Recent advances in respiratory monitory in nonoperating room anesthesia.

PURPOSE OF REVIEW: Sedation for nonoperating room procedures is experiencing a considerable increase in demand. Respiratory compromise is one of the most common adverse events seen in sedation. Capnography is a modality that has been widely adopted in this area, but may not be well suited to the special demands of nonoperating room sedation. This review is an assessment of new technologies that may improve outcomes beyond those achievable with capnography. RECENT FINDINGS: New devices for detecting the onset of apnea and for assessing respiratory depression have emerged which have advantages over conventional capnography for detecting apnea without excessive false positive and false negative rates. In addition, monitors that assess respiratory drive have become available, and these may prove useful in regulating depth of sedation. SUMMARY: No single monitor is ideal for all settings. During brief endoscopic sedation, detection of apnea is paramount, while during longer procedures, avoiding excessive respiratory depression is more critical. The clinician must choose the appropriate monitor based on an understanding of the challenges of the particular environment.

Understanding Infusion Pumps.

Infusion systems are complicated electromechanical systems that are used to deliver anesthetic drugs with moderate precision. Four types of systems are described-gravity feed, in-line piston, peristaltic, and syringe. These systems are subject to a number of failure modes-occlusion, disconnection, siphoning, infiltration, and air bubbles. The relative advantages of the various systems and some of the monitoring capabilities are discussed. A brief example of the use of an infusion system during anesthetic induction is presented. With understanding of the functioning of these systems, users may develop greater comfort.

Drug-induced sleep endoscopy: from obscure technique to diagnostic tool for assessment of obstructive sleep apnea for surgical interventions.

PURPOSE OF REVIEW: Provide a practical update on drug-induced sleep endoscopy (DISE) for anesthesia providers, which can also serve as a reference for those preparing to establish a DISE program. RECENT FINDINGS: New developments in surgical approaches to OSA and the growing global incidence of the condition have stimulated increased interest and demand for drug-induced sleep endoscopy. New techniques include transoral robotic surgery and hypoglossal nerve stimulation. Recent DISE literature has sought to address numerous debates including relevance of DISE findings to those during physiologic sleep and the most appropriate depth and type of sedation for DISE. Propofol and dexmedetomidine have supplanted midazolam as the drugs of choice for DISE. Techniques based on pharmacokinetic models of propofol are superior to empiric dosing with regard to risk of respiratory compromise and the reliability of dexmedetomidine to achieve adequate conditions for a complete DISE exam is questionable. SUMMARY: The role of DISE in surgical evaluation and planning for treatment of OSA continues to develop. Numerous questions as to the optimal anesthetic approach remain unanswered. Multicenter studies that employ a standardized approach using EEG assessment, pharmacokinetic-pharmacodynamic modelling, and objectively defined clinical endpoints will be helpful. There may be benefit to undertaking DISE studies in non-OSA patients.

Anesthesia in the Electrophysiology Laboratory.

The electrophysiology suite is a foreign location to many anesthesiologists. The initial experience was with shorter procedures under conscious sedation, and the value of greater tailoring of the sedation/anesthesia by anesthesiologists was not perceived until practice patterns had already been established. Although better control of ventilation with general anesthesia may be expected, suppression of arrhythmias, blunting of the hemodynamic adaptation to induced arrhythmias, and interference by muscle relaxants with identification of the phrenic nerve may be seen. We review a range of electrophysiology procedures and discuss anesthetic approaches that balance patient safety and favorable outcomes.

Hilbert-Huang Transform Yields Improved Minute Volume Estimates from Respiratory Inductance Plethysmography During Transitions to Paradoxical Breathing.

