|Year : 2013 | Volume
| Issue : 2 | Page : 155-159
Co-loading or pre-loading for prevention of hypotension after spinal anaesthesia! a therapeutic dilemma
Sukhminder Jit Singh Bajwa1, Ashish Kulshrestha1, Ravi Jindal2
1 Department of Anaesthesiology and Intensive Care, Gian Sagar Medical College and Hospital, Ram Nagar, Banur, Punjab, India
2 Department of Anaesthesiology and Intensive Care, Amar Hospital, Patiala, Punjab, India
|Date of Web Publication||26-Sep-2013|
Sukhminder Jit Singh Bajwa
House No-27-A, Ratan Nagar, Tripuri, Patiala, Punjab
Source of Support: None, Conflict of Interest: None
| Abstract|| |
Neuraxial blockade such as spinal anaesthesia can cause severe hypotension due to pharmacological sympathectomy resulting in potential deleterious consequences for the patient. Prevention of this spinal anaesthesia induced hypotension is of utmost importance especially in pregnant population as the life of mother as well as fetus is at risk. Several techniques and methodologies have been adopted for the prevention of this neuraxial hypotension with varying degree of success. The administration of intravenous fluids to optimize the blood volume during sympathectomy has been the most popular and widely used as the first line of therapy among these techniques. The intravenous fluids can be used both before and during the administration of spinal anaesthesia, the techniques appropriately named as pre-loading and co-loading respectively. Numerous research studies and available literary evidence suggests that both of these techniques can be equally effective in prevention of hypotension. The use of colloids has been observed to be more effective for pre-loading due to their longer half-life in the intravascular compartment. However, it has also been suggested that no technique is efficient in preventing the hypotension alone and has to be coupled with judicious use of vasopressors.
Keywords: Colloid, co-loading, crystalloid, hypotension, pre-loading, spinal anaesthesia
|How to cite this article:|
Bajwa SS, Kulshrestha A, Jindal R. Co-loading or pre-loading for prevention of hypotension after spinal anaesthesia! a therapeutic dilemma. Anesth Essays Res 2013;7:155-9
|How to cite this URL:|
Bajwa SS, Kulshrestha A, Jindal R. Co-loading or pre-loading for prevention of hypotension after spinal anaesthesia! a therapeutic dilemma. Anesth Essays Res [serial online] 2013 [cited 2021 May 16];7:155-9. Available from: https://www.aeronline.org/text.asp?2013/7/2/155/118943
| Introduction|| |
Hypotension following spinal anaesthesia is a common physiological complication with an incidence ranging from 25-75% among general population and a little higher in patients undergoing caesarean section. Occasionally, spinal anaesthesia induced hypotension can be significantly severe, more so in pregnant females, which can which can increase intra-op and post-op morbidity. , The present mini-review analyzes the various pros and cons associated with pre-loading and co-loading during spinal anesthesia and the potential comparative benefits of each of these methodologies with a specific emphasis on pregnant population.
| Pathophysiology of Hypotension Following Spinal Anesthesia|| |
Hypotension following spinal anaesthesia is mainly occurs due to sympathetic blockade leading to peripheral vasodilatation and venous pooling of blood. As a result, there is decreased venous return and cardiac output leading to hypotension.  The risk of hypotension is increased in a parturient due to the higher level of block (T 4 ) required for the cesarean section, unique physiologic and anatomic changes of pregnancy and increased susceptibility to the effects of sympathectomy due to reduced sensitivity to the endogenous vasoconstrictors coupled with increased synthesis of endothelium-derived vasodilators.  The various methods to prevent this hypotension following spinal anaesthesia are similar in both pregnant and non-pregnant patients.
| Hazards of Neuraxial Hypotension and Preventive Measures|| |
The spectrum of morbidity associated with hypotension may include but is not limited to a higher incidence of nausea, vomiting, dizziness, aspiration, syncope and cardiac arrhythmias.  The clinicians have used various methods and techniques such as leg wrapping, elastic stockings, optimizing patient's position, intravenous fluids and vasopressors from time to time to offset these hypotensive effects of spinal anaesthesia with varying degree of success. One of the foremost methods includes prophylactic administration of intravenous fluids before implementation of subarachnoid block to offset the hypotensive effects of sympathectomy by maintaining intravascular volume which is commonly called as pre-loading. The conflicting literary evidence and unequivocal results of the technique of pre-loading has made co-loading: A method of administration of intravenous fluid bolus immediately after the subarachnoid block equally popular.
| How Beneficial is Preloading? Literary Evidence|| |
One of the most commonly used methods to reduce spinal anaesthesia induced hypotension is administration of fluids before implementation of spinal anaesthesia, a technique named 'pre-loading' first described by Wollman and Marx.  This preloading with intravenous fluids offset the vasodilating effects of sympathetectomy caused by spinal anaesthesia thereby maintaining the venous return and thus the drop in blood pressure is prevented. Based on this literary evidence, a common methodology was being practiced to pre-load the patient with 10-20 ml/kg of intravenous fluids around 15-20 minutes prior to the administration of spinal anaesthesia for a long time. , Studies have shown that pre-loading decreases the incidence of hypotension after spinal anaesthesia in the first 5 minutes following subarachnoid injection as compared to the patients who did not receive any pre-loading. 
