Association between minor and major surgical complications after carotid endarterectomy: Results of the New York Carotid Artery Surgery study

Article Outline

• Abstract
• Methods
  • Study population
  • Data collection and measurement
  • Minor surgical complications and cardiac complications
  • Major complications
  • Analysis plan
• Results
  • Rates of complications
  • Univariate associations between minor and major surgical complications
  • Univariate associations between cardiac and major surgical complications
  • Multivariable associations between minor and major surgical complications
  • Multivariable associations between cardiac and major surgical complications
• Discussion
• Conclusion
• Author contributions
• Acknowledgment
• References
• Copyright

Objective

Most studies on outcomes of carotid endarterectomy (CEA) have focused on the major complications of death and stroke. Less is known about minor but more common surgical complications such as hematoma, cranial nerve palsy, and wound infection. This study used data from a large, population-based cohort study to describe the incidence of minor surgical complications after CEA and examine associations between minor and major complications.

Methods

The New York Carotid Artery Surgery (NYCAS) study examined all Medicare beneficiaries who underwent CEA from January 1998 to June 1999 in NY State. Detailed clinical information on preoperative characteristics and complications ≤30 days of surgery was abstracted from hospital charts. Associations between minor (cranial nerve palsies, hematoma, and wound infection) and major complications (death/stroke) were examined with χ² tests and multivariate logistic regression.

Results

The NYCAS study had data on 9308 CEAs performed by 482 surgeons in 167 hospitals. Overall, 10% of patients had a minor surgical complication (cranial nerve (CN) palsy, 5.5%; hematoma, 5.0%; and wound infection, 0.2%). Cardiac complications occurred in 3.9% (myocardial 1.1%, unstable angina 0.9%, pulmonary edema 2.1%, and ventricular tachycardia 0.8%). In both unadjusted and adjusted analyses, the occurrence of any minor surgical complication, CN palsy alone, or hematoma alone was associated with 3 to 4-fold greater odds of perioperative stroke or combined risk of death and nonfatal stroke (P < 0.0001). Patients with cardiac complications had 4 to 5-fold increased odds of stroke or combined risk of death and stroke.

Conclusion

Minor surgical complications are common after CEA and are associated with much higher risk of death and stroke. Patient factors, process factors, and direct causality are involved in this relationship, but future work will be needed to better understand their relative contributions.

Randomized controlled trials (RCTs) and national subspecialty practice guidelines for carotid endarterectomy (CEA) have focused on balancing the short-term risks of death or stroke due to the procedure with its long-term benefits of increasing long-term stroke-free survival. For these reasons, most studies on the outcomes of CEA both in clinical trials and real-world practice have primarily focused on rates of and risk factors for the major complications of perioperative death or stroke.¹, ², ³, ⁴, ⁵, ⁶, ⁷ In the RCTs and large population-based studies, the rates of death or stroke among symptomatic patients average about 6% among symptomatic patients⁸, ⁹, ¹⁰, ¹¹ and approximately 3% among asymptomatic ones.¹², ¹³

Less is known about rates of minor complications such as cranial nerve (CN) palsy, hematoma, bleeding, and wound infection. These minor complications are believed to be considerably more common than the major adverse events of death or stroke, but the incidence of such events has been less well studied. The reported rates of CN palsies are 2% to 27%,², ¹⁴, ¹⁵, ¹⁶, ¹⁷, ¹⁸, ¹⁹, ²⁰, ²¹, ²², ²³ and wound hematomas have been reported in 1.2% to 12% of cases.², ¹⁵, ²⁴, ²⁵, ²⁶, ²⁷ Prior studies of these minor complications have been limited by their focus on one type of surgical complication, single institutions,¹⁴, ¹⁵, ¹⁷, ¹⁸, ¹⁹, ²¹, ²⁵, ²⁶, ²⁷ small sample sizes, or highly selected surgeons and patients who participated in RCTs.¹⁶, ¹⁹

