Use of labetalol during hypotensive anaesthesia and in the management of phaeochromocytoma

Retrospective evaluation of labetalol as antihypertensive agent in dogs

Background

To evaluate the effect on arterial blood pressure (ABP) of labetalol infusion as treatment for perioperative non nociceptive acute hypertension in dogs. The clinical records of dogs receiving intra or postoperative labetalol infusion were retrospectively reviewed. Invasive systolic (SAP), mean (MAP) and diastolic (DAP) arterial pressure and heart rate (HR) before labetalol infusion (T0) and 15, 30, 45 and 60 min (T1, T2, T3 and T4 respectively) after infusion were retrieved. The dose rate of labetalol infusion and use of concurrently administered drugs that could have potentially affected ABP and/or HR were also recorded. ANOVA for repeated measures and Dunnett’s multiple comparison test were used to determine the effect of labetalol on ABP and HR. Differences were considered significant when p < 0.05.

Results

A total of 20 dogs met the inclusion criteria, and hypertension was documented after craniotomy (12/20), adrenalectomy (4/20) and other procedures (4/20). Five dogs received labetalol intraoperatively, 14 postoperatively, and 1 during the surgical procedure and recovery. Median infusion duration and rate were 463 (60-2120) minutes and 1.1 (0.2–3.4) mg/kg/h respectively. Median loading dose was 0.2 (0.2–0.4) mg/kg. Labetalol produced a significant decrease in SAP and DAP at all time points compared to T0 (p < 0.05), while the effect was not significant at T1 for MAP (p = 0.0519). Median maximum MAP decrease was 31 (20–90) mmHg. Heart rate did not increase significantly during treatment (p = 0.2454). Acepromazine given before or during labetalol treatment did not reduce significantly ABP (p = 0.735).

Conclusions

Labetalol produced a reliable and titratable decrease in ABP with non significant increase in HR.

Risks and benefits of deliberate hypotension in anaesthesia: a systematic review

This systematic review was performed to investigate and review the evidence on the risks and benefits of hypotensive anaesthesia in order to answer the following question: 'Should deliberate hypotension be used routinely during orthognathic surgery?' An electronic search on MEDLINE and the Cochrane Library database was carried out for all relevant articles using specific search keywords. All articles were classified by their levels of evidence. Studies with highest level of evidence and rated to have the lowest risk of bias were reviewed. Regarding the benefits of hypotensive anaesthesia, three studies reported significant decrease of blood loss in patients receiving hypotensive anaesthesia. Two studies reported a significant decrease in transfusion rate. Two studies demonstrated improved surgical field and significant reduction in operation time. In terms of risk, no significant changes in cerebral, cardiovascular, renal and hepatic functions in patients receiving hypotensive anaesthesia compared to control were reported. In conclusion, hypotensive anaesthesia appears to be effective in reducing blood loss. Serious consequences due to organ hypoperfusion are uncommon. Hypotensive anaesthesia can be justified as a routine procedure for orthognathic surgery especially bimaxillary osteotomy. Patient selection and appropriate monitoring are mandatory for this technique to be carried out safely.

Adverse drug reactions in patients with phaeochromocytoma: incidence, prevention and management

The dangers of phaeochromocytomas are mainly due to the capability of these neuroendocrine tumours to secrete large quantities of vasoactive catecholamines, thereby increasing blood pressure and causing other related adverse events or complications. Phaeochromocytomas are often missed, sometimes only becoming apparent during therapeutic interventions that provoke release or interfere with the disposition of catecholamines produced by the tumours. Because phaeochromocytomas are rare, evidence contraindicating use of specific drugs is largely anecdotal or based on case reports. The heterogeneous nature of the tumours also makes adverse reactions highly variable among patients. Some drugs, such as dopamine D(2) receptor antagonists (e.g. metoclopramide, veralipride) and beta-adrenergic receptor antagonists (beta-blockers) clearly carry high potential for adverse reactions, while others such as tricyclic antidepressants seem more inconsistent in producing complications. Other drugs capable of causing adverse reactions include monoamine oxidase inhibitors, sympathomimetics (e.g. ephedrine) and certain peptide and corticosteroid hormones (e.g. corticotropin, glucagon and glucocorticoids). Risks associated with contraindicated medications are easily minimised by adoption of appropriate safeguards (e.g. adrenoceptor blockade). Without such precautions, the state of cardiovascular vulnerability makes some drugs and manipulations employed during surgical anaesthesia particularly dangerous. Problems arise most often when drugs or therapeutic procedures are employed in patients in whom the tumour is not suspected. In such cases, it is extremely important for the clinician to recognise the possibility of an underlying catecholamine-producing tumour and to take the most appropriate steps to manage and treat adverse events and clinical complications.

