Blood gas analysis and critical care medicine

Technical Innovation in Critical Care in a World of Constraints: Lessons from the COVID-19 Pandemic

The COVID-19 crisis was characterized by a massive need for respiratory support, which has unfortunately not been met globally. This situation mimicked those which gave rise to critical care in the past. Since the polio epidemic in the 50's, the technological evolution of respiratory support has enabled health professionals to save the lives of critically-ill patients worldwide every year. However, much of the current innovation work has turned around developing sophisticated, complex, and high-cost standards and approaches whose resilience is still questionable upon facing constrained environments or contexts, as seen in resuscitation work outside intensive care units, during pandemics, or in low-income countries. Ventilatory support is an essential life-saving tool for patients with respiratory distress. It requires an oxygen source combined to a ventilatory assistance device, an adequate monitoring system, and properly trained caregivers to operate it. Each of these elements can be subject to critical constraints, which we can no longer ignore. The innovation process should incorporate them as a prima materia, whilst focusing on the core need of the field using the concept of frugal innovation. Having a universal access to oxygen and respiratory support, irrespective of the context and constraints, necessitates: i) developing cost-effective, energy-efficient, and maintenance-free oxygen generation devices; ii) improving the design of non-invasive respiratory devices (for example, with oxygen saving properties); iii) conceiving fully frugal ventilators and universal monitoring systems; iv) broadening ventilation expertise by developing end-user training programs in ventilator assistance. The frugal innovation approach may give rise to a more resilient and inclusive critical care system. This paradigm shift is essential for the current and future challenges.

A Toolbox to Investigate the Impact of Impaired Oxygen Delivery in Experimental Disease Models

Impaired oxygen utilization is the underlying pathophysiological process in different shock states. Clinically most important are septic and hemorrhagic shock, which comprise more than 75% of all clinical cases of shock. Both forms lead to severe dysfunction of the microcirculation and the mitochondria that can cause or further aggravate tissue damage and inflammation. However, the detailed mechanisms of acute and long-term effects of impaired oxygen utilization are still elusive. Importantly, a defective oxygen exploitation can impact multiple organs simultaneously and organ damage can be aggravated due to intense organ cross-talk or the presence of a systemic inflammatory response. Complexity is further increased through a large heterogeneity in the human population, differences in genetics, age and gender, comorbidities or disease history. To gain a deeper understanding of the principles, mechanisms, interconnections and consequences of impaired oxygen delivery and utilization, interdisciplinary preclinical as well as clinical research is required. In this review, we provide a "tool-box" that covers widely used animal disease models for septic and hemorrhagic shock and methods to determine the structure and function of the microcirculation as well as mitochondrial function. Furthermore, we suggest magnetic resonance imaging as a multimodal imaging platform to noninvasively assess the consequences of impaired oxygen delivery on organ function, cell metabolism, alterations in tissue textures or inflammation. Combining structural and functional analyses of oxygen delivery and utilization in animal models with additional data obtained by multiparametric MRI-based techniques can help to unravel mechanisms underlying immediate effects as well as long-term consequences of impaired oxygen delivery on multiple organs and may narrow the gap between experimental preclinical research and the human patient.

Prefer early tracheostomy

Tracheotomies are commonly performed for the patients with low GCS who needs a respiratory support. Still over the period there existed a controversy when to do tracheotomy ?  Early or late. Our study aimed at reassessing the complications of delayed tracheotomy versus the advantages of the early tracheostomy. This was a prospective comparative, observational study comprising of 140 patients in 2 different hospitals admitted to the neurosurgery ICU with poor GCS. Group A: Early tracheostomy (2-5 days) and Group B: Late tracheostomy (7-14 days). Both groups were followed ,Early tracheostomy required a mechanical ventilator support for average  5-8 days with early weaning  whereas late tracheostomy required 12-20 days of mechanical

Vitamin E and preterm infants

In evaluating vitamin E (VE) nutritional status of preterm infants, it is essential that any data should be compared with those of healthy term infants, and never with those of adults. Moreover, it should be evaluated in terms of gestational age (GA), not birth weight (BW), because placental transfer of most nutrients from mother to fetus is dependent on GA, not BW. Judging from the limited data during the last 75 years, there was no significant correlation between GA and VE concentrations in circulation or in the red blood cells (RBCs), leukocytes, and buccal mucosal cells. In addition, the oxidizability of polyunsaturated fatty acids (PUFAs) in plasma or RBCs, as targets for protection by VE chain-breaking ability, was lower in preterm infants. However, because of the minimal information available about hepatic VE levels, which is considered a key determinant of whole body VE status, the decision on whether VE status of preterm infants is comparable with that of term infants should be postponed. Clinical trials of VE supplementation in preterm infants were repeatedly undertaken to investigate whether VE reduces severity or inhibits development of several diseases specific to preterm infants, namely retinopathy of prematurity (ROP), bronchopulmonary dysplasia (BPD), and germinal matrix hemorrhage - intraventricular hemorrhage (GMH-IVH). Most of these trials resulted in a misfire, with a few exceptions for IVH prevention. However, almost all these studies were performed from 1980s to early 1990s, in the pre-surfactant era, and the study populations were composed of mid-preterm infants with GAs of approximately 30 weeks (wks). There is considerable difference in 'preterm infants' between the pre- and post-surfactant eras; modern neonatal medicine mainly treats preterm infants of 28 wks GA or less. Therefore, these results are difficult to apply in modern neonatal care. Before considering new trials of VE supplementation, we should fully understand modern neonatal medicine, especially the recent method of oxygen supplementation. Additionally, a deeper understanding of recent progress in pathophysiology and therapies for possible target diseases is necessary to decide whether VE administration is still worth re-challenging in modern neonatal intensive care units (NICUs). In this review, we present recent concepts and therapeutic trends in ROP, BPD, and GMH-IVH for those unfamiliar with neonatal medicine. Numerous studies have reported the possible involvement of reactive oxygen species (ROS)-induced damage in relation to supplemental oxygen use, inflammation, and immature antioxidant defense in the development of both BPD and ROP. Various antioxidants effectively prevented the exacerbation of BPD and ROP in animal models. In the future, VE should be re-attempted as a complementary factor in combination with various therapies for BPD, ROP, and GMH-IVH. Because VE is a natural and safe supplement, we are certain that it will attract attention again in preterm medicine.

