In the clinical literature, there is no consensus as to the meaning of terms such as “deep” or “moderate” neuromuscular block. To avoid confusion, we have defined depth of block as follows:
- Extreme block: a posttetanic count (PTC) of zero.
- Deep block: a PTC 1 or more; but a train-of-four (TOF) count of zero. Synonymous with profound or intense block.
- Moderate block: a TOF count of 1–3.
- Shallow block: a TOF count of 4 with fade.
There are clearly places in the practice of anesthesia where producing deep neuromuscular block is advantageous. Obtaining conditions favorable to tracheal intubation is an obvious example.1 There are also situations where maintaining deep block until the very end of a surgical procedure may enhance patient safety and decrease morbidity. Examples might include open-eye surgery under general anesthesia and intracranial surgery.2,3 However, as a general rule, because of the limited ability of anticholinesterases to antagonize deep nondepolarizing block, most clinicians wisely attempt to avoid deep block as the end of surgery approaches. More recently with the availability of sugammadex as an alternative to neostigmine, there has been renewed interest in other potential indications for the intraoperative maintenance of deep block, and especially on the potential advantages of maintaining deep neuromuscular block for laparoscopic surgery.4–9 Within the last 2 to 3 years, there has also been a flurry of education videos and conference panels on exactly this subject.a–f
There is some evidence that maintaining low inflation pressures during intra-abdominal laparoscopic surgery may reduce postoperative pain,10 and many surgeons certainly believe that deep neuromuscular block improves the quality of surgical conditions compared with moderate block and thus may contribute to less postoperative morbidity. Unfortunately, the relationship between deep block and an optimized surgical space is now first being explored. In this review, we will attempt to evaluate the available data supporting the premise that deep neuromuscular block for laparoscopic surgery has benefits for both the patient and the surgeon.
With the help of a health science librarian, a literature search was conducted on Ovid Medline (from 1996 to present), Ovid Excerpta Medica Database (EMBASE, from 1974 to present), Scopus (from 1966 to present), Cochrane database, Web of Science—SciSearch (from 1966 to present), Web of Science—Conference Proceedings (from 1990 to present), Web of Science—Biosis Previews (from 1969 to present), and Web of Science—Biosis Citation Index (from 1969 to present). Last update was on June 10, 2014. The number of articles identified in each database was 148, 194, 320, 10, 246, 21, 62, and 62, respectively. The 3 search strategies used in each database search were (1) Laparoscopy [index term] or “laparoscop…” [keyword] AND Neuromuscular Blockade [index term] or “neuromuscul…” adj “block…” [keywords] AND “deep…” or “profound” or “intense” or “extreme,” (2) Laparoscopy [index term] or “laparoscop…” [keyword] AND “abdominal” within 2 words of “relax…” [keywords], and (3) Laparoscopy [index term] or “laparoscop…” [keyword] AND “low…” within 2 words of “pressure” or “high…” within 2 words of “pressure” AND “pneumoperitoneum.” The search was not restricted to the English language. In addition, we studied the reference lists of the articles retrieved in the search and of other relevant articles known to the authors.
The 2 authors independently screened the titles and abstracts of all papers identified in our search. We retrieved and assessed the full manuscripts of what we considered to be potentially relevant articles. We only included studies that were published in peer-reviewed journals, and to the best of our knowledge, we did not cite studies from “pay to publish” journals. Although we cite several studies from surgical journals related to operating conditions at high versus low insufflation pressures, we rejected many because they were simply repetitious or had no relevance to our central question: Does deep neuromuscular block for laparoscopy have potential benefits for surgeon and patient when compared to more moderate block? We also cite 1 recent abstract because it had in our opinion extraordinary relevance to this question.
NONLAPAROSCOPIC SURGERY: ARE RELAXANTS ALWAYS NECESSARY?
