Beneficial effect of inhaled CO2 in a patient with non-obstructive sleep apnoea

Impact of concomitant medications on obstructive sleep apnoea

Obstructive sleep apnoea (OSA) is characterized by repeated episodes of apnoea and hypopnoea during sleep. Little is known about the potential impact of therapy drugs on the underlying respiratory disorder. Any influence should be taken into account and appropriate action taken, including drug withdrawal if necessary. Here, we review drugs in terms of their possible impact on OSA; drugs which (1) may worsen OSA; (2) are unlikely to have an impact on OSA; (3) those for which data are scarce or contradictory; and (4) drugs with a potentially improving effect. The level of evidence is ranked according to three grades: A - randomized controlled trials (RCTs) with high statistical power; B - RCTs with lower power, non-randomized comparative studies and observational studies; C - retrospective studies and case reports. Our review enabled us to propose clinical recommendations. Briefly, agents worsening OSA or inducing weight gain, that must be avoided, are clearly identified. Drugs such as 'Z drugs' and sodium oxybate should be used with caution as the literature contains conflicting results. Finally, larger trials are needed to clarify the potential positive impact of certain drugs on OSA. In the meantime, some, such as diuretics or other antihypertensive medications, are helpful in reducing OSA-associated cardiovascular morbidity.

Dynamic CO₂ inhalation: a novel treatment for CSR-CSA associated with CHF

BACKGROUND

Cheyne-Stokes respiration with central sleep apnea (CSR-CSA) is very common in patients with chronic congestive heart failure (CHF). A current concept of the key pathophysiological mechanism leading to CSR-CSA is a fluctuation of PaCO2 below and above the apneic threshold. A number of therapeutic approaches for CSR-CSA have been proposed-all with varying success, some of which include various modes of positive airway pressure among other strategies. However, CO2 oscillations seen in CSR-CSA have yet to be looked at as a specific therapeutic target by current treatments.

DISCUSSION

Previous studies have shown that delivery of constant CO2 is efficacious in eliminating CSR-CSA by raising PaCO2, but there are serious concerns about the potential side effects, such as unwanted elevations in ventilation, work of breathing, and sympathetic nerve activity (SNA), and consequently CO2 inhalation therapy has not been recommended as a routine option for therapy. However, recent new studies into CO2 inhalation therapy have been made that may reshape its role as therapeutic. In this review, we will focus on the recent developments of administration of dynamic CO2 in the management of CSR-CSA in CHF patients.

Dynamic CO2 therapy in periodic breathing: a modeling study to determine optimal timing and dosage regimes

We examine the potential to treat unstable ventilatory control (seen in periodic breathing, Cheyne-Stokes respiration, and central sleep apnea) with carefully controlled dynamic administration of supplementary CO₂, aiming to reduce ventilatory oscillations with minimum increment in mean CO₂. We used a standard mathematical model to explore the consequences of phasic CO₂ administration, with different timing and dosing algorithms. We found an optimal time window within the ventilation cycle (covering ∼1/6 of the cycle) during which CO₂ delivery reduces ventilatory fluctuations by >95%. Outside that time, therapy is dramatically less effective: indeed, for more than two-thirds of the cycle, therapy increases ventilatory fluctuations >30%. Efficiency of stabilizing ventilation improved when the algorithm gave a graded increase in CO₂ dose (by controlling its duration or concentration) for more severe periodic breathing. Combining gradations of duration and concentration further increased efficiency of therapy by 22%. The (undesirable) increment in mean end-tidal CO₂ caused was 300 times smaller with dynamic therapy than with static therapy, to achieve the same degree of ventilatory stabilization (0.0005 vs. 0.1710 kPa). The increase in average ventilation was also much smaller with dynamic than static therapy (0.005 vs. 2.015 l/min). We conclude that, if administered dynamically, dramatically smaller quantities of CO₂ could be used to reduce periodic breathing, with minimal adverse effects. Algorithms adjusting both duration and concentration in real time would achieve this most efficiently. If developed clinically as a therapy for periodic breathing, this would minimize excess acidosis, hyperventilation, and sympathetic overactivation, compared with static treatment.

