Perioperative Safety Podcast Series

Hi there, I am Dr. Robert Bilkovski and this is the beginning of a new podcast series on the topic of perioperative safety, where we take a look at concepts that apply to improving the perioperative journey which include topics on intraoperative paralysis, the depth of sedation, nociception monitoring, intraoperative awareness, and others. More importantly principles of a “systems approach” to improving patient outcomes will be covered throughout this podcast series.

Let us begin with a discussion on the concept of the perioperative surgical home and the Enhanced Recovery After Surgery, or ERAS.

To no one’s surprise, the field of medicine is constantly changing and so too are the requirements of anesthesiology, specifically as it looks to the perioperative space. Historically, the patient undergoing surgery will encounter the anesthesiologist relatively late in current surgical pathways where important decisions regarding sedation and pain management paradigms are made, in addition to patient counseling. The latter may or may not have been the focus of the anesthesiologist. ¹

The introduction of ERAS first spawned in the 1990s out of Denmark where researchers found that fast-tracking patients undergoing sigmoid colon surgery could have hospital stays reduced from an average of ten days, down to as little as two days. ²

The principles applied in this study evolved to shape the ERAS Society which was officially created in Sweden in 2010. There are multiple ERAS guidelines that have been published since, but common themes exist, which include the patient preparatory steps before surgery (such as patient counseling, education, and lifestyle modifications) through the post-operative period and all require coordination between surgeons, anesthesiologists, dietitians, physical medicine and rehabilitation professionals, psychiatrists, psychologists, and pharmacists to name a few.

Examples of ERAS protocols include: 

1. Multimodal analgesia: Multimodal analgesia protocols commence during the initial patient's evaluation as part of the preoperative evaluation clinic appointment. The preoperative evaluation also educates patients on different modalities that will be used during surgery and obtains the necessary informed consent for interventions such as neuraxial or regional blocks. The aim of these multimodal analgesia protocols extends into the intraoperative and postoperative periods, with emphasis on opioid sparing and opioid-free regimens that can bear impact on post-operative recovery in the PACU or in the hospital.
2. Goal-directed fluid therapy: Individualized goal-directed fluid therapy is a central element of ERAS in preoperative, intraoperative, and postoperative phases with the goal being to maintain euvolemia, which is a balance between fluids lost during surgery offset by fluids administered whether that is IV fluids, blood, or other products. Risk is stratified based on surgery type, where patients undergoing major surgery and/or with risk factors will benefit from an individualized goal-directed fluid plan. Of note, favorable outcomes have been reported with use of goal-directed fluid strategies and have been shown to reduce morbidity, mortality, and lengths of stay in the ICU and hospital.³
3. Post-Operative Nausea and Vomiting Prophylaxis: Similar to multimodal analgesia, the anesthesia care team will determine the most suitable strategy during the preoperative evaluation and will also leverage risk stratification based on surgery complexity and patient comorbidities to provide the optimal care plan.

In the United States, the American Society of Anesthesiologists have defined the Perioperative Surgical Home (or PSH) which builds off of the ERAS framework. The PSH serves as a patient-centric, team-based model of care to help meet the demands of a rapidly approaching health-care paradigm emphasizing value, patient satisfaction, and a reduction in costs. The goals of the PSH are to improve patient satisfaction, improve the quality of perioperative care delivered, and reduce the cost of surgical care. A notable concern is the focus during the intraoperative period with the interplay between depth of sedation and blood pressure can result in the “triple effect” where hypotension in the presence of a low mean alveolar concentration of inhaled anesthetics combined with a low sedation level  is an ominous predictor of morbidity and mortality. ⁴

This triple effect highlighted by Sessler et al.⁴ opens the door to consider concepts such as   AoA , or Adequacy of Anesthesia, whereby continuous monitoring of the depth of sedation, nociception-antinociception balance monitoring and quantitative neuromuscular monitoring may support the anesthesiologist in driving improvements in patient outcomes.

