DELIBERATE HYPOTENSION

Nitroprusside and metal nitroprusside nano analogues for cancer therapy

Sodium nitroprusside (SNP), U.S approved drug has been used in clinical emergency as a hypertensive drug for more than a decade. It is well established for its various biomedical applications such as angiogenesis, wound healing, neurological disorders including anti-microbial applications etc. Apart from that, SNP have been considered as excellent biomedical materials for its use as anti-cancer agent because of its behavior as NO-donor. Recent reports suggest that incorporation of metals in SNP/encapsulation of SNP in metal nanoparticles (metal nitroprusside analogues) shows better therapeutic anti-cancer activity. Although there are numerous reports available regarding the biological applications of SNP and metal-based SNP analogue nanoparticles, unfortunately there is not a single comprehensive review which highlights the anti-cancer activity of SNP and its derivative metal analogues in detail along with the future perspective. To this end, the present review article focuses the recent development of anti-cancer activity of SNP and metal-based SNP analogues, their plausible mechanism of action, current status. Furthermore, the future perspectives and challenges of these biomedical materials are also discussed. Overall, this review article represents a new perspective in the area of cancer nanomedicine that will attract a wider spectrum of scientific community.

Blood Loss Associated with Uncemented Total Hip Replacement: Hypotension Does not Affect Blood Loss

Twenty-seven patients who were moderately hypotensive during uncemented total hip replacement were compared with a group of normotensive patients. There was no statistical difference (P < 0.05) in blood loss measured at time of operation, following operation or in the calculated loss. Hypotension, which is known to be dangerous in the elderly, conferred no benefit and should be avoided.

Predictors of arterial blood pressure control during deliberate hypotension with sodium nitroprusside in children

BACKGROUND

Sodium nitroprusside (SNP) is used to decrease arterial blood pressure (BP) during certain surgical procedures. There are limited data regarding efficacy of BP control with SNP. There are no data on patient and clinician factors that affect BP control. We evaluated the dose-response relationship of SNP in infants and children undergoing major surgery and performed a quantitative assessment of BP control.

METHODS

One hundred fifty-three subjects at 7 sites received a blinded infusion followed by open-label SNP during operative procedures requiring controlled hypotension. SNP was administered by continuous infusion and titrated to maintain BP control (mean arterial BP [MAP] within ±10% of clinician-defined target). BP was recorded using an arterial catheter. Statistical process control methodology was used to quantify BP control. A multivariable model assessed the effects of patient and procedural factors.

RESULTS

BP was controlled an average 45.4% (SD 23.9%; 95% CI, 41.5%-49.18%) of the time. Larger changes in infusion rate were associated with worse BP control (7.99% less control for 1 μg·kg·min increase in average titration size, P = 0.0009). A larger difference between a patient's baseline and target MAP predicted worse BP control (0.93% worse control per 1-mm Hg increase in MAP difference, P = 0.0013). Both effects persisted in multivariable models.

CONCLUSIONS

SNP was effective in reducing BP. However, BP was within the target range less than half of the time. No clinician or patient factors were predictive of BP control, although 2 inverse relationships were identified. These relationships require additional study and may be best coupled with exposure-response modeling to propose improved dosing strategies when using SNP for controlled hypotension in the pediatric population.

Comparative induction of controlled circulation by magnesium and remifentanil in spine surgery

AIM: To evaluate the efficacy of magnesium sulfate (MGS) in comparison with remifentanil for induction of relative hypotension in posterior fusion of spine (PSF).

METHODS: In this randomized clinical trial, 40 patients with the American Society of Anesthesiologists I and II physical status undergoing lumbar PSF were randomized to receive remifentanil (REM) 0.15 μg/kg or MGS 50 mg/kg for controlled hypotension. The administering anesthesiologist was blinded to the medication. Continuous infusion was maintained at a fixed volume rate to deliver precalculated doses of either study drugs. All other aspects of anesthesia and surgery were similar in the two groups. The target mean arterial pressure (MAP) range used in this study was 60-70 mmHg. In the course of surgery, the hemodynamic variables, volume of blood loss, urine output, fluid intake and surgeon’s satisfaction were recorded. Data was analyzed with SPSS version 13.0 and P values less than 0.05 were considered significant.