Adaptive servo-ventilation and deadspace: effects on central sleep apnoea

Central Sleep Apnoea (CSA) occurs commonly in heart failure. Adaptive servo-ventilation (ASV) and deadspace (DS) have been shown in research settings to reverse CSA. The likely mechanism for this is the increase of PaCO(2) above the apnoeic threshold. However the role of increasing FiCO(2) on arousability remains unclear. To compare the effects of ASV and DS on sleep and breathing, in particular effects on Arousal Index (ArI), ten male patients with heart failure and CSA were studied during three nights with polysomnography plus measurements of PetCO(2). The order of the interventions control (C), ASV and DS was randomized. ASV and DS caused similar reductions in apnoea-hypopnoea index [(C) 30.0 +/- 6.6, (ASV) 14.0 +/- 3.8, (DS) 15.9 +/- 4.7 e h(-1); both P < 0.05]. However, DS was associated with decreased total sleep time compared with C (P < 0.02) and increased spontaneous ArI compared to C and ASV (both P < 0.01). Only DS was associated with increased DeltaPetCO(2) from resting wakefulness to eupnic sleep [(C) 2.1 +/- 0.9, (ASV) 1.3 +/- 1.0, (DS) 5.6 +/- 0.5 mmHg; P = 0.01]. ASV and DS both stabilized ventilation however DS application also increased sleep fragmentation with negative impacts on sleep architecture. We speculate that this effect is likely to be mediated by increased PetCO(2) and respiratory effort associated with DS application.

Pharmacological management of sleep apnoea

Obstructive sleep apnoea poses a significant health hazard that is associated with leading causes of mortality and morbidity. Nasal continuous positive airway pressure is the primary treatment modality, with surgical treatments as alternatives. Oral appliances and pharmacological therapy remain adjunctive modalities. Non-specific treatments include weight loss, postural therapy and behavioural measures. Pharmacotherapy goals include the reduction of risk factors for sleep apnoea; correction of underlying predisposing metabolic diseases, such as hypothyroidism or acromegaly; treatment of associated symptoms, including excessive daytime sleepiness; and prevention of apnoeas/hypopnoeas. This paper reviews data supporting the treatment of sleep apnoea with various pharmacological agents, including intranasal corticosteroids, decongestant sprays, nicotine therapy, opiate antagonists, methylxanthine derivatives, oestrogen and progesterone, testosterone, thyroid hormone, growth hormone therapy for acromegaly, beta-blockers, alpha-adrenergic agonists, angiotensin-converting enzyme inhibitors, glutamate antagonists, acetazolamide, selective serotonin re-uptake inhibitors, tricyclic antidepressants, physostigmine, modafinil and TNF-alpha antagonists, in addition to supplemental oxygen, and carbon dioxide inhalation. Some of these drugs have received very little testing and are the subject of few research articles.

Pharmacologic treatment of sleep-disordered breathing

Available literature on the use of pharmacologic agents for the treatment of sleep-disordered breathing was reviewed by evidenced-based methodology. Evidence tables were created and studies were graded according to study design and the number of subjects included. Scores for each group of studies evaluating each pharmacologic agent were established so that the quality of research for different drugs could be compared. The use of various ventilatory stimulants, psychotropic drugs, and antihypertensive agents were reviewed. The most objective data are available on theophylline and opioid antagonist/nicotine groups. Although more controlled studies would be helpful, relatively clear-cut indications for the use of ventilatory stimulants exist for hypercapnic obesity-hypoventilation patients (medroxyprogesterone), myxedema (thyroid replacement), central apnea (acetazolamide), and periodic breathing in congestive heart failure (theophylline). Few randomized, well-controlled trials have been published that evaluate pharmacologic agents in the treatment of classic OSA. To date, no one agent stands out as being useful for OSA. Future research will need to characterize subjects so that various subsets of patients can be tried on one or on a combination of various pharmacologic agents.