The study conducted by Vetter helped to shine a light on the clinical and economic outcomes that could result from implementation of the PSH construct. ⁵

Their study focused on process standardization in the management of patients undergoing either total hip or total knee arthroplasty. There was a standardization of care during the transitions of care throughout the continuum from the decision for surgery, to the post-discharge phase. They coined the term “Perioperativist” who is an anesthesiologist that specializes in the management of the surgical patient through this continuum and was deployed in the study. The study was a 2-group, before-and-after study wherein each group was observed for 24 months. The main variable deployed in the “after group” was the expansion of the PSH concept. The results from this study showed both clinical and economic outcome improvements. There was a 7.5% improvement in on-time day of surgery starts and a 2.2% reduction in ICU admission rates. In addition, there was a $432 decrease in direct non-surgery costs for total hip arthroplasty and $601 for total knee arthroplasty. 

These results help lay the foundation that structured operational efficiencies in the OR lead by anesthesiologists that touch the continuum of surgical care can improve outcomes to the patient and economically. Clearly more studies are needed to continue to grow awareness and understanding of both Perioperative Surgical Home model and Enhanced Recovery After Surgery framework. ⁶

This concludes the introductory podcast in this series, be on the lookout for more content as we take aim at means to further improve patient safety and operating room efficiencies. Thanks for listening.

References:

1. Elhassan A, Elhassan I, Elhassan A, Sekar KD, Cornett EM, Urman RD, Kaye AD. Perioperative surgical home models and enhanced recovery after surgery. J Anaesthesiol Clin Pharmacol. 2019 Apr;35(Suppl 1):S46-S50. doi: 10.4103/joacp.JOACP_47_18. PMID: 31142959; PMCID: PMC6515720.
2. Kehlet, H., 1997. Multimodal approach to control postoperative pathophysiology and rehabilitation. British journal of anaesthesia, 78(5), pp.606-617
3. Rollins, K.E. and Lobo, D.N., 2016. Intraoperative goal-directed fluid therapy in elective major abdominal surgery: a meta-analysis of randomized controlled trials. Annals of surgery, 263(3), p.465
4. Sessler, D.I., Sigl, J.C., Kelley, S.D., Chamoun, N.G., Manberg, P.J., Saager, L., Kurz, A. and Greenwald, S., 2012. Hospital stay and mortality are increased in patients having a “triple low” of low blood pressure, low bispectral index, and low minimum alveolar concentration of volatile anesthesia. The Journal of the American Society of Anesthesiologists, 116(6), pp.1195-1203
5. Vetter, Thomas R. MD, MPH; Barman, Joydip PhD, MBA; Hunter, James M. Jr MD; Jones, Keith A. MD; Pittet, Jean-Francois MD. The Effect of Implementation of Preoperative and Postoperative Care Elements of a Perioperative Surgical Home Model on Outcomes in Patients Undergoing Hip Arthroplasty or Knee Arthroplasty. Anesthesia & Analgesia 124(5):p 1450-1458, May 2017. | DOI: 10.1213/ANE.0000000000001743
6. Cannesson, Maxime MD, PhD; Mahajan, Aman MD, PhD. Anesthesiology and New Models of Perioperative Care: What Will Help Move the Needle?. Anesthesia & Analgesia 124(5):p 1392-1393, May 2017. | DOI: 10.1213/ANE.0000000000001952

Hello again and welcome to the second installment in the podcast series on perioperative safety. My name is Dr Robert Bilkovski and in this episode, we will review the topic of postoperative residual paralysis. Specifically, we will get a better understanding of the frequency of occurrence, the potential patient harms that may occur and the views coming from anesthesiology associations on this topic. 

