Cardio-puImonary arrest (CPA) complicating major regional blockade (MRB) in late pregnancy is uncommon. The cause(s) of the arrest and the timeliness of basic and advanced life support affect the outcome. Three causal patterns exist, all with common initial resuscitation requirements:
1. CPA causally related to the MRB, eg. total spinal block and primary respiratory arrest; local anaesthetic CNS and CVS toxic effects (1).
2. CPA causally related to obstetric or medical factors, with the MRB complicating management of the CPA, eg. haemorrhage; vagotonia (uterine inversion); anaphylaxis; complications of pregnancy induced hypertension; peri-partum cardiomyopathy; venous gas-, amniotic fluid- and thrombo-embolism (2); arrhythmia or congestive cardiac failure secondary to valvular or congenital heart disease (mitral stenosis, ASD).
3. CPA related to a complex interplay of multiple factors, eg. aortocaval compression (ACC) (Figure 28.1) with a "high epidural" on a background of hypovalaemia; MRB mediated hypotension and idiopathic hypertrophic subaortic stenosis; MRB with ACC mediated hypotension or a minor pulmonary embolism causing reversal of a left to right cardiac shunt in an otherwise asymptomatic atrial septal defect; primary cardiac tachyarrhythmia with a MRB and ACC.
Cardiac arrest complicating major regional blockade is associated with unexpectedly poor neurological outcomes (4). The physiological changes of pregnancy further complicate the situation. ACC can confound both the diagnosis of CPA and the monitoring of CPR because femoral pulses can be unreliable. A carotid pulse, apnoea and unconsciousness are more reliable clinical markers (Chapter 13).
Reports such as "Post-mortem caesarean section with recovery of both mother and offspring" (5, 6, 7) and cases of ACC masquerading behind esoteric diagnoses indicate that vigilance in avoiding ACC is required (8).
ACC is treated by:
1. Lateral patient positioning and uterine displacement,
2. Elevation of the legs,
3. Appropriate fluids, and
4. IV vasopressor.
Delivery of the fetus is ultimately the only way to eliminate ACC as a component of haemodynamic instability. Late term pregnancy is associated with a propensity for arterial hypoxaemia, airway management difficulty and pulmonary aspiration.
Local anaesthetics (LA) may directly cause circulatory instability via several mechanisms:
1. MRB related - denervation of vascular tree and venous pooling, attenuated cardiac sympathetic neural traffic, impaired sympathetic compensation for the ACC and in asymmetric blocks, QT interval changes;
2. CNS toxicity (Chapter 7);
3. Cardiac toxicity (Chapter 36). "Prevention" of LA toxicity with interval dosing of epidural LA etc is preferable to the "cure". Bupivacaine is more prone to induce complex arrhythmias than either lignocaine or ropivacaine (Table 36.6).
In true CPA during pregnancy, the usual resuscitation drugs are indicated. Pregnancy is associated with blunted responsiveness to beta-agonists. Adrenaline will reduce uteroplacental blood flow, but this must be weighed against the systemic effect of supporting cardiac perfusion and output. Drugs can have unexpected effects, eg. magnesium and verapamil can cause uterine atony. Bretylium may be the anti-arrhythmic of choice in LA toxicity with refractory ventricular tachyarrhythmia. Lateral patient positioning simplifies electrical cardioversion with anterior-posterior paddle placement.
References:
1. Dawson P. Cardiac Arrest following Epidural Overdose Anaesthesia and Intensive Care 23: 5; 650 1995.
2. Noble WH, St-Amand J. Amniotic Fluid embolism [review] Can J of Anaesthesia 40(10):971-980 1993.
3. Brown MA Pregnancy induced hypertension: pathogenesis and management Aust NZ J Med 1991 21:257-273.
4. Caplan PA. et al. Unexpected Cardiac arrest during spinal anesthesia: A closed claims analysis of predisposing factors Anesthesiology 68:5-11, 1988.
5. DePace NL, et al; 'Post-mortem' Caesarean Section with recovery of both mother and offspring JAMA 1982 248: 971-973.
6. Weber CE Post-mortem caesarean section: Review of the literature and case reports Am J Obst Gyn 1971 110: 2; 158-165
7. Strong TH, Lowe RA. Peri-mortem Caesarean Section Am J of Emergency Medicine 7: 5: 489-494 Sept 1989.
8. Sutherland SK, Duncan AW, et al 'Death from snake bite associated with the supine hypotensive syndrome of pregnancy' Med J Aust 1982 2: 238-239.