Bad news for rabbits & pregnant ladies…

Mendelson CL. The aspiration of stomach contents into the lungs during obstetric anesthesia. Anesthesiology 1946; 7: 694-695.

RHH Journal Club. May 31st, 2012. Dr Sireesha Aluri 

No free full-text available

To describe the presentation, pathology, diagnosis, prevention and management of aspiration pneumonia.

Study design:

– 1st study to describe the presentation, pathology, diagnosis, prevention and management of aspiration pneumonia.

– Retrospective case notes survey for 13 years, in single hospital in New York.

– With experimental work on rabbits.

Methodology: for retrospective case notes survey

Population

66 cases of 44016 pregnancies at the Lying-InHospital, Newyork, incidence 0.15%

Labour prolonged in these by 10%

Intervention

GA with gas/O2/ether.

Control:

None/ NoGA required.

Outcomes

– 66 out of 44016, incidence 0.15% aspirated.

– Solids- complete obstruction – suffocation/ incomplete obstruction – atelectasis, collapse. Liquids – asthma like syndrome.

– Liquid > common than solid, Rt lung > left lung. But massive aspiration both lungs involved.

– Cyanosis, tachycardia, dyspnoea occurred irrespective of the type of aspiration.

– Morbid group: temperature > 38 during any two 24 hr period after the first 24 hrs following delivery.

– < 30% cases were morbid, < 50% of them due to chest pathology.

– 2 deaths due to complete obstruction by solid particles.

For experimental work:

Study design:

Animal experiments to determine pathology of the 2 different types of aspiration and evaluate the role of hydrochloric acid.

Methodology:

Population

Adult rabbits weighing 5-6kgs.

Intervention:

– Introduction of material into trachea via tracheotomy or using a laryngoscope during sodium pentothal anaesthesia.

– Substances used; distilled water, Normal saline, Tenth normal hydrochloric acid, neutralised and unneutralised liquid vomitus, neutralised and unneutralised vomitus containing solid undigested food.

– Vomitus obtained from pregnant patients.

Control

Rabbits with distilled water into trachea.

Outcomes

Clinical presentation, X ray findings, pathological findings.

Validity

Observational study and animal experiments. No numbers, No blinding. ?Ethical approval for animal experiments. Follow up was complete.

Results can be extrapolated to current clinical practice (66 years since this paper)

Results:

  1. Aspiration of solid undigested food

–          picture of respiratory obstruction as in humans

–          no difference between acid or neutral material

–          complete obstruction – suffocation – not relieved – death.

–          Incomplete obstruction- massive atelectasis, collapse. If relieved of obstruction – recover completely.

  1. Aspiration of liquid containing HCl (tenth normal HCl / un-neutalised liquid vomitus)

–          picture similar to liquid aspiration in humans

–          clinical- cyanosis and laboured respirations with death in few hrs-minutes. Pink froth from respiratory passages in the terminal stage.

–          X ray: irregular, soft mottled shadows with out mediastinal shift.

  1. Aspiration of neutral liquid (distilled water, normal saline, neutralised liquid vomitus)

–          Clinical – brief phase of laboured respiration & cyanosis. With in a few hrs, back to normal and carry on rabbit activities uninhibited.

–          X ray: nil significant.

Conclusions:

–          gastric emptying time prolonged in labour.

–          Aspiration may occur while laryngeal reflexes are abolished under GA

–          Rt > Left lung, Liquid > Solid aspiration

–          Solids – complete / incomplete obstruction. Obstruction to be promptly relieved.

–          Liquid aspiration – asthma like syndrome. Diagnosis confused with cardiac failure

–          Animal experiments indicate HCl acid to be responsible.

–          Therapies to be directed against bronchiolar spasm, cardiac embarrassment.

–          O2, atropine, adrenaline, aminophylline to be used. Rapid digitalisation if cardiac failure develops.

–          Majority have an afebrile recovery in 7-10 days.

–          Sulphonamides, penicillin may help in preventing secondary infection.

Preventable by:

–          Withholding oral intake and substituting parenteral therapy if needed during labour.

–          Induced vomiting or warm alkaline solution to nullify the acid.

–          Wider use of local anaesthesia where indicated and feasible.

–          For GA- time of last intake along with pre op assessment to be noted.

–          Once retching occurs- mask to be removed and vomiting encouraged.

–          Competent administration of GA with appreciation of dangers of aspiration during induction and recovery.

–          Adequate delivery room equipment, including transparent anaesthetic masks, tiltable delivery table, suction, laryngoscope, bronchoscope to be available.

–          Early recognition and suitable treatment.

 

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