Arterial PCO2 Research Articles

Feasibility of non-intubated anesthesia and regional block for thoracoscopic surgery under spontaneous respiration: a prospective cohort study.

Data about the feasibility and safety of thoracoscopic surgery under non-intubated anesthesia and regional block are limited. In this prospective study, 57 consecutive patients scheduled for thoracoscopic surgery were enrolled. Patients were sedated with dexmedetomidine and anesthetized with propofol and remifentanil. Ropivacaine was used for intercostal nerve and paravertebral block. Lidocaine was used for vagal block. The primary outcomes were mean arterial pressure (MAP), heart rate (HR), oxygen saturation, and end-tidal carbon dioxide partial pressure (ETCO2) at T0 (pre-anesthesia), T1 (immediately after laryngeal mask/nasopharyngeal airway placement), T2 (immediately after skin incision), T3 (10 min after opening the chest), T4 (end of surgery), and T5 (immediately after laryngeal mask/nasopharyngeal airway removal). One patient required conversion to intubation, 15 developed intraoperative hypotension, and two had hypoxemia. MAP at T0 and T5 was higher than at T1–T4; MAP at T3 was lower (P<0.05 vs other time points). HR at T0 and T5 was higher (P<0.05 vs other time points). ETCO2 at T2 and T3 was higher (P<0.05 vs other time points). Arterial pH, PCO2, and lactic acid at T1 differed from values at T0 and T2 (P<0.05). The Quality of Recovery-15 (QoR-15) score at 24 h was lower (P<0.05). One patient experienced dysphoria during recovery. Thoracoscopic surgery with regional block under direct thoracoscopic vision is a feasible and safe alternative to conventional surgery under general anesthesia, intubation, and one-lung ventilation.

Role of central venous - Arterial pCO2 difference in determining microcirculatory hypoperfusion in off-pump coronary artery bypass grafting surgery.

Background:Cardiac surgery is frequently associated with macro and microcirculatory hypoperfusion. Patients with normal central venous oxygen saturation (Scvo2) also suffer from hypoperfusion. We hypothesized that monitoring central venous-arterial pco2 difference (dCO2) could also serve as additional marker in detecting hypoperfusion in cardiac surgery patient.Methods:This is a prospective observational study. Patients undergoing off-pump coronary artery bypass grafting included in this study. The dCO2 was measured postoperatively. The patients with a ScvO2 ≥70% were divided in to 2 groups, the high-dCO2 group (≥8 mmHg) and the low-dCO2 group (<8 mmHg).Results:The 65 patient had scvO2 ≥70%. Out of these, 20 patients were assigned to the high dCO2 group and 45 patients to the low dCO2 group. Patients with high dco2 had higher lactate levels after ICU admission. They also had significantly prolonged need for mechanical ventilation (14.90 ± 10.33 vs 10 ± 9.65, P = 0.0402), ICU stay (5.05 ± 2.52 d vs 3.75 ± 2.36 d, P = 0.049) and hospital stay (12.25 ± 5.90 d vs 8.57 ± 5.55 d P = 0.018). The overall rate of post-operative complications was similar in both the group.Conclusion:The present study demonstrates dCO2 as an easy to assess and routinely available tool to detect global and microcirculatory hypoperfusion in off-pump CABG patients, with assumed adequate fluid status and ScvO2 as a hemodynamic goal. We observed that high dCO2 (>8 mmHg) was associated with decreased DO2I, increased oxygen extraction ratio, the longer need for mechanical ventilation and longer ICU stay.

Comparison of Nasal bi-level Positive Airway Pressure Versus High-flow Nasal Cannula as a Means of Noninvasive Respiratory Support in Pediatric Cardiac Surgery.