Satisfactory surgical conditions are the end product of multiple factors that may range from the level of general anesthesia administered to the personal relationship between the surgeon and the anesthesiologist. This is equally true for both conventional and minimally invasive surgery. We believe that lessons learned from general surgery have applicability to laparoscopic surgery as well.
A 1995 article by Tammisto and Olkkola11 is instructive. They studied the intensity of neuromuscular block that was adequate for surgical relaxation at different end-tidal levels of enflurane during N2O–O2–fentanyl anesthesia in 30 patients undergoing upper abdominal surgery. All patients received vecuronium 0.07 mg/kg to facilitate tracheal intubation and thereafter the neuromuscular block was allowed to dissipate. Patients were then divided into 3 groups of 10 each, where end-tidal enflurane was maintained at 0.30, 0.60, or 1.2 percent. Additional increments of vecuronium were administered if (1) the surgeon complained about relaxation; (2) there were motor responses, e.g., coughing, bucking; or (3) there was a 30% increase in spontaneous electromyograph (EMG) activity in the muscles of the neck.12 The authors found a linear relationship between end-tidal concentration of enflurane and the degree of neuromuscular block required to produce adequate surgical muscle relaxation during abdominal surgery. As anesthesia deepened, less intense block was required.
Even major surgery does not necessarily require the continuous administration of neuromuscular blocking drugs. Gueret et al.13 report a series of 87 consecutive patients undergoing cardiac surgery in which no further relaxants were required after an intubation dose of either atracurium or cisatracurium. The absence of continuous neuromuscular block did not have any negative impact on surgery and neither diaphragmatic contraction nor patient movement was an issue. Surgeons were not concerned by the absence of neuromuscular blockade, and at the end of surgery TOF ratios recovered spontaneously to 0.90 or above in all of their patients.
Similarly, Li et al.14 question the need for neuromuscular blocking drugs during spinal surgery. They studied 86 patients under total IV anesthesia (TIVA) (average bispectral index = 50; range 40–60). In all patients, succinylcholine 2.0 mg/kg was used to facilitate tracheal intubation. Upon return of neuromuscular function, half of the subjects received atracurium 0.50 mg/kg (the frequency of or use of incremental doses was not reported). None of the surgeons realized that half of the patients had not received additional neuromuscular blocking drugs, and no patient in the control group required relaxant administration because of unsatisfactory operating conditions.
A rigorous and well-designed study of the need for neuromuscular block during abdominal surgery comes from King et al.15 They studied 124 patients scheduled for radical prostatectomy. In all patients, anesthesia was induced with sodium thiopental and tracheal intubation facilitated with succinylcholine. Anesthesia was maintained with an average end-tidal concentration of 1.3% isoflurane and a continuous infusion of fentanyl. Patients were vigorously hyperventilated (end-tidal pCO2 values of 26 ± 3 mm Hg). A mechanomyographic transducer was attached to the thumb for evoked force measurements of neuromuscular function in all patients. Both the anesthesia care team and the surgical team were blinded to this assessment by draping the hand. At this point, patients were divided into 2 groups. In the relaxant group, vecuronium 0.10 mg/kg was administered. In the placebo group, patients received a bolus of saline. After abdominal fascia was incised, surgeons were asked to rate the surgical field on a scale of 1 (excellent) to 4 (unacceptable). Based on this rating, additional doses of either vecuronium or saline were administered. In the placebo group, a rating of 4 was followed by a rescue dose of vecuronium. The surgeons were asked to give a final field assessment at the time of fascial closure. Discontinuation of the isoflurane was at the discretion of the anesthesia care team. Seventeen of 61 patients in the placebo group (28%) required rescue doses of vecuronium. Thus, good to excellent surgical conditions for the duration of the procedure were achieved in approximately 70% of patients without the use of neuromuscular blocking drugs. The authors conclude, “These findings suggest that anesthesiologists should at least consider whether muscle relaxants should be used routinely… or whether more selective application when inadequate surgical conditions are actually present might be more appropriate.”