Implementation of point-of-care blood gas testing at a large community hospital: Cost analysis, sepsis bundle compliance, and employee engagement

INTRODUCTION/BACKGROUND

Point-of-care testing (POCT) platforms support patient-centered approaches to health care delivery and may improve patient care. We evaluated implementation of a POCT platform at a large, acute care hospital in the Midwestern United States.

METHODS

We used lactate testing as part of a sepsis bundle protocol to evaluate compliance and mortality outcomes. Respiratory team members were surveyed to assess perception of efficiency, ease of use, timely patient care, and overall engagement with the POCT system. Annualized cost per test of a benchtop analyzer and a POCT platform were compared across 3 years for each platform.

RESULTS

Lactate testing volume increased from 61% to 91%, which was associated with improved sepsis bundle protocol compliance. Employees reported high levels of engagement, improvements in efficiency and time savings, and better patient care with POCT. Average cost per test was $10.02 for the benchtop system and $6.21 for the POCT platform. POCT saved our institution $88,476 annually in labor costs.

DISCUSSION

Combined with a robust training program emphasizing the use of lactate testing in the context of the overall clinical picture, POCT enabled adherence to the sepsis bundle protocol and may have contributed to lower mortality. Additionally, the COVID-19 pandemic has provided us with unanticipated benefits of using POCT; it has enhanced our ability to deal with stringent infectious disease protocols, saving time and minimizing patient and staff exposure.

CONCLUSIONS

Implementation of a POCT platform was associated with improved compliance to our sepsis protocol, reduced sepsis mortality, high employee engagement, and cost savings.

A Noninvasive Miniaturized Transcutaneous Oxygen Monitor

Transcutaneous monitoring is a noninvasive method to continuously measure the partial pressures of oxygen and carbon dioxide that diffuse through the skin and correlate closely with changes in blood gases. However, the contemporary commercially available electrochemical-based technology requires a heating mechanism and a bulky, corded, and expensive sensing unit. This study aims to demonstrate a prototype noninvasive, miniaturized monitor that uses luminescence-based technology to measure the partial pressure of transcutaneous oxygen, a surrogate of the partial pressure of arterial oxygen. To be able to build a robust measurement system, we conducted experiments to understand the temperature and humidity dependence of oxygen-sensitive platinum-porphyrin films. We performed a detailed analysis of both intensity and lifetime measurement techniques. To verify the performance, we tested the prototype in a small ex-vivo experiment involving three healthy human volunteers. We measured variations in the partial pressure of transcutaneous oxygen values due to pressure-induced arterial and venous occlusions on the volunteers' fingertips. The system resolves changes in the partial pressure of oxygen from 0 to 418 mmHg in the lab bench-top testing, covering the medically relevant range of 50-150 mmHg. Under fixed humidity, temperature, and the partial pressure of oxygen conditions, the sensor shows a 2% drift over 60 hours. The prototype consumes 9 mW of power from a 2.2 V external DC power supply.

Robust non-contact peripheral oxygenation saturation measurement using smartphone-enabled imaging photoplethysmography

We propose a robust non-contact method to accurately estimate peripheral oxygen saturation (SpO₂) using a smartphone-based imaging photoplethysmography. The method utilizes the built-in color camera as a remote sensor and the built-in flashlight as illumination to estimate the SpO₂. Following the ratio of ratios between green and red channels, we introduce a multiple linear regression algorithm to improve the SpO₂ estimation. The algorithm considers the ratio of ratios and the reflectance images recorded at the RGB channels during a calibration process to obtain a set of weighting coefficients to weigh each contributor to the final determination of SpO₂. We demonstrate the proposed smartphone-based method of estimating the SpO₂ on five healthy volunteers whose arms are conditioned by a manual pressure cuff to manipulate the SpO₂ between 90∼100% as detected simultaneously by a medical-grade pulse oximeter. Experimental results indicate that the overall estimated error between the smartphone and the reference pulse oximeter is 0.029 ± 1.141%, leading to a 43% improvement over the conventional ratio of ratios method (0.008 ± 2.008%). In addition, the data sampling time in the current method is 2 seconds, similar to the sampling cycle used in the commercial medical-grade pulse oximeters.

Respiratory Monitoring: Current State of the Art and Future Roads

In this article, we present current methodologies, available technologies, and demands for monitoring various respiratory parameters. We discuss the importance of noninvasive techniques for remote and continuous monitoring and challenges involved in the current "smart and connected health" era. We conducted an extensive literature review on the medical significance of monitoring respiratory vital parameters, along with the current methods and solutions with their respective advantages and disadvantages. We discuss the challenges of developing a noninvasive, wearable, wireless system that continuously monitors respiration parameters and opportunities in the field and then determines the requirements of a state-of-the-art system. Noninvasive techniques provide a significant amount of medical information for a continuous patient monitoring system. Contact methods offer more advantages than non-contact methods; however, reducing the size and power of contact methods is critical for enabling a wearable, wireless medical monitoring system. Continuous and accurate remote monitoring, along with other physiological data, can help caregivers improve the quality of care and allow patients greater freedom outside the hospital. Such monitoring systems could lead to highly tailored treatment plans, shorten patient stays at medical facilities, and reduce the cost of treatment.

Resting TcPO2 levels decrease during liner wear in persons with a transtibial amputation

Background

In our clinic, a substantial number of patients present with transtibial residual limb pain of no specific somatic origin. Silicone liner induced tissue compression may reduce blood flow, possibly causing residual limb pain. Thus, as a first step we investigated if the liner itself has an effect on transcutaneous oxygen pressure (TcPO2).

Methods

Persons with unilateral transtibial amputation and residual limb pain of unknown origin were included. Medical history, including residual limb pain, was recorded, and the SF-36 administered. Resting TcPO2 levels were measured in the supine position and without a liner at 0, 10, 20 and 30 minutes using two sensors: one placed in the Transverse plane over the tip of the Tibia End (= TTE), the other placed in the Sagittal plane, distally over the Peroneal Compartment (= SPC). Measurements were repeated with specially prepared liners avoiding additional pressure due to sensor placement. Statistical analyses were performed using SPSS.

