A Retrospective Analysis of Patients with Pulmonary Hypertension to Assess the Role of Overnight Oximetry in the Diagnosis of Sleep Disordered Breathing

C l i n M e d International Library Citation: Patel NM, Arunthari V, Heckman M Burger CD (2014) A Retrospective Analysis of Patients with Pulmonary Hypertension to Assess the Role of Overnight Oximetry in the Diagnosis of Sleep Disordered Breathing. Int J Respir Pulm Med 1:004 Received: August 14, 2014: Accepted: October 07, 2014: Published: October 10, 2014 Copyright: © 2014 Patel NM. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Patel, Int J Respir Pulm Med 2014, 1:1 ISSN: 2378-3516


Introduction
Sleep Disordered Breathing (SDB) is a known risk factor in the development of Pulmonary Hypertension (PH) [1].In patients with PH, the role of overnight oximetry as a means to screen for SDB has not been well established [2].Current recommendations are based on studies that have shown a high prevalence of nocturnal desaturation in patients with pulmonary arterial hypertension [3,4].The presence of sleep apneas and hypopneas has been found to be rare when measured during polysomnography [3].Nonetheless, the prevalence of patients with both SDB and PAH has been estimated at as high as 17 to 53% [5].
There exists evidence that overnight oximetry is a sensitive means of screening individuals for the presence of SDB [6,7].To date this data has not been extrapolated to patients with PH.In this study, we sought to evaluate whether overnight oximetry was additive to a standard sleep questionnaire in the diagnosis of SDB in patients with PH.

Patients
This study was approved by the Mayo Clinic Institutional Review Board.All patients seen at the Mayo Clinic Florida PH clinic from 1992 to Sept 2006 were studied retrospectively.A total of 318 patients were identified for analysis.The following number of patients were excluded from analysis: 183 patients because an overnight oximetry was not obtained at time of initial evaluation; 27 patients who were on oxygen at time of overnight oximetry; 4 patients who were being treated with non-invasive positive pressure therapy at the time of evaluation; 2 patients who had less than 4 hours of recording of overnight oximetry; and 2 patients who were found to have a normal Right Ventricular Systolic Pressure (RVSP) as measured by echocardiogram.

Statistical analysis
Numerical variables were summarized with the sample median, 25 th percentile, and 75 th percentile.Categorical variables were summarized with number and percentage.Kendall's correlation coefficient tau or a Cochran-Armitage trend test was used to investigate associations between patient characteristics and both overnight oximetry result as well as number of SDB symptoms.Kendall's correlation coefficient tau or a Cochran-Armitage trend test was used to examine associations between pulmonary function test information and overnight oximetry result.Odds Ratios (OR's) and corresponding 95% Confidence Intervals (CI's) from single variable logistic regression models were used to investigate associations between patient characteristics and individual SDB symptoms.
Logistic regression models were used to investigate the association between overnight oximetry test result and number of SDB symptoms; various dichotomizations of overnight oximetry result were considered.Sensitivity to the possible confounding effects of other variables was also considered; based on the relatively small sample size, no more than one variable in addition to number of SDB symptoms was included in any one model.Statistical significance was determined at the 5% level.No adjustments for multiple comparisons were made in these exploratory analyses.

Results
318 patients were reviewed of which 94 met inclusion criteria.Baseline patient characteristics are shown in Table 1.Of the 94 patients, 17 (18%) had abnormal overnight oximetry suggesting the presence of SDB.Low baseline hypoxemia was found in 23 (24%) of patients, and normal studies were found in 54 (57%) subjects.
There is strong evidence showing a higher prevalence of abnormal overnight oximetry results as the number of SDB symptoms increases (P<0.001).Of patients who had no symptoms of SDB (17), all oximetry results were found to be normal (Table 2).
The clinical symptoms of SDB were 100% sensitive for predicting an abnormal screening overnight oximetry (Table 3).
A PSG was performed on 18 of the 94 patients.Of the14 patients with abnormal PSG results, only one subject had a normal overnight oximetry (Table 4).
Associations between patient characteristics and number of SDB symptoms are shown in Table 5.Other analysis revealed evidence of a higher prevalence of snoring in men (P=0.005) and in patients with a higher BMI (P=0.038).There is no statistically significant evidence of any other associations between patient characteristics and either individual SDB symptoms or overnight oximetry results.
Other analysis revealed evidence of a lower oxygen saturation level, lower partial pressure of oxygen in arterial blood, lower DLCO, and lower TLC in patients with low baseline oximetry results (Table 6).

