End-tidal Research Articles

Comparison of end tidal CO2 levels between automated head up and conventional cardiopulmonary resuscitation: A pre-post intervention trial

BackgroundThe combination of controlled automated head/thorax elevation, active compression-decompression (ACD) cardiopulmonary resuscitation (CPR), and an impedance threshold device (ITD-16), termed AHUP-CPR, lowers intracranial pressure and increases circulation and neurologically-sound survival in pigs versus conventional (C) CPR. This study examined whether AHUP-CPR increased end tidal (ET) CO2, a non-invasive marker of cardiac output and organ perfusion, compared with C-CPR in witnessed out-of-hospital cardiac arrest patients. MethodWe conducted a prospective, single-arm, pre-post intervention trial in France between October 2019 and October 2022.Firefighters treated patients enrolled during the pre-intervention period with manual C-CPR and with AHUP-CPR during the post-intervention period. Advanced life support was provided by a physician-staffed 2nd-tier response vehicle for the two study periods. The primary outcome was the peak ETCO2 value measured during CPR. Results122 patients with a mean age of 67 years (standard deviation [SD], 17) were enrolled (59 in the pre-intervention period and 63 in the post-intervention period). Based on an intention-to-treat analysis, mean baseline ETCO2 values were comparable between pre- (20.1 mmHg, SD,16.3) and post-(19.2 mmHg, SD, 16.3) intervention periods. Mean peak ETCO2 values during CPR were 30.3 mmHg (SD, 13.1) versus 40.7 mmHg (SD, 17.8) for the pre- and post-intervention study periods (mean difference, 10.6, 95% confidence interval, 4.6 to 16.1, P < 0.001). Mean differences in peak ETCO2 between study periods did not vary according to the first recorded cardiac rhythm (P for interaction = 0.99). The proportion of return of spontaneous circulation [19 (32.2%) vs. 21 (33.3%)], survival on hospital admission [17 (28.8%) vs. 19 (30.2%)], and 30-day survival with favorable neurological outcome [8 (13.6%) vs. 7 (11.1%)] did not differ between study periods. ConclusionETCO2 values during AHUP-CPR reached the range of non-arrest normal physiological levels and were significantly higher than with C-CPR, regardless of the presenting cardiac rhythm.

COPD sleep phenotypes: Genesis of respiratory failure in COPD.

The chronic obstructive pulmonary disease (COPD) patients could have respiratory failure during sleep without daytime overt arterial blood gas (ABG) abnormality. We undertook a study first of its kind to attempt in distinguishing the underlying pathophysiological mechanisms. It was a prospective observational study in stable COPD patients. The inclusion criterion was presence of day time PaO2>60 mmHg and PaCO2<45 mmHg. Twenty five out of 110 patients were excluded because of the ABG abnormality. The remaining 85 patients were subjected to overnight pulse oximetry and end-tidal (ET)-CO2 monitoring. The nocturnal oxygen desaturation was defined as per Fletcher's criteria. The nocturnal hypoventilation was defined as per American academy of sleep medicine (AASM) guidelines. Patients having saw-tooth pattern on pulse oximetry and/or snoring were subjected to polysomnography. 38/85(44.8%) patients had nocturnal gas exchange abnormality in absence of daytime respiratory failure and were identified into 3 different phenotypes: obstructive sleep apnoea (OSA), nocturnal hypoventilation and nocturnal oxygen desaturation. The isolated abnormality was seen in 24 patients: 10 patients had OSA, 9 had nocturnal hypoventilation and 5 had nocturnal oxygen desaturation. Overlap of two or more phenotypes was seen in 14 patients. As compared to the nocturnal hypoventilation and desaturation phenotypes, the OSA phenotype had a significantly higher BMI & FEV1. The nocturnal hypoventilation and the desaturation phenotypes did not have significant difference in FEV1 and BMI, but the daytime SpO2 and PaO2 differed significantly. Such parameters could help in identifying the three distinct COPD-sleep phenotypes (OSA, nocturnal hypoventilation and nocturnal oxygen desaturation). A phenotype based nocturnal management may help in delaying the process of overt respiratory failure in COPD.

Hypercapnic ventilatory response in epilepsy patients treated with VNS: A case-control study.

