Randomized controlled trial of low vs high oxygen during neonatal anesthesia: Oxygenation, feasibility, and oxidative stress.

BACKGROUND: To reduce risk for intermittent hypoxia a high fraction of inspired oxygen is routinely used during anesthesia induction. This differs from the cautious dosing of oxygen during neonatal resuscitation and intensive care and may result in significant hyperoxia. AIM: In a randomized controlled trial, we evaluated oxygenation during general anesthesia with a low (23%) vs a high (80% during induction and recovery, and 40% during maintenance) fraction of inspired oxygen, in newborn infants undergoing surgery. METHOD: Thirty-five newborn infants with postconceptional age of 35-44 weeks were included (17 infants in low and 18 in high oxygen group). Oxygenation was monitored by transcutaneous partial pressure of oxygen, pulse oximetry, and cerebral oxygenation. Predefined SpO2 safety targets dictated when to increase inspired oxygen. RESULTS: At start of anesthesia, oxygenation was similar in both groups. Throughout anesthesia, the high oxygen group displayed significant hyperoxia with higher (difference-20.3 kPa, 95% confidence interval (CI)-28.4 to 12.2, p < .001) transcutaneous partial pressure of oxygen values than the low oxygen group. While SpO2 in the low oxygen group was lower (difference - 5.8%, 95% CI -9.3 to -2.4, p < .001) during anesthesia, none of the infants spent enough time below SpO2 safety targets to mandate supplemental oxygen, and cerebral oxygenation was within the normal range and not statistically different between the groups. Analysis of the oxidative stress biomarker urinary F2 -Isoprostane revealed no differences between the low and high oxygen group. CONCLUSION: We conclude that in healthy newborn infants, use of low oxygen during general anesthesia was feasible, while the prevailing practice of using high levels of inspired oxygen resulted in significant hyperoxia. The trade-off between careful dosing of oxygen and risks of hypo- and hyperoxia in neonatal anesthesia should be further examined.

Limitations of the ARDS criteria during high-flow oxygen or non-invasive ventilation: evidence from critically ill COVID-19 patients.

BACKGROUND: The ratio of partial pressure of arterial oxygen to inspired oxygen fraction (PaO2/FIO2) during invasive mechanical ventilation (MV) is used as criteria to grade the severity of respiratory failure in acute respiratory distress syndrome (ARDS). During the SARS-CoV2 pandemic, the use of PaO2/FIO2 ratio has been increasingly used in non-invasive respiratory support such as high-flow nasal cannula (HFNC) and non-invasive ventilation (NIV). The grading of hypoxemia in non-invasively ventilated patients is uncertain. The main hypothesis, investigated in this study, was that the PaO2/FIO2 ratio does not change when switching between MV, NIV and HFNC. METHODS: We investigated respiratory function in critically ill patients with COVID-19 included in a single-center prospective observational study of patients admitted to the intensive care unit (ICU) at Uppsala University Hospital in Sweden. In a steady state condition, the PaO2/FIO2 ratio was recorded before and after any change between two of the studied respiratory support techniques (i.e., HFNC, NIV and MV). RESULTS: A total of 148 patients were included in the present analysis. We find that any change in respiratory support from or to HFNC caused a significant change in PaO2/FIO2 ratio. Changes in respiratory support between NIV and MV did not show consistent change in PaO2/FIO2 ratio. In patients classified as mild to moderate ARDS during MV, the change from HFNC to MV showed a variable increase in PaO2/FIO2 ratio ranging between 52 and 140 mmHg (median of 127 mmHg). This made prediction of ARDS severity during MV from the apparent ARDS grade during HFNC impossible. CONCLUSIONS: HFNC is associated with lower PaO2/FIO2 ratio than either NIV or MV in the same patient, while NIV and MV provided similar PaO2/FIO2 and thus ARDS grade by Berlin definition. The large variation of PaO2/FIO2 ratio indicates that great caution should be used when estimating ARDS grade as a measure of pulmonary damage during HFNC.

A proof-of-concept study on mortality prediction with machine learning algorithms using burn intensive care data.

