Bench-to-bedside review: ventilatory abnormalities in sepsis

Are Deep Odontogenic Infections Associated With an Increased Risk for Sepsis?

BACKGROUND

Quick Sequential Organ Failure Assessment (qSOFA) is recommended to identify sepsis. Odontogenic infection (OI) can progress to sepsis, causing systematic inflammatory complications or organ failure.

PURPOSE

The purpose of the study was to measure the association between OI location and risk for sepsis at admission.

STUDY DESIGN, SETTING, AND SAMPLE

This retrospective cohort study included subjects treated for OI at Baylor University Medical Center in Dallas, TX, from January 9, 2019 to July 30, 2022. Subjects > 18 years old who were treated under general anesthesia were included. OI limited to periapical, vestibular, buccal, and/or canine spaces were excluded from the sample.

PREDICTOR VARIABLE

The primary predictor variable was OI anatomic location (superficial or deep). Superficial OI infection includes submental, submandibular, sublingual, submasseteric, and/or superficial temporal spaces. Deep OI includes pterygomandibular, deep temporal, lateral pharyngeal, retropharyngeal, pretracheal, and/or prevertebral.

MAIN OUTCOME VARIABLES

The primary outcome variable was risk for sepsis measured using a qSOFA score (0 to 3). A higher score (>0) indicates the patient has a high risk for sepsis.

COVARIATES

Covariates were demographics, clinical, laboratory, and radiological findings, antibiotic route, postoperative endotracheal intubation, tracheostomy, intensive care unit, admission, and length of stay.

ANALYSES

Descriptive and bivariate analyses were performed. A χ2 test was used for categorical variables. The Mann-Whitney U test was used for continuous variables. Statistical significance was P < .05.

RESULTS

The sample was composed of 168 subjects with a mean age of 42.8 ± 21.5 and 69 (48.6%) subjects were male. There were 11 (6.5%) subjects with a qSOFA score > 0. The relative risk of a qSOFA > 0 for a deep OI is 5.4 times greater than for a superficial OI (136 (95.8) versus 21 (80.8%): RR (95% confidence interval): 5.4 (1.51 to 19.27), P = .004). After adjusting for age, sex, American Society of Anesthesiologists score, and involved anatomical spaces, there was a significant correlation between laterality and the number of involved anatomical spaces and qSOFA score (odd ratio = 9.13, 95% confidence interval: 2.48 to 33.55, adjusted P = <.001).

CONCLUSION AND RELEVANCE

The study findings suggest that the OI location is associated with the qSOFA score >0.

The accuracy and feasibility of respiratory rate measurements in acutely ill adult patients by GPs: a mixed-methods study

BACKGROUND

Tachypnoea in acutely ill patients can be an early sign of a life-threatening condition such as sepsis. Routine measurement of the respiratory rate by GPs might improve the recognition of sepsis.

AIM

To assess the accuracy and feasibility of respiratory rate measurements by GPs.

DESIGN & SETTING

Observational cross-sectional mixed-methods study in the setting of out-of-hours (OOH) home visits at three GP cooperatives in The Netherlands.

METHOD

GPs were observed during the assessment of acutely ill patients, and semi-structured interviews were performed. The GP-assessed respiratory rate was compared with a reference measurement. In the event that the respiratory rate was not counted, GPs were asked to estimate the rate (dichotomised as ≥22 breaths per minute or <22 breaths per minute).

RESULTS

Observations of 130 acutely ill patients were included, and 14 GPs were interviewed. In 33 patients (25%), the GP counted the respiratory rate. A mean difference of 0.27 breaths per minute (95% confidence interval [CI] = -5.7 to 6.3) with the reference measurement was found. At a cut-off point of ≥22 breaths per minute, a sensitivity of 86% (95% CI = 57% to 98%) was found when the GP counted the rate, and a sensitivity of 43% (95% CI = 22% to 66%) when GPs estimated respiratory rates. GPs reported both medical and practical reasons for not routinely measuring the respiratory rate.

CONCLUSION

GPs are aware of the importance of assessing the respiratory rate of acutely ill adult patients, and counted measurements are accurate. However, in most patients the respiratory rate was not counted, and the rate was often underestimated when estimated.

