Pre‐oxygenation in pregnancy: an investigation using physiological modelling

McClelland, Siobhan; Bogod, David; Hardman, Jonathan G.

doi:10.1111/j.1365-2044.2007.05346.x

Cited by 32 publications

(26 citation statements)

References 27 publications

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“…Table 2 Length of pre-oxygenation by tidal breathing required in the average pregnant and non-pregnant subjects to achieve three different levels of pre-oxygenation. (From accompanying pre-oxygenation study [12]). …”

Section: Resultsmentioning

confidence: 99%

“…In this study, we set out to use the NPS to investigate how pregnant and non-pregnant women differ during apnoea. We wanted to determine the duration of apnoea tolerance that can be achieved in pregnancy, and to use this information to strengthen our recommendations regarding the optimal method of pre-oxygenation [12]. …”

mentioning

confidence: 99%

“…In an accompanying paper [12], we used the Nottingham Physiology Simulator (NPS) to investigate pre-oxygenation in pregnancy. In this study, we set out to use the NPS to investigate how pregnant and non-pregnant women differ during apnoea.…”

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confidence: 99%

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Apnoea in pregnancy: an investigation using physiological modelling

2008

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SummaryOxygen desaturation during apnoea following anaesthetic induction in obstetrics is hazardous for mother and baby. This study investigated apnoea during pregnancy using computer simulation. The Nottingham Physiology Simulator was configured to replicate normal pregnant physiology. Three pregnant and three non-pregnant subjects were created, representing population variation according to published physiological values. They each commenced apnoea from four levels of preoxygenation from none to 99% complete denitrogenation. During apnoea, the physiological changes of rapid sequence induction were simulated. We found reduced apnoea tolerance in pregnancy, the median [range] time taken to fall to S a O 2 < 90% after 99% complete denitrogenation being 4 min 52 s [3: 43-6:17] in the pregnant subjects, vs 7 min 25 s [5:49-9:42] in the non-pregnant subjects. The time taken to fall from S a O 2 90% to 40% was 35 s [32][33][34][35][36][37][38][39][40][41][42][43][44][45] in the pregnant vs 45 s [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54][55][56] in the non-pregnant subjects. Two minutes of pre-oxygenation by tidal breathing provides approximately 3.5-6 min before desaturation to < 90%. General anaesthesia for Caesarean section presents a hazard to both mother and baby from apnoeic hypoxaemia during rapid sequence induction. The normally brief period of apnoea can become prolonged if difficulties are experienced with airway management. The length of time prior to the onset of life-threatening oxygen desaturation can be extended by pre-oxygenation (denitrogenation) of the lungs [1].Significant changes to the cardiovascular and respiratory systems occur during pregnancy [2][3][4][5][6][7], and these predict differing effects on the physiology of preoxygenation and apnoea. During apnoea, reduced functional residual capacity, together with increased oxygen consumption, predicts quicker onset of hypoxaemia and desaturation. There are three small studies to support this [8][9][10]. However, research during pregnancy suffers from ethical and practical constraints, which have placed even greater limits on the in vivo study of apnoea than on preoxygenation. In addition, studies have used heterogeneous methodologies that are not necessarily applicable to clinical practice.Computer simulation can be employed to conduct precisely controlled investigations difficult or impossible to achieve in vivo [11]. In an accompanying paper [12], we used the Nottingham Physiology Simulator (NPS) to investigate pre-oxygenation in pregnancy. In this study, we set out to use the NPS to investigate how pregnant and non-pregnant women differ during apnoea. We wanted to determine the duration of apnoea tolerance that can be achieved in pregnancy, and to use this information to strengthen our recommendations regarding the optimal method of pre-oxygenation [12]. MethodsThe Nottingham Physiology Simulator is an integrated computational model of the respiratory and cardiovascular systems that has been described previously [13]...

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Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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Apnoea in pregnancy: an investigation using physiological modelling

2008

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“…A fresh gas flow rate of ≥ 10 l.min À1 is required for effective denitrogenation, and a tight mask-to-face seal is essential to reduce air entrainment [67]. Most anaesthetists pre-oxygenate for ≥ 3 min even during category-1 caesarean section [69]; however, previous clinical research and recent computer modelling shows that a 2-min period of pre-oxygenation is adequate for the term pregnant woman at term [66,70]. If the patient is apnoeic and the airway is not being instrumented, continued administration of 100% oxygen with a tightly fitting facemask and maintenance of a patent airway allows continued oxygenation by bulk flow to the alveoli (apnoeic oxygenation) [71].…”

Section: Rapid Sequence Inductionmentioning

confidence: 99%

Obstetric Anaesthetists’ Association and Difficult Airway Society Guidelines for the Management of Difficult and Failed Tracheal Intubation in Obstetrics