INTRODUCTION: Burn injuries are a common traumatic injury. Large burns have high mortality requiring intensive care and accurate mortality predictions. To assess if machine learning (ML) could improve predictions, ML algorithms were tested and compared with the original and revised Baux score. METHODS: Admission data and mortality outcomes were collected from patients at Uppsala University Hospital Burn Centre from 2002 to 2019. Prognostic variables were selected, ML algorithms trained and predictions assessed by analysis of the area under the receiver operating characteristic curve (AUC). Comparison was made with Baux scores using DeLong test. RESULTS: A total of 17 prognostic variables were selected from 92 patients. AUCs in leave-one-out cross-validation for a decision tree model, an extreme boosting model, a random forest model, a support-vector machine (SVM) model and a generalised linear regression model (GLM) were 0.83 (95% confidence interval [CI] = 0.72-0.94), 0.92 (95% CI = 0.84-1), 0.92 (95% CI = 0.84-1), 0.92 (95% CI = 0.84-1) and 0.84 (95% CI = 0.74-0.94), respectively. AUCs for the Baux score and revised Baux score were 0.85 (95% CI = 0.75-0.95) and 0.84 (95% CI = 0.74-0.94). No significant differences were observed when comparing ML algorithms with Baux score and revised Baux score. Secondary variable selection was made to analyse model performance. CONCLUSION: This proof-of-concept study showed initial credibility in using ML algorithms to predict mortality in burn patients. The sample size was small and future studies are needed with larger sample sizes, further variable selections and prospective testing of the algorithms. LAY SUMMARY: Burn injuries are one of the most common traumatic injuries especially in countries with limited prevention and healthcare resources. To treat a patient with large burns who has been admitted to an intensive care unit, it is often necessary to assess the risk of a fatal outcome. Physicians traditionally use simplified scores to calculate risks. One commonly used score, the Baux score, uses age of the patient and the size of the burn to predict the risk of death. Adding the factor of inhalation injury, the score is then called the revised Baux score. However, there are a number of additional causes that can influence the risk of fatal outcomes that Baux scores do not take into account. Machine learning is a method of data modelling where the system learns to predict outcomes based on previous cases and is a branch of artificial intelligence. In this study we evaluated several machine learning methods for outcome prediction in patients admitted for burn injury. We gathered data on 93 patients at admission to the intensive care unit and our experiments show that machine learning methods can reach an accuracy comparable with Baux scores in calculating the risk of fatal outcomes. This study represents a proof of principle and future studies on larger patient series are required to verify our results as well as to evaluate the methods on patients in real-life situations.

Intranasal dexmedetomidine and rectal ketamine for young children undergoing burn wound procedures.

BACKGROUND: Safe and effective methods for sedation and analgesia in pediatric burn patients are strongly warranted. This retrospective study of electronic health care records aims to evaluate the safety and efficacy of intranasal dexmedetomidine combined with rectal ketamine as procedural sedation for young children undergoing dressing changes and debridement of burn wounds. METHODS: Documentation was analyzed from 90 procedures in 58 pediatric patients aged <5 years. Safety and efficacy of the method were assessed based on documentation for complications, adverse effects, pain level, level of sedation and preoperative and recovery time. RESULTS: All 90 sedations were completed without significant adverse events with acute airway management or medical intervention. The combination of dexmedetomidine-ketamine produced acceptable analgesia during the procedure and effectively relieved postoperative pain. However, the approach was insufficient for 7/58 patients (7.8%); these patients were converted from the dexmedetomidine-ketamine combination to intravenous anesthesia. In 23% of the cases an extra dose of either ketamine of dexmedetomidine was administered. Moreover, there were two cases of delayed awakening with recovery time >120 min. CONCLUSION: The drug combination intranasal dexmedetomidine and rectal ketamine is a safe and reliable approach for procedural sedation and analgesia in pediatric patients undergoing burn wound procedures, producing a clinically stable sedative condition requiring only basic monitoring.

Expiratory Resistances Prevent Expiratory Diaphragm Contraction, Flow Limitation, and Lung Collapse.

