Induced hypotension

Correlation and Linear Regression between Blood Pressure Decreases after a Test Dose Injection of Propofol and that following Anaesthesia Induction

Propofol reduces systemic vascular resistance and suppresses cardiac function when injected rapidly. In this study we investigated whether blood pressure decrease after a minimal dose (test-dose) injection of propofol correlates with that after an induction-dose injection.

Patients were randomly divided into two groups; anaesthesia was induced in group A (n=60) using 1.5 mg/kg propofol and in group B (n=61) using 2.0 mg/kg. Blood pressure reduction after a minimal dose injection (0.4 mg/kg) was examined non-invasively prior to anaesthetic induction. Bispectral Index monitoring was measured and sedation level scored to evaluate anaesthetic depth.

After the minimal dose injection, 18 of 121 patients showed behaviour suggesting minor disinhibition, five patients were sedated and seven were drowsy. Oxygen saturation was not significantly changed after test-dose injection. Reduction in systolic blood pressure (mean±SD) was 17±11 mmHg after the minimal dose injection, 42±20 mmHg after a 1.5 mg/kg induction dose injection, and 42±22 mmHg after a 2.0 mg/kg induction-dose injection. In both groups, blood pressure after induction was significantly lower than the control value (P<0.05). In both groups, a positive correlation was observed between blood pressure reduction after the minimal dose injection and that after the induction-dose injection [P<0.01, R value for systolic blood pressure correlation in group A 0.712 (P<0.01) and in group B 0.758 (P<0.01)].

We concluded there was a positive correlation between blood pressure reduction after a minimal (test-dose) injection and that after an induction-dose injection.

Average blood loss and the risk of requiring perioperative blood transfusion in 506 orthognathic surgical procedures

PURPOSE

This study quantifies the estimated blood loss in seven groups of orthognathic surgical procedures and the risk of requiring perioperative blood transfusion, and identifies the factors relating to blood loss and need for transfusion.

PATIENTS AND METHODS

The records of 506 consecutive patients who underwent various orthognathic surgical procedures under hypotensive anesthesia from 1987 to 1990 were analyzed retrospectively. All procedures were performed by the authors in the same hospital setting. Patients were placed in seven groups based on the operation(s) performed, including single-jaw and double-jaw procedures. Estimated blood loss was calculated for each group and was correlated with patients' sex, age, and year of surgery, and whether they autodonated blood. The volume of intravenous (IV) fluids given was also recorded.

RESULTS

Average estimated blood loss for all groups was 273.23 mL. Double-jaw procedures resulted in more blood loss than single-jaw procedures. Men and boys had a higher average blood loss than women and girls, but average blood loss was not affected significantly by patients' age or year of surgery. Only four patients (0.8%) received blood transfusions, and their average estimated blood loss was 975 mL. The percentage of patients autodonating increased from 10.4% in 1987 to 54.9% in 1990. There was no significant difference in the percentage of autodonators by surgical procedure.

CONCLUSIONS

The need for blood transfusion in this study was extremely low. Factors contributing to this are believed to be use of hypotensive anesthesia; a single surgical team; and a constant surgical setting. Patients having double-jaw surgery are at greater risk for blood loss than those having single-jaw procedures, and should be so advised, along with the risks of blood transfusion. The authors believe that under the conditions of this study the use of autodonation is not necessary, with the possible exception of complex double-jaw procedures involving small patients.

Sodium nitroprusside induced hypotension: haemodynamic response and dose requirements during propofol or halothane anaesthesia

This study was designed to investigate the influence of anaesthesia induced and maintained with propofol on the haemodynamic effects and the dose requirements of SNP during the course of induced hypotension. Twenty-four adult ASA physical status I patients undergoing middle ear surgery were randomly assigned to receive anaesthesia with either morphine, thiopentone, d-tubocurarine, halothane 0.6% end-tidal and N2O 70% in oxygen (group I n = 12), or morphine, propofol, d-tubocurarine, propofol infusion 108 micrograms.kg-1.min-1 and N2O in oxygen (group 2 n = 12). Mean arterial blood pressure (MAP) was reduced to 60-65 mmHg in all patients using a continuous infusion of sodium nitroprusside (SNP) 0.01%. Propofol produced a significant (17%) reduction in the MAP before institution of SNP infusion. This was related to a 24% reduction in the systemic vascular resistance index (SVRI). In the halothane group SVRI was significantly reduced during SNP infusion. Halothane anaesthesia was associated with significant reflex tachycardia in response to SNP induced hypotension. Eight patients in the halothane group (66%) required propranolol 0.5-3 mg to control tachycardia. Propofol anaesthesia attenuated significantly the reflex tachycardia in response to SNP induced hypotension. Two patients in the propofol group (16%) required 0.5 mg propranolol to control reflex tachycardia. The mean SNP dose requirements were 7.25 +/- 1.6 and 2.1 +/- 1.4 micrograms. kg-1.min-1 in the halothane and propofol groups, respectively (P < 0.0001). None of the patients in the two groups developed rebound hypertension following SNP withdrawal.(ABSTRACT TRUNCATED AT 250 WORDS)

