Hypercapnia daytime

Although a Cochrane meta-analysis (73) does not recommend the institution of NIV for symptomatic sleep hypopneas, a prospective study from Mellies et al. (74) and a randomized controlled trial by Ward et al. (72) support the indication of NIV for patients with NMD and nocturnal hypercapnia. The consensus conference of the American College of Chest Physicians on MV beyond the ICU recommended that patients who develop symptomatic nocturnal hypercapnia, even in the absence of daytime hypercapnia, are candidates for long-term ventilatory assistance (75). 

Figure 1 Home oximetry (A) and split-night polysomnography (B) in an ALS patient with daytime hypercapnia and hypoventilation symptoms.

OHS, previously called the Pickwickian syndrome (6), is defined as the association of obesity, sleep-disordered breathing (SDB) with daytime h)q)ersomnolence, and hypercapnia (Pacc>2 > 45 mmHg) in the absence of any other respiratory disease (Fig. 1). SDB can present as obstructive apneas and hypopneas, obstructive hypoventilation due to increased upper airway resistance, and/or central hypoventilation (7). The prevalence of OHS is 36% in patients with BMI between 35 and 40 kg/m, and 48%, if BMI equals or exceeds 50 (8). Without adequate treatment, patients with OHS develop cor pulmonale and recurrent episodes of hypercapnic respiratory failure, and loss of survival (Fig. 2). OHS is one of the many etiologies of CRF and has become a growing indication to initiate longterm noninvasive ventilation (NIV) in most European countries (9,10). 

Approximately 10-15% of patients with OSAS present with daytime CRF along with hypoxia, hypercapnia, and PH (2). When these patients present with a stable respiratory status, their nocturnal pattern of predominant OSA leads to a discussion on the use of... 

Mechanical ventilation (MV) with bi-level NIV must be considered in the presence of nocturnal hypoventilation, especially if accompanied by cor pulmonale, nocturnal arryth-mias, morning headache, impaired cognitive function, or reduced daytime vigilance. Right heart failure is also frequently present. The obese sleepy patient (27) with chronic hypoxia and hypercapnia is the typical presentation of OHS. To adapt to NIV, it is important to identify the nocturnal respiratory pattern of such patients. 

Bi-level NIV may be used as a first-line treatment, with supplemental oxygen (27). Expiratory airway pressure is titrated to control h5q)opneas and apneas, and inspiratory airway pressure is added to control Paco2. If bi-level NIV fails, nasal volume ventilation may be used (29). In many patients with OHS and predominant OSA, once hypercapnia has improved (which may take several weeks) nCPAP may be used (29). Thirteen obese patients (n = 13) with a BMI > 35, aged 28-69 years with severe OSAS and hypercapnia (8.2 0.3 kPa) and failing to respond to initial CPAP therapy, were treated via a nasal nocturnal volume-cycled ventilator, which was tolerated by all patients. Significant improvements in daytime arterial blood gas levels were obtained after 7 to 18 days of nasal intermittent positive pressure ventilation (29) in 10 of the 13 patients three months later, 12 of the 13 patients could be converted to nCPAP therapy and one patient remained on NIV. In another study (37), the same results were observed after three months of home nocturnal bi-level NIV in seven patients, three of whom had severe obesity. 

Thus, the indications for a trial of bi-level NIV in obese patients with CRF are progressive respiratory failure with excessive sleepiness, with daytime hypercapnia and OHS in the setting of OSAS that has not correctly responded to nCPAP, with disorders of ventilatory control and daytime hypercapnia or sleepiness (27,38,39) (Fig. 5). 

The most accepted indication for NPPV is diurnal hypercapnia in a stable state because it is the signature of overt ventilatory failure. Most recommendations concern patients with NMD and, in particular, patients with Duchenne muscular dystrophy in whom ventilatory support should be considered when daytime Paco2 exceeds 6 kPa (45 mmHg) (23-27). No guidelines or recommendations are available for the other causes of hypoventilation such as OSA or CF, but it seems reasonable to also consider diurnal hypercapnia as a criterion to propose NPPV in these patients. 

Because sleep is an at-risk period in patients with chronic respiratory insufficiency and also for practical reasons, NPPV is preferentially performed during the night. However, daytime mechanical ventilation in awake adult patients has been reported to be equally effective in reversing chronic hypercapnia (42). 

Few studies have evaluated the effect of NPPV on quality of life in children (33,46). NPPV might influence both sleep and cognitive function, thereby influencing health-related quality of life. Early initiation of ventilatory support might improve school performance, even in the absence of permanent daytime hypercapnia (28). 

Most children are managed with NPPV (1,50). However, some require invasive ventilation through a tracheostomy. The main indications for a tracheostomy in children are airway abnormalities such as tracheobronchomalacia or tracheal stenosis, chronic disease of prematurity, and NMD (1,51,52). The indications for a tracheostomy are comparable to those of the adult population. They include the persistence of hypercapnia despite NPPV and additional measures such as daytime mouthpiece ventilation, aspiration, and bulbar dysfunction (53). In children, NPPV is more difficult to perform in those who might be 24-hour dependent, than in adults. Infants with primaiy alveolar hypoventilation (Ondine s curse) are preferentially ventilated by means of a tracheostomy (18). Tracheostomy ventilation favors airway inflammation (54) and may affect speech and language development (55). In children with progressive NMD, the decision of a tracheostomy has to be discussed on an individual basis, taking into account the familial environment and the parent s and child s perspective (52,56). In any case, sending children home with invasive ventilation is more difficult than when noninvasive ventilation is used (52). 

---