ACETAZOLAMIDE (Diamox)

 INDICATIONS: 1. Diuretic  (particularly  in  the  presence  of  metabolic  alkalosis) 2. Correction  of  severe  metabolic  alkalosis

Diamox  250mg  tablets  

 DOSAGE: For  diuresis,  the  dose  is  usually  250-375  mg  stat.  If,  after  an  initial  response,  the  patient fails  to  continue  to  diurese,  do  not  increase  the  dose  but  allow  for  kidney  recovery  by skipping  medication  for  a  day.  Acetazolamide  yields  best  diuretic  results  when  given  on alternate  days,  or  for  2  days  alternating  with  a  day  of  rest. 

DOSAGE  IN  PAEDIATRICS: The  safety  and  effectiveness  of  acetazolamide  in  paediatric  patients  below  the  age  of 12  years  have  not  been  established. 

DOSAGE  IN  RENAL FAILURE AND  RENAL REPLACEMENT THERAPY: No  dose  adjustment  is  required  when  administered  for  ICU  indications  (beware  that acetazolamide  is  contraindicated  in  the  presence  of  metabolic  acidosis). This  drug  is  not  indicated  in  patients  on  renal  replacement  therapy.   

CLINICAL  PHARMACOLOGY Acetazolamide  is  an  enzyme  inhibitor  that  acts  on  carbonic  anhydrase,  the  enzyme  that catalyzes  the  reversible  reaction  involving  the  hydration  of  carbon  dioxide  and  the dehydration  of  carbonic  acid.

 CONTRAINDICATIONS 1. Hypersensitivity  to  acetazolamide  or  other  sulphonamides 2. Metabolic  acidosis 3. Cirrhosis  (risk  of  development  of  hepatic  encephalopathy) 

General Increasing  the  dose  does  not  increase  the  diuresis  and  may  increase  the  incidence  of drowsiness  and/or  paraesthesia.  Increasing  the  dose  often  results  in  a  decrease  in diuresis. 

Acetazolamide  and  sodium  bicarbonate  used  concurrently  increases  the  risk  of  renal calculus  formation.

METABOLIC SIDE EFFECTS 

Metabolic  acidosis,  electrolyte  imbalance,  including  hypokalaemia,  hyponatraemia,  loss of  appetite,  taste  alteration,  hyper/hypoglycaemia.

ECG CHANGES IN SAH

🚩Deep T wave inversions. 

🚩Prolonged QT.

🚩Tall R waves. 

🚩ST depression

🚩Large U waves

🚩 ST elevations that seem to resolve while ‘T’ wave inversions appear to persist—even for months/years

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DO YOU KNOW?

ASA-2014 UPDATE

A social drinker is ASA II

A smoker is ASA II

Pregnant patient is ASA II

Obese patient is ASA II

Morbid obesity is not ASA II, but ASA III

Alcohol dependence without any documented systemic illness is also ASA III

Premature infant is ASA III

ESRD with regular HD is ASA III

ESRD without regular HD is ASA IV

Evidence of Sepsis or DIC- ASA IV

Intracranial bleed with mass effect is ASA V

A cardiac patient with bowel ischemia is ASA V

VISUAL IMPAIRMENT INTRACRANIAL PRESSURE SYNDROME & OCT

Visual acuity degradation in astronauts exposed to microgravity is a newly recognized phenomenon. Prompted by persistent reports of vision changes, NASA began a stepwise operational process to determine the cause 

        although  the exact mechanism is yet to be fully determined, many MRI findings suggest that intracranial hypertension is an important component. 

  

       OCT ( Optical Coherence Tomography ) is one technology that is operational @NASA's International Space Station, to study this Visual impairment Intracranial Pressure Syndrome. It is useful to analyse pathologies in the context of raised ICP. It can assess the Retinal Nerve Fibre Layer ( RNFL), total retinal thickness and the optic nerve head volume. But it can't provide a direct indication of raised ICP, is bulky, expensive and need an external energy source.

J Neurosurg Anesthesiol 27/4 Oct/2015

SPONDYLOEPIPHYSEAL DYSPLASIA

ANESTHETIC CONCERNS

1. Short trachea with 15 rings or less; high chance of accidental one lung ventilation

2. Chances of Laryngeal Stenosis... Some times an unanticipated difficulty for passing tube, may trigger edema and stridor ( one such case reported, needed emergency tracheostomy)

3. Atlanto axial instability, can cause, massive cord edema, even with moderate neck flexion ( one case suffered tetraparesis after intubation; so in clear words, explain to the relatives..,the anticipated amount of morbidity and mortality) Take LATERAL CERVICAL SPINE VIEWS IN FLEXION AND EXTENSION PREOPERATIVELY. If atlantoaxial instability is present and patient requires GA, give MANUAL IN LINE STABILIZATION/ do AWAKE FOB.