Results

Twenty persons (9 women, 11 men) with a mean age of 68.65 years (range 47–86 years) participated. The transtibial amputation occurred on average 43 months prior to study entry (range 3–119 months). With liner wear, both sensors measured TcPO2 levels that were significantly lower than those measured without a liner (TTE: p < 0.001; SPC: p = 0.002) after 10, 20 and 30 minutes. No significant differences were found between TcPO2 levels over time between the sensors. There were no significant associations between TcPO2 levels and pain, smoking status, age, duration of daily liner use, mobility level, and revision history.

Conclusion

Resting TcPO2 levels decreased significantly while wearing a liner alone, without a prosthetic socket. Further studies are required to investigate the effect of liner wear on exercise TcPO2 levels.

Enhanced Hemocompatibility and In Vivo Analytical Accuracy of Intravascular Potentiometric Carbon Dioxide Sensors via Nitric Oxide Release

In this letter, the innate ability of nitric oxide (NO) to inhibit platelet activation/adhesion/thrombus formation is employed to improve the hemocompatibility and in vivo accuracy of an intravascular (IV) potentiometric PCO₂ (partial pressure of carbon dioxide) sensor. The catheter-type sensor is fabricated by impregnating a segment of dual lumen silicone tubing with a proton ionophore, plasticizer, and lipophilic cation-exchanger. Subsequent filling of bicarbonate and strong buffer solutions and placement of Ag/AgCl reference electrode wires within each lumen, respectively, enables measurement of the membrane potential difference across the inner wall of the tube, with this potential changing as a function of the logarithm of sample PCO₂. The dual lumen device is further encapsulated within a S-nitroso-N-acetyl-DL-penicillamine (SNAP)-doped silicone tube that releases physiological levels of NO. The NO releasing sensor exhibits near-Nernstian sensitivity toward PCO₂ (slope = 59.31 ± 0.78 mV/decade) and low drift rates (<2 mV/24 h after initial equilibration). In vivo evaluation of the NO releasing sensors, performed in the arteries and veins of anesthetized pigs for 20 h, shows enhanced accuracy (vs non-NO releasing sensors) when benchmarked to measurements of discrete blood samples made with a commercial blood gas analyzer. The accurate, continuous monitoring of blood PCO₂ levels achieved with this new IV NO releasing PCO₂ sensor configuration could help better manage hospitalized patients in critical care units.

Arterio-VENouS Intra Subject agreement for blood gases within intensive care: The AVENSIS study

Background

In critically ill patients, who require multiple blood gas assessments, agreement between arterial and venous blood gas values for pH and partial pressure of carbon dioxide, is not clear. Good agreement would mean that venous values could be used to assess ventilation and metabolic status of patients in intensive care unit.

Methods

All adult patients admitted to Alfred intensive care unit, Melbourne, from February 2013 to January 2014, who were likely to have arterial and central venous lines for three days, were enrolled. Patients on extra-corporeal life support and pregnant women were excluded. After enrolment, near simultaneous arterial and central venous sampling and analysis were performed at least once per nursing shift till the lines were removed or the patient died. Bland-Altman analysis for repeated measures was performed to assess the agreement between arterio-venous pH and partial pressure of carbon dioxide.

Results

A total of 394 paired blood gas analyses were performed from 59 participants. The median (IQR) number of samples per patient was 6 (5-9) with the median (IQR) sampling interval 9.4 (5.2-18.5) h. The mean bias for pH was  + 0.036 with 95% limits of agreement ranging from - 0.005 to + 0.078. For partial pressure of carbon dioxide, the values were -2.58 and -10.43 to + 5.27 mmHg, respectively.

Conclusions

The arterio-venous agreement for pH in intensive care unit patients appears to be acceptable. However, the agreement for partial pressure of carbon dioxide was poor.

Measurement of absorption in scattering media using objective laser speckle: application to blood oximetry

Multi-spectral imaging enables non-invasive sensing of chemical concentrations in biological tissue based on measurement of optical absorption, but invariably in the presence of high levels of scatter. Absorption is normally inferred from measurement of contrast of biological features, such as the vasculature, and so accuracy is degraded by the poorly characterized modulation-transfer function of the imaging optics and overlying tissue. We report how experimental characterization of the spectral variation of the tissue point-spread function and associated objective speckle pattern can be used to characterize the absorption spectrum and chromophore concentration, with a particular emphasis on determination of the ratio of oxygenated to deoxygenated hemoglobin within blood. Absorption measurements are determined purely by the geometry of the experiment, without degradation due to optical aberrations and associated light scatter. The technique offers enhanced and low-cost determination of in vitro or in vivo chromophore characterizations, including blood-gas analysis.

The Physiology of Oxygen Transport by the Cardiovascular System: Evolution of Knowledge

The heart, vascular system, and red blood cells play fundamental roles in O₂ transport. The fascinating research history that led to the current understanding of the physiology of O₂ transport began in ancient Egypt in 3000 BC, when it was postulated that the heart was a pump serving a system of distributing vessels. Over 4 millennia elapsed before William Harvey (1578-1657) made the revolutionary discovery of blood circulation, but it was not until the 20th century that a lucid and integrative picture of O₂ transport finally emerged. This review describes major research achievements contributing to this evolution of knowledge. These achievements include the discovery of the systemic and pulmonary circulations, hemoglobin within red blood cells and its ability to bind O₂, and diffusion of O₂ from the capillary as the final step in its delivery to tissue. The authors also describe the classic studies that provided the initial description of the basic regulatory mechanisms governing heart function (Frank-Starling law) and the flow of blood through blood vessels (Poiseuille's law). The importance of technical advances, such as the pulmonary artery catheter, the blood gas analyzer and oximeter, and the radioactive microsphere technique to measure the regional blood flow in facilitating O₂ transport-related research, is recognized. The authors describe how religious and cultural constraints, as well as superstition-based medical traditions, at times impeded experimentation and the acquisition of knowledge related to O₂ transport.