BACKGROUND: Anesthesia and sedation are associated with paradoxical breathing. Respiratory inductance plethysmography (RIP) permits measurement of respiratory motion in clinical settings not conducive to spirometry, but correlation of RIP volume changes and spirometer flow in the time domain is degraded by the development of paradoxical breathing. The Hilbert-Huang transform (HHT) is a nonlinear signal analysis method that permits the instantaneous magnitude and phase of nonstationary signals to be estimated in the frequency domain. We hypothesized that these frequency domain estimates would provide higher correlation between RIP and spirometer signals than time domain signals during the transition between normal and paradoxical breathing. METHODS: From 51 patients undergoing sevoflurane anesthesia for minor procedures, a 5-minute epoch containing transitions between pressure support ventilation and spontaneous ventilation was selected for analysis. Pearson correlation for models based on HHT magnitude and phase was compared with models based on time domain signals. Bland-Altman analysis was performed to assess deviation from linearity in the models. RESULTS: For the 51 patients analyzed, the modulation of tidal volume over the epoch ranged from 30% to 215% of epoch mean. The coefficient of determination for time domain analysis was 0.62 ± 0.2 compared with 0.93 ± 0.07 for the HHT model incorporating phase. This improvement of 0.31 (99% confidence interval, 0.24-0.37) was significant (P < 0.0001). No trend was observed in prediction residuals. CONCLUSIONS: Under conditions of changing ventilation, HHT-derived magnitude and phase measures provide higher correlation with spirometry than those obtained with traditional time domain methods.

Provocation of atrial fibrillation triggers during ablation: does the use of general anesthesia affect inducibility?

INTRODUCTION: The autonomic nervous system exerts important effects upon atrial fibrillation (AF) initiation. The strategy of anesthesia used during AF ablation may impact the provocation of AF triggers. We hypothesized that the use of general anesthesia (GA) would reduce the incidence of provokable AF triggers in patients undergoing AF ablation compared to patients studied while receiving only conscious sedation (CS). METHODS AND RESULTS: We performed a prospective, case control study comparing the incidence of provokable AF triggers in a consecutive series of patients undergoing AF ablation under GA using a standard trigger induction protocol. We compared the frequency and distribution of AF triggers to a second cohort of historical controls (matched for age, gender, left atrial dimension, and AF phenotype) who underwent ablation while receiving CS. We calculated that 44 total subjects (22 patients in each group) were required to detect a 50% reduction in the incidence of AF triggers in the GA cohort. There was no difference between the 2 groups in the rate of AF trigger inducibility (77% vs. 68%, P = 0.26) or the number of triggers provoked per patient (1.2 ± 0.8 vs. 1.3 ± 0.8, P = 0.38). Patients ablated under GA required higher doses of phenylephrine during the trigger induction protocol (408.3 mg [52-600] vs. 158.3 mg [0-75]; P = 0.003), and tended to require higher doses of isoproterenol to initiate triggers (92.8 mg [20-111] vs. 63.6 mg [6-103]; P = 0.25). CONCLUSION: AF trigger induction during GA is both safe and efficacious.

Performance of Masimo rainbow acoustic monitoring for tracking changing respiratory rates under laryngeal mask airway general anesthesia for surgical procedures in the operating room: a prospective observational study.

BACKGROUND: Accurate monitoring of respiratory rate may be useful for the early detection of patient deterioration. Monitoring of respiratory rate in the operating room under general anesthesia by spirometry is technically straightforward and demonstrates high fidelity. Accurate measurement of the respiratory rate of an unattended patient outside the operating room is fraught with challenges. Monitors such as capnometry and thoracic impedance pneumography have significant drawbacks. Respiratory acoustic monitoring (RRa™) is a new technology for respiratory rate monitoring, which has been demonstrated to provide accurate respiratory rates in patients recovering from anesthesia, but the performance of this RRa-enabled monitor under conditions of major respiratory rate variation has not been evaluated. METHODS: We enrolled 53 patients undergoing urologic procedures in the operating room under general anesthesia with a laryngeal mask airway, spontaneous ventilation, and no muscle relaxation in an observational study. Respiratory signals (RRa and in-circuit pneumotachograph) were stored for later analysis. Artifacts were excluded based on visual inspection of the raw respiratory waveforms. Instantaneous respiratory rates were obtained from the pneumotachograph signal using the Hilbert-Huang Transform. Instantaneous rate estimates (IREs) were compared with RRa by 3 methods. First, the mean delay between IREs and RRa was determined. Second, precision was obtained by Bland-Altman analysis for repeated measures. Third, for all disparities in rates exceeding 4 breaths per minute (bpm), the probability of persistent error was determined as a function of time, with 95% confidence intervals estimated by bootstrap analysis. RESULTS: Data were collected from 53 patients. Three patients were excluded due to missing data. There were no adverse events related to RRa monitoring. RRa demonstrated a median delay of 45 seconds (interquartile range 20 seconds) to detect a 1- bpm change in IREs. Bland-Altman revealed 95% limits of agreement of -2.1 to 2.2 bpm across the range of 7 to 48 bpm. Disparities in respiratory rate >4 bpm between the 2 methods did not persist beyond 160 seconds, and 90% of these differences resolved within 33 seconds (95% confidence interval 23-48 seconds). CONCLUSIONS: The data demonstrate that, under conditions of general anesthesia with a laryngeal mask airway and spontaneous ventilation, the RRa rapidly detects changes in respiratory rate, demonstrates minimal bias, and when errors in rate occur, these do not persist. The utility of this monitoring technology in detecting rate changes in unattended patients will require further study.

