Hypotensive anaesthesia for spine surgery--nitroglycerin vs halothane.PP Kadam, SG Saksena, SR Jagtap, SM Pantavaidya
Dept. of Anaesthesiology, LTMMC and LTMG Hospital, Sion, Bombay, Maharashtra.
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 0008295141
Source of Support: None, Conflict of Interest: None
Thirty patients (ASA I or II) requiring spine surgery under general anesthesia were studied. To induce hypotension, halothane 0.5 to 2.5% (n = 15) or nitroglycerin infusion (1-2 micrograms/kg/min) (n = 15) was used. The parameters studied were blood pressure, blood loss, operating time and recovery score. The systolic blood pressure was maintained between 80-100 mmHg during surgery in both the groups. The blood loss with nitroglycerin was significantly less (202 +/- 114 ml) than halothane group (602 +/- 312 ml). All the patients were alert at the end of surgery in the nitroglycerin group (recovery score 9.8 +/- 0.76) as against the halothane group (7.98 +/- 0.9 p < 0.01). Tachycardia or tachyphylaxis was not observed with nitroglycerin. This study suggests that continuous intravenous infusion of nitroglycerin is effective and safe in reducing blood loss and operating time during spine surgery.
Keywords: Adult, Anesthesia, General, Blood Loss, Surgical, Blood Pressure, Halothane, Human, Hypotension, Controlled, Middle Age, Nitroglycerin, administration &dosage,Spine, surgery,
Extensive surgical procedures on spine such as scoliosis correction, posterior lumbar interbody fusion are associated with considerable haemorrhage during and after surgery. Induced hypotension has been advocated as means of reducing blood loss and improving the operating conditions during spine surgery, with the commonly used drugs, such as sodium nitroprusside, there are chances of tolerance, tachyphylaxis and cyanide toxicity, halothane induces hypotension by depressing myocardium. Nitroglycerin has been used to control blood pressure perioperatively during coronary artery surgery and to reduce the blood loss in total hip replacement. In the present study, we evaluated the effects of halothane and intravenous nitroglycerin on blood pressure and blood loss during spine surgery.
Thirty consecutive patients, belonging to ASA I or II scheduled for spine surgery [Table - 1] under general anaesthesia, were studied. Informed consent was obtained. They were divided into two groups depending upon the hypotensive agent used. Group I (n=15) received 0.5 to 2.5 % halothane and patients from Group II (n=15) were given intravenous nitroglycerin infusion 1-2 ?g/kg/min. The groups were comparable with regard to age (Gr I: 35 + 12, Gr II: 36 + 15 years) and weight (Gr I: 54 + II, Gr II: 50 + 13 kg).
All the patients were premedicated with pethidine 1 mg/kg and promethazine hydrochloride 0.5 mg/kg intramuscularly one hour before surgery. A 20 G Teflon catheter was inserted percutaneously into the radial artery for continuous direct intra-arterial blood pressure monitoring. The systolic, diastolic and mean blood pressure, and electrocardiogram were displayed continuously on oscilloscope. Two intravenous lines for fluid and drug administration were procured. A standard technique of general anaesthesia was employed consisting of nitrous oxide, oxygen and pancuronium bromide as muscle relaxant with controlled ventilation. All the patients were catheterised to measure urine output.
Halothane 0.5 - 2.5% was administered by Fluotec Mark III vaporiser to patients in Gr I. Nitroglycerin solution was prepared by addition of 25 mg to 500 ml of 5% dextrose. The infusion was begun at the rate of 1 ?g/kg/min and then adjusted upto 2 pg/kg/min for patients in Gr II. The systolic blood pressure was lowered to 80 - 100 mmHg before the skin incision and maintained throughout the surgery in both the groups.
