Daily Anesthesiology Research Analysis
A randomized trial shows high-flow nasal oxygen can safely replace laryngeal mask ventilation for short general anesthesia without neuromuscular blockade, though hypercarbia requires vigilance. A mechanistic study validates the recruitment-to-inflation ratio as a bedside indicator of recruitability to personalize PEEP. A nationwide ICU registry analysis from Japan challenges Western concepts of persistent critical illness onset, suggesting health system and cultural effects.
Summary
A randomized trial shows high-flow nasal oxygen can safely replace laryngeal mask ventilation for short general anesthesia without neuromuscular blockade, though hypercarbia requires vigilance. A mechanistic study validates the recruitment-to-inflation ratio as a bedside indicator of recruitability to personalize PEEP. A nationwide ICU registry analysis from Japan challenges Western concepts of persistent critical illness onset, suggesting health system and cultural effects.
Research Themes
- Intraoperative respiratory support strategies
- Personalized ventilation and recruitability metrics
- ICU outcomes and health-system variation
Selected Articles
1. High-Flow Nasal Oxygen versus Mechanical Ventilation Through a Laryngeal Mask During General Anesthesia Without Muscle Paralysis: A Randomized Clinical Trial.
In 180 ASA I–II patients undergoing 30-minute propofol anesthesia without paralysis, high-flow nasal oxygen achieved a 99% success rate, noninferior to laryngeal mask ventilation. HFNO reduced postoperative respiratory symptoms (2% vs 19%) but increased intraoperative hypercarbia (43% with TcCO2 >55 mm Hg).
Impact: This pragmatic RCT directly informs intraoperative airway strategy in short procedures, showing HFNO can obviate supraglottic devices while improving patient-reported respiratory outcomes.
Clinical Implications: HFNO is a viable alternative to laryngeal mask ventilation for short general anesthesia without neuromuscular blockade, potentially reducing postoperative throat/airway symptoms. However, clinicians must monitor for hypercarbia and select patients carefully (e.g., avoid those with limited CO2 reserve).
Key Findings
- Primary noninferiority outcome met: 99% intraoperative support success in both HFNO and LMA groups.
- Postoperative respiratory symptoms were significantly lower with HFNO (2% vs 19%).
- HFNO led to higher intraoperative transcutaneous CO2, with 43% >55 mm Hg.
Methodological Strengths
- Randomized noninferiority design with clear, objective primary endpoint.
- Complete follow-up of all 180 randomized patients and prespecified secondary outcomes.
Limitations
- Single-center study in operative hysteroscopy with 30-minute anesthesia, limiting generalizability.
- Exclusion of neuromuscular blockade; findings may not apply to longer or more complex surgeries.
Future Directions: Multicenter trials across varied surgical populations and anesthetic durations should evaluate HFNO protocols, CO2 monitoring strategies, and thresholds for rescue ventilation.
BACKGROUND: Apneic oxygenation with high-flow nasal oxygen is a novel intraoperative respiratory support strategy for patients undergoing general anesthesia, but data about its clinical effects are scarce. We conducted a randomized trial to assess whether high-flow nasal oxygen is noninferior to mechanical ventilation through a laryngeal mask in terms of success rate of intraoperative respiratory support among patients undergoing a 30-minute general anesthesia session. METHODS: Single-center, randomized, noninferiority trial conducted in Italy between May 2022 and June 2023 and involving American Society of Anesthesiologists class I and II patients undergoing general anesthesia for operative hysteroscopy. Participants were randomized to receive laryngeal mask ventilation (volume-controlled ventilation to obtain end-tidal carbon dioxide between 35 and 45 mm Hg, inhaled oxygen fraction to achieve peripheral oxygen saturation greater than 95%) or high-flow nasal oxygen (70 L per minute, inhaled oxygen fraction of 100%) for intraoperative respiratory support. Patients received general anesthesia with propofol target-controlled infusion without neuromuscular blockade. Primary outcome was intraoperative respiratory support success rate, which was defined as peripheral oxygen saturation greater than 94% and transcutaneous carbon dioxide lower than 65 mm Hg with no need for rescue airway interventions for the entire procedure. Secondary outcomes included the rate of airway-related complications (including need for bag-mask or laryngeal mask ventilation, or tracheal intubation), postoperative respiratory symptoms, and postoperative dyspnea. RESULTS: All 180 patients who were randomized completed the trial (90 patients in each group). Median [interquartile range] anesthesia duration was 25 [20-36] minutes in high-flow group and 32 minutes [27-44] in the laryngeal mask group. Intraoperative respiratory support was successful in 89 patients (99%) in both groups (absolute difference 0, unilateral 95% confidence interval, 3%, noninferiority P < .001). Incidence of postoperative respiratory symptoms was significantly lower in high-flow versus laryngeal mask group (2% vs 19%, P < .001), while airway-related complications and postoperative dyspnea were not different. Intraoperative transcutaneous carbon dioxide was significantly higher in high-flow group, with 43% of patients showing values greater than 55 mm Hg. CONCLUSIONS: High-flow nasal oxygen is noninferior to laryngeal mask ventilation for intraoperative respiratory support during 30-minute general anesthesia without muscle paralysis. The risk of hypercarbia warrants careful patient selection and monitoring.
