[Negative pressure pulmonary edema following a cholecystectomy - A case report]

Negative pressure pulmonary edema (NPPE) or post-obstructive pulmonary edema (POPE) is a rare but a life threatening respiratory situation. The most frequent cause of NPPE is a post anesthetic laryngospasm. Edema is developed after relief of upper airway obstruction. Its incidence is 0.1 % of general anesthesia with tracheal intubation. We report this clinical case of a 28-year-old woman, who developed dyspnea followed by acute respiratory distress with unilateral pulmonary edema after extubation following general anesthesia for cholecystectomy under celioscopy. After elimination of any other cause, context, clinical and radiological characteristics, and the favorable evolution under oxygen and furosemide made it possible for us to link this acute respiratory distress to a NPPE whose pathophysiological causes and mechanisms are discussed.

Negative Pressure Wound Therapy for Closed Surgical Wounds in Musculoskeletal Oncology Patients - A Case-Control Trial

Following excision of musculoskeletal tumours, patients are at high risk of wound issues such as infection, dehiscence and delayed healing. This is due to a multitude of factors including the invasive nature of the disease, extensive soft tissue dissection, disruption to blood and lymphatic drainage, residual cavity and adjuvant therapies. The use of negative pressure wound therapy (NPWT) has a growing body of evidence on its beneficial effect of wound healing such as promoting cell differentiation, minimising oedema and thermoregulation. Traditionally, these dressings have been used for open or dehisced wounds; however recent research has investigated its role in closed wounds.

Aim:

To evaluate the effect of NPWT in patients with closed wounds, either primarily or with flap coverage, in our high risk group. Consecutive patients who had a NPWT dressing applied were selected, and a control group was established by a blinded researcher with matching for tissue diagnosis, surgical site, gender and age. The primary outcome measured was documented for wound complications, with secondary data collected on radiotherapy and wound drainage.

Results:

Patients were well matched between the intervention (n=9) and control (n=9) groups for gender, age and tissue diagnosis. Both groups had 1 patient who underwent preoperative radiotherapy. A total of 3 wound infections occurred in the control group and none in the NPWT group. Overall there was a trend towards lower drain output and statistically significantly reduced infection rate in the NPWT group.

Conclusion:

In this short series, despite the NPWT patients having more additional risk factors for wound issues, they resulted in fewer infections. The sample size is not sufficient to have statistically significant reduction. Further evaluation on the value of NPWT in this patient group should be prospectively evaluated.

Acceleration of tendon-bone healing of anterior cruciate ligament graft using intermittent negative pressure in rabbits

Background

The purpose of this study was to test effects of negative pressure on tendon–bone healing after reconstruction of anterior cruciate ligament (ACL) in rabbits.

Methods

Hind legs of 24 New Zealand White rabbits were randomly selected as negative pressure group and the contralateral hind legs as control. Reconstruction of the ACL was done. Joints of the negative pressure side were placed with drainage tubes connecting the micro-negative pressure aspirator. Control side was placed with ordinary drainage tubes. Drainage tubes on both sides were removed at the same time 5 days after operation. After 6 weeks, joint fluid was drawn to detect the expression levels of interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α); at the same time, femur–ligament–tibia complex was obtained to determine tendon graft tension and to observe the histomorphology, blood vessels of the tendon–bone interface, and expression of vascular endothelial growth factor (VEGF).

Results

The maximum load breakage of tendon graft was significantly greater in the negative pressure group than in the control group (P < 0.05). Histological studies of the tendon–bone interface found that there was more new bone formation containing chondroid cells and aligned connective tissue in the negative pressure group than in the control group. Expression of VEGF was higher in the negative pressure group than in the control group (P < 0.01). Content of IL-1β and TNF-α in synovial fluid is lower in the negative pressure group than in the control group (P < 0.01).

Conclusions

Intermittent negative pressure plays an active role in tendon–bone healing and creeping substitution of ACL reconstruction in the rabbits.

Systematic review of the negative pressure wound therapy in kidney transplant recipients

AIM

To review negative pressure wound therapy (NPWT) as an important addition to the conventional methods of wound management.

METHODS

A systematic review, performed by searching the PubMed, EMBASE and Cochrane Library databases, showed 11 case reports comprising a total of 22 kidney transplantation (KT) patients (range, 1 to 9), who were treated with NPWT. Application of NPWT was associated with successful healing of wounds, leg ulcer, lymphocele and urine leak from ileal conduit.

