Fig. 31.1
Trendelenburg positioning for a da Vinci prostatectomy. The angle of the joint of the OR table emphasizes the extreme head-down-feet-up position. The knees are bent; legs are raised, spread, and fastened. Many clinics use shoulder pads, to prevent the patients from sliding cranially. However, the shoulder pads can cause pressure, which may cause the especially dreaded brachial plexus palsies
The duration of a da Vinci prostatectomy varies according to the patient’s anatomy, the type of procedure planned (e.g., a nerve sparing surgery), and the surgeon’s experience. Operating room times of 4–6 h are not unusual. The physiological effects of the positioning and the capnoperitoneum can be a challenge for the anesthesiologist (Fig. 31.2). The following problems should be anticipated:
Fig. 31.2
Anesthesiologist’s view of patient with a capnoperitoneum and placement of the first robotic arm. The position was not changed for the photo and highlights the steep Trendelenburg position and the massive pressure on the thorax
Drastic reduction in functional residual capacity and total lung capacity.
Difficulty in CO2 elimination.
Changes in the acid–base balance as a result of insufficient CO2 elimination and reduced renal perfusion.
Increase of the cerebral blood flow. The general anesthesia will be done as a balanced anesthesia; however, the choice of the anesthetics is not of primary concern. Muscle relaxation is very important, in order to minimize the effect of the extended pressure and to offer the surgeon optimal operative conditions.
>> CRNA Marid studied Mr. Scott’s medical record. The following information was noted:
65–year–old patient, 168 cm, 85 kg
Hypertension, therapy with metoprolol and a combination preparation with candesartan and hydrochlorothiazide. Cardiovascularly stable
Indigestion after eating certain foods (therapy with pantoprazole)
Renal insufficiency, in the compensated retention phase, with a creatinine of 1.43 mg/dl (reference 0.70–1.20 mg/dl), all other lab values unremarkable
A recent admission to a neurologist due to sudden headache
CRNA Marid stopped at that last detail and had to think about it for a minute.
31.1.3 Do You Have to Stop and Think, Too? Can You Think of Other Discoveries That May Cause You to Stop and Think?
You should take a minute to think about this, because a sudden headache can be a sign of a subarachnoid hemorrhage (see Sect. 2.1.1). As presented in Sect. 31.1.2, da Vinci prostatectomies increase the cerebral perfusion and intracranial pressure. Even when there was no previous case study reported in the literature, a cerebral artery aneurysm is a contraindication to the operation. The danger of aneurysm rupture cannot be equated with the benefits of the operative technique, especially since other techniques are available. For all other comorbidities, a risk–use analysis should be considered. Risks include:
Glaucoma (danger of an acute glaucoma episode) [4]
Serious pulmonary diseases, with emphysema-type changes, especially changes in the pulmonary parenchyma or formation of bullae
Heart failure
>> After further questioning, Mr. Scott shared with Marid the tip he had received from neurologist: If the headache arises again, try to breathe fresh oxygen. “I have a little oxygen tank at home now; it stands beside my bed, but I have only had to use it once so far.
“Alright, then it’s not an aneurysm – must be a cluster headache,” thought CRNA Marid to himself. He had had patients with headaches that went away with oxygen, but they were all much younger than Mr. Scott.
As a preoperative sedative, Mr. Scott had received 7.5 mg PO midazolam. His usual medications had not been held. “Oh dear,” thought Marid, but now he wanted to get started with the induction.
31.1.4 Would You Have Held the Usual Medications?
The discussion of preoperative ACE inhibitors and angiotensin receptor antagonists has been going around for many years. The basis of the debate is the observation that patients who take their usual dose before surgery often develop severe hypotension during surgery. Intraoperative hypotension is especially likely to occur when the patients have additionally taken a diuretic [6]. A pragmatic plan of action for this problem is to hold ACE inhibitors and angiotensin receptor antagonists when:
Large volume redistribution may be expected.
A volume restrictive anesthetic is planned (Case 21).
The patient takes an additional diuretic.
An additional indication worth considering is planned intraoperative thoracic epidural anesthesia, which almost always leads to relative hypovolemia.
An exception to this recommendation should be made when the patient’s hypertension is difficult to manage and when initiating treatment again postoperatively may be difficult. Furthermore, the European Society of Cardiology recommends continuing the therapy with ACE inhibitors in patients with left ventricular systolic dysfunction [14].