Very little is also known about the prognostic significance of minor complications after CEA. Although large hematomas can cause airway compromise, tracheal deviation, and airway compromise, they are typically considered to be minor and of no clinical consequence.² Cranial nerve injuries are rarely life threatening, but may cause discomfort or detract from quality of life, for example, tracheal obstruction by bilateral hypoglossal lesions or bilateral palsy of the vocal cords.², ¹⁴, ¹⁷ The importance of CN injuries has been questioned because most resolve over time.¹⁴, ¹⁷, ¹⁸

This study used data from a large, population-based cohort study to (1) describe the incidence of minor surgical complications after CEA, including hematoma, CN palsy, wound infection and cardiac complications and (2) examine the association between minor surgical complications and the major outcomes of perioperative death or stroke. We hypothesized that minor surgical complications, although often regarded as clinically insignificant outcomes, would be associated with a higher incidence of perioperative death and stroke even after adjusting for other factors known to influence the risk of major complications.

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Methods 

Study population 

The New York Carotid Artery Surgery (NYCAS) study examined all Medicare beneficiaries who underwent CEA between January 1, 1998, and June 30, 1999, in New York (NY) State. Details about the NYCAS study have been published previously.²⁸ Briefly, eligible cases (International Classification of Diseases, 9th Revision [ICD-9] code 38.12) with Medicare fee-for-service insurance were identified using Medicare Part A hospital claims. Medicare managed-care patients who had a CEA were identified with an algorithm that used the NY State hospital discharge database, age ≥65 years, and the Medicare eligibility files. The study was approved by the Mount Sinai Institutional Review Board.

We obtained the medical charts of 10,817 of 11,406 (94.8%) potentially eligible patients. We excluded 628 that were same-side operations for restenosis (n = 308), surgery combined with a major procedure in addition to coronary artery bypass graft surgery (CABG, n = 210), or no CEA was performed (n = 110). For the analyses presented here, we excluded an additional 280 patients who underwent simultaneous CEA and CABG surgery and 601 who were missing key clinical data. The results reported are based on 9308 patients, representing 93.9% of all eligible cases.

Data collection and measurement 

Detailed clinical information was abstracted from hospital charts by trained nurse abstractors, including sociodemographics, admission source; neurologic, medical, and surgical history; admission neurologic exam, functional status, laboratory values, medications, and diagnostic imaging test results. We collected data on individual comorbid conditions and calculated several comorbidity indices, including the Revised Cardiac Risk Index²⁹ and the Charlson comorbidity score.³⁰ Severe disability (modified Rankin score of 4 or 5) was defined as bedridden or unable to walk/attend bodily needs without assistance.³¹ There were several different indications for surgery.

The presence of a neurologic event in the 12 months before surgery was identified as a stroke or transient ischemic attack (TIA). Patients with crescendo TIAs or stroke-in-evolution were grouped as “acute syndromes.” Those without neurologic symptoms referable to a carotid artery distribution in the 12 months before surgery were considered asymptomatic.

We also abstracted the percentage of stenosis of the internal carotid arteries that were and were not operated on according to imaging tests. Carotid angiography was considered to be the most accurate test, followed by Doppler ultrasonography and magnetic resonance imaging. If no imaging test was available, we used stenosis information from preoperative notes.

The abstractors were required to pass a series of quality assurance and inter-rater reliability tests. All of the data elements reported here had substantial to nearly perfect agreement (κ = 0.60 to 1.0).

Minor surgical complications and cardiac complications 

Minor surgical complications were defined as CN palsy, hematoma, or wound infection. Cardiac complications were defined as myocardial infarction, angina, pulmonary edema, and ventricular tachycardia. Information about these complications was abstracted from the review of the inpatient medical record of the index admission and all readmissions ≤30 days of surgery anywhere in NY State. Trained, experienced research nurses abstracted data on these minor complications from a review of admission notes, the daily hospital notes, and discharge summaries, including notes from surgeons, neurologists, and medical consultants.

Symptoms were used to group CN palsies were into five categories: (1) tongue deviation toward operative side, (2) vocal cord paralysis, (3) lip or facial droop on the operative side, (4) ear numbness on the operative side, and (5) other. In the event that the abstractor could not determine whether CN palsy or a stroke had occurred, a study physician investigator reviewed the chart and made a determination.