Rationale: Tidal expiratory flow limitation (tidal-EFL) is not completely avoidable by applying positive end-expiratory pressure and may cause respiratory and hemodynamic complications in ventilated patients with lungs prone to collapse. During spontaneous breathing, expiratory diaphragmatic contraction counteracts tidal-EFL. We hypothesized that during both spontaneous breathing and controlled mechanical ventilation, external expiratory resistances reduce tidal-EFL.Objectives: To assess whether external expiratory resistances 1) affect expiratory diaphragmatic contraction during spontaneous breathing, 2) reduce expiratory flow and make lung compartments more homogeneous with more similar expiratory time constants, and 3) reduce tidal atelectasis, preventing hyperinflation.Methods: Three positive end-expiratory pressure levels and four external expiratory resistances were tested in 10 pigs after lung lavage. We analyzed expiratory diaphragmatic electric activity and respiratory mechanics. On the basis of computed tomography scans, four lung compartments-not inflated (atelectasis), poorly inflated, normally inflated, and hyperinflated-were defined.Measurements and Main Results: Consequently to additional external expiratory resistances, and mainly in lungs prone to collapse (at low positive end-expiratory pressure), 1) the expiratory transdiaphragmatic pressure decreased during spontaneous breathing by >10%, 2) expiratory flow was reduced and the expiratory time constants became more homogeneous, and 3) the amount of atelectasis at end-expiration decreased from 24% to 16% during spontaneous breathing and from 32% to 18% during controlled mechanical ventilation, without increasing hyperinflation.Conclusions: The expiratory modulation induced by external expiratory resistances preserves the positive effects of the expiratory brake while minimizing expiratory diaphragmatic contraction. External expiratory resistances optimize lung mechanics and limit tidal-EFL and tidal atelectasis, without increasing hyperinflation.

The time-course of the inflammatory response to major burn injury and its relation to organ failure and outcome.

Burn injury causes major inflammatory activation and cytokine release, however, the temporal resolution of the acute and sub-acute inflammatory response has not yet been fully delineated. To this end, we have quantified 20 inflammatory mediators in plasma from 44 adult patients 0-21 days after burn injury and related the time course of these mediators to % total body surface area (TBSA) burned, clinical parameters, organ failure and outcome. Of the cytokines analyzed in these patients, interleukin 6 (IL-6), IL-8, IL-10 and monocyte chemoattractant protein 1 (MCP-1) correlated to the size of the injury at 24-48h after burn injury. In our study, the concentration of IL-10 had prognostic value in patients with burn injury both measured at admission and at 24-48h after injury. However, simple demographic data such as age, % burned TBSA, inhalation injury and their combination, the Baux score and modified Baux score, outperform most of the cytokines, with the exception of IL-8 and MCP-1 levels on admission, in predicting death.

Optimal PEEP during one-lung ventilation with capnothorax: An experimental study.

BACKGROUND: One-lung ventilation (OLV) with induced capnothorax carries the risk of severely impaired ventilation and circulation. Optimal PEEP may mitigate the physiological perturbations during these conditions. METHODS: Right-sided OLV with capnothorax (16 cm H2 O) on the left side was initiated in eight anesthetized, muscle-relaxed piglets. A recruitment maneuver and a decremental PEEP titration from PEEP 20 cm H2 O to zero end-expiratory pressure (ZEEP) was performed. Regional ventilation and perfusion were studied with electrical impedance tomography and computer tomography of the chest was used. End-expiratory lung volume and hemodynamics were recorded and. RESULTS: PaO2 peaked at PEEP 12 cm H2 O (49 ± 14 kPa) and decreased to 11 ± 5 kPa at ZEEP (P < 0.001). PaCO2 was 9.5 ± 1.3 kPa at 20 cm H2 O PEEP and did not change when PEEP step-wise was reduced to 12 cm H2 O PaCO2. At lower PEEP, PaCO2 increased markedly. The ventilatory driving pressure was lowest at PEEP 14 cm H2 O (19.6 ± 5.8 cm H2 O) and increased to 38.3 ± 6.1 cm H2 O at ZEEP (P < 0.001). When reducing PEEP below 12-14 cm H2 O ventilation shifted from the dependent to the nondependent regions of the ventilated lung (P = 0.003), and perfusion shifted from the ventilated to the nonventilated lung (P = 0.02). CONCLUSION: Optimal PEEP was 12-18 cm H2 O and probably relates to capnothorax insufflation pressure. With suboptimal PEEP, ventilation/perfusion mismatch in the ventilated lung and redistribution of blood flow to the nonventilated lung occurred.

Matrix metalloproteinases -8 and -9 and tissue inhibitor of metalloproteinase-1 in burn patients. A prospective observational study.

