Central venous catheter tip misplacement: A multicentre cohort study of 8556 thoracocervical central venous catheterisations.

BACKGROUND: There is a paucity of data on the incidence of central venous catheter tip misplacements after the implementation of ultrasound guidance during insertion. The aims of the present study were to determine the incidence of tip misplacements and to identify independent variables associated with tip misplacement. METHODS: All jugular and subclavian central venous catheter insertions in patients ≥16 years with a post-procedural chest radiography at four hospitals were included. Each case was reviewed for relevant catheter data and radiologic evaluations of chest radiographies. Tip misplacements were classified as 'any tip misplacement', 'minor tip misplacement' or 'major tip misplacement'. Multivariable logistic regression analyses were used to investigate associations between predefined independent variables and tip misplacements. RESULTS: A total of 8556 central venous catheter insertions in 5587 patients were included. Real-time ultrasound guidance was used in 91% of all insertions. Any tip misplacement occurred (95% confidence interval) in 3.7 (3.3-4.1)% of the catheterisations, and 2.1 (1.8-2.4)% were classified as major tip misplacements. The multivariable logistic regression analyses showed that female patient gender, subclavian vein insertions, number of skin punctures and limited operator experience were associated with a higher risk of major tip misplacement, whereas increasing age and height were associated with a lower risk. CONCLUSIONS: In this large prospective multicentre cohort study, performed in the ultrasound-guided era, we demonstrated the incidence of tip misplacements to be 3.7 (3.3-4.1)%. Right internal jugular vein catheterisation had the lowest incidence of both minor and major tip misplacement.

Operator gender differences in major mechanical complications after central line insertions: a subgroup analysis of a prospective multicentre cohort study.

BACKGROUND: A previous study on mechanical complications after central venous catheterisation demonstrated differences in complication rates between male and female operators. The objective of this subgroup analysis was to further investigate these differences. The hypothesis was that differences in distribution of predefined variables between operator genders could be identified. METHODS: This was a subgroup analysis of a prospective, multicentre, observational cohort study conducted between March 2019 and December 2020 including 8 586 patients ≥ 16 years receiving central venous catheters at four emergency care hospitals. The main outcome measure was major mechanical complications defined as major bleeding, severe cardiac arrhythmia, pneumothorax, arterial catheterisation, and persistent nerve injury. Independent t-test and χ2 test were used to investigate differences in distribution of major mechanical complications and predefined variables between male and female operators. Multivariable logistic regression analysis was used to determine association between operator gender and major mechanical complications. RESULTS: Female operators had a lower rate of major mechanical complications than male operators (0.4% vs 0.8%, P = .02), were less experienced (P < .001), had more patients with invasive positive pressure ventilation (P < .001), more often chose the internal jugular vein (P < .001) and more frequently used ultrasound guidance (P < .001). Male operators more often chose the subclavian vein (P < .001) and inserted more catheters with bore size ≥ 9 Fr (P < .001). Multivariable logistic regression analysis showed that male operator gender was associated with major mechanical complication (OR 2.67 [95% CI: 1.26-5.64]) after correction for other relevant independent variables. CONCLUSIONS: The hypothesis was confirmed as differences in distribution of predefined variables between operator genders were found. Despite being less experienced, female operators had a lower rate of major mechanical complications. Furthermore, male operator gender was independently associated with a higher risk of major mechanical complications. Future studies are needed to further investigate differences in risk behaviour between male and female operators. TRIAL REGISTRATION: Clinicaltrials.gov identifier: NCT03782324. Date of registration: 20/12/2018.

Major immediate insertion-related complications after central venous catheterisation and associations with mortality, length of hospital stay, and costs: A prospective observational study.