Central CO2 chemoreception (CCR), a major chemical drive for breathing, can be quantified with a CO2 re-breathing test to measure the hypercapnic ventilatory response (HCVR). An attenuated HCVR correlates with the severity of respiratory dysfunction after generalized convulsive seizures and is a potential biomarker for sudden unexpected death in epilepsy (SUDEP) risk. Vagus nerve stimulation (VNS) may reduce SUDEP risk, but for unclear reasons the risk remains higher during the first 2 years after implantation. The vagus nerve has widespread connections in the brainstem, including key areas related to CCR. Here we examined whether chronic electrical stimulation of the vagus nerve induces changes in CCR. We compared the HCVR in epilepsy patients with or without an active VNS in a sex- and age-matched case-control study. Eligible subjects were selected from a cohort of patients who previously underwent HCVR testing. The HCVR slope, change in minute ventilation (VE) with respect to change in end tidal (ET) CO2 (∆ VE/ ∆ ETCO2) during the test was calculated for each subject. Key variables were compared between the two groups. Univariate and multivariate analyses were carried out for HCVR slope as dependent variable. A total of 86subjects were in the study. HCVR slope was significantly lower in the cases compared to the controls. Cases had longer duration of epilepsy and higher number of anti-epileptic drugs (AEDs) tried during lifetime. Having active VNS and ETCO2 were associated with a low HCVR slope while high BMI was associated with high HCVR slope in both univariate and multivariate analyses. We found having an active VNS was associated with relatively attenuated HCVR slope. Although duration of epilepsy and number of AEDs tried during lifetime was significantly different between the groups, they were not predictors of HCVR slope in subsequent analysis. Chronic electrical stimulation of the vagus nerve by VNS may be associated with an attenuated CCR [Correction added on 24 November 2021, after first online publication: The preceding sentence has been revised from “Chronic electrical stimulation of VNS nerve by VNS…”]. A larger prospective study may help to establish the time course of this effect in relation to the time of VNS implantation, whether there is a causal relationship, and determine how it affects SUDEP risk.

Differential regional cerebral blood flow reactivity to alterations in end-tidal gases in healthy volunteers.

Anesthesia is associated with alterations in end-tidal (ET) respiratory gases from the awake state. These alterations result in marked vasoactive changes in regional cerebral blood flow (rCBF). Altered regional cerebrovascular reactivity (rCVR) is linked to neurologic dysfunction. We examined these differences in reactivity from prior work by focusing on the ratio of vasoconstriction with hyperoxia/hypocapnia (HO/hc):vasodilation with hypercapnia (HC) using magnetic resonance imaging pseudo-continuous arterial spin labelling (pCASL) to measure rCBF and compare rCVR The distribution and magnitude of these ratios could provide insights into rCBF during clinical anesthesia and inform future research into the origins of postoperative delirium (POD). Ten healthy subjects underwent cerebral blood flow (CBF) studies using pCASL with computer-controlled delivery of ET gases to assess flow effects of hyperoxia, hypercapnia, and hyperoxia/hypocapnia as part of a larger study into cerebrovascular reactivity. The vasoconstrictor stimulus was compared with the vasodilator stimulus by the ratio HO/hc:HC. Hyperoxia minimally decreased whole brain CBF by -0.6%/100 mm Hg increase in ETO2. Hypercapnia increased CBF by +4.6%/mm Hg carbon dioxide (CO2) and with HO/hc CBF decreased by -5.1%/mm Hg CO2. The brain exhibited markedly different rCVR-regional HO/hc:HC ratios varied from 7.2:1 (greater response to vasoconstriction) to 0.49:1 (greater response to vasodilation). Many of the ratios greater than 1, where vasoconstriction predominated, were seen in regions associated with memory, cognition, and executive function, including the entorhinal cortex, hippocampus, parahippocampus, and dorsolateral prefrontal cortex. In awake humans, marked rCBF changes occurred with alterations in ET respiratory gases common under anesthesia. Such heterogeneous reactivity may be relevant to future studies to identify those at risk of POD.

Transcutaneous CO2 Monitoring in Children Undergoing Tonsillectomy for Sleep Disordered Breathing.

Children undergoing tonsillectomy for sleep-disordered breathing are at risk for respiratory compromise when narcotics are administered. Severe complications resulting from hypoxia can include neuro-devastation and death. The objective of this prospective study was to evaluate the feasibility, accuracy, and utility of transcutaneous carbon dioxide (tcPCO2) monitoring during and after adenotonsillectomy. Prospective, Observational study. Twenty-nine children with sleep-disordered breathing scheduled for adenotonsillectomy were included in the study. Peri-operative measurements of tcPCO2 were compared against a single venous blood sample (PaCO2) and end-tidal (ET) CO2. The differences between ETCO2, tcPCO2 measures, and PaCO2 were examined using non-paired t-tests and linear regression. Parameters from PSG were recorded and associations with tcPCO2 values were performed using linear regression analysis. Group comparisons were made between pre-, intra-, and post-operative tcPCO2 measurements. Similar to ETCO2, there was good correlation of tcPCO2 to PaCO2. Children with lower oxygen (O2) saturation nadirs had higher peak CO2 levels during surgery and spent a greater proportion of time with CO2 > 50 mmHg in the recovery room (P < .01 and P < .08). Other PSG measures (apnea-hypopnea index, O2 desaturation index, and peak CO2) did not have any significant correlation. Frequent episodes of hypercapnia were noted intra- and post-operatively and mean tcPCO2 values during both periods were significantly higher than baseline (P < .001). tcPCO2 monitoring is viable in children undergoing adenotonsillectomy and can provide a good estimate of hypoventilation. tcPCO2 measurements may have particular benefit in the post-operative setting and may assist in identifying children at greater risk for respiratory complications. 4 Laryngoscope, 131:1410-1415, 2021.

