Opioid Analgesia and Side Effects
Opioids are an effective therapy for severe pain, and their use remains a mainstay
of treatment for pain control after surgery. However, use of opioid medication comes
with significant side effects including ileus, respiratory depression, and nausea
and vomiting.
Postoperative Ileus
Opioid therapy has been implicated in postoperative ileus and prolonged recovery of
bowel function in a dose-dependent manner. Ileus can be an especially devastating
complication in patients following colorectal surgery in whom return of bowel function
is a key part of recovery. In a 2011 study of patients undergoing colorectal surgery,
Barletta et al found that a total daily hydromorphone dose of greater than 2 mg/day
was significantly associated with development of ileus; this risk was almost 10-fold
higher in patients undergoing open procedures (2.6 vs. 22%).[1] Though absolute rates were lower, risk of ileus was also significantly increased
for patients undergoing laparoscopic colorectal surgery. In addition to increased
rates of ileus, patients with a total daily hydromorphone dose exceeding 2 mg per
day had a mean LOS that was 2 days longer for open cases and 1 day longer for laparoscopic
cases.
Studies examining opioid-sparing analgesic regimens have shown a decrease in postoperative
ileus. Lidocaine,[2] celecoxib,[3] magnesium,[4] and epidural analgesia[5] have all been shown to decrease opioid consumption and decrease risk of postoperative
ileus formation. Postoperative ileus contributes significantly to both cost and LOS
in patients undergoing colorectal surgery. An analysis by Asgeirsson et al showed
that hospital costs were doubled for patients who developed postoperative ileus,[6] and a retrospective study by Vather and Bissett showed an increase in average LOS
from 6 to 13 days.[7]
Postoperative Respiratory Depression
One of the most feared complications of narcotic use is opioid-induced respiratory
depression. While it is rare compared with postoperative ileus, opioid-induced respiratory
depression can have devastating consequences. An analysis of the Anesthesia Closed
Claims Project database from 1990 to 2009 by Lee et al found that 92 out of the 9,799
claims in the database had “possible, probable, or definite” opioid-induced respiratory
depression events. Of these 92 claims, 77% resulted in severe brain damage or death;
the vast majority of these events (88%) occurred within 24 hours of surgery.[8]
Postoperative Nausea and Vomiting
Postoperative opioid use is a significant risk factor for postoperative nausea and
vomiting (PONV). A 2012 meta-analysis by Apfel et al identified opioid use as one
of the four major anesthesia-related factors contributing to PONV.[9] PONV contributes to prolonged LOS in the postanesthesia care unit (PACU); in addition,
patients often rate PONV as worse than postoperative pain. Vomiting has been associated
with aspiration, wound dehiscence, esophageal rupture, and pneumothorax.[10]
Use of nonopioid analgesics has been shown to decrease PONV in patients undergoing
colorectal surgery. Lidocaine,[11] gabapentin,[12] ketamine,[13] pregabalin,[14] acetaminophen,[15] as well as regional[16] and neuraxial[5] techniques have all been shown to decrease the incidence of PONV in colorectal surgery
patients compared with opioid-based analgesia alone.
Systemic Therapy
Acetaminophen
Acetaminophen is a mainstay of adjuvant analgesic therapy. Acetaminophen has a favorable
safety profile and has been shown to decrease postoperative opioid consumption. A
2010 review by Maund et al examining 12 trials of postoperative acetaminophen versus
placebo showed a decrease in morphine consumption of 8.68 mg over the first 24 hours,
though they did not find any improvement in PONV or sedation.[20] Acetaminophen is particularly effective in synergy with nonsteroidal anti-inflammatory
drugs (NSAIDs). A 2010 systematic review of 21 studies including over 1,900 patients
undergoing a variety of surgical procedures demonstrated a mean reduction in visual
analog scale (VAS) for pain scores of 35% and a reduction in opioid analgesic dose
of 38.8% with a combination of acetaminophen and NSAIDs versus acetaminophen alone.
