Analgesic duration of interscalene block after outpatient arthroscopic shoulder surgery with intravenous dexamethasone, intravenous dexmedetomidine, or their combination: a randomized-controlled trial.

PURPOSE: Both intravenous dexamethasone and dexmedetomidine prolong the analgesic duration of interscalene blocks (ISB) after arthroscopic shoulder surgery. This study compared their relative effectiveness and the benefit of their use in combination. METHODS: This single-centre, double-blinded, parallel three-group superiority trial randomized 198 adult patients undergoing ambulatory arthroscopic shoulder surgery. Patients received preoperative ISB with 30 mL 0.5% bupivacaine and 50 µg dexmedetomidine or 4 mg dexamethasone or both of these agents as intravenous adjuncts. The primary outcome was analgesic block duration. Secondary outcomes included the quality of recovery 15 score (range: 0-150) on day 1 and postoperative neurologic symptoms in the surgical arm. RESULTS: Block durations (n = 195) with dexamethasone (median [range], 24.5 [2.0-339.5] hr) and both adjuncts (24.0 [1.5-157.0] hr) were prolonged compared with dexmedetomidine (16.0 [1.5-154.0] hr). When analyzed by linear regression after an unplanned log transformation because of right-skewed data, the corresponding prolongations of block duration were 59% (95% confidence interval [CI], 28 to 97) and 46% (95% CI, 18 to 80), respectively (both P < 0.001). The combined adjuncts were not superior to dexamethasone alone (-8%; 95% CI, -26 to 14; P = 0.42). Median [IQR] quality of recovery 15 scores (n = 197) were significantly different only between dexamethasone (126 [79-149]) and dexmedetomidine (118.5 [41-150], P = 0.004), but by an amount less than the 8-point minimum clinically important difference. CONCLUSION: Dexamethasone is superior to dexmedetomidine as an intravenous adjunct for prolongation of bupivacaine-based ISB analgesic duration. There was no additional benefit to using both adjuncts in combination. TRIAL REGISTRATION: www.clinicaltrials.gov (NCT03270033); registered 1 September 2017.

RéSUMé: OBJECTIF: La dexaméthasone et la dexmédétomidine intraveineuses prolongent toutes deux la durée analgésique des blocs interscaléniques (BIS) après une chirurgie arthroscopique de l'épaule. Cette étude a comparé leur efficacité relative et les avantages d'une utilisation des deux agents en combinaison. MéTHODE: Cette étude de supériorité monocentrique en trois groupes parallèles à double insu a randomisé 198 patients adultes subissant une chirurgie arthroscopique de l'épaule en ambulatoire. Les patients ont reçu un BIS préopératoire composé de 30 mL de bupivacaïne 0,5 % avec 50 µg de dexmédétomidine, 4 mg de dexaméthasone, ou la combinaison de ces deux agents comme adjuvants intraveineux. Le critère d'évaluation principal était la durée analgésique du bloc. Les critères d'évaluation secondaires comprenaient le score de qualité de récupération (QoR) 15 (plage : 0-150) au jour 1 et les symptômes neurologiques postopératoires dans le bras opéré. RéSULTATS: Les durées des blocs (n = 195) avec la dexaméthasone (médiane [plage], 24,5 [2,0-339,5] heures) et la combinaison des deux adjuvants (24,0 [1,5-157,0] heures) ont été prolongées par rapport à la dexmédétomidine (16,0 [1,5-154,0] heures). Lorsqu'elles ont été analysées par régression linéaire après une transformation logarithmique non planifiée en raison de données biaisées vers la droite, les prolongations correspondantes de la durée du bloc étaient de 59 % (intervalle de confiance [IC] 95 %, 28 à 97) et de 46 % (IC 95 %, 18 à 80), respectivement (les deux P < 0,001). La combinaison des adjuvants n'était pas supérieure à la dexaméthasone seule (-8 %; IC 95 %, -26 à 14; P = 0,42). Les scores médians [ÉIQ] de qualité de récupération 15 (n = 197) n'étaient significativement différents qu'entre la dexaméthasone (126 [79-149]) et la dexmédétomidine (118,5 [41-150], P = 0,004), mais la différence observée était inférieure à la différence minimale de 8 points nécessaire pour être considérée cliniquement importante. CONCLUSION: La dexaméthasone est supérieure à la dexmédétomidine en tant qu'adjuvant intraveineux pour prolonger la durée analgésique d'un BIS à base de bupivacaïne. Aucun avantage supplémentaire n'a été observé lors de l'utilisation combinée des deux adjuvants. ENREGISTREMENT DE L'éTUDE: www.clinicaltrials.gov (NCT03270033); enregistrée le 1er septembre 2017.

