Adverse Outcomes and Prediction of Cardiopulmonary Complications in Elective Spine Surgery

Introduction

The United States is seeing an increasing utilization of complex surgical procedures on the spine, which leads to an increased risk of life-threatening complications and readmissions. ^1,2 Spine surgeries are typically longer than other elective surgeries and are associated with major blood loss, fluid shifts, and transfusions, all of which are factors that can induce or exacerbate hemodynamic stress in a patient. ³ Cardiopulmonary complications are among the most common after spine surgery and are known to increase the risk of mortality as well as generate long-term complications related to multiple mechanical failures of cardiac function. ^{4 –6} Respiratory complications can arise from the proximity of the respiratory system to the thoracic spine, and many spine surgeries even violate the thoracic cavity to perform surgery. ⁷ Furthermore, there is currently no clear indication to immediately begin anticoagulation in patients postoperatively. ⁸ These complications can detract significantly from postoperative quality of life.

Risk factors for cardiopulmonary complications, as established by the Revised Cardiac Risk Index (RCRI), include both intraperitoneal approach and intrathoracic approach, which are frequently indicated in spinal procedures. ⁹ Despite presumed additional risk factors for major morbidity, which include age, surgical invasiveness, and comorbidities, many of these links remain unvalidated in the context of spine. For example, Carabini et al in 2014 investigated the application of the RCRI to spinal fusion patients and were unable to determine the predictive value of the index in the context of spine surgeries. ³

Previous large database studies have evaluated the demographic and comorbid risk factors for complications following spine surgery, but none have focused specifically on cardiopulmonary risks and related mortality. For this reason, the authors queried the National Surgical Quality Improvement Program (NSQIP) database with the goal of elucidating the incidence of cardiopulmonary complications following elective spine surgery and their associated risk factors.

Methods

The American College of Surgeons’ NSQIP was implemented in 1991 by the US Department of Veterans Affairs in order to model patient risk-adjusted outcomes for patient factors and operative procedure. Patient data is collected by a Surgical Clinical Reviewer auditing participating hospitals. It samples all patient populations undergoing general, spinal, or epidural anesthesia. Patient data collected includes primary diagnosis in the form of an ICD-9-CM code, procedures underwent by Current Procedural Terminology (CPT) coding, 70 preoperative risk factors, 11 variables on the operation, and 24 postoperative outcomes. Complications, outcomes, and any further procedures are recorded for 30 days after enrollment. More detailed information on the NSQIP design is available at https://www.facs.org/quality-programs/acs-nsqip/about. ¹⁰ Institutional review board approval is exempt from studies using de-identified NSQIP data. CPT and ICD-9-CM codes used to identify patient diagnoses and procedures undergone are available in Appendix A (available online at http://journals.sagepub.com/home/gsj).

Results

This study examined 60 964 spine surgeries (average age 55.8 years, 55.3% female) and found 1285 major cardiopulmonary complications. Incidence rates per 1000 elective spine patients were 2.1 MIs, 1.3 cardiac arrests, 4.3 unplanned intubations, 3.5 on ventilator >48 hours, 6.1 perioperative pneumonia, and 3.7 pulmonary embolisms.

Demographic and Comorbidity Risk

Tables 1 and 2 details incidence of any cardiopulmonary event according to demographic and comorbidity status. The strongest predictors for any cardiopulmonary complication were >10% weight loss within 6 months of surgery (odds ratio [OR] = 3.0; confidence interval [CI] = 1.7-5.2), preoperative blood transfusion (OR = 2.1; CI = 1.0-4.1), and paraplegia (OR = 2.0; CI = 1.2-3.3). Black race was also predictive of a cardiopulmonary event (P = .006), as was increasing ASA class (P < .001).

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Table 1.

Demographics of Patients Experiencing a Cardiopulmonary Event.^a

	Event (N = 1285)	No Event (N = 60 964)	Univariate
Female	37.43%	49.59%	.023
Race
White	84.20%	83.35%	.226
Black	9.18%	6.90%	.006
Asian	1.09%	1.75%	.469
ASA class
1	0.78%	4.68%	<.001
2	25.60%	52.62%	<.001
3	61.79%	40.33%	<.001
4	11.52%	2.18%	<.001

Abbreviation: ASA, American Society for Anesthesiologists.

^aSignificance set at P < .05.

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Table 2.

