The crude odds ratio for CTS in NAs as compared with ORNs was 3.23 (CI, 1.27–8.17). This odds ratio was supported by a χ2 of 5.35 (P = 0.021) at a power of the χ2 of 75%.
Right-handed NAs were more likely to have left-hand and bilateral CTS than ORNs with an odds ratio of 3.85 (CI, 1.05–12.16) and a supporting χ2 of 5.08 (P = 0.024) at a power of the χ2 of 72%. Left-handed NAs did not seem to have the same risks for developing right-hand, left-hand, and bilateral CTS that right-handed NAs did as compared with similarly handed ORNs. Although not offering any protection from CTS as indicated by a negative odds ratio, left-hand dominance among NAs was associated with an insignificant risk of left unilateral and bilateral CTS with an OR of 1.44 (CI, 0.03–74.2) and a χ2 of 0.133 (P = 0.715).
Cumulative trauma disorders of the upper extremity are one of the fastest-growing occupational disorders in US industry (4). More than half (57%) of the occupational upper-extremity disorders reported in the federal work force were diagnosed as CTS (5). Product industries, especially meat packing and poultry processing, pose greater occupation-related risks of CTS in workers than service industries, such as health care (6). Some hobbies and avocations, such as knitting and string-instrument playing, also predispose individuals to CTS and may magnify and compound coexisting occupational risk factors (6).
Women between 31 and 50 years of age have now been identified as a high-risk population for CTS, predisposed to both occupation- and nonoccupation-related CTS (5). A recent shift to service industry work and more video display unit use, has, however, not correlated as well with increasing upper extremity cumulative trauma disorders in women as have increased numbers of women in the workforce and heightened public awareness of CTS (7). Despite increasing proportions of women in the US workforce, the distribution of Liberty Mutual Group Workers’ Compensation Insurance claims by sex has remained constant over the years, with women accounting for 65% of all upper-extremity cumulative trauma disorders, but only 30% of all claims (7). A compounding risks model has been proposed to illustrate the synergistic effects of work and home exposures on cumulative trauma disorders and can be easily adapted for CTS in women (8) (Fig. 1).
Several health care and allied health professions have been associated with unilateral CTS of the dominant hand and include interventional cardiology, dentistry, dental hygiene, and sign language communication (1). Repetitive pinching and advancement of small-bore vascular catheters with surgical gloves on may predispose interventional cardiologists to CTS (1). Vibrating dental buffers and drills may predispose dental hygienists and dentists, respectively, to CTS (1). Forced finger flexion during signing may predispose sign language interpreters to CTS (1). In all such cases among health industry workers, CTS is usually unilateral and confined to the dominant, preferred hand (1).
NAs have a number of unique, potentially neurodestructive, environmental and mechanical exposures in their professional workplace, the OR. The cumulative exposure of the upper extremity to these workplace exposures may predispose NAs to CTS. OR workers are habitually exposed to cold, ambient OR temperatures and waste anesthetics, especially nitrous oxide. Both cold and nitrous oxide exposures can reduce nerve conduction, and moderate nitrous oxide exposure can cause permanent symmetric, distal axonopathy (9). These environmental exposures can, however, be effectively mitigated by (1) wearing undergarments and layering OR garb (2), increasing OR temperatures, and (3) scavenging waste anesthetic gases.
Mechanical exposures unique to nurse anesthesia in this work site investigation included 1) rigid laryngoscopy for endotracheal intubation by using laryngoscopes and blades traditionally designed for left-hand use only and 2) wearing disposable, loose fitting gloves during laryngoscopy and other anesthesia procedures contaminated with body fluids. Rigid laryngoscopy performed with the left hand, in fact, exposed NAs to five of the six occupation-related risk factors for CTS as described by Silverstein et al. (10), with the single exception being use of vibrating, hand-held instruments, as in dentistry. These exposure risks during rigid laryngoscopy performed by NAs with the left hand included 1) repetitive left wrist deviation during laryngoscopy, 2) exaggerated left-hand grip during laryngoscopy, 3) left midpalmar compression by the laryngoscope handle during laryngoscopy, 4) extreme left-wrist flexion and extension during laryngoscopy, and 5) wearing poorly fitting gloves during laryngoscopy, which further exaggerated hand grip (10).
According to the classification of Silverstein et al. of mechanical exposures associated with work-related upper extremity cumulative trauma disorders, the task of rigid laryngoscopy may be classified as a high-force, low-repetition task (10,11). High force was defined as a force of 6 kg or more as estimated by surface electromyography (11). Low repetition was defined as a task lasting longer than 30 seconds or consisting of redundant tasks performed for 50% or more of the work-action cycle (11). Successful laryngoscopy for tracheal intubation often takes longer than 30 seconds, but less than one or two minutes, and requires a force that can extend the head (9% or more of body weight) off a flat surface and rigidly align to approximately 180 degrees the three axes of the airway (oral, laryngeal, and tracheal). The use of loose, bulky, or otherwise poorly fitted gloves, such as disposable, one-size-fits-all examination gloves, contributed to fingertip sensory feedback loss and resulted in hypercontraction of carpal tunnel tendons and increased grip forces in the model of Silverstein et al. (11).
In this investigation, NAs demonstrated a fivefold increased risk for CTS compared with ORNs. When risk adjustment was made for left-hand CTS, NAs continued to demonstrate an increased risk for nondominant, left-hand CTS and were nearly four times more likely to have been diagnosed clinically, and in some cases, electrophysiologically, with left-hand CTS than ORNs. The task of rigid laryngoscopy, which can be performed only with the left hand by using conventional laryngoscopes, and the wearing of loose-fitting, disposable gloves during rigid laryngoscopy contributed five of six known mechanical exposure forces associated with CTS in manual workers (10). Successful mitigation of these mechanical exposures might include laryngoscope redesign; replacing conventional, rigid laryngoscopy with flexible, fiberoptic laryngoscopy for tracheal intubation; and wearing fitted gloves for airway procedures (12).