Vasodilators during cerebral aneurysm surgery

The objective of this review is to review the anaesthetic implications of vasoactive compounds particularly with regard to the cerebral circulation and their clinical importance for the practicing anaesthetist. Material was selected on the basis of validity and application to clinical practice and animal studies were selected only if human studies were lacking. Hypotensive drugs have been used to induce hypotension and in the treatment of intraoperative hypertension during cerebral aneurysm surgery. After subarachnoid haemorrhage, cerebral blood flow is reduced and cerebral vasoreactivity is disturbed which may lead to brain ischaemia. Also, cerebral arterial vasospasm decreases cerebral blood flow, and may lead to delayed ischaemic brain damage which is a major problem after subarachnoid haemorrhage. Recently, the use of induced hypotension has decreased although it is still useful in patients with intraoperative aneurysm rupture, giant cerebral aneurysm, fragile aneurysms and multiple cerebral aneurysms. In this review, a variety of vasodilating agents, prostaglandin E1, sodium nitroprusside, nitroglycerin, trimetaphan, adenosine, calcium antagonists, and inhalational anaesthetics, are discussed for their clinical usefulness. Sodium nitroprusside, nitroglycerin and isoflurane are the drugs of choice for induced hypotension. Prostaglandin E1, nicardipine and nitroglycerin have the advantage that they do not alter carbon dioxide reactivity. Local cerebral blood flow is increased with nitroglycerin, decreased with trimetaphan and unchanged with prostaglandin E1. Intraoperative hypertension is a dangerous complication occurring during cerebral aneurysm surgery, but its treatment in association with subarachnoid haemorrhage is complicated in cases of cerebral arterial vasospasm because fluctuations in cerebral blood flow may be exacerbated. Hypertension should be treated immediately to reduce the risk of rebleeding and intraoperative aneurysmal rupture and the choice of drugs is discussed. Although the use of induced hypotension has declined, the control of arterial blood pressure with vasoactive drugs to reduce the risk of intraoperative cerebral aneurysm rupture is a useful technique. Intraoperative hypertension should be treated immediately but the cerebral vascular effects of each vasodilator should be understood before their use as hypotensive agents.

Anesthesia for intracranial aneurysm surgery

Aneurysmal rupture represents the most common cause of subarachnoid hemorrhage. Approximately two-thirds of persons who experience a subarachnoid hemorrhage will die or become disabled. Although advances in neurosurgical techniques, neuroanesthetic management, and neuroradiology have resulted in great progress in reducing the operative risk for patients with intracranial aneurysms, the overall outcome following subarachnoid hemorrhage remains disappointing. This article provides an overview of some current concepts related to the perioperative management of patients with intracranial aneurysms, such as the risk and management of rebleeding and vasospasm, and considerations related to the timing of surgery. The anesthetic management of these patients is reviewed, emphasizing principles relating to the facilitation of surgery--by optimizing operative conditions and minimizing the risks of intraoperative aneurysmal rupture or the aggravation of neurologic deficits--and to the provision of a smooth, stable recovery. Despite the disappointing overall prognosis following subarachnoid hemorrhage, adherence to these principles can optimize the outcome for those patients who reach the operating room.

Deliberate hypotension induced by labetalol with halothane, enflurane or isoflurane for middle-ear surgery

The feasibility of using labetalol, an alpha- and beta-adrenergic blocking agent, as a hypotensive agent in combination with inhalation anaesthetics (halothane, enflurane or isoflurane) was studied in 23 adult patients undergoing middle-ear surgery. The mean arterial pressure was decreased from 86 +/- 5 (s.e. mean) mmHg to 52 +/- 1 mmHg (11.5 +/- 0.7 to 6.9 +/- 0.1 kPa) for 98 +/- 10 min in the halothane (H) group, from 79 +/- 5 to 53 +/- 1 mmHg (10.5 +/- 0.7 to 7.1 +/- 0.1 kPa) for 129 +/- 11 min in the enflurane (E) group, and from 80 +/- 4 to 49 +/- 1 mmHg (10.7 +/- 0.5 to 6.5 +/- 0.1 kPa) for 135 +/- 15 min in the isoflurane (I) group. The mean H concentration during hypotension in the inspiratory gas was 0.7 +/- 0.1 vol%, the mean E concentration 1.6 +/- 0.2 vol%, and the mean I concentration 1.0 +/- 0.1 vol%. In addition, the patients received fentanyl and d-tubocurarine. The initial dose of labetalol for lowering blood pressure was similar, 0.52-0.59 mg/kg, in all the groups. During hypotension, the heart rate was stable without tachy- or bradycardia. The operating conditions regarding bleeding were estimated in a double-blind manner, and did not differ significantly between the groups. During hypotension, the serum creatinine concentration rose significantly in all groups from the values before hypotension and returned postoperatively to the initial level in the other groups, except the isoflurane group. After hypotension there was no rebound phenomenon in either blood pressure or heart rate. These results indicate that labetalol induces easily adjustable hypotension without compensatory tachycardia and rebound hypertension.