Effect of dexamethasone dose and route on the duration of interscalene brachial plexus block for outpatient arthroscopic shoulder surgery: a randomized controlled trial.

PURPOSE: Dexamethasone prolongs the duration of interscalene block, but the benefits of higher doses and perineural vs intravenous administration remain unclear. METHODS: This factorial design, double-blinded trial randomized 280 adult patients undergoing ambulatory arthroscopic shoulder surgery at a single centre in a 1:1:1:1 ratio. Patients received ultrasound-guided interscalene block with 30 mL 0.5% bupivacaine and 4 mg or 8 mg dexamethasone by either the perineural or intravenous route. The primary outcome (block duration measured as the time of first pain at the surgical site) and secondary outcomes (adverse effects, postoperative neurologic symptoms) were assessed by telephone. In this superiority trial, the predetermined minimum clinically important difference for comparisons between doses and routes was 3.0 hr. RESULTS: The perineural route significantly prolonged the mean block duration by 2.0 hr (95% confidence interval [CI], 0.4 to 3.5 hr; P = 0.01), but 8 mg of dexamethasone did not significantly prolong the mean block duration compared with 4 mg (1.3 hr; 95% CI, -0.3 to 2.9 hr, P = 0.10), and there was no significant statistical interaction (P = 0.51). The mean (95% CI) block durations, in hours, were 24.0 (22.9 to 25.1), 24.8 (23.2 to 26.3), 25.4 (23.8 to 27.0), and 27.2 (25.2 to 29.3) for intravenous doses of 4 and 8 mg and perineural doses of 4 and 8 mg, respectively. There were no marked differences in side effects between groups. At 14 postoperative days, 57 (20.4%) patients reported neurologic symptoms, including dyspnea and hoarseness. At six months postoperatively, only six (2.1%) patients had residual symptoms, with four (1.4%) patients' symptoms unlikely related to interscalene block. CONCLUSION: Compared with the intravenous route, perineural dexamethasone prolongs the mean interscalene block duration by a small amount that may or may not be clinically significant, regardless of dose. However, the difference in mean block durations between 8 mg and 4 mg of dexamethasone is highly unlikely to be clinically important, regardless of the administration route. TRIAL REGISTRATION: www.clinicaltrials.gov (NCT02426736). Registered 14 April 2015.

Perioperative implications of thoracic decortications: a retrospective cohort study.

PURPOSE: An increasing number of thoracic decortications have been performed in Manitoba, from five in 2007 to 45 in 2014. The primary objective of this study was to define the epidemiology of decortications in Manitoba. The secondary objective was to compare patients who underwent decortication due to primary infectious vs non-infectious etiology with respect to their perioperative outcomes. METHODS: Data for this cohort study were extracted from consecutive charts of all adult patients who underwent a decortication in Manitoba from 2007-2014 inclusive. RESULTS: One hundred ninety-two patients underwent a decortication. The most frequent disease processes resulting in a decortication were pneumonia (60%), trauma (13%), malignancy (8%), and procedural complications (5%). The number of decortications due to complications of pneumonia rose at the greatest rate, from three cases in 2007 to 29 cases in 2014. Performing a decortication for an infectious vs a non-infectious etiology was associated with a higher rate of the composite postoperative outcome of myocardial infarction, acute kidney injury, need of vasopressors for > 12 hr, and mechanical ventilation for > 48 hr (44.4% vs 24.2%, respectively; relative risk, 1.83; 95% confidence interval, 1.1 to 2.9; P = 0.01). CONCLUSION: There has been a ninefold increase in decortications over an eight-year period. Potential causes include an increase in the incidence of pneumonia, increased organism virulence, host changes, and changes in practice patterns. Patients undergoing decortication for infectious causes had an increased risk for adverse perioperative outcomes. Anesthesiologists need to be aware of the high perioperative morbidity of these patients and the potential need for postoperative admission to an intensive care unit.

Benefits of an individualized perioperative plan for children with autism spectrum disorder.

