The Physiological Basis of Ventilatory and Respiratory Support
The indications for support in acute respiratory failure are based on clinical, radiological and laboratory evidence: dyspnoea, tachypnoea and panlobar alveolar infiltrates of one or both lungs accompanied by severe hypoxaemia with an arterial oxygen tension (PaO2) or less than 75 mmHg when breathing a fraction of inspired oxygen (FiO2) of more than 0.5 (Artigas et al. 1985). These clinical signs often require an immediate response: in an attempt to improve arterial oxygenation, continuous positive airways pressure (CPAP) is applied via a facemask or an endotracheal tube, but frequently some sort of mechanical ventilation is required. However, the mode of mechanical ventilation depends essentially upon a process of trial and error in which success is monitored by blood gas analysis. Although reliable, this empirical method does not disclose where the failure or potential for improvement in ventilation lies. A method by which the optimal ventilatory pattern could be found should encompass the different anatomical levels of the lungs and their function as well as their mechanics.
KeywordsToxicity Dioxide Depression Cage Argon
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- Artigas A, Carlet J, Chastang C, Le Gall JR, Cox P (1985) Protocol of adult respiratory distress syndrome study: clinical predictors, prognostic factors and outcome. European Society of Intensive Care Medicine.Google Scholar
- Downs JB (1983) Ventilatory pattern and modes of ventilation in acute respiratory failure. Resp Care 28:586–591.Google Scholar
- Feiton CR, Montenegro HD, Saidel GM (1984) Inspiratory flow effects on mechanically ventilated patients: lung volume, inhomogeneity and arterial oxygenation. Intensive Care Med 10:281–286.Google Scholar
- Fischer AB (1980) Oxygen therapy: side effects and toxicity. Am Rev Respir Dis 122:61–69.Google Scholar
- Hillman DR (1986) Physiological aspects of intermittent positive pressure ventilation. Anaesthesiol Intensive Care 14:226–235.Google Scholar
- Ibanez J, Rawich JM, Moris SG (1983) Measurement of functional residual capacity during mechanical ventilation by simultaneous exchange of two insoluble gases. Anaesthesiol 54:413–417.Google Scholar
- Krogh A, Lindhard J (1917) The volume of dead space in breathing and the mixing of gases in the lungs of man. J Physiol (Lond) 51:59–90.Google Scholar
- Lanczos C (1957) Applied analysis. Prentice-Hall mathematics series. Pitman, London.Google Scholar
- Severinghaus JW (1966) Blood gas calculator. J Appl Physiol 4:102.Google Scholar
- West J (1979) Respiratory physiology. Williams and Wilkins, Baltimore.Google Scholar
- West J (1982) Ventilation-perfusion relationship. In: Scurr C, Feldman S (eds) Anaesthesia, scientific foundations. Heinemann, London.Google Scholar