Demographic and Comorbidity Status as Predictors of Cardiopulmonary Complications.^a

	Event	No Event	P Value	OR (CI)
Age ≥ 80	9.42%	4.91%	.001	1.5 (1.2-1.9)
BMI ≥ 30	46.85%	37.18%	.836	1.0 (0.8-1.1)
BMI ≥ 40	9.26%	7.28%	.476	1.0 (0.8-1.3)
Diabetes	26.54%	15.51%	<.001	0.7 (0.8-1.1)
Smoking status	20.00%	23.84%	<.001	1.3 (1.1-1.5)
Dyspnea	11.05%	6.04%	.040	1.2 (0.9-1.5)
COPD	11.05%	3.98%	.037	1.6 (1.3-2.1)
CHF	0.39%	0.21%	<.001	1.2 (0.5-2.9)
Hypertension	68.09%	49.88%	<.001	1.3 (1.1-1.5)
Steroid use	7.55%	3.73%	.860	1.3 (1.0-1.7)
Weight loss	1.87%	0.32%	.810	3.0 (1.7-5.2)
Bleeding disorder	5.37%	1.41%	<.001	2.0 (1.5-2.8)
Preoperative transfusion	1.40%	0.19%	<.001	2.1 (1.0-4.1)
Paraplegic	1.87%	0.60%	<.001	2.0 (1.2-3.3)

Abbreviations: OR, odds ratio; CI, confidence interval; BMI, body mass index; COPD, chronic obstructive pulmonary disorder; CHF, congestive heart failure.

^aSignificance set at P < .05.

Procedure Risk

Controlling for overall surgical invasiveness, anterior approach was an independent risk factor for any cardiopulmonary event (OR = 1.74; CI = 1.42-2.13; Table 3). Anterior approach including decompression resulted in particularly high risk for airway-related complications: unplanned reintubation (OR = 2.61; CI = 1.89-3.61), extended ventilation (OR = 3.2; CI = 2.28-4.5), and pneumonia (OR = 1.9; CI = 1.39-2.59). Conversely posterior approach procedures displayed decreased odds for airway-related complications (OR < 1). This trend was reversed in pulmonary embolism complications: anterior approach fusion procedures were protective against pulmonary embolism (OR = 0.55; CI = 0.38-0.79), while posterior approach fusion procedures increased risk (OR = 1.43; CI = 1.06-1.91). Procedure-derived odds ratios predicting cardiopulmonary complications were in general close to 1 (range = 0.35-3.81).

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Table 3.

Risk Factors for Sustaining a Cardiopulmonary Complication Based on Procedure Type, Spinal Region, and Diagnosis.^a

	Any Event	Myocardial Infarction	Pulmonary Embolism	Cardiac Arrest	Unplanned Reintubation	Extended Ventilation	Pneumonia
Procedure
Anterior fusion	0.95 (0.81-1.12)	0.68 (0.41-1.10)	0.55 (0.38-0.79)	1.29 (0.77-2.15)	1.53 (1.16-2.01)	1.43 (1.06-1.95)	1.17 (0.92-1.50)
Posterior fusion	0.87 (0.76-1.00)	1.42 (0.95-2.13)	1.43 (1.06-1.91)	0.68 (0.43-1.07)	0.60 (0.47-0.77)	0.58 (0.44-0.77)	0.70 (0.56-0.87)
Combined fusion	1.51 (1.15-1.96)	1.02 (0.41-2.53)	0.95 (0.48-1.88)	1.63 (0.64-4.12)	2.04 (1.29-3.22)	1.81 (1.09-3.00)	1.70 (1.12-2.60)
Anterior decompression	1.50 (1.21-1.86)	0.98 (0.49-1.96)	0.31 (0.13-0.71)	1.73 (0.88-3.39)	2.61 (1.89-3.61)	3.20 (2.28-4.50)	1.9 (1.39-2.59)
Posterior decompression	0.96 (0.82-1.13)	1.39 (0.93-2.07)	1.52 (1.13-2.04)	0.84 (0.48-1.48)	0.58 (0.41-0.82)	0.63 (0.43-0.90)	0.79 (0.60-1.04)
Interbody	0.59 (0.48-0.73)	0.45 (0.25-0.81)	0.51 (0.34-0.77)	0.75 (0.37-1.52)	0.73 (0.50-1.08)	0.79 (0.52-1.2)	0.68 (0.49-0.95)
Region
Cervical	1.16 (0.98-1.38)	0.77 (0.45-1.32)	0.67 (0.44-1.02)	1.54 (0.90-2.62)	1.65 (1.23-2.19)	2.15 (1.59-2.91)	1.33 (1.02-1.72)
Thoracic	2.47 (1.95-3.12)	1.59 (0.78-3.23)	2.31 (1.42-3.73)	1.11 (0.42-2.95)	2.31 (1.52-3.51)	3.11 (2.06-4.69)	2.27 (1.57-3.29)
Lumbar	0.94 (0.82-1.08)	1.36 (0.94-1.97)	1.66 (1.25-2.20)	0.87 (0.55-1.37)	0.62 (0.48-0.81)	0.47 (0.35-0.64)	0.76 (0.61-0.94)
Diagnosis
Stenosis	0.98 (0.83-1.17)	1.32 (0.87-2.01)	1.36 (0.99-1.87)	0.96 (0.54-1.71)	0.93 (0.67-1.29)	0.56 (0.36-0.86)	0.81 (0.61-1.09)
Spondylosis	0.80 (0.67-0.96)	0.77 (0.47-1.28)	0.78 (0.54-1.14)	1.39 (0.82-2.35)	1.00 (0.73-1.37)	0.94 (0.66-1.35)	0.90 (0.68-1.2)
Scoliosis	2.31 (1.75-3.04)	2.16 (1.03-4.51)	2.4 (1.39-4.14)	0.27 (0.03-2.06)	2.25 (1.37-3.68)	3.04 (1.89-4.90)	2.01 (1.30-3.10)
Cancer	1.68 (0.99-2.85)	0.74 (0.10-5.48)	2.21 (0.79-6.19)	1.00 (0.79-6.19)	0.47 (0.11-1.95)	1.51 (0.63-3.65)	2.1 (1.04-4.24)
Fracture	2.00 (1.08-3.67)	2.55 (0.61-10.62)	0.84 (0.11-6.1)	1.75 (0.23-12.96)	1.42 (0.44-4.56)	3.23 (1.36-7.63)	1.15 (0.36-3.69)