Hematoma was defined as documentation of a wound hematoma or wound-related bleeding that was described with adjectives such as, “significant,” “moderate,” “severe,” or “large.” Descriptions of “slight” or “small amount of” hematoma or bleeding or “oozing” were not coded as hematoma/bleeding.

Wound infections were coded when the term “wound infection” was used in the chart.

Cardiac complications included myocardial infarction, unstable angina, pulmonary edema, or ventricular tachycardia. Myocardial infarction was defined as subendocardial, transmural, Q-wave, and non-Q-wave myocardial infarctions. Unstable angina was coded if the word “unstable angina” or “class IV angina” was seen. Ventricular tachycardia was defined as more than five continuous premature ventricular contractions at a rate >100 beats/min.

Pulmonary edema included those cases of congestive heart failure with associated respiratory symptoms or signs, left-sided heart failure, pulmonary congestion, lung edema or paroxysmal nocturnal dyspnea.

Major complications 

Information about perioperative deaths, strokes, and TIAs was abstracted from the inpatient medical record of the index admission and all readmissions ≤30 days of surgery in a similar fashion as outlined and in our previous reports.²⁸ In addition, the records of all deaths, strokes, and TIAs were independently reviewed by two study physicians, including a neurologist. Initial agreement was 95%, and disagreements were resolved by consensus or a third reviewer, if necessary.

Analysis plan 

Descriptive statistics were used to display the characteristics of the study patients. The main analytic task was assessing association between minor surgical complications (CN palsy, hematoma, or wound infection) and major adverse events (death and stroke). We examined two main dependent variables in these analyses: (1) combined rate of death or nonfatal stroke ≤30 days of surgery (the main composite outcome in the RCT and practice guidelines of CEA), and (2) any fatal or nonfatal strokes ≤30 days of surgery.

Univariate relationships between each category of minor (CN palsy, hematoma, wound infection, cardiac) and major complication were examined with χ² tests. In addition, we calculated median and mean length of stay (LOS) for each individual complication and performed univariate tests to assess for significant differences from the group without the complication in question.

We then used multivariable logistic regression to assess if minor complications were associated with higher rates of combined death or stroke (or any stroke) after adjusting for other risk factors known to influence major outcomes. The risk-adjustment model contained other key preoperative patient characteristics associated with death or stroke, including age, sex, race/ethnicity, age, indication for CEA, admission source, admission from the emergency department, degree of stenosis of the nonoperative side, ulcer depth on the operative side, degree of disability, and Revised Cardiac Risk Index. When calculating the significance level for LOS for each individual complication, we added the occurrence of death/stroke to the risk adjustment model. We used generalized estimating equations to account for the hierarchic clustering of patients by surgeons and surgeons by hospitals. All analyses considered two-sided P = .05 as statistically significant and were performed using SAS 8.2 software (SAS Institute, Cary, NC).

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Results 

During the study, 9308 CEAs were performed in NY State. Characteristics of the patients are summarized in Table I. The mean age of the patients was 74.6 ± 6.8 years (range, 40 to 98), and 55.7% were men. Overall, 71.5% were operated on for asymptomatic carotid stenosis, 18.9% for carotid TIA, 9.3% for stroke, and 0.3% for acute syndromes. Nearly all patients (95.4%) were operated on for high-grade (70% to 99%) carotid stenosis. The degree of occlusion of the contralateral artery was variable. The CEAs in the NYCAS were performed by 482 surgeons in 167 hospitals. The median hospital length of stay was 2 days (interquartile range, 1 to 4 days).