BACKGROUND: It is well-known that infectious complications after central venous catheterisation are associated with increased mortality, length of hospital stay and costs. However, there are limited data regarding such associations for immediate insertion-related complications. Therefore, the aim of this study was to investigate whether major immediate insertion-related complications are associated with mortality, length of hospital stay and costs. METHODS: This was a preplanned substudy to the CVC-MECH trial on immediate insertion-related complications after central venous catheterisation in the ultrasound-guided era. Patients receiving central venous catheters at Skåne University Hospital from 2 March 2019 to 31 December 2020 were prospectively included. Patient characteristics, clinical data and costs were automatically collected from medical journals and the patient administration system. Associations between major immediate insertion-related complications and mortality, length of hospital stay and costs were studied by multivariable logistic and linear regression analyses. RESULTS: In total, 6671 patients were included, of whom 0.5% suffered major immediate insertion-related complications. Multivariable analyses, including surrogates for general morbidity, showed associations between major immediate insertion-related complications and 30-day (odds ratio 2.46 [95% CI 1.05-5.77]), 90-day (2.90 [1.35-6.21]) and 180-day (2.26 [1.05-4.83]) mortality. There were no associations between major immediate insertion-related complications and increased length of hospital stay or costs. CONCLUSION: This study showed that major immediate insertion-related complications, although not directly responsible for any death, were associated with increased 30-day, 90-day and 180-day mortality. These findings clearly demonstrate the importance of using all possible means to prevent avoidable insertion-related complications after central venous catheterisation.

Ultrasound-guided subclavian vein catheterisation with a needle guide (ELUSIVE): protocol for a randomised controlled study.

INTRODUCTION: Central venous catheters are indispensable in modern healthcare. Unfortunately, they are accompanied by minor as well as major complications, leading to increased morbidity, mortality and costs. Immediate insertion-related complications (mechanical complications) have decreased due to the implementation of real-time ultrasound guidance, but they still occur and additional efforts to enhance patient safety are warranted. This study aims to investigate whether the use of a needle guide mounted on the ultrasound probe in subclavian catheterisations may decrease the number of catheterisations with >1 skin puncture (primary outcome). METHODS AND ANALYSIS: This is an investigator-initiated, non-commercial, randomised, controlled, parallel-group study conducted at Skåne University Hospital, Lund, Sweden. Adults (≥18 years) with a clinical indication for a subclavian central venous catheter and the ability to give written informed consent will be eligible for inclusion. Exclusion criteria include subclavian catheterisation deemed unsuitable based on the preprocedural ultrasound examination. Patients will be randomised to catheterisation by certified operators using a microconvex probe (long-axis, in-plane technique) with (n=150) or without (n=150) a needle guide. The ultrasound imaging from the procedures will be recorded and assessed by two reviewers individually. The assessors will be blinded for group affiliation. Secondary outcomes include the total number of skin punctures, mechanical complications, time to successful venous puncture, number of failed catheterisations and operator satisfaction with the needle guide at the end of the study period.Recruitment started on 8 November 2022 and will continue until the sample size is achieved. ETHICS AND DISSEMINATION: This study was approved by the Swedish Ethical Review Authority (#2022-04073-01) and the Swedish Medical Products Agency (#5.1-2022-52130; CIV-21-12-038367). The findings will be submitted to an international peer-reviewed journal. TRIAL REGISTRATION NUMBER: NCT05513378, clinicaltrials.gov.

Central venous stenosis after subclavian versus internal jugular dialysis catheter insertion (CITES) in adults in need of a temporary central dialysis catheter: study protocol for a two-arm, parallel-group, non-inferiority randomised controlled trial.

