Hypoventilation defined

Hypoventilation is defined as a reduction in the rate and depth of breathing. Inadequate ventilation results in hypoxemia, or a decrease in the concentration of oxygen in the arterial blood. Hypoventilation may be induced inadvertently by various pharmacological agents, including opioid analgesics such as morphine. These medications cause hypoventilation by way of their effects on the respiratory centers in the brainstem. Doses of... 

The respiratory system is responsible for generating and regulating the transpulmonary pressures needed to inflate and deflate the lung. Normal gas exchange between the lung and blood requires breathing patterns that ensure appropriate alveolar ventilation. Ventilatory disorders that alter alveolar ventilation are defined as hypoventilation or hyperventilation syndromes. Hyperventilation results in an increase in the partial pressure of arterial CO2 above normal limits and can lead to acidosis, pulmonary hypertension, congestive heart failure, headache, and disturbed sleep. Hypoventilation results in a decrease in the partial pressure of arterial CO2 below normal limits and can lead to alkalosis, syncope, epileptic attacks, reduced cardiac output, and muscle weakness. 

On the graph of PCO2 [HCO3 ], indicate the immediate effects of hypoventilation and hyperventilation and deduce the effects on [HC03 ] and [H" ]. Also on the graph, indicate and explain the delayed effects, mediated by the kidney, occurring if the primary respiratory disorder persists. Hence define uncompensated and compensated respiratory acidosis and alkalosis. 

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). 

Nocturnal hypoventilation, which persists during the day in obese patients with nocturnal apneas and hypoventilation may be associated with COPD, defining the overlap syndrome (3). In 264 OSAS patients (32), 30 had coexistent COPD, with hypoxemia in 57%, hypercapnia in 27%, and PH in 37% of them. In the other 234 pure OSAS patients, only 26% were hypoxic, 8.5% were hypercapnic, and 11 % had PH at baseline. The same schedule may be proposed for OHS, but long-term studies are also warranted to confirm the initial choice and continuation of nCPAP or bi-level NIV. 

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