Background:Noninvasive respiratory support is often used in preventing postextubation respiratory failure in neonates and infants after cardiac surgery.Aim:We compared the efficacy of nasal Bilevel Positive Airway Pressure (N/BiPAP) with that of High- flow Nasal Cannula(HFNC) in prevention of post extubation respiratory failure and maintenance of gas exchange in neonates and infants undergoing cardiac surgery. The incidence of complications related to the use of these modes were also compared.Settings and Design:This is a retrospective review of medical records of patients in pediatric cardiac intensive unit of a high-volume center.Methods:A total of 100 patients who received noninvasive respiratory support postextubation were divided into N/BiPAP group and HFNC group. The two groups were compared for postextubation respiratory failure, gas exchange in arterial blood gas at 24 h of extubation, and incidence of complications, namely pneumothorax, abdominal distension, and device–interface-related pressure ulcers.Results:Fifty patients each received N/BiPAP and HFNC after extubation. Patients who received N/BiPAP were younger (2.68 ± 2.97 months vs. 6.94 ± 4.04 months, P = 0.001) and had longer duration of postoperative ventilation (106.98 ± 79.02 h vs. 62.72 ± 46.14 h, P = 0.001). The reintubation rates were similar (20% [n = 10] in N/BiPAP group vs. 8% [n = 4] in HFNC group, P = 0.074). The mean arterial PO2 values at 24 h of extubation was 119.17 ± 56.07 mmHg for N/BiPAP group versus 123.32 ± 64.33 mmHg for HFNC group (P = 0.732). Arterial PCO2 values at 24 h were similar (43.97 ± 43.64 mmHg in N/BiPAP vs. 37.67 ± 4.78 mmHg in HFNC, P = 0.318). N/BiPAP group had higher incidence of abdominal distension (16% [n = 8] vs. nil in HFNC group, P = 0.003) and interface-related pressure ulcers (86% [n = 43] vs. 14% [n = 7] P = 0.006).Conclusion:N/BiPAP and HFNC have comparable efficacy in preventing reintubation and maintaining gas exchange. HFNC has fewer complications compared to N/BiPAP.

A case of near-fatal asthma precipitated by H1N1 pneumonia with critical PCO2 successfully treated by multipharmacological approach

We describe a case of prolonged severe hypercapnia with respiratory acidosis occurring during an episode of near-fatal asthma in a 15-year-old boy, followed by complete recovery. After admission to the ICU, despite treatment with maximal conventional bronchodilatation therapy, the clinical picture deteriorated with evident signs of respiratory muscle fatigue. The patient was sedated, intubated, and mechanically ventilated. At 30 min after admission, arterial PCO2 reached 132 mmHg, pH was 6.94, and PO2 was 95 mmHg, and then the measurements repeated after 30 min revealed pH of 6.80, PCO2 of 209 mmHg, and PO2 of 73 mmHg. Oxygenation was initially hypoxic but rapidly maintained, and successful recovery followed without neurological or cardiovascular sequelae. This case shows the cardiovascular and neurological tolerance of a prolonged period of supercarbia in a young patient. The most important lesson to be learned is the extreme importance of maintaining adequate tissue perfusion and oxygenation during an asthma attack. The second lesson is that when conventional bronchodilators fail, the intensivist may resort to the use of drugs such as ketamine, magnesium sulfate, and inhalation anesthesia. In this context, deep sedation and curarization are important, not only to improve oxygenation but also to reduce cerebral metabolic requirements.

Effects of temperature on acid-base regulation, gill ventilation and air breathing in the clown knifefish, Chitala ornata.

Chitala ornata is a facultative air-breathing fish, which at low temperatures shows an arterial PCO2 (PaCO2 ) level only slightly elevated above that of water breathers. By holding fish with in-dwelling catheters at temperatures from 25 to 36°C and measuring blood gasses, we show that this animal follows the ubiquitous poikilotherm pattern of reducing arterial pH with increasing temperature. Surprisingly, the temperature increase caused an elevation of PaCO2 from 5 to 12 mmHg while the plasma bicarbonate concentration remained constant at around 8 mmol l-1 The temperature increase also gave rise to a larger fractional increase in air breathing than in gill ventilation frequency. These findings suggest that air breathing, and hence the partitioning of gas exchange, is to some extent regulated by acid-base status in air-breathing fish and that these bimodal breathers will be increasingly likely to adopt respiratory pH control as temperature rises, providing an interesting avenue for future research.

