心房缺与剖腹产 ASD for caesarean section

shenxiu2

You are asked to see a 30 years old, 34 weeks gravid female who requires emergency caesarian section, but refuses regional anaesthesia. She has a past history of a known medium size secundum atrial septal defect (ASD), and has been asymptomatic since birth. The cardiologists have reviewed her regularly in the outpatient clinic over the past years.

1) Describe the pathophysiology of this patient’s cardiac condition. What would you look for in preoperative assessment of this patient to indicate the severity of the ASD?

2) How would this cardiac condition affect your anaesthetic management of the patient?

3) Post-operatively, you are asked to see this patient in the recovery area because her SpO2 has decreased acutely to 70%. You confirm that her ventilation is not a problem. What are the possible causes and what is your immediate management.

-----Hong Kong Board final exam question 1 ,2009 March.------

jerryzhjj

非常受用                                 

jerryzhjj

非常受用                                 

shenxiu2

Translation of the above answer  :  

       Normal left atrial pressure is (8~10mmHg)> right atrial pressure （3~5mmHg)，in ASD, blood flow from the left atrium to the right atrium across the ASD. The shunt  amount  depends on the size of the ASD, the   pressure gradient  across the two atria and the filling resistance of both sides. In ASD primum, shunting  of blood is also affected by the degree of mitral regurgitation.

        Due to the long term shunting  of blood and an increase in volume load, the right atrium , right ventricle & pulmonary arteries dilate.The increase in pulmonary circulatory volume causes the pulmonary arterial pressure to rise, and also induces pulmonary arteriolar  reflex vasospasm .Chronic vasospasm brings about hypertrophy & fibrosis of the pulmonary arteriolar wall, and ultimately causes pulmonary hypertension.

    When the right atrial pressure is higher than the left atrial pressure , the shunt will  flow from the right to the left., and causes cyanosis , this is called Eisenmenger 's syndrome.。

　　In  this 30 years old ASD patient,  preoperatively we need to assess her  pulmonary arterial pressure , a color doppler echocardiogram , a pulmonary arterial  floatation catheter insertion and a blood gas test  should be done .Nitroglycerine infusion can be given via the PA floatation catheter, and an assessment of the response to the drug can be done, in order to  monitor  the progress and assess  the prognosis.  

   In this question , the preoperative description  of the patient is very little , but judging from the age of the patient, there is a high possibility that she has developed  pulmonary hypertension. In anesthetic management , we should give her adequate oxygen,avoid systemic hypotension which will increase  the right to left shunting and worsens  hypoxemia. Therefore , generally we do not use spinal  anesthesia , instead I will choose to use general anesthesia with endotracheal intubation.

      Postoperatively she desaturated even with normal ventilation, most probably she had developed right to left shunt. If the endotracheal tube is still in situ, then keep the tube , use ventilator to support the ventilation simultaneously , avoid high airway pressure, start intravenous nitroglycerin to reduce pulmonary arterial pressure ,if the systemic pressure drops, then dopamine may be used to maintain its pressure. A PA floatation catheter will be useful in assessing the pulmonary arterial pressure , and also in infusing nitroglycerins. If the patient has already been extubated, then maintain a facemask with supplemental oxygen ,and start her on the above mentioned vasoactive drugs.  

drlzw

　　正常左房压力(8~10mmHg)>右房压力（3~5mmHg)，房缺时左房血液经其向右房分流。分流量取决于缺损大小、两侧心房压力差和两侧充盈阻力，原发孔房间隔缺损的分流还与二尖瓣返流程度有关。分流所致的长期容量负荷增加造成右房、右室和肺动脉扩张。肺循环血量增加使肺动脉压力升高，并引发肺小动脉反应性痉挛，长期痉挛使肺小动脉管壁增厚和纤维化，最终导致梗阻性肺动脉高压。当右房压力高于左房压力时，出现右向左分流，引起发绀，称为艾森曼格（Eisenmenger）综合征。
　　30岁的房缺病人术前必须充分评估肺动脉压，可做心脏彩超和放置漂浮导管，血气分析。通过漂浮导管输注硝酸甘油还可以判断肺动脉小动脉对其反应情况以判断病情进展的程度和预后。本问题术前的情况描述较少，但从年龄上我们要警惕病情已经进展到严重的肺高压。这时麻醉处理上应该充分给氧，避免低血压加重右向左分流而加重缺氧，因此一般不再采用椎管内麻醉而采用全麻气管插管。
　　术后呼吸正常而发生低氧，应该认为右向左分流已经发生，如果气管导管尚未拔除，则暂不拔管，用呼吸机同步辅助，但压力不要太大，并自静脉输注硝酸甘油以降低肺动脉压力，如果血压下降需同时应用多巴胺，最好置入漂浮导管以确认肺动脉压力，并可以从其输入硝酸甘油。如果气管导管已经拔除，就先面罩吸氧，同上应用血管活性药。