The use of non-depolarizing paralytic agents during general anesthesia have been commonplace for decades and the risk for residual paralysis affecting patient safety in the post-operative setting has been reported dating back to the 1970s where nearly half of the patients arriving to the PACU had residual paralysis.^[1] Neuromuscular blockade is frequently used during anesthesia to support endotracheal intubation, optimize surgical conditions, and assist with mechanical ventilation in patients who have reduced lung compliance. In addition, the depth of paralysis should be closely monitored during the entire duration of surgery using train-of-four stimulation. Train of four monitoring is the most common method used to monitoring the extent of neuromuscular blockade.^[2] The train-of-four ratio is calculated by dividing the amplitude of the fourth twitch to the amplitude of the first twitch and monitoring technology exists to support the clinician in making this assessment. If the ratio is <0.9, it indicates that residual paralysis remains and there is a continued need to use a reversal agent. Other methodology used all focus on differing  patterns of stimulation patterns to assess residual paralysis which includes double-burst stimulation, post-tetanic count and tetanic stimulation.^[3]All leverage a similar method of stimulation, with the same pulse waveform and pulse duration. What differs is the frequency of impulses and means of evaluation between each stimulation. Double-burst stimulation delivers two bursts separated by 750 milliseconds, where the muscle contractions following the second burst is less than the first and allows clinicians to evaluate the fade of contraction between the two bursts. This method is more sensitive for tactile evaluation of a residual blockage and has been shown to be comparable to train of four assessments. Similarly with train of four, it has limited utility to assess deep blocks but useful during the onset of paralysis and at the time of recovery. Post-tetanic count (or PTC) is more useful during deep blocks where train of four is considered to be insensitive and supports bringing a patient out of very deep paralysis. The PTC delivers a stimulus (of 50 Hz for 5 sec) and is followed 3 seconds later by a single supramaximal stimuli and delivered once every second. The number of twitches recognized is inversely proportional to the degree of block, and is known as the post tetanic twitch count. Lastly, tetanic stimulation involves high frequency stimulation that is usually applied for 5 seconds. What is observed is for the presence or absence of a muscle contraction fade effect; where the absence of fading suggests acceptable levels of paralysis have been attained. paralysis is comparable to a train of for of approximately 0.85. Compared to DBS or train of four for use during recovery, the specificity has been reported to be low.

To further complicate matters, there are multiple device types that can be used for quantitative assessment for train of four and include acceler-myography, kine-myography and electro-myography, to name a few.^[4] Accelero-myography (or AMG) has been the most widely studied technology and uses a transducer placed on the muscle of interest to measure the response to an electrical stimuli when applied to that muscle; the muscle most commonly stimulated is the thumb. Kinemoyography (or KMG) is closely related to AMG and uses a special type of sensor placed in the groove between the thumb and index finger and senses bending of the thumb in response to electrical stimulation. Lastly, electro-myography (or EMG) is considered by experts to be the new gold standard which measures combined muscle action potentials rather than movement, in response to electrical stimuli. These amplitude of these action potentials is directly proportional to the number of muscle fibers activated, and thus the force of contraction. One limitation is that other forms of electrical stimuli during surgery, like electrocautery, may interfere with the measurements.

Literature shows that residual paralysis in the postoperative period is relatively common, where it has been reported to be as high as 40%.^[5][6]Unfortunately, clinicians frequently rely on clinical signs that include but not limited to head lift, hand grip and negative inspiratory force to determine if residual paralysis exists. These clinical signs are insensitive indicators in those patients coming out of general anesthesia and remain reliable only in awake patients.  The risk for residual paralysis while the patient remains in the post-anesthesia care unit includes:^[7]

1. the need for tracheal reintubation
2. impaired oxygenation and ventilation
3. impaired pulmonary function such as reduced forced vital capacity
4. increased risk for aspiration and pneumonia
5. pharyngeal dysfunction, and lastly may culminate in
6. a delayed discharge from the PACU

Re-intubation in and of itself is a notable risk to the patient and also bears an economic cost to the hospital system. In a publication in the British Journal of Anesthesia, re-intubation was shown to increase the risk for cardiac and respiratory complications, extended the length of stay in the PACU and the ICU on hospital, increased the duration of mechanical ventilation and ultimately an increased risk for death.^[8]

Some additional studies add further details on the frequency and importance of monitoring residual paralysis:

1. The RECITE-US study showed that in a 255-patient study in those undergoing abdominal surgery, almost 65% has a train of four ratio less than 0.9 at the time of extubation. This is despite the fact that the patients received reversing agents for neuromuscular blockade and qualitative peripheral nerve stimulation was monitored.^[9]
2. A large multi-center study from Spain reported that the patients with TOF ratios < 0.9 in the PACU were at an increased risk for postoperative adverse respiratory events, where the odd ratio was 2.57 and had a higher incidence of re-intubation.^[10]
3. A retrospective cohort study, which looked at the impact of postoperative residual paralysis on ICU admissions rates, hospital costs, and hospital length of stay, reported that patients with TOF ratios < 0.9 had a three-times higher risk of ICU admission than those with TOF ratios ≥ 0.9.^[11]and lastly, 
4. Several studies showed that failure to administer a reversal agent in the operating room was associated with increased complications such as post-operative pneumonia, failure to wean, re-intubation and unplanned ICU admissions.^[12][13][14]

