Differential Effect of Targeted Temperature Management Between 32 °C and 36 °C Following Cardiac Arrest According to Initial Severity of Illness: Insights From Two International Data Sets

BACKGROUND

Recent guidelines have emphasized actively avoiding fever to improve outcomes in patients who are comatose following resuscitation from cardiac arrest (ie, out-of-hospital cardiac arrest). However, whether targeted temperature management between 32 °C and 36 °C (TTM32-36) can improve neurologic outcome in some patients remains debated.

RESEARCH QUESTION

Is there an association between the use of TTM32-36 and outcome according to severity assessed at ICU admission using a previously derived risk score?

STUDY DESIGN AND METHODS

Data prospectively collected in the Sudden Death Expertise Center (SDEC) registry (France) between May 2011 and December 2017 and in the Resuscitation Outcomes Consortium Continuous Chest Compressions (ROC-CCC) trial (United States and Canada) between June 2011 and May 2015 were used for this study. Severity at ICU admission was assessed through a modified version of the Cardiac Arrest Hospital Prognosis (mCAHP) score, divided into tertiles of severity. The study explored associations between TTM32-36 and favorable neurologic status at hospital discharge by using multiple logistic regression as well as in tertiles of severity for each data set.

RESULTS

A total of 2,723 patients were analyzed in the SDEC data set and 4,202 patients in the ROC-CCC data set. A favorable neurologic status at hospital discharge occurred in 728 (27%) patients in the French data set and in 1,239 (29%) patients in the North American data set. Among the French data set, TTM32-36 was independently associated with better neurologic outcome in the tertile of patients with low (adjusted OR, 1.63; 95% CI, 1.15-2.30; P = .006) and high (adjusted OR, 1.94; 95% CI, 1.06-3.54; P = .030) severity according to mCAHP at ICU admission. Similar results were observed in the North American data set (adjusted ORs of 1.36 [95% CI, 1.05-1.75; P = .020] and 2.42 [95% CI, 1.38-4.24; P = .002], respectively). No association was observed between TTM32-36 and outcome in the moderate groups of the two data sets.

INTERPRETATION

TTM32-36 was significantly associated with a better outcome in patients with low and high severity at ICU admission assessed according to the mCAHP score. Further studies are needed to evaluate individualized temperature control following out-of-hospital cardiac arrest.

P-124 The impact of Fragile x premutation carrier state on embryo morphokinetic development, A comparison between genetically normal and abnormal embryos

Study question

Does inheritance of FMR1 pre mutant allele affect embryos morphokinetic development?

Summary answer

Embryos that inherit the FMR1 pre-mutant allele are of a lower morphokinetic quality at the blastocyte stage compared to those with the normal allele.

What is known already

Previous studies suggest lower oocyte yield and blastulation rate in FMR1 premutation carriers undergoing preimplantation genetic testing for monogenic diseases (PGT-M). Yet, data is lacking concerning embryo morphokinetic development in this group.

Study design, size, duration

Retrospective analysis, on 529 embryos from 126 in vitro fertilization (IVF)- PGT-M cycles of 39 FMR-1 premutation women carriers.

Participants/materials, setting, methods

Morphological and morphokinetic parameters acquired by the time-lapse monitoring system were compared between embryos carrying the FMR-1 permutated allele (FMR1 group n = 271) to those who inherited the normal allele (Normal group n = 258). Outcomes measures were embryos morphokinetic parameters up to day 3, the start of blasulation time (tSB) for day 5 embryos, and the rate of top-quality embryos at days 3 and 5.

Main results and the role of chance

No differences were found between the groups in all morphokinetic parameters from the time of ICSI until biopsy on day 3. Blastulation rate was comparable between the groups. However, FMR1 embryos exhibited delayed start of blastulation compared to the genetically normal embryos (median tSB 104.2 hrs (99.3-110.3) vs 101.6 hrs (94.5-106.7), P = 0.01) and had lower top quality embryo rate (25.6% vs 38.8%, P = 0.04).

Limitations, reasons for caution

This study is limited by its retrospective design and inability to assess CGG expansion in the embryo.

Wider implications of the findings

This study offers new insight into the impact of permutated FMR1 gene in the early stages of embryo development. Further studies are needed in order to apply these results in clinical decision-making.

Trial registration number

not applicable

Associations between breast implants and postpartum lactational mastitis in breastfeeding women: retrospective study

OBJECTIVE

To examine the putative associations between breast implants and postpartum lactational mastitis.