Utility of polysomnography and video swallow studies in the management of pediatric patients with congenital idiopathic bilateral vocal fold dysfunction

ObjectivesCongenital idiopathic bilateral vocal fold dysfunction (BVFD) is an uncommon cause of neonatal stridor and respiratory distress postnatally. Approximately 50% of affected neonates or infants will historically require tracheostomy for this condition. Timing and candidacy for tracheostomy in BVFD patients is often subjective and poorly understood. Polysomnography (PSG) and video swallow studies (VSS) may be helpful in the management of patients with BVFD prior to tracheostomy by quantifying their degree of upper airway obstruction during sleep and feeding dysfunction while awake. MethodsWe performed a single-institution retrospective case series of BVFD patients from 2000 to 2018 who had postnatal PSGs performed prior to tracheostomy. Demographics, gestational age, and VSS results prior to PSG were recorded for all patients. Findings from PSGs included non-REM AHI, REM AHI, oxygen nadir, % total sleep time (TST) O2<90%, peak end-tidal (ET) CO2, % TST ETCO2 >52 torr. Rates of post-PSG tracheostomy, gastrostomy tube (G-tube) placement, and home O2 supplementation were noted for all patients. ResultsFrom 2000 to 2018, 12/46 (26%) BVFD patients had postnatal PSGs performed prior to tracheostomy. Median patient age at BVFD diagnosis, VSS, and PSG was 5.5 days, 12.5 days, and 17.5 days, respectively. Mild, moderate, and severe obstructive sleep apnea (OSA) was found in 7/12, 3/12, and 4/12 patients, respectively. Hypercapnia (ETCO2 >52 torr) was found in 5/12 patients on PSG while hypoxemia (SpO2 <90% for >4% TST) was not found in any patient. VSS results demonstrated normal swallowing, inconsistent laryngeal penetration, and silent aspiration in 7/12, 2/12, and 3/12 patients, respectively. Tracheostomy and G-tube placement was performed in 3/12 and 2/12 patients, respectively. There was no association between the severity of OSA or any PSG abnormality, VSS findings, and the performance of tracheostomy in any BVFD patient. ConclusionsOSA was found in all BVFD patients undergoing postnatal PSG at our institution while feeding dysfunction was found in approximately 50% of patients. The presence of feeding dysfunction, severe OSA, or any PSG abnormality was not individually associated with the subsequent performance of a tracheostomy in our patients. PSG is likely useful in supporting but not supplanting one's clinical decision-making in the management of patients with congenital idiopathic BVFD.

Brain BOLD MRI O2 and CO2 stress testing: implications for perioperative neurocognitive disorder following surgery

BackgroundMechanical ventilation to alter and improve respiratory gases is a fundamental feature of critical care and intraoperative anesthesia management. The range of inspired O2 and expired CO2 during patient management can significantly deviate from values in the healthy awake state. It has long been appreciated that hyperoxia can have deleterious effects on organs, especially the lung and retina. Recent work shows intraoperative end-tidal (ET) CO2 management influences the incidence of perioperative neurocognitive disorder (POND). The interaction of O2 and CO2 on cerebral blood flow (CBF) and oxygenation with alterations common in the critical care and operating room environments has not been well studied.MethodsWe examine the effects of controlled alterations in both ET O2 and CO2 on cerebral blood flow (CBF) in awake adults using blood oxygenation level-dependent (BOLD) and pseudo-continuous arterial spin labeling (pCASL) MRI. Twelve healthy adults had BOLD and CBF responses measured to alterations in ET CO2 and O2 in various combinations commonly observed during anesthesia.ResultsDynamic alterations in regional BOLD and CBF were seen in all subjects with expected and inverse brain voxel responses to both stimuli. These effects were incremental and rapid (within seconds). The most dramatic effects were seen with combined hyperoxia and hypocapnia. Inverse responses increased with age suggesting greater risk.ConclusionsHuman CBF responds dramatically to alterations in ET gas tensions commonly seen during anesthesia and in critical care. Such alterations may contribute to delirium following surgery and under certain circumstances in the critical care environment.Trial registrationClincialTrials.gov NCT02126215 for some components of the study. First registered April 29, 2014.

