Abstract
Objective:
To examine the association between preoperative comorbidities and cochlear implant (CI) speech outcomes.
Study Design:
Retrospective cohort
Setting:
Tertiary referral center
Patients:
976 patients who underwent CI between January 2015 and May 2022. Adult patients with follow up, preoperative audiologic data, and a standardized anesthesia preoperative note were included.
Exposure:
Adult Comorbidity Evaluation 27 (ACE-27) based on standardized anesthesia preoperative notes.
Main Outcome Measures:
Postoperative change in CNC score, AzBio Sentence score in quiet, and AzBio + 10 dB signal-to-noise ratio (SNR) Sentence score of the implanted ear at three, six, and twelve months.
Results:
560 patients met inclusion criteria; 112 (20%) patients had no comorbidity, 204 (36.4%) had mild comorbidities, 161 (28.8%) had moderate comorbidities, and 83 (14.8%) had severe comorbidities. Mixed model analysis revealed all comorbidity groups achieved a clinically meaningful improvement in all speech outcome measures over time. This improvement was significantly different between comorbidity groups over time for AzBio Quiet (p=0.045) and AzBio + 10dB SNR (p=0.0096). Patients with severe comorbidities had worse outcomes. From preop to 12 months, the estimated mariginal mean difference (95% CI) between the no comorbidity group and the severe comorbidity group was 52.3 (45.7-58.9) and 32.5 (24.6-40.5), respectively for AzBio Quiet, 39.5 (33.8-45.2) and 21.2 (13.6-28.7) respectively for AzBio + 10 dB SNR, and 43.9 (38.7-49.0) and 31.1 (24.8-37.4) respectively for CNC.
Conclusions:
Comorbidities as assessed by ACE-27 are associated with CI performance. Patients with more severe comorbidities have clinically meaningful improvement but have worse outcome compared to patients with no comorbidities.
Introduction
Hearing loss affects more than a billion people worldwide and is the leading cause of years lived with disability for individuals greater than 70 years old.1 Cochlear implantation (CI) is the standard of care for patients with severe to profound sensorineural hearing loss who no longer benefit from amplification (i.e. hearing aids). CI is considered one of the most successful implantable devices to date with over 736,900 registered CI devices worldwide.2 CI utilization is only expected to grow over the next several decades with ongoing advancements in technology, expanding candidacy criteria,3 and given only 2% of eligible CI candidates in the US actually receive an implant.4,5 However, despite our best efforts, we continue to observe a wide range of post-implantation speech perception outcomes that cannot be adequately predicted.6-8
To better explain the wide range of post implantation speech outcomes, investigators have explored surgery-, device-, and patient-related factors that may account for the variability in CI performance. Surgical factors identified include cochleostomy approach, insertion technique to optimize scalar location, proximity to the modiolus, and methods for minimizing insertion trauma.9 Device-related factors include processing strategies, stimulation strategies, and electrode design.10,11 Patient-related factors include age at implantation, duration of hearing loss, preoperative hearing level, duration and use of amplification, cochlear nerve health, and baseline cognition.6,8,12 Nonetheless, multivariable models that include these predictors still only account for 20-30% of the variance observed in CI performance.8,13-15 As such, exploring additional factors that impact speech reception outcomes may improve preoperative counseling, prediction modeling, and ultimately the delivery of precision medicine in CI patient care.
For any type of medical decision making and delivery of quality medical care, providers take into consideration patients’ medical ailments (i.e. medical comorbidities). Medical comorbidities provide an overview of a patient’s health and drastically influence outcomes and quality of life in many chronic conditions such as diabetes, cancer, and heart disease.16-18 While studies have directly linked hearing loss with various comorbidities, such as diabetes and cardiovascular disease,19-21 the relationship between medical comorbidities and CI is not well established. One study utilized a modified frailty index and found no relationship between frailty and audiologic outcomes.22 A more recent investigation found that a higher number of comorbidities trended towards worse outcome, but conclusions are limited by small sample size and lack of a standardized comorbidity index.23
In this study, we perform a retrospective cohort study on 560 adult cochlear implant users to explore the association between the severity of comorbidities and CI hearing outcomes. We use the Adult Comorbidity Evaluation-27 (ACE-27), a validated comorbidity index utilized in head and neck cancer research, to define comorbidity severity.24,25 We hypothesize that patients with more severe comorbidities will have worse post-implantation speech perception outcomes compared to those with less severe comorbidities.