DESIGN

Observational retrospective study.

SETTING

Digital database of Maccabi Healthcare Services, integrated health maintenance organisation in Israel.

POPULATION

Breastfeeding mothers from 2003 to 2016 based on an initial health maintenance organisation data set of 28 383 singleton live births in Israel.

METHODS

Multivariate analysis and propensity score matching were used to test the extent to which breast implants were associated with lactational mastitis during the 6-month postpartum period in breastfeeding mothers. Analyses for potential confounders were adjusted for socio-economic status, smoking and parity.

MAIN OUTCOME MEASURE

Lactational mastitis among breastfeeding women with breast implants compared with women without breast implants.

RESULTS

Mothers with breast implants (n = 6099) were significantly (P < 0.001) more likely to be diagnosed with postpartum mastitis (8.3%) than mothers with no breast implants(n = 22 284) (6.6%) at an odds ratio of 1.22 (95% CI 1.09-1.35) after adjusting for confounders.

CONCLUSION

Breast augmentation is associated with an increased risk of postpartum lactational mastitis in the 6-month postpartum period. In light of these findings, it is important for health professionals to instruct women who have undergone breast augmentation on correct breastfeeding techniques, ways to avoid risk factors, and to be alert to signs permitting the early detection of lactational mastitis.

TWEETABLE ABSTRACT

A study of over 28,000 breastfeeding women has shown that breast augmentation is associated with an increased risk of postpartum lactational mastitis in the six-month postpartum period.

A multifunctional matching algorithm for sample design in agricultural plots

Collection of accurate and representative data from agricultural fields is required for efficient crop management. Since growers have limited available resources, there is a need for advanced methods to select representative points within a field in order to best satisfy sampling or sensing objectives. The main purpose of this work was to develop a data-driven method for selecting locations across an agricultural field given observations of some covariates at every point in the field. These chosen locations should be representative of the distribution of the covariates in the entire population and represent the spatial variability in the field. They can then be used to sample an unknown target feature whose sampling is expensive and cannot be realistically done at the population scale. An algorithm for determining these optimal sampling locations, namely the multifunctional matching (MFM) criterion, was based on matching of moments (functionals) between sample and population. The selected functionals in this study were standard deviation, mean, and Kendall's tau. An additional algorithm defined the minimal number of observations that could represent the population according to a desired level of accuracy. The MFM was applied to datasets from two agricultural plots: a vineyard and a peach orchard. The data from the plots included measured values of slope, topographic wetness index, normalized difference vegetation index, and apparent soil electrical conductivity. The MFM algorithm selected the number of sampling points according to a representation accuracy of 90% and determined the optimal location of these points. The algorithm was validated against values of vine or tree water status measured as crop water stress index (CWSI). Algorithm performance was then compared to two other sampling methods: the conditioned Latin hypercube sampling (cLHS) model and a uniform random sample with spatial constraints. Comparison among sampling methods was based on measures of similarity between the target variable population distribution and the distribution of the selected sample. MFM represented CWSI distribution better than the cLHS and the uniform random sampling, and the selected locations showed smaller deviations from the mean and standard deviation of the entire population. The MFM functioned better in the vineyard, where spatial variability was larger than in the orchard. In both plots, the spatial pattern of the selected samples captured the spatial variability of CWSI. MFM can be adjusted and applied using other moments/functionals and may be adopted by other disciplines, particularly in cases where small sample sizes are desired.

Two-year follow-up of 196 interstitial lung disease patients after ICU stay

OBJECTIVE: Interstitial lung diseases (ILDs) are associated with poor prognosis in the intensive care unit (ICU). We aimed to assess factors associated with hospital mortality in ILD patients admitted to the ICU and to investigate long-term outcome.MATERIAL AND METHODS: This was a retrospective study in a teaching hospital specialised in ILD management. Patients with ILD who were hospitalised in the ICU between 2000 and 2014 were included. Independent predictors of hospital mortality were identified using logistic regression.RESULTS: A total of 196 ILD patients were admitted to the ICU during the study period. Overall hospital mortality was 55%. Two years after ICU admission, 70 (36%) patients were still alive. Of the 196 patients, 108 (55%) required invasive mechanical ventilation, of whom 21 (20%) were discharged alive from hospital. Acute exacerbation of ILD and multi-organ failure were highly associated with hospital mortality (OR 5.4, 95% CI 1.9-15.5 and OR 12.6, 95% CI 4.9-32.5, respectively).CONCLUSION: Hospital mortality among ILD patients hospitalised in the ICU was high, but even where invasive mechanical ventilation was required, a substantial number of patients were discharged alive from hospital. Multi-organ failure could lead to major ethical concerns.