4. Restricted lung function accompanied by impending respiratory failure, is a situation, where we may be more inclined towards SAB in such patients (e.g. Pregnancy, where the uterus further compromise lung function).  So regional anesthesia may be appropriate, if technically feasible.

5. Technical difficulties with SAB/EDB; epidural space located 2.5 cm from skin was reported in one case.

KNOWN SECRETS! - COEXISTING ILLNESS AND ANESTHESIA

1. The evaluation of risk factors,  is for planning the anesthetic management, and will be of no use in predicting the outcome.
2. There is no justification for performing revascularisation purely to facilitate elective non cardiac surgery.
3. M.I. within the last 6 weeks, class iii-iv angina, decompensated heart failure, malignant arrhythmias, severe valvular heart disease, CABG/PTCA within the last 6 weeks constitute major Cardio Vascular risk factors for surgery.
4. Previous M.I. (>6weeks), class i-ii angina, compensated heart failure, T2 DM constitute intermediate C. V. risk factors.
5. Age > 70 years, uncontrolled systemic hypertension, arrhythmias, family h/o CAD, dyslipidemia, smoking, renal dysfunction, ECG abnormalities (LVH, RBBB/LBBB, ST segment anomalies) constitute minor C. V. risk factors.
6. Only emergency, life saving procedures should be performed during the first 6 weeks after a myocardial infarction (M. I.) and after CABG/PTCA with or without a coronary stent. The period between 6 weeks and 3 months are considered as a period of intermediate risk,  when non urgent elective surgery should be postponed.
7. SURGICAL PREDICTORS OF INCREASED PERIOPERATIVE CARDIOVASCULAR RISK
(i) HIGH RISK (complication rate >5%)
#Emergency major to intermediate surgery, especially in elderly patients
#Aortic & major and also peripheral vascular surgery
#Procedures involving: hem
dynamic instability, long duration or large fluid/blood loss
(ii) INTERMEDIATE RISK (complication rate 1-5%)
#Carotid endarterectomy
#Head & neck surgery
#Abdominal/thoracic surgery
#Orthopaedic surgery
#Prostatectomy
(iii)LOW RISK (complication rate <1%)
#Endoscopic procedure
#Breast and superficial surgery
#Eye surgery
8. ACE inhibitors are withheld for 24 hours by some anesthetists.
9. Perioperative beta blockade should be continued for 72 hours postoperatively.
10. The gold standard for detecting intraoperative ischemia and assessing volume status & valvular function is TEE.
11. Most perioperative myocardial infarctions occur in the first 3 days postoperatively. Patients at risk for M.I. require effective analgesia and humidified oxygen therapy for atleast 72 hours after major surgery.
12.  Severe hypertension (grade 3) has been associated with an increased incidence of perioperative hemodynamic instability, silent m.i. and arrhythmias; but evidence of a clinically significant increase in adverse outcome is lacking. The presence of endorgan damage due to hypertension is more important than the blood pressure per se.
13. Ideally the blood pressure should be maintained within 20% of the best estimate of preoperative pressure.
14. The treatment of arrhythmias produced by WPW syndrome includes Flecainide, Disopyramide, Procainamide and Amiodarone. Dgoxin and Verapamil are contraindicated.
15. There is no evidence to suggest that, frequent ventricular ectopics or asymptomatic non sustained ventricuar tachycardia is associated with an increased incidence of perioperative m.i..
16. Sick sinus syndrome is associated with a high ris of thromboemboism and may be anticoaguated. If the patient is not having a permanent pacemaker, he/she needs a, temporary pacing wire inserted preoperatively.
17. Complete heart block, type ii second degree A-V block and lesser degrees of heart block, in the presence of symptoms or cardiac failure requires preoperative insertion of permanent or temporary insertion of pacemaker. Vlatile agents prolong cardiac conduction and can worsen heart block. Atropine, Isoprenaline and facilities for external pacing should be kept ready.
18. ATRIOVENTRICULAR BLOCKS
(i) First degree block: P-R interval > 0.2 sec
(ii)Second degree block
Type I: progressive lengthening of PR interval,  until conduction fails and a beat is dropped.
Type II: intermittent failure of AV conduction without preceding PR prolongation.
(iii) Third degree block
Complete dissociation of atria and ventricles as atrial impulses fails to be transmitted. 
19. CHECKLIST FOR A PATIENT WITH PACEMAKER
a. Indication for pacemaker insertion
b. Mode of function of pacemaker
c. Functional status