BACKGROUND: Perioperative care for children with autism spectrum disorder may be challenging. Previous investigators recommend development of an individualized perioperative management plan with caregiver involvement. AIM: The primary goal was to determine the usefulness of an individualized plan based on the decision to provide preoperative sedation stratified by autism spectrum severity level. Secondary goals were to assess the effectiveness of the plan based on subjective assessment of patient behavior at induction of anesthesia and caregiver satisfaction. METHODS: We developed an individualized plan for each child with autism spectrum disorder scheduled for anesthesia. Children were categorized by autism spectrum disorder severity level. With institutional ethics approval, we conducted a retrospective chart review to document need for preoperative sedation, sedation stratified by autism spectrum disorder severity level, behavior at induction, and caregiver satisfaction. RESULTS: Between 2012 and 2014, we successfully prepared a plan for 246 (98%) of 251 surgical or diagnostic procedures in 224 patients. Severity level was distributed as 45% Severity Level 1 and Asperger's, 25% Severity Level 2, and 30% Severity Level 3. The majority (90%) of cases were scheduled as day surgery. Preoperative sedation increased with increasing severity level: Severity Level 1 (21%) or Asperger's (31%), Severity Level 2 (44%), and Severity Level 3 (56%). The odds ratio for sedation use was 5.5 [CI: 2.6-11.5, P<.001] with Severity Level 3 vs Severity Level 1 patients. Cooperation at induction of anesthesia was 90% overall with preoperative sedation administered to 94 (38%) of the entire cohort. Cooperation was greatest in Severity Level 1 (98%) and Asperger's patients (93%) and somewhat less (85%) in patients in Severity Levels 2 and 3. The plan was helpful to guide sedation choices as cooperation did not differ between sedated and unsedated children at any severity level (overall χ2 =2.87 P=.09). Satisfaction among caregivers contacted was 98%. CONCLUSION: The results suggest that an individualized plan is helpful in the perioperative management of children with autism spectrum disorder and that knowledge of autism spectrum disorder severity level may be helpful in determining the need for preoperative sedation.

Pulse pressure variability during hemorrhage and reinfusion in piglets: effects of age and tidal volume.

PURPOSE: The dynamic change in arterial pulse pressure during mechanical ventilation (PPV) predicts fluid responsiveness in adults but may not be applicable to pediatric patients. We compared PPV during hemorrhage and reinfusion in immature vs mature piglets at two clinically relevant tidal volumes (VT). METHODS: Following Institutional Animal Care Committee approval, we measured hemodynamics and PPV in two groups of piglets, 10-15 kg (immature, n = 9) and 25-30 kg (mature, n = 10), under stable intravenous anesthesia at VT = 8 and 10 mL·kg(-1). Measurements were taken at baseline, with blood withdrawal in 5 mL·kg(-1) steps up to 30 mL·kg(-1), and during stepwise reinfusion. For each age group and VT, we constructed receiver operating characteristic (ROC) curves to determine the threshold value that was predictive of fluid responsiveness. RESULTS: Pulse pressure variability was significantly lower in immature vs mature pigs and at VT 8 vs VT 10 at every measurement period. The difference in PPV induced by changing VT was less in immature animals. Significant areas under the ROC curve were obtained in immature pigs at both VTs but in mature animals at VT 10 alone. A PPV threshold was calculated to be 8.2% at VT 8 and 10.9% at VT 10 in immature animals vs 15.9% at VT 10 in mature animals, but sensitivity and specificity were only 0.7. CONCLUSION: Pulse pressure variability values are lower and less sensitive to VT in immature vs mature pigs. Adult PPV thresholds do not apply to pediatric patients, and a single PPV value representing fluid responsiveness should not be assumed.

Cerebral oxygen desaturation during one-lung ventilation: correlation with hemodynamic variables.

PURPOSE: Cerebral desaturation occurs frequently in patients undergoing one-lung ventilation for thoracic surgery. The mechanism of this desaturation is unclear regarding its etiology. The objective of this study was to investigate whether or not decreases in cerebral oxygen saturation associated with one-lung ventilation were a consequence of decreased cardiac output. METHODS: A blinded observational study was conducted in 23 patients undergoing one-lung ventilation with thoracic surgery. Eighteen patients completed the study. Cerebral oxygen saturation was monitored using near-infrared spectroscopy (FORE-SIGHT(®) monitor). Invasive blood pressure was monitored and hemodynamic variables were interrogated using the FloTrac(®) system. Anesthesia was maintained with sevoflurane with a F(i)O(2) of 1.0. Post-hoc analysis involved a comparison between baseline and integrated changes in cerebral saturation, heart rate, stroke index, cardiac index, and stroke volume variability. RESULTS: All patients showed cerebral desaturation from a baseline of two-lung ventilation in the lateral decubitus position following institution of one-lung ventilation. The cardiac index was stable at these times, but with one-lung ventilation, the heart rate decreased and the stroke index increased to maintain a stable product. The integral of heart rate × time was inversely correlated with the integral of cerebral desaturation × time (linear regression analysis; P = 0.02; (df) = 16)). CONCLUSIONS: Cerebral oxygen desaturation was universal during one-lung ventilation in this study. There was no correlation between cerebral desaturation and cardiac output or other hemodynamic variables.