^aReported as odds ratio (95% confidence interval). Significant items bolded (P < .05).

Outcomes after Cardiopulmonary Event

Table 4 follows inpatient outcomes in those patients who experienced a major cardiopulmonary event. Mortality, LOS, discharge status, and reoperation rate were all significantly worsened by cardiopulmonary events (P < .001). Mortality was highest among patients who suffered cardiac arrest (34.57%). Patients on a ventilator >48 hours had the longest LOS (17.58 days), followed by unplanned reintubations (13.04 days). Thirty-day reoperation rates also increased between 325% and 789%, P < .001. A total of 88.09% patients who did not experience any cardiopulmonary event were discharged home.

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Table 4.

Outcomes after Cardiopulmonary Event.^a

	No Event	Myocardial Infarction	Pulmonary Embolism	Cardiac Arrest	Unplanned Reintubation	Extended Ventilation	Pneumonia
LOS* (days)	2.86	8.52	7.61	9.62	13.04	17.58	10.58
Discharge status*
Expired	0.0985	5.343%	2.202%	34.57%	10.26%	11.74%	4.60%
Home*	88.09	57.3%	64.0%	56.6%	48.7%	35.6%	54.1%
Not home*	11.59	42.74%	57.26%	43.40%	64.36%	45.61%	35.6%
Unplanned reoperation*	1.832	8.870%	7.658%	9.434%	16.10%	16.49%	7.93%

Abbreviation: LOS, length of stay.

^aOnly contains data on patients who survived cardiopulmonary complication. All elements significant P < .001.

Discussion

This study demonstrates the incidence and predictors of cardiopulmonary complications following elective spine surgery. Understanding the incidence and risk factors for complications following spine surgery is essential for optimizing postoperative outcomes and improving patient perceptions of their care. Cardiopulmonary complications are the most common cause of death in patients undergoing spinal surgery. ¹² Despite this, no study to date has analyzed risk factors for these adverse events in the overall spine cohort.

In our cohort, cardiac arrest had the highest mortality rate following spine surgery. The importance of preoperative cardiac evaluation cannot be understated. Patients with history of coronary artery disease, heart failure, valvular heart disease, arrhythmias, and pulmonary vascular disease deserve special attention and risk stratification. ¹³ The preoperative assessment should include an evaluation of major adverse cardiac event (MACE) risk using at least one risk stratification tool, the most accepted of which are the RCRI, the NSQIP Myocardial Infarction and Cardiac Arrest, and the NSQIP Surgical Risk Calculator. The RCRI is the most well known and simplest to use, and incorporates high-risk surgery, history of ischemic heart disease, history of congestive heart failure, history of cerebrovascular disease, preoperative treatment with insulin, preoperative creatinine >2.0 mg/dL—interpolating them into a numerical score for interpretation. ⁹ Patients with MACE >1% according to the RCRI should undergo functional capacity evaluation prior to elective spine surgery.

