulations; by sampling points from the rheological models and adding a small amount of noise we create a synthetic data set which reveals that the problem of parameter identifiability is intrinsic to these models.

Influence of microvascular sutures on shear strain rate in realistic pulsatile flow.

Arterial thrombus formation is directly related to the mechanical shear experienced by platelets within flow. High shear strain rates (SSRs) and large shear gradients cause platelet activation, aggregation and production of thrombus. This study, for the first time, investigates the influence of pulsatile flow on local haemodynamics within sutured microarterial anastomoses. We measured physiological arterial waveform velocities experimentally using Doppler ultrasound velocimetry, and a representative example was applied to a realistic sutured microarterial geometry. Computational geometries were created using measurements taken from sutured chicken femoral arteries. Arterial SSRs were predicted using computational fluid dynamics (CFD) software, to indicate the potential for platelet activation, deposition and thrombus formation. Predictions of steady and sinusoidal inputs were compared to analyse whether the addition of physiological pulse characteristics affects local intravascular flow characteristics. Simulations were designed to evaluate flow in pristine and hand-sutured microarterial anastomoses, each with a steady-state and sinusoidal pulse component. The presence of sutures increased SSRmax in the anastomotic region by factors of 2.1 and 2.3 in steady-state and pulsatile flows respectively, when compared to a pristine vessel. SSR values seen in these simulations are analogous to the presence of moderate arterial stenosis. Steady-state simulations, driven by a constant inflow velocity equal to the peak systolic velocity (PSV) of the measured pulsatile flow, underestimated SSRs by ∼ 9% in pristine, and ∼ 19% in sutured vessels compared with a realistic pulse. Sinusoidal flows, with equivalent frequency and amplitude to a measured arterial waveform, represent a slight improvement on steady-state simulations, but still SSRs are underestimated by 1-2%. We recommend using a measured arterial waveform, of the form presented here, for simulating pulsatile flows in vessels of this nature. Under realistic pulsatile flow, shear gradients across microvascular sutures are high, of the order ∼ 7.9 × 106 m-1 s-1, which may also be associated with activation of platelets and formation of aggregates.

Microarterial anastomoses: A parameterised computational study examining the effect of suture position on intravascular blood flow.

This study investigates the extent to which individual aspects of suture placement influence local haemodynamics within microarterial anastomoses. An attempt to physically quantify flow characteristics of blood past microvascular sutures is made using computational fluid dynamics (CFD) software. Particular focus has been placed on increased shear strain rate (SSR), a known precipitant of intravascular platelet activation and thrombosis. Measurements were taken from micrographs of sutured anastomoses in chicken femoral vessels, with each assessed for bite width, suture angle and suture spacing. Computational geometries were then created to represent the anastomosis. Each suture characteristic was parameterised to allow independent or simultaneous adjustment. Flow rates were obtained from anonymised Doppler ultrasound scans of analogous vessels during preoperative assessment for autologous breast reconstruction. Vessel simulations were performed in 2.5mm ducts with blood as the working fluid. Vessel walls were non-compliant and a continuous Newtonian flow was applied, in accordance with current literature. Suture bite angle and spacing had significant effects on local haemodynamics, causing notably higher local SSRs, when simulated at extremes of surgical practice. A combined simulation, encompassing subtle changes of each suture parameter simultaneously i.e. representing optimum technique, created a more favourable SSR profile. As such, haemodynamic changes associated with optimum suture placement are unlikely to influence thrombus formation significantly. These findings support adherence to the basic principles of good microsurgical practice.

Reconstructive outcomes of Mohs surgery compared with conventional excision: A 13-month prospective study.

Established in 2012, the Mersey Regional Centre for Mohs Surgery is the first UK Mohs service to be led by a Mohs trained Plastic & Reconstructive surgeon. We evaluate the resection requirements and reconstructive techniques of our patient group and compare their surgical outcome to that which would have been gained with conventional excision (CE) and reconstruction for the same lesions. 157 patients were analysed over 13 months. Had CE and reconstruction been used, 56% of patients would have received a more invasive or cosmetically less desirable reconstruction, and 24% of margins would remain incomplete. The outcome was unchanged in 20% of patients. A small but significant subgroup (9%) of patients would have lost fundamental structures e.g. orbital exenteration, or undergone reconstructions unnecessarily crossing aesthetic subunits. Whilst in its infancy, the Plastic & Reconstructive Mohs surgery service has provided a valuable contribution to the care given to patients in the Mersey and Cheshire Skin Cancer Network. Detailed referral criteria, thorough preoperative patient evaluation, and appreciation of the abilities and limits of CE have enabled the service to produce a demonstrable reconstructive benefit in 80% of patients when compared to non-Mohs resection and reconstruction.

The plastic & reconstructive Mohs surgery service.

Mohs Micrographic Surgery (MMS) is the current 'gold-standard' for excision of a number of cutaneous lesions and provides a valuable addition to a skin cancer service. The Mersey Regional Centre for Mohs Surgery is the first MMS service in the UK to be led by an MMS trained Plastic and Reconstructive surgeon, and this article describes an overview of the processes involved in establishing such a service.

Dermal substitutes do well on dura: comparison of split skin grafting +/- artificial dermis for reconstruction of full-thickness calvarial defects.

Large, full-thickness calvarial defects present a series of significant reconstructive challenges involving a range of techniques, including local and free flaps. Occasionally these conventional methods may not be possible due to technical, or patient, factors. Artificial dermis is already widely used in burns surgery and is increasing in oncological reconstruction. We believe that artificial dermis coupled with split-thickness skin grafting provides an excellent option for closure of these defects when other techniques are not appropriate.

Dermal substitutes do well on dura: comparison of split skin grafting+/-artificial dermis for reconstruction of full-thickness calvarial defects.

Large, full-thickness calvarial defects present a series of significant reconstructive challenges involving a range of techniques, including local and free flaps. Occasionally these conventional methods may not be possible due to technical, or patient, factors. Artificial dermis is already widely used in burns surgery and is increasing in oncological reconstruction. We believe that artificial dermis coupled with split-thickness skin grafting provides an excellent option for closure of these defects when other techniques are not appropriate.