RESULTS: Twenty patients in the MGS group and 19 patients in the REM group were studied. There was no difference between the two groups in the hemodynamic variables, blood loss, urine output, fluid requirement and surgeon’s satisfaction for exposure. The target MAP was achieved in 75% of Mg and 58% of remifentanil groups. Although a higher number of patients in the REM group required nitroglycerin (42.1%) to reach the target MAP than those in the MGS group (25%), this difference was not statistically significant (P = 0.32).

CONCLUSION: Our findings showed that in patients undergoing lumbar PSF surgery, remifentanil and MGS have a similar hypotensive effect and comparable amount of blood loss without any significant adverse effects.

The assessment of blood loss in orthognathic surgery for prognathia

PURPOSE

It is difficult to predict the need for blood transfusion during orthognathic surgery. The purpose of this study was to evaluate differences between patients who underwent different orthognathic procedures, and to assess the need for transfusion in orthognathic surgery.

SUBJECTS AND METHODS

We examined 62 prognathic patients who underwent orthognathic surgery in our hospital. The subjects were divided into 4 groups according to procedure. Pre- and postoperative values of blood parameters were evaluated statistically.

RESULTS

A greater amount of blood was lost in the double-jaw surgeries than in the single-jaw surgeries. There was a significant difference between sagittal split ramus osteotomy (SSRO) combined with Le Fort I osteotomy and intraoral vertical ramus osteotomy (IVRO) ( P < .05). However, none of the patients required transfusion intraoperatively. In all groups except the IVRO group, there were significant differences in red blood cell count, hemoglobin, and hematocrit between preoperative values and 1 week postoperative values ( P < .05). Although the values of red blood cell, hemoglobin, and hematocrit tended to decrease until 2 weeks postoperative, no complications occurred. Simple regression analysis showed significant positive correlation between duration of operation and blood loss ( P < .05).

CONCLUSION

The present results indicate that there is little risk of marked bleeding in routine procedures, and that IVRO causes minimal bleeding. Transfusion was not necessary in IVRO or SSRO with or without Le Fort I osteotomy.

Differential pressor response to intravenous ephedrine during recovery from deliberate hypotension

STUDY OBJECTIVE

To determine whether nitroglycerin or trimethaphan alters pressor response to intravenous (i.v.) ephedrine.

DESIGN

Prospective, randomized study.

SETTING

Operating room of a university hospital.

PATIENTS

60 ASA physical status I female patients scheduled for mastectomy.

INTERVENTIONS

Patients were assigned to one of six groups (n = 10 in each). Group 1: nitroglycerin + normal saline (NS) i.v., Group 2: nitroglycerin + ephedrine 0.1 mg/kg i.v., Group 3: nitroglycerin + ephedrine 0.15 mg/kg i.v., Group 4: trimethaphan + NS i.v., Group 5: trimethaphan + ephedrine 0.1 mg/kg i.v., and Group 6: trimethaphan + ephedrine 0.15 mg/kg i.v.

MEASUREMENTS

Hemodynamic responses to ephedrine following withdrawal of vasodilators were observed for 15 minutes.

MAIN RESULTS

Ephedrine increased heart rate and mean blood pressure. After ephedrine 0.1 mg/kg i.v., the maximum pressor response in the trimethaphan group was approximately twofold that of the nitroglycerin group (p = 0.038).

CONCLUSIONS

Ephedrine restored BP more easily in those patients who had received trimethaphan compared with those who had received nitroglycerin for deliberate hypotension.

Sodium nitroprusside-induced deliberate hypotension to facilitate patent ductus arteriosus ligation in dogs

OBJECTIVE

To report the use of sodium nitroprusside to induce deliberate hypotension to reduce hemorrhage and facilitate surgical ligation of complicated patent ductus arteriosus (PDA) in dogs.

STUDY DESIGN

Retrospective study.

ANIMALS

Six dogs.