BACKGROUND: The right internal jugular vein is currently recommended for temporary central dialysis catheters (tCDC) based on results from previous studies showing a lower incidence of central vein stenosis compared to the subclavian vein. Data is however conflicting, and there are several advantages when the subclavian route is used for tCDCs. This prospective, controlled, randomised, non-inferiority study aims to compare the incidence of post-catheterisation central vein stenosis between the right subclavian and the right internal jugular routes. METHODS: Adult patients needing a tCDC will be included from several hospitals and randomised to either subclavian or internal jugular vein catheterisation with a silicone tCDC. Inclusion continues until 50 patients in each group have undergone a follow-up CT venography. The primary outcome is the incidence of post-catheterisation central vein stenosis detected by a CT venography performed 1.5 to 3 months after removal of the tCDC. Secondary outcomes include between-group comparisons of (I) the patients' experience of discomfort and pain, (II) any dysfunction of the tCDC during use, (III) catheterisation success rate and (IV) the number of mechanical complications. Furthermore, the ability to detect central vein stenosis by a focused ultrasound examination will be evaluated using the CT venography as golden standard. DISCUSSION: The use of the subclavian route for tCDC placement has largely been abandoned due to older studies with various methodological issues. However, the subclavian route offers several advantages for the patient. This trial is designed to provide robust data on the incidence of central vein stenosis after silicone tCDC insertion in the era of ultrasound-guided catheterisations. TRIAL REGISTRATION: Clinicaltrials.gov; NCT04871568. Prospectively registered on May 4, 2021.

Hypothermia versus normothermia after out-of-hospital cardiac arrest; the effect on post-intervention serum concentrations of sedatives and analgesics and time to awakening.

BACKGROUND: This study investigated the association of two levels of targeted temperature management (TTM) after out-of-hospital cardiac arrest (OHCA) with administered doses of sedative and analgesic drugs, serum concentrations, and the effect on time to awakening. METHODS: This substudy of the TTM2-trial was conducted at three centers in Sweden, with patients randomized to either hypothermia or normothermia. Deep sedation was mandatory during the 40-hour intervention. Blood samples were collected at the end of TTM and end of protocolized fever prevention (72 hours). Samples were analysed for concentrations of propofol, midazolam, clonidine, dexmedetomidine, morphine, oxycodone, ketamine and esketamine. Cumulative doses of administered sedative and analgesic drugs were recorded. RESULTS: Seventy-one patients were alive at 40 hours and had received the TTM-intervention according to protocol. 33 patients were treated at hypothermia and 38 at normothermia. There were no differences between cumulative doses and concentration and of sedatives/analgesics between the intervention groups at any timepoint. Time until awakening was 53 hours in the hypothermia group compared to 46 hours in the normothermia group (p = 0.09). CONCLUSION: This study of OHCA patients treated at normothermia versus hypothermia found no significant differences in dosing or concentration of sedatives or analgesic drugs in blood samples drawn at the end of the TTM intervention, or at end of protocolized fever prevention, nor the time to awakening.

Veno-arterial CO2 difference and lactate for prediction of early mortality after cardiac arrest.

Patients admitted to intensive care after cardiac arrest are at risk of circulatory shock and early mortality due to cardiovascular failure. The aim of this study was to evaluate the ability of the veno-arterial pCO2 difference (∆pCO2 ; central venous CO2 - arterial CO2 ) and lactate to predict early mortality in postcardiac arrest patients. This was a pre-planned prospective observational sub-study of the target temperature management 2 trial. The sub-study patients were included at five Swedish sites. Repeated measurements of ∆pCO2 and lactate were conducted at 4, 8, 12, 16, 24, 48, and 72 h after randomization. We assessed the association between each marker and 96-h mortality and their prognostic value for 96-h mortality. One hundred sixty-three patients were included in the analysis. Mortality at 96 h was 17%. During the initial 24 h, there was no difference in ∆pCO2 levels between 96-h survivors and non-survivors. ∆pCO2 measured at 4 h was associated with an increased risk of death within 96 h (adjusted odds ratio: 1.15; 95% confidence interval [CI]: 1.02-1.29; p = .018). Lactate levels were associated with poor outcome over multiple measurements. The area under the receiving operating curve to predict death within 96 h was 0.59 (95% CI: 0.48-0.74) and 0.82 (95% CI: 0.72-0.92) for ∆pCO2 and lactate, respectively. Our results do not support the use of ∆pCO2 to identify patients with early mortality in the postresuscitation phase. In contrast, non-survivors demonstrated higher lactate levels in the initial phase and lactate identified patients with early mortality with moderate accuracy.

Mechanical complications after central venous catheterisation in the ultrasound-guided era: a prospective multicentre cohort study.

