Question

Mr. C., age 68 with a history of COPD, presented in the emergency department 2 days ago febrile with a productive cough of large amounts of purulent sputum and in acute respiratory failure. He was diagnosed with community-acquired pneumonia and treated with antibiotics, hydration, aggressive pulmonary hygiene, and supplemental oxygen therapy. Although his oxygenation improved, he continued to be diaphoretic, using accessory muscles of respiration and complaining, "I am exhausted" and "I can't get enough air." Arterial blood gas revealed: pH 7.31, PaCO₂ 59 mm Hg, PaO₂ 89 mm Hg, SaO₂ 91%, HCO₃ 29 mEq/L. The decision was made to intubate and place him on mechanical ventilation with the following settings: assist control (AC) mode, tidal volume (V_T) 625 mL, respiratory rate 16 breaths/min, FiO₂ 0.70, and 5 cm H₂O of positive end-expiratory pressure (PEEP). He was transferred to the critical care unit.

Two days later, his presentation at 0500 is as follows:

• Ventilator settings: Mode AC, V_T625 mL, respiratory rate 12, FiO₂35, 5 cm H2O PEEP
• Total RR 16, peak inspiratory pressure (PIP) 22 mm Hg
• Moderate amounts sputum, rhonchi that clear with coughing, chest x-ray shows clearing pneumonia
• Negative inspiratory force ­-37 cm H₂O, spontaneous tidal volume 5 mL/kg, vital capacity (VC) 10 mL/kg, minute ventilation 10 L/min, rapid shallow breathing index of 37
• Temperature 99.0° F oral, heart rate 86 beats/min, blood pressure 132/84 mm Hg
• No vasopressor or inotropic agents, urinary output is good, NPO since admission.
• Alert and oriented to person, place and situation, hypervigilant and restless, has not slept well since admission

The team decides to perform a ventilator weaning trial. At 0620 Mr. C. is placed on 10 cm H₂O of pressure support with an FiO₂ 0.40.
Assessment at 0720 is as follows:

• Heart rate 108 beats/min
• Blood pressure 157/90 mm Hg
• Respiratory rate 36 breaths/min and labored
• SpO₂90%

He is diaphoretic and alternates between picking at his gown and falling asleep and needing to be aroused to stimulate breathing. He is placed back on the ventilator at the previous settings.
Late that morning, during rounds, Mr. C. is started on nutritional support via tube feeding and given trazodone at night for sleep. He is allowed a morning nap and has physical therapy that afternoon.

The following day he passes the pre-wean screening and is again placed on PS 5 above 5 cm H₂O PEEP. Assessment findings 30 minutes into the weaning trial are as follows:

• Heart rate of 84 beats/min
• Blood pressure 120/76 mm Hg
• Respiratory rate 18 breaths/min, unlabored
• SpO₂96%

Mr. C. is calm, cooperative, and oriented, so the weaning trial is continued for 90 minutes. Arterial blood gas results were pH 7.34, PaCO₂ 48 mm Hg, PaO₂ 74 mm Hg, HCO₃ 24 mEq/L, and SaO₂ 95%. The decision was made to extubate, and the patient was discharged from the critical care unit the following day.

Please answer the following questions concerning Mr. C,

1. What were the results of Mr. C.'s first arterial blood gas analysis? What factors contribute to these results?
2. What do the measures of negative inspiratory force, spontaneous tidal volume, vital capacity, minute ventilation, and rapid shallow breathing index assess?
3. What other parameters should/could be assessed as part of the initial wean screen?
4. Why is pressure support the mode used for the weaning trial?
5. How long does weaning the trial last?
6. Is Mr. C. tolerating weaning, and how do you know?
7. What interventions are indicated?

Answer 1

1)The intial ABG indicates the following:

i)PH < 7.40 so acidosis is present.

ii)PaCO2 is elevated indicating respiratory acidosis. The value consistent with PH is PaCO2 so it is respiratory acidosis.The acid-base which is consistent with PH is HCO3 as it is accounts for metabolic alkalosis so there is compensation signifying a primary disorder that is not acute because it takes days for mechanical compensation to be effective. lastly PaO2 is within normal range so no abnormality in oxygenation.

2)As the parameters are lower than the cutoff points the measures of negative insipiratory force,sponataneous tidal volume,vital capacity,minute ventilation and rapid shallow breathing clearly indicates that patient needs respiratory support such as mechanical ventillation.

3)Parameters like tidal volume ,vital capacity,minute ventillation,PaO2 could be assesed in intial weaning screen.

4)Pressure support volume reduces the work of breathing of a patient.The weaning process is performed by gradually reducing the amount if pressure support and transfering an increased amount of work to the patient.When patient can tolerate the level of ventillating support extubation can be successfully done.

5)Intial weaning trial lasts for 30- 120mins .if it is not clear in 120mins then the procedure is failure.It varies based on the severity and type of illness regularly takes 16 to 37 days for extubation.

6) yes Mr C is tolerating weaning as it continues to 90mins the ABG parameters are within the normal range indicating no signs of respiratory acidosis.

7)Interventions indicated are:

Prevention of disease progression, improve excerise tolerance, improve health status, prevent complications, smoking cessation, inspiratory muscle training which helps to improve breathing and diaphragmatic breathing which reducwes respiratory rate,increases alveolar ventillation, supportive care such as pneumococcal vaccination to reducevthe risk of respiratory infections, chest physiotherapy.