d. Consider conversion of rate responsive pacemakers to fixed rate in the perioperative period.
e. Ensure use of only bipolar diathermy
f. If unipolar diathermy must be used, then the ground plate should be placed on the same site as the operating site, as far away from the pacemaker as possible. The frequency and duration of use should be minimised and the lowest possible current used.
g. MRI is contraindicated
h. Magnets should not be placed over pacemakers during surgery,  as they have an unpredictable effect on the programming of modern pacemakers.
i. A backup pacing system, atropine, adrenaline, isoprenaline and a backup pacing system should be available, in case of pacemaker failure.
20. Anesthesia constitutes a significant risk in Hypertrophic Obstructive Cardiomyopathy. Patients will be having dynamic left ventricular outflow tract obstruction, often with secondary MR. They are prone to arrhythmias and sudden cardiac death. Look for an Ejection systolic murmur in auscultation and LVH in ecg. Confirmation is by ECHO. Avoid hypovolemia, vasodilatation and the use of catecholamines
21. Constrictive pericarditis poorly tolerate vasodilatation; especially at induction.
22. In valvular heart disease, antibiotic prophylaxis is especially required for dental surgeries and those involving instrumentation of upper respiratory tract and genitourinary system.
23. AORTIC STENOSIS
# Even an ejection systolic murmur in an asymptomatic patient also warrants careful preoperative examination/ ECHO, as symptoms tend to appear late in the disease only.
# Promptly treat tachycardia and AF.
# Maintain ventricular filling by avoiding hypovolemia and maintaining SVR.
# Vasodilatation may result in profound hypotension--> subendocardial ischemia and even sudden death.
# Aggressive treatment of hypotension is mandatory to prevent cardiogenic shock and/or cardiac arrest. Cardiopulmonary resuscitation is unlikely to be effective in patients with aortic stenosis because it is difficult, if not impossible, to create an adequate stroke volume across a stenotic aortic valve with cardiac compression.
24. AORTIC REGURGITATION
# Avoid vasoconstriction and bradycardia which increases the degree of regurgitation
# A mild tachycardia, moderate fluid loading, a degree of vasodilatation and avoidence of myocardial depression can improve the forward flow.
# Acute AR is a surgical emergency and may respond poorly to vasodilatation.
25. MITRAL STENOSIS
# Patients are prone to develop CCF and Pulmonary Edema.
# Atrial fibrillation is a trigger for acute deterioration; so should be treated preoperatively
# Avoid tachycardia, myocardial depression and excessive vasodilatation
# Hypovolemia compromises ventricular filling
# Fluid overload can easily precipitate pulmonary edema
# PCWP will be inaccurate in the presence of pulmonary hyperension. Avoid Nitrous oxide if there is evidence of pulmonary hypertension.
26. MITRAL REGURGITATION
# A mild tachycardia,  a slight reduction in SVR and avoidance of myocardial depression are desirable.
# Avoid hypovolemia
27. There is little evidence that GA in ADULTS with URTI is associated with an increased risk of adverse respiratory events, although upper airway reactivity may be increased
28. In children with URTI,  a higher incidence of adverse respiratory events have been demonstrated,  but few of these adverse events result in postoperative sequelae. It has been suggested that surgery need not necessarily be postponed in children with mild URTI. Increased airway reactivity may persist for 4-6 weeks and if surgery is postponed, it should be for a period of at least 6 weeks.
29. In COPD, if the patient is having copious secretions, better to avoid anticholinergics, as it will impair the ability to clear secretions.
30. Even though regional anesthesia has the advantage of avoiding respiratory complications of GA, most patients, even those with quite severe COPD may be managed safely under carefully c
ducted GA.
31. Pressure Controlled Ventilation with a low respiratory rate and prolonged expiratory phase is suitable in COPD patients.
32. Epidural analgesia has been shown to decrease the incidence of postoperative pulmonary complications in thoracic and upper abdomnal surgery.
33. In patients with bronchial asthma, good depth of anesthesia, good muscle relaxation and i. v.  Lidocaine can reduce the incidence of bronchospasm during intubation; topical lidocaine spray is not effective and may induce bronchoconstriction in some patients.
34. Circulatory disturbance during anesthesia and surgery may affect the absorption of subcutaneous insulin.

