Blood oxygenation and decarboxylation determinants during venovenous ECMO for respiratory failure in adults

Purpose

This study was designed to optimize the latest generation venovenous (vv)-extracorporeal membrane oxygenation (ECMO)-circuit configuration and settings based on the evaluation of blood oxygenation and CO₂ removal determinants in patients with severe acute respiratory distress syndrome (ARDS) on ultraprotective mechanical ventilation.

Methods

Blood gases and hemodynamic parameters were evaluated after changing one of three ECMO settings, namely, circuit blood flow, FiO_2ECMO (fraction of inspired oxygen in circuit), or sweep gas flow ventilating the membrane, while leaving the other two parameters at their maximum setting.

Results

Ten mechanically ventilated ARDS patients (mean age 44 ± 16 years; 6 males; mean hemoglobin 8.0 ± 1.8 g/dL) on ECMO for a mean of 9.0 ± 3.8 days) receiving femoro–jugular vv-ECMO were evaluated. vv-ECMO blood flow and FiO_2ECMO determined arterial oxygenation. Decreasing the ECMO flow from its baseline maximum value (5.8 ± 0.8 L/min) to 40 % less (2.4 ± 0.3 L/min) significantly decreased mean PaO₂ (arterial oxygen tension; 88 ± 24 to 45 ± 9 mm Hg; p < 0.001) and SaO₂ (oxygen saturation; 97 ± 2 to 82 ± 10 %; p < 0.001). When the ECMO flow/cardiac output was >60 %, SaO₂ was always >90 %. Alternatively, the rate of sweep gas flow through the membrane lung determined blood decarboxylation, while PaCO₂ (arterial carbon dioxide tension) was unaffected when the ECMO blood flow and FiO_2ECMO were reduced to <2.5 L/min and 40 %, respectively. In three additional patients evaluated before and after red blood cell transfusion, O₂ delivery increased after transfusion, allowing lower ECMO flows to reach adequate SaO₂.

Conclusions

For severe ARDS patients receiving femoro–jugular vv-ECMO, blood flow was the main determinant of arterial oxygenation, while CO₂ elimination depended on sweep gas flow through the oxygenator. An ECMO flow/cardiac output >60 % was constantly associated with adequate blood oxygenation and oxygen transport and delivery.     

A mathematical model of oxygenation during venovenous extracorporeal membrane oxygenation support

PurposeTo develop a mathematical model of oxygenation during venovenous extracorporeal membrane oxygenation (vv-ECMO).Material and methodsTotal oxygen consumption, cardiac output, blood flow, recirculation, intrapulmonary shunt, hemoglobin, natural lung, and membrane lung oxygen fractions were chosen as inputs. Content, partial pressure, and hemoglobin saturation of oxygen in arterial, venous, pulmonary, and extracorporeal blood were outputs. To assess accuracy and predictive power of the model, we retrospectively analyzed data of 25 vv-ECMO patients. We compiled 2 software (with numerical, 2D and 3D graphical outputs) to study the impact of each variable on oxygenation.ResultsThe model showed high accuracy and predictive power. Raising blood flow and oxygen fraction to the membrane lung or reducing total oxygen consumption improves arterial and venous oxygenation, especially in severe cases; raising oxygen fraction to the natural lung improves oxygenation only in milder cases; raising hemoglobin always improves oxygenation, especially in the venous district; recirculation fraction severely impairs oxygenation. In severely ill patients, increasing cardiac output worsens arterial oxygenation but enhances venous oxygenation. Oxygen saturation of ECMO inlet is critical to evaluate the appropriateness of oxygen delivery.ConclusionsThe model with the software can be a useful teaching tool and a valuable decision-making aid for the management of hypoxic patients supported by vv-ECMO.     