Supreme\u2122 laryngeal mask airway insertion requires a lower concentration of sevoflurane than ProSeal\u2122 laryngeal mask airway insertion during target-controlled remifentanil infusion: a prospective randomised controlled study

BackgroundProSeal (PLMA) and Supreme (SLMA) laryngeal mask airways are effective ventilator devices with distinctive designs that may require different anaesthetics for insertion. Sevoflurane induction provides acceptable conditions for laryngeal mask insertion, and remifentanil significantly decreases the minimum alveolar concentration of sevoflurane required for that insertion. The study aimed to evaluate the optimal end-tidal (ET) sevoflurane concentration for successful insertion of PLMA versus SLMA in patients receiving a remifentanil infusion without a neuromuscular blocking agent.MethodsAltogether, 45 patients ASA (American Society Anaesthesiologists) physical status I–II, aged 18–60 years were scheduled for elective ambulatory surgery. Exclusion criteria were a difficult airway, recent respiratory infection, reactive airway, obstructive sleep apnoea syndrome, gastric aspiration’s risk factors, pregnancy, and lactation. Patients were randomly allocated to receive the SLMA or the PLMA. Sevoflurane induction with co-administration of remifentanil was performed at an effect-site concentration of 4 ng mL− 1. ET50 was calculated with a modified Dixon’s up-and-down method (starting at 2.5% in steps of 0.5%). Predetermined sevoflurane concentration was kept constant during the 10 min before LMA insertion. Patient’s response to LMA insertion was classified as “movement” or “no movement”. Sevoflurane ET50 was determined as the midpoint concentration of all the independent pairs that manifested crossover from “movement” to “no movement”.ResultsThe ET50 sevoflurane concentration co-administered with remifentanil required for PLMA insertion was 1.20 ± 0.41% (95% confidence interval 0.76 to 1.63%). For SLMA insertion, it was 0.55 ± 0.38% (95% confidence interval 0.14 to 0.95%) (p = 0.019).ConclusionsThe end-tidal sevoflurane concentration with co-administered remifentanil required to allow insertion of the SLMA was 54% lower than that needed for inserting the PLMA.Trial registrationClinicaltrials.gov identifier: NCT03003377. Retrospectively registered. Date of registration: December 28, 2016.

Ventilatory response to CO2 in patients with epilepsy.

Severe periictal respiratory depression is thought to be linked to risk of sudden unexpected death in epilepsy (SUDEP) but its determinants are largely unknown. Interindividual differences in the interictal ventilatory response to CO2 (hypercapnic ventilatory response [HCVR] or central respiratory CO2 chemosensitivity) may identify patients who are at increased risk for severe periictal hypoventilation. HCVR has not been studied previously in patients with epilepsy; therefore we evaluated a method to measure it at bedside in an epilepsy monitoring unit (EMU) and examined its relationship to postictal hypercapnia following generalized convulsive seizures (GCSs). Interictal HCVR was measured by a respiratory gas analyzer using a modified rebreathing technique. Minute ventilation (VE ), tidal volume, respiratory rate, end tidal (ET) CO2 and O2 were recorded continuously. Dyspnea during the test was assessed using a validated scale. The HCVR slope (ΔVE /ΔETCO2 ) for each subject was determined by linear regression. During the video-electroencephalography (EEG) study, subjects underwent continuous respiratory monitoring, including measurement of chest and abdominal movement, oronasal airflow, transcutaneous (tc) CO2 , and capillary oxygen saturation (SPO2 ). Sixty-eight subjects completed HCVR testing in 151 ± (standard deviation) 58 seconds, without any serious adverse events. HCVR slope ranged from -0.94 to 5.39 (median 1.71) L/min/mm Hg. HCVR slope correlated with the degree of unpleasantness and intensity of dyspnea and was inversely related to baseline ETCO2 . Both the duration and magnitude of postictal tcCO2 rise following GCSs were inversely correlated with HCVR slope. Measurement of the HCVR is well tolerated and can be performed rapidly and safely at the bedside in the EMU. A subset of individuals has a very low sensitivity to CO2 , and this group is more likely to have a prolonged increase in postictal CO2 after GCS. Low interictal HCVR may increase the risk of severe respiratory depression and SUDEP after GCS and warrants further study.

Poor performance of main-stream capnography in newborn infants during general anesthesia.

Endtidal (ET) measurement of carbon dioxide is well established for intraoperative respiratory monitoring of adults and children, but the method's accuracy for intraoperative use in small newborn infants has been less extensively investigated. The aim of this study was to compare carbon dioxide from ET measurements with arterialized capillary blood samples in newborn infants during general anesthesia and surgery. Endtidal carbon dioxide was continuously measured during anesthesia and surgery and compared with simultaneous blood gas analyses obtained from capillary blood samples. Fifty-nine sample sets of ET to blood gas carbon dioxide were obtained from 23 prospectively enrolled infants with a gestational age of 23-41 weeks and a birth weight of 670-4110 g. Endtidal levels of carbon dioxide were considerably lower in all sample sets and only 4/23 individual ET-blood gas sample pairs differed <7.5 mm Hg (1 kPa). Bland-Altman analysis indicated a poor agreement with a bias of -13 ± 7 mm Hg and a precision of ±14 mm Hg. The performance of ET measurements was particularly poor in infants weighing below 2.5 kg, in infants in need of respiratory support prior to anesthesia, and when the true (blood gas) carbon dioxide level was high, above 45 mm Hg. Main-stream capnography during anesthesia and surgery correlated poorly to blood gas values in small and/or respiratory compromised infants. We conclude that caution should be exercised when relying solely on ET measurements to guide mechanical ventilation in the OR.