Safety and efficacy of drug-induced sleep endoscopy using a probability ramp propofol infusion system in patients with severe obstructive sleep apnea.

BACKGROUND: Drug-induced sleep endoscopy (DISE) uses sedative-hypnotics to induce moderate obstruction in sleep apnea patients, thereby facilitating anatomic assessment of obstructive physiology. Implementation of DISE with propofol requires a dosing strategy that reliably and efficiently produces obstruction while minimizing oxygen desaturation. METHODS: The surgeon in a prospective study of transoral robotic resection of the tongue base enrolled 97 patients with obstructive sleep apnea confirmed by polysomnography who failed continuous positive airway pressure. All patients were screened by DISE. Propofol dose was determined using custom software written in MATLAB, which has been previously described. Studies were performed in an operating room with standard monitors and resuscitation equipment. No topical anesthesia was used, and no IV drugs other than propofol were used. All patients received 2 L/min supplemental oxygen via a nasal cannula placed in the mouth. After initiation of propofol sedation, a pediatric bronchoscope was positioned via the naris to observe the velopharynx. The sedation sequence was continued until the clinical end point of obstruction onset was noted. Observation of the pharynx was performed for a sufficient period to obtain images of the anatomic site(s) of obstruction. The infusion was then terminated. Statistical analysis was performed with MATLAB (MathWorks, version 2012b). Comparison of saturation nadirs between DISE and subject sleep studies was performed with both the paired and unpaired Student t test. RESULTS: The subject population was characterized by a median body mass index of 32.1 (interquartile range [IQR] 6.8) kg/m and apnea-hypopnea index of 48 (IQR 32). All patients demonstrated obstruction within the design variables. Obstruction was observed after 236 (±57.9) seconds at an estimated effect-site concentration of 4.2 ± 1.3 mcg/mL. The median saturation nadir during DISE was significantly higher (91.4% (IQR 5.1)) than that during standard sleep studies (81.0% [IQR 11.2], P < 0.0001). Ninety-five percent confidence intervals for correlations between DISE saturation nadir and body mass index, age, apnea-hypopnea index, or administered propofol dose included zero in all cases. CONCLUSIONS: A propofol infusion strategy that requires limited experience with propofol dose selection and only 1 pump dosing change reliably produced airway obstruction in patients with severe sleep apnea. Clinical obstruction was achieved faster than target-controlled infusion-based systems for similar procedures reported in the literature. The observed degree of oxygen desaturation in the model system was within a clinically acceptable range.

Considerations for the use of short-acting opioids in general anesthesia.

Anesthesiologists play a critical role in facilitating a positive perioperative experience and early recovery for patients. Depending on the kind of procedure or surgery, a wide variety of agents and techniques are currently available to anesthesiologists to administer safe and efficacious anesthesia. Notably, the fast-track or ambulatory surgery environment requires the use of agents that enable rapid induction, maintenance, and emergence combined with minimal adverse effects. Short-acting opioids demonstrate a safe and rapid onset/offset of effect; that short effect is both predictable and precise. It also ensures easier titration and reduced or rapidly reversed side effects. Due to their distinct pharmacokinetic and pharmacodynamic properties, and, in one case, rapid extra-hepatic clearance of remifentanil, these agents have several applications in general anesthesia.