Analysis of respiratory kinematics: a method to characterize breaths from motion signals

Breathing motion (respiratory kinematics) can be characterized by the interval and depth of each breath, and by magnitude-synchrony relationships between locations. Such characteristics and their breath-by-breath variability might be useful indicators of respiratory health. To enable breath-by-breath characterization of respiratory kinematics, we developed a method to detect breaths using motion sensors. In 34 volunteers who underwent maximal exercise testing, we used 8 motion sensors to record upper rib, lower rib and abdominal kinematics at 3 exercise stages (rest, lactate threshold and exhaustion). We recorded volumetric air flow signals using clinical exercise laboratory equipment and synchronized them with kinematic signals. Using instantaneous phase landmarks from the analytic representation of kinematic and flow signals, we identified individual breaths and derived respiratory rate (RR) signals at 1Hz. To evaluate the fidelity of kinematics-derived RR, we calculated bias, limits of agreement, and cross-correlation coefficients (CCC) relative to flow-derived RR. To identify coupling between kinematics and flow, we calculated the Shannon entropy of the relative frequency with which flow landmarks were distributed over the phase of the kinematic cycle. We found good agreement in the kinematics-derived and flow-derived RR signals [bias (95% limit of agreement) = 0.1 (± 7) breaths/minute; CCC median (IQR) = 0.80 (0.48 - 0.91)]. In individual signals, kinematics and flow were well-coupled (entropy 0.9-1.4 across sensors), but the relationship varied within (by exercise stage) and between individuals. The final result was that the flow landmarks did not consistently localize to any particular phase of the kinematic signals (entropy 2.2-3.0 across sensors). The Analysis of Respiratory Kinematics method can yield highly resolved respiratory rate signals by separating individual breaths. This method will facilitate characterization of clinically significant breathing motion patterns on a breath-by-breath basis. The relationship between respiratory kinematics and flow is much more complex than expected, varying between and within individuals.

Respiratory Drive in Patients with Sepsis and Septic Shock: Modulation by High-flow Nasal Cannula

BACKGROUND

Experimental and pilot clinical data suggest that spontaneously breathing patients with sepsis and septic shock may present increased respiratory drive and effort, even in the absence of pulmonary infection. The study hypothesis was that respiratory drive and effort may be increased in septic patients and correlated with extrapulmonary determinant and that high-flow nasal cannula may modulate drive and effort.

METHODS

Twenty-five nonintubated patients with extrapulmonary sepsis or septic shock were enrolled. Each patient underwent three consecutive steps: low-flow oxygen at baseline, high-flow nasal cannula, and then low-flow oxygen again. Arterial blood gases, esophageal pressure, and electrical impedance tomography data were recorded toward the end of each step. Respiratory effort was measured as the negative swing of esophageal pressure (ΔPes); drive was quantified as the change in esophageal pressure during the first 500 ms from start of inspiration (P0.5). Dynamic lung compliance was calculated as the tidal volume measured by electrical impedance tomography, divided by ΔPes. The results are presented as medians [25th to 75th percentile].

RESULTS

Thirteen patients (52%) were in septic shock. The Sequential Organ Failure Assessment score was 5 [4 to 9]. During low-flow oxygen at baseline, respiratory drive and effort were elevated and significantly correlated with arterial lactate (r = 0.46, P = 0.034) and inversely with dynamic lung compliance (r = -0.735, P < 0.001). Noninvasive support by high-flow nasal cannula induced a significant decrease of respiratory drive (P0.5: 6.0 [4.4 to 9.0] vs. 4.3 [3.5 to 6.6] vs. 6.6 [4.9 to 10.7] cm H2O, P < 0.001) and effort (ΔPes: 8.0 [6.0 to 11.5] vs. 5.5 [4.5 to 8.0] vs. 7.5 [6.0 to 12.6] cm H2O, P < 0.001). Oxygenation and arterial carbon dioxide levels remained stable during all study phases.

CONCLUSIONS

Patients with sepsis and septic shock of extrapulmonary origin present elevated respiratory drive and effort, which can be effectively reduced by high-flow nasal cannula.