Table I. Characteristics of 9308 patients undergoing carotid endarterectomy

Patient risk factor	Prevalence (%)	Patient risk factor	Prevalence (%)
Male sex	55.7	Neurologic indication
Age (years)		Asymptomatic	71.5
<60	2.1	Carotid TIA⁎	18.9
60-69	21.0	Stroke⁎	9.3
70-79	53.3	Acute Syndrome†	0.3
80+	23.6	Revised Cardiac Risk Index
Race/ethnicity		0	19.2
White	93.6	1	44.5
Black	2.5	2	28.1
Hispanic	2.2	≥3	8.2
Other/unknown	2.3	Charlson Comorbidity Score
Admitted from ED	10.1	0	17.4
Admit source		1	32.2
Home	96.5	2	26.4
Transfer	3.5	≥3	24.0
Stenosis of operated artery		Severe neurologic disability	2.6
Occluded	0.2	Coronary artery disease	60.8
70-99	95.4	Active coronary disease	4.0
60-69	2.9	Operated artery on left	50.9
50-59	1.0	Valvular heart disease	14.2
30-49	0.5	Hypertension	78.2
0-29	0.1	Congestive heart failure	9.4
Stenosis of nonoperated artery		Peripheral vascular disease	30.1
Occluded	5.8	Renal insufficiency	4.8
70-99	21.7	Cerebrovascular disease	44.1
60-69	5.4	Diabetes mellitus	29.7
50-59	5.2	Diabetes on insulin	7.4
30-49	11.3	Pulmonary disease	19.1
0-29	50.6	Current smoking	14.9
Ulcerated plaque		Alcohol use	9.1
None	94.4
Shallow	4.7
Deep	0.9

TIA, Transient ischemic attack.

Rates of complications 

Within 30 days of surgery, 106 patients died (1.14%) and 305 strokes (3.28%) occurred, of which 265 (2.85%) were nonfatal and 40 were fatal. Given the overlap of 40 cases, there were thus 371 cases of perioperative death or nonfatal stroke for a combined rate of perioperative death or nonfatal stroke of 3.99%. Overall, 932 patients (10%) had one or more minor surgical complications. Cranial nerve palsies occurred in 514 (5.5%), hematoma in 461 (5.0%), and wound infection in 22 (0.2%). More than one minor surgical complication occurred in 65 patients (0.7%): 60 (0.6%) had hematoma and CN palsy, three (0.03%) had a hematoma and a wound infection, and two (0.02%) had CN palsy and a wound infection.

Table II summarizes additional details about the CN palsies. The two most common deficits were described as tongue deviation towards the operative side (33%) and lip/facial droop on the side of surgery (24%). More than one nerve was affected in 117 patients (23%) who had a CN palsy, and all of these had one or more cutaneous nerve injury as well as a single motor cranial nerve injury. The distribution of motor nerve injuries was as follows: 47 hypoglossal (40%), 43 facial or branch or both (37%), 14 branch of Vagus (12%), and 13 glossopharyngeal (11%). Reoperation was required in 146 of the 461 patients (32%) who developed postoperative bleeding or a hematoma, representing 64% of all patients who were taken back to the operating room.

Table II. Description of cranial nerve palsies in 9308 patients

A total of 451 cardiac complications occurred in 365 cases (3.9%). The perioperative myocardial infarction rate was 1.1% (n = 104), unstable angina rate was 0.87% (n = 81), pulmonary edema rate was 2.1% (n = 194), and ventricular tachycardia rate was 0.77% (n = 72).

Univariate associations between minor and major surgical complications 

Univariate associations between minor surgical complications and death/stroke are summarized in Table III. Patients with any minor surgical complication had approximately three times the rate of death or stroke (10.7% vs 3.2%) and nearly a four-times higher risk of stroke (9.7% vs 2.6%) or death (2.9% vs 0.9%, P < .001 for all). Those who had a CN palsy had three times the risk of death/stroke or any stroke (P < .001), with a trend towards higher rates of death as well (P = .08). Hematoma was also associated with a three- to four-times greater risk of combined death/stroke, any stroke, or death (P < .001). Wound infection had a similar pattern, but because there were very few of these outcomes, the trends were not statistically significant (P > .05). In addition, each group had a significantly longer LOS (all P < .001 except wound infection, for whom P = .03).