MUSCLE RELAXANTS AND LAPAROSCOPIC SURGERY
Is There Something Special About Laparoscopic Surgery?
Perhaps anesthesia for routine abdominal laparoscopy is a special case. The rationale for promoting the use of extreme or deep neuromuscular block for laparoscopic and robotic surgeries is based on the assumption that it will improve surgical operating conditions and patient outcome while allowing lower abdominal inflation pressures to be used. Controlled ventilation would seem to be indicated because pneumoperitoneum is associated with reduced airway compliance, a decreased functional residual capacity, and increased airway pressures and carbon dioxide (CO2) production. Thus, “common sense” would dictate that neuromuscular blocking drugs should play an important and perhaps critical role in anesthesia for abdominal laparoscopy. But is this necessarily always true?
Does Deep Neuromuscular Block Provide Better Laparoscopic Surgical Conditions Than Moderate Levels of Block?
Chassard et al.16 studied 50 patients having laparoscopies for gynecological surgery under TIVA. Half of the patients received atracurium in doses sufficient to maintain twitch height at 10% of control as measured by EMG. The control group received no blocking drugs. Surgeons were unable to identify differences in operating conditions between the 2 groups. The authors pointed out that these results were compatible with an animal study they conducted in which they observed that high peak inspiratory airway pressures and intraabdominal pressures during laparoscopy were not affected by neuromuscular block.17 Thus, they questioned the necessity of administering muscle relaxants in clinical anesthetic practice during laparoscopic surgery. Similarly, Putensen et al.18 also using an animal model concluded that, “Neuromuscular blockade does not alter the elastic properties of the lungs, chest wall, or total respiratory system in mechanically ventilated pigs receiving sodium pentobarbital anesthesia to suppress spontaneous breathing efforts.”
Chen et al.19 report findings similar to Chassard et al.17 in a larger study (n = 120) of gynecological laparoscopies also under TIVA anesthesia (remifentanil 0.25 μg/kg/min and propofol 75–125 μg/kg/min). In half the patients, a ProSeal™ laryngeal mask airway (LMA) was inserted after rocuronium 0.60 mg/kg (the authors do not make clear if incremental doses of rocuronium were ever administered or if neuromuscular function was monitored). In the remainder, the LMA was placed without relaxant facilitation. Ventilation was controlled in both groups. Satisfactory conditions for ventilation and operation were consistently achieved with and without muscle relaxants using LMAs in all patients. The authors could see no benefits (reduced operative or recovery times) in the use of neuromuscular blocking drugs for laparoscopy gynecological surgery.
Swann et al.20 also questioned the requirement for muscle relaxant administration for gynecological laparoscopy. They studied 60 patients scheduled for very short (average duration < 15 minutes) laparoscopic procedures. Anesthesia in all subjects was induced with propofol 2.5 mg/kg and fentanyl 1.0 μg/kg. Anesthesia was maintained with 67% N2O and enflurane 0.5% to 2.0% inspired. In half the patients, this was followed by insertion of an LMA. The remainder of subjects had an endotracheal tube placed after a 0.30 mg/kg dose of atracurium. Ventilation was spontaneous in the LMA group and controlled in the atracurium group. There were no clinically significant differences in the intraoperative conditions of the 2 groups. No adverse consequences were reported. It is unclear, however, if the authors’ results are applicable to longer surgical procedures. We suspect that many clinicians would not opt for spontaneous ventilation via an LMA for laparoscopic procedures with anticipated durations of 20 to 30 minutes or more.
