Trans-cerebral HCO3− and PCO2 exchange during acute respiratory acidosis and exercise-induced metabolic acidosis in humans

This study investigated trans-cerebral internal jugular venous-arterial bicarbonate ([HCO3−]) and carbon dioxide tension (PCO2) exchange utilizing two separate interventions to induce acidosis: 1) acute respiratory acidosis via elevations in arterial PCO2 (PaCO2) (n = 39); and 2) metabolic acidosis via incremental cycling exercise to exhaustion (n = 24). During respiratory acidosis, arterial [HCO3−] increased by 0.15 ± 0.05 mmol ⋅ l−1 per mmHg elevation in PaCO2 across a wide physiological range (35 to 60 mmHg PaCO2; P < 0.001). The narrowing of the venous-arterial [HCO3−] and PCO2 differences with respiratory acidosis were both related to the hypercapnia-induced elevations in cerebral blood flow (CBF) (both P < 0.001; subset n = 27); thus, trans-cerebral [HCO3−] exchange (CBF × venous-arterial [HCO3−] difference) was reduced indicating a shift from net release toward net uptake of [HCO3−] (P = 0.004). Arterial [HCO3−] was reduced by −0.48 ± 0.15 mmol ⋅ l−1 per nmol ⋅ l−1 increase in arterial [H+] with exercise-induced acidosis (P < 0.001). There was no relationship between the venous-arterial [HCO3−] difference and arterial [H+] with exercise-induced acidosis or CBF; therefore, trans-cerebral [HCO3−] exchange was unaltered throughout exercise when indexed against arterial [H+] or pH (P = 0.933 and P = 0.896, respectively). These results indicate that increases and decreases in systemic [HCO3−] – during acute respiratory/exercise-induced metabolic acidosis, respectively – differentially affect cerebrovascular acid-base balance (via trans-cerebral [HCO3−] exchange).

Simulating effect of neonate body position on carbon dioxide tension in oxygen tent

Oxygen therapy is a common method of respiratory support, but its use involves the risk of carbon dioxide recycling and the development of hypercapnia in the patient.The aim of the study. Assess the carbon dioxide tension in the oxygen tent depending on the patient's body position in the experimental newborn Model.Materials and Methods. The study was performed on the phantom of the newborn. Influence of 3 patient positions at fresh mixture feed rate 2.5, 5, 7 and 10 l/min is evaluated. Monitoring of the carbon dioxide tension was carried out using Testo 480, measurements were carried out for 60 minutes.Results of the study. A clear relationship was established between the position of the newborn's body and the tension of carbon dioxide in the oxygen tent. The minimum tension of carbon dioxide is noted in the patient's position ≪on the back≪ at a fresh mixture feed rate of 7.5 l/minute and is 527 ± 64 ppm, and the maximum ‒ in the child's position ≪on the stomach≪ at the same oxygen-air mixture feed rate: 1180 ± 63 ppm.Conclusion. The position of the newborn baby's body is the main factor affecting the carbon dioxide stress in the oxygen tent.

Comparison of Intra and Post-operative Sedation efficacy of Dexmedetomidine-Midazolam and Dexmedetomidine-Propofol for Major Abdominal Surgery

Background: The effectiveness and side effects of dexmedetomidine (DEX) in combination with midazolam and propofol have not been comparatively studied in a single clinical trial as sedative agents to general anesthesia before. Objective: The objective of this study is to compare intra and post-operative sedation between DEX-Midazolam and DEX-Propofol in patients who underwent major abdominal surgery on the duration of general anesthesia, hemodynamic and sedation effect. Method: This prospective, randomized, double-blinded clinical trial included 50 patients who were 20 to 60 years of age and admitted for major abdominal surgery. The patients were randomly assigned by a computer-generated random numbers table to sedation with DEX plus midazolam (DM group) (n=25) or DEX plus propofol (DP group) (n=25). In the DM group, patients received a bolus dose of 0.1 mg/kg of midazolam and immediately initiated the intravenous (i.v.) infusion of DEX 1 µg/kg over a 10 min and 0.5 µg/kg/hr by continuous i.v. infusion within operation period. In the DP group, patients received pre-anesthetic i.v. DEX 1 µg/kg over 15 min before anesthesia induction and 0.2-1 µg/kg/hr by continuous i.v. infusion during the operative period. After preoxygenation for at least 2 min, during the surgery, patients received propofol infusion dose of 250 μg/kg/min for 15 min then a basal infusion dose of 50 μg/kg/min. The bispectral index (BIS) value, as well as mean arterial pressure (MAP), heart rate (HR), respiratory rate (RR), oxygen saturation (SaO2), percutaneous arterial oxygen saturation (SpO2) and end-tidal carbon dioxide tension (ETCO2) were recorded before anesthesia (T0), during anesthesia (at 15-min intervals throughout the surgical procedure), by a blinded observer. Evidence of apnea, hypotension, hypertension and hypoxemia were recorded during surgery. Results: The hemodynamic changes, including HR, MAP, BIS, VT, SaO2, and RR had a downward tendency with time, but no significant difference was observed between the groups (P>0.05). However, the two groups showed no significant differences in ETCO2 and SPO2 values in any of the assessed interval (P>0.05). In this study, the two groups showed no significant differences in the incidence of nausea, vomiting, coughing, apnea, hypotension, hypertension, bradycardia and hypoxemia (P>0.05). Respiratory depression and Conclusion: Our study showed no significant differences between the groups in hemodynamic and respiratory changes in each of the time intervals. There were also no significant differences between the two groups in the incidence of complication intra and post-operative. Further investigations are required to specify the optimum doses of using drugs which provide safety in cardiovascular and respiratory system without adverse disturbance during surgery.