METHODS

Hemorrhage occurred during surgical ligation of PDA in 5 dogs. Surgical dissection and isolation of the PDA were very difficult in a sixth dog that was considered to be at increased risk for ductus rupture. Sodium nitroprusside (5 to 25 microg/kg/min intravenously) was administered to these 6 dogs to induce hypotension to reduce blood loss and facilitate surgical ligation of the PDA.

RESULTS

Sodium nitroprusside infusion reduced blood pressure (mean arterial pressure, 45 to 60 mm Hg) within 5 to 10 minutes and hemorrhage from the PDA, facilitating its surgical ligation. Recovery from surgery and anesthesia was uneventful in all 6 dogs.

CONCLUSIONS

Sodium nitroprusside infusion can be used to induce deliberate hypotension in dogs to facilitate surgical ligation of PDA.

CLINICAL RELEVANCE

Sodium nitroprusside infusion produces hypotension within 5 to 10 minutes and is easy to control, rapidly abates, and should help to facilitate surgical ligation of PDA.

Hypotensive anaesthesia and blood loss in orthognathic surgery: a clinical study

OBJECTIVES

To find out whether hypotensive anaesthesia minimized blood loss during orthognathic surgery.

DESIGN

A prospective randomized clinical study.

SUBJECTS AND METHODS

53 consecutive patients, 15-33 years old, who were to have orthognathic operations were admitted to the study. They were randomly allocated to either normotensive or hypotensive anaesthesia.

RESULTS

Median (range) blood loss/operation (ml) under hypotensive anaesthesia was 200 (90-400)ml and under normotensive anaesthesia was 350 (130-1575)ml (P= 0.01), and those for maxillary segmental osteotomy under hypotensive anaesthesia were 85 (40-240)ml and, under normotensive anaesthesia, 175 (100-190)ml (P= 0.05).

CONCLUSION

There was pronounced reduction in blood loss during orthognathic operations done under hypotensive anaesthesia compared with those done under normotensive anaesthesia.

Effect of isoflurane versus nicardipine on blood flow of lumbar paraspinal muscles during controlled hypotension for spinal surgery

STUDY DESIGN

This study compared the effects of isoflurane and nicardipine on regional blood flow of the lumbar paraspinal muscles.

OBJECTIVES

The purpose of this study was to determine whether treatment with hypotensive agents result in ischemia of the lumbar paraspinal muscles, thereby facilitating surgical procedures.

SUMMARY OF BACKGROUND DATA

Despite the general acceptance of controlled hypotension as effective in reducing blood loss during spinal surgery, the changes of blood flow that occur at the lumbar paraspinal muscles when this technique is applied remain unclear. The use of laser Doppler flowmetry allows changes of muscle blood flow to be easily detected in real time with minimal invasion, thereby allowing differences among distinct pharmacological approaches for induction and maintenance of controlled hypotension to be evaluated.

METHODS

The prehypotensive and hypotensive (reduction of mean arterial pressure by 20 mm Hg) blood flow of the lumbar paraspinal muscles were assessed with a laser Doppler flowmeter in 40 patients undergoing lumbar spinal surgery. The first half of the patients (n = 20) received isoflurane, whereas the second half received nicardipine to achieve arterial hypotension.

RESULTS

Compared with the prehypotensive state, during the hypotensive state, patients in the isoflurane group exhibited a 17% to 46% (mean, 33.7%) decrease in lumbar paraspinal muscle blood flow, whereas patients in the nicardipine group exhibited a 24% to 177% (mean, 82.5%) increase in lumbar paraspinal muscle blood flow. Statistical analysis showed a significant difference in the changes of flux after induced hypotension between the isoflurane and nicardipine group (P < 0.001).

CONCLUSIONS

Depending on the pharmacological treatment used to achieve arterial hypotension in spine surgery, there will be either a reduction in paraspinal muscle blood flow (ischemia) or an enhancement of this blood flow (hyperemia).

Effect of patient position and hypotensive anesthesia on inferior vena caval pressure

STUDY DESIGN

This is a prospective study to measure the inferior vena caval pressure of 20 patients in different positions and different states of blood pressure.