Williams et al.21 also studied the necessity of neuromuscular blockade for procedures of short duration in 40 women scheduled for diagnostic laparoscopy or laparoscopic sterilization. Anesthesia in all patients was induced with propofol and fentanyl, and anesthesia was maintained with isoflurane 1% to 2% and nitrous oxide 66% in oxygen. In half the subjects, an LMA was then inserted and patients were allowed to breathe spontaneously during the procedure. In the remaining patients, endotracheal intubation was accomplished after atracurium 0.50 mg/kg. In this group, ventilation was controlled. Blinding of the surgeons was attempted by screening of the patient’s airway and the anesthetic machine. However, despite this, the surgeons could identify the technique used by observing the abdominal movements of the patient. Although the surgical view was rated as similar in both groups, in 5 of 18 patients in the LMA group, the pneumoperitoneum was rated as inadequate for trocar insertion. In the atracurium group, the pneumoperitoneum was rated as adequate in all 19 cases. Thus, spontaneous ventilation via an LMA must be considered a suboptimal technique for pelvic laparoscopy. Had the authors used controlled ventilation via the LMA, perhaps their results might have been different.
A more universally applicable study comes from Paek et al.22 They studied 56 subjects scheduled for laparoscopic pelvic surgery. In all patients, anesthesia was induced with propofol and remifentanil, and tracheal intubation was facilitated with rocuronium 0.60 mg/kg. Anesthesia was maintained with TIVA. In half the patients (group A), incremental doses of rocuronium were given whenever the TOF count returned to 2, and block was maintained until the peritoneum was closed. In group B, no additional doses of rocuronium were administered. In this group, the fourth response to TOF stimulation returned in 72 ± 10 minutes. The total pneumoperitoneal time in both groups approximated 100 ± 20 minutes. Thus in group B, the level of block for the final 30 minutes of the pneumoperitoneum was minimal. There was no difference between groups in intraoperative hemodynamics, peak airway pressures, or arterial blood gases. “There were no occasions when difficulty, such as coughing, bucking, and any voluntary movement during the procedure, led to the withdrawal of a patient from the study. Moreover, there were no complaints from any of the participating surgeons.” The authors concluded that supplemental muscle relaxants were not required for laparoscopy pelvic surgery under TIVA.
Martini et al.5 randomized 24 patients undergoing elective laparoscopic surgery for prostatectomy or nephrectomy under TIVA to receive moderate neuromuscular block (n = 12; TOF count = 1–2) using the combination of atracurium/mivacurium, or deep neuromuscular block (n = 12; PTC = 1–2) using high-dose rocuronium. After surgery, neuromuscular block was antagonized with neostigmine (in patients in the moderate neuromuscular block group) or sugammadex (in patients in the deep neuromuscular block group). During all surgeries, 1 surgeon scored the quality of surgical conditions using a 5-point surgical rating scale ranging from 1 (extremely poor conditions) to 5 (optimal conditions). Video images were obtained and 12 anesthesiologists rated a random selection of images. On a rating scale of 1 to 5, the authors reported a mean value of 4.0 ± 0.4 during moderate and 4.7 ± 0.4 during deep neuromuscular block.