The American Society of Anesthesia issued a recommendation where quantitative neuromuscular monitoring should be used whenever neuromuscular blocking agents are being utilized, throughout all phases of anesthesia.^[15] It is important to highlight that a quantitative monitor is the ideal for qualitative monitors lack the needed fidelity to determine sufficient reversal from neuromuscular blockade.^[16]  Furthermore, train of four determinations with qualitative monitors are suitable up to the 0.4 level which is lower than the 0.9 threshold recommended by the ASA in this guideline. The Anesthesia Patient Safety Foundation has issued a position and state that residual neuromuscular blockade in the postoperative period is a patient safety hazard that could be addressed partially by better and consistent use of our qualitative standard train-of-four nerve stimulator monitors, but will ultimately require quantitative (or objective TOF) monitoring along with traditional subjective observations to eliminate this problem completely. The need for intraoperative train of four monitoring is quite clear and further emphasis on routine use can drive further improvements in patient safety. 

Adding an additional layer of complexity is the use of sugammadex, which is a reversal agent of neuromuscular blocking agents that has grown in clinical use over the past decade or two and is highlighted by a faster recovery time and improved safety profile than legacy reversal agents.^[17] However, the risk of incomplete reversal remains an important clinical problem and use of train-of-four  in combination has been show to reduced as compared to use of sugammadex without quantitative monitoring.^[18]

This ends this podcast on the topic of perioperative residual paralysis and you were able to take away the fact that this problem remains common and is associated with increased risk for complications that increase the patient’s risk for a poor post-operative outcome. Thank you for listening and be sure to visit again on other topics pertaining perioperative safety in coming podcasts. Thank you.

References:

[1]     Jørgen Viby-Mogensen, Bent Chraemmer Jørgensen, Helle Ørding; Residual Curarization in the Recovery Room. Anesthesiology 1979; 50:539–541.

[2]     Cook, D. and Simons, D.J., 2021. Neuromuscular blockade. In StatPearls [Internet]. StatPearls Publishing.

[3]     Fuchs-Buder, T., Schreiber, J.-.-U. and Meistelman, C. (2009), Monitoring neuromuscular block: an update. Anaesthesia, 64: 82-89.

[4]     Renew, J.R., Advancements in Quantitative Neuromuscular Monitoring. Perioperative Hypotension, p.117.

[5]     Todd MM, Hindman BJ, King BJ. The implementation of quantitative electromyographic neuromuscular monitoring in an academic anesthesia department. Anesth Analg 2014;119:323–331.

[6]     Checketts MR, Alladi R, Ferguson K, et al. Recommendations for standards of monitoring during anaesthesia and recovery 2015: Association of Anaesthetists of Great Britain and Ireland. Anaesthesia 2015.

[7]     Stoelting, R.K., 2016. Monitoring of neuromuscular blockade: what would you expect if you were the patient. APSF Newslett, 30(3), pp.45-47.

[8]     Rujirojindakul, P., Geater, A.F., McNeil, E.B., Vasinanukorn, P., Prathep, S., Asim, W. and Naklongdee, J., 2012. Risk factors for reintubation in the post-anaesthetic care unit: a case–control study. British journal of Anesthesia, 109(4), pp.636-642.

[9]     Saager L, Maiese EM, Bash LD, et al. Incidence, risk factors, and consequences of residual neuromuscular block in the United States: The prospective, observational, multicenter RECITE-US study. J Clin Anesth. 2019;55:33–41.

[10]   Errando CL, Garutti I, Mazzinari G, et al. Residual neuromuscular blockade in the postanesthesia care unit: observational cross-sectional study of a multicenter cohort. Minerva Anestesiol. 2016;82:1267–1277.