BACKGROUND: Limited data are available on the incidence of mechanical complications after ultrasound-guided central venous catheterisation. We aimed to determine the incidence of mechanical complications in hospitals where real-time ultrasound guidance is clinical practice for central venous access and to identify variables associated with mechanical complications. METHODS: All central venous catheter insertions in patients ≥16 yr at four emergency care hospitals in Sweden from March 2, 2019 to December 31, 2020 were eligible for inclusion. Every insertion was monitored for complete documentation and occurrence of mechanical complications within 24 h after catheterisation. Multivariable logistic regression analyses were used to determine associations between predefined variables and mechanical complications. RESULTS: In total, 12 667 catheter insertions in 8586 patients were included. The incidence (95% confidence interval [CI]) of mechanical complications was 7.7% (7.3-8.2%), of which 0.4% (0.3-0.5%) were major complications. The multivariable analyses showed that patient BMI <20 kg m-2 (odds ratio 2.69 [95% CI: 1.17-5.62]), male operator gender (3.33 [1.60-7.38]), limited operator experience (3.11 [1.64-5.77]), and increasing number of skin punctures (2.18 [1.59-2.88]) were associated with major mechanical complication. Subclavian vein catheterisation was associated with pneumothorax (5.91 [2.13-17.26]). CONCLUSIONS: The incidence of major mechanical complications is low in hospitals where real-time ultrasound guidance is the standard of care for central venous access. Several variables independently associated with mechanical complications can be used for risk stratification before catheterisation procedures, which might further reduce complication rates. CLINICAL TRIAL REGISTRATION: NCT03782324.

Biomarkers of brain injury after cardiac arrest; a statistical analysis plan from the TTM2 trial biobank investigators.

Background: Several biochemical markers in blood correlate with the magnitude of brain injury and may be used to predict neurological outcome after cardiac arrest. We present a protocol for the evaluation of prognostic accuracy of brain injury markers after cardiac arrest. The aim is to define the best predictive marker and to establish clinically useful cut-off levels for routine implementation. Methods: Prospective international multicenter trial within the Targeted Hypothermia versus Targeted Normothermia after Out-of-Hospital Cardiac Arrest (TTM2) trial in collaboration with Roche Diagnostics International AG. Samples were collected 0, 24, 48, and 72 hours after randomisation (serum) and 0 and 48 hours after randomisation (plasma), and pre-analytically processed at each site before storage in a central biobank. Routine markers neuron-specific enolase (NSE) and S100B, and neurofilament light, total-tau and glial fibrillary acidic protein will be batch analysed using novel Elecsys® electrochemiluminescence immunoassays on a Cobas e601 instrument. Results: Statistical analysis will be reported according to the Standards for Reporting Diagnostic accuracy studies (STARD) and will include comparisons for prediction of good versus poor functional outcome at six months post-arrest, by modified Rankin Scale (0-3 vs. 4-6), using logistic regression models and receiver operating characteristics curves, evaluation of mortality at six months according to biomarker levels and establishment of cut-off values for prediction of poor neurological outcome at 95-100% specificities. Conclusions: This prospective trial may establish a standard methodology and clinically appropriate cut-off levels for the optimal biomarker of brain injury which predicts poor neurological outcome after cardiac arrest.

Minimal guidewire length for central venous catheterization of the right subclavian vein: A CT-based consecutive case series.

