Basic Science – Physiologic Monitoring of the Surgical Patient
Respiratory Monitoring: 1. A 76 year old man has just undergone a sigmoid colectomy for perforated sigmoid diverticulitis. He is returned to the ICU intubated post‐operatively for continued care. His ventilator settings are as follows: Mode: Pressure Regulated Volume Control (PRVC) Tidal Volume (Tv): 500cc Respirator Rate (RR): 15 FiO2: 40% PEEP: 5 Electrolytes: 140 109 7 3.6 24 0.6 ABG: pH = 7.25 PaCO2 = 55 PaO2 = 120 a. What is the acid/base disturbance? b. Assuming the patient is not over‐breathing the set ventilator rate of 15, what is his minute ventilation (Mv)? c. What adjustments can you make on the ventilator to correct this patients acid/base disturbance? d. Two days later, you believe the patient is ready to be weanedoff of the ventilator. You place him on Pressure Support. How will the patient tell you he is not ready for extubation? e. Assuming the patient appears comfortable on minimal settings of Pressure Support, what might you want to know prior to extubation? 2. A 76 year‐old man has just undergone an aorto‐bifemoral bypass for aorto‐occlusive disease. He is sent to the ICU post‐
operatively intubated. His ventilator settings are: Mode: PRVC Tidal volume: 800cc Respiratory rate; 16 FiO2: 50% PEEP: +5 His initial peak airway pressure (Ppeak) is 30 mmHg, and his initial plateau pressure (Pplateau) is 25 mmHg. PIP = Ppeak
a. a. Over the course of the next several hours, the respiratory therapist reports that on these same ventilator settings, the patients Ppeak has increased to 40mmHg and his Pplateau has increased to 37mmHg. What does this suggest? What are the common etiologies of this problem? b. You treat the patients’ Pneumothorax and his Ppeak returns to 30mmHg and his Pplateau returns to 25mmHg. Three hours later, the respiratory therapist call to tell you that now the patients Ppeak is 40mmHg and his Pplateauremains 25mmHg. What does this suggest? What are the common etiologies of this problem? c. The respiratory therapist decides to place a capnometer in‐
line with the ventilator for continuous monitoring of the patients partial pressure of CO2 in the end‐tidal exhaled gas (PETCO2). She re‐checks an ABG and notes a PaCO2 of 40. The capnometer is recording a PETCO2 of 37. Over the course of the next several hours, the respiratory therapist notes a sudden decrease in the patients PETCO2 to 25. What does this suggest? d. The patient now develops acute renal failure. He is hypertensive and the covering OMFS intern decides to manage this patients’ hypertension by placing him on a high‐
dose nitroglycerin drip. The next morning, you find your patient to have a profound metabolic acidosis with altered mental status. The patient appears cyanotic; however, his pulse‐oximeter reveals a saturation of 90%. What is going on? How can you diagnose metHb?
What would this patients’ blood look like?
How can you treat metHb?
Renal Monitoring: 1. A 76 year old woman is post‐operative day #3 following an abdominoperineal resection for rectal cancer. The nurse notes that she has had minimal urine output over the last 24 hours. You order a BMP, which reveals the following: 136 107 40 5.5 21 3.2 a. What are the categories of acute renal failure? b. How do you calculate a fractional excretion of sodium (FENa)? c. How can you differentiate between pre‐renal and intrinsic renal failure? Pre‐Renal Failure Intrinsic Renal Failure Urine Na FENa UCr/PCr Urine Microscopy d. What are the 5 indications for dialysis? 2. A 63 year old man has just undergone an open repair of an abdominal aortic aneurysm. It was a prolonged case and the patient requires significant resuscitation in the immediate post‐
operative period. The nurse calls you to bedside to re‐evaluate the patient as he is now persistently tachycardic and hypotensive and no longer is responding to fluid resuscitation. a. What is your differential diagnosis? b. On arrival to the ICU, you find the patient with a heart rate of 135 and a blood pressure of 80/60. His Ppeak is 50mmHg and he has made only 10cc of urine over the last hour. His abdomen is firm, distended, and tight. You suspect the patient may have abdominal compartment syndrome (ACS). How can you confirm the diagnosis? c. What is the pathophysiology of ACS? d. What is the management of ACS? Neurologic Monitoring: 24 year old man was the non‐helmeted driver of a motorcycle that collided with a parked car. He was intubated in the field for a GCS of 7 and was brought to the nearest Level I Trauma center. He remained hemodynamically stable in transport. Workup subsequently revealed multiple facial fractures as well as a TBI with diffuse SAH and frontal contusions. 1. What are the basic tenets in managing this patients TBI in the next several days in order to optimize outcome? 2. How do you calculate the cerebral perfusion pressure (CPP)? 3. In the ICU, the neurosurgeons place a ventriculostomy catheter to measure the patients ICP. The nurse notes n ICP of 30 and a MAP of 90. What interventions could be done to decrease this patients’ ICP? 4. You medically optimize the patients ICP, which is now 10mmHg, but the nurse notes that the patients MAP is now 60, giving you a CPP of 50. What next? 5. The neurosurgery resident decides to place a jugular bulb to assess the patients’ jugular venous O2 saturation (SjO2). The measured SjO2 is 40%. What does this suggest? How would you manage this SjO2 of 40%?