2. Evaluation of the Potential for Lung Recruitment with the Recruitment-to-Inflation Ratio during General Anesthesia.
In a prospective physiologic study of 20 patients, the recruitment-to-inflation ratio correlated strongly with recruitable volume by electrical impedance tomography (r=0.82). Patients with R/I>0.40 benefited from higher PEEP with reduced dead space, collapse, and dynamic strain, supporting R/I as a bedside metric to individualize PEEP.
Impact: Provides a practical, equipment-free ventilator-derived index to gauge recruitability under general anesthesia, advancing personalized ventilation strategies.
Clinical Implications: Anesthesiologists can consider using a single-breath PEEP-release maneuver to calculate R/I and tailor PEEP—particularly when R/I >0.4—to minimize collapse and overdistension.
Key Findings
- R/I correlated strongly with EIT-derived recruitable volume (r=0.82) and moderately with gas-dilution metrics.
- Patients with R/I >0.40 required higher optimal PEEP (median 10 vs 8 cmH2O; P=0.03).
- Higher PEEP in high R/I patients reduced dead space (−2% vs +3%), collapse (−44% vs −30%), and dynamic lung strain (−0.06 vs −0.04).
Methodological Strengths
- Comprehensive multimodal physiology (EIT, nitrogen dilution, gas exchange, mechanics).
- Standardized protocol with within-patient comparisons across PEEP steps.
Limitations
- Small single-center sample (n=20) limits external validity.
- Short-term physiologic endpoints without clinical outcomes; open abdominal surgery only.
Future Directions: Validate R/I-guided PEEP strategies in larger, diverse surgical cohorts with clinical outcomes (oxygenation failure, postoperative pulmonary complications).
BACKGROUND: During general anesthesia, the effect of positive end-expiratory pressure (PEEP) on lung injury depends on the potential for lung recruitment, which is variable among patients. The recruitment-to-inflation ratio (R/I) is measured from ventilator data during a single-breath PEEP-release maneuver and has been proposed to assess recruitability without the need for additional equipment during acute respiratory distress syndrome. This study hypothesized that R/I reliably estimates the individual potential for lung recruitment during general anesthesia. METHODS: Twenty patients undergoing open abdominal surgery received mechanical ventilation with PEEP of 12 cm H 2 O for 30 min, which was then abruptly reduced to 2 cm H 2 O. Finally, a decremental PEEP trial was performed to measure collapse and overdistension at each level. Gas exchange, end-tidal carbon dioxide, respiratory mechanics by ventilator waveform analysis, regional overdistension and collapse by electrical impedance tomography, end-expiratory lung volume, and functional residual capacity by nitrogen dilution were measured. The R/I was calculated during the single-breath derecruitment maneuver from ventilator data. RESULTS: The R/I (median = 0.41, range = 0 to 0.86) was linearly correlated with recruited volume normalized to functional residual capacity measured by gas dilution (r = 0.48, slope = 0.27 [0.03, 0.52]), and recruited volume scaled to PEEP-induced inflation volume measured by tomography (r = 0.82, slope = 1.2 [0.77, 1.64]). Compared to patients with R/I of less than or equal to 0.40 (n = 10), those with R/I greater than 0.40 (n = 10) required higher PEEP to optimize regional mechanics and balance collapse and overdistension (median [quartile 1, quartile 3]: 10 [8, 11] cm H 2 O vs . 8 [7, 9]; P = 0.03) and showed decreases in dead space (-2 [-5, 1] % vs . 3 [0, 5]%; P = 0.013) and greater reductions in collapse (-44 [-31, -47] % vs . -30 [-20, -38]%; P = 0.016) and dynamic lung strain (-0.06 [-0.09, -0.05] vs . -0.04 [-0.05, -0.02]; P = 0.04) with higher PEEP. CONCLUSIONS: During general anesthesia, the R/I reflects potential for lung recruitment. The R/I may help identify patients in whom higher PEEP improves physiology and may favor less injurious ventilation.