RESULTS

No complications related to NPWT were reported. However, there was paucity of robust data on the effectiveness of NPWT in KT recipients; therefore, prospective studies assessing its safety and efficacy of NPWT and randomised trials comparing the effectiveness of NPWT with alternative modalities of wound management in KT recipients is recommended.

CONCLUSION

Negative pressure incision management system, NPWT with instillation and endoscopic vacuum-assisted closure system are in investigational stage.

Slow-pull and different conventional suction techniques in endoscopic ultrasound-guided fine-needle aspiration of pancreatic solid lesions using 22-gauge needles

AIM

To evaluate the cytological diagnostic capacity and sample quality of the slow-pull technique and compare them with different suction techniques.

METHODS

From July 2010 to December 2015, 102 patients with pancreatic solid lesions who underwent endoscopic ultrasound-guided fine-needle aspiration (EUS-FNA) with 22-gauge needles were retrospectively evaluated. EUS-FNA diagnosis was based on a cytological examination, and final diagnosis was based on a comprehensive standard of cytological diagnosis, surgical pathology and clinical or imaging follow-up. Cytological specimens were characterized for cellularity and blood contamination. The cytological diagnostic capacity and sample quality of the slow-pull technique and suction techniques with 5-mL/10-mL/20-mL syringes were analyzed.

RESULTS

Of all of the EUS-FNA procedures, the slow-pull technique and suction techniques with 5-mL/10-mL/20-mL syringes were used in 31, 19, 34 and 18 procedures, respectively. There were significant differences between these four suction techniques in terms of cytological diagnostic accuracy (90.3% vs 63.2% vs 58.8% vs 55.6%, P = 0.019), sensitivity (88.2% vs 41.7% vs 40.0% vs 36.4%, P = 0.009) and blood contamination (score ≥ 2 for 29.0% vs 52.6% vs 70.6% vs 72.2%, P = 0.003). The accuracy and sensitivity of the slow-pull technique were significantly higher than those of the suction techniques using 5-mL (P = 0.03, P = 0.014), 10-mL (P = 0.005; P = 0.006) and 20-mL syringes (P = 0.01, P = 0.01). Blood contamination was significantly lower in the slow-pull technique than in the suction techniques with 10-mL (P = 0.001) and 20-mL syringes (P = 0.007).

CONCLUSION

The slow-pull technique may increase the cytological diagnostic accuracy and sensitivity with slight blood contamination during EUS-FNA when using 22-gauge needles for solid pancreatic masses.

Potential airborne pathogen transmission in a hospital with and without surge control ventilation system modifications

To better understand the transport of airborne particulate matter (PM) in hospital environments when surge control strategies are implemented, tests were conducted in a recently decommissioned hospital during a one-week period. An aerosol was released within a patient room and concentrations measured in the room and hallway with and without surge control ventilation system modifications. The average hallway protection efficiencies were high (>98%) both for the baseline ventilation configuration and when the ventilation system was modified for whole floor negative pressure, indicating very little PM reached the hallway. During entry/exit events through the patient room door into the hallway, the average minimum hallway protection efficiencies were lower during the modified ventilation operation (93-94%) than for the baseline operation (98-99%). These lower hallway protection efficiencies may be explained by the 52% reduction in the outdoor air ventilation being supplied to the hallway during the modified operation mode. This suggests that patient room doors should remain closed to control PM movement into the hallway. In addition, if there is concern about airborne infection transmission, an anteroom may be used to further reduce the transport of particles from the patient rooms to the hallways of the ward.

Well-promising outcomes with vacuum-assisted closure in an infected wound following laparotomy: A case report

Introducation

Negative pressure wound therapy (NPWT) represents an alternative method to optimize conditions for wound healing. Delayed wound closure is a significant health problem, which is directly associated with pain and suffering from patient's aspect, as well with social and financial burden.

Presentation of case

We report a case of vacuum-assisted wound therapy with hypertonic solution distillation and continuous negative pressure application, in an infected wound after laparotomy for incisional hernia reconstruction with mesh placement. Negative pressure was initiated at the wound margins after failure of conventional treatment with great outcomes, achieving a total closure of the incision within two weeks.

Discussion

Each wound has particular characteristics which must be managed. Vacuum assisted closure (VAC) with continuous negative pressure and simultaneous wound instillation and cleanse can provide optimum results, reducing the cavity volume, by newly produced granulated tissue.