Table III. Prevalence of minor surgical and cardiac complications, association with death and stroke outcomes in 9308 patients

Complication	Prevalence (%)	Death/stroke rate (%)	P	Stroke rate (%)	P	Death rate (%)	P	Median LOS	P
Any surgical⁎
Yes	10.0	10.73	<.001	9.66	<.001	2.90	<.001	3.0	<.001
No	90.0	3.24		2.57		0.94
Cranial nerve palsy
Yes	5.5	10.31	<.001	9.53	<.001	1.95	.08	2.5	<.001
No	94.5	3.62		2.91		1.09
Hematoma
Yes	5.0	12.80	<.001	11.06	<.001	4.56	<.001	3.0	<.001
No	95.0	3.53		2.87		0.96
Wound infection
Yes	0.2	9.09	0.22	4.55	0.74	4.55	.13	2.0	0.03
No	99.8	3.97		3.27		1.13
Cardiac complications†
Yes	3.9	18.90	<.001	12.88	<.001	9.86	<.001	6.0	<.001
No	96.1	3.38		2.88		0.78

LOS, Length of stay.

The timing of the minor complications in relation to when a stroke was recorded was as follows: 23 minor complications occurred before the stroke, 38 were noted on the same day as a stroke, and 29 were mentioned after the day of the operation. Secondary analyses that excluded these 29 minor complications that occurred after the index CEA produced similar results to those summarized in Table II.

Univariate associations between cardiac and major surgical complications 

Univariate associations between cardiac complications and death/stroke are also in Table III. Patients with cardiac complication had approximately a five times the rate of death or stroke (18.9% vs 3.4%) and stroke alone (12.9% vs 2.9%) and approximately 12 times the rate of death (9.9% vs 0.8%, P < .001 for all), and had a significantly longer LOS (P < .001).

Multivariable associations between minor and major surgical complications 

Table IV shows that minor complications remained strongly correlated with major adverse events even after controlling for other key prognostic factors. Patients who had a minor surgical complication had triple the odds of combined death or stroke (odds ratio [OR], 3.39, 95% confidence interval [CI], 2.65 to 4.33) or death alone (OR, 2.89; 95% CI, 1.84 to 4.54) and nearly quadruple the odds of any stroke (OR, 3.83; 95% CI, 2.95 to 4.97). Hematoma approximately quadrupled the odds of death and stroke (OR, 3.69 95% CI, 2.72 to 5.00), death alone (OR, 4.30; 95% CI, 2.61 to 7.08), and stroke alone (OR, 3.89; 95% CI, 2.82 to 5.38). Patients who required operations for hematoma had higher odds of death/stroke than patients with hematomas who were observed (adjust odds ratios OR = 5.5 [3.5-8.5] v. OR = 2.6 [1.7-3.9], P < 0.0001 for both).

Table IV. Adjusted^⁎ odds ratios for minor surgical and cardiac complications in 9308 patients

CI, Confidence inteval; LOS, length of stay; OR, odds ratio.

A multivariate subanalysis for death/stroke of these patients showed a relative risk of 5.5 (95% CI, 3.5 to 8.5; P < .0001) vs a relative risk of 2.6 (95% CI, 1.7 to 3.9; P < .0001) for those patients with a hematoma that was observed. Cranial nerve palsy tripled the odds of combined death/stroke (OR, 2.92; 95% CI, 2.13 to 4.00) and any stroke (OR, 3.34; 95% CI, 2.41 to 4.63), although the relationship with death was borderline (OR, 1.71; 95% CI, 0.88 to 3.34; P = .11).

Amongst the CN palsies, post hoc subgroup analyses revealed increased odds of major complications for most but not all of the individual CN palsies. For example, death and stroke rates were higher in those with hypoglossal (XII) palsy (OR, 2.0; 95% CI, 1.2 to 3.3; P < 0.01), facial or branch (VII) palsy (OR, 4.0; 95% CI, 2.6 to 6.2; P < .0001), or both, and vagus nerve (X) palsy (OR, 6.5; 95% CI, 2.3 to 18.8; P < .001), but not for glossopharyngeal (IX) palsy (OR, 1.6; 95% CI, 0.6 to 4.3; P = .30). No statistically significant relationship was found between wound infection and major complications. On multivariate analysis controlling for death/stroke, each individual complication was significantly associated with an increase in LOS.