OBJECTIVES

Because the inferior vena caval pressure could affect the vertebral venous pressure, which in turn may influence blood loss during lumbar spinal surgery, this study was designed to provide the quantitative data necessary to stress the importance of patient positioning and to assess the effect of controlled hypotension on inferior vena caval pressure.

SUMMARY OF BACKGROUND DATA

Positioning patients with a pendulous abdomen and controlled hypotension has been practiced widely during lumbar spinal surgery. It is generally believed that the former will help reduce vertebral venous engorgement and the latter will produce a bloodless surgical wound. However, there have been no complete studies in which quantitative changes of inferior vena caval pressure resulting from different positions was examined. In addition, it would be interesting to know what happens to inferior vena caval pressure during induced hypotension. Could there be an adverse effect on the inferior vena caval pressure during the hypotensive state?

METHODS

An intravenous catheter was introduced into the inferior vena cava in each of 20 patients undergoing spinal surgery. In each patient, the inferior vena caval pressure was measured when the patient was supine, prone on a conventional pad, and prone on a Relton-Hall frame. It was followed by isoflurane-induced hypotension with reduction of mean arterial pressure by 20 mm Hg.

RESULTS

In this series, the inferior vena caval pressure ranged from 8.2 to 23.4 mm Hg (with a mean of 15.3 mm Hg) when patients were positioned prone on a conventional pad. However, when they were subsequently positioned prone on a Relton-Hall frame, the inferior vena caval pressure decreased dramatically to a range of 4.6 to 13.6 mm Hg (with a mean of 8.2 mm Hg). In each patient the measured inferior vena caval pressure when positioned prone on a conventional pad was 1.5 times greater than that measured with the patient positioned on a Relton-Hall frame. There was a statistically significant difference between these two positions (F = 75.996; P < 0.05). The patients' mean arterial pressure ranged from 92 to 105 mm Hg before induced hypotension. During this time, the inferior vena caval pressure ranged from 4.1 to 13.1 mm Hg (mean, 8.2 mm Hg). During the hypotensive state, the patients' inferior vena caval pressure was found to range from 4.2 to 13.6 mm Hg (mean, 8.1 mm Hg). In each patient the hypotensive interior vena caval pressure may be slightly higher or lower than the baseline pressure. However, the variation never exceeded 1.7 mm Hg. Statistically, there was no significant difference between these two periods (t = 0.956; P > 0.05).

CONCLUSIONS

A device allowing the patient's abdominaL viscera to hang freely while the patient is in a prone position significantly reduces their inferior vena caval pressure. The patients also has a constant inferior vena caval pressure during isoflurane-induced hypotension.

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.

Circulatory and metabolic changes in the brain during induced hypotension--comparison among trimetaphan, glycerin trinitrate and prostaglandin E1

Induced hypotension was carried out using trimetaphan (TMP), glycerin trinitrate (GTN) and prostaglandin E(1) (PGE(1)) in 45 patients received elective abdominal surgery under anesthesia with enflurane in N(2)O/O(2) in order to evaluate and compare the effects of these three agents on cerebral circulation and metabolism. Upon reduction of mean arterial blood pressure to 60-65 mmHg, cerebral blood flow decreased in the TMP and GTN groups but increased in the PGE(1) group. The changes were quite proportional to those in cardiac index in the three groups. Cerebral oxygen consumption decreased only in the TMP group. Changes in cerebrospinal fluid pressure were not in parallel with those in cerebral blood flow. The former decreased slightly in the TMP group but increased in the GTN and PGE(1) groups. These results offered a great caution for induction of artificial hypotension using these agents.

