Final answer:
The PN should monitor the water-sealed chambers of the chest tubes after a lobectomy to ensure suction is maintaining negative pressure in the chest cavity, which prevents the lungs from collapsing.
Step-by-step explanation:
When a client is admitted to the postoperative surgical unit after a left lobectomy with two chest tubes and the prescribed suction of 20 cm H2O is set, the practical nurse (PN) should observe the water-sealed chambers to ensure that the suction is effectively reestablishing negative pressure within the chest cavity. This negative pressure is required to prevent the lungs from collapsing by counteracting the surface tension in the alveoli which is maintained by liquid adhesion. The PN should confirm that the chest tube system is functioning correctly and no air leaks are present that would disrupt the suction process. The gauge pressure in the liquid that keeps the lungs attached to the inside of the chest wall should range from -4 to -8 mm Hg during exhalation and inhalation, respectively. If any abnormalities are noticed in the water seal's expected fluctuations or the pressure readings, the PN should take immediate action to rectify the situation, following hospital protocols and alerting the supervising nurse or physician as needed.