Discussion
During routine evaluation of patients with PH, an assessment for the presence of SDB is recommended.[1].Whether this assessment

ISSN: 2378-3516
should consist of a questionnaire, overnight oximetry, or PSG is unknown.One such recommended approach would be to obtain an overnight oximetry if evidence of daytime resting or exercise desaturation exists.Subsequently, if the overnight tracing reveals a "sawtooth" pattern and patient has risk factors such as snoring, excessive daytime sleepiness, witnessed apneas, obesity, systemic hypertension, or old age then one should proceed on to full PSG [8,9].
We found that in patients with PH, clinical screening may suffice as the initial tool to screen for the presence of SDB.When symptoms were present, overnight oximetry added little to the diagnosis of SDB.In the absence of symptoms, there were no abnormal overnight oximetry results [10].
Proponents for the use of overnight oximetry often argue that it aids in the diagnosis of nocturnal hypoxemia.A small study of 13 primary PH patients reported that 10 (77%) had significant nocturnal hypoxemia, which were unrelated to apneas and hypopneas [3].A second study of 43 patients with pulmonary arterial hypertension demonstrated that 70% had at least 10% of the night with an oxygen saturation of less than 90% [4].Our subset of patients did not show nearly such high a prevalence, with only 24% of patients found to have nocturnal hypoxemia.These 23 patients tended to have lower baseline oxygen saturation (94% vs 96%), as well as lower resting PaO 2 (65 vs 71 mmHg).Also these patients were found to have a lower % predicted DLCO (57% vs 68%).Perhaps alternative measures (i.e.resting or exercise induced hypoxemia, low DLCO etc.) could be used as clues to identify those at high risk for nocturnal hypoxemia, thus increasing the pretest probability of further testing by overnight oximetry.
Of the subset of patients (18) who were prompted to undergo PSG based on an abnormal oximetry or history suggestive of SDB, a majority 14 (77.8%) were found to have an abnormal study (Apnea/ Hypopnea Index>5).All patients who had SDB confirmed by an abnormal PSG had at least one symptom suggestive of SDB (i.e.snoring, excessive daytime sleepiness, witnessed apneas).Only a single patient was reported to have a normal overnight oximetry, and found to have an abnormal PSG.Of note, this patient did report symptoms of snoring, excessive daytime sleepiness, and witnessed apneic events.The PSG confirmed mild SDB (AHI 8.3) despite normal overnight oximetry.The experience with this patient emphasizes the point that in patients who have a clinical history suggestive of SDB, proceeding to PSG may be the correct course of action, rather than obtaining an overnight oximetry.
Limitations of our analysis include the single center, retrospective design and lack of a control group to non-PH patients.Also the population was drawn from a tertiary referral practice and may not reflect a general medical practice.The diagnosis of PH was based on ECHO estimates of RVSP and not all patients underwent the standard of RHC [2].Finally, not all patients underwent PSG which remains the standard in diagnosis of SDB.

Conclusion
Future practices may consider exclusion of routine overnight oximetry as the initial screening tool for SDB in the evaluation of patients with PH.Overnight oximetry may still have a role in the initial evaluation of nighttime basal hypoxemia if suspected by history and physical examination.
In PH patients who have no symptoms of SDB, an overnight oximetry may not be additive in screening for SDB.In those patients with SDB symptoms, an overnight oximetry will be predictably abnormal.
Reporting of results was either: normal, baseline hypoxemia (mean SpO2 < 91%), or a number representing the ODI.ODI < 15 was defined as normal, 16 to 30 as mild SDB, 31 to 45 as moderate SDB, and > 45 as severe SDB.

Table 2 :
Associations between individual sleep disordered breathing symptoms and overnight oximetry test result.

Table 3 :
Estimated sensitivity and specificity of number of SDB symptoms for predicting an abnormal overnight oximetry.
-An exact binomial 95% confidence interval (CI) is given for each estimated sensitivity and specificity.

Table 4 :
Overnight oximetry result and polysomnography result.

Table 5 :
Associations between patient characteristics and number of sleep disordered breathing symptoms.