The strengths of this investigation included 1) a double-blinded design at the time of data collection and analysis; 2) the same workplace occupational stresses, cold-temperatures, and scavenged waste-gas environmental exposures for all study subjects; and 3) the most sensitive and specific combination of two historical and two physical findings to confirm a clinical diagnosis of CTS with or without electrophysiologic diagnosis (13).
In making a clinical diagnosis of CTS, a positive Tinel’s sign (sensitivity 44%–63%, specificity 55%–94%) or a positive Phalen’s test (sensitivity 25%–71%, 47%–80%) do not offer the dependability that a combination of clinical tests and examinations can offer (6). A hand pain diagram as a diagnostic tool for CTS is an even weaker and more subjective indicator of CTS than provocative physical tests with a sensitivity of 61% and a specificity of 71%(6). When combined, however, as in this investigation, a Tinel’s sign and a hand pain diagram can offer a specificity of 89% and a positive predictive value of 71%(6). A combination of a positive Phalen’s test and a hand pain diagram can offer a specificity of 83% and a positive predictive value of 83%(6). This study was not designed to compare the sensitivity and specificity of combined nocturnal hand pain history, hand pain diagram, positive Tinel’s sign, and positive Phalen’s sign with the “gold standard” electrophysiologic diagnosis of CTS. The predetermined sensitivities and specificities of combined clinical tests as compared with nerve conduction tests were, however, assumed to be additive.
Weaknesses of this investigation included 1) the small sample size (n = 244) with no male nurses included; 2) a cross-sectional study design comparing prevalent cases, which could estimate only relative risk for incident cases of CTS; 3) no physiologic mea-surements of force and force duration (force × time) during rigid laryngoscopy, such as surface electromyography, grip force, force-posture interactions, and carpal tunnel compartment pressures; and 4) an inability to confirm the clinical diagnosis of CTS in 17 of 20 cases with electrodiagnostic testing. In addition, the temporal, synergistic risk factors for CTS could not be measured in this study, including shift lengths, repetitive laryngoscopies per day, work-rest ratios, and off-duty or sick-leave times (Fig. 1). The exact temporal responses and the repetitive stress exposures per day could not even be estimated because of rotating duty rosters, vacation and call schedules, and sick leaves, which institutions were not required to reveal for purposes of subject confidentiality and anonymity. Finally, the investigators were not permitted to contact off-duty nonresponders on call, vacation, or sick leave, creating two types of information bias (nonresponse and volunteer biases) that could not be controlled for in a prevalent study.
In adapting Kerk’s (8) model of compounding risk factors for musculoskeletal injuries in the workplace, a personal risk factor model for CTS in NAs should also have included a number of observed physical risk factors (solid boxes, Fig. 1) compounded by many unknown occupational, nonoccupational, and psychosocial risk factors (open boxes, Fig. 1) (8). Such a model cannot be replicated in a cross-sectional, bivariate investigation and will require prospective studies with multivariate analysis (Fig. 1) (8). This cross-sectional investigation at 11 work sites will require further confirmation of its findings in larger, both-sex, historical cohorts of OR workers from multiple professions in many work sites before generalizing its findings on CTS, left-hand CTS, and bilateral CTS to the universe of all NAs performing rigid laryngoscopy with the left hand.
On the basis of our data analysis, however, other female anesthesiology workers, such as female anesthesiologists and female anesthesiology physician assistants, will have the same increased exposure odds ratios for left-hand and bilateral CTS as female NAs. Although CTS occurred with increased frequency in both sexes in other health professions, such as interventional cardiology and dentistry; it was always a unilateral disorder of the dominant hand in these professions and not uniquely lateralized to the nondominant left hand (1). Male anesthesiology workers, such as male NAs, anesthesiologists, and physician assistants, will remain at decreased risk of CTS compared with female anesthesiology workers because of sex and increased upper extremity strength, but they could be predisposed to CTS by coexisting conditions, such as arthritis and endocrinopathy.
In conclusion, the answers to the research questions posed by this regional prevalence study included the following: 1) There were significant sentinel clusters of CTS in female NAs as compared with other OR workers, specifically female ORNs in 11 regional work sites. 2) Nurse anesthesia may represent another high-risk health care occupation for upper-extremity cumulative trauma disorders. Nondominant left-hand CTS and bilateral CTS were significantly more common among female NAs than female ORNs. As compared with other health care workers at increased risk of unilateral and dominant hand CTS, the cases of CTS in NAs observed in this study were bilateral or lateralized to the left hand and affected by hand dominance (1). Rigid laryngoscopy performed with the left hand exposed NAs to five of the six occupation-related risk factors for CTS as identified by Silverstein et al. (10,11). Despite precise inclusion criteria, the physical risk factors for CTS in all study subjects may have been magnified by sex, musculoskeletal strength, endocrine activity, and other physiologic variables, such as menses and premenstrual edema (1,8). Nevertheless, any possible confounding from risk magnification in women was evenly represented in same-sex cases and controls. On the basis of our data analysis, nondominant left-hand CTS and bilateral CTS were significantly more prevalent in NAs than ORNs.
The author acknowledges and appreciates the statistical advice and support of Professor and Chair Miguel A. Guzman, PhD, and Assistant Professor Donald E. Mercante, PhD, of the Department of Biometry and Genetics, Louisiana State University School of Medicine.
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© 2001 International Anesthesia Research Society
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