Carbon dioxide tolerability and toxicity in rat and man: A translational study.

Background: Due the increasing need for storage of carbon dioxide (CO2) more individuals are prone to be exposed to high concentrations of CO2 accidentally released into atmosphere, with deleterious consequences. Methods: We tested the effect of increasing CO2 concentrations in humans (6-12%) and rats (10-50%) at varying inhalation times (10-60 min). In humans, a continuous positive airway pressure helmet was used to deliver the gas mixture to the participants. Unrestrained rats were exposed to CO2 in a transparent chamber. In both species regular arterial blood gas samples were obtained. After the studies, the lungs of the animals were examined for macroscopic and microscopic abnormalities. Results: In humans, CO2 concentrations of 9% inhaled for >10 min, and higher concentrations inhaled for <10 min were poorly or not tolerated due to exhaustion, anxiety, dissociation or acidosis (pH < 7.2), despite intact oxygenation. In rats, concentrations of 30% and higher were associated with CO2 narcosis, epilepsy, poor oxygenation and, at 50% CO2, spontaneous death. Lung hemorrhage and edema were observed in the rats at inhaled concentrations of 30% and higher. Conclusion: This study provides essential insight into the occurrence of physiological changes in humans and fatalities in rats after acute exposure to high levels of CO2. Humans tolerate 9% CO2 and retain their ability to function coherently for up to 10 min. These data support reconsideration of the current CO2 levels (<7.5%) that pose a risk to exposed individuals (<7.5%) as determined by governmental agencies to ≤9%.

Respiratory Effects of the Atypical Tricyclic Antidepressant Tianeptine in Human Models of Opioid-induced Respiratory Depression.

BACKGROUND: Animal data suggest that the antidepressant and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor modulator tianeptine is able to prevent opioid-induced respiratory depression. The hypothesis was that oral or intravenous tianeptine can effectively prevent or counteract opioid-induced respiratory depression in humans. METHODS: Healthy male and female volunteers participated in two studies that had a randomized, double blind, placebo-controlled, crossover design. First, oral tianeptine (37.5-, 50-, and 100-mg doses with 8 subjects) pretreatment followed by induction of alfentanil-induced respiratory depression (alfentanil target concentration, 100 ng/ml) was tested. Primary endpoint was ventilation at an extrapolated end-tidal carbon dioxide concentration of 55 mmHg (V̇E55). Next, the ability of four subsequent and increasing infusions of intravenous tianeptine (target tianeptine plasma concentrations 400, 1,000, 1,500, and 2,000 ng/ml, each given over 15 min) to counteract remifentanil-induced respiratory depression was determined in 15 volunteers. Ventilation was measured at isohypercpania (baseline ventilation 20 ± 2 l/min). The primary endpoint was minute ventilation during the 60 min of tianeptine versus placebo infusion. RESULTS: Alfentanil reduced V̇E55 to 13.7 (95% CI, 8.6 to 18.8) l/min after placebo pretreatment and to 17.9 (10.2 to 25.7) l/min after 50-mg tianeptine pretreatment (mean difference between treatments 4.2 (-11.5 to 3.0) l/min, P = 0.070). Intravenous tianeptine in the measured concentration range of 500 to 2,000 ng/ml did not stimulate ventilation but instead worsened remifentanil-induced respiratory depression: tianeptine, 9.6 ± 0.8 l/min versus placebo 15.0 ± 0.9 l/min; mean difference, 5.3 l/min; 95% CI, 2.5 to 8.2 l/min; P = 0.001, after 1 h of treatment. CONCLUSIONS: Neither oral nor intravenous tianeptine were respiratory stimulants. Intravenous tianeptine over the concentration range of 500 to 2000 ng/ml worsened respiratory depression induced by remifentanil.

The impact of deep versus standard neuromuscular block on intraoperative safety during laparoscopic surgery: an international multicenter randomized controlled double-blind strategy trial - EURO-RELAX TRIAL.

BACKGROUND: Muscle relaxants are routinely used during anesthesia to facilitate endotracheal intubation and to optimize surgical conditions. However, controversy remains about the required depth of neuromuscular block (NMB) needed for optimal surgical working conditions and how this relates to other outcomes. For instance, a deep neuromuscular block yields superior surgical working conditions compared to a standard NMB in laparoscopic surgery, however, a robust association to other (safety) outcomes has not yet been established. METHODS: Trial design: an international multicenter randomized controlled double-blind strategy trial. Trial population: 922 patients planned for elective, laparoscopic or robotic, abdominal surgery. INTERVENTION: Patients will be randomized to a deep NMB (post-tetanic count 1-2 twitches) or standard care (single-dose muscle relaxant administration at induction and repeated only if warranted by surgical team). Main trial endpoints: Primary endpoint is the difference in incidence of intraoperative adverse events during laparoscopic surgery graded according to ClassIntra® classification (i.e., ClassIntra® grade ≥ 2) between both groups. Secondary endpoints include the surgical working conditions, 30-day postoperative complications, and patients' quality of recovery. DISCUSSION: This trial was designed to analyze the effect of deep neuromuscular block compared to standard neuromuscular block on intra- and postoperative adverse events in patients undergoing laparoscopic surgery. TRIAL REGISTRATION: ClinicalTrials.gov NCT04124757 (EURO-RELAX); registration URL: https://clinicaltrials.gov/ct2/show/NCT04124757 , registered on October 11th, 2019.