A recent study by Dubois et al.7 also addressed this issue. The authors randomly assigned 100 women scheduled to have laparoscopic hysterectomies under 1 minimum alveolar concentration desflurane anesthesia into 2 groups. In group D (deep block; as defined by the authors), patients received rocuronium 0.60 mg/kg before tracheal intubation and top-up doses of 5 mg whenever the TOF-count (as determined by EMG) exceeded 2. In group S (shallow block), the intubation dose of rocuronium was 0.45 mg/kg and no further relaxant was administered unless surgical conditions were unacceptable. The senior surgeon in charge of the study (blinded to the EMG values) assessed the exposure of the surgical field on a 4-grade numerical scale: excellent (1), good but not optimal (2), poor but acceptable (3), or unacceptable and impossible to continue the operation (4). Multiple assessments (348 in group S; 306 in group D) were made as surgery progressed. In group S, there were 14 episodes where the surgical field score was 4. In the D group, there were no such scores. The authors concluded: “Inducing deep neuromuscular block (TOF count < 1) significantly improved surgical field scores and made it possible to completely prevent unacceptable surgical conditions.” However, several points need to be remembered. First, the preceding quote notwithstanding, group D included individuals with TOF counts of 1 and 2. Thus, an unknown number of their surgical field score observations were made during moderate block, not deep block as we define it. Second, the average field scores between the S and D groups did not differ statistically (1.3 ± 0.8 vs 1.1 ± 0.4; P > 0.10). Half of the scores of 4 occurred at TOF ratios >0.40 (a point when no fade can be detected by tactile evaluation) and only 1 such score was associated with a TOF count <4. Thus, it was only when the TOF count was 3 or more that the surgical field score was not excellent in the shallow block group. Although the authors refer to group S as having “shallow block,” that was not really the case. The average duration of surgery in that group was 74 ± 23 minutes. Within 25 minutes after rocuronium 0.45 mg, one would expect to see a TOF count of 4,23 and by 45 minutes, twitch height was probably 90% of control.24 Thus, for probably half the duration of surgery, the authors were comparing deep block with essentially no block at all. A more instructive study would have been a comparison of deep block with moderate block (TOF counts maintained at 1–3). The authors’ results are entirely compatible with the premise that a less intense block would have produced comparable results. A study by Staehr-Rye et al.6 raises a similar issue. The authors conclude, “Deep neuromuscular blockade was associated with surgical space conditions that were marginally better than with moderate muscle relaxation during low-pressure laparoscopic cholecystectomy.” However, at a point half way through the surgical procedure, T1 in the “moderate NMB” group was 47% of control (a TOF count of 4 with fade), and at the 75% time point, T1 was 89% of control (a TOF ratio >0.40).25 Thus, the authors were really comparing deep versus very shallow or minimal block for a considerable portion of the surgical procedure.
What is still missing from the peer-reviewed literature are studies of surgical operating conditions during deep versus moderate block at comparable levels of anesthesia and their respective effects on outcome and patient safety. However, a recent abstract by Barrio et al.8 is a positive move in that direction. They attempted to compare the effect of 2 different levels of rocuronium-induced neuromuscular blockade on abdominal compliance (work space) during the pneumoperitoneum in 28 ASA 1 to 2 women under propofol- remifentanil anesthesia. Depth of block was monitored by acceleromyography. The volume-pressure relationship was measured twice during pneumoperitoneum establishment before surgery, once at moderate block (1–3 TOF responses) and 1 time at profound block (PTC 1–3). After the insertion of the abdominal trocar, all CO2 introduced with the Verres needle was allowed to escape. Then, during insufflation at a flow of 1.5 L/min, the abdominal pressure was measured at delivered volumes of 1, 2, 3, and 4 liters during moderate block. After this first set of measurements, all CO2 was again allowed to escape and the same protocol was repeated once deep block was established. Volume-pressure data were fit by a linear least-square regression to calculate the compliance and a paired t test was used for comparison. They concluded that abdominal compliance was not increased by a significant amount when deep block was established when compared with moderate neuromuscular block.
Does Deep Neuromuscular Block Allow the Use of Lower Insufflation Pressures?
The list of undesirable physiologic consequences and potential side effects associated with pneumoperitoneum is lengthy and beyond the scope of this review.26,27 It has been hypothesized that high insufflation pressures may exacerbate many of these effects; therefore, efforts to keep abdominal pressures at a minimum consistent with satisfactory surgical exposure may be beneficial. Because neuromuscular blocking drugs can decrease muscle tone in lightly or inadequately anesthetized patients, the hypothesis that deep neuromuscular block may allow laparoscopic surgery to proceed with lower CO2 insufflation pressures is not unreasonable. However, we have not been able to find any clinical studies or data to substantiate this position. The surgical literature on the potential virtues of low versus high insufflation pressures that we reviewed generally provided little information on the respective studies’ anesthetic protocol and often none on the management of muscle relaxant administration.