A similar benefit was seen with the combination versus NSAIDs alone, with reductions
of 37.7 and 31.3%, respectively.[21]
Acetaminophen is available in both oral and intravenous (IV) preparations, though
the latter is considerably more expensive. IV acetaminophen has become a popular adjunct
in place of oral or rectal acetaminophen given the ease of administration, particularly
in patients who cannot take oral medications. IV acetaminophen has been shown to have
both a faster time to peak cerebrospinal fluid (CSF) levels as well as a much larger
CSF concentration–area under the curve (AUC); however, direct comparison studies between
IV and oral acetaminophen have failed to show a benefit in terms of pain control or
opiate requirement in patients undergoing total joint arthroplasty[22] or oral surgery.[23] Direct comparison studies of IV acetaminophen versus oral or rectal routes for abdominal
surgery are lacking. Absorption of rectal acetaminophen has been shown to be quite
variable (though in a very small population) with peak CSF levels and AUC less than
half of those in the IV group and 50% less than the PO group.[24]
A 2013 meta-analysis by Apfel et al showed a decrease in PONV with use of IV acetaminophen.
In a review of 30 trials encompassing 2,300 patients, they found a relative risk (RR)
of 0.73 for nausea and 0.63 for vomiting leading to a number needed to treat (NNT)
of 12 and 14, respectively.[15] Decreased rates of PONV from the study of Apfel et al were maintained whether acetaminophen
was given intraoperatively, preoperatively, or postoperatively as a prophylactic measure;
however, it was not effective if given as a reactive measure after patients experienced
postoperative pain.
Lidocaine
Lidocaine is an amide local anesthetic and antiarrhythmic agent that blocks voltage-gated
sodium channels in neurons, preventing depolarization and inhibiting the propagation
of nerve impulses. Lidocaine infusions have been shown to be a safe and effective
adjunct for multimodal pain control. A Cochrane review from 2015 examining 45 trials
with 2,502 subjects found that lidocaine infusions significantly reduced postoperative
pain in the first 24 hours postoperatively.[2] This effect was most pronounced for laparoscopic abdominal surgery. In addition,
their review found that risk of postoperative ileus was significantly reduced by IV
lidocaine with an RR of 0.38. Lidocaine also reduced overall hospital LOS, opioid
requirements, and PONV.
Lidocaine may also have a beneficial effect on inflammatory mediators. A three-armed
study examining thoracic epidural analgesia, lidocaine, and placebo for patients undergoing
colon surgery not only found a significant decrease in opioid requirement and faster
return of bowel function but also showed significantly lower levels of inflammatory
cytokines interleukin 6 and interleukin 8 in patients who were given IV lidocaine
versus controls.[25]
Studies have not been able to demonstrate efficacy of lidocaine infusions for pain
beyond 24 hours. A meta-analysis by Vigneault et al in 2011 showed improved pain scores
and decreased morphine requirement at 6, 12, and 24 hours but failed to find any benefit
at later time points.[11] Grady et al in 2015 failed to find any benefit to lidocaine in addition to ketamine
or either drug alone versus placebo in terms of effect on 6-minute walk distance on
postoperative day (POD) 2 in abdominal hysterectomy patients.[26]
Optimal dosing of IV lidocaine is not clear. The standard dosing regimen in the trials
reviewed by the Cochrane group was 2 mg/kg/hour; however, significant heterogeneity
existed as far as duration of infusion, which ranged from intraoperative use only
up to 48 hours postoperatively.[2] Despite lack of clear data regarding optimal dosing regimen or timing, neither of
the two large meta-analyses referenced previously were able to find any significant
increase in adverse events as a result of perioperative IV lidocaine use.
Gabapentinoids
Gabapentin and pregabalin (collectively referred to as “gabapentinoids”) are antiepileptic
drugs which have traditionally been used as therapies for chronic and neuropathic
pain; however, their use in the acute pain arena has increased recently as data have
shown benefit for perioperative pain control and nausea. While gabapentinoids have
structural similarity to the inhibitory neurotransmitter γ-aminobutyric acid (GABA)
receptor, their mechanism of action is not well understood. A randomized controlled
trial (RCT) of 60 patients undergoing abdominal hysterectomy demonstrated a substantial
decrease in postoperative tramadol use in patients who received a single 1,200 mg
dose of gabapentin preoperatively. Tramadol use was 420 mg in the control group versus
270 mg in the intervention group.[27] Sen et al examined gabapentin or ketamine versus placebo in hysterectomy patients
and showed that patients who received gabapentin 1,200 mg orally preoperatively required
42% less opioid medication over the first 24 hours postoperatively, which was similar
to the group which received intraoperative ketamine (35% reduction). Patients who
received gabapentin (but not patients who received ketamine) also had a decrease in
self-reported pain scores in follow-up phone interviews at 1, 3, and 6 months postoperatively,
suggesting gabapentin may have a role in reducing development of chronic pain after
surgery.[28]
In addition, gabapentin may have a benefit on PONV. A recent meta-analysis of 1,605
patients showed a reduction in PONV for patients who received preoperative gabapentin.