COMPARATIVE STUDY OF PULMONARY FUNCTION TESTS IN SEDENTARY INDIVIDUALS AND DYNAMIC EXERCISING PEOPLE

The field of exercise physiology is at the dawn of a new era. Exercise can play a role in shaping one's life style.Jogging, and walking are dynamic exercises, play a dominant role in individual's total health. The pulmonary physicians admit the dynamic exercise is beneficial to prevent respiratory diseases . The dynamic exercise's positive impact includes pulmonary physioloy. The pulmonary function tests evaluate the respiratory system. They are ventilatory function tests. The oxygen consumption and carbon dioxide production may go up to 25 times depending on severity of the exercise and the alveolar and arterial PO2 and PCO2 are maintained normal during the strenuous exercise, by increase in pulmonary ventilation and changes at the tissues level. Materials and Methods: study was conducted on subjects ranging from 24-26 years, 44-46 years and 64-66 years male in good health and their hemoglobin is more than 10gms/ 100ml. Different parameters (FVC, FEV1, FEV1/FVC %, PEF 50%, RR) of the study are recorded on the computerized Spirometer. Results and Conclusion: The results showed significantly increased (p<0.001) mean FVC, mean FEV1, mean FEV% and mean PEF in male atheletes practicing regular dynamic exercise and more so in young persons. This suggests that regular dynamic exercise has improved lung function.

Mild Hyperventilation in Traumatic Brain Injury—Relation to Cerebral Energy Metabolism, Pressure Autoregulation, and Clinical Outcome

Hyperventilation is a controversial treatment in traumatic brain injury (TBI). Prophylactic severe hyperventilation (below 3.3 kPa/25 mm Hg) is generally avoided, due to the risk of cerebral ischemia. Mild hyperventilation (arterial pCO2 within 4.0-4.5 kPa/30-34 mm Hg) in cases of intracranial hypertension is commonly used, but its safety and benefits are not fully elucidated. The aim of this study was to evaluate the use of mild hyperventilation and its relation to cerebral energy metabolism, pressure autoregulation, and clinical outcome in TBI. This retrospective study was based on 120 patients with severe TBI treated at the neurointensive care unit, Uppsala University Hospital, Sweden, between 2008 and 2018. Data from cerebral microdialysis (glucose, pyruvate, and lactate), arterial pCO2, and pressure reactivity index were analyzed for the first 3 days post-injury. Mild hyperventilation, 4.0-4.5 kPa (30-34 mm Hg), was more frequently used early and the patients were gradually normoventilated. Low pCO2 was associated with slightly higher intracranial pressure and slightly lower cerebral perfusion pressure (P < 0.01). There was no univariate correlation between low pCO2 and worse cerebral energy metabolism. Multiple linear regression analysis showed that mild hyperventilation was associated with lower pressure reactivity index on day 2 (P= 0.03), suggesting better pressure autoregulation. Younger age and lower intracranial pressure were also associated with lower pressure reactivity index. These findings support the notion that mild hyperventilation is safe and may improve cerebrovascular reactivity.

Ventilatory responses of the clown knifefish, Chitala ornata, to arterial hypercapnia remain after gill denervation.

The aim of this study was to corroborate the presence of CO2/H+-sensitive arterial chemoreceptors involved in producing air-breathing responses to aquatic hypercarbia in the facultative air-breathing clown knifefish (Chitala ornata) and to explore their possible location. Progressively increasing levels of CO2 mixed with air were injected into the air-breathing organ (ABO) of one group of intact fish to elevate internal PCO2 and decrease blood pH. Another group of fish in which the gills were totally denervated was exposed to aquatic hypercarbia (pH ~ 6) or arterial hypercapnia in aquatic normocarbia (by injection of acetazolamide to increase arterial PCO2 and decrease blood pH). Air-breathing frequency, gill ventilation frequency, heart rate and arterial PCO2 and pH were recorded during all treatments. The CO2 injections into the ABO induced progressive increases in air-breathing frequency, but did not alter gill ventilation or heart rate. Exposure to both hypercarbia and acetazolamide post-denervation of the gills also produced significant air-breathing responses, but no changes in gill ventilation. While all treatments produced increases in arterial PCO2 and decreases in blood pH, the modest changes in arterial PCO2/pH in the acetazolamide treatment produced the greatest increases in air-breathing frequency. These results strengthen the evidence that internal CO2/H+ sensing is involved in the stimulation of air breathing in clown knifefish and suggest that it involves extra-branchial chemoreceptors possibly situated either centrally or in the air-breathing organ.

