Resistant Hypertension in Chronic Kidney Disease

203

Respiratory events are characterized as either apneas (defined as a >90% reduc-
tion in tidal volume lasting ≥10 s) or hypopneas (defined as a ≥30% reduction in
airflow lasting ≥10 s and accompanied by either a ≥3% reduction in oxygen satura-
tion or an arousal from sleep as seen on electroencephalogram [ 44 ].
OSA severity is defined according to the apnea-hypopnea index (AHI), where
mild OSA is defined by AHI 5–14 events/hour, moderate OSA by AHI 15–29
events/hour, and severe OSA by ≥30 or more events per hour. While somewhat
clinically arbitrary, these thresholds have provided a structure for research purposes
and may influence treatment decisions and in some cases insurance reimbursement
for CPAP therapy.

Clinical Features of OSA

History and Risk Factors

Snoring and daytime sleepiness are common symptoms of OSA, but are not specific
to the disorder. Nocturnal gasping or choking appears to be the most reliable indica-
tor or sleep apnea [ 45 ]. Table 13.2 lists the varied clinical characteristics that may
be seen in association with obstructive sleep apnea. While many patients may pres-
ent with several of the features listed, some may have very few. It is common for a
bedpartner’s concerns to outweigh those of the patient. Risk factors for OSA include
male gender, smoking, older age, larger neck circumference, and obesity.

Table 13.1 Diagnostic criteria for OSA. The presence either of both A and B, or of C alone, is
needed for diagnosis

A. The presence of one or more of the following

1. The patient complains of sleepiness, non-restorative sleep, fatigue, or insomnia symptoms


2. The patient wakes with breath holding, gasping, or choking


3. The bed partner or other observer reports habitual snoring, breathing interruptions, or both
   during the patient’s sleep


4. The patient has been diagnosed with hypertension, mood disorder, cognitive dysfunction,
   coronary artery disease, stroke, congestive heart failure, atrial fibrillation, or type 2 diabetes
   mellitus
   B. Polysomnography (PSG) or out-of-center sleep testing (OCST) demonstrates


5. Five or more obstructive respiratory events (obstructive or mixed apneas, hypopneas, or
   respiratory effort-related arousals) per hour of sleep during PSG or per hour of monitoring
   (OCST)
   C. PSG or OCST demonstrates


6. Fifteen or more obstructive respiratory events per hour of sleep during PSG or per hour of
   monitoring (OCST)
   Adapted from American Academy of Sleep Medicine [ 43 ]

13 Obstructive Sleep Apnea and Resistant Hypertension