Time-delay when updating infusion rates in the Graseby 3400 pump results in reduced drug delivery.

Infusion pumps are commonly used for infusion of drugs for physiologic control, and infusion rate has been demonstrated to affect the parameters of pharmacokinetic models. In attempting to develop a model that explained this behavior, we examined the behavior of the Graseby 3400 syringe pump under a range of flow conditions and with variations in syringe characteristics. Two issues were identified: start-up loss (the difference between actual and ideal delivery on initial infusion) and update loss (the difference between actual and ideal delivery when transmitting a command to change infusion rate). Under worst-case conditions, this may result in a 20-second period of zero delivery during start-up, and when updating infusion rates once per second, zero output. These effects are influenced by syringe characteristics and vary sufficiently as to make it impossible to isolate this effect from the pharmacokinetic process being controlled. The implications of this for previous published results and clinical application of target-controlled infusions are discussed.

Nintendo® Wii Fit based sleepiness tester detects impairment of postural steadiness due to 24 h of wakefulness.

A field-usable sleepiness tester could reduce sleepiness related accidents. 15 subjects' postural steadiness was measured with a Nintendo(®) Wii Fit balance board every hour for 24 h. Body sway was quantified with complexity index, CI, and the correlation between CI and alertness predicted by a three-process model of sleepiness was calculated. The CI group average was 8.9 ± 1.3 for alert and 7.9 ± 1.4 for sleep deprived subjects (p < 0.001, ρ = 0.94). The Wii Fit board detects the impairment of postural steadiness. This may allow large scale sleepiness testing outside the laboratory setting.

Abdominal relaxation during emergence from general anesthesia with propofol and remifentanil.

STUDY OBJECTIVE: To characterize respiratory dynamics during emergence from propofol-remifentanil anesthesia using noninvasive respiratory inductance plethysmography (RIP). DESIGN: Observational pilot study. SETTING: Operating room in a university-affiliated teaching hospital. PATIENTS: 50 ASA physical status 1, 2, and 3 patients scheduled for microdirect laryngoscopy or bronchoscopy using total intravenous anesthesia (TIVA) with high-frequency jet ventilation. INTERVENTIONS: Patients were fitted with plethysmography bands around the chest and abdomen prior to induction. Following completion of surgery in patients undergoing brief airway procedures using propofol-remifentanil general anesthesia, the anesthetic infusions were stopped and ventilation suspended until resumption of spontaneous ventilation or desaturation below 90%. During this period of apnea, abdominal and thoracic girth was assessed with noninvasive RIP. MEASUREMENTS: Cross-sectional area of the thorax and abdomen during emergence were measured. MAIN RESULTS: Useful data were obtained from 41 patients, with stable apnea lasting 404 ± 193.1 seconds; of these, 34 exhibited a slow and significant decrease in abdominal girth over a period of 267.8 ± 128.5 seconds. Resumption of spontaneous ventilation generally coincided with the end of this abdominal relaxation. CONCLUSION: Slow expiration is the initial step in the resumption of spontaneous ventilation during apnea induced with TIVA using propofol-remifentanil.

Efforts to enhance catheter stability improve atrial fibrillation ablation outcome.

BACKGROUND: Contemporary techniques to enhance anatomical detail and catheter contact during atrial fibrillation (AF) ablation include (1) the integration of preacquired tomographic reconstructions with electroanatomical mapping (3-dimensional image integration [I-EAM]), (2) the use of steerable introducers (SIs), and (3) high-frequency jet ventilation (HFJV). OBJECTIVE: To prove that using these stabilizing techniques during AF ablation improves 1-year procedural outcome. METHODS: We studied 300 patients undergoing AF ablation at our institution. Patients were divided into 3 equal treatment groups (100 patients each) on the basis of the tools utilized: (1) group 1: AF ablation performed without I-EAM, SI, or HFJV; (2) group 2: AF ablation performed using I-EAM and SI, but without HFJV; and (3) group 3: AF ablation performed with I-EAM, SI, and HFJV. The primary outcome was freedom from AF 1 year after a single ablation procedure. The burden of both acute and chronic pulmonary vein reconnection was also assessed. RESULTS: Patients from groups 2 and 3 had significantly more nonparoxysmal AF (17% vs 30% vs 39%; P = .002), larger left atria (4.2 ± 0.8 cm vs 4.4 ± 0.7 cm vs 4.5 ± 0.8 cm; P<.001), and higher body mass index (BMI; 28.5 ± 5.8 kg/m² vs 29.1 ± 4.8 kg/m² vs 31.2 ± 5.4 kg/m²; P<.001). Despite these differences, with adoption of I-EAM, SI, and HFJV we noted a significant improvement in 1-year freedom from AF (52% vs 66% vs 74%; P = .006) as well as fewer acute (1.1 ± 1.2 vs 0.9 ± 1.1 vs 0.6 ± 0.9; P = .03) and chronic (3.5 ± 0.9 vs 3.2 ± 0.9 vs 2.4 ± 1.0; P = .02) pulmonary vein reconnections. CONCLUSIONS: The incorporation of contemporary tools to enhance anatomical detail and ablation catheter stability significantly improved 1-year freedom from AF after ablation.

