Introduction

Neuroendocrine tumors (NETs) are a rare malignancy arising throughout the aerodigestive tract. These tumors have recently been recognized to be increasing in incidence, reaching 6.98 per 100,000 per year. The term carcinoid was first coined in 1907 as “karzinoide” and describes a multitude of primary locations of NETs. These tumors have the unique property of production of an array of neurotransmitters such as serotonin and histamine, peptides such as those in the kinin-kallikrein system, and catecholamines, among others.

Carcinoid syndrome is a constellation of symptoms (classically flushing, diarrhea, and bronchospasm) thought to be mediated by the various hormones secreted by NETs. Carcinoid syndrome is present in 19% of patients with NETs of any primary tumor type, and 40% of those with duodenal, jejunal, or ileal primary NETs. The mechanism of carcinoid syndrome is incompletely understood, and in spite of this incomplete understanding, carcinoid crisis is hypothesized to be an extension of carcinoid syndrome. Carcinoid crisis has no universal accepted definition, but is frequently defined as a life-threatening form of carcinoid syndrome with marked hemodynamic instability. Historically, carcinoid crisis has also been hypothesized to be caused by a massive release of hormones as described above due to their vasoactive effects.

The literature on carcinoid crisis is very limited given the rarity of these tumors and the spontaneity of crisis occurrence. To date, only seven single-center retrospective reviews and one prospective single-center review have been published. This leaves clinicians with the challenge of accepting expert opinion. More recently, studies have begun to challenge the paradigm that carcinoid crisis is caused by a massive release of hormones as an extension of carcinoid syndrome, which will be discussed within the chapter. Given the variety of origins of NETs and the differences in intraabdominal and cardiac operations, this chapter will not cover cardiac operations but will attempt to focus specifically on abdominal operations, though this may be challenging in the setting of small retrospective studies being the only available literature.

As expected from the lack of consensus definition and the recent questioning of the paradigm of carcinoid crisis, controversy exists over the management of carcinoid crisis. Two areas of disagreement exist: first, the use of somatostatin analogues (i.e., octreotide) as prophylaxis and treatment, and second, the use of β-adrenergic agonists. Much has changed about our understanding of carcinoid crisis in recent years and much remains to be learned about this unique endocrine emergency’s pathophysiology and treatment strategies.

Definition

Carcinoid syndrome was first described in 1954 in a case series of 16 patients. In this series, the principal findings were described as a malignant carcinoid tumor with metastases to the liver having dependent edema, diarrhea, borborygmi, abdominal pain, generalized widening of the small vessels of the skin, peculiar patchy flushing, right-sided heart valvular disease, and attacks of bronchial asthma. In this work, serotonin is attributed as the major mediator for many of these symptoms. Crisis was first described in a 1964 case report of a patient with peripheral vascular collapse, leading to the beginnings of the definition as “profound hypotension in patients with the malignant carcinoid syndrome has been noted during anesthesia, palpation of the tumor at operation, or spontaneous bouts of flushing.” The cause of the crisis was unknown and was postulated once again to be due to serotonin, as the patient had no response to norepinephrine and did respond to cyproheptadine, an antiserotonergic agent.

Currently, there is no strict definition of carcinoid crisis. Most studies define carcinoid crisis as an acute change with profound, life-threatening hemodynamic instability, though the degree of symptomatology and duration of crisis varies. Consensus guidelines, such as those published by the North American Neuroendocrine Tumor Society (NANETS) in 2017, defined crisis as “the sudden onset of hemodynamic instability that can occur during anesthesia, operations, or other invasive procedures.” There have been seven retrospective reviews and one prospective study of patients with NETs undergoing operation; the definitions of carcinoid crisis by each study are summarized in Table 17.1 . Not having an accepted definition of carcinoid crisis has created two major challenges. First, studies on carcinoid crisis are difficult to compare directly, as different authors define carcinoid crisis in different ways. Second, there is a wealth of individual case reports on carcinoid crisis, but these must be interpreted with caution, as no accepted definition of crisis exists.

