Spinal anesthesia for surgical repair of hip fracture in the elderly is associated with a high incidence of hypotension. The synergism between intrathecal opioids and local anesthetics may make it possible to achieve reliable spinal anesthesia with minimal hypotension using a minidose of local anesthetic.
Twenty patients aged > or = 70 yr undergoing surgical repair of hip fracture were randomized into two groups of 10 patients each. Group A received a spinal anesthetic of bupivacaine 4 mg plus fentanyl 20 microg, and group B received 10 mg bupivacaine. Hypotension was defined as a systolic pressure of < 90 mmHg or a 25% decrease in mean arterial pressure from baseline. Hypotension was treated with intravenous ephedrine boluses 5-10 mg up to a maximum 50 mg, and thereafter by phenylephrine boluses of 100-200 microg.
All patients had satisfactory anesthesia. One of 10 patients in group A required ephedrine, a single dose of 5 mg. Nine of 10 patients in group B required vasopressor support of blood pressure. Group B patients required an average of 35 mg ephedrine, and two patients required phenylephrine. The lowest recorded systolic, diastolic, and mean blood pressures as fractions of the baseline pressures were, respectively, 81%, 84%, and 85% versus 64%, 69%, and 64% for group A versus group B.
A "minidose" of 4 mg bupivacaine in combination with 20 microg fentanyl provides spinal anesthesia for surgical repair of hip fracture in the elderly. The minidose combination caused dramatically less hypotension than 10 mg bupivacaine and nearly eliminated the need for vasopressor support of blood pressure.
SPINAL anesthesia is often used for surgical repair of traumatic hip fracture, a procedure largely restricted to the geriatric population. These patients have a particularly high incidence of hypotension during spinal anesthesia. 1–3Moreover, the high incidence of coronary disease in this population increases the risk of ischemia secondary to the hypotension. 4
There is considerable controversy over the use of vasopressors and intravenous fluids to treat or prevent the hypotension of spinal anesthesia (HSA). 1,5Unfortunately, none of these methods is without potential ill effect. Another approach has been to minimize HSA by using very small or titrated doses of local anesthetic. A comparison of continuous spinal with titrated dosing versus single-dose spinal anesthesia found that the former technique led to less frequent and less pronounced decreases in mean arterial pressure with significantly less use of ephedrine. 6Spinal anesthesia with a single dose of 5 mg bupivacaine for elderly patients undergoing hip surgery yielded only a moderate incidence of hypotension (37.5% for isobaric, 42.5% for hyperbaric), but in 15% of patients this low dosage did not provide an adequate level of sensory block. 7Similarly, spinal anesthesia failed in 25% of young patients receiving 5 mg of bupivacaine for arthroscopic surgery. 8,9
Therefore, although the use of a single-shot low-dosage local anesthetic for spinal blockade may limit hypotension, it may not provide acceptable anesthesia. Opioids and local anesthetics administered together intrathecally have a potent synergistic analgesic effect. 10,11Intrathecal opioids enhance analgesia from subtherapeutic doses of local anesthetic and make it possible to achieve successful spinal anesthesia using otherwise inadequate doses of local anesthetic. 8,12,13Yet because intrathecal fentanyl causes neither by itself nor in combination with bupivacaine any further depression of efferent sympathetic activity, 12it is possible to enhance the sensory blockade without altering the degree of sympathetic blockade. In a clinical demonstration of this, spinal anesthesia for cesarean section using intrathecal sufentanil (3.3 μg) combined with low-dosage bupivacaine (6.6 mg) produced only a 6% incidence of intraoperative hypotension. 14No hypotension at all was seen with a low-dosage lidocaine–fentanyl spinal anesthetic in ambulatory surgery patients. 15
The goal of this study was to compare the hemodynamic and sensory effects of a “minidose” bupivacaine–fentanyl spinal anesthetic versus a conventional dose of spinal bupivacaine in elderly patients undergoing surgical repair of traumatic hip fracture.
This study was approved by the hospital’s ethics committee and conducted after obtaining written informed consent of the subjects. The subjects included 20 patients aged > 70 yr presenting for open surgical repair of hip fracture. Surgeries included only Richard’s plate-screw internal fixation of femoral neck fractures and Austin–Moore hemiarthroplasty for subcapital fractures of the femoral neck. The subjects were randomly assigned to two groups (defined by the spinal injectate) using a sealed-envelope technique. Patient groups were as follows: group A, 4 mg glucose-free bupivacaine 0.5% (Astra, Södertälje, Sweden) plus 20 μg fentanyl (prepared by withdrawing 2 ml of a solution of glucose-free bupivacaine 20 mg plus 100 μg fentanyl diluted to 10 ml with saline); and group B, 2 ml (10 mg) of glucose-free bupivacaine 0.5%. Injectate volume for both groups was 2 ml. The syringe was prepared by one researcher and administered by a second who remained blinded to its contents. Patient assessment and care were conducted and study data were recorded by the second blinded researcher.