Perioperative stroke. Part I: General surgery, carotid artery disease, and carotid endarterectomy

Although stroke, defined as a focal neurological deficit lasting more than 24 hr, is uncommon in the perioperative period, its associated mortality and long-term disability are high. No large-scale data are available to identify the importance of recognized risk factors for stroke in the perioperative period. A review of the literature shows that the incidence and mechanism of its occurrence are influenced by the presence of cardiovascular disease and the type of surgery. The most common cause of perioperative stroke is embolism. In non-cardiac surgery, the incidence of perioperative stroke is higher among the elderly. Properly administered, controlled hypotension is associated with minimal risk of stroke. Cerebral vasospasm may be the cause of focal cerebral ischaemia in eclamptic patients, and the aggressive treatment of hypertension may exacerbate the neurological damage. The risk of stroke associated with carotid endarterectomy is closely related to the preoperative neurological presentation, and the experience of the surgical/anaesthetic team. Symptomatic cerebrovascular disease, acute stroke, asymptomatic carotid lesions, preoperative assessment of risk, local and general anaesthesia, cerebral protection and monitoring during carotid endarterectomy are discussed with reference to reducing the risk of perioperative stroke. Adequate monitoring and protection have minimized the risk of ischaemia from carotid clamping, and the major mechanism of stroke is embolization.

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.

Effects of hypotension induced by adenosine on brain surface oxygen pressure and cortical cerebral blood flow in the pig

Six pigs were anaesthetized with ketamine in combination with fentanyl and droperidol and paralysed with pancuronium. The pigs were tracheotomized and ventilated mechanically. Mean arterial blood pressure, MABP, was lowered from 97 +/- 21 mmHg stepwise to 58 +/- 2, 33 +/- 4 and 22 +/- 4 mmHg by intravenous infusion of adenosine (4-8 mg kg-1 min-1). Regional cerebral blood flow (rCBF) was measured directly onto the cortex of the brain by local atraumatic application of 133xenon. Brain surface oxygen pressure (PtO2) was obtained using a multiwire oxygen surface electrode. At the level of 60 mmHg, rCBF showed a significant increase, while flow values were not changed from initial values with further hypotension. Ten minutes after adenosine was discontinued, rCBF showed a rebound effect with higher values than initially. During normotension mean cortical PtO2 varied between 2.1 KPa and 3.9 kPa. During adenosine infusion PtO2 was increased at MABP-levels of 60 and 30 mmHg, while at 20 mmHg a decrease was seen in all animals. After discontinuation of the adenosine infusion, PtO2 values were higher than those measured at the initial normotension, a similar rebound phenomenon as seen with rCBF. During the experiments all hypotensive levels could be maintained at constant level without progressively increasing infusion rates, indicating no tachyphylaxis during these time periods. After discontinuation of the drug, blood pressure did not fully reach pre-hypotensive level within 10 min. Thus, hypotension induced by adenosine down to a MABP of 30 mmHg in animal experiments does not cause deterioration in either cerebral blood flow or oxygen pressure.

Trimethaphan-induced hypotension: effect on renal function

This study was designed to evaluate the effects of trimethaphan-induced hypotension on renal function in healthy young patients undergoing maxillofacial surgery. Anaesthesia was induced with thiopentone and was maintained with halothane 1.5-2.0 per cent in oxygen. Each patient served as his own control, and data were analyzed using the paired t-test. Trimethaphan was infused at a rate of 45-52 microgram.kg-1.min-1 for an average hypotensive period of 53 +/- 4 (mean +/- SEM) minutes to reduce the mean arterial pressure (MAP) to 49 +/- 2 torr. Endogenous creatinine clearance, urinary Po2, sodium reabsorption rate (Tna), and serum and urine osmolalities were determined before, during and after arterial hypotension with trimethaphan. Urine flow averaged 2.9 +/- 1 ml/min during the period of hypotension. Endogenous creatinine clearance and Tna were significantly decreased (p less than 0.05) in the hypotensive period. These values returned to normal levels within one hour upon discontinuation of trimethaphan and restoration of blood pressure. We found no statistical difference in urine Po2, and serum and urine osmolalities during control, hypotensive and recovery periods. These results suggest that medullary renal tissue oxygenation, an index of tissue viability, may have remained adequate despite a significant reduction in endogenous creatinine clearance during the hypotensive period. Furthermore, it appears that the effect of trimethaphan-induced hypotension on renal function is similar to the sodium nitroprusside-induced hypotension in man which we have reported previously.