[11]   Grabitz SD, Rajaratnam N, Chhagani K, et al. The effects of postoperative residual neuromuscular blockade on hospital costs and intensive care unit admission: a population-based cohort study. Anesth Analg. 2019;128:1129–1136

[12]   Bulka CM, Terekhov MA, Martin BJ, et al. Nondepolarizing neuromuscular blocking agents, reversal, and risk of postoperative pneumonia. Anesthesiology. 2016;125:647–55.

[13]   Bronsert MR, Henderson WG, Monk TG, et al. Intermediate-acting nondepolarizing neuromuscular blocking agents and risk of postoperative 30-day morbidity and mortality, and long-term survival. Anesth Analg. 2017;124:1476–1483.

[14]   Belcher AW, Leung S, Cohen B, et al. Incidence of complications in the post-anesthesia care unit and associated healthcare utilization in patients undergoing non-cardiac surgery requiring neuromuscular blockade 2005–2013: a single center study. J Clin Anesth. 2017;43:33–38.  15

[15]   Klein AA, Meek T, Allcock E, Cook TM, Mincher N, Morris C, Nimmo AF, Pandit JJ, Pawa A, Rodney G, Sheraton T. Recommendations for standards of monitoring during anaesthesia and recovery 2021: Guideline from the Association of Anaesthetists. Anaesthesia. 2021 Sep;76(9):1212-23.

[16]   Brull SJ, Murphy GS. Residual neuromuscular block: lessons unlearned. Part II: methods to reduce the risk of residual weakness. Anesth Analg. 2010 Jul;111(1):129-40.

[17]   Mirakhur, R.K., 2009. Sugammadex in clinical practice. Anaesthesia, 64, pp.45-54.

[18]   Thilen, S.R., Weigel, W.A., Todd, M.M., Dutton, R.P., Lien, C.A., Grant, S.A., Szokol, J.W., Eriksson, L.I., Yaster, M., Grant, M.D. and Agarkar, M., 2023. 2023 American Society of Anesthesiologists practice guidelines for monitoring and antagonism of neuromuscular blockade: a report by the American Society of Anesthesiologists task force on neuromuscular blockade. Anesthesiology, 138(1), pp.13-41.

Welcome back to the third installment in the podcast series on perioperative safety. My name is Dr. Robert Bilkovski and in this episode, we will review the topic of intraoperative depth of anesthesia monitoring and the use of Entropy^TM monitoring. Specifically, we will get a better understanding of this technology that is one of several solutions available to the anesthesiologist and how it can support improved patient outcomes. 

In an attempt to minimize patient risk and to standardize practice, anesthesiology associations have issued guidelines for monitoring during sedation.^[1] These associations include the American Society of Anesthesiologists (ASA), the Association of Anesthetists of Great Britain and Ireland (AAGBI), the European Society of Anesthesiologists (ESA), the Australian and New Zealand College of Anesthetists (ANZCA), and the Anesthesia Patient Safety Foundation (APSF). The guidelines universally require assessment of the depth of sedation and the use of pulse oximetry and non-invasive arterial pressure monitoring. 

Taking aim at the depth of sedation monitoring, there are several means by which this can be accomplished which includes:

1. Clinical scales such as the Modified Observer's Assessment of Alertness/Sedation Scale (MOASS), and the Ramsay Sedation Scale (RSS), and
2. Processed EEG, which is based on the understanding that the EEG waveform changes in accordance to varying depths of sedation.

There are several EEG-based sedation monitoring technologies and one such technique is Entropy monitoring, where Entropy collects both the EEG and frontal EMG signals to provide two readings: State Entropy and Response Entropy. Simply stated, Entropy monitoring measures the amount of irregularity in the EEG and frontal EMG waveforms. Entropy values have been shown to correlate to the patient’s anesthetic state. High values of Entropy indicate high irregularity of the signal, signifying that the patient is awake. A more regular signal produces low Entropy values which can be associated with low probability of consciousness.^[2][3]

Response Entropy is sensitive to the activation of facial muscles, namely the frontal EMG and its response time is very fast at less than 2 seconds. Frontal EMG is especially active during the awake state but may also activate during surgery. Facial muscles may also give an early indication of emergence, and this can be seen as a quick rise in RE. The display range is from 0-100.