Materials and Methods
A retrospective cohort study was performed on a cohort of 976 patients undergoing cochlear implantation at a tertiary referral center from a novel workflow integrated CI data registry.26,27 Approval was obtained by the authors’ local institutional review board (IRB #202211010).
Inclusion and Exclusion
Adult patients who underwent cochlear implantation at a tertiary referral center between January 2015 and May 2022 were included. Pediatric patients, those without preoperative consonant-nucleus consonant (CNC) score, those without follow-up, those with disqualifying surgical complications (i.e., explanted, migrated stimulator), and those without a standardized preoperative anesthesia assessment were excluded.
Exposure and Outcomes
Severity of comorbidities, as defined by the ACE-27 scale, was the main exposure of interest. The ACE-27 is a validated index that assesses 26 comorbid ailments from different organ systems and scores them by severity of decompensation.28 These scores were then categorized into an overall comorbidity assessment, reported as none, mild, moderate, and severe. Other comorbidity indices exist, such as the American Society of Anesthesiologists Physical Status (ASA status) or Charleston Comorbidity Index, but they are more subjective and susceptible to misclassification than the ACE-27.29-34 Comorbidity data were extracted from standardized preoperative anesthesia notes. This preoperative assessment included a comprehensive review of medical history, medications, and preoperative testing (including laboratory testing and specialized testing as indicated).
Post-operative speech recognition scores were the primary outcome of interest. Speech recognition in quiet was presented at 60 dB using CNC words and AzBio sentences. AzBio sentences were also presented with background noise (signal-to-noise ratio [SNR] + 10 dB). Speech recognition scores were obtained from audiology records at 3, 6, and 12 months post-operatively. Similar to prior studies, a 15% change in AzBio and AzBio + 10 dB SNR score was considered clinically meaningful.35-38 A 10% change in CNC was considered clinically meaningful.38,39
Additional variables collected through chart review included demographics, body mass index (BMI), functional capacity, ASA status, hearing history (i.e. duration of hearing loss, duration of severe-profound hearing loss, prelingual hearing loss), Montreal Cognitive Assessment (MoCA), sequential CI, preoperative audiologic data, functional status (as defined by number of metabolic equivalents), CI manufacturer (Cochlear, Advanced Bionics, and MedEL), and data-logging history. Data logging was collected from sound processor data and defined as the average hours of processor use per day.
Statistical Analysis
Statistical analysis was performed in SAS (Version 9.4 statistical software (SAS Institute, Cary, NC). Descriptive statistics were used to describe the study population. Normal distribution assumption was evaluated through histogram analysis and Shapiro-Wilks test. Mean with standard deviation (SD) was used to describe normally distributed data while median with minimum-maximum was used to describe non-normally distributed data. A p-value of <0.05 was set as statistically significant.
A mixed general linear model (GLM) analysis was used to explore the change in CI speech perception outcomes (i.e. CNC, AzBio in quiet, AzBio +10dB SNR) through time and compare changes between ACE-27 groups through the exploration of ACE-27 by time interaction. A mixed GLM model allows exploration of fixed and random effects after controlling for potential confounders. Subjects were treated as random effects in the model and the unstructured covariance matrix was employed for the repeated measures. Post-operative visit timepoint, ACE-27 group, and other covariates were evaluated as fixed effects. Clinically important confounders were included in the mixed-effects model (age and sequential CI). Least squares marginal means and 95% confidence intervals were used as measures of effect size.
Results
A total of 976 patients were pulled from our institution’s CI data registry. Patients were excluded as follows: 42 pediatric patients (<18 years), 155 patients without preoperative CNC score, 103 patients without postoperative follow-up, 11 patients with surgical complication (migrated stimulators, explanted), and 105 patients without a preoperative anesthesia evaluation (for consistent ACE-27 collection). A total of 560 patients remained for analysis.