ANESTHETIC MANAGEMENT OF PATIENT, WITH HYPERTROPHIC OBSTRUCTIVE CARDIOMYOPATHY

Tachycardias from emotion, exercise and pain, and drugs such as digoxin and beta stimulators, will all increase the outflow tract gradients and may considerably reduce the cardiac output to essential organs, such as the myocardium and brain.Preoperative beta blockers should be maintained.(Patients are often already taking beta blockers to prevent tachycardias.)

Hypotension from blood loss, regional anaesthesia, or vasodilator drugs, cause similar reductions in cardiac output and can worsen obstruction.Drugs and techniques that cause vasodilatation and hypotension must be avoided,contraindicated. However, with the greater ability to control the onset of epidural and by the use of continuous infusions and opiates, it has been suggested that regional blocks are no longer contraindicated. Hypotension should be treated by restoring vascular volume. If vasopressors are required, an alpha1agonist, such as phenylephrine or methoxamine, is the most suitable.

An adequate preload should be given and blood loss should be replaced promptly.

KNOWN SECRETS!-PREANESTHETIC CHECK

Y1. Two cardinal symptoms of cardiac illness are exercise intolerance and chest pain
2.Systemic illness in : ASA 2- not incapacitating , ASA 3- incapacitating, ASA 4- life threatening
3. Take history of syncope, seriously, as it may point towards undetected significant CVS issues.
4. Cardiac catheterisation is indicated in whom, a non invasive test is strongly positive or whose symptoms are unequvivocal.
5. Postponing of surgery is considered, ONLY IF, BP is consistently >180/110 mm of Hg
6. Preoperative administration of bronchodilators and topical application of local anesthetics , are some strategies practiced to reduce bronchospasm at induction, in asthmatic patients.
7.  TOTAL LUNG CAPACITY: reduced in RLD and increased in OLD
FORCED VITAL CAPACITY(4-5L): reduced in both OLD and RLD
FEV1(75% of FVC): reduced in both OLD and RLD
FEV1/FVC(>75%): reduced in OLD
PEFR(450-650L/min):<120L/min if severe obstruction
MVV(70-100L/min): index of total cardiorespiratory function
(OLD-Obstructive Lung Disease, RLD-Restrictive Lung Disease, F-Fibrosis)
8. Mallampati score
G1-all structures visible
G2-uvula obscured by base of tongue
G3-only soft palate
G4-only hard palate
Thyro Mental Distance >6.5cm is normal
Mallampati score + TMD provides a positive predictive value of upto 100%
9. Volatile agents other than halothane also may cause jaundice
10. Non Alcoholic Steato Hepatitis (NASH-comprises obesity, T2 DM and elevated blood lipids) is an advanced form of Non Alcoholic Fatty Liver Disease (NAFLD). Incidence of NAFLD is rising in the western world.
11. Child Pugh Grade B patients should be optimised preoperatively. Grade C patients should not undergo elective surgery if possible.
12. Look for the development of Hepatorenal syndrome in the jaundiced patient, document it, and consider prophylactic measures like mannitol administration.
13. Cirrhotic patients are at risk of hypovolemia and so, consider CVP monitoring.
14. Anticipate higher incidence of PONV in E.N.T. and Gynecological surgeries. If more than one among the following risk factors is present, a prophylactic antiemetic should be administered: 1) female gender 2) non smoker 3) h/o PONV or motion sickness 4) predicted opioid use
15. The obese patient is at risk of perioperative hypoxia, because of (a) hypoventilation and (b) restriction of diaphragmatic excursion. Volume of epidural space will be less, reducing drug requirement. NIBP cuff may overestimate BP; so consider IBP, if required.
16. If planning to give transfusion, complete it 24 hours prior to surgery
17. DVT PROPHYLAXIS :
Low risk- Compressive stockings/ Pneumatic Compression Device
Medium risk- +LMWH (e.g.20-40 mg ENOXOPARIN s/c )
High risk- +LMWH. Maintain anticoagulation with Warfarin.
18. Patients of African or Afro-Caribbean descent should be screened for Sickle cell disease, using a Sickledex test.
19. Malignant hyperthermia, is a preventable cause of anesthetic death. Ask for family history; the standard test is the in vitro sensitivity of striated muscle to caffiene and halothane.
20. Clonidine reduces requirements for volatile anesthetics.
21. The amnesia produced by benzodiazepines is anterograde and lasts for about 10 mins,  if given i.v. , but much longer after oral doses
22. Benzodiazepines potentiate propofol.