BACKGROUND: Central venous catheter (CVC) misplacement occurs frequently after right subclavian vein catheterization. It can be avoided by using ultrasound to confirm correct guidewire tip position in the lower superior vena cava prior to CVC insertion. However, retraction of the guidewire during the CVC insertion may dislocate the guidewire tip from its desired and confirmed position, thereby resulting in CVC misplacement. The aim of this study was to determine the minimal guidewire length required to maintain correct guidewire tip position in the lower superior vena cava throughout an ultrasound-guided CVC placement in the right subclavian vein. METHODS: One hundred adult patients with a computed tomography scan of the chest were included. By using multiplanar reconstructions from thin-sliced images, the distance from the most plausible distal puncture site of the right subclavian vein to the optimal guidewire tip position in the lower superior vena cava was measured (vessel length). In addition, measurements of equipment in common commercial over-the-wire percutaneous 15-16 cm CVC kits were performed. The 95th percentile of the vessel length was used to calculate the required minimal guidewire length for each CVC kit. RESULTS: The 95th percentile of the vessel length was 153 mm. When compared to the calculated minimal guidewire length, the guidewires were up to 108 mm too short in eight of eleven CVC kits. CONCLUSION: After confirmation of a correct guidewire position, retraction of the guidewire tip above the junction of the brachiocephalic veins should be avoided prior to CVC insertion in order to preclude dislocation of the catheter tip towards the right internal jugular vein or the left subclavian vein. This study shows that many commercial over-the-wire percutaneous 15-16 cm CVC kits contain guidewires that are too short for right subclavian vein catheterization, i.e., guidewire retraction is needed prior to CVC insertion.

Hypothermia versus Normothermia after Out-of-Hospital Cardiac Arrest.

BACKGROUND: Targeted temperature management is recommended for patients after cardiac arrest, but the supporting evidence is of low certainty. METHODS: In an open-label trial with blinded assessment of outcomes, we randomly assigned 1900 adults with coma who had had an out-of-hospital cardiac arrest of presumed cardiac or unknown cause to undergo targeted hypothermia at 33°C, followed by controlled rewarming, or targeted normothermia with early treatment of fever (body temperature, ≥37.8°C). The primary outcome was death from any cause at 6 months. Secondary outcomes included functional outcome at 6 months as assessed with the modified Rankin scale. Prespecified subgroups were defined according to sex, age, initial cardiac rhythm, time to return of spontaneous circulation, and presence or absence of shock on admission. Prespecified adverse events were pneumonia, sepsis, bleeding, arrhythmia resulting in hemodynamic compromise, and skin complications related to the temperature management device. RESULTS: A total of 1850 patients were evaluated for the primary outcome. At 6 months, 465 of 925 patients (50%) in the hypothermia group had died, as compared with 446 of 925 (48%) in the normothermia group (relative risk with hypothermia, 1.04; 95% confidence interval [CI], 0.94 to 1.14; P = 0.37). Of the 1747 patients in whom the functional outcome was assessed, 488 of 881 (55%) in the hypothermia group had moderately severe disability or worse (modified Rankin scale score ≥4), as compared with 479 of 866 (55%) in the normothermia group (relative risk with hypothermia, 1.00; 95% CI, 0.92 to 1.09). Outcomes were consistent in the prespecified subgroups. Arrhythmia resulting in hemodynamic compromise was more common in the hypothermia group than in the normothermia group (24% vs. 17%, P<0.001). The incidence of other adverse events did not differ significantly between the two groups. CONCLUSIONS: In patients with coma after out-of-hospital cardiac arrest, targeted hypothermia did not lead to a lower incidence of death by 6 months than targeted normothermia. (Funded by the Swedish Research Council and others; TTM2 ClinicalTrials.gov number, NCT02908308.).

Bedside interpretation of simplified continuous EEG after cardiac arrest.

BACKGROUND: Continuous EEG-monitoring (cEEG) in the ICU is recommended to assess prognosis and detect seizures after cardiac arrest but implementation is often limited by the lack of EEG-technicians and experts. The aim of the study was to assess ICU physicians ability to perform preliminary interpretations of a simplified cEEG in the post cardiac arrest setting. METHODS: Five ICU physicians received training in interpretation of simplified cEEG - total training duration 1 day. The ICU physicians then interpreted 71 simplified cEEG recordings from 37 comatose survivors of cardiac arrest. The cEEG included amplitude-integrated EEG trends and two channels with original EEG-signals. Basic EEG background patterns and presence of epileptiform discharges or seizure activity were assessed on 5-grade rank-ordered scales based on standardized EEG terminology. An EEG-expert was used as reference. RESULTS: There was substantial agreement (κ 0.69) for EEG background patterns and moderate agreement (κ 0.43) for epileptiform discharges between ICU physicians and the EEG-expert. Sensitivity for detecting seizure activity by ICU physicians was limited (50%), but with high specificity (87%). CONCLUSIONS: After cardiac arrest, preliminary bedside interpretations of simplified cEEGs by trained ICU physicians may allow earlier detection of clinically relevant cEEG changes, prompting changes in patient management as well as additional evaluation by an EEG-expert. This strategy requires awareness of limitations of both the simplified electrode montage and the cEEG interpretations performed by ICU physicians. cEEG evaluation by an expert should not be delayed.