The RR was 0.76 for postoperative nausea, 0.63 for postoperative vomiting, and 0.6
for use of rescue antiemetic medication for patients who received gabapentin versus
controls.[12]
Pregabalin has also been used as an adjunct for multimodal analgesic therapy. An RCT
examining pregabalin 150 mg every 8 hours starting preoperatively and continuing for
5 days postoperatively showed significantly lower morphine consumption at 4, 8, 24,
and 48 hours in the intervention group. No increase in sedation was noted; however,
there was an increase in dizziness, diplopia, and ataxia in patients receiving pregabalin.[14]
While individual studies have not shown an increase in side effects in patients receiving
gabapentin, a recent retrospective review by Cavalcante et al showed a significant
increase in respiratory depression in these patients.[29] They retrospectively reviewed 8,500 patients who underwent laparoscopic surgery
and found that gabapentin use was associated with an odds ratio (OR) of 1.47 for respiratory
depression during phase I recovery in the PACU. Patients who experienced respiratory
depression had a longer phase I recovery and an increased rate of admission to higher
level of care. These risks were increased for those receiving intrathecal opioids,
large doses of IV opioids, and older patients. Increasing age in particular was correlated
with increased risk, with a univariate analysis showing an OR of 1.43 for age between
60 and 69 years and OR of 1.86 for patients older than 70 years.[29]
Nonsteroidal Anti-inflammatory Drugs
The term NSAID describes a group of nonsteroidal drugs that have anti-inflammatory,
antipyretic, and analgesic effects. Most NSAIDs act via inhibition of cyclooxygenase-1
(COX-1) and cyclooxygenase-2 (COX-2), enzymes which play a role in the downstream
signaling of both inflammation and pain. NSAIDs are a mainstay of multimodal analgesic
therapy and have been shown to decrease postoperative opioid requirements as well
as PONV.[20] NSAIDs have also shown synergy with acetaminophen in terms of postoperative pain
relief. One review encompassing 21 studies with patients undergoing a variety of surgical
procedures showed a reduction in postoperative VAS scores of 35% and opioid dose of
38.8% for patients treated with a combination of NSAIDs and acetaminophen.[21] A 2004 RCT comparing patient-controlled analgesia (PCA) with morphine plus ketorolac
to morphine PCA alone for patients undergoing open colorectal surgery showed a significant
decrease in morphine consumption over the first 24 hours (66 vs. 80 mg) and a decrease
to return of bowel function of 0.6 days.[30]
COX-2 selective inhibitors (coxibs) have also been proposed as an analgesic adjunct
to achieve analgesia while reducing side effects associated with nonselective drugs.
An RCT of patients undergoing laparoscopic cholecystectomy showed that coxibs are
effective at reducing both pain and opioid requirements in this population[31]; in addition, patients in this study who received NSAID therapy had lower rates
of sedation, itchiness, urinary retention, and fatigue. However, another study examining
diclofenac or celecoxib versus placebo in patients undergoing open colorectal surgery
failed to show improvement in pain control or total narcotic used with either NSAID,
although patients receiving celecoxib had a 10-fold reduction in rates of postoperative
ileus (1 vs. 10%, p < 0.05).[32]
While NSAIDs have shown excellent analgesic effectiveness, studies have raised concerns
about an increased risk of anastomotic leak associated with NSAID use. One retrospective
study showed that use of nonselective NSAIDs was associated with a higher rate of
anastomotic leak as compared with controls (14.5 vs. 9.9% overall, OR: 2.13). Longer
duration of NSAID use correlated with higher risk of leak. However, no increased risk
of anastomotic leak was seen in patients taking COX-2 selective inhibitors.[33]
NMDA Receptor Antagonists
Ketamine, a N-methyl-D-aspartate (NMDA) receptor antagonist, is used for both pain
control and general anesthesia. It's minimal effects on respiratory drive and strong
analgesic effect have led to its popularity as an adjunct to opioid therapy for pain
control; however, concern about psychomimetic effects in conscious patients have limited
its role.