Decreasing transfusion exposure risk during extracorporeal membrane oxygenation (ECMO)

Extracorporeal membrane oxygenation (ECMO) is a lifesaving therapy for neonatal pulmonary hypertension but carries a significant risk for transfusion-related complications. Packed red blood cell (PRBC) and platelet exposure were quantified and reviewed in 17 ECMO survivors prior (Group I, n = 9) and subsequent to (Group II, n = 8) changes in transfusion protocols. Blood product requirements included ECMO circuit priming, maintenance of haematocrit > 0.40 or platelet count > 50 x 10(9)/l, and colloid volume expansion. Group I was exposed to 13.8 +/- 10.2 (x +/- SD) different PRBC units. In Group II, multiple transfusions from single donor units decreased exposure 71% to 3.9 +/- 0.7 units (P < 0.05). Decreases in blood withdrawn (11%) and transfusion volume (7%) were coincident with a 15% reduction in mean bypass time. Platelet volume transfusion decreased from 159 +/- 213 to 93 +/- 64 ml using volume-reduced platelet packs. Total transfusion exposure decreased 59% from 20.8 +/- 17.8 units to 8.6 +/- 2.4 donor units. No transfusion complications occurred during the aggregate 1,926 h on bypass. We conclude that neonates on ECMO have a significant transfusion exposure risk increasing with prolonged duration of ECMO therapy. In addition we noted that concentrated platelet packs decreased transfusion volume by 41%, and multiple PRBC transfusions from single donor units decreased donor exposure by 71% while both strategies decreased the overall transfusion exposure risk by 59%.     

A new formula for determining arterial oxygen saturation during venovenous extracorporeal oxygenation

Purpose

Venovenous extracorporeal membrane oxygenation (VV-ECMO) is used to treat severe forms of acute respiratory distress syndrome (ARDS). VV-ECMO management may be confusing due to the lack of information about the interplay between the determinant parameters and their impact on oxygenation. We found a relationship between arterial oxygen saturation (SaO₂) and its relevant parameters. The aim of this study was to assess the validity of this model.

Methods

We report our experience in 17 patients under VV-ECMO for severe ARDS. We compared, at two different levels of pump flow, SaO₂ and the oxygen saturation measured in the pulmonary artery (SpaO₂) with the predicted saturation using the formula: SpaO₂ = (EF/CO)SmO₂ + (1 ? EF/CO)SvO₂ + 10^?2PmO₂, where PF is pump flow, R is recirculation, EF is effective flow [= (1 ? R)PF], SmO₂ is saturation of the oxygenator outgoing blood, CO is cardiac output, SvO₂ is saturation of mixed venous blood, and PmO₂ is oxygen partial pressure of the oxygenator outgoing blood.

Results

There was no significant difference between predicted and measured SpaO₂: the mean predicted and measured SpaO₂ values were 90.7 ± 2.8 % and 90.4 ± 2.7 % , respectively (p = 0.696, r = 0.966). Bland-Altman analysis showed good agreement between predicted and measured SpaO₂. Predicted SpaO₂ and SaO₂ was well correlated (r = 0.80).

Conclusions

We have presented an explicit relationship between SaO₂ and its direct determinants during VV-ECMO. Good agreement was found with the measured values of SaO₂, but the model remains to be fully validated before its use in clinical practice.     

A numerical model of blood oxygenation during veno-venous ECMO: analysis of the interplay between blood oxygenation and its delivery parameters

Veno-venous extracorporeal membrane oxygenation (VV-ECMO) is an important tool in the management of most severe forms of acute respiratory failure. The determinants and management of oxygen delivery in patients treated with VV-ECMO is a complex topic. The physiological principles of oxygenation on VV-ECMO are reviewed in many textbooks. However a numerical model is an additional instrument to be used in understanding and exploring this intricate subject matter. We present a numerical model of blood oxygenation during VV-ECMO. Using this model we examined the role and impact of each determinant on blood oxygenation. The numerical analysis of variation and interplay between each oxygenation determinants during VV-ECMO is presented in graphical form. These results corroborate all the findings of previous studies. The proposed numerical model facilitates understanding of oxygenation physiology during VV-ECMO; it can be used for a medical simulation system and for teaching the principles of oxygenation during VV-ECMO.     

Nutrition support during extracorporeal membrane oxygenation (ECMO) in adults: a retrospective audit of 86 patients

Purpose

Extracorporeal membrane oxygenation (ECMO) is increasingly being used to support critically ill patients with severe cardiac and/or respiratory failure. It has been claimed that the resulting haemodynamic alterations, particularly in venoarterial ECMO, mean that enteral feeding is unsafe and/or poorly tolerated. This study aims to investigate this question and to identify any barriers to optimal nutrition.