Research protocol for mechanical complications after central venous catheterisation: a prospective controlled multicentre observational study to determine incidence and risk factors of mechanical complications within 24 hours after cannulation.

INTRODUCTION: Central venous catheterisation is a common procedure in intensive care therapy and the use of central venous catheters is essential for treatment of many medical disorders. Although rare, central venous catheterisation is associated with mechanical complications that can be life-threatening if untreated. Real-time ultrasound guidance reduces the incidence of mechanical complications when compared with the anatomic landmark method. The purpose of this study is to determine the incidence of and potential risk factors associated with early mechanical complications of central venous catheterisation in an era where real-time ultrasound guidance has become clinical practice. METHODS AND ANALYSIS: This is a prospective, controlled, multicentre, observational study. All participating hospitals follow the same clinical guidelines for central venous catheterisation. Each central venous catheter insertion will be recorded in the common electronic chart system according to a recently revised template. An automated script-based search will identify all recorded central venous catheter insertion templates during the study period and relevant variables will be extracted. Outcome measures and independent variables are pre-defined in this study protocol. Multivariable and univariable logistic regression analysis will be used to determine associations and risk factors of mechanical complications. ETHICS AND DISSEMINATION: The Regional Ethical Review Board in Lund, Sweden has approved this study. The results will be submitted for publication in peer-reviewed medical journals and presented at national and international scientific meetings. TRIAL REGISTRATION NUMBER: NCT03782324.

Mechanical effects of negative pressure wound therapy on abdominal wounds - effects of different pressures and wound fillers.

The mechanical deformation of the wound edge resulting from negative pressure wound therapy (NPWT) at the standard setting of around -120 mmHg has positive effects in promoting wound healing. However, it may cause pain to the patient during treatment. It is therefore important to study the mechanical effects of the wound edges using lower pressure and different wound fillers. Abdominal wounds were created on eight pigs. The wounds were sealed for NPWT using foam or gauze. Negative pressures between -20 and -160 mmHg were applied, and the decrease in wound diameter and the force with which the edges of the wound were drawn together (wound edge force) were measured. Increasing levels of negative pressure resulted in a gradual decrease in wound diameter and increase in wound edge force and reached a maximum at -120 mmHg, which is the pressure commonly used in clinical practice. Both the decrease in wound diameter and the increase in wound edge force was greater with foam than with gauze. A pressure of -80 mmHg has only 15% less effect than -120 mmHg, while a lower pressure (-40 mmHg) diminished the effects on diameter and force markedly. The NPWT-induced decrease in wound diameter and increase in wound edge force are greater at higher levels of negative pressure and when using foam than when using gauze as a wound filler. It may be possible to tailor the type of wound filler and level of negative pressure to obtain the best balance between wound healing and patient comfort.

Dysglycemia, Glycemic Variability, and Outcome After Cardiac Arrest and Temperature Management at 33°C and 36°C.

