Deliberate hypotension in head and neck surgery

Hypotensive anesthesia versus normotensive anesthesia during major maxillofacial surgery: a review of the literature

Steady blood pressure within normal limits during surgery is one of the markers of the ideal and skillful anesthesia. Yet, reduced blood pressure is advantageous in some settings because it can contribute to a reduction in overall blood loss and improve the surgical field conditions. Controlled hypotension during anesthesia or hypotensive anesthesia is often used in major maxillofacial operations. Since hypotensive anesthesia carries the risk of hypoperfusion to important organs and tissues, mainly the brain, heart, and kidneys, it cannot be applied safely in all patients. In this paper we review the medical literature regarding hypotensive anesthesia during major maxillofacial surgery, the means to achieve it, and the risks and benefits of this technique, in comparison to normotensive anesthesia.

Effectiveness of dexmedetomidine in reducing bleeding during septoplasty and tympanoplasty operations

STUDY OBJECTIVE

To determine the effect of dexmedetomidine on intraoperative bleeding during septoplasty and tympanoplasty operations.

DESIGN

Randomized, placebo-controlled study.

SETTING

Univesity medical center.

PATIENTS

80 ASA physical status I and II patients, aged 18 to 65 years, 40 of whom were scheduled for septoplasty and 40 to undergo tympanoplasty operations.

INTERVENTIONS

Patients undergoing septoplasty (S) and tympanoplasty (T) operations were randomly divided into 4 groups. Dexmedetomidine (D) was administered to Group SD and Group TD first as a bolus dose of one microg kg(-1), then intraoperative maintenance was supplied with dexmedetomidine 0.7 microg kg(-1) hour(-1). Groups S and T (controls) were given identical amounts of saline. If systolic blood pressure measurements are greater than 20% preoperative values, then fentanyl one microg kg(-1) was given.

MEASUREMENTS

Intraoperative blood loss was determined with suction volumes and gauze counting. Bleeding was rated according to a 6-point scale. Hemodynamic parameters and fentanyl administration were recorded.

MAIN RESULTS

Group SD had less bleeding and lower bleeding scores (P < 0.05). In addition, this group received less intraoperative fentanyl (P < 0.05). The only significant difference between Groups TD and T was the amount of intraoperative fentanyl given (35.4 +/- 58.8 vs 110.0 +/- 81.0 microg) (P < 0.05).

CONCLUSION

Dexmedetomidine reduces bleeding, bleeding scores, and intraoperative fentanyl consumption during general anesthesia in septoplasty operations.

The effects of prolonged controlled hypotension induced by prostaglandin E1 on renal tubular function

The effects of the prolonged 3-hour and 6-hour controlled hypotension induced by prostaglandin E(1) (PGE(1)) on renal tubular function have been comparatively studied with trimethaphan (TMP; 3-hour hypotensive anesthesia) and enflurane deep anesthesia (6-hour hypotensive anesthesia), using the urine N-acetyl-Beta-D-glucosaminidase (NAG index) and the serum and urine Beta(2)-microglobulin (fractional clearance of Beta(2)-m; Fc-Beta(2)-m) as markers. During 3-hour and 6-hour controlled hypotension PGE(1), NAG index and Fc-Beta(2)-m and urine volume could be maintained without remarkable changes. In the group with TPM, NAG index and Fc-Beta(2)-m significantly increased. The increasing trend was also noted over time in deep anesthesia with enflurane. On 1st postoperative day, Fc-Beta(2)-m significantly increased in PGE(1) group in both 3-hour and 6-hour hypotensive anesthesia, whereas it restored to normal on 2nd postoperative day. Also, in TMP and enflurane deep anesthesia, Fc-Beta(2)-m significantly increased on 1st postoperative day. With the latter, significant increase was also observed on 2nd postoperative day. These results suggest that, in 3-hour and 6-hour controlled hypotension induced by PGE(1), renal tubular function is normally maintained and that it is useful for prolonged controlled hypotensive anesthesia. However, further study is necessary because tubular dysfunction might appear on 1st postoperative day.

Microvascular response in cancellous bone to halothane-induced hypotension in pigs

The microvascular response in cancellous bone to halothane-induced hypotension was studied simultaneously using Laser Doppler Flowmetry (LDF) and clearance of locally injected 133Xe in the subapical mandibular bone of 16 young pigs. During halothane inhalation, a significant reduction in mean blood pressure to values ranging from 22 to 60 mm Hg was observed. The blood flow, as measured with LDF, increased in more than 60% of the animals with hypotension levels above 30 mm Hg. At hypotension levels below 30 mm Hg, blood flow decreased in all cases. The individual regional vascular resistance, calculated as the quotient between blood pressure and recorded blood flow value, was significantly reduced (p less than 0.001) during hypotension. Rhythmical flow variations, observed in some animals at normotension, disappeared immediately following the start of halothane inhalation, but returned when blood pressure was stabilized at a lower level. For recordings made with 133Xe-clearance, a significant reduction (p less than 0.001) in the logarithmic decay of the washout curves was observed during hypotension. This logarithmic decay was correlated to the reduced blood pressure levels (r = 0.73). No average change in regional vascular resistance could, however, be demonstrated. The lack of correlation between results obtained by the 2 methods may be due to the fact that LDF is sensitive to the total blood flow in a limited tissue volume, while the 133Xe isotope seems to be washed out mainly by the capillary blood flow. It can be further concluded that halothane-induced hypotension levels, applicable to clinical routines, may produce an increase rather than a decrease in total blood flow in cancellous bone tissue.