Spinal Anaesthesia in Obstetrics - Essay Example

Anaesthetic Nursing ANAESTHETIC NURSING POST-SPINAL HYPOTENSION Mary, a 28-year old, was scheduled for caesarean section because of expected difficult delivery due to a narrow pelvis. She had a past medical history of asthma at her early childhood which was treated. Mary’s height was 1.72m and weighed 90kg. After discussion with the patient, spinal anaesthesia was planned. In the theatre, a standard monitoring by the electrocardiogram (ECG) was done to monitor the cardiac rhythm of Mary. Her pulse rate was 68 beats/min, oxygen saturation 100%; non-invasive blood pressure 124/76mm Hg. A peripheral venous access was established. A litre bag of Hartman was also started. The spinal anaesthesia was performed in the sitting position at L4/L5 with 2.4mls of bupivacaine 0.5% in hyperbaric dextrose solution of “Heavy Marcaine”. Immediately following the spinal block, the patient was put back in the supine position, and the operating table altered with left lateral tilt to diminish aorto-caval compression. About 3 minutes later the patient’s blood pressure fell to 103/56mmhg which was the first sign of the effect of spinal anaesthesia. As the medical team was waiting for the spinal to take full effect, the blood pressure further dropped to 86/51mmHg. The patient also complained of nausea and “not feeling well” and experienced progressive difficulty to breathe. The features that need to be considered are the increasing hypotension that she has suffered, the progressive difficulty in breathing and the nauseous feeling with general unease. Spinal anaesthesia Modern anaesthesiology uses spinal anaesthesia as a cost-effective method with sophisticated equipment along with the advantage of developed techniques. Operations are being performed on an ambulatory basis with advanced technologies to meet the demands of a busy environment (Tarkkila 2007). Providing anaesthesia without complications ensures a high degree of satisfaction. However the potential risk is a failure of spinal anaethesia due to incorrect needle placement unlike the other anaesthetic methods where the risk of failure is low. Haemodynamic complications are also possible. Hypotension is one such event which occurs due to the cardiovascular side effects (Tarkkila 1991). The hypotension is a normal physiological effect but it can turn into a complication if the level falls low enough to cause problems. The blood pressure at which interventions are necessary to correct the hypotension has not been decided yet. Clinical judgement by the anaesthesiologist is the method to decide the point to intervene (Tarkkila 2007). Spinal anaesthesia in obstetrics Spinal anaesthesia produces a fast, effective and high quality sensory and motor block of the necessary nerves in women having caesarian sections (Lee et al 2002). The incidence of hypotension in non pregnant patients occurring due to spinal anaesthesia ranges from 0 to more than 50% while that in pregnant patients ranges from 50% to more than 90%. Hypotension is defined as “the systolic blood pressure less than 85-90 mm Hg or a decrease of more than 25-30% from the pre-anaesthetic value” (Carpenter 1992). Another definition said that it was a “decrease of mean arterial blood pressure of more than 30% within 10 minutes and relevance was defined as a therapeutic intervention with fluids or pressors within 20 minutes” (Hartman 2002). The normal physiological change leading to hypotension The hypotension in the spinal anaesthesia is attributed to the pre-ganglionic sympathetic blockade. The sympathetic tone of the arterial circulation is directly related to the systemic vascular resistance (Tarkkila 2007). The blockade thereby causes a reduction in the systemic vascular resistance. Peripheral arterial vasodilatation follows suit as a compensatory mechanism. The extent of this would depend on the number of spinal segments involved. Other mechanisms have been proposed for the hypotension. Local anaesthetics are believed to produce a direct depressive circulatory effect (Tarkkila 2007). Relative adrenal insufficiency has been found to be another cause. The skeletal muscle paralysis which has been induced with a relaxant as part of the procedure could further increase the level of hypotension. One reason may be the ascending medullary vasomotor