OBJECTIVES: Dysglycemia and glycemic variability are associated with poor outcomes in critically ill patients. Targeted temperature management alters blood glucose homeostasis. We investigated the association between blood glucose concentrations and glycemic variability and the neurologic outcomes of patients randomized to targeted temperature management at 33°C or 36°C after cardiac arrest. DESIGN: Post hoc analysis of the multicenter TTM-trial. Primary outcome of this analysis was neurologic outcome after 6 months, referred to as "Cerebral Performance Category." SETTING: Thirty-six sites in Europe and Australia. PATIENTS: All 939 patients with out-of-hospital cardiac arrest of presumed cardiac cause that had been included in the TTM-trial. INTERVENTIONS: Targeted temperature management at 33°C or 36°C. MEASUREMENTS AND MAIN RESULTS: Nonparametric tests as well as multiple logistic regression and mixed effects logistic regression models were used. Median glucose concentrations on hospital admission differed significantly between Cerebral Performance Category outcomes (p < 0.0001). Hyper- and hypoglycemia were associated with poor neurologic outcome (p = 0.001 and p = 0.054). In the multiple logistic regression models, the median glycemic level was an independent predictor of poor Cerebral Performance Category (Cerebral Performance Category, 3-5) with an odds ratio (OR) of 1.13 in the adjusted model (p = 0.008; 95% CI, 1.03-1.24). It was also a predictor in the mixed model, which served as a sensitivity analysis to adjust for the multiple time points. The proportion of hyperglycemia was higher in the 33°C group compared with the 36°C group. CONCLUSION: Higher blood glucose levels at admission and during the first 36 hours, and higher glycemic variability, were associated with poor neurologic outcome and death. More patients in the 33°C treatment arm had hyperglycemia.

A rigid disc for protection of exposed blood vessels during negative pressure wound therapy.

BACKGROUND: There are increasing reports of serious complications and deaths associated with negative pressure wound therapy (NPWT). Bleeding may occur when NPWT is applied to a wound with exposed blood vessels. Inserting a rigid disc in the wound may protect these structures. The authors examined the effects of rigid discs on wound bed tissue pressure and blood flow through a large blood vessel in the wound bed during NPWT. METHODS: Wounds were created over the femoral artery in the groin of 8 pigs. Rigid discs were inserted. Wound bed pressures and arterial blood flow were measured during NPWT. RESULTS: Pressure transduction to the wound bed was similar for control wounds and wounds with discs. Blood flow through the femoral artery decreased in control wounds. When a disc was inserted, the blood flow was restored. CONCLUSIONS: NPWT causes hypoperfusion in the wound bed tissue, presumably as a result of mechanical deformation. The insertion of a rigid barrier alleviates this effect and restores blood flow.

The use of a rigid disc to protect exposed structures in wounds treated with negative pressure wound therapy: effects on wound bed pressure and microvascular blood flow.

There are increasing reports of deaths and serious complications associated with the use of negative pressure wound therapy (NPWT). Bleeding may occur in patients when NPWT is applied to a wound with exposed blood vessels or vascular grafts, possibly due to mechanical deformation and hypoperfusion of the vessel walls. Recent evidence suggests that using a rigid barrier disc to protect underlying tissue can prevent this mechanical deformation. The aim of this study was to examine the effect of rigid discs on the tissue exposed to negative pressure with regard to tissue pressure and microvascular blood flow. Peripheral wounds were created on the backs of eight pigs. The pressure and microvascular blood flow in the wound bed were measured when NPWT was applied. The wound was filled with foam, and rigid discs of different designs were inserted between the wound bed and the foam. The discs were created with or without channels (to accommodate exposed sensitive structures such as blood vessels and nerves), perforations, or a porous dressing that covered the underside of the discs (to facilitate pressure transduction and fluid evacuation). When comparing the results for pressure transduction to the wound bed, no significant differences were found using different discs covered with dressing, whereas pressure transduction was lower with bare discs. Microvascular blood flow in the wound bed decreased by 49 ± 7% when NPWT was applied to control wounds. The reduction in blood flow was less in the presence of a protective disc (e.g., -6 ± 5% for a dressing-covered, perforated disc, p = 0.006). In conclusion, NPWT causes hypoperfusion of superficial tissue in the wound bed. The insertion of a rigid barrier counteracts this effect. The placement of a rigid disc over exposed blood vessels or nerves may protect these structures from rupture and damage.

Measurements of wound edge microvascular blood flow during negative pressure wound therapy using thermodiffusion and transcutaneous and invasive laser Doppler velocimetry.