Application of P(jv-a) CO2 in monitoring cerebral oxygen supply-demand balance in injured brain

Transcranial Doppler sonography (TCD) assayed cerebral blood flow (CBF) may vary between different intracranial pathologies. Blood gas analysis of the jugular bulb provides a novel way to estimate the global relationship between CBF and oxygen metabolism. In this study, 25 patients with brain trauma, spontaneous intracerebral hemorrhage, and acute cerebral infarction were recruited. Jugular venous oxygen saturation (SjvO₂) increased significantly at different time points after hyperventilation (p < 0.05). A negative correlation between the partial pressure of CO₂ between jugular venous bulb and radial artery blood (P(jv-a)CO₂) and CBF could be observed in acute brain injury and spontaneous intracerebral hemorrhage groups, while P(jv-a)CO₂ and CBF show positive correlation in acute cerebral infarction group. Our results suggest that serial P(jv-a)CO₂ analysis combing with SjvO₂ can be utilized to monitor the change of CBF for patients undergoing craniocerebral surgery.

Transcutaneous PCO2 monitoring in critically ill patients: update and perspectives

The physiology of venous and tissue CO₂ monitoring has a long and well-established physiological background, leading to the technological development of different tissue capnometric devices, such as transcutaneous capnometry monitoring (TCM). To outline briefly, measuring transcutaneous PCO₂ (tcPCO₂) depends on at least three main phenomena: (I) the production of CO₂ by tissues (VCO₂), (II) the removal of CO₂ from the tissues by perfusion (wash-out phenomenon), and (III) the reference value of CO₂ at tissue inlet represented by arterial CO₂ content (approximated by arterial PCO₂, or artPCO₂). For this reason, there are, at present, roughly two clinical uses for tcPCO₂ measurement: a respiratory approach where tcPCO₂ is likely to estimate and non-invasively track artPCO₂; and a hemodynamic under-estimate use where tcPCO₂ can reflect tissue perfusion, summarized by a so-called "tc-art PCO₂ gap". Recent research shows that these two uses are not incompatible and could be combined. The spectrum of indications and validation studies in ICUs is summarized in this review to give a survey of the potential applications of TCM in critically ill patients, focusing mainly on its potential (micro)circulatory monitoring contribution. We strongly believe that the greatest benefit of measuring tcPCO₂ is not to only to estimate artPCO₂, but also to quantify the gap between these two values, which can then help clinicians continuously and noninvasively assess both respiratory and hemodynamic failures in critically ill patients.

The role of the clinical laboratory in diagnosing acid-base disorders

Acid-base homeostasis is fundamental for life. The body is exceptionally sensitive to changes in pH, and as a result, potent mechanisms exist to regulate the body's acid-base balance to maintain it in a very narrow range. Accurate and timely interpretation of an acid-base disorder can be lifesaving but establishing a correct diagnosis may be challenging. The underlying cause of the acid-base disorder is generally responsible for a patient's signs and symptoms, but laboratory results and their integration into the clinical picture is crucial. Important acid-base parameters are often available within minutes in the acute hospital care setting, and with basic knowledge it should be easy to establish the diagnosis with a stepwise approach. Unfortunately, many caveats exist, beginning in the pre-analytical phase. In the post-analytical phase, studies on the arterial reference pH are scarce and therefore many different reference values are used in the literature without any solid evidence. The prediction models that are currently used to assess the acid-base status are approximations that are mostly based on older studies with several limitations. The two most commonly used methods are the physiological method and the base excess method, both easy to use. The secondary response equations in the base excess method are the most convenient. Evaluation of acid-base disorders should always include the assessment of electrolytes and the anion gap. A major limitation of the current acid-base laboratory tests available is the lack of rapid point-of-care laboratory tests to diagnose intoxications with toxic alcohols. These intoxications can be fatal if not recognized and treated within minutes to hours. The surrogate use of the osmolal gap is often an inadequate substitute in this respect. This article reviews the role of the clinical laboratory to evaluate acid-base disorders.

The Relationship between Arterial and Central Venous Blood Gases Values in Patients Undergoing Mechanical Ventilation after Cardiac Surgery

Background

The most straightforward method of ascertaining arterial PO₂, PCO₂, and other components of blood gas is to measure them directly from a blood sample. In situations in which arterial puncture cannot be achieved or may be technically difficult, the venous blood sample can be used.

Methods

In a prospective analytical study, 80 patients undergoing mechanical ventilation after open-heart surgery in the intensive care unit were evaluated. Simultaneous, matched arterial and central venous blood gas samples were taken from radial artery line and central vein, respectively, when the ABG (arterial blood gases) assessment was needed. Arterial and central venous blood samples were analyzed and data were expressed as mean and ± SD.

Results

The Pearson correlation coefficient for pH, PCO₂, HCO₃, and SatO₂ was 0.898, 0.940, 0.840, and 0.567, respectively. There was a significant correlation between arterial and central venous values of pH, PCO₂, and HCO₃ (P < 0.0001). The mean difference between arterial and central venous PCO₂ was -2.44 ± 2.6 mmHg, and the mean venous pH value was only 0.021 ± 0.037 units lower than the mean arterial value. In addition, the calculated mean bicarbonate concentration in venous blood was only about 0.06 ± 1.5 mEq.L higher than the mean arterial value.

Conclusions

The central venous PCO₂, pH, and HCO₃ measured during mechanical ventilation in the intensive care unit approximate arterial values closely enough to permit the estimation of the adequacy of ventilation and acid-base status. The central venous Sat O₂ does not reliably parallel the arterial Sat O₂. In conclusion, venous blood sampling can potentially reduce the requirement for ABG sampling in special situations.

Timing of tracheotomy in ICU patients: a systematic review of randomized controlled trials

Introduction

The optimal timing of tracheotomy in critically ill patients remains a topic of debate. We performed a systematic review to clarify the potential benefits of early versus late tracheotomy.

Methods

We searched PubMed and CENTRAL for randomized controlled trials that compared outcomes in patients managed with early and late tracheotomy. A random-effects meta-analysis, combining data from three a priori-defined categories of timing of tracheotomy (within 4 versus after 10 days, within 4 versus after 5 days, within 10 versus after 10 days), was performed to estimate the weighted mean difference (WMD) or odds ratio (OR).