A meta-analysis by Laskowski et al in 2011 including 4,701 total patients undergoing
a variety of surgical procedures showed that ketamine decreased postoperative opioid
requirements, increased time to first rescue analgesic dose postoperatively, decreased
VAS scores, and decreased PONV. These effects were most pronounced for patients undergoing
abdominal and thoracic surgical procedures. However, after excluding trials where
ketamine was not efficacious, a significant increase in neuropsychiatric side effects
was noted (7.7 vs. 3%). Their study did not reveal a relevant dose-dependent effect
of ketamine and significant heterogeneity existed between studies with respect to
total ketamine dose and timing.[13]
An RCT by Zakine et al of patients undergoing major abdominal surgery compared analgesia
in patients given a single dose of 0.5 mg/kg ketamine intraoperatively, 0.5 mg/kg
intraoperative ketamine plus 2 μg/kg/min postoperative infusion, and controls.[34] They found an almost 50% reduction in morphine requirement in the perioperative
group (27 vs. 48 mg morphine equivalent dose [MED]) versus intraoperative or control
groups. VAS scores were also lower in both the intraoperative and perioperative groups
at 4, 24, and 48 hours versus controls. They reported no neuropsychiatric side effects
in any of their three groups.[34]
Ketamine may also decrease perioperative inflammation. A 2012 systematic review examined
11 studies looking at pro- and anti-inflammatory markers (interleukin-6 [IL-6] and
IL-10, respectively) postoperatively in patients who did and did not receive ketamine
as part of general anesthesia. They found a significant decrease in the proinflammatory
IL-6 levels and a correlated increase in anti-inflammatory IL-10 levels; these effects
seemed to be most pronounced with patients undergoing cardiopulmonary bypass. Their
analysis did not detect a dose-dependent effect but had a high degree of heterogeneity
in terms of dosing between studies.[35]
While ketamine has been proposed as a possible adjunct to reduce chronic postsurgical
pain, there remains disagreement in the literature about its effectiveness for this
indication. One study did demonstrate a reduction in chronic postoperative pain in
patients undergoing total hip arthroplasty[36]; however, a study on patients undergoing abdominal hysterectomy showed improved
pain scores immediately postoperatively but failed to find any long-term benefit to
pain scores at 1, 3, or 6 months between ketamine and placebo.[28]
Magnesium has also been raised by some as a possible adjunct due to its antagonism
at the NMDA receptor. Early reviews failed to find any evidence of benefit for magnesium
administration[37]; however, a small recent RCT examining magnesium versus placebo in open abdominal
surgery showed a decrease in postoperative morphine consumption as well as a remarkable
decrease in postoperative ileus, with average ileus duration of 2.3 days in the magnesium
group versus 4.2 days in the control group.[4]
Dexamethasone
The corticosteroid dexamethasone has well-established effects on reduction of PONV,[10] but its role as an analgesic has been less well established. A meta-analysis from
Waldron et al in 2013 showed that a single perioperative dose of dexamethasone reduced
both VAS scores and morphine consumption over the first 24 hours after surgery in
patients who had open abdominal procedures; however, the overall effects were relatively
modest with a mean difference in morphine consumption of −2.33 mg (∼10% of total morphine
consumption in the intervention group). Interestingly, the improvement in pain scores
was preserved when only patients undergoing laparoscopic surgery were considered but
the difference in morphine consumption was not.[38] The most common dose of dexamethasone given in the studies analyzed was 8 mg, though
doses ranged from 1.25 to 20 mg; no difference was observed when pooled data were
compared between 4 to 5 mg and 8 to 10 mg doses.
Dexamethasone can have a potent immunosuppressive effect which has led to concerns
about an increase in wound infection rates in patients who receive it intraoperatively.