The surgeon was asked to grade the drynes of surgical field on a scale 1 - 10; 1 being “dry and ideal" with little or no oozing and 10 being "wet and hopeless" which interfered with the surgical dissection. Intravenous infusion of 5% dextrose or Hartmarm's solution was administered at the rate of 8-10 m]/kg/hr to maintain hourly urine output of 50 ml or more. The blood loss was replaced by whole blood when the loss exceeded 10% of the estimated blood volume. It was assessed by weighing sponges and measuring the volume of blood in the suction bottle during surgery. Postoperative drainage from the operation site within next 24 hours was also noted.
The hypotensive agents were discontinued before suturing the wound. The systolic blood pressure was allowed to return to pre-hypotensive level to check the haemostasis. The operative time was measured from the start of skin incision to the end of skin closure. At the end of surgery the recovery score was assessed.
The data was subjected to statistical analysis using student T test.
The hypotension achieved by nitroglycerin (Gr II) appeared to be more sustained than that by halothane (Gr I). With the latter there appears to be a tendency for gradual rise in systolic blood pressure, though at any given point of time, difference between the groups was not statistically significant [Figure:1]. Systolic blood pressure returned to control value immediately after discontinuation of both the agents [Table - 2] Rebound hypertension was not observed in any patient. Similar pattern was observed with mean blood pressure. After an hour of nitroglycerin infusion there was marginal reduction in diastolic blood pressure. With planned dosage of both the agents there were no significant variations in heart rate [Figure:2]. However, two patients developed ventricular arrhythmias when halothane concentration was increased to more than 2.5%. Urine output was adequate in all the patients.
The mean intra-operative blood loss in Gr II was significantly less (202 + 13 ml). Only one patient required blood transfusion. The blood loss in Gr I was 602 + 312 ml and nine patients needed blood transfusion. the postoperative drainage was similar in both the groups. (Gr I : 61 + 17 ml, Gr II : 57 + 22 ml)
The surgeon's score (2.2 + 1.5) and operating time (143 + 57 mins) were significantly less in Gr II than in Gr I. The patients receiving nitroglycerin were alert at the end of the operation whereas six patients were drowsy for 4-6 hours following halothane [Table - 2]. There was no evidence of tachyphylaxis or tolerance to action of nitroglycerin.
The benefits of induced hypotension during spine surgery include reduction in blood loss and need for blood transfusion, improved operating conditions and shorter duration of surgery. It is reported that decrease in systolic blood pressure to 80-100 mm Hg was enough to reduce the blood loss,. Fahmy used nitroglycerin infusion during total hip replacement for the similar purpose. The present study shows that nitroglycerin, induced hypotension was more effective than that by halothane in reducing blood loss intra-operatively. Only one patient in the nitroglycerin group required blood transfusion. The bleeding during operation is mainly of venous origin. Nitroglycerin predominantly dilates venous capacitance vessels causing pooling of blood away from operation site and decreasing blood loss. The dose of nitroglycerin was adjusted to maintain systolic blood pressure between 80-100 mmHg in this study. Prys Roberts et al reported that halothane induces hypotension mainly due to its myocardial depressant effect, with overall systemic vascular resistance remaining unchanged. They observed arrhythmias in two out of fifteen patients with 3% halothane. When an attempt was made to increase halothane concentration to more than 2.5% to achieve desired systolic blood pressure for longer period, two patients developed ventricular arrhythmia in our study. Arterial blood gas analysis was done to rule out other causes of arrhythmias.
In our study there was no significant effect on the heart rate with halothane as well as nitroglycerin. Kaplan et al, did not observe significant change in heart rate when nitroglycerin was used to control blood pressure during coronary artery surgery. They suggested that gradual reduction in blood pressure by nitrolgycerin prevented an increase in heart rate. Similar results were reported by Fahmy, Dauchet and Bale et al.
Thus intravenous nitroglycerin 1-2 ?g/Kg/min is a safe and useful adjuvant to anaesthesia as suggested by less blood loss, better working field for the surgeon, reduced operative time and faster recovery.
[Table - 1], [Table - 2]