Benchmarking a Canadian Anesthesiology Resident Research Program against national norms using a logic model framework: a quality improvement study.

Background: Canadian specialty training programs are expected to deliver curriculum content and assess competencies related to the CanMEDS Scholar role. We evaluated our residency research program and benchmarked it against national norms for quality improvement purposes. Methods: In 2021 we reviewed departmental curriculum documents and surveyed current and recently graduated residents. We applied a logic model framework to assess if our program's inputs, activities, and outputs addressed the relevant CanMeds Scholar competencies. We then descriptively benchmarked our results against a 2021 environmental scan of Canadian anesthesiology resident research programs. Results: Local program content was successfully mapped to competencies. The local survey response rate was 40/55 (73%). In benchmarking, our program excelled in providing milestone-related assessments, research funding, administrative, supervisory, and methodologic support, and requiring a literature review, proposal presentation, and local abstract submission as output. Acceptable activities to meet research requirements vary greatly among programs. Balancing competing clinical and research responsibilities was a frequently reported challenge. Conclusions: The logic model framework was easily applied and demonstrated our program benchmarked well against national norms. National level dialogue is needed to develop specific, consistent scholar role activities and competency assessments to bridge the gap between expected outcome standards and education practice.

Contexte: Les programmes de spécialité canadiens doivent proposer un contenu de formation en lien avec le rôle CanMEDS d'érudit et évaluer les compétences qui s'y attachent. Nous avons évalué notre programme de résidence en recherche par rapport aux normes nationales en la matière à des fins d'amélioration de la qualité. Méthodes: En 2021, nous avons examiné les documents du programme d'études du département et interrogé des résidents et des médecins récemment diplômés. Nous avons utilisé un modèle logique pour déterminer si les intrants, les activités et les extrants de notre programme couvraient adéquatement les compétences pertinentes liées au rôle CanMeds d'érudit. Nous avons ensuite comparé de façon descriptive nos résultats à une analyse du milieu des programmes de résidence canadiens en recherche en anesthésiologie effectuée la même année. Résultats: Nous avons établi une correspondance entre le contenu du programme local et les compétences. Le taux de réponse à l'enquête était de 40/55 (73 %). D'après l'analyse comparative, notre programme se démarque par l'offre d'évaluations d'étape, de fonds de recherche, de soutien administratif, de supervision, d'orientation méthodologique, et, en ce qui concerne les extrants, par l'exigence d'une analyse documentaire, de la présentation d'une proposition et de la soumission d'un résumé à l'université. Les activités admissibles pour répondre aux exigences de la recherche varient considérablement d'un programme à l'autre. De nombreux répondants ont signalé la difficulté de concilier les responsabilités cliniques et de recherche. Conclusions: L'application du modèle logique a été aisée et elle a permis de montrer que notre programme respecte les normes nationales. Un dialogue au niveau national est nécessaire pour définir de manière précise et cohérente les activités et les évaluations des compétences en lien avec le rôle d'érudit afin de combler le fossé entre les normes quant aux résultats attendus et les pratiques des programmes.

Quantitative computed tomography in porcine lung injury with variable versus conventional ventilation: recruitment and surfactant replacement.