A retrospective analysis by Bolac et al on women undergoing laparotomies for endometrial
cancer failed to show any difference in wound complication rates among patients who
received intraoperative dexamethasone.[39] This was corroborated by a 2015 RCT in patients undergoing colorectal surgery where
no difference was observed between patients who received 4 mg of dexamethasone versus
placebo.[40]
Dexamethasone has been shown to potentially raise blood glucose levels in the first
24 hours postoperatively, though the clinical relevance of this finding is unclear
as it has not been correlated to an increase in side effects.[38]
Central α-2 Agonists
Central α-2 agonists decrease postsynaptic release of norepinephrine and are thought
to play a role in central pain modulation. Clonidine and, more recently, dexmedetomidine
both have been explored as possible adjunctive medications for postoperative pain
control. A randomized trial of patients undergoing laparoscopic bariatric surgery
showed a decrease in rescue narcotic required in the PACU as well as a decrease in
time to PACU discharge for patients who received intraoperative dexmedetomidine as
compared with controls; however, they failed to show any change in 24-hour opioid
requirements or other complications.[41]
A meta-analysis by Blaudszun et al examined the impact of both dexmedetomidine and
clonidine on postoperative pain and morphine requirements. Their analysis found that
both clonidine and dexmedetomidine decreased morphine requirements at 12 and 24 hours
postoperatively. Interestingly, while clonidine's effect was most pronounced within
the first 12 hours (mean morphine use decreased by 9.8 mg at 12 hours vs. 4.1 mg at
24 hours), the effect of dexmedetomidine was more pronounced over time—decreased by
6 mg at 12 hours and by 14.5 mg at 24 hours. Both clonidine and dexmedetomidine were
shown to decrease PONV in their analysis (NNT of 8.9 and 9.3, respectively). However,
cardiovascular side effects were common: patients who received dexmedetomidine had
significantly higher rates of bradycardia (number needed to harm [NNH]: 3.1) and patients
who received clonidine had higher rates of intra- and postoperative hypotension (NNH:
9 and 20).[42]
Esmolol
Intraoperative β-blockade has gained interest as a therapy to improve both hemodynamic
response to surgical stimuli and postoperative pain control. A 2007 RCT examined esmolol
infusions versus fentanyl boluses or remifentanil infusions for patients undergoing
laparoscopic cholecystectomy. Rescue fentanyl administration in the PACU was significantly
decreased in patients who received intraoperative esmolol, with an average of 91 versus
168 µg in the control group and 237 µg in the remifentanil group. Patients who received
esmolol infusions also met discharge criteria from the PACU and left the hospital
faster than patients who received remifentanil.[43]
A 2004 RCT by Chia et al examining intraoperative esmolol in patients undergoing open
hysterectomy also showed a significant improvement in opioid requirement. Patients
who received intraoperative esmolol consumed 37.3 mg of morphine over PODs 1 to 3
versus 54.7 mg for patients in the control group.[44]
Regional Anesthetic Techniques
Thoracic Epidural Analgesia
Thoracic epidural analgesia has been used as an effective analgesic technique for
both open and laparoscopic abdominal surgery, and it is identified as a key part of
postoperative pain control in colorectal surgery in the ERAS group recommendations.[19]
Epidural analgesia provides excellent pain control while minimizing narcotic use and
promoting return of bowel function. Block et al showed in a 2004 meta-analysis that
epidural analgesia has improved postoperative VAS scores versus parenteral opioids
for a variety of surgical procedures, including abdominal surgery.[45] A subsequent meta-analysis examining epidural analgesia solely in patients who underwent
colorectal surgery showed improved VAS scores at 24 and 48 hours as well as decreased
opioid use. In addition, this analysis by Marret et al showed shortened duration of
postoperative ileus for patients who received epidurals by an average of 36 hours.[46] A 2016 Cochrane review confirmed improved pain control and faster return to bowel
function in patients who received epidural analgesia for colorectal surgery.[47]
Even excluding postoperative ileus, epidural analgesia may have advantageous effects
on postoperative morbidity and mortality. A 2014 meta-analysis showed that epidural
analgesia significantly reduced postoperative mortality, though this finding did not
reach significance when cardiac surgical trials were excluded. In addition, rates
of postoperative atrial fibrillation, supraventricular tachycardia, respiratory depression,
atelectasis, pneumonia, ileus, and PONV were significantly decreased with epidural
analgesia versus controls.[5]
Disagreement exists on the impact of epidural analgesia on hospital LOS. Studies have
shown improvement in LOS for open colorectal surgery in patients who receive epidurals[48]; however, other analyses have failed to find any benefit.[46] A recent Cochrane meta-analysis showed decreased LOS for patients who underwent
open but not laparoscopic surgery.[47] Other studies have shown either no difference in LOS[49] or even increased LOS[50] in patients undergoing laparoscopic colorectal surgery who received epidurals.
The role of epidural analgesia in patients undergoing laparoscopic surgery is less
well defined than in those undergoing open procedures. A 2013 meta-analysis by Khan
et al showed improved postoperative pain control in patients who received epidurals
for laparoscopic colorectal surgery; however, they found no impact on overall LOS.[49] Other studies have failed to show any benefit for postoperative recovery of bowel
function or complications from epidural analgesia in these patients.[50]
[51]
Serious complications from epidural analgesia such as hematoma and abscess are feared
but extremely rare, with no events reported in any of the meta-analyses examining
epidural versus PCA analgesia. However, less morbid complications are more common.