FMRpolyG accumulates in FMR1 premutation granulosa cells

Background

Fragile X premutation (Amplification of CGG number 55–200) is associated with increased risk for fragile X-Associated Premature Ovarian Insufficiency (FXPOI) in females and fragile X-associated tremor/ataxia syndrome (FXTAS) predominantly in males. Recently, it has been shown that CGG repeats trigger repeat associated non-AUG initiated translation (RAN) of a cryptic polyglycine-containing protein, FMRpolyG. This protein accumulates in ubiquitin-positive inclusions in neuronal brain cells of FXTAS patients and may lead to protein-mediated neurodegeneration. FMRpolyG inclusions were also found in ovary stromal cells of a FXPOI patient. The role of FMRpolyG expression has not been thoroughly examined in folliculogenesis related cells. The main goal of this study is to evaluate whether FMRpolyG accumulates in mural granulosa cells of FMR1 premutation carriers. Following FMRpolyG detection, we aim to examine premutation transfected COV434 as a suitable model used to identify RAN translation functions in FXPOI pathogenesis.

Results

FMRpolyG and ubiquitin immunostained mural granulosa cells from six FMR1 premutation carriers demonstrated FMRpolyG aggregates. However, co-localization of FMRpolyG and ubiquitin appeared to vary within the FMR1 premutation carriers’ group as three exhibited partial ubiquitin and FMRpolyG double staining and three premutation carriers demonstrated FMRpolyG single staining. None of the granulosa cells from the five control women expressed FMRpolyG. Additionally, human ovarian granulosa tumor, COV434, were transfected with two plasmids; both expressing 99CGG repeats but only one enables FMRpolyG expression. Like in granulosa cells from FMR1 premutation carriers, FMRpolyG aggregates were found only in COV434 transfected with expended CGG repeats and the ability to express FMRpolyG.

Conclusions

Corresponding with previous studies in FXTAS, we demonstrated accumulation of FMRpolyG in mural granulosa cells of FMR1 premutation carriers. We also suggest that following further investigation, the premutation transfected COV434 might be an appropriate model for RAN translation studies. Detecting FMRpolyG accumulation in folliculogenesis related cells supports previous observations and imply a possible common protein-mediated toxic mechanism for both FXPOI and FXTAS.

Does the presence of AGG interruptions within the CGG repeat tract have a protective effect on the fertility phenotype of female FMR1 premutation carriers?

PURPOSE

While FMR1 premutation carriers (CGG 55-200) were shown to have reduced success with IVF treatment (lower oocyte yield), studies reporting on the association between the number of CGG repeats and patients' response to controlled ovarian hyperstimulation (COH) are inconsistent. In the present study, we aim to explore whether the number of CGG repeats in women with premutation in FMR1 gene, undergoing COH for IVF, correlates with COH variables and whether the number of AGG interruptions may function as a "protective factor" by improving the ovarian response to COH.

METHODS

Retrospective study, in an academic IVF-PGD unit. Fifty-seven consecutive FMR1 premutation carriers who underwent 285 IVF treatment cycles were included. The numbers of CGG repeats and AGG interruptions were retrieved and correlated to the demographics and COH variables.

RESULTS

There were no significant association between the numbers of CGG or the AGG interruptions and the number of oocyte retrieved or the peak estradiol levels. The lack of association was also observed when including all the IVF treatment cycles or only the first or last IVF treatment cycle. Moreover, no associations were found between the number of CGG repeats or AGG interruptions and other COH variables, i.e., duration of stimulation, the total dose of gonadotropin used, or the number of top-quality embryos.

CONCLUSIONS

No associations were observed between the number of CGG repeats or AGG interruptions and any of the COH variables. Further studies are required to identify early biomarkers of POI to empower FMR1 premutation carriers with risk assessment tools to consider procedures such as fertility preservation.