Results

Of the 142 studies identified in the search, 12, including a total of 2,689 patients, met the inclusion criteria. The tracheotomy rate was significantly higher with early than with late tracheotomy (87 % versus 53 %, OR 16.1 (5.7-45.7); p <0.01). Early tracheotomy was associated with more ventilator-free days (WMD 2.12 (0.94, 3.30), p <0.01), a shorter ICU stay (WMD -5.14 (-9.99, -0.28), p = 0.04), a shorter duration of sedation (WMD -5.07 (-10.03, -0.10), p <0.05) and reduced long-term mortality (OR 0.83 (0.69-0.99), p = 0.04) than late tracheotomy.

Conclusions

This updated meta-analysis reveals that early tracheotomy is associated with higher tracheotomy rates and better outcomes, including more ventilator-free days, shorter ICU stays, less sedation, and reduced long-term mortality, compared to late tracheotomy.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-015-1138-8) contains supplementary material, which is available to authorized users.

Erratum: Concordance and limits between transcutaneous and arterial carbon dioxide pressure in emergency department patients with acute respiratory failure: a single-center, prospective, and observational study

Abstract

After publication of this article (Scand J Trauma Resusc Emerg Med 23:40, 2015), it came to light that an earlier version had been published in error. This erratum contains the correct version of the article, which incorporates revisions made in response to reviewer comments. Additionally, one of the authors was inadvertently omitted from the author list. This author, Justin Yan, has been included in the corrected author list above.

Background

Transcutaneous CO₂ (PtCO₂) is a continuous and non-invasive measure recommended by scientific societies in the management of respiratory distress. The objective of this study was to evaluate the correlation between PtCO₂ and arterial partial pressure of CO₂ (PaCO₂) by arterial blood gas analysis in emergency patients with dyspnoea, and to determine the factors that interfere with this correlation.

Methods

From January to June 2014, all adult patients admitted to the RR with dyspnoea during business hours were included in the study if arterial blood gas measurements were indicated. A sensor measuring the PtCO₂ was attached to the ear lobe of the patient before the gas analysis. Anamnesis, clinical and laboratory parameters were identified.

Results

Ninety patients with dyspnoea were included (104 pairs of measurements). The median (IQR) age was 79 years (69 – 85). The correlation between PtCO₂ and PaCO₂ was R² =.83 (p<.001) but became lower for values of PaCO₂ above 60 mm Hg. The mean bias (± SD) between the two methods of measurement (Bland-Altman analysis) was −1.4 mm Hg (± 7.7) with limits of agreement from −16.4 to 13.7 mm Hg. In univariate analysis, PaO₂ interfered with this correlation. After multivariate analysis, temperature (OR = 3.01; 95 % CIs [1.16, 7.80]) and PaO₂ (OR = 1.22; 95 % CIs [1.02, 1.47]) significantly interfered with this correlation.

Conclusions

There is a significant correlation between PaCO₂ and PtCO₂ values for patients admitted to the emergency department for acute respiratory failure. One limiting factor to routine use of PtCO₂ measurements in the emergency department is the presence of hyperthermia.

Concordance and limits between transcutaneous and arterial carbon dioxide pressure in emergency department patients with acute respiratory failure: a single-center prospective observational study

Introduction

Transcutaneous CO ₂ (PtCO ₂) is a continuous and non-invasive measure recommended by scientific societies in the management of respiratory distress. The objective of this study is to evaluate the correlation between PtCO ₂ and blood pressure of CO ₂ (PaCO ₂) by blood gas analysis in emergency patients with dyspnoea and to determine the factors that interfere in this correlation.

Methods

From January to June 2014, all patients admitted to resuscitation room of the emergency department targeted for arterial blood gases were included prospectively. A sensor measuring the PtCO ₂ was attached to the ear lobe of the patient before the gas analysis. Anamnesis, clinical and laboratory parameters were identified.

Results

90 patients with dyspnoea were included (with 104 pairs of measurements), the median age was 79 years [69-85]. The correlation between PtCO ₂ and PaCO ₂ was R ²= 0.83 (p <0.001) but became lower for values of PaCO ₂>60 mm Hg. The mean bias (±SD) between the two methods of measurement (Bland-Altman analysis) was -1.4 mm Hg (±7.7) with limits of agreement of -16.4 to 13.7 mm Hg. In univariate analysis, PaO ₂ interfered in this correlation. After multivariate analysis, the temperature (OR = 3.01, 95% CI = 1.16-7.09) and the PaO ₂ (OR = 1.22, 95% CI = 1.02-1.47) were found to be significant.

Conclusions

In patients admitted in emergency unit for acute respiratory failure, there is a significant correlation between PaCO ₂ and PtCO ₂, mainly for values below 60 mm Hg. The two limiting factors of use are hyperthermia and users training.

Update on pediatric neurocritical care

Paralytic poliomyelitis, Reye syndrome, Hemophilus Influenzae type B epiglottitis, bacterial meningitis, and meningococcal septic shock are catastrophic illnesses that in the last 60 years have shaped the development of pediatric intensive care. Neurocritical care has been at the forefront of our thinking and, more latterly, as a specialty we have had the technology and means to develop this focus, educate the next generation and show that outcomes can be improved-first in adult critical care and now the task is to translate these benefits to critically ill children. In our future we will need to advance interventions in patient care with clinical trials. MeSH terms: Neurocritical care; child; traumatic brain injury; status epilepticus; cerebrovascular.

Comparison of central venous saturation by standard ABG machine versus co-oximeter: Is 18 carat as good as the 24 carat gold standard?

AIMS

Aggressive therapy aimed at desired end-points of Early Goal Directed Therapy (EGDT) is the cornerstone of septic shock management. A key endpoint that improves outcomes is achieving central venous saturation (ScvO2) >70%. The gold standard to measure ScvO2 is by a co-oximeter (co-ox).

SETTINGS AND DESIGN

This prospective, observational study from a multidisciplinary pediatric intensive care unit (PICU) was conducted to assess the validity of ScvO2 levels by standard ABG (stand ABG) machine in comparison with co-ox in conditions that shifted the oxygen dissociation curve (ODC) to the right or left in sick children and controls.

MATERIALS AND METHODS

Data from paired samples was tested for correlation coefficient for pH, paCO2, paO2, and ScvO2. Tests for correlation (Pearson's coefficient) and agreement (Bland-Altman analysis) were performed on ScvO2 values obtained in various subgroups. Sensitivity and specificity for ScvO2 values determined by standard ABG machine versus co-ox were calculated in reference to EGDT endpoints.