>> In CRNA Marid’s department, it was usual to do da Vinci prostatectomies with total intravenous anesthesia (TIVA). Student nurse anesthetist Al had already prepared the TIVA “tower” with propofol and remifentanil and started the pressure infusions. After an initial bolus of 1 mg/kg body weight propofol and 0.5 μg/kg body weight remifentanil, Mr. Scott slowly fell asleep and CRNA Marid began with the mask ventilation, which went well. Student nurse anesthetist Al turned on the twitch monitor, finally administering rocuronium 0.5 mg/kg. As they each waited for the muscle relaxant to take effect, the monitor’s alarm sounded. The heart rate was only 30 beats/min.
31.1.5 You Know the Cause, Don’t You?
In Mr. Scott’s case, three factors have affected the heart rate:
Bradycardia is a typical side effect of μ-agonists. The bradycardia is probably mediated by central vagus stimulation [8]. It is often seen after administration of a bolus of remifentanil.
Propofol, depending on the dose, causes cardiovascular depression, which is usually not accompanied by reflex tachycardia.
Mr. Scott had taken his β-blocker before surgery.
>> “Please give him 0.5 mg atropine,” CRNA Marid said to student nurse anesthetist Al. “I don’t want the laryngoscopy to cause asystole.” The vagolytic effect appeared quickly, and intubation went without complications. “Now we’ve just got to complete the monitoring,” thought CRNA Marid, and began preparations.
31.1.6 Which Monitoring Would You Choose Now?
The choice of perioperative monitoring should be guided by two factors:
Patient Factors
The patient’s individual comorbidities must be considered independently of the surgery scheduled (see Case 9, Discussion in Sect. 9.2.1). Mr. Scott’s main comorbidities include systemic hypertension, renal failure in the stage of compensated retention, and obesity.
Procedural Factors
The reverse is also true; the factors of the procedure must be independently considered, independent of the patient-specific factors. For a da Vinci prostatectomy, these factors include blood loss and ventilation problems. In addition, just as in abdominal surgery, the anesthesia is done increasingly with restrictive volume therapy, in order to reduce perioperative blood loss. Carrying out restrictive volume therapy was already discussed in Sect. 21.1.3; however, urine production and central venous pressure are not measurable during a da Vinci prostatectomy. Therefore, the decision to place a central venous line is based on patient, not procedural, characteristics. Quantitative assessment of neuromuscular blockade was already set up for Mr. Scott.
>> CRNA Marid cannulated the left radial artery, as nurse anesthetist student Al placed 2 more large bore venous lines. CRNA Mark wiped the sweat from his face and thought, “I’m not quite healthy today; when we’re finished with these preparations, I’ll take a little break.” Turning to the student he said, “Al, let’s hook up the BIS. Come on, let’s make the surgeons happy and let them begin prepping the patient.”
31.1.7 What Do You Know About BIS Monitoring?
Anesthetics have a dose-dependent effect on the synchronized electrical activity of cortical neurons. Electroencephalography (EEG) can be used for the measurement of the level of consciousness [5]. BIS monitoring (BIS = bispectral index) is a commercial neurological monitoring procedure which processes the EEG signals and transforms it into an easy-to-understand index value. The BIS value ranges from 0 (no electrical activity) to 100 (awake). During anesthesia, the desired value is between 40 and 60. The BIS monitoring can be used for individual titration of anesthetics or for automated computer-controlled anesthesia [7].
Neurological monitoring techniques for the measurement of anesthesia depth have two goals:
Reduction of side effects by unnecessarily high doses of anesthetics
Prevention of awareness episodes as a result of insufficient anesthetic depth.
The original hopes of neuromonitoring have only partly been realized. There have been reports that titrating anesthetics according to clinical criteria tends to lead to excessive administration, so that the neuromonitoring helps. On the other hand, some users tend to employ the BIS to maintain the anesthesia depth as light as possible, whereby the danger of an awareness episode is increased. Therefore, an awareness episode can occur during BIS monitoring [2, 3, 10]. In addition, BIS-guided anesthesia (titrated to maintain BIS levels of 40–60) is equally efficacious in reducing awareness as maintaining end-tidal gas concentrations at 0.7–1.3 age-adjusted MAC [2, 3].
A disadvantage of the technique is that there is a latency period in the index value before a change is registered. If the value increases over the threshold, this means that the patient had an insufficient depth of anesthesia for about 30 s. In order to maintain a reliable EEG signal, artifacts must be excluded. Electromyographic activity may also interfere with the EEG signal in some models.
BIS-guided anesthesia reduced the incidence of awareness compared to routine care when the anesthetic is titrated to BIS levels of 40–60 in patients at high risk for awareness [10]. In addition, a recent comparative effectiveness study demonstrated a decrease in awareness with BIS-guided anesthesia compared to routine care, especially for TIVA, as end-tidal anesthetic gas concentrations are not available [9]. Despite the weaknesses, neuromonitoring techniques are increasing year to year, and it is probably only a question of time until the costs, technical developments, and time make this technique a standard part of patient monitoring.