Conclusion

The simultaneous use of instillation and constant pressure seemed to be superior in comparison with NPWT alone. Compared to conventional methods, the use of VAC ends to better outcomes, in cases of infected wounds following laparotomy.

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A VAC device with automated solution distribution (with saline solution plus hypertonic saline), continuous pressure of −125 mmHg with equal distribution was applied.

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Within 4 days bacterial culture was negative.

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On the 7th day the wound was half in diameter and depth.

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After 15 days in total, therapy was discontinued achieving closure.

A quantitative cell modeling and wound-healing analysis based on the Electric Cell-substrate Impedance Sensing (ECIS) method

In this paper, a quantitative modeling and wound-healing analysis of fibroblast and human keratinocyte cells is presented. Our study was conducted using a continuous cellular impedance monitoring technique, dubbed Electric Cell-substrate Impedance Sensing (ECIS). In fact, we have constructed a mathematical model for quantitatively analyzing the cultured cell growth using the time series data directly derived by ECIS in a previous work. In this study, the applicability of our model into the keratinocyte cell growth modeling analysis was assessed first. In addition, an electrical "wound-healing" assay was used as a means to evaluate the healing process of keratinocyte cells at a variety of pressures. Two innovative and new-defined indicators, dubbed cell power and cell electroactivity, respectively, were developed for quantitatively characterizing the biophysical behavior of cells. We then employed the wavelet transform method to perform a multi-scale analysis so the cell power and cell electroactivity across multiple observational time scales may be captured. Numerical results indicated that our model can well fit the data measured from the keratinocyte cell culture for cell growth modeling analysis. Also, the results produced by our quantitative analysis showed that the wound healing process was the fastest at the negative pressure of 125mmHg, which consistently agreed with the qualitative analysis results reported in previous works.

Potential Danger of Pre-Pump Clamping on Negative Pressure-Associated Gaseous Microemboli Generation During Extracorporeal Life Support--An In Vitro Study

The objectives of this study were to investigate the relationship between revolution speed of a conventional centrifugal pump and negative pressure at the inlet of the pump by clamping the tubing upstream of the pump, and to verify whether negative pressure leads to gaseous microemboli (GME) production in a simulated adult extracorporeal life support (ECLS) system. The experimental circuit, including a Maquet Rotaflow centrifugal pump and a Medos Hilite 7000 LT polymethyl-pentene membrane oxygenator, was primed with packed red blood cells (hematocrit 35%). Negative pressure was created in the circuit by clamping the tubing upstream of the pump for 10 s, and then releasing the clamp. An emboli detection and classification quantifier was used to record GME volume and count at pre-oxygenator and post-oxygenator sites, and pressure and flow rate data were collected using a custom-based data acquisition system. All trials were conducted at 36°C at revolution speeds of 2000-4000 rpm (500 rpm increment). The flow rates were 1092.5-4708.4 mL/min at the revolution speeds of 2000-4000 rpm. Higher revolution speed generated higher negative pressure at the pre-pump site when clamping the tubing upstream of the pump (-108.3 ± 0.1 to -462.0 ± 0.5 mm Hg at 2000-4000 rpm). Moreover, higher negative pressure was associated with a larger number and volume of GME at pre-oxygenator site after de-clamp (GME count 10,573 ± 271 at pre-oxygenator site at 4000 rpm). The results showed that there was a potential danger of delivering GME to the patient when clamping pre-pump tubing during ECLS using a centrifugal pump. Our results warrant further clinical studies to investigate this phenomenon.

A comparative study to evaluate the effect of limited access dressing (LAD) on burn wound healing