Labetalol Pretreatment Reduces Blood Pressure Instability During Surgical Resection of Pheochromocytoma

BACKGROUND

To evaluate the effect of pretreatment with the mixed alpha- and beta-adrenergic blocker, labetalol, on blood pressure instability during surgical resection of pheochromocytoma.

METHODS

Blood pressure stability and surgical results were compared between patients in the saline (n = 11) and labetalol (n = 15) groups. Anesthesia was induced with fentanyl, sodium thiopental and atracurium, and maintained with isoflurane in a 50% oxygen/nitrous oxide mixture. Intravenous labetalol was administered in the labetalol group before surgical incision, with the maximal dose being 1.2 mg/kg, while normal saline was administered to patients in the control, saline, group. Supplemental intravenous sodium nitroprusside (SNP) infusion was administered whenever systolic blood pressure exceeded 180 mmHg. The number of patients with intraoperative hypertension or hypotension, dosage of SNP administered, number of intraoperative hypertension episodes, use of fluid and blood transfusion, and heart rate (defined as the mean of heart rate every 5 minutes throughout the operation) were compared between these two groups.

RESULTS

The number of patients with intraoperative hypertension, number of patients receiving SNP, dose of SNP administered, and number of hypertension episodes were significantly lower in patients who received labetalol pretreatment than in control patients.

CONCLUSION

This study has demonstrated that labetalol pretreatment (1.2 mg/kg) with supplemental SNP provides more favorable blood pressure control during surgical resection of pheochromocytoma than with SNP alone.

[Beta blockers and anesthesia]

Beta-adrenoceptor antagonists (BB) demonstrate a competitive antagonism with endogenous catecholamines. Beta-1 receptor blockade mediates the depressive action on contractility, heart rate and atrio-ventricular conduction. Beta-2 receptor blockade mediates vascular, bronchial and uterine smooth muscle constriction. BB with beta-1 selective and intrinsec sympathomimetic activity do not increase systemic vascular resistance. BB are mostly used to treat ischaemic heart disease, hypertension and arrhythmias. Bradycardia, hypotension and bronchospasm are the main hazards in BB treated patients undergoing anaesthesia. However giving BB with premedication to patients taking usely this treatment allows better perioperative haemodynamic stability and avoids rebound effect. Experimentally, oxprenolol reverses regional dysfunction in ischaemic myocardium under halothane anaesthesia. During and after anaesthesia, intravenous (i.v.) BB must be used with caution to treat hypertension associated with tachycardia. In controlled hypotension, i.v. BB potentialise other agents. In phaechromocytoma surgery, alpha-blocking drugs are essential but additional BB can control tachycardia successfully. In coronary artery bypass surgery, giving BB prior to induction decreases cardiac enzymes serum levels. Esmolol, a new ultra-short-acting BB, would control perioperative tachycardia and hypertension without risk of prolonged cardiac depression.

A randomized comparison of labetalol and nitroprusside for induced hypotension

In a randomized study, labetalol-induced hypotension and nitroprusside-induced hypotension were compared in 20 patients (10 in each group) scheduled for major orthopedic procedures. Each patient was subjected to an identical anesthetic protocol and similar drug-induced reductions in mean arterial blood pressure (BP) (50 to 55 mmHg). Nitroprusside infusion was associated with a significant (p less than 0.05) increase in heart rate and cardiac output; rebound hypertension was observed in three patients after discontinuation of nitroprusside. Labetalol administration was not associated with any of these findings. Arterial PO2 decreased in both groups. It was concluded that labetalol offers advantages over nitroprusside.