Multivariable associations between cardiac and major surgical complications 

Table IV also shows that cardiac complications remained strongly correlated with major adverse events, even after controlling for other key prognostic factors. Patients who had a cardiac complication had four to five times the odds of combined death or stroke (OR, 5.42; 95% CI, 4.01 to 7.34) or stroke alone (OR, 4.14; 95% CI, 2.93 to 5.84) and approximately ten times the odds of death (OR, 10.4; 95% CI, 6.68 to 16.2). Finally, on multivariate analysis controlling for death/stroke, cardiac complications were significantly associated with an increase in LOS.

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Discussion 

In this statewide study of all 9308 CEAs performed by 482 surgeons in Medicare beneficiaries in NY State, we found that one in 10 patients had a minor surgical complication (CN palsy, hematoma, or wound infection). Cranial nerve palsies occurred in 5.5% of patients and hematomas in 5.0%. Although minor surgical complications have traditionally been considered outcomes of little or no consequence, we found that patients with a minor surgical complication had an increased LOS and a threefold to fourfold greater odds of perioperative death or stroke, even after risk adjustment.

This study confirms and extends the literature on minor complications after CEA in the following ways. Prior studies of minor complications after CEA focused on single types of complications, were based at single institutions, had small sample sizes, or were based on the highly selected samples enrolled in RCTs. To the best of our knowledge, the incidence of CN palsy, hematoma, and wound infection we report here represents the largest, most generalizable estimate of these complications in widespread community practice.¹⁴, ¹⁵, ¹⁶, ¹⁷, ¹⁸, ¹⁹, ²¹, ²⁵, ²⁶, ²⁷

Although incidence of CN palsies after CEA reported by others have varied widely, from 2% to 27%.², ¹⁴, ¹⁵, ¹⁶, ¹⁷, ¹⁸, ¹⁹, ²⁰, ²¹, ²², ²³ the rate of 5.5% we found in NYCAS is higher than that reported in a large single-site study of 5425 by Chiesa et al¹⁵ and somewhat lower than rates of 6.3% and 8.6% reported in the European Carotid Surgery Trial and North American Symptomatic Carotid Endarterectomy Trial (NASCET) RCTs.², ¹⁶ The higher rate of CN palsies in these RCTs may be partly because all CEAs were among symptomatic patients and our NYCAS study were three-quarters asymptomatic. Alternatively, the differences can also be attributed to the different protocols of the studies. In the RCTs, there was routine prospective evaluation by neurologists, whereas the data in our study are from a retrospective chart review based primarily on clinically significant findings reported in everyday practice. The current study reports on all CN palsies (both transient and permanent), whereas others have focused exclusively on permanent deficits.

The hematoma rate of 5.0% that we found is in the middle of the range reported by others (1.2% to 12%)², ¹⁵, ²⁴, ²⁵, ²⁶, ²⁷ and slightly lower than the 7.1% incidence in NASCET.² Comparison with other studies in the case of hematoma is more challenging and should be made with caution because of the substantial differences in definitions used in other investigations. For example, one series that classified a hematoma as a radiographically evident reduction in airway cross section reported an incidence as high as 26%,³² whereas another series that reported only hematomas that led to wound revision published a rate of 1.4%.¹⁵

Finally, the wound infection rate in this study of 0.2% was low and consistent with other studies of CEA, as well as clean head and neck cases in general,¹⁵, ³³, ³⁴, ³⁵ and the rate of 2.1% reported in NASCET.²

To our knowledge, this is the first study to demonstrate a multivariable relationship between minor and major surgical complications of CEA or any other major procedure. There are several potential explanations for this association.

First, both types of outcomes could be correlated because the risk of minor and major complications is related to other underlying patient factors. For example, if a case were technically challenging due to unusual carotid anatomy or a high internal carotid artery lesion, there might be a greater chance of a CN injury or bleeding, or both, on that basis, and a similarly increased chance of death or stroke due to the more difficult repair. From the NYCAS study nurses review of the operative notes, we obtained information on key surgical processes of care but were not able to know the fine details regarding the difficulty of repair. Such information may be incompletely documented in operative notes and this was a level of detail that was not part of the chart review protocol in the parent study. It is also possible that this association reflects the impact of subtle differences in patients’ underlying severity of carotid disease, comorbid illness burden, or hemostasis/bleeding risk of the patient. Our multivariable models adjusted for several markers of carotid disease, comorbidity, and death/stroke risk after CEA, so we think this is a less likely explanation.