In addition, defining carcinoid crisis has been challenged by its unknown pathophysiology. Historically, carcinoid crisis was thought of as an extreme of carcinoid syndrome with a massive release of vasoactive substances, and some authors still define carcinoid crisis as an extreme of carcinoid syndrome. More recently, other studies have begun to systemically disprove this theory with the fact that octreotide (a somatostatin analogue that causes inhibition of hormonal synthesis and release) does not help prevent or treat carcinoid crisis. ^, In addition, a prospective trial from 2019, which collected intraoperative levels of hormones and data on pulmonary vasculature via a pulmonary artery catheter and cardiac function via a transesophageal echocardiogram, found that carcinoid crisis is most consistent with distributive shock, and intraoperative hormone levels were not elevated with crisis.

There is also an ethical consideration in defining carcinoid crisis—it is not ethical to subject a patient to 10 minutes of sustained, life-threatening hemodynamic instability in the interest of fulfilling a definition of carcinoid crisis. In addition, a study published in 2013 found higher rates of postoperative complications occur in those with intraoperative crises, and a follow-up study in 2016 demonstrated that those who have hypotension in excess of 10 minutes are more likely to have postoperative complications, and those with prompt treatment of crisis are less likely to have carcinoid crisis. We implore specialty societies to define carcinoid crisis with a clinically relevant definition that allows for patient safety while also allowing studies on the incidence and risk factors, prevention, and treatment of carcinoid crisis to occur.

Incidence

A literature search on carcinoid crises reveals a surprising number of case reports of carcinoid crises during anesthesia and operations, physical examinations, or diagnostic procedures or examinations (such as echocardiograms, mammograms, biopsies, or endoscopic procedures). As these case reports often do not include any definition of carcinoid crisis and no denominator is given for the number for patients undergoing these events, the incidence cannot be determined from these. In addition, as there is no accepted definition of carcinoid crisis, individual case reports must be interpreted with caution as being true carcinoid crises.

A summary of incidence rates of carcinoid crisis found in retrospective and prospective studies cited in the literature are summarized in Table 17.1 . These vary between 0% and 35% but are difficult to generalize, as these studies classify things such as intraoperative complications (which in definition appear similar to carcinoid crisis), hemodynamic instability (in definition appears as a surrogate for intraoperative complication or crisis), intraoperative carcinoid syndrome (as reported by a single study), or carcinoid crisis (defined differently by each study).

Risk Factors

Historically, carcinoid crisis was considered an extension of carcinoid syndrome, so logically patients with functional tumors (i.e., patients who experience carcinoid syndrome) would be at risk of carcinoid crisis. In addition, it has long been thought that patients with hepatic metastases, metastases or primary tumors in locations that drain systemically, or high tumor burden were considered at risk. There are several hypotheses about the pathogenesis of carcinoid syndrome and crisis. First, tumors with hepatic metastases are hypothesized to bypass liver enzyme breakdown, leading to higher risk of carcinoid syndrome and crisis. Second, tumors that develop from or spread to sites with systemic drainage (i.e., lungs or ovaries) are hypothesized to bypass portal circulation and breakdown, thus leading to higher risk of carcinoid syndrome and crisis. Third, it is hypothesized that tumor burden can become so large that enzymatic breakdown systems are overwhelmed, leading to higher risk of carcinoid syndrome and crisis. However, cases of carcinoid crisis have been documented in patients without functional tumors, systemically drained metastases or primary tumors, or hepatic metastases. ^,