Patient Demographics and Characteristics
Patient characteristics are summarized in Table 1. Patients were categorized by the ACE-27 index: a total of 112 patients (20.0%) had no comorbidities, 204 patients (36.4%) had mild comorbidities, 161 patients (28.8%) had moderate comorbidities, and 83 patients (14.8%) had severe comorbidities. Patients without comorbidities were on average younger than patients with comorbidities (Total: mean age 64.5, None: mean age 56.6, Mild: mean age 70.4, Moderate: mean age 71.7, Severe: mean age 73.6). The majority of patients were Caucasian (95.3%) and there was equal gender distribution throughout all four comorbidity groups. The median duration of hearing loss, duration of severe to profound loss, and cognition as assessed with MoCA were similar across all groups. A greater number of patients with no comorbidities had prelingual hearing loss (Total: 6.5%, None: 14.4%, Mild: 6.4%, Moderate: 3.2%, Severe: 3.7%).
Table 1.
Patient demographics and preoperative characteristics categorized by ACE-27 score (reported as none, mild, moderate, and severe). SD = standard deviation; BMI = body mass index; MET = metabolic equivalent; ASA = American Society of Anesthesiologists (classification system); HL = hearing loss; MoCA = Montreal Cognitive Assessment. *Statistically significant differences across ACE-27 groups.
| Total (n=560) n (%) |
None (n=112) n (%) |
Mild (n=204) n (%) |
Moderate (n=161) n (%) |
Severe (n=83) n (%) |
|
|---|---|---|---|---|---|
| Age at CI (years)* | |||||
| Mean (SD) | 64.5 (16.4) | 56.6 (18.6) | 70.4 (14.1) | 71.7 (15.4) | 73.6 (12.5) |
| Sex | |||||
| Female | 244 (43.6%) | 53 (47.3%) | 79 (38.7%) | 76 (47.2%) | 36 (43.4%) |
| Male | 316 (56.4%) | 59 (52.2%) | 125 (61.3%) | 85 (52.8%) | 47 (56.6%) |
| Race | |||||
| Caucasian | 532 (95.3%) | 105 (93.8%) | 200 (98.5%) | 150 (93.8%) | 77 (92.8%) |
| African American | 20 (3.6%) | 6 (5.4%) | 3 (1.5%) | 6 (3.8%) | 5 (6.0%) |
| Hispanic | 2 (0.4%) | 0 (0%) | 0 (0%) | 1 (0.6%) | 1 (1.2%) |
| Asian | 4 (0.7%) | 1 (0.9%) | 0 (0%) | 3 (1.9%) | 0 (0%) |
| Other | 0 (0%) | 0 (0%) | 0 (0%) | 0 (0%) | 0 (0%) |
| BMI (kg/m2)* | |||||
| Mean (SD) | 29.1 (5.9) | 26.8 (4.2) | 28.1 (4.4) | 30.7 (6.7) | 31.5 (7.2) |
| Functional Capacity* | |||||
| 1-4 METs | 27 (14.8%) | 1 (3.3%) | 3 (4.8%) | 10 (18.9%) | 13 (41.9%) |
| 5-9 METs | 148 (81.3%) | 27 (90.0%) | 57 (91.9%) | 46 (86.8%) | 18 (58.1%) |
| >10 METs | 6 (3.3%) | 2 (6.7%) | 2 (3.2%) | 2 (3.8%) | 0 (0%) |
| ASA | |||||
| 1 | 28 (5.0%) | 23 (20.7%) | 5 (2.5%) | 0 (0%) | 0 (0%) |
| 2 | 315 (56.5%) | 84 (75.7%) | 146 (71.6%) | 66 (41.3%) | 19 (22.9%) |
| 3 | 212 (38.0%) | 4 (3.6%) | 53 (26.0%) | 93 (58.1%) | 62 (74.7%) |
| 4 | 3 (0.5%) | 0 (0%) | 0 (0%) | 1 (0.6%) | 2 (2.4%) |
| Duration HL (years) | |||||
| Median (min-max) | 20 (0-85) | 19 (0-85) | 20 (0-76) | 20 (0-80) | 20 (0-59) |
| Duration Severe-Profound HL (years) | |||||
| Median (min-max) | 5 (0-85) | 5 (0-85) | 5 (0-62) | 5 (0-55) | 4 (0-42) |
| Prelingual HL* | |||||
| Yes | 36 (6.5%) | 16 (14.4%) | 13 (6.4%) | 5 (3.2%) | 3 (3.7%) |
| No | 515 (93.5%) | 93 (85.3%) | 190 (93.6%) | 152 (96.8%) | 79 (96.3%) |