The risk of MI in spine surgery has been previously studied with reported incidences 30 days postoperatively ranging from 0.13% to 1.6%, with odds significantly increasing with age >65 years, postoperative stay >7 days, operative time >5 hours, intraoperative blood transfusion, baseline creatinine >1 mg/dL, and fusions greater than 1 level. ^14,15 Our data supports these previous conclusions and again demonstrate the importance of preoperative cardiac risk stratification. We found that low invasive posterior fusions were associated with a 2-fold rate of MI. Posterior approaches requires going through more layers of tissue, which can increase perioperative blood loss and can lead to hemodynamic instability.

In this study, thoracic and anterior approaches were associated with a significantly higher risk of an adverse cardiopulmonary event, which is consistent with previously reported data. We report an unplanned reintubation rate of 0.43% for all elective spine surgery, with OR significantly higher for anterior cervical procedures. Unplanned reintubation is a well-known complication of anterior cervical spine fusions, the incidence of which has been reported to be 0.5%, which increases to 1.6% with ≥3-level fusions. ^{16 –19} Possible causes have been attributed to soft tissue swelling, hematoma, and injury from instrumentation. ^{16 –19} Duration of intubation was also an identified risk factor for perioperative mortality. It is worth noting that this measure may reflect the complex medical circumstances surrounding these patients, which may confound the effect of duration of ventilator dependence itself on mortality rate.

The incidence of pneumonia after anterior cervical discectomy and fusion has been reported to be 0.45% with age being greatest risk factor for this complication. ²⁰ For posterior lumbar interbody fusion, a rate of 0.59% has been reported with comorbid COPD presenting the greatest risk factor. ²¹ Our cohort is consistent with these previous reports, with a pneumonia rate of 0.61% for all patients in this cohort. The slight increase may be attributable to the fact that our data included patients with thoracic approaches, which may predispose to postoperative respiratory issues.

We found that patients with preoperative chronic spinal cord injury were at higher risk of cardiopulmonary complication following spine surgery. This patient population has been described as vulnerable to thromboembolic disease and autonomic dysreflexia, which can cause rapid changes in hemodynamic stability. ²² Although not without its own risks, inferior vena cava filters have been demonstrated to be protective against pulmonary embolism in patients at high risk for thromboembolic disease and should be considered in these patients prior to surgery. ²³

Undergoing any cardiopulmonary event significantly increased the LOS in patients. Yadla et al found the mean LOS increased the most in patients who experienced a pulmonary complication. ²⁴ Similarly, our study found that the LOS was increased the most in patients who had extended ventilation (mean 17.58 days) followed by unplanned reintubation (mean 13.04 days). Similarly, discharge status was significantly poorer in patients who experienced an adverse event. While 88.09% of patients who experienced no event were discharged home, only 35.6%% of patients who required extended ventilation were discharged home. The percentage of people who were discharged to places other than home were increased up to nearly 6-fold in those experienced an adverse event. Discharge to a subacute or nursing facility has been found to be highly correlated with an increased LOS. ²⁵ This change in discharge disposition is expected as these patients may require prolonged care at rehabilitation centers or nursing homes that are equipped to deal with any further complications that may arise.

We found that patients who experienced any cardiopulmonary event also had much higher rates of unplanned reoperation. It is important to note that this includes any and all types of surgical procedures so those patients who experienced an adverse event may not have necessarily had to undergo further spinal surgery. Even so, patients who experience such events are more prone to receiving additional procedures, which may be necessary not only to treat those pathologies but also expose patients to the risks that come along with them.

This study has several limitations, including its retrospective nature. A problem inherent to large database studies is that data analysis is limited to what was included in the database design. Specifics of surgical technique, diagnostic imaging, and a complete list of medical comorbidities are not reported and therefore there are likely some outcomes which are not captured or which are influenced by confounding variables for which there is no control. In general, however, the NSQIP database is a representative national sample with generalizable results.

Conclusion

This study reports the rates of cardiopulmonary complications after spinal surgery. The strongest risk factors for these events include thoracic approaches, as well as patients with anterior or combined approach procedures, and patients indicated for high-risk procedures. This agrees with risk factors seen in the RCRI. These patients deserve special attention during presurgical planning, with emphasis on cardiac risk stratification in order to prevent or anticipate complications during the hospital stay.

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