block. Another cause is the “concurrent mechanical respiratory insufficiency” (Greene 1981). Maternal haemodynamics in pregnancy The patient Mary is in an advanced pregnancy and the gravid uterus produces aorto-caval compression which increases the hypotensive effects of spinal anaesthesia (Tarkkila 2007). The effect of the local anaesthetics is exaggerated due to the chronic exposure of the highly sensitive nerve fibres of the patient to circulating progesterone which has changed the protein synthesis in the nerve tissue in pregnancy. Several changes occur in the maternal haemodynamics in pregnancy. The autonomic nervous system plays a huge role in the cardiovascular adjustments. Ladies prone to orthostatic changes in blood pressure are prone to hypotension after spinal anaesthesia (Frolich and Caton 2002). The pathophysiology in both have similar mechanisms: decreased venous return and decreased arteriolar resistance. During pregnancy, central venous return after standing shows no change and the heart rate is higher indicating a sympathetic outflow to the heart. The pre-hydrated pregnant woman shows a rise in heart rate and BP in an orthostatic challenge. Baseline heart rate prior to the hydration is predictive of hypotension after the spinal anaesthesia (Frolich and Caton 2002). Relevant symptoms Nausea and the feeling of unease could be mostly symptoms of hypotension. Progressive difficulty in breathing is another symptom and it could be at the root cause of the hypotension. Though the nausea could be due to the hypotension, the other causes of nausea must be remembered at this point. They are “cerebral hypoxia, inadequate anaesthesia and traction-related parasympathetic reflexes stimulated during surgical manipulation.” (Tarkkila 2007). Nausea is also seen in females and those who had prior opiate pre-medication (Tarkkila 1992). A history of motion sickness has also been attributed as a reason for the nausea (Carpenter 1992). The most frequent complication of spinal anaesthesia for caesarian section is maternal hypotension (Cyna et al 2006). Serious risks occur when the hypotension is combined with nausea or vomiting. Unconsciousness or pulmonary aspiration may be the consequence in the mother while hypoxia, acidosis and neurological injury may be seen in the baby. A study found that hypotension could be prevented by ephedrine, administration of colloids or leg compression (Cyna et al 2006). Spinal Block for Mary Many factors influence the extent of block. The volume of the local anaesthetic dose and baricity affect the level of block. Here the Heavy Marcaine administered as the spinal anaesthesia in the sitting position was distributed further than expected as the patient was placed in the supine position immediately. The table was also immediately adjusted to the left lateral tilt in order to avoid the compression of the aorta and inferior vena cava. The raised intra-abdominal pressure in the pregnant lady and the decreased volume of lumbar spinal canal was taken into consideration when the dose of anaesthetic was administered. The local anaesthetic was lesser than normal (2.4 ml. bupivacaine in 0.5 hyberbaric dextrose solution). The spinal block could have become a high one and progressing in Mary. The total block which depresses the brain stem and the cervical spinal cord has not occurred in the case of Mary. Pathophysiology of the hypotension The initial symptoms of nausea and the feeling of unease followed by increasing hypotension and the progressive difficulty in breathing in Mary are indicative of a high spinal block. Venous and arterial dilatation cause a diminished venous return, cardiac output and systemic vascular resistance (Tarkkila 2007). The widespread sympathetic block causes a block of the cardioaccelerator fibres leading to a reduced atrial filling and a decreased heart rate The stroke volume is decreased because venous dilatation reduces the return of blood to the heart. Maternal hypotension could have deleterious effects on the blood flow of the uterus. This would in turn affect the foetal health and finally the newborn outcome measured by APGAR scores (Lee 2002). The difficulty in breathing starts when the nerve supply to the intercoastal muscles is affected (Lee 2002). Inspiration would appear normal even though the respiratory muscles are affected and the