| MoCA | |||||
| Median (min-max) | 24 (8-30) | 24 (12-30) | 24 (8-30) | 24 (11-29) | 24 (8-29) |
| Etiology | |||||
| Unknown | 201 (35.9%) | 43 | 73 | 52 | 33 |
| Presbycusis | 96 (17.1%) | 6 | 41 | 26 | 23 |
| Noise Exposure | 62 (11.1%) | 5 | 21 | 27 | 9 |
| Sudden Hearing Loss | 62 (11.1%) | 18 | 22 | 16 | 6 |
| Meniere’s Disease | 42 (7.5%) | 15 | 10 | 10 | 7 |
| Autoimmune | 4 (0.7%) | 0 | 2 | 1 | 1 |
| Congenital | 45 (8.0%) | 17 | 11 | 12 | 5 |
| Infectious | 16 (2.9%) | 3 | 9 | 4 | 0 |
| Temporal Bone Fracture | 10 (1.8%) | 1 | 4 | 5 | 0 |
| Other | 22 (3.9%) | 4 | 8 | 8 | 2 |
Functional capacity was missing for the majority of patients (67.7%). Available data demonstrated most patients had 5-9 metabolic equivalents (MET) (Total: 81.3%, None: 90.0%, Mild: 91.9%, Moderate: 86.8%, Severe: 58.1%). The proportion of 1-4 METs was higher amongst patients with moderate and severe comorbidities (Total: 14.8%, None: 3.3%, Mild: 4.8%, Moderate: 18.9%, Severe: 41.9%). ASA also trended towards a higher classification in patients with more severe comorbidities (% ASA 3 - Total: 38.0%, None: 3.6%, Mild: 26.0%, Moderate: 58.1%, Severe: 74.7%).
Preoperative speech perception scores are summarized in Table 2. Preoperative CNC words, AzBio sentences in quiet, and AzBio sentences +10 dB scores were similar across comorbidity groups. The percentage of data-logging reported was also similar across comorbidity groups.
Table 2.
Preoperative speech recognition scores and postoperative data logging categorized by ACE-27 score (reported as none, mild, moderate, and severe). CNC = consonant-nucleus-consonant; AzBio = Arizona Bioindustry Sentences; SNR = signal to noise ratio. There was no statistical significance between preoperative speech perception measures across ACE-27 comorbidity groups.
| Total (n=560) n (%) |
None (n=112) n (%) |
Mild (n=204) n (%) |
Moderate (n=161) n (%) |
Severe (n=83) n (%) |
|
|---|---|---|---|---|---|
| Preoperative CNC | |||||
| Median (min-max) | 10 (0-86) | 7 (0-72) | 12 (0-66) | 10 (0-76) | 12 (0-86) |
| Preoperative AzBio Quiet | |||||
| Median (min-max) | 12 (0-98) | 12 (0-80) | 12 (0-81) | 7.5 (0-91) | 17 (0-98) |
| Preoperative AzBio + 10dB SNR | |||||
| Median (min-max) | 2 (0-67) | 1 (0-39) | 4 (0-65) | 1 (0-67) | 2 (0-64) |
| Data Logging | |||||
| 3 Months Postop | |||||
| Reported | 398 (77.9) | 81 (77.9) | 155 (81.6) | 106 (76.3) | 56 (70.9) |
| Unreported | 113 (22.1) | 23 (22.1) | 35 (18.4) | 33 (23.7) | 23 (29.1) |
| 6 Months Postop | |||||
| Reported | 339 (78.1) | 75 (80.7) | 134 (82.2) | 88 (74.0) | 42 (71.2) |
| Unreported | 95 (21.9) | 18 (19.4) | 29 (17.8) | 31 (26.1) | 17 (28.8) |
| 12 Months Postop | |||||
| Reported | 248 (74.5) | 45 (65.2) | 105 (80.8) | 69 (72.6) | 29 (74.4) |
| Unreported | 85 (25.5) | 24 (34.8) | 25 (19.2) | 26 (27.4) | 10 (25.6) |
Postoperative speech perception outcomes are summarized in Table 3. Patients with severe comorbidities trended towards worse speech recognition, especially in noise (Median AzBio + 10 dB SNR at 12 months – Total: 36.0, None: 44.0, Mild: 36.5, Moderate: 33.5, Severe: 18.0).