Extracorporeal cardiopulmonary resuscitation in out-of-hospital cardiac arrest: a registry study

Aims

Out-of-hospital cardiac arrest (OHCA) without return of spontaneous circulation (ROSC) despite conventional resuscitation is common and has poor outcomes. Adding extracorporeal membrane oxygenation (ECMO) to cardiopulmonary resuscitation (extracorporeal-CPR) is increasingly used in an attempt to improve outcomes.

Methods and results

We analysed a prospective registry of 13 191 OHCAs in the Paris region from May 2011 to January 2018. We compared survival at hospital discharge with and without extracorporeal-CPR and identified factors associated with survival in patients given extracorporeal-CPR. Survival was 8% in 525 patients given extracorporeal-CPR and 9% in 12 666 patients given conventional-CPR (P = 0.91). By adjusted multivariate analysis, extracorporeal-CPR was not associated with hospital survival [odds ratio (OR), 1.3; 95% confidence interval (95% CI), 0.8–2.1; P = 0.24]. By conditional logistic regression with matching on a propensity score (including age, sex, occurrence at home, bystander CPR, initial rhythm, collapse-to-CPR time, duration of resuscitation, and ROSC), similar results were found (OR, 0.8; 95% CI, 0.5–1.3; P = 0.41). In the extracorporeal-CPR group, factors associated with hospital survival were initial shockable rhythm (OR, 3.9; 95% CI, 1.5–10.3; P = 0.005), transient ROSC before ECMO (OR, 2.3; 95% CI, 1.1–4.7; P = 0.03), and prehospital ECMO implantation (OR, 2.9; 95% CI, 1.5–5.9; P = 0.002).

Conclusions

In a population-based registry, 4% of OHCAs were treated with extracorporeal-CPR, which was not associated with increased hospital survival. Early ECMO implantation may improve outcomes. The initial rhythm and ROSC may help select patients for extracorporeal-CPR.

P4509The cardiopulmonary vicious cycle in patients with heart failure, a mechanism for accelerated decompensation

Background

Hemodynamic congestion appears days prior to the development of clinical congestion. Lung congestion is associated with increased respiratory effort and dyspnoea. The effects of increased respiratory effort on pulmonary circulation were not well-defined.

Purpose

The study investigates the cardiopulmonary interactions and the role of the respiratory effort in the development of decompensation. It is well-accepted that lung congestion affects the lung mechanics and increases the respiratory effort. On the other hand, changes in the intrathoracic and alveolar pressures, due to the increase in the respiratory effort, may have detrimental effects on the pulmonary circulation and the workloads of the heart.

Methods

We have simultaneously measured the hemodynamic indices and the respiratory mechanics in patients undergoing right heart catheterization (n=56) for the diagnosis of dyspnoea. The patients were classified either as heart failure (HF) or lung disease, according to their clinical history, symptoms and signs. The pulmonary capillary wedge pressure (PCWP) was decomposed into cardiac and respiratory waves. The respiratory effort (Presp) was defined as the respiratory wave amplitude that modulates the PCWP. Lung compliance was calculated as the ratio of the tidal volume to Presp.

Results and discussion

The HF patients (n=35) exhibited huge Presp of 9.6±3.7 mmHg [2.6–16.7], ∼4 fold the normal Presp, of about 2–3 mmHg (figure below). Their lung compliance decreased with increasing PCWP (2.0±0.4%/mmHg of PCWP). Both PCWP and pulmonary artery pressure (PAP) rose with Presp, by 0.92±0.36 mmHg and 1.68±0.47 mmHg, for 1 mmHg of Presp, respectively (Figure below). Interestingly, PCWP always exceeded Presp, leading to the stipulation of a novel fundamental constraint/law: the continuous pulmonary flow throughout the respiratory cycle requires that PCWP > Presp (above the identity line in figure A), otherwise the capillary pressure will decrease below the surrounding alveolar pressure and the pulmonary circulation will collapse, especially during inspiration. This constraint imposes a positive feedback of Presp on the pulmonary circulatory pressures. It is also supported by the increase in PWCP with Presp in the patients with lung diseases (Figure A). The bigger rise in PAP than in PWCP is attributed to the increase in the pulmonary vascular resistance (PVR) with Presp (0.3±0.06 wood units for 1mmHg Presp). The latter constructs additional positive feedback of Presp on the cardiac workload. A decrease in the intrathoracic pressure that surrounds the heart increases the LV apparent afterload. The increase in PAP and PVR elevates the right ventricle afterload.