3. Timing of onset of persistent critical illness in Japan: a nationwide registry study.
Analyzing 285,567 ICU patients in Japan, the AUROC for acute illness consistently exceeded antecedent characteristics through day 28, indicating no identifiable onset of persistent critical illness. This contrasts with Western reports and implies system-level differences in ICU trajectories and end-of-life practices.
Impact: A very large, multicenter registry challenges a widely cited ICU paradigm, reframing how we conceptualize and measure transitions to persistent critical illness in different health systems.
Clinical Implications: Risk stratification tools and resource planning based on Western PerCI timing may not generalize to Japan; local validation is essential for palliative triggers, staffing, and rehabilitation pathways.
Key Findings
- In 285,567 ICU admissions, acute illness AUROC remained higher than antecedent characteristics through day 28.
- No crossover point indicating PerCI onset was observed; overall in-hospital mortality was 8.2%.
- Findings suggest health-system and cultural factors may influence ICU trajectories and PerCI definitions.
Methodological Strengths
- Nationwide, multicenter registry with very large sample size and predefined AUROC-based framework.
- Robust multivariable logistic models assessed daily from ICU day 1 to day 28.
Limitations
- Observational design cannot establish causality; unmeasured confounding may persist.
- Findings may be specific to Japan’s ICU practices; external validation is needed.
Future Directions: Cross-national comparative analyses using harmonized methods could clarify how end-of-life policies, rehabilitation timing, and ICU discharge practices shape PerCI onset.
BACKGROUND: Persistent critical illness (PerCI) occurs in patients whose ongoing ICU stay is no longer primarily driven by their presenting illness, but rather by new clinical instability. Studies in Western countries have found PerCI onset at 5-11 days, but timing in Japan or other Asian countries is unknown. METHODS: Using the Japanese Intensive Care Patient Database (JIPAD), PerCI onset was assessed by comparing the predictive ability of antecedent characteristics components (demographics, comorbidities) and acute illness components (physiological status at ICU admission) for in-hospital mortality, analyzed through multivariable logistic regression models among patients still in ICU from day 1 to day 28. The day when the Area Under the Receiver Operating Characteristic curve (AUROC) of antecedent characteristics exceeded that of acute illness was defined as the onset of PerCI. FINDINGS: We studied 285,567 patients from 101 ICUs in Japan between April 2015 and March 2023. Overall in-hospital mortality was 8.2%. The AUROCs of antecedent characteristics and acute illness components for in-hospital mortality was 0.752 and 0.920 on day 1, 0.669 and 0.779 on day 7, 0.668 and 0.743 on day 14 and 0.667 and 0.700 on day 28, respectively. Through day 28, the AUROC of acute illness component remained consistently higher than that of antecedent characteristics component, with no observed onset of PerCI. INTERPRETATION: Unlike findings from Western countries, PerCI onset was not observed in ICU in Japan. This suggests that variation in end-of-life decision making and the critical care delivery system may influence the onset of PerCI. FUNDING: None.