Regarding the hypothesis that functional tumors are more likely to have carcinoid crisis, several investigators have looked at the correlation between 24-hour levels of urinary 5-hydroxyindoleacetic acid (5-HIAA), a breakdown product of serotonin, and rates of carcinoid crisis. In a series of 119 patients in 2001, it was found that most patients (94%) had a high preoperative 24-hour level of urinary 5-HIAA, and the median 5-HIAA was significantly higher in those who experienced complications. In contrast, a series of 97 cases found 21% of patients with functioning tumors had intraoperative complications compared to 28% of patients with nonfunctioning tumors, although the authors did not define what made the diagnosis of functional versus nonfunctional tumors and no serum chromogranin A (CgA) or 5-HIAA levels were reported. A later series of 127 patients who underwent 150 operations found that neither preoperative CgA nor 5-HIAA levels correlated with intraoperative crisis. In a series of 75 patients published in 2019, there were no clinicopathologic characteristics that was associated with the development of carcinoid crisis or hemodynamic instability, including preprocedure 24-hour level of urinary 5-HIAA levels greater than twice the upper limit of normal. With only one author documenting a high 5-HIAA level as a significant risk, others documenting no correlation, ^, and one inconclusive, review articles are mixed in the recommendation to include a high 5-HIAA level as a risk factor for carcinoid crisis. ^, Regarding hepatic metastases as a risk factor for carcinoid crisis, this was confirmed in two studies. ^, The theory of systemic drainage primary tumors or metastatic tumors has not been reported in these studies as a risk factor. Interestingly, the single prospective study found only preincisional serotonin levels to be related to carcinoid crisis.

With the only prospective study showing preincisional serotonin level to correlate with carcinoid crisis, the variability in the risk factors for carcinoid crisis as described above, and the observation that crisis occurred even in patients without the associated risk factors of hepatic metastases or carcinoid syndrome, ^, we are left to conclude that all patients with NETs are at risk for developing crisis.

Many of these articles were written on patients undergoing large operations under general anesthesia, but in light of case reports of carcinoid crisis with smaller procedures for which patients may not be under sedation at all (i.e., percutaneous biopsy or mammogram), questions remain regarding when these patients are at risk and when to provide prophylactic treatment for carcinoid crisis. A review article published in 2014 identified 28 articles with 53 unique patients identified who had carcinoid crisis. In this review, triggering factors included anesthesia/operation in 63.5%, interventional therapy in 11.5%, radionuclide therapy in 9.6%, physical examination in 7.7%, medication in 3.8%, biopsy in 2%, and spontaneous in 2%.

With an inability to know who is most at risk or when carcinoid crisis will occur, and given its obvious life-threatening possibility, clinicians are attempting to develop appropriate preventative and therapeutic measures for these patients. There have been several review articles published on the anesthetic management of patients with neuroendocrine tumors, ^{, ,} but we caution against accepting these as dogma when they are expert review and published before many of the articles cited previously were published. The 2017 NANETS guidelines state, “physicians should be prepared to manage carcinoid crisis events in patients with SBNETs [small bowel neuroendocrine tumors] who undergo operations or invasive procedures,” and give no firm criteria for risk factors.

Current Understanding of Pathophysiology

The mechanism of carcinoid syndrome and crisis is incompletely understood, and several theories exist regarding their pathogenesis as discussed in the “Risk Factors” section. Many theories of the mechanism of carcinoid crisis are based in biochemical studies in the mid-1950s, starting with isolation of serotonin from carcinoid tumors in 1953 and increased levels of histamine in the blood of a patient with a carcinoid tumor in 1956. A later publication in 1964 that reported a case of carcinoid crisis being successfully treated with cyproheptadine (an antiserotonin and antihistamine compound) while having no response to norepinephrine supported this theory. Subsequent studies began to propose that serotonin may not be the sole mediator or a mediator at all for the following reasons. First, a breakdown product of serotonin, 24-hour urinary 5-HIAA, was not elevated in all patients with carcinoid syndrome. Second, it became apparent that other hormones and peptides were produced by carcinoid tumors. The first of these was published in 1966 when bradykinin was demonstrated to be high in patients with carcinoid syndrome. This finding was echoed in a publication from 2008, which found that tachykinin was independently correlated with carcinoid diarrhea. In 1980, another publication showed substantial amounts of dopamine and norepinephrine were present in the mesenteric mass of an ileal carcinoid tumor. This finding was confirmed in a 1994 publication that demonstrated 38% of patients with midgut carcinoids had elevated urinary dopamine metabolites (3-methoxytyramine) and 33% of patients with midgut NETs had elevated norepinephrine and epinephrine urinary metabolites (normetanephrine and metanephrine). Each of these products, upon being isolated in patients with NETs, have been postulated to have a different role in the symptomatology of carcinoid syndrome. Additionally, each tumor likely has its own unique secretory pattern, making every patient’s experience of carcinoid syndrome different.