| Controversies of Pre-Loading and Co-Loading|| |
However, the efficacy of such fluid administration is largely questioned by the fact that pre-loading, especially with crystalloids, results in rapid redistribution of the fluid into the extravascular compartment thus offsetting the increase in the intravascular fluid volume.  Also, this method may induce the secretion of atrial natriuretic peptide (ANP) which causes peripheral vasodilatation increasing the rate of excretion of pre-load fluid.  It has also been established that maternal hypotension occurs in the period just following the spinal injection and even the rapid bolus infusion of intravenous fluids in that period, a technique named 'co-load', does not prevent it while during the same period pre-load may be more beneficial. , The various observational and prospective studies provide literary evidence from which it can be concluded that pre-loading may still be beneficial. However, there is another school of thought which has based their assumptions through numerous studies showing that even large volumes of intravenous fluids given as pre-load before spinal anaesthesia may not prevent spinal induced hypotension and therefore this practice has become less popular. 
It has been suggested by some studies that pre-loading with colloid solutions may be more beneficial in preventing spinal induced hypotension as the colloid solutions remain in intravascular space for a longer duration so as to resist any decrease in intravascular volume following spinal anaesthesia.  However, prophylactic administration of colloids is not popular routinely due to increased cost, possibility of derangement of coagulation, suppression of platelet activity and risk of anaphylaxis. 
| Co-loading vs. Pre-loading: Comparative Literary Evidence|| |
Most of the studies comparing pre-loading with co-loading have been done in parturients but the results of these studies can also be extrapolated to the general population receiving spinal anaesthesia. Due to inconsistent results of benefits of pre-loading, the concept of co-loading has also gained a widespread acceptance among the clinicians. Results of few studies have shown a sustained increase in cardiac output with rapid administration of crystalloids after initiation of spinal anaesthesia.  Studies with regards to kinetics of intravenous infusion of crystalloids as co-load have shown to reduce the incidence of spinal induced hypotension.  Co-loading seems to be more appropriate physiologically as the increase in intravascular volume brought about by co-loading coincides with the time of maximal vasodilatation effect of spinal anaesthesia, thus reducing the degree of hypotension. 
Co-loading is found to be a safer technique except for few concerns related to decreased oxygen carrying capacity and increased risk of pulmonary oedema in pregnant patients.  in a bid to find the superiority of one methodology over the other, various studies have compared pre-loading and co-loading during spinal anaesthesia but have produced inconsistent and mixed results without any substantial evidence of superiority of one method over the other. Majority of these clinical research studies have compared pre-loading with co-loading by administration of colloid solutions and concluded that the incidence of hypotension following spinal anaesthesia was similar as was the requirement of vasopressors in both the methodologies. , The results are almost similar when colloids have been replaced with crystalloids in studies of similar designs comparing the potential benefits of pre-loading and co-loading. ,
In one of the major meta-analysis involving 8 studies and a total of 518 patients, it was observed that incidence of hypotension was observed to be similar during comparison of pre-load and co-load. 
Even the spectrum of side effects was observed to be similar in two groups receiving pre-loading and co-loading as the incidence of nausea and vomiting have been found to be similar and is mainly due to reduced perfusion of the chemoreceptor trigger zone leading to hypoxia and its stimulation.
Recently, Williamson et al., studied the effect of timing of fluid bolus on reduction of spinal induced hypotension in which they divided the total amount of crystalloid solution to be given (20 ml/kg) into two parts: The first part was (10 ml/kg) given before and the second half (10 ml/kg) was given after the successful administration of spinal anaesthesia. From the observations of the study, it was concluded that this method is equally effective in prevention of spinal induced hypotension and can reduce the amount of perioperative intravenous fluids required in caesarean sections effectively without increasing the postoperative morbidity and mortality. 
| Pre-Loading and Co-loading with Crystalloids or Colloids?: The Never Ending Controversies|| |
The controversies surrounding these two classes of fluids have been never ending. Till date it has not been successfully established which one is superior to other. Even the type of fluid used for pre-loading or co-loading remains a controversial issue. Both types of fluids have been used for pre-loading as well as co-loading and have been extensively studied.
Crystalloids have shorter half-life in the intravascular compartment and generally exit the intravascular space within 1 hour so that their ability to expand the intravascular volume is limited due to shorter duration of action. Pre-loading with crystalloids has been found to be less effective due to the shorter half-life as they are less successful in maintaining the intravascular volume during the dynamic establishment of spinal anaesthesia effect and the resulting vasodilatation. 
Colloids, on the other hand, have a longer half-life in the intravascular compartment and are able to maintain the increase in intravascular volume for longer durations. Hence, they have been observed to be more effective in preventing the hypotension following spinal anaesthesia when used for pre-loading as compared to crystalloid solutions. 