EDITOR’S PERSPECTIVE

Assessment of Sepsis in the ICU by Linear and Complex Characterization of Cardiovascular Dynamics

Sepsis is one of the pathological conditions with the highest incidence in intensive care units. Sepsis-induced cardiac and autonomic dysfunction are well-known effects, among others, caused by a dysregulated host response to infection. In this context, we investigate the role of complex cardiovascular dynamics quantified through sample entropy indices from the inter-beat interval, systolic and diastolic blood pressure time series as well as the cross-entropy between heartbeat and systolic blood pressure in patients with sepsis in the first hour of intensive care when compared with non-septic subjects. Results show a significant (p<0.05) reduction in the probability of being septic for a unitary increase in entropy for systolic and diastolic time series (odds equal to 0.038 and 0.264, respectively) when adjusting for confounding factors. A significant (p<0.001) odds ratio (0.248) is observed also in cross-entropy, showing a reduced probability of being septic for an increase in heartbeat and systolic pressure asynchrony. The inclusion of our measures of complexity also determines an increase in the predictive ability (+0.03) of a logistic regression model reaching an area under the receiving operating and precision recall curves both equal to 0.95.Clinical relevance The study demonstrates the ability of information theory in catching a reduction of complex cardiovascular dynamics from vital signs commonly recorded in ICU. The considered complexity measures contribute to characterize sepsis development by showing a general loss of the interaction between heartbeat and pressure regulation. The extracted measures also improve the ability to identify sepsis in the first hour of intensive care.

Hemodynamics of the sternocleidomastoid measured with frequency domain near-infrared spectroscopy towards non-invasive monitoring during mechanical ventilation

Mechanical ventilation (MV) is used to assist spontaneous breathing in critically ill patients in the intensive care unit (ICU). MV is a cornerstone of critical care medicine but it is now known that inspiratory muscle dysfunction due to injury, disuse, and/or atrophy during MV plays a major role in outcomes for these patients. For example, prolonged MV is strongly correlated with dysfunction of the sternocleidomastoid (SCM), an accessory inspiratory muscle that has been linked to weaning failure from MV. Hemodynamic monitoring of the SCM may provide an important non-invasive and real-time means to monitor MV. In this work, we first conducted multi-layer Monte Carlo simulations to confirm the ability of near infrared light to detect changes in the oxygenation of the SCM over wide ranges of skin tones and adipose layer thicknesses. We then optimized a custom digital frequency domain near-infrared spectroscopy (FD-NIRS) system for continuous 10 Hz measurements of the SCM at 730 nm and 850 nm. A healthy volunteer study was conducted (N=10); subjects performed sets of isometric neck flexions of the SCM. Substantial changes in oxyhemoglobin + oxymyoglobin (oxy[Hb + Mb]), deoxyhemoglobin + deoxymyoglobin (deoxy[Hb + Mb]), and total hemoglobin + myoglobin (total[Hb + Mb]) were observed during sustained and intermittent isometric flexions. There were notable sex differences observed in the magnitude of hemodynamic changes (∼2x larger changes in males for oxy[Hb + Mb] and deoxy[Hb + Mb]). The magnitude of hemodynamic changes when taking into account µ_s' changes during flexions was ∼ 2-2.5x larger as compared to assuming constant scattering (CS), which is a common assumption used for continuous wave (CW) NIRS methods. This study suggests that FD-NIRS provides improved accuracy for hemodynamic monitoring of the SCM compared to CW-NIRS, and that FD-NIRS may provide value for SCM monitoring during MV.

Clinical and experimental aspects of breathing modulation by inflammation

Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.

Regulation of Akt-mTOR, ubiquitin-proteasome and autophagy-lysosome pathways in locomotor and respiratory muscles during experimental sepsis in mice

Sepsis induced loss of muscle mass and function contributes to promote physical inactivity and disability in patients. In this experimental study, mice were sacrificed 1, 4, or 7 days after cecal ligation and puncture (CLP) or sham surgery. When compared with diaphragm, locomotor muscles were more prone to sepsis-induced muscle mass loss. This could be attributed to a greater activation of ubiquitin-proteasome system and an increased myostatin expression. Thus, this study strongly suggests that the contractile activity pattern of diaphragm muscle confers resistance to atrophy compared to the locomotor gastrocnemius muscle. These data also suggest that a strategy aimed at preventing the activation of catabolic pathways and preserving spontaneous activity would be of interest for the treatment of patients with sepsis-induced neuromyopathy.