The theory that these hormones are the cause of carcinoid crisis should be questioned because, first only one of the published seven retrospective reviews have shown 5-HIAA levels are related. In addition, the single prospective study of 46 patients with liver metastases from NETs undergoing operation published in 2019 had fascinating results from their hormone assays. The investigators measured plasma levels of serotonin, histamine, kallikrein, and bradykinin at preincision, mid-crisis, and closing. The authors report that only preincision serotonin levels were significantly elevated for those who had a carcinoid crisis versus those who did not. Remarkably, the other measured hormones did not have any other significant increase in patients with carcinoid crises. The investigators concluded that without an increase in these measured hormones during a crisis, these hormones cannot be the direct cause for triggering a crisis.

These studies are the basis on which we question the paradigm of carcinoid crisis being a massive release of hormones in functional tumors only. Acceptance of this paradigm would limit prophylaxis and treatment to only those with functional tumors and crises have been observed in those without the classically cited risk factors of carcinoid syndrome and hepatic metastases. ^, In addition, specialty societies recommend being ready to treat crisis in all NET patients. These modern-era studies will need to be validated in future studies, although this does have several challenges: the rarity of NETs and spontaneity of carcinoid crises making it difficult for a single center to gather enough cases to power a study; the ethics of allowing a crisis to proceed for 10 minutes in order to fulfill a definition; and the life-threatening hemodynamic instability that mandates urgent treatment.

Treatment With Somatostatin Analogues (Octreotide)

The paradigm that carcinoid crisis was precipitated by a massive release of hormones was perpetuated by case reports showing the effectiveness of somatostatin (a 14-amino acid inhibitory hormone) for both carcinoid syndrome and carcinoid crisis. Carcinoid tumors are known to express somatostatin receptors, which are G-protein–coupled receptors with five subtypes. The mechanism of somatostatin is a reduction of hormone synthesis (see previous section on pathophysiology—these tumors have been demonstrated to secrete an array of serotonin, histamine, tachykinins, dopamine, and catecholamines) and inhibition of the release of these hormones. ^, As somatostatin has very rapid breakdown in circulation and would have to be given as a continuous infusion to be effective, a somatostatin analogue (i.e., octreotide) was developed later, which had a longer duration of action, allowing for bolus doses intravenously (IV) or subcutaneously (SQ). Octreotide is known to bind to somatostatin receptor subtypes 2, 3, and 5 with high, low, and moderate affinity, causing the previously described effects—inhibition of hormone synthesis and release. Somatostatin analogues were used to treat patients with carcinoid syndrome, and it has been shown that patients treated with octreotide had decreased 5-HIAA levels, proving its inhibition of serotonin release. In addition, somatostatin and octreotide also cause reduced splanchnic blood flow via visceral vasoconstriction.

Regarding carcinoid syndrome and crisis treatment, publications in 1978 began to demonstrate inhibition of carcinoid flush by somatostatin and the use of somatostatin for the treatment of intraoperative hypotension, though the term “carcinoid crisis” was not used by the authors. Thus the credit for the first use of a somatostatin analogue for the treatment of carcinoid crisis is generally given to Larry Kvols who published a letter to the editor in 1985 with a case report of a patient with an intraoperative carcinoid crisis that resolved with a somatostatin analogue, with a full publication following in 1987. ^, In addition to its treatment of carcinoid crisis, publications in the late 1980s also began to report the use of pretreatment with somatostatin analogues for its prevention. ^, Because of these case reports, many anesthesia reviews recommend the use of octreotide to prevent and treat carcinoid crises. ^{, ,} Recommendations on preoperative and intraoperative regimen dosage, timing/duration, and routes (IV or SQ) vary widely between these sources. In more recent years several retrospective reviews and one prospective study were published, which comment on the use of octreotide prophylactically or therapeutically for carcinoid crisis, which lend a higher level of evidence than the previously discussed individual case reports and review articles.