Anaesthesia for hip surgery in the elderly

Surgical repair of hip fracture and total hip arthroplasty are primarily performed on elderly patients. Patients presenting for hip fracture surgery have a high prevalence of preoperative medical problems and may require medical stabilization before surgery. Regional anaesthesia for hip fracture repair may be contraindicated due to perioperative pharmacologic prophylaxis for deep venous thrombosis. The use of regional anaesthesia increases the magnitude and frequency of hypotensive episodes when compared with general anaesthesia. Intraoperative blood losses, averaging 250-300 ml, are not affected by anaesthetic technique. Following hip fracture surgery under spinal anaesthesia, patients exhibit better oxygenation in the early postoperative period than those after general anaesthesia. The frequency of postoperative confusion is unrelated to anaesthetic technique. The incidence of deep venous thrombosis is reduced following spinal anaesthesia as compared with general anaesthesia. The one-month mortality rate, approximately eight per cent, is unrelated to anaesthetic technique. Spinal, epidural and general anaesthesia have been used successfully for total hip arthroplasty. Intraoperative blood loss of 0.5-1.5 litres is reduced with regional anaesthesia. General anaesthesia with controlled hypotension also significantly reduces blood loss. Intraoperative instability with hypoxaemia, hypotension and cardiac arrest may follow impaction of the femoral prosthesis and are related to absorption of acrylic cement monomers and pulmonary embolism of fat, air, and platelet-fibrin aggregates. Postoperative deep venous thrombosis is common and the incidence may be reduced with epidural anaesthesia. Operative mortality is less than one per cent and pulmonary embolism is the commonest cause of death.(ABSTRACT TRUNCATED AT 250 WORDS)

Additive effects of dihydralazine during enflurane or isoflurane hypotensive anaesthesia for spinal fusion

Sixteen patients (13-38 yr) undergoing spinal fusion for scoliosis under controlled hypotension were studied to determine the haemodynamic and neuroendocrine responses to IV dihydralazine (1.0 mg.kg-1) followed by 0.5 and 1 MAC of enflurane or isoflurane. Twenty minutes after dihydralazine administration mean arterial pressure (-20 per cent) and systemic vascular resistance (-50 per cent) decreased, and cardiac index (+57 per cent), heart rate (+37 per cent) and intrapulmonary shunt increased. Plasma renin activity and aldosterone and norepinephrine levels increased. Further decreases in mean arterial pressure and in systemic vascular resistance were observed when 0.5 MAC enflurane or isoflurane were added. With 1 MAC anaesthetic levels a further decrease in mean arterial pressure was observed in both groups, but pressure fell to a lower level with isoflurane than with enflurane (p less than 0.01). The reduction of arterial blood pressure to a level of 50-60 mmHg for three to four hours was easy to control and was free of complications. The preliminary IV administration of dihydralazine allowed a reduced volatile agent concentration which attenuated undesirable haemodynamic effects, in spite of renin and norepinephrine release, and permitted a rapid intraoperative awakening.

Comparison of intravenous nitroprusside, nitroprusside-captopril, and nitroglycerin for deliberate hypotension during posterior spine fusion in adults

Three techniques for deliberate hypotension (mean arterial pressure, 60 to 70 mmHg) were prospectively compared in adults undergoing posterior spine fusion. Patients received either IV sodium nitroprusside, sodium nitroprusside with oral captopril pretreatment, or IV nitroglycerin. Patient groups were comparable in age, sex, weight, baseline hemodynamic and laboratory parameters, duration of surgery, and duration of hypotension. Absolute blood loss was significantly less in the group receiving nitroglycerin; however, there were no differences between groups when corrected for operative exposure (milliliter per spine segment exposed). Nitroprusside was effective in producing target blood pressure in all patients. Nitroglycerin was ineffective in two patients and two other patients required greater than 20 micrograms/kg/min. Both groups receiving nitroprusside developed significant postinfusion increases in arterial pressure. Blood pressure fell significantly after induction of anesthesia in patients receiving captopril. Cardiac index, heart rate, pulmonary capillary wedge pressure, intrapulmonary shunt, and arterial blood gases were comparable and did not change significantly in any group. Systemic vascular resistance fell during infusion in all groups and remained depressed after infusion in patients receiving nitroglycerin. Plasma renin activity was significantly increased in the group receiving captopril due to loss of feedback inhibition of renin release and rose significantly during infusion in those patients receiving nitroprusside alone. There were no complications. Nitroprusside with and without captopril pretreatment was associated with postoperative increases in arterial pressure, although not to hypertensive levels, probably due to loss of captopril activity after single-dose administration. The use of nitroglycerin was limited by lack of potency. There was no demonstrable clinical advantage for any of the three techniques.