Preservation of renal blood flow by the antioxidant EUK-134 in LPS-treated pigs

Sepsis is associated with an increase in reactive oxygen species (ROS), however, the precise role of ROS in the septic process remains unknown. We hypothesized that treatment with EUK-134 (manganese-3-methoxy N,N'-bis(salicyclidene)ethylene-diamine chloride), a compound with superoxide dismutase and catalase activity, attenuates the vascular manifestations of sepsis in vivo. Pigs were instrumented to measure cardiac output and blood flow in renal, superior mesenteric and femoral arteries, and portal vein. Animals were treated with saline (control), lipopolysaccharide (LPS; 10 µg·kg-1·h-1), EUK-134, or EUK-134 plus LPS. Results show that an LPS-induced increase in pulmonary artery pressure (PAP) as well as a trend towards lower blood pressure (BP) were both attenuated by EUK-134. Renal blood flow decreased with LPS whereas superior mesenteric, portal and femoral flows did not change. Importantly, EUK-134 decreased the LPS-induced fall in renal blood flow and this was associated with a corresponding decrease in LPS-induced protein nitrotyrosinylation in the kidney. PO2, pH, base excess and systemic vascular resistance fell with LPS and were unaltered by EUK-134. EUK-134 also had no effect on LPS-associated increase in CO. Interestingly, EUK-134 alone resulted in higher CO, BP, PAP, mean circulatory filling pressure, and portal flow than controls. Taken together, these data support a protective role for EUK-134 in the renal circulation in sepsis.

Respiratory distress in the newborn

Respiratory distress presents as tachypnea, nasal flaring, retractions, and grunting and may progress to respiratory failure if not readily recognized and managed. Causes of respiratory distress vary and may not lie within the lung. A thorough history, physical examination, and radiographic and laboratory findings will aid in the differential diagnosis. Common causes include transient tachypnea of the newborn, neonatal pneumonia, respiratory distress syndrome (RDS), and meconium aspiration syndrome (MAS). Strong evidence reveals an inverse relationship between gestational age and respiratory morbidity. (1)(2)(9)(25)(26) Expert opinion recommends careful consideration about elective delivery without labor at less than 39 weeks’ gestation. Extensive evidence, including randomized control trials, cohort studies, and expert opinion, supports maternal group B streptococcus screening, intrapartum antibiotic prophylaxis, and appropriate followup of high-risk newborns according to guidelines established by the Centers for Disease Control and Prevention. (4)(29)(31)(32)(34) Following these best-practice strategies is effective in preventing neonatal pneumonia and its complications. (31)(32)(34). On the basis of strong evidence, including randomized control trials and Cochrane Reviews, administration of antenatal corticosteroids (5) and postnatal surfactant (6) decrease respiratory morbidity associated with RDS. Trends in perinatal management strategies to prevent MAS have changed. There is strong evidence that amnioinfusion, (49) oropharyngeal and nasopharyngeal suctioning at the perineum, (45) or intubation and endotracheal suctioning of vigorous infants (46)(47) do not decrease MAS or its complications. Some research and expert opinion supports endotracheal suctioning of nonvigorous meconium-stained infants (8) and induction of labor at 41 weeks’ gestation (7) to prevent MAS.

From data patterns to mechanistic models in acute critical illness

The complexity of the physiologic and inflammatory response in acute critical illness has stymied the accurate diagnosis and development of therapies. The Society for Complex Acute Illness was formed a decade ago with the goal of leveraging multiple complex systems approaches to address this unmet need. Two main paths of development have characterized the society's approach: (i) data pattern analysis, either defining the diagnostic/prognostic utility of complexity metrics of physiologic signals or multivariate analyses of molecular and genetic data and (ii) mechanistic mathematical and computational modeling, all being performed with an explicit translational goal. Here, we summarize the progress to date on each of these approaches, along with pitfalls inherent in the use of each approach alone. We suggest that the next decade holds the potential to merge these approaches, connecting patient diagnosis to treatment via mechanism-based dynamical system modeling and feedback control and allowing extrapolation from physiologic signals to biomarkers to novel drug candidates. As a predicate example, we focus on the role of data-driven and mechanistic models in neuroscience and the impact that merging these modeling approaches can have on general anesthesia.

