THE EFFECT OF SUCTIONING ON PASSIVE RESPIRATORY SYSTEM MECHANICS IN INTUBATED PREMATURE INFANTS

Abstract

Based on the hypothesis that mucous accumulation increases airway resistance, we measured passive respiratory system compliance (Crs), resistance (Rrs) and the product of these mechanical variables, time constant (Trs), just prior to and immediately following suctioning in 11 studies on 8 premature infants. All infants were intubated (3 mmlD endotracheal tube (ETT)) and artificially ventilated with peak pressures ranging from 12-27 cmH₂O and with 3-4 cmH₂O end expiratory pressure. Ventilator rates ranged from 5-40 per minute. Inspired oxygen concentration varied from 0.21 to 0.35. A valve was inserted between the ventilator circuit and the ETT connector of the infant who continued to receive the required ventilation. Crs, Rrs, and Trs were obtained by occluding the airway at end-inspiration, measuring occlusion pressure and the flow and volume of the subsequent passive expiration. Rrs and Trs fell significantly (p<.02)after suctioning by an average of 19 and 25% respectively while Crs did not change in a systematic manner. The high resistance in intubated infants is not entirely a function of the diameter of the ETT. It also depends on the amount of mucous accumulating within and at the tip of the tube. While a high inspiratory resistance is inconsequential to the ventilated infant, a high expiratory resistance is not. If the resistance is sufficiently high to increase Trs to a value close to expiratory time, an occult PEEP may be generated and hyperinflation will occur.

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