Table 3.
Postoperative speech recognition scores categorized by ACE-27 score (reported as none, mild, moderate, severe). CNC = consonant-nucleus-consonant; AzBio = Arizona Bioindustry Sentences; SNR = signal to noise ratio.
| Total (n=560) | None (n=112) | Mild (n=204) | Moderate (n=161) | Severe (n=83) | |
|---|---|---|---|---|---|
| 3 month | |||||
| CNC | |||||
| Median (min-max) | 48 (0-93) | 52 (0-93) | 48 (0-92) | 48 (0-85) | 40 (4-83) |
| AzBio Quiet | |||||
| Median (min-max) | 59 (0-99) | 70.5 (2-99) | 61 (0-97) | 56.5 (0-99) | 53 (0-92.6) |
| AzBio + 10dB SNR | |||||
| Median (min-max) | 27 (0-91) | 30 (0-91) | 29 (0-88) | 26.5 (0-90) | 20.5 (0-77) |
| 6 month | |||||
| CNC | |||||
| Median (min-max) | 52.5 (0-97) | 60 (0-92) | 55.5 (0-97) | 52 (0-92) | 48 (2-88) |
| AzBio Quiet | |||||
| Median (min-max) | 66 (0-100) | 71 (0-100) | 66.5 (0-98) | 66 (0-98) | 56.5 (3-94) |
| AzBio + 10dB SNR | |||||
| Median (min-max) | 32 (0-100) | 38 (0-100) | 33 (0-93) | 31.5 (0-86) | 19 (0-79) |
| 12 month | |||||
| CNC | |||||
| Median (min-max) | 56 (0-93) | 64 (4-93) | 56 (0-92) | 52 (6-88) | 56 (4-90) |
| AzBio Quiet | |||||
| Median (min-max) | 67 (0-100) | 75.5 (0-100) | 70 (0-96) | 63 (0-99) | 60 (4-98) |
| AzBio + 10dB SNR | |||||
| Median (min-max) | 36 (0-95) | 44 (0-87) | 36.5 (0-87) | 33.5 (0-95) | 18 (0-78) |
Mixed Model Analysis
After controlling for age and sequential CI, there was a clinically important improvement in CNC, AzBio, and AzBio + 10dB SNR from preop to 3, 6, and 12 months follow-up, and this improvement varied between ACE-27 groups over time with p-values 0.11, 0.045, and 0.0096, respectively (Figure 1). As can be seen in Table 4, clinically important improvement was noted in each of the follow-up assesssments as compared to preop for each of the speech perception outcomes. The largest improvement was noted between preop and 12 months assessments among patients with no comorbidities with estimated marginal mean (EMM) difference (95% CI) for CNC: 43.9 (38.7-49.0), AzBio: 52.3 (45.7-58.9) and AzBio + 10dB SNR: 39.5 (33.8-45.2). Patients with more severe comorbidities had worse outcome. For AzBio Quiet, EMM difference between preop and 12 month assessments (95% CI) was 52.3 (45.7-58.9) in the no comorbidity group and 32.5 (24.6-40.5) in the severe comorbidity group. For AzBio + 10dB SNR, EMM difference between preop and 12 month assessments (95% CI) was 39.5 (33.8-45.2) for the no comorbidity group and 21.2 (13.6-28.7) for the severe comorbidity group. For CNC, EMM difference between preop and and 12 month assessments (95% CI) was 43.9 (38.7-49.0) for no comorbidity group and 31.1 (24.8-37.4) for the severe comorbidity group.
Figure 1.
Comparison of change in speech perception outcomes between comorbidity groups through time while controlling for age and sequential CI. Estimated marginal means and 95% confidence intervals are plotted.
Table 4.