31.1.8 Is BIS Monitoring Indicated in This Case?
Mr. Scott is receiving general anesthesia without volatile anesthetics with simultaneous continuous muscle relaxation – therefore, he is at increased risk for awareness (see Sects. 8.1.8 and 8.1.19). The ASA practice advisory on intraoperative awareness [1] recommends use of brain functioning monitoring on a case-to-case basis, depending upon the risk of awareness. Given the absence of end-tidal gas monitoring during TIVA, use of the BIS monitor is indicated, despite its imperfections.
>> It took 30 min until CRNA Marid found a moment to responsibly excuse himself for a break. “Thank goodness I’ve got Al by my side today,” he thought. “He’s so experienced and clever, I can trust him to watch over my patient.” In the OR, the two of them had together hooked up the monitoring and ventilation and carefully checked the patient positioning to make sure there would be no problems later. The urologist created a capnoperitoneum and inserted the trocars. As expected, the peak airway pressure (Paw) increased to 25 cmH 2 O, even though the nerve stimulator showed a TOF value of 0. CRNA Mark had set a PEEP of 6 cmH 2 O and the respiratory rate was 18/min with a tidal volume of 450 ml.
“Do you think you’ll be all right for a minute without me?” he asked student nurse anesthetist Al. “I gotta get a cup of Joe to get myself movin’. I’ll be in the break room when or if you need me.” Student Al nodded in agreement. He valued Marid for his cautious and calm demeanor, and he had already noticed that Marid wasn’t performing at his peak this morning.
On the way to the break room, Marid grabbed an ibuprofen “to help with the sweating.” In the break room, he encountered his attending, Dr. Eldridge, who was immersed in a medical journal. “I only want to drink a quick cup of coffee; the patient is stable and Al is with him.” CRNA Marid knew his boss didn’t like patients left alone with uncertified students. “And who is watching over Al?” was his sarcastic response as he looked up. “Hey, are you OK? You look a little pale around your nose,” the boss said, softening a bit. “I’m fine,” said CRNA Marid, “but my little daughter has the flu. Perhaps a little of her pale color rubbed off on me.”
As usual, there was no coffee made. Marid set a new pot on and, as the coffee filtered, conversed with Dr. Eldridge about his career perspectives in – and around – the hospital. This was a theme which was occupying his mind at the moment. After a little more than half an hour, he found himself in his OR again, “Anything special happen?” he asked his tech. Al replied, “No, not really. I gave more muscle relaxant, and set the remifentanil infusion higher. The urologist seems satisfied. The Paw has increased a bit, because the ventilator was truncating the inspiration. With the maximum pressure cutoff level, I increased the frequency.” CRNA Marid glanced at the monitor and saw the following value:
Blood pressure: 92/60 mmHg
Heart rate: 90 beats/min
Respiratory rate: 20/min
V T : 400 ml
Paw: 30 cmH 2 O
PEEP: 6 cmH 2 O
End–tidal CO 2 : 63 mmHg
31.1.9 Do You See a Problem?
You should see two problems:
The blood pressure is borderline for a patient who has hypertension, and the heart rate is relatively high, especially for a patient who took his β-blocker before the surgery. Many factors could cause this including hypervolemia, hypovolemia, anesthetic overdose, acute heart failure, etc.
The second problem is the ventilation: Mr. Scott is receiving a minute volume of 8 l. Simultaneously, the CO2 is increased. A 63 mmHg CO2 equates to a relative partial pressure of 8 % in room air. This means that Mr. Scott’s oxygen consumption is about 8 % of 8 l, or 640 ml/min. An oxygen consumption of 7.5 ml/kg min – Mr. Scott weighs 85 kg – is unusual for a patient under general anesthesia – especially with the additional muscle relaxant. Usually an oxygen consumption of 4 ml/kg min is assumed, a value which is seldom exceeded. Higher values are seen with states of high metabolism. Examples include sepsis, postoperative shivering, and the commonly feared, but seldom seen, malignant hyperthermia.
In the presented case, the cause is probably not increased endogenous CO2 production, but exogenous CO2 influx via the capnoperitoneum. The CO2 absorption is so high that the set respiratory minute volume is not sufficient to breathe it off. The result is relative hypoventilation with an increased expiratory CO2.
>> CRNA Marid studied the BIS monitor. “40,” he thought, “Mr. Scott isn’t awake. I’ll give a vasopressor and optimize the ventilation.” Shortly after beginning a phenylephrine infusion, the systolic increased to 110 mmHg. The blood loss was minimal so CRNA Mark saw no reason to increase the fluid administration. He set the ventilator to:
Respiratory rate: 26/min
V T : 450 mlRelated posts:
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