Patients received no premedication before arrival in the operating theater. Before spinal block, each patient received a rapid infusion of 8 ml/kg of lactated Ringer’s solution. Patients received 1 mg midazolam and 1 μg/kg fentanyl intravenously several minutes before being turned into the lateral position for performing the lumbar puncture. Standard monitoring included continuous electrocardiogram and pulse oximetry. Noninvasive automated blood pressure measurements were recorded at 2.5-min intervals. The baseline mean arterial pressure was determined from the average of three consecutive readings taken after the administration of fluids, midazolam, and fentanyl. Lumbar puncture was performed in the lateral position with the fractured side up, using a 22-gauge Quincke point needle (Kobayashi Shoji K.K., Tokyo, Japan) positioned midline at the L3–L4 interspace. Injections were made over 10–15 s. After completion of injections the patients were immediately returned to the supine position.
For the purpose of the study hypotension was defined as a systolic blood pressure of < 90 mmHg or a decrease of more than 25% from the baseline mean arterial pressure. Reaching either criterion was considered hypotension and was treated with an intravenous bolus of ephedrine 5–10 mg. If 50 mg ephedrine was used and hypotension persisted, the protocol called for a switch to phenylephrine 100–200 μg boluses. In addition to the loading dose of intravenous fluids, patients received additional lactated Ringer’s solution as deemed necessary by the blinded anesthesiologist. No additional sedative medications were given during the operation. Inadequate anesthesia (patient complaint of pain) was to be treated with an additional bolus of intravenous fentanyl 1 μg/kg, with a second bolus allowable. The protocol allowed for conversion to general anesthesia as deemed necessary by the blinded anesthesiologist.
Pinprick testing in the midline every 2 min was used to establish onset and peak level of sensory blockade. Blood pressures and heart rates were recorded by an automated printer. The number of hypotensive measurements, total vasopressor use for each patient, and intraoperative patient complaints of pain, nausea, and vomiting were recorded.
Statistical analysis was performed using GB Stat (Dynamic Microsystems, Silver Spring, MD). Analysis of variance was used to analyze demographic data including baseline heart rate and pressures, lowest pressures, ratios of lowest:baseline pressures, peak block level, and fluid requirements. The Mann–Whitney test was used to analyze surgical times, the number of measurements of hypotension for each patient, and ephedrine dose. The Fisher exact test was used for the number of patients treated for hypotension and the number requiring phenylephrine. Results were considered significant at P = 0.05.
There were 10 patients in each of the two groups. There were no differences between the demographic characteristics of the two groups (table 1) Though systolic blood pressures were slightly higher in group B, this was not a significant difference. Two patients in each group underwent Austin–Moore hemiarthroplasty, and eight in each group underwent Richard’s plate-screw internal fixation.
Study results are summarized in table 2. Peak sensory block height (to pinprick) was only two dermatomes higher in group B. No patient in either group complained of intraoperative pain or required supplemental analgesics intraoperatively. Likewise, no patient complained of nausea or vomited intraoperatively.
The lowest recorded systolic, diastolic, and mean blood pressures are reported in table 2, as well as their percentages of the baseline pressures. For group A these were, respectively, 81%, 84%, and 85%versus 64%, 69%, and 64% for group B. These lower pressures in group B were despite of the use of vasopressors. In group A only 1 of 10 patients required treatment for hypotension as per the protocol definition of hypotension. That patient received a single dose of 5 mg ephedrine. In contrast, 9 of the 10 patients in group B required vasopressor support of blood pressure. Patients in group B averaged (median) seven hypotensive measurements and received an average of 35 mg ephedrine each. Two patients required additional use of phenylephrine because hypotension persisted even after a total dose of 50 mg ephedrine. Fluid requirements in the two groups were comparable.
Postoperative follow-up revealed 19 patients with uneventful recoveries. One patient in group B developed atrial fibrillation postoperatively after a suspected pulmonary embolism. This patient’s recovery, although delayed, ultimately proceeded well.
This study demonstrates that the use of a minidose bupivacaine plus fentanyl spinal anesthetic (4 mg bupivacaine plus 20 μg fentanyl) for surgical hip-fracture repair in the elderly provides successful anesthesia and incurs a minimum of hypotension. The hemodynamic stability of these patients was reflected in the minimal need for vasopressor support of blood pressure. In the minidose group only 1 of 10 patients required treatment for hypotension, and in that patient a single dose of 5 mg ephedrine sufficed. This stood in contrast to the marked reductions in blood pressure and the significant vasopressor requirements seen in the group receiving a spinal anesthetic of bupivacaine 10 mg.