Biochemical and histopathological analyses are commonly used objective parameters in research and clinical fields to assess the healing status of burn wounds. In this study, the effect of newer intermittent negative-pressure wound therapy in combination with moist environment [limited access dressing (LAD)] on burn wound healing is studied. Various biochemical parameters like hydroxyproline, hexosamine and total protein, and antioxidants like reduced glutathione (GSH), glutathione peroxidase (GPx) and oxidative biomarker malondialdhyde (MDA) were measured in the granulation tissue. Histopathologically, necrotic tissue, amount of inflammatory infiltrate, angiogenesis and extracellular matrix deposition (ECM) were studied to determine wound healing. A total of 55 patients were divided into two groups as follows: LAD group (n = 28) and conventional dressing group (n = 27). Patients treated with LAD have shown significant increase in the mean levels of (±SD) hydroxyproline (75·2 ± 26·30 versus 27·8 ± 15·5; P = 0·010), hexosamine (9·0 ± 1·99 versus 8·0 ± 1·18; P = 0·038), total protein (15·6 ± 8·23 versus 10·26 ± 4·94; P = 0·003), GSH (7·40 ± 1·91 versus 5·1 ± 1·28; P = 0·037), GPx (112·6 ± 46·4 versus 92 ± 32·4; P = 0·016), and decrease in MDA (6·5 ± 2·24 versus 1 0·6 ± 3·8; P = 0·002). Histopathologically, between LAD and conventional dressing groups, there was a significant difference after 10 days of treatment (mean±SE) in necrotic tissue of (LAD versus conventional dressing groups = 10 ± 1·8 versus 11·9 ± 2·6; P = 0·033), inflammatory cells (8·4 ± 1·9 versus 13 ± 3·46; P = 0·021), new blood vessels (12·5 ± 2·87 versus 9·4 ± 1·7; P = 0·047), ECM deposit (12·9 ± 2·41 versus 9·68 ± 1·3; P = 0·018) and showed comparatively fewer inflammatory cells, increased and well-organised extracellular matrix deposit, more angiogenesis in LAD group as compared with that in conventional dressing group. To conclude, LAD exerts its beneficial effects on wound healing by reducing oxidative stress, decreasing necrotic tissue and amount of inflammatory infiltrate, and increasing ECM deposition and angiogenesis.

Bench-top testing of suction forces generated through endoscopic ultrasound-guided aspiration needles

BACKGROUND

Adequate needle size and tissue acquisition techniques for endoscopic ultrasound-guided fine needle aspiration (EUS-FNA) need further elucidation. Moreover, the actual negative pressure and suction forces of FNA needles remain unknown. We evaluated the suction forces of 19-gauge, 22-gauge, and 25-gauge conventional FNA needles and side hole aspiration needles using conventional negative pressure and the slow pull technique.

METHODS

Using a manometer, we determined the mean (SD) negative pressure and suction force for needle gauge, aspiration volume, and aspiration technique. We also evaluated the time to reach the maximum negative pressure.

RESULTS

Suction force was comparatively higher in the 19-gauge needle when 50 ml of negative pressure was applied. Suction force using the slow pull method was very weak at 5% of pressure found with conventional methods. With the use of a 20-ml syringe, the time to reach the maximum negative pressure was 4 s in the 19-gauge needle, 11 s in the 22-gauge needle, and 80 s in the 25-gauge needle.

CONCLUSIONS

Bench-top testing showed that suction force increases with a larger gauge needle and larger aspiration volume. The slow pull method produces a very weak suction force. The time to reach the maximum negative pressure was longest in the 25-gauge needle.

Long-term follow-up of negative pressure wound therapy with instillation: a limb salvage procedure?

Negative pressure wound therapy (NPWT) is a treatment to reduce oedema, stimulate granulation tissue formation, remove wound exudate and diminish wound area, thus preparing it for secondary healing, skin grafting or coverage with flaps. The association of instillation to NPWT (NPWTi) is a new method for treating severe wounds, in particular, limb lesions at high risk for amputation. This therapy helps to deliver instillation fluid automatically into the contaminated wound, before application of negative pressure. These steps, repeated cyclically, help to remove infectious material, leading to a better moist environment, a necessary condition for wound healing. We report our experience of treating three patients with complex wounds and associated noble structure exposition conservatively with NPWTi and flap coverage. In a long-term follow-up (5 years), we were able to achieve a stable surgery reconstruction on preserved limbs, without evidence of chronic infection and other sequelae or complications. Despite the fact that our experience is limited , as it is based on only a few cases, it suggests how NPWTi could be considered useful in a conservative approach to the treatment of acute complex wounds of the lower extremities. In these patients with high risk of amputation, a long-term follow-up becomes fundamental in order to evaluate wound bed status after NPTWi.

Negative pressure wound therapy: past, present and future

Negative pressure wound therapy (NPWT), which was introduced as a commercial product (V.A.C. Therapy, KCI USA, Inc., San Antonio, TX) less than 20 years ago, has revolutionised the treatment of complex wounds. Indicated for wide variety of wound types, NPWT is an adjunctive therapy that can be used safely in a range of care settings. Current research indicates that there are four primary NPWT mechanisms of action: macrodeformation, microdeformation, fluid removal and environmental control of the wound. The interaction of the primary mechanisms results in secondary effects through cell signalling (e.g. granulation tissue formation, cell proliferation and modulation of inflammation). Better understanding of the mechanisms of action also provides insight into future directions for NPWT research that could create better solutions for patients with complex wounds.

