Clinical Adult Literature Updates from May 2014

Normal Hypercapnic Cerebrovascular Conductance in Obstructive Sleep Apnea

“In this study, the authors hypothesized that cerebrovascular reactivity (CVR, ratio of the change in cerebral blood flow to the change in vasodilatory stimulus such as hypercapnia) would be decreased in OSA patients as a possible mechanism for stroke. Middle cerebral artery blood flow velocity (MCAv) and mean arterial blood pressure (MAP) responses to hypercapnia were measured to determine cerebrovascular conductance (MCAv/MAP). It was assumed that the MCAv was an estimate of cerebral blood flow. Overnight changes in conductance CVR were assessed in treatment naïve, otherwise healthy OSA (n=13) and non-OSA (n=9) subjects at two isoxic tensions (150 and 50mmHg). There were no differences in CVR between the two groups for either isoxic tension. CVR was increased in hypoxia, indicating other alterations in CVR may raise the risk of stroke in OSA patients.“


New Frontiers in Obstructive Sleep Apnoea

“In this good quality scoping review, authors describe and summarize cutting-edge research with respect to OSA in three sections. In the animal section, various simulation strategies used to simulate OSA airway physiology and understand the mechanisms of OSA are discussed. In the diabetes section, current evidence is summarized in human and animal models demonstrating how intermittent hypoxia and sleep fragmentation could have a negative impact on glucose tolerance. The last section describes the use of cardiovascular biomarkers to measure some of the negative consequences of OSA, and response to OSA therapies.“


Effect of Rostral Fluid Shift on Pharyngeal Resistance in Men With and Without Obstructive Sleep Apnea

In this randomized controlled cross-over trial, the authors hypothesized that increased pharyngeal resistance (Rph) will increase more in men with than without OSA in response to rostral fluid redistribution. Seventeen men with, and 12 without obstructive sleep apnea (OSA) were randomized to lower body positive pressure (LBPP) for 15min or control, then crossed over. LBPP displaced similar amounts of fluid from the legs in both groups. However, compared to the non-OSA group, Rph increased significantly more during LBPP in the OSA group (p=0.016). Moreover, change in Rph during LBPP correlated directly with baseline Rph in the OSA group, but inversely in the non-OSA group. This study adds to the increasing body of literature that OSA patients have increased susceptibility to pharyngeal obstruction and collapse in response to overnight rostral fluid redistribution during sleep. Future research is needed to evaluate treatment strategies targeted to prevent the rostral fluid shift, and its impact on hard clinical outcomes in OSA patients.


Incidence of Perioperative Sleep-Disordered Breathing in Patients Undergoing Major Surgery — A Prospective Cohort Study

“In this study, polygraphic recordings have been obtained from 37 inpatients without a diagnosis of obstructive sleep apnea syndrome during the preoperative night before and six nights following major surgical procedures. Median (IQR [range]) apnea-hypopnea-index (AHI) for the whole group was 6,0 (2,5 — 14,7 [0–32,6]) in the preoperative night and increased in the following six nights post surgery: second night: 5,6 (2,6–15,0 [1,1 — 59,3]); third night: 16,9 (5,6 — 38,8 [2,9 — 64,3]); fourth night: 11,6 (5,9 — 17,3 [0,4 — 39,3]); fifth night: 15,2 (5,7 — 22,2 [0,2 — 55,5]); sixth night: 22,5 (5,2 — 35,4 [0,2 — 67,7]). AHI-scores of the third to sixth night post surgery differed significantly from data observed in the preoperative night. Sleep-disordered breathings in the late postoperative period deserve attention, as they potentially increase the risk of postoperative complications.”

Emerging Risk Factors and Prevention of Perioperative Pulmonary Complications

“In this review article the authors discuss the fact that “modern surgery is faced with the emergence of newer “risk factors” and the challenges associated with identifying and managing these risks in the perioperative period. Obstructive sleep apnea and obesity hypoventilation syndrome pose unique challenges in the perioperative setting.”

Obesity Does Not Increase Mortality After Emergency Surgery

The authors “aim of this study was to evaluate the impact of obesity on patient outcomes after emergency surgery. 341 patients were identified during the study period. 202 (59%) were obese.” The authors concluded that “after reviewing A higher BMI is not an independent predictor of mortality after emergency surgery. Obese patients are at a higher risk of developing wound infections and requiring ICU admission after emergent general surgical procedure.

Incremental Shuttle Walk Test in the Assessment of Patients With Obstructive Sleep Apnea-Hypopnea Syndrome

The authors’ findings support the use of the incremental shuttle walk test for monitoring the effects of continuous positive airway pressure treatment and may suggest its use in rehabilitation programmes designed to reduce obesity and cardiovascular risk factors in patients with obstructive sleep apnea-hypopnea syndrome.“\

Clinical Implications of Sleep Disordered Breathing in Acute Myocardial Infarction

There is a high prevalence of previously undiagnosed SDB among patients with AMI. SDB in the setting of AMI is associated with higher pulmonary artery systolic pressure. SDB was not associated with adverse clinical outcomes.

Diagnostic Predictors of Obesity-Hypoventilation Syndrome in Patients Suspected of Having Sleep Disordered Breathing

PO2 and HCO3 were independent predictors of OHS, explaining 27.7% of pCO2 variance (p < 0.0001). A calculated HCO3 cutoff > 27 mmol/L had 85.7% sensitivity and 89.5% specificity for diagnosis of OHS, with 68.1% positive and 95.9% negative predictive value.

Sleep Apnea is Associated With Subclinical Myocardial Injury in the Community. The ARIC-SHHS Study

In middle-aged to older individuals, OSA severity is independently associated with higher levels of high-sensitivity troponin T (hs-TnT), suggesting that subclinical myocardial injury may play a role in the association between OSA and risk of heart failure. OSA was not associated with N-terminal proB-type natriuretic peptide (NT-proBNP) levels after adjusting for multiple possible confounders.