RESULTS

A total of 141 paired samples were collected from 82 children. Despite a statistically significant difference in the pH and ScvO2, there was good linear correlation between these parameters. Limits of agreement between ScvO2 measured by standard ABG machine and co-ox by Bland-Altman gave 2.3% bias with 95% CI of -24.2% to 19.5%. Sensitivity and specificity of standard ABG machine in detecting low ScvO2 in shock was 84.21% and 93.18% respectively, while it was false positive in 4 samples.

CONCLUSIONS

The less expensive standard ABG machine showed satisfactory correlation with gold standard co-ox over a range of patient conditions; however, the wide range for agreement was of concern and it performed particularly poorly in anemic patients.

The development of continuous positive airway pressure: an interview with Dr. George Gregory

George Gregory, M.D. (1934-), Professor Emeritus at the University of California, San Francisco, has made numerous contributions to neonatology and pediatric anesthesia through his research efforts and authoritative textbook, Gregory's Pediatric Anesthesia. However he identified his defining moment as the occasion he saved the life of an infant suffering from neonatal respiratory distress syndrome by using continuous positive airway pressure (CPAP) ventilation. The development of CPAP by Gregory revolutionized the treatment of premature infants with respiratory failure. Prior to the creation of this treatment, the mortality rate of neonates with respiratory distress syndrome was >50%. The innovation markedly improved the ventilation of infants with respiratory distress and led to significant improvements in survival rates. Based on an interview with Dr. Gregory, this article describes the discovery of CPAP and reviews his career in advancing pediatric anesthesia and critical care medicine.

Evaluation of a transcutaneous carbon dioxide monitor in patients with acute respiratory failure

BACKGROUND

Non-invasive measurement of oxygenation is a routine procedure in clinical practice, but transcutaneous monitoring of PCO(2)(PtCO(2)) is used much less than expected.

METHODS

The aim of our study was to analyze the value of a commercially available combined SpO(2)/PtCO(2) monitor (TOSCA-Linde Medical System, Basel, Switzerland) in adult non-invasive ventilated patients with acute respiratory failure. Eighty critically ill adult patients, requiring arterial blood sample gas analyses, underwent SpO(2) and PtCO(2) measurements (10 min after the probe was attached to an earlobe) simultaneously with arterial blood sampling. The level of agreement between PaCO(2) - PtCO(2) and SaO(2) - SpO(2)was assessed by Bland-Altman analyses.

RESULTS

Both, SaO(2) from blood gas analysis and SpO(2) from the transcutaneous monitor, and PaCO(2) and PtCO(2) were equally useful. No measurements were outside of the acceptable clinical range of agreement of ± 7.5 mmHg.

CONCLUSIONS

The accuracy of estimation of the TOSCA transcutaneous electrode (compared with the "gold standard" blood sample gas analysis) was generally good. Moreover, TOSCA presents the advantage of the possibility of continuous non-invasive measurement. The level of agreement of the two methods of measurement allows us to state that the TOSCA sensor is useful in routine monitoring of adults admitted to an intermediate respiratory unit and undergoing non-invasive ventilation.

Evolution and revolution: the formation of today's American Thoracic Society, part 1

The American Thoracic Society (ATS), the preeminent professional organization in the field of respiratory, critical care, and sleep medicine, is now 107 years old. For the most part, the Society's administrative and medical-scientific interests evolved in an orderly fashion, but two "revolutions" took place that should be remembered. What ultimately metamorphosed into the ATS in 1960 began in 1905 as the 34-member American Sanatorium Association, which in 1915 became the medical section of the National Association for the Study and Prevention of Tuberculosis (NASPT). In 1918, the NASPT became the National Tuberculosis Association and in 1939, the ASA became the American Trudeau Society, cosmetic revisions having no effect on either the medical section-parent relationship or the one-disease orientation of both organizations. After World War II, the narrow focus of the ATS on tuberculosis was progressively enlarged through coalescence of several factors that transformed the practice of pulmonary medicine: the growth of intensive care units and pulmonary function laboratories and the advent of fiberoptic bronchoscopy; the rise of asthma, chronic obstructive pulmonary disease, and lung cancer coincident with the withering of tuberculosis; and the arrival of pulmonary physician-scientists who sought enrichment through a professional society. The newcomers found a home in the ATS, but it was slow to fulfill their needs for scientific communication and administrative responsibility. The first revolution, the formation of Scientific Assemblies, got the job done quickly and well, as described in Part 1 of this perspective. The second revolution, separation from the American Lung Association, is described in Part 2.

[Relationship between the alveolar-arterial oxygen gradient and PaO₂/FiO₂-introducing PEEP into the model]

OBJECTIVES

To determine whether the alveolar-arterial oxygen gradient (Grad[A-a]O₂) helps confirm the influence of PEEP on PaFi (PaO₂/FiO₂).

DESIGN

Observational study; we used linear regression to perform a multivariate study to improve the PaFi formula by taking PEEP into account.

SETTING

Tertiary hospital.

PATIENTS

We included all patients who were admitted to the intensive care unit, regardless of pulmonary damage.

VARIABLES

We recorded personal history, clinical judgment, intensive care data, severity scores on the first day and progression. Two calculated variables: PaFi and Grad(A-a)O₂.

RESULTS

A total of 956 patients were included: 63.9% men; median age 68 years. On the first day, 31.8% did not have mechanical ventilation (MV), 13.1% had non-invasive MV and 55.1% had invasive MV. PaFi values: 32.9% 0-200, 32.2% 201-300, and 34.8% >300. PEEP values: 0-5 69.8%, 6-10 27.5% and >10 2.6%. We observed a correlation (Pearson) between Grad(A-a)O₂ and PaFi of -0.84 (p<0.001). On performing multiple regression (dependent variable: Grad[A-a]O₂), the following variables were included in the model: PaFi, PEEP, APACHE IV and SOFA; coefficient of determination (R²) of 0.62 without PEEP and 0.72 with PEEP. We changed the PaFi formula, referring to it as PaFip (PaFi plus PEEP): Ln (PaFi/[PEEP+12]). Correlation index between PaFip and Grad(A-a)O₂: -0.9 (p<0.001). We performed linear regression (dependent variable: Grad[A-a]O₂) and used PaFip instead of PaFi. Only PaFi remained in the model, and was discretely complemented by APACHE IV; R²=0.8.

