A 57- year old 62-inch female with rheumatoid arthritis is scheduled for a total knee replacement. She has Raynaud's phenomenon in her hands, and a history of bronchiectasis. She is status post right lower lobectomy ten years ago for this. She had a lumbar laminectomy five years ago, and current medications include: ibuprofen, aspirin, prednisone 10 mg/day, and Theodur. Blood pressure is 120/80 mm Hg, pulse is 75 bpm, respirations are 16, temperature is 98 degrees Fahrenheit, and hemoglobin is 9.5 gm/dl,
I. Pulmonary status
1. What are your concerns about bronchiectasis and lung resection?
2. Would you obtain sputum cultures and pulmonary function tests preoperatively?
3. How will these results affect your management?
4. Wheezing is evident. Would you delay surgery to control wheezing?
5. Would you delay surgery to treat infection?
6. Would you administer prophylactic antibiotics?
II. Rheumatoid arthritis
1. How does it affect the airway?
2. How do you evaluate chest radiograms?
3. Are coagulation tests needed?
4. Which ones would you order?
5. Would you order platelets?
6. What are causes of her anemia?
7. Would you transfuse preoperatively?
No. There is no definite minimally acceptable hematocrit. Since she has anemia of a chronic nature, no impaired cardiac function, and estimated blood loss will be minimal with tourniquet use, there is no evidence that her anemia would prolong her recovery. But since her coexisting pulmonary disease places her in a category where she would be more likely to exhibit myocardial ischemia at higher hemoglobin compared to normal patients, it would be prudent to transfuse preoperatively. Oxygen delivery is dependent on the hematocrit, cardiac output, oxygen saturation, and viscosity. She should have well-compensated systemic disease, and a hematocrit over 30% would be preferable.
8. Is she malnourished?
9. What are the anesthetic implications of malnourishment?
I. Regional anesthesia
1. The patient refuses general anesthesia. Do you agree?
2. What is your choice of technique? Explain.
3. Are you concerned about the previous laminectomy?
4. Are you concerned about a coagulopathy or platelet dysfunction?
5. What sensory level is necessary to prevent tourniquet pain?
6. What will be the effect of a spinal or an epidural to this level on pulmonary function?
7. What is your management of intraoperative restlessness?
8. Compare sedatives vs nitrous oxide.
9. You disagree with the use of regional anesthesia for this case. Explain.
10. What agent is your choice for general anesthesia? Explain.
11. Would you intubate the patient? Explain.
12. What is the risk of pulmonary infection?
13. How do you prevent bronchoconstriction?
14. Would you use muscle relaxant? Why or why not?
15. What are the advantages of spontaneous vs mechanical ventilation?
16. Would you reduce the tidal volume, in light of the previous lung resection?
1. Do you plan to obtain arterial blood gases?
2. What sampling site do you plan to use?
3. Would you insert an arterial cannula? Explain.
4. What alternatives are there to an arterial blood gas?
Pulse oximetry and end-tidal CO2 can be used to estimate PaO2 and paCO2. The pulse oximeter can only estimate the paO2 when the oxyhemoglobin curve is not shifted, and when there are no abnormal hemoglobin species. Therefore, acidosis, alkalosis, hypo- or hyperthermia, and altered 2, 3 diphosphoglycerate can alter the value, as can saturation below 50%. The correlation between end-tidal CO2 and paCO2 is altered by chronic pulmonary disease, bronchospasm, and increased CO2 production Therefore, pulse oximetry and end-tidal CO2 may be sufficient alternatives in a patient with no ventilation abnormalities, and a normal oxyhemoglobin curve. One would not receive information of blood pH, bicarbonate concentration, or base excess.
5. What is the base excess or deficit?
The blood pH is titrated to 7.4, and then the bicarbonate concentration is measured. The difference from a normal value of 24 mEq/l is the excess or deficit of bicarbonate.
5. Why must the arterial blood gas sample be heparinized?
So that the sample does not clot in the complex and expensive blood gas analyzer.
6. How does heparin affect the sample of arterial blood?
It has a minimal effect, because the volume is so small compared to the sample volume. Heparin is acidic, and can decrease the pH and dilute the sample if an excess amount is used.
5. What pulse oximetry site would you use?
6. Is transcutaneous oxygen better?
7. Would you insert a central venous catheter? Explain.
8. Would this be useful for blood gas analysis?
9. How would you obtain a mixed venous sample?
10. Is a Foley catheter a satisfactory substitute for central venous pressures, in order to guide fluid management? Why or why not?
III. Hemodynamic complications
1. What is your acceptable blood loss before requiring a transfusion?
2. The fear of AIDS led the patient to request no blood products unless it is a life-threatening situation. What are your alternatives to maintain circulation?
3. Upon release of the tourniquet at the end of the case, the blood pressure decreases from 100/70 mmHg to 60/40 mmHg. What is your immediate treatment?
4. What is your differential diagnosis?
I. Postoperative hypoxia
1. The patient refuses the oxygen mask in the recovery room. Is it necessary?
2. How will you determine if it is necessary?
3. What is diffusion hypoxia?
When nitrous oxide is given as a part of a general anesthetic, and then the patient is immediately awakened on room air, the rapid outward movement of nitrous oxide displaces alveolar oxygen, leading to a decrease in paO2, and hypoxia. It can be prevented by giving the patient 100% oxygen for a period of time, once the general anesthetic is discontinued.
3. The pulse oximeter shows an oxygen saturation of 85%. The patient is combative, and will not accept the oxygen mask. What could be done?
Possible management for improving ventilation in any patient include increasing FIO2, increasing minute ventilation, cardiac output, or oxygen carrying capacity, optimizing ventilation/perfusion by using positive end-pressure ventilation or continuous positive airway pressure, decreasing oxygen consumption from pain, shivering, or fever, or instituting cardiopulmonary bypass.
4. What effects do inhalational agents have on ventilation?
CO2 is the most important regulator of ventilation, with medullary chemoreceptors regulating CO2. Receptors in the carotid and aortic bodies are sensitive to changes in oxygen. Increasing concentrations of all inhalational agents shifts the CO2 response curve to the right, resulting in a decreased minute volume response to increasing hypercarbia.
I. Postoperative Oliguria
1. The urine output for the first two hours in the recovery room is only 10 ml/hr. What is your differential diagnosis? Consider the anesthetic technique.
2. When is a diuretic indicated?
1. Would you use epidural local anesthetic vs opioid?
2. Would you use epidural morphine vs fentanyl? Explain.
3. What epidural orders do you write?
4. Is it necessary for this patient to go to the intensive care unit?
5. What methods of monitoring ventilatory function do you have?