Use of expiratory change in bladder pressure to assess expiratory muscle activity in patients with large respiratory excursions in central venous pressure

BACKGROUND

Expiratory muscle activity may cause the end-expiratory central venous pressure (CVP) to greatly overestimate right atrial transmural pressure.

METHODS

We recorded CVP and expiratory change in intra-abdominal pressure (ΔIAP) in 39 patients who had a respiratory excursion in CVP from end-expiration to end-inspiration (CVP(ee)-CVP(ei)) ≥ 8 mmHg. Uncorrected CVP was measured at end-expiration, and corrected CVP was calculated as uncorrected CVP-ΔIAP. In 13 patients measurements were repeated during relaxed breathing.

RESULTS

The CVP(ee)-CVP(ei) was 15.2 ± 6.3 mmHg (range 8-34 mmHg), and ΔIAP was 7.4 ± 6.0 mmHg (range 0-30 mmHg). Uncorrected CVP was 18.3 ± 6.1 mmHg, and corrected CVP was 10.9 ± 3.9 mmHg. There was a significant positive correlation between CVP(ee)-CVP(ei) and ΔIAP (r = 0.814). However, some patients with a large CVP(ee)-CVP(ei) had negligible ΔIAP. In a subset of 13 patients with active expiration who had a relaxed CVP tracing available for comparison, the difference between uncorrected CVP and relaxed CVP was much greater than the difference between corrected CVP and relaxed CVP (7.3 ± 3.0 vs. 1.1 ± 0.7 mmHg, p < 0.001).

CONCLUSION

Patients with large respiratory excursions in CVP often have significant expiratory muscle activity that will cause their CVP to overestimate transmural right atrial pressure. The magnitude of expiratory muscle activity can be assessed by measuring ΔIAP. Subtracting ΔIAP from the end-expiratory CVP usually provides a reasonable estimate of the CVP that would be obtained if exhalation were passive.

Sepsis: from pattern to mechanism and back

Sepsis is a clinical entity in which complex inflammatory and physiological processes are mobilized, not only across a range of cellular and molecular interactions, but also in clinically relevant physiological signals accessible at the bedside. There is a need for a mechanistic understanding that links the clinical phenomenon of physiologic variability with the underlying patterns of the biology of inflammation, and we assert that this can be facilitated through the use of dynamic mathematical and computational modeling. An iterative approach of laboratory experimentation and mathematical/computational modeling has the potential to integrate cellular biology, physiology, control theory, and systems engineering across biological scales, yielding insights into the control structures that govern mechanisms by which phenomena, detected as biological patterns, are produced. This approach can represent hypotheses in the formal language of mathematics and computation, and link behaviors that cross scales and domains, thereby offering the opportunity to better explain, diagnose, and intervene in the care of the septic patient.

Sepsis: Something old, something new, and a systems view

Sepsis is a clinical syndrome characterized by a multisystem response to a microbial pathogenic insult consisting of a mosaic of interconnected biochemical, cellular, and organ-organ interaction networks. A central thread that connects these responses is inflammation that, while attempting to defend the body and prevent further harm, causes further damage through the feed-forward, proinflammatory effects of damage-associated molecular pattern molecules. In this review, we address the epidemiology and current definitions of sepsis and focus specifically on the biologic cascades that comprise the inflammatory response to sepsis. We suggest that attempts to improve clinical outcomes by targeting specific components of this network have been unsuccessful due to the lack of an integrative, predictive, and individualized systems-based approach to define the time-varying, multidimensional state of the patient. We highlight the translational impact of computational modeling and other complex systems approaches as applied to sepsis, including in silico clinical trials, patient-specific models, and complexity-based assessments of physiology.