In comparison, the State Entropy value is always less than or equal to Response Entropy. During general anesthesia the hypnotic effect of certain anesthetic drugs on the brain may be estimated by the State Entropy value. Of note, State Entropy is less affected by sudden reactions to the facial muscles because it is mostly based on the EEG signal. The display range is from 0-91. In addition, neuromuscular blocking agents (NMBA), administered in surgically appropriate doses are not known to affect the EEG, but are known to affect the EMG signal.

The clinically relevant target range during general anesthesia for Entropy monitoring values is 40-60. RE and SE values near 40 indicate a low probability of consciousness.^[4] In addition, both Entropy measures and other EEG-based sedation monitoring technologies have shown a strong ability to discriminate between consciousness and unconsciousness states during propofol, sevoflurane and thiopental anesthesia.⁴ Lastly, Vakkuri et al concluded that Response Entropy informed emergence from anesthesia faster than State Entropy or other EEG-based sedation monitoring signals.

The use of Entropy monitoring has been shown in a variety of studies to inform clinical benefits and some of these benefits include:

1. Improved hemodynamic stability. Where a 2008 study found that Entropy monitoring provides more reliable hemodynamic control, specifically need for antihypertensive medications and fewer occurrences of hemodynamic fluctuations during total knee replacement surgery.^[5]
2. Reduction in the use of anesthetics. Studies have shown that Entropy monitoring is associated with a 30% reduction in Sevoflurane/Isoflurane and a 15% reduction in Propofol.^[6]
3. A lower risk of postoperative delirium. The use of Entropy monitoring may help avoid reaching unnecessarily deep states of hypnosis, including burst suppression that has been associated with increased risk of delirium.^[7]

The use of Entropy monitoring has been shown to benefit the hospital as well, via reductions in drug consumption,reducing perioperative adverse events and improved recovery time and operating room throughput.⁵  In a UK-based Health Technology Assessment amongst the general surgical population undergoing general anesthesia with TIVA (or total intravenous anesthesia). Entropy monitoring was modeled as being associated with 3.8 cases of awareness, compared with 16 cases for patients receiving standard clinical monitoring and the incremental cost-effectiveness ratio ICER for Entropy monitoring compared with standard clinical monitoring was £14,421.^[8]  It is likely that these patient and hospital benefits supported the implementation of entropy monitoring use in guidelines published by the Enhanced Recovery After Surgery Society.^[9] Implementation of the ERAS protocol, notably in head and neck surgery as shown a significant impact in the reduction of hospital lengths of stay.

This ends this podcast on the topic of intraoperative sedation and the use of entropy monitoring. You were able to take away the fact that intraoperative sedation is recommended by many international anesthesia societies globally and that there are several approaches including EEG-based entropy levels of consciousness monitoring. Thank you for listening and be sure to visit again on other topics pertaining perioperative safety in coming podcasts. 

References:

[1]     C. G. Sheahan , D. M. Mathews, Monitoring and delivery of sedation, BJA: British Journal of Anaesthesia, Volume 113, Issue suppl_2, December 2014, Pages ii37–ii47.

[2]     Viertiö-Oja et al. Description of the Entropy algorithm as applied in the Datex-Ohmeda S/5 Entropy Module. Acta Anaesthesiologica Scandinavica, 48 (2): 154-161 (2004).

[3]    Entropy Monitoring: A Valuable Tool for Guiding Delivery of Anesthesia; ClinicalView GE Healthcare, https://clinicalview.gehealthcare.com/quick-guide/entropy-monitoring-valuable-tool-guiding-delivery-anesthesia

[4]     Vakkuri, A., Yli‐Hankala, A., Talja, P., Mustola, S., Tolvanen‐Laakso, H., Sampson, T. and Viertiö‐Oja, H., 2004. Time‐frequency balanced spectral entropy as a measure of anesthetic drug effect in central nervous system during sevoflurane, propofol, and thiopental anesthesia. Acta Anaesthesiologica Scandinavica, 48(2), pp.145-153.