The first of these studies was a retrospective review published by Kinney et al. in 2001. In this review of 119 patients with metastatic carcinoids undergoing abdominal operation, 15 (12.6%) had perioperative complications (see Table 17.1 for definition of complication) or death. The overall rate of intraoperative complications was 7%, with events occurring in seven (10%) of 67 patients who received no octreotide preoperatively or intraoperatively and one (17%) of six patients who received only a preoperative dose (median dose 300 µg IV or SQ, range 50 to 1000 μg). In the 45 patients who received intraoperative octreotide (median dose 350 μg, range 30 to 4000 μg), either alone or with a preoperative dose, no intraoperative complications occurred. In the results section, it is stated the authors have “no evidence that preoperative administration of octreotide is associated with a reduced frequency of intraoperative complications or that intraoperative administration is associated with a reduced frequency of postoperative complications.” However, their conclusion hints heavily that “no intraoperative complications occurred in those who received octreotide intraoperatively,” and many subsequent anesthesia review articles cite this paper as a reason to give intraoperative octreotide. ^{, ,}

As this article was unable to provide specific recommendations on optimal dosage, a systematic review was published in 2013 of 18 articles on the dosage of octreotide. The authors found that doses of 25 to 500 μg given IV effectively managed carcinoid crises. These authors were unable to describe any secondary outcomes of deaths, length of stay in an intensive care unit or the hospital. However, they note that a small sample size, the inconsistent use of the term “carcinoid crisis,” and the paucity of outcomes were limitations to their study.

Massimino et al. published a retrospective review in 2013 of 97 cases of patients with carcinoid tumors undergoing abdominal operations in which 90% were given preoperative prophylactic octreotide (median dose 500 μg, range 100 to 1100 μg) and 70% of patients were on outpatient octreotide. Five of the 97 (5%) had life-threatening carcinoid crisis and 23 (24%) had an intraoperative complication (see Table 17.1 for definitions). In this series, it was found that significant intraoperative complications occur frequently in patients with hepatic metastases regardless of the presence of carcinoid syndrome, even though events were observed in those without hepatic metastases. The authors found no correlation between long-acting octreotide preoperatively or single-dose prophylactic octreotide with intraoperative complications. Fifty-six patients also received intraoperative boluses of octreotide (250 to 500 μg), and 46% of these patients still had a subsequent event. The authors of this study concluded that neither preoperative octreotide (whether long-acting dosage or prophylactic dosage as described earlier) nor intraoperative boluses of octreotide are sufficient to prevent carcinoid crises.

Further support that octreotide is not an effective prophylaxis for carcinoid crisis was demonstrated in a publication of a metaanalysis of 28 articles with 53 unique patients identified who had carcinoid crises, which was published in 2014. This group found the overall pooled risk of perioperative carcinoid crisis was similar despite the prophylactic administration of octreotide. These authors concluded that the prophylactic use of somatostatin analogues was not effective in the prevention of carcinoid crisis.

A third retrospective review was published in 2016 by Woltering et al. of 150 patients with small bowel NETs who underwent 179 cytoreductive operations. Their standard practice is a 500-μg/hour infusion preoperatively, intraoperatively, and postoperatively. They identified six cases (3.4%) who experienced a carcinoid crisis (see Table 17.1 for authors’ definition of crisis for this particular study). Given their low rates of carcinoid crisis, the authors recommend clinicians give a high-dose continuous infusion of octreotide during surgical intervention, commenting specifically that a bolus dose without a continuous infusion will defeat the purpose of the bolus dose because of its short half-life.