Comparison of trapezius squeeze test and jaw thrust as clinical indicators for laryngeal mask airway insertion in spontaneously breathing children.

Background and Aims:It is not known whether trapezius squeeze test (TPZ) is a better clinical test than jaw thrust (JT) to assess laryngeal mask airway (LMA) insertion conditions in children under sevoflurane anesthesia.Material and Methods:After the Institutional Ethics Committee approval and written informed parental consent, 124 American Society of Anesthesiologists I and II children of 2–8 years of age undergoing minor surgical procedures were randomized into TPZ and JT groups. The children were induced with 8% sevoflurane in oxygen at a fresh gas flow of 4 L/min. TPZ or JT was performed after 1 min of start of sevoflurane and then every 20 s till the test was negative, when end-tidal (ET) sevoflurane concentration was noted. Classic LMA of requisite size was inserted by a blinded anesthetist and conditions at the insertion of LMA, insertion time, and the number of attempts of LMA insertion were recorded.Results:The mean LMA insertion time was significantly longer (P < 0.001) for TPZ (145 ± 28.7 sec) compared to JT group (111.8 ± 31.0 sec). ET sevoflurane concentration at the time of LMA insertion was comparable in the two groups. LMA insertion conditions were similar in the two groups. There was no difference between the two groups regarding total number of attempts of LMA insertion. Heart rate (HR) decreased in both groups after LMA insertion (P < 0.001) but TPZ group had significantly lower HR compared with the JT group up to 5 min after LMA insertion (P = 0.03).Conclusion:Both JT and TPZ are equivalent clinical indicators in predicting the optimal conditions of LMA insertion in spontaneously breathing children; however, it takes a longer time to achieve a negative TPZ squeeze test.

Clinical Use of a Multivariate Electroencephalogram (Narcotrend) for Assessment of Anesthetic Depth in Horses during Isoflurane-Xylazine Anesthesia.

To investigate the use of the Narcotrend electroencephalogram (EEG) monitor for the assessment of anesthetic depth in horses undergoing xylazine balanced isoflurane anesthesia. Blinded experimental study. Seven healthy warm-blooded horses, aged 10.6 ± 5.9 years, weighing 535 ± 55 kg. Horses were anesthetized for a terminal surgical trial with xylazine, thiopentone, and guaiphenesin for induction and isoflurane and xylazine continuous rate infusion for maintenance. After surgery, an EEG was recorded and processed by the Narcotrend monitor. It displays an index [Narcotrend index (NI)] between 0 and 100, which is supposed to indicate anesthetic depth. This index was recorded and correlated with eight different end tidal (ET) isoflurane concentrations between 0.8 and 2.2 vol%. In addition, anesthetic depth was numerically scored based on common clinical signs with a score of 1 (plane "too deep") to 4 (plane "too light"). After testing for normal distribution, both clinical scores and NI were correlated with different ET isoflurane concentrations using Spearman rank correlation. Correlation of NI with ET isoflurane concentrations was poor (r s = 0.24). The NI ranged between maximal 48 and minimal 13 in the horses. The clinical scores decreased with increasing ET isoflurane concentrations (r s = 0.80). They ranged from 1 to 4 in different horses at the concentrations investigated. In this study, the NI did not seem to be useful for assessment of anesthetic depth in horses receiving isoflurane anesthesia balanced with a xylazine constant rate infusion.

Cost efficiency of target-controlled inhalational anesthesia.

Background:Cost and environmental pollution are two prime concerns with general anesthesia. We hypothesized that target-controlled (TC) anesthesia drug delivery system also called as end-tidal (ET) control is an effective and safe system that would reduce the cost and also environmental pollution.Materials and Methods:We studied 200 patients undergoing laparoscopic abdominal and pelvic surgeries and randomly distributed those in 2 groups of 100 each, TC and manual-controlled (MC) group. We reviewed the two groups in term of consumption of gases, time required to achieve the ET concentration of sevoflurane of 1.5%, maximum inspired concentration of sevoflurane achieved, and number of adjustments required to maintain the depth of anesthesia.Results:We found that the consumption of nitrous oxide and sevoflurane was significantly less in TC group than MC group (P < 0.05), oxygen consumption was also less in TC group but not statistically significant. The time required to achieve the desired levels, maximum inspired sevoflurane concentration achieved, and the number of drug delivery adjustments required were statistically significant in TC group (P < 0.05). As the consumption reduced in TC group, the cost of the inhalational anesthesia reduced by approximately Rs. 64/h ($1.12) and thus the environmental pollution.Conclusion:We concluded from our study that ET control is a good system for conserving the consumption of gases and thus is efficient as it reduces both the cost and the environmental pollution.