COVID-19 pneumonia: pathophysiology and management

Coronavirus disease 2019 (COVID-19) pneumonia is an evolving disease. We will focus on the development of its pathophysiologic characteristics over time, and how these time-related changes determine modifications in treatment. In the emergency department: the peculiar characteristic is the coexistence, in a significant fraction of patients, of severe hypoxaemia, near-normal lung computed tomography imaging, lung gas volume and respiratory mechanics. Despite high respiratory drive, dyspnoea and respiratory rate are often normal. The underlying mechanism is primarily altered lung perfusion. The anatomical prerequisites for PEEP (positive end-expiratory pressure) to work (lung oedema, atelectasis, and therefore recruitability) are lacking. In the high-dependency unit: the disease starts to worsen either because of its natural evolution or additional patient self-inflicted lung injury (P-SILI). Oedema and atelectasis may develop, increasing recruitability. Noninvasive supports are indicated if they result in a reversal of hypoxaemia and a decreased inspiratory effort. Otherwise, mechanical ventilation should be considered to avert P-SILI. In the intensive care unit: the primary characteristic of the advance of unresolved COVID-19 disease is a progressive shift from oedema or atelectasis to less reversible structural lung alterations to lung fibrosis. These later characteristics are associated with notable impairment of respiratory mechanics, increased arterial carbon dioxide tension (PaCO2), decreased recruitability and lack of response to PEEP and prone positioning.

Changes in central venous-to-arterial carbon dioxide tension induced by fluid bolus in critically ill patients

Background In this prospective observational study, we evaluated the effects of fluid bolus (FB) on venous-to-arterial carbon dioxide tension (PvaCO2) in 42 adult critically ill patients with pre-infusion PvaCO2 > 6 mmHg. Results FB caused a decrease in PvaCO2, from 8.7 [7.6−10.9] mmHg to 6.9 [5.8−8.6] mmHg (p < 0.01). PvaCO2 decreased independently of pre-infusion cardiac index and PvaCO2 changes during FB were not correlated with changes in central venous oxygen saturation (ScvO2) whatever pre-infusion CI. Pre-infusion levels of PvaCO2 were inversely correlated with decreases in PvaCO2 during FB and a pre-infusion PvaCO2 value < 7.7 mmHg could exclude a decrease in PvaCO2 during FB (AUC: 0.79, 95%CI 0.64–0.93; Sensitivity, 91%; Specificity, 55%; p < 0.01). Conclusions Fluid bolus decreased abnormal PvaCO2 levels independently of pre-infusion CI. Low baseline PvaCO2 values suggest that a positive response to FB is unlikely.

Intraventricular haemorrhage

Like other problems of preterm infants, cerebral bleeding was barely known before special hospital units for ‘weaklings’ were established. Its symptoms were unspecific, the infants were considered miscarriages, and autopsies were rarely performed. Based on those postmortem findings, the theory arose at the end of the 18th century that brain haemorrhages in preterm infants result from birth trauma. Such mechanical explanations persisted for two centuries, even when it became ever more evident that this brain disorder was associated with postnatal respiratory distress. When in vivo imaging techniques (computed tomography, ultrasound scanning through the fontanelle) became available in the 1970s, the view changed and respiratory insufficiency was acknowledged as the major causative factor. Relying on these imaging techniques, Pape and Wigglesworth developed a model that explained the origin of periventricular haemorrhage and ischaemia in 1978. With the understanding of pressure-passive perfusion and cerebral flow dependent on carbon dioxide tension, the stage was set for effective preventive strategies.

Inverse Ratio Ventilation for Preventing Intra-Operative Hypercapnia in Children Undergoing Laparoscopic Surgery

BackgroundHigh end-tidal carbon dioxide tension (PETCO2) and respiratory acidosis occurs frequently in patients undergoing laparoscopic surgery. The aim of this study is to be investigate the effect of pressure-controlled inverse ratio ventilation (IRV) with inspiratory to expiratory ratio (I: E) of 2:1 on children undergoing laparoscopic surgery. MethodsEighty children undergoing elective laparoscopic surgery were allocated randomly to the IRV group (1: E=2:1) and the control group (I: E=1:2). Children received pressure-controlled ventilation with I: E ratio of 2:1 or 1:2. Hemodynamic parameters and respiratory mechanics were recorded. Side effects were also recorded. ResultsAt 30 min after CO2 pneumoperitoneum, tidal volume (Vt) and arterial partial pressure of oxygen (PaO2) were greater in the IRV group than the control group (100.6 ± 6.6 vs. 95.1±7.9 ml, 282.7 ± 45.6 vs.246.5 ± 40.1mmHg, respectively) (P < 0.01), but PaCO2 was lower than the control group (43.9 ± 5.45 vs. 46.7 ± 4.90 mmHg, P = 0.013). The incidence of intra-operative hypercapnia was lower in the IRV group (25% vs. 42.5%, P= 0.03). ConclusionIRV may reduce the incidence of intra-operative hypercapnia as well as increasing Vt and thus improving CO2 elimination in children undergoing laparoscopy. (Registration number: ChiCTR2000035589)