23. The dose of Flumazenil, the benzodiazepine antagonist, is 100-200 microgram iv, followed by 100-400 microgram/hr. S/E: tachycardia,  hypertension, seizures
24. Lorazepam : Oral dose 1-4 mg (30-50 ug/kg).  Duration : 4-24 hours.  Produces appreciable anterograde amnesia. Abolishes vasoconstriction that accompanies fear.
25. Diazepam: Oral dose : 10-20 mg,  duration : 4-8 hours,  When given in combination with metoprolol, its anxiolytic effect is greatly enhanced.
26. Patients with alcoholic liver disease are very sensitive to promethazine. Promethazine has antihypertensive property.
27. Complete vagal block requires a dose of 3 mg of atropine.
28. Atropine should be avoided in small children with pyrexia or sepsis ; may result in overdose and febrile convulsions can occur
29. Patients with Downs syndrome may show resistance to parenteral atropine
30. Antisecretory effect of atropine,  is much more pronounced, if given as i.m. 1 hour before,  than immediately before induction as i.v.
31. Hyoscine,  glycopyrrolate and atropine increases chances of regurgitation by relaxing cardiac sphinctor of stomach. 
32. Atropine crosses the placenta and can protect foetus from vagal reflexes.
33. Hyoscine butylbromide is a gi or urinary antispasmodic at doses, of 10-30 mg oral/i.v.
34. Hyoscine hydrobromide is a mild respiratory stimulant and an antiemetic at doses of 0.3-0.6 mg im.
35. Glycopyrronium bromide (dose: 0.2-0.4 mg  /  4-8 ug/kg) is a better, antisecretory agent than atropine and emergence is faster, than after giving atropine; is effective in  preventing bradycardia after suxamethonium; but has no antiemetic effect.
36. The treatment of Central anticholinergic syndrome is with Physostigmine salicylate (2mg iv); it can also be used to modify the psychotic side effects of ketamine.
37. For major surgery,  Lithium should be stopped 2 days prior, as it will potentiate NDMR; if case is posted as emergency, may have to consider regional anesthesia or suxamethonium. Hydrate well and take care of fluid, and electrolyte balance.
38. NON SELECTIVE MAO INHIBITORS :
# May react with pethidine, morphine and fentanyl and can cause fits, coma, muscle twitching, hypertension, ataxia and ocular paralysis. Deaths have occurred. Chlorpromazine (25 mg) has found to be effective, in treating this. Regional anesthesia,  NSAIDs and a combination of chorpromazine and codeine are choices for postoperative analgesia. Severe hypertension and even death may occur with administration of vasopressor drugs (even with adrenaline contained in local anesthetic preparations). Treatment is with phentoamine. So non specific MAO inhibitors should be stopped,  2 weeks prior to surgery.
39. SELECTIVE MAO INHIBITORS:
# The specific,  reversible MAO-A inhibitors (moclobemide) and MAO-B inhibitors ( Selegiline,  used in treatment of Parkinsonism) are less dangerous and can be continued upto the day before surgery; but caution is still needed; avoid pethidine and sympathomimetic agents
40. SSRIs may prolong the action of warfarin; fluvoxamine an SSRI, may reduce the metabolism of ropivacaine; otherwise SSRIs are relatively safe in the perioperative period.
41. To avoid the recurrence of severe Parkinsonism, dysphagia and the risk of aspiration pneumonia, antiparkinsonian drugs like levodopa should be continued upto the time of surgery.
42. During the perioperative period, in response to the stress, cortisol secretion from the adrenal cortex may rise upto 500 mg/day from the normal value of ~25 mg/day. This response cannot occur in patients on corticosteroid therapy, due to adrenal suppression. Even a one week course of steroids or inhaled steroids can cause this suppression. But <10 mg prednisone per day or equivalents,  has no effect. For higher dose therapy,  it requires extra hydrocortisone e.g. 25 mg at induction,  followed by 25 mg 6 hourly for 24-48 hours (48 hours for major surgeries). i.m. route gives more sustained release.
43. Combined Oral Contraceptive Pills, if possible,  should be discontinued 4 weeks before major elective surgery or leg surgery, and started again at the first menstrual period, following an interval of 2 weeks after the surgery, if the patient is fully mobile. If this is not feasible, prophylactic heparin/LMWH should be considered. Risk for DVT is higher in case of pelvic/cancer/orthopaedic surgeries, old age, smoking, obesity and factor V Leiden mutation.