The recent article by Staehr-Rye et al.6 demonstrates that there are limits to what even deep block can accomplish. The authors divided 48 patients scheduled for laparoscopic cholecystectomy under TIVA into 2 groups. In 25 patients, PTC was maintained at 0 to 1 responses. In 23 patients, only shallow to moderate block (as defined in the present manuscript) was maintained. The goal was to perform surgery at an inflation pressure of only 8 mm Hg. Although deep or extreme block allowed surgery to be completed with a 60% success rate (versus only 35% with less intense block), they still experienced a 40% failure rate. Even with intense block only 7 of 25 individuals (28%) were deemed to have optimal surgical space conditions during the entire procedure.
The above observations should not be interpreted to mean that muscle relaxants are never indicated. Certainly, they occupy an important place in the anesthesiologist’s armamentarium. However, they should not be used as a substitute for adequate depth of anesthesia. More often than not resumption of respiratory efforts under anesthesia in the presence of 1 to 2 twitches to TOF stimulation should be viewed as an indication that the depth of anesthesia is inadequate or that minute ventilation needs to be increased.
Does the Low Pressure Pneumoperitoneum Offer Advantages over a Standard Pressure Pneumoperitoneum?
A Cochrane review10 comparing the safety and effectiveness of low pressure (12 mm Hg) versus standard pressure (16 mm Hg) pneumoperitoneum in laparoscopic cholecystectomy (1092 patients from 21 trials) concluded that there was no difference between the 2 groups with respect to (1) surgical morbidity, (2) conversion to open cholecystectomy, (3) hemodynamic effects, (4) length of hospital stay, or (5) patient satisfaction. Operating time was about 2 minutes longer in the low pressure group than in the standard pressure group.
Oliguria is equally associated with low (10 mm Hg)28 or standard pressure (15 mm Hg)29 pneumoperitoneum, possibly due to reduction in renal cortical perfusion30 and increases in plasma antidiuretic hormone levels.31 Urinary output returned to normal levels after the release of pneumoperitoneum. Serum creatinine levels are not altered by pneumoperitoneum.28 There is no evidence to suggest that a low pressure (10 mm Hg) pneumoperitoneum32 would have less effect on venous hemodynamics than a standard pressure (13 to 15 mm Hg) pneumoperitoneum.33 There is no evidence that low or standard pressure pneumoperitoneum is associated with a lower incidence of gas embolization. Gas embolization was not seen during laparoscopic partial nephrectomy with insufflation pressures of 30 mm Hg in the porcine model.34
Factors implicated in pain after laparoscopic surgery35 include (1) distension-induced neurapraxia of the phrenic nerves, (2) acid intraperitoneal milieu during the operation, (3) residual intraabdominal gas after laparoscopy, (4) lack of humidity of the insufflated gas, (5) volume of the insufflated gas, (6) wound size, (7) presence of drains, and (8) sociocultural and individual factors. A clinically significant reduction in pain score is likely to result in shorter hospital stay, earlier return to normal activity and to work. However, the overall quality of evidence in this regard with respect to low pressure versus standard pressure pneumoperitoneum is equivocal.
Sandhu et al.36 reported that there was no significant difference in shoulder pain in 140 patients undergoing elective cholecystectomy randomized to low (7 mm Hg) or standard pressure (14 mm Hg) pneumoperitoneum. Similar findings were reported by others.37,38 In contrast, Bogani et al.39 studied fewer patients (n = 42) undergoing laparoscopic hysterectomy and reported that the incidence of shoulder tip pain was reduced with low (8 mm Hg) as compared with standard pressure (12 mm Hg) pneumoperitoneum at 1 and 3 hours (but not 24 hours) postoperatively. There were no between-group differences in abdominal pain noted. Sarli et al.,40 however, reported that shoulder tip pain scores after laparoscopic cholecystectomy were lower in patients randomized to low (9 mm Hg) rather than standard pressure (13 mm Hg) pneumoperitoneum at 12 and 24 hours, but not at 1, 3, 6, or 48 hours. Despite the higher incidence of shoulder pain, the analgesic requirements were not significantly different between low versus standard pressure groups in the aforementioned studies.39,40 In a double-blind randomized controlled study, the use of low pressure (8 mm Hg) versus standard pressure (12 mm Hg) pneumoperitoneum for laparoscopic cholecystectomy was associated with significantly less postoperative pain. However, the authors noted that the use of low-pressure pneumoperitoneum was often associated with a substantial reduction in visibility and in available working space.41 The authors hypothesized that these factors could negatively affect patient outcome in terms of increased difficulty in dissection and might result in increased risk of organ injury and operating time.