[5]     Wu et al, 2008, Use of Spectral Entropy Monitoring in Reducing the Quantity of Sevoflurane as Sole Inhalational Anesthetic and in Decreasing the Need for Antihypertensive Drugs in Total Knee Replacement Surgery

[6]     Vakkuri A. et al.. Spectral Entropy Monitoring Is Associated with Reduced Propofol Use and Faster Emergence in Propofol–Nitrous Oxide–Alfentanil Anaesthesia. Anesthesiology. 2005;103:274–9. El Hor, Tarek. Impact of Entropy Monitoring on Volatile Anesthetic Uptake. Anesthesiology. 2013;118:868-73 Aiméet al. Does Monitoring BispectralIndex or Spectral Entropy Reduce Sevoflurane Use? AnesthAnalg. 2006;103:1469 –77

[7]     Daiello LA, et al.. Postoperative Delirium and Postoperative Cognitive Dysfunction: Overlap and Divergence. Anesthesiology. 2019 Sep;131(3):477-491.

[8]     Shepherd J, Jones J, Frampton G, Bryant J, Baxter L, Cooper K. Clinical effectiveness and cost-effectiveness of depth of anaesthesia monitoring (E-Entropy, Bispectral Index and Narcotrend): a systematic review and economic evaluation. Health Technol Assess. 2013 Aug;17(34):1-264. 

[9]     Bertazzoni G, Testa G, Tomasoni M, Mattavelli D, Del Bon F, Montalto N, Ferrari M, Andreoli M, Morello R, Sbalzer N, Vecchiati D, Piazza C, Nicolai P, Deganello A. The Enhanced Recovery After Surgery (ERAS) protocol in head and neck cancer: a matched-pair analysis. Acta Otorhinolaryngol Ital. 2022 Aug;42(4):325-333.

Hello again, this is Dr Robert Bilkovski and we continue on our next installment in the podcast series on perioperative safety, where we look at lung recruitment during anesthesia. This podcast will help you get a grounding on the negative effects general anesthesia has on the lungs and the importance alveolar recruitment maneuvers can provide. 

[note: basis for this podcast leverages Alveolar Recruitment Maneuvers to Help Improve Lung Function During General Anesthesia https://clinicalview.gehealthcare.com/white-paper/alveolar-recruitment-…]

When a patient is undergoing surgery, they undergo a transition from standing to a supine position along with the induction of general anesthesia which may negatively affect lung function. Specifically, the collapse of alveolar units can result in the development of atelectasis and as a result may make ventilation and oxygenation more difficult. There are multiple additional factors that can contribute to lung collapse and include: the high FiO2 used during induction, diaphragm dysfunction during anesthesia and the central anesthetic effects on respiratory muscle tone.^[1]  In addition, changes in abdominal pressure, chest wall compliance, and neuromuscular blockade all produce additive effects that can further compromise lung function, notably reduction in the functional residual capacity which represents the end-expiratory lung volume.  As a result of these changes, the lung has a smaller volume and can require greater pressures in order to support the patient's ventilatory needs. 

For more information on oxygen exchange and the alveolar unit, I suggest revisiting a podcast from the   series on end-tidal oximetry, specifically podcast #1 of the series that looked at the principles of oxygen exchange.

Of note, up to 90% of patients undergoing general anesthesia may develop hypoxemia due to progressive atelectasis. Early studies found that the use of a tidal volume of 12 – 15 mL/kg body weight was effective in reducing atelectasis and restoring compliance for normal pulmonary gas exchange in the operating room. [2] Since then, researchers have turned their focus to lower tidal volumes for the adverse effects of high tidal volume ventilation has been recognized both in patients with acute respiratory distress syndrome and those with healthy lungs undergoing anesthesia. This has shifted recommendations away from high tidal volume to low tidal volume ventilation, where now the tidal volume goal is between 6 to 8 ml per kg body weight.^[3]

The basis for lung protective strategies is to minimize the burden of volutrauma and barotrauma. Volutrauma refers to the damage that can be imposed to the lungs as a result of high tidal volumes which causes excessive inflation of the alveoli, whereas barotrauma is the result of excessive tranpulmonary pressure which is the difference between pressures inside and outside the lungs.^[4]

