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Her current ventilator settings are assist control (AC), respiratory rate (RR) of 12/min, tidal volume (TV)of 500 ml, fraction of inspired oxygen (FiO2) is 50%, positive end expiratory pressures (PEEP) of 5 mm/Hg. The most appropriate intervention at this time is toA. decrease set respiratory rateB. increase the fraction of inspired oxygenC. increase PEEPD. increase tidal volumeE. make no adjustments at this timeExplanation:The correct answer is D. The key to this question is to recognize that this patient remains acidoticand hypercarbic despite intubation. In order to "blow off" more carbon dioxide and normalize theblood pH, you must increase minute ventilation (MV).If you remember that MV=TV X RR, you can
quickly recognize that the two ways to decrease carbon dioxide is to increase the RR or increase the TV.Decreasing RR (choice A) will increase carbon dioxide because we are decreasing minuteventilation as described above. This will result in worsening acidosis. In addition, our set respiratoryrate is lower than the patient's actual rate. If we decreased the respiratory rate, our patient wouldcontinue to breathe at a high rate and receive the same tidal volume (thereby not even changing theMV).Increasing FiO2 (choice B) will not be beneficial. First, the patient already has a paO2 of greaterthan 60 mm Hg. If you remember the hemoglobin binding curve, you should remember oxygensaturations remain above 90% for paO2>60 mm Hg. Therefore, our goal is to keep paO2>60 mm Hgfor most patients. Second, maintaining patients on greater than 60% oxygen may have someassociated lung toxicity. Therefore, if possible, keeping the inspired oxygen less than 60% is animportant part of management. Of course, if high levels of inspired oxygen are necessary, you shouldnot hesitate to use them. Please remember that patients on ventilators need not (and should not) haveoxygen saturations of 100% or paO2 much greater than 60 mm Hg.PEEP (choice C) is the use of positive airway pressures at the end of expiration. PEEP is useful inhypoxic respiratory failure such as ARDS or cardiogenic pulmonary edema. Low levels of PEEP canbe used in COPD to keep airways open. Our patient's oxygenation is acceptable so increasingPEEP would not be beneficial now. In addition, our patients blood pressure is only borderlineacceptable. Increasing PEEP will decrease venous return to the heart and might leadto furtherreductions in blood pressures. High levels of PEEP might also predispose patients to barotraumawhich is a form of ventilator induced lung damage.Making no adjustments (choice E) is not acceptable. This patient is severely acidotic andhypercarbic and should not be left in this state.
A 45-year-old woman is planning a trip from the United States to Hong Kong on a direct flight. Shecomes to the office inquiring about advice for any travel precautions that she should take. She hasfibrocystic disease of the breast and takes oral contraceptive pills. Physical examination isunremarkable. Her estimated