The Cochrane review10 also concluded that low pressure pneumoperitoneum appeared to be associated with a decrease in the incidence of shoulder pain after laparoscopic cholecystectomy; however, there was no difference in the postoperative analgesic requirements between low (12 mm Hg) and standard (16 mm Hg) pressure pneumoperitoneum. Because of the high risk of bias due to incomplete outcome data in 7 trials, it was not possible to make any conclusions about the safety of low pressure pneumoperitoneum in the Cochrane review. A very recent meta-analysis42 also concluded that cholecystectomies performed under low pressure pneumoperitoneum were associated with a reduction in postoperative pain scores and postoperative analgesic consumption compared with those performed under standard pressure pneumoperitoneum. Donatsky et al.43 in a systematic review of 12 papers investigating the effects of low versus high pressure pneumoperitoneum found that only half reported a reduction of shoulder pain after low pressure pneumoperitoneum. Residual CO2 may be a contributing factor for shoulder pain. Extended assisted ventilation with an open umbilical trocar valve for 5 minutes after laparoscopic hysterectomy was found to be an effective and safe method to reduce postoperative abdominal and shoulder pain levels in patients undergoing laparoscopic hysterectomy.44
An article by Warlé et al.45 demonstrates that the use of low insufflation pressures is not without potential drawbacks even in the presence of fairly deep neuromuscular block. The authors studied 20 kidney donors randomly assigned to either standard (14 mm Hg) or low (7 mm Hg) pressure laparoscopic nephrectomy. Anesthesia was maintained with IV propofol and remifentanil infusions and tracheal intubation was facilitated with rocuronium 0.80 mg/kg. In all subjects, if the TOF count exceeded 2 responses additional boluses of rocuronium 10 to 20 mg were administered. Surgery was successfully completed in both groups. The authors concluded “Our data show that low-pressure pneumoperitoneum during [laparoscopic nephrectomy] is feasible and may contribute to increased … donors’ comfort during the early postoperative phase.” However, skin-to-skin time in the low pressure group was significantly longer and more variable (147 ± 86 vs 111 ± 19 minutes, P = <0.01). Thus, low insufflation pressures apparently resulted in a less than optimal surgical field. Inferior operating conditions plus an increased duration of the procedure may be a recipe for an increased incidence of surgical complications. However, the study was probably inadequately powered (n = 10 per group) to address this issue.
REVERSAL OF DEEP BLOCK: CLINICAL IMPLICATIONS
As noted earlier, maintaining deep block until the termination of pneumoperitoneum is not a wise idea if antagonism with neostigmine is planned. Reversal of block with an acetylcholinesterase inhibitor at a time when no response to TOF stimulation can be elicited is slow and incomplete. When neostigmine 0.07 mg/kg is used to reverse rocuronium at a PTC of 1 to 2, the mean time to TOF ratio of 0.80 is 41 minutes (IQR = 26–56 minutes).46 Since the average time interval from the end of pneumoperitoneum to the last skin stitch is rarely more than 15 minutes and often considerably less,22 the potential for postoperative residual neuromuscular weakness in these circumstances is considerable. Thus, continuous maintenance of deep block during laparoscopic surgery should only be contemplated by clinicians who have access to sugammadex. However, even for those anesthesiologists fortunate enough to have this drug in their armamentarium, the obligatory addition of sugammadex to any anesthetic protocol based on the maintenance of deep block is not without associated caveats.