INTRODUCTION: Matrix metalloproteinases (MMPs) -8 and -9 are released from neutrophils in acute inflammation and may contribute to permeability changes in burn injury. In retrospective studies on sepsis, levels of MMP-8, MMP-9, and tissue inhibitor of metalloproteinase-1 (TIMP-1) differed from those of healthy controls, and TIMP-1 showed an association with outcome. Our objective was to investigate the relationship between these proteins and disease severity and outcome in burn patients. METHODS: In this prospective, observational, two-center study, we collected plasma samples from admission to day 21 post-burn, and burn blister fluid samples on admission. We compared MMP-8, -9, and TIMP-1 levels between TBSA<20% (N = 19) and TBSA>20% (N = 30) injured patients and healthy controls, and between 90-day survivors and non-survivors. MMP-8, -9, and TIMP-1 levels at 24-48 hours from injury, their maximal levels, and their time-adjusted means were compared between groups. Correlations with clinical parameters and the extent of burn were analyzed. MMP-8, -9, and TIMP-1 levels in burn blister fluids were also studied. RESULTS: Plasma MMP-8 and -9 were higher in patients than in healthy controls (P<0.001 and P = 0.016), but only MMP-8 differed between the TBSA<20% and TBSA>20% groups. MMP-8 and -9 were not associated with clinical severity or outcome measures. TIMP-1 differed significantly between patients and controls (P<0.001) and between TBSA<20% and TBSA>20% groups (P<0.002). TIMP-1 was associated with 90-day mortality and correlated with the extent of injury and clinical measures of disease severity. TIMP-1 may serve as a new biomarker in outcome prognostication of burn patients.

Hypercapnic acidosis transiently weakens hypoxic pulmonary vasoconstriction without affecting endogenous pulmonary nitric oxide production.

PURPOSE: Hypercapnic acidosis often occurs in critically ill patients and during protective mechanical ventilation; however, the effect of hypercapnic acidosis on endogenous nitric oxide (NO) production and hypoxic pulmonary vasoconstriction (HPV) presents conflicting results. The aim of this study is to test the hypothesis that hypercapnic acidosis augments HPV without changing endogenous NO production in both hyperoxic and hypoxic lung regions in pigs. METHODS: Sixteen healthy anesthetized pigs were separately ventilated with hypoxic gas to the left lower lobe (LLL) and hyperoxic gas to the rest of the lung. Eight pigs received 10% carbon dioxide (CO(2)) inhalation to both lung regions (hypercapnia group), and eight pigs formed the control group. NO concentration in exhaled air (ENO), nitric oxide synthase (NOS) activity, cyclic guanosine monophosphate (cGMP) in lung tissue, and regional pulmonary blood flow were measured. RESULTS: There were no differences between the groups for ENO, Ca(2+)-independent or Ca(2+)-dependent NOS activity, or cGMP in hypoxic or hyperoxic lung regions. Relative perfusion to LLL (Q (LLL)/Q (T)) was reduced similarly in both groups when LLL hypoxia was induced. During the first 90 min of hypercapnia, Q (LLL)/Q (T) increased from 6% (1%) [mean (standard deviation, SD)] to 9% (2%) (p < 0.01), and then decreased to the same level as the control group, where Q (LLL)/Q (T) remained unchanged. Cardiac output increased during hypercapnia (p < 0.01), resulting in increased oxygen delivery (p < 0.01), despite decreased PaO(2) (p < 0.01)(.) CONCLUSIONS: Hypercapnic acidosis does not potentiate HPV, but rather transiently weakens HPV, and does not affect endogenous NO production in either hypoxic or hyperoxic lung regions.

Distant effects of nitric oxide inhalation in endotoxemic pigs.

OBJECTIVE: Inhalation of nitric oxide (INO) has distant effects. By a blood- borne factor, INO down-regulates endogenous nitric oxide production in healthy pig lungs, resulting in vasoconstriction in lung regions not directly reached by INO. The aim of this study was to investigate whether INO has distant effects in endotoxemic pig lungs. The hypothesis was that INO down-regulates endogenous NO production in lung regions not reached by INO. DESIGN: Prospective, randomized animal study. SETTING: University hospital research laboratory. SUBJECTS: Twenty-two pairs of domestic pigs. INTERVENTIONS: Cross-circulation was established in 22 pairs of anesthetized pigs. Nine pairs received endotoxin (control group) and 13 pairs received endotoxin, with one pig inhaling NO (80 ppm) and one pig receiving blood from that pig (NO-blood recipient group). MEASUREMENTS AND MAIN RESULTS: NO in exhaled air, NO synthase activity in lung tissue, endothelin-1 in the blood, ETA and ETB receptor immunoreactivity in lung tissue, vital parameters, and blood gases were measured. Endotoxin per se increased NO in exhaled air by 100% compared to baseline (control group). In the NO-blood recipient group, i.e., pigs receiving blood from the NO-inhaling pigs, NO in exhaled air increased by 300% (p = .03). The Ca-dependent NO synthase activity was higher in these pigs (p = .02), indicating increased endogenous NO production. The ET B receptor immunoreactivity was higher in the NO-blood recipient group (p = .004). CONCLUSIONS: As opposed to findings in healthy pigs, INO in endotoxemic pigs causes an increase in endogenous NO production in lung regions not reached by INO. Increased NO production in nonventilated lung regions may cause vasodilatation, counteracting the INO-induced increase in blood flow to the ventilated lung regions.