CONCLUSIONS

By adding PEEP to the PaFi model (PaFip), we clearly improve the latter, as reflected by a better goodness of fit.

Quantitation of dissolved gas content in emulsions and in blood using mass spectrometric detection

Quantitation of dissolved gases in blood or in other biological media is essential for understanding the dynamics of metabolic processes. Current detection techniques, while enabling rapid and convenient assessment of dissolved gases, provide only direct information on the partial pressure of gases dissolved in the aqueous fraction of the fluid. The more relevant quantity known as gas content, which refers to the total amount of the gas in all fractions of the sample, can be inferred from those partial pressures, but only indirectly through mathematical modeling. Here we describe a simple mass spectrometric technique for rapid and direct quantitation of gas content for a wide range of gases. The technique is based on a mass spectrometer detector that continuously monitors gases that are rapidly extracted from samples injected into a purge vessel. The accuracy and sample processing speed of the system is demonstrated with experiments that reproduce within minutes literature values for the solubility of various gases in water. The capability of the technique is further demonstrated through accurate determination of O(2) content in a lipid emulsion and in whole blood, using as little as 20 μL of sample. The approach to gas content quantitation described here should greatly expand the range of animals and conditions that may be used in studies of metabolic gas exchange, and facilitate the development of artificial oxygen carriers and resuscitation fluids.

Pediatric neurocritical care: is it time to come of age?

PURPOSE OF REVIEW

Neurocritical care in adults with life-threatening neurological disease is a distinct discipline that has developed out of critical care medicine and neurology. This review considers whether it is time for such a specialized service to be developed in pediatrics.

RECENT FINDINGS

Recent reports describe how some institutions and pediatric professional bodies have set about transferring the specialist neurocritical care experience in adults to pediatric practice. The issue, now, is whether such a development would improve pediatric healthcare, medical education and training in the newly defined field. Adult neurocritical care did not develop in a void. The historical influences were the polio epidemics and the investment in experimental neuroprotection. These traditions provided a foundation for success in recent clinical trials, patient outcomes and healthcare research. Pediatric neurocritical care does not have the equivalent parallels and track record in healthcare research. Size of practice and casemix is also significantly different, with one-third of potential beneficiaries of the new field having a primary medical, rather than neurological, disorder. Three types of development for pediatric neurocritical services are, therefore, suggested by the literature and the implications of these on cross-discipline staffing and education are discussed.

SUMMARY

Pediatric neurocritical care is the new frontier for pediatric critical care medicine and pediatric neurology. There is sufficient specialist interest and momentum for the development of a multidisciplinary collaboration that has the aim of improving patient care.

Clinical review: long-term noninvasive ventilation

Noninvasive positive ventilation has undergone a remarkable evolution over the past decades and is assuming an important role in the management of both acute and chronic respiratory failure. Long-term ventilatory support should be considered a standard of care to treat selected patients following an intensive care unit (ICU) stay. In this setting, appropriate use of noninvasive ventilation can be expected to improve patient outcomes, reduce ICU admission, enhance patient comfort, and increase the efficiency of health care resource utilization. Current literature indicates that noninvasive ventilation improves and stabilizes the clinical course of many patients with chronic ventilatory failure. Noninvasive ventilation also permits long-term mechanical ventilation to be an acceptable option for patients who otherwise would not have been treated if tracheostomy were the only alternative. Nevertheless, these results appear to be better in patients with neuromuscular/-parietal disorders than in chronic obstructive pulmonary disease. This clinical review will address the use of noninvasive ventilation (not including continuous positive airway pressure) mainly in diseases responsible for chronic hypoventilation (that is, restrictive disorders, including neuromuscular disease and lung disease) and incidentally in others such as obstructive sleep apnea or problems of central drive.

Heights and haematology: the story of haemoglobin at altitude

In order to compensate for the low partial pressure of oxygen at altitude, the human body undergoes a number of physiological changes. A vital component in this process is the increase in the concentration of circulating haemoglobin. The role of HIF-1alpha, erythropoietin and red blood cells in this acclimatisation process is described, together with the fall in plasma volume that increases the concentration of haemoglobin in the early stages of hypoxic exposure.

Chronic respiratory failure in patients with neuromuscular diseases: diagnosis and treatment

Neuromuscular diseases affect alveolar air exchange and therefore cause chronic respiratory failure. The onset of respiratory failure can be acute, as in traumas, or progressive (slow or rapid), as in amyotrophic lateral sclerosis, muscular dystrophies, diseases of the myoneural junction, etc. Respiratory muscle impairment also affects cough efficiency and, according to the current knowledge regarding the type of treatment available in Brazil to these patients, it can be said that the high rates of morbidity and mortality in these individuals are more often related to the fact that they cough inefficiently rather than to the fact that they ventilate poorly. In this review, with the objective of presenting the options of devices available to support and substitute for natural ventilation in patients with neuromuscular diseases, we have compiled a brief history of the evolution of orthopedic braces and prostheses used to aid respiration since the end of the 19th century. In addition, we highlight the elements that are fundamental to the diagnosis of alveolar hypoventilation and of failure of the protective cough mechanism: taking of a clinical history; determination of peak cough flow; measurement of maximal inspiratory and expiratory pressures; spirometry in two positions (sitting and supine); pulse oximetry; capnography; and polysomnography. Furthermore, the threshold values available in the literature for the use of nocturnal ventilatory support and for the extension of this support through the daytime period are presented. Moreover, the maneuvers used to increase cough efficiency, as well as the proper timing of their introduction, are discussed.

Laboratory monitoring of mechanical ventilation

This article examines the use of laboratory tests for managing mechanical ventilation. Blood gas analysis is a common test widely used for this purpose, and this is evaluated in detail. Other tests, however, provide valuable insight into the management of patients receiving mechanical ventilation. These include serum electrolytes, thyroid function tests, and adrenal function tests.