First, monitoring of neuromuscular function is still essential. Results from a study of Kotake et al.47 in which intraoperative monitoring of neuromuscular block was not used are instructive. The authors studied 117 patients who were given sugammadex (2.0 to 4.0 mg/kg based on clinical signs) to reverse rocuronium-induced block. After tracheal extubation, the TOF ratio was measured by acceleromyography. The frequency of TOF values <0.90 was 4.3% (95% confidence limits 1.7%–9.4%). However, these values were not normalized and thus probably overestimate the extent of recovery. The incidence of TOF ratios <1.0 was 46% (CI 37%–56%). Finally, antagonism at PTCs of 1 to 3 necessitates a dose of sugammadex of at least 4.0 mg/kg. Thus, maintenance of deep block has important economic repercussions. The acquisition price for sugammadex approximates $100 (€73) for a 200 mg single dose vial. Adequate dosage for a 70 kg patient at a PTC of 1 to 2 would require opening 2 vials, an expenditure of $200 (€146). Consequently, the cost of the routine application of deep block for laparoscopic surgery becomes an issue of importance. This is especially true because the actual benefits of deep block may be nonexistent.
Although the depth of neuromuscular block is easy enough to measure objectively, there has been a paucity of research into the subject of what level of block is associated with optimal conditions for surgery. Nevertheless, work by de Jong48,49 now almost 50 years-old deserves mention. He was able to demonstrate that when single twitch height (T1) at the hand as measured by EMG was in the range of 5% to 10% of control (equivalent to a TOF-count of 1) that 24 of 25 patients under halothane anesthesia (0.8%–1.3% inspired) were deemed to have excellent abdominal relaxation compared to only 4 of 25 when T1 was in the range of 51% to 75% (a TOF-count of 4 with fade). He concluded that “total [deep] neuromuscular block … is not a prerequisite for profound muscle relaxation, at least not in the adequately anesthetized patient.” A half century later these words are no less true.
On the basis of our review of the relevant literature, there is little or no evidence to suggest that using deep block (as opposed to block of moderate degree) for laparoscopic surgery will improve surgical operating conditions. Even if deep block is maintained, it does not necessarily follow that surgeons will automatically ask for lower inflation pressures. Current practice in the United States where sugammadex is not available and deep block is not routinely practiced for laparoscopic surgery suggests that there is no pressing need to change current clinical routines.
Name: Aaron F. Kopman, MD.
Contribution: This author helped write the manuscript.
Attestation: Aaron F. Kopman approved the final manuscript.
Name: Mohamed Naguib, MB, BCh, MSc, FCARCSI, MD.
Contribution: This author helped write the manuscript.
Attestation: Mohamed Naguib approved the final manuscript.
This manuscript was handled by: Ken B. Johnson, MD.
The authors thank Gretchen Hallerberg, MS, MSLS, AHIP, Director, Cleveland Clinic Alumni Library, for performing the literature search for this review.
a Available at: http://ispub.com/IJOS/7/2/7856. Accessed September 25, 2014.
b Available at: http://www.medscape.org/viewarticle/818024. Accessed September 25, 2014.
c Available at: http://www.medscape.org/viewarticle/814476. Accessed September 25, 2014.
d Available at: http://www.medscape.org/viewarticle/810637_transcript. Accessed September 25, 2014.
e Available at: http://publicationslist.org/data/jan.mulier/ref-357/Best%20practice%20in%20NMB%20management%209%2020121%20FARC%20ST%20Petersburg.pdf. Accessed September 25, 2014.
f Available at: http://publicationslist.org/data/jan.mulier/ref-355/deep%20block%20and%20enhanced%20surgical%20view%2022%206%202012%20EAES%20.pdf. Accessed September 25, 2014.
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