Practical Clinical Application of an Extracorporeal Carbon Dioxide Removal System in Acute Respiratory Distress Syndrome and Acute on Chronic Respiratory Failure.

We retrospectively reviewed the medical records of 11 patients supported with a veno-venous low-flow extracorporeal carbon dioxide (CO2) removal (ECCO2R) device featuring a large gas exchange surface membrane lung (ML) (i.e., 1.8 m). Seven patients suffered from exacerbation of a chronic pulmonary disease, while four subjects were affected by acute respiratory distress syndrome (ARDS). Twenty-four hours of ECCO2R treatment reduced arterial PCO2 from 63 ± 12 to 54 ± 11 mm Hg (p < 0.01), increased arterial pH from 7.29 ± 0.07 to 7.39 ± 0.06 (p < 0.01), and decreased respiratory rate from 32 ± 10 to 21 ± 8 bpm (p < 0.05). Extracorporeal blood flow and CO2 removal were 333 ± 37 and 94 ± 18 ml/min, respectively. The median duration of ECCO2R treatment was 7 days (6.5-9.5). All four ARDS patients were invasively ventilated at the time of treatment start, no one was extubated and they all died. Among the seven patients with exacerbation of chronic pulmonary diseases, four were managed with noninvasive ventilation at ECCO2R institution, while three were extubated after starting the extracorporeal treatment. No one of these seven patients was intubated or re-intubated after ECCO2R institution and five (71%) survived to hospital discharge. A low-flow ECCO2R device with a large surface ML removes a relevant amount of CO2 resulting in a decreased arterial PCO2, an increased arterial pH, and in a reduced ventilatory load.

Impact of different intraoperative CO2 pressure levels (8 and 15 mmHg) during laparoscopic hysterectomy performed due to benign uterine pathologies on postoperative pain and arterial pCO2: a prospective randomised controlled clinical trial

To compare the effects of two different intraoperative CO2 pressures (8 and 15mmHg) during laparoscopic hysterectomy for benign uterine pathologies in terms of postoperative abdominal and shoulder pain, laparoscopy-mediated vegetative alterations, pain medication requirement, arterial CO2 pressure (pCO2 ), surgical parameters, and safety. Prospective randomised controlled study. German university hospital. Female patients undergoing laparoscopic hysterectomy for benign uterine pathologies. Patients were randomised to a standard pressure (SP; 15mmHg, control) or low-pressure (LP; 8mmHg, experimental) group. Primary outcomes were postoperative abdominal and shoulder pain intensities, measured via numeric rating scale (NRS) and vegetative parameters (fatigue, nausea, vomiting, bloating) at 3, 24, and 48hours postoperatively. Secondary outcomes were pain medication requirement (mg) and arterial pCO2 (mmHg). Surgical parameters and intra- and postoperative complications were also recorded. In total, 178 patients were included. Patients in the LP group (n=91) showed significantly lower postoperative abdominal and shoulder pain scores, fewer vegetative alterations, lower pain medication requirements, a shorter postoperative hospitalization, and lower intra- and postoperative arterial pCO2 values compared with the SP group (n=87; P≤0.01). No differences in intra- and postoperative complications were observed between groups. Low-pressure laparoscopy seems to be an effective and safe technique for the reduction of postoperative pain and laparoscopy-induced metabolic and vegetative alterations following laparoscopic hysterectomy for benign indications. Low-pressure laparoscopy seems to be an effective and safe technique for reduction of pain following laparoscopic hysterectomy.