OBJECTIVES: Biologically variable ventilation improves lung function in acute respiratory distress models. If enhanced recruitment is responsible for these results, then biologically variable ventilation might promote distribution of exogenous surfactant to nonaerated areas. Our objectives were to confirm model predictions of enhanced recruitment with biologically variable ventilation using computed tomography and to determine whether surfactant replacement with biologically variable ventilation provides additional benefit in a porcine oleic acid injury model. DESIGN: Prospective, randomized, controlled experimental animal investigation. SETTING: University research laboratory. SUBJECTS: Domestic pigs. INTERVENTIONS: Standardized oleic acid lung injury in pigs randomized to conventional mechanical ventilation or biologically variable ventilation with or without green dye labeled surfactant replacement. MEASUREMENTS AND MAIN RESULTS: Computed tomography-derived total and regional masses and volumes were determined at injury and after 4 hrs of ventilation at the same average low tidal volume and minute ventilation. Hemodynamics, gas exchange, and lung mechanics were determined hourly. Surfactant distribution was determined in postmortem cut lung sections. Biologically variable ventilation alone resulted in 7% recruitment of nonaerated regions (p < .03) and 15% recruitment of nonaerated and poorly aerated regions combined (p < .04). Total and normally aerated regional volumes increased significantly with biologically variable ventilation, biologically variable ventilation with surfactant replacement, and conventional mechanical ventilation with surfactant replacement, while poorly and nonaerated regions decreased after 4 hrs of ventilation with biologically variable ventilation alone (p < .01). Biologically variable ventilation showed the greatest improvement (p < .003, biologically variable ventilation vs. all other groups). Hyperaerated regional gas volume increased significantly with biologically variable ventilation, biologically variable ventilation with surfactant replacement, and conventional mechanical ventilation with surfactant replacement. Biologically variable ventilation was associated with restoration of respiratory compliance to preinjury levels and significantly greater improvements in gas exchange at lower peak airway pressures compared to all other groups. Paradoxically, gas exchange and lung mechanics were impaired to a greater extent initially with biologically variable ventilation with surfactant replacement. Peak airway pressure was greater in surfactant-treated animals with either ventilation mode. Surfactant was distributed to the more caudal/injured lung sections with biologically variable ventilation. CONCLUSIONS: Quantitative computed tomography analysis confirms lung recruitment with biologically variable ventilation in a porcine oleic acid injury model. Surfactant replacement with biologically variable ventilation provided no additional recruitment benefit and may in fact be harmful.

Resolution of pulmonary edema with variable mechanical ventilation in a porcine model of acute lung injury.

OBJECTIVE: Resolution of the acute respiratory distress syndrome (ARDS) requires clearance of pulmonary edema. Biologically variable ventilation (BVV) strategies that improve gas exchange, lung mechanics, and inflammatory mediators in ARDS may be beneficial in this regard. We used quantitative computed tomography (CT), a single indicator thermodilution system (PiCCO®) to determine extravascular lung water (EVLW), and the change in edema protein concentration over time to compare edema clearance with BVV vs conventional mechanical ventilation (CMV) in a porcine ARDS model. METHODS: Sixteen pigs with oleic acid lung injury were randomized to four hours of ventilation with either CMV (n = 8) or BVV (n = 8) at identical low tidal volume and minute ventilation over time. Hemodynamic variables, gas exchange, lung mechanics, and PiCCO derived EVLW were determined hourly. Computed tomography images and edema fluid samples were obtained at baseline lung injury and after four hours of ventilation. Wet and dry lung weights were determined postmortem. RESULTS: At four hours with BVV, peak airway pressure was decreased significantly and lung compliance improved compared with CMV (P = 0.003; P < 0.001, respectively). Hemodynamic variables and gas exchange were not different between groups. Also at four hours, computed tomography revealed an increase in total gas volume (P = 0.001) and a decrease in total lung weight and global lung density (P = 0.005; P = 0.04 respectively) with BVV. These findings were associated with a significant increase in the gas volume of normally aerated lung regions (P < 0.001) and a decrease in the poorly and non-aerated lung regions (P = 0.001). No change in any CT parameter occurred with CMV. The lung weights derived from computed tomography correlated well with postmortem wet weights (R(2) = 0.79; P < 0.01). The decrease in PiCCO derived EVLW from injury to four hours did not differ significantly between BVV and CMV. Extravascular lung water showed no correlation with postmortem wet weights and significantly underestimated lung water. Average alveolar fluid clearance rates were positive (1.4%·hr(-1) (3%)) with BVV and negative with CMV (-2.0%·hr(-1) (4%)). CONCLUSIONS: In a comparison between BVV and CMV, computed tomography evidence suggests that BVV facilitates enhanced clearance and/or redistribution of edema fluid with improved recruitment of atelectatic and poorly aerated lung regions; no such evidence was seen with either single thermodilution measurement of EVLW or edema clearance rates. The results of computed tomography provide further evidence of the benefit of BVV over conventional ventilation in ARDS.

Lactate flux during carotid endarterectomy under general anesthesia: correlation with various point-of-care monitors.