PCWP (A) and PAP (B) vs. Presp

Conclusions

The respiratory effort is not just a hallmark of HF but plays a pivotal role in the cardiopulmonary vicious cycle. An increase in the respiratory effort increases the PWCP, PAP, PVR, and the afterloads of both ventricles, and thereby may accelerate cardiac decompensation.

A 2-year multicenter, observational, prospective, cohort study on extracorporeal CO2 removal in a large metropolis area

Background

Extracorporeal carbon dioxide removal (ECCO₂R) is a promising technique for the management of acute respiratory failure, but with a limited level of evidence to support its use outside clinical trials and/or data collection initiatives. We report a collaborative initiative in a large metropolis.

Methods

To assess on a structural basis the rate of utilization as well as efficacy and safety parameters of 2 ECCO₂R devices in 10 intensive care units (ICU) during a 2-year period.

Results

Seventy patients were recruited in 10 voluntary and specifically trained centers. The median utilization rate was 0.19 patient/month/center (min 0.04; max 1.20). ECCO₂R was started under invasive mechanical ventilation (IMV) in 59 patients and non-invasive ventilation in 11 patients. The Hemolung Respiratory Assist System (Alung) was used in 53 patients and the iLA Activve iLA kit (Xenios Novalung) in 17 patients. Main indications were ultraprotective ventilation for ARDS patients (n = 24), shortening the duration of IMV in COPD patients (n = 21), preventing intubation in COPD patients (n = 9), and controlling hypercapnia and dynamic hyperinflation in mechanically ventilated patients with severe acute asthma (n = 6). A reduction in median V_T was observed in ARDS patients from 5.9 to 4.1 ml/kg (p <0.001). A reduction in PaCO₂ values was observed in AE-COPD patients from 67.5 to 51 mmHg (p< 0.001). Median duration of ECCO₂R was 5 days (IQR 3–8). Reasons for ECCO₂R discontinuation were improvement (n = 33), ECCO₂R-related complications (n = 18), limitation of life-sustaining therapies or measures decision (n = 10), and death (n = 9). Main adverse events were hemolysis (n = 21), bleeding (n = 17), and lung membrane clotting (n = 11), with different profiles between the devices. Thirty-five deaths occurred during the ICU stay, 3 of which being ECCO₂R-related.

Conclusions

Based on a registry, we report a low rate of ECCO₂R device utilization, mainly in severe COPD and ARDS patients. Physiological efficacy was confirmed in these two populations. We confirmed safety concerns such as hemolysis, bleeding, and thrombosis, with different profiles between the devices. Such results could help to design future studies aiming to enhance safety, to demonstrate a still-lacking strong clinical benefit of ECCO₂R, and to guide the choice between different devices.

Trial registration

ClinicalTrials.gov: Identifier: NCT02965079 retrospectively registered https://clinicaltrials.gov/ct2/show/NCT02965079

[Rhabdomyolysis in patients treated by corticosteroids for acute asthma in intensive care unit]

INTRODUCTION

Acute muscle involvement is an infrequent complication of corticosteroids, characterized by muscle weakness and a rhabdomyolysis, rapidly regressive after withdrawal of corticosteroids.

CASE REPORT

We report the case of a woman admitted in intensive care unit for acute severe asthma, treated with high doses of methylprednisolone. Serum CPK level raised with a peak at 28,160 UI/L (n<250 UI/L) at day 15, suggesting acute rhabdomyolysis with renal failure. CPK rapidly normalized when corticosteroids were discontinued. Other causes of rhabdomyolysis were ruled out.

CONCLUSION

This necrosing myopathy under high doses of corticosteroids has been described in patients with severe acute asthma. The mechanism of the muscle damage results from a combination of corticosteroids toxicity, respiratory acidosis and mechanic ventilation.

Probing the internal micromechanical properties of Pseudomonas aeruginosa biofilms by Brillouin imaging

Biofilms are organised aggregates of bacteria that adhere to each other or surfaces. The matrix of extracellular polymeric substances that holds the cells together provides the mechanical stability of the biofilm. In this study, we have applied Brillouin microscopy, a technique that is capable of measuring mechanical properties of specimens on a micrometre scale based on the shift in frequency of light incident upon a sample due to thermal fluctuations, to investigate the micromechanical properties of an active, live Pseudomonas aeruginosa biofilm. Using this non-contact and label-free technique, we have extracted information about the internal stiffness of biofilms under continuous flow. No correlation with colony size was found when comparing the averages of Brillouin shifts of two-dimensional cross-sections of randomly selected colonies. However, when focusing on single colonies, we observed two distinct spatial patterns: in smaller colonies, stiffness increased towards their interior, indicating a more compact structure of the centre of the colony, whereas, larger (over 45 μm) colonies were found to have less stiff interiors.