Improving the prognostic value of ∆PCO2 following cardiac surgery: a prospective pilot study.

Conflicting results have been published on prognostic significance of central venous to arterial PCO2 difference (∆PCO2) after cardiac surgery. We compared the prognostic value of ∆PCO2 on intensive care unit (ICU) admission to an original algorithm combining ∆PCO2, ERO2 and lactate to identify different risk profiles. Additionally, we described the evolution of ∆PCO2 and its correlations with ERO2 and lactate during the first postoperative day (POD1). In this monocentre, prospective, and pilot study, 25 patients undergoing conventional cardiac surgery were included. Central venous and arterial blood gases were collected on ICU admission and at 6, 12 and 24 h postoperatively. High ∆PCO2 (≥ 6 mmHg) on ICU admission was found to be very frequent (64% of patients). Correlations between ∆PCO2 and ERO2 or lactate for POD1 values and variations were weak or non-existent. On ICU admission, a high ∆PCO2 did not predict a prolonged ICU length of stay (LOS). Conversely, a significant increase in both ICU and hospital LOS was observed in high-risk patients identified by the algorithm: 3.5 (3.0–6.3) days versus 7.0 (6.0–8.0) days (p = 0.01) and 12.0 (8.0–15.0) versus 8.0 (8.0–9.0) days (p < 0.01), respectively. An algorithm incorporating ICU admission values of ∆PCO2, ERO2 and lactate defined a high-risk profile that predicted prolonged ICU and hospital stays better than ∆PCO2 alone.

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 Relationship between Pulmonary Function Testing Including Cardiopulmonary Exercise Testing (CPET) and Outcomes in Patients with Oesophagogastric Cancer Undergoing Neo-adjuvant Chemotherapy

Background: In the field of gastro-oesophageal cancer, the effect of chemotherapy treatment on patients’ cardiopulmonary fitness as well as on the incidence of post-operative cardiopulmonary complications remains controversial. Objectives: To examine the effect of chemotherapy on cardiopulmonary fitness. Further, to examine the association between cardiopulmonary exercise testing and other measurements on outcomes in patients with gastro-oesophageal cancer undergoing neo-adjuvant chemotherapy. And to compare post chemotherapy cardiopulmonary exercise testing with surgical outcome. Patients and methods: Forty-one patients with gastroesophageal cancer who underwent chemotherapy were referred to the Pulmonary Function Laboratory, Respiratory Medicine, Glasgow Royal Infirmary during the period August 2008 to December 2011. 35 of these patients underwent both pre- and post-chemotherapy pulmonary function testing and 31 of these 35 patients had their chemotherapy followed by surgery. A further 6 patients underwent chemotherapy followed by pulmonary function testing and surgery but without pre-chemotherapy testing Results: There were significant differences between the pre- and post-chemotherapy results in arterial PCO2 (p<0.01), t hemoglobin (p<0.001) and heart rate at anaerobic threshold as a % of maximum predicted heart rate (p<0.05). There were significant differences between those patients without post-operative complications and those with post-operative complications, in length of high dependency care stay (p<0.01), length of ward stay (p<0.05) and length of hospital stay (p<0.001) Conclusion: the results of the present study show that there was no significant change in cardiopulmonary fitness in patients with gastro-oesophageal cancer who underwent chemotherapy apart from correctable side effect such as anaemia. In addition, CPET parameters, pulmonary function tests and other related factors did not predict an increase in the risk of post-operative complications. There was, however, a relationship between deprivation and an increased risk of postoperative complications.

Volume Capnography in the Intensive Care Unit: Potential Clinical Applications.