In direct contradiction to the Woltering study is a fourth retrospective review published by Condron et al. in 2016 of 127 patients with carcinoid tumors who underwent 150 operations. All patients received a 500-μg/hour continuous infusion, but carcinoid crisis (see definition of crisis for this study in Table 17.1 ) occurred in 30% of cases. In addition, they did find that with an earlier initiation of treatment for hypotension, the carcinoid crises events were no longer associated with complications, except when hypotension persisted for more than 10 minutes. The authors concluded that intraoperative continuous infusions of octreotide do not prevent crisis but prompt treatment was important to reduce postoperative complications. These two studies were not commented upon by the opposing author, as one was accepted but not published for a year, and during this time the other study was under review.

To continue to attempt to answer the question of octreotide prophylaxis and treatment for carcinoid crisis, a fifth retrospective review published in 2018 by Kinney et al. included 169 patients with metastatic NETs who underwent 196 procedures. Of these 169 patients, 77% received prophylactic octreotide SQ and 23% were given additional intraoperative octreotide. No episodes of carcinoid crisis were observed (see Table 17.1 for definition according to this author). As no crises were observed, these authors are unable to comment on octreotide’s efficacy.

A sixth retrospective review was published by Fouché et al. in 2018 of 81 patients undergoing operation for small bowel NETs. The perioperative octreotide regimen is a continuous intravenous infusion of 40 μg/hour to 80 μg/hour for 12 to 48 hours prior to operation. In addition, an observation of intraoperative carcinoid syndromes (see Table 17.1 for the authors’ definition) initiated treatment with additional octreotide boluses of 0.5 to 2 μg/kg. The authors observed 139 episodes of intraoperative carcinoid syndrome and no episodes of carcinoid crisis. These authors suggest that with no patients having a carcinoid crisis in their series, there is clinical relevance of a standardized octreotide prophylactic protocol.

The last retrospective review was published by Kwon et al. in 2019 of 75 patients with hepatic metastases from NETs undergoing hepatic resection, ablation, or embolotherapy. The authors found that 24 (32%) experienced carcinoid crisis or hemodynamic instability (see Table 17.1 for authors’ definition). They found that periprocedural octreotide use was not associated with lower carcinoid crisis/hemodynamic instability occurrence. This supported the previous findings of Condron in 2016 and Massimino in 2013. These authors hypothesized that carcinoid crisis may be a phenomenon different from carcinoid syndrome.

In summary of these seven retrospective reviews, three of these articles ^{, ,} have little statistical support for the use of octreotide as a preventative or therapeutic strategy for carcinoid crisis, with three articles ^{, ,} showing that it has no efficacy, and one is inconclusive. The only single prospective study was published in 2019 by Condron et al. In this study, 46 patients with hepatic metastases from NETs undergoing operation were studied between 2015 and 2017 and 16 (35%) experienced intraoperative hypotensive crisis. In this series, the preoperative bolus of octreotide (500 μg) and continuous infusion (500 μg/hour) were given to eliminate the variable of not having octreotide from their results. These patients had invasive monitoring intraoperatively with pulmonary artery catheters, transesophageal echocardiographs, and arterial lines placed, as well as hormonal measurements of serotonin, histamine, kallikrein, and bradykinin at three time points (preincision, mid-crisis, and at case conclusion). The fascinating results of this study showed none of the hormone levels changed during a carcinoid crisis, which questions the theory that carcinoid crisis is a massive release of hormones. However, as all these patients received a preoperative bolus and continuous infusion of octreotide, we may be seeing that octreotide does effectively block the hormone release but does not block the physiologic changes of carcinoid crisis, questioning the theory that carcinoid crisis is due to the massive release of hormones. To expand upon this further, on the invasive monitoring equipment described earlier the authors observed a decrease in pulmonary vascular resistance, consistent cardiac hypovolemia on echocardiography, and a decrease in systemic vascular resistance. From this the authors concluded that carcinoid crisis is a distributive shock. Last, as all patients were receiving continuous octreotide infusions but a crisis incidence rate of 35% was still observed, these authors also concluded octreotide was not a preventative agent.