PURPOSE: The ability to assess the brain-at-risk during carotid endarterectomy (CEA) under general anesthesia remains a major clinical problem. Point-of-care monitoring can potentially dictate changes to management intraoperatively. In this observational study, we examined the correlation between a series of point-of-care monitors and lactate flux during CEA. METHODS: Both neurosurgeons and vascular surgeons participated in the study. The patients underwent arterial-jugular venous blood sampling for oxygen, carbon dioxide, glucose, and lactate, n = 26; bispectral index (BIS) monitoring ipsilateral to side of surgery, n = 26; raw and processed electroencephalogram (EEG), n = 22; and bi-frontal cerebral oximetry using the Fore-Sight monitor, n = 20. RESULTS: One patient experienced a new neurological deficit when assessed at 24 hr following surgery. Lactate flux into the brain was correlated with the greatest decrease in cerebral oximetry with carotid cross-clamping; lactate efflux was correlated with the least. The most noticeable changes in processed EEG (density spectral analysis) were also seen with lactate influx, but at a slower time resolution than cerebral oximetry. Loss of autoregulatory behaviour was demonstrated with lactate influx; however, no correlation was seen between lactate flux and BIS monitoring. CONCLUSION: There was a correlation between cerebral oximetry and lactate flux during carotid cross-clamping. The Fore-Sight monitor may be of value as a point-of-care monitor during CEA under general anesthesia. A novel finding of this study is lactate flux into the brain in the presence of a large difference in cerebral oxygenation during cross-clamping of the carotid artery. Registered at clinicaltrials.gov: NCT000737334.

Effect of Daytime Versus Night-time on Outcome in Patients Undergoing Emergent Neurosurgical Procedures.

BACKGROUND: Timing of neurosurgical procedures is controversial. Challenges identified with night-time surgeries include physician fatigue and sleep deprivation, and fewer staff and resources compared with daytime surgery. These might contribute to medical errors and complications, and, hence, worse patient outcomes. METHODS: This single center retrospective study of 304 patients who underwent emergent neurosurgical procedures between January 1, 2010 and December 31, 2016 included 2 groups based on the timing of surgery: daytime (7:00 AM to 6:59 PM) and night-time (7:00 PM to 6:59 AM) surgery groups. Patient demographics, diagnosis, surgical characteristics, complications, and neurological outcome were obtained from the medical records. RESULTS: There was no difference in patient demographics, intraoperative complications, and length of surgery between the 2 groups. Although there was no statistically significant difference in neurological outcome between the 2 groups at hospital discharge and 1 month postdischarge, there was a higher proportion of patients in the night-time surgical group with unfavorable neurological outcome (Glasgow Outcome Score 1 to 3) at both these times. There were differences in hospital length of stay, location of postoperative management (postanesthesia care unit or intensive care unit), midline shift, baseline Glasgow Coma Scale score, and acuity of surgery between the 2 groups. Logistic regression analysis showed that age, baseline Glasgow Coma Scale score, surgery acuity status, procedure type, and intraoperative complications influenced neurological outcome. CONCLUSIONS: This study found no difference in the rate of unfavorable neurological outcome in patients undergoing emergent neurosurgical procedures during the daytime and night-time. However, our findings cannot exclude the possibility of an association between timing of surgery and outcome given its limitations, including small sample size and omission of potentially confounding variables. Further well-designed prospective trials are warranted to confirm our findings.

Does eliminating the preoperative history and physical make a difference in low-risk cataract surgery patients? A before and after study of 30-day morbidity and mortality.

OBJECTIVE: To evaluate the safety of omitting the conventional preoperative history and physical examination (H&P) for low-risk cataract surgery patients. DESIGN: Comparison of outcomes before and after the January 1, 2015 system wide implementation of a program that eliminated the conventional preoperative H&P for low-risk patients as identified by a 12-item risk stratification questionnaire. PARTICIPANTS: Two separate groups of Winnipeg residents who had cataract surgery at the city's sole ophthalmological referral centre between July 1 and December 31, 2014 (preimplementation reference group) or between October 1, 2015 and March 31, 2016 (postimplementation intervention group). METHODS: A detailed chart review was completed for cataract surgery patients who experienced a postoperative medical event (a composite of death or hospital admission or emergency department visit, identified within administrative databases) within 30 days of surgery. Nonfatal events were captured for all 7 hospitals and urgent care centres in the city, including the ophthalmological referral centre. RESULTS: Postoperative medical events occurred in 114 of 2981 (3.82%) intervention group surgeries and 125 of 3037 (4.12%) reference group surgeries (Relative risk 0.92, 95% confidence interval 0.72 to 1.19, p = 0.6 Fisher exact test). Subgroup analyses of major medical events and medical events by affected organ system yielded no significant differences between the 2 groups. In the opinion of the physician chart reviewers, none of the events among low-risk patients in the intervention group were related to the omission of a conventional preoperative H&P. CONCLUSIONS: The risk of adverse medical events within 30 days of cataract surgery was not higher after the omission of the conventional preoperative H&P in patients screened to be low risk by a validated preoperative questionnaire.