Nasal cannula end-tidal CO2 correlates with serum lactate levels and odds of operative intervention in penetrating trauma patients

Penetrating trauma patients in shock often require urgent operative intervention. Studies have demonstrated that variables obtained in the emergency department, such as lactate levels, can help the physician determine the presence of hemorrhagic shock, leading to more rapid intervention and improve prognosis in trauma patients. The purpose of the study is to determine if end-tidal (ET) CO2 correlates with serum lactate levels, a measure of tissue hypoxia and subsequently shock, in penetrating trauma patients. Secondarily, we sought to determine whether ET CO2 could be used to determine the patient's odds of requiring operative intervention. A prospective observational cohort study was undertaken at an urban Level 1 trauma center. Baseline ET CO2 from nasal cannula and serum lactate level were recorded in all patients in whom the trauma team was activated. Outcomes defined were whether operative intervention was needed. Pearson correlation (R), correlation coefficient (r(2)), and odds ratio were calculated. One hundred five patients were enrolled. Pearson correlations and coefficients calculated for serum lactate level to ET CO2 were R = -0.86 (r(2) = 0.74, p < 0.0001). Of patients requiring operative intervention, 81.97% had abnormally low ET CO2 and 54.1% had abnormally high serum lactate levels. Odds ratios of patients needing an emergent operation with abnormally low ET CO2 was 20.4 (95% confidence interval, 7.47-55.96) and with abnormally high serum lactate levels was 4 (95% confidence interval, 1.68-5.93). ET CO2 has a strong inverse correlation to serum lactate levels. Abnormally low ET CO2 values were associated with greater increased odds compared with serum lactate levels of penetrating trauma patients requiring operative intervention. Prognostic/diagnostic study, level I.

Intrathoracic pressure regulation during cardiopulmonary resuscitation: A feasibility case-series

Aim of the studyIntrathoracic pressure regulation (IPR) is a novel, noninvasive therapy intended to increase cardiac output and blood pressure in hypotensive states by generating a negative end expiratory pressure of −12cm H2O between positive pressure ventilations. In this first feasibility case-series, we tested the hypothesis that IPR improves End tidal (ET) CO2 during cardiopulmonary resuscitation (CPR). ETCO2 was used as a surrogate measure for circulation. MethodsAll patients were treated initially with manual CPR and an impedance threshold device (ITD). When IPR-trained medics arrived on scene the ITD was removed and an IPR device (CirQLATOR™) was attached to the patient's advanced airway (intervention group). The IPR device lowered airway pressures to −9mmHg after each positive pressure ventilation for the duration of the expiratory phase. ETCO2, was measured using a capnometer incorporated into the defibrillator system (LifePak™). Values are expressed as mean±SEM. Results were compared using paired and unpaired Student's t test. p values of <0.05 were considered statistically significant. ResultsETCO2 values in 11 patients in the case series were compared pre and during IPR therapy and also compared to 74 patients in the control group not treated with the new IPR device. ETCO2 values increased from an average of 21±1mmHg immediately before IPR application to an average value of 32±5mmHg and to a maximum value of 45±5mmHg during IPR treatment (p<0.001). In the control group ETCO2 values did not change significantly. Return of spontaneous circulation (ROSC) rates were 46% (34/74) with standard CPR and ITD versus 73% (8/11) with standard CPR and the IPR device (p<0.001). ConclusionsETCO2 levels and ROSC rates were significantly higher in the study intervention group. These findings demonstrate that during CPR circulation may be significantly augmented by generation of a negative end expiratory pressure between each breath.

Remifentanil or dexmedetomidine for monitored anesthesia care during cataract surgery under topical anesthesia