The most recent NANETs guidelines published in 2017 have discussed that recent literature does not support the notion that routine administration of octreotide prevents carcinoid crisis though it does not appear to increase complication rates and is generally safe. As we have now found that the pathophysiology of carcinoid crisis is fundamentally different and several authors have proven octreotide’s ineffectiveness at prevention of crises, ^, future studies in the pathophysiology of crisis and different treatment strategies are advised. We question if the known effect of splanchnic vasoconstriction causes the improvements in blood pressure, which is why there are so many reports of carcinoid crisis improving with octreotide administration.

Treatment With Vasopressors, Including β-Adrenergic Agonists

The use of vasopressors, including β-adrenergic agonists in patients with carcinoid syndrome and crisis, is historically controversial. The basis of this argument are physiology studies from the 1960s, starting with a publication of 10 normal subjects compared to 8 patients with carcinoid tumors, which implicated bradykinin in the understanding of carcinoid flushing. They found that bradykinin resulted in venoconstriction during a phase of arteriolar hypotension, followed by venodilation. In addition, this study found that epinephrine caused flushing in carcinoid patients as well as a marked decline in forearm resistance that was significantly longer than normal subjects, which the authors interpreted as that “a substantial portion of the vascular phenomena might be the result of an indirect effect of epinephrine.” In addition, they found a few of the carcinoid patients showed obvious venodilatation instead of venoconstriction with the administration of epinephrine.

Later physiology studies done in the 1980s began to show adrenergic control of serotonin release, particularly β-adrenergic receptors. This was perpetuated by anesthetic review articles that recommended against the use of these drugs, as they could cause a canonical process of crisis. ^, However, outside of these physiology studies from the 1960s and 1980s, data to support the avoidance of β-adrenergic agonists are limited. In addition, some tertiary referral centers have also demonstrated β-adrenergic agonist safety when other traditionally used agents (phenylephrine and vasopressin) were insufficient. ^,

To investigate this area further, a retrospective review of 293 operations that identified 58 operations on 56 patients with carcinoid tumors, with 161 crisis events, was published in 2019. Of these patients, 36 were treated with phenylephrine or vasopressin only and 22 were treated with β-adrenergic agonists as well. There was no significant difference in the incidence of paradoxical hypotension between patients treated with β-adrenergic agonists compared with non–β-adrenergic agonists. In addition, the dose-response curve for the administration of ephedrine or epinephrine showed no significant linear association in the percent decrease in mean arterial pressure (MAP). There were also no differences in crises duration or postoperative complications. Based on the results of this study, the authors conclude that β-adrenergic agonists may be considered to treat refractory hypotension in patients with carcinoid if phenylephrine and vasopressin are proven insufficient.

The fact that β-adrenergic receptors can safely be given without precipitation of secondary crises supports the theory that there is a different mechanism at play as β-adrenergic agents would otherwise cause a canonical process of crises.

Conclusion

We implore specialty societies to decide upon a strict definition of carcinoid crisis in order to give generalizability to on-going research efforts. This will also help clinicians determine the true incidence and risk factors of carcinoid crisis. There is much to be learned about the unique pathophysiologic process of carcinoid crisis and its treatment. The unpredictability and urgency of these crises make research very difficult, especially in light of the ethical considerations of leaving a crisis untreated for greater than 10 minutes to fulfill a definition and a demonstrated higher complication rate if hypotension exceeds this threshold. Current recommendations would be not to rely on octreotide, as it has been demonstrated to not prevent or treat carcinoid crises. For the treatment of carcinoid crisis, we recommend intravenous fluids and vasopressors in the following order: vasopressin, phenylephrine, and finally β-adrenergic agents. β-Adrenergic agents are considered third-line agents, as the data are emerging that these are safe and do not provoke secondary crises. With these emerging studies showing that octreotide is not helpful and challenging the paradigm that the crisis is triggered by a massive release of hormones, much remains to be learned about the pathophysiology of crisis, and this should be investigated further in multicenter, prospective trials.