Hypotension has been shown as a consequence of epidural analgesia in many but not
all studies.[45]
[46]
[49] Both pruritus and urinary retention are known complications of epidural analgesia[5]; the latter results in many institutions leaving urinary catheters in place while
patients are receiving epidural analgesia, which has been attributed to an increased
incidence of urinary tract infections in these patients.[51]
Intrathecal Morphine
Intrathecal opioid administration has been suggested as a possible alternative to
epidural analgesia for postoperative pain control. Intrathecal injection results in
less pain during placement and requires less time than epidural placement.[52] Intrathecal injection examining local anesthetic plus morphine versus local anesthetic
alone showed a decrease in parenteral opioid requirements at 24 hours (7 vs. 25 mg)
and 48 hours (11.5 vs. 31 mg) while improving pain control in patients undergoing
laparoscopic colorectal surgery.[53] A subsequent study by Wongyingsinn et al on patients undergoing laparoscopic colorectal
surgery with an ERAS protocol confirmed an improvement in postoperative pain control
and opioid requirement but failed to show a benefit in postoperative ileus or hospital
LOS.[54]
An RCT of intrathecal morphine versus epidural analgesia in laparoscopic colorectal
surgery showed improved postoperative pain control, early return to mobility, and
shorter hospital LOS for the intrathecal morphine group.[55] In addition, patients in the intrathecal morphine group had lower rates of insertion
failure, hypotension, and sedation versus patients receiving epidural analgesia.
In contrast, a 2014 RCT examining intrathecal morphine versus epidural analgesia for
open gastrectomy actually showed worse outcomes in the intrathecal group, suggesting
that intrathecal morphine may be inadequate for postoperative pain control for open
cases.[52] In this study, patients who received intrathecal morphine consumed significantly
more fentanyl, had higher rates of postoperative ileus, and had longer latency to
ambulation than patients who received epidural analgesia.
Transversus Abdominis Plane Blocks
The transversus abdominis plane (TAP) block is an analgesic technique which delivers
local anesthetic to the plane between the internal oblique and transversus abdominis
muscles to anesthetize the thoracolumbar nerves delivering sensation to the anterior
abdominal wall. TAP blocks were originally described based on a landmark-guided technique
but have evolved to predominantly ultrasound-guided,[56] though meta-analyses have failed to demonstrate superiority of ultrasound over landmark
guidance.[57]
A 2010 Cochrane review found evidence that TAP blocks for abdominal surgery reduced
morphine requirements over the first 48 hours postoperatively as well as increased
the latency to request for first rescue analgesic dose; however, their analysis showed
no evidence of effect on sedation or PONV.[56] These data were based on several moderately sized studies with significant heterogeneity
between them. A more recent meta-analysis by Brogi et al, however, found that while
TAP blocks were effective for a variety of gynecologic and urologic procedures, when
only the data for major abdominal surgery (excluding appendectomy) were analyzed there
was no significant reduction in pain scores or morphine requirements over the first
24 hours.[57] Interestingly, while their analysis had insufficient numbers to examine TAP blocks
versus epidural analgesia, a subgroup analysis of TAP blocks versus intrathecal morphine
in women undergoing cesarean sections showed significantly improved pain scores and
morphine consumption in the intrathecal morphine group versus the TAP group.[57]
TAP blocks have also been examined for possible analgesic benefit in laparoscopic
surgery. A 2013 RCT by Walter et al examining TAP blocks for laparoscopic colorectal
surgery showed a decrease in 24-hour morphine requirement of 20 mg (60 vs. 40 mg,
p < 0.05), though they did not show any significant difference in VAS scores, LOS,
or morbidity in the intervention group.[58] Interestingly, patients who received TAP blocks in this study actually had an increased
incidence of PONV, though the mechanism behind this is unclear and it has not been
seen in prior studies.[16]
Data for TAP blocks in laparoscopic colorectal surgery remains quite mixed, with several
recent trials failing to show any benefit,[59]
[60] while a recent RCT examining the combination of wound infiltration and TAP block
versus infiltration alone showed benefit in terms of both opioid sparing and reduction
in postoperative nausea and ileus.[61] Further data are necessary to clarify which patient populations may benefit.