Cataract surgery is usually performed under topical anesthesia. The procedure is quick and simple to perform and topical anesthesia avoids the potential hazards of a nerve block. However, topical anesthesia may not provide complete anesthesia and may cause anxiety or uncontrolled and unexpected movement. Monitored anesthesia care (MAC) is intended to provide anxiety relief, patient comfort, and safety during eye surgery. Propofol, benzodiazepines, and opioids have been used for sedation during cataract surgery [1]. However each of these drugs causes respiratory depression, hypoxemia, and apnea. The adverse respiratory complications of these drugs may impede the patient’s cooperation during surgery and increase the need for a sedative drug that can be used safely during MAC. Dexmedetomidine is a central α2 agonist that can be titrated to the desired sedation level without significant respiratory depression and has been used as a primary sedative drug for various surgical and diagnostic procedures [2]. Unlike other opioids, remifentanil, which is a μ-opioid receptor agonist, has a short elimination half life of 3-10 min and a short context sensitive half life of 3-5 min. These properties of remifentanil suggest that it may be useful for MAC either combined with propofol or alone [3]. The aim of this study was to compare dexmedetomidine with remifentanil during cataract surgery in patients under topical anesthesia. The protocol was approved by the Institutional Review Board of our hospital, and all patients provided written informed consent. Eighty American Society of Anesthesiology physical status class 1-3 patients (age, 60-80 years), who were scheduled for elective cataract surgery under topical anesthesia, were enrolled in this study. Patients were randomized to receive either dexmedetomidine (group D) or remifentanil (group R). Group D patients received an infusion of 0.5 μg/kg dexmedetomidine over 10 minutes followed by a main tenance infusion at a rate of 0.2 μg/kg/hr. Group R patients received remifentanil by target controlled infusion to reach a 1 ng/ml target effect site concentration (Cet). Heart rate (HR), systolic blood pressure, diastolic blood pressure, mean arterial pressure (MAP), respiratory rate (RR), oxygen saturation (SpO2), bispectral index monitor (BIS) and end tidal (ET)CO2 were recorded before infusion (baseline), after the start of infusion, and every 5 minutes after infusion. The degree of sedation was evaluated using the Ramsay sedation scale by an anesthesiologist who was unaware of the type of sedative used. The satisfaction of the patients and surgeon was assessed immediately after surgery using a 7-point Likert-like verbal rating scale. Recovery time was the interval from stopping the infusion to the time when the patient’s Ramsay sedation score was 2. Demographic variables were compared using the t-test. Physiological data were analyzed by repeated-measures analysis of variance. The chi-square test was used to compare the sedation and satisfaction scores. No differences in baseline characteristics were observed between the groups. Significantly lower MAP, ETCO2, and higher RR were observed over time in group D compared with those in group R. No significant differences in HR or SpO 2 were observed between the groups. BIS scores decreased at 10, 15, and 20 minutes after infusion, but no significant differences in BIS scores were observed between the groups. More patients

Abstract 39: Intrathoracic Pressure Regulation During and After Cardiopulmonary Resuscitation: A Feasibility Study

Objective: Reduction of intrathoracic pressures to -10 cm H2O during the decompression phase of cardiopulmonary resuscitation (CPR) increases cardiac preload, lowers intracranial pressures, and increases circulation and survival rates in pigs undergoing standard CPR. In this proof of concept study, we tested the hypothesis that augmentation of negative intrathoracic pressure during standard (S) CPR with intrathoracic pressure regulation (IPR) providing continuous negative intrathoracic pressure of -10 cm H2O between positive pressure ventilations will improve circulation, using end tidal (ET) CO2 as a non-invasive surrogate of organ perfusion, in patients receiving S-CPR. Methods: In this first clinical evaluation of IPR (CirQLatorTM, Advanced Circulatory Systems Inc, Roseville, MN) paramedic supervisors in Toledo OH performed CPR, applied IPR in 12 adult patients, and measured ETCO2, blood pressure and O2 saturation upon return of spontaneous circulation (ROSC) rates. IPR was continued after ROSC to help maintain perfusion. Values are expressed as mean ± SEM and statistical significance was determined by a paired Student's t-test. ETCO2 and blood pressure are expressed in mmHg. Results: IPR was used together with S-CPR to treat cardiac arrest in 12 patients: mean age 64 ± 3; 4 were male and the initial recorded rhythms were ventricular fibrillation (n=2), pulseless electrical activity (n=3), and asystole (n=7). Time from the initial 911 call to IPR application was 16±1 min. Initial ETCO2 when IPR was applied was 21± 3. Maximum ETCO2 during CPR was 44 ± 4, (p &lt; 0.001 compared with initial ETCO2). There was ROSC in 9/12 patients: 3 patients with asystole did not have ROSC. Time from IPR application to ROSC was 16 ± 3 minutes. Systolic/diastolic blood pressures immediately after ROSC were 126 ±13/72 ± 8. O2 saturation at ROSC was 96 ± 1%. IPR was used in 8/9 patients post ROSC for 8 ± 3 min. There were no observed adverse events. Conclusion: Clinical application of IPR during CPR increased ETCO2 values and resulted in ROSC in 9/12 patients, providing first clinical proof-of-concept that this new non-invasive technology increases circulation during CPR. Based upon these positive data, further study of IPR in patients in cardiac arrest is warranted.

Treatment of Positive Airway Pressure Treatment-Associated Respiratory Instability with Enhanced Expiratory Rebreathing Space (EERS)