Benefit versus Severe Side Effects of Opioid Analgesia: Novel Utility Functions of Probability of Analgesia and Respiratory Depression.

BACKGROUND: Previous studies integrated opioid benefit and harm into one single function-the utility function-to determine the drug toxicity (respiratory depression) in light of its wanted effect (analgesia). This study further refined the concept of the utility function using the respiratory and analgesic effects of the opioid analgesic alfentanil as example. METHODS: Data from three previous studies in 48 healthy volunteers were combined and reanalyzed using a population pharmacokinetic-pharmacodynamic analysis to create utility probability functions. Four specific conditions were defined: probability of adequate analgesia without severe respiratory depression, probability of adequate analgesia with severe respiratory depression, probability of inadequate analgesia without severe respiratory depression, and probability of inadequate analgesia with severe respiratory depression. RESULTS: The four conditions were successfully identified with probabilities varying depending on the opioid effect-site concentration. The optimum analgesia probability without serious respiratory depression is reached at an alfentanil effect-site concentration of 68 ng/ml, and exceeds the probability of the most unwanted effect, inadequate analgesia with severe respiratory depression (odds ratio, 4.0). At higher effect-site concentrations the probability of analgesia is reduced and exceeded by the probability of serious respiratory depression. CONCLUSIONS: The utility function was successfully further developed, allowing assessment of specific conditions in terms of wanted and unwanted effects. This approach can be used to compare the toxic effects of drugs relative to their intended effect and may be a useful tool in the development of new compounds to assess their advantage over existing drugs.

Influence of Ethanol on Oxycodone-induced Respiratory Depression: A Dose-escalating Study in Young and Elderly Individuals.

BACKGROUND: Respiratory depression is a potentially fatal complication of opioid use, which may be exacerbated by simultaneous ethanol intake. In this three-way sequential crossover dose-escalating study, the influence of coadministration of oral oxycodone and intravenous ethanol was assessed on resting ventilation, apneic events and the hypercapnic ventilatory response in healthy young and older volunteers. METHODS: Twelve young (21 to 28 yr) and 12 elderly (66 to 77 yr) opioid-naive participants ingested one 20 mg oxycodone tablet combined with an intravenous infusion of 0, 0.5, or 1 g/l ethanol. Resting respiratory variables and the primary outcome, minute ventilation at isohypercapnia (end-tidal partial pressure of carbon dioxide of 55 mmHg or VE55), were obtained at regular intervals during treatment. RESULTS: Oxycodone reduced baseline minute ventilation by 28% (P < 0.001 vs. control). Ethanol caused a further decrease of oxycodone-induced respiratory depression by another 19% at 1 g/l ethanol plus oxycodone (P < 0.01 vs. oxycodone). Ethanol combined with oxycodone caused a significant increase in the number of apneic events measured in a 6-min window with a median (range) increase from 1 (0 to 3) at 0 g/l ethanol to 1 (0 to 11) at 1 g/l ethanol (P < 0.01). Mean (95% CI) VE55 decreased from 33.4 (27.9 to 39.0) l/min (control) to 18.6 (15.6 to 21.6) l/min (oxycodone, P < 0.01 vs. control) and to 15.7 (12.7 to 18.6) l/min (oxycodone combined with ethanol, 1 g/l; P < 0.01 vs. oxycodone). CONCLUSIONS: Ethanol together with oxycodone causes greater ventilatory depression than either alone, the magnitude of which is clinically relevant. Elderly participants were more affected than younger volunteers.

Opioid-induced respiratory depression: reversal by non-opioid drugs.

The human body is critically dependent on the ventilatory control system for adequate uptake of oxygen and removal of carbon dioxide (CO2). Potent opioid analgesics, through their actions on µ-opioid receptor (MOR) expressed on respiratory neurons in the brainstem, depress ventilation. Opioid-induced respiratory depression (OIRD) is potentially life threatening and the cause of substantial morbidity and mortality. One possible way of prevention of OIRD is by adding a respiratory stimulant to the opioid treatment, which through activation of non-opioidergic pathways will excite breathing and consequently will offset OIRD and should not affect analgesia. Various new respiratory stimulants are currently under investigation including (a) potassium channel blockers acting at the carotid bodies, and (b) ampakines and (c) serotonin receptor agonists acting within the brainstem. (a) GAL-021 targets BKCa-channels. Initial animal and human experimental evidence indicates that this potassium channel blocker is a potent respiratory stimulant that reverses OIRD without affecting antinociception. GAL021 is safe and better tolerated than the older K(+)-channel blocker doxapram and more efficacious in its effect on respiration. (b) Ampakines modulate glutamatergic respiratory neurons in brainstem respiratory centers. Various ampakines have been studied showing their ability to increase respiratory drive during OIRD by increasing respiratory rate. Currently, CX717 is the most promising ampakine for use in humans as it is safe and does not affect opioid analgesia. (c) While animal studies show that serotonin receptor agonists increase respiratory drive via activation of serotonin receptors in brainstem respiratory centers, human studies are without success. Further clinical studies are required to improve our care of patients that are treated with potent opioid analgesics. The use of non-opioid adjuvants may reduce the probability of OIRD but does never relieve us of our duty to continuously monitor these patients, irrespective whether they are treated in-house or in an ambulatory setting.