Second, both minor and major complications might be related to the overall skill and quality of the surgical repair or perioperative management, or both. Extremely skilled and proficient surgeons and surgical teams would be expected to possess superior technical and cognitive skills and resources that might decrease the chance of CN injuries, bleeding, and infection as well as translate into lower rates of death or stroke. As such, the rate of minor complications might be seen as a surrogate marker of overall quality of surgical care at either the surgeon or hospital level. Conversely, a less-experienced surgeon might have higher rates of inadvertent CN injuries and perform a less skillful arterial reconstruction, which might be manifested in higher rates of postoperative stroke. That we found a significant association between CN palsy and stroke (and combined death/stroke) but not with death alone may provide additional support for this hypothesis. Although post-CEA stroke is most commonly due to thromboembolic phenomena stemming from the endarterectomy site, many post-CEA deaths are due to cardiac events. Strokes are thus more likely than deaths to be related to the same process of care factors that affect minor surgical complications (like CN palsies), explaining their stronger association.

Third, there might be occasions where there is a direct causal link; that is, the minor complication causes stroke or death. In rare cases, a very large hematoma could cause airway compromise and hypoxia, increasing the risk of both death and stroke. Alternatively, in the presence of a serious postoperative wound hematoma, perioperative aspirin or other antiplatelet/anticoagulation therapy might be withheld, which might then increase the risk of perioperative stroke. It is most likely that a combination of these different pathways could contribute to the overall relationship between minor and major complications. Better understanding of these relationships will require further investigation.

Fourth, it is conceivable that a major complication such as stroke could make the documentation of a minor complication more likely. Amongst other factors, the occurrence of a major complication is more likely to be associated with additional physicians being involved in the care of the patient, thereby increasing the chance of more detailed assessment and documentation.

Our study has several strengths, but it is worth commenting on a few limitations. First, this was a retrospective observational cohort study that depended on documentation of complications of CN palsies, hematomas, wound infections, and strokes in the medical charts. Because we evaluated outcomes of CEA in real-world practice, no standardized approach was used to assess or document subtle changes in neurologic function after surgery the way there would have been in a clinical trial. It is possible the some mild CN deficits or small hematomas were not documented in the inpatient notes and that we underestimated the wound infection rate because we did not have access to data from outpatient visits. Thus, the rates of minor complications that we report here represent events that were serious enough to merit documentation in real-world practice. Because the degree of postoperative assessment and documentation varies in community practice, the rates of minor complications reported here may be biased on the lower side.

Second, because we only reviewed inpatient medical records (and the median LOS was 2 days), we do not have any data on the extent to which the CN deficits persisted over time or resolved, as many commonly do.

Third, our results may not be generalizable to other states or patient populations. However, NY State accounts for 14% of the Medicare population,³⁶ 8% of all CEAs performed nationwide,³⁶, ³⁷ and three-quarters of CEAs are performed on Medicare beneficiaries.³⁸

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Conclusion 

We found that minor surgical complications are common after CEA and are associated with a much higher risk of death and stroke. Future work is needed to better understand the reason for these associations, as well as to identify potential interventions to reduce their occurrence.

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Author contributions 

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We acknowledge the assistance of the Island Peer Review Organization (IPRO) and the Centers for Medicare and Medicaid Services (CMS) in providing the data that made this research possible. The conclusions presented are solely those of the authors and do not represent those of IPRO or CMS. We would acknowledge the assistance of Patricia Formisano, MPH, R. Edward Park, PhD, Hugh Dai, Virginia Chan, Bernadette Rynne, RN, Wilfredo Gaerlan, Anna Arreglado, Camille Cohen, RN, Larry Hollier, MD, Chiaki Nakazono, Ying Qiu, Diane Thomas, MD, Kathleen Burger, MD, and Matthew Press, MD.

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