Methods

Data were retrospectively collected for 86 patients who received ECMO between January 2007 and July 2012 in a tertiary critical care unit/ECMO referral centre. All were fed using existing protocols that emphasise early enteral feeding in preference over parenteral or delayed enteral nutrition.

Results

Thirty-one patients required ECMO for cardiac failure, and all of these received venoarterial ECMO; the remainder received venovenous ECMO. Enteral feeds started for all patients at average 13.1 h [standard deviation (SD) 16.7 h] after ICU admission, reaching goal rate on day 2.6 (SD 1.4). Thirty-three patients experienced significant feeding intolerance during the first 5 days, but of these 20 were managed effectively with prokinetic medications; 18 required parenteral nutrition to supplement inadequately tolerated tube feeds. Intolerance did not differ between ECMO modes. Overall patients tolerated 79.7 % of goal nutrition each day in the first 2 weeks.

Conclusions

Enteral feeding can be well tolerated by patients who are receiving ECMO, whether in venovenous or venoarterial mode. ECMO should not exclude patients from receiving the well-documented benefits of early enteral feeding in critical illness.     

A new technique for measuring cardiac output and shunt fraction during venovenous extracorporeal membrane oxygenation

A new indicator dilution technique is described for measuring cardiac output and shunt fraction in patients undergoing venovenous extracorporeal membrane oxygenation (ECMO). Shunt fraction is the proportion of the ECMO pump flow which recirculates through the ECMO circuit (passing directly from the inflow cannula to the outflow cannula) instead of flowing through the pulmonary and systemic circulations. The indicator is an isotonic (150 mmol/l) solution of lithium chloride which is injected into the ECMO flow returning to the patient. Two lithium sensors are used simultaneously to record the resulting lithium dilution curves in arterial blood and in the blood in the ECMO circuit. Cardiac output and shunt fraction are derived from these curves. The techniques, which is simple and safe, provides measurements that allow optimal adjustment of ECMO flow and cardiovascular support.     

Pressure-guided positioning of bicaval dual-lumen catheters for venovenous extracorporeal gas exchange

Purpose

Bicaval dual-lumen catheters allow for single-site cannulation venovenous extracorporeal gas exchange and facilitate early mobilization of patients. Using these catheters blood is drained from the superior and inferior venae cavae, pumped through a respiratory membrane, and returned into the right atrium. The insertion of these catheters is challenging as their correct positioning is fundamental to reduce recirculation and avoid severe complications. We describe here a new technique for the positioning of bicaval dual-lumen catheters.

Materials and methods

The right internal jugular vein was percutaneously cannulated in nine sheep. The distance between skin and tricuspid valve was measured from the point of pressure change in the waveform of a Swan–Ganz catheter being retracted from the right ventricle into the right atrium. The atrium-tricuspid valve-ventricle axis was determined by observing the fluctuations of the tip of the Swan–Ganz entering the ventricle during fluoroscopy. A bicaval dual-lumen catheter was placed on the basis of these evaluations and connected to an extracorporeal respiratory support system.

Results

The position of the catheter was verified at necropsy approximately 18 h after insertion. In all cases the catheter was correctly placed, with the central port situated in front of the tricuspid valve.

Conclusions

The described technique may help to position bicaval dual-lumen catheters for venovenous extracorporeal gas exchange without the use of transesophageal echocardiography or contrast media during fluoroscopy.     

The potential of accurate SvO2 monitoring during venovenous extracorporeal membrane oxygenation: an in vitro model using ultrasound dilution