Interactions between nimodipine and general anaesthesia--clinical investigations in 124 patients during neurosurgical operations

Haemodynamic, respiratory, metabolic and endocrine investigations were performed in a total number of 124 patients, divided into four different groups, during opiate anaesthesia for neurosurgical operations in order to characterize general effects of nimodipine, a calcium channel blocking agent with a preferential cerebrovascular action. These studies led to the following conclusions: Nimodipine is a vasodilator drug with a hypotensive action, which is especially obvious in hypertensive patients and in combination with similarly acting agents, such as sodium nitroprusside or nitroglycerin. This vascular hypotensive effect may be also enhanced by combined cardiodepressive activity if nimodipine is applied together with inhaled anaesthetics, such as halothane or isoflurane. Nimodipine as well as other vasodilator drugs may lead to increased pulmonary shunting in patients with artificial ventilation, which, however, can be reduced by adequate positive end-exspiratory pressure. With high doses the decrease of oxygen extraction and consumption, seen with nimodipine, is accompanied by a moderate rise of lactate. Determination of stress hormones did not reveal analgesia potentiation of nimodipine, as has been assumed in other studies.

Systemic haemodynamic and metabolic effects of deliberate hypotension with isoflurane anaesthesia or sodium nitroprusside during total hip arthroplasty

Isoflurane (ISO) was examined as an alternative hypotensive agent to nitroprusside (SNP) in 16 patients (mean age: 60 years) anaesthetized for total hip arthroplasty. MAP was decreased to 50 per cent of the awake level by infusion of SNP in Group I (n = 8) and with ISO in Group II (n = 8). Fentanyl (10-16 micrograms X kg-1) was administered to both groups. Haemodynamic measurements were repeated in the lateral position before, during and after hypotension. Polygeline and fresh frozen plasma were infused throughout the study period in volumes sufficient to maintain pulmonary capillary wedge pressure in the 7-9 mmHg range. The MAP decrease was the same in both groups, as were perioperative blood replacement (mean 500 ml), and postoperative haematocrits. Total perioperative fluid replacement was higher (p less than 0.01) in Group I (mean 2500 ml) than in Group II (mean 1300 ml). Venous tone was more affected by SNP than by ISO. ISO decreased the systemic vascular resistance index and oxygen consumption (VO2) without any change in CI or in Qs/Qt, in contrast to SNP which increased CI, VO2 and Qs/Qt.

Hypotensive actions of diltiazem and nitroprusside compared during fentanyl anaesthesia for total hip arthroplasty

The potential for inducing hypotension during fentanyl anaesthesia by administering either diltiazem (n = 7) or sodium nitroprusside (n = 7) was investigated during total hip arthroplasty. Haemodynamic variables were obtained in the lateral position before, during and after administration of the hypotensive agent. Diltiazem 0.15 mg X kg-1 given as an IV bolus followed by a 12.5 +/- 3 micrograms X kg-1 X min-1 continuous infusion decreased mean arterial pressure (MAP) from 77 +/- 11 mmHg to 63 +/- 16 mmHg (p less than 0.05) while other haemodynamic parameters showed only minor and insignificant changes. Hypotension continued for at least 30 min after the cessation of diltiazem. With sodium nitroprusside MAP decreased immediately from 81 +/- 11 mmHg to 59 +/- 9 mmHg (p less than 0.01) and rapidly returned to its control value after cessation of the infusion. CI and Qs/Qt rose significantly (p less than 0.05) while the systemic vascular resistance index (SVRI) (p less than 0.01) and pulmonary vascular resistance index (PVRI) (p less than 0.05) fell significantly. The haemodynamic profile was significantly different between hypotensive agents for MAP (p less than 0.02), heart rate (HR) (p less than 0.01), SVRI (p less than 0.05), and PVRI (p less than 0.05). HR was lower with diltiazem than with nitroprusside. A bradycardia less than 50 beats/min was observed in five patients in the diltiazem group. MAP, SVRI and PVRI were lower with nitroprusside than with diltiazem. Diltiazem can induce and maintain moderate hypotension without tachycardia and decreased cardiac output in humans during fentanyl anaesthesia but the modulation of the level of arterial pressure and the depression of atrioventricular conduction are unpredictable.