End-Tidal Hypocapnia Under Anesthesia Predicts Postoperative Delirium.

Background: Postoperative delirium (POD) might be associated with anesthetic management, but research has focused on choice or dosage of anesthetic drugs. We examined potential contributions of intraoperative ventilatory and hemodynamic management to POD. Methods: This was a sub-study of the ENGAGES-Canada trial (NCT02692300) involving non-cardiac surgery patients enrolled in Winnipeg, Canada. Patients received preoperative psychiatric and cognitive assessments, and intraoperatively underwent high-fidelity data collection of blood pressure, end-tidal respiratory gases and anesthetic agent concentration. POD was assessed by peak and mean POD scores using the Confusion Assessment Method-Severity (CAM-S) tool. Bivariate and multiple linear regression models were constructed controlling for age, psychiatric illness, and cognitive dysfunction in the examination of deviations in intraoperative end-tidal carbon dioxide (areas over (AOC) and under the curve (AUC)) on POD severity scores. Results: A total of 101 subjects [69 (6) years of age] were studied; 89 had comprehensive intraoperative hemodynamic and end-tidal gas measurements (data recorded at 1 Hz). The incidence of POD was 11.9% (12/101). Age, cognitive dysfunction, anxiety, depression, and intraoperative end-tidal CO2 (AUC) were significant correlates of POD severity. In the multiple regression model, cognitive dysfunction and AUC end-tidal CO2 (0.67 kPa below median intra-operative value) were the only independent significant predictors across both POD severity (mean and peak) scores. There was no association between cumulative anesthetic agent exposure and POD. Conclusions: POD was associated with intraoperative ventilatory management, reflected by low end-tidal CO2 concentrations, but not with cumulative anesthetic drug exposure. These findings suggest that maintenance of intraoperative normocapnia might benefit patients at risk of POD.

Fractal ventilation enhances respiratory sinus arrhythmia.

BACKGROUND: Programming a mechanical ventilator with a biologically variable or fractal breathing pattern (an example of 1/f noise) improves gas exchange and respiratory mechanics. Here we show that fractal ventilation increases respiratory sinus arrhythmia (RSA) -- a mechanism known to improve ventilation/perfusion matching. METHODS: Pigs were anaesthetised with propofol/ketamine, paralysed with doxacurium, and ventilated in either control mode (CV) or in fractal mode (FV) at baseline and then following infusion of oleic acid to result in lung injury. RESULTS: Mean RSA and mean positive RSA were nearly double with FV, both at baseline and following oleic acid. At baseline, mean RSA = 18.6 msec with CV and 36.8 msec with FV (n = 10; p = 0.043); post oleic acid, mean RSA = 11.1 msec with CV and 21.8 msec with FV (n = 9, p = 0.028); at baseline, mean positive RSA = 20.8 msec with CV and 38.1 msec with FV (p = 0.047); post oleic acid, mean positive RSA = 13.2 msec with CV and 24.4 msec with FV (p = 0.026). Heart rate variability was also greater with FV. At baseline the coefficient of variation for heart rate was 2.2% during CV and 4.0% during FV. Following oleic acid the variation was 2.1 vs. 5.6% respectively. CONCLUSION: These findings suggest FV enhances physiological entrainment between respiratory, brain stem and cardiac nonlinear oscillators, further supporting the concept that RSA itself reflects cardiorespiratory interaction. In addition, these results provide another mechanism whereby FV may be superior to conventional CV.

Mathematical modelling to centre low tidal volumes following acute lung injury: a study with biologically variable ventilation.