INTRODUCTION: Some degree of recirculation occurs during venovenous extracorporeal membrane oxygenation (VV ECMO) which, (1) reduces oxygen (O2) delivery, and (2) renders venous line oxygen saturation monitoring unreliable as an index of perfusion adequacy. Ultrasound dilution allows clinicians to rapidly monitor and quantify the percent of recirculation that is occurring during VV ECMO. The purpose of this paper is to test whether accurate patient mixed venous oxygen saturation (SvO2) can be calculated once recirculation is determined. It is hypothesized that it is possible to derive patient mixed venous saturations by integrating recirculation data with the ECMO circuit arterial and venous line oxygen saturation data. METHODS: A test system containing sheep blood adjusted to three venous saturations (low-30%, med-60%, high-80%) was interfaced via a mixing chamber with a standard VV ECMO circuit. Recirculation, arterial line and venous line oxygen saturations were measured and entered into a derived equation to calculate the mixed venous saturation. The resulting value was compared to the actual mixed venous saturation. RESULTS: Recirculation was held constant at 30.5 +/- 2.0% for all tests. A linear regression comparison of "actual" versus "calculated" mixed venous saturations produced a correlation coefficient of R2 = 0.88. Direct comparison of actual versus calculated saturations for all three test groups respectively are as follows; Low: 31.8 +/- 3.95% vs. 37.0 +/- 6.7% (NS), Med: 61.7 +/- 1.5% vs. 72.3 +/- 1.8% (p < 0.05), High: 84.4 +/- 0.9% vs. 91.2 +/- 1.1% (p < 0.05). DISCUSSION: There was a strong correlation between actual and calculated mixed venous saturations; however, significant differences between actual and calculated values where observed at the Med and High groups. While this data suggests that using quantified recirculation data to calculate SvO2 is promising, it appears that a straightforward derivative of the oxygen saturation-based equation may not be sufficient to produce clinically accurate calculations of actual mixed venous saturations.     

Infiltration during intravenous therapy in neonates: comparison of Teflon and Vialon catheters.

Infiltration is a frequent complication of intravenous therapy using peripheral venous lines in neonatal patients. In a randomized trial of two catheter materials, Vialon (Becton Dickinson) and Teflon (DuPont), we studied 19 putative risk factors for infiltration, including 11 infusates, in 772 peripheral venous lines in patients aged 1 to 67 days. The best-fit Cox regression model identified six significant predictors of infiltration (P less than .05): catheter material, age, anatomic insertion site, hyperalimentation, and use of furosemide and dopamine. For the subsample of patients weighing less than or equal to 1500 g, a second Cox regression model identified time spent inserting the catheter and the number of insertion attempts as additional significant predictors. These multivariate models showed that Vialon catheter material reduced the risk of infiltration by 18% (95% CI, 1% to 32% reduction) in the total sample and by 35% (95% CI, 15% to 50% reduction) in the higher risk low-weight (less than or equal to 1500 g) subsample.     

Securing central venous catheters: a comparison of sutures with staples

Methods: Prospective, randomised trial of 20 patients requiring insertion of a central venous catheter during elective surgery.

Results: Mean (SD) times were significantly shorter in the staples group than in the sutures group (staples 10.1 (3.5) seconds; sutures 50.5 (9.6) seconds; p<0.0001). However, 3 of 10 central venous catheters in the staples group were accidentally pulled out within the first three days.

Conclusions: The use of staples significantly reduces the time to secure a central venous catheter. However, staples failed to secure the central venous catheters adequately and therefore cannot be recommended instead of sutures.

     

Exit-site infection in children on peritoneal dialysis: comparison of two types of peritoneal catheters.

OBJECTIVE: To review our experience with two types of peritoneal catheters, the standard Tenckhoff catheter and the swan-neck presternal catheter (SNPC). DESIGN: A retrospective study was undertaken to compare exit-site infection (ESI) rates using two types of peritoneal catheters in children. SETTING: Medical University of Warsaw, Warsaw, Poland. PATIENTS: During the past 10 years, 60 peritoneal catheters were implanted in 50 children with end-stage renal failure: 46 straight, double-cuffed Tenckhoff in 37 children (mean age 11.8 +/- 4.2 years, range 3.1 - 18.5 years), and 14 presternal in 13 children (mean age 10.6 +/- 5 years, range 0.3-17.7 years). The SNPCs were used in special clinical situations such as recurrent ESI with previous abdominal peritoneal catheters, obesity, presence of ureterocutaneostomies, use of diapers, and young age. For the statistical analysis, only the first catheter placed in each child was chosen: 34 standard Tenckhoff catheters and 9 SNPCs. INTERVENTION: In all children, peritoneal catheters were implanted surgically under general anesthesia by one surgeon; uniform operative technique and perioperative management was used. RESULTS: The mean observation time for 46 standard Tenckhoff catheters was 23.8 +/- 21.1 months, and for 14 SNPCs 25.1 +/- 27.0 months. The ESI rate was 1/17.4 patient-months (0.69 episodes/year) for Tenckhoff catheters and 1/70.2 patient-months (0.17 episodes/year) for SNPCs. The observed differences in ESI rates between the groups reported did not achieve statistical significance. CONCLUSIONS: The risk of ESI may be lower with presternal catheters. Confirmation of these findings requires further prospective clinical investigation in large numbers of patients.     