Hypocapnia is an important mediator of sleep-dependent respiratory instability. Positive pressure-associated ventilatory control instability results in poor control of sleep apnea and persistent sleep fragmentation. We tested the adjunctive efficacy of low volumes of dead space (enhanced expiratory rebreathing space [EERS]) using a non-vented mask to minimize sleep hypocapnia. Retrospective chart review. American Academy of Sleep Medicine accredited sleep center and laboratory. Enhanced expiratory rebreathing space 204 patients diagnosed with continuous positive pressure (CPAP)-refractory sleep apnea between 1/1/04 and 7/1/06 were included in this retrospective review. All patients had in-lab attended polysomnography for diagnosis, conventional CPAP titration, and further assessments of added EERS. EERS volume was titrated to control of disease, which was typically obtained when end-tidal (ET) CO₂ during sleep was 1-2 mm Hg above wake eupneic CO₂ levels. The clinic records were reviewed for clinical outcomes. Poor laboratory response to, and initial clinical abandonment of CPAP, was very common (89.2%) in this group of patients, who as a group demonstrated mild resting wake hypocapnia (ETCO₂ = 38.1 ± 3.1 mm Hg). Minimizing sleep hypocapnia by adding 100-150 mL EERS (mean ETCO₂) at optimal therapy 38.6 ± 2.9 mm Hg) markedly improved polysomnographic control of sleep apnea, without inducing tachypnea or tachycardia. Follow-up (range 30-1872 days) showed improved clinical tolerance, compliance, and sustained clinical improvement. Leak and sleep fragmentation modified clinical outcomes. EERS is a potentially useful adjunctive therapy for positive pressure-associated respiratory instability and salvage of some CPAP treatment failures.

An Evaluation of Remifentanil-Sevoflurane Response Surface Models in Patients Emerging from Anesthesia

We previously reported models that characterized the synergistic interaction between remifentanil and sevoflurane in blunting responses to verbal and painful stimuli. This preliminary study evaluated the ability of these models to predict a return of responsiveness during emergence from anesthesia and a response to tibial pressure when patients required analgesics in the recovery room. We hypothesized that model predictions would be consistent with observed responses. We also hypothesized that under non-steady-state conditions, accounting for the lag time between sevoflurane effect-site concentration (Ce) and end-tidal (ET) concentration would improve predictions. Twenty patients received a sevoflurane, remifentanil, and fentanyl anesthetic. Two model predictions of responsiveness were recorded at emergence: an ET-based and a Ce-based prediction. Similarly, 2 predictions of a response to noxious stimuli were recorded when patients first required analgesics in the recovery room. Model predictions were compared with observations with graphical and temporal analyses. While patients were anesthetized, model predictions indicated a high likelihood that patients would be unresponsive (> or = 99%). However, after termination of the anesthetic, models exhibited a wide range of predictions at emergence (1%-97%). Although wide, the Ce-based predictions of responsiveness were better distributed over a percentage ranking of observations than the ET-based predictions. For the ET-based model, 45% of the patients awoke within 2 min of the 50% model predicted probability of unresponsiveness and 65% awoke within 4 min. For the Ce-based model, 45% of the patients awoke within 1 min of the 50% model predicted probability of unresponsiveness and 85% awoke within 3.2 min. Predictions of a response to a painful stimulus in the recovery room were similar for the Ce- and ET-based models. Results confirmed, in part, our study hypothesis; accounting for the lag time between Ce and ET sevoflurane concentrations improved model predictions of responsiveness but had no effect on predicting a response to a noxious stimulus in the recovery room. These models may be useful in predicting events of clinical interest but large-scale evaluations with numerous patients are needed to better characterize model performance.

Precision of Cerebrovascular Reactivity Assessment with Use of Different Quantification Methods for Hypercapnia Functional MR Imaging

Tools for noninvasive mapping of hemodynamic function including cerebrovascular reactivity are emerging and may become clinically useful to predict tissue at hemodynamic risk. One such technique assesses blood oxygen level-dependent (BOLD) MR imaging contrast in response to hypercapnia, but the reliability of its quantification is uncertain. The aim of this study was to prospectively investigate the intersubject and interhemispheric variability and short-term reproducibility of hypercapnia functional MR imaging (fMRI) in healthy volunteers and to assess the effects of different methods of quantification and normalization. Sixteen healthy volunteers, (7 women and 9 men) underwent hypercapnia fMRI with a clinical 1.5T scanner; 8 underwent scanning twice. We determined BOLD amplitude changes using a visually defined block design or automated regression to end-tidal (ET) carbon dioxide (CO2). Absolute percent signal intensity changes (PSC) were extracted for whole-brain, gray matter, and middle cerebral artery territory, and also normalized to ETCO2 change. Intersubject and intrasubject (between hemispheres and sessions) coefficients of variation (COV) were derived. We assessed the effects of different quantification methods on reproducibility indices using the t test and U tests. The mean change in ETCO2 was 7.8 +/- 3.3 mm Hg. Averaged BOLD increases varied from 2.54% to 2.92%. Short-term reproducibility was good for absolute PSC (4.8% to 10%) but poor for normalized PSC (range, 24% to 27% COV). Intersubject reproducibility varied between 11% and 23% for absolute PSC and, again, was poorer for normalized data (32% to 39%). Interhemispheric reproducibility of absolute PSC was excellent ranging between 1.24 and 2.16% COV. In conclusion, quantification of cerebrovascular reactivity with use of hypercapnia fMRI was found to have good between-session and very good interhemispheric reproducibility. The technique holds promise as a diagnostic tool, especially for sensitive detection of unilateral disease.