A specialized microscopy technique can monitor biofilm stiffness in a non-destructive manner, yielding insights into biofilm structure and development. The technique, called Brillouin imaging, uses changes in the frequency of light interacting with a substance to reveal fine detail about the material’s mechanical properties. Peter Török and colleagues at Imperial College London, with co-workers in Singapore, used Brillouin imaging to study biofilms of Pseudomonas aeruginosa bacteria at different stages in their life cycle. In young colonies, stiffness increased towards the interior of the biofilm, while mature colonies had less stiff interiors. The older biofilms may therefore have hollow interiors or may have been moving towards a phase of bacterial dispersal from the biofilm state. This non-disruptive method to study mechanical variations within and between living biofilms may help efforts to combat biofilms in clinical, environmental and industrial situations.

Eustachian tube dysfunction leading to middle-ear pathology in patients on chronic mechanical ventilation

OBJECTIVE

This study aimed to investigate the prevalence of and risk factors for Eustachian tube dysfunction leading to middle-ear pathology in patients on chronic mechanical ventilation via tracheostomy tube.

METHODS

A total of 40 patients on chronic ventilation were included in a prospective cohort study. Middle-ear status was determined by tympanometry. Tympanograms were categorised as types A, B or C; types B and C were defined as middle-ear pathology.

RESULTS

In all, 57 ears of 40 patients were examined. Disease was found in at least 1 ear in 26 out of 40 patients. Middle-ear pathology was found in 25 out of 34 patients who were tube fed (via nasogastric tube or percutaneous endoscopic gastrostomy) vs 1 patient out of the 6 fed orally (p = 0.014), and in 23 out of 31 with conscious or cognitive impairment vs 3 out of 9 cognitively intact patients (p = 0.044).

CONCLUSION

Middle-ear pathology is common in patients on chronic mechanical ventilation via tracheostomy tube. The highest prevalence was in those with impaired consciousness or cognition, and oral feeding appeared protective.

High-frequency measurement of depressive severity in a patient treated for severe treatment-resistant depression with deep-brain stimulation

Although there have been previous studies of deep-brain stimulation (DBS), we present, to our knowledge, the first example of high-frequency depressive severity measurement-based DBS treatment in particular and psychiatric treatment in general. Daily post-surgical e-mail prompts for a period of 6 months resulted in 93 administrations of a computerized adaptive test (CAT) of depression severity (CAT-Depression Inventory or CAT-DI) via the internet. There was an average of 3.37 weekly measurements with an average separation of 2.12 days. No additional incentive was provided to the patient for completing the adaptive tests. The patient is a 55-year-old female with six psychiatric hospitalizations for depression, two suicide attempts, marginal response to eight electroconvulsive therapy (ECT) treatments and 35 psychotropic medications. We report results after high-frequency stimulation of the superolateral branch of the medial forebrain bundle. The CAT-DI was used for daily assessments before, during and after (remotely in response to an e-mail prompt) the DBS procedure. Two follow-up Hamilton Depression Scales (HAM-Ds) were also collected. Response to treatment varied markedly, with a decrease from severe (>75) to mild (60), which is three times the size of the uncertainty level. Although the HAM-D scores decreased, they missed the more complete temporal pattern identified by CAT-DI daily monitoring. We demonstrated feasibility of daily depressive severity measurement at high levels of precision and compliance. Clinician ratings confirm the general pattern of treatment benefit, but mask the marked variability in mood and more marked periods of benefit and decline.

Laplacian networks: Growth, local symmetry, and shape optimization

Inspired by river networks and other structures formed by Laplacian growth, we use the Loewner equation to investigate the growth of a network of thin fingers in a diffusion field. We first review previous contributions to illustrate how this formalism reduces the network's expansion to three rules, which respectively govern the velocity, the direction, and the nucleation of its growing branches. This framework allows us to establish the mathematical equivalence between three formulations of the direction rule, namely geodesic growth, growth that maintains local symmetry, and growth that maximizes flux into tips for a given amount of growth. Surprisingly, we find that this growth rule may result in a network different from the static configuration that optimizes flux into tips.