Estimated Marginal Mean (EMM) Difference from pre-operative scores for each outcome measure, categorized by ACE-27 score (reported as none, mild, moderate, and severe). For each model, the estimates are adjusted for age and sequential CI. CNC = consonant-nucleus-consonant; AzBio = Arizona Bioindustry Sentences; SNR = signal to noise ratio. P-value measures whether the respective speech perception measure changes significantly over time and whether that change is significantly different across comorbidity groups.
| Time of Assessment |
None EMM Difference from Pre-Op (95% CI) |
Mild EMM Difference from Pre-Op (95% CI) |
Moderate EMM Difference from Pre-Op (95% CI) |
Severe EMM Difference from Pre-Op (95% CI) |
p-value | |
|---|---|---|---|---|---|---|
| CNC | 3 months | 35.5 (30.5-40.0) | 28.6 (25.0-32.1) | 29.9 (25.9-33.9) | 22.7 (17.2-28.2) | |
| 6 months | 42.0 (37.1-47.0) | 33.9 (30.2-37.6) | 35.3 (31.1-39.5) | 30.3 (24.3-36.2) | 0.11 | |
| 12 months | 43.9 (38.7-49.0) | 36.1 (32.3-39.9) | 37.4 (33.1-39.5) | 31.1 (24.8-37.4) | ||
| AzBio Quiet | 3 months | 44.4 (38.2-50.6) | 36.0 (31.5-40.4) | 35.2 (30.1-40.2) | 28.4 (21.4-35.4) | |
| 6 months | 48.2 (41.8-54.5) | 41.4 (36.8-46.0) | 41.0 (35.7-46.2) | 32.5 (25.1-39.9) | 0.045 | |
| 12 months | 52.3 (45.7-58.9) | 42.3 (37.5-47.2) | 41.1 (35.6-46.6) | 32.5 (24.6-40.5) | ||
| AzBio + 10dB SNR | 3 months | 26.8 (21.9-31.8) | 21.8 (18.2-25.4) | 21.2 (17.0-25.5) | 15.1 (−9.0-21.3) | |
| 6 months | 33.2 (27.8-38.7) | 26.1 (21.9-30.2) | 24.7 (19.8-29.6) | 19.9 (12.8-27.1) | 0.0096 | |
| 12 months | 39.5 (33.8-45.2) | 27.4 (23.3-31.6) | 25.9 (21.1-30.8) | 21.2 (13.6-28.7) |
Discussion
Our limited ability to identify prognostic factors for CI performance is a critical barrier to the advancement of precision medicine in CI patient care. Comorbidities offer objective data about the overall health of an individual patient. They are a predictor of cancer survival independent of tumor stage, and a predictor of outcomes in several chronic conditions such as diabetes, heart disease, and hearing loss.16-18,20,28,40 To our knowledge, this is the largest study to date evaluating the role of medical comorbidities in CI outcomes. This study suggests that individual patient comorbidities are a prognostic factor for CI speech recognition outcomes. Using a mixed model analysis on 560 CI recipients while controlling for age at CI, we demonstrate that all comorbidity groups achieve a clinically meaningful improvement in speech perception outcomes. However, patients with more severe comorbidities perform significantly worse over time when compared to those with less severe comorbidities. Clinical and statistical significance was demonstrated for AzBio Quiet and AzBio + 10 dB SNR, but we also show clinically meaningful differences in improvement CNC between no comorbidity and severe comorbidity groups.
While these findings that sicker patients do worse may be intuitive, the causality of between comorbidities and CI performance is unclear and needs to be further explored. The association between comorbidities and age, social determinants of health, and cognitive function gives us some insight into their significance for CI patients. Comorbidities are associated with age, as reflected by the younger mean age in our no-comorbidities group. While some studies have found an association between age and performance,6,14,15,41,42 other studies have not.43,44 The variability in prior studies may be related to differences in the comorbidity burden between patients as they may be discrepancies between chronological and biological age. To fully evaluate the influence of comorbidities on CI speech perception performance, particularly given differences in age across ACE-27 comorbidity groups, age was controlled for in the mixed model analysis. Our findings strongly support patient’s individual comorbidities are significantly associated with CI outcomes regardless of age at CI.