Labetalol as a hypotensive agent for middle ear microsurgery

Labetalol, an alpha- and beta-adrenergic receptor-blocking agent, was studied as a hypotensive agent during halothane (mostly 0.5 vol.%)-N2O-fentanyl-d-tubocurarine anaesthesia with a head-up tilt of 5 degrees in 41 patients undergoing middle ear microsurgery. After the mean initial dose of 0.3 mg/kg, the mean need for labetalol ranged from 0.05 to 0.07 mg/kg at 30 +/- 5-min intervals. The mean duration of the hypotensive period was 102 min. During the hypotension, the average mean arterial pressure ranged from 59 to 62 mmHg (7.9-8.3 kPa) and the mean heart rate from 61 to 66 b.p.m. After labetalol the maximum cardiac output decrease was 7%. Before labetalol the mean PaO2 value was 158 mmHg (21.1 kPa) and during hypotension it ranged from 145 to 149 mmHg (19.3-19.9 kPa) when FiO2 was 40%. The only peroperative side effects were ECG changes (middle junctional rhythm and sinus bradycardia) which occurred in 10% of the patients. The mean value for the degree of haemostasis rated by the otologist on a visual analogue scale between poor (0 mm) and excellent (100 mm) was 91 mm. The patients were able to open their eyes and to give their names 8-9 min after the end of anaesthesia. After extubation the patients were normotensive and there were no clinically significant changes in the cardiovascular parameters during the 4-h recovery room period. Acid-base status showed slight metabolic acidosis. The most common postoperative side effects were nausea only and nausea + vomiting, which occurred in 39% and 20% of the patients, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

[Disclosure of a fatal pheochromocytoma during general anesthesia]

A case is reported of a phaeochromocytoma revealed during a general anaesthesia by a sudden hypertensive crisis associated with acute pulmonary oedema and signs of extreme sympathetic stimulation (bilateral mydriasis, piloerection, peripheral vasoconstriction). Aortic angiography revealed the tumour lying in an ectopic retroperitoneal situation and spasm in the superior mesenteric arterial territory. The patient died at the thirtieth hour from septic shock due to necrotizing colitis.

Labetalol: a review of its pharmacology, pharmacokinetics, clinical uses and adverse effects

Labetalol is a combined alpha- and beta-adrenoceptor blocking agent for oral and intravenous use in the treatment of hypertension. It is a nonselective antagonist at beta-adrenoceptors and a competitive antagonist of postsynaptic alpha 1-adrenoceptors. Labetalol is more potent at beta that at alpha 1 adrenoceptors in man; the ratio of beta-alpha antagonism is 3:1 after oral and 6.9:1 after intravenous administration. Labetalol is readily absorbed in man after oral administration, but the drug, which is lipid soluble, undergoes considerable hepatic first-pass metabolism and has an absolute bioavailability of approximately 25%. There are no active metabolites, and the elimination half-life of the drug is approximately 6 hours. Unlike conventional beta-adrenoceptor blocking drugs without intrinsic sympathomimetic activity, labetalol, when given acutely, produces a decrease in peripheral vascular resistance and blood pressure with little alteration in heart rate or cardiac output. However, like conventional beta-blockers, labetalol may influence the renin-angiotensin-aldosterone system and respiratory function. Clinical studies have shown that the antihypertensive efficacy of labetalol is superior to placebo and to diuretic therapy and is at least comparable to that of conventional beta-blockers, methyldopa, clonidine and various adrenergic neuronal blockers. Labetalol administered alone or with a diuretic is often effective when other antihypertensive regimens have failed. Studies have shown that labetalol is effective in the treatment of essential hypertension, renal hypertension, pheochromocytoma, pregnancy hypertension and hypertensive emergencies. In addition, preliminary studies indicate that labetalol may be of value in the management of ischemic heart disease. The most troublesome side effect of labetalol therapy is posture-related dizziness. Other reported side effects of the drug include gastrointestinal disturbances, tiredness, headache, scalp tingling, skin rashes, urinary retention and impotence. Side effects related to the beta-adrenoceptor blocking effect of labetalol, including asthma, heart failure and Raynaud's phenomenon, have been reported in rare instances.

Effect of labetalol on intracranial pressure in dogs with and without intracranial hypertension

Intracranial pressure measurements and ventricular volume pressure response curves were made during induced hypotension with labetalol, a combined alpha- and beta-adrenoceptor antagonist, in dogs without (group I) and with (group II) intracranial hypertension. The administration of 600 mg labetalol resulted in a percentage decrease of mean systemic arterial blood pressure (MAP) of 27% (+/- 10%) in group I, and 32% (+/- 9%) in group II from control values without changes in intracranial pressure and the ventricular volume pressure response curve. Larger decreases in MAP were not possible, even with a dose 3 times that clinically recommended. Labetalol may be a safe hypotensive agent to supplement neurolept analgesia, but it is not the drug of choice to induce deliberate hypotension.