Patient-perceived discomfort with two coated urinary catheters

Intermittent catheterization is now the preferred method for urethral catheterization of the urinary bladder when an indwelling catheter is not required. Nevertheless, the procedure may cause discomfort or pain. This randomized, prospective study was done to compare patient-perceived discomfort between two commonly used hydrophilic, single-use catheters in women. A total of 196 women referred to the urogynaecology section in the outpatient department were randomized to be catheterized with either a LoFric (n=102) or a SpeediCath (n=94) catheter. Both catheters are hydrophilic, low friction, single-use, disposable catheters. Discomfort was measured using a visual analogue scale (VAS). The results showed no difference in degree of patient-perceived discomfort between the two groups. Median score was 0.75 VAS points in both groups, which indicates little discomfort. Half of all the patients stated that they experienced no discomfort at all.     

Outcomes of severe Legionella pneumonia requiring extracorporeal membrane oxygenation (ECMO)

BackgroundLegionella pneumonia with acute respiratory failure may necessitate extracorporeal membrane oxygenation (ECMO). The medical literature in this area is comprised primarily of case reports and small case series. Our goal was to summarize published data and contribute our institutional experience regarding survival in severe Legionella pneumonia requiring ECMO.MethodsA National Library of Medicine (PubMed) search was conducted, identifying reports of ECMO therapy in patients with severe Legionella pneumonia. Electronic health records of Montefiore Medical Center (Bronx, NY) captured all such patients treated at our institution during the 10-year period 2010–2019.Results23 articles reported 73 patients. Survival to hospital discharge was 78.1%. In an attempt to avoid publication bias, we culled from the search four series (53 patients), reporting surviving and non-surviving patients. Survival in this group was 71.7%. Our institutional experience included 10 patients with survival rate 80%.ConclusionsReview of clinical experience with ECMO for severe Legionella pneumonia yields a survival rate of over 70%. The similarity in survival rates among all published cases (78.1%), case series reporting surviving and non-surviving patients (71.7%), our institutional experience (80%), and recently reported Extracorporeal Life Support Organization (ELSO) registry data (71%) supports the veracity of this encouraging survival rate.     

应用扇形拨开器与常规置管术在腹膜透析置管中的效果比较

目的 比较应用扇形拨开器的腹膜透析(peritoneal dialysis,PD)置管术与常规PD置管术术后引起的并发症,探讨应用扇形拨开器的PD置管术的临床效果. 方法 随机入选三峡大学人民医院肾内科2009年2月至2012年4月首次PD置管并接受PD治疗且观察满6个月的终末期肾病(end stage renal disease,ESRD)患者共69例,随机分为用扇形拨开器引导组(A组),常规手术组(B组),A组35例,B组34例,纪录2组术前的基本情况、术后感染并发症;同时观察比较2组术后6个月内的PD管移位率、导管阻塞率、渗漏、疼痛等机械并发症发生情况. 结果 2组患者的年龄、原发病情况无差别(P＞0.05);A组患者导管移位3例(8.57％),B组患者导管移位10例(29.41％),两组相比有显著性差异(x2=4.899,P=0.027);A组患者重新置管2例(5.71％),B组患者重新置管8例(23.53％),2组相比有显著性差异(x2=4.417,P0.036);2组患者发生导管阻塞、渗漏、疼痛等并发症差异均无统计学意义(P＞0.05).2组患者发生感染并发症无统计学差异(P＞0.05). 结论 应用扇形拨开器的PD置管术可降低置管术后PD导管移位率,需重新置管率低.不增加PD置管术后感染率及机械并发症.