patient may talk. Inability to cough may be an early symptom. The difficulty then progresses further if the high spinal block affects the cervical nerve supply cutting the innervation to the diaphragm.and respiratory difficulty becomes more pronounced. If the respiratory centre in the brainstem is affected, sudden respiratory arrest results. The commonest reason for the hypotension in obstetric patients is the fasting status. Sufficient pre-loading can prevent the hypotension (Musaid and Naranjo 2006). Lateral uterine positioning of the patient and a prophylactic vasopressor drug like ephedrine or phenyl ephrine could act in unison to prevent hypotension (Lee 2007). Hypotension is less seen in pre-eclamptic patients. Subdural block complicating spinal anaesthesia Extensive spread, slow onset of neural block, lack of sympathetic block, progressive respiratory depression and incoordination are features of the spread of local anaesthetic in the subdural space in a case of subarachnoid block, a rare incident (Singh 2002). However the hypotension would be moderate. Conclusion Mary is a pregnant lady who was to have a caesarian section for the delivery of her baby. She needed a caesarian section as her pelvis was narrow, not allowing a normal vaginal delivery. Spinal anaesthesia being the best of the techniques for anaesthesia, Mary was subjected to this procedure. Following the spinal anaesthesia, Mary suffered hypotension with symptoms of nausea and unease and progressive respiratory difficulty due to a high spinal block which had occurred incidentally. Spinal anaesthesia has a normal lowering of blood pressure as a side effect due to the normal physiological change caused by a pre-ganglionic sympathetic block. However Mary’s hypotension became pathologic in that there was more than 30% change in the blood pressure and she had a progressive breathing difficulty. The probable cause for the hypotension is her advanced pregnancy with altered haemodynamics. The immediate alteration into a supine position from a sitting position and the lateral tilt must have contributed to it. Her symptoms of nausea, uneasy disposition and the difficulty in breathing were quickly diagnosed. As hypotension is expected in about 80% of pregnant ladies who undergo spinal anaesthesia, Mary was watched for hypotension. References: Carpenter, R. L., Caplan, R.A. and Brown, D.L. et al, 1992. Incidence and risk factors for side effects of spinal anaesthesia. Anaesthesiology, Vol. 76, p. 906-916 Cyna, A. M., Andrew, M., Emmett R.S., Middleton, P. and Simmons, S.W., 2006. Techniques for preventing hypotension during spinal anaesthesia for caesarean section. Cochrane Database of Systematic Reviews Issue 4. Art. No.: CD002251. DOI: 10.1002/14651858.CD002251.pub2 Frolich, M.A. and Caton, D. 2002. Baseline heart rate may predict hypotension after spinal anaesthesia in pre-hydrated obstetric patients, Can J. Anaesthesia, Vol. 49(2), p.185-189 Greene, N.M., 1981. Physiology of Spinal anaesthesia. Baltimore: Williams and Wilkins, p. 112-115. Hartmann, B. et al., 2002. The incidence and risk factors for hypotension after spinal Anaesthesia Induction: An analysis with automated data collection. Anesth Analg, Vol.94, p. 1521-1529 Lee, A. et al, 2002. Prophylactic ephedrine prevents hypotension during spinal anaesthesia for Caesarian delivery but does not improve neonatal outcome: a quantitative systematic review. Can J. of Anaesthesia, 2002, Vol. 49 (6), p. 588-599 Musaid, R.A and Naranjo, T.M., 2006. Spinal block complications in obstetrics and gynaecology patients. Neurosciences, Vol. 11(3), p.140-144 Singh, B. and Sharma, P., 2002. Subdural block complicating spinal anaesthesia. Anesth Analg, Vol. 94, p. 1007-1009, International Anaesthesia Society Tarkkila, P. and Kaukinen, S., 1991. Complications during spinal anaesthesia: A prospective study. Regional Anaesthesia, Vol. 16, p. 101-106 Tarkkila, P. J. and Isola, J., 1992. Identification of patients in high risk of hypotension, bradycardia and nausea during spinal anaesthesia with a regression model of separate risk factors. Acta Anaesthesiology Scandinavia, Vol. 36, p. 554-558 Tarkkila, P., 2007, Complications associated with spinal anaesthesia in Complications of Regional anaesthesia 2nd Ed, (Eds.) Brendan T.Finucaine, New York:Springer Science and Business Media Read More