During surgery, an approach by which the anesthesiologist can reduce the incidence of atelectasis is to conduct a recruitment maneuver. The basis of recruitment maneuvers is to bring a collapsed alveolus back to normal function via the application of sufficient positive pressure ventilation. The opening pressure of an alveolus or terminal airway is the specific amount of positive pressure that results in their reopening; but the opening pressure will vary from one alveolus to another. Most collapsed alveoli can be opened during general anesthesia with an alveolar recruitment maneuver that consists of peak inspiratory pressure of 40 cm H2O being applied for 7-10 seconds. ^[5] However, there are different ways to perform a recruitment maneuver: 

1. Pressure can be delivered manually, but this approach is ill-advised for it may be associated with a paradoxical increased rate of post-operative complications^[6]
2. What is preferred is to conduct a step-wise changes in volume settings on the ventilator component of the anesthesia delivery device. In this setting, the delivered volume and/or pressure can be increased every 3 – 6 breaths until the target opening pressure is achieved. After delivering several breaths at the target pressure one can return to the previous low tidal volume ventilation. 

The importance of alveolar recruitment maneuvers was summarized by an international expert panel which published a consensus statement in 2019 and in it the panel concluded that recruitment maneuvers should be used:^[7]

1. Whenever the patient is disconnected from the breathing circuit and whenever the patient’s hemoglobin saturation is consistently ≤94%;
2. One should evaluate change in respiratory system compliance and driving pressure after an alveolar recruitment maneuver and repeat maneuver with a longer inspiratory hold or higher pressure if recruitment is assessed as ineffective; and
3. Alveolar recruitment maneuvers should be performed using the lowest effective peak inspiratory pressure and shortest effective time or fewest number of breaths

 

In closing a meta-analysis published in 2019 showed that the effect of alveolar recruitment maneuvers from 12 selected studies had a statistically significant reduction in postoperative pulmonary complications, especially when lung-protective ventilation strategies were also deployed,^[8] thereby stressing the clinical utility of recruitment maneuvers during general anesthesia.

This concludes this podcast on lung recruitment strategies during general anesthesia. Thank you for listening and be sure to listen in again on future topics pertaining to perioperative safety.

References:

[1]     Tusman, G. and Belda, J.F., 2010. Treatment of anesthesia-induced lung collapse with lung recruitment maneuvers. Current anaesthesia & critical care, 21(5-6), pp.244-249.

[2]     The Acute Respiratory Distress Syndrome Network: Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med 2000, 342:1301–1308.

[3]     Futier, E., Constantin, J. M., Paugam-Burtz, C., Pascal, J., Eurin, M., Neuschwander, A., ... & Jaber, S. (2013). A trial of intraoperative low-tidal-volume ventilation in abdominal surgery. New England Journal of Medicine, 369(5), 428-43

[4]     Beitler JR, Malhotra A, Thompson BT. Ventilator-induced Lung Injury. Clin Chest Med. 2016 Dec;37(4):633-646.

[5]     Hartland BL, Newell TJ, Damico N. Alveolar recruitment maneuvers under general anesthesia: a systematic review of the literature. Respiratory care. 2015 Apr 1;60(4):609-20.

[6]     Ball, L., Hemmes, S. N. T., Neto, A. S., Bluth, T., Canet, J., Hiesmayr, M., ... & Pelosi, P. (2018). Intraoperative ventilation settings and their associations with postoperative pulmonary complications in obese patients. British Journal of Anaesthesia, 121(4), 899-908.

[7]     Young, C. C., Harris, E. M., Vacchiano, C., Bodnar, S., Bukowy, B., Elliott, R. R. D., ... & Sprung, J. (2019). Lung-protective ventilation for the surgical patient: international expert panel-based consensus recommendations. British Journal of Anaesthesia, 123(6), 898-913.

[8]     Cui, Y., Cao, R., Li, G., Gong, T., Ou, Y. and Huang, J., 2019. The effect of lung recruitment maneuvers on post-operative pulmonary complications for patients undergoing general anesthesia: a meta-analysis. *PLoS One*, *14*(5), p.e0217405.

 

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Dr. Bilkovski is a paid consultant of GE HealthCare. GE is a trademark of General Electric Company used under trademark license. Reproduction in any form is forbidden without prior written permission from GE HealthCare. Nothing in this material should be used to diagnose or treat any disease or condition. Readers must consult a healthcare professional.

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