Quantitative airway analysis during drug-induced sleep endoscopy for evaluation of sleep apnea.

OBJECTIVES/HYPOTHESIS: To quantitatively measure changes in airway caliber at multiple anatomical levels during drug-induced sleep endoscopy (DISE) for evaluation of sleep apnea. We hypothesize that patients undergoing DISE will show: 1) collapse at multiple upper airway regions (retropalatal, retroglossal, and retroepiglottic), with greater collapse in the retropalatal region; and 2) greater anterior-posterior dimensional narrowing than the lateral. STUDY DESIGN: Case series. METHODS: Patients underwent DISE employing propofol as part of a nonrandomized prospective trial assessing candidacy for transoral robotic surgery intervention for sleep apnea. Images of the retropalatal, retroglossal, and retroepiglottic regions were captured during an initial period of light sedation and again in a period of deep sedation. Images were analyzed using software to measure the percent change in regional airway measurements as a result of DISE. RESULTS: Thirty-seven sleep endoscopy videos were analyzed from patients with obstructive sleep apnea (apnea-hypopnea index: 42.9 ± 27.0 events/hour). Analyzable images were in the retropalatal (n = 24), retroglossal (n = 27), and retroepiglottic (n = 29) regions. The patients demonstrated mean reductions in airway area in the retropalatal (84.1 ± 18.7%), retroglossal (39.3 ± 37.5%), and retroepiglottic region (44.6 ± 42.8%). No statistically significant differences were found between lateral and anterior-posterior airway dimensional changes. CONCLUSIONS: Patients undergoing DISE had significant reductions in airway area at multiple regions under deep sedation with propofol. We conclude that collapse in the retropalatal region is greater than the hypopharyngeal region. This method can be used to quantitatively measure DISE upper airway changes, which could potentially be used as a means for understanding surgical outcomes in patients with sleep apnea.

The use of high-frequency jet ventilation for out of operating room anesthesia.

PURPOSE OF REVIEW: High-frequency jet ventilation is a novel technique for providing mechanical ventilation in the out of operating room (OOR) setting. Case reports and a small series of patients have shown it to be useful in patients undergoing cardiac arrhythmia ablations, interventional radiology procedures, and extracorporeal shock wave lithotripsy. Recently, interest in the technique has grown tremendously as the ability to provide superior surgical conditions may lead to improved efficiency and less side-effects in a variety of procedures. RECENT FINDINGS: Atrial fibrillation ablation procedures, liver tumor ablations, and extracorporeal shock wave lithotripsy are all the procedures that benefit from minimal movement of the heart, liver, and kidney, respectively, during the procedure. Although randomized controlled trials are lacking, increasing data suggest that by maintaining the thoracic and abdominal structures relatively immobile throughout the respiratory cycle, the efficiency and safety of these procedures may be improved. SUMMARY: Technological advances are allowing an increasing number of surgical procedures to be performed in the OOR setting. Such procedures often depend on the precise application of ablation catheters or shock waves. High-frequency jet ventilation facilitates the improved accuracy of catheter and shock wave placement, as well as efficiency of a variety of procedures. Improved efficiency, with fewer side-effects, has tremendous implications for the growth of such procedures in the OOR setting.