Influence of continuous negative pressure in the rat middle ear

OBJECTIVES/HYPOTHESIS

High negative pressure in the middle ear was thought to be closely related to the etiology of retraction-type cholesteatoma. Recently, it has been detected that mechanical forces are important factors in epithelial turnover and affect cytoskeletal remodeling. Continuous negative pressure in the middle ear may possibly accelerate the proliferation and differentiation of epithelial cells of the tympanic membrane.

STUDY DESIGN

Animal experimental study.

METHODS

Eleven adult male Sprague-Dawley rats were used, and continuous negative pressure was loaded by connecting a catheter from the rat's middle ear to the supply route of an implantable microinfusion pump, iPRECIO. At 7 days after implantation of the device, an otoendoscopic examination and micro-computed tomography (CT) analysis of the temporal bone were performed; the temporal bones were then collected for histological and immunohistochemical analysis. The degree of proliferation and differentiation of epithelial cells of the tympanic membrane was investigated immunohistochemically using the anti-cytokeratin-5 and anti-cytokeratin-10 antibodies.

RESULTS

Otoendoscopic examination revealed retraction of the pars flaccida in all of the ears under negative pressure. In the micro-CT analysis, soft tissue density area in the hypotympanum was observed in all ears under negative pressure. Histological analysis revealed thickened epithelium of the pars flaccida. In this region, the thickness of layers with cytokeratin-5-positive cells and cytokeratin-10-positive cells were increased.

CONCLUSIONS

Continuous negative pressure in the middle ear can lead to thickening of the epithelium of the pars flaccida, and may accelerate the proliferation and differentiation of epithelial cells.

Management of fistula of ileal conduit in open abdomen by intra-condoit negative pressure system

INTRODUCTION

We aimed to present the management of a patient with fistula of ileal conduit in open abdomen by intra-condoid negative pressure in conjunction with VAC Therapy and dynamic wound closure system (ABRA).

PRESENTATION OF CASE

65-Year old man with bladder cancer underwent radical cystectomy and ileal conduit operation. Fistula from uretero-ileostomy anastomosis and ileus occurred. The APACHE II score was 23, Mannheim peritoneal index score was 38 and Björck score was 3. The patient was referred to our clinic with ileus, open abdomen and fistula of ileal conduit. Patient was treated with intra-conduid negative pressure, abdominal VAC therapy and ABRA.

DISCUSSION

Management of urine fistula like EAF in the OA may be extremely challenging. Especially three different treatment modalities of EAF are established in recent literature. They are isolation of the enteric effluent from OA, sealing of EAF with fibrin glue or skin flep and resection of intestine including EAF and re-anastomosis. None of these systems were convenient to our case, since urinary fistula was deeply situated in this patient with generalized peritonitis and ileus.

CONCLUSION

Application of intra-conduid negative pressure in conjunction with VAC therapy and ABRA is life saving strategies to manage open abdomen with fistula of ileal conduit.

Comparison of central line-associated bloodstream infection rates when changing to a zero fluid displacement intravenous needleless connector in acute care settings

This was a multicenter, quasiexperimental, 140-month, acute care study comparing central line-associated bloodstream infection rates associated with positive or negative intravenous connectors to a zero fluid displacement connector. A decrease in central line-associated bloodstream infections was found after changing from either negative or positive intravenous connectors to the zero fluid displacement connector (P = .004) with total cost savings of over $3 million.

Intrarectal negative pressure system in the management of open abdomen with colorectal fistula: A case report

INTRODUCTION

To present the management of open abdomen with colorectal fistula by application of intrarectal negative pressure system (NPS) in addition to abdominal NPS.

PRESENTATION OF CASE

Twenty-year old man had a history of injuries by a close-range gunshot to the abdomen eight days ago and he had been treated by bowel repairs, resections, jejunal anastomosis and Hartman's procedure. He was referred to our center after deterioration, evisceration with open abdomen and enteric fistula in septic shock. There were edematous, fibrinous bowels and large multiple fistulas from the edematous rectal stump. APACHE II, Mannheim Peritoneal Index and Björck scores were 18, 33 and 3, respectively (expected mortality 100%). After intensive care for 5 days, he was treated by abdominal and intrarectal NPS. NPS repeated for 5 times and the fistula was recovered on day 18 completely. Fascial closure was facilitated with a dynamic abdominal closure system (ABRA) and he was discharged on day 33 uneventfully. There was no herniation and any other problem after 12 months follow-up.