Deliberate hypotension for elective major maxillofacial surgery: a balance halothane and morphine technique

The deliberate hypotensive technique presented here reduces blood loss and operating time during elective major maxillofacial surgery. All the patients in this study had an uneventful course following surgery and were dismissed in satisfactory condition. The one death, while possibly related to halothane, was not related to the hypotensive technique employed. Only one patient required blood replacement and this was due to preoperative anaemia. The hypotensive properties of halothane and morphine are synergistic and sufficient to reduce and control arterial blood pressure during surgery. Further, the use of controlled intermittent ventilation, fluid management, and body position complement the induced hypotension. This yields a technique which is capable of producing significant reduction in arterial blood pressure without the use of potent vasodilators and ganglionic blocking agents with associated undesirable effects.

Blood flow to oral tissues: and experimental study with enflurane, sodium nitroprusside, and nitroglycerin

Hypotensive anesthesia is currently being used in oral and maxillofacial surgery to reduce blood loss and provide a relatively bloodless surgical field. Radioactively labeled microspheres were used to determine and compare the hemodynamic effects of sodium nitroprusside (SNP), nitroglycerin (NTG), and deep enflurane anesthesia on oral tissues during controlled hypotension when compared with controls. Sodium nitroprusside and NTG produced significant reductions in blood flow to the maxilla, mandible, and tongue, while deep enflurane anesthesia did not. In the masseter and suprahyoid muscles, increases in tissue blood flow were found with SNP and enflurane. Nitroglycerin produced no significant change in blood flow in the masseter and the suprahyoid. These results demonstrate that in spite of a similar cardiac index with all agents tested, local oral blood flow varied significantly with the different agents tested. These differences in tissue blood flow suggest that SNP and NTG may be preferable to deep enflurane anesthesia for maxillary osteotomies to achieve greater flow reduction and diminish blood loss.

Clinical applications of sodium nitroprusside

Sodium nitroprusside has its place in two main spheres of medical practice. It is used for the production of deliberate hypotension during anaesthesia to reduce surgical bleeding, and in the management of the acute phase of certain cardiac conditions. This paper considers the value of the drug separately in these two clinical situations.

Deliberate hypotension in head and neck surgery

The deliberate reduction of blood pressure in an attempt to reduce intraoperative blood loss has generated significant controversy in the 30 years since its clinical introduction. Numerous series have been reported, but few have met generally accepted, current criteria for controlled studies. In this article, the effect of blood pressure reduction on organ perfusion will be presented together with a review of techniques of achieving hypotension. A summary of results is included and, based on this data, recommendations are offered regarding the application and limits of deliberate hypotension.

Coarctation in children. Controlled hypotension using labetalol and halothane

Hypotension was induced with halothane and labetalol, an alpha and beta adrenergic blocking agent, in nine children undergoing operation for postductal coarctation of the aorta. The mean arterial pressure decreased by an average of 30% following labetalol, and in six patients the initial halothane concentration (1%) had to be reduced during this period. The heart rate decreased by an average of 8% after labetalol. Profound beta-blockade did not occur, and operating conditions were considered satisfactory. The usefulness of labetalol in the postoperative period is suggested.

Sodium nitroprusside as a hypotensive agent in intracranial aneurysm surgery

Sodium nitroprusside (SNP) was used to induce hypotension during intracranial aneurysm surgery in 67 patients. The effects of SNP infusion (0.1 mg/ml) on blood pressure were rapid and it was easy to adjust blood pressure to desired levels in most patients. When SNP was stopped, the blood pressure returned instantly to the initial level. In eight patients an increase to about 25% or more above prehypotensive level was seen, counteracted in two patients by administration of small doses of halothane. There was a mean increase of 36% in heart rate. Total doses of SNP were 0.05--120 mg (mean: 10.8), corresponding to 0.08--6.8 micrograms/kg/min (mean: 1.9). No metabolic acidosis indicating cyanide intoxication was observed. Tachyphylaxis was seen in three patients, and SNP had to be discontinued in one. It is concluded that SNP gives a rapid and effective hypotension but tachyphylaxis and subsequent danger of cyanide intoxication exist. Therefore, in some cases SNP has to be replaced by or combined with some other hypotensive agent to achieve the desired effect. As there is a risk of impairment of cerebral autoregulation after the use of SNP, it is important to avoid sudden and prolonged blood pressure fluctuations, and to continue with controlled hyperventilation in the postoperative period to reduce the risk of brain oedema and high intracranial pressure.

