Chronic Respiratory Failure due to Kyphoscoliosis

Arterial blood gases showed severe chronic hypercapnic respiratory failure with a pH of 7,374, pCO2 of 8,11 kPa and pO2 of 4,55 kPa, which was compensated by retention of bicarbonates.

The chest X ray in posteroanterior projection showed severe deformity of thoracic spine with a removal of middle structures (Figure 1). No infiltrations were detected in visible part of lung parenchyma.
Pulmonary function tests proved severe restrictive ventilatory defect, forced vital capacity was decreased to 0,62 l (25% of predicted values).

In view of presented results of arterial blood gases, noninvasive ventilation via nasal mask with bilevel positive airway pressures delivering two different pressures between inhalation and exhalation creating the pressure support was started. We used the optional average volume assured pressure support mode that automatically adapts the inspiratory positive airway pressure to provide the preset patient´s tidal volume. Due to severe hypoxaemia, supplemental oxygen therapy was added to the ventilation circuit. The patient's tolerance of the treatment was good, during 17 days in hospital we found an improvement of patient´s clinical status and blood gases values. There was gradual decrease in daytime values of pCO2 and increase in daytime values of pO2. The NIV in combination with long-term supplemental oxygen therapy was recommended for chronic everyday use. The patient compliance to treatment has remained very good (average day usage 8 hours) throughout 3 years of follow-up with normalization of pCO2 levels (Figure 2). Patient´s quality of life has improved as well, she is still employed.

Chronic hypercapnic respiratory failure
Kyphoscoliosis

The respiratory system consists of two parts. The lung performs gas exchange and the pump ventilates the lung. The pump consists of the chest wall, including the respiratory muscles, and the respiratory controllers in the central nervous system (CNS) linked to respiratory muscles through spinal and peripheral nerves. When respiratory failure ensues, the respiratory system fails in one or both of its gas exchange functions - oxygenation of mixed venous blood and/or elimination of carbon dioxide (Figure 3).
The diagnose of respiratory failure is based on arterial blood gas assessment and it may present as acute, chronic or acute on chronic. Respiratory failure due to lung diseases (pneumonia, acute respiratory distress syndrome, cardiogenic pulmonary oedema, emphysema or interstitial lung disease) leads to hypoxaemia with normocapnia or even hypocapnia (type I respiratory failure = hypoxaemic respiratory failure). Failure of the pump results in alveolar hypoventilation and hypercapnia with parallel hypoxaemia (type II respiratory failure = hypercapnic respiratory failure). In some diseases, both conditions may coexist, hypoxaemia usually appearing first. Hypercapnic respiratory failure may be the result of CNS depression, functional or mechanical defects of the chest wall, an imbalance of energy demands and supplies of the respiratory muscles.
Kyphoscoliosis is a well-recognized cause of respiratory pump failure. The most common cause is idiopathic scoliosis which begins in childhood but it may occur also secondary to other disorders (Figure 4). Scoliosis (spinal curvature in the lateral plane) is usually associated with kyphosis (spinal curvature in the sagittal plane). In scoliosis, there is a relationship between the severity of the scoliosis as measured by the angle of the curvature in the spine (Cobb angle), and the risk of development of respiratory failure (Figure 5). The disorder affects the respiratory system due to decreased compliance of the chest wall. The stiff chest wall requires greater inspiratory effort for relatively small tidal breaths, which increases the work of breathing. However, respiratory muscle strength might be decreased because of intrinsic muscle weakness (as in secondary kyphoscoliosis due to neuromuscular disease) or because of the respiratory muscles act at a mechanically disadvantageous position because of the altered chest wall configuration. To prevent respiratory muscle fatigue patients adopt a pattern of rapid shallow breathing with a low tidal volume, leading to unequal ventilation of the lungs and pulmonary microatelectasis. Respiratory failure eventually develops once the output that can be generated by the respiratory muscles is insufficient to overcome the additional load placed on the system.
Once respiratory failure or cor pulmonale develops, life expectancy with conservative therapy is poor. Ventilatory support has been used in different forms in the treatment of patients with kyphoscoliosis and acute or chronic respiratory failure for the past 50 years.
Noninvasive ventilation is the application of respiratory support via a face-mask or helmet. NIV avoids intubation and its risks while preserving functions such as speaking and swallowing (picture 6). In the modern era it implies the application of positive airway pressure, however some classifications include the application of a negative-pressure generator to the chest (iron lung) as NIV, which was used in the past. Positive pressure ventilatory support may be with continuous positive airway pressure (CPAP) or bilevel positive airway pressure (BiPAP) modes and delivered by a range of ventilators from specifically designed devices to full-service ICU ventilators.
In patients with kyphoscoliosis NIV improves sleep architecture, and nocturnal and daytime arterial blood gases almost immediately after initiation. It might improve pulmonary mechanics, relieve work of breathing, as endurance time of the respiratory muscles may increase. Long-term usage of NIV has been reported to reduce hypoventilation related symptoms and dyspnea, improve mental function, reduce number of days spent in hospital and increase quality of life. Start of NIV in patients with kyphoscoliosis is indicated in combination of daytime hypercapnia and symptoms reflecting hypoventilation or the development of its associated complications. There is no evidence to start NIV “prophylactically” when patients at risk still have normal diurnal arterial gases. In many cases, ventilatory support via NIV may itself correct hypoxaemia, however in some patients supplemental oxygen is required as well. Survival in patient with chest wall disorders on long-term NIV is quite good, with a 5-year survival rate reported between 76% and 90%.