DISCUSSION

Management of fistula in OA can be extremely challenging. Floating stoma, fistula VAC, nipple VAC, ring and silo VAC, fistula intubation systems are used for isolation of the enteric effluent from OA. Several biologic dressings such as acellular dermal matrix, pedicled flaps have been used to seal the fistula opening with various success. Resection of the involved enteric loop and a new anastomosis of the intestine is very hard and rarely possible. In all of these reports, usually patients are left to heal with a giant hernia. In contrast to this, there is no hernia in our case during one year follow up period.

CONCLUSION

Combination of intra and extra luminal negative pressure systems and ABRA is a safe and successful method to manage open abdomen with colorectal fistula.

Vacuum-assisted closure therapy as an alternative treatment of subcutaneous emphysema

Vacuum-assisted closure therapy is an alternative method for a massive subcutaneous emphysema treatment. It is easily applicable and shows rapid effectiveness in massive subcutaneous emphysema, intractable with chest tube drainage.

Negative pressure wound therapy for inguinal lymphatic complications in critically ill patients

Purpose

In this study, we investigated the therapeutic potential of regulated negative pressure vacuum-assisted wound therapy for inguinal lymphatic complications in critically ill, liver transplant recipients.

Methods

The great saphenous vein was harvested for hepatic vein reconstruction during liver transplantation in 599 living-donor liver transplant recipients. Fourteen of the recipients (2.3%) developed postoperative inguinal lymphatic complications and were treated with negative pressure wound therapy, and they were included in this study.

Results

The average total duration of negative pressure wound therapy was 23 days (range, 11 to 42 days). Complete resolution of the lymphatic complications and wound healing were achieved in all 14 patients, 5 of whom were treated in hospital and 9 as outpatients. There was no clinically detectable infection, bleeding or recurrence after an average follow-up of 27 months (range, 7 to 36 months).

Conclusion

Negative pressure wound therapy is an effective, readily-available treatment option that is less invasive than exploration and ligation of leaking lymphatics and provides good control of drainage and rapid wound closure in critically ill patients.

The use of negative-pressure wound therapy to manage enteroatmospheric fistulae in two patients with large abdominal wounds

Enteric fistulae are a relatively common complication of bowel surgery or in surgery where the bowel has been exposed. Fistulae can present a significant threat to patients' well-being. Changes in surgical techniques and in particular the rise in damage control surgery for emergency patients have led to an increase in open abdominal wounds. The presence of an enteroatmospheric fistula on the surface of a wound can cause a number of distressing symptoms/issues for the patient whilst providing a significant challenge for the clinician. The loss of fluid, proteins and electrolytes will place the patient in danger of becoming hypokalaemic and malnourished. A variety of techniques are available, most refer to a method of isolating the fistula using stoma rings or washers and ostomy paste. The role of negative pressure in the management of wounds with fistula is in its infancy; however, there is evidence to suggest that isolation techniques can be advantageous in managing wounds with fistulae.

Negative pressure pulmonary oedema after septoplasty

Negative pressure pulmonary oedema (NPPO) is an anaesthetic complication due to acute obstruction of the upper airway, whose main cause is laryngospasm. The pathophysiology involves a strong negative intrapleural pressure during inspiration against a closed glottis, which triggers excessive pressure in the pulmonary microvasculature. Although its diagnosis can be difficult, its recognition helps to minimise morbidity and mortality. This article presents a case of NPPO due to postextubation laryngospasm.

Mechanical behaviour analyses of sap ascent in vascular plants

A pure mechanical anisotropic model of a tree trunk has been developed based on the 3D finite element method. It simulates the microscopic structure of vessels in the trunk of a European beech (Fagus sylvatica) in order to study and analyse its mechanical behaviour with different configurations of pressures in the conduits of xylem and phloem. The dependence of the strains at the inner bark was studied when sap pressure changed. The comparison with previously published experimental data leads to the conclusion that a great tensile stress-or 'negative pressure'-must exist in the water column in order to achieve the measured strains if only the mechanical point of view is taken into account. Moreover, the model can help to design experiments where qualitatively knowing the strains and the purely mechanical behaviour of the tree is required.