The intravenous fluid preload of 8 ml/kg lactated Ringer’s solution used in the study was chosen to represent a middle-ground position on this somewhat controversial issue. Fluid loading, whether with crystalloid or colloidal solutions, has repeatedly been shown to be of little benefit if used without an adrenergic agonist. 2,16–19Fluid administration may prevent a decrease in central venous pressure and may diminish or even reverse the decrease in cardiac index, but blood pressure falls nevertheless because of a substantial decrease in systemic vascular resistance. 3,18,19Excessive fluid loading may also lead to additional complications such as pulmonary edema or urinary retention and is therefore to be avoided. 1In view of this literature it is doubtful that the choice of an alternative fluid regimen would have changed the findings of the study. Compressive stockings or tightly wrapping the legs with elastic bandages may be of some benefit, 20but these were not used, as this did not reflect the practice of our orthopedic department.
Various adrenergic agonists (ephedrine, metaraminol, methoxamine, phenylephrine, epinephrine) have been used either prophylactically or as treatment of HSA. Prophylactic treatment has included both intramuscular injection 2,17,21and intravenous infusion 17–19of these drugs. Ephedrine, although probably the most commonly used pressor for HSA, may not in fact be the agent of choice in this situation. It is not a potent vasoconstrictor and thus does not well address the primary mechanism of the hypotension, which is the decrease in systemic vascular resistance. 3,22Careful study has indeed shown that ephedrine may not reliably reverse HSA. 17,19Moreover, ephedrine treatment of hypotension increases heart rate. 17,22A combination of decreased diastolic pressure and increased heart rate would be expected to be particularly deleterious in the patient with ischemic cardiac disease. Epinephrine infusion has been shown to restore systolic arterial pressure and increase both cardiac output and heart rate, but with no increase in diastolic or mean arterial pressure. 23Phenylephrine, an α agonist, restores diastolic and mean arterial pressure as well as systolic arterial pressure and decreases heart rate, but at the cost of a reduction in cardiac output. 23This hemodynamic profile has led some investigators to suggest that α agonists are to be preferred in the treatment of HSA and should be used in association with only modest fluid loading. 1,18Our choice of ephedrine as the first-line vasopressor in the study was based on what we believed to represent common clinical practice.
One possible explanation for the large difference between the two groups could be that our group B experienced more hypotension than is typically seen with a comparable dose of bupivacaine spinal. However, our findings for group B are not at odds with the literature. The small number of patients in each group does not appear to be a problem in interpreting the results of this study. The study was discontinued at this number of patients because with the blatant differences between groups we felt we could no longer justify using the higher- dosage spinal anesthetic. Even with these small numbers the differences between groups were so profound as to have reached strong levels of significance.
Although some of the operations lasted as long as 110 min from the time of the spinal injection, none of the patients complained of pain intraoperatively. Based on work with younger adults, this duration of effect was not expected with the minidose group, 9and it suggests delayed pharmacokinetics in these elderly patients. Because we did not map the change in sensory levels with time we do not have data to compare with previously published data on younger patients. Certainly this issue of block duration versus age warrants further study. One should be cautious in extrapolating the results of this study to younger patients either in terms of the adequacy of the dosage for hip surgery or in terms of the duration of surgical anesthesia with it. Neither can one extrapolate these findings to other surgeries for which a higher cephalad level of block may be required.
Although the use of low doses of local anesthetic for spinal anesthesia may reduce the severity and incidence of hypotension, it has not been possible to develop a reliable single-shot low-dosage technique. Recent work has shown a strong correlation between cephalad spread of spinal block and the lumbosacral cerebrospinal fluid volume. 24Those data also indicated the great variability and unpredictability of the cerebrospinal fluid volume and therefore of the cephalad spread and effect of a given dose of intrathecal local anesthetic in any given patient. This information suggests that efforts to use single-shot low-dosage spinal anesthesia to minimize hypotension are doomed to failure in a certain percentage of patients. However, by intensifying the nociceptive blockade of a low-dosage local anesthetic through the synergistic action of an opioid such as fentanyl, it is possible to achieve a functional blockade that does provide surgical anesthesia for virtually all patients. These results are therefore potentially of great practical value to the practitioner in presenting a technique most useful in this and perhaps other clinical situations.
In summary, this study shows that a “minidose” of 4 mg isobaric bupivacaine in combination with 20 μg fentanyl provides completely satisfactory spinal anesthesia for surgical repair of hip fracture in the elderly. The minidose combination, in comparison with a 10-mg dose of isobaric bupivacaine, caused dramatically less hypotension and nearly eliminated the need for vasopressor support of blood pressure.