Co-loading with crystalloids and colloids has been observed to give comparable results as the literary evidence show that the incidence of hypotension remains similar and no significant differences was observed in vasopressor requirements or hemodynamic stability with both crystalloid and colloid co-loading. 
| Special Population: Pregnancy|| |
Regional anaesthesia has been considered as the most appropriate for caesarean section in a parturient due to its beneficial effects on both mother and foetus.  However, spinal anaesthesia is usually accompanied with hypotension often defined as a systolic blood pressure of 90 or 100 mmHg or a 20% fall in blood pressure from the baseline, which mainly occurs as a result of decreased systemic vascular resistance due to pharmacological sympathectomy. The discussion on controversies of pre-loading vs co-loading would be incomplete without mentioning the pathophysiological alterations in pregnant patients as most of the studies have been done during operative deliveries. Thus, prevention of hypotension is of utmost importance in this subset of patients as it involves two lives, the mother and the foetus.
| Pathophysiological Evidence|| |
The linear relationship between maternal blood pressure and cardiac output is somewhat offset by significant changes in peripheral resistance. These clinical changes are further strengthened by the fact that instead of maternal hypotension, correlation of decreased cardiac output with spinal anaesthesia, increased umbilical artery pulsatility index and acidic changes in umbilical arterial blood are better predictors of uteroplacental perfusion.  The aortocaval compression due to the gravid uterus further aggravates this hypotension. The degree and severity of the hypotension following spinal anaesthesia depends on the height of the block, position of the patient and the preventive measures taken to prevent the hypotension. The risk of hypotension is increased in a parturient due to the higher level of block (T 4 ) required for the caesarean section, unique physiological and anatomical changes of pregnancy and increased susceptibility to the effects of sympathectomy due to reduced sensitivity to the endogenous vasoconstrictors coupled with increased synthesis of endothelium-derived vasodilators. 
| Risk Factors and Complications of Maternal Hypotension|| |
The risk factors ,,, for development of severe hypotension in pregnant patients are:
- Age ≥ 35 years,
- Obesity (body mass index ≥29-35 kg/m 2 ),
- Pre-operative hypertension,
- Associated co-morbidities
- Baricity of the injectate used and
- Higher foetal weight.
The catastrophic effects of maternal hypotension are not limited in causing complications in the mother only but also cause severe adverse effects in foetus namely neurological injury due to reduced placental perfusion, low APGAR scores, prolonged time for sustained spontaneous respirations, prolonged foetal acidosis, weak neonatal breastfeeding reflexes and permanent neurological damage. , Thus prevention of severe hypotension during caesarean section is much more important than that in normal population for a favourable maternal and foetal outcome. [31 ]
| Prophylactic Measures and Management Modalities|| |
The use of epidural anaesthesia technique over spinal anaesthesia did not find much favour as the former is associated with higher cost and increased duration for its administration which may not be feasible in emergency caesarean sections. ,. Numerous methods and techniques have been described in literatures which have been able to prevent maternal hypotension following spinal anaesthesia with a varying degree of success. These include intravenous fluid administration (pre-loading and co-loading), lateral uterine displacement to prevent aortocaval compression, use of Esmarch's bandage to mobilise blood from lower extremities and use of vasopressors. Use of vasopressors should be restricted to management rather than prevention of hypotension as they can jeopardise the foetal well being due to uteroplacental vasoconstriction with resultant reduced placental blood flow.
| Intravenous Fluids: The First Line of Management|| |
The use of intravenous fluids has been the most popular measure to prevent maternal hypotension over the last few decades and use of both pre-load as well as co-load techniques has been equally accepted by the clinicians. As compared to crystalloid, pre-loading with colloid has been observed to be more effective in prevention of spinal anaesthesia induced maternal hypotension whereas during co-loading, crystalloids are considered better than colloids.  However, due to the conflicting evidence in literature, a general consensus exists among the medical fraternity that precious time should not be wasted to administer a pre-defined amount of fluid to the mother, especially during emergent conditions, as co-loading has been found to be equally effective in prevention of maternal hypotension.
Lastly, it is being emphasized that no single modality is effective for prevention of maternal hypotension following spinal anaesthesia alone and should be combined with timely and judicious use of vasopressors.
| Conclusion|| |
In conclusion, the clinical implications of this discussion are that the colloids appear to be more efficient than crystalloids (especially in pre-loading) in prevention of hypotension following spinal anaesthesia but the decision to use depends upon the clinician's assessment of benefits when compared to the disadvantages of colloids namely cost, effect on coagulation and hypersensitivity reactions. Several studies have shown that the incidence of hypotension remains significant irrespective of the type or timing of the fluid following spinal anaesthesia and the clinician should judiciously use appropriate vasopressors.
As enough literary evidence exists that pre-loading is not superior to co-loading irrespective of the type of fluid used, significant amount of time should not be spent for administration of predetermined volume of fluid before the spinal anaesthesia especially in urgency.
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