Volume capnography provides a noninvasive, continuous display of the fractional concentration or partial pressure of carbon dioxide (Pco2) versus exhaled volume. Derived measurements and calculations are influenced by changes in both ventilation and perfusion and are therefore useful for assessing both respiratory and cardiovascular function. This article provides an evidence-based review of several potential uses of volume capnography in the intensive care unit: 1) monitoring the effectiveness of ventilation by using end-tidal Pco2 as a surrogate for arterial Pco2, 2) assessing volume responsiveness, 3) measuring cardiac output, 4) determining prognosis in patients with the acute respiratory distress syndrome, 5) optimizing alveolar recruitment, and 6) excluding pulmonary embolism. Studies performed during the past few decades have clearly shown that volume capnography can provide important prognostic information in patients with acute respiratory distress syndrome and that end-tidal Pco2 should not be used to estimate or even to monitor the direction of change in the arterial Pco2 in mechanically ventilated intensive care unit patients. Unfortunately, few conclusions can be made from studies evaluating other potential applications. Of these, the most promising are the noninvasive measurement of cardiac output and optimization of alveolar recruitment in patients with acute respiratory distress syndrome and in mechanically ventilated, morbidly obese patients.

Sucrose but Not Nitrate Ingestion Reduces Strenuous Cycling-induced Intestinal Injury.

Strenuous exercise induces intestinal injury, which is likely related to splanchnic hypoperfusion and may be associated with gastrointestinal complaints commonly reported during certain exercise modalities. Increasing circulating nitric oxide (NO) levels or inducing postprandial hyperemia may improve splanchnic perfusion, thereby attenuating intestinal injury during exercise. Therefore, we investigated the effects of both dietary nitrate ingestion and sucrose ingestion on splanchnic perfusion and intestinal injury induced by prolonged strenuous cycling. In a randomized crossover manner, 16 well-trained male athletes (age, 28 ± 7 yr; Wmax, 5.0 ± 0.3 W·kg) cycled 60 min at 70% Wmax after acute ingestion of sodium nitrate (NIT; 800 mg NO3), sucrose (SUC; 40 g), or a water placebo (PLA). Splanchnic perfusion was assessed by determining the gap between gastric and arterial pCO2 (gapg-apCO2) using gastric air tonometry. Plasma intestinal fatty acid-binding protein (I-FABP) concentrations, reflecting enterocyte damage, were assessed every 20 min during and up to 60 min of postexercise recovery. The exercise protocol resulted in splanchnic hypoperfusion, as gapg-apCO2 levels increased during exercise (P < 0.001), with no differences between treatments (P = 0.47). Although plasma I-FABP concentrations increased during exercise and postexercise recovery for all treatments (P < 0.0001), the increase was different between treatments (P < 0.0001). Post hoc comparisons showed an attenuated increase in I-FABP in SUC versus PLA (P = 0.020). In accordance, I-FABP area under the curve (AUC0-120) was significantly lower in SUC versus PLA (57,270 ± 77,425 vs 114,907 ± 91,527 pg·mL per 120 min, P = 0.002). No differences were observed between NIT and PLA (P = 0.99). Sucrose but not nitrate ingestion lowers intestinal injury evoked during prolonged strenuous cycling. These results suggest that sucrose ingestion, but not nitrate, prevents hypoperfusion-induced gastrointestinal damage during exercise and, as such, may help to lower exercise-related gastrointestinal complaints.

TP1-6 Pathological patterns of spinal cord blood flow after injury visualised with laser speckle contrast imaging

ObjectivesIn humans the effect of spinal cord injury (SCI) on spinal cord blood flow (SCBF) is poorly understood. We imaged SCBF intraoperatively using laser speckle contrast imaging (LSCI).MethodsWe recruited 4 patients without SCI and 22 patients with SCI. Inclusion criteria for SCI patients are: AIS A–C, 18–70 years old, surgery within 72 hour of injury. In the SCI patients, we monitored spinal cord perfusion pressure and microdialysis from the injury site for 24 hour postoperatively. Mean patient follow-up after SCI was 7 m.ResultsLSCI signal is dampened by cerebrospinal fluid, but not dura. In patients without SCI we observed intact autoregulation, as well as SCBF variation with cardiac cycle, respiratory cycle and arterial pCO2. In SCI patients three pathological SCBF patterns were seen: necrosis-penumbra, patchy-perfusion and hyper-perfusion. Increase in MAP (&gt;20 mmHg) increased overall injury site SCBF, but in 5/22 SCI patients there was a local steal effect where SCBF increased in some regions but decreased in others. In 7 SCI patients there was diastolic ischaemia, with regions only perfused in systole, but not diastole. Low injury site SCBF correlated with low spinal cord perfusion pressure, low tissue glucose, high tissue lactate and less improvement in combined sensory AIS score at follow-up.ConclusionsLSCI can be used to visualise SCBF non-invasively with high spatial-temporal resolution. We observed pathological SCBF patterns after SCI and some unanticipated SCBF responses to blood pressure changes.