Contactless multiple wavelength photoplethysmographic imaging: a first step toward "SpO2 camera" technology

We describe a route toward contactless imaging of arterial oxygen saturation (SpO2) distribution within tissue, based upon detection of a two-dimensional matrix of spatially resolved optical plethysmographic signals at different wavelengths. As a first step toward SpO2-imaging we built a monochrome CMOS-camera with apochromatic lens and 3lambda-LED-ringlight (lambda1 = 660 nm, lambda2 = 810 nm, lambda3 = 940 nm; 100 LEDs lambda(-1)). We acquired movies at three wavelengths while simultaneously recording ECG and respiration for seven volunteers. We repeated this experiment for one volunteer at increased frame rate, additionally recording the pulse wave of a pulse oximeter. Movies were processed by dividing each image frame into discrete Regions of Interest (ROIs), averaging 10 x 10 raw pixels each. For each ROI, pulsatile variation over time was assigned to a matrix of ROI-pixel time traces with individual Fourier spectra. Photoplethysmograms correlated well with respiration reference traces at three wavelengths. Increased frame rates revealed weaker pulsations (main frequency components 0.95 and 1.9 Hz) superimposed upon respiration-correlated photoplethysmograms, which were heartbeat-related at three wavelengths. We acquired spatially resolved heartbeat-related photoplethysmograms at multiple wavelengths using a remote camera. This feasibility study shows potential for non-contact 2-D imaging reflection-mode pulse oximetry. Clinical devices, however, require further development.

Transcutaneous Pco2 monitoring in critically ill adults: Clinical evaluation of a new sensor*

OBJECTIVE

In critically ill patients, arterial blood gas analysis is the gold standard for evaluating systemic oxygenation and carbon dioxide partial pressure. A new miniaturized carbon dioxide tension Pco2-Spo2 single sensor (TOSCA, Linde Medical Sensors AG, Basel, Switzerland) continuously and noninvasively (transcutaneously) monitors both Paco2 and oxygen saturation by pulse oximetry (Spo2). The present study was designed to investigate the usability and the accuracy of this device in critically ill patients.

DESIGN

Prospective clinical investigation.

SETTING

A 20-bed, university-affiliated, surgical intensive care unit.

PATIENTS

Patients admitted after major surgery, multiple trauma, or septic shock equipped with an arterial catheter.

INTERVENTIONS

The heated (42 degrees C) sensor was fixed at the earlobe using an attachment clip. Transcutaneous Pco2 (TcPco2) measurements were correlated with Paco2 values (measured using a blood gas analyzer). In addition, the differences between Paco2 and TcPco2 values were evaluated using the method of Bland-Altman.

MEASUREMENTS AND MAIN RESULTS

We studied 55 patients, aged 18-80 (mean 57 +/- 15) yrs. A total of 417 paired measurements were compared. Correlation between TcPco2 and Paco2 was r = .86 (p < .01) in the Paco2 range of 24-101 mm Hg. Mean bias (+/-sd) between the two methods of measurement (Bland-Altman analysis) was 1.2 +/- 6.0 mm Hg with TcPco2 slightly overestimating arterial carbon dioxide tension. Nineteen percent of the measured values were outside of the acceptable clinical range of agreement of +/-7.5 mm Hg.

CONCLUSIONS

The present study suggests that Paco2 can be acceptably assessed by measuring TcPco2 using the TOSCA Pco2-Spo2 sensor.

The physiological challenges of the 1952 Copenhagen poliomyelitis epidemic and a renaissance in clinical respiratory physiology

The 1952 Copenhagen poliomyelitis epidemic provided extraordinary challenges in applied physiology. Over 300 patients developed respiratory paralysis within a few weeks, and the ventilator facilities at the infectious disease hospital were completely overwhelmed. The heroic solution was to call upon 200 medical students to provide round-the-clock manual ventilation using a rubber bag attached to a tracheostomy tube. Some patients were ventilated in this way for several weeks. A second challenge was to understand the gas exchange and acid-base status of these patients. At the onset of the epidemic, the only measurement routinely available in the hospital was the carbon dioxide concentration in the blood, and the high values were initially misinterpreted as a mysterious "alkalosis." However, pH measurements were quickly instituted, the Pco(2) was shown to be high, and modern clinical respiratory acid-base physiology was born. Taking a broader view, the problems highlighted by the epidemic underscored the gap between recent advances made by physiologists and their application to the clinical environment. However, the 1950s ushered in a renaissance in clinical respiratory physiology. In 1950 the coverage of respiratory physiology in textbooks was often woefully inadequate, but the decade saw major advances in topics such as mechanics and gas exchange. An important development was the translation of the new knowledge from departments of physiology to the clinical setting. In many respects, this period was therefore the beginning of modern clinical respiratory physiology.

Further commentary on Denmark's 1952-53 poliomyelitis epidemic, especially regarding mortality; with a correction

Berthelsen and Cronqvist recently published an article in Acta Anaesthesiologica Scandinavica including aspects which could lead on to further discussion about the Danish 1952-53 poliomyelitis epidemic. This paper considers how Bjørn Ibsen's initial approach to treatment during the epidemic was successful, as well as how it could have failed; the roles played by ventilatory failure vs. gross neurologic destruction in causing deaths; and compilations from publications of statistics concerning mortality of the epidemic. The Blegdam Hospital concept of 'life-threatening poliomyelitis' is revisited, along with its division into six anatomico-clinical categories for the 345 patients so classified. Attention is drawn to the severity of assorted cerebral lesions demonstrated in 114 of the 115 autopsies conducted from the 144 fatal cases. Despite an overall mortality rate of 41.6% among the entire epidemic's sickest patients, a lowest mortality rate of 11% in the last 18 of such patients is identified. Note is made of the difficulty in reconciling various sources for certain features -- for which the 1956 book on the epidemic, edited by H.C.A. Lassen, has been freely used. Some folklore about aspects of management is mentioned. In the light of other recent research by Dr Berthelsen an essential correction is needed in dating 'Bjørn Ibsen's Day', amending 26 August 1952 to the 27th.

The significance of the blood gas analyzer

This essay looks at the historical significance of an APS classic paper that is freely available online:

Severinghaus JW and Bradley AF. Electrodes for blood Po2 and Pco2 determination. J Appl Physiol 13: 515—520, 1958 ( http://jap.physiology.org/cgi/reprint/13/3/515 ).