Opioid-induced respiratory depression in the acute care setting: a compendium of case reports.

Opioid-induced respiratory depression (OIRD) is a potentially fatal complication of treatment with opioids. Little is known about patient- and case-related factors associated with OIRD. One-hundred-and-five available case reports on OIRD in 134 patients (12 years and older) in the perioperative, obstetric or emergency care setting, published since 1980, were retrieved from the literature. The most frequently reported case-related factors were: morphine use, perioperative setting and obstetrics, neuraxial or intravenous administration. The most frequently reported patient-related factors involved were: female gender, sleep-disordered breathing, obesity, renal impairment, pulmonary disease and CYP450 enzyme polymorphisms. While the analysis has limitations, it confirms that OIRD in the acute setting involves complex and interrelated factors and is a significant cause of preventable morbidity and mortality.

Two studies on reversal of opioid-induced respiratory depression by BK-channel blocker GAL021 in human volunteers.

BACKGROUND: Opioid-induced respiratory depression is potentially lethal. GAL021 is a calcium-activated potassium (BKCa) channel blocker that causes reversal of opioid-induced respiratory depression in animals due to a stimulatory effect on ventilation at the carotid bodies. To assess in humans whether GAL021 stimulates breathing in established opioid-induced respiratory depression and to evaluate its safety, a proof-of-concept double-blind randomized controlled crossover study on isohypercapnic ventilation (study 1) and subsequent double-blind exploratory study on poikilocapnic ventilation and nonrespiratory end points (study 2) was performed. METHODS: In study 1, intravenous low- and high-dose GAL021 and placebo were administrated on top of low- and high-dose alfentanil-induced respiratory depression in 12 healthy male volunteers on two separate occasions. In study 2, the effect of GAL021/placebo on poikilocapnic ventilation, analgesia, and sedation were explored in eight male volunteers. Data are mean difference between GAL021 and placebo (95% CI). RESULTS: Study 1: Under isohypercapnic conditions, a separation between GAL021 and placebo on minute ventilation was observed by 6.1 (3.6 to 8.6) l/min (P < 0.01) and 3.6 (1.5 to 5.7) l/min (P < 0.01) at low-dose alfentanil plus high-dose GAL021 and high-dose-alfentanil plus high-dose GAL021, respectively. Study 2: Similar observations were made on poikilocapnic ventilation and arterial pCO2. GAL021 had no effect on alfentanil-induced sedation, antinociception and no safety issues or hemodynamic effects became apparent. CONCLUSION: GAL021 produces respiratory stimulatory effects during opioid-induced respiratory depression with containment of opioid-analgesia and without any further increase of sedation. Further studies are needed to confirm these preliminary data.

Prior medical conditions and the risk of amyotrophic lateral sclerosis.

Sporadic amyotrophic lateral sclerosis (ALS) is believed to be a complex disease in which multiple exogenous and genetic factors interact to cause motor neuron degeneration. Elucidating the association between medical conditions prior to the first symptoms of ALS could lend support to the theory that specific subpopulations are at risk of developing ALS and provide new insight into shared pathogenic mechanisms. We performed a population-based case-control study in the Netherlands, including 722 sporadic ALS patients and 2,268 age and gender matched controls. Data on medical conditions and use of medication were obtained through a structured questionnaire. Multivariate analyses showed that hypercholesterolemia (OR 0.76, 95% CI 0.63-0.92, P = 0.006), the use of statins (OR 0.45, 95% CI 0.35-0.59, P = 1.86 × 10(-9)) or immunosuppressive drugs (OR 0.26, 95% CI 0.08-0.86, P = 0.03) were associated with a decreased risk of ALS. Head trauma was associated with an increased ALS susceptibility (OR 1.95, 95% CI 1.11-3.43, P = 0.02). No association was found with autoimmune diseases, cancer, psychiatric disorders or cardiovascular diseases, or survival. The lower frequency of hypercholesterolemia and less use of statins in ALS patients indicate a favorable lipid profile prior to symptom onset in at least a subpopulation of ALS. Prior head trauma is a risk factor for ALS and the significantly lower use of immunosuppressive drugs in ALS patients could suggest a protective effect. The identification of specific subpopulations at risk for ALS may provide clues towards possible pathogenic mechanisms.