How does homeostasis happen? Integrative physiological, systems biological, and evolutionary perspectives.

Homeostasis is a founding principle of integrative physiology. In current systems biology, however, homeostasis seems almost invisible. Is homeostasis a key goal driving body processes, or is it an emergent mechanistic fact? In this perspective piece, I propose that the integrative physiological and systems biological viewpoints about homeostasis reflect different epistemologies, different philosophies of knowledge. Integrative physiology is concept driven. It attempts to explain biological phenomena by continuous formation of theories that experimentation or observation can test. In integrative physiology, "function" refers to goals or purposes. Systems biology is data driven. It explains biological phenomena in terms of "omics"-i.e., genomics, gene expression, epigenomics, proteomics, and metabolomics-it depicts the data in computer models of complex cascades or networks, and it makes predictions from the models. In systems biology, "function" refers more to mechanisms than to goals. The integrative physiologist emphasizes homeostasis of internal variables such as Pco2 and blood pressure. The systems biologist views these emphases as teleological and unparsimonious in that the "regulated variable" (e.g., arterial Pco2 and blood pressure) and the "regulator" (e.g., the "carbistat" and "barostat") are unobservable constructs. The integrative physiologist views systems biological explanations as not really explanations but descriptions that cannot account for phenomena we humans believe exist, although they cannot be observed directly, such as feelings and, ultimately, the conscious mind. This essay reviews the history of the two epistemologies, emphasizing autonomic neuroscience. I predict rapprochement of integrative physiology with systems biology. The resolution will avoid teleological purposiveness, transcend pure mechanism, and incorporate adaptiveness in evolution, i.e., "Darwinian medicine."

Agreement and Correlation of Arterial and Venous Blood Gas Analysis in a Diverse Population

Introduction: Agreement and correlation of arterial blood gases (ABGs) and venous blood gases (VBGs) at near normal values are well described but have not been well validated at extremes of values. We evaluated the agreement and correlation of ABG and VBG at extremes of values and assessed the utility of VBG as a screening tool. Methods: We performed a retrospective, observational study of ABG and VBG collected at the same time. Statistical analysis included Bland-Altman plot analysis, Pearson correlations, and sensitivity/specificity tests. For limits of agreement (LOA), we set a threshold of ±0.10 units for pH and ±2.4 mm Hg for partial pressure of carbon dioxide (pCO2). A threshold of 80% sensitivity was considered appropriate for VBG to be used as a screening tool for abnormal ABG values. Results: There were 1684, 1744, and 1769 paired pH, pCO2, and HCO3¯ results, respectively. Mean difference (MD) for arterial and venous pH was 0.017 (95% confidence interval [CI]: 0.014-0.020; 95% LOA: −0.11 to 0.15), and Pearson correlation was 0.78 ( P &lt; .0001). At venous pH &lt;7.35, MD was 0.025 (95% CI: 0.019-0.030; 95% LOA: −0.12 to 0.17). Sensitivity of venous pH &lt;7.35 identifying arterial pH &lt;7.35 was 85.0%. MD for arterial and venous pCO2 was −2.5 (95% CI: −2.9 to −2.0; 95% LOA: −21.7 to 16.8), and Pearson correlation was 0.70 ( P &lt; .0001). At venous pCO2 &gt;45 mm Hg, MD was −4.1 (95% CI: −4.9 to −3.3; 95% LOA: −25.7 to 17.5). Sensitivity of venous pCO2 &gt;45 mm Hg identifying arterial pCO2 &gt;45 mm Hg was 67.6%. MD for arterial and venous HCO3¯ was −0.3 (95% CI: −0.4 to −0.2; 95% LOA: −4.8 to 4.2), and Pearson correlation was 0.90 ( P &lt; .0001). Conclusions: Venous blood gases cannot reliably replace ABGs due to poor agreement in acidemia and hypercarbia. Venous blood gases can be used as a screening tool for acidemia but are unsuitable for hypercarbia.