Clinical evaluation of intravenous nitroglycerin for neurosurgery

Moment-to-moment control of blood pressure is important in the management of the neurosurgical patient. The ideal agent to control blood pressure or induce hypotension should be non-toxic, maintain cerebrovascular autoregulation, and not alter cardiac output or change intracranial pressure. Intravenous nitroglycerin has been used to control blood pressure in 54 neurosurgical cases. This agent produces a rapid, controllable, but not precipitous fall in blood pressure without rebound, is non-toxic, may not alter cerebrovascular autoregulation, and does not raise intracranial pressure. Our clinical experience with intravenous nitroglycerin indicates that it has an important role as a hypotensive agent for the neurosurgical patient.

Serious cerebral complications following unilateral ligation of the internal jugular vein. Review of the literature and a case report

Serious intracranial sequelae of unilateral internal jugular vein ligation or resection are extremely rare. 22 cases including our own, were found in the literature, eight of them with a fatal outcome. Factors involved such as abnormalities of the cerebral venous sinus system, controlled hypotension, hypovolemia, posture, and dressings are discussed, as well as safeguards and possible preoperative diagnostic measures.

Systemic hypotension in neurosurgery

The authors review the intraoperative use of elective hypotension to reduce the probability of hemorrhage, to increase pliability of the aneurysmal sac for ease of clip application, and to control hemorrhage. The optimum agent and techniques for lowering systemic blood pressure remain controversial, but trimethaphan, sodium nitroprusside, and halothane have been found most useful. When cerebral blood flow falls below the brain's capacity to autoregulate, distinct time-related alterations occur biochemically and histologically. The profile of prolonged reduced adenosine triphosphate (ATP), low phosphocreatine, low glucose, and elevated lactate and lactate/pyruvate ratio is associated with swelling of perivascular astrocytes and "blebbing" of vascular endothelial cells with subsequent cerebral damage. To prevent permanent alteration it is desirable to observe time constraints and to employ other means of protection such as hypothermia, although the authors believe the latter unnecessary for short hypotensive periods. It has been proposed, but not substantiated, that anesthetics which depress rate of cerebral oxygen consumption but do not affect cerebral ATP level protect the brain from hypotension. Several investigations suggest that halothane, a vasodiltor, satisfies the safety requirement. The most prominent contraindication to halothane, however, is elevation of intracranial pressure. At present hypotensive surgery for aneurysmorrhapy is usually performed when intracranial pressure has returned to normal. Experimentally the electroencephalogram has been observed to show alterations prior to biochemical parameters for following brain vulnerability, so that it conceivably could be an effective monitoring technique during prolonged profound hypotension.

Deliberate hypotension

Deliberate hypotension can reduce major blood loss and indelicate operations can produce a drier field increasing the ease of surgery and the likelihood of a good result. The techniques used to induce hypotension can also be used to avoid dangerous hypertension during and after surgery. These benefits must be weighed against the risks of inadequate perfusion: especially cerebral, myocardial, or renal. In previously normotensive patients these risks are minimal when the arterial pressure is held above 80 torr systolic, and may be acceptably small even at mean pressure of 50 to 60 torr. Previously hypertensive patients show signs of cerebral ischemia at higher pressures; they should probably not be subjected to deliberate hypotension, but they also can be harmed by severe hypertension which can be avioded by the proper use of hypotensive agents. For most situations a balanced technique is suitable: after a stable anesthetic level has been achieved using halothane or enflurane, hypotension can be induced with sodium nitroprusside or trimethaphan camsylate. Longer-acting agents such as pentolinium are sometimes desirable, but the shorter-acting agents are easier to control. Careful monitoring with observation of intra-arterial pressure, electroencephalogram, electrocardiogram, and determination arterial blood gas tensions is likely to make for safer conduct. Close postoperative observation is essential. With careful preparation and monitoring deliberate hypotension can be a safe technique for reducing blood loss or facilitating delicate procedures.