Additionally, comorbidity indices may provide insight about a patient’s social determinants of health. Chronic disease outcomes are intricately connected with an individual’s income, social support, and access to healthcare.45-47 When evaluating race, black adults are also more likely to die from heart disease compared to other races.48 Income and education are also associated with cardiovascular disease, with one study demonstrating each $10,000 increment increase in neighborhood income was associated with a 10% reduction in mortality after myocardial infarction.49 Social determinants of health are therefore closely related to overall frailty, and comorbidity indices allow for a more comprehensive evaluation of an individual’s health status. Further work is needed to explore this potential relationship.
Interestingly, we observed CI outcomes between comorbidity severity groups is most pronounced with the addition of background noise. These findings suggest patients with more severe comorbid ailments may have decreased central auditory processing. Background noise and central processing has primarily been studied as it relates to age. Prior literature has suggested that older patients tend to perform worse in background noise,50-52 and may have decreased central processing efficiency.51,53 Comorbidities may offer a quick and easy partial surrogate maker for central processing and cognition. While there are no studies to our knowledge evaluating the direct relationship between comorbidities, cognition, and hearing loss; there are several studies that have demonstrated a strong correlation between severity of comorbid ailments and patient cognition. Post-ICU cognitive impairment has been associated with higher comorbidity index.54 Higher comorbidity index is also associated with rates of dementia and polypharmacy in geriatric patients.55 Similarly, the Lancet commission has demonstrated patients with more comorbid conditions (e.g. hypertension, obesity) are at higher risk for dementia.56 Of particular interest, a recent prospective trial demonstrated hearing aids may have a protective effect on the rate of cognitive decline in patients at higher risk for dementia, a subgroup of patients with more comorbid conditions (e.g. cardiovascular risk factors).57 Future work will need to carefully explore the relationship and predictive capabilities of comorbidities on central auditory processing and impact on CI speech perception outcomes.
In a subgroup analysis, we found the median MoCA is the same across all comorbidity groups (mild cognitive impairment). However, MoCA was not included in the mixed model analysis due to a large amount of missing data, thus limiting conclusions. The ACE-27 also has a central nervous system domain that captures conditions like history of stroke, TIA, dementia, paralysis, and neuromuscular disease. Out of 560 patients, only 41 patients had an CNS comorbid conditions and sub-analysis of this group did not demonstrate any significant correlation with CNC scores (supplemental data). As we look to the future of precision medicine, an ideal model for CI performance prediction necessitates measurements of both peripheral and central function.58 While comorbidities demonstrate a significant impact on CI speech perception outcomes that is most pronounced in noise, future studies will need to further evaluate the relationship cognition and comorbidity index in the CI population.
While patient comorbidities may offer a novel insight into CI performance stratification, this study has several limitations. The ACE-27 was first developed as a comorbidity index in newly diagnosed cancer patients. However, the ACE-27 has several advantages; first, it is the only comorbidity index to grade based on severity of decompensation across different organ systems. Second, it relies on information extracted from the medical charts in a standard fashion and information is not based on claims data and ICD coding.28 ICD based claims data for comorbidity assessment, like the Charleston Comorbidity index, is used for hospital billing and therefore may be inaccurate and misleading.29 Additionally, as any retrospective study, information was extracted from the electronic medical record resulting in a variable amount of missing data. To limit bias when calculating the ACE-27, only patients with a preoperative standardized anesthesia note were included. This study was not structured to evaluate the causality behind the associations noted, and this is an important area of future research. We additionally did not evaluate the relationship between quality of life and comorbidities. This study has limited generalizability as data is from a single center and the pediatric population was excluded.
Conclusions
Medical comorbidities are an important and often overlooked factor in post-operative CI speech perception performance. A comprehensive comorbidity evaluation is routinely performed by anesthesia prior to major surgery and can be utilized in preoperative counseling to help frame patient expectations and potential future use in CI prediction modeling. Future studies are needed to elucidate the causation behind this association.
Supplementary Material
Footnotes
Conflicts of Interests:
DK and JFP own stock options for PotentiaMetrics, but the work of the company is not related to the present article. CCW – Consultant for Stryker Coporation and Cochlear Ltd.; JAH – Consultant for Cochlear Ltd., CAB – consultant for Advanced Bionics, Cochlear Ltd., Envoy, and IotaMotion, and has equity interest in Advanced Cochlear Diagnostics, LLC.; MAS – consultant for Cochlear Ltd.
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