Comparison of arterial and venous blood gases in patients with obesity hypoventilation syndrome and neuromuscular disease.

OBJECTIVES:Obesity hypoventilation syndrome (OHS) and some neuromuscular diseases (NMD) present with hypercapnic respiratory failure. Arterial blood gas (ABG) analysis is important in the diagnosis, follow-up, and treatment response of these diseases. However, ABG sampling is difficult in these patients because of excessive subcutaneous fat tissue, muscle atrophy, or contracture. The aim of this study is to investigate the value of venous blood gas (VBG), which is an easier and less complicated method, among stable patients with OHS and NMD.METHODS:The study included stable OHS and NMD patients who had been previously diagnosed and followed up between March 2017 and May 2017 in the outpatient clinic. ABG was taken from all patients in room air, and peripheral VBG was taken within 5 min after ABG sampling.RESULTS:Thirty-six patients with OHS and 46 patients with NMD were included in the study. There was a moderate positive correlation between arterial and venous pH values for all patients (rs = 0.590, P < 0.001). There were a strong and very strong positive correlations between arterial and venous pCO2 and HCO3 values (rs = 0.725 and rs = 0.934, respectively) (P < 0.001). There was no correlation between arterial and venous pO2 and saturation values. There was an agreement in Bland–Altman method for the values of ABG and VBG (pH, pCO2, and HCO3).CONCLUSIONS:There was a correlation between ABG and VBG values (pH, pCO2, and HCO3). VBG parameters (pH, pCO2, and HCO3) can be used safely instead of ABG parameters which have many risks, during treatment and follow-up of patients with OHS and NMD.

Extracorporeal CO2 Removal: The Minimally Invasive Approach, Theory, and Practice.

Minimally invasive extracorporeal CO2 removal is an accepted supportive treatment in chronic obstructive pulmonary disease patients. Conversely, the potential of such technique in treating acute respiratory distress syndrome patients remains to be investigated. The aim of this study was: 1) to quantify membrane lung CO2 removal (VCO2ML) under different conditions and 2) to quantify the natural lung CO2 removal (VCO2NL) and to what extent mechanical ventilation can be reduced while maintaining total expired CO2 (VCO2tot = VCO2ML + VCO2NL) and arterial PCO2 constant. Experimental animal study. Department of Experimental Animal Medicine, University of Göttingen, Germany. Eight healthy pigs (57.7 ± 5 kg). The animals were sedated, ventilated, and connected to the artificial lung system (surface 1.8 m, polymethylpentene membrane, filling volume 125 mL) through a 13F catheter. VCO2ML was measured under different combinations of inflow PCO2 (38.9 ± 3.3, 65 ± 5.7, and 89.9 ± 12.9 mm Hg), extracorporeal blood flow (100, 200, 300, and 400 mL/min), and gas flow (4, 6, and 12 L/min). At each setting, we measured VCO2ML, VCO2NL, lung mechanics, and blood gases. VCO2ML increased linearly with extracorporeal blood flow and inflow PCO2 but was not affected by gas flow. The outflow PCO2 was similar regardless of inflow PCO2 and extracorporeal blood flow, suggesting that VCO2ML was maximally exploited in each experimental condition. Mechanical ventilation could be reduced by up to 80-90% while maintaining a constant PaCO2. Minimally invasive extracorporeal CO2 removal removes a relevant amount of CO2 thus allowing mechanical ventilation to be significantly reduced depending on extracorporeal blood flow and inflow PCO2. Extracorporeal CO2 removal may provide the physiologic prerequisites for controlling ventilator-induced lung injury.