The effects of negative pressure wound therapy (NPWT) on wound edge microvascular blood flow are not clear. The aim of the present study was therefore to further elucidate the effects of NPWT on periwound blood flow in a porcine peripheral wound model using different blood flow measurement techniques. NPWT at -20, -40, -80, and -125 mmHg was applied to a peripheral porcine wound (n = 8). Thermodiffusion, transcutaneous, and invasive laser Doppler velocimetry were used to measure the blood perfusion 0.5, 1.0, and 2.5 cm from the wound edge. Thermodiffusion (an invasive measurement technique) generally showed a decrease in perfusion close to the wound edge (0.5 cm), and an increase further from the edge (2.5 cm). Invasive laser Doppler velocimetry showed a similar response pattern, with a decrease in blood flow 0.5 cm from the wound edge and an increase further away. However, 1.0 cm from the wound edge blood flow decreased with high pressure levels and increased with low pressure levels. A different response pattern was seen with transcutaneous laser Doppler velocimetry, showing an increase in blood flow regardless of the distance from the wound edge (0.5, 1.0, and 2.5 cm). During NPWT, both increases and decreases in blood flow can be seen in the periwound tissue depending on the distance from the wound edge and the pressure level. The pattern of response depends partly on the measurement technique used. The combination of hypoperfusion and hyperperfusion caused by NPWT may accelerate wound healing.

The influence of different sizes and types of wound fillers on wound contraction and tissue pressure during negative pressure wound therapy.

Negative pressure wound therapy (NPWT) contracts the wound and alters the pressure in the tissue of the wound edge, which accelerates wound healing. The aim of this study was to examine the effect of the type (foam or gauze) and size (small or large) of wound filler for NPWT on wound contraction and tissue pressure. Negative pressures between --20 and --160 mmHg were applied to a peripheral porcine wound (n = 8). The pressure in the wound edge tissue was measured at distances of 0·1, 0·5, 1·0 and 2·0 cm from the wound edge and the wound diameter was determined. At 0·1 cm from the wound edge, the tissue pressure decreased when NPWT was applied, whereas at 0·5 cm it increased. Tissue pressure was not affected at 1·0 or 2·0 cm from the wound edge. The tissue pressure, at 0·5 cm from the wound edge, was greater when using a small foam than when using than a large foam. Wound contraction was greater when using a small foam than when using a large foam during NPWT. Gauze resulted in an intermediate wound contraction that was not affected by the size of the gauze filler. The use of a small foam to fill the wound causes considerable wound contraction and may thus be used when maximal mechanical stress and granulation tissue formation are desirable. Gauze or large amounts of foam result in less wound contraction which may be beneficial, for example when NPWT causes pain to the patient.

The influence on wound contraction and fluid evacuation of a rigid disc inserted to protect exposed organs during negative pressure wound therapy.

The use of a rigid disc as a barrier between the wound bed and the wound filler during negative pressure wound therapy (NPWT) has been suggested to prevent damage to exposed organs. However, it is important to determine that the effects of NPWT, such as wound contraction and fluid removal, are maintained during treatment despite the use of a barrier. This study was performed to examine the effect of NPWT on wound contraction and fluid evacuation in the presence of a rigid disc. Peripheral wounds were created on the backs of eight pigs. The wounds were filled with foam, and rigid discs of different designs were inserted between the wound bed and the foam. Wound contraction and fluid evacuation were measured after application of continuous NPWT at -80 mmHg. Wound contraction was similar in the presence and the absence of a rigid disc (84 ± 4% and 83 ± 3%, respectively, compared with baseline). Furthermore, the rigid disc did not affect wound fluid removal compared with ordinary NPWT (e.g. after 120 seconds, 71 ± 4 ml was removed in the presence and 73 ± 3 ml was removed in the absence of a disc). This study shows that a rigid barrier may be placed under the wound filler to protect exposed structures during NPWT without affecting wound contraction and fluid removal, which are two crucial features of NPWT.