Prevention of atelectasis in morbidly obese patients during general anesthesia and paralysis: a computerized tomography study.

BACKGROUND: Morbidly obese patients show impaired pulmonary function during anesthesia and paralysis, partly due to formation of atelectasis. This study analyzed the effect of general anesthesia and three different ventilatory strategies to reduce the amount of atelectasis and improve respiratory function. METHODS: Thirty patients (body mass index 45 +/- 4 kg/m) scheduled for gastric bypass surgery were prospectively randomized into three groups: (1) positive end-expiratory pressure of 10 cm H2O (PEEP), (2) a recruitment maneuver with 55 cm H2O for 10 s followed by zero end-expiratory pressure, (3) a recruitment maneuver followed by PEEP. Transverse lung computerized tomography scans and blood gas analysis were recorded: awake, 5 min after induction of anesthesia and paralysis at zero end-expiratory pressure, and 5 min and 20 min after intervention. In addition, spiral computerized tomography scans were performed at two occasions in 23 of the patients. RESULTS: After induction of anesthesia, atelectasis increased from 1 +/- 0.5% to 11 +/- 6% of total lung volume (P < 0.0001). End-expiratory lung volume decreased from 1,387 +/- 581 ml to 697 +/- 157 ml (P = 0.0014). A recruitment maneuver + PEEP reduced atelectasis to 3 +/- 4% (P = 0.0002), increased end-expiratory lung volume and increased Pao2/Fio2 from 266 +/- 70 mmHg to 412 +/- 99 mmHg (P < 0.0001). PEEP alone did not reduce the amount of atelectasis or improve oxygenation. A recruitment maneuver + zero end-expiratory pressure had a transient positive effect on respiratory function. All values are presented as mean +/- SD. CONCLUSIONS: A recruitment maneuver followed by PEEP reduced atelectasis and improved oxygenation in morbidly obese patients, whereas PEEP or a recruitment maneuver alone did not.

Central hemodynamics during lung recruitment maneuvers at hypovolemia, normovolemia and hypervolemia. A study by echocardiography and continuous pulmonary artery flow measurements in lung-injured pigs.

OBJECTIVE: The impact of lung-recruitment maneuvers on heart function at different volemic levels has not been studied in detail. We therefore investigated the effect on central hemodynamics of lung recruitment maneuvers at hypovolemia, normovolemia and hypervolemia in experimental lung injury. DESIGN: Randomized, controlled, cross-over experimental study. SETTING: Animal laboratory at a university hospital. PARTICIPANTS: Eleven anesthetized and lung-lavaged pigs. INTERVENTION: The animals were randomized to 10-s lung recruitment maneuvers followed by 30-s maneuvers (40 cm H(2)O airway pressure) or vice versa, performed under hypovolemia, normovolemia and hypervolemia. MEASUREMENTS AND MAIN RESULTS: Left-ventricular end-diastolic diameter and cardiac output were measured before, during, and 1 min and 5 min after the lung recruitment maneuver and left-ventricular eccentricity index was calculated for before and during the maneuver. Cardiac output and left-ventricular end-diastolic diameter (within parentheses) decreased significantly during both the 10-s and 30-s lung recruitment maneuvers at hypovolemia, by a mean of 89% (35) and 92% (33), at normovolemia by 75% (33) and 86% (32), and at hypervolemia by 56% (32) and 64% (43), respectively. At hypovolemia, cardiac output was increased above baseline 1-5 min following the 30-s maneuver. Left-ventricular eccentricity index increased significantly during the maneuver, indicating right ventricular dysfunction. CONCLUSIONS: In this animal lung injury model, lung recruitment maneuvers significantly decreased left-ventricular end-diastolic volume and cardiac output at hypovolemia. Hypervolemia did partly counteract this compromise. In addition, a marked right-ventricular dysfunction during the maneuver was found.