This study found that compared with patients without mental disorders, patients with mental disorders experienced higher rate of several potentially preventable complications and injuries during hospitalization for CABG surgery. The higher rate of postoperative adverse events for mentally ill patients persisted after adjusting for patient characteristics and hospital effects. Complication rates after CABG surgery may vary across hospitals for all patients and for patients with mental disorders.
Our data showed that CABG patients with concurrent mental disorders had a higher prevalence of medical comorbidities than other CABG patients, and were more likely to be admitted for unscheduled surgery, which would suggest that they were sicker and presented later in the course of their cardiac disease. Their higher disease burden may be caused by adverse effects of antipsychotic drugs, potential direct effects of mental abnormalities on medical vulnerability, and poor health behaviors such as increased smoking and alcohol consumption, unhealthy diet, and sedentary lifestyle (Shah et al. 2004
). In addition, earlier studies report that mentally ill patients may have delayed hospital admission for myocardial infarction (Bunde and Martin 2006
In this study, although we cannot totally rule out the possibility that unobserved clinical and health care factors lead to their increased postoperative injuries, the increased odds of overall and several individual adverse outcomes associated with mental disorders remained significant after adjusting for available patient diagnoses and hospital effects. This suggests that mentally ill patients undergoing CABG surgery may have received lower quality of care than other CABG patients. The likelihood of deficiency in care and its manifestation in safety outcomes among these patients are supported by the existing literature showing that mentally ill patients tend to receive suboptimal quality of medical care (Druss et al. 2001
) and surgical care (Li et al. 2007
) during hospitalizations for CHD.
Multiple plausible factors may explain the association between mental disorders and the increased risk of postoperative complications. Surgical patients with mental disorders may present a variety of problems during anesthesia including difficulty in provider–patient communication, interactions between antipsychotics and anesthetic drugs, hazardous behaviors such as agitation, and lack of patient cooperation (Kudoh 2005
). In addition, physicians and other health professionals may have less experience treating these “difficult” patients, who are more likely to have adverse reactions to anesthetic and analgesic drugs, including arrhythmias, hypotension, torsade de pointes, and postoperative confusion (Buckley and Sanders 2000
; Shah et al. 2004
; Kudoh 2005
). If this is the reason behind the safety issues faced by patients with mental disorders, specific interventions to sensitize medical providers to their complex care needs are necessary so as to bridge the gap in safety outcomes and improve the quality of cardiac services that they receive.
Patients with mental disorders also tend to have reduced sensation and pain responsiveness, poor compliance with recommended postoperative health behaviors such as ambulating and self-hygiene, and more frequent restraint use, all of which can contribute to their increased risk of developing decubitus ulcer during hospital stay. The threefold increase in postoperative hip fractures in these patients may be partially related to the undesirable sedative and autonomic effects of psychotropic drugs such as confusion, drowsiness, and ataxia (Ray et al. 1987
). In addition, some of these patients may exhibit abusive, aggressive, or other disruptive behaviors, which may lead to physical injuries and falls due to nurse aides' reluctance to provide necessary supportive care.
Our study has several strengths. It is based on the innovative AHRQ PSIs that have been shown to be associated with longer length of stay, higher hospital charges, and increased mortality (Zhan and Miller 2003
). The AHRQ PSI, with its rigorous measurement design, allowed this study to identify patient safety events that likely reflect consequences of hospital care failures. Although not all flagged cases may reflect problematic care and the PSI algorithm may miss a portion of cases with compromised safety, the AHRQ PSI provides an important tool for population-based comparisons of hospital care safety. In addition, our access to multiple years of New York hospital claims databases makes it feasible to conduct the analysis with a large sample of a well-defined patient population (i.e., patients undergoing CABG surgery). To the extent that most complications occur in rare circumstances, our large sample allowed for meaningful statistical comparisons between patients with and without mental disorders.
The use of hospital claims data, however, is also associated with several limitations. First, the validity of the PSI outcomes depends on the completeness and precision of recorded administrative and clinical information. Because ICD-9-CM diagnoses can be undercoded or miscoded, and are relatively insensitive in capturing medical conditions, the prevalence of safety events is likely to be underestimated in our data. However, the overall underestimation of outcomes would bias our result towards the null hypothesis or lack of associations between mental disorder and postoperative complications. Second, we used ICD-9-CM codes to identify mental disorders, which is a widely used approach in mental disparity studies (Druss et al. 2000
; Daumit et al. 2006
; Li et al. 2007
). Several validation studies, including one conducted over 10 years ago, have shown that hospital administrative data can be a reliable source of mental diagnoses for Veteran Affairs patients and Medicaid patients (Lurie et al. 1992
; Kashner 1998
; Walkup, Boyer, and Kellermann 2000
), but similar studies do not exist that examine the validity of mental diagnoses in the general population. Therefore, mental disorder could be underdetected in our sample due to undercoding or underdocumentation by medical providers. The underdocumentation of mental disorder may be more likely to occur when its symptom is less severe. However, the misclassification of mentally ill patients would also bias the estimated result toward the null hypothesis and thus make it a conservative estimate of the true effect of mental disorder.
Third, the administrative data do not contain as detailed clinical information as in chart review data for risk adjustment. Although we statistically adjusted for over 20 medical comorbidities defined by a validated ICD-9-CM algorithm (Elixhauser et al. 1998
), it is possible that uncontrolled clinical confounders mediate a part of the effect of mental disorders, and thus lead to an overestimation of the effect.
Finally, our analyses included only New York patients undergoing CABG surgery and therefore may not be generalized to patients in other states. New York State might be unique in open heart surgery because of its long-standing, highly reputed quality report cards for CABG outcomes, which likely have affected patient access and physician and hospital practice (Li et al. 2007
). Therefore, although we do not believe the effect of mental disorder on post-CABG complications is unique to this state, similar studies in other states are needed to confirm our findings.