ANESTHESIA FOR ESOPHAGEAL SURGERIES

Approaches: Ivor Lewis (laparotomy and right thoracotomy, transhiatal (abdominal and neck incisions), left thoraco abdominal approach

Concerns:

Preoperative Chemotherapy
1. Less distinct tissue planes and increased bleeding
2. Bleomycin : pulmonary toxicity ; worsened by high oxygen concentrations
3. Doxorubicin: acute dysrhythmia, chronic cardiomyopathy

Incomplete Obstruction
1. Recurrent aspiration pneumonitis- decreased pulmonary reserve
2. Retained food products @ induction - increased risk of aspiration

History of smoking, alcoholism
1. Associated COPD
2. Alcoholic cardiomyopathy
3. If on antiplatelets for CAD, use of epidural may be contraindicated

Evaluation

1. CBC: check for infections
2. PFT-ABG-FLOW VOLUME LOOPS
3. CT/MRI- bronchoscopy; if required, to evaluate for presence of tracheal or bronchial compression
4. ECG, ECHO

Special points on Anesthetic technique

1. In thoracic or thoraco abdominal approach, placement of a DLT is indicated to provide OLV. If difficult airway, single lumen can be inserted first and then changed using a tube exchange catheter.
2. Surgeries involving only cervical or endoscopic approach don't require epidural
3. If epidural is planned placement and testing before induction is recommended
4. Significant third space loss : close monitoring of BP and Urine output
5. Transient compression of myocardium can produce dysrhythmia and hypotension : IBP will be helpful
6. PEEP- low tidal volume - low ventilator pressures can be lung protective strategies in OLV
7. Avoid excess fluids: anastamotic edema, pulmonary edema
8. Patients with significant intraoperative fluid shifts may develop airway edema- avoid premature extubation
8. If patient requires prolonged postoperative ventilation, DLT can be exchanged with single lumen tube, before shifting to icu.
9. Arrange platelets, ffp, cryoprecipitate etc.
10. CVP cannulation site should be determined by surgical approach
11. Prevent hypothermia
12. Take necessary precautions to avoid position related injuries; check radial pulse after placement of axillary roll. Can place pulseoximeter probe on down arm to check perfusion
13. Ensure normal potassium ( dysrhythmias)
14. Hypoxia during OLV : PEEP to ventilated lung, CPAP to non ventilated lung, return to double lung ventilation
15. Adequate BP is necessary for maintaining integrity of the anastamosis

16. POSTOPERATIVE

a. Recovery in head up position, ig risk of aspiration high
b. High index of suspicion for pneumothorax
c. Hoarseness = RLN injury
d.  SVT: adenosine. 6 mg iv push and repeat if needed to 12 mg ; AF - DC cardioversion, beta blockers, Amiodarone,  CCBs, pacing
e. DVT prophylaxis

Magnesium Sulphate therapy in preeclampsia

Continuous Intravenous Infusion

Magnesium sulfate 4-g to 6-g loading dose diluted in 100 mL fluid  administered intravenously over 15 minutes, followed by continuous intravenous infusion at 1 to 2 g per hour. Discontinue 24 hours after delivery or last seizure.

If convulsions persist after 15 min, give up to 2  gram more intravenously as a 20% solution at a rate not to exceed 1g/min. If the woman is large (> 70 kg) then an additional 2 grams may be given slowly

Only give the next IM dose, or only continue the IV infusion if:

Respiratory rate > 16/min
Urine output > 25 ml/h
Patellar reflexes are present

If urine output < 100 ml in 4 h and there are no other signs of magnesium toxicity, reduce the IV infusion to 0.5 g/h.

If patellar reflexes are depressed and respiration is normal, withhold further doses of magnesium sulfate until the reflexes return and request magnesium level.

If there is concern about respiratory depression , stop magnesium, give oxygen by mask and give:

Calcium gluconate (10mL of 10% solution over 10 minutes)

ACOG TASK FORCE 2013

... For women with severe preeclampsia, the administration of intrapartum and postpartum magnesium sulfate to prevent eclampsia is recommended.  For women with preeclampsia undergoing cesarean delivery, the continued intraoperative administration of parenteral magnesium sulfate to prevent eclampsia is recommended.