Mushambi¹,

Kinsella²,

Popat³

et al. 2016

Obstetric Anesthesia Digest

114

221

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SummaryThe Obstetric Anaesthetists' Association and Difficult Airway Society have developed the first national obstetric guidelines for the safe management of difficult and failed tracheal intubation during general anaesthesia. They comprise four algorithms and two tables. A master algorithm provides an overview. Algorithm 1 gives a framework on how to optimise a safe general anaesthetic technique in the obstetric patient, and emphasises: planning and multidisciplinary communication; how to prevent the rapid oxygen desaturation seen in pregnant women by advocating nasal oxygenation and mask ventilation immediately after induction; limiting intubation attempts to two; and consideration of early release of cricoid pressure if difficulties are encountered. Algorithm 2 summarises the management after declaring failed tracheal intubation with clear decision points, and encourages early insertion of a (preferably secondgeneration) supraglottic airway device if appropriate. Algorithm 3 covers the management of the 'can't intubate, can't oxygenate' situation and emergency front-of-neck airway access, including the necessity for timely perimortem caesarean section if maternal oxygenation cannot be achieved. Table 1 gives a structure for assessing the individual factors relevant in the decision to awaken or proceed should intubation fail, which include: urgency related to maternal or fetal factors; seniority of the anaesthetist; obesity of the patient; surgical complexity; aspiration risk; potential difficulty with provision of alternative anaesthesia; and post-induction airway device and airway patency. This decision should be considered by the team in advance of performing a general anaesthetic to make a provisional plan should failed intubation occur. The table is also intended to be used as a teaching tool to facilitate discussion and learning regarding the complex nature of decision-making when faced with a failed intubation. Table 2 gives practical considerations of how to awaken or proceed with surgery. The background paper covers recommendations on drugs, new equipment, teaching and training.

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“…At least 2 minutes of pre-oxygenation and denitrogenation with 100% oxygen administered through a tightly fitting face mask is strongly recommended before tracheal intubation of pregnant patients. 12) III. Anesthetic management Hemodynamic considerations: To preserve cerebral and uteroplacental perfusion, every effort should be made to maintain hemodynamic stability during neurosurgical intervention.…”

Section: Anesthesia Inductionmentioning

confidence: 99%

Anesthetic Management of Pregnant Women With Stroke

Yoshitani

Inatomi

Kuwajima

et al. 2013

Neurol. Med. Chir.(Tokyo)

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Stroke during pregnancy is rare, but after occurring, most patients develop serious neurological conditions. Hemorrhagic stroke, including intracerebral hemorrhage and subarachnoid hemorrhage, often requires emergency surgical intervention. In addition to significant maternal physiological changes, the potential for fetal harm should be considered during anesthetic management of these patients. Whether cesarean section or neurosurgical intervention should be prioritized or performed simultaneously in pregnant women with stroke is an important issue. Whether the patients receive general or spinal and epidural anesthesia is another clinically significant issue. Finally neurosurgeons, anesthesiologists, and obstetricians should cooperate to manage pregnant women with stroke.Key words: pregnant woman, cerebral stroke, anesthesia Maternal Physiological Changes During PregnancyImportant physiological changes occur in pregnancy that could affect anesthetic management. Such physiological changes are mainly the result of hormonal and anatomical changes. I. Hormonal changesVarious hormonal alterations occur to sustain the pregnancy. Human chorionic gonadotropin allows the corpus luteum, which produces progesterone and estrogen, to be maintained. Endorphins and aldosterone are also secreted as shown in Fig. 1. Both estrogen and progesterone are important pregnancy-sustaining hormones that lead to endometrial hyperplasia. These hormones lead to dilation of blood vessels, which may cause cerebral aneurysms to increase in size. 4) In addition, meningiomas and other neoplasms expressing estrogen and progesterone receptors experience faster growth during pregnancy. 17) Increased levels of progesterone along with an increased rate of carbon dioxide production during pregnancy are responsible for increases in ventilation. Oxygen consumption also increases by as much as 60% during pregnancy. 20) As a result, functional residual capacity decreases by as much as 20% by the end of the third trimester. 11) Progesterone sensitizes the respiratory center to carbon dioxide. PaCO 2 falls to approximately 30 mmHg by the 12 th week of gestation. In the central nervous system, increased concentrations of endorphins have been found during pregnancy in animal models. 6) Beta-endorphin was identified as an endogenous agonist for

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Pre‐oxygenation in pregnancy: an investigation using physiological modelling

Cited by 32 publications

References 27 publications

Apnoea in pregnancy: an investigation using physiological modelling

Apnoea in pregnancy: an investigation using physiological modelling

Obstetric Anaesthetists’ Association and Difficult Airway Society Guidelines for the Management of Difficult and Failed Tracheal Intubation in Obstetrics

Anesthetic Management of Pregnant Women With Stroke

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