BACKGROUND: With biologically variable ventilation [BVV--using a computer-controller to add breath-to-breath variability to respiratory frequency (f) and tidal volume (VT)] gas exchange and respiratory mechanics were compared using the ARDSNet low VT algorithm (Control) versus an approach using mathematical modelling to individually optimise VT at the point of maximal compliance change on the convex portion of the inspiratory pressure-volume (P-V) curve (Experimental). METHODS: Pigs (n = 22) received pentothal/midazolam anaesthesia, oleic acid lung injury, then inspiratory P-V curve fitting to the four-parameter logistic Venegas equation F(P) = a + b[1 + e-(P-c)/d]-1 where: a = volume at lower asymptote, b = the vital capacity or the total change in volume between the lower and upper asymptotes, c = pressure at the inflection point and d = index related to linear compliance. Both groups received BVV with gas exchange and respiratory mechanics measured hourly for 5 hrs. Postmortem bronchoalveolar fluid was analysed for interleukin-8 (IL-8). RESULTS: All P-V curves fit the Venegas equation (R2 > 0.995). Control VT averaged 7.4 +/- 0.4 mL/kg as compared to Experimental 9.5 +/- 1.6 mL/kg (range 6.6 - 10.8 mL/kg; p < 0.05). Variable VTs were within the convex portion of the P-V curve. In such circumstances, Jensen's inequality states "if F(P) is a convex function defined on an interval (r, s), and if P is a random variable taking values in (r, s), then the average or expected value (E) of F(P); E(F(P)) > F(E(P))." In both groups the inequality applied, since F(P) defines volume in the Venegas equation and (P) pressure and the range of VTs varied within the convex interval for individual P-V curves. Over 5 hrs, there were no significant differences between groups in minute ventilation, airway pressure, blood gases, haemodynamics, respiratory compliance or IL-8 concentrations. CONCLUSION: No difference between groups is a consequence of BVV occurring on the convex interval for individualised Venegas P-V curves in all experiments irrespective of group. Jensen's inequality provides theoretical proof of why a variable ventilatory approach is advantageous under these circumstances. When using BVV, with VT centred by Venegas P-V curve analysis at the point of maximal compliance change, some leeway in low VT settings beyond ARDSNet protocols may be possible in acute lung injury. This study also shows that in this model, the standard ARDSNet algorithm assures ventilation occurs on the convex portion of the P-V curve.

A comparison of biologically variable ventilation to recruitment manoeuvres in a porcine model of acute lung injury.

BACKGROUND: Biologically variable ventilation (return of physiological variability in rate and tidal volume using a computer-controller) was compared to control mode ventilation with and without a recruitment manoeuvre - 40 cm H2O for 40 sec performed hourly; in a porcine oleic acid acute lung injury model. METHODS: We compared gas exchange, respiratory mechanics, and measured bronchoalveolar fluid for inflammatory cytokines, cell counts and surfactant function. Lung injury was scored by light microscopy. Pigs received mechanical ventilation (FIO2 = 0.3; PEEP 5 cm H2O) in control mode until PaO2 decreased to 60 mm Hg with oleic acid infusion (PaO2/FIO2 <200 mm Hg). Additional PEEP to 10 cm H2O was added after injury. Animals were randomized to one of the 3 modes of ventilation and followed for 5 hr after injury. RESULTS: PaO2 and respiratory system compliance was significantly greater with biologically variable ventilation compared to the other 2 groups. Mean and mean peak airway pressures were also lower. There were no differences in cell counts in bronchoalveolar fluid by flow cytometry, or interleukin-8 and -10 levels between groups. Lung injury scoring revealed no difference between groups in the regions examined. No differences in surfactant function were seen between groups by capillary surfactometry. CONCLUSIONS: In this porcine model of acute lung injury, various indices to measure injury or inflammation did not differ between the 3 approaches to ventilation. However, when using a low tidal volume strategy with moderate levels of PEEP, sustained improvements in arterial oxygen tension and respiratory system compliance were only seen with BVV when compared to CMV or CMV with a recruitment manoeuvre.

Obstetrical and neonatal outcomes in obese parturients.

OBJECTIVE: Obstetrical risk is increased with maternal obesity. This prospective study was designed to simultaneously evaluate the outcomes in obese parturients and their newborns. METHODS: Patients with a body mass index (BMI) > or =35 were prospectively identified and compared to an equal number of normal weight parturients. Maternal and neonatal outcome measures were compared for the peripartum and neonatal period. RESULTS: We identified 580 obese parturients over a 6 month period and compared them to an equal number of normal weight parturients. The incidence of obesity in this population was 23%. Obesity was associated with increased rates of hypertension, diabetes, and cesarean section. Obese patients were more likely to develop postpartum complications. Neonatal outcomes were compared for infants > or =37 weeks gestation excluding multiple births (496 neonates in the obese group and 520 in the control group). The neonates of obese parturients were more likely to be macrosomic, have 1-minute Apgar scores of < or =7.0 and require admission to a special care unit. Sub-group analysis showed that negative outcomes for parturients and their neonates correlated with increasing BMI. Neonates born to obese diabetic parturients had the highest risk of poor outcomes. CONCLUSIONS: Maternal obesity confers increased risks for both the parturient and their newborn.