Discussion
Use of illicit stimulant drugs has been associated with increased morbidity in both the trauma and perioperative setting.1 10 To help manage this risk, UDS is used to identify drug-positive patients. However, a positive UDS does not always correlate with acute drug intoxication. For instance, the UDS for cocaine measures levels of an inactive metabolite, which can remain in the urine up to a week after use, making it an unreliable indicator of acute intoxication.11 This makes risk stratification after a positive UDS challenging. Currently, there are no universal guidelines to evaluate a patient’s perioperative risk after a positive UDS, but a result positive for stimulant drugs is widely considered a contraindication for elective general anesthesia. A study conducted by Elkassabany et al found that two-thirds of the clinicians surveyed would elect to cancel surgery for these patients, even in the absence of any symptoms of acute intoxication.5 Canceling elective surgery can delay care in a vulnerable patient population, resulting in adverse health outcomes. It can also result in financial losses and waste of resources. It is difficult to measure the effect that illicit substance use has on elective perioperative complications, given the reluctance to operate on this population. Trauma patients, however, regularly undergo emergency procedures despite having a positive drug screen, allowing us to examine the impact of substance use on perioperative complications.
Our analysis showed protective or neutral association of stimulant drugs with cardiovascular morbidity or mortality on the overall population, and on the subset who underwent major surgery. This lack of harmful association also applied to the group of patients who underwent immediate surgery. If the effects of the substances measured on a UDS conferred excess cardiovascular risk, one would expect this population to be especially vulnerable because the substances had less time for excretion or metabolism. However, even for the group requiring immediate surgery, stimulant-positive UDS is not associated with increased cardiovascular morbidity or mortality.
While these findings are consistent with our previous study,8 they still seem counterintuitive given the evidence of cardiotoxicity with stimulant use.3 4 The protective effects observed with stimulant use may be a result of unknown confounding variables; however, it is also possible that these protective effects are based on a true pharmacologic effect. Evidence of protective effects with stimulant use in trauma patients has been observed in previous studies. Ryb and Cooper showed that patients who had a positive UDS for cocaine had decreased rates of cardiovascular complications when undergoing surgery during the first day of admission12 and Cheng et al showed amphetamine use to be associated with lower rates of mortality.1 There are also studies that show no significant difference in mortality or cardiovascular complications in trauma patients who test positive for stimulants.13–16 This is further validated by recent studies examining the incidence of hemodynamic events under anesthesia to be similar between patients who screen positive for stimulants and patients who have a negative UDS, with the rates of vasopressor use during surgery similar between both groups.17–19
It can be difficult to separate the effects of acute and chronic stimulant use. While we do not know the duration of substance use for each patient, 28.6% and 31.6% of the amphetamine and cocaine group, respectively, in our population had a documented history of chronic substance use. Chronic substance abuse could potentially have a harmful or protective effect. On one hand, chronic stimulant use can result in dilated cardiomyopathy and an increased risk of acute coronary syndrome.3 4 However, an alternative hypothesis is that chronic users of methamphetamine and cocaine may have undergone a selection process that leaves survivors less vulnerable to catecholamine-induced cardiovascular stress. Having already survived a stimulant stressor, this population may be relatively resistant to further cardiovascular compromise. Most of our UDS-positive patients did not have a diagnosis of chronic substance abuse. Since we do not know the timing of substance use based on a positive UDS, it is possible that, in spite of positive results, many of our patients were not suffering from acute or chronic effects of illicit drugs at the time of the trauma and subsequent treatment.
While our study findings do not show an association of stimulant use with increased risk of MI, stroke, and mortality, both stimulants are associated with increased rates of surgical site infections, sepsis, and ventilator-associated pneumonia. Stimulants can cause vasoconstriction, resulting in poor wound healing and more susceptibility to surgical site infections. In addition, chronic stimulant abuse can result in malnutrition which can further increase a patient’s susceptibility to infections.20 Other studies have shown that cocaine can negatively impact the functioning of immune cells and mediators.20 21
Strengths of study
We used a large multicenter database for greater statistical power. We were able to show associations between the use of individual drugs and a wide variety of complications. Our study further investigated the use of stimulant drugs and the interaction with surgical procedures to help assess the influence on perioperative risk.
Limitations of study
Not all patients were evaluated for drug use because facilities did not have standardized criteria for choosing which patients to screen. Inconsistent selection of patients for UDS could potentially introduce bias. The UDS does not provide data about the level of the substance present or the time that the substance was used, thus UDS-positive patients may not have been acutely intoxicated. Our analysis shows lower rates of surgical interventions in positive amphetamine/cocaine groups. It is possible that some higher risk patients were excluded from surgery based on UDS results, which could mask a harmful effect. Terms were included in the multivariate analysis to adjust for surgical treatment, but this could still represent a subtle bias. The multivariate analysis adjusts for baseline imbalance; however, the retrospective nature of the study introduces the possibility of unknown and unmeasured confounding variables, thus it cannot establish cause and effect.